The RID is A 32-bit dotted decimal value which is used to uniquely identify a specific OSPF-enabled device in an autonomous system.   Uniquely means that different devices shouldn’t have the same router-id configured.

It is a best practice to hard code the Router-ID but is optional.

OSPF has its own automatic RID election process:

• The IP Address of the first loopback interface.
• If there is no Loopback interface, then the Router ID will be the highest IP Address a physical interface.

We have to understand that the Router-ID looks like an IP address in format, but is not.   Is just and ID and is used to represent a Router in the OSPF topology graph.   We can assign something like 0.0.0.1, 0.0.10.10, for example.

With RID election, we are subject to undesired changes or outages when the process is cleared.   Another reason to manually assign the RID is because other technologies such OSPF virtual links.

Configuring RID

Configuring the RID in OSPF is very straight-forward.  It’s done using the command router-id x.x.x.x under the process.

!
router ospf 1
router-id 1.1.1.1
!

If the OSPF process was previously started or pre-configured, you will receive a notification informing that it will be necessary to clear the process for the change to take effect.

Yes, Clear the OSPF process is a Resume Generating Event if done in production, especially during business hours.

Clearing the OSPF process is a DISRUPTIVE command which forces OSPF to reconverge.

To clear the OSPF process use the clear ip ospf process command in exec mode.

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