Allied Telesis BGP, BGP4+ User Manual

BGP & BGP4+ (Border Gateway Protocol IPv4 & IPv6) Software Reference Supplement for x-Series Switches

AlliedWare Plus™ Operating System

Version 5.4.3-2.6

SwitchBlade® x8112 SwitchBlade

x900-24XS and x900-24XT x900-12XT/S

x610-24Ts and x610-24Ts/X x610-48Ts and x610-48Ts/X x610-24Ts-PoE+ and x610-24Ts/X-PoE+ x610-48Ts-PoE+ and x610-48Ts/X-PoE+ x610-24SPs/X

C613-50032-01 REV D

® x908

Acknowledgments

This product includes software developed by the OpenSSL Project for use in the OpenSSL Tool k it (http://www.openssl.org/).

This product includes software licensed under the GNU General Public License available from:

http://www.gnu.org/licenses/gpl2.html

Source code for all GPL licensed software in this product can be obtained from the Allied Telesis GPL Code Download Center at:

http://www.alliedtelesis.com/support/default.aspx

Allied Telesis is committed to meeting the requirements of the open source licenses including the GNU General Public License (GPL) and will make all required source code available.

If you would like a copy of the GPL source code contained in Allied Telesis products, please send us a request by registered mail including a check for US$15 to cover production and shipping costs and a CD with the GPL code will be mailed to you.

GPL Code Request Allied Telesis Labs (Ltd) PO Box 8011 Christchurch. New Zealand

This documentation is subject to change without notice. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or any means electronic or mechanical, including photocopying and recording for any purpose other than the purchaser’s internal use without the written permission of Allied Telesis, Inc.

Allied Telesis, AlliedWare Plus, EPSRing, SwitchBlade, and VCStack are trademarks or registered trademarks in the United States and elsewhere of Allied Telesis, Inc. Adobe, Acrobat, and Reader are either registered trademarks or trademarks of Adobe Systems Incorporated in the United States and/or other countries. Additional brands, names and products mentioned herein may be trademarks of their respective companies.

Getting the most from this manual

Although you can view this document using Acrobat version 5, to get the best from this manual, we recommend using Adobe Acrobat Reader version 8. You can download Acrobat Reader 8 free from http://www.adobe.com/.

New features in this software version

For a list of new and enhanced features and commands in this version, see the Software Release Note for Software Version 5.4.3-2.6. Documentation can be downloaded from the Support area of our website at http://www.alliedtelesis.com. Note that to download software files, you need a valid user account.

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

i.ii AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 C613-50032-01 REV D

Chapter 1 BGP and BGP4+ Introduction

Introduction...................................................................................................................................................................... 1.3

BGP and BGP4+ ASNs and AS_Path Attributes............................................................................................. 1.4

Internal and External BGP Concepts ........................................................................................................................ 1.5

Public and Private ASNs ........................................................................................................................................ 1.5

Outbound Routing Toward the Internet......................................................................................................... 1.5

External BGP (eBGP) Concepts................................................................................................................................... 1.6

External BGP (eBGP)................................................................................................................................................ 1.6

Verifying BGP............................................................................................................................................................. 1.7

Advertising eBGP routes to ISPs......................................................................................................................... 1.8

Internal BGP (iBGP) Concepts..................................................................................................................................... 1.9

iBGP between Internet connected routers..................................................................................................... 1.9

Configuring iBGP ..................................................................................................................................................... 1.9

Verifying iBGP .........................................................................................................................................................1.10

How to configure BGP and BGP4+......................................................................................................................... 1.12

Initial BGP and BGP4+ Configuration Tasks ................................................................................................. 1.12

How to enable BGP and BGP4+ Routing.......................................................................................................1.12

How to configure BGP and BGP4+ Neighbors ............................................................................................ 1.12

BGP and BGP4+ Neighbor Route Filtering ..........................................................................................................1.13

BGP and BGP4+ Path Filtering by Neighbor ................................................................................................ 1.13

How to disable next hop processing for BGP or BGP4+ updates........................................................ 1.14

How to use Route Maps for BGP or BGP4+ updates ................................................................................. 1.15

BGP and BGP4+ Peer Groups ...................................................................................................................................1.16

How to create a Peer Group for BGP............................................................................................................... 1.16

How to assign options to the created Peer Group ....................................................................................1.16

How to make neighbors members of a Peer Group ................................................................................. 1.19

BGP and BGP4+ Prefix Lists ....................................................................................................................................... 1.20

How to create and configure a Prefix List for BGP or BGP4+................................................................. 1.21

How to delete Prefix List Entries.......................................................................................................................1.21

How to display IPv4 and IPv6 Prefix Entries .................................................................................................1.22

BGP and BGP4+ Route Dampening .......................................................................................................................1.23

How to enable BGP and BGP4+ Route Dampening.................................................................................. 1.24

How to monitor BGP and BGP4+ Route Dampening ...............................................................................1.24

BGP and BGP4+ Synchronization ...........................................................................................................................1.26

BGP and BGP4+ Weights............................................................................................................................................ 1.27

BGP and BGP4+ Aggregate Addresses .................................................................................................................1.28

How to enable and disable Automatic Summarization...........................................................................1.28

BGP and BGP4+ monitoring ..................................................................................................................................... 1.29

How to clear BGP and BGP4+ tables...............................................................................................................1.29

How to display BGP and BGP4+ statistics .....................................................................................................1.30

BGP Neighbor status logging................................................................................................................................... 1.31

BGP Connections Reset ..............................................................................................................................................1.32

BGP Versions................................................................................................................................................................... 1.32

BGP Confederations.....................................................................................................................................................1.32

BGP Route Reflectors...................................................................................................................................................1.33

BGP Community Filtering ..........................................................................................................................................1.34

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

C613-50032-01 REV D AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 i.iii

BGP Optimization .........................................................................................................................................................1.35

How to determine Backdoor Routes ..............................................................................................................1.35

How to set the BGP Administrative Distance .............................................................................................. 1.35

How to change BGP default local preference value ................................................................................. 1.35

How to redistribute the default network 0.0.0.0 ........................................................................................ 1.36

How to adjust BGP Timers ..................................................................................................................................1.36

How to adjust the eBGP advertisement interval ........................................................................................1.37

How to adjust the iBGP advertisement interval ......................................................................................... 1.37

How to adjust the AS origination interval ....................................................................................................1.38

How to remove private AS numbers for BGP .............................................................................................. 1.39

BGP and BGP4+ Terminology ..................................................................................................................................1.42

Chapter 2 BGP and BGP4+ Configuration

Introduction...................................................................................................................................................................... 2.2

BGP Configurations........................................................................................................................................................ 2.3

Enabling BGP Peers In The Same Autonomous System ............................................................................ 2.3

Enabling BGP Between Different Autonomous Systems .......................................................................... 2.5

Configuring a BGP Route Reflector ................................................................................................................... 2.6

Configuring a BGP Confederation..................................................................................................................... 2.8

Configuring BGP Authentication ..................................................................................................................... 2.11

Configuring BGP Graceful Reset....................................................................................................................... 2.13

Configuring BGP Distance ..................................................................................................................................2.15

Configuring BGP Graceful Restart....................................................................................................................2.18

Configuring BGP Weight per Peer...................................................................................................................2.20

BGP4+ Configurations ................................................................................................................................................ 2.23

Enabling iBGP Peering using a Global Address ..........................................................................................2.23

Enabling iBGP Peering using a Link-local Address .................................................................................... 2.26

Enabling eBGP Peering between different Autonomous Systems...................................................... 2.29

Configuring Route-Maps with BGP4+............................................................................................................ 2.31

Configuring BGP4+ Graceful Restart ..............................................................................................................2.35

Configuring BGP4+ Distance.............................................................................................................................2.39

Configuring BGP4+ Graceful Reset ................................................................................................................. 2.43

Chapter 3 BGP and BGP4+ Commands

Introduction ..................................................................................................................................................................... 3.5

Controlling “show” Command Output...................................................................................................................3.6

Command List .................................................................................................................................................................3.8

address-family (BGP and BGP4+) ............................................................................................................................. 3.8

aggregate-address (BGP and BGP4+)...................................................................................................................3.10

auto-summary (BGP)...................................................................................................................................................3.12

bgp aggregate-nexthop-check (BGP and BGP4+) ...........................................................................................3.13

bgp always-compare-med (BGP and BGP4+) ....................................................................................................3.14

bgp bestpath as-path ignore (BGP and BGP4+) ...............................................................................................3.15

bgp bestpath compare-confed-aspath (BGP and BGP4+) ............................................................................3.15

bgp bestpath compare-routerid (BGP and BGP4+).........................................................................................3.16

bgp bestpath med (BGP and BGP4+) ...................................................................................................................3.17

bgp bestpath med remove-recv-med (BGP and BGP4+) ..............................................................................3.18

bgp bestpath med remove-send-med (BGP and BGP4+) .............................................................................3.18

bgp client-to-client reflection (BGP and BGP4+) ..............................................................................................3.19

bgp cluster-id (BGP and BGP4+).............................................................................................................................3.20

bgp confederation identifier (BGP and BGP4+) ................................................................................................3.21

bgp confederation peers (BGP and BGP4+) .......................................................................................................3.22

bgp config-type (BGP and BGP4+) ........................................................................................................................3.24

bgp dampening (BGP and BGP4+) ........................................................................................................................3.26

bgp default ipv4-unicast (BGP and BGP4+)........................................................................................................3.27

bgp default local-preference (BGP) .......................................................................................................................3.28

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

i.iv AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 C613-50032-01 REV D

bgp deterministic-med (BGP and BGP4+) ..........................................................................................................3.29

bgp enforce-first-as (BGP and BGP4+)..................................................................................................................3.30

bgp fast-external-failover (BGP and BGP4+) ......................................................................................................3.31

bgp graceful-restart (BGP and BGP4+).................................................................................................................3.32

bgp graceful-restart graceful-reset (BGP and BGP4+) ....................................................................................3.33

bgp log-neighbor-changes (BGP and BGP4+)...................................................................................................3.34

bgp memory maxallocation (BGP and BGP4+) .................................................................................................3.36

bgp nexthop-trigger-count (BGP and BGP4+) ..................................................................................................3.37

bgp nexthop-trigger delay (BGP and BGP4+)....................................................................................................3.38

bgp nexthop-trigger enable (BGP and BGP4+).................................................................................................3.39

bgp rfc1771-path-select (BGP) ................................................................................................................................3.40

bgp rfc1771-strict (BGP).............................................................................................................................................3.40

bgp router-id (BGP and BGP4+)..............................................................................................................................3.41

bgp scan-time (BGP) ...................................................................................................................................................3.42

bgp update-delay (BGP and BGP4+).....................................................................................................................3.43

clear bgp * (BGP and BGP4+) ...................................................................................................................................3.44

clear bgp (IPv4 or IPv6 address) (BGP and BGP4+) ..........................................................................................3.45

clear bgp (ASN) (BGP and BGP4+)..........................................................................................................................3.47

clear bgp external (BGP and BGP4+).....................................................................................................................3.48

clear bgp peer-group (BGP and BGP4+) ..............................................................................................................3.49

clear ip bgp * (BGP)......................................................................................................................................................3.50

clear ip bgp (IPv4) (BGP) ............................................................................................................................................3.52

clear ip bgp dampening (BGP) ................................................................................................................................3.53

clear ip bgp flap-statistics (BGP) .............................................................................................................................3.53

clear ip bgp (ASN) (BGP) ............................................................................................................................................3.54

clear ip bgp external (BGP) .......................................................................................................................................3.55

clear ip bgp peer-group (BGP).................................................................................................................................3.56

clear bgp ipv6 (ipv6 address) (BGP4+) .................................................................................................................3.57

clear bgp ipv6 dampening (BGP4+) ......................................................................................................................3.58

clear bgp ipv6 flap-statistics (BGP4+) ...................................................................................................................3.58

clear bgp ipv6 (ASN) (BGP4+) ..................................................................................................................................3.59

clear bgp ipv6 external (BGP4+) .............................................................................................................................3.60

clear bgp ipv6 peer-group (BGP4+) ......................................................................................................................3.61

debug bgp (BGP) ..........................................................................................................................................................3.62

distance (BGP and BGP4+) ........................................................................................................................................3.63

exit-address-family (BGP and BGP4+)...................................................................................................................3.65

ip as-path access-list (BGP and BGP4+)................................................................................................................3.66

ip community-list (BGP and BGP4+)......................................................................................................................3.67

ip community-list expanded (BGP and BGP4+) ................................................................................................3.68

ip community-list standard (BGP and BGP4+)...................................................................................................3.70

ip extcommunity-list expanded (BGP and BGP4+) ..........................................................................................3.72

ip extcommunity-list standard (BGP and BGP4+) ............................................................................................3.74

ip prefix-list (IPv4 Prefix List) ....................................................................................................................................3.76

ipv6 prefix-list (IPv6 Prefix List) ...............................................................................................................................3.78

match as-path (Route Map) ......................................................................................................................................3.80

match community (Route Map)..............................................................................................................................3.81

neighbor activate (BGP and BGP4+) .....................................................................................................................3.82

neighbor advertisement-interval (BGP and BGP4+) .......................................................................................3.85

neighbor allowas-in (BGP and BGP4+) .................................................................................................................3.88

neighbor as-origination-interval (BGP and BGP4+).........................................................................................3.91

neighbor attribute-unchanged (BGP and BGP4+) ...................................................................................

ighbor capability graceful-restart (BGP and BGP4+)..................................................................................3.96

neighbor capability orf prefix-list (BGP and BGP4+) .......................................................................................3.99

neighbor capability route-refresh (BGP and BGP4+) ................................................................................... 3.102

neighbor collide-established (BGP and BGP4+) ............................................................................................ 3.105

neighbor default-originate (BGP and BGP4+) ................................................................................................ 3.107

neighbor description (BGP and BGP4+)............................................................................................................ 3.110

........3.93

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

C613-50032-01 REV D AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 i.v

neighbor disallow-infinite-holdtime (BGP and BGP4+) .............................................................................. 3.112

neighbor distribute-list (BGP and BGP4+)........................................................................................................ 3.114

neighbor dont-capability-negotiate (BGP and BGP4+)............................................................................... 3.117

neighbor ebgp-multihop (BGP and BGP4+).................................................................................................... 3.119

neighbor enforce-multihop (BGP and BGP4+)............................................................................................... 3.122

neighbor filter-list (BGP and BGP4+).................................................................................................................. 3.125

neighbor interface (BGP4+)...................................................................................................................................3.128

neighbor local-as (BGP and BGP4+) ................................................................................................................... 3.129

neighbor maximum-prefix (BGP and BGP4+)................................................................................................. 3.131

neighbor next-hop-self (BGP and BGP4+) ....................................................................................................... 3.134

neighbor override-capability (BGP and BGP4+) ............................................................................................ 3.137

neighbor passive (BGP and BGP4+) ...................................................................................................................3.139

neighbor password (BGP and BGP4+)............................................................................................................... 3.141

neighbor peer-group (add a neighbor) (BGP and BGP+) ........................................................................... 3.144

neighbor peer-group (create a peer-group) (BGP and BGP4+)................................................................ 3.146

neighbor port (BGP and BGP4+).......................................................................................................................... 3.147

neighbor prefix-list (BGP and BGP4+) ...............................................................................................................3.149

neighbor remote-as (BGP and BGP4+).............................................................................................................. 3.152

neighbor remove-private-AS (BGP) .................................................................................................................... 3.155

neighbor restart-time (BGP and BGP4+)........................................................................................................... 3.156

neighbor route-map (BGP and BGP4+)............................................................................................................. 3.159

neighbor route-reflector-client (BGP)................................................................................................................3.164

neighbor route-server-client (BGP) .................................................................................................................... 3.165

neighbor send-community (BGP and BGP4+)................................................................................................ 3.166

neighbor shutdown (BGP and BGP4+).............................................................................................................. 3.170

neighbor soft-reconfiguration inbound (BGP and BGP4+)........................................................................ 3.172

neighbor timers (BGP and BGP4+)...................................................................................................................... 3.175

neighbor transparent-as (BGP and BGP4+) ..................................................................................................... 3.178

neighbor transparent-nexthop (BGP and BGP4+) ........................................................................................ 3.180

neighbor unsuppress-map (BGP and BGP4+) ................................................................................................ 3.182

neighbor update-source (BGP and BGP4+).....................................................................................................3.185

neighbor version (BGP) ........................................................................................................................................... 3.188

neighbor weight (BGP and BGP4+) ....................................................................................................................3.190

network (BGP and BGP4+) ..................................................................................................................................... 3.193

network synchronization (BGP and BGP4+).................................................................................................... 3.196

redistribute (into BGP or BGP4+) (BGP and BGP4+) ..................................................................................... 3.197

restart bgp graceful (BGP)...................................................................................................................................... 3.199

router bgp (BGP and BGP4+) ................................................................................................................................ 3.200

route-map (Route Map) .......................................................................................................................................... 3.201

set as-path (Route Map).......................................................................................................................................... 3.203

set community (Route Map)..................................................................................................................................3.204

show bgp ipv6 (BGP4+) .......................................................................................................................................... 3.205

show bgp ipv6 community (BGP4+)..................................................................................................................3.206

show bgp ipv6 community-list (BGP4+)...........................................................................................................3.207

show bgp ipv6 dampening (BGP4+).................................................................................................................. 3.208

show bgp ipv6 filter-list (BGP4+)......................................................................................................................... 3.209

show bgp ipv6 inconsistent-as (BGP4+)........................................................................................................... 3.209

show bgp ipv6 longer-prefixes (BGP4+)........................................................................................................... 3.210

show bgp ipv6 neighbors (BGP4+)..................................................................................................................... 3.211

show bgp ipv6 paths (BGP4+).............................................................................................................................. 3.214

show bgp ipv6 prefix-list (BGP4+) ......................................................................................................................3.214

show bgp ipv6 quote-regexp (BGP4+).............................................................................................

w bgp ipv6 regexp (BGP4+) ...........................................................................................................................3.216

sho

show bgp ipv6 route-map (BGP4+)....................................................................................................................3.217

show bgp ipv6 summary (BGP4+) ...................................................................................................................... 3.217

show bgp nexthop-tracking (BGP) ..................................................................................................................... 3.218

show bgp nexthop-tree-details (BGP) ............................................................................................................... 3.218

................. 3.215

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

i.vi AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 C613-50032-01 REV D

show bgp memory maxallocation (BGP).......................................................................................................... 3.218

show debugging bgp (BGP) .................................................................................................................................. 3.219

show ip bgp (BGP) ....................................................................................................................................................3.220

show ip bgp attribute-info (BGP) ........................................................................................................................ 3.221

show ip bgp cidr-only (BGP)..................................................................................................................................3.222

show ip bgp community (BGP) ............................................................................................................................3.223

show ip bgp community-info (BGP)................................................................................................................... 3.224

show ip bgp community-list (BGP)..................................................................................................................... 3.225

show ip bgp dampening (BGP) ............................................................................................................................3.226

show ip bgp filter-list (BGP) ................................................................................................................................... 3.228

show ip bgp inconsistent-as (BGP) ..................................................................................................................... 3.229

show ip bgp longer-prefixes (BGP)..................................................................................................................... 3.230

show ip bgp neighbors (BGP) ............................................................................................................................... 3.231

show ip bgp neighbors connection-retrytime (BGP) ................................................................................... 3.234

show ip bgp neighbors hold-time (BGP).......................................................................................................... 3.234

show ip bgp neighbors keepalive (BGP)........................................................................................................... 3.235

show ip bgp neighbors keepalive-interval (BGP) .......................................................................................... 3.235

show ip bgp neighbors notification (BGP).......................................................................................................3.236

show ip bgp neighbors open (BGP) ...................................................................................................................3.236

show ip bgp neighbors rcvd-msgs (BGP) ......................................................................................................... 3.237

show ip bgp neighbors sent-msgs (BGP) ......................................................................................................... 3.237

show ip bgp neighbors update (BGP) ...............................................................................................................3.238

show ip bgp paths (BGP) ........................................................................................................................................ 3.238

show ip bgp prefix-list (BGP)................................................................................................................................. 3.239

show ip bgp quote-regexp (BGP)........................................................................................................................ 3.240

show ip bgp regexp (BGP) ..................................................................................................................................... 3.241

show ip bgp route-map (BGP).............................................................................................................................. 3.242

show ip bgp scan (BGP) .......................................................................................................................................... 3.243

show ip bgp summary (BGP)................................................................................................................................. 3.244

show ip community-list (BGP and BGP4+)....................................................................................................... 3.245

show ip extcommunity-list (BGP and BGP4+) ................................................................................................ 3.245

show ip prefix-list (IPv4 Prefix List) .....................................................................................................................3.246

show ipv6 prefix-list (IPv6 Prefix List) ................................................................................................................ 3.246

show ip protocols bgp (BGP) ................................................................................................................................ 3.247

show route-map (Route Map) .............................................................................................................................. 3.248

synchronization (BGP and BGP4+)......................................................................................................................3.249

timers (BGP and BGP4+) ......................................................................................................................................... 3.250

undebug bgp (BGP)..................................................................................................................................................3.251

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

C613-50032-01 REV D AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 i.vii

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

i.viii AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 C613-50032-01 REV D

Chapter 1: BGP and BGP4+ Introduction

Introduction ...........................................................................................................................................1.3

BGP and BGP4+ ASNs and AS_Path Attributes ..................................................................1.4

Internal and External BGP Concepts .............................................................................................1.5

Public and Private ASNs..............................................................................................................1.5

Outbound Routing Toward the Internet..............................................................................1.5

External BGP (eBGP) Concepts ........................................................................................................1.6

External BGP (eBGP) .....................................................................................................................1.6

Verifying BGP..................................................................................................................................1.7

Advertising eBGP routes to ISPs ..............................................................................................1.8

Internal BGP (iBGP) Concepts ..........................................................................................................1.9

iBGP between Internet connected routers..........................................................................1.9

Configuring iBGP...........................................................................................................................1.9

Verifying iBGP.............................................................................................................................. 1.10

How to configure BGP and BGP4+.............................................................................................. 1.12

Initial BGP and BGP4+ Configuration Tasks ..................................................................... 1.12

How to enable BGP and BGP4+ Routing ........................................................................... 1.12

How to configure BGP and BGP4+ Neighbors ................................................................ 1.12

BGP and BGP4+ Neighbor Route Filtering ............................................................................... 1.13

BGP and BGP4+ Path Filtering by Neighbor .................................................................... 1.13

How to disable next hop processing for BGP or BGP4+ updates............................ 1.14

How to use Route Maps for BGP or BGP4+ updates ..................................................... 1.15

BGP and BGP4+ Peer Groups ........................................................................................................1.16

How to create a Peer Group for BGP................................................................................... 1.16

How to assign options to the created Peer Group ........................................................ 1.16

How to make neighbors members of a Peer Group...................................................... 1.19

BGP and BGP4+ Prefix Lists ........................................................................................................... 1.20

How to create and configure a Prefix List for BGP or BGP4+ ..................................... 1.21

How to delete Prefix List Entries........................................................................................... 1.21

How to display IPv4 and IPv6 Prefix Entries ..................................................................... 1.22

BGP and BGP4+ Route Dampening............................................................................................ 1.23

How to enable BGP and BGP4+ Route Dampening ...................................................... 1.24

How to monitor BGP and BGP4+ Route Dampening.................................................... 1.24

BGP and BGP4+ Synchronization ................................................................................................ 1.26

BGP and BGP4+ Weights ................................................................................................................ 1.27

BGP and BGP4+ Aggregate Addresses...................................................................................... 1.28

How to enable and disable Automatic Summarization............................................... 1.28

BGP and BGP4+ monitoring.......................................................................................................... 1.29

How to clear BGP and BGP4+ tables................................................................................... 1.29

How to display BGP and BGP4+ statistics ......................................................................... 1.30

BGP Neighbor status logging ....................................................................................................... 1.31

BGP Connections Reset................................................................................................................... 1.32

BGP Versions ....................................................................................................................................... 1.32

BGP Confederations ......................................................................................................................... 1.32

BGP Route Reflectors ....................................................................................................................... 1.33

BGP Community Filtering............................................................................................................... 1.34

BGP Optimization..............................................................................................................................1.35

How to determine Backdoor Routes................................................................................... 1.35

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

C613-50032-01 REV D AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 1.1

BGP and BGP4+ Introduction

How to set the BGP Administrative Distance .................................................................. 1.35

How to change BGP default local preference value...................................................... 1.35

How to redistribute the default network 0.0.0.0 ............................................................ 1.36

How to adjust BGP Timers ...................................................................................................... 1.36

How to adjust the eBGP advertisement interval ............................................................ 1.37

How to adjust the iBGP advertisement interval ............................................................. 1.37

How to adjust the AS origination interval ........................................................................ 1.38

How to remove private AS numbers for BGP .................................................................. 1.39

BGP and BGP4+ Terminology .......................................................................................................1.42

Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches

1.2 AlliedWare Plus

Operating System - Software Version 5.4.3-2.6 C613-50032-01 REV D

BGP and BGP4+ Introduction

Introduction

This chapter introduces terminology and concepts about BGP for IPv4 and BGP4+ for IPv6, including the concepts of autonomous system numbers (ASN), path attributes (PA), and both internal and external BGP and BGP4+.

For basic BGP and BGP4+ configuration examples, see Chapter 2, BGP and BGP4+

Configuration.

For details about the commands used in these examples, or the outputs from validation commands, see Chapter 3, BGP and BGP4+ Commands. This chapter provides an alphabetical reference of commands used to configure the Border Gateway Protocol for IPv4 (BGP) and for IPv6 (BGP4+).

BGP and BGP4+ Overview

Border Gateway Protocol (BGP for IPv4 and BGP4+ for IPv6) is an exterior gateway protocol (EGP). The purpose of BGP is to advertise, learn, and choose the best paths inside the Internet.

ISPs (Internet Service Providers) use BGP to exchange the Internet routing table with each other. Enterprises also use BGP to exchange routing information with ISPs, allowing the Enterprise routers to learn Internet routes.

RFCs 1771 (BGP4), 1654 (first BGP4 specification), 1105, 1163, 1267 (older version of BGP) describe BGP and BGP4. RFC 2283 Multiprotocol Extensions for BGP-4 describes BGP4+.

BGP not only enables ISPs to exchange routes with each other, but also to control what data passed through their networks. ISPs need to keep fine control over the routes that they advertise out of their network, and who they advertise those networks to. They have commercial reasons for sending different traffic through different paths. In particular, ISPs whose main service is to provide bulk Internet backbone transport need to be very sure whose data they are transporting, as they do not want to be transporting data on behalf of people who have not paid for the service.

Since the paths via which Internet data is directed are subject to commercial agreements, network providers need to be able to implement policies that control the content of their route tables, and control the routes that they advertise to which neighbors. Internal routing protocols like OSPF and RIP do not have facilities for the types of policies that BGP needs. Although some filtering can be performed in OSPF and RIP, the sets of parameters that can be filtered on are rather limited.

So, instead of just using metric as the criterion for choosing the best route to a destination, BGP uses a process with path attributes, where path attributes are a variety of parameters that are associated with routes and exchanged in routing updates. BGP has an elaborate best path algorithm that is controlled by these path attributes, and allows network engineers flexibility in how routers choose the best BGP routes.

Moreover, the routing protocols used between ISPs are advertising huge numbers of routes (potentially hundreds of thousands of routes), so the routing protocol they use needs to be efficient, not a protocol that requires regular updates of all the routes (as the 30 minute refresh OSPF requires). BGP was developed to operate quite differently from OSPF or RIP.

BGP does not send route updates to multiple neighbors in the local subnet (as is typical with IGPs), but uses TCP (port 179) to establish connections to just a specific set of peer routers with which it will exchange routing information. BGP peer routers can be in the same subnet, or can be separated by several routers.

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BGP does not send any more route updates than it absolutely has to. When routers first peer up, they exchange the route table data that they wish to inform each other of. Thereafter, they only send each other route information if anything changes.

BGP and BGP4+ ASNs and AS_Path Attributes

BGP and BGP4+ uses BGP path attributes (PAs). PAs define information about a path, or route, through a network. Some BGP and BGP4+ PAs describe information that is used to choose the best BGP or BGP4+ route. PAs are also used for other purposes, such as preventing routing loops.

If no BGP or BGP4+ PAs have been explicitly set, BGP and BGP4+ routers use the BGP and BGP4+ AS_Path (autonomous system path) PA when choosing the best route among competing routes. The AS_Path PA itself has many subcomponents, one of which is the autonomous system number (ASN)

The integer ASN identifies one organization that considers itself autonomous from other organizations. Each company with a network that connects to the Internet can be considered to be an autonomous system and can be assigned an ASN. (IANA assigns unique ASNs.) Each ISP has an ASN. Some large ISPs have multiple ASNs.

When a router uses BGP or BGP4+ to advertise a route, the prefix/ length is associated with a set of PAs, including the AS_Path. The AS_Path PA associated with a prefix/ length lists the ASNs that would be part of an end-to-end route for that prefix as learned using BGP or BGP4+.

BGP and BGP4+ use the AS_Path for two key functions:

■ Choose the best route for a prefix based on the shortest AS_Path.

■ Prevent routing loops.

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Internal and External BGP Concepts

BGP defines two classes of neighbors (peers): internal BGP (iBGP) and external BGP (eBGP). These terms use the perspective of a single router, with the terms referring to whether a BGP neighbor is in the same ASN (iBGP) or a different ASN (eBGP).

A BGP router behaves differently in several ways depending on whether the peer (neighbor) is an iBGP or eBGP peer. The differences include different rules about what must be true before the two routers can become neighbors, different rules about which routes the BGP best path algorithm chooses as best, and even some different rules about how the routers update the BGP AS_Path PA.

When advertising to an eBGP peer, a BGP router updates the AS_Path PA, but it does not do so when advertising to an iBGP peer.

Public and Private ASNs

IANA administers the assignment of ASNs as it does with IP address prefixes. ASNs must be assigned as unique values since if ASNs are duplicated, the BGP loop prevention process may prevent parts of the Internet learning about a route.

IANA controls the ASN numbering space. Using the same process as for IPv4 addresses, ASNs are assigned to different organizations. The previous 16-bit BGP ASN has a decimal range of 0 through 65,535. The 32-bit BGP ASN has a decimal range of 1 through 4,294,967,295.

Like the public IPv4 address space, the public BGP ASN space has similar issues. To help overcome this issue, the ASN assignment process requires that each AS justify whether it truly needs a publicly unique ASN or whether it can just as easily use a private ASN. RFC 5398 reserves a small range of ASNs for use in documentation so that documentation avoids the use of ASNs assigned to organizations.

Private ASNs allow routers inside an AS to participate with BGP, using the same ASN as other organizations. An AS can use a private AS where the AS connects to only one other ASN. Loops cannot occur at that point in the BGP topology, so unique ASNs in that network do not exist. Loops cannot occur with BGP advertising the best path for a prefix.

Outbound Routing Toward the Internet

The main reason to use BGP between an Enterprise and an ISP is to influence the choice of best path (or best route). However, since the majority of the end-to-end routes exist inside the Internet, it is hard to determine which exit point from the Enterprise is a better route.

Enterprises typically have two major classes of options for outbound routing toward the Internet: default routing and BGP. Using default routes is reasonable. This section discusses default routes toward the Internet, and outbound routes toward the Internet.

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BGP is useful when you have at least two Internet connections. BGP is most useful when you want to choose one outbound path over another path for particular destinations in the Internet. Consider BGP when you have multiple Internet connections, where you want to make some packets take one path and you want other packets to take another path.

External BGP (eBGP) Concepts

This section describes the basics of eBGP to configure, verify, and advertise eBGP routes:

■ External BGP (eBGP): describes connections, configuration and commands to verify

eBGP.

■ Verifying BGP: describes the contents of the BGP table, and routes learned with eBGP.

■ Advertising eBGP routes to ISPs: shows how to configure eBGP to advertise routes.

External BGP (eBGP)

BGP first forms a neighbor relationship with peers. BGP then learns information from its neighbors, placing information in a table named the BGP table. BGP analyzes the BGP table to choose the best route for each prefix in the BGP table, placing those routes into the IP routing table.

This section discusses the configuration of eBGP peers (called neighbors), with settings that may be needed for eBGP connections to result in working BGP neighborships, then discusses the BGP table, listing the learned prefix/ length and path attributes (PA).

eBGP Neighbor Configuration

At a minimum, a router participating in BGP needs to configure the following settings:

■ The ASN for the router configured from a router bgp (BGP and BGP4+) command

from Global Configuration mode on the router to enter Router Configuration mode.

■ The IP address and ASN of each neighbor from a neighbor remote-as (BGP and

BGP4+) command from Router Configuration mode, once the ASN is configured with

the router bgp (BGP and BGP4+) command in the Global Configuration mode.

How Routers become eBGP Neighbors

Routers must meet several requirements to become BGP neighbors:

■ A local router’s ASN must match the reference from the neighboring router to that

ASN as specified from the router bgp (BGP and BGP4+) command.

■ The BGP router IDs of the two routers must not be the same.

■ Each router must establish a TCP connection with the other router.

The remote router’s IP address specified from the neighbor remote-as (BGP and

BGP4+) command and used in that TCP connection must match what the local router

configures from a router bgp (BGP and BGP4+) command.

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How to verify eBGP Neighbor Status

The two most common commands to display a BGP neighbor’s status are:

show ip bgp summary (BGP) and show ip bgp neighbors (BGP).

The show ip bgp neighbors (BGP) command shows detailed output per neighbor.

The show ip bgp summary (BGP) command shows summary output per neighbor.

Administratively Controlling Neighbor Status

To administratively disable any BGP neighbor, enter BGP configuration mode with the router bgp command and issue the neighbor <neighborid> shutdown command to set an idle state.

To administratively enable any BGP neighbor, enter BGP configuration mode with the router bgp command and issue the no neighbor <neighborid> shutdown command to set an idle state.

Use the debug bgp (BGP) command to see the BGP messages.

Verifying BGP

When a BGP router has established its eBGP neighbor relationships, that router can advertise and learn routes using BGP. To learn routes, a BGP router does not need additional configuration beyond the configuration of eBGP neighbor.

To advertise routes to eBGP peers, particularly the public IP address prefix(es) used by that Enterprise, the Enterprise BGP router needs some additional configuration.

The BGP table is important in the process of learning and using routing information with BGP. A router stores all learned BGP prefixes and PAs in its BGP table. The BGP router chooses which route for each prefix is the best BGP route. The BGP router advertises its BGP table to its neighbors, so the best route for each prefix is advertised to neighbors.

BGP Update Messages

When a BGP neighborship reaches the established state, those neighbors begin sending BGP Update messages to each other. The router receiving an Update places those learned prefixes into its BGP table, regardless of whether the route appears to be the best route. BGP puts all learned routing information into its table, and then BGP processes all such potential routes to choose the best route for each prefix.

The format of the Update message tells us about BGP as a Path Vector algorithm. The message lists a set of PAs and then a long list of prefixes that use that set of PAs. So, you might view the BGP Update message as focusing on advertising paths, or a set of PAs, along with the associated list of prefixes that use the advertised path. BGP uses the information in the combined set of PAs to make a decision of which path is best.

Verify the BGP Table

Verify BGP to check the prefixes in the BGP table and confirm that the right prefixes have been learned from the expected neighbors. The BGP table should hold all learned prefixes, from each neighbor, except for any prefixes filtered by an inbound BGP filter.

For a router configured with a neighbor route-map (BGP and BGP4+) command, the local router would first filter the routes and then add the allowed routes into the BGP table. The show ip bgp (BGP) command lists the entire BGP routing table.

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Viewing a subset of the BGP Table

When accepting full BGP updates, the number of BGP table entries may be too large for the show ip bgp (BGP) command listing thousands of prefixes. So instead use the show

ip bgp summary (BGP) command that only lists the number of prefixes received from

each neighbor.

Advertising eBGP routes to ISPs

Outbound routes let the Enterprise routers forward packets toward the Internet. At the same time, the ISPs need to learn routes for the Enterprise’s public IP address space. This section of this chapter examines the options for advertising these routes. In particular, this section looks at two options:

■ BGP network (BGP and BGP4+) command

■ Redistribute from an IGP (RIP/RIPng/OSPF/OSPFv3)

Advertising eBGP routes with the network command

The BGP network (BGP and BGP4+) command installs the prefix defined in the BGP table to be advertised to peers. The route does not have to exist in the routing table. BGP does not use this command to enable BGP on interfaces. This command compares the command’s parameters and the contents of that router’s IP routing table, as follows:

Look for a route in the router’s current IP routing table that exactly matches the parameters of the network (BGP and BGP4+) command. If a route for that exact prefix/ length exists, then put the equivalent prefix/ length into the local BGP table.

This assumes a BGP default setting of no auto-summary. With auto-summary configured, the router adds a route for that classful network to the BGP table:

■ If the exact classful route is in the IP routing table

■ If any subset routes of that classful network are in the routing table

Advertising eBGP routes with the redistribute command

Instead of using the network (BGP and BGP4+) command to add routes to the BGP table, BGP routers can use a redistribute command for OSPF, OSPFv3, RIPng, and RIP to redistribute routes from an IGP into BGP.

■ Advertise the public address range, not the private IP address range, to the BGP table.

■ Advertise one route for the public address range, not individual subnets of the range.

Routers that run BGP may already run an IGP and have learned routes for either the entire public range either as one route or with subset routes. If a single route exists for the entire public range, then you need to add a redistribute command for OSPF, OSPFv3, RIPng, and RIP to the BGP configuration to redistribute only that single route into BGP.

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BGP and BGP4+ Introduction

Internal BGP (iBGP) Concepts

Routers that run BGP often run an IGP, such as OSPF, and have learned routes for the public range either as one route or with subset routes. If a single route exists for the public range, then you can add a redistribute (into BGP or BGP4+) (BGP and BGP4+) command to the BGP configuration to redistribute that route, and only that route, into BGP.

IGPs do not handle the public routing table. Internally peered BGP routers are capable of exchanging routing information without redistributing into an IGP. But an IGP can be used to connect two or more distant iBGP peers, and redistribution into an IGP may be used.

iBGP between Internet connected routers

When an organization uses more than one router to connect to the Internet, and those routers use BGP to exchange routing information with their ISPs, those same routers need to exchange BGP routes with each other as well. The BGP neighbor relationships occur inside that organization, making these routers iBGP peers.

iBGP with two Internet connected routers

Two Internet-connected routers in an Enterprise need to communicate BGP routes to each other because these routers may want to forward IP packets to the other Internetconnected router, which in turn would forward the packets into the Internet.

With an iBGP peer connection, each Internet-connected router can learn routes from the other router and decide if that other router has a better route to reach some destinations in the Internet. Without that iBGP connection, the routers have no way to know if the other router has a better BGP path.

Configuring iBGP

The most basic iBGP configuration differs only slightly compared to eBGP configuration. The configuration does not explicitly identify an eBGP versus an iBGP peer. Instead, for iBGP, the neighbor’s ASN listed on the neighbor remote-as (BGP and BGP4+) command lists the same ASN as the local router’s router bgp (BGP and BGP4+) command. This is because the local router and the neighbor are in the same ASN.

For eBGP, the neighbor remote-as (BGP and BGP4+) command lists a different ASN.

The configuration to use loopback interfaces as the update source mirrors configuration for eBGP peers, except that iBGP peers do not need to configure the neighbor ebgp-

multihop (BGP and BGP4+) command.

For iBGP connections, only the following steps are required to make two iBGP peers use a loopback interface:

1. Configure an IP address on a loopback interface on each router.

2. Configure each router to use the loopback IP address as the source IP address, for the

neighborship with the other router, using the neighbor update-source (BGP and

BGP4+) command.

3. Configure the BGP neighbor remote-as (BGP and BGP4+) command on each router

to refer to the other router’s loopback IP address as the neighbor IP address in the

neighbor remote-as (BGP and BGP4+) command.

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4. Make sure each router has IP routes so that they can forward packets to the loopback

interface IP address of the other router.

Verifying iBGP

iBGP neighbors use the same messages and neighbor states as eBGP peers. The same commands for BGP neighbor verification can be used to verify iBGP peers. The show ip

bgp summary (BGP) command lists neighbors. The show ip bgp neighbors (BGP) and show bgp ipv6 neighbors (BGP4+) commands list many details specifically for the

neighbor for BGP and BGP4+ respectively.

Understanding Next-Hop Reachability Issues with iBGP

With IGPs, the IP routes added to the IP routing table list a next-hop IP address. With few exceptions, the next-hop IP address routes exist in a connected subnet.

BGP advertises these particular IP addresses as the next-hop IP addresses because of a default behavior for BGP. By default, when a router advertises a route using eBGP, the advertising router lists its own update-source IP address as the next-hop address of the route. In other words, the next-hop IP address is the IP address of the eBGP neighbor, as listed on the neighbor remote-as (BGP and BGP4+) command. However, when advertising a route to an iBGP peer, the advertising router (by default) does not change the next-hop address.

The IP routing process can use routes whose next-hop addresses are not in connected subnets as long as each router has an IP route that matches the next-hop IP address. Two main options exist to ensure reachability to these next-hop addresses:

■ Create IP routes so that each router can reach these next-hop addresses that exist in

other ASNs.

■ Change the default iBGP behavior with the neighbor next-hop-self (BGP and

BGP4+) command.

Using neighbor next-hop-self to change Next-Hop Address

The second option for dealing with these unconnected next-hop IP addresses changes the iBGP configuration, so that a router changes the next-hop IP address on iBGPadvertised routes. This option requires the neighbor next-hop-self (BGP and BGP4+) command to be configured for the iBGP neighbor relationship.

With this command configured, the router advertises iBGP routes with its own updatesource IP address as the next-hop IP address. Because the iBGP neighborship already relies on a working route for these update source IP addresses, if the neighborship is up, then IP routes already exist for these next-hop addresses.

IGP Redistribution and BGP Synchronization

Redistributing BGP routes into the IGP can solve routing loop problems. Redistributing BGP routes into the IGP prevents routing loops by giving routers the best exit point for each destination.

Redistributing eBGP-learned Internet routes into the IGP is the BGP feature started with the synchronization (BGP and BGP4+) command, where iBGP learned routes must be synchronized with IGP-learned routes for the same prefix before they can be used. If an iBGP learned route is to be considered to be a usable route, then that same prefix must be in the IP routing table and learned locally or via an IGP, such as OSPF.

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The synchronization feature tells a BGP router not to consider an iBGP-learned route as best unless the prefix is learned locally or via an IGP and is currently in the IP routing table.

BGP synchronization prevents reachability issues by preventing a BGP router advertising routes learned from an iBGP peer unless the route is learned locally, or via an IGP.

If the route does not exist in the routing table, because an IGP has not learned the route, then BGP will not use or advertise the learned prefix. If BGP advertised the route to an external peer, then the external peer would consider that path valid. This is the resulting problem if synchronization is not enabled and there are non-BGP routers in the transit AS.

The eBGP peer would send traffic to the BGP router advertising the prefix and that router would be able to pass the traffic on since the IGP routers between the two iBGP routers do not know the prefix.

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How to configure BGP and BGP4+

This section describes BGP and BGP4+ configuration tasks and the commands required. For example configurations with sample topologies, see Chapter 2, BGP and BGP4+

Configuration.

Initial BGP and BGP4+ Configuration Tasks

There are two initial BGP and BGP4+ configuration tasks described in the below sections. More advanced BGP and BGP4+ configuration tasks are described later in this chapter and are also available separately in the How to Configure BGP and BGP4+ Technical Guide:

■ How to enable BGP and BGP4+ Routing

■ How to configure BGP and BGP4+ Neighbors

How to enable BGP and BGP4+ Routing

To enable BGP or BGP4+ routing and establish a BGP or BGP4+ routing process, use the following commands starting in Global Configuration mode:

awplus(config)#

router bgp <asn>

awplus(config-router)#

network {<ip-prefix/length>|

<ip-network-addr>} [mask

<network-mask>] [route-map

<route-map-name>] [backdoor]

awplus(config-router)#

network {<ipv6-prefix/length>|

<ipv6-network-addr>} [route-map

<route-map-name>]

How to configure BGP and BGP4+ Neighbors

Like other EGPs, BGP must completely understand the relationships it has with its neighbors. Therefore, this task is required.

BGP supports two kinds of neighbors: internal and external. Internal neighbors are in the same autonomous system; external neighbors are in different autonomous systems. Normally, external neighbors are adjacent to each other and share a subnet, while internal neighbors may be anywhere in the same autonomous system.

This command enables a BGP or BGP4+ routing process, which places the router in Router Configuration mode.

This command flags an IPv4 network as local to this autonomous system and enters it to the BGP table.

This command flags an IPv6 network as local to this autonomous system and enters it to the BGP4+ table.

To configure BGP neighbors, use the following command in Router Configuration mode:

awplus(config-router)#

neighbor <neighborid> remote-as

<as-number>

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This command specifies a BGP neighbor.

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BGP and BGP4+ Neighbor Route Filtering

You can filter BGP and BGP4+ advertisements in two ways with neighbors:

■ Use autonomous system path filters, as with the ip as-path access-list (BGP and

BGP4+) Global Configuration mode command and the neighbor filter-list (BGP and BGP4+) Router Configuration mode command

■ Use access or prefix lists, as with the neighbor distribute-list (BGP and BGP4+)

Router Configuration mode command.

If you want to restrict routing information that is learned or advertised, you can filter BGP routing updates to and from neighbors. You can define an access list or a prefix list and apply it to the updates.

To filter BGP routing updates for IPv4 routes, use the command below in Router Configuration mode:

awplus(config-router)#

neighbor <neighborid>

distribute-list <access-list>

{in|out}

BGP and BGP4+ Introduction

This command filters BGP routing updates to and from neighbors as specified in an access list for IPv4 routers in Router Configuration mode.

To filter BGP4+ routing updates for IPv6 routes, use the command below in Address Family Configuration mode:

awplus(config-router-af)#

neighbor <neighborid>

distribute-list <access-list>

{in|out}

BGP and BGP4+ Path Filtering by Neighbor

You can specify an access list filter on both incoming and outbound updates based on the BGP autonomous system paths. Each filter is an access list based on regular expressions. To specify the access list filter, define an autonomous system path access list and apply it to updates to and from particular neighbors.

To configure BGP path filtering, use the following commands starting in Global Configuration mode:

awplus(config)#

ip as-path access-list (BGP and

BGP4+)

awplus(config)#

router bgp <asn>

This command filters BGP routing updates to and from neighbors as specified in an access list for IPv6 routes in Address Family Configuration mode.

This command defines a BGP-related access list.

This command enters Router configuration mode

awplus(config-router)#

neighbor <neighborid>

filter-list <listname> {in|out}

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This command establishes a BGP filter for an IPv4 path in the Router Configuration mode.

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To configure BGP4+ path filtering, use the following commands starting in Global Configuration mode:

awplus(config)#

ip as-path access-list (BGP and

BGP4+)

This command defines a BGP-related access list.

awplus(config)#

router bgp <asn>

awplus(config-router)#

address-family ipv6 [unicast]

awplus(config-router-af)#

neighbor <neighborid>

filter-list <listname> {in|out}

How to disable next hop processing for BGP or BGP4+ updates

You can configure the software to disable next hop processing for BGP and BGP4+ updates to a neighbor.

For BGP, to disable next hop processing and provide a specific address to be used instead of the next hop address, use the command below in Router Configuration mode:

awplus(config-router)#

neighbor <neighborid>

next-hop-self

This command enters Router Configuration mode

This command enters Address Family Configuration mode

This command establishes a BGP4+ filter for an IPv6 path in the Address Family Configuration mode.

This command disables next hop processing on BGP updates to an IPv4 neighbor in Router Configuration mode.

For BGP4+, to disable next hop processing and provide a specific address to be used instead of the next hop address, use the command below in Address Family Configuration

mode:

awplus(config-router-af)#

neighbor <neighborid>

next-hop-self

Configuring this command causes the current router to advertise its peering address as the next hop for the specified neighbor. Therefore, other BGP neighbors will forward to it packets for that address.

This command disables next hop processing on BGP4+ updates to an IPv6 neighbor in Address Family Configuration mode.

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How to use Route Maps for BGP or BGP4+ updates

You can use a route map on a per-neighbor basis to filter updates and modify various attributes. A route map can be applied to either inbound or outbound updates. Only the routes that pass the route map are sent or accepted in updates.

Note that community based matching requires the ip community-list (BGP and BGP4+) Global Configuration command.

See the section BGP Community Filtering for more information. See also the related route-map commands that are included in the BGP and BGP4+ Commands chapter of this Supplement: set community (Route Map) and match community (Route Map).

For BGP, to apply a route map to incoming and outgoing IPv4 routes, use the command below in the Router Configuration mode:

awplus(config-router)#

neighbor <neighborid> route-map

<mapname> {in|out}

BGP and BGP4+ Introduction

This command applies a route map to incoming or outgoing IPv4 routes in the Router Configuration mode.

For BGP4+, to apply a route map to incoming and outgoing IPv6 routes, use the following command in Address Family Configuration mode:

awplus(config-router-af)#

neighbor <neighborid> route-map

<mapname> {in|out}

This command applies a route map to incoming or outgoing IPv6 routes in the Address Family Configuration mode.

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BGP and BGP4+ Peer Groups

Often, in a BGP speaker, many neighbors are configured with the same update policies. Neighbors with the same update policies can be grouped into peer groups to simplify configuration and, more importantly, to make updating more efficient.

Three steps to configure a BGP peer group, described in following sections, are as below:

1. How to create a Peer Group for BGP

2. How to assign options to the created Peer Group

3. How to make neighbors members of a Peer Group

You can disable a BGP peer or peer group without removing all the configuration information using the neighbor shutdown (BGP and BGP4+) Router Configuration mode command.

Note the steps differ slightly for BGP4+ peer groups. First you create a peer group in Global Configuration mode. Next you activate the peer group in Address Family Configuration mode, not Router Configuration mode. Then you assign options to the created peer group in Address Family Configuration mode, not Router Configuration mode as used for BGP.

How to create a Peer Group for BGP

To create a BGP peer group, use the following command in Router Configuration mode:

awplus(config-router)#

neighbor peer-group (create a

peer-group) (BGP and BGP4+)

How to assign options to the created Peer Group

After you create a peer group, you configure the peer group with neighbor commands. By default, members of the peer group inherit all the configuration options of the peer group. Members can also be configured to override the options that do not affect outbound updates.

Peer group members will always inherit the following attributes: minimumadvertisement-interval, next-hop-self, out-route-map, out-filter-list, out-dist-list, remoteas (if configured), version, and update-source. All the peer group members will inherit changes made to the peer group.

This command creates a BGP peer group.

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To assign configuration options to an individual neighbor, specify any of the following commands using the IP address as the <neighborid>. To assign the options to a peer group, specify any of the commands using the peer group name as the <neighborid>.

Use the following commands in Router Configuration mode as needed.

awplus(config-router)#

neighbor <neighborid> remote-as

<as-number>

awplus(config-router)#

neighbor <neighborid>

description <description>

awplus(config-router)#

neighbor {<neighborid>}

default-originate [route-map

<routemap-name>]

awplus(config-router)#

neighbor <neighborid>

send-community {both|extended|

standard}

BGP and BGP4+ Introduction

This command specifies a BGP neighbor.

This command associates a description with a neighbor.

This command allows a BGP speaker (the local router) to send the default route 0.0.0.0 to a neighbor for use as a default route.

This command specifies that the community attribute be sent to the neighbor at this IP address.

awplus(config-router)#

neighbor <neighborid>

update-source <interface>

awplus(config-router)#

neighbor <neighborid>

ebgp-multihop [<count>]

awplus(config-router)#

neighbor <neighborid>

advertisement-interval <time>

awplus(config-router)#

neighbor <neighborid>

maximum-prefix <maximum>

awplus(config-router)#

neighbor <neighborid> weight

awplus(config-router)#

neighbor <neighborid>

distribute-list <access-list>

{in|out}

This command allows iBGP sessions to use any operational interface for TCP connections.

This command allows BGP sessions, even when the neighbor is not on a directly connected segment. The multihop session is not established if the only route to the address of the multihop peer is the default route (0.0.0.0).

This command sets the minimum interval between sending BGP routing updates.

This command limits the number of prefixes allowed from a neighbor.

This command specifies a weight for all routes from a neighbor.

This command filters BGP routing updates to and from neighbors, as specified in an access list..

awplus(config-router)#

neighbor <neighborid>

This command establishes a BGP filter.

filter-list <listname> {in|out}

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BGP and BGP4+ Introduction

awplus(config-router)#

neighbor <neighborid>

next-hop-self

awplus(config-router)#

neighbor <neighborid> version

awplus(config-router)#

neighbor {<ip-address>|

<peer-group-name>} password

awplus(config-router)#

neighbor <neighborid> route-map

<mapname> {in|out}

awplus(config-router)#

neighbor <neighborid>

soft-reconfiguration inbound

This command disables next hop processing on the BGP updates to a neighbor.

This command specifies the BGP version to use when communicating with a neighbor.

This command starts MD5 authentication on a TCP connection to a BGP peer. You can enter a case-sensitive password of up to 25 characters. The string can contain any alphanumeric characters.

This command applies a route map to incoming or outgoing routes.

This command configures the software to start storing received updates.

If a peer group is not configured with a remote-as attribute, the members can be configured with the neighbor remote-as (BGP and BGP4+) command in Router Configuration mode. This command allows you to create peer groups containing external BGP (eBGP) neighbors.

You can customize inbound policies for peer group members (using a distribute list, a route map, or a filter list) because one identical copy of an update is sent to every member of a group. Neighbor options for outgoing updates cannot be customized for peer groups.

External BGP (eBGP) peers must reside on a directly connected network. But you may want to change this to test BGP or BGP4+. You can do this by specifying the neighbor ebgp-

multihop (BGP and BGP4+) command in Router Configuration mode. Members of a peer

group can pass routes from one member of the peer group to another. For example, if router B is peering with routers A and C, router B can pass routes from router A to router C.

For Internal BGP (iBGP) peers, you may want to allow BGP or BGP4+ connections to stay up if any interface is used. To enable this configuration, configure a loopback interface and assign it an IPv4 or an IPv6 address. Next, configure the BGP or BGP4+ update source to be the loopback interface. Then configure your neighbor to use the address on the loopback interface. Now the iBGP session will be up as long as there is a route on any interface.

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How to configure authentication for BGP Peering Sessions

You can configure authentication between two BGP peers, meaning that each segment sent on the TCP connection between the peers is verified. Authentication must be configured with the same password on both BGP peers; otherwise, the connection between them will not be made. Configuring authentication causes the software to generate and check the MD5 digest of every segment sent on the TCP connection. If authentication is invoked and a segment fails authentication, then an error message will

be displayed in the console.

awplus(config-router)#

neighbor {<ip-address>|

<peer-group-name>} password

When configuring authentication, you can enter a case-sensitive password of up to 25 characters.The string can contain any alphanumeric characters, including spaces. A password cannot be configured in the number-space-anything format. The space after the number can cause authentication to fail.

BGP and BGP4+ Introduction

This command starts MD5 authentication on a TCP connection to a BGP peer. You can enter a case-sensitive password of up to 25 characters.

How to make neighbors members of a Peer Group

To configure a BGP neighbor to be a member of a BGP peer group, use the following command in Router Configuration mode, using the same peer group name:

awplus(config-router)#

neighbor <ipv6-addr> peer-group

<peer-group>

How to disable a Peer or Peer Group

To disable an existing BGP neighbor or neighbor peer group, use the following command in Router Configuration mode:

awplus(config-router)#

neighbor <neighborid> shutdown

To enable a previously existing neighbor or neighbor peer group that had been disabled using the neighbor shutdown (BGP and BGP4+) command in Router Configuration

mode, use the following command in Router Configuration mode:

This command makes a BGP neighbor a member of the peer group.

This command shuts down or disables a BGP neighbor or peer group.

awplus(config-router)#

no neighbor <neighborid>

shutdown

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This command enables a BGP neighbor or peer group.

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BGP and BGP4+ Prefix Lists

Prefix lists can be used as an alternative to access lists in many BGP or BGP4+ route filtering commands. The advantages of using IPv4 or IPv6 prefix lists are as follows:

■ More of a performance improvement in loading and route lookup of large lists.

■ Support for updates. Filtering using access lists does not support updates.

■ The command-line interface to use access lists to filter BGP updates is more difficult.

■ More flexibility

Before using a prefix list in a BGP or BGP4+ command, first set up the prefix list, and assign sequence numbers to entries in the prefix list.

BGP and BGP4+ filtering by prefix lists involves matching the prefixes of IPv4 or IPv6 routes with those listed in the prefix list. When there is a match, the route is used. Whether a prefix is permitted or denied is based upon these rules:

■ An empty prefix list permits all prefixes.

■ An implicit deny is assumed if a given prefix does not match any entries of a prefix list.

The router begins the search at the top of the prefix list, with the sequence number 1. Once a match or deny occurs, the router need not go through the rest of the prefix list.

For efficiency, add the most common matches or denies near the top of the list, using the

seq parameter in the ip prefix-list (IPv4 Prefix List) and ipv6 prefix-list (IPv6 Prefix

List) Global Configuration mode commands. The show ip prefix-list (IPv4 Prefix List)

command and the show ipv6 prefix-list (IPv6 Prefix List) command output includes sequence numbers.

Sequence numbers are generated automatically unless you disable automatic generation. If you disable the automatic generation of sequence numbers, you need to specify the sequence number for each entry with the seq parameter of the ip prefix-list (IPv4 Prefix

List) and ipv6 prefix-list (IPv6 Prefix List) Global Configuration mode commands.

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How to create and configure a Prefix List for BGP or BGP4+

To create a prefix list for BGP, use the following command in Global Configuration mode. Note you can add individual prefix list entries to a defined prefix list as well.

awplus(config)#

ip prefix-list <list-name> [seq <1-429496725>] {deny|

permit} {any|<ip-prefix>} [ge

<0-32>] [le <0-32>]

awplus(config)#

ipv6 prefix-list <list-name>

[seq <1-429496725>] {deny|

permit} {any|<ipv6-prefix>} [ge

<0-128>] [le <0-128>]

BGP and BGP4+ Introduction

This command creates an IPv4 prefix list with the name specified for the <list-name> parameter. To create a prefix list you must enter at least one permit or deny clause. Once an IPv4 prefix list is created, this command creates a prefix list entry, and assigns a sequence number to the IPv4 prefix list entry.

This command creates an IPv6 prefix list with the name specified for the <list-name> parameter. To create a prefix list you must enter at least one permit or deny clause. Once an IPv6 prefix list is created, this command creates a prefix list entry and assigns a sequence number to the IPv6 prefix list entry.

The optional ge and le keywords can be used to specify the range of the prefix length to be matched for prefixes that are more specific than the network/length parameter. An exact match is assumed when neither ge nor le is specified.

You can specify sequence values for prefix list entries in any increments you want. If you specify the sequence values in increments of 1, you cannot insert additional entries into the prefix list. If you choose very large increments, you could run out of sequence values.

How to delete Prefix List Entries

To remove a prefix list, and optionally specific entries, use the following commands as appropriate in Global Configuration mode:

awplus(config)#

no ip prefix-list <list-name>

[seq <1-429496725>]

awplus(config)#

no ipv6 prefix-list <list-name>

[seq <1-429496725>]

This command removes an IPv4 prefix list with the name specified for the required <list-name> parameter and the sequence number specified in the range <1-429496725>.

This command removes an IPv6 prefix list with the name specified for the <list-name> parameter and the sequence number specified in the range <1-429496725>.

The sequence number of an entry is optional when you delete the prefix list entry. If you omit the sequence number then all entries are deleted for the prefix list.

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BGP and BGP4+ Introduction

How to display IPv4 and IPv6 Prefix Entries

To display information about IPv4 and IPv6 prefix tables, prefix table entries, the policy associated with a node, or specific information about an entry, use the following

commands in Privileged Exec mode as appropriate:

awplus#

show ip prefix-list [<name>|

detail|summary]

awplus#

show ipv6 prefix-list [<name>|

detail|summary]

This command displays information about IPv4 prefix lists.

This command displays information about IPv6 prefix lists.

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+ 320 hidden pages

Allied Telesis BGP, BGP4+ User Manual

Acknowledgments

Table of Contents

Chapter 1: BGP and BGP4+ Introduction

Introduction

BGP and BGP4+ Overview

BGP and BGP4+ ASNs and AS_Path Attributes

Internal and External BGP Concepts

Public and Private ASNs

Outbound Routing Toward the Internet

External BGP (eBGP) Concepts

External BGP (eBGP)

eBGP Neighbor Configuration

How Routers become eBGP Neighbors

How to verify eBGP Neighbor Status

Administratively Controlling Neighbor Status

Verifying BGP

BGP Update Messages

Verify the BGP Table

Viewing a subset of the BGP Table

Advertising eBGP routes to ISPs

Advertising eBGP routes with the network command

Advertising eBGP routes with the redistribute command

Internal BGP (iBGP) Concepts

iBGP between Internet connected routers

iBGP with two Internet connected routers

Configuring iBGP

Verifying iBGP

Understanding Next-Hop Reachability Issues with iBGP

Using neighbor next-hop-self to change Next-Hop Address

IGP Redistribution and BGP Synchronization

How to configure BGP and BGP4+

Initial BGP and BGP4+ Configuration Tasks

How to enable BGP and BGP4+ Routing

How to configure BGP and BGP4+ Neighbors

BGP and BGP4+ Neighbor Route Filtering

BGP and BGP4+ Path Filtering by Neighbor

How to disable next hop processing for BGP or BGP4+ updates

How to use Route Maps for BGP or BGP4+ updates

BGP and BGP4+ Peer Groups

How to create a Peer Group for BGP

How to assign options to the created Peer Group

How to configure authentication for BGP Peering Sessions

How to make neighbors members of a Peer Group

How to disable a Peer or Peer Group

BGP and BGP4+ Prefix Lists

How to create and configure a Prefix List for BGP or BGP4+

How to delete Prefix List Entries

How to display IPv4 and IPv6 Prefix Entries