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Configuring BGP
Configuring Advanced BGP Features
IPC-316
Cisco IOS IP Configuration Guide
Inbound soft reconfiguration allowed
NEXT_HOP is always this router
Community attribute sent to this neighbor
Condition-map old-route, Advertise-map new-route, status:Uninitialized
2 accepted prefixes consume 72 bytes
Prefix advertised 7, suppressed 0, withdrawn 4
Connections established 1; dropped 0
Last reset 01:05:29, due to Soft reconfig change
BGP Conditional Advertisement Troubleshooting Tips
This section provides troubleshooting information for the BGP conditional advertisement feature.
The BGP Conditional Advertisement feature is based on the nonexistence of a prefix and the
advertisement of another. Normally, only two problems can occur:
• The tracked prefix exists, but the conditional advertisement occurs.
• The tracked prefix does not exist, and the conditional advertisement does not occur.
The same method of troubleshooting is used for both problems:
• Verify the existence (or not) of the tracked prefix in the BGP table with the show ip bgp EXEC
command.
• Verify the advertisement (or not) of the other prefix using the show ip bgp neighbor
advertised-routes EXEC command.
The user needs to ensure that all of the characteristics specified in the route maps match the routes in the
BGP table.
Configuring a Routing Domain Confederation
One way to reduce the iBGP mesh is to divide an autonomous system into multiple subautonomous
systems and group them into a single confederation. To the outside world, the confederation looks like
a single autonomous system. Each autonomous system is fully meshed within itself, and has a few
connections to other autonomous systems in the same confederation. Even though the peers in different
autonomous systems have eBGP sessions, they exchange routing information as if they were iBGP peers.
Specifically, the next hop, MED, and local preference information is preserved. This feature allows the
you to retain a single IGP for all of the autonomous systems.
To configure a BGP confederation, you must specify a confederation identifier. To the outside world, the
group of autonomous systems will look like a single autonomous system with the confederation
identifier as the autonomous system number. To configure a BGP confederation identifier, use the
following command in router configuration mode:
Command Purpose
Router(config-router)# bgp confederation identifier
as-number
Configures a BGP confederation.