Identifying a Router Within an Autonomous System

The router identifier (ID) is commonly one of the router’s defined IP addresses. Although the router ID is, by convention, formatted as an IP address, it is not required to be a configured address of the router. If you do not use the ip router-id command to assign a router ID, the router uses one of its configured IP addresses as the router ID. The router ID is a unique identifier that IP routing protocols use to identify the router within an autonomous system

To assign a router ID:

• Issue the ip router-id command in Global Configuration mode.
  host1(config)#ip router-id 192.32.15.23

  Use the no version to remove the router ID assignment.