Cisco Systems OL-14356-01 User Manual

Cisco IOS XR Routing Configuration Guide

Cisco IOS XR Software Release 3.4

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Cisco IOS XR Routing Configuration Guide

© 2007 Cisco Systems, Inc. All rights reserved.

CONTENTS

Preface RC-xiii

Changes to This Document RC-xiii

Obtaining Documentation and Submitting a Service Request RC-xiii

Implementing BGP on Cisco IOS XR Software RC-1

Contents RC-2

Prerequisites for Implementing BGP on Cisco IOS XR Software RC-2

Information About Implementing BGP on Cisco IOS XR Software RC-2

BGP Functional Overview RC-3
BGP Router Identifier RC-3
BGP Default Limits RC-4
BGP Next Hop Tracking RC-5
Autonomous System Number Formats in BGP RC-7
BGP Configuration RC-7
No Default Address Family RC-19
Routing Policy Enforcement RC-20
Table Policy RC-21
Update Groups RC-22
BGP Cost Community RC-22
BGP Best Path Algorithm RC-27
Administrative Distance RC-30
Multiprotocol BGP RC-32
Route Dampening RC-33
BGP Routing Domain Confederation RC-34
BGP Route Reflectors RC-34
Default Address Family for show Commands RC-37
Distributed BGP RC-37
MPLS VPN Carrier Supporting Carrier RC-38
BGP Keychains RC-39
IPv6/IPv6 VPN Provider Edge Transport over MPLS RC-39
VPNv4/VPNv6 over the IP Core Using L2TPv3 Tunnels RC-40

How to Implement BGP on Cisco IOS XR Software RC-42

Enabling BGP Routing RC-44
Configuring a Routing Domain Confederation for BGP RC-47

Cisco IOS XR Routing Configuration Guide

RC-iii

Contents

Resetting an eBGP Session Immediately Upon Link Failure RC-49
Logging Neighbor Changes RC-49
Adjusting BGP Timers RC-50
Changing the BGP Default Local Preference Value RC-51
Configuring the MED Metric for BGP RC-53
Configuring BGP Weights RC-54
Tuning the BGP Best-Path Calculation RC-56
Indicating BGP Back-door Routes RC-58
Configuring Aggregate Addresses RC-60
Redistributing iBGP Routes into IGP RC-61
Redistributing Prefixes into Multiprotocol BGP RC-63
Configuring BGP Route Dampening RC-66
Applying Policy When Updating the Routing Table RC-71
Setting BGP Administrative Distance RC-73
Configuring a BGP Neighbor Group and Neighbors RC-74
Configuring a Route Reflector for BGP RC-77
Configuring BGP Route Filtering by Route Policy RC-79
Configuring BGP Next-hop Trigger Delay RC-81
Disabling Next-hop Processing on BGP Updates RC-83
Configuring BGP Community and Extended-Community Advertisements RC-84
Configuring the BGP Cost Community RC-86
Configuring Software to Store Updates from a Neighbor RC-91
Configuring Distributed BGP RC-93
Configuring a VPN Routing and Forwarding Instance in BGP RC-96
Configuring Keychains for BGP RC-114
Configuring an MDT Address Family Session in BGP RC-115
Disabling a BGP Neighbor RC-118
Resetting Neighbors Using BGP Inbound Soft Reset RC-120
Resetting Neighbors Using BGP Outbound Soft Reset RC-120
Resetting Neighbors Using BGP Hard Reset RC-121
Clearing Caches, Tables, and Databases RC-122
Displaying System and Network Statistics RC-123
Displaying BGP Process Information RC-125
Monitoring BGP Update Groups RC-126

RC-iv

Configuration Examples for Implementing BGP on Cisco IOS XR Software RC-127

Enabling BGP: Example RC-127
Displaying BGP Update Groups: Example RC-129
BGP Neighbor Configuration: Example RC-129
BGP Confederation: Example RC-130
BGP Route Reflector: Example RC-131

Cisco IOS XR Routing Configuration Guide

BGP MDT Address Family Configuration: Example RC-132

Where to Go Next RC-132

Additional References RC-133

Related Documents RC-133
Standards RC-133
MIBs RC-134
RFCs RC-134
Technical Assistance RC-134

Implementing EIGRP on Cisco IOS XR Software RC-135

Contents RC-135

Prerequisites for Implementing EIGRP on Cisco IOS XR Software RC-136

Restrictions for Implementing EIGRP on Cisco IOS XR Software RC-136

Information About Implementing EIGRP on Cisco IOS XR Software RC-136

EIGRP Functional Overview RC-137
EIGRP Features RC-137
EIGRP Components RC-138
EIGRP Configuration Grouping RC-139
EIGRP Configuration Modes RC-139
EIGRP Interfaces RC-140
Redistribution for an EIGRP Process RC-140
Metric Weights for EIGRP Routing RC-141
Percentage of Link Bandwidth Used for EIGRP Packets RC-142
Floating Summary Routes for an EIGRP Process RC-142
Split Horizon for an EIGRP Process RC-144
Adjustment of Hello Interval and Hold Time for an EIGRP Process RC-145
Stub Routing for an EIGRP Process RC-145
Route Policy Options for an EIGRP Process RC-146
EIGRP Layer 3 VPN PE-CE Site-of-Origin RC-147
IPv6 and IPv6 VPN Provider Edge Support over MPLS and IP RC-148

Contents

How to Implement EIGRP on Cisco IOS XR Software RC-148

Enabling EIGRP Routing RC-149
Configuring Route Summarization for an EIGRP Process RC-151
Redistributing Routes for EIGRP RC-153
Creating a Route Policy and Attaching It to an EIGRP Process RC-155
Configuring Stub Routing for an EIGRP Process RC-158
Configuring EIGRP as a PE-CE Protocol RC-159
Redistributing BGP Routes into EIGRP RC-161
Monitoring EIGRP Routing RC-163

Cisco IOS XR Routing Configuration Guide

RC-v

Contents

Configuration Examples for Implementing EIGRP on Cisco IOS XR Software RC-166

Configuring a Basic EIGRP Configuration: Example RC-166
Configuring an EIGRP Stub Operation: Example RC-167
Configuring an EIGRP PE-CE Configuration with Prefix-Limits: Example RC-167

Additional References RC-168

Related Documents RC-168
Standards RC-168
MIBs RC-168
RFCs RC-168
Technical Assistance RC-169

Implementing OSPF on Cisco IOS XR Software RC-171

Contents RC-172

Prerequisites for Implementing OSPF on Cisco IOS XR Software RC-172

Information About Implementing OSPF on Cisco IOS XR Software RC-173

OSPF Functional Overview RC-173
Key Features Supported in the Cisco IOS XR OSPF Implementation RC-175
Comparison of Cisco IOS XR OSPFv3 and OSPFv2 RC-175
OSPF Hierarchical CLI and CLI Inheritance RC-176
OSPF Routing Components RC-176
OSPF Process and Router ID RC-179
Supported OSPF Network Types RC-179
Route Authentication Methods for OSPF RC-180
Neighbors and Adjacency for OSPF RC-181
Designated Router (DR) for OSPF RC-181
Default Route for OSPF RC-181
Link-State Advertisement Types for OSPF Version 2 RC-181
Link-State Advertisement Types for OSPFv3 RC-182
Virtual Link and Transit Area for OSPF RC-183
OSPFv2 Shamlink Support for MPLS VPN RC-184
Route Redistribution for OSPF RC-186
OSPF Shortest Path First Throttling RC-186
Nonstop Forwarding for OSPF Version 2 RC-187
Graceful Restart for OSPFv3 RC-188
Warm Standby and Nonstop Routing for OSPF Version 2 RC-190
Multicast-Intact Support for OSPF RC-190
Load Balancing in OSPF Version 2 and OSPFv3 RC-191
Multi-Area Adjacency for OSPF Version 2 RC-191
Label Distribution Protocol IGP Auto-configuration for OSPF RC-192
OSPF Authentication Message Digest Management RC-193

RC-vi

Cisco IOS XR Routing Configuration Guide

GTSM TTL Security Mechanism for OSPF RC-193
Path Computation Element for OSPFv2 RC-193

How to Implement OSPF on Cisco IOS XR Software RC-194

Enabling OSPF RC-194
Configuring Stub and Not-So-Stubby Area Types RC-197
Configuring Neighbors for Nonbroadcast Networks RC-199
Configuring Authentication at Different Hierarchical Levels for OSPF Version 2 RC-204
Controlling the Frequency That the Same LSA Is Originated or Accepted for OSPF RC-207
Creating a Virtual Link with MD5 Authentication to Area 0 for OSPF RC-209
Summarizing Subnetwork LSAs on an OSPF ABR RC-213
Redistributing Routes from One IGP into OSPF RC-215
Configuring OSPF Shortest Path First Throttling RC-219
Configuring Nonstop Forwarding Specific to Cisco for OSPF Version 2 RC-224
Configuring OSPF Version 2 for MPLS Traffic Engineering RC-226
Configuring OSPFv3 Graceful Restart RC-230
Configuring an OSPFv2 Sham Link RC-233
Enabling Nonstop Routing for OSPFv2 RC-236
Enabling Multicast-intact for OSPFv2 RC-237
Associating Interfaces to a VRF RC-238
Configuring OSPF as a Provider Edge to Customer Edge (PE-CE) Protocol RC-240
Creating Multiple OSPF Instances (OSPF Process and a VRF) RC-243
Configuring Multi-area Adjacency RC-244
Configuring Label Distribution Protocol IGP Auto-configuration for OSPF RC-246
Configuring Authentication Message Digest Management for OSPF RC-247
Configuring Generalized TTL Security Mechanism (GTSM) for OSPF RC-251
Verifying OSPF Configuration and Operation RC-254

Contents

Configuration Examples for Implementing OSPF on Cisco IOS XR Software RC-255

Cisco IOS XR for OSPF Version 2 Configuration: Example RC-255
CLI Inheritance and Precedence for OSPF Version 2: Example RC-257
MPLS TE for OSPF Version 2: Example RC-258
ABR with Summarization for OSPFv3: Example RC-258
ABR Stub Area for OSPFv3: Example RC-258
ABR Totally Stub Area for OSPFv3: Example RC-258
Route Redistribution for OSPFv3: Example RC-259
Virtual Link Configured Through Area 1 for OSPFv3: Example RC-259
Virtual Link Configured with MD5 Authentication for OSPF Version 2: Example RC-260
VPN Backbone and Sham Link Configured for OSPF Version 2: Example RC-260

Where to Go Next RC-262

Additional References RC-262

Cisco IOS XR Routing Configuration Guide

RC-vii

Contents

Related Documents RC-262
Standards RC-262
MIBs RC-263
RFCs RC-263
Technical Assistance RC-264

Implementing IS-IS on Cisco IOS XR Software RC-265

Contents RC-266

Prerequisites for Implementing IS-IS on Cisco IOS XR Software RC-266

Restrictions for Implementing IS-IS on Cisco IOS XR Software RC-266

Information About Implementing IS-IS on Cisco IOS XR Software RC-266

IS-IS Functional Overview RC-267
Key Features Supported in the Cisco IOS XR IS-IS Implementation RC-267
IS-IS Configuration Grouping RC-268
IS-IS Configuration Modes RC-268
IS-IS Interfaces RC-269
Multitopology Configuration RC-269
IPv6 Routing and Configuring IPv6 Addressing RC-269
Limit LSP Flooding RC-269
Maximum LSP Lifetime and Refresh Interval RC-270
Overload Bit Configuration During Multitopology Operation RC-270
Single-Topology IPv6 Support RC-271
Multitopology IPv6 Support RC-271
IS-IS Authentication RC-271
Nonstop Forwarding RC-272
Multi-Instance IS-IS RC-272
Multiprotocol Label Switching Traffic Engineering RC-273
Overload Bit on Router RC-273
Default Routes RC-273
Attached Bit on an IS-IS Instance RC-273
IS-IS Support for Route Tags RC-274
Multicast-Intact Feature RC-274
Multicast Topology Support Using IS-IS RC-275
MPLS Label Distribution Protocol IGP Synchronization RC-275
Label Distribution Protocol IGP Auto-configuration RC-276
MPLS TE Forwarding Adjacency RC-276
MPLS TE Interarea Tunnels RC-276
IP Fast Reroute RC-276

RC-viii

How to Implement IS-IS on Cisco IOS XR Software RC-277

Enabling IS-IS and Configuring Level 1 or Level 2 Routing RC-277

Cisco IOS XR Routing Configuration Guide

Configuring Single Topology for IS-IS RC-280
Configuring Multitopology for IS-IS RC-284
Controlling LSP Flooding for IS-IS RC-285
Configuring Nonstop Forwarding for IS-IS RC-289
Configuring Authentication for IS-IS RC-291
Configuring Keychains for IS-IS RC-293
Configuring MPLS Traffic Engineering for IS-IS RC-295
Tuning Adjacencies for IS-IS RC-298
Setting SPF Interval for a Single-Topology IPv4 and IPv6 Configuration RC-301
Customizing Routes for IS-IS RC-303
Configuring MPLS LDP IS-IS Synchronization RC-306
Enabling Multicast-Intact RC-308
Tagging IS-IS Interface Routes RC-309
Setting the Priority for Adding Prefixes to the RIB RC-311
Configuring IP Fast Reroute Loop-free Alternate RC-313

Contents

Configuration Examples for Implementing IS-IS on Cisco IOS XR Software RC-314

Configuring Single-Topology IS-IS for IPv6: Example RC-315
Configuring Multitopology IS-IS for IPv6: Example RC-315
Redistributing IS-IS Routes Between Multiple Instances: Example RC-315
Tagging Routes: Example RC-316

Where to Go Next RC-316

Additional References RC-317

Related Documents RC-317
Standards RC-317
MIBs RC-318
RFCs RC-318
Technical Assistance RC-318

Implementing and Monitoring RIB on Cisco IOS XR Software RC-319

Contents RC-320

Prerequisites for Implementing RIB on Cisco IOS XR Software RC-320

Information About RIB Configuration RC-320

Overview of RIB RC-320
RIB Data Structures in BGP and Other Protocols RC-321
RIB Administrative Distance RC-321
RIB Support for IPv4 and IPv6 RC-322
RIB Statistics RC-322
IPv6 and IPv6 VPN Provider Edge Transport over MPLS RC-322
IP Fast Reroute RC-323

Cisco IOS XR Routing Configuration Guide

RC-ix

Contents

RIB Quarantining RC-323

How to Deploy and Monitor RIB RC-324

Verifying RIB Configuration Using the Routing Table RC-324
Verifying Networking and Routing Problems RC-324
Disabling RIB Next-hop Dampening RC-326

Configuration Examples for RIB Monitoring RC-327

Output of show route Command: Example RC-328
Output of show route backup Command: Example RC-328
Output of show route best-local Command: Example RC-328
Output of show route connected Command: Example RC-329
Output of show route local Command: Example RC-329
Output of show route longer-prefixes Command: Example RC-329
Output of show route next-hop Command: Example RC-329

Where to Go Next RC-330

Additional References RC-330

Related Documents RC-331
Standards RC-331
MIBs RC-332
RFCs RC-332
Technical Assistance RC-332

Implementing RIP on Cisco IOS XR Software RC-333

Contents RC-333

Information About Implementing RIP on Cisco IOS XR Software RC-334

Prerequisites for Implementing RIP on Cisco IOS XR Software RC-334
RIP Functional Overview RC-334
Split Horizon for RIP RC-335
Route Timers for RIP RC-335
Route Redistribution for RIP RC-336
Default Administrative Distances for RIP RC-336
Routing Policy Options for RIP RC-337

How to Implement RIP on Cisco IOS XR Software RC-337

Enabling RIP RC-338
Customize RIP RC-339
Control Routing Information RC-342
Creating a Route Policy for RIP RC-344

Configuration Examples for Implementing RIP on Cisco IOS XR Software RC-347

Configuring a Basic RIP Configuration: Example RC-347
Configuring RIP on the Provider Edge: Example RC-348

RC-x

Cisco IOS XR Routing Configuration Guide

Adjusting RIP Timers for each VRF Instance: Example RC-348
Configuring Redistribution for RIP: Example RC-349
Configuring Route Policies for RIP: Example RC-349
Configuring Passive Interfaces and Explicit Neighbors for RIP: Example RC-350
Controlling RIP Routes: Example RC-350

Additional References RC-350

Related Documents RC-351
Standards RC-351
MIBs RC-351
RFCs RC-351
Technical Assistance RC-352

Implementing Routing Policy on Cisco IOS XR Software RC-353

Contents RC-354

Prerequisites for Implementing Routing Policy on Cisco IOS XR Software RC-354

Contents

Information About Implementing Routing Policy on Cisco IOS XR Software RC-354

Routing Policy Language RC-354
Routing Policy Language Overview RC-355
Routing Policy Configuration Basics RC-363
Policy Definitions RC-363
Parameterization RC-364
Semantics of Policy Application RC-365
Policy Statements RC-370
Attach Points RC-374
Attached Policy Modification RC-406
Nonattached Policy Modification RC-406

How to Implement Routing Policy on Cisco IOS XR Software RC-408

Defining a Route Policy RC-409
Attaching a Routing Policy to a BGP Neighbor RC-410
Modifying a Routing Policy Using a Text Editor RC-412

Configuration Examples for Implementing Routing Policy on Cisco IOS XR Software RC-413

Routing Policy Definition: Example RC-414
Simple Inbound Policy: Example RC-414
Modular Inbound Policy: Example RC-415
Translating Cisco IOS Route Maps to Cisco IOS XR Routing Policy Language: Example RC-416

Additional References RC-416

Related Documents RC-416
Standards RC-417
MIBs RC-417

Cisco IOS XR Routing Configuration Guide

RC-xi

Contents

RFCs RC-417
Technical Assistance RC-417

Implementing Static Routes on Cisco IOS XR Software RC-419

Contents RC-420

Prerequisites for Implementing Static Routes on Cisco IOS XR Software RC-420

Information About Implementing Static Routes on Cisco IOS XR Software RC-420

Static Route Functional Overview RC-420
Default Administrative Distance RC-421
Directly Connected Routes RC-421
Recursive Static Routes RC-422
Fully Specified Static Routes RC-422
Floating Static Routes RC-423
Default VRF RC-423
IPv4 and IPv6 Static VRF Routes RC-423
IPv6/IPv6 VPN Provider Edge Transport over MPLS RC-423

How to Implement Static Routes on Cisco IOS XR Software RC-424

Configuring a Static Route RC-424
Configuring a Floating Static Route RC-425
Configuring Static Routes Between PE-CE Routers RC-427
Changing the Maximum Number of Allowable Static Routes RC-429
Associating a VRF with a Static Route RC-430

Configuration Examples RC-432

Configuring Traffic Discard: Example RC-432
Configuring a Fixed Default Route: Example RC-432
Configuring a Floating Static Route: Example RC-432
Configuring a Static Route Between PE-CE Routers: Example RC-432

Where to Go Next RC-433

Additional References RC-433

Related Documents RC-433
Standards RC-433
MIBs RC-434
RFCs RC-434
Technical Assistance RC-434

RC-xii

Index

Cisco IOS XR Routing Configuration Guide

Preface

The Cisco IOS XR Routing Configuration Guide provides information and procedures related to routing
on Cisco IOS XR software.

The preface contains the following sections:

• Changes to This Document

• Obtaining Documentation and Submitting a Service Request

Changes to This Document

Table 1 lists the technical changes made to this document since it was first printed.

Table 1 Changes to This Document

Revision Date Change Summary

OL-14356-01 December 2007 Initial release of this document.

Obtaining Documentation and Submitting a Service Request

For information on obtaining documentation, submitting a service request, and gathering additional
information, see the monthly What’s New in Cisco Product Documentation, which also lists all new and
revised Cisco technical documentation, at:

http://www.cisco.com/en/US/docs/general/whatsnew/whatsnew.html

Subscribe to the What’s New in Cisco Product Documentation as a Really Simple Syndication (RSS) feed
and set content to be delivered directly to your desktop using a reader application. The RSS feeds are a free
service and Cisco currently supports RSS version 2.0.

OL-14356-01

Cisco IOS XR Routing Configuration Guide

RC-xiii

Preface

RC-xiv

Cisco IOS XR Routing Configuration Guide

OL-14356-01

Implementing BGP on Cisco IOS XR Software

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 provides the conceptual and configuration information for BGP on 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 performing a configuration task, search
online in the Cisco IOS XR software master command index.

Feature History for Implementing BGP on Cisco IOS XR Software

Release Modification

Release 2.0 This feature was introduced on the Cisco CRS-1.

Release 3.0 No modification.

Release 3.2 Support was added for the Cisco XR 12000 Series Router.

Release 3.3.0 VPN routing and forwarding (VRF) support was added, including

information on VRF command modes and command syntax.

OL-14356-01

BGP cost community information was added.

Release 3.4.0 The following features were supported:

• Four-byte autonomous system (AS) number

• Carrier supporting carrier (CSC) for BGP was added. See

Cisco IOS XR Multiprotocol Label Switching Protocol Configuration
Guide for information

• Key chains

Cisco IOS XR Routing Configuration Guide

RC-1

Contents

Contents

Implementing BGP on Cisco IOS XR Software

Release 3.5.0 The following features were supported:

• IPv6 Provider Edge and IPv6 VPN Provider Edge over Multiprotocol

Label Switching

• Neighbor-specific VRF IPv6 address family configurations

• Address family group-specific VPNv6 configurations

• VPN4/VPNv6 over IP Core using L2TPv3 Tunnels

• Multicast Distribution Tree (MDT) Subaddress Family Identifier

Information (SAFI) support for Multicast VPN (MVPN)

Release 3.6.0 No modification.

• Prerequisites for Implementing BGP on Cisco IOS XR Software, page RC-2

• Information About Implementing BGP on Cisco IOS XR Software, page RC-2

• How to Implement BGP on Cisco IOS XR Software, page RC-42

• Configuration Examples for Implementing BGP on Cisco IOS XR Software, page RC-127

• Where to Go Next, page RC-132

• Additional References, page RC-133

Prerequisites for Implementing BGP on Cisco IOS XR Software

You must be in a user group associated with a task group that includes the proper task IDs for BGP
commands. For detailed information about user groups and task IDs, see the Configuring AAA Services
on Cisco IOS XR Software module of 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, page RC-3

• BGP Router Identifier, page RC-3

• BGP Default Limits, page RC-4

• BGP Next Hop Tracking, page RC-5

• Autonomous System Number Formats in BGP, page RC-7

• BGP Configuration, page RC-7

• No Default Address Family, page RC-19

RC-2

• Routing Policy Enforcement, page RC-20

• Table Policy, page RC-21

• Update Groups, page RC-22

• BGP Best Path Algorithm, page RC-27

Cisco IOS XR Routing Configuration Guide

OL-14356-01

Implementing BGP on Cisco IOS XR Software

• Administrative Distance, page RC-30

• Administrative Distance, page RC-30

• Multiprotocol BGP, page RC-32

• Route Dampening, page RC-33

• BGP Routing Domain Confederation, page RC-34

• BGP Route Reflectors, page RC-34

• Default Address Family for show Commands, page RC-37

• Distributed BGP, page RC-37

• MPLS VPN Carrier Supporting Carrier, page RC-38

• BGP Keychains, page RC-39

• IPv6/IPv6 VPN Provider Edge Transport over MPLS, page RC-39

• VPNv4/VPNv6 over the IP Core Using L2TPv3 Tunnels, page RC-40

BGP Functional Overview

Information About Implementing BGP on Cisco IOS XR Software

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.

Note For information on configuring BGP to distribute Multiprotocol Label Switching (MPLS) Layer 3

virtual private network (VPN) information, see Cisco IOS XR Multiprotocol Label Switching
Configuration Guide.

Note For information on BGP support for Bidirectional Forwarding Detection (BFD), see Cisco IOS XR

Interface and Hardware Configuration Guide and Cisco IOS XR Interface and Hardware Command
Reference.

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):

OL-14356-01

Cisco IOS XR Routing Configuration Guide

RC-3

Information About Implementing BGP on Cisco IOS XR Software

• By means of the address configured using the bgp router-id command in router configuration mode.

• 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.

Note 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).

Implementing BGP on Cisco IOS XR Software

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 4000. The default can be changed

using the bgp maximum neighbor command. The limit range is 1 to 15000. 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:

–

–

–

–

–

–

512K (524,288) prefixes for IPv4 unicast.

128K (131,072) prefixes for IPv4 multicast.

128K (131,072) prefixes for IPv6 unicast.

128K (131,072) prefixes for IPv6 multicast

512K (524,288) prefixes for VPNv4 unicast

512K (524,288) prefixes for VPNv6 unicast

RC-4

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

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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 Next Hop Tracking

BGP receives notifications from the Routing Information Base (RIB) when next-hop information
changes (event-driven notifications). BGP obtains next-hop information from the RIB to:

• Determine whether a next hop is reachable.

• Find the fully recursed IGP metric to the next hop (used in the best-path calculation).

• Validate the received next hops.

• Calculate the outgoing next hops.

• Verify the reachability and connectedness of neighbors.

BGP is notified when any of the following events occurs:

• Next hop becomes unreachable

Information About Implementing BGP on Cisco IOS XR Software

• Next hop becomes reachable

• Fully recursed IGP metric to the next hop changes

• First hop IP address or first hop interface change

• Next hop becomes connected

• Next hop becomes unconnected

• Next hop becomes a local address

• Next hop becomes a nonlocal address

Note Reachability and recursed metric events trigger a best-path recalculation.

Event notifications from the RIB are classified as critical and noncritical. Notifications for critical and
noncritical events are sent in separate batches. However, a noncritical event is sent along with the critical
events if the noncritical event is pending and there is a request to read the critical events.

• Critical events are related to the reachability (reachable and unreachable), connectivity (connected

and unconnected), and locality (local and nonlocal) of the next hops. Notifications for these events
are not delayed.

• Noncritical events include only the IGP metric changes. These events are sent at an interval of 3

seconds. A metric change event is batched and sent 3 seconds after the last one was sent.

The next-hop trigger delay for critical and noncritical events can be configured to specify a minimum
batching interval for critical and noncritical events using the nexthop trigger-delay command. The
trigger delay is address family dependent.

The BGP next-hop tracking feature allows you to specify that BGP routes are resolved using only next
hops whose routes have the following characteristics:

• To avoid the aggregate routes, the prefix length must be greater than a specified value.

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• The source protocol must be from a selected list, ensuring that BGP routes are not used to resolve

next hops that could lead to oscillation.

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Information About Implementing BGP on Cisco IOS XR Software

This route policy filtering is possible because RIB identifies the source protocol of route that resolved a
next hop as well as the mask length associated with the route. The nexthop route-policy command is
used to specify the route-policy.

For information on route policy filtering for next hops using the next-hop attach point, see the

Implementing Routing Policy Language on Cisco IOS XR Software module of Cisco IOS XR Routing
Configuration Guide.

Scoped IPv4/VPNv4 Table Walk

To determine which address family to process, a next-hop notification is received by first dereferencing
the gateway context associated with the next hop, then looking into the gateway context to determine
which address families are using the gateway context. The IPv4 unicast and VPNv4 unicast address
families share the same gateway context, because they are registered with the IPv4 unicast table in the
RIB. As a result, both the global IPv4 unicast table and the VPNv4 table are processed when an IPv4
unicast next-hop notification is received from the RIB. A mask is maintained in the next hop, indicating
whether the next hop belongs to IPv4 unicast or VPNv4 unicast, or both. This scoped table walk localizes
the processing in the appropriate address family table.

Implementing BGP on Cisco IOS XR Software

Reordered Address Family Processing

The Cisco IOS XR software walks address family tables based on the numeric value of the address
family. When a next-hop notification batch is received, the order of address family processing is
reordered to the following order:

• IPv4 tunnel

• VPNv4 unicast

• VPNv6 unicast

• IPv4 labeled unicast

• IPv4 unicast

• IPv4 MDT

• IPv4 multicast

• IPv6 unicast

• IPv6 multicast

• IPv6 labeled unicast

New Thread for Next-Hop Processing

The critical-event thread in the spkr process handles only next-hop, Bidirectional Forwarding Detection
(BFD), and fast-external-failover (FEF) notifications. This critical-event thread ensures that BGP
convergence is not adversely impacted by other events that may take a significant amount of time.

show, clear, and debug Commands

The show bgp nexthops command provides statistical information about next-hop notifications, the
amount of time spent in processing those notifications, and details about each next hop registered with
the RIB. The clear bgp nexthop performance-statistics command ensures that the cumulative statistics
associated with the processing part of the next-hop show command can be cleared to help in monitoring.

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The clear bgp nexthop registration command performs an asynchronous registration of the next hop
with the RIB. See the BGP Commands on Cisco IOS XR Software module of Cisco IOS XR Routing
Commands for information on the next-hop show and clear commands.

The debug bgp nexthop command displays information on next-hop processing. The
provides debug information only about BGP registration of next hops with RIB. The in keyword displays
debug information about next-hop notifications received from RIB. The out keyword displays debug
information about next-hop notifications sent to the RIB. See BGP Debug Commands on Cisco IOS XR
Software.

Autonomous System Number Formats in BGP

Autonomous system numbers (ASNs) are globally unique identifiers used to identify autonomous
systems (ASs) and enable ASs to exchange exterior routing information between neighboring ASs. A
unique ASN is allocated to each AS for use in BGP routing.

Currently, ASNs are encoded as 2-byte numbers in BGP. The 2-byte range is 1 to 65535. To prepare for
the eventual exhaustion of 2-byte ASNs, BGP has the capability to support 4-byte ASNs. The 4-byte
range is 1.0 to 65535.65535 and the format is high-order 16-bit value in decimal . low-order 16-bit value
in decimal. The BGP 4-byte ASN capability is used to propagate 4-byte-based AS path information
across BGP speakers that do not support 4-byte AS numbers. This capability allows for the gradual
transition from 2-byte ASNs to 4-byte ASNs. See draft-ietf-idr-as4bytes-12.txt for information on
increasing the size of an ASN from 2 bytes to 4 bytes.

Information About Implementing BGP on Cisco IOS XR Software

out keyword

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:

• Router Configuration Mode, page RC-8

• Router Address Family Configuration Mode, page RC-8

• Neighbor Configuration Mode, page RC-8

• Neighbor Address Family Configuration Mode, page RC-8

• VRF Configuration Mode, page RC-8

• VRF Address Family Configuration Mode, page RC-8

• VRF Neighbor Configuration Mode, page RC-8

• VRF Neighbor Address Family Configuration Mode, page RC-9

Configuration Modes

The following sections show how to enter some of the configuration modes. From a mode, you can enter
the ? command to display the commands available in that mode.

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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)#

Router Address Family Configuration Mode

The following example shows how to enter router address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 112
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)#

Implementing BGP on Cisco IOS XR Software

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 112
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)#

VRF Configuration Mode

The following example shows how to enter VPN routing and forwarding (VRF) configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_A
RP/0/RP0/CPU0:router(config-bgp-vrf)#

VRF Address Family Configuration Mode

The following example shows how to enter VRF address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 112
RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_A
RP/0/RP0/CPU0:router(config-bgp-vrf)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-vrf-af)#

VRF Neighbor Configuration Mode

The following example shows how to enter VRF neighbor configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 140
RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_A
RP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 11.0.1.2
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)#

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VRF Neighbor Address Family Configuration Mode

The following example shows how to enter VRF neighbor address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 112
RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_A
RP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 11.0.1.2
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)#

VPNv4 Address Family Configuration Mode

The following example shows how to enter VPNv4 address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 152
RP/0/RP0/CPU0:router(config-bgp)# address-family vpnv4 unicast
RP/0/RP0/CPU0:router(config-bgp-af)#

VPNv6 Address Family Configuration Mode

The following example shows how to enter VPNv6 address family configuration mode:

RP/0/RP0/CPU0:router(config)# router bgp 150
RP/0/RP0/CPU0:router(config-bgp)# address-family vpnv6 unicast
RP/0/RP0/CPU0:router(config-bgp-af)#

Information About Implementing BGP on Cisco IOS XR Software

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:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.23.1.2
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002
RP/0/RP0/CPU0: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:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 2002::2
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2023
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv6 unicast
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# next-hop-self
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy one in

• You must enter neighbor-specific IPv4, IPv6, VPNv4, or VPNv6 commands in neighbor

address-family configuration submode. In Cisco IOS XR software, the configuration is as follows:

RP/0/RP0/CPU0:router(config)# router bgp 109
RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.40.24
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# maximum-prefix 1000

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• You must enter neighbor-specific IPv4 and IPv6 commands in VRF neighbor address-family

configuration submode. In Cisco IOS XR software, the configuration is as follows:

RP/0/RP0/CPU0:router(config)# router bgp 110

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Information About Implementing BGP on Cisco IOS XR Software

RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_A
RP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 11.0.1.2
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)# route-policy pass all in

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,
IPv6, VPNv4, or VPNv6 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)#

Implementing BGP on Cisco IOS XR Software

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 123
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)#

RC-10

• 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.

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Configuration grouping has the following effects in 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.

Information About Implementing BGP on Cisco IOS XR Software

• 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

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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

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Information About Implementing BGP on Cisco IOS XR Software

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 00:00:14, 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 of the parent, the configuration
of the parent of the 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

Implementing BGP on Cisco IOS XR Software

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.

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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:

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

Information About Implementing BGP on Cisco IOS XR Software

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) and 25 (from the neighbor group). The advertisement interval set in the
session group overrides the one set 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 ADV_2
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# advertisement-interval 25
RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# route-policy POLICY_1 in
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)# exit
RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.2.2
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1

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Information About Implementing BGP on Cisco IOS XR Software

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:

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%

Implementing BGP on Cisco IOS XR Software

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)# 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

RC-14

For Address Family: IPv4 Unicast
BGP neighbor version 0
Update group: 0.2
eBGP neighbor with no inbound or outbound policy; defaults to 'drop'

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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 00:00:25, 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, page RC-15

• show bgp af-group, page RC-16

• show bgp session-group, page RC-17

• show bgp neighbor-group, page RC-18

Information About Implementing BGP on Cisco IOS XR Software

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 142
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-bgp-afgrp)# 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

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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: n:GROUP_1 s:GROUP_2
IPv4 Unicast: 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 [n:GROUP_1 s:GROUP_2]
ebgp-multihop 3 [n:GROUP_1]
address-family ipv4 unicast []
next-hop-self [a:GROUP_3]
route-policy POLICY_1 in [a:GROUP_3]
weight 200 []
address-family ipv4 multicast [n:GROUP_1]
default-originate [n:GROUP_1]

Implementing BGP on Cisco IOS XR Software

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 sample commands that follow are based on 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 both

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