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Network Working Group C. Brown Request for Comments: 2427 Consultant STD: 55 A. Malis Obsoletes: 1490, 1294 Ascend Communications, Inc. Category: Standards Track September 1998

            Multiprotocol Interconnect over Frame Relay

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

 This memo describes an encapsulation method for carrying network
 interconnect traffic over a Frame Relay backbone.  It covers aspects
 of both Bridging and Routing.
 Systems with the ability to transfer both the encapsulation method
 described in this document, and others must have a priori knowledge
 of which virtual circuits will carry which encapsulation method and
 this encapsulation must only be used over virtual circuits that have
 been explicitly configured for its use.

Acknowledgments

 This document could not have been completed without the support of
 Terry Bradley of Avici Systems, Inc..  Comments and contributions
 from many sources, especially those from Ray Samora of Proteon, Ken
 Rehbehn of Visual Networks, Fred Baker and Charles Carvalho of Cisco
 Systems, and Mostafa Sherif of AT&T have been incorporated into this
 document. Special thanks to Dory Leifer of University of Michigan for
 his contributions to the resolution of fragmentation issues (though
 it was deleted in the final version) and Floyd Backes and Laura
 Bridge of 3Com for their contributions to the bridging descriptions.
 This document could not have been completed without the expertise of
 the IP over Large Public Data Networks and the IP over NBMA working
 groups of the IETF.

Brown & Malis Standards Track [Page 1] RFC 2427 Multiprotocol over Frame Relay September 1998

1. Conventions and Acronyms

 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
 document, are to be interpreted as described in [16].
 All drawings in this document are drawn with the left-most bit as the
 high order bit for transmission.  For example, the drawings might be
 labeled as:
            0   1   2   3   4   5   6   7 bits
            +---+---+---+---+---+---+---+
            +---------------------------+
            |    flag (7E hexadecimal)  |
            +---------------------------+
            |       Q.922 Address*      |
            +--                       --+
            |                           |
            +---------------------------+
            :                           :
            :                           :
            +---------------------------+
 Drawings that would be too large to fit onto one page if each octet
 were presented on a single line are drawn with two octets per line.
 These are also drawn with the left-most bit as the high order bit for
 transmission.  There will be a "+" to distinguish between octets as
 in the following example.
      |---   octet one     ---|---   octet two  ---|
      0  1  2  3  4  5  6  7  0  1  2  3  4  5  6  7
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      +--------------------------------------------+
      | Organizationally Unique                    |
      +--                     +--------------------+
      | Identifier            | Protocol           |
      +-----------------------+--------------------+
      | Identifier            |
      +-----------------------+
 The following are common acronyms used throughout this document.
    BECN - Backward Explicit Congestion Notification
    BPDU - Bridge Protocol Data Unit
    C/R  - Command/Response bit
    DCE  - Data Communication Equipment

Brown & Malis Standards Track [Page 2] RFC 2427 Multiprotocol over Frame Relay September 1998

    DE   - Discard Eligibility bit
    DTE  - Data Terminal Equipment
    FECN - Forward Explicit Congestion Notification
    PDU  - Protocol Data Unit
    PTT  - Postal Telephone & Telegraph
    SNAP - Subnetwork Access Protocol

2. Introduction

 The following discussion applies to those devices which serve as end
 stations (DTEs) on a public or private Frame Relay network (for
 example, provided by a common carrier or PTT.  It will not discuss
 the behavior of those stations that are considered a part of the
 Frame Relay network (DCEs) other than to explain situations in which
 the DTE must react.
 The Frame Relay network provides a number of virtual circuits that
 form the basis for connections between stations attached to the same
 Frame Relay network.  The resulting set of interconnected devices
 forms a private Frame Relay group which may be either fully
 interconnected with a complete "mesh" of virtual circuits, or only
 partially interconnected.  In either case, each virtual circuit is
 uniquely identified at each Frame Relay interface by a Data Link
 Connection Identifier (DLCI).  In most circumstances, DLCIs have
 strictly local significance at each Frame Relay interface.
 The specifications in this document are intended to apply to both
 switched and permanent virtual circuits.

3. Frame Format

 All protocols must encapsulate their packets within a Q.922 Annex A
 frame [1].  Additionally, frames shall contain information necessary
 to identify the protocol carried within the protocol data unit (PDU),
 thus allowing the receiver to properly process the incoming packet.
 The format shall be as follows:

Brown & Malis Standards Track [Page 3] RFC 2427 Multiprotocol over Frame Relay September 1998

                +---------------------------+
                |    flag (7E hexadecimal)  |
                +---------------------------+
                |       Q.922 Address*      |
                +--                       --+
                |                           |
                +---------------------------+
                |    Control (UI = 0x03)    |
                +---------------------------+
                | Pad (when required) (0x00)|
                +---------------------------+
                |           NLPID           |
                +---------------------------+
                |             .             |
                |             .             |
                |             .             |
                |           Data            |
                |             .             |
                |             .             |
                +---------------------------+
                |   Frame Check Sequence    |
                +--           .           --+
                |       (two octets)        |
                +---------------------------+
                |   flag (7E hexadecimal)   |
                +---------------------------+
  • Q.922 addresses, as presently defined, are two octets and

contain a 10-bit DLCI. In some networks Q.922 addresses

           may optionally be increased to three or four octets.
 The control field is the Q.922 control field.  The UI (0x03) value is
 used unless it is negotiated otherwise.  The use of XID (0xAF or
 0xBF) is permitted and is discussed later.
 The pad field is used to align the data portion (beyond the
 encapsulation header) of the frame to a two octet boundary.  If
 present, the pad is a single octet and must have a value of zero.
 Explicit directions of when to use the pad field are discussed later
 in this document.
 The Network Level Protocol ID (NLPID) field is administered by ISO
 and the ITU.  It contains values for many different protocols
 including IP, CLNP, and IEEE Subnetwork Access Protocol (SNAP)[10].
 This field tells the receiver what encapsulation or what protocol
 follows.  Values for this field are defined in ISO/IEC TR 9577 [3]. A
 NLPID value of 0x00 is defined within ISO/IEC TR 9577 as the Null
 Network Layer or Inactive Set.  Since it cannot be distinguished from

Brown & Malis Standards Track [Page 4] RFC 2427 Multiprotocol over Frame Relay September 1998

 a pad field, and because it has no significance within the context of
 this encapsulation scheme, a NLPID value of 0x00 is invalid under the
 Frame Relay encapsulation. Appendix A contains a list of some of the
 more commonly used NLPID values.
 There is no commonly implemented minimum maximum frame size for Frame
 Relay.  A network must, however, support at least a 262 octet
 maximum.  Generally, the maximum will be greater than or equal to
 1600 octets, but each Frame Relay provider will specify an
 appropriate value for its network.  A Frame Relay DTE, therefore,
 must allow the maximum acceptable frame size to be configurable.
 The minimum frame size allowed for Frame Relay is five octets between
 the opening and closing flags assuming a two octet Q.922 address
 field.  This minimum increases to six octets for three octet Q.922
 address and seven octets for the four octet Q.922 address format.

4. Interconnect Issues

 There are two basic types of data packets that travel within the
 Frame Relay network: routed packets and bridged packets.  These
 packets have distinct formats and therefore, must contain an
 indicator that the destination may use to correctly interpret the
 contents of the frame.  This indicator is embedded within the NLPID
 and SNAP header information.
 For those protocols that do not have a NLPID already assigned, it is
 necessary to provide a mechanism to allow easy protocol
 identification.  There is a NLPID value defined indicating the
 presence of a SNAP header.
 A SNAP header is of the form:
          +--------------------------------------------+
          | Organizationally Unique                    |
          +--                     +--------------------+
          | Identifier            | Protocol           |
          +-----------------------+--------------------+
          | Identifier            |
          +-----------------------+
 The three-octet Organizationally Unique Identifier (OUI) identifies
 an organization which administers the meaning of the Protocol
 Identifier (PID) which follows.  Together they identify a distinct
 protocol.  Note that OUI 0x00-00-00 specifies that the following PID
 is an Ethertype.

Brown & Malis Standards Track [Page 5] RFC 2427 Multiprotocol over Frame Relay September 1998

4.1. Routed Frames

 Some protocols will have an assigned NLPID, but because the NLPID
 numbering space is limited, not all protocols have specific NLPID
 values assigned to them. When packets of such protocols are routed
 over Frame Relay networks, they are sent using the NLPID 0x80 (which
 indicates the presence of a SNAP header) followed by SNAP.  If the
 protocol has an Ethertype assigned, the OUI is 0x00-00-00 (which
 indicates an Ethertype follows), and PID is the Ethertype of the
 protocol in use.
 When a SNAP header is present as described above, a one octet pad is
 used to align the protocol data on a two octet boundary as shown
 below.
                     Format of Routed Frames
                       with a SNAP Header
                +-------------------------------+
                |         Q.922 Address         |
                +---------------+---------------+
                | Control  0x03 | pad     0x00  |
                +---------------+---------------+
                | NLPID    0x80 | Organization- |
                +---------------+               |
                | ally Unique Identifier (OUI)  |
                +-------------------------------+
                |   Protocol Identifier (PID)   |
                +-------------------------------+
                |                               |
                |         Protocol Data         |
                |                               |
                +-------------------------------+
                |              FCS              |
                +-------------------------------+
 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              |
                +-------------------------------+

Brown & Malis Standards Track [Page 6] 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:

Brown & Malis Standards Track [Page 7] 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              |
                +-------------------------------+

Brown & Malis Standards Track [Page 8] 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              |
                +-------------------------------+

Brown & Malis Standards Track [Page 9] 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              |
                +-------------------------------+

Brown & Malis Standards Track [Page 10] 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              |
                +-------------------------------+

Brown & Malis Standards Track [Page 11] 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    |
                :                               :
                |                               |
                +-------------------------------+
                |   (remainder of MAC frame)    |
                +-------------------------------+
                |                               |
                +-     Common PDU Trailer      -+
                |                               |
                +-------------------------------+
                |              FCS              |
                +-------------------------------+
 Note that in bridge 802.6 PDUs, there is only one choice for the PID
 value, since the presence of a CRC-32 is indicated by the CIB bit in
 the header of the MAC frame.
 The Common Protocol Data Unit (CPDU) Header and Trailer are conveyed
 to allow pipelining at the egress bridge to an 802.6 subnetwork.
 Specifically, the CPDU Header contains the BAsize field, which
 contains the length of the PDU.  If this field is not available to
 the egress 802.6 bridge, then that bridge cannot begin to transmit
 the segmented PDU until it has received the entire PDU, calculated
 the length, and inserted the length into the BAsize field.  If the
 field is available, the egress 802.6 bridge can extract the length
 from the BAsize field of the Common PDU Header, insert it into the
 corresponding field of the first segment, and immediately transmit
 the segment onto the 802.6 subnetwork.  Thus, the bridge can begin
 transmitting the 802.6 PDU before it has received the complete PDU.

Brown & Malis Standards Track [Page 12] RFC 2427 Multiprotocol over Frame Relay September 1998

 One should note that the Common PDU Header and Trailer of the
 encapsulated frame should not be simply copied to the outgoing 802.6
 subnetwork because the encapsulated BEtag value may conflict with the
 previous BEtag value transmitted by that bridge.
                       Format of BPDU Frame
                +-------------------------------+
                |         Q.922 Address         |
                +-------------------------------+
                |        Control   0x03         |
                +-------------------------------+
                |          PAD     0x00         |
                +-------------------------------+
                |         NLPID    0x80         |
                +-------------------------------+
                |        OUI 0x00-80-C2         |
                +-------------------------------+
                |          PID 0x00-0E          |
                +-------------------------------+
                |                               |
                |       BPDU as defined by      |
                |     802.1(d) or 802.1(g)[12]  |
                |                               |
                +-------------------------------+
                |              FCS              |
                +-------------------------------+
               Format of Source Routing BPDU Frame
                +-------------------------------+
                |         Q.922 Address         |
                +-------------------------------+
                |        Control   0x03         |
                +-------------------------------+
                |          PAD     0x00         |
                +-------------------------------+
                |         NLPID    0x80         |
                +-------------------------------+
                |        OUI 0x00-80-C2         |
                +-------------------------------+
                |          PID 0x00-0F          |
                +-------------------------------+
                |                               |
                |      Source Routing BPDU      |
                |                               |
                |                               |
                +-------------------------------+
                |              FCS              |
                +-------------------------------+

Brown & Malis Standards Track [Page 13] RFC 2427 Multiprotocol over Frame Relay September 1998

5. Data Link Layer Parameter Negotiation

 Frame Relay stations may choose to support the Exchange
 Identification (XID) specified in Appendix III of Q.922 [1].  This
 XID exchange allows the following parameters to be negotiated at the
 initialization of a Frame Relay circuit: maximum frame size N201,
 retransmission timer T200, and the maximum number of outstanding
 Information (I) frames K.
 A station may indicate its unwillingness to support acknowledged mode
 multiple frame operation by specifying a value of zero for the
 maximum window size, K.
 If this exchange is not used, these values must be statically
 configured by mutual agreement of Data Link Connection (DLC)
 endpoints, or must be defaulted to the values specified in Section
 5.9 of Q.922:
                   N201: 260 octets
                      K:  3 for a 16 Kbps link,
                          7 for a 64 Kbps link,
                         32 for a 384 Kbps link,
                         40 for a 1.536 Mbps or above link
                  T200: 1.5 seconds [see Q.922 for further details]
 If a station supporting XID receives an XID frame, it shall respond
 with an XID response.  In processing an XID, if the remote maximum
 frame size is smaller than the local maximum, the local system shall
 reduce the maximum size it uses over this DLC to the remotely
 specified value.  Note that this shall be done before generating a
 response XID.
 The following diagram describes the use of XID to specify non-use of
 acknowledged mode multiple frame operation.

Brown & Malis Standards Track [Page 14] RFC 2427 Multiprotocol over Frame Relay September 1998

             Non-use of Acknowledged Mode Multiple Frame Operation
                    +---------------+
                    |    Address    |     (2,3 or 4 octets)
                    |               |
                    +---------------+
                    | Control 0xAF  |
                    +---------------+
                    | format  0x82  |
                    +---------------+
                    | Group ID 0x80 |
                    +---------------+
                    | Group Length  |     (2 octets)
                    |    0x00-0E    |
                    +---------------+
                    |      0x05     |     PI = Frame Size (transmit)
                    +---------------+
                    |      0x02     |     PL = 2
                    +---------------+
                    |    Maximum    |     (2 octets)
                    |   Frame Size  |
                    +---------------+
                    |      0x06     |     PI = Frame Size (receive)
                    +---------------+
                    |      0x02     |     PL = 2
                    +---------------+
                    |    Maximum    |     (2 octets)
                    |   Frame Size  |
                    +---------------+
                    |      0x07     |     PI = Window Size
                    +---------------+
                    |      0x01     |     PL = 1
                    +---------------+
                    |      0x00     |
                    +---------------+
                    |      0x09     |     PI = Retransmission Timer
                    +---------------+
                    |      0x01     |     PL = 1
                    +---------------+
                    |      0x00     |
                    +---------------+
                    |      FCS      |     (2 octets)
                    |               |
                    +---------------+

6. Address Resolution for PVCs

 This document only describes address resolution as it applies to
 PVCs.  SVC operation will be discussed in future documents.

Brown & Malis Standards Track [Page 15] RFC 2427 Multiprotocol over Frame Relay September 1998

 There are situations in which a Frame Relay station may wish to
 dynamically resolve a protocol address over PVCs.  This may be
 accomplished using the standard Address Resolution Protocol (ARP) [6]
 encapsulated within a SNAP encoded Frame Relay packet as follows:
         +-----------------------+-----------------------+
         |                 Q.922 Address                 |
         +-----------------------+-----------------------+
         | Control (UI)  0x03    |     pad     0x00      |
         +-----------------------+-----------------------+
         |    NLPID    0x80      |                       |  SNAP Header
         +-----------------------+  OUI   0x00-00-00     +  Indicating
         |                                               |  ARP
         +-----------------------+-----------------------+
         |                  PID   0x0806                 |
         +-----------------------+-----------------------+
         |                   ARP packet                  |
         |                       .                       |
         |                       .                       |
         |                       .                       |
         +-----------------------+-----------------------+
   Where the ARP packet has the following format and values:
       Data:
         ar$hrd   16 bits     Hardware type
         ar$pro   16 bits     Protocol type
         ar$hln    8 bits     Octet length of hardware address (n)
         ar$pln    8 bits     Octet length of protocol address (m)
         ar$op    16 bits     Operation code (request or reply)
         ar$sha   noctets     source hardware address
         ar$spa   moctets     source protocol address
         ar$tha   noctets     target hardware address
         ar$tpa   moctets     target protocol address
         ar$hrd - assigned to Frame Relay is 15 decimal
                   (0x000F) [7].
         ar$pro - see assigned numbers for protocol ID number for
                  the protocol using ARP. (IP is 0x0800).
         ar$hln - length in bytes of the address field (2, 3, or 4)
         ar$pln - protocol address length is dependent on the
                  protocol (ar$pro) (for IP ar$pln is 4).

Brown & Malis Standards Track [Page 16] RFC 2427 Multiprotocol over Frame Relay September 1998

         ar$op -  1 for request and 2 for reply.
         ar$sha - Q.922 source hardware address, with C/R, FECN,
                  BECN, and DE set to zero.
         ar$tha - Q.922 target hardware address, with C/R, FECN,
                  BECN, and DE set to zero.
 Because DLCIs within most Frame Relay networks have only local
 significance, an end station will not have a specific DLCI assigned
 to itself.  Therefore, such a station does not have an address to put
 into the ARP request or reply.  Fortunately, the Frame Relay network
 does provide a method for obtaining the correct DLCIs. The solution
 proposed for the locally addressed Frame Relay network below will
 work equally well for a network where DLCIs have global significance.
 The DLCI carried within the Frame Relay header is modified as it
 traverses the network.  When the packet arrives at its destination,
 the DLCI has been set to the value that, from the standpoint of the
 receiving station, corresponds to the sending station.  For example,
 in figure 1 below, if station A were to send a message to station B,
 it would place DLCI 50 in the Frame Relay header.  When station B
 received this message, however, the DLCI would have been modified by
 the network and would appear to B as DLCI 70.
                            ~~~~~~~~~~~~~~~
                           (                )
         +-----+          (                  )             +-----+
         |     |-50------(--------------------)---------70-|     |
         |  A  |        (                      )           |  B  |
         |     |-60-----(---------+            )           |     |
         +-----+         (        |           )            +-----+
                          (       |          )
                           (      |         )  <---Frame Relay
                            ~~~~~~~~~~~~~~~~         network
                                  80
                                  |
                               +-----+
                               |     |
                               |  C  |
                               |     |
                               +-----+
                               Figure 1
    Lines between stations represent data link connections (DLCs).
    The numbers indicate the local DLCI associated with each
    connection.

Brown & Malis Standards Track [Page 17] RFC 2427 Multiprotocol over Frame Relay September 1998

            DLCI to Q.922 Address Table for Figure 1
            DLCI (decimal)  Q.922 address (hex)
                 50              0x0C21
                 60              0x0CC1
                 70              0x1061
                 80              0x1401
    For authoritative description of the correlation between DLCI and
    Q.922 [1] addresses, the reader should consult that specification.
    A summary of the correlation is included here for convenience. The
    translation between DLCI and Q.922 address is based on a two byte
    address length using the Q.922 encoding format.  The format is:
              8   7   6   5   4   3    2   1
            +------------------------+---+--+
            |  DLCI (high order)     |C/R|EA|
            +--------------+----+----+---+--+
            | DLCI (lower) |FECN|BECN|DE |EA|
            +--------------+----+----+---+--+
    For ARP and its variants, the FECN, BECN, C/R and DE bits are
    assumed to be 0.
 When an ARP message reaches a destination, all hardware addresses
 will be invalid.  The address found in the frame header will,
 however, be correct. Though it does violate the purity of layering,
 Frame Relay may use the address in the header as the sender hardware
 address.  It should also be noted that the target hardware address,
 in both ARP request and reply, will also be invalid.  This should not
 cause problems since ARP does not rely on these fields and in fact,
 an implementation may zero fill or ignore the target hardware address
 field entirely.
 As an example of how this address replacement scheme may work, refer
 to figure 1.  If station A (protocol address pA) wished to resolve
 the address of station B (protocol address pB), it would format an
 ARP request with the following values:
            ARP request from A
              ar$op     1 (request)
              ar$sha    unknown
              ar$spa    pA
              ar$tha    undefined
              ar$tpa    pB

Brown & Malis Standards Track [Page 18] RFC 2427 Multiprotocol over Frame Relay September 1998

 Because station A will not have a source address associated with it,
 the source hardware address field is not valid.  Therefore, when the
 ARP packet is received, it must extract the correct address from the
 Frame Relay header and place it in the source hardware address field.
 This way, the ARP request from A will become:
            ARP request from A as modified by B
              ar$op     1 (request)
              ar$sha    0x1061 (DLCI 70) from Frame Relay header
              ar$spa    pA
              ar$tha    undefined
              ar$tpa    pB
 Station B's ARP will then be able to store station A's protocol
 address and Q.922 address association correctly.  Next, station B
 will form a reply message.  Many implementations simply place the
 source addresses from the ARP request into the target addresses and
 then fills in the source addresses with its addresses.  In this case,
 the ARP response would be:
            ARP response from B
              ar$op     2 (response)
              ar$sha    unknown
              ar$spa    pB
              ar$tha    0x1061 (DLCI 70)
              ar$tpa    pA
 Again, the source hardware address is unknown and when the response
 is received, station A will extract the address from the Frame Relay
 header and place it in the source hardware address field.  Therefore,
 the response will become:
            ARP response from B as modified by A
              ar$op     2 (response)
              ar$sha    0x0C21 (DLCI 50)
              ar$spa    pB
              ar$tha    0x1061 (DLCI 70)
              ar$tpa    pA
 Station A will now correctly recognize station B having protocol
 address pB associated with Q.922 address 0x0C21 (DLCI 50).
 Reverse ARP (RARP) [8] works in exactly the same way.  Still using
 figure 1, if we assume station C is an address server, the following
 RARP exchanges will occur:

Brown & Malis Standards Track [Page 19] RFC 2427 Multiprotocol over Frame Relay September 1998

        RARP request from A             RARP request as modified by C
           ar$op  3 (RARP request)         ar$op  3  (RARP request)
           ar$sha unknown                  ar$sha 0x1401 (DLCI 80)
           ar$spa undefined                ar$spa undefined
           ar$tha 0x0CC1 (DLCI 60)         ar$tha 0x0CC1 (DLCI 60)
           ar$tpa pC                       ar$tpa pC
 Station C will then look up the protocol address corresponding to
 Q.922 address 0x1401 (DLCI 80) and send the RARP response.
       RARP response from C            RARP response as modified by A
               ar$op  4  (RARP response)       ar$op  4 (RARP response)
               ar$sha unknown                  ar$sha 0x0CC1 (DLCI 60)
               ar$spa pC                       ar$spa pC
               ar$tha 0x1401 (DLCI 80)         ar$tha 0x1401 (DLCI 80)
               ar$tpa pA                       ar$tpa pA
 This means that the Frame Relay interface must only intervene in the
 processing of incoming packets.
 In the absence of suitable multicast, ARP may still be implemented.
 To do this, the end station simply sends a copy of the ARP request
 through each relevant DLC, thereby simulating a broadcast.
 The use of multicast addresses in a Frame Relay environment, as
 specified by [19], is presently being considered by Frame Relay
 providers.  In time, multicast addressing may become useful in
 sending ARP requests and other "broadcast" messages.
 Because of the inefficiencies of emulating broadcasting in a Frame
 Relay environment, a new address resolution variation was developed.
 It is called Inverse ARP [11] and describes a method for resolving a
 protocol address when the hardware address is already known.  In
 Frame Relay's case, the known hardware address is the DLCI.  Support
 for Inverse ARP is not required to implement this specification, but
 it has proven useful for Frame Relay interface autoconfiguration.
 See [11] for its description and an example of its use with Frame
 Relay.
 Stations must be able to map more than one IP address in the same IP
 subnet (CIDR address prefix) to a particular DLCI on a Frame Relay
 interface. This need arises from applications such as remote access,
 where servers must act as ARP proxies for many dial-in clients, each
 assigned a unique IP address while sharing bandwidth on the same DLC.
 The dynamic nature of such applications result in frequent address
 association changes with no affect on the DLC's status as reported by
 Frame Relay PVC Status Signaling.

Brown & Malis Standards Track [Page 20] RFC 2427 Multiprotocol over Frame Relay September 1998

 As with any other interface that utilizes ARP, stations may learn the
 associations between IP addresses and DLCIs by processing unsolicited
 ("gratuitous") ARP requests that arrive on the DLC.  If one station
 (perhaps a terminal server or remote access server) wishes to inform
 its peer station on the other end of a Frame Relay DLC of a new
 association between an IP address and that PVC, it should send an
 unsolicited ARP request with the source IP address equal to the
 destination IP address, and both set to the new IP address being used
 on the DLC.  This allows a station to "announce" new client
 connections on a particular DLCI.  The receiving station must store
 the new association, and remove any old existing association, if
 necessary, from any other DLCI on the interface.

7. IP over Frame Relay

 Internet Protocol [9] (IP) datagrams sent over a Frame Relay network
 conform to the encapsulation described previously.  Within this
 context, IP could be encapsulated in two different ways.
       1.  NLPID value indicating IP
       +-----------------------+-----------------------+
       |                 Q.922 Address                 |
       +-----------------------+-----------------------+
       | Control (UI)  0x03    |       NLPID  0xCC     |
       +-----------------------+-----------------------+
       |                   IP packet                   |
       |                       .                       |
       |                       .                       |
       |                       .                       |
       +-----------------------+-----------------------+

Brown & Malis Standards Track [Page 21] RFC 2427 Multiprotocol over Frame Relay September 1998

       2.  NLPID value indicating SNAP
       +-----------------------+-----------------------+
       |                 Q.922 Address                 |
       +-----------------------+-----------------------+
       | Control (UI)  0x03    |     pad     0x00      |
       +-----------------------+-----------------------+
       |   NLPID       0x80    |                       |  SNAP Header
       +-----------------------+  OUI = 0x00-00-00     +  Indicating
       |                                               |  IP
       +-----------------------+-----------------------+
       |                  PID   0x0800                 |
       +-----------------------+-----------------------+
       |                   IP packet                   |
       |                       .                       |
       |                       .                       |
       |                       .                       |
       +-----------------------+-----------------------+
 Although both of these encapsulations are supported under the given
 definitions, it is advantageous to select only one method as the
 appropriate mechanism for encapsulating IP data.  Therefore, IP data
 shall be encapsulated using the NLPID value of 0xCC indicating IP as
 shown in option 1 above.  This (option 1) is more efficient in
 transmission (48 fewer bits), and is consistent with the
 encapsulation of IP in X.25.

8. Other Protocols over Frame Relay

 As with IP encapsulation, there are alternate ways to transmit
 various protocols within the scope of this definition.  To eliminate
 the conflicts, the SNAP encapsulation is only used if no NLPID value
 is defined for the given protocol.
 As an example of how this works, ISO CLNP has a NLPID defined (0x81).
 Therefore, the NLPID field will indicate ISO CLNP and the data packet
 will follow immediately.  The frame would be as follows:
                +---------------------------------------------+
                |                Q.922 Address                |
                +----------------------+----------------------+
                | Control (UI)  0x03   | NLPID   0x81 (CLNP)  |
                +----------------------+----------------------+
                |           remainder of CLNP packet          |
                |                      .                      |
                |                      .                      |
                +---------------------------------------------+

Brown & Malis Standards Track [Page 22] RFC 2427 Multiprotocol over Frame Relay September 1998

 In this example, the NLPID is used to identify the data packet as
 CLNP.  It is also considered part of the CLNP packet and as such, the
 NLPID should not be removed before being sent to the upper layers for
 processing.  The NLPID is not duplicated.
 Other protocols, such as IPX, do not have a NLPID value defined.  As
 mentioned above, IPX would be encapsulated using the SNAP header.  In
 this case, the frame would be as follows:
                +---------------------------------------------+
                |               Q.922 Address                 |
                +----------------------+----------------------+
                | Control (UI)  0x03   |      pad  0x00       |
                +----------------------+----------------------+
                | NLPID    0x80 (SNAP) | OUI - 0x00 00 00     |
                +----------------------+                      |
                |                                             |
                +---------------------------------------------+
                |                PID    0x8137                |
                +---------------------------------------------+
                |                 IPX packet                  |
                |                      .                      |
                |                      .                      |
                +---------------------------------------------+

9. Bridging Model for Frame Relay

 The model for bridging in a Frame Relay network is identical to the
 model for remote bridging as described in IEEE P802.1g "Remote MAC
 Bridging" [13] and supports the concept of "Virtual Ports". Remote
 bridges with LAN ports receive and transmit MAC frames to and from
 the LANs to which they are attached. They may also receive and
 transmit MAC frames through virtual ports to and from other remote
 bridges.  A virtual port may represent an abstraction of a remote
 bridge's point of access to one, two or more other remote bridges.
 Remote Bridges are statically configured as members of a remote
 bridge group by management. All members of a remote bridge group are
 connected by one or more virtual ports. The set of remote MAC bridges
 in a remote bridge group provides actual or *potential* MAC layer
 interconnection between a set of LANs and other remote bridge groups
 to which the remote bridges attach.
 In a Frame Relay network there must be a full mesh of Frame Relay VCs
 between bridges of a remote bridge group.  If the frame relay network
 is not a full mesh, then the bridge network must be divided into
 multiple remote bridge groups.

Brown & Malis Standards Track [Page 23] RFC 2427 Multiprotocol over Frame Relay September 1998

 The frame relay VCs that interconnect the bridges of a remote bridge
 group may be combined or used individually to form one or more
 virtual bridge ports.  This gives flexibility to treat the Frame
 Relay interface either as a single virtual bridge port, with all VCs
 in a group, or as a collection of bridge ports (individual or grouped
 VCs).
 When a single virtual bridge port provides the interconnectivity for
 all bridges of a given remote bridge group (i.e. all VCs are combined
 into a single virtual port), the standard Spanning Tree Algorithm may
 be used to determine the state of the virtual port.  When more than
 one virtual port is configured within a given remote bridge group
 then an "extended" Spanning Tree Algorithm is required.  Such an
 extended algorithm is defined in IEEE 802.1g [13].  The operation of
 this algorithm is such that a virtual port is only put into backup if
 there is a loop in the network external to the remote bridge group.
 The simplest bridge configuration for a Frame Relay network is the
 LAN view where all VCs are combined into a single virtual port.
 Frames, such as BPDUs,  which would be broadcast on a LAN, must be
 flooded to each VC (or multicast if the service is developed for
 Frame Relay services). Flooding is performed by sending the packet to
 each relevant DLC associated with the Frame Relay interface. The VCs
 in this environment are generally invisible to the bridge.  That is,
 the bridge sends a flooded frame to the frame relay interface and
 does not "see" that the frame is being forwarded to each VC
 individually.  If all participating bridges are fully connected (full
 mesh) the standard Spanning Tree Algorithm will suffice in this
 configuration.
 Typically LAN bridges learn which interface a particular end station
 may be reached on by associating a MAC address with a bridge port.
 In a Frame Relay network configured for the LAN-like single bridge
 port (or any set of VCs grouped together to form a single bridge
 port), however, the bridge must not only associated a MAC address
 with a bridge port, but it must also associate it with a connection
 identifier.  For Frame Relay networks, this connection identifier is
 a DLCI.  It is unreasonable and perhaps impossible to require bridges
 to statically configure an association of every possible destination
 MAC address with a DLC.  Therefore, Frame Relay LAN-modeled bridges
 must provide a mechanism to allow the Frame Relay bridge port to
 dynamically learn the associations.  To accomplish this dynamic
 learning, a bridged packet shall conform to the encapsulation
 described within section 4.2.  In this way, the receiving Frame Relay
 interface will know to look into the bridged packet to gather the
 appropriate information.

Brown & Malis Standards Track [Page 24] RFC 2427 Multiprotocol over Frame Relay September 1998

 A second Frame Relay bridging approach, the point-to-point view,
 treats each Frame Relay VC as a separate bridge port.  Flooding and
 forwarding packets are significantly less complicated using the
 point-to-point approach because each bridge port has only one
 destination.  There is no need to perform artificial flooding or to
 associate DLCIs with destination MAC addresses.  Depending upon the
 interconnection of the VCs, an extended Spanning Tree algorithm may
 be required to permit all virtual ports to remain active as long as
 there are no true loops in the topology external to the remote bridge
 group.
 It is also possible to combine the LAN view and the point-to-point
 view on a single Frame Relay interface.  To do this, certain VCs are
 combined to form a single virtual bridge port while other VCs are
 independent bridge ports.
 The following drawing illustrates the different possible bridging
 configurations.  The dashed lines between boxes represent virtual
 circuits.
                                               +-------+
                            -------------------|   B   |
                           /            -------|       |
                          /            /       +-------+
                         /             |
               +-------+/              \       +-------+
               |   A   |                -------|   C   |
               |       |-----------------------|       |
               +-------+\                      +-------+
                         \
                          \                    +-------+
                           \                   |   D   |
                            -------------------|       |
                                               +-------+
 Since there is less than a full mesh of VCs between the bridges in
 this example, the network must be divided into more than one remote
 bridge group.  A reasonable configuration is to have bridges A, B,
 and C in one group, and have bridges A and D in a second.
 Configuration of the first bridge group combines the VCs
 interconnection the three bridges (A, B, and C) into a single virtual
 port.  This is an example of the LAN view configuration.  The second
 group would also be a single virtual port which simply connects
 bridges A and D.  In this configuration the standard Spanning Tree
 Algorithm is sufficient to detect loops.

Brown & Malis Standards Track [Page 25] RFC 2427 Multiprotocol over Frame Relay September 1998

 An alternative configuration has three individual virtual ports in
 the first group corresponding to the VCs interconnecting bridges A, B
 and C.  Since the application of the standard Spanning Tree Algorithm
 to this configuration would detect a loop in the topology, an
 extended Spanning Tree Algorithm would have to be used in order for
 all virtual ports to be kept active.  Note that the second group
 would still consist of a single virtual port and the standard
 Spanning Tree Algorithm could be used in this group.
 Using the same drawing, one could construct a remote bridge scenario
 with three bridge groups.  This would be an example of the point-to-
 point case.  Here, the VC connecting A and B, the VC connecting A and
 C, and the VC connecting A and D are all bridge groups with a single
 virtual port.

10. Security Considerations

 This document defines mechanisms for identifying the multiprotocol
 encapsulation of datagrams over Frame Relay.  There is obviously an
 element in trust in any encapsulation protocol - a receiver must
 trust that the sender has correctly identified the protocol being
 encapsulated.  In general, there is no way for a receiver to try to
 ascertain that the sender did indeed use the proper protocol
 identification, nor would this be desired functionality.
 It also specifies the use of ARP and RARP with Frame Relay, and is
 subject to the same security constraints that affect ARP and similar
 address resolution protocols.  Because authentication is not a part
 of ARP, there are known security issues relating to its use (e.g.,
 host impersonation).  No additional security mechanisms have been
 added to ARP or RARP for use with Frame Relay networks.

Brown & Malis Standards Track [Page 26] RFC 2427 Multiprotocol over Frame Relay September 1998

11. Appendix A - NLPIDS and PIDs

 List of Commonly Used NLPIDs
 0x00    Null Network Layer or Inactive Set
         (not used with Frame Relay)
 0x08    Q.933 [2]
 0x80    SNAP
 0x81    ISO CLNP
 0x82    ISO ESIS
 0x83    ISO ISIS
 0x8E    IPv6
 0xB0    FRF.9 Data Compression [14]
 0xB1    FRF.12 Fragmentation [18]
 0xCC    IPv4
 0xCF    PPP in Frame Relay [17]
 List of PIDs of OUI 00-80-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
                      0x00-0D              Fragments
                      0x00-0E              BPDUs as defined by
                                             802.1(d) or
                                             802.1(g)[12].
                      0x00-0F              Source Routing BPDUs

Brown & Malis Standards Track [Page 27] RFC 2427 Multiprotocol over Frame Relay September 1998

12. Appendix B - Connection Oriented Procedures

 This Appendix contains additional information and instructions for
 using ITU Recommendation Q.933 [2] and other ITU standards for
 encapsulating data over frame relay.  The information contained here
 is similar (and in some cases identical) to that found in Annex E to
 ITU Q.933.  The authoritative source for this information is in Annex
 E and is repeated here only for convenience.
 The Network Level Protocol ID (NLPID) field is administered by ISO
 and the ITU.  It contains values for many different protocols
 including IP, CLNP (ISO 8473), ITU Q.933, and ISO 8208.  A figure
 summarizing a generic encapsulation technique over frame relay
 networks follows.  The scheme's flexibility consists in the
 identification of multiple alternative to identify different
 protocols used either by
  1. end-to-end systems or
  2. LAN to LAN bride and routers or
  3. a combination of the above.
 over frame relay networks.
                            Q.922 control
                                 |
                                 |
            --------------------------------------------
            |                                          |
           UI                                       I Frame
            |                                          |
      ---------------------------------         --------------
      | 0x08    | 0x81      |0xCC     | 0x80    |..01....    |..10....
      |         |           |         |         |            |
     Q.933     CLNP        IP        SNAP     ISO 8208    ISO 8208
      |                               |       Modulo 8    Modulo 128
      |                               |
      --------------------           OUI
      |                  |            |
     L2 ID              L3 ID      -------
      |               User         |     |
      |               Specified    |     |
      |               0x70        802.3 802.6
      |
      ---------------------------
      |0x51 |0x4E |     |0x4C   |0x50
      |     |     |     |       |
     7776  Q.922 Others 802.2  User
                               Specified

Brown & Malis Standards Track [Page 28] RFC 2427 Multiprotocol over Frame Relay September 1998

 For those protocols which do not have a NLPID assigned or do not have
 a SNAP encapsulation, the NLPID value of 0x08, indicating ITU
 Recommendation Q.933 should be used.  The four octets following the
 NLPID include both layer 2 and layer 3 protocol identification.  The
 code points for most protocols are currently defined in ITU Q.933 low
 layer compatibility information element.  The code points for "User
 Specified" are described in Frame Relay Forum FRF.3.1 [15].  There is
 also an escape for defining non-standard protocols.
                    Format of Other Protocols
                        using Q.933 NLPID
                +-------------------------------+
                |         Q.922 Address         |
                +---------------+---------------+
                | Control  0x03 | NLPID   0x08  |
                +---------------+---------------+
                |        L2 Protocol ID         |
                |   octet 1     |   octet 2     |
                +---------------+---------------+
                |         L3 Protocol ID        |
                |    octet 1    |   octet 2     |
                +---------------+---------------+
                |         Protocol Data         |
                +-------------------------------+
                |              FCS              |
                +-------------------------------+
                    ISO 8802/2 with user specified
                            layer 3
                +-------------------------------+
                |         Q.922 Address         |
                +---------------+---------------+
                | Control  0x03 | NLPID   0x08  |
                +---------------+---------------+
                |  802/2   0x4C |      0x80     |
                +---------------+---------------+
                |User Spec. 0x70|     Note 1    |
                +---------------+---------------+
                |     DSAP      |     SSAP      |
                +---------------+---------------+
                |       Control  (Note 2)       |
                +-------------------------------+
                |       Remainder of PDU        |
                +-------------------------------+
                |              FCS              |
                +-------------------------------+

Brown & Malis Standards Track [Page 29] RFC 2427 Multiprotocol over Frame Relay September 1998

          Note 1: Indicates the code point for user specified
                  layer 3 protocol.
          Note 2: Control field is two octets for I-format and
                  S-format frames (see 88002/2)
 Encapsulations using I frame (layer 2)
 The Q.922 I frame is for supporting layer 3 protocols which require
 acknowledged data link layer (e.g., ISO 8208).  The C/R bit will be
 used for command and response indications.
                    Format of ISO 8208 frame
                            Modulo 8
                +-------------------------------+
                |         Q.922 Address         |
                +---------------+---------------+
                |   ....Control I frame         |
                +---------------+---------------+
                | 8208 packet (modulo 8) Note 3 |
                |                               |
                +-------------------------------+
                |              FCS              |
                +-------------------------------+
               Note 3: First octet of 8208 packet also identifies the
                       NLPID which is "..01....".
                    Format of ISO 8208 frame
                            Modulo 128
                +-------------------------------+
                |         Q.922 Address         |
                +---------------+---------------+
                |   ....Control I frame         |
                +---------------+---------------+
                |    8208 packet (modulo 128)   |
                |            Note 4             |
                +-------------------------------+
                |              FCS              |
                +-------------------------------+
               Note 4: First octet of 8208 packet also identifies the
                       NLPID which is "..10....".

Brown & Malis Standards Track [Page 30] RFC 2427 Multiprotocol over Frame Relay September 1998

13. Appendix C - Modifications from RFC 1490

 RFC 1490 has been widely implemented and used, and has been adopted
 by the Frame Relay Forum in FRF.3.1 [15] and by the ITU in Q.933 [2].
 This section describes updates to RFC 1490 that have been made as a
 result of this implementation and interoperability experience, and
 which reflect current implementation practice.
 Some language changes were necessary to clarify RFC 1490.  None of
 these changes impacted the technical aspects of this document, but
 were required to keep diagrams and language specific and consistent.
 Specifics of these changes will not be listed here.  Below are listed
 those changes which were significant.
 a) The requirement for stations to accept SNAP encapsulated protocols
    for which a NLPID was available, was removed.  RFC 1490 indicated
    that, if a protocol, such as IP, had a designated NLPID value, it
    must be used.  Later the document required stations to accept a
    SNAP encapsulated version of this same protocol.  This is clearly
    inconsistent.  A compliant station must send and accept the NLPID
    encapsulated version of such a protocol.  It MAY accept the SNAP
    encapsulation but should not be required to do so as these frames
    are noncompliant.
 b) Fragmentation was removed.  To date there are no interoperable
    implementations of the fragmentation algorithm presented in RFC
    1490.  Additionally, there have been several suggestions that the
    proposed mechanisms are insufficient for some frame relay
    applications.  To this end, fragmentation was removed from this
    document, and has been replaced by the fragmentation specified in
    FRF.12 [18].
 c) The address resolution presented in RFC 1490 referred only to PVC
    environments and is insufficient for SVC environments.  Therefore
    the section title was changed to reflect this.  Further work on
    SVC address resolution will take place in the ION working group.
 d) The encapsulation for Source Routing BPDUs was added, and the
    lists in Appendix A were augmented.
 e) The use of canonical and non-canonical MAC destination addresses
    in the bridging encapsulations was clarified.
 f) The Inverse ARP description was moved to the Inverse ARP
    specification [11].
 g) A new security section was added.

Brown & Malis Standards Track [Page 31] RFC 2427 Multiprotocol over Frame Relay September 1998

14. References

 [1] International Telecommunication Union, "ISDN Data Link Layer
     Specification for Frame Mode Bearer Services", ITU-T
     Recommendation Q.922, 1992.
 [2] International Telecommunication Union, "Signalling Specifications
     for Frame Mode Switched and Permanent Virtual Connection Control
     and Status Monitoring", ITU-T Recommendation Q.933, 1995.
 [3] Information technology - Telecommunications and Information
     Exchange between systems - Protocol Identification in the Network
     Layer, ISO/IEC TR 9577: 1992.
 [4] Baker, F., and R. Bowen, "PPP Bridging Control Protocol (BCP)",
     RFC 1638, June 1994.
 [5] International Standard, Information Processing Systems - Local
     Area Networks - Logical Link Control, ISO 8802-2, ANSI/IEEE,
     Second Edition, 1994-12-30.
 [6] Plummer, D., "An Ethernet Address Resolution Protocol - or -
     Converting Network Protocol Addresses to 48.bit Ethernet Address
     for Transmission on Ethernet Hardware", STD 37, RFC 826, November
     1982.
 [7] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
     October 1994.  See also: http://www.iana.org/numbers.html
 [8] Finlayson, R., Mann, R., Mogul, J., and M. Theimer, "A Reverse
     Address Resolution Protocol", STD 38, RFC 903, June 1984.
 [9] Postel, J., and J. Reynolds, "A Standard for the Transmission of
     IP Datagrams over IEEE 802 Networks", RFC 1042, February 1988.
 [10] IEEE, "IEEE Standard for Local and Metropolitan Area Networks:
      Overview and architecture", IEEE Standard 802-1990.
 [11] Bradley, T., Brown, C., and A. Malis, "Inverse Address
      Resolution Protocol", RFC 2390, September 1998.
 [12] IEEE, "IEEE Standard for Local and Metropolitan Networks:  Media
      Access Control (MAC) Bridges", IEEE Standard 802.1D-1990.
 [13] ISO/IEC 15802-5 : 1998 (IEEE Standard 802.1G), Remote Media
      Access Control (MAC) Bridging, March 12, 1997.

Brown & Malis Standards Track [Page 32] RFC 2427 Multiprotocol over Frame Relay September 1998

 [14] Frame Relay Forum, "Data Compression Over Frame Relay
      Implementation Agreement", FRF.9, January 22, 1996.
 [15] Frame Relay Forum, "Multiprotocol Encapsulation Implementation
      Agreement", FRF.3.1, June 22, 1995.
 [16] Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [17] Simpson, W., "PPP in Frame Relay", RFC 1973, June 1996.
 [18] Frame Relay Forum, "Frame Relay Fragmentation Implementation
      Agreement", FRF.12, December 1997.
 [19] Frame Relay Forum, "Frame Relay PVC Multicast Service and
      Protocol Implementation Agreement", FRF.7, October 21, 1994.

15. Authors' Addresses

 Caralyn Brown
 Consultant
 EMail:  cbrown@juno.com
 Andrew Malis
 Ascend Communications, Inc.
 1 Robbins Road
 Westford, MA  01886
 Phone: (978) 952-7414
 EMail:  malis@ascend.com

Brown & Malis Standards Track [Page 33] RFC 2427 Multiprotocol over Frame Relay September 1998

16. Full Copyright Statement

 Copyright (C) The Internet Society (1998).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
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Brown & Malis Standards Track [Page 34]

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