# BGP Loopback Interface and Router ID Overview

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 because a loopback interface is inherently stable.

After you configure the loopback interface, 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.