rfc2590.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

         6  |                   "DLCI"                      |
            +                                               +
         7  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+

            Fig.1 Frame Relay Pseudo-Interface Identifier

   The Duplicate Address Detection specified in [AUTOCONF] is used
   repeatedly during the interface identifier and local-link address
   generation process, until the generated identifier and consequently
   the link-local address on the link -- VC -- are unique.

4.1  Generating the "Mid" field.

   The "Mid" can be generated in multiple ways. This specification
   suggests two mechanisms:

 (b.1)  "Use of Local Administrative Numbers"

        The "Mid" is filled with the result of merging:

   (b.1.1)  A random number of 6 bits in length (Fig.2).


   (b.1.2)  The Frame Relay Node Identifier -- 16 bits -- is a user
            administered value used to locally identify a Frame Relay
            node (Fig.2).

   (b.1.3)  The Frame Relay Link Identifier -- 16 bits -- is a numerical
            representation of the Frame Relay interface or link (Fig.2).







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RFC 2590             IPv6 over Frame Relay Networks             May 1999


             7     6     5     4     3     2     1     0  (bit order)
            +-----+-----+-----+-----+-----+-----+-----+-----+
(Octets) 0  |          Random Number            |    MBZ    |
            +-----------------------------------+-----+-----+
         1  |                                               |
            +          Frame Relay Node Identifier          +
         2  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+
         3  |                                               |
            +          Frame Relay Link Identifier          +
         4  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+
         5  |                                               |
            +                                               +
         6  |                    "DLCI"                     |
            +                                               +
         7  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+

            Fig.2  Frame Relay Pseudo-Interface Identifier

   or,

 (b.2)  "Use of The Frame Relay address - E.164 [E164], X.121
       [X25] numbers, or NSAP [NSAP] address"

       If a Frame Relay interface has an E.164 or a X.121 number, or an
       NSAP address, the "Mid" field MUST be filled in with a number
       resulted from it as follows:  the number represented by the BCD
       encoding of the E.164 or X.121 number, or the binary encoding of
       the NSAP address is truncated to 38 bits (Fig.3). Since the Frame
       Relay interface identifier has a "local" significance, the use of
       such a value has no real practical purposes other than adding to
       the uniqueness of the interface identifier on the link. Therefore
       the truncation can be performed on the high order or low order
       bits. If the high order bits truncation does not provide
       uniqueness on the link -- perhaps the DLCI value is not unique --
       this most likely means that the VC spans more for instance than a
       national and/or international destination area for an E.164
       number, and therefore the truncation of the low order bits should
       be performed next, which most likely will provide the desired
       uniqueness.









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RFC 2590             IPv6 over Frame Relay Networks             May 1999


             7     6     5     4     3     2     1     0     (bit order)
            +-----+-----+-----+-----+-----+-----+-----+-----+
(Octets) 0  |                                   |    MBZ    |
            +                                   +-----+-----+
         1  |                                               |
            +          E.164, X.121 (BCD encoding)          +
         2  |               or NSAP Address                 |
            +                                               +
         3  |            (truncated to 38 bits)             |
            +                                               +
         4  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+
         5  |                                               |
            +                                               +
         6  |                    "DLCI"                     |
            +                                               +
         7  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+

            Fig.3   Frame Relay (Pseudo) Interface Identifier

5. Link-Local Addresses

   The IPv6 link-local address [AARCH] for an IPv6 Frame Relay interface
   is formed by appending the interface identifier, formed as defined
   above, to the prefix FE80::/64 [AARCH].

       10 bits            54 bits                  64 bits
     +----------+-----------------------+----------------------------+
     |1111111010|         (zeros)       |Frame Relay Interface Ident.|
     +----------+-----------------------+----------------------------+

6. Address Mapping -- Unicast, Multicast

   The procedure for mapping IPv6 addresses to link-layer addresses is
   described in [IPv6-ND]. Additionally, extensions to Neighbor
   Discovery (ND) that allow the mapping of link-layer addresses to IPv6
   addresses are defined as Inverse Neighbor Discovery (IND) in [IND].
   This document defines the formats of the link-layer address fields
   used by ND and IND. This specification does not define an algorithmic
   mapping of IPv6 multicast addresses to Frame Relay link-layer
   addresses.

   The Source/Target Link-layer Address option used in Neighbor
   Discovery and Inverse Neighbor Discovery messages for a Frame Relay
   link follows the general rules defined by [IPv6-ND]. IPv6 addresses
   can map two type of identifiers equivalent to link-layer addresses:




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RFC 2590             IPv6 over Frame Relay Networks             May 1999


   DLCIs, and Frame Relay Addresses.  Therefore, for Frame Relay, this
   document defines two distinct formats for the ND and IND messages
   Link-Layer Address field:

   (a)  DLCI Format -- used in ND and/or IND messages on VCs that were
        established prior to the ND or IND message exchange --  mostly
        PVCs. The use on SVCs makes sense with Inverse Neighbor
        Discovery [IND] messages if IND is employed after the successful
        establishing of an SVC to gather information about other IPv6
        addresses assigned to the remote node and that SVC.

   (b)  Frame Relay Address Format -- used mostly prior to establishing
        a new SVC, to get the  Frame Relay remote node identifier
        (link-layer address) mapping to a certain IPv6 address.

        Note: An implementation may hold both types of link layer
        identifiers in the Neighbor Discovery cache. Additionally, in
        case of multiple VCs between two nodes, one node's Neighbor
        Discovery cache may hold a mapping of one of the remote node's
        IPv6 addresses to each and every DLCI identifying the VCs.

        The mechanisms which in such an implementation would make the
        distinction between the Neighbor Discovery Cache mapping of an
        IPv6 address to a "Frame Relay Address Format" and a "DLCI
        Format" link-layer address, or among several mappings to a "DLCI
        Format" addresses are beyond the scope of this specification.

        The use of the override "O" bit in the advertisement messages
        that contain the above Link-Layer Address formats SHOULD be
        consistent with the [ND] specifications. Additionally, there
        should be consistency related to the type of Link-Layer Address
        format: an implementation should override one address format in
        its Neighbor Discovery cache with the same type of address
        format.

   The "DLCI Format" is defined as follows:

              7     6     5     4     3     2     1     0    (bit order)
             +-----+-----+-----+-----+-----+-----+-----+-----+
          0  |                      Type                     |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          1  |                     Length                    |
             +-----+-----+-----+-----+-----+-----+-----+-----+








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RFC 2590             IPv6 over Frame Relay Networks             May 1999


   with a DLCI (Q.922 address) encoded as option value:

              7     6     5     4     3     2     1     0    (bit order)
             +-----+-----+-----+-----+-----+-----+-----+-----+
          2  |                                   |  1  |  1  |
             +              unused               +-----+-----+
          3  |                                               |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          4  |            DLCI(high order)       |  0  |  0  |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          5  |  DLCI(low order)      |  0  |  0  |  0  |  1  |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          6  |                                               |
             +                   Padding                     +
          7  |                   (zeros)                     |
             +-----+-----+-----+-----+-----+-----+-----+-----+

                 10 bits DLCI

              7     6     5     4     3     2     1     0    (bit order)
             +-----+-----+-----+-----+-----+-----+-----+-----+
          2  |                                   |  1  |  1  |
             +              unused               +-----+-----+
          3  |                                               |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          4  |            DLCI(high order)       |  0  |  0  |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          5  |  DLCI                 |  0  |  0  |  0  |  0  |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          6  |             DLCI(low order)             |  0  |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          7  |       unused (set to 0)           |  1  |  1  |
             +-----+-----+-----+-----+-----+-----+-----+-----+

                 17 bits DLCI
















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RFC 2590             IPv6 over Frame Relay Networks             May 1999


              7     6     5     4     3     2     1     0    (bit order)
             +-----+-----+-----+-----+-----+-----+-----+-----+
          2  |                                   |  1  |  1  |
             +              unused               +-----+-----+
          3  |                                               |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          4  |            DLCI(high order)       |  0  |  0  |
             +-----+-----+-----+-----+-----+-----+-----+-----
          5  |  DLCI                 |  0  |  0  |  0  |  0  |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          6  |             DLCI                        |  0  |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          7  |       DLCI (low order)            |  0  |  1  |
             +-----+-----+-----+-----+-----+-----+-----+-----+

                 23 bits DLCI


     Option fields:

        Type        1 for Source Link-layer address.
                    2 for Target Link-layer address.

        Length      The Length of the Option (including the Type
                    and Length fields) in units of 8 octets.
                    It has the value 1.

        Link-Layer Address        The DLCI encoded as a Q.922 address.

      Description

        The "DLCI Format" option value field has two components:


        (a)  Address Type -- encoded in the first two bits of the first
             two octets. Both bits are set to 1 to indicate the DLCI
             format. The rest of the bits in the two first octets are
             not used -- they MUST be set to zero on transmit and MUST
             be ignored by the receiver.

        (b)  DLCI -- encoded as a Q.922 address padded with zeros to the
             last octet of the 6 octets available for the entire Link-
             Layer Address field of this format.








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RFC 2590             IPv6 over Frame Relay Networks             May 1999


   The "Frame Relay Address Format" is defined as follows:

              7     6     5     4     3     2     1     0    (bit order)
             +-----+-----+-----+-----+-----+-----+-----+-----+
          0  |                      Type                     |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          1  |                     Length                    |
             +-----+-----+-----+-----+-----+-----+-----+-----+

   with an E.164, X.121, number or NSAP  address encoded as option
   value:

              7     6     5     4     3     2     1     0    (bit order)
             +-----+-----+-----+-----+-----+-----+-----+-----+
          2  |             size                  |  1  |  0  |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          3  |            E.164 or X.121, or NSAP            |
             +---          Address Family Number          ---+
          4  |               (Assigned Number)               |
             +-----+-----+-----+-----+-----+-----+-----+-----+
          5  |                                               |
             /       E.164, or X.121 number (BCD encoded)    /
             /               or  NSAP address                /
      4+size |                                               |
             +-----+-----+-----+-----+-----+-----+-----+-----+
      5+size |                                               |
             /                    Padding                    /
             /                    (zeros)                    /
   8*Length-1|                                               |
             +-----+-----+-----+-----+-----+-----+-----+-----+


      Option fields: