Why cannot configure OSPF ?

[eigrpy]

Hi I am configuring OSPF in C3645. It is strange that I got error message and failed to configure OSPF. Please see below

R2(config)#router ospf 1
R2(config-router)#
*Mar  1 00:37:17.671: %OSPF-4-NORTRID: OSPF process 1 cannot pick a router-id.
  Please configure manually or bring up an interface with an ip address.

interface is up 

[Mark Malone]

Hey have you any ips enabled yet ?

edit:bring up a loopback give it an ip address

[eigrpy]

Thank you for your reply. You are right. After i added loopback ip, it began to work.

In fact, the router has a physical interface, and it is up, why the interface cannot work for the ospf ? 

[Jon Marshall]

It should work as long as the physical interface has an IP address assigned to it and is up/up.

The message you are seeing is because OSPF needs to select a router id and if you don't configure one within the OSPF process itself it selects one from the interfaces with IPs that are up.

It will choose the highest IP and use loopbacks first and then physical interfaces.

Jon