For a GRE tunnel to be up between two routers, which of the following must be configured?
A.
Loopback Interface
B.
IP reachability between the loopback interfaces
C.
Dynamic Routing between routers.
D.
Tunnel interfaces must be in the same subnet.
Explanation:
GRE tunnels don’t require loopbacks. They work quite well using physical interfaces as
the source and destination. They also don’t require dynamic routing; static routes work just fine.
Place the IP addresses assigned to the tunnels in different subnets and there won’t be any
connectivity over the tunnels… that is unless you place static routes at both endpoints pointing to
the remote tunnel IP address via the tunnel. Host routes work just fine.