OSPF Loopback

bmauro · October 2006

Hi guys,

I'm messing around with OSPF on my lab and I have a quick question on loopback interfaces.

If you start OSPF ip before you config your loopback (so it already has picked the Router ID) and then configure your loopback is there anyway to force the OSPF process to use the loopback rather than the highest physical IP?

I thought I read somewhere that the clear ip ospf process would restart ospf, but that didn't do it. Is rebooting the router the only option?

keenon · October 2006

yes

those are the 2 choices other than deleting the process and rebuilding it

bmauro · October 2006

Thanks keenon, but I think you might have mis-understood.

The " clear ip ospf process" did NOT change the loopback interface.

It's no big deal to reboot the router, I just did know if there was a quicker - easier way that is used in the real world.

Thanks again.

loboernesto · October 2006

I was thinking.... maybe if you do show run then copy the ospf configuration (if you are using telnet do right click-->mark select what you want, press ctrl+c, to paste it right click-->paste). Go to global configuration, do no router ospf processId and then just paste what you copied from your show run output...That would reset the ospf, quicker than reloading (it may depend on your configs...) but it's surely more secure and adequate in a "real world" situation because you are not compromising the whole router just to influence the RID selection...it sounds a lot of hassle but I've just done a couple of times and it doesn't take more than 15 seconds.
I've also tried using clear ip ospf process with no success...
hope that helps your. Cheers

steve-o87 · October 2006

In the Real world you don't want to be unnecessarily rebooting routers. But if you had to choose a different Loopback for some reason You would use

Clear ip ospf process will restart it and it should pick the highest Loopback address.

bmauro · October 2006

Sorry steve - I'm afraid to say that "clear ip ospf process" does not change the router id.

I was playing around with it last night.

Two interfaces when I first config'ed the ospf process
172.16.1.6 /30
172.16.30.1 /24

So after that - the Router ID was 172.16.30.1 - no surprise.

I then created the loopback interface - 10.0.6.160 /24 <- Loopback

Did a "no shut" and then a "clear ip ospf process"

172.16.30.1 remained the Router ID even after the command.

Maybe I'm doing it wrong - but a few people have also mentioned the "clear ip ospf process" not reassigning the router id.

OSPF Loopback

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