Cisco IOS Cookbook, 2nd Edition

Connecting to Two ISPs

Problem

You want to set up BGP to support two redundant Internet connections.

Solution

The following configuration shows how to make the basic BGP connections, but it has serious problems that we will show how to fix in other recipes in this chapter:

Router1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#interface Serial0
Router1(config-if)#description connection to ISP #1, ASN 65510
Router1(config-if)#ip address 192.168.1.6 255.255.255.252
Router1(config-if)#exit
Router1(config)#interface Serial1
Router1(config-if)#description connection to ISP #2, ASN 65520
Router1(config-if)#ip address 192.168.2.6 255.255.255.252
Router1(config-if)#exit
Router1(config)#interface Ethernet0
Router1(config-if)#description connection to internal network, ASN 65500
Router1(config-if)#ip address 172.18.5.2 255.255.255.0
Router1(config-if)#exit
Router1(config)#router bgp 65500
Router1(config-router)#network 172.18.5.0 mask 255.255.255.0
Router1(config-router)#neighbor 192.168.1.5 remote-as 65510
Router1(config-router)#neighbor 192.168.2.5 remote-as 65520
Router1(config-router)#no synchronization
Router1(config-router)#exit
Router1(config)#end
Router1#

Warning

We do not recommend using this configuration as printed for a real Internet connection because it leaves out several key components. A more complete example is shown in Recipe 9.19.

Discussion

Perhaps the most common BGP application involves connecting a single router to two different ...