718 CHAPTER 49: T UNNELING CONFIGURATIONc CAUTION:■ If the addresses of the tunnel interfaces at the two ends of a tunnel are not inthe same subnet, a forwarding route through the tunnel to the peer must beconfigured so that the encapsulated packet can be forwarded normally. Youcan configure static or dynamic routes. For the detailed configuration, refer to“Static Routing and Dynamic Routing” on page 817.■ Two or more tunnel interfaces using the same encapsulation protocol musthave different source and destination addresses.■ If the tunnel interface is the source interface, the source address is the primaryIP address of the source interface.■ Before configuring dynamic routes, you must enable the dynamic routingprotocol on the tunnel interfaces at both ends of the tunnel. Such a route mustbe configured at both ends of the tunnel. For related configurations, refer torelated contents in “Static Routing and Dynamic Routing” on page 817.Configuration Example Network requirementsThe two subnets Group 1 and Group 2 running IPv4 are interconnected via an IPv4over IPv4 tunnel between Router A and Router B.Configure an IPv4 address forthe tunnel interfaceip address ip-address { mask |mask-length } [ sub ]RequiredBy default, no IPv4 address isconfigured for the tunnelinterface.Set the tunnel to an IPv4 overIPv4 tunneltunnel-protocol ipv4-ipv4 OptionalBy default, the tunnel is a GREtunnel. The same tunnel typeshould be configured at bothends of the tunnel. Otherwise,packet delivery will fail.Configure a source address orinterface for the tunnelsource { ip-address |interface-typeinterface-number }RequiredBy default, no source addressor interface is configured forthe tunnel.Configure a destinationaddress for the tunneldestination ip-address RequiredBy default, no destinationaddress is configured for thetunnel.Configure the MTU for thetunnel interfacemtu mtu-size OptionalThe default value varies withdevices.To do... Use the command... Remarks
