loopback interface

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Dec 23rd, 2005
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Can anyone tell me why use loopback interfaces for routing protocols, I cant see why we would need to set one up ? I have set one up on my routers and for a test I removed the ip address from the ethernet interface to see if I could still see the loopback interface from another router , this did not work ?

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mheusinger Fri, 12/23/2005 - 06:20
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a loopback IP is more stable. This is however only true when you have more than one link to the router.

Infact it depends on the routing protocol. In OSPF f.e. you could set the router ID to any value (f.e. and have no negative side effects.

The advantage of a loopback in this case would be to have the router ID set to an IP which you can telnet to as long as the router is reachable through any interface. It simplifies thins when troubleshooting.

In BGP the IP is used to setup a TCP session. And you do not want to loose BGP in case an interface goes down. So use a loopback for stability reasons.

Hope this helps



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