Sometimes a router ID needs to be changed, for example, when a network administrator establishes a new router ID scheme for the network. However, after a router selects a router ID, an active OSPF router does not allow the router ID to be changed until the router is reloaded or the OSPF process cleared.
In Figure 1, notice that the current router ID is 192.168.10.5. The router ID should be 1.1.1.1.
In Figure 2, the router ID 1.1.1.1 is being assigned to R1. Notice how an informational message appears stating that the OSPF process must be cleared or that the router must be reloaded. The reason is because R1 already has adjacencies with other neighbors using the router ID 192.168.10.5. Those adjacencies must be renegotiated using the new router IP 1.1.1.1.
Clearing the OSPF process is the preferred method to reset the router ID.
In Figure 3, the OSPF routing process is cleared using the clear ip ospf process privileged EXEC mode command. This forces OSPF on R1 to transition to the Down and Init states. Notice the adjacency change messages from full to down and then from loading to full. The show ip protocols command verifies that the router ID has changed.
Use the Syntax Checker in Figure 4 to modify the router ID for R1.