Notice that when the networks for the serial links from R3 to R1 and R3 to R2 are added to the
OSPF configuration, the router sends a notification message to the console stating that a
neighbor relationship with another OSPF router has been established.
Task 6: Configure OSPF Router IDs
The OSPF router ID is used to uniquely identify the router in the OSPF routing domain. A router
ID is an IP address. Cisco routers derive the Router ID in one of three ways and with the following
precedence:
1. IP address configured with the OSPF router-id command.
2. Highest IP address of any of the router’s loopback addresses.
3. Highest active IP address on any of the router’s physical interfaces.
Step 1: Examine the current router IDs in the topology.
Since no router IDs or loopback interfaces have been configured on the three routers, the router
ID for each router is determined by the highest IP address of any active interface.