Concept Guide

Table Of Contents
Origin.............................................................................................................................................................................173
AS Path.........................................................................................................................................................................173
Next Hop...................................................................................................................................................................... 174
Multiprotocol BGP........................................................................................................................................................... 174
Implement BGP ............................................................................................................................................................... 174
Advertise IGP Cost as MED for Redistributed Routes..................................................................................... 175
Ignore Router-ID for Some Best-Path Calculations.......................................................................................... 175
Four-Byte AS Numbers............................................................................................................................................ 175
AS4 Number Representation...................................................................................................................................176
AS Number Migration................................................................................................................................................177
BGP4 Management Information Base (MIB)...................................................................................................... 178
Important Points to Remember.............................................................................................................................. 179
Configuration Information..............................................................................................................................................179
BGP Configuration.......................................................................................................................................................... 180
Enabling BGP.............................................................................................................................................................. 180
Configuring AS4 Number Representations..........................................................................................................183
Configuring Peer Groups......................................................................................................................................... 185
Configuring BGP Fast Fail-Over.............................................................................................................................187
Configuring Passive Peering................................................................................................................................... 188
Maintaining Existing AS Numbers During an AS Migration..............................................................................189
Allowing an AS Number to Appear in its Own AS Path.................................................................................... 189
Filtering on an AS-Path Attribute.......................................................................................................................... 190
Regular Expressions as Filters.................................................................................................................................191
Redistributing Routes............................................................................................................................................... 192
Enabling Additional Paths........................................................................................................................................ 193
Configuring IP Community Lists.............................................................................................................................193
Configuring an IP Extended Community List...................................................................................................... 194
Filtering Routes with Community Lists.................................................................................................................195
Manipulating the COMMUNITY Attribute............................................................................................................196
Changing MED Attributes........................................................................................................................................ 197
Changing the LOCAL_PREFERENCE Attribute................................................................................................. 197
Configuring the local System or a Different System to be the Next Hop for BGP-Learned Routes....198
Changing the WEIGHT Attribute........................................................................................................................... 198
Enabling Multipath.....................................................................................................................................................199
Filtering BGP Routes................................................................................................................................................ 199
Filtering BGP Routes Using Route Maps............................................................................................................ 200
Filtering BGP Routes Using AS-PATH Information.......................................................................................... 200
Configuring BGP Route Reflectors....................................................................................................................... 201
Aggregating Routes...................................................................................................................................................201
Configuring BGP Confederations..........................................................................................................................202
Enabling Route Flap Dampening............................................................................................................................202
Changing BGP Timers..............................................................................................................................................204
Setting the extended timer.................................................................................................................................... 205
Enabling BGP Neighbor Soft-Reconfiguration...................................................................................................205
Enabling or disabling BGP neighbors....................................................................................................................206
Route Map Continue................................................................................................................................................ 207
Enabling MBGP Configurations................................................................................................................................... 208
Configure IPv6 NH Automatically for IPv6 Prefix Advertised over IPv4 Neighbor.................................. 208
BGP Regular Expression Optimization.......................................................................................................................209
Debugging BGP............................................................................................................................................................... 209
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