The Cisco IOS router-id command manually assigns the 32-bit router ID (RID) used by an OSPF process. The RID must be unique within the OSPF autonomous system. section 18.2.1
Enter router ospf process-id first, then use router-id value in router configuration mode. OSPF chooses a manual RID before considering the highest address on an operational loopback interface or physical interface. section 18.2.1
Manually configure and verify the RID
R1(config)# router ospf 1 R1(config-router)# router-id 172.16.1.1 R1(config-router)# do show ip protocols Router ID 172.16.1.1 The show ip protocols command verifies the configured RID.
Remember these operational points:
- Creating an OSPF process before configuring a RID means the router initially selects an eligible loopback or physical-interface address. section 18.2.1
- If no operational interface has an IP address, configure the RID or bring an addressed interface up so the process can start. section 18.2.1
- Use a loopback address when a stable virtual interface is preferred over an address tied to a physical interface. section 18.2.1
