Cisco IOS Cookbook, 2nd Edition

Configuring BGP

Problem

You want to run BGP in a simple network.

Solution

In its simplest configuration, BGP exchanges routes between a router in one AS and another router in a different AS. The first router is in AS 65500:

Router1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#interface Serial0
Router1(config-if)#ip address 192.168.55.6 255.255.255.252
Router1(config-if)#exit
Router1(config)#router bgp 65500
Router1(config-router)#network 192.168.1.0
Router1(config-router)#neighbor 192.168.55.5 remote-as 65501
Router1(config-router)#no synchronization
Router1(config-router)#exit
Router1(config)#end
Router1#

The second router is in AS 65501:

Router2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router2(config)#interface Serial0
Router2(config-if)#ip address 192.168.55.5 255.255.255.252
Router2(config-if)#exit
Router2(config)#router bgp 65501
Router2(config-router)#network 172.25.17.0 mask 255.255.255.0
Router2(config-router)#neighbor 192.168.55.6 remote-as 65500
Router2(config-router)#no synchronization
Router2(config-router)#exit
Router2(config)#end
Router2#

Discussion

This example shows two routers in different Autonomous Systems. Router1 is in AS 65500, and is configured to share routing information only for a single network using the command network 192.168.1.0. Because this is a classful network, we don’t need to include a mask. However, you will notice that the syntax of the network command on Router2 ...