I created a GRE tunnel in GNS3

The GRE tunnel, Tunnel1 is established between Router1 and Router3. A static route is used to reach nework 10.1.10.4/30 from Router1 and in the same way to reach 10.1.10.0/30 from Router3. Router2 may or may not be in the same management domain (ownershipwise) as Routers 1 and 3 but so long as it can forward the tunnel traffic as between its G0/0 and G0/, the tunnel should be okay.