Hello Sanjiv.
In order to clarify why you’re getting the error, first let’s look back on how a router chooses its router ID. A router ID is always in the format of an IPv4 address. The router ID is chosen in the following order:
- If a router ID is configured in the ospf configuration, this is used as the router ID.
- If no router ID is configured, then it uses the highest IP address of a loopback interface
- If no loopback interface exists, it will use the highest IP address of any physical interface in the “up” state.
Now if you’re using IPv4, then one of the above will be configured so you will NEVER get the above error message. If you’re using ONLY IPV6, you may have NONE of the above configured. So if that is the case, you get the error message that you observed in your configuration.
To solve the problem, define a router ID using one of the above three entities. It is always best practice however, whether you use IPv4 or IPv6, to define a router ID in the ospf configuration. This will allow you to more easily identify routers in neighbor tables when troubleshooting and when changing configurations.
I hope this has been helpful!
Laz