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When we dealing with bgp, osp. Why do we especially use loopback interfaces with / 32!? Is there an advantage or something different from other subnets like 24.

  • Loopback interfaces never go down from line errors, etc. If the router has multiple ways to get to it, the loopback interface is guaranteed to be up, unless you specifically disable it. It is often the case that you will configure a loopback as the IP address for routing protocols and other services because as long as the router has a working interface, the loopback is a constant address that you can use to reach the router. – Ron Maupin Dec 23 '19 at 6:31
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/32 is represent one single IP address or host address. If you use /32, It mean only one ip address available in that particular range.

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A loopback interface isn't connected to any other host, so using anything else for it than a /32 - single IP address - doesn't really make much sense.

Referring to a router using the loopback IP has the benefit of it always being up and never changing with interface states and configurations.

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    Not really true, there are times when you use loopback interfaces with proper network addresses in order to always make sure a route gets installed in the the FIB specifically when BGP is used as it requires the route to be in the FIB before it will get advertised, there are also other scenarios where it makes a lot of sense but thats just one example. – Matt Douhan Dec 23 '19 at 14:27

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