Using the GRE to establish the TUNNEL between NE80E and NE40E during subcontactor engineers did PAT test. The GRE tunnel can not be established.
1.On NE80E/NE40E using the "disp interface tunnel " command to check the interface status.
2.On NE80E end, tunnel interface physical up ,but the link-protocol is down;On NE40E end, tunnel interface physcial up and link-protocol are up.
1.Using the disp command to check the tunnel interface status.tunnel interface line protocol is not up on one end .
2.Check the configuration on both end ,the parameters including the Tunnel protocol,GRE key.source ip ,destination ip. the confugration is ok.
3.Execute Ping test. the tunnel destination is unreachable from both ends.
4.Check the routing table, there is no tunnel destination route in the routing table.
5.Configing the static route or using routing protocol to import the route,Tunnel destination ip is reachable.
6.Check the status of tunnel interface, it is ok .GRE tunnel is established.
The reason cause the GRE tunnel can not be estabilished is that tunnel destination ip is unreachable.
The Network is reachable is pre-condition .Troubleshooting step must be familiar.