RFC 2473 (rfc2473) - Page 7 of 36
Generic Packet Tunneling in IPv6 Specification
Alternative Format: Original Text Document
RFC 2473 Generic Packet Tunneling in IPv6 December 1998
Tunnel extension headers should appear in the order recommended by
the specifications that define the extension headers, such as [IPv6-
Spec].
A source of original packets and a tunnel entry-point that
encapsulates those packets can be the same node.
3.2 Packet Processing in Tunnels
The intermediate nodes in the tunnel process the IPv6 tunnel packets
according to the IPv6 protocol. For example, a tunnel Hop by Hop
Options extension header is processed by each receiving node in the
tunnel; a tunnel Routing extension header identifies the intermediate
processing nodes, and controls at a finer granularity the forwarding
path of the tunnel packet through the tunnel; a tunnel Destination
Options extension header is processed at the tunnel exit-point node.
3.3 IPv6 Decapsulation
Decapsulation is graphically shown in Fig.4:
+---------+- - - - - -+----------------------------------//-----+
| IPv6 | IPv6 | |
| | Extension | Original Packet |
| Header | Headers | |
+---------+- - - - - -+----------------------------------//-----+
< Tunnel IPv6 Packet >
|
v
+----------------------------------//-----+
| Original | |
| | Original Packet Payload |
| Headers | |
+----------------------------------//-----+
< Original Packet >
Fig.4 Decapsulating a Packet
Upon receiving an IPv6 packet destined to an IPv6 address of a tunnel
exit-point node, its IPv6 protocol layer processes the tunnel
headers. The strict left-to-right processing rules for extension
headers is applied. When processing is complete, control is handed to
the next protocol engine, which is identified by the Next Header
field value in the last header processed. If this is set to a tunnel
protocol value, the tunnel protocol engine discards the tunnel
headers and passes the resulting original packet to the Internet or
lower layer protocol identified by that value for further processing.
Conta & Deering Standards Track