Why Loopback an Interface?

What is the benefit of a loopback interface on a router?

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In article , AC writes

Is it so that a router has an IP address which will not change irrespective of which subnets its various interfaces are placed on from time to time?

I think there's more reasons too, but I'd have to check some notes for them.

Reply to
Andrew W Young

The main advantage is that it never goes down. Therefore it's very useful for management, router id's or such things like tunnel anchors.


Reply to
Buzz Lightbeer

As others have mentioned, it's useful in cases where you can't have an interface go down. OSPF, for example, behaves very badly when an interface fails and it has to choose a new router ID. The BGP process won't even start if you don't have a loopback interface configured that it can use as its router ID.

It also can allow you to avoid having multiple adjacencies, because a router can be reached by a number of paths. Without a loopback, you would have to form an adjacency between every single interface on every single router. With a loopback, you just make one adjacency, and it doesn't matter how traffic gets there, as long as it can.

Finally, it can allow you to do load-balancing on a protocol that doesn't support it, or without the additional configuration that usually goes along with it. For example, you have two redundant links between routers, and you're running BGP. BGP will not load-balance unless you create two adjacencies and use the maximum-paths option. Instead, you can create a single adjacency to the loopback, set two static routes to that loopback, one out each interface, and voila you have BGP load-balancing, with one less memory-hogging neighbor relationship to boot!

There's a bunch of other reas>What is the benefit of a loopback interface on a router?

Reply to
Deez Nutz

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