Use the router-id rid router configuration mode command to manually assign a 32-bit value expressed as an IPv4 address to a router. An OSPF router identifies itself to other routers using this router ID.
As shown in Figure 1, R1 is configured with a router ID of 1.1.1.1, R2 with 2.2.2.2, and R3 with 3.3.3.3.
In Figure 2, the router ID 1.1.1.1 is assigned to R1. Use the show ip protocols command to verify the router ID.
Note: R1 had never been configured with an OSPF router ID. If it had, then the router ID would have to be modified.
If the router ID is the same on two neighboring routers, the router displays an error message similar to the one below:
%OSPF-4-DUP_RTRID1: Detected router with duplicate router ID.
To correct this problem, configure all routers so that they have unique OSPF router IDs.
Use the Syntax Checker in Figure 3 to assign the router ID to R2 and R3.