rfc2427.txt

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   In the few cases when a protocol has an assigned NLPID (see Appendix
   A), 48 bits can be saved using the format below:

                   Format of Routed NLPID Protocol
                  +-------------------------------+
                  |         Q.922 Address         |
                  +---------------+---------------+
                  | Control  0x03 |     NLPID     |
                  +---------------+---------------+
                  |         Protocol Data         |
                  +-------------------------------+
                  |              FCS              |
                  +-------------------------------+



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RFC 2427             Multiprotocol over Frame Relay       September 1998


   When using the NLPID encapsulation format as described above, the pad
   octet is not used.

   In the case of ISO protocols, the NLPID is considered to be the first
   octet of the protocol data.  It is unnecessary to repeat the NLPID in
   this case.  The single octet serves both as the demultiplexing value
   and as part of the protocol data (refer to "Other Protocols over
   Frame Relay for more details). Other protocols, such as IP, have a
   NLPID defined (0xCC), but it is not part of the protocol itself.

                    Format of Routed IP Datagram
                  +-------------------------------+
                  |         Q.922 Address         |
                  +---------------+---------------+
                  | Control  0x03 |  NLPID  0xCC  |
                  +---------------+---------------+
                  |          IP Datagram          |
                  +-------------------------------+
                  |              FCS              |
                  +-------------------------------+

4.2.  Bridged Frames

   The second type of Frame Relay traffic is bridged packets. These
   packets are encapsulated using the NLPID value of 0x80 indicating
   SNAP.  As with other SNAP encapsulated protocols, there will be one
   pad octet to align the data portion of the encapsulated frame.  The
   SNAP header which follows the NLPID identifies the format of the
   bridged packet.  The OUI value used for this encapsulation is the
   802.1 organization code 0x00-80-C2.  The PID portion of the SNAP
   header (the two bytes immediately following the OUI) specifies the
   form of the MAC header, which immediately follows the SNAP header.
   Additionally, the PID indicates whether the original FCS is preserved
   within the bridged frame.

   Following the precedent in RFC 1638 [4], non-canonical MAC
   destination addresses are used for encapsulated IEEE 802.5 and FDDI
   frames, and canonical MAC destination addresses are used for the
   remaining encapsulations defined in this section.

   The 802.1 organization has reserved the following values to be used
   with Frame Relay:









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RFC 2427             Multiprotocol over Frame Relay       September 1998


           PID Values for OUI 0x00-80-C2

        with preserved FCS   w/o preserved FCS    Media
        ------------------   -----------------    ----------------
        0x00-01              0x00-07              802.3/Ethernet
        0x00-02              0x00-08              802.4
        0x00-03              0x00-09              802.5
        0x00-04              0x00-0A              FDDI
                             0x00-0B              802.6

      In addition, the PID value 0x00-0E, when used with OUI 0x00-80-C2,
      identifies Bridge Protocol Data Units (BPDUs) as defined by
      802.1(d) or 802.1(g) [12], and the PID value 0x00-0F identifies
      Source Routing BPDUs.

   A packet bridged over Frame Relay will, therefore, have one of the
   following formats:

                Format of Bridged Ethernet/802.3 Frame
                  +-------------------------------+
                  |         Q.922 Address         |
                  +---------------+---------------+
                  | Control  0x03 | pad     0x00  |
                  +---------------+---------------+
                  | NLPID    0x80 | OUI     0x00  |
                  +---------------+             --+
                  |        OUI     0x80-C2        |
                  +-------------------------------+
                  |    PID 0x00-01 or 0x00-07     |
                  +-------------------------------+
                  |    MAC destination address    |
                  :                               :
                  |                               |
                  +-------------------------------+
                  |   (remainder of MAC frame)    |
                  +-------------------------------+
                  |  LAN FCS (if PID is 0x00-01)  |
                  +-------------------------------+
                  |              FCS              |
                  +-------------------------------+











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RFC 2427             Multiprotocol over Frame Relay       September 1998


                    Format of Bridged 802.4 Frame
                  +-------------------------------+
                  |         Q.922 Address         |
                  +---------------+---------------+
                  | Control  0x03 | pad     0x00  |
                  +---------------+---------------+
                  | NLPID    0x80 | OUI     0x00  |
                  +---------------+             --+
                  |        OUI     0x80-C2        |
                  +-------------------------------+
                  |    PID 0x00-02 or 0x00-08     |
                  +---------------+---------------+
                  | pad      0x00 | Frame Control |
                  +---------------+---------------+
                  |    MAC destination address    |
                  :                               :
                  |                               |
                  +-------------------------------+
                  |   (remainder of MAC frame)    |
                  +-------------------------------+
                  |  LAN FCS (if PID is 0x00-02)  |
                  +-------------------------------+
                  |              FCS              |
                  +-------------------------------+



























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RFC 2427             Multiprotocol over Frame Relay       September 1998


                    Format of Bridged 802.5 Frame
                  +-------------------------------+
                  |         Q.922 Address         |
                  +---------------+---------------+
                  | Control  0x03 | pad     0x00  |
                  +---------------+---------------+
                  | NLPID    0x80 | OUI     0x00  |
                  +---------------+             --+
                  |        OUI     0x80-C2        |
                  +-------------------------------+
                  |    PID 0x00-03 or 0x00-09     |
                  +---------------+---------------+
                  | pad      0x00 | Frame Control |
                  +---------------+---------------+
                  |    MAC destination address    |
                  :                               :
                  |                               |
                  +-------------------------------+
                  |   (remainder of MAC frame)    |
                  +-------------------------------+
                  |  LAN FCS (if PID is 0x00-03)  |
                  |                               |
                  +-------------------------------+
                  |              FCS              |
                  +-------------------------------+


























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RFC 2427             Multiprotocol over Frame Relay       September 1998


                    Format of Bridged FDDI Frame
                  +-------------------------------+
                  |         Q.922 Address         |
                  +---------------+---------------+
                  | Control  0x03 | pad     0x00  |
                  +---------------+---------------+
                  | NLPID    0x80 | OUI     0x00  |
                  +---------------+             --+
                  |        OUI     0x80-C2        |
                  +-------------------------------+
                  |    PID 0x00-04 or 0x00-0A     |
                  +---------------+---------------+
                  | pad      0x00 | Frame Control |
                  +---------------+---------------+
                  |    MAC destination address    |
                  :                               :
                  |                               |
                  +-------------------------------+
                  |   (remainder of MAC frame)    |
                  +-------------------------------+
                  |  LAN FCS (if PID is 0x00-04)  |
                  |                               |
                  +-------------------------------+
                  |              FCS              |
                  +-------------------------------+


























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RFC 2427             Multiprotocol over Frame Relay       September 1998


                    Format of Bridged 802.6 Frame
                  +-------------------------------+
                  |        Q.922 Address          |
                  +---------------+---------------+
                  | Control  0x03 | pad     0x00  |
                  +---------------+---------------+
                  | NLPID    0x80 | OUI     0x00  |
                  +---------------+             --+
                  |        OUI     0x80-C2        |
                  +-------------------------------+
                  |        PID     0x00-0B        |
                  +---------------+---------------+ -------
                  |   Reserved    |     BEtag     |  Common
                  +---------------+---------------+  PDU
                  |            BAsize             |  Header
                  +-------------------------------+ -------
                  |    MAC destination address    |
                  :                               :