RFC 2473 (rfc2473) - Page 8 of 36

Generic Packet Tunneling in IPv6 Specification

RFC 2473            Generic Packet Tunneling in IPv6       December 1998


   For example, in the case the Next Header field has the IPv6 Tunnel
   Protocol value, the resulting original packet is passed to the IPv6
   protocol layer.

   The tunnel exit-point node, which decapsulates the tunnel packets,
   and the destination node, which receives the resulting original
   packets can be the same node.

3.4 IPv6 Tunnel Protocol Engine

   Packet flow (paths #1-7) through the IPv6 Tunnel Protocol Engine on a
   node is graphically shown in Fig.5:

   Note:

   In Fig.5, the Upper-Layer Protocols box represents transport
   protocols such as TCP, UDP, control protocols such as ICMP, routing
   protocols such as OSPF, and internet or lower-layer protocol being
   "tunneled" over IPv6, such as IPv4, IPX, etc.  The Link-Layer
   Protocols box represents Ethernet, Token Ring, FDDI, PPP, X.25, Frame
   Relay, ATM, etc..., as well as internet layer "tunnels" such as IPv4
   tunnels.

   The IPv6 tunnel protocol engine acts as both an "upper-layer" and a
   "link-layer", each with a specific input and output as follows:

   (u.i) "tunnel upper-layer input" - consists of  tunnel  IPv6  packets
         that are going to be decapsulated.  The tunnel packets are
         incoming through the IPv6 layer from:

         (u.i.1) a link-layer - (path #1, Fig.5)

                 These are tunnel packets destined to this node and will
                 undergo decapsulation.

         (u.i.2) a tunnel link-layer - (path #7, Fig.5)

                 These are tunnel packets that underwent one or more
                 decapsulations on this node, that is, the packets had
                 one or more nested tunnel headers and one nested tunnel
                 header was just discarded. This node is the exit-point
                 of both an outer tunnel and one or more of its inner
                 tunnels.

         For both above cases the resulting original packets are passed
         back to the IPv6 layer as "tunnel link-layer" output for
         further processing (see b.2).




Conta & Deering             Standards Track