-/** \brief A GRE tunnel
- @param client_index - opaque cookie to identify the sender
- @param context - sender context, to match reply w/ request
- @param tunnel_type - 0: L3, 1: TEB, 2: ERSPAN
+/** \brief A composite type uniquely defining a GRE tunnel.
+ @param type - tunnel type (see enum definition), 0: L3, 1: TEB, 2: ERSPAN
+ @param mode - P2P or P2MP
+ @param flags - to control encap/decap behaviour
+ @param session_id - session for ERSPAN tunnel, range 0-1023