Configuring the Loopback Interface and Router ID for VPLS

A loopback interface provides a stable address for BGP or LDP to use so that they can avoid any impact if a physical interface goes down. The loopback interface sends packets back to the router or access server for local processing. Any packets routed from the loopback interface, but not destined to the loopback interface, are dropped.

To establish a BGP session, BGP uses the IP address of the outgoing interface towards the BGP peer as the update source IP address for the TCP connection over which the BGP session runs. Typically, you configure a loopback interface as the update source interface.

LDP uses the loopback interface as the associated interface for the targeted neighbors configured with the mpls ldp vpls neighbor command, as described in Configuring LDP Signaling for VPLS.

After you configure the loopback interface, you use the ip router-id command to assign a router ID to uniquely identify the router within a BGP AS. The router ID is the IP address of the loopback interface.

To configure the loopback interface and router ID on the PE router:

1. Configure a loopback interface on the PE router and assign it an IP address.
   host1(config)#interface loopback 0 host1(config-if)#ip address 10.3.3.3 255.255.255.255 host1(config-if)#exit
2. Assign the router ID using the IP address you configured for the loopback interface.
   host1(config)#ip router-id 10.3.3.3