Best Path Selection Criteria.........................................................................................................155
Weight..........................................................................................................................................157
Local Preference..........................................................................................................................157
Multi-Exit Discriminators (MEDs)................................................................................................158
Origin...........................................................................................................................................159
AS Path.........................................................................................................................................160
Next Hop.....................................................................................................................................160
Multiprotocol BGP............................................................................................................................160
Implement BGP ................................................................................................................................161
Additional Path (Add-Path) Support............................................................................................161
Advertise IGP Cost as MED for Redistributed Routes.................................................................161
Ignore Router-ID for Some Best-Path Calculations..................................................................162
Four-Byte AS Numbers...............................................................................................................162
AS4 Number Representation......................................................................................................162
AS Number Migration..................................................................................................................164
BGP4 Management Information Base (MIB)..............................................................................166
Important Points to Remember..................................................................................................166
Configuration Information................................................................................................................167
BGP Configuration............................................................................................................................167
Enabling BGP...............................................................................................................................168
Configuring AS4 Number Representations................................................................................172
Configuring Peer Groups............................................................................................................173
Configuring BGP Fast Fail-Over..................................................................................................176
Configuring Passive Peering.......................................................................................................178
Maintaining Existing AS Numbers During an AS Migration........................................................179
Allowing an AS Number to Appear in its Own AS Path..............................................................180
Enabling Neighbor Graceful Restart...........................................................................................180
Filtering on an AS-Path Attribute................................................................................................181
Regular Expressions as Filters.....................................................................................................183
Redistributing Routes..................................................................................................................184
Enabling Additional Paths............................................................................................................185
Configuring IP Community Lists.................................................................................................185
Configuring an IP Extended Community List.............................................................................187
Filtering Routes with Community Lists.......................................................................................188
Manipulating the COMMUNITY Attribute...................................................................................188
Changing MED Attributes...........................................................................................................190
Changing the LOCAL_PREFERENCE Attribute..........................................................................190
Changing the NEXT_HOP Attribute............................................................................................191
Changing the WEIGHT Attribute.................................................................................................192
Enabling Multipath.......................................................................................................................192
Filtering BGP Routes....................................................................................................................192
Filtering BGP Routes Using Route Maps....................................................................................194