router loopback question.

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Apr 14th, 2009
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I would like to set up a loopback interface on a remote router I have so I can take the link down and make changes on the remote end...

far end address is

ofcourse there is a route to it from my core...

I tried a loopback address

and get a confliction with my fastethernet? What am I doing wrong?

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thotsaphon Tue, 04/14/2009 - 09:25
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What's the ip address of fastethernet you mentioned?

Please do a "sh run int fx/x" command.


Richard Burts Tue, 04/14/2009 - 09:27
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Based on what you posted there should not be a conflict. Is it possible that the masks that you posted are not the same as the masks in the config? Or is it possible that there are several interfaces on the router?

Could you post the output of:

show interface | include address

from the remote router.

Also I am a little concerned about what you are trying to do. When you say that:"so I can take the link down and make changes on the remote end" it sounds like you expect the loopback interface to still be accessible when the link to the remote is down. The loopback will still have a status of up/up. But if the link to the router is taken down then neither the physical interface address nor the loopback address will be reachable.



Does the loopback address show up in the route table? If not you would be unable to access it.

Is the ip address in a subnet that exists somewhere? If so then the route would go to that router and not the one with the lookback.

I have always seen the loopback ip addresses with a subnet. That way you are not wasting 255 addresses for each loopback.


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