Chapter 2 discussed the purpose and function of the OSPF router ID (RID) and how it is randomly determined. In certain circumstances, you might not want to use a loopback address or you might want to statically assign the RID in a different way. Fortunately, Cisco IOS Software Release 12.0(1)T or later provides this capability with the router-id command, as follows:
Trinity(config)#router ospf 100 Trinity(config-router)#router-id ?
A.B.C.D OSPF router-id in IP address format Trinity(config-router)#router-id
Remember that each RID must be unique. If you apply a RID, via this command, to a router already running OSPF, the OSPF process or the router must be restarted. You can do this either with a clear ip ospf process command or a reload command.
Trinity#clear ip ospf ?
<1-4294967295> Process ID number counters OSPF counters process Reset OSPF process redistribution Clear OSPF route redistribution
Trinity#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
NOTE Another way to restart OSPF is to cut and paste no router ospf xx followed by router ospf etc... to restart the process without a reload of the router.
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