Cisco IOS XR Routing Configuration Guide
Cisco IOS XR Software Release 3.2
Corporate Headquarters
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
USA
800 553-NETS (6387)
Fax: 408 526-4100
Text Part Number: OL-5554-05
Download from Www.Somanuals.com. All Manuals Search And Download.
Contents
Cisco IOS XR Routing Configuration Guide
RC-iv
Download from Www.Somanuals.com. All Manuals Search And Download.
Contents
Standards RC-203
MIBs RC-203
RFCs RC-204
Contents RC-205
Parameterization RC-214
Cisco IOS XR Routing Configuration Guide
RC-viii
Download from Www.Somanuals.com. All Manuals Search And Download.
Contents
Cisco IOS XR Routing Configuration Guide
RC-x
Download from Www.Somanuals.com. All Manuals Search And Download.
Preface
This is the preface for the Cisco IOS XR Routing Configuration Guide.
The preface contains the following sections:
•
•
•
•
•
•
Document Revision History
The Document Revision History table records technical changes to this document. Table 1 shows the
document revision number for the change, the date of the change, and a brief summary of the change.
Note that not all Cisco documents use a Document Revision History table.
Table 1
Document Revision History
Revision
Date Change Summary
OL-5554-05 November
2005
Added description for the OSPFv3 Graceful Restart feature.
Added descriptions for the multicast-intact option in IS-IS and OSPFv2.
Implementing IS-IS on Cisco IOS XR Software changes:
OL-5554-04 August 31,
2005
Updated the IS-IS module to include the ability to configure a broadcast
medium connecting two networking devices as a point-to-point link.
OL-5554-02 October 31, Implementing IS-IS on Cisco IOS XR Software changes:
2004
Changes to lsp-gen-interval, spf-interval, and show isis spf-log information.
OL-5554-01 July 30, 2004 Initial release of this document.
Cisco IOS XR Routing Configuration Guide
xi
Download from Www.Somanuals.com. All Manuals Search And Download.
Preface
Obtaining Documentation
Obtaining Documentation
Cisco documentation and additional literature are available on Cisco.com. Cisco also provides several
ways to obtain technical assistance and other technical resources. These sections explain how to obtain
technical information from Cisco Systems.
Cisco.com
You can access the most current Cisco documentation at this URL:
You can access the Cisco website at this URL:
You can access international Cisco websites at this URL:
Product Documentation DVD
Cisco documentation and additional literature are available in the Product Documentation DVD package,
which may have shipped with your product. The Product Documentation DVD is updated regularly and
may be more current than printed documentation.
The Product Documentation DVD is a comprehensive library of technical product documentation on
portable media. The DVD enables you to access multiple versions of hardware and software installation,
configuration, and command guides for Cisco products and to view technical documentation in HTML.
With the DVD, you have access to the same documentation that is found on the Cisco website without
being connected to the Internet. Certain products also have .pdf versions of the documentation available.
The Product Documentation DVD is available as a single unit or as a subscription. Registered Cisco.com
users (Cisco direct customers) can order a Product Documentation DVD (product number
DOC-DOCDVD=) from Cisco Marketplace at this URL:
Ordering Documentation
Beginning June 30, 2005, registered Cisco.com users may order Cisco documentation at the Product
Documentation Store in the Cisco Marketplace at this URL:
Nonregistered Cisco.com users can order technical documentation from 8:00 a.m. to 5:00 p.m.
(0800 to 1700) PDT by calling 1 866 463-3487 in the United States and Canada, or elsewhere by
calling 011 408 519-5055. You can also order documentation by e-mail at
[email protected] or by fax at 1 408 519-5001 in the United States and Canada,
or elsewhere at 011 408 519-5001.
Cisco IOS XR Routing Configuration Guide
xii
Download from Www.Somanuals.com. All Manuals Search And Download.
Preface
Documentation Feedback
Documentation Feedback
You can rate and provide feedback about Cisco technical documents by completing the online feedback
form that appears with the technical documents on Cisco.com.
You can submit comments by using the response card (if present) behind the front cover of your
document or by writing to the following address:
Cisco Systems
Attn: Customer Document Ordering
170 West Tasman Drive
San Jose, CA 95134-9883
We appreciate your comments.
Cisco Product Security Overview
Cisco provides a free online Security Vulnerability Policy portal at this URL:
From this site, you can perform these tasks:
•
•
•
Report security vulnerabilities in Cisco products.
Obtain assistance with security incidents that involve Cisco products.
Register to receive security information from Cisco.
A current list of security advisories and notices for Cisco products is available at this URL:
If you prefer to see advisories and notices as they are updated in real time, you can access a Product
Security Incident Response Team Really Simple Syndication (PSIRT RSS) feed from this URL:
Reporting Security Problems in Cisco Products
Cisco is committed to delivering secure products. We test our products internally before we release them,
and we strive to correct all vulnerabilities quickly. If you think that you might have identified a
vulnerability in a Cisco product, contact PSIRT:
•
An emergency is either a condition in which a system is under active attack or a condition for which
a severe and urgent security vulnerability should be reported. All other conditions are considered
nonemergencies.
•
In an emergency, you can also reach PSIRT by telephone:
•
•
1 877 228-7302
1 408 525-6532
Cisco IOS XR Routing Configuration Guide
xiii
Download from Www.Somanuals.com. All Manuals Search And Download.
Preface
Obtaining Technical Assistance
Tip
We encourage you to use Pretty Good Privacy (PGP) or a compatible product to encrypt any sensitive
information that you send to Cisco. PSIRT can work from encrypted information that is compatible with
PGP versions 2.x through 8.x.
Never use a revoked or an expired encryption key. The correct public key to use in your correspondence
with PSIRT is the one linked in the Contact Summary section of the Security Vulnerability Policy page
at this URL:
The link on this page has the current PGP key ID in use.
Obtaining Technical Assistance
Cisco Technical Support provides 24-hour-a-day award-winning technical assistance. The Cisco
Technical Support & Documentation website on Cisco.com features extensive online support resources.
In addition, if you have a valid Cisco service contract, Cisco Technical Assistance Center (TAC)
engineers provide telephone support. If you do not have a valid Cisco service contract, contact your
reseller.
Cisco Technical Support & Documentation Website
The Cisco Technical Support & Documentation website provides online documents and tools for
troubleshooting and resolving technical issues with Cisco products and technologies. The website is
available 24 hours a day, at this URL:
Access to all tools on the Cisco Technical Support & Documentation website requires a Cisco.com user
ID and password. If you have a valid service contract but do not have a user ID or password, you can
register at this URL:
Note
Use the Cisco Product Identification (CPI) tool to locate your product serial number before submitting
a web or phone request for service. You can access the CPI tool from the Cisco Technical Support &
Documentation website by clicking the Tools & Resources link under Documentation & Tools. Choose
Cisco Product Identification Tool from the Alphabetical Index drop-down list, or click the Cisco
Product Identification Tool link under Alerts & RMAs. The CPI tool offers three search options: by
product ID or model name; by tree view; or for certain products, by copying and pasting show command
output. Search results show an illustration of your product with the serial number label location
highlighted. Locate the serial number label on your product and record the information before placing a
service call.
Cisco IOS XR Routing Configuration Guide
xiv
Download from Www.Somanuals.com. All Manuals Search And Download.
Preface
Obtaining Additional Publications and Information
Submitting a Service Request
Using the online TAC Service Request Tool is the fastest way to open S3 and S4 service requests. (S3
and S4 service requests are those in which your network is minimally impaired or for which you require
product information.) After you describe your situation, the TAC Service Request Tool provides
recommended solutions. If your issue is not resolved using the recommended resources, your service
request is assigned to a Cisco engineer. The TAC Service Request Tool is located at this URL:
For S1 or S2 service requests or if you do not have Internet access, contact the Cisco TAC by telephone.
(S1 or S2 service requests are those in which your production network is down or severely degraded.)
Cisco engineers are assigned immediately to S1 and S2 service requests to help keep your business
operations running smoothly.
To open a service request by telephone, use one of the following numbers:
Asia-Pacific: +61 2 8446 7411 (Australia: 1 800 805 227)
EMEA: +32 2 704 55 55
USA: 1 800 553-2447
For a complete list of Cisco TAC contacts, go to this URL:
Definitions of Service Request Severity
To ensure that all service requests are reported in a standard format, Cisco has established severity
definitions.
Severity 1 (S1)—Your network is “down,” or there is a critical impact to your business operations. You
and Cisco will commit all necessary resources around the clock to resolve the situation.
Severity 2 (S2)—Operation of an existing network is severely degraded, or significant aspects of your
business operation are negatively affected by inadequate performance of Cisco products. You and Cisco
will commit full-time resources during normal business hours to resolve the situation.
Severity 3 (S3)—Operational performance of your network is impaired, but most business operations
remain functional. You and Cisco will commit resources during normal business hours to restore service
to satisfactory levels.
Severity 4 (S4)—You require information or assistance with Cisco product capabilities, installation, or
configuration. There is little or no effect on your business operations.
Obtaining Additional Publications and Information
Information about Cisco products, technologies, and network solutions is available from various online
and printed sources.
•
Cisco Marketplace provides a variety of Cisco books, reference guides, documentation, and logo
merchandise. Visit Cisco Marketplace, the company store, at this URL:
Cisco IOS XR Routing Configuration Guide
xv
Download from Www.Somanuals.com. All Manuals Search And Download.
Preface
Obtaining Additional Publications and Information
•
•
Cisco Press publishes a wide range of general networking, training and certification titles. Both new
and experienced users will benefit from these publications. For current Cisco Press titles and other
information, go to Cisco Press at this URL:
Packet magazine is the Cisco Systems technical user magazine for maximizing Internet and
networking investments. Each quarter, Packet delivers coverage of the latest industry trends,
technology breakthroughs, and Cisco products and solutions, as well as network deployment and
troubleshooting tips, configuration examples, customer case studies, certification and training
information, and links to scores of in-depth online resources. You can access Packet magazine at
this URL:
•
iQ Magazine is the quarterly publication from Cisco Systems designed to help growing companies
learn how they can use technology to increase revenue, streamline their business, and expand
services. The publication identifies the challenges facing these companies and the technologies to
help solve them, using real-world case studies and business strategies to help readers make sound
technology investment decisions. You can access iQ Magazine at this URL:
or view the digital edition at this URL:
•
Internet Protocol Journal is a quarterly journal published by Cisco Systems for engineering
professionals involved in designing, developing, and operating public and private internets and
intranets. You can access the Internet Protocol Journal at this URL:
•
•
Networking products offered by Cisco Systems, as well as customer support services, can be
obtained at this URL:
Networking Professionals Connection is an interactive website for networking professionals to share
questions, suggestions, and information about networking products and technologies with Cisco
experts and other networking professionals. Join a discussion at this URL:
•
World-class networking training is available from Cisco. You can view current offerings at
this URL:
Cisco IOS XR Routing Configuration Guide
xvi
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
The Border Gateway Protocol (BGP) is an Exterior Gateway Protocol (EGP) that allows you to create
loop-free interdomain routing between autonomous systems. An autonomous system is a set of routers
under a single technical administration. Routers in an autonomous system can use multiple Interior
Gateway Protocols (IGP) to exchange routing information inside the autonomous system and an EGP to
route packets outside the autonomous system.
This module describes information that is unique to BGP for IP Version 4 (IPv4) and IP Version 6 (IPv6)
implementation in Cisco IOS XR Software.
Note
For more information about BGP on the Cisco IOS XR software and complete descriptions of the BGP
commands listed in this module, you can see the “Related Documents” section of this module. To locate
documentation for other commands that might appear while executing a configuration task, search online
in the Cisco IOS XR software master command index.
Feature History for Implementing BGP on Cisco IOS XR Configuration Module
Release
Modification
Release 2.0
Release 3.0
Release 3.2
This feature was introduced on the Cisco CRS-1.
No modification.
Support was added for the Cisco XR 12000 Series Router.
Contents
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-1
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Prerequisites for Implementing BGP on Cisco IOS XR Software
Prerequisites for Implementing BGP on Cisco IOS XR Software
To use this command, you must be in a user group associated with a task group that includes the proper
task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on
Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Information About Implementing BGP on Cisco IOS XR Software
To implement BGP, you need to understand the following concepts:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
BGP Functional Overview
BGP uses TCP as its transport protocol. Two BGP routers form a TCP connection between one another
(peer routers) and exchange messages to open and confirm the connection parameters.
BGP routers exchange network reachability information. This information is mainly an indication of the
full paths (BGP autonomous system numbers) that a route should take to reach the destination network.
This information helps construct a graph that shows which autonomous systems are loop free and where
routing policies can be applied to enforce restrictions on routing behavior.
Any two routers forming a TCP connection to exchange BGP routing information are called peers or
neighbors. BGP peers initially exchange their full BGP routing tables. After this exchange, incremental
updates are sent as the routing table changes. BGP keeps a version number of the BGP table, which is
the same for all of its BGP peers. The version number changes whenever BGP updates the table due to
routing information changes. Keepalive packets are sent to ensure that the connection is alive between
the BGP peers and notification packets are sent in response to error or special conditions.
Cisco IOS XR Routing Configuration Guide
RC-2
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
BGP Router Identifier
For BGP sessions between neighbors to be established, BGP must be assigned a router ID. The router
ID is sent to BGP peers in the OPEN message when a BGP session is established.
BGP attempts to obtain a router ID in the following ways (in order of preference):
•
•
By means of the address configured using the bgp router-id command in router configuration mode.
By assigning a primary IPv4 address to the interface specified using the bgp router-id command in
router configuration mode.
Note
If the specified interface does not have an IPv4 address, or is not up, BGP will fail to obtain a router ID.
•
By using the address specified with the router-id command in global configuration mode if the
router is booted with the saved router-id command and if the ID from this command is available
when the last saved loopback configuration is applied.
•
By using the primary IPv4 address on the interface specified with the router-id command in global
configuration mode if the box is booted with the saved router-id command in global configuration
mode and if the router ID is up by the time all saved loopback configurations are applied.
•
•
By using the highest IPv4 address on a loopback interface in the system if the router is booted with
saved loopback address configuration.
By using the primary IPv4 address of the first loopback address that gets configured if there are not
any in the saved configuration.
If none of these methods for obtaining a router ID succeeds, BGP does not have a router ID and cannot
establish any peering sessions with BGP neighbors. In such an instance, an error message is entered in
the system log, and the show bgp summary command displays a router ID of 0.0.0.0.
After BGP has obtained a router ID, it continues to use it even if a better router ID becomes available.
This usage avoids unnecessary flapping for all BGP sessions. However, if the router ID currently in use
becomes invalid (because the interface goes down or its configuration is changed), BGP selects a new
router ID (using the rules described) and all established peering sessions are reset.
We strongly recommend that the bgp router-id command is configured to prevent unnecessary changes
to the router ID (and consequent flapping of BGP sessions).
BGP Default Limits
Cisco IOS XR BGP imposes maximum limits on the number of neighbors that can be configured on the
router and on the maximum number of prefixes that are accepted from a peer for a given address family.
This limitation safeguards the router from resource depletion caused by misconfiguration, either locally
or on the remote neighbor. The following limits apply to BGP configurations:
•
•
The default maximum number of peers that can be configured is 1024. The default can be changed
using the bgp maximum neighbor command. The limit range is 1 to 1500. Any attempt to configure
additional peers beyond the maximum limit or set the maximum limit to a number that is less than
the number of peers currently configured will fail.
To prevent a peer from flooding BGP with advertisements, a limit is placed on the number of
prefixes that are accepted from a peer for each supported address family. The default limits can be
overridden through configuration of the maximum-prefix limit command for the peer for the
appropriate address family. The following default limits are used if the user does not configure the
maximum number of prefixes for the address family:
Cisco IOS XR Routing Configuration Guide
RC-3
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
–
–
–
512K (524,288) prefixes for IPv4 unicast.
128K (131,072) prefixes for IPv4 multicast.
128K (131,072) prefixes for IPv6 unicast.
A cease notification message is sent to the neighbor and the peering with the neighbor is terminated
when the number of prefixes received from the peer for a given address family exceeds the maximum
limit (either set by default or configured by the user) for that address family.
It is possible that the maximum number of prefixes for a neighbor for a given address family has been
configured after the peering with the neighbor has been established and a certain number of prefixes have
already been received from the neighbor for that address family. A cease notification message is sent to
the neighbor and peering with the neighbor is terminated immediately after the configuration if the
configured maximum number of prefixes is fewer than the number of prefixes that have already been
received from the neighbor for the address family.
BGP Validation of Local Next-Hop Addresses
When Cisco IOS XR BGP receives a route advertisement from a neighbor, it validates the next-hop
address contained in the route by verifying that the next-hop address is not the same as an IP address
assigned to an interface on this router (for example, a local address). If the received next-hop address is
a local address, the update is dropped. However, if the next-hop address is set to a local address by the
configured inbound policy, the update is not dropped, is treated as a valid next-hop address, and is
processed normally in Cisco IOS XR BGP. This verification means that the router advertises to its
neighbors that it has a route to the prefix, but any traffic received for that prefix is dropped.
This “blackholing” effect is often used to automatically protect against Denial of Service (DOS) attacks
on user hosts. An inbound policy is configured that sets the next hop to a local address (for example, the
address of a loopback interface) when a route with a particular community is received. When a user finds
that a host is under a DOS attack, a BGP advertisement is sent to the address of the attacked host with
the special community attached. The advertisement causes the Internet service provider (ISP) router to
install a route with a local next hop for that address that drops all traffic destined for it.
BGP Configuration
Cisco IOS XR BGP follows a neighbor-based configuration model that requires that all configurations
for a particular neighbor be grouped in one place under the neighbor configuration. Peer groups are not
supported for either sharing configuration between neighbors or for sharing update messages. The
concept of peer group has been replaced by a set of configuration groups to be used as templates in BGP
configuration and automatically generated update groups to share update messages between neighbors.
BGP configurations are grouped into four major categories:
–
–
–
–
Configuration Modes
The following sections show how to enter each of the configuration modes. From a mode, you can enter
the ? command to display the commands available in that mode.
Cisco IOS XR Routing Configuration Guide
RC-4
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Router Configuration Mode
The following example shows how to enter router configuration mode:
RP/0/RP0/CPU0:router# configuration
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)#
Global Address Family Configuration Mode
The following example shows how to enter global address family configuration mode:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 multicast
RP/0/RP0/CPU0:router(config-bgp-af)#
Neighbor Configuration Mode
The following example shows how to enter neighbor configuration mode:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.1
RP/0/RP0/CPU0:router(config-bgp-nbr)#
Neighbor Address Family Configuration Mode
The following example shows how to enter neighbor address family configuration mode:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.1
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbr-af)#
Neighbor Submode
Cisco IOS XR BGP uses a neighbor submode to make it possible to enter configurations without having
to prefix every configuration with the neighbor keyword and the neighbor address:
•
Cisco IOS XR software has a submode available for neighbors in which it is not necessary for every
command to have a “neighbor x.x.x.x” prefix.
In Cisco IOS XR software, the configuration is as follows:
Router(config-bgp-af)# neighbor 192.23.1.2
Router(config-bgp-nbr)# remote-as 2002
Router(config-bgp-nbr)# address-family ipv4 multicast
•
An address family configuration submode inside the neighbor configuration submode is available
for entering address family-specific neighbor configurations. In Cisco IOS XR, the configuration is
as follows:
Router(config-bgp-af)# neighbor 2002::2
Router(config-bgp-nbr)# remote-as 2002
Router(config-bgp-nbr)# address-family ipv6 unicast
Router(config-bgp-nbr-af)# next-hop-self
Router(config-bgp-nbr-af)# route-policy one in
•
You must enter neighbor-specific IPv4 or IPv6 commands in neighbor address-family configuration
submode. In Cisco IOS XR software, the configuration is as follows:
Router(config-bgp)# router bgp 109
Router(config-bgp)# neighbor 192.168.40.24
Cisco IOS XR Routing Configuration Guide
RC-5
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Router(config-bgp-nbr)# remote-as 1
Router(config-bgp-nbr)# address-family ipv4 unicast
Router(config-bgp-nbr-af)# maximum-prefix 1000
Configuration Templates
The af-group, session-group, and neighbor-group configuration commands provide template support
for the neighbor configuration in Cisco IOS XR software:
The af-group command is used to group address family-specific neighbor commands within an IPv4 or
IPv6 address family. Neighbors that have the same address family configuration are able to use the
address family group (af-group) name for their address family-specific configuration. A neighbor
inherits the configuration from an address family group by way of the use command. If a neighbor is
configured to use an address family group, the neighbor (by default) inherits the entire configuration
from the address family group. However, a neighbor does not inherit all of the configuration from the
address family group if items are explicitly configured for the neighbor. The address family group
configuration is entered under the BGP router configuration mode. The following example shows how
to enter address family group configuration mode.
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# af-group afmcast1 address-family ipv4 multicast
RP/0/RP0/CPU0:router(config-bgp-afgrp)#
The session-group command allows you to create a session group from which neighbors can inherit
address family-independent configuration. A neighbor inherits the configuration from a session group
by way of the use command. If a neighbor is configured to use a session group, the neighbor (by default)
inherits the entire configuration of the session group. A neighbor does not inherit all of the configuration
from a session group if a configuration is done directly on that neighbor. The following example shows
how to enter session group configuration mode:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# session-group session1
RP/0/RP0/CPU0:router(config-bgp-sngrp)#
The neighbor-group command helps you apply the same configuration to one or more neighbors.
Neighbor groups can include session groups and address family groups and can comprise the complete
configuration for a neighbor. After a neighbor group is configured, a neighbor can inherit the
configuration of the group using the use command. If a neighbor is configured to use a neighbor group,
the neighbor inherits the entire BGP configuration of the neighbor group.
The following example shows how to enter neighbor group configuration mode:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group nbrgroup1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
The following example shows how to enter neighbor group address family configuration mode:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group nbrgroup1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)#
•
However, a neighbor does not inherit all of the configuration from the neighbor group if items are
explicitly configured for the neighbor. In addition, some part of the configuration of the neighbor
group could be hidden if a session group or address family group was also being used.
Configuration grouping has the following effects in Cisco IOS XR software:
Cisco IOS XR Routing Configuration Guide
RC-6
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
•
•
Commands entered at the session group level define address family-independent commands (the
same commands as in the neighbor submode).
Commands entered at the address family group level define address family-dependent commands
for a specified address family (the same commands as in the neighbor-address family configuration
submode).
•
Commands entered at the neighbor group level define address family-independent commands and
address family-dependent commands for each address family (the same as all available neighbor
commands), and define the use command for the address family group and session group commands.
Template Inheritance Rules
In Cisco IOS XR software, BGP neighbors or groups inherit configuration from other configuration
groups.
For address family-independent configurations:
•
•
•
•
Neighbors can inherit from session groups and neighbor groups.
Neighbor groups can inherit from session groups and other neighbor groups.
Session groups can inherit from other session groups.
If a neighbor uses a session group and a neighbor group, the configurations in the session group are
preferred over the global address family configurations in the neighbor group.
For address family-dependent configurations:
•
•
•
Address family groups can inherit from other address family groups.
Neighbor groups can inherit from address family groups and other neighbor groups.
Neighbors can inherit from address family groups and neighbor groups.
Configuration group inheritance rules are numbered in order of precedence as follows:
1. If the item is configured directly on the neighbor, that value is used. In the example that follows, the
advertisement interval is configured both on the neighbor group and neighbor configuration and the
advertisement interval being used is from the neighbor configuration:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group AS_1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 15
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.1.1.1
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1
RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group AS_1
RP/0/RP0/CPU0:router(config-bgp-nbr)# advertisement-interval 20
The following output from the show bgp neighbors command shows that the advertisement interval
used is 20 seconds:
RP/0/RP0/CPU0:router# show bgp neighbors 10.1.1.1
BGP neighbor is 10.1.1.1, remote AS 1, local AS 140, external link
Remote router ID 0.0.0.0
BGP state = Idle
Last read 00:00:00, hold time is 180, keepalive interval is 60 seconds
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Minimum time between advertisement runs is 20 seconds
For Address Family: IPv4 Unicast
BGP neighbor version 0
Cisco IOS XR Routing Configuration Guide
RC-7
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Update group: 0.1
eBGP neighbor with no inbound or outbound policy; defaults to 'drop'
Route refresh request: received 0, sent 0
0 accepted prefixes
Prefix advertised 0, suppressed 0, withdrawn 0, maximum limit 524288
Threshold for warning message 75%
Connections established 0; dropped 0
Last reset 00:00:14, due to BGP neighbor initialized
External BGP neighbor not directly connected.
2. Otherwise, if the neighbor uses a session group or address family group, the configuration value is
obtained from the session group or address family group. If the address family group or session
group has a parent and an item is configured on the parent, the parent configuration is used. If the
item is not configured on the parent, but is configured on the parent ‘s parent, the configuration of
the parent’s parent is used, and so on. In the example that follows, the advertisement interval is
configured on a neighbor group and a session group and the advertisement interval value being used
is from the session group:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# session-group AS_2
RP/0/RP0/CPU0:router(config-bgp-sngrp)# advertisement-interval 15
RP/0/RP0/CPU0:router(config-bgp-sngrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group AS_1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 20
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.0.1
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1
RP/0/RP0/CPU0:router(config-bgp-nbr)# use session-group AS_2
RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group AS_1
The following output from the show bgp neighbors command shows that the advertisement interval
used is 15 seconds:
RP/0/RP0/CPU0:router# show bgp neighbors 192.168.0.1
BGP neighbor is 192.168.0.1, remote AS 1, local AS 140, external link
Remote router ID 0.0.0.0
BGP state = Idle
Last read 00:00:00, hold time is 180, keepalive interval is 60 seconds
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Minimum time between advertisement runs is 15 seconds
For Address Family: IPv4 Unicast
BGP neighbor version 0
Update group: 0.1
eBGP neighbor with no inbound or outbound policy; defaults to 'drop'
Route refresh request: received 0, sent 0
0 accepted prefixes
Prefix advertised 0, suppressed 0, withdrawn 0, maximum limit 524288
Threshold for warning message 75%
Connections established 0; dropped 0
Last reset 00:03:23, due to BGP neighbor initialized
External BGP neighbor not directly connected.
3. Otherwise, if the neighbor uses a neighbor group and does not use a session group or address family
group, the configuration value can be obtained from the neighbor group either directly or through
inheritance. In the example that follows, the advertisement interval from the neighbor group is used
because it is not configured directly on the neighbor and no session group is used:
Cisco IOS XR Routing Configuration Guide
RC-8
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
RP/0/RP0/CPU0:router(config)# router bgp 150
RP/0/RP0/CPU0:router(config-bgp)# session-group AS_2
RP/0/RP0/CPU0:router(config-bgp-sngrp)# advertisement-interval 20
RP/0/RP0/CPU0:router(config-bgp-sngrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group AS_1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 15
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.1.1
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1
RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group AS_1
The following output from the show bgp neighbors command shows that the advertisement interval
used is 15 seconds:
RP/0/RP0/CPU0:router# show bgp neighbors 192.168.1.1
BGP neighbor is 192.168.2.2, remote AS 1, local AS 140, external link
Remote router ID 0.0.0.0
BGP state = Idle
Last read 00:00:00, hold time is 180, keepalive interval is 60 seconds
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Minimum time between advertisement runs is 15 seconds
For Address Family: IPv4 Unicast
BGP neighbor version 0
Update group: 0.1
eBGP neighbor with no outbound policy; defaults to 'drop'
Route refresh request: received 0, sent 0
Inbound path policy configured
Policy for incoming advertisements is POLICY_1
0 accepted prefixes
Prefix advertised 0, suppressed 0, withdrawn 0, maximum limit 524288
Threshold for warning message 75%
Connections established 0; dropped 0
Last reset 00:01:14, due to BGP neighbor initialized
External BGP neighbor not directly connected.
To illustrate the same rule, the following example shows how to set the advertisement interval to 15
(from the session group). The timers are set to the default (60/180) because the neighbor uses a
session group, thus hiding the timers command in the neighbor group. The inbound policy is set to
POLICY_1 from the neighbor group.
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# session-group ADV
RP/0/RP0/CPU0:router(config-bgp-sngrp)# advertisement-interval 15
RP/0/RP0/CPU0:router(config-bgp-sngrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group TIMER
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# timers 10 30
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# route-policy POLICY_1 in
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.2.2
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1
RP/0/RP0/CPU0:router(config-bgp-nbr)# use session-group ADV
RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group TIMER
The following output from the show bgp neighbors command shows that the advertisement interval
used is 15 seconds:
Cisco IOS XR Routing Configuration Guide
RC-9
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
RP/0/RP0/CPU0:router# show bgp neighbors 192.168.2.2
BGP neighbor is 192.168.2.2, remote AS 1, local AS 140, external link
Remote router ID 0.0.0.0
BGP state = Idle
Last read 00:00:00, hold time is 180, keepalive interval is 60 seconds
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Minimum time between advertisement runs is 15 seconds
For Address Family: IPv4 Unicast
BGP neighbor version 0
Update group: 0.1
eBGP neighbor with no inbound or outbound policy; defaults to 'drop'
Route refresh request: received 0, sent 0
0 accepted prefixes
Prefix advertised 0, suppressed 0, withdrawn 0, maximum limit 524288
Threshold for warning message 75%
Connections established 0; dropped 0
Last reset 00:02:03, due to BGP neighbor initialized
External BGP neighbor not directly connected.
4. Otherwise, the default value is used. In the example that follows, neighbor 10.0.101.5 has the
minimum time between advertisement runs set to 30 seconds (default) because the neighbor is not
configured to use the neighbor configuration or the neighbor group configuration:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group AS_1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# remote-as 1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# neighbor-group adv_15
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# remote-as 10
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 15
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.101.5
RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group AS_1
RP/0/RP0/CPU0:router(config-bgp-nbr)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.101.10
RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group adv_15
The following output from the show bgp neighbors command shows that the advertisement interval
used is 30 seconds:
RP/0/RP0/CPU0:router# show bgp neighbors 10.0.101.5
BGP neighbor is 10.0.101.5, remote AS 1, local AS 140, external link
Remote router ID 0.0.0.0
BGP state = Idle
Last read 00:00:00, hold time is 180, keepalive interval is 60 seconds
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Minimum time between advertisement runs is 30 seconds
For Address Family: IPv4 Unicast
BGP neighbor version 0
Update group: 0.2
eBGP neighbor with no inbound or outbound policy; defaults to 'drop'
Route refresh request: received 0, sent 0
0 accepted prefixes
Prefix advertised 0, suppressed 0, withdrawn 0, maximum limit 524288
Threshold for warning message 75%
Connections established 0; dropped 0
Cisco IOS XR Routing Configuration Guide
RC-10
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Last reset 00:00:25, due to BGP neighbor initialized
External BGP neighbor not directly connected.
The inheritance rules used when groups are inheriting configuration from other groups are the same
as the rules given for neighbors inheriting from groups.
Template Inheritance
You can use the following show commands described to monitor BGP inheritance information:
•
•
•
•
show bgp neighbors
Use the show bgp neighbors command to display information about the BGP configuration for
neighbors.
•
Use the configuration keyword to display the effective configuration for the neighbor, including any
settings that have been inherited from session groups, neighbor groups, or address family groups
used by this neighbor.
•
Use the inheritance keyword to display the session groups, neighbor groups, and address family
groups from which this neighbor is capable of inheriting configuration .
The show bgp neighbors command examples that follow are based on the sample configuration:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# af-group GROUP_3 address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-afgrp)# next-hop-self
RP/0/RP0/CPU0:router(config-bgp-afgrp)# route-policy POLICY_1 in
RP/0/RP0/CPU0:router(config-bgp0afgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# session-group GROUP_2
RP/0/RP0/CPU0:router(config-bgp-sngrp)# advertisement-interval 15
RP/0/RP0/CPU0:router(config-bgp-sngrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group GROUP_1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# use session-group GROUP_2
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# ebgp-multihop 3
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# weight 100
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# send-community-ebgp
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# exit
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 multicast
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# default-originate
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# exit
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.0.1
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2
RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group GROUP_1
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# use af-group GROUP_3
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# weight 200
Cisco IOS XR Routing Configuration Guide
RC-11
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
The following example displays sample output from the show bgp neighbors command using the
inheritance keyword. The example shows that the neighbor inherits session parameters from neighbor
group GROUP_1, which in turn inherits from session group GROUP_2. The neighbor inherits IPv4
unicast parameters from address family group GROUP_3 and IPv4 multicast parameters from neighbor
group GROUP_1:
RP/0/RP0/CPU0:router# show bgp neighbors 192.168.0.1 inheritance
Session:
IPv4 Unicast:
n:GROUP_1 s:GROUP_2
a:GROUP_3
IPv4 Multicast: n:GROUP_1
The following example displays sample output from the show bgp neighbors command using the
configuration keyword. The example shows from where each item of configuration was inherited, or if
it was configured directly on the neighbor (indicated by [ ]). For example, the ebgp-multihop 3
command was inherited from neighbor group GROUP_1 and the next-hop-self command was inherited
from the address family group GROUP_3:
RP/0/RP0/CPU0:router# show bgp neighbors 192.168.0.1 configuration
neighbor 192.168.0.1
remote-as 2
[]
advertisement-interval 15
ebgp-multihop 3
address-family ipv4 unicast
next-hop-self
route-policy POLICY_1
weight 200
[n:GROUP_1 s:GROUP_2]
[n:GROUP_1]
[]
[a:GROUP_3]
[a:GROUP_3]
[]
in
address-family ipv4 multicast [n:GROUP_1]
default-originate [n:GROUP_1]
show bgp af-group
Use the show bgp af-group command to display address family groups:
•
Use the configuration keyword to display the effective configuration for the address family group,
including any settings that have been inherited from address family groups used by this address
family group.
•
•
Use the inheritance keyword to display the address family groups from which this address family
group is capable of inheriting configuration.
Use the users keyword to display the neighbors, neighbor groups, and address family groups that
inherit configuration from this address family group.
The show bgp af-group command examples that follow are based on the this sample configuration:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# af-group GROUP_3 address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-afgrp)# remove-private-as
RP/0/RP0/CPU0:router(config-bgp-afgrp)# route-policy POLICY_1 in
RP/0/RP0/CPU0:router(config-bgp-afgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# af-group GROUP_1 address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-afgrp)# use af-group GROUP_2
RP/0/RP0/CPU0:router(config-bgp-afgrp)# maximum-prefix 2500 75 warning-only
RP/0/RP0/CPU0:router(config-bgp-afgrp)# default-originate
RP/0/RP0/CPU0:router(config-bgp-afgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# af-group GROUP_2 address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-afgrp)# use af-group GROUP_3
RP/0/RP0/CPU0:router(config-bgp-afgrp)# send-community-ebgp
RP/0/RP0/CPU0:router(config-bgp-afgrp)# send-extended-community-ebgp
RP/0/RP0/CPU0:router(config-bgp-afgrp)# capability orf prefix-list both
Cisco IOS XR Routing Configuration Guide
RC-12
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
The following example displays sample output from the show bgp af-group command using the
configuration keyword. This example shows from where each configuration item was inherited. The
default-originate command was configured directly on this address family group (indicated by [ ]). The
remove-private-as command was inherited from address family group GROUP_2, which in turn
inherited from address family group GROUP_3:
RP/0/RP0/CPU0:router# show bgp af-group GROUP_1 configuration
af-group GROUP_1 address-family ipv4 unicast
capability orf prefix-list both
default-originate
[a:GROUP_2]
[]
maximum-prefix 2500 75 warning-only
route-policy POLICY_1 in
remove-private-AS
send-community-ebgp
send-extended-community-ebgp
[]
[a:GROUP_2 a:GROUP_3]
[a:GROUP_2 a:GROUP_3]
[a:GROUP_2]
[a:GROUP_2]
The following example displays sample output from the show bgp af-group command using the users
keyword:
RP/0/RP0/CPU0:router# show bgp af-group GROUP_2 users
IPv4 Unicast: a:GROUP_1
The following example displays sample output from the show bgp af-group command using the
inheritance keyword. This shows that the specified address family group GROUP_1 directly uses the
GROUP_2 address family group, which in turn uses the GROUP_3 address family group:
RP/0/RP0/CPU0:router# show bgp af-group GROUP_1 inheritance
IPv4 Unicast: a:GROUP_2 a:GROUP_3
show bgp session-group
Use the show bgp session-group command to display session groups:
•
•
•
Use the configuration keyword to display the effective configuration for the session group,
including any settings that have been inherited from session groups used by this session group.
Use the inheritance keyword to display the session groups from which this session group is capable
of inheriting configuration.
Use the users keyword to display the session groups, neighbor groups, and neighbors that inherit
configuration from this session group.
The examples that follow sample output from the show bgp session-group command with the
configuration keyword in EXEC mode. The examples are based on the following session group
configuration:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# session-group GROUP_1
RP/0/RP0/CPU0:router(config-bgp-sngrp)# use session-group GROUP_2
RP/0/RP0/CPU0:router(config-bgp-sngrp)# update-source Loopback 0
RP/0/RP0/CPU0:router(config-bgp-sngrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# session-group GROUP_2
RP/0/RP0/CPU0:router(config-bgp-sngrp)# use session-group GROUP_3
RP/0/RP0/CPU0:router(config-bgp-sngrp)# ebgp-multihop 2
RP/0/RP0/CPU0:router(config-bgp-sngrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# session-group GROUP_3
RP/0/RP0/CPU0:router(config-bgp-sngrp)# dmz-link-bandwidth
The following is sample output from the show bgp session-group command with the configuration
keyword in EXEC mode:
Cisco IOS XR Routing Configuration Guide
RC-13
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
RP/0/RP0/CPU0:router# show bgp session-group GROUP_1 configuration
session-group GROUP_1
ebgp-multihop 2
[s:GROUP_2]
update-source Loopback0 []
dmz-link-bandwidth [s:GROUP_2 s:GROUP_3]
The following is sample output from the show bgp session-group command with the inheritance
keyword showing that the GROUP_1 session group inherits session parameters from the GROUP_3 and
GROUP_2 session groups:
RP/0/RP0/CPU0:router# show bgp session-group GROUP_1 inheritance
Session: s:GROUP_2 s:GROUP_3
The following is sample output from the show bgp session-group command with the users keyword
showing that both the GROUP_1 and GROUP_2 session groups inherit session parameters from the
GROUP_3 session group:
RP/0/RP0/CPU0:router# show bgp session-group GROUP_3 users
Session: s:GROUP_1 s:GROUP_2
show bgp neighbor-group
Use the show bgp neighbor-group command to display neighbor groups:
•
•
•
Use the configuration keyword to display the effective configuration for the neighbor group,
including any settings that have been inherited from neighbor groups used by this neighbor group.
Use the inheritance keyword to display the address family groups, session groups, and neighbor
groups from which this neighbor group is capable of inheriting configuration.
Use the users keyword to display the neighbors and neighbor groups that inherit configuration from
this neighbor group.
The examples are based on the following group configuration:
RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# af-group GROUP_3 address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-afgrp)# remove-private-as
RP/0/RP0/CPU0:router(config-bgp-afgrp)# soft-reconfiguration inbound
RP/0/RP0/CPU0:router(config-bgp-afgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# af-group GROUP_2 address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-afgrp)# use af-group GROUP_3
RP/0/RP0/CPU0:router(config-bgp-afgrp)# send-community-ebgp
RP/0/RP0/CPU0:router(config-bgp-afgrp)# send-extended-community-ebgp
RP/0/RP0/CPU0:router(config-bgp-afgrp)# capability orf prefix-list both
RP/0/RP0/CPU0:router(config-bgp-afgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# session-group GROUP_3
RP/0/RP0/CPU0:router(config-bgp-sngrp)# timers 30 90
RP/0/RP0/CPU0:router(config-bgp-sngrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group GROUP_1
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# remote-as 1982
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# use neighbor-group GROUP_2
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# exit
RP/0/RP0/CPU0:router(config-nbrgrp)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor-group GROUP_2
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# use session-group GROUP_3
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# use af-group GROUP_2
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# weight 100
Cisco IOS XR Routing Configuration Guide
RC-14
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
The following is sample output from the show bgp neighbor-group command with the configuration
keyword. The configuration setting source is shown to the right of each command. In the output shown
previously, the remote autonomous system is configured directly on neighbor group GROUP_1, and the
send community setting is inherited from neighbor group GROUP_2, which in turn inherits the setting
from address family group GROUP_3:
RP/0/RP0/CPU0:router# show bgp neighbor-group GROUP_1 configuration
neighbor-group GROUP_1
remote-as 1982
[]
timers 30 90
address-family ipv4 unicast
[n:GROUP_2 s:GROUP_3]
[]
capability orf prefix-list both [n:GROUP_2 a:GROUP_2]
remove-private-AS
[n:GROUP_2 a:GROUP_2 a:GROUP_3]
send-community-ebgp
send-extended-community-ebgp
soft-reconfiguration inbound
weight 100
[n:GROUP_2 a:GROUP_2]
[n:GROUP_2 a:GROUP_2]
[n:GROUP_2 a:GROUP_2 a:GROUP_3]
[n:GROUP_2]
The following is sample output from the show bgp neighbor-group command with the inheritance
keyword. This output shows that the specified neighbor group GROUP_1 inherits session (address
family-independent) configuration parameters from neighbor group GROUP_2. Neighbor group
GROUP_2 inherits its session parameters from session group GROUP_3. It also shows that the
GROUP_1 neighbor group inherits IPv4 unicast configuration parameters from the GROUP_2 neighbor
group, which in turn inherits them from the GROUP_2 address family group, which itself inherits them
from the GROUP_3 address family group:
RP/0/RP0/CPU0:router# show bgp neighbor-group GROUP_1 inheritance
Session:
n:GROUP-2 s:GROUP_3
IPv4 Unicast: n:GROUP_2 a:GROUP_2 a:GROUP_3
The following is sample output from the show bgp neighbor-group command with the users keyword.
This output shows that the GROUP_1 neighbor group inherits session (address family-independent)
configuration parameters from the GROUP_2 neighbor group. The GROUP_1 neighbor group also
inherits IPv4 unicast configuration parameters from the GROUP_2 neighbor group:
RP/0/RP0/CPU0:router# show bgp neighbor-group GROUP_2 users
Session:
n:GROUP_1
IPv4 Unicast: n:GROUP_1
No Default Address Family
BGP does not support the concept of a default address family. An address family must be explicitly
configured under the BGP router configuration for the address family to be activated in BGP. Similarly,
an address family must be explicitly configured under a neighbor for the BGP session to be activated
under that address family. It is not required to have any address family configured under the BGP router
configuration level for a neighbor to be configured. However, it is a requirement to have an address
family configured at the BGP router configuration level for the address family to be configured under a
neighbor.
Cisco IOS XR Routing Configuration Guide
RC-15
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Routing Policy Enforcement
External BGP (eBGP) neighbors must have an inbound and outbound policy configured. If no policy is
configured, no routes are accepted from the neighbor, nor are any routes advertised to it. This added
security measure ensures that routes cannot accidentally be accepted or advertised in the case of a
configuration omission error.
Note
This enforcement affects only eBGP neighbors (neighbors in a different autonomous system than this
router). For internal BGP (iBGP) neighbors (neighbors in the same autonomous system), all routes are
accepted or advertised if there is no policy.
In the following example, for an eBGP neighbor, if all routes should be accepted and advertised with no
modifications, a simple pass-all policy is configured:
RP/0/RP0/CPU0:router(config)# route-policy pass-all
RP/0/RP0/CPU0:router(config-rpl)# pass
RP/0/RP0/CPU0:router(config-rpl)# end-policy
RP/0/RP0/CPU0:router(config)# commit
Use the route-policy (BGP) command in the neighbor address-family configuration mode to apply the
pass-all policy to a neighbor. The following example shows how to allow all IPv4 unicast routes to be
received from neighbor 192.168.40.42 and advertise all IPv4 unicast routes back to it:
RP/0/RP0/CPU0:router(config)# router bgp 1
RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.40.24
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy pass-all in
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy pass-all out
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Use the show bgp summary command to display eBGP neighbors that do not have both an inbound and
outbound policy for every active address family. In the following example, such eBGP neighbors are
indicated in the output with an exclamation (!) mark:
RP/0/RP0/CPU0:router# show bgp all all summary
Address Family: IPv4 Unicast
============================
BGP router identifier 10.0.0.1, local AS number 1
BGP generic scan interval 60 secs
BGP main routing table version 41
BGP scan interval 60 secs
BGP is operating in STANDALONE mode.
Process
Speaker
RecvTblVer
41
bRIB/RIB SendTblVer
41
41
Neighbor
10.0.101.1
10.0.101.2
Spk
0
0
AS MsgRcvd MsgSent
TblVer InQ OutQ Up/Down St/PfxRcd
1
2
919
0
925
0
41
0
0
0
0 15:15:08
0 00:00:00 Idle
10
Address Family: IPv4 Multicast
==============================
BGP router identifier 10.0.0.1, local AS number 1
BGP generic scan interval 60 secs
BGP main routing table version 1
Cisco IOS XR Routing Configuration Guide
RC-16
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
BGP scan interval 60 secs
BGP is operating in STANDALONE mode.
Process
Speaker
RecvTblVer
1
bRIB/RIB SendTblVer
1
1
Some configured eBGP neighbors do not have both inbound and
outbound policies configured for IPv4 Multicast address family.
These neighbors will default to sending and/or receiving no
routes and are marked with ’!’ in the output below. Use the
’show bgp neighbor <nbr_address>’ command for details.
Neighbor
10.0.101.2
Spk
0
AS MsgRcvd MsgSent
TblVer InQ OutQ Up/Down St/PfxRcd
0 00:00:00 Idle!
2
0
0
0
0
Address Family: IPv6 Unicast
============================
BGP router identifier 10.0.0.1, local AS number 1
BGP generic scan interval 60 secs
BGP main routing table version 2
BGP scan interval 60 secs
BGP is operating in STANDALONE mode.
Process
Speaker
RecvTblVer
2
bRIB/RIB SendTblVer
2
2
Neighbor
2222::2
2222::4
Spk
0
0
AS MsgRcvd MsgSent
TblVer InQ OutQ Up/Down St/PfxRcd
2
3
920
0
918
0
2
0
0
0
0 15:15:11
0 00:00:00 Idle
1
Address Family: IPv6 Multicast
==============================
BGP router identifier 10.0.0.1, local AS number 1
BGP generic scan interval 60 secs
BGP main routing table version 1
BGP scan interval 60 secs
BGP is operating in STANDALONE mode.
Process
Speaker
RecvTblVer
1
bRIB/RIB SendTblVer
1
1
Some configured eBGP neighbors do not have both inbound and
outbound policies configured for IPv6 Multicast address family.
These neighbors will default to sending and/or receiving no
routes and are marked with ’!’ in the output below. Use the
’show bgp neighbor <nbr_address>’ command for details.
Neighbor
2222::2
2222::4
Spk
0
0
AS MsgRcvd MsgSent
TblVer InQ OutQ Up/Down St/PfxRcd
2
3
920
0
918
0
0
0
0
0
0 15:15:11
0 00:00:00 Idle!
0
Cisco IOS XR Routing Configuration Guide
RC-17
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Table Policy
The table policy feature in BGP allows you to configure traffic index values on routes as they are
installed in the global routing table. This feature is enabled using the table-policy command and
supports the BGP policy accounting feature.
BGP policy accounting uses traffic indices that are set on BGP routes to track various counters. See
Implementing Routing Policy on Cisco IOS XR Software for details on table policy use. See the Cisco
Express Forwarding Commands on Cisco IOS XR Software module in the Cisco IOS XR IP Addresses
and Services Command Reference for details on BGP policy accounting.
Table policy also provides the ability to drop routes from the RIB based on match criteria. This feature
can be useful in certain applications and should be used with caution as it can easily create a routing
‘black-hole’ where BGP advertises routes to neighbors that BGP does not install in its global routing
table but in the forwarding table .
Update Groups
The BGP Update Groups feature contains an algorithm that dynamically calculates and optimizes update
groups of neighbors that share outbound policies and can share the update messages. The BGP Update
Groups feature separates update group replication from peer group configuration, improving
convergence time and flexibility of neighbor configuration.
To use this feature, you must understand the following concepts:
•
•
BGP Update Generation and Update Groups
The BGP Update Groups feature separates BGP update generation from neighbor configuration. The
BGP Update Groups feature introduces an algorithm that dynamically calculates BGP update group
membership based on outbound routing policies. This feature does not require any configuration by the
network operator. Update group-based message generation occurs automatically and independently.
BGP Update Group
When a change to the configuration occurs, the router automatically recalculates update group
memberships and applies the changes.
For the best optimization of BGP update group generation, we recommend that the network operator
keeps outbound routing policy the same for neighbors that have similar outbound policies. This feature
contains commands for monitoring BGP update groups. For more information about the commands, see
BGP Best Path Algorithm
BGP routers typically receive multiple paths to the same destination. The BGP best path algorithm
determines the best path to install in the IP routing table and to use for forwarding traffic. This section
describes the IOS XR implementation of BGP best path algorithm, as specified in Section 9.1 of the
Internet Engineering Task Force (IETF) Network Working Group draft-ietf-idr-bgp4-24.txt document.
Cisco IOS XR Routing Configuration Guide
RC-18
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
The BGP best path algorithm implementation is in three parts:
•
•
Part 1—Compares two paths to determine which is better.
Part 2—Iterates over all paths and determines which order to compare the paths to select the overall
best path.
•
Part 3—Determines whether the old and new best paths differ enough so that the new best path
should be used.
Note
The order of comparison determined by Part 2 is important because the comparison operation is not
transitive; that is, if three paths, A, B, and C exist, such that when A and B are compared, A is better,
and when B and C are compared, B is better, it is not necessarily the case that when A and C are
compared, A is better. This nontransitivity arises because the multi exit discriminator (MED) is
compared only among paths from the same neighboring autonomous system (AS) and not among all
paths.
Comparing Pairs of Paths
The following steps are completed to compare two paths and determine the better path:
1. If either path is invalid (for example, it has the maximum possible MED value, or it has an
unreachable nexthop), then the other path is chosen (provided that the path is valid).
2. If the paths have unequal weights, the path with the highest weight is chosen. Note: the weight is
entirely local to the router, and can be set with the weight command or using a routing policy.
3. If the paths have unequal local preferences, the path with the higher local preference is chosen. Note:
If a local preference attribute was received with the path or was set by a routing policy, then that
value is used in this comparison. Otherwise, the default local preference value of 100 is used. The
default value can be changed using the bgp default local-preference command.
4. If one of the paths is a redistributed path, which results from a redistribute or network command,
then it is chosen. Otherwise, if one of the paths is a locally generated aggregate, which results from
an aggregate-address command, it is chosen.
Note
Steps 1 through 4 implement the “Degree of Preference” calculation from Section 9.1.1 of
draft-ietf-idr-bgp4-24.txt.
5. If the paths have unequal AS path lengths, the path with the shorter AS path is chosen. This step is
skipped if bgp bestpath as-path ignore command is configured. Note: when calculating the length
of the AS path, confederation segments are ignored, and AS sets count as 1. (See Section 9.1.2.2a
of draft-ietf-idr-bgp4-24.txt.)
6. If the paths have different origins, the path with the lower origin is selected. Interior Gateway
Protocol (IGP) is considered lower than EGP, which is considered lower than INCOMPLETE. (See
Section 9.1.2.2b of draft-ietf-idr-bgp4-24.txt.)
7. If appropriate, the MED of the paths is compared. If they are unequal, the path with the lower MED
is chosen.
A number of configuration options exist that affect whether or not this step is performed. In general,
the MED is compared if both paths were received from neighbors in the same AS; otherwise the
MED comparison is skipped. However, this behavior is modified by certain configuration options,
and there are also some corner cases to consider. (See Section 9.1.2.2c of draft-ietf-idr-bgp4-24.txt.)
Cisco IOS XR Routing Configuration Guide
RC-19
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
If the bgp bestpath med always command is configured, then the MED comparison is always
performed, regardless of neighbor AS in the paths. Otherwise, MED comparison depends on the AS
paths of the two paths being compared, as follows:
a. If a path has no AS path or the AS path starts with an AS_SET, then the path is considered to
be internal, and the MED is compared with other internal paths
b. If the AS path starts with an AS_SEQUENCE, then the neighbor AS is the first AS number in
the sequence, and the MED is compared with other paths that have the same neighbor AS
c. If the AS path contains only confederation segments or starts with confederation segments
followed by an AS_SET, then the MED is not compared with any other path unless the bgp
bestpath med confed command is configured. In that case, the path is considered internal and
the MED is compared with other internal paths.
d. If the AS path starts with confederation segments followed by an AS_SEQUENCE, then the
neighbor AS is the first AS number in the AS_SEQUENCE, and the MED is compared with
other paths that have the same neighbor AS.
Note: if no MED attribute was received with the path, then the MED is considered to be 0 unless the
bgp bestpath med missing-as-worst command is configured. In that case, if no MED attribute was
received, the MED is considered to be the highest possible value.
8. If one path is received from an external peer and the other is received from an internal (or
confederation) peer, the path from the external peer is chosen. (See Section 9.1.2.2d of
draft-ietf-idr-bgp4-24.txt.)
9. If the paths have different IGP metrics to their next hops, the path with the lower IGP metric is
chosen. (See Section 9.1.2.2e of draft-ietf-idr-bgp4-24.txt.)
10. If all path parameters in steps 1 through 10 are the same, then the router IDs are compared. If the
path was received with an originator attribute, then that is used as the router ID to compare;
otherwise, the router ID of the neighbor from which the path was received is used. If the paths have
different router IDs, the path with the lower router ID is chosen. Note: where the originator is used
as the router ID, it is possible to have two paths with the same router ID. It is also possible to have
two BGP sessions with the same peer router, and therefore receive two paths with the same router
ID. (See Section 9.1.2.2f of draft-ietf-idr-bgp4-24.txt.)
11. If the paths have different cluster lengths, the path with the shorter cluster length is selected. If a
path was not received with a cluster list attribute, it is considered to have a cluster length of 0.
12. Finally, the path received from the neighbor with the lower IP address is chosen. Locally generated
paths (for example, redistributed paths) are considered to have a neighbor IP address of 0. (See
Section 9.1.2.2g of draft-ietf-idr-bgp4-24.txt.)
Order of Comparisons
The second part of the BGP best path algorithm implementation determines the order in which the paths
should be compared. The order of comparison is determined as follows:
1. The paths are partitioned into groups such that within each group the MED can be compared among
determine whether MED can be compared between any two paths. Normally, this comparison results
in one group for each neighbor AS. If the bgp bestpath med always command is configured, then
there is just one group containing all the paths.
Cisco IOS XR Routing Configuration Guide
RC-20
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
2. The best path in each group is determined. Determining the best path is achieved by iterating through
all paths in the group and keeping track of the best one seen so far. Each path is compared with the
best-so-far, and if it is better, it becomes the new best-so-far and is compared with the next path in
the group.
3. A set of paths is formed containing the best path selected from each group in step 2. The overall best
path is selected from this set of paths, by iterating through them as in step 2.
Best Path Change Suppression
The third part of the implementation is to determine whether the best path change can be suppressed or
not—whether the new best path should be used, or continue using the existing best path. The existing
best path can continue to be used if the new one is identical to the point at which the best path selection
algorithm becomes arbitrary (if the router-id is the same). Continuing to use the existing best path can
avoid churn in the network.
Note
This suppression behavior does not comply with the IETF Networking Working Group
draft-ietf-idr-bgp4-24.txt document, but is specified in the IETF Networking Working Group
draft-ietf-idr-avoid-transition-00.txt document.
The suppression behavior can be turned off by configuring the bgp bestpath compare-routerid
command. If this command is configured, the new best path is always preferred to the existing one.
Otherwise, the following steps are used to determine whether the best path change can be suppressed:
1. If the existing best path is no longer valid, the change cannot be suppressed.
2. If either the existing or new best paths were received from internal (or confederation) peers or were
locally generated (for example, by redistribution), then the change cannot be suppressed. That is,
suppression is possible only if both paths were received from external peers.
3. If the paths were received from the same peer (the paths would have the same router-id), the change
cannot be suppressed. The router ID is calculated using rules in the “Comparing Pairs of Paths”
4. If the paths have different weights, local preferences, origins, or IGP metrics to their next hops, then
the change cannot be suppressed. Note that all of these values are calculated using the rules in the
5. If the paths have different-length AS paths and the bgp bestpath as-path ignore command is not
configured, then the change cannot be suppressed. Again, the AS path length is calculated using the
6. If the MED of the paths can be compared and the MEDs are different, then the change cannot be
suppressed. The decision as to whether the MEDs can be compared is exactly the same as the rules
7. If all path parameters in steps 1 through 6 do not apply, the change can be suppressed.
Multiprotocol BGP
Multiprotocol BGP is an enhanced BGP that carries routing information for multiple network layer
protocols and IP multicast routes. BGP carries two sets of routes, one set for unicast routing and one set
for multicast routing. The routes associated with multicast routing are used by the Protocol Independent
Multicast (PIM) feature to build data distribution trees.
Cisco IOS XR Routing Configuration Guide
RC-21
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Multiprotocol BGP is useful when you want a link dedicated to multicast traffic, perhaps to limit which
resources are used for which traffic. Multiprotocol BGP allows you to have a unicast routing topology
different from a multicast routing topology providing more control over your network and resources.
In BGP, the only way to perform interdomain multicast routing was to use the BGP infrastructure that
was in place for unicast routing. Perhaps you want all multicast traffic exchanged at one network access
point (NAP). If those routers were not multicast capable, or there were differing policies for which you
wanted multicast traffic to flow, multicast routing could not be supported without multiprotocol BGP.
Note
It is possible to configure BGP peers that exchange both unicast and multicast network layer reachability
information (NLRI), but you cannot connect multiprotocol BGP clouds with a BGP cloud. That is, you
cannot redistribute multiprotocol BGP routes into BGP.
Figure 1 illustrates simple unicast and multicast topologies that are incongruent, and therefore are not
possible without multiprotocol BGP.
Autonomous systems 100, 200, and 300 are each connected to two NAPs that are FDDI rings. One is
used for unicast peering (and therefore the exchange of unicast traffic). The Multicast Friendly
Interconnect (MFI) ring is used for multicast peering (and therefore the exchange of multicast traffic).
Each router is unicast and multicast capable.
Figure 1
Incongruent Unicast and Multicast Routes
FDDI
FDDI
MFI
Unicast
AS 100
AS 200
ISP B
AS 300
ISP A
ISP C
Figure 2 is a topology of unicast-only routers and multicast-only routers. The two routers on the left are
unicast-only routers (that is, they do not support or are not configured to perform multicast routing). The
two routers on the right are multicast-only routers. Routers A and B support both unicast and multicast
routing. The unicast-only and multicast-only routers are connected to a single NAP.
In Figure 2, only unicast traffic can travel from Router A to the unicast routers to Router B and back.
Multicast traffic could not flow on that path, so another routing table is required. Multicast traffic uses
the path from Router A to the multicast routers to Router B and back.
Figure 2 illustrates a multiprotocol BGP environment with a separate unicast route and multicast route
from Router A to Router B. Multiprotocol BGP allows these routes to be incongruent. Both of the
autonomous systems must be configured for internal multiprotocol BGP (IMBGP) in the figure.
Cisco IOS XR Routing Configuration Guide
RC-22
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
A multicast routing protocol, such as PIM, uses the multicast BGP database to perform Reverse Path
Forwarding (RPF) lookups for multicast-capable sources. Thus, packets can be sent and accepted on the
multicast topology but not on the unicast topology.
Figure 2
Multicast BGP Environment
Router B
AS 200
Unicast
router
Multicast
router
IMBGP
NAP
Unicast
router
Multicast
router
IMBGP
AS 100
Unicast route
Multicast route
Router A
Route Dampening
Route dampening is a BGP feature that minimizes the propagation of flapping routes across an
internetwork. A route is considered to be flapping when it is repeatedly available, then unavailable, then
available, then unavailable, and so on.
For example, consider a network with three BGP autonomous systems: autonomous system 1,
autonomous system 2, and autonomous system 3. Suppose the route to network A in autonomous system
1 flaps (it becomes unavailable). Under circumstances without route dampening, the eBGP neighbor of
autonomous system 1 to autonomous system 2 sends a withdraw message to autonomous system 2. The
border router in autonomous system 2, in turn, propagates the withdrawal message to autonomous
system 3. When the route to network A reappears, autonomous system 1 sends an advertisement message
to autonomous system 2, which sends it to autonomous system 3. If the route to network A repeatedly
becomes unavailable, then available, many withdrawal and advertisement messages are sent. Route
flapping is a problem in an internetwork connected to the Internet because a route flap in the Internet
backbone usually involves many routes.
Cisco IOS XR Routing Configuration Guide
RC-23
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Note
No penalty is applied to a BGP peer reset when route dampening is enabled. Although the reset
withdraws the route, no penalty is applied in this instance, even if route flap dampening is enabled.
Minimizing Flapping
The route dampening feature minimizes the flapping problem as follows. Suppose again that the route
to network A flaps. The router in autonomous system 2 (in which route dampening is enabled) assigns
network A a penalty of 1000 and moves it to history state. The router in autonomous system 2 continues
to advertise the status of the route to neighbors. The penalties are cumulative. When the route flaps so
often that the penalty exceeds a configurable suppression limit, the router stops advertising the route to
network A, regardless of how many times it flaps. Thus, the route is dampened.
The penalty placed on network A is decayed until the reuse limit is reached, upon which the route is once
again advertised. At half of the reuse limit, the dampening information for the route to network A is
removed.
BGP Routing Domain Confederation
One way to reduce the iBGP mesh is to divide an autonomous system into multiple subautonomous
systems and group them into a single confederation. To the outside world, the confederation looks like
a single autonomous system. Each autonomous system is fully meshed within itself and has a few
connections to other autonomous systems in the same confederation. Although the peers in different
autonomous systems have eBGP sessions, they exchange routing information as if they were iBGP peers.
Specifically, the next hop, MED, and local preference information is preserved. This feature allows the
you to retain a single IGP for all of the autonomous systems.
BGP Route Reflectors
BGP requires that all iBGP speakers be fully meshed. However, this requirement does not scale well
when there are many iBGP speakers. Instead of configuring a confederation, another way to reduce the
iBGP mesh is to configure a route reflector.
Figure 3 illustrates a simple iBGP configuration with three iBGP speakers (routers A, B, and C). Without
route reflectors, when Router A receives a route from an external neighbor, it must advertise it to both
routers B and C. Routers B and C do not readvertise the iBGP learned route to other iBGP speakers
because the routers do not pass on routes learned from internal neighbors to other internal neighbors,
thus preventing a routing information loop.
Cisco IOS XR Routing Configuration Guide
RC-24
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Figure 3
Three Fully Meshed iBGP Speakers
Fully meshed
autonomous
system
Router C
Routes
Routes not
advertised
Routes
advertised
Router A
Router A
External
BGP
Routes
speaker
Router B
With route reflectors, all iBGP speakers need not be fully meshed because there is a method to pass
learned routes to neighbors. In this model, an iBGP peer is configured to be a route reflector responsible
for passing iBGP learned routes to a set of iBGP neighbors. In Figure 4, Router B is configured as a route
reflector. When the route reflector receives routes advertised from Router A, it advertises them to Router
C, and vice versa. This scheme eliminates the need for the iBGP session between routers A and C.
Figure 4
Simple BGP Model with a Route Reflector
Partially meshed autonomous system
Routes
Router A
Router C
Router A
External
BGP
speaker
Routes
Reflected
routes
Router B
Route
reflector
The internal peers of the route reflector are divided into two groups: client peers and all other routers in
the autonomous system (nonclient peers). A route reflector reflects routes between these two groups.
The route reflector and its client peers form a cluster. The nonclient peers must be fully meshed with
each other, but the client peers need not be fully meshed. The clients in the cluster do not communicate
with iBGP speakers outside their cluster.
Cisco IOS XR Routing Configuration Guide
RC-25
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
Figure 5
More Complex BGP Route Reflector Model
Partially meshed
autonomous system
Nonclient
Router G
Route reflector
Router A
Nonclient
Nonclient
Routes
advertised
Router F
Router A
External
BGP
speaker
Cluster
Router E
Router B
Client
Router C
Client
Router D
Client
Figure 5 illustrates a more complex route reflector scheme. Router A is the route reflector in a cluster
with routers B, C, and D. Routers E, F, and G are fully meshed, nonclient routers.
When the route reflector receives an advertised route, depending on the neighbor, it takes the following
actions:
•
•
•
A route from an external BGP speaker is advertised to all clients and nonclient peers.
A route from a nonclient peer is advertised to all clients.
A route from a client is advertised to all clients and nonclient peers. Hence, the clients need not be
fully meshed.
Along with route reflector-aware BGP speakers, it is possible to have BGP speakers that do not
understand the concept of route reflectors. They can be members of either client or nonclient groups,
allowing an easy and gradual migration from the old BGP model to the route reflector model. Initially,
you could create a single cluster with a route reflector and a few clients. All other iBGP speakers could
be nonclient peers to the route reflector and then more clusters could be created gradually.
An autonomous system can have multiple route reflectors. A route reflector treats other route reflectors
just like other iBGP speakers. A route reflector can be configured to have other route reflectors in a client
group or nonclient group. In a simple configuration, the backbone could be divided into many clusters.
Each route reflector would be configured with other route reflectors as nonclient peers (thus, all route
reflectors are fully meshed). The clients are configured to maintain iBGP sessions with only the route
reflector in their cluster.
Usually, a cluster of clients has a single route reflector. In that case, the cluster is identified by the router
ID of the route reflector. To increase redundancy and avoid a single point of failure, a cluster might have
more than one route reflector. In this case, all route reflectors in the cluster must be configured with the
Cisco IOS XR Routing Configuration Guide
RC-26
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
cluster ID so that a route reflector can recognize updates from route reflectors in the same cluster. All
route reflectors serving a cluster should be fully meshed and all of them should have identical sets of
client and nonclient peers.
By default, the clients of a route reflector are not required to be fully meshed and the routes from a client
are reflected to other clients. However, if the clients are fully meshed, the route reflector need not reflect
routes to clients.
As the iBGP learned routes are reflected, routing information may loop. The route reflector model has
the following mechanisms to avoid routing loops:
•
Originator ID is an optional, nontransitive BGP attribute. It is a 4-byte attributed created by a route
reflector. The attribute carries the router ID of the originator of the route in the local autonomous
system. Therefore, if a misconfiguration causes routing information to come back to the originator,
the information is ignored.
•
Cluster-list is an optional, nontransitive BGP attribute. It is a sequence of cluster IDs that the route
has passed. When a route reflector reflects a route from its clients to nonclient peers, and vice versa,
it appends the local cluster ID to the cluster-list. If the cluster-list is empty, a new cluster-list is
created. Using this attribute, a route reflector can identify if routing information is looped back to
the same cluster due to misconfiguration. If the local cluster ID is found in the cluster-list, the
advertisement is ignored.
Default Address Family for show Commands
Most of the show commands require the address family (afi) and subsequent address family (safi) to be
specified as arguments. The Cisco IOS XR software parser provides the ability to set the afi and safi so
it is not necessary to specify them while executing a show command. The parser commands are:
•
•
set default-afi {ipv4 | ipv6 | all}
set default-safi {unicast | multicast | all}
The parser automatically sets the default afi value to ipv4 and default safi value to unicast. It is
necessary to use only the parser commands to change the default afi value from ipv4 or default safi value
from unicast. Any afi or safi keyword specified in a show command overrides the values set using the
parser commands. Use the following command to check the currently set value of the afi and safi:
•
show default-afi-safi
How to Implement BGP on Cisco IOS XR Software
This section contains instructions for the following tasks:
•
•
•
•
•
•
•
•
Enabling BGP Routing, page RC-28 (required)
Logging Neighbor Changes, page RC-34 (optional)
Adjusting BGP Timers, page RC-34 (optional)
Configuring BGP Weights, page RC-38 (optional)
Cisco IOS XR Routing Configuration Guide
RC-27
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Indicating BGP Backdoor Routes, page RC-41 (optional)
Configuring Aggregate Addresses, page RC-43 (optional)
Configuring BGP Route Dampening, page RC-48 (optional)
Configuring a BGP Neighbor Group, page RC-55 (optional)
Configuring a BGP Neighbor, page RC-58 (required)
Disabling a BGP Neighbor, page RC-69 (optional)
Monitoring BGP Update Groups, page RC-75 (optional)
Enabling BGP Routing
Perform this task to enable BGP routing and establish a BGP routing process. Configuring BGP
neighbors is included as part of enabling BGP routing.
Note
At least one neighbor and at least one address family must be configured to enable BGP routing. At least
one neighbor with both a remote AS and an address family must be configured globally using the
address family and remote as commands.
Prerequisites
BGP must be able to obtain a router identifier (for example, a configured loopback address). At least,
one address family must be configured in the BGP router configuration and the same address family must
also be configured under the neighbor.
Cisco IOS XR Routing Configuration Guide
RC-28
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Restrictions
If the neighbor is configured as an external BGP (eBGP) peer, you must configure an inbound and
outbound route policy on the neighbor using the route-policy command.
SUMMARY STEPS
1. configure
2. route-policy name
3. end-policy
4. end
or
commit
5. configure
6. router bgp autonomous-system-number
7. bgp router-id {ip-address | interface-type interface-instance}
8. neighbor ip-address
9. remote-as autonomous-system-number
10. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
11. route-policy route-policy-name {in | out}
12. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
route-policy name
Step 2
(Optional) Defines a route policy named drop-as-1234 and
enters route policy configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# route-policy
drop-as-1234
RP/0/RP0/CPU0:router(config-rpl)# if as-path
passes-through '1234' then
RP/0/RP0/CPU0:router(config-rpl)# apply
check-communities
RP/0/RP0/CPU0:router(config-rpl)# else
RP/0/RP0/CPU0:router(config-rpl)# pass
RP/0/RP0/CPU0:router(config-rpl)# endif
Cisco IOS XR Routing Configuration Guide
RC-29
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
end-policy
Step 3
(Optional) Ends the definition of a route policy and exits
route policy configuration mode.
Example:
RP/0/RP0/CPU0:router(config-rpl)# end-policy
end
Step 4
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
configure
Step 5
Step 6
Step 7
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
bgp router-id {ip-address | interface-type
interface-instance}
Configures the local router with a router id of
192.168.70.24.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp router-id
192.168.70.24
neighbor ip-address
Step 8
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
Cisco IOS XR Routing Configuration Guide
RC-30
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
remote-as autonomous-system-number
Step 9
Creates a neighbor and assigns it a remote autonomous
system number of 2002.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as
2002
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Step 10
Enters global address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
route-policy route-policy-name {in | out}
Step 11
Step 12
(Optional) Applies the In-Ipv4 policy to inbound IPv4
unicast routes.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)#
route-policy In-Ipv4 in
end
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring a Routing Domain Confederation for BGP
Perform this task to configure the routing domain confederation for BGP. This includes specifying a
confederation identifier and autonomous systems that belong to the confederation.
Configuring a routing domain confederation reduces the internal BGP (iBGP) mesh by dividing an
autonomous system into multiple autonomous systems and grouping them into a single confederation.
Each autonomous system is fully meshed within itself and has a few connections to another autonomous
system in the same confederation. The confederation maintains the next hop and local preference
information, and that allows you to retain a single Interior Gateway Protocol (IGP) for all autonomous
systems. To the outside world, the confederation looks like a single autonomous system.
Cisco IOS XR Routing Configuration Guide
RC-31
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. bgp confederation identifier autonomous-system-number
4. bgp confederation peers autonomous-system-number
5. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Step 3
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
bgp confederation identifier
autonomous-system-number
Specifies a BGP confederation identifier of 5.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp
confederation identifier 5
Cisco IOS XR Routing Configuration Guide
RC-32
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
bgp confederation peers
autonomous-system-number
Step 4
Specifies that the BGP autonomous systems 1091, 1092,
1093, 1094, 1095, and 1096 belong to BGP confederation
identifier 5.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp
confederation peers 1091
RP/0/RP0/CPU0:router(config-bgp)# bgp
confederation peers 1092
RP/0/RP0/CPU0:router(config-bgp)# bgp
confederation peers 1093
RP/0/RP0/CPU0:router(config-bgp)# bgp
confederation peers 1094
RP/0/RP0/CPU0:router(config-bgp)# bgp
confederation peers 1095
RP/0/RP0/CPU0:router(config-bgp)# bgp
confederation peers 1096
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Resetting eBGP Session Immediately Upon Link Failure
Immediately resetting BGP sessions of any directly adjacent external peers if the link used to reach them
goes down is enabled by default. Use the bgp fast-external-fallover disable command to disable
automatic resetting. The bgp fast-external-fallover disable command can also be used to turn the
automatic reset back on.
Cisco IOS XR Routing Configuration Guide
RC-33
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Logging Neighbor Changes
Logging neighbor changes is enabled by default. Use the log neighbor changes disable command to
turn off logging. The log neighbor changes disable command can also be used to turn logging back on
if it has been disabled.
Adjusting BGP Timers
Perform this task to set the timers for BGP neighbors.
BGP uses certain timers to control periodic activities, such as the sending of keepalive messages and the
interval after which a neighbor is assumed to be down if no messages are received from the neighbor
during the interval. The values set using the timers bgp command can be overridden on particular
neighbors using the timers command in the neighbor configuration mode.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. timers bgp keepalive hold-time
4. neighbor ip-address
5. timers keepalive hold-time
6. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Step 3
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
timers bgp keepalive hold-time
Sets a default keepalive time of 30 seconds and a default
hold time of 90 seconds for all neighbors.
Example:
RP/0/RP0/CPU0:router(config-bgp)# timers bgp 30
90
Cisco IOS XR Routing Configuration Guide
RC-34
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
neighbor ip-address
Step 4
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
timers keepalive hold-time
Step 5
Step 6
(Optional) Sets the keepalive timer to 60 seconds and the
hold-time timer to 220 seconds for BGP neighbor
172.168.40.24.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# timers 60
220
end
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Changing the BGP Default Local Preference Value
Perform this task to set the default local preference value for BGP paths.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. bgp default local-preference value
4. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-35
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
bgp default local-preference value
Step 3
Sets the default local preference value from the default of
100 to 200, making it a more preferable path.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp default
local-preference 200
end
Step 4
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring the MED Metric for BGP
Perform this task to set the multi exit discriminator (MED) to advertise to peers for routes that do not
already have a metric set (routes that were received with no MED attribute).
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. default-metric value
Cisco IOS XR Routing Configuration Guide
RC-36
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
4. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
default-metric value
Step 3
Sets the default metric to 10, which is used to set the MED
to advertise to peers for routes that do not already have a
metric set (routes that were received with no MED
attribute).
Example:
RP/0/RP0/CPU0:router(config-bgp)# default
metric 10
end
Step 4
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-37
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Configuring BGP Weights
Perform this task to assign a weight to routes received from a neighbor. A weight is a number that you
can assign to a path so that you can control the best path selection process. If you have particular
neighbors that you want to prefer for most of your traffic, you can use the weight command to assign a
higher weight to all routes learned from that neighbor.
Restrictions
The clear bgp command must be used for the newly configured weight to take effect.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. neighbor ip-address
4. remote-as autonomous-system-number
5. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
6. weight weight-value
7. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Step 3
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
neighbor ip-address
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
remote-as autonomous-system-number
Step 4
Creates a neighbor and assigns it a remote autonomous
system number of 2002.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as
2002
Cisco IOS XR Routing Configuration Guide
RC-38
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Step 5
Enters neighbor address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
weight weight-value
Step 6
Step 7
Assigns a weight of 41150 to all IPv4 unicast routes learned
through 172.168.40.24.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# weight
41150
end
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Tuning the BGP Best Path Calculation
Perform this task to change the default BGP best path calculation behavior.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. bgp bestpath med missing-as-worst
4. bgp bestpath med always
5. bgp bestpath med confed
6. bgp bestpath as-path ignore
7. bgp bestpath compare-routerid
Cisco IOS XR Routing Configuration Guide
RC-39
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
8. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
bgp bestpath med missing-as-worst
Step 3
Directs the BGP software to consider a missing MED
attribute in a path as having a value of infinity, making this
path the least desirable path.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath
med missing-as-worst
bgp bestpath med always
Step 4
Configures the BGP speaker in autonomous system 120 to
compare MEDs among alternative paths, regardless of the
autonomous system from which the paths are received.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath
med always
bgp bestpath med confed
Step 5
Enables BGP software to compare MED values for paths
learned from confederation peers.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath
med confed
bgp bestpath as-path ignore
Step 6
Configures the BGP software to ignore the autonomous
system length when performing best path selection.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath
as-path ignore
Cisco IOS XR Routing Configuration Guide
RC-40
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
bgp bestpath compare-routerid
Step 7
Configure the BGP speaker in autonomous system 120 to
compare the router IDs of similar paths.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath
compare-routerid
end
Step 8
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Indicating BGP Backdoor Routes
Perform this task to set the administrative distance on an external Border Gateway Protocol (eBGP) route
to that of a locally sourced BGP route, causing it to be less preferred than an Interior Gateway Protocol
(IGP) route.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
4. network {ip-address /prefix-length | ip-address mask} backdoor
5. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-41
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Step 3
Enters global address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp)#
address-family ipv4 unicast
network {ip-address /prefix-length | ip-address
mask} backdoor
Step 4
Configures the local router to originate and advertise the
IPv4 unicast network 172.20.0.0/16.
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# network
172.20.0.0/16
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-42
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Configuring Aggregate Addresses
Perform this task to create aggregate entries in a BGP routing table.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
4. aggregate-address address/mask-length [as-set] [as-confed-set] [summary-only] [route-policy
route-policy-name]
5. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Step 3
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Enters global address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp)#
address-family ipv4 unicast
Cisco IOS XR Routing Configuration Guide
RC-43
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
aggregate-address address/mask-length [as-set]
[as-confed-set] [summary-only] [route-policy
route-policy-name]
Step 4
Creates an aggregate address. The path advertised for this
route is an autonomous system set consisting of all elements
contained in all paths that are being summarized.
•
The as-set keyword generates autonomous system set
path information and community information from
contributing paths.
Example:
RP/0/RP0/CPU0:router(config-bgp-af)#
aggregate-address 10.0.0.0/8 as-set
•
The as-confed-set keyword generates autonomous
system confederation set path information from
contributing paths.
•
•
The summary-only keyword filters all more specific
routes from updates.
The route-policy route-policy-name keyword and
argument specify the route policy used to set the
attributes of the aggregate route.
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Redistributing iBGP Routes into IGP
Perform this task to redistribute iBGP routes into an Interior Gateway Protocol (IGP), such as
Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF).
Note
Use of the bgp redistribute-internal command requires the clear route * command to be issued to
reinstall all BGP routes into the IP routing table.
Caution
Redistributing iBGP routes into IGPs may cause routing loops to form within an autonomous system.
Use this command with caution.
Cisco IOS XR Routing Configuration Guide
RC-44
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. bgp redistribute-internal
4. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Step 3
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
bgp redistribute-internal
Allows the redistribution of iBGP routes into an IGP, such
as IS-IS or OSPF.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp
redistribute-internal
end
Step 4
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-45
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Redistributing Prefixes into Multiprotocol BGP
Perform this task to redistribute prefixes from another protocol into multiprotocol BGP.
Redistribution is the process of injecting prefixes from one routing protocol into another routing
protocol. This task shows how to inject prefixes from another routing protocol into multiprotocol BGP.
Specifically, prefixes that are redistributed into multiprotocol BGP using the redistribute command are
injected into the unicast database, the multicast database, or both.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
4. redistribute connected [metric metric-value] [route-policy route-policy-name]
or
redistribute isis process-id [level {1 | 1-inter-area | 2}] [metric metric-value] [route-policy
route-policy-name]
or
redistribute ospf process-id [match {external [1 | 2] | internal | nssa-external [1 | 2]]} [metric
metric-value] [route-policy route-policy-name]
or
redistribute ospfv3 process-id [match {external [1 | 2] | internal | nssa-external [1 | 2]]} [metric
metric-value] [route-policy route-policy-name]
or
redistribute static [metric metric-value] [route-policy route-policy-name]
5. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Step 3
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Enters global address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp)#
address-family ipv4 unicast
Cisco IOS XR Routing Configuration Guide
RC-46
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
redistribute connected [metric metric-value]
[route-policy route-policy-name]
Step 4
Causes IPv4 unicast OSPF routes from OSPF instance 110
to be redistributed into BGP.
or
redistribute isis process-id [level {1 |
1-inter-area | 2}] [metric metric-value]
[route-policy route-policy-name]
or
redistribute ospf process-id [match {external
[1 | 2] | internal | nssa-external [1 | 2]]}
[metric metric-value] [route-policy
route-policy-name]
or
redistribute ospfv3 process-id [match {external
[1 | 2] | internal | nssa-external [1 | 2]]}
[metric metric-value] [route-policy
route-policy-name]
or
redistribute static [metric metric-value]
[route-policy route-policy-name]
Example:
RP/0/RP0/CPU0:router(config-bgp-af)#
redistribute ospf 110
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-47
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Configuring BGP Route Dampening
Perform this task to configure and monitor BGP route dampening.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
4. bgp dampening [half-life [reuse suppress max-suppress-time] | route-policy route-policy-name]
5. end
or
commit
6. show bgp [ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}]
flap-statistics
7. show bgp [ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}]
flap-statistics regexp regular-expression
8. show bgp [ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}]
flap-statistics route-policy route-policy-name
9. show bgp [ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}]
flap-statistics {ip-address [{mask | /prefix-length}
10. show bgp [ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}]
flap-statistics {ip-address [{mask | /prefix-length} [longer-prefixes]]
11. clear bgp {ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}}
flap-statistics
12. clear bgp {ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}}
flap-statistics regexp regular-expression
13. clear bgp {ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}}
flap-statistics route-policy route-policy-name
14. clear bgp {ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}}
flap-statistics network/mask-length
15. clear bgp {ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}}
flap-statistics ip-address
16. show bgp [ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}]
dampened-paths
17. clear bgp {ipv4 {unicast | multicast | all} | ipv6 {unicast | all} | all {unicast | multicast | all}}
dampening [ip-address/mask-length]
Cisco IOS XR Routing Configuration Guide
RC-48
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Step 3
Enters global address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp)#
address-family ipv4 unicast
bgp dampening [half-life [reuse suppress
max-suppress-time] | route-policy
route-policy-name]
Step 4
Configures BGP dampening for the IPv4 address family.
The half-life argument is set to 30, the reuse argument is set
to 1500, the suppress argument is set to 10000, and the
max-suppress-time argument is set to 120.
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# bgp
dampening 30 1500 10000 120
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-49
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
show bgp [ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}] flap-statistics
Step 6
Displays BGP flap statistics for all paths.
Example:
RP/0/RP0/CPU0:router# show bgp flap statistics
show bgp [ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}] flap-statistics regexp
Step 7
Step 8
Step 9
Step 10
Step 11
Displays BGP flap statistics for all paths that match the
regular expression _1$.
regular-expression
Example:
RP/0/RP0/CPU0:router# show bgp flap-statistics
regexp _1$
show bgp [ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}] flap-statistics route-policy
route-policy-name
Displays BGP flap statistics for route policy policy_A.
Example:
RP/0/RP0/CPU0:router(config)# show bgp
flap-statistics route-policy policy_A
show bgp [ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}] flap-statistics {ip-address [{mask |
/prefix-length}
Displays BGP flap statistics for neighbor 172.20.1.1.
Example:
RP/0/RP0/CPU0:router# show bgp flap-statistics
172.20.1.1
show bgp [ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}] flap-statistics {ip-address [{mask |
/prefix-length} [longer-prefixes]
Displays BGP flap statistics for more specific entries for
neighbor 172.20.1.1.
Example:
RP/0/RP0/CPU0:router# show bgp flap-statistics
172.20.1.1 longer-prefixes
clear bgp {ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}} flap-statistics
Clears BGP flap statistics for all routes.
Example:
RP/0/RP0/CPU0:router# clear bgp all all
flap-statistics
Cisco IOS XR Routing Configuration Guide
RC-50
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
clear bgp {ipv4 {unicast | multicast | all} |
Step 12
Clears BGP flap statistics for all paths that match the
regular expression _1$.
ipv6 {unicast | all} | all {unicast | multicast
| all}} flap-statistics regexp
regular-expression
Example:
RP/0/RP0/CPU0:router# clear bgp ipv4 unicast
flap-statistics _1$
clear bgp {ipv4 {unicast | multicast | all} |
Step 13
Clears BGP flap statistics for route policy policy_A.
ipv6 {unicast | all} | all {unicast | multicast
| all}} flap-statistics route-policy
route-policy-nane
Example:
RP/0/RP0/CPU0:router# clear bgp ipv4 unicast
flap-statistics route-policy policy_A
clear bgp {ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}} flap-statistics network/mask-length
Step 14
Clears BGP flap statistics for network 192.168.40.0/24.
Example:
RP/0/RP0/CPU0:router# clear bgp ipv4 unicast
flap-statistics 192.168.40.0/24
clear bgp {ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}} flap-statistics ip-address
Step 15
Clears BGP flap statistics for routes received from this
neighbor 172.20.1.1.
Example:
RP/0/RP0/CPU0:router# clear bgp ipv4 unicast
flap-statistics 172.20.1.1
show bgp [ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}] dampened-paths
Step 16
Displays the dampened routes, including the time
remaining before they are unsuppressed.
Example:
RP/0/RP0/CPU0:router# show bgp dampened paths
clear bgp {ipv4 {unicast | multicast | all} |
ipv6 {unicast | all} | all {unicast | multicast
| all}} dampening [ip-address/mask-length]
Step 17
Clears route dampening information and unsuppresses the
suppressed routes.
Example:
RP/0/RP0/CPU0:router# clear bgp dampening
Cisco IOS XR Routing Configuration Guide
RC-51
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Applying Policy When Updating the Routing Table
Perform this task to apply a routing policy to routes being installed into the routing table.
Prerequisites
See the Implementing Routing Policy on Cisco IOS XR Software module of the Cisco IOS XR Routing
Configuration Guide for a list of the supported attributes and operations that are valid for table policy
filtering.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
4. table-policy policy-name
5. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Step 3
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Enters global address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp)#
address-family ipv4 unicast
Cisco IOS XR Routing Configuration Guide
RC-52
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
table-policy policy-name
Step 4
Applies the tbl-plcy-A policy to IPv4 unicast routes being
installed into the routing table.
Example:
RP/0/RP0/CPU0:router(config-bgp-af)#
table-policy tbl-plcy-A
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Setting BGP Administrative Distance
Perform this task to specify the use of administrative distances that can be used to prefer one class of
route over another.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
4. distance bgp external-distance internal-distance local-distance
5. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-53
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Step 3
Enters global address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp)#
address-family ipv4 unicast
distance bgp external-distance
internal-distance local-distance
Step 4
Sets the external, internal, and local administrative
distances to prefer one class of routes over another. The
higher the value, the lower the trust rating. The
external-distance argument is set to 20, the
internal-distance argument is set to 20, and the
local-distance argument is set to 200.
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# distance
bgp 20 20 200
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-54
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Configuring a BGP Neighbor Group
Perform this task to configure BGP neighbor groups and apply the neighbor group configuration to a
neighbor.
After a neighbor group is configured, each neighbor can inherit the configuration through the use
command. If a neighbor is configured to use a neighbor group, the neighbor (by default) inherits the
entire configuration of the neighbor group, which includes the address family-independent and address
family-dependent configurations. The inherited configuration can be overridden if you directly
configure commands for the neighbor or configure session groups or address family groups through the
use command.
From neighbor group configuration mode, you can configure address family-independent parameters for
the neighbor group. Use the address-family command when in the neighbor group configuration mode.
After specifying the neighbor group name using the neighbor group command, you can assign options
to the neighbor group.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. neighbor-group name
4. remote-as autonomous-system-number
5. advertisement-interval seconds
6. description text
7. dmz-link-bandwidth
8. ebgp-multihop [ttl-value]
9. local-as autonomous-system-number
10. password {clear | encrypted} password
11. password-disable
12. receive-buffer-size socket-size [bgp-size]
13. send-buffer-size socket-size [bgp-size]
14. timers keepalive hold-time
15. ttl-security
16. update-source interface-type interface-number
17. exit
18. neighbor ip-address
19. use neighbor-group group-name
20. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-55
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
neighbor-group name
Step 3
Places the router in neighbor group configuration mode.
Example:
RP/0/RP0/CPU0:router(config-bgp)#
neighbor-group nbr-grp-A
remote-as autonomous-system-number
Step 4
Creates a neighbor and assigns it a remote autonomous
system number of 2002.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
remote-as 2002
advertisement-interval seconds
Step 5
(Optional) Sets the minimum time between sending BGP
routing updates to 10 seconds.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
advertisement-interval 10
description text
Step 6
(Optional) Configures the description “Neighbor on BGP
120” for neighbor group nbr-grp-A.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
description Neighbor on BGP 120
dmz-link-bandwidth
Step 7
(Optional) Advertises the bandwidth of links on router bgp
120.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
dmz-link-bandwidth
ebgp-multihop [ttl-value]
Step 8
(Optional) Allows a BGP connection to neighbor group
nbr-grp-A.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
ebgp-multihop
local-as autonomous-system-number
Step 9
(Optional) Specifies that BGP use autonomous system 30
for the purpose of peering with neighbor group nbr-grp-A.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
local-as 30
Cisco IOS XR Routing Configuration Guide
RC-56
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
password {clear | encrypted} password
Step 10
(Optional) Configures neighbor group nbr-grp-A to use
MD5 authentication with the password pswd123.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
password clear pswd123
password-disable
Step 11
(Optional) Overrides any inherited password configuration
from the neighbor group.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
password-disable
receive-buffer-size socket-size [bgp-size]
Step 12
(Optional) Sets the receive buffer sizes for neighbor group
nbr-grp-A to 45215 bytes for the socket buffer and 5156
bytes for the BGP buffer.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
receive-buffer-size 45215 5156
send-buffer-size socket-size [bgp-size]
Step 13
(Optional) Sets the send buffer sizes for neighbor group
nbr-grp-A to 8741 bytes for the socket buffer and 8741
bytes for the BGP buffer.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
send-buffer-size 8741 8741
timers keepalive hold-time
Step 14
(Optional) Sets the keepalive timer to 60 seconds and the
hold-time timer to 220 seconds for the BGP neighbor group
nbr-grp-A.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# timers
60 220
ttl-security
Step 15
(Optional) Enables TTL security for eBGP neighbor group
nbr-grp-A.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
ttl-security
update-source interface-type interface-number
Step 16
(Optional) Configures the router to use the IP address from
the Loopback0 interface when trying to open a session with
neighbor group nbr-grp-A.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)#
update-source Loopback0
exit
Step 17
Exits the current configuration mode.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit
neighbor ip-address
Step 18
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
Cisco IOS XR Routing Configuration Guide
RC-57
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
use neighbor-group group-name
Step 19
(Optional) Specifies that BGP neighbor 172.168.40.24
inherit configuration from neighbor group nbr-grp-A.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# use
neighbor-group nbr-grp-A
end
Step 20
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring a BGP Neighbor
Perform this task to configure BGP neighbors.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. neighbor ip-address
4. remote-as autonomous-system-number
5. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
6. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-58
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
neighbor ip-address
Step 3
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
remote-as autonomous-system-number
Step 4
Creates a neighbor and assigns it a remote autonomous
system number of 2002.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as
2002
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Step 5
Enters neighbor address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
end
Step 6
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-59
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Configuring a Route Reflector for BGP
Perform this task to configure a route reflector for BGP.
All the neighbors configured with the route-reflector-client command are members of the client group,
and the remaining iBGP peers are members of the nonclient group for the local route reflector.
Together, a route reflector and its clients form a cluster. A cluster of clients usually has a single route
reflector. In such instances, the cluster is identified by the software as the router ID of the route reflector.
To increase redundancy and avoid a single point of failure in the network, a cluster can have more than
one route reflector. If it does, all route reflectors in the cluster must be configured with the same 4-byte
cluster ID so that a route reflector can recognize updates from route reflectors in the same cluster. The
bgp cluster-id command is used to configure the cluster ID when the cluster has more than one route
reflector.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. bgp cluster-id cluster-id
4. neighbor ip-address
5. remote-as autonomous-system-number
6. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
7. route-reflector-client
8. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Step 3
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
bgp cluster-id cluster-id
Configures the local router as one of the route reflectors
serving the cluster. It is configured with the cluster ID of
192.168.70.1 to identify the cluster.
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp
cluster-id 192.168.70.1
Cisco IOS XR Routing Configuration Guide
RC-60
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
neighbor ip-address
Step 4
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
remote-as autonomous-system-number
Step 5
Step 6
Creates a neighbor and assigns it a remote autonomous
system number of 2002.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as
2002
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Enters neighbor address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
route-reflector-client
Step 7
Step 8
Configures the router as a BGP route reflector and
configures the neighbor 172.168.40.24 as its client.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)#
route-reflector-client
end
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-61
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Configuring BGP Route Filtering by Route Policy
Perform this task to configure BGP routing filtering by route policy.
Prerequisites
See the Implementing Routing Policy on Cisco IOS XR Software module of the Cisco IOS XR Routing
Configuration Guide for a list of the supported attributes and operations that are valid for inbound and
outbound neighbor policy filtering.
SUMMARY STEPS
1. configure
2. route-policy name
3. end-policy
4. router bgp autonomous-system-number
5. neighbor ip-address
6. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
7. route-policy route-policy-name {in | out}
8. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
route-policy name
Step 2
(Optional) Defines a route policy named drop-as-1234 and
enters route policy configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# route-policy
drop-as-1234
RP/0/RP0/CPU0:router(config-rpl)# if as-path
passes-through '1234' then
RP/0/RP0/CPU0:router(config-rpl)# apply
check-communities
RP/0/RP0/CPU0:router(config-rpl)# else
RP/0/RP0/CPU0:router(config-rpl)# pass
RP/0/RP0/CPU0:router(config-rpl)# endif
end-policy
Step 3
(Optional) Ends the definition of a route policy and exits
route policy configuration mode.
Example:
RP/0/RP0/CPU0:router(config-rpl)# end-policy
Cisco IOS XR Routing Configuration Guide
RC-62
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
router bgp autonomous-system-number
Step 4
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
neighbor ip-address
Step 5
Step 6
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Enters neighbor address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
route-policy route-policy-name {in | out}
Step 7
Step 8
Applies the In-Ipv4 policy to inbound IPv4 unicast routes.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)#
route-policy In-Ipv4 in
end
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-63
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Disabling Next Hop Processing on BGP Updates
Perform this task to disable next hop calculation for a neighbor and insert your own address in the next
hop field of BGP updates. Disabling the calculation of the best next hop to use when advertising a route
causes all routes to be advertised with the network device as the next hop.
Note
Next hop processing can be disabled for address family group, neighbor group, or neighbor address
family.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. neighbor ip-address
4. remote-as autonomous-system-number
5. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
6. next-hop-self
7. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Step 3
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
neighbor ip-address
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
remote-as autonomous-system-number
Step 4
Creates a neighbor and assigns it a remote autonomous
system number of 2002.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as
2002
Cisco IOS XR Routing Configuration Guide
RC-64
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Step 5
Enters neighbor address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
next-hop-self
Step 6
Step 7
Sets the next hop attribute for all IPv4 unicast routes
advertised to neighbor 172.168.40.24 to the address of the
local router. Disabling the calculation of the best next hop
to use when advertising a route causes all routes to be
advertised with the local network device as the next hop.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)#
next-hop-self
end
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring BGP Community and Extended-Community Filtering
Perform this task to specify that community attributes should be sent to an eBGP neighbor.
Perform this task to specify that community/extended-community attributes should be sent to an eBGP
neighbor. These attributes are not sent to an eBGP neighbor by default. By contrast, they are always sent
to iBGP neighbors. This section provides examples on how to enable sending community attributes. The
send-community-ebgp keyword can be replaced by the send-extended-community-ebgp keyword to
enable sending extended-communities.
Note
If the send-community-ebgp command is configured for a neighbor group or address family group, all
neighbors using the group inherit the configuration. Configuring the command specifically for a
neighbor overrides inherited values.
Cisco IOS XR Routing Configuration Guide
RC-65
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. neighbor ip-address
4. remote-as autonomous-system-number
5. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
6. send-community-ebgp
7. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Step 3
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
neighbor ip-address
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
remote-as autonomous-system-number
Step 4
Step 5
Creates a neighbor and assigns it a remote autonomous
system number of 2002.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as
2002
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Enters neighbor address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
Cisco IOS XR Routing Configuration Guide
RC-66
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
send-community-ebgp
Step 6
Specifies that the router send community attributes (which
are disabled by default for eBGP neighbors) to eBGP
neighbor 172.168.40.24 for IPv4 multicast routes.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)#
send-community-ebgp
end
Step 7
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring Software to Store Updates from a Neighbor
Perform this task to configure the software to store updates received from a neighbor.
The soft-reconfiguration inbound command causes a route refresh request to be sent to the neighbor if
the neighbor is route refresh capable. If the neighbor is not route refresh capable, the neighbor must be
reset to relearn received routes using the clear bgp soft command. See the “Resetting Neighbors Using
Note
Storing updates from a neighbor works only if either the neighbor is route refresh capable or if the
soft-reconfiguration inbound command is configured. Even if the neighbor is route refresh capable and
the soft-reconfiguration inbound command is configured, the original routes are not stored unless the
always option is used with the command. The original routes can be easily retrieved with a route refresh
request. Route refresh sends a request to the peer to resend its routing information. The
soft-reconfiguration inbound command stores all paths received from the peer in an unmodified form
and refers to these stored paths during the clear. Soft reconfiguration is memory intensive.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. neighbor ip-address
Cisco IOS XR Routing Configuration Guide
RC-67
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
4. address-family {ipv4 unicast | ipv4 multicast | ipv6 unicast | ipv6 multicast}
5. soft-reconfiguration inbound always
6. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Step 3
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
neighbor ip-address
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
address-family {ipv4 unicast | ipv4 multicast |
ipv6 unicast | ipv6 multicast}
Step 4
Enters neighbor address family configuration mode for the
IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
Cisco IOS XR Routing Configuration Guide
RC-68
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
soft-reconfiguration inbound always
Step 5
Configures the software to store updates received from
neighbor 172.168.40.24. Soft reconfiguration inbound
causes the software to store the original unmodified route in
addition to a route that is modified or filtered. This allows a
“soft clear” to be performed after the inbound policy is
changed.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)#
soft-reconfiguration inbound always
end
Step 6
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Disabling a BGP Neighbor
Perform this task to administratively shut down a neighbor without removing the configuration.
SUMMARY STEPS
1. configure
2. router bgp autonomous-system-number
3. neighbor ip-address
4. shutdown
5. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-69
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp autonomous-system-number
Step 2
Enters BGP configuration mode allowing you to configure
the BGP routing process.
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
neighbor ip-address
Step 3
Places the router in neighbor configuration mode for BGP
routing and configures the neighbor IP address
172.168.40.24 as a BGP peer.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
172.168.40.24
shutdown
Step 4
Disables all active sessions for neighbor 172.168.40.24.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# shutdown
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-70
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Resetting Neighbors Using BGP Dynamic Inbound Soft Reset
Perform this task to trigger an inbound soft reset of the specified address families for the specified group or
neighbors.
Resetting neighbors is useful if you change the inbound policy for the neighbors or any other
configuration that affects the sending or receiving of routing updates. If an inbound soft reset is
triggered, BGP sends a REFRESH request to the neighbor if the neighbor has advertised the
ROUTE_REFRESH capability. To determine whether the neighbor has advertised the
ROUTE_REFRESH capability, use the show bgp neighbors command.
SUMMARY STEPS
1. show bgp neighbors
2. clear bgp {ipv4 | ipv6 | all} {unicast | multicast | all} {* | ip-address | as-number | external} soft in
DETAILED STEPS
Command or Action
Purpose
show bgp neighbors
Step 1
Step 2
Verifies that received route refresh capability from the
neighbor is enabled.
Example:
RP/0/RP0/CPU0:router# show bgp neighbors
clear bgp {ipv4 | ipv6 | all} {unicast |
multicast | all} {* | ip-address | as-number |
external} soft in
Soft resets a BGP neighbor.
•
•
The * keyword resets all BGP neighbors.
The ip-address argument specifies the address of the
neighbor to be reset.
Example:
RP/0/RP0/CPU0:router# clear bgp ipv4 unicast
10.0.0.1 soft in
•
•
The as-number argument specifies that all neighbors
that match the autonomous system number be reset.
The external keyword specifies that all external
neighbors are reset.
Resetting Neighbors Using BGP Outbound Soft Reset
Perform this task to trigger an outbound soft reset of the specified address families for the specified group
or neighbors.
Resetting neighbors is useful if you change the outbound policy for the neighbors or any other
configuration that affects the sending or receiving of routing updates.
If an outbound soft reset is triggered, BGP resends all routes for the address family to the given
neighbors.
To determine whether the neighbor has advertised the ROUTE_REFRESH capability, use the show bgp
neighbors command.
Cisco IOS XR Routing Configuration Guide
RC-71
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
SUMMARY STEPS
1. show bgp neighbors
2. clear bgp {ipv4 | ipv6 | all} {unicast | multicast | all} {* | ip-address | as-number | external} soft
out
DETAILED STEPS
Command or Action
Purpose
show bgp neighbors
Step 1
Step 2
Verifies that received route refresh capability from the
neighbor is enabled.
Example:
RP/0/RP0/CPU0:router# show bgp neighbors
clear bgp {ipv4 | ipv6 | all} {unicast |
multicast | all} {* | ip-address | as-number |
external} soft out
Soft resets a BGP neighbor.
•
•
The * keyword resets all BGP neighbors.
The ip-address argument specifies the address of the
neighbor to be reset.
Example:
RP/0/RP0/CPU0:router# clear bgp ipv4 unicast
10.0.0.2 soft out
•
•
The as-number argument specifies that all neighbors
that match the autonomous system number be reset.
The external keyword specifies that all external
neighbors are reset.
Resetting Neighbors Using BGP Hard Reset
Perform this task to reset neighbors using a hard reset. A hard reset removes the TCP connection to the
neighbor, removes all routes received from the neighbor from the BGP table, and then re-establishes the
session with the neighbor. If the graceful keyword is specified, the routes from the neighbor are not
removed from the BGP table immediately, but are marked as stale. After the session is re-established,
any stale route that has not been received again from the neighbor is removed.
SUMMARY STEPS
DETAILED STEPS
1. clear bgp {* | ip-address | as-number | external} [graceful]
Command or Action
Purpose
clear bgp {* | ip-address | as-number |
external} [graceful]
Step 1
Clears a BGP neighbor. The graceful keyword specifies a
graceful restart.
Example:
RP/0/RP0/CPU0:router# clear bgp 10.0.0.3
Cisco IOS XR Routing Configuration Guide
RC-72
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Clearing Caches, Tables and Databases
Perform this task to remove all contents of a particular cache, table, or database. Clearing a cache, table,
or database can become necessary when the contents of the particular structure have become, or are
suspected to be, invalid.
SUMMARY STEPS
DETAILED STEPS
1. clear bgp ip-address
2. clear bgp external
3. clear bgp *
Command or Action
Purpose
clear bgp ip-address
Step 1
Step 2
Step 3
Clears neighbor 172.20.1.1.
Example:
RP/0/RP0/CPU0:router# clear bgp 172.20.1.1
clear bgp external
Clears all external peers.
Clears all BGP neighbors.
Example:
RP/0/RP0/CPU0:router# clear bgp external
clear bgp *
Example:
RP/0/RP0/CPU0:router# clear bgp *
Displaying System and Network Statistics
Perform this task to display specific statistics, such as the contents of BGP routing tables, caches, and
databases. Information provided can be used to determine resource usage and solve network problems.
You can also display information about node reachability and discover the routing path that the packets
of your device are taking through the network.
SUMMARY STEPS
1. show bgp cidr-only
2. show bgp count-only
3. show bgp community community-list [exact-match]
4. show bgp regexp regular-expression
5. show bgp
6. show bgp neighbors ip-address [advertised-routes | dampened-routes | flap-statistics |
performance-statistics | received prefix-filter | routes]
7. show bgp paths
Cisco IOS XR Routing Configuration Guide
RC-73
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
8. show bgp neighbor-group group-name configuration
9. show bgp summary
DETAILED STEPS
Command or Action
Purpose
show bgp cidr-only
Step 1
Step 2
Step 3
Displays routes with nonnatural network masks (classless
interdomain routing [CIDR]) routes.
Example:
RP/0/RP0/CPU0:router# show bgp cidr-only
show bgp count-only
Displays the number of paths.
Example:
RP/0/RP0/CPU0:router# show bgp count-only
show bgp community community-list [exact-match]
Displays routes that match the BGP community 1081:5.
Example:
RP/0/RP0/CPU0:router# show bgp community 1081:5
exact-match
show bgp regexp regular-expression
Step 4
Step 5
Step 6
Displays routes that match the autonomous system path
regular expression "^3 ".
Example:
RP/0/RP0/CPU0:router# show bgp regexp "^3 "
show bgp
Displays entries in the BGP routing table.
Example:
RP/0/RP0/CPU0:router# show bgp
show bgp neighbors ip-address
Displays information about the BGP connection to neighbor
10.0.101.1.
[advertised-routes | dampened-routes |
flap-statistics | performance-statistics |
received prefix-filter | routes]
•
•
•
•
The advertised-routes keyword displays all routes the
router advertised to the neighbor.
The dampened-routes keyword displays the dampened
routes that are learned from the neighbor.
Example:
RP/0/RP0/CPU0:router# show bgp neighbors
10.0.101.1
The flap-statistics keyword displays flap statistics of
the routes learned from the neighbor.
The performance-statistics keyword displays
performance statistics relating to work done by the
BGP process for this neighbor.
•
•
The received prefix-filter keyword and argument
display the received prefix list filter.
The routes keyword displays routes learned from the
neighbor.
Cisco IOS XR Routing Configuration Guide
RC-74
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
Command or Action
Purpose
show bgp paths
Step 7
Displays all BGP paths in the database.
Example:
RP/0/RP0/CPU0:router# show bgp paths
show bgp neighbor-group group-name
configuration
Step 8
Step 9
Displays the effective configuration for neighbor group
group_1, including any configuration inherited by this
neighbor group.
Example:
RP/0/RP0/CPU0:router# show bgp neighbor-group
group_1 configuration
show bgp summary
Displays the status of all BGP connections.
Example:
RP/0/RP0/CPU0:router# show bgp summary
Monitoring BGP Update Groups
This task displays information related to the processing of BGP update groups.
SUMMARY STEPS
1. show bgp [{ipv4 | ipv6 | all} {unicast | multicast | all]} update-group [neighbor ip-address |
process-id.index [summary | performance-statistics]]
DETAILED STEPS
Command or Action
Purpose
show bgp[{ipv4 | ipv6 | all} {unicast|
Step 1
Displays information about BGP update groups.
multicast | all}] update-group [neighbor
ip-address | process-id.index [summary|
performance-statistics]]
•
The ip-address argument displays the update groups to
which that neighbor belongs.
•
The process-id.index argument selects a particular
update group to display and is specified as follows:
process id (dot) index. Process ID range is from 0 to
254. Index range is from 0 to 4294967295.
Example:
RP/0/RP0/CPU0:router# show bgp update-group 0.0
•
•
The summary keyword displays summary information
for neighbors in a particular update group.
If no argument is specified, this command displays
information for all update groups (for the specified
address family).
•
The performance-statistics keyword displays
performance statistics for an update group.
Cisco IOS XR Routing Configuration Guide
RC-75
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Configuration Examples for Implementing BGP on Cisco IOS XR Software
Configuration Examples for Implementing BGP on Cisco IOS XR
Software
This section provides the following configuration examples:
•
•
•
•
•
Enabling BGP: Example
The following shows how to enable BGP.
prefix-set static
2020::/64,
2012::/64,
10.10.0.0/16,
10.2.0.0/24
end-set
route-policy pass-all
pass
end-policy
route-policy set_next_hop_agg_v4
set next-hop 10.0.0.1
end-policy
route-policy set_next_hop_static_v4
if (destination in static) then
set next-hop 10.1.0.1
else
drop
endif
end-policy
route-policy set_next_hop_agg_v6
set next-hop 2003::121
end-policy
route-policy set_next_hop_static_v6
if (destination in static) then
set next-hop 2011::121
else
drop
endif
end-policy
router bgp 65000
bgp fast-external-fallover disable
bgp confederation peers
65001
65002
bgp confederation identifier 1
bgp router-id 1.1.1.1
address-family ipv4 unicast
aggregate-address 10.2.0.0/24 route-policy set_next_hop_agg_v4
aggregate-address 10.3.0.0/24
redistribute static route-policy set_next_hop_static_v4
Cisco IOS XR Routing Configuration Guide
RC-76
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Configuration Examples for Implementing BGP on Cisco IOS XR Software
address-family ipv4 multicast
aggregate-address 10.2.0.0/24 route-policy set_next_hop_agg_v4
aggregate-address 10.3.0.0/24
redistribute static route-policy set_next_hop_static_v4
address-family ipv6 unicast
aggregate-address 2012::/64 route-policy set_next_hop_agg_v6
aggregate-address 2013::/64
redistribute static route-policy set_next_hop_static_v6
address-family ipv6 multicast
aggregate-address 2012::/64 route-policy set_next_hop_agg_v6
aggregate-address 2013::/64
redistribute static route-policy set_next_hop_static_v6
neighbor 10.0.101.60
remote-as 65000
address-family ipv4 unicast
address-family ipv4 multicast
neighbor 10.0.101.61
remote-as 65000
address-family ipv4 unicast
address-family ipv4 multicast
neighbor 10.0.101.62
remote-as 3
address-family ipv4 unicast
route-policy pass-all in
route-policy pass-all out
address-family ipv4 multicast
route-policy pass-all in
route-policy pass-all out
neighbor 10.0.101.64
remote-as 5
update-source Loopback0
address-family ipv4 unicast
route-policy pass-all in
route-policy pass-all out
address-family ipv4 multicast
route-policy pass-all in
route-policy pass-all out
Displaying BGP Update Groups: Example
The following is sample output from the show bgp update-group command executed in EXEC mode:
RP/0/RP0/CPU0:router# show bgp update-group
Update group for IPv4 Unicast, index 0.1:
Attributes:
Outbound Route map:rm
Minimum advertisement interval:30
Messages formatted:2, replicated:2
Neighbors in this update group:
10.0.101.92
Update group for IPv4 Unicast, index 0.2:
Attributes:
Minimum advertisement interval:30
Messages formatted:2, replicated:2
Neighbors in this update group:
10.0.101.91
Cisco IOS XR Routing Configuration Guide
RC-77
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Configuration Examples for Implementing BGP on Cisco IOS XR Software
BGP Neighbor Configuration: Example
The following example shows how BGP neighbors on an autonomous system are configured to share
information. In the example, a BGP router is assigned to autonomous system 109, and two networks are
listed as originating in the autonomous system. Then the addresses of three remote routers (and their
autonomous systems) are listed. The router being configured shares information about networks
131.108.0.0 and 192.31.7.0 with the neighbor routers. The first router listed is in a different autonomous
system; the second neighbor and remote-as commands specify an internal neighbor (with the same
autonomous system number) at address 131.108.234.2; and the third neighbor and remote-as
commands specify a neighbor on a different autonomous system.
router bgp 109
network 131.108.0.0
network 192.31.7.0
neighbor 131.108.200.1
remote-as 167
neighbor 131.108.234.2
remote-as 109
neighbor 150.136.64.19
remote-as 99
BGP Confederation: Example
The following is a sample configuration that shows several peers in a confederation. The confederation
consists of three internal autonomous systems with autonomous system numbers 6001, 6002, and 6003.
To the BGP speakers outside the confederation, the confederation looks like a normal autonomous
system with autonomous system number 666 (specified using the bgp confederation identifier
command).
In a BGP speaker in autonomous system 6001, the bgp confederation peers command marks the peers
from autonomous systems 6002 and 6003 as special eBGP peers. Hence, peers 171.69.232.55 and
171.69.232.56 get the local preference, next hop, and MED unmodified in the updates. The router at
160.69.69.1 is a normal eBGP speaker and the updates received by it from this peer are just like a normal
eBGP update from a peer in autonomous system 666.
router bgp 6001
bgp confederation identifier 666
bgp confederation peers 6002 6003
neighbor 171.69.232.55
remote-as 6002
neighbor 171.69.232.56
remote-as 6003
neighbor 160.69.69.1
remote-as 777
In a BGP speaker in autonomous system 6002, the peers from autonomous systems 6001 and 6003 are
configured as special eBGP peers. Peer 170.70.70.1 is a normal iBGP peer and peer 199.99.99.2 is a
normal eBGP peer from autonomous system 700.
router bgp 6002
bgp confederation identifier 666
bgp confederation peers 6001 6003
neighbor 170.70.70.1
remote-as 6002
neighbor 171.69.232.57
remote-as 6001
neighbor 171.69.232.56
remote-as 6003
Cisco IOS XR Routing Configuration Guide
RC-78
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Where to Go Next
neighbor 199.99.99.2
remote-as 700
In a BGP speaker in autonomous system 6003, the peers from autonomous systems 6001 and 6002 are
configured as special eBGP peers. Peer 200.200.200.200 is a normal eBGP peer from autonomous
system 701.
router bgp 6003
bgp confederation identifier 666
bgp confederation peers 6001 6002
neighbor 171.69.232.57
remote-as 6001
neighbor 171.69.232.55
remote-as 6002
neighbor 200.200.200.200
remote-as 701
The following is a part of the configuration from the BGP speaker 200.200.200.205 from autonomous
system 701 in the same example. Neighbor 171.69.232.56 is configured as a normal eBGP speaker from
autonomous system 666. The internal division of the autonomous system into multiple autonomous
systems is not known to the peers external to the confederation.
router bgp 701
neighbor 171.69.232.56
remote-as 666
neighbor 200.200.200.205
remote-as 701
BGP Route Reflector: Example
The following example shows how to use an address family to configure internal BGP peer 10.1.1.1 as
a route reflector client for both unicast and multicast prefixes:
router bgp 140
neighbor 10.1.1.1
remote-as 140
address-family ipv4 unicast
route-reflector-client
router bgp 140
neighbor 10.1.1.1
remote-as 140
address-family ipv4 multicast
route-reflector-client
Where to Go Next
For detailed information about BGP commands, see the Cisco IOS XR Routing Command Reference
document.
Cisco IOS XR Routing Configuration Guide
RC-79
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Additional References
Additional References
The following sections provide references related to implementing BGP for Cisco IOS XR software.
Related Documents
Related Topic
Document Title
BGP commands: complete command syntax, command Cisco IOS XR Routing Command Reference, Release 3.2
modes, command history, defaults, usage guidelines,
and examples
Standards
Standards
Title
draft-ietf-idr-bgp4-26.txt
draft-ietf-idr-bgp4-mib-15.txt
A Border Gateway Protocol 4, by Y. Rekhter, T.Li, S. Hares
Definitions of Managed Objects for the Fourth Version of Border
Gateway Protocol (BGP-4), by J. Hass and S. Hares
draft-ietf-idr-cease-subcode-05.txt
Subcodes for BGP Cease Notification Message, by Enke Chen, V.
Gillet
MIBs
MIBs
MIBs Link
•
•
BGP4-MIB
To locate and download MIBs for selected platforms using
Cisco IOS XR software, use the Cisco MIB Locator found at the
following URL:
CISCO-BGP4-MIB
RFCs
RFCs
Title
RFC 1997
RFC 2385
RFC 2439
RFC 2545
BGP Communities Attribute
Protection of BGP Sessions via the TCP MD5 Signature Option
BGP Route Flap Damping
Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain
Routing
RFC 2796
RFC 2858
RFC 2918
BGP Route Reflection - An Alternative to Full Mesh IBGP
Multiprotocol Extensions for BGP-4
Route Refresh Capability for BGP-4
Cisco IOS XR Routing Configuration Guide
RC-80
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Additional References
RFCs
Title
RFC 3065
RFC 3392
Autonomous System Confederations for BGP
Capabilities Advertisement with BGP-4
Technical Assistance
Description
Link
The Cisco Technical Support website contains
thousands of pages of searchable technical content,
including links to products, technologies, solutions,
technical tips, and tools. Registered Cisco.com users
can log in from this page to access even more content.
Cisco IOS XR Routing Configuration Guide
RC-81
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing BGP on Cisco IOS XR Software
Additional References
Cisco IOS XR Routing Configuration Guide
RC-82
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Integrated Intermediate System-to-Intermediate System (IS-IS), Internet Protocol Version 4 (IPv4), is a
standards-based Interior Gateway Protocol (IGP).
Cisco IOS XR implements the IP routing capabilities described in International Organization for
Standardization (ISO)/International Engineering Consortium (IEC) 10589 and RFC 1995, and adds the
standard extensions for single topology and multitopology IS-IS for IP Version 6 (IPv6).
This module describes the new and revised tasks you need to implement IS-IS (IPv4 and IPv6) on your
Cisco IOS XR network.
Note
For more information about IS-IS on the Cisco IOS XR software and complete descriptions of the IS-IS
locate documentation for other commands that might appear while of executing a configuration task,
search online in the Cisco IOS XR software master command index.
Feature History for Implementing IS-IS on Cisco IOS XR Software
Release
Modification
Release 2.0
Release 3.0
Release 3.2
This feature was introduced on the Cisco CRS-1.
No modification.
Support was added for the Cisco XR 12000 Series Router. The ability to
configure a broadcast medium connecting two networking devices as a
point-to-point link was added.
Release 3.2.2
Support was added for the multicast-intact feature.
Contents
•
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-83
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Prerequisites for Implementing IS-IS on Cisco IOS XR Software
Prerequisites for Implementing IS-IS on Cisco IOS XR Software
The following are prerequisites for implementing IS-IS on Cisco IOS XR software:
•
You must be in a user group associated with a task group that includes the proper task IDs for IS-IS
commands. Task IDs for commands are listed in the Cisco IOS XR Task ID Reference Guide. For
detailed information about user groups and task IDs, see the Configuring AAA Services on
Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Restrictions for Implementing IS-IS on Cisco IOS XR Software
When multiple instances of IS-IS are being run, an interface can be associated with only one instance
(process). Instances may not share an interface. Additionally, if Multiprotocol Label Switching traffic
engineering (MPLS TE) is being employed, then MPLS must be enabled for only one instance. The
MPLS process is not multi-instance aware.
Information About Implementing IS-IS on Cisco IOS XR Software
To implement IS-IS you need to understand the following concepts:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-84
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Information About Implementing IS-IS on Cisco IOS XR Software
IS-IS Functional Overview
Small IS-IS networks are typically built as a single area that includes all routers in the network. As the
network grows larger, it may be reorganized into a backbone area made up of the connected set of all
Level 2 routers from all areas, which is in turn connected to local areas. Within a local area, routers know
how to reach all system IDs. Between areas, routers know how to reach the backbone, and the backbone
routers know how to reach other areas.
The IS-IS routing protocol supports the configuration of backbone Level 2 and Level 1 areas and the
necessary support for moving routing information between the areas. Routers establish Level 1
adjacencies to perform routing within a local area (intra-area routing). Routers establish Level 2
adjacencies to perform routing between Level 1 areas (interarea routing).
For Cisco IOS XR software, each IS-IS instance can support either a single Level 1 or Level 2 area, or
one of each. By default, all IS-IS instances automatically support Level 1 and Level 2 routing. You can
change the level of routing to be performed by a particular routing instance using the is-type command.
Key Features Supported in the Cisco IOS XR IS-IS Implementation
The Cisco IOS XR implementation of IS-IS conforms to the IS-IS Version 2 specifications detailed in
RFC 1195 and the IPv6 IS-IS functionality based on the Internet Engineering Task Force (IETF) IS-IS
Working Group draft-ietf-isis-ipv6.txt document.
The following list outlines key features supported in the Cisco IOS XR implementation:
•
•
•
•
•
•
•
•
Improved configuration syntax and enhanced show commands
Single topology IPv6
Multitopology
Nonstop forwarding (NSF), both Cisco proprietary and IETF
Three-way handshake
Mesh groups
Multiple IS-IS instances
Configuration of a broadcast medium connecting two networking devices as a point-to-point link
IS-IS Configuration Grouping
Cisco IOS XR groups all of the IS-IS configuration in router configuration mode, including the portion
of the interface configurations associated with IS-IS. The grouping makes the configuration process
clearer, and eliminates some of the clutter in the global interface stanza. To display the IS-IS
configuration in its entirety, use the show isis interface command.
The command output displays the running configuration for all configured IS-IS instances, including the
interface assignments and interface attributes.
Cisco IOS XR Routing Configuration Guide
RC-85
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Information About Implementing IS-IS on Cisco IOS XR Software
IS-IS Interfaces
IS-IS interfaces can be configured as one of the following types:
•
•
active—advertises connected prefixes and forms adjacencies. This is the default for interfaces.
passive—advertises connected prefixes but does not form adjacencies. The passive command is
used to configure interfaces as passive. Passive interfaces should be used sparingly for important
prefixes such as loopback addresses that need to be injected into the IS-IS domain. If many
connected prefixes need to be advertised then the redistribution of connected routes with the
appropriate policy should be used instead.
•
•
suppressed—does not advertise connected prefixes but forms adjacencies. The suppress command
is used to configure interfaces as suppressed.
shutdown—does not advertise connected prefixes and does not form adjacencies. The shutdown
command is used to disable interfaces without removing the IS-IS configuration.
Multitopology Configuration
Cisco IOS XR software supports multitopology for IPv6 IS-IS unless single topology is explicitly
configured in IPv6 address-family configuration mode.
Note
IS-IS supports IP routing and not Open Systems Interconnection (OSI) Connectionless Network Service
(CLNS) routing.
IPv6 Routing and Configuring IPv6 Addressing
By default, IPv6 routing is disabled in the Cisco IOS XR software. To enable IPv6 routing, you must
assign IPv6 addresses to individual interfaces in the router using the ipv6 enable or ipv6 address
command. See the Network Stack IPv4 and IPv6 Commands on Cisco IOS XR Software module of the
Cisco IOS XR IP Addresses and Services Command Reference.
Limit LSP Flooding
Limiting link-state packets (LSP) may be desirable in certain “meshy” network topologies. An example
of such a network might be a highly redundant one such as a fully meshed set of point-to-point links over
a nonbroadcast multiaccess (NBMA) transport. In such networks, full LSP flooding can limit network
scalability. One way to restrict the size of the flooding domain is to introduce hierarchy by using multiple
Level 1 areas and a Level 2 area. However, two other techniques can be used instead of or with hierarchy:
Block flooding on specific interfaces and configure mesh groups.
Both techniques operate by restricting the flooding of LSPs in some fashion. A direct consequence is
that although scalability of the network is improved, the reliability of the network (in the face of failures)
is reduced because a series of failures may prevent LSPs from being flooded throughout the network,
even though links exist that would allow flooding if blocking or mesh groups had not restricted their use.
In such a case, the link-state databases of different routers in the network may no longer be synchronized.
Consequences such as persistent forwarding loops can ensue. For this reason, we recommend that
blocking or mesh groups be used only if specifically required, and then only after careful network
design.
Cisco IOS XR Routing Configuration Guide
RC-86
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Information About Implementing IS-IS on Cisco IOS XR Software
Flood Blocking on Specific Interfaces
With this technique, certain interfaces are blocked from being used for flooding LSPs, but the remaining
interfaces operate normally for flooding. This technique is simple to understand and configure, but may
be more difficult to maintain and more error prone than mesh groups in the long run. The flooding
topology that IS-IS uses is fine-tuned rather than restricted. Restricting the topology too much (blocking
too many interfaces) makes the network unreliable in the face of failures. Restricting the topology too
little (blocking too few interfaces) may fail to achieve the desired scalability.
To improve the robustness of the network in the event that all nonblocked interfaces drop, use the
csnp-interval command in interface configuration mode to force periodic complete sequence number
PDUs (CSNPs) packets to be used on blocked point-to-point links. The use of periodic CSNPs enables
the network to become synchronized.
Mesh Group Configuration
Configuring mesh groups (a set of interfaces on a router) can help to limit flooding. All routers reachable
over the interfaces in a particular mesh group are assumed to be densely connected with each router
having at least one link to every other router. Many links can fail without isolating one or more routers
from the network.
In normal flooding, a new LSP is received on an interface and is flooded out over all other interfaces on
the router. With mesh groups, when a new LSP is received over an interface that is part of a mesh group,
the new LSP is not flooded over the other interfaces that are part of that mesh group.
Maximum LSP Lifetime and Refresh Interval
By default, the router sends a periodic LSP refresh every 15 minutes. LSPs remain in a database for
20 minutes by default. If they are not refreshed by that time, they are deleted. You can change the LSP
refresh interval or maximum LSP lifetime. The LSP interval should be less than the LSP lifetime or else
LSPs time out before they are refreshed. In the absence of a configured refresh interval, the software
adjusts the LSP refresh interval, if necessary, to prevent the LSPs from timing out.
Overload Bit Configuration During Multitopology Operation
Because the overload bit applies to forwarding for a single topology, it may be configured and cleared
independently for IPv4 and IPv6 during multitopology operation. For this reason, the overload is set
from the router address family configuration mode. If the IPv4 overload bit is set, all routers in the area
do not use the router for IPv4 transit traffic. However, they can still use the router for IPv6 transit traffic.
Single-Topology IPv6 Support
Single-topology IPv6 support on Cisco IOS XR software allows IS-IS for IPv6 to be configured on
interfaces along with an IPv4 network protocol. All interfaces must be configured with the identical set
of network protocols, and all routers in the IS-IS area (for Level 1 routing) or the domain (for Level 2
routing) must support the identical set of network layer protocols on all interfaces.
Cisco IOS XR Routing Configuration Guide
RC-87
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Information About Implementing IS-IS on Cisco IOS XR Software
When single-topology support for IPv6 is used, only narrow link metrics, also known as old-style type,
length, and value (TLV) arguments, may be employed. During single-topology operation, one shortest
path first (SPF) computation for each level is used to compute both IPv4 and IPv6 routes. Using a single
SPF is possible because both IPv4 IS-IS and IPv6 IS-IS routing protocols share a common link topology.
Because multitopology is the default behavior in the software, you must explicitly configure IPv6 to use
the same topology as IPv4 enable single-topology IPv6. Configure the single-topology command in
IPv6 router address family configuration submode of the IS-IS router stanza.
Multitopology IPv6 Support
Multitopology IPv6 support on Cisco IOS XR software for IS-IS assumes that multitopology support is
required as soon as it detects interfaces configured for both IPv6 and IPv4 within the IS-IS stanza.
Nonstop Forwarding
On Cisco IOS XR software, NSF minimizes the amount of time a network is unavailable to its users
following a route processor (RP) failover. The main objective of NSF is to continue forwarding IP
packets and perform a graceful restart following an RP failover.
When a router restarts, all routing peers of that device usually detect that the device went down and then
came back up. This transition results in what is called a routing flap, which could spread across multiple
routing domains. Routing flaps caused by routing restarts create routing instabilities, which are
detrimental to the overall network performance. NSF helps to suppress routing flaps in NSF-aware
devices, thus reducing network instability.
NSF allows for the forwarding of data packets to continue along known routes while the routing protocol
information is being restored following an RP failover. When the NSF feature is configured, peer
networking devices do not experience routing flaps. Data traffic is forwarded through intelligent line
cards or dual forwarding processors (FPs) while the standby RP assumes control from the failed active
RP during a failover. The ability of line cards and FPs to remain up through a failover and to be kept
current with the Forwarding Information Base (FIB) on the active RP is key to NSF operation.
When the Cisco IOS XR router running IS-IS routing performs an RP failover, the router must perform
two tasks to resynchronize its link-state database with its IS-IS neighbors. First, it must relearn the
available IS-IS neighbors on the network without causing a reset of the neighbor relationship. Second,
it must reacquire the contents of the link-state database for the network.
The IS-IS NSF feature offers two options when configuring NSF:
•
•
IETF NSF
Cisco NSF
If neighbor routers on a network segment are NSF aware, meaning that neighbor routers are running a
software version that supports the IETF Internet draft for router restartability, they assist an IETF NSF
router that is restarting. With IETF NSF, neighbor routers provide adjacency and link-state information
to help rebuild the routing information following a failover.
In Cisco IOS XR software, Cisco NSF checkpoints (stores persistently) all the state necessary to recover
from a restart without requiring any special cooperation from neighboring routers. The state is recovered
from the neighboring routers, but only using the standard features of the IS-IS routing protocol. This
capability makes Cisco NSF suitable for use in networks in which other routers have not used the IETF
standard implementation of NSF.
Cisco IOS XR Routing Configuration Guide
RC-88
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Information About Implementing IS-IS on Cisco IOS XR Software
Note
If you configure IETF NSF on the Cisco IOS XR router and a neighbor router does not support IETF
NSF, the affected adjacencies flap, but nonstop forwarding is maintained to all neighbors that do support
IETF NSF. A restart reverts to a cold start if no neighbors support IETF NSF.
Multi-Instance IS-IS
You may configure as many IS-IS instances as system resources (memory and interfaces) allow. Each
interface may be associated with only a single IS-IS instance, and MPLS may be enabled for only a
single IS-IS instance. Cisco IOS XR software prevents the double-booking of an interface by two
instances at configuration time—two instances of MPLS configuration causes an error.
Because the Routing Information Base (RIB) treats each of the IS-IS instances as equal routing clients,
you must be careful when redistributing routes between IS-IS instances. The RIB does not know to prefer
Level 1 routes over Level 2 routes. For this reason, if you are running Level 1 and Level 2 instances, you
must enforce the preference by configuring different administrative distances for the two instances.
Multiprotocol Label Switching Traffic Engineering
The MPLS TE feature enables an MPLS backbone to replicate and expand the traffic engineering
capabilities of Layer 2 ATM and Frame Relay networks. MPLS is an integration of Layer 2 and Layer 3
technologies.
For IS-IS, MPLS TE automatically establishes and maintains MPLS TE label-switched paths across the
backbone by using Resource Reservation Protocol (RSVP). The route that a label-switched path uses is
determined by the label-switched paths resource requirements and network resources, such as
bandwidth. Available resources are flooded by using special IS-IS TLV extensions in the IS-IS. The
label-switched paths are explicit routes and are referred to as traffic engineering (TE) tunnels.
Overload Bit on Router
The overload bit is a special bit of state information that is included in an LSP of the router. If the bit is
set on the router, it notifies routers in the area that the router is not available for transit traffic. This
capability is useful in four situations:
1. During a serious but nonfatal error, such as limited memory.
2. During the startup and restart of the process. The overload bit can be set until the routing protocol
has converged. However, it is not employed during a normal NSF restart or failover because doing
so causes a routing flap.
3. During a trial deployment of a new router. The overload bit can be set until deployment is verified,
then cleared.
4. During the shutdown of a router. The overload bit can be set to remove the router from the topology
before the router is removed from service.
Cisco IOS XR Routing Configuration Guide
RC-89
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Information About Implementing IS-IS on Cisco IOS XR Software
Default Routes
You can force a default route into an IS-IS routing domain. Whenever you specifically configure
redistribution of routes into an IS-IS routing domain, the Cisco IOS XR software does not, by default,
redistribute the default route into the IS-IS routing domain. The default-information originate
command generates a default route into IS-IS, which can be controlled by a route map. You can use the
route map to identify the level into which the default route is to be announced, and you can specify other
filtering options configurable under a route map. You can use a route map to conditionally advertise the
default route, depending on the existence of another route in the routing table of the router.
Attached Bit on an IS-IS Instance
The attached bit is set in a router that is configured with the is-type command and level-1-2 keyword.
The attached bit indicates that the router is connected to other areas (typically through the backbone).
This functionality means that the router can be used by Level 1 routers in the area as the default route to
the backbone. The attached bit is usually set automatically as the router discovers other areas while
computing its Level 2 SPF route. The bit is automatically cleared when the router becomes detached
from the backbone. To simulate this behavior when using multiple processes to represent the level-1-2
keyword functionality, you would manually configure the attached bit on the Level 1 process.
Caution
If the connectivity for the Level 2 instance is lost, the attached bit in the Level 1 instance LSP would
continue sending traffic to the Level 2 instance and cause the traffic to be dropped.
Multicast-Intact Feature
The multicast-intact feature provides the ability to run multicast routing (PIM) when IGP shortcuts are
configured and active on the router. Both OSPFv2 and IS-IS support the multicast-intact feature.
You can enable multicast-intact in the IGP when multicast routing protocols (PIM) are configured and
IGP shortcuts are configured on the router. IGP shortcuts are MPLS tunnels that are exposed to IGP. The
IGPs route the IP traffic over these tunnels to destinations that are downstream from the egress router of
the tunnel (from an SPF perspective). PIM cannot use IGP shortcuts for propagating PIM joins because
reverse path forwarding (RPF) cannot work across a unidirectional tunnel.
When you enable multicast-intact on an IGP, the IGP publishes a parallel or alternate set of equal-cost
next-hops for use by PIM. These next-hops are called mcast-intact next-hops. The mcast-intact
next-hops have the following attributes:
•
•
They are guaranteed not to contain any IGP shortcuts.
They are not used for unicast routing but are used only by PIM to look up an IPv4 next-hop to a PIM
source.
•
•
They are not published to the FIB.
When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through
link-state advertisements are published with a set equal-cost mcast-intact next-hops to the RIB. This
attribute applies even when the native next-hops have no IGP shortcuts.
•
In IS-IS, the max-paths limit is applied by counting both the native and mcast-intact next-hops
together. (In OSPFv2, the behavior is slightly different.)
Cisco IOS XR Routing Configuration Guide
RC-90
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
This section contains the following procedures:
•
•
•
•
•
•
•
•
•
•
Note
To save configuration changes, you must commit changes when the system prompts you.
Enabling IS-IS and Configuring Level 1 or Level 2 Routing
This task explains how to enable IS-IS and configure the routing level for an area.
Note
Configuring the routing level in Step 4 is optional, but is highly recommended to establish the proper
level of adjacencies.
Prerequisites
Although you can configure IS-IS before you configure an IP address, no IS-IS routing occurs until at
least one IP address is configured.
SUMMARY STEPS
1. configure
2. router isis instance-id
3. net network-entity-title
4. is-type {level-1 | level-1-2 | level-2-only}
5. end
or
commit
6. show isis [instance instance-id] protocol
Cisco IOS XR Routing Configuration Guide
RC-91
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Step 2
Enables IS-IS routing for the specified routing instance, and
places the router in router configuration mode.
•
By default, all IS-IS instances are automatically
Level 1 and Level 2. You can change the level of
routing to be performed by a particular routing instance
using the is-type router configuration command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
net network-entity-title
Step 3
Configures network entity titles (NETs) for the routing
instance.
•
Specify a NET for each routing instance if you are
configuring multi-instance IS-IS. You can specify a
name for a NET and for an address.
Example:
RP/0/RP0/CPU0:router(config-isis)# net
47.0004.004d.0001.0001.0c11.1110.00
•
•
This example configures a router with area ID
47.0004.004d.0001 and system ID 0001.0c11.1110.00.
To specify more than one area address, specify
additional NETs. Although the area address portion of
the NET differs, the systemID portion of the NET must
match exactly for all of the configured items.
is-type {level-1 | level-1-2 | level-2-only}
Step 4
(Optional) Configures the system type (area or backbone
router).
•
By default, every IS-IS instance acts as a level-1-2
router.
Example:
RP/0/RP0/CPU0:router(config-isis)# is-type
level-2-only
•
The level-1 keyword configures the software to perform
Level 1 (intra-area) routing only. Only Level 1
adjacencies are established. The software learns about
destinations inside its area only. Any packets
containing destinations outside the area are sent to the
nearest level-1-2 router in the area.
•
•
The level-2-only keyword configures the software to
perform Level 2 (backbone) routing only, and the router
establishes only Level 2 adjacencies, either with other
Level 2-only routers or with level-1-2 routers.
The level-1-2 keyword configures the software to
perform both Level 1 and Level 2 routing. Both Level 1
and Level 2 adjacencies are established. The router acts
as a border router between the Level 2 backbone and its
Level 1 area.
Cisco IOS XR Routing Configuration Guide
RC-92
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
Saves configuration changes.
end
Step 5
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show isis [instance instance-id] protocol
Step 6
(Optional) Displays summary information about the IS-IS
instance.
Example:
RP/0/RP0/CPU0:router# show isis protocol
Configuring Single Topology for IS-IS
After an IS-IS instance is enabled, it must be configured to compute routes for a specific network
topology.
This task explains how to configure the operation of the IS-IS protocol on an interface for an IPv4 or
IPv6 topology.
Restrictions
To enable the router to run in single-topology mode, configure each of the IS-IS interfaces with all of
the address families enabled and “single-topology” in the address-family IPv6 unicast in the IS-IS router
stanza. You can use either the IPv6 address family or both IPv4 and IPv6 address families, but your
configuration must represent the set of all active address families on the router. In addition, you should
explicitly enable single-topology operation by configuring it in the IPv6 router address family submode.
Exceptions to these instructions exist:
1. If the address-family stanza in the IS-IS process contains the adjacency-check disable command,
then an interface is not required to have the address family enabled.
2. If the interface is configured to Level 2 only. (This exception permits the running of IPv4 and IPv6
areas.)
3. The single-topology command is not valid in the ipv4 address-family submode.
Cisco IOS XR Routing Configuration Guide
RC-93
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
The default metric style for single topology is narrow metrics. However, you can use either wide metrics
or narrow metrics. How to configure them depends on how single topology is configured. If both IPv4
and IPv6 are enabled and single topology is configured, the metric style is configured in the
address-family ipv4 stanza. You may configure the metric style in the address-family ipv6 stanza, but
it is ignored in this case. If only IPv6 is enabled and single topology is configured, then the metric style
is configured in the address-family ipv6 stanza.
SUMMARY STEPS
1. configure
2. interface type number
3. ipv4 address address mask
or
ipv6 address ipv6-prefix/prefix-length [eui-64]
or
ipv6 address ipv6-address {/prefix-length | link-local}
or
ipv6 enable
4. exit
5. router isis instance-id
6. net network-entity-title
7. address-family ipv6 [unicast]
8. single-topology
9. exit
10. interface type instance
11. circuit-type {level-1 | level-1-2 | level-2-only}
12. address-family {ipv4 | ipv6} [unicast]
13. end
or
commit
14. show isis [instance instance-id] interface [type instance] [detail] [level {1 | 2}]
15. show isis [instance instance-id] topology [systemid system-id] [level {1 | 2}] [summary]
Cisco IOS XR Routing Configuration Guide
RC-94
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
interface type number
Step 2
Enters interface configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# interface POS
0/1/0/3
ipv4 address address mask
Step 3
Defines the IPv4 address for the interface. An IP address is
required on all interfaces in an area enabled for IS-IS if any
one interface is configured for IS-IS routing.
or
ipv6 address ipv6-prefix/prefix-length [eui-64]
or
or
ipv6 address ipv6-address {/prefix-length
| link-local}
Specifies an IPv6 network assigned to the interface and
enables IPv6 processing on the interface with the eui-64
keyword.
or
ipv6 enable
or
Specifies an IPv6 address assigned to the interface and
enables IPv6 processing on the interface with the link-local
keyword.
Example:
RP/0/RP0/CPU0:router(config-if)# ipv4 address
10.0.1.3 255.255.255.0
or
or
RP/0/RP0/CPU0:router(config-if)# ipv6 address
3ffe:1234:c18:1::/64 eui-64
Automatically configures an IPv6 link-local address on the
interface while also enabling the interface for IPv6
processing.
or
RP/0/RP0/CPU0:router(config-if)# ipv6 address
FE80::260:3EFF:FE11:6770 link-local
•
The link-local address can be used only to
communicate with nodes on the same link.
or
RP/0/RP0/CPU0:router(config-if)# ipv6 enable
•
Specifying the ipv6 address ipv6-prefix/prefix-length
interface configuration command without the eui-64
keyword configures site-local and global IPv6
addresses.
•
•
Specifying the ipv6 address ipv6-prefix/prefix-length
command with the eui-64 keyword configures
site-local and global IPv6 addresses with an interface
ID in the low-order 64 bits of the IPv6 address. Only the
64-bit network prefix for the address needs to be
specified; the last 64 bits are automatically computed
from the interface ID.
Specifying the ipv6 address command with the
link-local keyword configures a link-local address on
the interface that is used instead of the link-local
address that is automatically configured when IPv6 is
enabled on the interface.
Cisco IOS XR Routing Configuration Guide
RC-95
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
exit
Step 4
Exits interface configuration mode, and returns the router to
global configuration mode.
Example:
RP/0/RP0/CPU0:router(config-if)# exit
router isis instance-id
Step 5
Step 6
Enables IS-IS routing for the specified routing instance, and
places the router in router configuration mode.
•
By default, all IS-IS instances are Level 1 and Level 2.
You can change the level of routing to be performed by
a particular routing instance using the is-type
command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
net network-entity-title
Configures NETs for the routing instance.
•
Specify a NET for each routing instance if you are
configuring multi-instance IS-IS. You can specify a
name for a NET and for an address.
Example:
RP/0/RP0/CPU0:router(config-isis)# net
47.0004.004d.0001.0001.0c11.1110.00
•
•
This example configures a router with area ID
47.0004.004d.0001 and system ID 0001.0c11.1110.00.
To specify more than one area address, specify
additional NETs. Although the area address portion of
the NET differs, the system ID portion of the NET must
match exactly for all of the configured items.
address-family ipv6 [unicast]
Step 7
Step 8
Specifies the IPv6 address family and enters router address
family configuration mode.
•
This example specifies the unicast IPv6 address family.
Example:
RP/0/RP0/CPU0:router(config-isis)#
address-family ipv6 unicast
single-topology
(Optional) Configures the link topology for IPv4 when IPv6
is configured.
•
The single-topology command is valid only in IPv6
submode. The command instructs IPv6 to use the single
topology rather than the default configuration of a
separate topology in the multitopology mode.
Example:
RP0/0/RP0/CPU0:router(config-isis-af)#
single-topology
•
page RC-87 for more information.
exit
Step 9
Exits router address family configuration mode, and returns
the router to router configuration mode.
Example:
RP/0/RP0/CPU0:router(config-isis-af)# exit
interface type instance
Step 10
Enters interface configuration mode.
Example:
RP/0/RP0/CPU0:router(config-isis)# interface
POS 0/1/0/3
Cisco IOS XR Routing Configuration Guide
RC-96
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
(Optional) Configures the type of adjacency.
circuit-type {level-1 | level-1-2 |
level-2-only}
Step 11
•
The default circuit type is the configured system type
(configured through the is-type command).
Example:
•
Typically, the circuit type must be configured when the
router is configured as only level-1-2 and you want to
constrain an interface to form only level-1 or
level-2-only adjacencies.
RP/0/RP0/CPU0:router(config-isis-if)#
circuit-type level-1-2
address-family {ipv4 | ipv6} [unicast]
Step 12
Specifies the IPv4 or IPv6 address family, and enters
interface address family configuration mode.
•
This example specifies the unicast IPv6 address family
on the interface.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
address-family ipv6 unicast
end
Step 13
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show isis [instance instance-id] interface
[type instance] [detail] [level {1 | 2}]
Step 14
(Optional) Displays information about the IS-IS interface.
Example:
RP/0/RP0/CPU0:router# show isis interface
POS0/1/0/1
show isis [instance instance-id] topology
[systemid system-id] [level {1 | 2}][summary]
Step 15
(Optional) Displays a list of connected routers in all areas.
Example:
RP/0/RP0/CPU0:router# show isis topology
Cisco IOS XR Routing Configuration Guide
RC-97
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Configuring Multitopology for IS-IS
This task explains how to configure multitopology IS-IS. This task is optional. Multitopology is
configured in much the same way as the single topology for IPv4 and IPv6 address families. The single-
topology command is omitted, invoking the default multitopology behavior.
SUMMARY STEPS
1. configure
2. interface type instance
3. ipv4 address address mask
or
ipv6 address ipv6-prefix/prefix-length [eui-64]
or
ipv6 address ipv6-address {/prefix-length | link-local}
or
ipv6 enable
4. exit
5. router isis instance-id
6. net network-entity-title
7. interface type instance
8. address-family ipv4 [unicast]
9. exit
10. address-family ipv6 [unicast]
11. end
or
commit
12. show isis [instance instance-id] interface [type number] [brief | detail] [level {1 | 2}]
13. show isis [instance instance-id] topology [systemid system-id] [level {1 | 2}] [ipv4 | ipv6]
[summary] [unicast]
14. show isis [instance instance-id] adjacency [level {1 | 2}] [interface-type interface-instance]
[detail] [systemid system-id]
15. show isis adjacency-log [level {1 | 2}]
Cisco IOS XR Routing Configuration Guide
RC-98
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
interface type instance
Step 2
Enters interface configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# interface POS
0/1/0/3
ipv4 address address mask
Step 3
Defines the IPv4 address for the interface.
or
•
An IP address is required on all interfaces in an area
enabled for IS-IS if any one interface is configured for
IS-IS routing.
ipv6 address ipv6-prefix/prefix-length [eui-64]
or
ipv6 address ipv6-address {/prefix-length |
link-local}
or
or
Specifies an IPv6 network assigned to the interface and
enables IPv6 processing on the interface.
ipv6 enable
or
Example:
Specifies an IPv6 address assigned to the interface and
enables IPv6 processing on the interface.
RP/0/RP0/CPU0:router(config-if)# ipv4 address
10.0.1.3 255.255.255.0
or
or
RP/0/RP0/CPU0:router(config-if)# ipv6 address
3ffe:1234:c18:1::/64 eui-64
Automatically configures an IPv6 link-local address on the
interface while also enabling the interface for IPv6
processing.
or
RP/0/RP0/CPU0:router(config-if)# ipv6 address
FE80::260:3EFF:FE11:6770 link-local
•
The link-local address can be used to communicate
only with nodes on the same link.
or
RP/0/RP0/CPU0:router(config-if)# ipv6 enable
•
Specifying the ipv6 address ipv6-prefix/prefix-length
interface configuration command without the eui-64
keyword configures site-local and global IPv6
addresses.
•
•
Specifying the ipv6 address ipv6-prefix/prefix-length
command with the eui-64 keyword configures
site-local and global IPv6 addresses with an interface
ID in the low-order 64 bits of the IPv6 address. Only the
64-bit network prefix for the address needs to be
specified; the last 64 bits are automatically computed
from the interface ID.
Specifying the ipv6 address command with the
link-local keyword configures a link-local address on
the interface that is used instead of the link-local
address that is automatically configured when IPv6 is
enabled on the interface.
Cisco IOS XR Routing Configuration Guide
RC-99
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
exit
Step 4
Exits interface configuration mode, and returns the router to
global configuration mode.
Example:
RP/0/RP0/CPU0:router(config-if)# exit
router isis instance-id
Step 5
Step 6
Enables IS-IS routing for the specified routing instance, and
places the router in router configuration mode.
•
You can change the level of routing to be performed by
a particular routing instance using the is-type router
configuration command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
net network-entity-title
Configures NETs for the routing instance.
•
Specify a NET for each routing instance if you are
configuring multi-instance IS-IS. You can specify a
name for a NET and for an address.
Example:
RP/0/RP0/CPU0:router(config-isis)# net
47.0004.004d.0001.0001.0c11.1110.00
•
•
This example configures a router with area ID
47.0004.004d.0001 and system ID 0001.0c11.1110.10.
To specify more than one area address, specify
additional NETs. Although the area address portion of
the NET differs, the system ID portion of the NET must
match exactly for all of the configured items.
interface type instance
Step 7
Step 8
Enters interface configuration mode.
Example:
RP/0/RP0/CPU0:router(config-isis)# interface
POS 0/1/0/4
address-family ipv4 [unicast]
Specifies the IPv4 address family and enters interface
address family configuration mode.
•
This example specifies the unicast IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
address-family ipv4 unicast
exit
Step 9
Exits interface configuration mode, and returns the router to
interface configuration mode.
Example:
RP/0/RP0/CPU0:router(config-if)# exit
address-family ipv6 [unicast]
Step 10
Specifies the IPv6 address family and enters interface
address family configuration mode.
•
This example specifies the unicast IPv6 address family.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
address-family ipv6 unicast
Cisco IOS XR Routing Configuration Guide
RC-100
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
Saves configuration changes.
end
Step 11
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-if-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-if-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show isis [instance instance-id] interface
[type instance] [brief | detail] [level {1 |
2}]
Step 12
(Optional) Displays information about the IS-IS interface.
Example:
RP/0/RP0/CPU0:router# show isis interface POS
0/1/0/1 brief
show isis [instance instance-id] topology
[systemid system-id] [level {1 | 2}][ipv4 |
ipv6] [summary] [unicast]
Step 13
(Optional) Displays a list of connected routers in all areas.
Example:
RP/0/RP0/CPU0:router# show isis topology
show isis [instance instance-id] adjacency
Step 14
(Optional) Displays state information about established
adjacencies.
[level {1 | 2}] [interface-type
interface-instance] [detail] [systemid
system-id]
Example::
RP/0/RP0/CPU0:router# show isis adjacency
show isis adjacency-log [level {1 | 2}]
Step 15
(Optional) Displays the history of recent adjacency state
transitions.
Example:
RP/0/RP0/CPU0:router# show isis adjacency-log
level 1
Cisco IOS XR Routing Configuration Guide
RC-101
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Controlling LSP Flooding for IS-IS
Flooding of LSPs can limit network scalability. You can control LSP flooding by tuning your LSP
database parameters on the router globally or on the interface. This task is optional.
Many of the commands to control LSP flooding contain an option to specify the level to which they
apply. Without the option, the command applies to both levels. If an option is configured for one level,
the other level continues to use the default value. To configure options for both levels, use the command
twice. For example:
RP/0/RP0/CPU0:router(config-isis)# lsp-refresh-interval 1200 level 2
RP/0/RP0/CPU0:router(config-isis)# lsp-refresh-interval 1100 level 1
SUMMARY STEPS
1. configure
2. router isis instance-id
3. lsp-refresh-interval seconds [level {1 | 2}]
4. lsp-check-interval seconds [level {1 | 2}]
5. lsp-gen-interval {[initial-wait initial | secondary-wait secondary | maximum-wait maximum]
...}[level {1 | 2}]
6. lsp-mtu bytes [level {1 | 2}]
7. max-lsp-lifetime seconds [level {1 | 2}]
8. ignore-lsp-errors disable
9. interface type instance
10. lsp-interval milliseconds [level {1 | 2}]
11. csnp-interval seconds [level {1 | 2}]
12. retransmit-interval seconds [level {1 | 2}]
13. retransmit-throttle-interval milliseconds [level {1 | 2}]
14. mesh-group {number | blocked}
15. end
or
commit
16. show isis interface [type instance | level {1 | 2}] [brief]
17. show isis [instance instance-id] database [level {1 | 2}] [detail | summary | verbose] [* | lsp-id]
18. show isis [instance instance-id] lsp-log [level {1 | 2}]
19. show isis database-log [level {1 | 2}]
Cisco IOS XR Routing Configuration Guide
RC-102
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Step 2
Enables IS-IS routing for the specified routing instance, and
places the router in router configuration mode.
•
You can change the level of routing to be performed by
a particular routing instance using the is-type router
configuration command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
lsp-refresh-interval seconds [level {1 | 2}]
Step 3
(Optional) Sets the time between regeneration of LSPs that
contain different sequence numbers
•
The refresh interval should always be set lower than the
max-lsp-lifetime command.
Example:
RP/0/RP0/CPU0:router(config-isis)#
lsp-refresh-interval 10800
lsp-check-interval seconds [level {1 | 2}]
Step 4
(Optional) Configures the time between periodic checks of
the entire database to validate the checksums of the LSPs in
the database.
Example:
RP/0/RP0/CPU0:router(config-isis)#
lsp-check-interval 240
•
This operation is costly in terms of CPU and so should
be configured to occur infrequently.
lsp-gen-interval {[initial-wait initial |
secondary-wait secondary | maximum-wait
maximum] ...}[level {1| 2}]
Step 5
(Optional) Reduces the rate of LSP generation during
periods of instability in the network. Helps reduce the CPU
load on the router and number of LSP transmissions to its
IS-IS neighbors.
Example:
•
During prolonged periods of network instability,
repeated recalculation of LSPs can cause an increased
CPU load on the local router. Further, the flooding of
these recalculated LSPs to the other Intermediate
Systems in the network causes increased traffic and can
result in other routers having to spend more time
running route calculations.
RP/0/RP0/CPU0:router(config-isis)#
lsp-gen-interval maximum-wait 15 initial-wait 5
lsp-mtu bytes [level {1 | 2}]
Step 6
Step 7
(Optional) Sets the maximum transmission unit (MTU) size
of LSPs.
Example:
RP/0/RP0/CPU0:router(config-isis)# lsp-mtu 1300
max-lsp-lifetime seconds [level {1 | 2}]
(Optional) Sets the initial lifetime given to an LSP
originated by the router.
•
This is the amount of time that the LSP persists in the
database of a neighbor unless the LSP is regenerated or
refreshed.
Example:
RP/0/RP0/CPU0:router(config-isis)#
max-lsp-lifetime 11000
Cisco IOS XR Routing Configuration Guide
RC-103
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
ignore-lsp-errors disable
Step 8
(Optional) Sets the router to purge LSPs received with
checksum errors.
Example:
RP/0/RP0/CPU0:router(config-isis)#
ignore-lsp-errors disable
interface type instance
Step 9
Enters interface configuration mode.
Example:
RP/0/RP0/CPU0:router(config-isis)# interface
POS 0/1/0/3
lsp-interval milliseconds [level {1 | 2}]
Step 10
Step 11
(Optional) Configures the amount of time between each
LSP sent on an interface.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
lsp-interval 100
csnp-interval seconds [level {1 | 2}]
(Optional) Configures the interval at which periodic CSNP
packets are sent on broadcast interfaces.
•
Sending more frequent CSNPs means that adjacent
routers must work harder to receive them.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
csnp-interval 30 level 1
•
Sending less frequent CSNP means that differences in
the adjacent routers may persist longer.
retransmit-interval seconds [level {1 | 2}]
Step 12
Step 13
(Optional) Configures the amount of time that the sending
router waits for an acknowledgment before it considers that
the LSP was not received and subsequently resends.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
retransmit-interval 60
retransmit-throttle-interval milliseconds
[level {1 | 2}]
(Optional) Configures the amount of time between
retransmissions on each LSP on a point-to-point interface.
•
This time is usually greater than or equal to the
lsp-interval command time because the reason for lost
LSPs may be that a neighboring router is busy. A longer
interval gives the neighbor more time to receive
transmissions.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
retransmit-throttle-interval 1000
mesh-group {number | blocked}
Step 14
(Optional) Optimizes LSP flooding in NBMA networks
with highly meshed, point-to-point topologies.
•
This command is appropriate only for an NBMA
network with highly meshed, point-to-point topologies.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
mesh-group blocked
Cisco IOS XR Routing Configuration Guide
RC-104
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
Saves configuration changes.
end
Step 15
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-if)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-if)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show isis interface [type instance | level {1 |
2}] [brief]
Step 16
(Optional) Displays information about the IS-IS interface.
Example:
RP/0/RP0/CPU0:router# show isis interface
POS0/1/0/1 brief
show isis [instance instance-id] database
[level {1 | 2}] [detail | summary | verbose] [*
Step 17
(Optional) Displays the IS-IS LSP database.
| lsp-id]
Example:
RP/0/RP0/CPU0:router# show isis database
level 1
show isis [instance instance-id] lsp-log [level
{1 | 2}]
Step 18
(Optional) Displays LSP log information.
Example:
RP/0/RP0/CPU0:router# show isis lsp-log
show isis database-log [level {1 | 2}]
Step 19
(Optional) Display IS-IS database log information.
Example:
RP/0/RP0/CPU0:router# show isis database-log
level 1
Cisco IOS XR Routing Configuration Guide
RC-105
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Configuring Nonstop Forwarding for IS-IS
This task explains how to configure your router with NSF that allows the Cisco IOS XR software to
resynchronize the IS-IS link-state database with its IS-IS neighbors after a process restart. The process
restart could be due to an:
•
•
•
RP failover (for a warm restart)
Simple process restart (due to an IS-IS reload or other administrative request to restart the process)
IS-IS software upgrade
In all cases, NSF mitigates link flaps and loss of user sessions. This task is optional.
SUMMARY STEPS
1. configure
2. router isis instance-id
3. nsf {cisco | ietf}
4. nsf interface-expires number
5. nsf interface-timer seconds
6. nsf lifetime seconds
7. end
or
commit
8. show running-config [command]
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Step 2
Step 3
Enables IS-IS routing for the specified routing instance, and
places the router in router configuration mode.
•
You can change the level of routing to be performed by
a particular routing instance using the is-type router
configuration command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
nsf{cisco| ietf}
Enables NSF on the next restart.
•
Enter the cisco keyword to run IS-IS in heterogeneous
networks that might not have adjacent NSF-aware
networking devices.
Example:
RP/0/RP0/CPU0:router(config-isis)# nsf ietf
•
Enter the ietf keyword to enable IS-IS in homogeneous
networks where all adjacent networking devices
support IETF draft-based restartability.
Cisco IOS XR Routing Configuration Guide
RC-106
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
nsf interface-expires number
Step 4
Configures the number of resends of an acknowledged
NSF-restart acknowledgment.
•
If the resend limit is reached during the NSF restart, the
restart falls back to a cold restart.
Example:
RP/0/RP0/CPU0:router(config-isis)# nsf
interface-expires 1
nsf interface-timer seconds
Step 5
Step 6
Configures the number of seconds to wait for each restart
acknowledgment.
Example:
RP/0/RP0/CPU0:router(config-isis) nsf
interface-timer 15
nsf lifetime seconds
Configures the maximum route lifetime following an NSF
restart.
•
This command should be configured to the length of
time required to perform a full NSF restart because it is
the amount of time that the Routing Information Base
(RIB) retains the routes during the restart.
Example:
RP/0/RP0/CPU0:router(config-isis)# nsf lifetime
20
•
•
Setting this value too high results in stale routes.
Setting this value too low could result in routes purged
too soon.
end
Step 7
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show running-config [command]
Step 8
(Optional) Displays the entire contents of the currently
running configuration file or a subset of that file.
Example:
•
Verify that “nsf” appears in the IS-IS configuration of
the NSF-aware device.
RP/0/RP0/CPU0:router# show running-config
router isis isp
•
This example shows the contents of the configuration
file for the “isp” instance only.
Cisco IOS XR Routing Configuration Guide
RC-107
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Configuring Authentication for IS-IS
This task explains how to configure authentication for IS-IS. This task is optional.
Authentication is available to limit the establishment of adjacencies by using the hello-password
configuration, and to limit the exchange of LSPs by using the LSP password.
IS-IS supports plain-text authentication, which does not provide security against hackers or other
unauthorized users. Plain-text authentication allows you to configure a password to prevent unauthorized
networking devices from forming adjacencies with this router. The password is exchanged as plain text
and is potentially visible to an agent able to view the IS-IS packets.
IS-IS stores a configured password using simple encryption. However, the plain-text form of the
password is used in LSPs, sequence number protocols (SNPs), and hello packets, which would be visible
to a process that can view IS-IS packets. The passwords can be entered in plain text (preceded by a 0) or
encrypted (preceded by a 7) form.
To set the domain password, configure the lsp-password for Level 2; to set the area password, configure
the lsp-password for Level 1.
SUMMARY STEPS
1. configure
2. router isis instance-id
3. lsp-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only] [snp
send-only]
4. interface type instance
5. hello-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only]
6. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Step 2
Enables IS-IS routing for the specified routing instance, and
places the router in router configuration mode.
•
You can change the level of routing to be performed by
a particular routing instance using the is-type
command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
Cisco IOS XR Routing Configuration Guide
RC-108
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
Configures the LSP authentication password.
lsp-password {hmac-md5 | text} {clear |
encrypted} password [level {1 | 2}] [send-only]
[snp send-only]
Step 3
•
•
•
•
•
•
•
The hmac-md5 keyword specifies that the password is
used in HMAC-MD5 authentication.
The text keyword specifies that the password uses
cleartext password authentication.
Example:
RP/0/RP0/CPU0:router(config-isis)# lsp-password
hmac-md5 encrypted password1 level 1
The clear keyword specifies that the password is
unencrypted when entered.
The encrypted keyword specifies that the password is
encrypted using a two-way algorithm when entered.
The level 1 keyword sets a password for authentication
in the area (in Level 1 LSPs and Level SNPs).
The level 2 keywords set a password for authentication
in the backbone (the Level 2 area).
The send-only keyword adds authentication to LSP and
sequence number protocol data units (SNPs) when they
are sent. It does not authenticate received LSPs or
SNPs.
•
The snp send-only keyword adds authentication to
SNPs when they are sent. It does not authenticate
received SNPs.
Note
To disable SNP password checking, the snp
send-only keywords must be specified in the
lsp-password command.
interface type instance
Step 4
Enters interface configuration mode.
Example:
RP/0/RP0/CPU0:router(config-isis)# interface
POS 0/1/0/3
Cisco IOS XR Routing Configuration Guide
RC-109
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
hello-password {hmac-md5 | text} {clear |
encrypted} password [level {1 | 2}] [send-only]
Step 5
Configures the authentication password for an IS-IS
interface.
Example:
RP/0/RP0/CPU1:router(config-isis-if)#
hello-password text clear mypassword
end
Step 6
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-if)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-if)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring MPLS Traffic Engineering for IS-IS
This task explains how to configure IS-IS for MPLS TE. This task is optional.
For a description of the MPLS TE tasks and commands that allow you to configure the router to support
tunnels, configure an MPLS tunnel that IS-IS can use, and troubleshoot MPLS TE, see the Implementing
MPLS Traffic Engineering on Cisco IOS XR Software.
Prerequisite
Your network must support the following Cisco IOS XR software features before you enable MPLS TE
for IS-IS on your router:
•
•
MPLS
IP Cisco Express Forwarding (CEF)
Note
You must enter the commands in the following task list on every IS-IS router in the traffic-engineered
portion of your network.
Cisco IOS XR Routing Configuration Guide
RC-110
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Restrictions
MPLS traffic engineering currently supports only a single IS-IS level and does not support routing and
signaling of LSPs over unnumbered IP links. Therefore, do not configure the feature over those links.
SUMMARY STEPS
1. configure
2. router isis instance-id
3. address-family {ipv4 | ipv6} [unicast]
4. mpls traffic-eng level {1 | 2}
5. mpls traffic-eng router-id {ip-address | interface-name}
6. metric-style wide [level {1 | 2}]
7. end
or
commit
8. show isis [instance instance-id] mpls traffic-eng tunnel
9. show isis [instance instance-id] mpls traffic-eng adjacency-log
10. show isis [instance instance-id] mpls traffic-eng advertisements
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Step 2
Enables IS-IS routing for the specified routing instance, and
places the router in router configuration mode.
•
You can change the level of routing to be performed by
a particular routing instance using the is-type router
configuration command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
address-family {ipv4 | ipv6} [unicast]
Step 3
Step 4
Specifies the IPv4 or IPv6 address family, and enters router
address family configuration mode.
•
This example specifies the unicast IPv6 address family.
Example:
RP/0/RP0/CPU0:router(config-isis)#
address-family ipv6 unicast
mpls traffic-eng level {1 | 2}
Configures a router running IS-IS to flood MPLS TE link
information into the indicated IS-IS level.
Example:
RP/0/RP0/CPU0:router(config-isis-af)# mpls
traffic-eng level 1
Cisco IOS XR Routing Configuration Guide
RC-111
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
mpls traffic-eng router-id {ip-address |
interface-name}
Step 5
Specifies that the MPLS TE router identifier for the node is
the IP address and or name associated with a given
interface.
Example:
RP/0/RP0/CPU0:router(config-isis-af)# mpls
traffic-eng router-id loopback0
metric-style wide [level {1 | 2}]
Step 6
Step 7
Configures a router to generate and accept only wide link
metrics in the Level 1 area.
Example:
RP/0/RP0/CPU0:router(config-isis-af)#
metric-style wide level 1
end
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show isis [instance instance-id] mpls
traffic-eng tunnel
Step 8
Step 9
Step 10
(Optional) Displays MPLS TE tunnel information.
Example:
RP/0/RP0/CPU0:router# show isis instance isp
mpls traffic-eng tunnel
show isis [instance instance-id] mpls
traffic-eng adjacency-log
(Optional) Displays a log of MPLS TE IS-IS adjacency
changes.
Example:
RP/0/RP0/CPU0:router# show isis instance isp
mpls traffic-eng adjacency-log
show isis [instance instance-id] mpls
traffic-eng advertisements
(Optional) Displays the latest flooded record from MPLS
TE.
Example:
RP/0/RP0/CPU0:router# show isis instance isp
mpls traffic-eng advertisements
Cisco IOS XR Routing Configuration Guide
RC-112
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Tuning Adjacencies for IS-IS on Point-to-Point Interfaces
This task explains how to enable logging of adjacency state changes, alter the timers for IS-IS adjacency
packets, and display various aspects of adjacency state. Tuning your IS-IS adjacencies increases network
stability when links are congested. This task is optional.
For point-to-point links, IS-IS sends only a single hello for Level 1 and Level 2, which means that the
level modifiers are meaningless on point-to-point links. To modify hello parameters for a point-to-point
interface, omit the specification of the level options.
The options configurable in the interface submode apply only to that interface. By default, the values are
applied to both Level 1 and Level 2.
The hello-password command can be used to prevent adjacency formation with unauthorized or
undesired routers. This ability is particularly useful on a LAN, where connections to routers with which
you have no desire to establish adjacencies are commonly found.
SUMMARY STEPS
1. configure
2. router isis instance-id
3. log adjacency changes
4. interface type number
5. hello-padding {disable | sometimes} [level {1 | 2}]
6. hello-interval seconds [level {1 | 2}]
7. hello-multiplier multiplier [level {1 | 2}]
8. hello-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only]
9. end
or
commit
10. show isis [instance instance-id] adjacency [interface-type interface-instance] [detail] [systemid
system-id]
11. show isis adjacency-log
12. show isis [instance instance-id] interface [type instance] [brief | detail] [level {1 | 2}]
13. show isis [instance instance-id] neighbors [interface-type interface-instance] [summary] [detail]
[systemid system-id]
Cisco IOS XR Routing Configuration Guide
RC-113
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Step 2
Enables IS-IS routing for the specified routing instance,
and places the router in router configuration mode.
•
You can change the level of routing to be performed
by a particular routing instance using the is-type
command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
log adjacency changes
Step 3
Generates a log message when an IS-IS adjacency
changes state (up or down).
Example:
RP/0/RP0/CPU0:router(config-isis)# log adjacency
changes
interface type number
Step 4
Enters interface configuration mode.
Example:
RP/0/RP0/CPU0:router(config-isis)# interface POS
0/1/0/3
hello-padding {disable | sometimes} [level {1 |
2}]
Step 5
Configures padding on IS-IS hello PDUs for all IS-IS
interfaces on the router.
•
Hello padding applies to only this interface and not
to all interfaces.
Example:
RP/0/RP0/CPU0:router(config-isis-if)# hello-paddi
ng sometimes
hello-interval seconds [level {1 | 2}]
Step 6
Specifies the length of time between hello packets that
the software sends.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
hello-interval 6
hello-multiplier multiplier [level {1 | 2}]
Step 7
Specifies the number of IS-IS hello packets a neighbor
must miss before the router should declare the adjacency
as down.
Example:
RP/0/RP0/CPU0:router(config-isis-if)#
hello-multiplier 10
•
A higher value increases the networks tolerance for
dropped packets, but also may increase the amount
of time required to detect the failure of an adjacent
router.
•
Conversely, not detecting the failure of an adjacent
router can result in greater packet loss.
Cisco IOS XR Routing Configuration Guide
RC-114
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
hello-password {hmac-md5 | text} {clear |
encrypted} password [level {1 | 2}] [send-only]
Step 8
Specifies that this system include authentication in the
hello packets and requires successful authentication of
the hello packet from the neighbor to establish an
adjacency.
Example:
RP/0/RP0/CPU1:router(config-isis-if)#
hello-password text clear mypassword
end
Step 9
Saves configuration changes.
or
•
When you issue the end command, the system
commit
prompts you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-if)# end
or
–
Entering yes saves configuration changes to the
running configuration file, exits the
configuration session, and returns the router to
EXEC mode.
RP/0/RP0/CPU0:router(config-isis-if)# commit
–
–
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show isis [instance instance-id] adjacency
[interface-type interface-instance] [detail]
[systemid system-id]
Step 10
Step 11
(Optional) Displays IS-IS adjacencies.
Example:
RP/0/RP0/CPU0:router# show isis instance isp
adjacency ipv4
show isis adjacency-log
(Optional) Displays a log of the most recent adjacency
state transitions.
Example:
RP/0/RP0/CPU1:router# show isis adjacency-log
Cisco IOS XR Routing Configuration Guide
RC-115
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
show isis [instance instance-id] interface [type
instance] [brief | detail] [level {1 | 2}]
Step 12
(Optional) Displays information about the IS-IS
interface.
Example:
RP/0/RP0/CPU0:router# show isis interface POS
0/1/0/1 brief
show isis [instance instance-id] neighbors
[interface-type interface-instance] [summary]
[detail] [systemid system-id]
Step 13
(Optional) Displays information about IS-IS neighbors.
Example:
RP/0/RP0/CPU0:router# show isis neighbors summary
Setting SPF Interval for a Single-Topology IPv4 and IPv6 Configuration
This task explains how to make adjustments to the SPF calculation to tune router performance. This task
is optional.
Because the SPF calculation computes routes for a particular topology, the tuning attributes are located
in the router address family configuration submode. SPF calculation computes routes for Level 1 and
Level 2 separately.
When IPv4 and IPv6 address families are used in a single-topology mode, only a single SPF for the IPv4
topology exists. The IPv6 topology “borrows” the IPv4 topology; therefore, no SPF calculation is
required for IPv6. To tune the SPF calculation parameters for single-topology mode, configure the
address-family ipv4 unicast command.
The incremental SPF algorithm can be enabled separately. When enabled, the incremental shortest path
first (ISPF) is not employed immediately. Instead, the full SPF algorithm is used to “seed” the state
information required for the ISPF to run. The startup delay prevents the ISPF from running for a
specified interval after an IS-IS restart (to permit the database to stabilize). After the startup delay
elapses, the ISPF is principally responsible for performing all of the SPF calculations. The reseed
interval enables a periodic running of the full SPF to ensure that the iSFP state remains synchronized.
SUMMARY STEPS
1. configure
2. router isis instance-id
3. address-family {ipv4 | ipv6} [unicast]
4. spf-interval {[initial-wait initial | secondary-wait secondary | maximum-wait maximum]
...}[level {1 | 2}]
5. ispf [startup-delay seconds] [level {1 | 2}]
6. ispf startup-delay seconds [level {1 | 2}]
7. end
or
commit
8. show isis [instance instance-id] spf-log [level {1 | 2}] [ipv4 | ipv6] [unicast] [ispf | fspf | prc]
[detail] [internal] [last number | first number]
Cisco IOS XR Routing Configuration Guide
RC-116
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Step 2
Enables IS-IS routing for the specified routing instance, and
places the router in router configuration mode.
•
You can change the level of routing to be performed by
a particular routing instance using the is-type router
configuration command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
address-family {ipv4 | ipv6} [unicast]
Step 3
Specifies the IPv4 or IPv6 address family, and enters router
address family configuration mode.
•
This example specifies the unicast IPv6 address family.
Example:
RP/0/RP0/CPU0:router(config-isis)#
address-family ipv6 unicast
spf-interval {[initial-wait initial |
secondary-wait secondary | maximum-wait
maximum] ...} [level {1 | 2}]
Step 4
(Optional) Controls the minimum time between successive
SPF calculations.
•
This value imposes a delay in the SPF computation
after an event trigger and enforces a minimum elapsed
time between SPF runs.
Example:
RP/0/RP0/CPU0:router(config-isis-af)#
spf-interval initial-wait 10 maximum-wait 30
•
•
•
If this value is configured too low, the router can lose
too many CPU resources when the network is unstable.
Configuring the value too high delays changes in the
network topology that result in lost packets.
The SPF interval does not apply to the running of the
ISPF because that algorithm runs immediately on
receiving a changed LSP.
ispf [startup-delay seconds] [level {1 | 2}]
Step 5
Step 6
(Optional) Configures incremental IS-IS ISPF to calculate
network topology.
Example:
RP/0/RP0/CPU0:router(config-isis-af)# ispf
ispf startup-delay seconds [level {1 | 2}]
(Optional) Configures the time delay between the starting
of the IS-IS instance and the activation of ISPF.
Example:
RP/0/RP0/CPU0:router(config-isis-af)# ispf
startup-delay 600
Cisco IOS XR Routing Configuration Guide
RC-117
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
Saves configuration changes.
end
Step 7
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show isis [instance instance-id] spf-log [level
{1| 2}] [ipv4| ipv6] [unicast] [ispf| fspf | prc]
[detail] [internal] [last number | first number]
Step 8
(Optional) Displays how often and why the router has run a
full SPF calculation.
Example:
RP/0/RP0/CPU0:router# show isis instance 1
spf-log ipv4
Enabling Multicast-Intact for IS-IS
This optional task describes how to enable multicast-intact for IS-IS routes that use IPv4 addresses.
Summary Steps
1. configure
2. router isis instance-id
3. address-family {ipv4 | ipv6} [unicast]
4. mpls traffic-eng multicast-intact
5. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-118
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Step 2
Enables IS-IS routing for the specified routing process, and
places the router in router configuration mode. In this
example, the IS-IS instance is called isp.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
address-family {ipv4 | ipv6} [unicast]
Step 3
Specifies the IPv4 or IPv6 address family, and enters router
address family configuration mode. This example specifies
the unicast IPv4 address family.
Example:
RP/0/RP0/CPU0:router(config-isis)#
address-family ipv4
mpls traffic-eng multicast-intact
Step 4
Enables multicast-intact.
Example:
RP/0/RP0/CPU0:router(config-isis)# mpls
traffic-eng multicast-intact
end
Step 5
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Customizing Routes for IS-IS
This task describes how to perform route functions that include injecting default routes into your IS-IS
routing domain and redistributing routes learned at one IS-IS level into a different level. This task is
optional.
Cisco IOS XR Routing Configuration Guide
RC-119
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
SUMMARY STEPS
1. configure
2. router isis instance-id
3. set-overload-bit [on-startup {delay | wait-for-bgp}] [level {1 | 2}]
4. address-family {ipv4 | ipv6} [unicast]
5. default-information originate [route-map map-name]
6. redistribute isis instance [level-1 | level-2 | level-1-2] [metric metric] [metric-type {internal |
external}] policy policy-name]
7. summary-prefix [address/prefix-length] [level {1 | 2}]
or
summary-prefix [ipv6-prefix/prefix-length] [level {1 | 2}]
8. maximum-paths route-number
9. distance weight [address/prefix-length [route-list-name]]
10. set-attached-bit
11. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router isis instance-id
Enables IS-IS routing for the specified routing process, and
places the router in router configuration mode.
•
By default, all IS-IS instances are automatically
Level 1 and Level 2. You can change the level of
routing to be performed by a particular routing instance
using the is-type command.
Example:
RP/0/RP0/CPU0:router(config)# router isis isp
set-overload-bit [on-startup {delay |
wait-for-bgp}] [level {1 | 2}]
Step 3
Step 4
(Optional) Sets the overload bit.
Note
The configured overload bit behavior does not apply
to NSF restarts because the NSF restart does not set
the overload bit during restart.
Example:
RP/0/RP0/CPU0:router(config-isis)#
set-overload-bit
address-family {ipv4 | ipv6} [unicast]
Specifies the IPv4 or IPv6 address family, and enters router
address family configuration mode.
•
This example specifies the unicast IPv6 address family.
Example:
RP/0/RP0/CPU0:router(config-isis)#
address-family ipv6 unicast
Cisco IOS XR Routing Configuration Guide
RC-120
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
How to Implement IS-IS on Cisco IOS XR Software
Command or Action
Purpose
default-information originate [route-map
map-name]
Step 5
(Optional) Injects a default IPv4 or IPv6 route into an IS-IS
routing domain.
•
The route-map keyword and map-name argument
specify the conditions under which the IPv4 or IPv6
default route is advertised.
Example:
RP/0/RP0/CPU0:router(config-isis-af)#
default-information originate
•
If the route-map keyword is omitted, then the IPv4 or
IPv6 default route is unconditionally advertised at
Level 2.
redistribute isis instance [level-1 | level-2 |
level-1-2] [metric metric] [metric-type
{internal | external}] [policy policy-name]
Step 6
Step 7
(Optional) Redistributes routes from one IS-IS instance into
another instance.
•
In this example, an IS-IS instance redistributes IS-IS
instance 2 routes into its Level 1 area.
Example:
RP/0/RP0/CPU0:router(config-isis-af)#
redistribute isis 2 level-1
summary-prefix [address/prefix-length] [level
{1 | 2}]
(Optional) Allows a Level 1-2 router to summarize Level 1
IPv4 and IPv6 prefixes at Level 2, instead of advertising the
Level 1 prefixes directly when the router advertises the
summary.
or
summary-prefix [ipv6-prefix/prefix-length]
[level {1 | 2}]
•
or
•
This example specifies an IPv4 address and mask.
Example:
RP/0/RP0/CPU0:router(config-isis-af)#
summary-prefix 10.1.0.0/16 level 1
This example specifies an IPv6 prefix, and the
command must be in the form documented in RFC 2373
in which the address is specified in hexadecimal using
16-bit values between colons.
or
RP/0/RP0/CPU0:router(config-isis-af)#
summary-prefix 3003:xxxx::/24 level 1
•
Note that IPv6 prefixes must be configured only in the
IPv6 router address family configuration submode, and
IPv4 prefixes in the IPv4 router address family
configuration submode.
maximum-paths route-number
Step 8
Step 9
(Optional) Configures the maximum number of parallel
paths allowed in a routing table.
Example:
RP/0/RP0/CPU0:router(config-isis-af)#
maximum-paths 16
distance weight [address/prefix-length
[route-list-name]]
(Optional) Defines the administrative distance assigned to
routes discovered by the IS-IS protocol.
•
A different administrative distance may be applied for
IPv4 and IPv6.
Example:
RP/0/RP0/CPU0:router(config-isis-af)# distance
90
Cisco IOS XR Routing Configuration Guide
RC-121
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Configuration Examples for Implementing IS-IS on Cisco IOS XR Software
Command or Action
Purpose
set-attached-bit
Step 10
(Optional) Configures an IS-IS instance with an attached bit
in the Level 1 LSP.
Example:
RP/0/RP0/CPU0:router(config-isis-af)#
set-attached-bit
end
Step 11
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuration Examples for Implementing IS-IS on Cisco IOS XR
Software
This section provides the following configuration examples:
•
•
•
Configuring Single-Topology IS-IS for IPv6: Example
The following example shows single-topology mode being enabled, an IS-IS instance being created, the
NET being defined, IPv6 being configured along with IPv4 on an interface, and IPv4 link topology being
used for IPv6.
This configuration allows POS interface 0/3/0/0 to form adjacencies for both IPv4 and IPv6 addresses.
router isis isp
net 49.0000.0000.0001.00
address-family ipv6 unicast
single-topology
interface POS0/3/0/0
Cisco IOS XR Routing Configuration Guide
RC-122
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Configuration Examples for Implementing IS-IS on Cisco IOS XR Software
address-family ipv4 unicast
!
address-family ipv6 unicast
!
exit
!
interface POS0/3/0/0
ipv4 address 10.0.1.3 255.255.255.0
ipv6 address 2001::1/64
Configuring Multitopology IS-IS for IPv6: Example
The following example shows multitopology IS-IS being configured in IPv6. You need not enable IS-IS
for IPv6 globally on the router.
router isis isp
net 49.0000.0000.0001.00
interface POS0/3/0/0
address-family ipv6 unicast
metric-style wide level 1
exit
!
interface POS0/3/0/0
ipv6 address 2001::1/64
Redistributing IS-IS Routes Between Multiple Instances: Example
The following example shows the attached bit being set for a Level 1 instance. This example shows the
other Level 1 routers in the area being informed that this router is a suitable candidate to get from the
area to the backbone. The Level 1 instance is also propagating routes to the Level 2 instance using
redistribution. Note that the administrative distance is explicitly configured higher on the Level 2
instance to ensure that Level 1 routes are preferred.
router isis 1
is-type level-2-only
net 49.0001.0001.0001.0001.00
address-family ipv4 unicast
distance 116
redistribute isis 2 level 2
!
interface POS0/3/0/0
address-family ipv4 unicast
!
!
router isis 2
is-type level-1
net 49.0002.0001.0001.0002.00
address-family ipv4 unicast
set-attached-bit
!
interface POS0/1/0/0
address-family ipv4 unicast
Cisco IOS XR Routing Configuration Guide
RC-123
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Where to Go Next
Where to Go Next
To implement more IP routing protocols, see the following document modules:
•
•
Implementing OSPF on Cisco IOS XR Software
Implementing BGP on Cisco IOS XR Software
Additional References
The following sections provide references related to implementing IS-IS on Cisco IOS XR software.
Related Documents
Related Topic
Document Title
IS-IS commands: complete command syntax,
command modes, command history, defaults, usage
guidelines, and examples
Cisco IOS XR Routing Command Reference, Release 3.2
MPLS TE feature information
Implementing MPLS Traffic Engineering on Cisco IOS XR Software
module in the Cisco IOS XR Multiprotocol Label Switching
Configuration Guide, Release 3.2
Standards
Standards
Title
Draft-ietf-isis-ipv6-05.txt
Draft-ietf-isis-wg-multi-topology-06.txt
Routing IPv6 with IS-IS, by Christian E. Hopps
M-ISIS: Multi Topology (MT) Routing in IS-IS, by Tony Przygienda,
Naiming Shen, and Nischal Sheth
Draft-ietf-isis-traffic-05.txt
IS-IS Extensions for Traffic Engineering, by Henk Smit and Toni Li
Restart Signalling for IS-IS, by M. Shand and Les Ginsberg
Draft-ietf-isis-restart-04.txt
Draft-ietf-isis-igp-p2p-over-lan-05.txt
Point-to-point operation over LAN in link-state routing protocols, by
Naiming Shen
MIBs
MIBs
MIBs Link
There are no applicable MIBs for this module.
To locate and download MIBs for selected platforms using
Cisco IOS XR software, use the Cisco MIB Locator found at the
following URL:
Cisco IOS XR Routing Configuration Guide
RC-124
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Additional References
RFCs
RFCs
Title
RFC 1142
RFC 1195
RFC 2763
RFC 2966
RFC 2973
RFC 3277
RFC 3373
RFC 3567
OSI IS-IS Intra-domain Routing Protocol
Use of OSI IS-IS for Routing in TCP/IP and Dual Environments
Dynamic Hostname Exchange Mechanism for IS-IS
Domain-wide Prefix Distribution with Two-Level IS-IS
IS-IS Mesh Groups
IS-IS Transient Blackhole Avoidance
Three-Way Handshake for IS-IS Point-to-Point Adjacencies
IS-IS Cryptographic Authentication
Technical Assistance
Description
Link
The Cisco Technical Support website contains
thousands of pages of searchable technical content,
including links to products, technologies, solutions,
technical tips, and tools. Registered Cisco.com users
can log in from this page to access even more content.
Cisco IOS XR Routing Configuration Guide
RC-125
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing IS-IS on Cisco IOS XR Software
Additional References
Cisco IOS XR Routing Configuration Guide
RC-126
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Open Shortest Path First (OSPF) is an Interior Gateway Protocol (IGP) developed by the OSPF working
group of the Internet Engineering Task Force (IETF). Designed expressly for IP networks, OSPF
supports IP subnetting and tagging of externally derived routing information. OSPF also allows packet
authentication and uses IP multicast when sending and receiving packets.
Implementing OSPF version 3 (OSPFv3) expands on OSPF Version 2, to provide support for IPv6
routing prefixes.
This module describes the concepts and tasks you need to implement both versions of OSPF on your
Cisco IOS XR router. The term “OSPF” implies both versions of the routing protocol, unless otherwise
noted.
Note
For more information about OSPF on the Cisco IOS XR software and complete descriptions of the OSPF
documentation for other commands that might appear during execution of a configuration task, search
online in the Cisco IOS XR software master command index.
Feature History for Implementing OSPF on Cisco IOS XR Software
Release
Modification
Release 2.0
Release 3.0
Release 3.2
Release 3.2.2
This feature was introduced on the Cisco CRS-1.
No modification.
Support was added for the Cisco XR 12000 Series Router.
Support was added for the multicast-intact feature.
Contents
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-127
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Prerequisites for Implementing OSPF on Cisco IOS XR Software
Prerequisites for Implementing OSPF on Cisco IOS XR Software
The following are prerequisites for implementing OSPF on Cisco IOS XR Software:
•
•
•
You must be in a user group associated with a task group that includes the proper task IDs for OSPF
commands. Task IDs for commands are listed in the Cisco IOS XR Task ID Reference Guide. For
detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS
XR Software module of the Cisco IOS XR System Security Configuration Guide.
Configuration tasks for OSPFv3 assume that you are familiar with IPv6 addressing and basic
configuration. See the Implementing Network Stack IPv4 and IPv6 on Cisco IOS XR Software
module of the Cisco IOS XR IP Addresses and Services Configuration Guide for information on
IPv6 routing and addressing.
Before you enable OSPFv3 on an interface, you must perform the following tasks:
–
Complete the OSPF network strategy and planning for your IPv6 network. For example, you
must decide whether multiple areas are required.
–
Enable IPv6 on the interface.
•
Configuring authentication (IP Security) is an optional task. If you choose to configure
authentication, you must first decide whether to configure plain text or Message Digest 5 (MD5)
authentication, and whether the authentication applies to an entire area or specific interfaces.
Information About Implementing OSPF on Cisco IOS XR
Software
To implement OSPF you need to understand the following concepts:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-128
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
•
•
OSPF Functional Overview
OSPF is a routing protocol for IP. It is a link-state protocol, as opposed to a distance-vector protocol. A
link-state protocol makes its routing decisions based on the states of the links that connect source and
destination machines. The state of the link is a description of that interface and its relationship to its
neighboring networking devices. The interface information includes the IP address of the interface,
network mask, type of network to which it is connected, routers connected to that network, and so on.
This information is propagated in various types of link-state advertisements (LSAs).
A router stores the collection of received link-state advertisement (LSA) data in a link-state database.
This database includes LSA data for the links of the router. The contents of the database, when subjected
to the Dijkstra algorithm, extract data to create an OSPF routing table. The difference between the
database and the routing table is that the database contains a complete collection of raw data; the routing
table contains a list of shortest paths to known destinations through specific router interface ports.
OSPF is the IGP of choice because it scales to large networks. It uses areas to partition the network into
more manageable sizes and to introduce hierarchy in the network. A router is attached to one or more
areas in a network. All of the networking devices in an area maintain the same complete database
information about the link states in their area only. They do not know about all link states in the network.
The agreement of the database information among the routers in the area is called convergence.
At the intradomain level, OSPF can import routes learned using Intermediate System-to-Intermediate
System (IS-IS). OSPF routes can also be exported into IS-IS. At the interdomain level, OSPF can import
routes learned using Border Gateway Protocol (BGP). OSPF routes can be exported into BGP.
Unlike Routing Information Protocol (RIP), OSPF does not provide periodic routing updates. On
becoming neighbors, OSPF routers establish an adjacency by exchanging and synchronizing their
databases. After that, only changed routing information is propagated. Every router in an area advertises
the costs and states of its links, sending this information in an LSA. This state information is sent to all
OSPF neighbors one hop away. All the OSPF neighbors, in turn, send the state information unchanged.
This flooding process continues until all devices in the area have the same link-state database.
To determine the best route to a destination, the software sums all of the costs of the links in a route to
a destination. After each router has received routing information from the other networking devices, it
runs the shortest path first (SPF) algorithm to calculate the best path to each destination network in the
database.
The networking devices running OSPF detect topological changes in the network, flood link-state
updates to neighbors, and quickly converge on a new view of the topology. Each OSPF router in the
network soon has the same topological view again. OSPF allows multiple equal-cost paths to the same
destination. Since all link-state information is flooded and used in the SPF calculation, multiple equal
cost paths can be computed and used for routing.
On broadcast and nonbroadcast multiaccess (NBMA) networks, the designated router (DR) or backup
DR performs the LSA flooding. On point-to-point networks, flooding simply exits an interface directly
to a neighbor.
OSPF runs directly on top of IP; it does not use TCP or User Datagram Protocol (UDP). OSPF performs
its own error correction by means of checksums in its packet header and LSAs.
In OSPFv3, the fundamental concepts are the same as OSPF Version 2, except that support is added for
the increased address size of IPv6. New LSA types are created to carry IPv6 addresses and prefixes, and
the protocol runs on an individual link basis rather than on an individual IP-subnet basis.
Cisco IOS XR Routing Configuration Guide
RC-129
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
OSPF typically requires coordination among many internal routers: Area Border Routers (ABRs), which
are routers attached to multiple areas, and Autonomous System Border Routers (ASBRs) that export
reroutes from other sources (for example, IS-IS, BGP, or static routes) into the OSPF topology. At a
minimum, OSPF-based routers or access servers can be configured with all default parameter values, no
authentication, and interfaces assigned to areas. If you intend to customize your environment, you must
ensure coordinated configurations of all routers.
Key Features Supported in the Cisco IOS XR OSPF Implementation
The Cisco IOS XR implementation of OSPF conforms to the OSPF Version 2 and OSPF Version 3
specifications detailed in the Internet RFC 2328 and RFC 2740, respectively.
The following key features are supported in the Cisco IOS XR implementation:
•
•
•
•
•
•
•
Hierarchy—CLI hierarchy is supported.
Inheritance—CLI inheritance is supported.
Stub areas—Definition of stub areas is supported.
NSF—Nonstop forwarding is supported.
SPF throttling—Shortest path first throttling feature is supported.
LSA throttling—LSA throttling feature is supported.
Fast convergence—SPF and LSA throttle timers are set, configuring fast convergence. The OSPF
LSA throttling feature provides a dynamic mechanism to slow down LSA updates in OSPF during
network instability. LSA throttling also allows faster OSPF convergence by providing LSA rate
limiting in milliseconds.
•
•
•
Route redistribution—Routes learned using any IP routing protocol can be redistributed into any
other IP routing protocol.
Authentication—Plain text and MD5 authentication among neighboring routers within an area is
supported.
Routing interface parameters—Configurable parameters supported include interface output cost,
retransmission interval, interface transmit delay, router priority, router “dead” and hello intervals,
and authentication key.
•
•
•
Virtual links—Virtual links are supported.
Not-so-stubby area (NSSA)—RFC 1587 is supported.
OSPF over demand circuit—RFC 1793 is supported.
Cisco IOS XR Routing Configuration Guide
RC-130
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
Comparison of Cisco IOS XR OSPFv3 and OSPFv2
Much of the OSPFv3 protocol is the same as in OSPFv2. OSPFv3 is described in RFC 2740.
The key differences between the Cisco IOS XR OSPFv3 and OSPFv2 protocols are as follows:
•
•
OSPFv3 expands on OSPFv2 to provide support for IPv6 routing prefixes and the larger size of IPv6
addresses.
When using an NBMA interface in OSPFv3, users must manually configure the router with the list
of neighbors. Neighboring routers are identified by the link local address of the attached interface
of the neighbor.
•
•
•
Unlike in OSPFv2, multiple OSPFv3 processes can be run on a link.
LSAs in OSPFv3 are expressed as “prefix and prefix length” instead of “address and mask.”
The router ID is a 32-bit number with no relationship to an IPv6 address.
Importing Addresses into OSPFv3
When importing into OSPFv3 the set of addresses configured on an OSPFv3 interface, users cannot
select specific addresses to be imported. Either all addresses are imported or no addresses are imported.
OSPF Hierarchical CLI and CLI Inheritance
Cisco IOS XR software introduces new OSPF configuration fundamentals consisting of hierarchical
CLI and CLI inheritance.
Hierarchical CLI is the grouping of related network component information at defined hierarchical
levels such as at the router, area, and interface levels. Hierarchical CLI allows for easier configuration,
maintenance, and troubleshooting of OSPF configurations. When configuration commands are
displayed together in their hierarchical context, visual inspections are simplified. Hierarchical CLI is
intrinsic for CLI inheritance to be supported.
With CLI inheritance support, you need not explicitly configure a parameter for an area or interface. In
Cisco IOS XR, the parameters of interfaces in the same area can be exclusively configured with a single
command, or parameter values can be inherited from a higher hierarchical level—such as from the area
configuration level or the router ospf configuration levels.
For example, the hello interval value for an interface is determined by this precedence “IF” statement:
If the hello interval command is configured at the interface configuration level, then use the
interface configured value, else
If the hello interval command is configured at the area configuration level, then use the area
configured value, else
If the hello interval command is configured at the router ospf configuration level, then use the
router ospf configured value, else
Use the default value of the command.
Cisco IOS XR Routing Configuration Guide
RC-131
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
Tip
Understanding hierarchical CLI and CLI inheritance saves you considerable configuration time. See the
page RC-155 to understand how to implement these fundamentals. In addition, Cisco IOS XR examples
are provided in the “Configuration Examples for Implementing OSPF on Cisco IOS XR Software”
OSPF Routing Components
Before implementing OSPF, you must know what the routing components are and what purpose they
serve. They consist of the autonomous system, area types, interior routers, ABRs, and ASBRs.
Figure 6 illustrates the routing components in an OSPF network topology.
Figure 6
OSPF Routing Components
OSPF Domain
(BGP autonomous
system 109)
Area 0
backbone
R3
Area 2
Area 1
stub area
ABR 2
ABR 1
R1
R2
ASBR 1
ASBR 2
OSPF Domain
(BGP autonomous
system 65200)
Area 3
Autonomous Systems
The autonomous system is a collection of networks, under the same administrative control, that share
routing information with each other. An autonomous system is also referred to as a routing domain.
Figure 6 shows two autonomous systems: A and B. An autonomous system can consist of one or more
OSPF areas.
Cisco IOS XR Routing Configuration Guide
RC-132
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
Areas
Areas allow the subdivision of an autonomous system into smaller, more manageable networks or sets
of adjacent networks. As shown in Figure 6, autonomous system A consists of three areas: Area 0, Area
1, and Area 2.
OSPF hides the topology of an area from the rest of the autonomous system. The network topology for
an area is visible only to routers inside that area. When OSPF routing is within an area, it is called
intra-area routing. This routing limits the amount of link-state information flood into the network,
reducing routing traffic. It also reduces the size of the topology information in each router, conserving
processing and memory requirements in each router.
Also, the routers within an area cannot see the detailed network topology outside the area. Because of
this restricted view of topological information, you can control traffic flow between areas and reduce
routing traffic when the entire autonomous system is a single routing domain.
Backbone Area
A backbone area is responsible for distributing routing information between multiple areas of an
autonomous system. OSPF routing occurring outside of an area is called interarea routing.
The backbone itself has all properties of an area. It consists of ABRs, routers, and networks only on the
reserved area ID of 0.0.0.0.
Stub Area
A stub area is an area that does not accept or detailed network information external to the area. A stub
area typically has only one router that interfaces the area to the rest of the autonomous system. The stub
ABR advertises a single default route to external destinations into the stub area. Routers within a stub
area use this route for destinations outside the area and the autonomous system. This relationship
conserves LSA database space that would otherwise be used to store external LSAs flooded into the area.
In Figure 6, Area 2 is a stub area that is reached only through ABR 2. Area 0 cannot be a stub area.
Not-so-Stubby Area (NSSA)
NSSA is similar to the stub area. NSSA does not flood Type 5 external LSAs from the core into the area,
but can import autonomous system external routes in a limited fashion within the area.
NSSA allows importing of Type 7 autonomous system external routes within an NSSA area by
redistribution. These Type 7 LSAs are translated into Type 5 LSAs by NSSA ABRs, which are flooded
throughout the whole routing domain. Summarization and filtering are supported during the translation.
Use NSSA to simplify administration if you are a network administrator that must connect a central site
using OSPF to a remote site that is using a different routing protocol.
Before NSSA, the connection between the corporate site border router and remote router could not be
run as an OSPF stub area because routes for the remote site could not be redistributed into a stub area,
and two routing protocols needed to be maintained. A simple protocol like RIP was usually run and
handled the redistribution. With NSSA, you can extend OSPF to cover the remote connection by
defining the area between the corporate router and remote router as an NSSA. Area 0 cannot be an
NSSA.
Cisco IOS XR Routing Configuration Guide
RC-133
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
Routers
The OSPF network is composed of ABRs, ASBRs, and interior routers.
Area Border Routers (ABR)
ABRs are routers with multiple interfaces that connect directly to networks in two or more areas. An
ABR runs a separate copy of the OSPF algorithm and maintains separate routing data for each area that
is attached to, including the backbone area. ABRs also send configuration summaries for their attached
areas to the backbone area, which then distributes this information to other OSPF areas in the
ABR 2 interfaces the backbone Area 0 to Area 2, a stub area.
Autonomous System Boundary Routers (ASBR)
ASBRs provide connectivity from one autonomous system to another system. ASBRs exchange their
autonomous system routing information with boundary routers in other autonomous systems. Every
router inside an autonomous system knows how to reach the boundary routers for its autonomous
system.
ASBRs can import external routing information from other protocols like BGP and redistribute them as
AS-external (ASE) Type 5 LSAs to the OSPF network. If the Cisco IOS XR router is an ASBR, you can
configure it to advertise VIP addresses for content as autonomous system external routes. In this way,
ASBRs flood information about external networks to routers within the OSPF network.
ASBR routes can be advertised as a Type 1 or Type 2 ASE. The difference between Type 1 and Type 2
is how the cost is calculated. For a Type 2 ASE, only the external cost (metric) is considered when
multiple paths to the same destination are compared. For a Type 1 ASE, the combination of the external
cost and cost to reach the ASBR is used. Type 2 external cost is the default and is always more costly
than an OSPF route and used only if no OSPF route exists.
Interior Routers
The interior routers (such as R1 in Figure 6) attached to one area (for example, all the interfaces reside
in the same area).
OSPF Process and Router ID
An OSPF process is a logical routing entity running OSPF in a physical router. This logical routing entity
should not be confused with the logical routing feature that allows a system administrator (known as the
Cisco IOS XR Owner) to partition the physical box into separate routers.
A physical router can run multiple OSPF processes, although the only reason to do so would be to
connect two or more OSPF domains. Each process has its own link-state database. The routes in the
routing table are calculated from the link-state database. One OSPF process does not share routes with
another OSPF process unless the routes are redistributed.
Each OSPF process is identified by a router ID. The router ID must be unique across the entire routing
domain. OSPFv2 obtains a router ID from the following sources, in order of decreasing preference:
OSPF attempts to obtain a router ID in the following ways (in order of preference):
•
The 32-bit numeric value specified by the OSPF router-id command in router configuration mode.
(This value can be any 32-bit value. It is not restricted to the IPv4 addresses assigned to interfaces
on this router, and need not be a routable IPv4 address.)
Cisco IOS XR Routing Configuration Guide
RC-134
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
•
•
The primary IPv4 address of the interface specified by the OSPF router-id command.
The 32-bit numeric value specified by the router-id command in global configuration mode. (This
value must be an IPv4 address assigned to an interface on this router.)
•
•
By using the highest IPv4 address on a loopback interface in the system if the router is booted with
saved loopback address configuration.
The primary IPv4 address of an interface over which this OSPF process is running.
We recommend that the router ID be set by the router-id command in router configuration mode.
Separate OSPF processes could share the same router ID, in which case they cannot reside in the same
OSPF routing domain.
Supported OSPF Network Types
OSPF classifies different media into the following three types of networks by default:
•
•
•
NBMA networks (POS)
Point-to-point networks (POS)
Broadcast networks (Gigabit Ethernet)
You can configure your Cisco IOS XR network as either a broadcast or an NBMA network. Using this
feature, you can configure broadcast networks as NBMA networks when, for example, you have routers
in your network that do not support multicast addressing.
Route Authentication Methods for OSPF Version 2
OSPF Version 2 supports two types of route authentication: plain text authentication and MD5
authentication. By default, no authentication is enabled (referred to as null authentication in RFC 2178).
Both plain text and MD5 authentication are performed on changed routing information that arrive on an
interface. The sender and receiver must know the authentication password or key. For both types of
authentication, a router sends a routing update packet with a key and corresponding key number. The
receiving router checks the key number and key against its own stored key number and key. If the key
numbers and keys match, the router accepts the routing update packet. If they do not match, the routing
update is discarded.
Plain Text Authentication
Plain text authentication (also known as Type 1 authentication) uses a password that travels on the
physical medium and is easily visible to someone that does not have access permission and could use
the password to infiltrate a network. Therefore, plain text authentication does not provide security. It
might protect against a faulty implementation of OSPF or a misconfigured OSPF interface trying to send
erroneous OSPF packets.
MD5 Authentication
MD5 authentication provides a means of security. No password travels on the physical medium. Instead,
the router uses MD5 to produce a message digest of the OSPF packet plus the key, which is sent on the
physical medium. Using MD5 authentication prevents a router from accepting unauthorized or
deliberately malicious routing updates, which could compromise your network security by diverting
your traffic.
Cisco IOS XR Routing Configuration Guide
RC-135
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
Note
MD5 authentication supports multiple keys, requiring that a key number be associated with a key.
Authentication Strategies
Authentication can be specified for an entire process or area, or on an interface or a virtual link. An
interface or virtual link can be configured for only one type of authentication, not both. Authentication
configured for an interface or virtual link overrides authentication configured for the area or process.
If you intend for all interfaces in an area to use the same type of authentication, you can configure fewer
commands if you use the area authentication command (and specify the message-digest keyword if
you want the entire area to use MD5 authentication). This strategy requires fewer commands than
specifying authentication for each interface.
Key Rollover
To support the changing of a plain text key or MD5 key in an operational network without disrupting
OSPF adjacencies (and hence the topology), a key rollover mechanism is supported. As a network
administrator configures the new key into the multiple networking devices that communicate, some time
exists when different devices are using both a new key and an old key. If an interface is configured with
a new key, the software sends two copies of the same packet, each authenticated by the old key and new
key. The software tracks which devices start using the new key, and the software stops sending duplicate
packets after it detects that all of its neighbors are using the new key. The software then discards the old
key. The network administrator must then remove the old key from each the configuration file of each
router.
Neighbors and Adjacency for OSPF
Routers that share a segment (Layer 2 link between two interfaces) become neighbors on that segment.
OSPF uses the hello protocol as a neighbor discovery and keep alive mechanism. The hello protocol
involves receiving and periodically sending hello packets out each interface. The hello packets list all
known OSPF neighbors on the interface. Routers become neighbors when they see themselves listed in
the hello packet of the neighbor. After two routers are neighbors, they may proceed to exchange and
synchronize their databases, which creates an adjacency. On broadcast and NBMA networks all
neighboring routers have an adjacency.
Designated Router (DR) for OSPF
On point-to-point and point-to-multipoint networks, the Cisco IOS XR software floods routing updates
to immediate neighbors. No DR or backup DR (BDR) exists; all routing information is flooded to each
router.
On broadcast or NBMA segments only, OSPF minimizes the amount of information being exchanged on
a segment by choosing one router to be a DR and one router to be a BDR. Thus, the routers on the
segment have a central point of contact for information exchange. Instead of each router exchanging
routing updates with every other router on the segment, each router exchanges information with the DR
and BDR. The DR and BDR relay the information to the other routers. On broadcast network segments
the number of OSPF packets is further reduced by the DR and BDR sending such OSPF updates to a
multicast IP address that all OSPF routers on the network segment are listening on.
Cisco IOS XR Routing Configuration Guide
RC-136
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
The software looks at the priority of the routers on the segment to determine which routers are the DR
and BDR. The router with the highest priority is elected the DR. If there is a tie, then the router with the
higher router ID takes precedence. After the DR is elected, the BDR is elected the same way. A router
with a router priority set to zero is ineligible to become the DR or BDR.
Default Route for OSPF
Type 5 (ASE) LSAs are generated and flooded to all areas except stub areas. For the routers in a stub
area to be able to route packets to destinations outside the stub area, a default route is injected by the
ABR attached to the stub area.
The cost of the default route is 1 (default) or is determined by the value specified in the default-cost
command.
Link-State Advertisement Types for OSPF Version 2
Each of the following LSA types has a different purpose:
•
Router LSA (Type 1)—Describes the links that the router has within a single area, and the cost of
each link. These LSAs are flooded within an area only. The LSA indicates if the router can compute
paths based on quality of service (QoS), whether it is an ABR or ASBR, and if it is one end of a
virtual link. Type 1 LSAs are also used to advertise stub networks.
•
Network LSA (Type 2)—Describes the link state and cost information for all routers attached a
multiaccess network segment. This LSA lists all the routers that have interfaces attached to the
network segment. It is the job of the designated router of a network segment to generate and track
the contents of this LSA.
•
•
•
Summary LSA for ABRs (Type 3)—Advertises internal networks to routers in other areas (interarea
routes). Type 3 LSAs may represent a single network or a set of networks aggregated into one prefix.
Only ABRs generate summary LSAs.
Summary LSA for ASBRs (Type 4)—Advertises and ASBR and the cost to reach it. Routers that
are trying to reach an external network use these advertisements to determine the best path to the
next hop. ABRs generate Type 4 LSAs.
Autonomous system external LSA (Type 5)—Redistributes routes from another autonomous
system, usually from a different routing protocol into OSPF.
Link-State Advertisement Types for OSPFv3
Each of the following LSA types has a different purpose:
•
Router LSA (Type 1)—Describes the link state and costs of a the router link to the area. These LSAs
are flooded within an area only. The LSA indicates whether the router is an ABR or ASBR and if it
is one end of a virtual link. Type 1 LSAs are also used to advertise stub networks. In OSPFv3, these
LSAs have no address information and are network protocol independent. In OSPFv3, router
interface information may be spread across multiple router LSAs. Receivers must concatenate all
router LSAs originated by a given router before running the SPF calculation.
Cisco IOS XR Routing Configuration Guide
RC-137
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
•
•
Network LSA (Type 2)—Describes the link state and cost information for all routers attached to a
multiaccess network segment. This LSA lists all OSPF routers that have interfaces attached to the
network segment. Only the elected designated router for the network segment can generate and track
the network LSA for the segment. In OSPFv3, network LSAs have no address information and are
network-protocol-independent.
Interarea-prefix LSA for ABRs (Type 3)—Advertises internal networks to routers in other areas
(interarea routes). Type 3 LSAs may represent a single network or set of networks aggregated into
one prefix. Only ABRs generate Type 3 LSAs. In OSPFv3, addresses for these LSAs are expressed
as “prefix and prefix length” instead of “address and mask.” The default route is expressed as a
prefix with length 0.
•
•
Interarea-router LSA for ASBRs (Type 4)—Advertises an ASBR and the cost to reach it. Routers
that are trying to reach an external network use these advertisements to determine the best path to
the next hop. ABRs generate Type 4 LSAs.
Autonomous system external LSA (Type 5)—Redistributes routes from another autonomous
system, usually from a different routing protocol into OSPF. In OSPFv3, addresses for these LSAs
are expressed as “prefix and prefix length” instead of “address and mask.” The default route is
expressed as a prefix with length 0.
•
•
Link LSA (Type 8)—Has link-local flooding scope and is never flooded beyond the link with which
it is associated. Link LSAs provide the link-local address of the router to all other routers attached
to the link or network segment, inform other routers attached to the link of a list of IPv6 prefixes to
associate with the link, and allow the router to assert a collection of Options bits to associate with
the network LSA that is originated for the link.
Intra-area-prefix LSAs (Type 9)—A router can originate multiple intra-area-prefix LSAs for every
router or transit network, each with a unique link-state ID. The link-state ID for each
intra-area-prefix LSA describes its association to either the router LSA or network LSA and
contains prefixes for stub and transit networks.
An address prefix occurs in almost all newly defined LSAs. The prefix is represented by three fields:
Prefix Length, Prefix Options, and Address Prefix. In OSPFv3, addresses for these LSAs are expressed
as “prefix and prefix length” instead of “address and mask.” The default route is expressed as a prefix
with length 0.
Inter-area-prefix and intra-area-prefix LSAs carry all IPv6 prefix information that, in IPv4, is included
in router LSAs and network LSAs. The Options field in certain LSAs (router LSAs, network LSAs,
interarea-router LSAs, and link LSAs) has been expanded to 24 bits to provide support for OSPF in IPv6.
In OSPFv3, the sole function of link-state ID in interarea-prefix LSAs, interarea-router LSAs, and
autonomous system external LSAs is to identify individual pieces of the link-state database. All
addresses or router IDs that are expressed by the link-state ID in OSPF Version 2 are carried in the body
of the LSA in OSPFv3.
Virtual Link and Transit Area for OSPF
In OSPF, routing information from all areas is first summarized to the backbone area by ABRs. The same
ABRs, in turn, propagate such received information to their attached areas. Such hierarchical
distribution of routing information requires that all areas be connected to the backbone area (Area 0).
Occasions might exist for which an area must be defined, but it cannot be physically connected to Area 0.
Examples of such an occasion might be if your company makes a new acquisition that includes an OSPF
area, or if Area 0 itself is partitioned.
Cisco IOS XR Routing Configuration Guide
RC-138
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
In the case in which an area cannot be connected to Area 0, you must configure a virtual link between
that area and Area 0. The two endpoints of a virtual link are ABRs, and the virtual link must be
configured in both routers. The common nonbackbone area to which the two routers belong is called a
transit area. A virtual link specifies the transit area and the router ID of the other virtual endpoint (the
other ABR).
A virtual link cannot be configured through a stub area or NSSA.
Figure 7 illustrates a virtual link from Area 3 to Area 0.
Figure 7
Virtual Link to Area 0
OSPF Domain (BGP autonomous system 109)
Area 0
Backbone
Area 1
Area 3
ABR 2
ABR 1
ABR 3
Transit Area
ASBR 1
Router ID 5.5.5.5
Router ID 4.4.4.4
ASBR 2
Route Redistribution for OSPF
Redistribution allows different routing protocols to exchange routing information. This technique can
be used to allow connectivity to span multiple routing protocols. It is important to remember that the
redistribute command controls redistribution into an OSPF process and not from OSPF. See the
for an example of route redistribution for OSPF.
OSPF Shortest Path First Throttling
OSPF SPF throttling makes it possible to configure SPF scheduling in millisecond intervals and to
potentially delay SPF calculations during network instability. SPF is scheduled to calculate the Shortest
Path Tree (SPT) when there is a change in topology. One SPF run may include multiple topology change
events.
Cisco IOS XR Routing Configuration Guide
RC-139
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
The interval at which the SPF calculations occur is chosen dynamically and based on the frequency of
topology changes in the network. The chosen interval is within the boundary of the user-specified value
ranges. If network topology is unstable, SPF throttling calculates SPF scheduling intervals to be longer
until topology becomes stable.
SPF calculations occur at the interval set by the timers throttle spf command. The wait interval
indicates the amount of time to wait until the next SPF calculation occurs. Each wait interval after that
calculation is twice as long as the previous interval until the interval reaches the maximum wait time
specified.
The SPF timing can be better explained using an example. In this example, the start interval is set at
5 milliseconds (ms), initial wait interval at 1000 ms, and maximum wait time at 90,000 ms.
timers spf 5 1000 90000
Figure 8 shows the intervals at which the SPF calculations occur as long as at least one topology change
event is received in a given wait interval.
Figure 8
SPF Calculation Intervals Set by the timers spf Command
5 ms
2000 ms
4000 ms
8000 ms
32000 ms
90000 ms
1000 ms
16000 ms
64000 ms
Notice that the wait interval between SPF calculations doubles when at least one topology change event
is received during the previous wait interval. After the maximum wait time is reached, the wait interval
remains the same until the topology stabilizes and no event is received in that interval.
If the first topology change event is received after the current wait interval, the SPF calculation is
delayed by the amount of time specified as the start interval. The subsequent wait intervals continue to
follow the dynamic pattern.
If the first topology change event occurs after the maximum wait interval begins, the SPF calculation is
again scheduled at the start interval and subsequent wait intervals are reset according to the parameters
received after the start of the maximum wait time interval and that the SPF intervals have been reset.
Figure 9
Timer Intervals Reset After Topology Change Event
Topology change event
64000 ms
1000 ms
5 ms 2000 ms
4000 ms
16000 ms
90000 ms
8000 ms
90000 ms
SPF scheduled at
start interval
Nonstop Forwarding for OSPF Version 2
Cisco IOS XR NSF for OSPF Version 2 allows for the forwarding of data packets to continue along
known routes while the routing protocol information is being restored following a failover. With NSF,
peer networking devices do not experience routing flaps. During failover, data traffic is forwarded
Cisco IOS XR Routing Configuration Guide
RC-140
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
through intelligent line cards while the standby Route Processor (RP) assumes control from the failed
RP. The ability of line cards to remain up through a failover and to be kept current with the Forwarding
Information Base (FIB) on the active RP is key to Cisco IOS XR NSF operation.
Routing protocols, such as OSPF, run only on the active RP or DRP and receive routing updates from
their neighbor routers. When an OSPF NSF-capable router performs an RP failover, it must perform two
tasks to resynchronize its link-state database with its OSPF neighbors. First, it must relearn the available
OSPF neighbors on the network without causing a reset of the neighbor relationship. Second, it must
reacquire the contents of the link-state database for the network.
As quickly as possible after an RP failover, the NSF-capable router sends an OSPF NSF signal to
neighboring NSF-aware devices. This signal is in the form of a link-local LSA generated by the
failed-over router. Neighbor networking devices recognize this signal as a cue that the neighbor
relationship with this router should not be reset. As the NSF-capable router receives signals from other
routers on the network, it can begin to rebuild its neighbor list.
After neighbor relationships are re-established, the NSF-capable router begins to resynchronize its
database with all of its NSF-aware neighbors. At this point, the routing information is exchanged
between the OSPF neighbors. After this exchange is completed, the NSF-capable device uses the routing
information to remove stale routes, update the RIB, and update the FIB with the new forwarding
information. OSPF on the router as well as the OSPF neighbors are now fully converged.
Note
The standardized IETF version of NSF, known as OSPF graceful restart (RFC 3623) is also supported.
Load Balancing in OSPF Version 2 and OSPFv3
When a router learns multiple routes to a specific network by using multiple routing processes (or
routing protocols), it installs the route with the lowest administrative distance in the routing table.
Sometimes the router must select a route from among many learned by using the same routing process
with the same administrative distance. In this case, the router chooses the path with the lowest cost (or
metric) to the destination. Each routing process calculates its cost differently; the costs may need to be
manipulated to achieve load balancing.
OSPF performs load balancing automatically. If OSPF finds that it can reach a destination through more
than one interface and each path has the same cost, it installs each path in the routing table. The only
restriction on the number of paths to the same destination is controlled by the maximum-paths (OSPF)
command. The default number of maximum paths is 32 for Cisco CRS-1 routers and 16 for
Cisco XR 12000 Series Routers. The range is from 1 to 32 for Cisco CRS-1 routers and 1 to 16 for
Cisco XR 12000 Series Routers.
Graceful Restart for OSPFv3
In the current release, various restart scenarios in the control plane of an IPv6-enabled router can disrupt
data forwarding. The OSPFv3 Graceful Restart feature can preserve the data plane capability in the
following circumstances:
•
•
•
RP failure, resulting in a switchover to the backup processor
Planned OSPFv3 process restart, such as software upgrade or downgrade
Unplanned OSPFv3 process restart, such as a process crash
This feature supports non-stop data forwarding on established routes while the OSPFv3 routing protocol
is restarting. (Therefore, this feature enhances high availability of IPv6 forwarding.)
Cisco IOS XR Routing Configuration Guide
RC-141
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
Modes of Graceful Restart Operation
The two operational modes that a router can be in for this feature are restart mode and helper mode.
Restart mode occurs when the OSPFv3 process is doing a graceful restart. Helper mode refers to the
neighbor routers that continue to forward traffic on established OSPFv3 routes while OSPFv3 is
restarting on a neighboring router.
Restart Mode
When the OSPFv3 process starts up, it determines whether it must attempt a graceful restart. The
determination is based on whether graceful restart was previously enabled. (OSPFv3 does not attempt a
graceful restart upon the first-time startup of the router.) When OSPFv3 graceful restart is enabled, it
changes the purge timer in the RIB to a non-zero value. See Configuring OSPFv3 Graceful Restart,
page RC-181, for descriptions of how to enable and configure the Graceful Restart feature.
During a graceful restart, the router does not populate OSPFv3 routes in the RIB. It tries to bring up full
adjacencies with the fully-adjacent neighbors that OSPFv3 had before the restart. Eventually, the
OSPFv3 process indicates to the RIB that it has converged either for the purpose of terminating the
graceful restart (for any reason) or because it has completed the graceful restart.
The following are general details about restart mode. More detailed information on behavior and certain
•
•
•
If the OSPFv3 attempts a restart too soon after the most recent restart, the OSPFv3 process is most
likely crashing repeatedly, so the new graceful restart stops running. To control the period between
allowable graceful restarts, use the graceful-restart interval command. A description of how to set
this time period appears in the section Configuring the Minimum Time Required Between Restarts,
When OSFPv3 starts a graceful restart with the first interface that comes up, a timer starts running
to limit the duration (or lifetime) of the graceful restart. You can configure this period with the
graceful-restart lifetime command. On each interface that comes up, a grace LSA (type 11) is
flooded to indicate to the neighboring routers that this router is attempting graceful restart. The
neighbors enter into helper mode.
The designated router and backup designated router check of the hello packet received from the
restarting neighbor is bypassed because it might not be valid.
Helper Mode
Helper mode is enabled by default. When a (helper) router receives a grace LSA (type 11) from a router
that is attempting a graceful restart, the following events occur:
•
If helper mode has been disabled through the graceful-restart helper disable command, the router
drops the LSA packet.
•
If helper mode is enabled, the router enters helper mode if all of the following conditions are met.
–
–
–
–
The local router itself is not attempting a graceful restart.
The local (helping) router has full adjacency with the sending neighbor.
The value of lsage (link state age) in the received LSA is less than the requested grace period.
The sender of the grace LSA is the same as the originator of the grace LSA.
Cisco IOS XR Routing Configuration Guide
RC-142
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
•
Upon entering helper mode, a router performs its helper function for a specific period of time. This
time period is the lifetime value from the router that is in restart mode—minus the value of lsage in
the received grace LSA. If the graceful restart succeeds in time, the helper’s timer is stopped before
it expires. If the helper’s timer does expire, the adjacency to the restarting router is brought down,
and normal OSPFv3 functionality resumes.
•
•
The dead timer is not honored by the router that is in helper mode.
A router in helper mode ceases to perform the helper function in any of the following cases:
–
–
The helper router is able to bring up a FULL adjacency with the restarting router.
The local timer for the helper function expires.
Graceful Restart Requirements and Restrictions
The requirements for supporting the Graceful Restart feature include:
•
Cooperation of a router’s neighbors during a graceful restart. In relation to the router on which
OSPFv3 is restarting, each router is called a helper.
•
•
•
•
•
All neighbors of the router that does a graceful restart must be capable of doing a graceful restart.
A graceful restart does not occur upon the first-time startup of a router.
OSPFv3 neighbor information and database information are not check-pointed.
An OSPFv3 process rebuilds adjacencies after it restarts.
To ensure consistent databases after a restart, the OSPFv3 configuration must be identical to the
configuration before the restart. (This requirement applies to self-originated information in the local
database.) A graceful restart can fail if configurations change during the operation. In this case, data
forwarding would be affected. OSPFv3 resumes operation by regenerating all its LSAs and
resynchronizing its database with all its neighbors.
•
•
Although IPv6 FIB tables remain unchanged during a graceful restart, these tables eventually mark
the routes as stale through the use of a holddown timer. Enough time is allowed for the protocols to
rebuild state information and converge.
The router on which OSPFv3 is restarting must send OSPFv3 hellos within the dead interval of the
process restart. Protocols must be able to retain adjacencies with neighbors before the adjacency
dead timer expires. The default for the dead timer is 40 seconds. If hellos do not arrive on the
adjacency before the dead timer expires, the router takes down the adjacency. The OSPFv3 Graceful
Restart feature does not function properly if the dead timer is configured to be less than the time
required to send hellos after the OSPFv3 process restarts.
•
•
Simultaneous graceful restart sessions on multiple routers are not supported on a single network
segment. If a router determines that multiple routers are in restart mode, it terminates any local
graceful restart operation.
This feature utilizes the available support for changing the purge time of existing OSPFv3 routes in
the routing information base (RIB). When graceful restart is enabled, the purge timer is set to 90
seconds by default. If graceful restart is disabled, the purge timer setting is 0.
•
•
This feature has an associated grace LSA. This link-scope LSA is type 11.
According to the RFC, the OSPFv3 process should flush all old, self-originated LSAs during a
restart. With the Graceful Restart feature, however, the router delays this flushing of unknown
self-originated LSAs during a graceful restart. OSPFv3 can learn new information and build new
LSAs to replace the old LSAs. When the delay is over, all old LSAs are flushed.
Cisco IOS XR Routing Configuration Guide
RC-143
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
•
If graceful restart is enabled, the adjacency creation time of all the neighbors is saved in the system
database (SysDB). The purpose for saving the creation time is so that OSPFv3 can use the original
adjacency creation time to display the uptime for that neighbor after the restart.
Multicast-Intact Feature
The multicast-intact feature provides the ability to run multicast routing (PIM) when IGP shortcuts are
configured and active on the router. Both OSPFv2 and IS-IS support the multicast-intact feature.
You can enable multicast-intact in the IGP when multicast routing protocols (PIM) are configured and
IGP shortcuts are configured on the router. IGP shortcuts are MPLS tunnels that are exposed to IGP. The
IGPs routes IP traffic over these tunnels to destinations that are downstream from the egress router of
the tunnel (from an SPF perspective). PIM cannot use IGP shortcuts for propagating PIM joins because
reverse path forwarding (RPF) cannot work across a unidirectional tunnel.
When you enable multicast-intact on an IGP, the IGP publishes a parallel or alternate set of equal-cost
next-hops for use by PIM. These next-hops are called mcast-intact next-hops. The mcast-intact
next-hops have the following attributes:
•
•
They are guaranteed not to contain any IGP shortcuts.
They are not used for unicast routing but are used only by PIM to look up an IPv4 next-hop to a PIM
source.
•
•
They are not published to the FIB.
When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through
link-state advertisements are published with a set equal-cost mcast-intact next-hops to the RIB. This
attribute applies even when the native next-hops have no IGP shortcuts.
•
In OSPF, the max-paths (number of equal-cost next-hops) limit is applied separately to the native
and mcast-intact next-hops. The number of equal cost mcast-intact next-hops is the same as that
configured for the native next-hops. (In IS-IS, the behavior is slightly different.)
How to Implement OSPF on Cisco IOS XR Software
This section contains the following procedures:
•
•
•
•
Enabling OSPF, page RC-145 (required)
(optional)
•
(optional)
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-144
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
•
•
•
Enabling OSPF
This task explains how to perform the minimum OSPF configuration on your router that is to enable an
OSPF process with a router ID, configure a backbone or nonbackbone area, and then assign one or more
interfaces on which OSPF runs.
Prerequisites
Although you can configure OSPF before you configure an IP address, no OSPF routing occurs until at
least one IP address is configured.
SUMMARY STEPS
1. configure
2. router ospf process-name
or
router ospfv3 process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. area area-id
5. interface type instance
6. Repeat Step 5 for each interface that use OSPF.
7. log adjacency changes [detail] [enable | disable]
8. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-145
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Step 2
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
or
router ospfv3 process-name
or
Enables OSPFv3 routing for the specified routing process,
and places the router in router ospfv3 configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
Note
The process-name argument is any alphanumeric
or
string no longer than 40 characters.
RP/0/RP0/CPU0:router(config)# router ospfv3 1
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Configures a router ID for the OSPF process.
Note
We recommend using a stable IP address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
area area-id
Step 4
Enters area configuration mode and configures an area for
the OSPF process.
•
•
•
Backbone areas have an area ID of 0.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 0
Nonbackbone areas have a nonzero area ID.
The area-id argument can be entered in dotted-decimal
or IPv4 address notation, such as area 1000 or
area 0.0.3.232. However, you must choose one form or
the other for an area. We recommend using the IPv4
address notation.
interface type instance
Step 5
Enters interface configuration mode and associates one or
more interfaces for the area configured in Step 4.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
POS 0/1/0/3
Step 6
Repeat Step 5 for each interface that uses OSPF.
—
Cisco IOS XR Routing Configuration Guide
RC-146
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
(Optional) Requests notification of neighbor changes.
log adjacency changes [detail] [enable |
disable]
Step 7
•
•
By default, this feature is enabled.
The messages generated by neighbor changes are
considered notifications, which are categorized as
severity Level 5 in the logging console command. The
logging console command controls which severity
level of messages are sent to the console. By default, all
severity level messages are sent.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-if)# log
adjacency changes detail
end
Step 8
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-if)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf-ar-if)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring Stub and Not-so-Stubby Area Types
This task explains how to configure the stub area and the NSSA for OSPF.
SUMMARY STEPS
1. configure
2. router ospf process-name
or
router ospfv3 process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. area area-id
5. stub [no-summary]
or
nssa [no-redistribution] [default-information-originate] [no-summary]
Cisco IOS XR Routing Configuration Guide
RC-147
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
6. stub
or
nssa
7. default-cost cost
8. end
or
commit
9. Repeat this task on all other routers in the stub area or NSSA.
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
or
router ospfv3 process-name
or
Enables OSPFv3 routing for the specified routing process,
and places the router in router ospfv3 configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
Note
The process-name argument is any alphanumeric
or
string no longer than 40 characters.
RP/0/RP0/CPU0:router(config)# router ospfv3 1
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Step 4
Configures a router ID for the OSPF process.
Note
We recommend using a stable IP address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
area area-id
Enters area configuration mode and configures a
nonbackbone area for the OSPF process.
•
The area-id argument can be entered in dotted-decimal
or IPv4 address notation, such as area 1000 or
area 0.0.3.232. However, you must choose one form or
the other for an area. We recommend using the IPv4
address notation.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 1
Cisco IOS XR Routing Configuration Guide
RC-148
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
Defines the nonbackbone area as a stub area.
stub [no-summary]
Step 5
or
•
nssa [no-redistribution]
[default-information-originate] [no-summary]
•
Specify the no-summary keyword to further reduce the
number of LSAs sent into a stub area. This keyword
prevents the ABR from sending summary link-state
advertisements (Type 3) in the stub area.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# stub no
summary
or
or
RP/0/RP0/CPU0:router(config-ospf-ar)# nssa
no-redistribution
Defines an area as an NSSA.
•
stub
Step 6
(Optional) Turns off the options configured for stub and
NSSA areas.
or
nssa
•
•
If you configured the stub and NSSA areas using the
optional keywords (no-summary, no-redistribution,
default-information-originate, and no-summary) in
Step 5, you must now reissue the stub and nssa
commands without the keywords—rather than using
the no form of the command.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# stub
or
RP/0/RP0/CPU0:router(config-ospf-ar)# nssa
For example, the no nssa
default-information-originate form of the command
changes the NSSA area into a normal area that
inadvertently brings down the existing adjacencies in
that area.
default-cost cost
Step 7
(Optional) Specifies a cost for the default summary route
sent into a stub area or an NSSA.
•
Use this command only on ABRs attached to the NSSA.
Do not use it on any other routers in the area.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)#
default-cost 15
•
The default cost is 1.
Cisco IOS XR Routing Configuration Guide
RC-149
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
Saves configuration changes.
end
Step 8
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf-ar)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Step 9
Repeat this task on all other routers in the stub area or
NSSA.
—
Configuring Neighbors for Nonbroadcast Networks
This task explains how to configure neighbors for a nonbroadcast network. This task is optional.
Prerequisites
Configuring NBMA networks as either broadcast or nonbroadcast assumes that there are virtual circuits
from every router to every other router or a fully meshed network.
SUMMARY STEPS
1. configure
2. router ospf process-name
or
router ospfv3 process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. area area-id
5. network {broadcast | non-broadcast | {point-to-multipoint [non-broadcast] | point-to-point}}
6. dead-interval seconds
7. hello-interval seconds
8. interface type number
Cisco IOS XR Routing Configuration Guide
RC-150
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
9. neighbor ip-address [priority number] [poll-interval seconds] [cost number]
or
neighbor ipv6-link-local-address [priority number] [poll-interval seconds] [cost number]
[database-filter [all]]
10. Repeat Step 9 for all neighbors on the interface.
11. exit
12. interface type instance
13. neighbor ip-address [priority number] [poll-interval seconds][cost number] [database-filter
[all]]
or
neighbor ipv6-link-local-address [priority number] [poll-interval seconds][cost number]
[database-filter [all]]
14. Repeat Step 13 for all neighbors on the interface.
15. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
or
router ospfv3 process-name
or
Enables OSPFv3 routing for the specified routing process,
and places the router in router ospfv3 configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
Note
The process-name argument is any alphanumeric
or
string no longer than 40 characters.
RP/0/RP0/CPU0:router(config)# router ospfv3 1
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Step 4
Configures a router ID for the OSPF process.
Note
We recommend using a stable IP address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
area area-id
Enters area configuration mode and configures an area for
the OSPF process.
•
•
This example configures a backbone area.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 0
The area-id argument can be entered in dotted-decimal
or IPv4 address notation, such as area 1000 or
area 0.0.3.232. However, you must choose one form or
the other for an area. We recommend using the IPv4
address notation.
Cisco IOS XR Routing Configuration Guide
RC-151
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
network {broadcast | non-broadcast |
{point-to-multipoint [non-broadcast] |
point-to-point}}
Step 5
Configures the OSPF network type to a type other than the
default for a given medium.
•
The example sets the network type to NBMA.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# network
non-broadcast
dead-interval seconds
Step 6
Step 7
Step 8
(Optional) Sets the time to wait for a hello packet from a
neighbor before declaring the neighbor down.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)#
dead-interval 40
hello-interval seconds
(Optional) Specifies the interval between hello packets that
OSPF sends on the interface.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)#
hello-interval 10
interface type instance
Enters interface configuration mode and associates one or
more interfaces for the area configured in Step 4.
•
In this example, the interface inherits the nonbroadcast
network type and the hello and dead intervals from the
areas because the values are not set at the interface
level.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
POS 0/2/0/0
Cisco IOS XR Routing Configuration Guide
RC-152
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
neighbor ip-address [priority number]
[poll-interval seconds][cost number]
Step 9
Configures the IPv4 address of OSPF neighbors
interconnecting to nonbroadcast networks.
or
or
neighbor ipv6-link-local-address [priority
number][poll-interval seconds][cost number]
[database-filter [all]]
Configures the link-local IPv6 address of OSPFv3
neighbors.
•
The ipv6-link-local-address must be in the form that is
specified in RFC 2373. The address is specified in
hexadecimal using 16-bit values between colons.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-if)#
neighbor 10.20.20.1 priority 3 poll-interval 15
•
The priority keyword notifies the router that this
neighbor is eligible to become a DR or BDR. The
priority value should match the actual priority setting
on the neighbor router. The neighbor priority default
value is 0. This keyword does not apply to
point-to-multipoint interfaces.
or
RP/0/RP0/CPU0:router(config-ospf-ar-if)#
neighbor fe80::3203:a0ff:fe9d:f3fe
•
•
The poll-interval keyword does not apply to
point-to-multipoint interfaces. RFC 1247 recommends
that this value be much larger than the hello interval.
The default is 120 seconds (2 minutes).
Neighbors with no specific cost configured assumes the
cost of the interface, based on the cost command. On
point-to-multipoint interfaces, cost number is the only
keyword and argument combination that works. The
cost keyword does not apply to NBMA networks.
•
The database-filter keyword filters outgoing LSAs to
an OSPF neighbor. If you specify the all keyword,
incoming and outgoing LSAs are filtered. Use with
extreme caution because filtering might cause the
routing topology to be seen as entirely different
between two neighbors, resulting in black-holing of
data traffic or routing loops.
Step 10
Step 11
Repeat Step 9 for all neighbors on the interface.
—
exit
Enters area configuration mode.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-if)# exit
interface type instance
Step 12
Enters interface configuration mode and associates one or
more interfaces for the area configured in Step 4.
•
In this example, the interface inherits the nonbroadcast
network type and the hello and dead intervals from the
areas because the values are not set at the interface
level.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
POS 0/3/0/1
Cisco IOS XR Routing Configuration Guide
RC-153
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
neighbor ip-address [priority number]
[poll-interval seconds][cost number]
[database-filter [all]]
Step 13
Configures the IPv4 address of OSPF neighbors
interconnecting to nonbroadcast networks.
or
or
neighbor ipv6-link-local-address [priority
number] [poll-interval seconds][cost number]
[database-filter [all]]
Configures the link-local IPv6 address of OSPFv3
neighbors.
•
The ipv6-link-local-address argument must be in the
form documented in RFC 2373 in which the address is
specified in hexadecimal using 16-bit values between
colons.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# neighbor
10.34.16.6
•
The priority keyword notifies the router that this
neighbor is eligible to become a DR or BDR. The
priority value should match the actual priority setting
on the neighbor router. The neighbor priority default
value is zero. This keyword does not apply to
point-to-multipoint interfaces.
or
RP/0/RP0/CPU0:router(config-ospf-ar)# neighbor
fe80::3203:a0ff:fe9d:f3f
•
•
The poll-interval keyword does not apply to
point-to-multipoint interfaces. RFC 1247 recommends
that this value be much larger than the hello interval.
The default is 120 seconds (2 minutes).
Neighbors with no specific cost configured assumes the
cost of the interface, based on the cost command. On
point-to-multipoint interfaces, cost number is the only
keyword and argument combination that works. The
cost keyword does not apply to NBMA networks.
•
The database-filter keyword filters outgoing LSAs to
an OSPF neighbor. If you specify the all keyword,
incoming and outgoing LSAs are filtered. Use with
extreme caution since filtering may cause the routing
topology to be seen as entirely different between two
neighbors, resulting in ‘black-holing’ or routing loops.
Cisco IOS XR Routing Configuration Guide
RC-154
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
Step 14
Step 15
Repeat Step 13 for all neighbors on the interface.
—
end
Saves configuration changes.
or
•
When you issue the end command, the system prompts
you to commit changes:
commit
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf-ar)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring Authentication at Different Hierarchical Levels for OSPF Version 2
This task explains how to configure MD5 (secure) authentication on the OSPF router process, configure
one area with plain text authentication, and then apply one interface with clear text (null) authentication.
Note
Authentication configured at the interface level overrides authentication configured at the area level and
the router process level. If an interface does not have authentication specifically configured, the interface
inherits the authentication parameter value from a higher hierarchical level. See the “OSPF Hierarchical
CLI and CLI Inheritance” section on page RC-131 for more information about hierarchy and inheritance.
Prerequisites
If you choose to configure authentication, you must first decide whether to configure plain text or MD5
authentication, and whether the authentication applies to all interfaces in a process, an entire area, or
page RC-135 for information about each type of authentication and when you should use a specific
method for your network.
SUMMARY STEPS
1. configure
2. router ospf process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. authentication [message-digest | null]
Cisco IOS XR Routing Configuration Guide
RC-155
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
5. message-digest-key key-id md5 {key | clear key | encrypted key}
6. area area-id
7. interface type instance
8. Repeat Step 7 for each interface that must communicate, using the same authentication.
9. exit
10. area area-id
11. authentication [message-digest | null]
12. interface type instance
13. Repeat Step 7 for each interface that must communicate, using the same authentication.
14. interface type instance
15. authentication [message-digest | null]
16. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
Note
The process-name argument is any alphanumeric
string no longer than 40 characters.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Configures a router ID for the OSPF process.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
authentication [message-digest | null]
Step 4
Step 5
Enables MD5 authentication for the OSPF process.
•
This authentication type applies to the entire router
process unless overridden by a lower hierarchical level
such as the area or interface.
Example:
RP/0/RP0/CPU0:router(config-ospf)#
authentication message-digest
message-digest-key key-id md5 {key | clear key
| encrypted key}
Specifies the MD5 authentication key for the OSPF process.
The neighbor routers must have the same key identifier.
•
Example:
RP/0/RP0/CPU0:router(config-ospf)#
message-digest-key 4 md5 yourkey
Cisco IOS XR Routing Configuration Guide
RC-156
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
area area-id
Step 6
Enters area configuration mode and configures a backbone
area for the OSPF process.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 0
interface type instance
Step 7
Enters interface configuration mode and associates one or
more interfaces to the backbone area.
•
All interfaces inherit the authentication parameter
values specified for the OSPF process (Step 4, Step 5,
and Step 6).
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
POS 0/1/0/3
Step 8
Step 9
Repeat Step 7 for each interface that must
communicate, using the same authentication.
—
exit
Enters area OSPF configuration mode.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# exit
area area-id
Step 10
Enters area configuration mode and configures a
nonbackbone area 1 for the OSPF process.
•
The area-id argument can be entered in dotted-decimal
or IPv4 address notation, such as area 1000 or
area 0.0.3.232. However, you must choose one form or
the other for an area. We recommend using the IPv4
address notation.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 1
authentication [message-digest | null]
Step 11
Step 12
Enables Type 1 (plain text) authentication that provides no
security.
•
The example specifies plain text authentication (by not
specifying a keyword). Use the authentication-key
interface command to specify the plain text password.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)#
authentication
interface type instance
Enters interface configuration mode and associates one or
more interfaces to the nonbackbone area 1 specified in
Step 7.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
POS 0/1/0/0
•
All interfaces configured inherit the authentication
parameter values configured for area 1.
Step 13
Step 14
Repeat Step 12 for each interface that must
communicate, using the same authentication.
—
interface type instance
Enters interface configuration mode and associates one or
more interfaces to a different authentication type.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
POS 0/3/0/0
Cisco IOS XR Routing Configuration Guide
RC-157
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
authentication [message-digest | null]
Step 15
Specifies no authentication on POS interface 0/3/0/0,
overriding the plain text authentication specified for area 1.
•
By default, all of the interfaces configured in the same
area inherit the same authentication values of the area.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-if)#
authentication null
end
Step 16
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-if)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf-ar-if)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Controlling the Frequency that the Same LSA Is Originated or Accepted for
OSPF
This task explains how to tune the convergence time of OSPF routes in the routing table when many
LSAs need to be flooded in a very short time interval.
SUMMARY STEPS
1. configure
2. router ospf process-name
or
router ospfv3 process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. Do Step 5, Step 6 or both to control the frequency that the same LSA is originated or accepted.
5. timers lsa gen-interval seconds
6. timers lsa min-arrival seconds
7. timers lsa group-pacing seconds
8. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-158
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Step 2
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
or
router ospfv3 process-name
or
Enables OSPFv3 routing for the specified routing process,
and places the router in router ospfv3 configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
Note
The process-name argument is any alphanumeric
or
string no longer than 40 characters.
RP/0/RP0/CPU0:router(config)# router ospfv3 1
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Configures a router ID for the OSPF process.
Note
We recommend using a stable IP address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
Step 4
Step 5
Perform Step 5 or Step 6 or both to control the
frequency that the same LSA is originated or accepted.
—
timers lsa gen-interval seconds
Changes the minimum interval between the same OSPF
LSAs that the router originates.
•
The default is 5 seconds for both OSPF and OSPFv3.
Example:
RP/0/RP0/CPU0:router(config-ospf)# timers lsa
gen-interval 10
timers lsa min-arrival seconds
Step 6
Limits the frequency that new processes of any particular
OSPF Version 2 LSA can be accepted during flooding.
•
The default is 1 second.
Example:
RP/0/RP0/CPU0:router(config-ospf)# timers lsa
min-arrival 2
Cisco IOS XR Routing Configuration Guide
RC-159
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
timers lsa group-pacing seconds
Step 7
Changes the interval at which OSPF link-state LSAs are
collected into a group for flooding. The default is 240
seconds.
Example:
RP/0/RP0/CPU0:router(config-ospf)# timers lsa
group-pacing 1000
end
Step 8
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Creating a Virtual Link with MD5 Authentication to Area 0 for OSPF
This task explains how to create a virtual link to your backbone (area 0) and apply MD5 authentication.
You must perform the steps described on both ABRs, one at each end of the virtual link. To understand
Note
After you explicitly configure area parameter values, they are inherited by all interfaces bound to that
area—unless you override the values and configure them explicitly for the interface. An example is
Prerequisites
Meet the following prerequisites before you create a virtual link with MD5 authentication to area 0:
•
Have the router ID of the neighbor router at the opposite end of the link to configure the local router.
You can use the show ospf or show ospfv3 command on the remote end to get its router ID.
Cisco IOS XR Routing Configuration Guide
RC-160
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
•
For a virtual link to be successful, you need a stable router ID at each end of the virtual link. You
do not want them to be subject to change, which could happen if they are assigned by default (See
is determined.) Therefore, we recommend that you perform one of the following tasks before
configuring a virtual link:
–
–
Use the router-id command to set the router ID. This strategy is preferable.
Configure a loopback interface so that the router has a stable router ID.
•
Before configuring your virtual link for OSPF Version 2, you must decide whether to configure plain
text authentication, MD5 authentication, or no authentication (which is the default). Your decision
determines whether you need to perform additional tasks related to authentication.
Note
If you decide to configure plain text authentication or no authentication, see the authentication
command provided in the OSPF Commands on Cisco IOS XR Software module in the Cisco IOS XR
Routing Command Reference.
SUMMARY STEPS
1. show ospf [process-name]
or
show ospfv3 [process-name]
2. configure
3. router ospf process-name
or
router ospfv3 process-name
4. router-id {ipv4-address | interface-type interface-instance}
5. area area-id
6. virtual link router-id
7. authentication message-digest
8. message-digest-key key-id md5 {key | clear key | encrypted key}
9. Repeat all of the steps in this task on the ABR that is at the other end of the virtual link. Specify the
same key ID and key that you specified for the virtual link on this router.
10. end
or
commit
11. show ospf [process-name] [area-id] virtual-links
or
show ospfv3 [process-name] virtual-links
Cisco IOS XR Routing Configuration Guide
RC-161
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
show ospf [process-name]
Step 1
(Optional) Displays general information about OSPF
routing processes.
or
show ospfv3 [process-name]
•
The output displays the router ID of the local router.
You need this router ID to configure the other end of
the link.
Example:
RP/0/RP0/CPU0:router# show ospf
or
RP/0/RP0/CPU0:router# show ospfv3
configure
Step 2
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Step 3
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
or
router ospfv3 process-name
or
Enables OSPFv3 routing for the specified routing process,
and places the router in router ospfv3 configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
Note
The process-name argument is any alphanumeric
or
string no longer than 40 characters.
RP/0/RP0/CPU0:router(config)# router ospfv3 1
router-id {ipv4-address | interface-type
interface-instance}
Step 4
Configures a router ID for the OSPF process.
Note
We recommend using a stable IPv4 address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
area area-id
Step 5
Enters area configuration mode and configures a
nonbackbone area for the OSPF process.
•
The area-id argument can be entered in dotted-decimal
or IPv4 address notation, such as area 1000 or
area 0.0.3.232. However, you must choose one form or
the other for an area. We recommend using the IPv4
address notation.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 1
virtual-link router-id
Step 6
Defines an OSPF virtual link.
•
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# virtual
link 10.3.4.5
authentication message-digest
Step 7
Selects MD5 authentication for this virtual link.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-vl)#
authentication message-digest
Cisco IOS XR Routing Configuration Guide
RC-162
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
Defines an OSPF virtual link.
message-digest-key key-id md5 {key | clear key
| encrypted key}
Step 8
•
section on page RC-138 to understand a virtual link.
Example:
•
The key-id argument is a number in the range from 1 to
255. The key argument is an alphanumeric string of up
to 16 characters. The routers at both ends of the virtual
link must have the same key identifier and key to be
able to route OSPF traffic.
RP/0/RP0/CPU0:router(config-ospf-ar-vl)#
message-digest-key 4 md5 yourkey
•
The authentication-key key command is not supported
for OSPFv3.
•
Once the key is encrypted it must remain encrypted.
Step 9
Repeat all of the steps in this task on the ABR that is
at the other end of the virtual link. Specify the same
key ID and key that you specified for the virtual link
on this router.
—
end
Step 10
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-vl)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf-ar-vl)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show ospf [process-name] [area-id]
virtual-links
Step 11
(Optional) Displays the parameters and the current state of
OSPF virtual links.
or
show ospfv3 [process-name] virtual-links
Example:
RP/0/RP0/CPU0:router# show ospf 1 2
virtual-links
or
RP/0/RP0/CPU0:router# show ospfv3 1
virtual-links
Cisco IOS XR Routing Configuration Guide
RC-163
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Examples
In the following example, the show ospfv3 virtual links EXEC command verifies that the OSPF_VL0
virtual link to the OSPFv3 neighbor is up, the ID of the virtual link interface is 2, and the IPv6 address
of the virtual link endpoint is 2003:3000::1.
RP/0/RP0/CPU0:router# show ospfv3 virtual-links
Virtual Links for OSPFv3 1
Virtual Link OSPF_VL0 to router 10.0.0.3 is up
Interface ID 2, IPv6 address 2003:3000::1
Run as demand circuit
DoNotAge LSA allowed.
Transit area 0.1.20.255, via interface POS 0/1/0/1, Cost of using 2
Transmit Delay is 5 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Adjacency State FULL (Hello suppressed)
Index 0/2/3, retransmission queue length 0, number of retransmission 1
First 0(0)/0(0)/0(0) Next 0(0)/0(0)/0(0)
Last retransmission scan length is 1, maximum is 1
Last retransmission scan time is 0 msec, maximum is 0 msec
Check for lines:
Virtual Link OSPF_VL0 to router 10.0.0.3 is up
Adjacency State FULL (Hello suppressed)
State is up and Adjacency State is FULL
Summarizing Subnetwork LSAs on an OSPF ABR
If you configured two or more subnetworks when you assigned your IP addresses to your interfaces, you
might want the software to summarize (aggregate) into a single LSA all of the subnetworks that the local
area advertises to another area. Such summarization would reduce the number of LSAs and thereby
conserve network resources. This summarization is known as interarea route summarization. It applies
to routes from within the autonomous system. It does not apply to external routes injected into OSPF by
way of redistribution.
This task configures OSPF to summarize subnetworks into one LSA, by specifying that all subnetworks
that fall into a range are advertised together. This task is performed on an ABR only.
SUMMARY STEPS
1. configure
2. router ospf process-name
or
router ospfv3 process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. area area-id
5. range ip-address mask [advertise | not-advertise]
or
range ipv6-prefix/prefix-length [advertise | not-advertise]
6. interface type instance
Cisco IOS XR Routing Configuration Guide
RC-164
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
7. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Step 2
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
or
router ospfv3 process-name
or
Enables OSPFv3 routing for the specified routing process,
and places the router in router ospfv3 configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
Note
The process-name argument is any alphanumeric
or
string no longer than 40 characters.
RP/0/RP0/CPU0:router(config)# router ospfv3 1
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Configures a router ID for the OSPF process.
Note
We recommend using a stable IPv4 address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
area area-id
Step 4
Enters area configuration mode and configures a
nonbackbone area for the OSPF process.
•
The area-id argument can be entered in dotted-decimal
or IPv4 address notation, such as area 1000 or
area 0.0.3.232. However, you must choose one form or
the other for an area. We recommend using the IPv4
address notation.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 0
range ip-address mask [advertise |
not-advertise]
Step 5
Consolidates and summarizes OSPF routes at an area
boundary.
or
•
The advertise keyword causes the software to advertise
the address range of subnetworks in a Type 3 summary
LSA.
range ipv6-prefix/prefix-length [advertise |
not-advertise]
•
The not-advertise keyword causes the software to
suppress the Type 3 summary LSA, and the
subnetworks in the range remain hidden from other
areas.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# range
192.168.0.0 255.255.0.0 advertise
or
•
•
In the first example, all subnetworks for network
192.168.0.0 are summarized and advertised by the
ABR into areas outside the backbone.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# range
4004:f000::/32 advertise
In the second example, two or more IPv4 interfaces are
covered by a 192.x.x network.
Cisco IOS XR Routing Configuration Guide
RC-165
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
interface type instance
Step 6
Enters interface configuration mode and associates one or
more interfaces to the area.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
POS 0/2/0/3
end
Step 7
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf-ar)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Redistributing Routes from One IGP into OSPF
This task redistributes routes from an IGP (could be a different OSPF process) into OSPF.
Prerequisites
For information about configuring routing policy, see the Implementing Routing Policy on Cisco IOS XR
Software module.
SUMMARY STEPS
1. configure
2. router ospf process-name
or
router ospfv3 process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. redistribute protocol [process-id] {level-1 | level-1-2 | level-2} [metric metric-value] [metric-type
type-value] [match {internal | external [1 | 2} | nssa-external [1 | 2}] [tag tag-value] [route-map
map-tag | policy policy-tag]
Cisco IOS XR Routing Configuration Guide
RC-166
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
5. summary-prefix address mask [not-advertise] [tag tag]
or
summary-prefix ipv6-prefix/prefix-length [not-advertise] [tag tag]
6. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
or
router ospfv3 process-name
or
Enables OSPFv3 routing for the specified routing process,
and places the router in router ospfv3 configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
Note
The process-name argument is any alphanumeric
string no longer than 40 characters.
or
RP/0/RP0/CPU0:router(config)# router ospfv3 1
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Configures a router ID for the OSPF process.
Note
We recommend using a stable IPv4 address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
Cisco IOS XR Routing Configuration Guide
RC-167
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
redistribute protocol[process-id] {level-1 |
Step 4
Redistributes OSPF routes from one routing domain to
another routing domain.
level-1-2 | level-2} [metric metric-value]
[metric-type type-value] [match {internal |
external [1 | 2} | nssa-external [1 | 2}] [tag
tag-value] [route-map map-tag | policy
policy-tag]
or
Redistributes OSPFv3 routes from one routing domain to
another routing domain.
•
•
•
•
This command causes the router to become an ASBR
by definition.
Example:
RP/0/RP0/CPU0:router(config-ospf)# redistribute
bgp 1 level-1
OSPF tags all routes learned through redistribution as
external.
or
RP/0/RP0/CPU0:router(config-router)#
redistribute bgp 1 level-1-2 metric-type 1
The protocol and its process ID, if it has one, indicate
the protocol being redistributed into OSPF.
The metric is the cost you assign to the external route.
The default is 20 for all protocols except BGP, whose
default metric is 1.
•
•
The OSPF example redistributes BGP autonomous
system 1, Level 1 routes into OSPF as Type 2 external
routes.
The OSPFv3 example redistributes BGP autonomous
system 1, Level 1 and 2 routes into OSPF. The external
link type associated with the default route advertised
into the OSPFv3 routing domain is the Type 1 external
route.
Note
RPL is not supported for OSPFv3.
Cisco IOS XR Routing Configuration Guide
RC-168
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
summary-prefix address mask [not-advertise]
[tag tag]
Step 5
(Optional) Creates aggregate addresses for OSPF.
or
or
(Optional) Creates aggregate addresses for OSPFv3.
summary-prefix ipv6-prefix/prefix-length
[not-advertise] [tag tag]
•
This command provides external route summarization
of the non-OSPF routes.
Example:
•
External ranges that are being summarized should be
contiguous. Summarization of overlapping ranges from
two different routers could cause packets to be sent to
the wrong destination.
RP/0/RP0/CPU0:router(config-ospf)#
summary-prefix 10.1.0.0 255.255.0.0
or
RP/0/RP0/CPU0:router(config-router)#
summary-prefix 2010:11:22::/32
•
•
This command is optional. If you do not specify it, each
route is included in the link-state database and
advertised in LSAs.
In the OSPFv2 example, the summary address 10.1.0.0
includes address 10.1.1.0, 10.1.2.0, 10.1.3.0, and so on.
Only the address 10.1.0.0 is advertised in an external
LSA.
•
In the OSPFv3 example, the summary address
2010:11:22::/32 has addresses such as
2010:11:22:0:1000::1, 2010:11:22:0:2000:679:1, and
so on. Only the address 2010:11:22::/32 is advertised in
the external LSA.
end
Step 6
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-169
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Configuring OSPF Shortest Path First Throttling
This task explains how to configure SPF scheduling in millisecond intervals and potentially delay SPF
calculations during times of network instability. This task is optional.
Prerequisites
throttling.
SUMMARY STEPS
1. configure
2. router ospf process-name
or
router ospfv3 process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. timers throttle spf spf-start spf-hold spf-max-wait
5. area area-id
6. interface type instance
7. end
or
commit
8. show ospf [process-name]
or
show ospfv3 [process-name]
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Step 2
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
or
router ospfv3 process-name
or
Enables OSPFv3 routing for the specified routing process,
and places the router in router ospfv3 configuration mode.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
Note
The process-name argument is any alphanumeric
or
string no longer than 40 characters.
RP/0/RP0/CPU0:router(config)# router ospfv3 1
Cisco IOS XR Routing Configuration Guide
RC-170
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
Configures a router ID for the OSPF process.
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Note
We recommend using a stable IPv4 address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
timers throttle spf spf-start spf-hold
spf-max-wait
Step 4
Step 5
Sets SPF throttling timers.
Example:
RP/0/RP0/CPU0:router(config-ospf)# timers
throttle spf 10 4800 90000
area area-id
Enters area configuration mode and configures a backbone
area.
•
The area-id argument can be entered in dotted-decimal
or IPv4 address notation, such as area 1000 or
area 0.0.3.232. However, you must choose one form or
the other for an area. We recommend using the IPv4
address notation.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 0
interface type instance
Step 6
Enters interface configuration mode and associates one or
more interfaces to the area.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
POS 0/1/0/3
Cisco IOS XR Routing Configuration Guide
RC-171
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
Saves configuration changes.
end
Step 7
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-if)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf-ar-if)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show ospf [process-name]
Step 8
(Optional) Displays SPF throttling timers.
or
show ospfv3 [process-name]
Example:
RP/0/RP0/CPU0:router# show ospf 1
or
RP/0/RP0/CPU0:router# show ospfv3 2
Examples
In the following example, the show ospf EXEC command is used to verify that the initial SPF schedule
delay time, minimum hold time, and maximum wait time are configured correctly. Additional details are
displayed about the OSPF process, such as the router type and redistribution of routes.
RP/0/RP0/CPU0:router# show ospf 1
Routing Process "ospf 1" with ID 192.168.4.3
Supports only single TOS(TOS0) routes
Supports opaque LSA
It is an autonomous system boundary router
Redistributing External Routes from,
ospf 2
Initial SPF schedule delay 5 msecs
Minimum hold time between two consecutive SPFs 100 msecs
Maximum wait time between two consecutive SPFs 1000 msecs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 00000000
Number of opaque AS LSA 0. Checksum Sum 00000000
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
External flood list length 0
Cisco IOS XR Routing Configuration Guide
RC-172
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Non-Stop Forwarding enabled
Note
For a description of each output display field, see the show ospf command in the OSPF Commands on
Cisco IOS XR Software module in the Cisco IOS XR Routing Command Reference document.
Configuring Nonstop Forwarding for OSPF Version 2
This task explains how to configure OSPF NSF on your NSF-capable router. This task is optional.
Prerequisites
OSPF NSF requires that all neighbor networking devices be NSF aware, which happens automatically
after you install the Cisco IOS XR image on the router. If an NSF-capable router discovers that it has
non-NSF-aware neighbors on a particular network segment, it disables NSF capabilities for that
segment. Other network segments composed entirely of NSF-capable or NSF-aware routers continue to
provide NSF capabilities.
Restrictions
The following are restrictions when configuring nonstop forwarding:
•
•
OSPF Cisco NSF for virtual links is not supported.
Neighbors must be NSF aware.
SUMMARY STEPS
1. configure
2. router ospf process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. nsf
or
nsf enforce global
5. nsf interval seconds
6. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-173
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Step 2
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
Note
The process-name argument is any alphanumeric
string no longer than 40 characters.
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
router-id {ipv4-address | interface-type
interface-instance}
Step 3
Configures a router ID for the OSPF process.
Note
We recommend using a stable IPv4 address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
nsf
Step 4
Enables OSPF NSF operations.
or
•
Use the nsf command without the optional enforce and
global keywords to abort the NSF restart mechanism on
the interfaces of detected non-NSF neighbors and allow
NSF neighbors to function properly.
nsf enforce global
Example:
RP/0/RP0/CPU0:router(config-ospf)# nsf
•
Use the nsf command with the optional enforce and
global keywords if the router is expected to perform
NSF during restart. However, if non-NSF neighbors are
detected, NSF restart is canceled for the entire OSPF
process.
or
RP/0/RP0/CPU0:router(config-ospf)# nsf enforce
global
Cisco IOS XR Routing Configuration Guide
RC-174
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
Sets the minimum time between NSF restart attempts.
nsf interval seconds
Step 5
Note
When you use this command, the OSPF process
must be up for at least 90 seconds before OSPF
attempts to perform an NSF restart.
Example:
RP/0/RP0/CPU0:router(config-ospf)# nsf interval
120
end
Step 6
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring OSPF Version 2 for MPLS Traffic Engineering
This task explains how to configure OSPF for MPLS TE. This task is optional.
For a description of the MPLS TE tasks and commands that allow you to configure the router to support
tunnels, configure an MPLS tunnel that OSPF can use, and troubleshoot MPLS TE, see the Implementing
MPLS Traffic Engineering Configuration Guide.
Prerequisites
Your network must support the following Cisco IOS XR features before you enable MPLS TE for OSPF
on your router:
•
•
MPLS
IP Cisco Express Forwarding (CEF)
Note
You must enter the commands in the following task on every OSPF router in the traffic-engineered
portion of your network.
Cisco IOS XR Routing Configuration Guide
RC-175
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Restrictions
MPLS traffic engineering currently supports only a single OSPF area.
SUMMARY STEPS
1. configure
2. router ospf process-name
3. router-id {ipv4-address | interface-type interface-instance}
4. mpls traffic-eng area area-id
5. mpls traffic-eng router-id {ip-address | interface-type interface-instance}
6. area area-id
7. interface type instance
8. end
or
commit
9. show ospf [process-name] [area-id] mpls traffic-eng {link | fragment}
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf process-name
Step 2
Step 3
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode.
Note
The process-name argument is any alphanumeric
Example:
RP/0/RP0/CPU0:router(config)# router ospf 1
string no longer than 40 characters.
router-id {ipv4-address | interface-type
interface-instance}
Configures a router ID for the OSPF process.
Note
We recommend using a stable IPv4 address as the
router ID.
Example:
RP/0/RP0/CPU0:router(config-ospf)# router-id
192.168.4.3
mpls traffic-eng area area-id
Step 4
Configures the OSPF area for MPLS TE.
Example:
RP/0/RP0/CPU0:router(config-ospf)# mpls
traffic-eng area 0
Cisco IOS XR Routing Configuration Guide
RC-176
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
mpls traffic-eng router-id {ip-address |
interface-type interface-instance}
Step 5
(Optional) Specifies that the traffic engineering router
identifier for the node is the IP address associated with a
given interface.
Example:
•
•
This IP address is flooded to all nodes in TE LSAs.
RP/0/RP0/CPU0:router(config-ospf)# mpls
traffic-eng router-id loopback 0
For all traffic engineering tunnels originating at other
nodes and ending at this node, you must set the tunnel
destination to the traffic engineering router identifier of
the destination node because that is the address that the
traffic engineering topology database at the tunnel head
uses for its path calculation.
•
We recommend that loopback interfaces be used for
MPLS TE router ID because they are more stable than
physical interfaces.
area area-id
Step 6
Step 7
Enters area configuration mode and configures an area for
the OSPF process.
•
The area-id argument can be entered in dotted-decimal
or IPv4 address notation, such as area 1000 or
area 0.0.3.232. However, you must choose one form or
the other for an area.
Example:
RP/0/RP0/CPU0:router(config-ospf)# area 0
interface type instance
Enters interface configuration mode and associates one or
more interfaces to the area.
Example:
RP/0/RP0/CPU0:router(config-ospf-ar)# interface
interface loopback0
Cisco IOS XR Routing Configuration Guide
RC-177
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
Saves configuration changes.
end
Step 8
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-ospf-ar-if)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-ospf-ar-if)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
show ospf [process-name] [area-id] mpls
traffic-eng {link | fragment}
Step 9
(Optional) Displays information about the links and
fragments available on the local router for MPLS TE.
Example:
RP/0/RP0/CPU0:router# show ospf 1 0 mpls
traffic-eng link
Examples
This section provides the following output examples:
•
•
•
Sample Output for the show ospf Command Before Configuring MPLS TE
In the following example, the show route ospf EXEC command verifies that POS interface 0/3/0/0 exists
and MPLS TE is not configured:
RP/0/RP0/CPU0:router# show route ospf 1 0
O E2 192.168.10.0/24 [110/20] via 192.168.1.2, 00:02:50, POS 0/3/0/0
[110/20] via 192.168.4.1, 00:02:50, POS 0/3/0/1
O E2 192.168.11.0/24 [110/20] via 192.168.1.2, 00:02:50, POS 0/3/0/0
[110/20] via 192.168.4.1, 00:02:50, POS 0/3/0/1
O E2 192.168.244.0/24 [110/20] via 192.168.1.2, 00:02:50, POS 0/3/0/0
[110/20] via 192.168.4.1, 00:02:50, POS 0/3/0/1
O
192.168.12.0/24 [110/2] via 192.168.1.2, 00:02:50, POS 0/3/0/0
[110/2] via 192.168.4.1, 00:02:50, POS 0/3/0/1
Cisco IOS XR Routing Configuration Guide
RC-178
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Sample Output for the show ospf mpls traffic-eng Command
In the following example, the show ospf mpls traffic-eng EXEC command verifies that the MPLS TE
fragments are configured correctly:
RP/0/RP0/CPU0:router# show ospf 1 mpls traffic-eng fragment
OSPF Router with ID (192.168.4.3) (Process ID 1)
Area 0 has 1 MPLS TE fragment. Area instance is 3.
MPLS router address is 192.168.4.2
Next fragment ID is 1
Fragment 0 has 1 link. Fragment instance is 3.
Fragment has 0 link the same as last update.
Fragment advertise MPLS router address
Link is associated with fragment 0. Link instance is 3
Link connected to Point-to-Point network
Link ID :55.55.55.55
Interface Address :192.168.50.21
Neighbor Address :192.168.4.1
Admin Metric :0
Maximum bandwidth :19440000
Maximum global pool reservable bandwidth :25000000
Maximum sub pool reservable bandwidth
Number of Priority :8
:3125000
Global pool unreserved BW
Priority 0 : 25000000 Priority 1 : 25000000
Priority 2 : 25000000 Priority 3 : 25000000
Priority 4 : 25000000 Priority 5 : 25000000
Priority 6 : 25000000 Priority 7 : 25000000
Sub pool unreserved BW
Priority 0 :
Priority 2 :
Priority 4 :
Priority 6 :
Affinity Bit :0
3125000 Priority 1 :
3125000 Priority 3 :
3125000 Priority 5 :
3125000 Priority 7 :
3125000
3125000
3125000
3125000
In the following example, the show ospf mpls traffic-eng EXEC command verifies that the MPLS TE
links on area instance 3 are configured correctly:
RP/0/RP0/CPU0:router# show ospf mpls traffic-eng link
OSPF Router with ID (192.168.4.1) (Process ID 1)
Area 0 has 1 MPLS TE links. Area instance is 3.
Links in hash bucket 53.
Link is associated with fragment 0. Link instance is 3
Link connected to Point-to-Point network
Link ID :192.168.50.20
Interface Address :192.168.20.50
Neighbor Address :192.168.4.1
Admin Metric :0
Maximum bandwidth :19440000
Maximum global pool reservable bandwidth :25000000
Maximum sub pool reservable bandwidth
Number of Priority :8
:3125000
Global pool unreserved BW
Priority 0 : 25000000 Priority 1 : 25000000
Priority 2 : 25000000 Priority 3 : 25000000
Priority 4 : 25000000 Priority 5 : 25000000
Priority 6 : 25000000 Priority 7 : 25000000
Sub pool unreserved BW
Cisco IOS XR Routing Configuration Guide
RC-179
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Priority 0 :
Priority 2 :
Priority 4 :
Priority 6 :
Affinity Bit :0
3125000 Priority 1 :
3125000 Priority 3 :
3125000 Priority 5 :
3125000 Priority 7 :
3125000
3125000
3125000
3125000
Sample Output for the show ospf Command After Configuring MPLS TE
In the following example, the show route ospf EXEC command verifies that the MPLS TE tunnels
replaced POS interface 0/3/0/0 and that configuration was performed correctly:
RP/0/RP0/CPU0:router# show route ospf 1 0
O E2 192.168.10.0/24 [110/20] via 0.0.0.0, 00:00:15, tunnel2
O E2 192.168.11.0/24 [110/20] via 0.0.0.0, 00:00:15, tunnel2
O E2 192.168.1244.0/24 [110/20] via 0.0.0.0, 00:00:15, tunnel2
O
192.168.12.0/24 [110/2] via 0.0.0.0, 00:00:15, tunnel2
Verifying OSPF Configuration and Operation
This task explains how to verify the configuration and operation of OSPF.
Note
To execute OSPFv3 commands for this task, replace ospf with ospfv3 in Steps 1 through 7.
SUMMARY STEPS
1. show ospf [process-name]
2. show ospf [process-name] border-routers [router-id]
3. show ospf [process-name] database
4. show ospf [process-name] [area-id] flood-list interface type instance
5. show ospf [process-name] [area-id] neighbor [interface-type interface-instance] [neighbor-id]
[detail]
6. clear ospf [process-name] process
7. clear ospf [process-name] statistics [neighbor [interface-type interface-instance] [ip-address]]
DETAILED STEPS
Command or Action
Purpose
show ospf [process-name]
Step 1
Step 2
(Optional) Displays general information about OSPF
routing processes.
Example:
RP/0/RP0/CPU0:router# show ospf group1
show ospf [process-name] border-routers
[router-id]
(Optional) Displays the internal OSPF routing table entries
to an ABR and ASBR.
Example:
RP/0/RP0/CPU0:router# show ospf group1
border-routers
Cisco IOS XR Routing Configuration Guide
RC-180
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Command or Action
Purpose
show ospf [process-name] database
Step 3
(Optional) Displays the lists of information related to the
OSPF database for a specific router.
•
The various forms of this command deliver information
about different OSPF LSAs.
Example:
RP/0/RP0/CPU0:router# show ospf group2 database
show ospf [process-name] [area-id] flood-list
interface type instance
Step 4
Step 5
(Optional) Displays a list of OSPF LSAs waiting to be
flooded over an interface.
Example:
RP/0/RP0/CPU0:router# show ospf 100 flood-list
interface pos 0/3/0/0
show ospf [process-name] [area-id] neighbor
[interface-type interface-instance]
[neighbor-id] [detail]
(Optional) Displays OSPF neighbor information on an
individual interface basis.
Example:
RP/0/RP0/CPU0:router# show ospf 100 neighbor
clear ospf [process-name] process
Step 6
Step 7
(Optional) Resets an OSPF router process without stopping
and restarting it.
Example:
RP/0/RP0/CPU0:router# clear ospf 100 process
clear ospf [process-name] statistics [neighbor
[interface-type interface-instance]
[ip-address]]
(Optional) Clears the OSPF statistics of neighbor state
transitions.
Example:
RP/0/RP0/CPU0:router# clear ospf 100 statistics
Configuring OSPFv3 Graceful Restart
This section describes the following tasks for configuring a graceful restart of an OSPFv3 process:
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-181
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Enabling Graceful Restart
This section describes how to enable an OSPFv3 graceful restart on the current router. By default, this
feature is disabled.
SUMMARY STEPS
DETAILED STEPS
1. configuration
2. router ospfv3
3. graceful-restart
Command or Action
Purpose
config
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:single10-hfr#config
RP/0/RP0/CPU0:single10-hfr(config)
router ospfv3 process-name
Step 2
Step 3
Enters router configuration mode for OSPFv3. The process
name is a WORD that uniquely identifies an OSPF routing
process. The process name is any alphanumeric string no
longer than 40 characters without spaces.
Example:
RP/0/RP0/CPU0:single10-hfr(config)# router
ospfv3 test
graceful-restart
Enable graceful restart on the current router.
Example:
RP/0/RP0/CPU0:single10-hfr(config-ospfv3)#grace
ful-restart
Configuring the Maximum Lifetime of a Graceful Restart
This section describes the task of modifying the total time that a router can be in graceful restart mode.
The default lifetime is 95 seconds. The range is 90–3600 seconds.
SUMMARY STEPS
1. configuration
2. router ospfv3
3. graceful-restart lifetime
Cisco IOS XR Routing Configuration Guide
RC-182
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
config
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:single10-hfr#config
RP/0/RP0/CPU0:single10-hfr(config)
router ospfv3 <process-name>
Step 2
Step 3
Enters router configuration mode for OSPFv3. The process
name is a WORD that uniquely identifies an OSPF routing
process. The process name is any alphanumeric string no
longer than 40 characters without spaces.
Example:
RP/0/RP0/CPU0:single10-hfr(config)# router
ospfv3 test
graceful-restart lifetime
Specifies a maximum duration for a graceful restart.
Example:
RP/0/RP0/CPU0:single10-hfr(config-ospfv3)#grace
ful-restart lifetime 120
Configuring the Minimum Time Required Between Restarts
This section describes the task of modifying the minimal time that is required between allowable
graceful restarts. The purpose of this interval is to prevent the waste of system resources if the OSPFv3
process is repeatedly crashing for reasons that must be diagnosed. The default value for the interval is
90 seconds. The range is 90–3600 seconds.
SUMMARY STEPS
1. configuration
2. router ospfv3
3. graceful-restart interval
Cisco IOS XR Routing Configuration Guide
RC-183
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
config
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:single10-hfr#config
RP/0/RP0/CPU0:single10-hfr(config)
router ospfv3 <process-name>
Step 2
Enters router configuration mode for OSPFv3. The process
name is a WORD that uniquely identifies an OSPF routing
process. The process name is any alphanumeric string no
longer than 40 characters without spaces.
Example:
RP/0/RP0/CPU0:single10-hfr(config)# router
ospfv3 test
graceful-restart interval <seconds>
Step 3
Specifies the interval (minimal time) between graceful
restarts on the current router.
Example:
RP/0/RP0/CPU0:single10-hfr(config-ospfv3)#grace
ful-restart interval 120
Configuring the Helper Level of the Router
This section describes the task of disabling the helper mode on the current router. By default, a router
that is capable of doing an OSPFv3 graceful restart is also enabled to be a helper to a node in graceful
mode. The graceful-restart helper command lets you disable the current router’s helper capability.
SUMMARY STEPS
1. configuration
2. router ospfv3
3. graceful-restart helper [disable]
Cisco IOS XR Routing Configuration Guide
RC-184
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
config
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:single10-hfr#config
RP/0/RP0/CPU0:single10-hfr(config)
router ospfv3 <process-name>
Step 2
Step 3
Enters router configuration mode for OSPFv3. The process
name is a WORD that uniquely identifies an OSPF routing
process. The process name is any alphanumeric string no
longer than 40 characters without spaces.
Example:
RP/0/RP0/CPU0:single10-hfr(config)# router
ospfv3 test
graceful-restart helper
Disables the helper capability.
Example:
RP/0/RP0/CPU0:single10-hfr(config-ospfv3)#grace
ful-restart helper disable
Displaying Information About Graceful Restart
This section describes the tasks you can use to display information about a graceful restart.
•
To see if the feature is enabled and when the last graceful restart ran, use the show ospf command.
To see details for an OSPFv3 instance, use the show ospf process-name database grace command.
Displaying the State of the Graceful Restart Feature
The following screen output shows the state of the graceful restart capability on the local router:
RP/0/0/CPU0:LA#show ospfv3 test database grace
Routing Process “ospfv3 test” with ID 2.2.2.2
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
Initial LSA throttle delay 0 msecs
Minimum hold time for LSA throttle 5000 msecs
Maximum wait time for LSA throttle 5000 msecs
Minimum LSA arrival 1000 msecs
LSA group pacing timer 240 secs
Interface flood pacing timer 33 msecs
Retransmission pacing timer 66 msecs
Maximum number of configured interfaces 255
Number of external LSA 0. Checksum Sum 00000000
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Graceful Restart enabled, last GR 11:12:26 ago (took 6 secs)
Area BACKBONE(0)
Number of interfaces in this area is 1
SPF algorithm executed 1 times
Number of LSA 6. Checksum Sum 0x0268a7
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
RP/0/0/CPU0:LA#
Cisco IOS XR Routing Configuration Guide
RC-185
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
How to Implement OSPF on Cisco IOS XR Software
Displaying Graceful Restart Information for an OSPFv3 Instance
The following screen output shows the link state for the instance of OSPFv3 called test:
RP/0/0/CPU0:LA#show ospfv3 test database grace
OSPFv3 Router with ID (2.2.2.2) (Process ID test)
Router Link States (Area 0)
ADV Router
1.1.1.1
2.2.2.2
Age
Seq#
Fragment ID Link count Bits
1949
2007
0x8000000e
0x80000011
0
0
1
1
None
None
Link (Type-8) Link States (Area 0)
Age Seq#
ADV Router
1.1.1.1
s2.2.2.2
Link ID
1
1
Interface
PO0/2/0/0
PO0/2/0/0
180
0x80000006
0x80000006
2007
Intra Area Prefix Link States (Area 0)
ADV Router
1.1.1.1
2.2.2.2
Age
Seq#
Link ID
0
0
Ref-lstype Ref-LSID
0x2001
180
2007
0x80000006
0x80000006
0
0x2001
0
Grace (Type-11) Link States (Area 0)
Age Seq#
ADV Router
2.2.2.2
Link ID
1
Interface
PO0/2/0/0
2007
0x80000005
RP/0/0/CPU0:LA#
Enabling Multicast-Intact for OSPFv2
This optional task describes how to enable multicast-intact for OSPFv2 routes that use IPv4 addresses.
Summary Steps
1. configure
2. router ospf instance-id
3. mpls traffic-eng multicast-intact
4. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Step 2
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router ospf instance-id
Enables OSPF routing for the specified routing process, and
places the router in router configuration mode. In this
example, the OSPF instance is called isp.
Example:
RP/0/RP0/CPU0:router(config)# router ospf isp
Cisco IOS XR Routing Configuration Guide
RC-186
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Configuration Examples for Implementing OSPF on Cisco IOS XR Software
Command or Action
Purpose
mpls traffic-eng multicast-intact
Step 3
Enables multicast-intact.
Example:
RP/0/RP0/CPU0:router(config-isis)# mpls
traffic-eng multicast-intact
end
Step 4
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-isis-af)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config-isis-af)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuration Examples for Implementing OSPF on Cisco IOS XR
Software
This section provides the following configuration examples:
•
•
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-187
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Configuration Examples for Implementing OSPF on Cisco IOS XR Software
Cisco IOS XR for OSPF Version 2 Configuration: Example
The following example shows how an OSPF interface is configured for an area in
Cisco IOS XR software.
In Cisco IOS XR software, area 0 must be explicitly configured with the area command and all
interfaces that are in the range from 10.1.2.0 to 10.1.2.255 are bound to area 0. Interfaces are configured
with the interface command (while the router is in area configuration mode) and the area keyword is
not included in the interface statement.
Cisco IOS XR Software Configuration
interface POS 0/3/0/0
ip address 10.1.2.1 255.255.255.255
negotiation auto
!
router ospf 1
router-id 10.2.3.4
area 0
interface POS 0/3/0/0
!
!
The following example shows how OSPF interface parameters are configured for an area in
Cisco IOS XR software.
In Cisco IOS XR software, OSPF interface-specific parameters are configured in interface configuration
mode and explicitly defined for area 0. In addition, the ip ospf keywords are no longer required.
Cisco IOS XR Software Configuration
interface POS 0/3/0/0
ip address 10.1.2.1 255.255.255.0
negotiation auto
!
router ospf 1
router-id 10.2.3.4
area 0
interface POS 0/3/0/0
cost 77
mtu-ignore
authentication message-digest
message-digest-key 1 md5 0 test
!
!
The following example shows the hierarchical CLI structure of Cisco IOS XR software.
In Cisco IOS XR software, OSPF areas must be explicitly configured, and interfaces configured under
the area configuration mode are explicitly bound to that area. In this example, interface 10.1.2.0/24 is
bound to area 0 and interface 10.1.3.0/24 is bound to area 1.
Cisco IOS XR Software Configuration
interface POS 0/3/0/0
ip address 10.1.2.1 255.255.255.0
negotiation auto
!
interface POS 0/3/0/1
ip address 10.1.3.1 255.255.255.0
negotiation auto
!
Cisco IOS XR Routing Configuration Guide
RC-188
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Configuration Examples for Implementing OSPF on Cisco IOS XR Software
router ospf 1
router-id 10.2.3.4
area 0
interface POS 0/3/0/0
!
area 1
interface POS 0/3/0/1
!
!
CLI Inheritance and Precedence for OSPF Version 2: Example
The following example configures the cost parameter at different hierarchical levels of the OSPF
topology, and illustrates how the parameter is inherited and how only one setting takes precedence.
According to the precedence rule, the most explicit configuration is used.
The cost parameter is set to 5 in router configuration mode for the OSPF process. Area 1 sets the cost to
15 and area 6 sets the cost to 30. All interfaces in area 0 inherit a cost of 5 from the OSPF process because
the cost was not set in area 0 or its interfaces.
In area 1, every interface has a cost of 15 because the cost is set in area 1 and 15 overrides the value 5
that was set in router configuration mode.
Area 4 does not set the cost, but POS interface 01/0/2 sets the cost to 20. The remaining interfaces in
area 4 have a cost of 5 that is inherited from the OSPF process.
Area 6 sets the cost to 30, which is inherited by POS interfaces 0/1/0/3 and 0/2/0/3. POS interface 0/3/0/3
uses the cost of 1, which is set in interface configuration mode.
router ospf 1
router-id 10.5.4.3
cost 5
area 0
interface POS 0/1/0/0
!
interface POS 0/2/0/0
!
interface POS 0/3/0/0
!
!
area 1
cost 15
interface POS 0/1/0/1
!
interface POS 0/2/0/1
!
interface POS 0/3/0/1
!
!
area 4
interface POS 0/1/0/2
cost 20
!
interface POS 0/2/0/2
!
interface POS 0/3/0/2
!
!
area 6
cost 30
interface POS 0/1/0/3
!
Cisco IOS XR Routing Configuration Guide
RC-189
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Configuration Examples for Implementing OSPF on Cisco IOS XR Software
interface POS 0/2/0/3
!
interface POS 0/3/0/3
cost 1
!
!
MPLS TE for OSPF Version 2: Example
The following example shows how to configure the OSPF portion of MPLS TE. However, you still need
to build an MPLS TE topology and create an MPLS TE tunnel. See the Cisco IOS XR MPLS
Configuration Guide for information.
In this example, loopback interface 0 is associated with area 0 and area 0 is declared to be an MPLS area:
interface Loopback 0
ip address 10.10.10.10 255.255.255.0
!
interface POS 0/2/0/0
ip address 10.1.2.2 255.255.255.0
!
router ospf 1
router-id 10.10.10.10
nsf
auto-cost reference-bandwidth 10000
area 0
interface POS 0/2/0/0
interface Loopback 0
mpls traffic-eng area 0
mpls traffic-eng router-id Loopback 0
ABR with Summarization for OSPFv3: Example
The following example shows the prefix range 2300::/16 summarized from area 1 into the backbone:
router ospfv3 1
router-id 192.168.0.217
area 0
interface POS 0/2/0/1
area 1
range 2300::/16
interface POS 0/2/0/0
ABR Stub Area for OSPFv3: Example
The following example shows that area 1 is configured as a stub area:
router ospfv3 1
router-id 10.0.0.217
area 0
interface POS 0/2/0/1
area 1
stub
interface POS 0/2/0/0
Cisco IOS XR Routing Configuration Guide
RC-190
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Configuration Examples for Implementing OSPF on Cisco IOS XR Software
ABR Totally Stub Area for OSPFv3: Example
The following example shows that area 1 is configured as a totally stub area:
router ospfv3 1
router-id 10.0.0.217
area 0
interface POS 0/2/0/1
area 1
stub no-summary
interface POS 0/2/0/0
Route Redistribution for OSPFv3: Example
The following example uses prefix lists to limit the routes redistributed from other protocols.
Only routes with 9898:1000 in the upper 32 bits and with prefix lengths from 32 to 64 are redistributed
from BGP 42. Only routes not matching this pattern are redistributed from BGP 1956.
ipv6 prefix-list list1
seq 10 permit 9898:1000::/32 ge 32 le 64
ipv6 prefix-list list2
seq 10 deny 9898:1000::/32 ge 32 le 64
seq 20 permit ::/0 le 128
router ospfv3 1
router-id 10.0.0.217
redistribute bgp 42
redistribute bgp 1956
distribute-list prefix-list list1 out bgp 42
distribute-list prefix-list list2 out bgp 1956
area 1
interface POS 0/2/0/0
Virtual Link Configured Through Area 1 for OSPFv3: Example
This example shows how to set up a virtual link to connect the backbone through area 1 for the OSPFv3
topology that consists of areas 0 and 1 and virtual links 10.0.0.217 and 10.0.0.212:
ABR 1 Configuration
router ospfv3 1
router-id 10.0.0.217
area 0
interface POS 0/2/0/1
area 1
virtual-link 10.0.0.212
interface POS 0/2/0/0
ABR 2 Configuration
router ospfv3 1
router-id 10.0.0.212
area 0
interface POS 0/3/0/1
area 1
virtual-link 10.0.0.217
interface POS 0/2/0/0
Cisco IOS XR Routing Configuration Guide
RC-191
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Where to Go Next
Virtual Link Configured with MD5 Authentication for OSPF Version 2: Example
The following examples show how to configure a virtual link to your backbone and apply MD5
authentication. You must perform the steps described on both ABRs at each end of the virtual link.
After you explicitly configure the ABRs, the configuration is inherited by all interfaces bound to that
area—unless you override the values and configure them explicitly for the interface.
To understand virtual links, see the “Virtual Link and Transit Area for OSPF” section on page RC-138.
In this example, all interfaces on router ABR1 use MD5 authentication:
router ospf ABR1
router-id 10.10.10.10
authentication message-digest
message-digest-key 100 md5 0 cisco
area 0
interface pos 0/2/0/1
interface pos 0/3/0/0
area 1
interface pos 0/3/0/1
virtual-link 10.10.5.5
!
!
In this example, only area 1 interfaces on router ABR3 use MD5 authentication:
router ospf ABR2
router-id 10.10.5.5
area 0
area 1
authentication message-digest
message-digest-key 100 md5 0 cisco
interface pos 0/9/0/1
virtual-link 10.10.10.10
area 3
interface Loopback 0
interface pos 0/9/0/0
!
!
Where to Go Next
To configure route maps through the RPL for OSPF Version 2, see the Implementing Routing Policy on
Cisco IOS XR Software document.
To build an MPLS TE topology, create tunnels, and configure forwarding over the tunnel for OSPF
Version 2; see the Cisco IOS XR MPLS Configuration Guide.
Cisco IOS XR Routing Configuration Guide
RC-192
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Additional References
Additional References
The following sections provide references related to implementing OSPF on Cisco IOS XR software.
Related Documents
Related Topic
Document Title
OSPF and OSPFv3 commands: complete command
syntax, command modes, command history, defaults,
usage guidelines, and examples
Cisco IOS XR Routing Command Reference, Release 32
MPLS TE feature information
Implementing MPLS Traffic Engineering on Cisco IOS XR Software
module in the Cisco IOS XR MPLS Configuration Guide, Release
3.2
Standards
Standards
Title
No new or modified standards are supported by this
feature, and support for existing standards has not been
modified by this feature.
—
MIBs
MIBs
MIBs Link
•
OSPF-MIB
To locate and download MIBs for selected platforms using
Cisco IOS XR software, use the Cisco MIB Locator found at the
following URL:
RFCs
RFCs
Title
RFC 1587
RFC 1793
RFC 2328
RFC 2740
RFC 3623
Not so Stubby Area (NSSA)
OSPF over demand circuit
OSPF Version 2
OSPFv3
Graceful OSPF Restart (OSPFv2)
Cisco IOS XR Routing Configuration Guide
RC-193
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing OSPF on Cisco IOS XR Software
Additional References
Technical Assistance
Description
Link
The Cisco Technical Support website contains
thousands of pages of searchable technical content,
including links to products, technologies, solutions,
technical tips, and tools. Registered Cisco.com users
can log in from this page to access even more content.
Cisco IOS XR Routing Configuration Guide
RC-194
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on
Cisco IOS XR Software
Routing Information Base (RIB) is a distributed collection of information about routing connectivity
among all nodes of a network.
Each router maintains a RIB containing the routing information for that router. RIB stores the best routes
from all routing protocols that are running on the system.
This module describes the tasks you need to perform to implement and monitor RIB on your
Cisco IOS XR network.
Note
For more information about RIB on the Cisco IOS XR software and complete descriptions of RIB
for other commands that might appear during the execution of a configuration task, search online in the
Cisco IOS XR software master command index.
Feature History for Implementing and Monitoring RIB on Cisco IOS XR Software
Release
Modification
Release 2.0
Release 3.0
Release 3.2
This feature was introduced on the Cisco CRS-1.
No modification.
Support was added for the Cisco XR 12000 Series Router.
Contents
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-195
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
Prerequisites for Implementing RIB on Cisco IOS XR Software
Prerequisites for Implementing RIB on Cisco IOS XR Software
•
To use this command, you must be in a user group associated with a task group that includes the
proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA
Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration
Guide.
•
RIB is distributed with the base Cisco IOS XR software; as such, it does not have any special
requirements for installation. The following are the requirements for base software installation:
–
–
–
Router
Cisco IOS XR software
Base package
Information About RIB Configuration
To implement the Cisco RIB feature, you must understand the following concepts:
•
•
•
•
Overview of RIB
Each routing protocol selects its own set of best routes and installs those routes and their attributes in
RIB. RIB stores these routes and selects the best ones from among all routing protocols. Those routes
are downloaded to the line cards for use in forwarding packets. The acronym RIB is used both to refer
to RIB processes and the collection of route data contained within RIB.
Within a protocol, routes are selected based on the metrics in use by that protocol. A protocol downloads
its best routes (lowest or tied metric) to RIB. RIB selects the best overall route by comparing the
administrative distance of the associated protocol.
RIB Data Structures in BGP and Other Protocols
RIB uses processes and maintains data structures distinct from other routing applications, such as Border
Gateway Protocol (BGP) and other unicast routing protocols, or multicast protocols, such as Protocol
Independent Multicast (PIM) or Multicast Source Discovery Protocol (MSDP). However, these routing
protocols use internal data structures similar to what RIB uses, and may internally refer to the data
structures as a RIB. For example, BGP routes are stored in the BGP RIB (BRIB), and multicast routes,
computed by multicast routing protocols such as PIM and MSDP, are stored in the Multicast RIB
(MRIB). RIB processes are not responsible for the BRIB and MRIB, which are handled by BGP and
multicast processes, respectively.
The table used by the line cards and RP to forward packets is called the Forwarding Information Base
(FIB). RIB processes do not build the FIBs. Instead, RIB downloads the set of selected best routes to the
FIB processes, by the Bulk Content Downloader (BCDL) process, onto each line card. FIBs are then
constructed.
Cisco IOS XR Routing Configuration Guide
RC-196
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
Information About RIB Configuration
RIB Administrative Distance
Forwarding is done based on the longest prefix match. If you are forwarding a packet destined to
10.0.2.1, you prefer 10.0.2.0/24 over 10.0.0.0/16 because the mask /24 is longer (and more specific) than
a /16.
Routes from different protocols that have the same prefix and length are chosen based on administrative
distance. For instance, the Open Shortest Path First (OSPF) protocol has an administrative distance of
110, and the Intermediate System-to-Intermediate System (IS-IS) protocol has an administrative
distance of 115. If IS-IS and OSPF both download 10.0.1.0/24 to RIB, RIB would prefer the OSPF route
because OSPF has a lower administrative distance. Administrative distance is used only to choose
between multiple routes of the same length.
Table 2
Default Administrative Distances
Protocol
Administrative Distance Default
Connected or local routes
Static routes
0
1
External BGP routes
OSPF routes
20
110
115
200
IS-IS routes
Internal BGP routes
The administrative distance for some routing protocols (for instance IS-IS, OSPF, and BGP) can be
changed. See the protocol-specific documentation for the proper method to change the administrative
distance of that protocol.
Note
Changing the administrative distance of a protocol on some but not all routers can lead to routing loops
and other undesirable behavior. Doing so is not recommended.
RIB Support for IPv4 and IPv6
In Cisco IOS XR software, RIB tables support multicast and unicast routing.
The default routing table for Cisco IOS XR RIB are the unicast and the multicast-unicast RIB tables for
IPv4 and IPv6 routing, respectively. For multicast routing, routing protocols insert unicast routes into
the multicast-unicast RIB table. Multicast protocols then use the information to build multicast routes
(which in turn are stored in the MRIB). See the multicast documentation for more information on using
and configuring multicast.
RIB processes ipv4_rib and ipv6_rib run on the RP card. If process placement functionality is available
and supported by multiple RPs in the router, RIB processes can be placed on any available node.
Cisco IOS XR Routing Configuration Guide
RC-197
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
How to Deploy and Monitor RIB
How to Deploy and Monitor RIB
To deploy and monitor RIB, you must understand the following concepts:
•
•
Verifying RIB Configuration Using the Routing Table
This task verifies the RIB configuration to ensure that RIB is running on the RP and functioning properly
by checking the routing table summary and details.
SUMMARY STEPS
DETAILED STEPS
1. show route [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] summary
2. show route [protocol [process-id]] [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] [ip-address
[mask]]
Command or Action
Purpose
show route [afi-all | ipv4 | ipv6] [unicast |
multicast | safi-all] summary
Step 1
Step 2
Displays route summary information on the specified
routing table.
•
The default table summarized is the IPv4 unicast
routing table.
Example:
RP/0/RP0/CPU0:router# show route summary
show route [protocol[process-id]] [afi-all |
ipv4 | ipv6] [unicast | multicast | safi-all]
[ip-address [mask]]
Displays more detailed route information on the specified
routing table.
•
This command is usually issued with an IP address or
other optional filters to limit its display. Otherwise, it
displays all routes from the default IPv4 unicast routing
table, which can result in an extensive list, depending
on the configuration of the network.
Example:
RP/0/RP0/CPU0:router# show route ipv4 unicast
Verifying Networking and Routing Problems
This task verifies the operation of the routes between nodes.
SUMMARY STEPS
1. show route [protocol [instance]] [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] [ip-address
[mask]]
2. show route [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] backup [ip-address]
3. show route [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] best-local ip-address
4. show route [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] connected
Cisco IOS XR Routing Configuration Guide
RC-198
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
How to Deploy and Monitor RIB
5. show route [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] local [interface]
6. show route [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] ip-address mask longer-prefixes
7. show route [afi-all | ipv4 | ipv6] [unicast | multicast | safi-all] next-hop ip-address
DETAILED STEPS
Command or Action
Purpose
show route [protocol [instance]] [afi-all |
ipv4 | ipv6] [unicast | multicast | safi-all]
Step 1
Displays the current routes in RIB.
[ip-address [mask]]
Example:
RP/0/RP0/CPU0:router# show route list list1 bgp
aspo ipv4 unicast 192.168.111/8
show route [afi-all | ipv4 | ipv6] [unicast |
multicast | safi-all] backup [ip-address]
Step 2
Step 3
Step 4
Step 5
Displays backup routes in RIB.
Example:
RP/0/RP0/CPU0:router# show route ipv4 unicast
backup 192.168.111/8
show route [afi-all | ipv4 | ipv6] [unicast |
multicast | safi-all] best-local ip-address
Displays the best-local address to use for return packets
from the given destination.
Example:
RP/0/RP0/CPU0:router# show route ipv4 unicast
best-local 192.168.111/8
show route [afi-all | ipv4 | ipv6] [unicast |
multicast | safi-all] connected
Displays the current connected routes of the routing table.
Displays local routes for receive entries in the routing table.
Example:
RP/0/RP0/CPU0:router# show route ipv4 unicast
connected
show route [afi-all | ipv4 | ipv6] [unicast |
multicast | safi-all] local [interface]
Example:
RP/0/RP0/CPU0:router# show route ipv4 unicast
local
Cisco IOS XR Routing Configuration Guide
RC-199
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
Configuration Examples for RIB Monitoring
Command or Action
Purpose
show route [afi-all | ipv4 | ipv6] [unicast |
multicast | safi-all] ip-address mask
longer-prefixes
Step 6
Displays the current routes in RIB that share a given
number of bits with a given network.
Example:
RP/0/RP0/CPU0:router# show route ipv4 unicast
192.168.111/8 longer-prefixes
show route [afi-all | ipv4 | ipv6] [unicast |
multicast | safi-all] next-hop ip-address
Step 7
Displays the next hop gateway or host to a destination
address.
Example:
RP/0/RP0/CPU0:router# show route ipv4 unicast
next-hop 192.168.1.34
Configuration Examples for RIB Monitoring
RIB is not configured separately for the Cisco IOS XR system. RIB computes connectivity of the router
with other nodes in the network based on input from the routing protocols. RIB may be used to monitor
and troubleshoot the connections between RIB and its clients, but it is essentially used to monitor routing
connectivity between the nodes in a network. This section contains displays from the show commands
used to monitor that activity. The following sample output is provided:
•
•
•
•
•
•
•
Output of show route Command: Example
The following is sample output from the show route command when entered without an address:
RP/0/RP0/CPU0:router# show route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
O - OSPF, IA - OSPF inter area, N1 - OSPF NSSA external type 1
N2 - OSPF NSSA external type 2, E1 - OSPF external type 1
E2 - OSPF external type 2, E - EGP, i - ISIS, L1 - IS-IS level-1
L2 - IS-IS level-2, ia - IS-IS inter area
su - IS-IS summary null, * - candidate default
U - per-user static route, o - ODR, L - local
Gateway of last resort is 172.23.54.1 to network 0.0.0.0
C
L
C
10.2.210.0/24 is directly connected, 1d21h, Ethernet0/1/0/0
10.2.210.221/32 is directly connected, 1d21h, Ethernet0/1/1/0
172.20.16.0/24 is directly connected, 1d21h, ATM4/0.1
Cisco IOS XR Routing Configuration Guide
RC-200
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
Configuration Examples for RIB Monitoring
L
C
L
S
172.20.16.1/32 is directly connected, 1d21h, ATM4/0.1
10.6.100.0/24 is directly connected, 1d21h, Loopback1
10.6.200.21/32 is directly connected, 1d21h, Loopback0
192.168.40.0/24 [1/0] via 172.20.16.6, 1d21h
Output of show route backup Command: Example
The following is sample output from the show route backup command:
RP/0/RP0/CPU0:router# show route backup
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
O - OSPF, IA - OSPF inter area, N1 - OSPF NSSA external type 1
N2 - OSPF NSSA external type 2, E1 - OSPF external type 1
E2 - OSPF external type 2, E - EGP, i - ISIS, L1 - IS-IS level-1
L2 - IS-IS level-2, ia - IS-IS inter area
su - IS-IS summary null, * - candidate default
U - per-user static route, o - ODR, L - local
S
172.73.51.0/24 is directly connected, 2d20h, GigabitEthernet2/2
Backup O E2 [110/1] via 10.12.12.2, POS3/0
Output of show route best-local Command: Example
The following is sample output from the show route best-local command:
RP/0/RP0/CPU0:router# show route best-local 10.12.12.1
Routing entry for 10.12.12.1/32
Known via "local", distance 0, metric 0 (connected)
Routing Descriptor Blocks
10.12.12.1 directly connected, via POS3/0
Route metric is 0
Output of show route connected Command: Example
The following is sample output from the show route connected command:
RP/0/RP0/CPU0:router# show route connected
Gateway of last resort is 172.23.54.1 to network 0.0.0.0
C
C
C
10.2.210.0/24 is directly connected, 1d21h, Ethernet0
172.20.16.0/24 is directly connected, 1d21h, ATM4/0.1
10.6.100.0/24 is directly connected, 1d21h, Loopback1
Output of show route local Command: Example
The following is sample output from the show route local command:
RP/0/RP0/CPU0:router# show route local
L
L
L
10.10.10.1/32 is directly connected, 00:14:36, Loopback0
10.91.36.98/32 is directly connected, 00:14:32, Ethernet0/0
172.22.12.1/32 is directly connected, 00:13:35, POS3/0
Cisco IOS XR Routing Configuration Guide
RC-201
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
Where to Go Next
L
L
192.168.20.2/32 is directly connected, 00:13:27, GigabitEthernet2/0
10.254.254.1/32 is directly connected, 00:13:26, GigabitEthernet2/2
Output of show route longer-prefixes Command: Example
The following is sample output from the show route longer-prefixes command:
RP/0/RP0/CPU0:router# show route ipv4 172.16.0.0/8 longer-prefixes
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
O - OSPF, IA - OSPF inter area, N1 - OSPF NSSA external type 1
N2 - OSPF NSSA external type 2, E1 - OSPF external type 1
E2 - OSPF external type 2, E - EGP, i - ISIS, L1 - IS-IS level-1
L2 - IS-IS level-2, ia - IS-IS inter area
su - IS-IS summary null, * - candidate default
U - per-user static route, o - ODR, L - local
Gateway of last resort is 172.23.54.1 to network 0.0.0.0
S
S
S
S
S
S
S
S
172.16.2.0/32 is directly connected, 00:00:24, Loopback0
172.16.3.0/32 is directly connected, 00:00:24, Loopback0
172.16.4.0/32 is directly connected, 00:00:24, Loopback0
172.16.5.0/32 is directly connected, 00:00:24, Loopback0
172.16.6.0/32 is directly connected, 00:00:24, Loopback0
172.16.7.0/32 is directly connected, 00:00:24, Loopback0
172.16.8.0/32 is directly connected, 00:00:24, Loopback0
172.16.9.0/32 is directly connected, 00:00:24, Loopback0
Output of show route next-hop Command: Example
The following is sample output from the show route next-hop command:
RP/0/RP0/CPU0:router# show route next-hop 10.0.0.1
Routing entry for 10.0.0.0/24
Known via "connected", distance 0, metric 0 (connected)
Routing Descriptor Blocks
10.0.0.50 directly connected, via GigabitEthernet6/0
Route metric is 0
Where to Go Next
For additional information on the protocols that interact with RIB, you may want to see the following
publications:
•
•
•
•
Implementing BGP on Cisco IOS XR Software
Implementing IS-IS on Cisco IOS XR Software
Implementing OSPF on Cisco IOS XR Software
RIB Commands on Cisco IOS XR Software
Cisco IOS XR Routing Configuration Guide
RC-202
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
Additional References
Additional References
The following sections provide references related to implementing RIB on Cisco IOS XR software:
Related Documents
Related Topic
Document Title
Routing Information Base commands: complete
RIB Commands on Cisco IOS XR Software in the Cisco IOS XR
command syntax, command modes, command history, Routing Command Reference, Release 3.2
defaults, usage guidelines, and examples
BGP commands: complete command syntax, command BGP Commands on Cisco IOS XR Software, in the Cisco IOS XR
modes, command history, defaults, usage guidelines,
and examples
Routing Command Reference, Release 3.2
IS-IS commands: complete command syntax,
command modes, command history, defaults, usage
guidelines, and examples
IS-IS Commands on Cisco IOS XR Software in the Cisco IOS XR
Routing Command Reference, Release 3.2
OSPF commands: complete command syntax,
command modes, command history, defaults, usage
guidelines, and examples
OSPF Commands on Cisco IOS XR Software in the Cisco IOS XR
Routing Command Reference, Release 3.2
OSPFv3 commands: complete command syntax,
command modes, command history, defaults, usage
guidelines, and examples
OSPFv3 Commands on Cisco IOS XR Software in the Cisco IOS XR
Routing Command Reference, Release 3.2
Multicast commands: complete command syntax,
command modes, command history, defaults, usage
guidelines, and examples
Cisco IOS XR Multicast Command Reference, Release 3.2
Cisco IOS XR Multicast Configuration Guide, Release 3.2
Multicast configuration: complete command syntax,
command modes, command history, defaults, usage
guidelines, and examples
Standards
Standards
Title
No new or modified standards are supported by this
feature, and support for existing standards has not been
modified by this feature.
—
MIBs
MIBs
MIBs Link
•
•
IP-FORWARD-MIB
RFC1213-MIB
To locate and download MIBs for selected platforms using
Cisco IOS XR software, use the Cisco MIB Locator found at the
following URL:
Cisco IOS XR Routing Configuration Guide
RC-203
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing and Monitoring RIB on Cisco IOS XR Software
Additional References
RFCs
RFCs
Title
No new or modified RFCs are supported by this
feature, and support for existing RFCs has not been
modified by this feature.
—
Technical Assistance
Description
Link
The Cisco Technical Support website contains
thousands of pages of searchable technical content,
including links to products, technologies, solutions,
technical tips, and tools. Registered Cisco.com users
can log in from this page to access even more content.
Cisco IOS XR Routing Configuration Guide
RC-204
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR
Software
A routing policy instructs the router to inspect routes, filter them, and potentially modify their attributes
as they are accepted from a peer, advertised to a peer, or redistributed from one routing protocol to
another. Routing protocols make decisions to advertise, aggregate, discard, distribute, export, hold,
import, redistribute and otherwise modify routes based on configured routing policy.
The routing policy language (RPL) has been designed to provide a single, straightforward language in
which all routing policy needs can be expressed. RPL was designed to support large-scale routing
configurations. It greatly reduces the redundancy inherent in previous routing policy configuration
methods. RPL has been designed to streamline routing policy configuration, to reduce system resources
required to store and process these configurations, and to simplify troubleshooting.
Note
For more information about routing policy on the Cisco IOS XR software and complete descriptions of
the routing policy commands listed in this module, see the “Related Documents” section of this module.
To locate documentation for other commands that might appear during execution of a configuration task,
search online in the Cisco IOS XR software master command index.
Feature History for Implementing Routing Policy on Cisco IOS XR Software
Release
Modification
Release 2.0
Release 3.0
Release 3.2
This feature was introduced on the Cisco CRS-1.
No modification.
Support was added for the Cisco XR 12000 Series Router.
Contents
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-205
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Prerequisites for Implementing Routing Policy
Prerequisites for Implementing Routing Policy
The following are prerequisites for implementing Routing Policy on Cisco IOS XR Software:
•
To use this command, you must be in a user group associated with a task group that includes the
proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA
Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration
Guide.
•
Border Gateway Protocol (BGP), integrated Intermediate System-to-Intermediate System (IS-IS),
or Open Shortest Path First (OSPF) must be configured in your network.
Information About Implementing Routing Policy
To implement RPL, you need to understand the following concepts:
•
•
•
•
•
•
•
•
•
•
Routing Policy Language
This section contains the following information:
•
•
•
•
Routing Policy Language Overview
RPL was developed to support large-scale routing configurations. RPL has several fundamental
capabilities that differ from those present in configurations oriented to traditional route maps, access
lists, and prefix lists. The first of these capabilities is the ability to build policies in a modular form.
Common blocks of policy can be defined and maintained independently. These common blocks of policy
can then be applied from other blocks of policy to build complete policies. This capability reduces the
amount of configuration information that needs to be maintained. In addition, these common blocks of
policy can be parameterized. This parameterization allows for policies that share the same structure but
differ in the specific values that are set or matched against to be maintained as independent blocks of
Cisco IOS XR Routing Configuration Guide
RC-206
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
policy. For example, three policies that are identical in every way except for the local preference value
they set can be represented as one common parameterized policy that takes the varying local preference
value as a parameter to the policy.
The policy language introduces the notion of sets. Sets are containers of similar data that can be used in
route attribute matching and setting operations. Four set types exist: prefix-sets, community-sets,
as-path-sets, and extcommunity-sets. These sets hold groupings of IPv4 or IPv6 prefixes, community
values, AS path regular expressions, and extended community values, respectively. Sets are simply
containers of data. Most sets also have an inline variant. An inline set allows for small enumerations of
values to be used directly in a policy rather than having to refer to a named set. Prefix lists, community
lists, and AS path lists must be maintained even when only one or two items are in the list. An inline set
in RPL allows the user to place small sets of values directly in the policy body without having to refer
to a named set.
Decision making, such as accept and deny, is explicitly controlled by the policy definitions themselves.
RPL combines matching operators, which may use set data, with the traditional Boolean logic operators
and, or, and not into complex conditional expressions. All matching operations return a true or false
result. The execution of these conditional expressions and their associated actions can then be controlled
by using simple if then, elseif, and else structures, which allow the evaluation paths through the policy
to be fully specified by the user.
Routing Policy Language Structure
This section describes the basic structure of RPL.
Names
The policy language provides two kinds of persistent, namable objects: sets and policies. Definition of
these objects is bracketed by beginning and ending command lines. For example, to define a policy
named test, the configuration syntax would look similar to the following:
route-policy test
[ . . . policy statements . . . ]
end-policy
Legal names for policy objects can be any sequence of the upper- and lowercase alphabetic characters;
the numerals 0 to 9; and the punctuation characters period, hyphen, and underscore. A name must begin
with a letter or numeral.
Sets
In this context, the term set is used in its mathematical sense to mean an unordered collection of unique
elements. The policy language provides sets as a container for groups of values for matching purposes.
Sets are used in conditional expressions. The elements of the set are separated by commas. Null (empty)
sets are not allowed.
Four kinds of sets exist: as-path-set, community-set, extcommunity-set, and prefix-set. You may want to
perform comparisons against a small number of elements, such as two or three community values, for
example. To allow for these comparisons, the user can enumerate these values directly. These
enumerations are referred to as inline sets. Functionally, inline sets are equivalent to named sets, but
allow for simple tests to be inline. Thus, comparisons do not require that a separate named set be
maintained when only one or two elements are being compared. See the set types described in the
following sections for the syntax. In general, the syntax for an inline set is a comma-separated list
Cisco IOS XR Routing Configuration Guide
RC-207
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
surrounded by parentheses as follows: (<element-entry>,<element-entry>,<element-entry>,
...<element-entry>), where <element-entry> is an entry of an item appropriate to the type of usage such
as a prefix or a community value.
The following is an example using an inline community set:
route-policy sample-inline
if community matches-any ([10..15]:100) then
set local-preference 100
endif
end-policy
The following is an equivalent example using the named set test-communities:
community-set test-communities
10:100,
11:100,
12:100,
13:100,
14:100,
15:100
end-set
route-policy sample
if community matches-any test-communities then
set local-preference 100
endif
end-policy
Both of these policies are functionally equivalent, but the inline form does not require the configuration
of the community set just to store the six values. You can choose the form appropriate to the
configuration context. In the following sections, examples of both the named set version and the inline
form are provided where appropriate.
as-path-set
An AS path set comprises operations for matching an AS path attribute. The only matching operation is
a regular expression match.
Named Set Form
The named set form uses the ios-regex keyword to indicate the type of regular expression and requires
single quotation marks around the regular expression.
The following is a sample definition of a named AS path set:
as-path-set aset1
ios-regex ’_42$’,
ios-regex ’_127$’
end-set
This AS path set comprises two elements. When used in a matching operation, this AS path set matches
any route whose AS path ends with either the autonomous system (AS) number 42 or 127.
To remove the named AS path set, use the no as-path-set aset1 command-line interface (CLI) command.
Inline Set Form
The inline set form is a parenthesized list of comma-separated expressions, as follows:
(ios-regex '_42$', ios-regex '_127$')
Cisco IOS XR Routing Configuration Guide
RC-208
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
This set matches the same AS paths as the previously named set, but does not require the extra effort of
creating a named set separate from the policy that uses it.
community-set
A community-set holds community values for matching against the BGP community attribute. A
community is a 32-bit quantity. Integer community values must be split in half and expressed as two
unsigned decimal integers in the range from 0 to 65535, separated by a colon. Single 32-bit community
values are not allowed. The following is the named set form:
Named Set Form
community-set cset1
12:34,
12:56,
12:78,
internet
end-set
Inline Set Form
(12:34, 12:56, 12:78)
($as:34, $as:$tag1, 12:78, internet)
The inline form of a community-set also supports parameterization. Each 16-bit portion of the
information.
RPL provides symbolic names for the standard well-known community values: internet is 0:0, no-export
is 65535:65281, no-advertise is 65535:65282, and local-as is 65535:65283.
RPL also provides a facility for using wildcards in community specifications. A wildcard is specified by
inserting an asterisk (*) in place of one of the 16-bit portions of the community specification; the
wildcard indicates that any value for that portion of the community matches. Thus, the following policy
matches all communities in which the autonomous system part of the community is 123:
community-set cset3
123:*
end-set
Every community set must contain at least one community value. Empty community sets are invalid and
are rejected.
extcommunity-set
An extended community-set is analogous to a community-set except that it contains extended
community values instead of regular community values. It also supports named forms and inline forms.
The following are syntactic examples:
Named Form
extcommunity-set extcomm-set1
RT:1.2.3.4:666,
RT:1234:666,
SoO:1.2.3.4:777,
SoO :4567:777
end-set
Cisco IOS XR Routing Configuration Guide
RC-209
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Inline Form
(RT:1.2.3.4:666, RT:1234:6667, SoO:1.2.3.4:777, SoO:45678:777)
(RT:$ipaddr:666, RT:1234:$tag, SoO:1.2.3.4:777, SoO:$tag2:777)
As with community sets, the inline form supports parameterization within parameterized policies. Either
portion of the extended community value can be parameterized.
Every extended community-set must contain at least one extended community value. Empty extended
community-sets are invalid and rejected.
prefix-set
A prefix-set holds IPv4 or IPv6 prefix match specifications, each of which has four parts: an address, a
mask length, a minimum matching length, and a maximum matching length. The address is required, but
the other three parts are optional. The address is a standard dotted-decimal IPv4 or colon-separated
hexadecimal IPv6 address. The mask length, if present, is a nonnegative decimal integer in the range
from 0 to 32 (0 to 128 for IPv6) following the address and separated from it by a slash. The optional
minimum matching length follows the address and optional mask length and is expressed as the keyword
ge (mnemonic for greater than or equal to), followed by a nonnegative decimal integer in the range from
0 to 32 (0 to 128 for IPv6). The optional maximum matching length follows the rest and is expressed by
the keyword le (mnemonic for less than or equal to), followed by yet another nonnegative decimal integer
in the range from 0 to 32 (0 to 128 for IPv6). A syntactic shortcut for specifying an exact length for
prefixes to match is the eq keyword (mnemonic for equal to).
If a prefix match specification has no mask length, then the default mask length is 32 for IPv4 and 128
for IPv6. The default minimum matching length is the mask length. If a minimum matching length is
specified, then the default maximum matching length is 32 for IPv4 and 128 for IPv6. Otherwise, if
neither minimum nor maximum is specified, the default maximum is the mask length.
The prefix-set itself is a comma-separated list of prefix match specifications. The following are
examples:
prefix-set legal-ipv4-prefix-examples
10.0.1.1,
10.0.2.0/24,
10.0.3.0/24 ge 28,
10.0.4.0/24 le 28,
10.0.5.0/24 ge 26 le 30,
10.0.6.0/24 eq 28
end-set
prefix-set legal-ipv6-prefix-examples
2001:0:0:1::/64,
2001:0:0:2::/64 ge 96,
2001:0:0:2::/64 ge 96 le 100,
2001:0:0:2::/64 eq 100
end-set
The first element of the prefix-set matches only one possible value, 10.0.1.1/32 or the host address
10.0.1.1. The second element matches only one possible value, 10.0.2.0/24. The third element matches
a range of prefix values, from 10.0.3.0/28 to 10.0.3.255/32. The fourth element matches a range of
values, from 10.0.4.0/24 to 10.0.4.240/28. The fifth element matches prefixes in the range from
10.0.5.0/26 to 10.0.5.252/30. The sixth element matches any prefix of length 28 in the range from
10.0.6.0/28 through 10.0.6.240/28.
Cisco IOS XR Routing Configuration Guide
RC-210
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
The following prefix-set consists entirely of invalid prefix match specifications:
prefix-set ILLEGAL-PREFIX-EXAMPLES
10.1.1.1 ge 16,
10.1.2.1 le 16,
10.1.3.0/24 le 23,
10.1.4.0/24 ge 33,
10.1.5.0/25 ge 29 le 28
end-set
Neither the minimum length nor maximum length is valid without a mask length. The maximum length
must be at least the mask length. For IPv4, the minimum length must be less than 32, the maximum
length of an IPv4 prefix. For IPv6, the minimum length must be less than 128, the maximum length of
an IPv6 prefix. The maximum length must be equal to or greater than the minimum length.
Routing Policy Language Components
Four main components in the routing policy language are involved in defining, modifying, and using
policies: the configuration front end, policy repository, execution engine, and policy clients themselves.
The configuration front end (CLI) is the mechanism to define and modify policies. This configuration is
then stored on the router using the normal storage means and can be displayed using the normal
configuration show commands.
The second component of the policy infrastructure, the policy repository, has several responsibilities.
First, it compiles the user-entered configuration into a form that the execution engine can understand.
Second, it performs much of the verification of policies; and it ensures that defined policies can actually
be executed properly. Third, it tracks which attach points are using which policies so that when policies
are modified the appropriate clients are properly updated with the new policies relevant to them.
The third component is the execution engine. This component is the piece that actually runs policies as
the clients request. The process can be thought of as receiving a route from one of the policy clients and
then executing the actual policy against the specific route data.
The fourth component is the policy clients (the routing protocols). This component calls the execution
engine at the appropriate times to have a given policy be applied to a given route, and then perform some
number of actions. These actions may include deleting the route if policy indicated that it should be
dropped, passing along the route to the protocol decision tree as a candidate for the best route, or
advertising a policy modified route to a neighbor or peer as appropriate.
Routing Policy Language Usage
This section provides basic routing policy language usage examples. See the “How to Implement
Routing Policy” section on page RC-237 for detailed information on how to implement routing policy
language.
The pass policy
The following example shows how the policy accepts all presented routes without modifying the routes.
route-policy quickstart-pass
pass
end-policy
The drop everything policy
The following example shows how the policy explicitly rejects all routes presented to it. This type of
policy is used to ignoring everything coming from a misbehaving peer.
Cisco IOS XR Routing Configuration Guide
RC-211
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
route-policy quickstart-drop
drop
end-policy
Ignore routes with specific AS numbers in the path
The following example shows the policy definition in three parts. First, the as-path-set command
defines three regular expressions to match against an AS path. Second, the route-policy command
applies the AS path set to a route. If the AS path attribute of the route matches the regular expression
defined with the as-path-set command, the protocol refuses the route. Third, the route policy is attached
to BGP neighbor 10.0.1.2. BGP consults the policy named ignore_path_as on routes received (imported)
from neighbor 10.0.1.2.
as-path-set ignore_path
ios-regex '_11_',
ios-regex '_22_',
ios-regex '_33_'
end-set
route-policy ignore_path_as
if as-path in ignore_path then
drop
else
pass
endif
end-policy
router bgp 2
neighbor 10.0.1.2 address-family ipv4 unicast policy ignore_path_as in
Set community based on MED
The following example shows how the policy tests the MED of a route and modifies the community
attribute of the route based on the value of the MED. If the MED value is 127, the policy adds the
community 123:456 to the route. If the MED value is 63, the policy adds the value 123:789 to the
community attribute of the route. Otherwise, the policy removes the community 123:123 from the route.
In any case, the policy instructs the protocol to accept the route.
route-policy quickstart-med
if med eq 127 then
set community (123:456) additive
elseif med eq 63 then
set community (123:789) additive
else
delete community in (123:123)
endif
pass
end-policy
Set local preference based on community
The following example shows how the community-set named quickstart-communities defines
community values. The route policy named quickstart-localpref tests a route for the presence of the
communities specified in the quickstart-communities community set. If any of the community values are
present in the route, the route policy sets the local preference attribute of the route to 31. In any case, the
policy instructs the protocol to accept the route.
community-set quickstart-communities
987:654,
987:543,
987:321,
987:210
end-set
Cisco IOS XR Routing Configuration Guide
RC-212
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
route-policy quickstart-localpref
if community matches-any quickstart-communities then
set local-preference 31
endif
pass
end-policy
Persistent Remarks
The following example shows how comments are placed in the policy to clarify the meaning of the
entries in the set and the statements in the policy. The remarks are persistent, meaning they remain
attached to the policy. For example, remarks are displayed in the output of the show running-config
command. Adding remarks to the policy makes the policy easier to understand, modify at a later date,
and troubleshoot if an unexpected behavior occurs.
prefix-set rfc1918
# These are the networks defined as private in RFC1918 (including
# all subnets thereof)
10.0.0.0/8 ge 8,
172.16.0.0/12 ge 12,
192.168.0.0/16 ge 16
end-set
route-policy quickstart-remarks
# Handle routes to RFC1918 networks
if destination in rfc1918 then
# Set the community such that we do not export the route
set community (no-export) additive
endif
end-policy
Routing Policy Configuration Basics
Route policies comprise series of statements and expressions that are bracketed with the route-policy
and end-policy keywords. Rather than a collection of individual commands (one for each line), the
statements within a route policy have context relative to each other. Thus, instead of each line being an
individual command, each policy or set is an independent configuration object that can be used, entered,
and manipulated as a unit.
Each line of a policy configuration is a logical subunit. At least one new line must follow the then, else,
and end-policy keywords. A new line must also follow the closing parenthesis of a parameter list and
the name string in a reference to an AS path set, community set, extended community set, or prefix set.
At least one new line must precede the definition of a route policy, AS path set, community set, extended
community set, or prefix set. One or more new lines can follow an action statement. One or more new
lines can follow a comma separator in a named AS path set, community set, extended community set, or
prefix set. A new line must appear at the end of a logical unit of policy expression and may not appear
anywhere else.
Policy Definitions
Policy definitions create named sequences of policy statements. A policy definition consists of the CLI
route-policy keyword followed by a name, a sequence of policy statements, and the end-policy
keyword. For example, the following policy drops any route it encounters:
Cisco IOS XR Routing Configuration Guide
RC-213
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
route-policy drop-everything
drop
end-policy
The name serves as a handle for binding the policy to protocols. To remove a policy definition, issue the
no route-policy name command.
Policies may also refer to other policies such that common blocks of policy can be reused. This reference
to other policies is accomplished by using the apply statement, as shown in the following example:
route-policy check-as-1234
if as-path passes-through ‘1234’ then
apply drop-everything
else
pass
endif
end-policy
The apply statement indicates that the policy drop-everything should be executed if the route under
consideration passed through autonomous system 1234 before it is received. If a route that has
autonomous system 1234 in its AS path is received, the route is dropped; otherwise, the route is accepted
without modification. This policy is an example of a hierarchical policy. Thus, the semantics of the apply
statement are just as if the applied policy were cut and pasted into the applying policy:
route-policy check-as-1234-prime
if as-path passes-through '1234' then
drop
else
pass
endif
end-policy
You may have as many levels of hierarchy as desired. However, many levels may be difficult to maintain
and understand.
Parameterization
In addition to supporting reuse of policies using the apply statement, policies can be defined that allow
for parameterization of some of the attributes. The following example shows how to define a
parameterized policy named param-example. In this case, the policy takes one parameter, $mytag.
Parameters always begin with a dollar sign and consist otherwise of any alphanumeric characters.
Parameters can be substituted into any attribute that takes a parameter.
In the following example, a 16-bit community tag is used as a parameter:
route-policy param-example ($mytag)
set community (1234:$mytag) additive
end-policy
This parameterized policy can then be reused with different parameterizations, as shown in the following
example. In this manner, policies that share a common structure but use different values in some of their
individual statements can be modularized. For details on which attributes can be parameterized, see the
individual attribute sections.
Cisco IOS XR Routing Configuration Guide
RC-214
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
route-policy origin-10
if as-path originates-from ‘10’ then
apply param-example(10)
else
pass
endif
end-policy
route-policy origin-20
if as-path originates-from ‘20’ then
apply param-example(20)
else
pass
endif
end-policy
The parameterized policy param-example provides a policy definition that is expanded with the values
provided as the parameters in the apply statement. Note that the policy hierarchy is always maintained,
Thus, if the definition of param-example changes, then the behavior of origin_10 and origin_20 changes
to match.
The effect of the origin-10 policy is that it adds the community 1234:10 to all routes that pass through
this policy and have an AS path indicating the route originated from autonomous system 10. The
origin-20 policy is similar except that it adds to community 1234:20 for routes originating from
autonomous system 20.
Semantics of Policy Application
This section discusses how routing policies are evaluated and applied. The following concepts are
discussed:
•
•
•
•
•
•
Boolean Operator Precedence
Boolean expressions are evaluated in order of operator precedence, from left to right. The highest
precedence operator is not, followed by and, and then or. The following expression:
med eq 10 and not destination in (10.1.3.0/24) or community matches-any ([10..25]:35)
if fully parenthesized to display the order of evaluation, would look like this:
(med eq 10 and (not destination in (10.1.3.0/24))) or community matches-any ([10..25]:35)
The inner not applies only to the destination test; the and combines the result of the not expression with
the Multi Exit Discriminator (MED) test; and the or combines that result with the community test. If the
order of operations are rearranged:
not med eq 10 and destination in (10.1.3.0/24) or community matches-any ([10..25]:35)
Cisco IOS XR Routing Configuration Guide
RC-215
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
then the expression, fully parenthesized, would look like the following:
((not med eq 10) and destination in (10.1.3.0/24)) or community matches-any ([10..25]:35)
Multiple Modifications of the Same Attribute
When a policy replaces the value of an attribute multiple times, the last assignment wins because all
actions are executed. Because the MED attribute in BGP is one unique value, the last value to which it
gets set to wins. Therefore, the following policy results in a route with a MED value of 12:
set med 9
set med 10
set med 11
set med 12
This example is trivial, but the feature is not. It is possible to write a policy that effectively changes the
value for an attribute. For example:
set med 8
if community matches-any cs1 then
set local-preference 122
if community matches-any cs2 then
set med 12
endif
endif
The result is a route with a MED of 8, unless the community list of the route matches both cs1 and cs2,
in which case the result is a route with a MED of 12.
In the case in which the attribute being modified can contain only one value, it is easy to think of this
case as the last statement wins. However, a few attributes can contain multiple values and the result of
multiple actions on the attribute is cumulative rather than as a replacement. The first of these cases is the
use of the additive keyword on community and extended community evaluation. Consider a policy of
the form:
route-policy community-add
set community (10:23)
set community (10:24) additive
set community (10:25) additive
end-policy
This policy sets the community string on the route to contain all three community values: 10:23, 10:24,
and 10:25.
The second of these cases is AS path prepending. Consider a policy of the form:
route-policy prepend-example
prepend as-path 2 3
prepend as-path 666 2
end-policy
This policy prepends the following to the AS path (666 666 2 2 2). This prepending is a result of all
actions being taken and to AS path being an attribute that contains an array of values rather than a simple
scalar value.
When Attributes Are Modified
A policy does not modify route attribute values until all tests have been completed. In other words,
comparison operators always run on the initial data in the route. Intermediate modifications of the route
attributes do not have a cascading effect on the evaluation of the policy. Take the following example:
Cisco IOS XR Routing Configuration Guide
RC-216
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
if med eq 12 then
set med 42
if med eq 42 then
drop
endif
endif
This policy never executes the drop statement because the second test (med eq 42) sees the original,
unmodified value of the MED in the route. Because the MED has to be 12 to get to the second test, the
second test always returns false.
Default Drop Disposition
All route policies have a default action to drop the route under evaluation unless the route has been
modified by a policy action or explicitly passed. Applied (nested) policies implement this disposition as
though the applied policy were pasted into the point where it is applied.
Consider a policy to allow all routes in the 10 network and set their local preference to 200 while
dropping all other routes. You might write the policy as follows:
route-policy two
if destination in (10.0.0.0/8 ge 8 le 32) then
set local-preference 200
endif
end-policy
route-policy one
apply two
end-policy
It may appear that policy one drops all routes because it neither contains an explicit pass statement nor
modifies a route attribute. However, the applied policy does set an attribute for some routes and this
disposition is passed along to policy one. The result is that policy one passes routes with destinations in
network 10, and drops all others.
Control Flow
Policy statements are processed sequentially in the order in which they appear in the configuration.
Policies that hierarchically reference other policy blocks are processed as if the referenced policy blocks
had been directly substituted inline. For example, if the following policies are defined:
route-policy one
set weight 100
end-policy
route-policy two
set med 200
end-policy
route-policy three
apply two
set community (2:666) additive
end-policy
route-policy four
apply one
apply three
pass
end-policy
Cisco IOS XR Routing Configuration Guide
RC-217
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Policy four could be rewritten in an equivalent way as follows:
route-policy four-equivalent
set weight 100
set med 200
set community (2:666) additive
pass
end-policy
Note
The pass statement is not required and can be removed to represent the equivalent policy in another way.
Policy Verification
Several different types of verification occur when policies are being defined and used.
Range Checking
As policies are being defined, some simple verifications, such as range checking of values, is done. For
example, the MED that is being set is checked to verify that it is in a proper range for the MED attribute.
However, this range checking cannot cover parameter specifications because they may not have defined
values yet. These parameter specifications are verified when a policy is attached to an attach point. The
policy repository also verifies that there are no recursive definitions of policy, and that parameter
numbers are correct. At attach time, all policies must be well formed. All sets and policies that they
reference must be defined and have valid values. Likewise, any parameter values must also be in the
proper ranges.
Incomplete Policy and Set References
As long as a given policy is not attached at an attach point, the policy is allowed to refer to nonexistent
sets and policies, which allows for freedom of workflow. You can build configurations that reference sets
or policy blocks that are not yet defined, and then can later fill in those undefined policies and sets,
thereby achieving much greater flexibility in policy definition. Every piece of policy you want to
reference while defining a policy need not exist in the configuration. Thus, a user can define a policy
sample that references the policy bar using an apply statement even if the policy bar does not exist.
Similarly, a user can enter a policy statement that refers to a nonexistent set.
However, the existence of all referenced policies and sets is enforced when a policy is attached. If you
attempt to attach the policy sample with the reference to an undefined policy bar at an inbound BGP
policy using the neighbor 1.2.3.4 address-family ipv4 unicast policy sample in command, the
configuration attempt is rejected because the policy bar does not exist.
Likewise, you cannot remove a route policy or set that is currently in use at an attach point because this
removal would result in an undefined reference. An attempt to remove a route policy or set that is
currently in use results in an error message to the user.
A condition exists that is referred to as a null policy in which the policy bar exists but has no statements,
actions, or dispositions in it. In other words, the policy bar does exist as follows:
route-policy bar
end-policy
This is a valid policy block. It effectively forces all routes to be dropped because it is a policy block that
never modifies a route, nor does it include the pass statement. Thus, the default action of drop for the
policy block is followed.
Cisco IOS XR Routing Configuration Guide
RC-218
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Attached Policy Modification
Policies that are in use do, on occasion, need to be modified. Traditionally, configuration changes are
done by completely removing the relevant configuration and then re-entering it. However, this allows for
a window of time in which no policy is attached and the default action takes place. RPL provides a
mechanism for an atomic change so that if a policy is redeclared, or edited using the emacs editor, the
new configuration is applied immediately, which allows for policies that are in use to be changed without
having a window of time in which no policy is applied at the given attach point.
Verification of Attribute Comparisons and Actions
The policy repository knows which attributes, actions, and comparisons are valid at each attach point.
When a policy is attached, these actions and comparisons are verified against the capabilities of that
particular attach point. Take, for example, the following policy definition:
route-policy bad
set med 100
set level level-1-2
set cost 200
end-policy
This policy attempts to perform actions to set the BGP attribute med, IS-IS attribute level, and OSPF
attribute cost. The system allows you to define such a policy, but it does not allow you to attach such a
policy. If you had defined the policy bad and then attempted to attach it as an inbound BGP policy using
the BGP configuration statement neighbor 1.2.3.4 address-family ipv4 unicast route-policy bad in the
system would reject this configuration attempt. This rejection results from the verification process
checking the policy and realizing that while BGP could set the MED, it has no way of setting the level
or cost as the level and cost are attributes of IS-IS and OSPF, respectively. Instead of silently omitting
the actions that cannot be done, the system generates an error to the user. Likewise, a valid policy in use
at an attach point cannot be modified in such a way as to introduce an attempt to modify a nonexistent
attribute or to compare against a nonexistent attribute. The verifiers test for nonexistent attributes and
reject such a configuration attempt.
Policy Statements
Four types of policy statements exist: remark, disposition (drop and pass), action (set), and if
(comparator).
Remark
A remark is text attached to policy configuration but otherwise ignored by the policy language parser.
Remarks are useful for documenting parts of a policy. The syntax for a remark is text that has each line
prepended with a pound sign (#):
# This is a simple one-line remark.
# This
# is a remark
# comprising multiple
# lines.
In general, remarks are used between complete statements or elements of a set. Remarks are not
supported in the middle of statements or within an inline set definition.
Cisco IOS XR Routing Configuration Guide
RC-219
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Unlike traditional !-comments in the CLI, RPL remarks persist through reboots and when configurations
are saved to disk or a TFTP server and then loaded back onto the router.
Disposition
By default, a route is dropped at the end of policy processing unless either the policy modifies a route
attribute or it passes the route by means of an explicit pass statement. For example, the following policy
drops all routes because it neither modifies the attribute of any route nor explicitly passes it.
route-policy EMPTY
end-policy
Whereas the following policies pass all routes that they evaluate.
route-policy PASS-ALL
pass
end-policy
route-policy SET-LPREF
set local-preference 200
end-policy
In addition to being implicitly dropped, a route may be dropped by an explicit drop statement. Drop
statements cause a route to be dropped immediately so that no further policy processing is done. Note
also that a drop statement overrides any previously processed pass statements or attribute modifications.
For example, the following policy drops all routes. The first pass statement is executed, but is then
immediately overridden by the drop statement. The second pass statement never gets executed.
route-policy DROP-EXAMPLE
pass
drop
pass
end-policy
When one policy applies another, it is as if the applied policy were copied into the right place in the
applying policy, and then the same drop-and-pass semantics are put into effect. For example, policies
ONE and TWO are equivalent to policy ONE-PRIME:
route-policy ONE
apply route-policy two
if as-path neighbor-is '123' then
pass
endif
end-policy
route-policy TWO
if destination in (10.0.0.0/16 le 32) then
drop
endif
end-policy
route-policy ONE-PRIME
if destination in (10.0.0.0/16 le 32) then
drop
endif
if as-path neighbor-is '123' then
pass
endif
end-policy
Cisco IOS XR Routing Configuration Guide
RC-220
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Because the effect of an explicit drop statement is immediate, routes in 10.0.0.0/16 le 32 are dropped
without any further policy processing. Other routes are then considered to see if they were advertised by
autonomous system 123. If they were advertised, they are passed; otherwise, they are implicitly dropped
at the end of all policy processing.
Action
An action is a sequence of primitive operations that modify a route. Most actions, but not all, are
distinguished by the set keyword. In a route policy, actions can be grouped together. For example, the
following is a route policy comprising three actions:
route-policy actions
set med 217
set community (12:34) additive
delete community in (12:56)
end-policy
If
In its simplest form, an if statement uses a conditional expression to decide which actions or dispositions
should be taken for the given route. For example:
if as-path in as-path-set-1 then
drop
endif
The example indicates that any routes whose AS path is in the set as-path-set-1 are dropped. The contents
of the then clause may be an arbitrary sequence of policy statements.
The following example contains two action statements:
if origin is igp then
set med 42
prepend as-path 73 5
endif
The CLI provides support for the exit command as an alternative to the endif command.
The if statement also permits an else clause, which is executed if the if condition is false:
if med eq 8 then
set community (12:34) additive
else
set community (12:56) additive
endif
The policy language also provides syntax, using the elseif keyword, to string together a sequence of tests:
if med eq 150 then
set local-preference 10
elseif med eq 200 then
set local-preference 60
elseif med eq 250 then
set local-preference 110
else
set local-preference 0
endif
Cisco IOS XR Routing Configuration Guide
RC-221
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
The statements within an if statement may themselves be if statements, as shown in the following
example:
if community matches-any (12:34,56:78) then
if med eq 150 then
drop
endif
set local-preference 100
endif
This policy example sets the value of the local preference attribute to 100 on any route that has a
community value of 12:34 or 56:78 associated with it. However, if any of these routes has a MED value
of 150, then these routes with either the community value of 12:34 or 56:78 and a MED of 150 are
dropped.
Boolean Conditions
In the previous section describing the if statement, all of the examples use simple Boolean conditions
that evaluate to either true or false. RPL also provides a way to build compound conditions from simple
conditions by means of Boolean operators.
Three Boolean operators exist: negation (not), conjunction (and), and disjunction (or). In the policy
language, negation has the highest precedence, followed by conjunction, and then by disjunction.
Parentheses may be used to group compound conditions to override precedence or to improve
readability.
The following simple condition:
med eq 42
is true only if the value of the MED in the route is 42, otherwise it is false.
A simple condition may also be negated using the not operator:
not next-hop in (10.0.2.2)
Any Boolean condition enclosed in parentheses is itself a Boolean condition:
(destination in prefix-list-1)
A compound condition takes either of two forms. It can be a simple expression followed by the and
operator, itself followed by a simple condition:
med eq 42 and next-hop in (10.0.2.2)
A compound condition may also be a simpler expression followed by the or operator and then another
simple condition:
origin is igp or origin is incomplete
An entire compound condition may be enclosed in parentheses:
(med eq 42 and next-hop in (10.0.2.2))
The parentheses may serve to make the grouping of subconditions more readable, or they may force the
evaluation of a subcondition as a unit.
In the following example, the highest-precedence not operator applies only to the destination test, the
and operator combines the result of the not expression with the community test, and the or operator
combines that result with the MED test.
med eq 10 or not destination in (10.1.3.0/24) and community matches-any
([12..34]:[56..78])
Cisco IOS XR Routing Configuration Guide
RC-222
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
With a set of parentheses to express the precedence, the result is the following:
med eq 10 or ((not destination in (10.1.3.0/24)) and community matches-any
([12..34]:[56..78])
The following is another example of a complex expression:
(origin is igp or origin is incomplete or not med eq 42) and next-hop in (10.0.2.2)
The left conjunction is a compound condition enclosed in parentheses. The first simple condition of the
inner compound condition tests the value of the origin attribute; if it is Interior Gateway Protocol (IGP),
then the inner compound condition is true. Otherwise, the evaluation moves on to test the value of the
origin attribute again, and if it is incomplete, then the inner compound condition is true. Otherwise, the
evaluation moves to check the next component condition, which is a negation of a simple condition.
apply
As discussed in the sections on policy definitions and parameterization of policies, the apply command
executes another policy (either parameterized or unparameterized) from within another policy, which
allows for the reuse of common blocks of policy. When combined with the ability to parameterize
common blocks of policy, the apply command becomes a powerful tool for reducing repetitive
configuration.
Attach Points
Policies do not become useful until they are applied to routes, and for policies to be applied to routes
they need to be made known to routing protocols. In BGP, for example, there are several situations where
policies can be used, the most common of these is defining import and export policy. The policy attach
point is the point in which an association is formed between a specific protocol entity, in this case a BGP
neighbor, and a specific named policy. It is important to note that a verification step happens at this point.
Each time a policy is attached, the given policy and any policies it may apply are checked to ensure that
the policy can be validly used at that attach point. For example, if a user defines a policy that sets the
IS-IS level attribute and then attempts to attach this policy as an inbound BGP policy, the attempt would
be rejected because BGP routes do not carry IS-IS attributes. Likewise, when policies are modified that
are in use, the attempt to modify the policy is verified against all current uses of the policy to ensure that
the modification is compatible with the current uses.
Each protocol has a distinct definition of the set of attributes (commands) that compose a route. For
example, BGP routes may have a community attribute, which is undefined in OSPF. Routes in IS-IS have
a level attribute, which is unknown to BGP. Routes carried internally in the RIB may have a tag attribute.
When a policy is attached to a protocol, the protocol checks the policy to ensure the policy operates using
route attributes known to the protocol. If the protocol uses unknown attributes, then the protocol rejects
the attachment. For example, OSPF rejects attachment of a policy that tests the values of BGP
communities.
The situation is made more complex by the fact that each protocol has access to at least two distinct route
types. In addition to native protocol routes, for example BGP or IS-IS, some protocol policy attach points
operate on RIB routes, which is the common central representation. Using BGP as an example, the
protocol provides an attach point to apply policy to routes redistributed from the RIB to BGP. An attach
point dealing with two different kinds of routes permits a mix of operations: RIB attribute operations for
matching and BGP attribute operations for setting.
Cisco IOS XR Routing Configuration Guide
RC-223
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Note
The protocol configuration rejects attempts to attach policies that perform unsupported operations.
The following sections describe the protocol attach points, including information on the attributes
(commands) and operations that are valid for each attach point.
•
•
•
•
See the Cisco IOS XR Routing Command Reference for more information on the attributes and
operations.
BGP Policy Attach Points
This section describes each of the BGP policy attach points and provides a summary of the BGP
attributes and operators.
Aggregation
The aggregation attach point generates an aggregate route to be advertised based on the conditional
presence of subcomponents of that aggregate. Policies attached at this attach point are also able to set
any of the valid BGP attributes on the aggregated routes. For example, the policy could set a community
value or a MED on the aggregate that is generated. The specified aggregate is generated if any routes
evaluated by the named policy pass the policy. More specifics of the aggregate are filtered using the
suppress-route keyword. Any actions taken to set attributes in the route affect attributes on the
aggregate.
In the policy language, the configuration is controlled by which routes pass the policy. The suppress map
was used to selectively filter or suppress specific components of the aggregate when the summary-only
flag is not set. In other words, when the aggregate and more specific components are being sent, some
of the more specific components can be filtered using a suppress map. In the policy language, this is
controlled by selecting the route and setting the suppress flag. The attribute-map allowed the user to set
specific attributes on the aggregated route. In the policy language, setting attributes on the aggregated
route is controlled by normal action operations.
In the following example, the aggregate address 10.0.0.0/8 is generated if there are any component routes
in the range 10.0.0.0/8 ge 8 le 25 except for 10.2.0.0/24. Because summary-only is not set, all
components of the aggregate are advertised. However, the specific component 10.1.0.0 are suppressed.
route-policy sample
if destination in (10.0.0.0/8 ge 8 le 25) then
set community (10:33)
endif
if destination in (10.2.0.0/24) then
drop
endif
if destination in (10.1.0.0/24) then
suppress-route
endif
end-policy
Cisco IOS XR Routing Configuration Guide
RC-224
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
router bgp 2
address-family ipv4
aggregate-address 10.0.0.0/8 policy sample
.
.
.
Dampening
The dampening attach point controls the default route-dampening behavior within BGP. Unless
overridden by a more specific policy on the associate peer, all routes in BGP apply the associated policy
to set their dampening attributes.
The following policy sets dampening values for BGP IPv4 unicast routes. Those routes that are more
specific than a /25 take longer to recover after they have been dampened than routes that are less specific
than /25.
route-policy sample_damp
if destination in (0.0.0.0/0 ge 25) then
set dampening halflife 30 others default
else
set dampening halflife 20 others default
endif
end-policy
router bgp 2
address-family ipv4 unicast
bgp dampening policy sample_damp
.
.
.
Default Originate
The default originate attach point allows the default route (0.0.0.0/0) to be conditionally generated and
advertised to a peer, based on the presence of other routes. It accomplishes this configuration by
evaluating the associated policy against routes in the Routing Information Base (RIB). If any routes pass
the policy, the default route is generated and sent to the relevant peer.
The following policy generates and sends a default-route to the BGP neighbor 10.0.0.1 if any routes that
match 10.0.0.0/8 ge 8 le 32 are present in the RIB.
route-policy sample-originate
if rib-has-route in (10.0.0.0/8 ge 8 le 32) then
pass
endif
end-policy
router bgp 2
neighbor 10.0.0.1
remote-as 3
address-family ipv4 unicast
default-originate policy sample-originate
.
.
.
Note
The current implementation of default origination policy permits matching only on destination address.
Cisco IOS XR Routing Configuration Guide
RC-225
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Neighbor Export
The neighbor export attach point selects the BGP routes to send to a given peer or group of peers. The
routes are selected by running the set of possible BGP routes through the associated policy. Any routes
that pass the policy are then sent as updates to the peer or group of peers. The routes that are sent may
have had their BGP attributes altered by the policy that has been applied.
The following policy sends all BGP routes to neighbor 10.0.0.5. Routes that are tagged with any
community in the range 2:100 to 2:200 are sent with a MED of 100 and a community of 2:666. The rest
of the routes are sent with a MED of 200 and a community of 2:200.
route-policy sample-export
if community matches-any (2:[100-200]) then
set med 100
set community (2:666)
else
set med 200
set community (2:200)
endif
end-policy
router bgp 2
neighbor 10.0.0.5
remote-as 3
address-family ipv4 unicast
route-policy sample-export out
.
.
.
Neighbor Import
The neighbor import attach point controls the reception of routes from a specific peer. All routes that are
received by a peer are run through the attached policy. Any routes that pass the attached policy are passed
to the BGP Routing Information Base (BRIB) as possible candidates for selection as best path routes.
When a BGP import policy is modified, it is necessary to rerun all the routes that have been received
from that peer against the new policy. The modified policy may now discard routes that were previously
allowed through, allow through previously discarded routes, or change the way the routes are modified.
A new configuration option in BGP (bgp auto-policy-soft-reset) that allows this modification to happen
automatically in cases for which either soft reconfiguration is configured or the BGP route-refresh
capability has been negotiated.
The following example shows how to receive routes from neighbor 10.0.0.1. Any routes received with
the community 3:100 have their local preference set to 100 and their community tag set to 2:666. All
other routes received from this peer have their local preference set to 200 and their community tag set to
2:200.
route-policy sample_import
if community matches-any (3:100) then
set local-preference 100
set community (2:666)
else
set local-preference 200
set community (2:200)
endif
end-policy
Cisco IOS XR Routing Configuration Guide
RC-226
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
router bgp 2
neighbor 10.0.0.1
remote-as 3
address-family ipv4 unicast
route-policy sample_import in
.
.
.
Network
The network attach point controls the injection of routes from the RIB into BGP. A route policy attached
at this point is able to set any of the valid BGP attributes on the routes that are being injected.
The following example shows a route policy attached at the network attach point that sets the well-known
community no-export for any routes more specific than /24:
route-policy NetworkControl
if destination in (0.0.0.0/0 ge 25) then
set community (no-export) additive
endif
end-policy
router bgp 2
address-family ipv4 unicast
network 172.16.0.5/27 route-policy NetworkControl
Redistribute
The redistribute attach point allows routes from other sources to be advertised by BGP. The policy
attached at this point is able to set any of the valid BGP attributes on the routes that are being
redistributed. Likewise, selection operators allow a user to control what route sources are being
redistributed and which routes from those sources.
The following example shows how to redistribute all routes from OSPF instance 12 into BGP. If OSPF
were carrying a default route, it is dropped. Routes carrying a tag of 10 have their local preference set
to 300 and the community value of 2:666 and no-advertise attached. All other routes have their local
preference set to 200 and a community value of 2:100 set.
route-policy sample_redistribute
if destination in (0.0.0.0/0) then
drop
endif
if tag eq 10 then
set local-preference 300
set community (2:666, no-advertise)
else
set local-preference 200
set community (2:100)
endif
end-policy
router bgp 2
address-family ipv4 unicast
redistribute ospf 12 route-policy sample_redistribute
.
.
Cisco IOS XR Routing Configuration Guide
RC-227
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Show bgp
The show bgp attach point allows the user to display selected BGP routes that pass the given policy. Any
routes that are not dropped by the attached policy are displayed in a manner similar to the output of the
show ip bgp command.
In the following example, the show bgp route-policy command is used to display any BGP routes
carrying a MED of 5:
route-policy sample-display
if med eq 5 then
pass
endif
end-policy
!
show bgp route-policy sample-display
A show bgp policy route-policy command also exists, which runs all routes in the RIB past the named
policy as if the RIB were an outbound BGP policy. This command then displays what each route looked
like before it was modified and after it was modified, as shown in the following example:
RP/0/RP0/CPU0:router# show rpl route-policy test2
route-policy test2
if (destination in (10.0.0.0/8 ge 8 le 32)) then
set med 333
endif
end-policy
!
RP/0/RP0/CPU0:router# show bgp
BGP router identifier 10.0.0.1, local AS number 2
BGP main routing table version 11
BGP scan interval 60 secs
Status codes:s suppressed, d damped, h history, * valid, > best
i - internal, S stale
Origin codes:i - IGP, e - EGP, ? - incomplete
Network
*> 10.0.0.0
Next Hop
10.0.1.2
10.0.1.2
10.0.1.2
10.0.1.2
10.0.1.2
10.0.1.2
10.0.1.2
10.0.1.2
10.0.101.2
10.0.101.2
Metric LocPrf Weight Path
10
10
0 3 ?
0 3 ?
0 3 ?
0 3 ?
0 3 ?
0 3 ?
0 3 ?
0 3 ?
0 100 e
0 100 e
*> 10.0.0.0/9
*> 10.0.0.0/10
*> 10.0.0.0/11
*> 10.1.0.0/16
*> 10.3.30.0/24
*> 10.3.30.128/25
*> 10.128.0.0/9
*> 10.255.0.0/24
*> 10.255.64.0/24
....
10
10
10
10
10
10
1000
1000
555
555
Cisco IOS XR Routing Configuration Guide
RC-228
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
RP/0/RP0/CPU0:router# show bgp policy route-policy test2
10.0.0.0/8 is advertised to 10.0.101.2
Path info:
neighbor:10.0.1.2
neighbor router id:10.0.1.2
valid external best
Attributes after inbound policy was applied:
next hop:10.0.1.2
MET ORG AS
origin:incomplete neighbor as:3 metric:10
aspath:3
Attributes after outbound policy was applied:
next hop:10.0.1.2
MET ORG AS
origin:incomplete neighbor as:3 metric:333
aspath:2 3
...
Table Policy
The table policy attach point allows the user to configure traffic-index values on routes as they are
installed into the global routing table. This attach point supports the BGP policy accounting feature.
BGP policy accounting uses the traffic indexes that are set on the BGP routes to track various counters.
This way, router operators can select different sets of BGP route attributes using the matching operations
and then set different traffic indexes for each different class of route they are interested in tracking.
The following example shows how to set the traffic index to 10 in IPv4 unicast routes that originated
from autonomous system 10. Likewise, any IPv4 unicast routes that originated from autonomous system
11 have their traffic index set to 11 when they are installed into the FIB. These traffic indexes are then
used to count traffic being forwarded on these routes in line cards by enabling the BGP policy accounting
counters on the interfaces of interest.
route-policy sample-table
if as-path originates-from ‘10’ then
set traffic-index 10
elseif as-path originates-from ‘11’ then
set traffic-index 11
endif
end-policy
router bgp 2
address-family ipv4 unicast
table-policy sample-table
.
.
.
BGP Attributes and Operators
Table 3 summarizes the BGP attributes and operators.
Cisco IOS XR Routing Configuration Guide
RC-229
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Table 3
BGP Attributes and Operators
Attribute
Match
Set
as-path
in
prepend
is-local
length
neighbor-is
originates-from
passes-though
unique-length
is-empty
community
dampening
delete
set
matches-any
matches-every
n/a
set dampening... to set
values that control the
dampening (see
destination
in
n/a
extended community
is-empty
matches-any
matches-every
n/a
delete
set
local-preference
med
set
is, eq, ge, le
set
set +
set -
next-hop
in
set
origin
is
set
rib-has-route
route-type
source
in
n/a
is
n/a
in
n/a
suppress-route
tag
n/a
suppress-route
is, eq, ge, le
set
traffic-index
unsuppress-route
weight
n/a
n/a
n/a
set
unsuppress-route
set
Some BGP route attributes are inaccessible from some BGP attach points for various reasons. For
example, the set med igp-cost only command makes sense when there is a configured igp-cost to
Cisco IOS XR Routing Configuration Guide
RC-230
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Table 4
Restricted BGP Operations by Attach Point
import
export
aggregation
n/a
redistribution
n/a
prepend as-path
set med igp-cost
set weight
eBGP only
forbidden
n/a
eBGP only
eBGP only
forbidden
forbidden
forbidden
n/a
forbidden
n/a
suppress
forbidden
n/a
forbidden
OSPF Policy Attach Points
This section describes each of the OSPF policy attach points and provides a summary of the OSPF
attributes and operators.
Default Originate
The default originate attach point allows the user to conditionally inject the default route 0.0.0.0/0 into
the OSPF link-state database, which is done by evaluating the attached policy. If any routes in the local
RIB pass the policy, then the default route is inserted into the link-state database.
The following example shows how to generate a default route if any of the routes that match 10.0.0.0/8
ge 8 le 25 are present in the RIB:
route-policy ospf-originate
if rib-has-route in (10.0.0.0/8 ge 8 le 25) then
pass
endif
end-policy
router ospf 1
default-information originate policy ospf-originate
.
.
.
Redistribute
The redistribute attach point within OSPF injects routes from other routing protocol sources into the
OSPF link-state database, which is done by selecting the route types it wants to import from each
protocol. It then sets the OSPF parameters of cost and metric type. The policy can control how the routes
are injected into OSPF by using the set level command.
The following example shows how to redistribute routes from IS-IS instance instance_10 into OSPF
instance 1 using the policy OSPF-redist. The policy sets the metric type to type-2 for all redistributed
routes. IS-IS routes with a tag of 10 have their cost set to 100, and IS-IS routes with a tag of 20 have
their OSPF cost set to 200. Any IS-IS routes not carrying a tag of either 10 or 20 are not be redistributed
into the OSPF link-state database.
Cisco IOS XR Routing Configuration Guide
RC-231
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
route-policy OSPF-redist
set metric-type type-2
if tag eq 10 then
set cost 100
elseif tag eq 20 then
set cost 200
else
drop
endif
end-policy
router ospf 1
redistribute isis instance_10 policy OSPF-redist
.
.
.
OSPF Attributes and Operators
Table 5 summarizes the OSPF attributes and operators.
Table 5
OSPF Attributes and Operators
Attribute
cost
Match
n/a
Set
set
n/a
set
n/a
n/a
set
destination
metric-type
in
n/a
rib-has-route
route-type
tag
in
is
eq, ge, le
OSPFv3 Policy Attach Points
This section describes each of the OSPFv3 policy attach points and provides a summary of the BGP
attributes and operators.
Default Originate
The default originate attach point allows the user to conditionally inject the default route 0::/0 into the
OSPFv3 link-state database, which is done by evaluating the attached policy. If any routes in the local
RIB pass the policy, then the default route is inserted into the link-state database.
The following example shows how to generate a default route if any of the routes that match 2001::/96
are present in the RIB:
route-policy ospfv3-originate
if rib-has-route in (2001::/96) then
pass
endif
end-policy
Cisco IOS XR Routing Configuration Guide
RC-232
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
router ospfv3 1
default-information originate policy ospfv3-originate
.
.
.
Redistribute
The redistribute attach point within OSPFv3 injects routes from other routing protocol sources into the
OSPFv3 link-state database, which is done by selecting the route types it wants to import from each
protocol. It then sets the OSPFv3 parameters of cost and metric type. The policy can control how the
routes are injected into OSPFv3 by using the metric type command.
The following example shows how to redistribute routes from BGP instance instance_15 into OSPF
instance 1 using the policy OSPFv3-redist. The policy sets the metric type to type-2 for all redistributed
routes. BGP routes with a tag of 10 have their cost set to 100, and BGP routes with a tag of 20 have their
OSPFv3 cost set to 200. Any BGP routes not carrying a tag of either 10 or 20 are not be redistributed
into the OSPFv3 link-state database.
route-policy OSPFv3-redist
set metric-type type-2
if tag eq 10 then
set cost 100
elseif tag eq 20 then
set cost 200
else
drop
endif
end-policy
router ospfv3 1
redistribute bgp instance_15 policy OSPFv3-redist
.
.
.
OSPFv3 Attributes and Operators
Table 6 summarizes the OSPFv3 attributes and operators.
Table 6
OSPFv3 Attributes and Operators
Attribute
cost
Match
n/a
Set
set
n/a
set
n/a
n/a
set
destination
metric-type
in
n/a
rib-has-route
route-type
tag
in
is
eq, ge, le
Cisco IOS XR Routing Configuration Guide
RC-233
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
IS-IS Policy Attach Points
This section describes each of the IS-IS policy attach points and provides a summary of the BGP
attributes and operators.
Redistribute
The redistribute attach point within IS-IS allows routes from other protocols to be readvertised by IS-IS.
The policy is a set of control structures for selecting the types of routes that a user wants to redistribute
into IS-IS. The policy can also control which IS-IS level the routes are injected into and at what metric
values.
The following example shows how to redistribute routes from IS-IS instance 1 into IS-IS instance
instance_10 using the policy ISIS-redist. This policy sets the level to level-1-2 for all redistributed
routes. OSPF routes with a tag of 10 have their metric set to 100, and IS-IS routes with a tag of 20 have
their IS-IS metric set to 200. Any IS-IS routes not carrying a tag of either 10 or 20 are not be redistributed
into the IS-IS database.
route-policy ISIS-redist
set level level-1-2
if tag eq 10 then
set metric 100
elseif tag eq 20 then
set metric 200
else
drop
endif
end-policy
router isis instance_10
address-family ipv4 unicast
redistribute ospf 1 policy ISIS-redist
.
.
.
IS-IS Attributes and Operators
Table 7 summarizes the IS-IS attributes and operators.
Table 7
IS-IS Attributes and Operators
Attribute
Destination
Level
Match
in
Set
n/a
set
set
set
n/a
n/a
n/a
n/a
metric
n/a
metric-type
n/a
rib-has-route
route-type
tag
in
is
eq, ge, le
Cisco IOS XR Routing Configuration Guide
RC-234
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
Attached Policy Modification
Policies that are in use do, on occasion, need to be modified. In the traditional configuration model, a
policy modification would be done by completely removing the policy and re-entering it. However, this
model allows for a window of time in which no policy is attached and default actions to be used, which
is an opportunity for inconsistencies to exist. To close this window of opportunity, you can modify a
policy in use at an attach point by respecifying it, which allows for policies that are in use to be changed,
without having a window of time in which no policy is applied at the given attach point.
Note
A route policy or set that is in use at an attach point cannot be removed because this removal would result
in an undefined reference. An attempt to remove a route policy or set that is in use at an attach point
results in an error message to the user.
Nonattached Policy Modification
As long as a given policy is not attached at an attach point, the policy is allowed to refer to nonexistent
sets and policies. Configurations can be built that reference sets or policy blocks that are not yet defined,
and then later those undefined policies and sets can be filled in. This method of building configurations
gives much greater flexibility in policy definition. Every piece of policy you want to reference while
defining a policy need not exist in the configuration. Thus, you can define a policy sample1 that
references a policy sample2 using an apply statement even if the policy sample2 does not exist. Similarly,
you can enter a policy statement that refers to a nonexistent set.
However, the existence of all referenced policies and sets is enforced when a policy is attached. Thus, if
a user attempts to attach the policy sample1 with the reference to an undefined policy sample2 at an
inbound BGP policy using the statement neighbor 1.2.3.4 address-family ipv4 unicast policy sample1
in, the configuration attempt is rejected because the policy sample2 does not exist.
Editing Routing Policy Configuration Elements
RPL is based on statements rather than on lines. That is, within the begin-end pair that brackets policy
statements from the CLI, a new line is merely a separator, the same as a space character.
The CLI provides the means to enter and delete route policy statements. RPL provides a means to edit
the contents of the policy between the begin-end brackets using a microemacs editor.
Editing Routing Policy Configuration Elements Using the EMACS Editor
To edit the contents of a routing policy, use the following CLI command in EXEC mode:
edit {route-policy | prefix-set | as-path-set | community-set | extended-community-set}
name
A copy of the route policy is copied to a temporary file and the editor is launched. After editing, save
the changes by using the save-buffer command, C-X C-S (Control-X Control-S). To exit the editor, use
the quit command, Control-X Control-C. When you quit the editor, the buffer is committed. If there are
no parse errors, the configuration is committed:
Cisco IOS XR Routing Configuration Guide
RC-235
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Information About Implementing Routing Policy
RP/0/RP0/CPU0:router# edit route-policy policy_A
----------------------------------------
== MicroEMACS 3.8b () == rpl_edit.139281 ==
if destination in (2001::/8) then
drop
endif
end-policy
!
== MicroEMACS 3.8b () == rpl_edit.139281 ==
Parsing.
83 bytes parsed in 1 sec (82)bytes/sec
Committing.
1 items committed in 1 sec (0)items/sec
Updating.
Updated Commit database in 1 sec
RP/0/RP0/CPU0:router#
If there are parse errors, you are asked whether editing should continue:
RP/0/RP0/CPU0:router#edit route-policy policy_B
== MicroEMACS 3.8b () == rpl_edit.141738
route-policy policy_B
set metric-type type_1
if destination in (2001::/8) then
drop
endif
end-policy
!
== MicroEMACS 3.8b () == rpl_edit.141738 ==
Parsing.
105 bytes parsed in 1 sec (103)bytes/sec
% Syntax/Authorization errors in one or more commands.!! CONFIGURATION
FAILED DUE TO SYNTAX/AUTHORIZATION ERRORS
set metric-type type_1
if destination in (2001::/8) then
drop
endif
end-policy
!
Continue editing? [no]:
If you answer yes, the editor continues on the text buffer from where you left off. If you answer no, the
running configuration is not changed and the editing session is ended.
Editing Routing Policy Configuration Elements Using the CLI
The CLI allows you to enter and delete route policy statements. You can complete a policy configuration
block by entering applicable commands such as end-policy or end-set. Alternatively, the CLI interpreter
allows you to use the exit command to complete a policy configuration block. The abort command is
used to discard the current policy configuration and return to global configuration mode.
Cisco IOS XR Routing Configuration Guide
RC-236
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
How to Implement Routing Policy
How to Implement Routing Policy
This section contains the following procedures:
•
•
•
Defining a Route Policy, page RC-237 (required)
Defining a Route Policy
This task explains how to define a route policy.
Note
If you want to modify an existing routing policy using the command-line interface (CLI), you must
redefine the policy by completing this task.
SUMMARY STEPS
1. configure
2. route-policy name
3. end-policy
4. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
route-policy name
Step 2
Enters route-policy configuration mode.
•
After the route-policy has been entered, a group of
commands can be entered to define the route-policy.
Example:
RP/0/RP0/CPU0:router(config)# route-policy
sample1
Cisco IOS XR Routing Configuration Guide
RC-237
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
How to Implement Routing Policy
Command or Action
Purpose
end-policy
Step 3
Ends the definition of a route policy and exits route-policy
configuration mode.
Example:
RP/0/RP0/CPU0:router(config-rpl)# end-policy
end
Step 4
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
Use the commit command to save the configuration
changes to the running configuration file and remain within
the configuration session.
Attaching a Routing Policy to a BGP Neighbor
This task explains how to attach a routing policy to a BGP neighbor. The procedure to attach a routing
policy to an IS-IS or OSPF neighbor is the same as BGP, except that the commands and applicable
arguments vary.
Prerequisites
A routing policy must be preconfigured and well defined prior to it being applied at an attach point. If a
policy is not predefined, an error message is generated stating that the policy is not defined.
SUMMARY STEPS
1. configure
2. router bgp as-number
3. neighbor ip-address
4. address-family {ipv4 | ipv6} {multicast | unicast}
5. route-policy route-policy-name {in | out}
6. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-238
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
How to Implement Routing Policy
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
router bgp as-number
Step 2
Configures a BGP routing process and enters router
configuration mode.
•
The as-number argument identifies the
Example:
RP/0/RP0/CPU0:router(config)# router bgp 125
autonomous system in which the router resides.
Valid values are from 0 to 65535. Private
autonomous system numbers that can be used in
internal networks range from 64512 to 65535.
neighbor ip-address
Step 3
Specifies a neighbor IP address.
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor
10.0.0.20
address-family {ipv4 | ipv6} {multicast | unicast}
Step 4
Specifies the address family, the version of IP that is
in use, and either multicast or unicast.
•
Enters address family configuration mode.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)#
address-family ipv4 unicast
Cisco IOS XR Routing Configuration Guide
RC-239
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
How to Implement Routing Policy
Command or Action
Purpose
route-policy policy-name {in | out}
Step 5
Attaches the route-policy, which must be well formed
and predefined.
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)#
route-policy example1 in
end
Step 6
Saves configuration changes.
or
•
When you issue the end command, the system
commit
prompts you to commit changes:
Uncommitted changes found, commit them
before exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# end
or
–
Entering yes saves configuration changes to
the running configuration file, exits the
configuration session, and returns the router
to EXEC mode.
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
–
–
Entering no exits the configuration session
and returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the
current configuration session without exiting
or committing the configuration changes.
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Modifying a Routing Policy Using the Microemacs Editor
This task explains how to modify an existing routing policy using the microemacs editor.
SUMMARY STEPS
1. edit {route-policy | prefix-set | as-path-set | community-set | extended-community-set} name
2. show rpl route-policy name [detail]
3. show rpl prefix-set name
Cisco IOS XR Routing Configuration Guide
RC-240
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Configuration Examples for Implementing Routing Policy
DETAILED STEPS
Command or Action
Purpose
edit {route-policy | prefix-set | as-path-set |
community-set | extended-community-set} name
Step 1
Identifies the route policy, prefix set, AS path set,
community set, or extended community set name to be
modified.
Example:
•
A copy of the route policy, prefix set, AS path set,
community set, or extended community set is copied to
a temporary file and the microemacs editor is launched.
When you finish editing the policy or set, save the
changes by using the save-buffer command, ^X^S
(Control-X Control-S).
RP/0/RP0/CPU0:router# edit route-policy sample1
To commit the changed configuration:
•
•
save the buffer (Control-X Control-S)
exit MicroEmacs (Control-X Control-C)
show rpl route-policy name [detail]
Step 2
(Optional) Displays the configuration of a specific named
route policy.
•
Use the detail keyword to display all policies and sets
that a policy uses.
Example:
RP/0/RP0/CPU0:router# show rpl route-policy
sample2
show rpl prefix-set name
Step 3
(Optional) Displays the contents of a named prefix set.
•
To display the contents of a named AS path set,
community set, or extended community set, replace the
prefix-set keyword with as-path-set, community-set,
or extcommunity-set, respectively.
Example:
RP/0/RP0/CPU0:router# show rpl prefix-set
prefixset1
Configuration Examples for Implementing Routing Policy
This section provides the following configuration examples:
•
•
•
•
Routing Policy Definition: Example
In the following example, a BGP route policy named sample1 is defined using the route-policy name
command. The policy compares the network layer reachability information (NLRI) to the elements in
the prefix set test. If it evaluates to true, the policy performs the operations in the then clause. If it
evaluates to false, the policy performs the operations in the else clause, that is, sets the MED value to
200 and adds the community 2:100 to the route. The final steps of the example commit the configuration
to the router, exit configuration mode, and display the contents of route policy sample1.
Cisco IOS XR Routing Configuration Guide
RC-241
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Configuration Examples for Implementing Routing Policy
configure
route-policy sample1
if destination in test then
drop
else
set med 200
set community (2:100) additive
endif
end-policy
end
show config running route-policy sample1
Building configuration...
route-policy sample1
if destination in test then
drop
else
set med 200
set community (2:100) additive
endif
end-policy
Simple Inbound Policy: Example
The following policy discards any route whose network layer reachability information (NLRI) specifies
a prefix longer than /24, and any route whose NLRI specifies a destination in the address space reserved
by RFC 1918. For all remaining routes, it sets the MED and local preference, and adds a community to
the list in the route.
For routes whose community lists include any values in the range from 101:202 to 106:202 that have a
16-bit tag portion containing the value 202, the policy prepends autonomous system number 2 twice, and
adds the community 2:666 to the list in the route. Of these routes, if the MED is either 666 or 225, then
the policy sets the origin of the route to incomplete, and otherwise sets the origin to IGP.
For routes whose community lists do not include any of the values in the range from 101:202 to 106:202,
the policy adds the community 2:999 to the list in the route.
prefix-set too-specific
0.0.0.0/0 ge 25 le 32
end-set
prefix-set rfc1918
10.0.0.0/8 le 32,
172.16.0.0/12 le 32,
192.168.0.0/16 le 32
end-set
route-policy inbound-tx
if destination in too-specific or destination in rfc1918 then
drop
endif
set med 1000
set local-preference 90
set community (2:1001) additive
if community matches-any ([101..106]:202) then
prepend as-path 2 2
set community (2:666) additive
if med is 666 or med is 225 then
set origin incomplete
else
set origin igp
Cisco IOS XR Routing Configuration Guide
RC-242
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Configuration Examples for Implementing Routing Policy
endif
else
set community (2:999) additive
endif
end-policy
router bgp 2
neighbor 10.0.1.2 address-family ipv4 unicast route-policy inbound-tx in
Modular Inbound Policy: Example
The following policy example shows how to build two inbound policies, in-100 and in-101, for two
different peers. In building the specific policies for those peers, the policy reuses some common blocks
of policy that may be common to multiple peers. It builds a few basic building blocks, the policies
common-inbound, filter-bogons, and set-lpref-prepend.
The filter-bogons building block is a simple policy that filters all undesirable routes, such as those from
the RFC 1918 address space. The policy set-lpref-prepend is a utility policy that can set the local
preference and prepend the AS path according to parameterized values that are passed in. The
common-inbound policy uses these filter-bogons building blocks to build a common block of inbound
policy. The common-inbound policy is used as a building block in the construction of in-100 and in-101
along with the set-lpref-prepend building block.
This is a simple example that illustrates the modular capabilities of the policy language.
prefix-set bogon
10.0.0.0/8 ge 8 le 32,
0.0.0.0,
0.0.0.0/0 ge 27 le 32,
192.168.0.0/16 ge 16 le 32
end-set
!
route-policy in-100
apply common-inbound
if community matches-any ([100..120]:135) then
apply set-lpref-prepend (100,100,2)
set community (2:1234) additive
else
set local-preference 110
endif
if community matches-any ([100..666]:[100..999]) then
set med 444
set local-preference 200
set community (no-export) additive
endif
end-policy
!
route-policy in-101
apply common-inbound
if community matches-any ([101..200]:201) then
apply set-lpref-prepend(100,101,2)
set community (2:1234) additive
else
set local-preference 125
endif
end-policy
!
route-policy filter-bogons
if destination in bogon then
drop
else
Cisco IOS XR Routing Configuration Guide
RC-243
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Additional References
pass
endif
end-policy
!
route-policy common-inbound
apply filter-bogons
set origin igp
set community (2:333)
end-policy
!
route-policy set-lpref-prepend($lpref,$as,$prependcnt)
set local-preference $lpref
prepend as-path $as $prependcnt
end-policy
Translating Cisco IOS Route Maps to Cisco IOS XR Routing Policy Language:
Example
RPL performs the same functions as route-maps. See the Converting Cisco IOS Configurations to
Cisco IOS XR Configurations guide.
Additional References
The following sections provide references related to implementing RPL.
Related Documents
Related Topic
Document Title
Routing policy language commands: complete
Routing Policy Language Commands on Cisco IOS XR Software,
command syntax, command modes, command history, Release 3.2
defaults, usage guidelines, and examples
Regular expression syntax
“Understanding Regular Expressions, Special Characters and
Patterns” appendix in the Cisco IOS XR Getting Started Guide
Standards
Standards
Title
Draft-ietf-idr-bgp4-26.txt
A Border Gateway Protocol 4, by Y. Rekhter, T.Li, S. Hares
Cisco IOS XR Routing Configuration Guide
RC-244
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Additional References
MIBs
MIBs
MIBs Link
There are no applicable MIBs for this module.
To locate and download MIBs for selected platforms using
Cisco IOS XR software, use the Cisco MIB Locator found at the
following URL:
RFCs
RFCs
Title
No new or modified RFCs are supported by this
feature, and support for existing RFCs has not been
modified by this feature.
—
Technical Assistance
Description
Link
The Cisco Technical Support website contains
thousands of pages of searchable technical content,
including links to products, technologies, solutions,
technical tips, and tools. Registered Cisco.com users
can log in from this page to access even more content.
Cisco IOS XR Routing Configuration Guide
RC-245
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Routing Policy on Cisco IOS XR Software
Additional References
Cisco IOS XR Routing Configuration Guide
RC-246
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR
Software
Static routes are user-defined routes that cause packets moving between a source and a destination to
take a specified path. Static routes can be important if the Cisco IOS XR software cannot build a route
to a particular destination. They are useful for specifying a gateway of last resort to which all unroutable
packets are sent.
This module describes the tasks you need to implement static routes on your Cisco IOS XR network.
Note
For more information about static routes on the Cisco IOS XR software and complete descriptions of the
static routes commands listed in this module, see the “Related Documents” section of this module. To
locate documentation for other commands that might appear while executing a configuration task, search
online in the Cisco IOS XR software master command index.
Feature History for Implementing Static Routes on Cisco IOS XR Software
Release
Modification
Release 2.0
Release 3.0
Release 3.2
This feature was introduced on the Cisco CRS-1.
No modification.
Support was added for the Cisco XR 12000 Series Router.
Contents
•
•
•
•
•
•
Cisco IOS XR Routing Configuration Guide
RC-247
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
Prerequisites for Implementing Static Routes on Cisco IOS XR Software
Prerequisites for Implementing Static Routes on Cisco IOS XR
Software
To use this command, you must be in a user group associated with a task group that includes the proper
task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on
Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.
Information About Implementing Static Routes on Cisco IOS XR
Software
To implement static routes you need to understand the following concepts:
•
•
•
Static Route Functional Overview
Static routes are entirely user configurable and can point to a next-hop interface, next-hop IP address, or
both. In Cisco IOS XR software, if an interface was specified, then the static route is installed in the
Routing Information Base (RIB) if the interface is reachable. If an interface was not specified, the route
is installed if the next-hop address is reachable. The only exception to this configuration is when a static
route is configured with the permanent attribute, in which case it is installed in RIB regardless of
reachability.
Networking devices forward packets using route information that is either manually configured or
dynamically learned using a routing protocol. Static routes are manually configured and define an
explicit path between two networking devices. Unlike a dynamic routing protocol, static routes are not
automatically updated and must be manually reconfigured if the network topology changes. The benefits
of using static routes include security and resource efficiency. Static routes use less bandwidth than
dynamic routing protocols, and no CPU cycles are used to calculate and communicate routes. The main
disadvantage to using static routes is the lack of automatic reconfiguration if the network topology
changes.
Static routes can be redistributed into dynamic routing protocols, but routes generated by dynamic
routing protocols cannot be redistributed into the static routing table. No algorithm exists to prevent the
configuration of routing loops that use static routes.
Static routes are useful for smaller networks with only one path to an outside network and to provide
security for a larger network for certain types of traffic or links to other networks that need more control.
In general, most networks use dynamic routing protocols to communicate between networking devices
but may have one or two static routes configured for special cases.
Default Administrative Distance
Static routes have a default administrative distance of 1. A low number indicates a preferred route. By
default, static routes are preferred to routes learned by routing protocols. Therefore, you can configure
an administrative distance with a static route if you want the static route to be overridden by dynamic
Cisco IOS XR Routing Configuration Guide
RC-248
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
Information About Implementing Static Routes on Cisco IOS XR Software
routes. For example, you could have routes installed by the Open Shortest Path First (OSPF) protocol
with an administrative distance of 120. To have a static route that would be overridden by an OSPF
dynamic route, specify an administrative distance greater than 120.
Directly Connected Routes
The routing table considers the static routes that point to an interface as “directly connected.” Directly
connected networks are advertised by IGP routing protocols if a corresponding interface command is
contained under the router configuration stanza of that protocol.
In directly attached static routes, only the output interface is specified. The destination is assumed to be
directly attached to this interface, so the packet destination is used as the next hop address. The following
example shows how to specify that all destinations with address prefix 2001:0DB8::/32 are directly
reachable through interface GigabitEthernet 0/5/0/0:
RP/0/RP0/CPU0:router(config)# route ipv6 unicast 2001:0DB8::/32 gigabitethernet 0/5/0/0
Directly attached static routes are candidates for insertion in the routing table only if they refer to a valid
interface; that is, an interface that is both up and has IPv4 or IPv6 enabled on it.
Recursive Static Routes
In a recursive static route, only the next hop is specified. The output interface is derived from the next
hop. The following example shows how to specify that all destinations with address prefix
2001:0DB8::/32 are reachable through the host with address 2001:0DB8:3000::1:
RP/0/RP0/CPU0:router(config)# route ipv6 unicast 2001:0DB8::/32 2001:0DB8:3000::1
A recursive static route is valid (that is, it is a candidate for insertion in the routing table) only when the
specified next hop resolves, either directly or indirectly, to a valid output interface, provided the route
does not self-recurse, and the recursion depth does not exceed the maximum IPv6 forwarding recursion
depth.
A route self-recurses if it is itself used to resolve its own next hop. If a static route becomes
self-recursive, RIB sends a notification to static routes to withdraw the recursive route.
The following example shows how to define a recursive IPv6 static route:
RP/0/RP0/CPU0:router(config)# route ipv6 unicast 2001:0DB8::/32 2001:0DB8:3000::1
This static route is not inserted into the IPv6 routing table because it is self-recursive. The next hop of
the static route, 2001:0DB8:3000:1, resolves through the BGP route 2001:0DB8:3000:0/16, which is
itself a recursive route (that is, it only specifies a next hop). The next hop of the BGP route,
2001:0DB8::0104, resolves through the static route. Therefore, the static route would be used to resolve
its own next hop.
It is not normally useful to manually configure a self-recursive static route, although it is not prohibited.
However, a recursive static route that has been inserted in the routing table may become self-recursive
as a result of some transient change in the network learned through a dynamic routing protocol. If this
occurs, the fact that the static route has become self-recursive will be detected and it will be removed
from the routing table, although not from the configuration. A subsequent network change may cause
the static route to no longer be self-recursive, in which case it will be re-inserted in the routing table.
Cisco IOS XR Routing Configuration Guide
RC-249
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
How to Implement Static Routes on Cisco IOS XR Software
Fully Specified Static Routes
In a fully specified static route, both the output interface and next hop are specified. This form of static
route is used when the output interface is a multiaccess one and it is necessary to explicitly identify the
next hop. The next hop must be directly attached to the specified output interface. The following
example shows a definition of a fully specified static route:
RP/0/RP0/CPU0:router(config)# route ipv6 unicast 2001:0DB8::/32 2001:0DB8:3000::1
A fully specified route is valid (that is, a candidate for insertion into the routing table) when the specified
interface is IPv4 or IPv6 enabled and up.
Floating Static Routes
Floating static routes are static routes that are used to back up dynamic routes learned through configured
routing protocols. A floating static route is configured with a higher administrative distance than the
dynamic routing protocol it is backing up. As a result, the dynamic route learned through the routing
protocol is always preferred to the floating static route. If the dynamic route learned through the routing
protocol is lost, the floating static route is used in its place. The following example shows how to define
a floating static route:
RP/0/RP0/CPU0:router(config)# route ipv6 unicast 2001:0DB8::/32 2001:0DB8:3000::1 210
Any of the three types of static routes can be used as a floating static route. A floating static route must
be configured with an administrative distance that is greater than the administrative distance of the
dynamic routing protocol because routes with smaller administrative distances are preferred.
Note
By default, static routes have smaller administrative distances than dynamic routes, so static routes
preferred to dynamic routes.
How to Implement Static Routes on Cisco IOS XR Software
This section contains the following procedures:
•
•
•
Configuring a Static Route, page RC-250 (required)
Configuring a Static Route
This task explains how to configure a static route.
SUMMARY STEPS
1. configure
2. route {ipv4 | ipv6} {unicast | multicast} prefix mask {ip-address | interface-type
interface-instance} [distance] [tag tag] [permanent]
Cisco IOS XR Routing Configuration Guide
RC-250
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
How to Implement Static Routes on Cisco IOS XR Software
3. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
route {ipv4 | ipv6} {unicast | multicast}
Step 2
Configures an administrative distance of 110.
prefix mask {ip-address | interface-type
interface-instance} [distance] [tag tag]
[permanent]
•
This example shows how to route packets for network
10.0.0.0 through to a router at 172.20.16.6 if dynamic
information with administrative distance less than 110
is not available.
Example:
RP/0/RP0/CPU0:router(config)# route ipv4
unicast 10.0.0.0/8 172.20.16.6 110
end
Step 3
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Configuring a Floating Static Route
This task explains how to configure a floating static route.
SUMMARY STEPS
1. configure
2. route {ipv4 | ipv6} {unicast | multicast} prefix mask {ip-address | interface-type
interface-instance} [distance] [tag tag] [permanent]
Cisco IOS XR Routing Configuration Guide
RC-251
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
How to Implement Static Routes on Cisco IOS XR Software
3. end
or
commit
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
route {ipv4 | ipv6} {unicast | multicast}
Step 2
In this example, a floating static IPv6 route is being
configured. An administrative distance of 201 is configured
prefix mask {ip-address | interface-type
interface-instance} [distance] [tag tag]
[permanent]
Default administrative distances are as follows:
•
•
Connected interface—0
Static route—1
Example:
RP/0/RP0/CPU0:router(config)# route ipv6
unicast 2001:0DB8::/32 2001:0DB8:3000::1 201
end
Step 3
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-252
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
How to Implement Static Routes on Cisco IOS XR Software
Changing the Maximum Number of Allowable Static Routes
This task explains how to change the maximum number of allowable static routes.
Restrictions
The number of static routes that can be configured on a router for a given address family is limited by
default to 4000. The limit can be raised or lowered using the route maximum command. Note that if
you use the route maximum command to reduce the configured maximum allowed number of static
routes for a given address family below the number of static routes currently configured, the change is
rejected. In addition, understand the following behavior: If you commit a batch of routes that would,
when grouped, push the number of static routes configured above the maximum allowed, the first n
routes in the batch are accepted. The number previously configured is accepted, and the remainder are
rejected. The n argument is the difference between the maximum number allowed and number previously
configured.
SUMMARY STEPS
1. configure
2. route maximum {ipv4 | ipv6} value
3. end
or
commit
Cisco IOS XR Routing Configuration Guide
RC-253
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
How to Implement Static Routes on Cisco IOS XR Software
DETAILED STEPS
Command or Action
Purpose
configure
Step 1
Enters global configuration mode.
Example:
RP/0/RP0/CPU0:router# configure
route maximum {ipv4 | ipv6} value
Step 2
Changes the maximum number of allowable static routes.
•
•
Specify IPv4 or IPv6 address prefixes.
Example:
Specify the maximum number of static routes for the
given address family. The range is from 1 to 128000.
RP/0/RP0/CPU0:router(config)# route maximum
ipv4 10000
•
This example sets the maximum number of static IPv4
routes to 10000.
end
Step 3
Saves configuration changes.
or
•
When you issue the end command, the system prompts
commit
you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
Example:
RP/0/RP0/CPU0:router(config)# end
or
–
–
–
Entering yes saves configuration changes to the
running configuration file, exits the configuration
session, and returns the router to EXEC mode.
RP/0/RP0/CPU0:router(config)# commit
Entering no exits the configuration session and
returns the router to EXEC mode without
committing the configuration changes.
Entering cancel leaves the router in the current
configuration session without exiting or
committing the configuration changes.
•
Use the commit command to save the configuration
changes to the running configuration file and remain
within the configuration session.
Cisco IOS XR Routing Configuration Guide
RC-254
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
Configuration Examples
Configuration Examples
This section provides the following configuration examples:
•
•
•
Configuring Traffic Discard: Example
Configuring a static route to point at interface null 0 may be used for discarding traffic to a particular
prefix. For example, if it is required to discard all traffic to prefix 2001:0DB8:42:1/64, the following
static route would be defined:
configure
route ipv6 unicast 2001:0DB8:42:1::/64 null 0
end
Configuring a Fixed Default Route: Example
A default static route is often used in simple router topologies. In the following example, a router is
configured with an administrative distance of 110.
configure
route ipv4 unicast 10.0.0.0/8 172.20.16.6 110
end
Configuring a Floating Static Route: Example
A floating static route often is used to provide a backup path if connectivity fails. In the following
example, a router is configured with an administrative distance of 201.
configure
route ipv6 unicast 2001:0DB8::/32 2001:0DB8:3000::1 201
end
Where to Go Next
For additional information on static routes, routing protocols, and RIB, consult the following
publications:
•
•
•
•
•
•
Implementing and Monitoring RIB on Cisco IOS XR Software
Implementing BGP on Cisco IOS XR Software
Implementing IS-IS on Cisco IOS XR Software
Implementing OSPF on Cisco IOS XR Software
Implementing OSPFv3 on Cisco IOS XR Software
RIB Commands on Cisco IOS XR Software
Cisco IOS XR Routing Configuration Guide
RC-255
Download from Www.Somanuals.com. All Manuals Search And Download.
Implementing Static Routes on Cisco IOS XR Software
Additional References
Additional References
The following sections provide references related to implementing static routes on Cisco IOS XR
software.
Related Documents
Related Topic
Document Title
Static routes commands: complete command syntax,
command modes, command history, defaults, usage
guidelines, and examples
Static and Utility Routing Commands on Cisco IOS XR Software,
Release 3.2
Standards
Standards
Title
No new or modified standards are supported by this
feature, and support for existing standards has not been
modified by this feature.
—
MIBs
MIBs
MIBs Link
There are no applicable MIBs for this module.
To locate and download MIBs for selected platforms using
Cisco IOS XR software, use the Cisco MIB Locator found at the
following URL:
RFCs
RFCs
Title
No new or modified RFCs are supported by this
feature, and support for existing RFCs has not been
modified by this feature.
—
Technical Assistance
Description
Link
The Cisco Technical Support website contains
thousands of pages of searchable technical content,
including links to products, technologies, solutions,
technical tips, and tools. Registered Cisco.com users
can log in from this page to access even more content.
Cisco IOS XR Routing Configuration Guide
RC-256
Download from Www.Somanuals.com. All Manuals Search And Download.
I N D E X
BGP (Border Gateway Protocol)
configuration
HC
Cisco IOS XR Interface and Hardware Component
Configuration Guide
IC
Cisco IOS XR IP Addresses and Services Configuration Guide
Cisco IOS XR Multicast Configuration Guide
Cisco IOS XR MPLS Configuration Guide
MCC
MPC
QC
grouping RC-5
inheriting RC-7
Cisco IOS XR Modular Quality of Service Configuration
Guide
description RC-1
RC
Cisco IOS XR Routing Configuration Guide
SC
Cisco IOS XR System Security Configuration Guide
Cisco IOS XR System Management Configuration Guide
SMC
multiprotocol RC-21
A
policy attach points
dampening RC-225
network RC-227
redistribute RC-227
authentication
router identifier
strategies RC-136
routing policy
enforcing RC-16
update groups
description RC-18
example RC-77
B
Cisco IOS XR Routing Configuration Guide
RC-257
Download from Www.Somanuals.com. All Manuals Search And Download.
Index
draft-ietf-idr-cease-subcode-05.txt RC-80
Draft-ietf-isis-igp-p2p-over-lan-05.txt, Point-to-point
Draft-ietf-isis-ipv6-05.txt, Routing IPv6 with
IS-IS RC-124
Draft-ietf-isis-restart-04.txt, Restart Signalling for
IS-IS RC-124
show isis mpls traffic-eng adjacency-log
Draft-ietf-isis-traffic-05.txt, IS-IS Extensions for Traffic
command RC-112
Engineering RC-124
show isis mpls traffic-eng advertisements
Draft-ietf-isis-wg-multi-topology-06.txt, M-ISIS
command RC-112
E
G
H
I
inheritance
monitoring RC-11
Cisco IOS XR Routing Configuration Guide
RC-259
Download from Www.Somanuals.com. All Manuals Search And Download.
Index
IPv6
configuring RC-106
overload bit
IS-IS support
configuring RC-87
multitopology RC-88
single-topology RC-87
policy attach points
redistribute RC-234
single topology
routing RC-86
IS-IS (Intermediate System-to-Intermediate System)
configuring RC-93
single-topology
Cisco IOS and Cisco IOS XR software differences,
configuration
isis router submode
grouped RC-85
configuration
multitopology RC-98
restrictions RC-84
L
link-state advertisement (LSA)
OSPFv2 RC-137
description RC-83
LSP flooding
controlling RC-102
LSP flooding
limiting RC-86
controlling RC-102
limiting RC-86
MPLS TE
configuring RC-110
description RC-89
Cisco IOS XR Routing Configuration Guide
RC-260
Download from Www.Somanuals.com. All Manuals Search And Download.
Index
M
MPLS TE (Multiprotocol Label Switching traffic
engineering) configuring
O
IS-IS RC-110
ospf area configuration submode
OSPFv2 RC-175
multicast-intact
IS-IS RC-90
OSPFv2 RC-144
multitopology
ospf area submode
ospf interface configuration submode
configuring RC-98
example RC-123
N
OSPFv2 (Open Shortest Path First Version 2)
configuration
neighbors
description RC-127
enabling RC-145
LSA
Cisco IOS XR Routing Configuration Guide
RC-261
Download from Www.Somanuals.com. All Manuals Search And Download.
Index
types RC-137
description RC-127
nonstop forwarding
enabling RC-145
LSA
configuring RC-173
types RC-137
description RC-140
policy attach points
route authentication methods
neighbors
policy attach points
MD5 RC-135
ospfv3 area configuration submode
strategies RC-136
route redistribution
configuring RC-166
description RC-139
Shortest Path First (SPF) throttling
configuring RC-170
description RC-139
supported OSPF network types
virtual link
creating RC-160
adjacency RC-143
OSPFv2 (Open Shortest Path Fisrt version 2)
ospfv3 interface configuration submode
overload bit
configuration RC-87
configuration
Cisco IOS XR Routing Configuration Guide
RC-262
Download from Www.Somanuals.com. All Manuals Search And Download.
Index
RFC 3065, Autonomous System Confederations for
P
BGP RC-81
policy, modifying
RFC 3373, Three-Way Handshake for IS-IS Point-to-Point
Adjacencies RC-125
attached RC-235
nonattached RC-235
RIB (Routing Information Base)
deploying RC-198
R
description RC-195
examples RC-200
monitoring RC-198
prerequisites RC-196
RFC 1142, OSI IS-IS Intra-domain Routing
Protocol RC-125
RFC 1195, Use of OSI IS-IS for Routing in TCP/IP and
See route-policy command
RFC 2385, Protection of BGP Sessions via the TCP MD5
router bgp neighbor group address family configuration
mode
RFC 2545, Use of BGP-4 Multiprotocol Extensions for
RFC 2763, Dynamic Hostname Exchange Mechanism for
IS-IS RC-125
router isis address family submode
RFC 2796, BGP Route Reflection - An Alternative to Full
RFC 2966, Domain-wide Prefix Distribution with
Cisco IOS XR Routing Configuration Guide
RC-263
Download from Www.Somanuals.com. All Manuals Search And Download.
Index
router isis interface submode
router isis configuration submode
router ospf configuration submode command
router ospf submode
router ospfv3 configuration submode
router isis interface configuration submode
routes
default
IS-IS RC-90
routing components
Cisco IOS XR Routing Configuration Guide
RC-264
Download from Www.Somanuals.com. All Manuals Search And Download.
Index
Autonomous System Boundary Routers
(ASBRs) RC-134
verification RC-218
structure
defining RC-237
names RC-207
prefix-set RC-210
sets RC-207
implementing
S
prerequisites RC-206
modifying RC-240
statements
action RC-221
disposition RC-220
elseif RC-221
if RC-221
remark RC-219
RPL (routing policy language)
components RC-211
overview RC-206
policy
attributes
modification RC-216
parameterization RC-214
definitions RC-213
Cisco IOS XR Routing Configuration Guide
RC-265
Download from Www.Somanuals.com. All Manuals Search And Download.
Index
U
show isis mpls traffic-eng adjacency-log
command RC-112
update groups
show isis mpls traffic-eng advertisements
monitor RC-75
command RC-112
V
virtual link
single-topology
command RC-96
W
SPF throttling, configuring
static route
Cisco IOS static route and Cisco IOS XR static route
differences RC-247
T
Cisco IOS XR Routing Configuration Guide
RC-266
Download from Www.Somanuals.com. All Manuals Search And Download.
|