Users Guide
8 Border Gateway Protocol IPv4 (BGPv4)......................................................................................................... 164
Autonomous Systems (AS)................................................................................................................................... 164
Sessions and Peers.................................................................................................................................................166
Establish a Session............................................................................................................................................167
Route Reflectors..................................................................................................................................................... 167
Communities.....................................................................................................................................................168
BGP Attributes.........................................................................................................................................................168
Best Path Selection Criteria............................................................................................................................169
Weight................................................................................................................................................................. 170
Local Preference................................................................................................................................................171
Multi-Exit Discriminators (MEDs)................................................................................................................... 171
Origin...................................................................................................................................................................172
AS Path................................................................................................................................................................ 172
Next Hop.............................................................................................................................................................173
Multiprotocol BGP..................................................................................................................................................173
Implement BGP ......................................................................................................................................................173
Additional Path (Add-Path) Support..............................................................................................................173
Advertise IGP Cost as MED for Redistributed Routes............................................................................... 174
Ignore Router-ID for Some Best-Path Calculations................................................................................. 174
Four-Byte AS Numbers....................................................................................................................................174
AS4 Number Representation..........................................................................................................................175
AS Number Migration.......................................................................................................................................176
BGP4 Management Information Base (MIB)............................................................................................... 178
Important Points to Remember.....................................................................................................................178
Configuration Information....................................................................................................................................179
BGP Configuration................................................................................................................................................. 179
Enabling BGP.....................................................................................................................................................180
Configuring AS4 Number Representations.................................................................................................183
Configuring Peer Groups................................................................................................................................184
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............................................................................ 190
Enabling Neighbor Graceful Restart.............................................................................................................190
Filtering on an AS-Path Attribute................................................................................................................... 191
Regular Expressions as Filters........................................................................................................................ 192
Redistributing Routes.......................................................................................................................................194
Enabling Additional Paths............................................................................................................................... 194
Configuring IP Community Lists................................................................................................................... 195
Configuring an IP Extended Community List............................................................................................. 196
Filtering Routes with Community Lists........................................................................................................ 197
Manipulating the COMMUNITY Attribute.................................................................................................... 197
Changing MED Attributes............................................................................................................................... 199
Changing the LOCAL_PREFERENCE Attribute...........................................................................................199
Configuring the local System or a Different System to be the Next Hop for BGP-Learned
Routes.................................................................................................................................................................200
Contents
7