Dynamic routing

Router ID

Also called RID, OSPF router ID, router-id, loopback

The 32-bit name an OSPF (or BGP) router goes by, written like an IPv4 address and unique in the domain.

It names the router in Hellos, in neighbour tables and as the author of its LSAs. On IOS it is the router-id command; else the highest loopback address; else the highest address on an active interface. It is chosen when the process starts, so a change waits for clear ip ospf process. Two routers with one ID ignore each other's Hellos and overwrite each other's LSAs.

See it on real machines

Learn it on real machines.