How is OSPF router ID determined

Question

How is OSPF router ID determined?

Answer 1

When physical interfaces are only employed, the OSPF router ID is the maximum IP address allocated to an active physical interface. When loopback interfaces are utilized, the OSPF router ID is the maximum IP address allocated to a loopback interface. When the router-id command is employed with the OSPF configuration, the address utilized with this command will be the router ID.