rfc2473.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   the tunnel header immediately preceding the original packet in the
   ICMP message payload.

   From here the processing depends on the protocol of the original
   packet:




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RFC 2473            Generic Packet Tunneling in IPv6       December 1998


        (a)  - for an IPv6 original packet

     Fig.7 path #3 and Fig.8 (c.1)- for an IPv6 original packet, the
     ICMPv6 error report builds an ICMP message of a type and code
     according to the "internal error code", containing the "original
     packet" as ICMP payload.

     Fig.7 path #4 and Fig.8 (d.1)- The ICMP message has the tunnel
     entry-point node address as source address, and the original packet
     source node address as destination address. The tunnel entry-point
     node sends the ICMP message to the source node of the original
     packet.

        (b)  - for an IPv4 original packet

     Fig.7 path #5 and Fig.8 (c.2) - for an IPv4 original packet, the
     ICMPv4 error report builds an ICMP message of a type and code
     derived from the the "internal error code", containing the
     "original packet" as ICMP payload.

     Fig.7 path #6 and Fig.8 (d.2) - The ICMP message has the tunnel
     entry-point node IPv4 address as source address, and the original
     packet IPv4 source node address as destination address. The tunnel
     entry-point node sends the ICMP message to the source node of the
     original packet.

   A graphical description of the header processing taking place is  the
   following:























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RFC 2473            Generic Packet Tunneling in IPv6       December 1998


    <                     Tunnel Packet                                >
   +--------+- - - - - -+--------+------------------------------//------+
   | IPv6   | IPv6      | ICMP   |             Tunnel                   |
(a)|        | Extension |        |             IPv6                     |
   | Header | Headers   | Header |             Packet in error          |
   +--------+- - - - - -+--------+------------------------------//------+
    < Tunnel Headers   > <       Tunnel ICMP Message                   >
                                  <         ICMPv6 Message Payload     >
                                 |
                                 v
        <                    Tunnel ICMP Message                   >
                        <       Tunnel IPv6 Packet in Error        >
       +--------+      +---------+      +----------+--------//------+
       | ICMP   |      | Tunnel  |      | Original | Original       |
(b)    |        |  +   | IPv6    |  +   |          | Packet         |
       | Header |      | Headers |      | Headers  | Payload        |
       +--------+      +---------+      +----------+--------//------+
           |                             <Original Packet in Error >
           -----------------              |
                           |              |
             --------------|---------------
             |             |
             V             V
       +---------+      +--------+      +-------------------//------+
       | New     |      | ICMP   |      |                           |
(c.1)  | IPv6    |  +   |        |  +   | Orig. Packet in Error     |
       | Headers |      | Header |      |                           |
       +---------+      +--------+      +-------------------//------+
                             |
                             v
                 +---------+--------+-------------------//------+
                 | New     | ICMP   |  Original                 |
(d.1)            | IPv6    |        |                           |
                 | Headers | Header |  Packet in Error          |
                 +---------+--------+-------------------//------+
                  <             New ICMP Message               >















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RFC 2473            Generic Packet Tunneling in IPv6       December 1998


                  or for an IPv4 original packet

       +---------+      +--------+      +-------------------//------+
       | New     |      | ICMP   |      |                           |
(c.2)  | IPv4    |  +   |        |  +   | Orig. Packet in Error     |
       | Header  |      | Header |      |                           |
       +---------+      +--------+      +-------------------//------+
                             |
                             v
                 +---------+--------+-------------------//------+
                 | New     | ICMP   |  Original                 |
(d.2)            | IPv4    |        |                           |
                 | Header  | Header |  Packet in Error          |
                 +---------+--------+-------------------//------+
                  <             New ICMP Message               >

                Fig.8 ICMP Error Reporting and Processing

8.1 Tunnel ICMP Messages

   The tunnel ICMP messages that are reported to the source of the
   original packet are:

        hop limit exceeded

             The tunnel has a misconfigured hop limit, or contains a
             routing loop, and packets do not reach the tunnel exit-
             point node. This problem is reported to the tunnel entry-
             point node, where the tunnel hop limit can be reconfigured
             to a higher value. The problem is further reported to the
             source of the original packet as described in section 8.2,
             or 8.3.

        unreachable node

             One of the nodes in the tunnel is not or is no longer
             reachable.  This problem is reported to the tunnel entry-
             point node, which should be reconfigured with a valid and
             active path between the entry and exit-point of the tunnel.

             The problem is further reported to the source of the
             original packet as described in section 8.2, or 8.3.

        parameter problem

             A Parameter Problem ICMP message pointing to a valid Tunnel
             Encapsulation Limit Destination header with a Tun Encap Lim
             field value set to one is an indication that the tunnel



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RFC 2473            Generic Packet Tunneling in IPv6       December 1998


             packet exceeded the maximum number of encapsulations
             allowed. The problem is further reported to the source of
             the original packet as described in section 8.2, or 8.3.

   The above three problems detected inside the tunnel, which are a
   tunnel configuration and a tunnel topology problem, are reported to
   the source of the original IPv6 packet, as a tunnel generic
   "unreachable" problem caused by a "link problem" - see section 8.2
   and 8.3.

        packet too big

             The tunnel packet exceeds the tunnel Path MTU.

             The information carried by this type of ICMP message is
             used as follows:

             - by a receiving tunnel entry-point node to set or adjust
             the tunnel MTU

             - by a sending tunnel entry-point node to indicate to the
             source of an original packet the MTU size that should be
             used in sending IPv6 packets towards the tunnel entry-point
             node.

8.2 ICMP Messages for IPv6 Original Packets

   The tunnel entry-point node builds the ICMP and IPv6 headers of the
   ICMP message that is sent to the source of the original packet as
   follows:

   IPv6 Fields:

   Source Address

                  A valid unicast IPv6 address of the outgoing
                  interface.

   Destination Address

                  Copied from the Source Address field of the Original
                  IPv6 header.

   ICMP Fields:

   For any of the following tunnel ICMP error messages:

     "hop limit exceeded"



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     "unreachable node"

     "parameter problem" - pointing to a valid Tunnel Encapsulation
     Limit destination header with the Tun Encap Lim field set to a
     value zero:

     Type           1 - unreachable node

     Code           3 - address unreachable

   For tunnel ICMP error message "packet too big":

     Type           2 - packet too big

     Code           0

     MTU            The MTU field from the tunnel ICMP message minus
                    the length of the tunnel headers.

   According to the general rules described in 7.1, an ICMP "packet too
   big" message is sent to the source of the original packet only if the
   original packet size is larger than the minimum link MTU size
   required for IPv6 [IPv6-Spec].

8.3 ICMP Messages for IPv4 Original Packets

   The tunnel entry-point node builds the ICMP and IPv4 header of the
   ICMP message that is sent to the source of the original packet as
   follows:

   IPv4 Fields:

   Source Address

                  A valid unicast IPv4 address of the outgoing
                  interface.

   Destination Address

                  Copied from the Source Address field of the Original
                  IPv4 header.

   ICMP Fields:

   For any of the following tunnel ICMP error messages:

     "hop limit exceeded"




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RFC 2473            Generic Packet Tunneling in IPv6       December 1998


     "unreachable node"

     "parameter problem" - pointing to a valid Tunnel Enacpsulation
     Limit destination header with the Tun Encap Lim field set to a
     value zero:

     Type           3 - destination unreachable

     Code           1 - host unreachable

   For a tunnel ICMP error message "packet too big":

     Type           3 - destination unreachable

     Code           4 - packet too big

     MTU            The MTU field from the tunnel ICMP message minus
                    the length of the tunnel headers.

   According to the general rules described in section 7.2, an ICMP
   "packet too big" message is sent to the original IPv4 packet source
   node if the the original IPv4 header has the DF - don't fragment -
   bit flag SET.

8.4 ICMP Messages for Nested Tunnel Packets

   In case of an error uncovered with a nested tunnel packet, the inner
   tunnel entry-point, which receives the ICMP error message from the
   inner tunnel reporting node, relays the ICMP message to the outer
   tunnel entry-point following the mechanisms described in sections
   8.,8.1, 8.2, and 8.3. Further, the outer tunnel entry-point relays
   the ICMP message to the source of the original packet, following the
   same mechanisms.

9. Security Considerations

   An IPv6 tunnel can be secured by securing the IPv6 path between the
   tunnel entry-point and exit-point node. The security architecture,
   mechanisms, and services are described in [RFC2401], [RFC2402], and
   [RFC24