The tunnel mode determines the encapsulation capabilities of the tunnel. GRE mode provides for all four IPv4 and IPv6 encapsulation types. GRE mode is used when you do not want to limit the tunnel to a particular encapsulation type. There is also a tunnel mode specific to each of the four encapsulation types. Use a tunnel mode specific to an encapsulation type if you wish to limit the tunnel to that encapsulation type.
Use the tunnel mode command in tunnel configuration mode to configure the tunnel encapsulation type. The supported encapsulation types and their associated command keywords are: