Using Loopback Addresses for GRE Tunnels

drewbert87

Hey Folks,

Can anyone explain why it's best practice to use a loopback interface for a GRE tunnel as opposed to just an IP address? Do the tunnels have to be tied to an interface or can you simply make up an address? Looking for some clarification on this.

Thank you!

fredrikjj

It allows the tunnel to be rerouted around a link failure.

PS.
Most basic case would be that you have two links between routers A and B. If you use the physical addresses of one of the links as source/destination of the tunnel, the tunnel would die if that link dies. You could instead use the loopback addresses of each router and, assuming that they are reachable via both links, the tunnel would survive one of the links going down.