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Community Member

OSPF loopback router ID

I have found out that if you configure the loopback address after you have configured the OSPF on a router, the loopback address is not recognised as the Router ID.

Am I right???

Community Member

Re: OSPF loopback router ID

This is correct. When the OSPF process is turned on, it selects the best router id. It will try the loopbacks first, and then it will select the highest ip address (non loopback) next.

If you should change something on the router AFTER OSPF is started, such as creating a loopback that wasn't there before, or even just numbering an interfaces with a higher IP address than what was found to be the highest when OSPF was enabled, it will not preempt the previous router id.

This can REALLY mess you up, becuase when the router reboots, at that time, the newly added address WILL be recognized by OSPF and will become the new router id. Some things depend on the router id, such as OSPF virtual-links, and these can all break a the time the router is reloaded! So the best practice is to hard code your OSPF router id's using the "router-id" command under the OSPF process.


Community Member

Re: OSPF loopback router ID


Yes, only to first reboot.

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