Tunnel spec
Describes the requirements for a tunnel and is defined as a set of parameters that are used in tunnel setup and selection process. The tunnel-spec is defined in the CLI or can be supplied through RADIUS.
Tunnel (instance)
A run-time object with a unique ID terminating at a specific peer. Any change in the tunnel spec after the tunnel has been created has no bearing on the tunnel itself. The list of tunnels can be obtained using the show router l2tp tunnel command.
Peer
A run-time object that is defined by an ip-address/port combination. Multiple tunnels can be terminated on the same peer. The list of peers can be obtained using the show router l2tp peer command.