I am issuing the command "cdp enable" on tunnel interface of routers. On some of the routers its accepting the command and I can see it in the "sh run" but on some of the routers its giving the error "% CDP is not supported on this interface, or for this encapsulation". I have checked the encapsulation on every gre tunnel interface and its "tunnel" no matter cdp can be enabled or no. Pls help me to know why am I getting this error. Thanks.