Cisco Systems 78-11741-02 manual Configuring a Routing Domain Confederation, IPC-316

Configuring BGP

Configuring Advanced BGP Features

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Prefix advertised 7, suppressed 0, withdrawn 4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	Configures a BGP confederation.
as-number

Cisco IOS IP Configuration Guide

IPC-316