A GRE tunnel is much like other interfaces in terms of how you get traffic to go through them. There must be entries in the routing table which specify this interface as the exit point to reach the next hop address. These entries might be static routes as suggested in the previous responses or might be routes from a dynamic routing protocol. If you are running a dynamic routing protocol (RIP, OSPF, EIGRP) just make sure that there is a network entry in the routing protocol configuration that matches the IP or subnet of the GRE tunnel.

HTH

Rick

thanks for your answer.i know how to send traffic via static route.May i know how to do it via dynamic route

For dynamic routing, you treat the tunnel link much as you would as any other link.  However, what you have to be careful of, is recursive routing, which is where both the tunnel link and the underlying physical links are both in the same dynamic routing protocol.  Normally you would have static routes for the tunnel endpoints that have a better AD than the dynamic routing protocol.

Hi

For example 

R4

Router ospf 100
Network 10.1.1.2 0.0.0.0 area 0
net 4.4.4.4 0.0.0.0 area 0 

R6

Router ospf 100
Network 10.1.1.1 0.0.0.0 area 0
net 6.6.6.6 0.0.0.0 area 0

The tunnel IPs is added to the dynamic routing protocol and if you want to advertise the loopbacks it should be included as well.

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