





Network Working Group                                          A. Conta
Request for Comments: 2590                                       Lucent
Category: Standards Track                                      A. Malis
                                                                 Ascend
                                                             M. Mueller
                                                                 Lucent
                                                               May 1999


         Transmission of IPv6 Packets over Frame Relay Networks
                             Specification

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 (1999).  All Rights Reserved.

Abstract

   This memo describes mechanisms for the transmission of IPv6 packets
   over Frame Relay networks.

Table of Contents

   1. Introduction.................................................2
   2. Maximum Transmission Unit....................................3
   3. Frame Format.................................................4
   4. Stateless Autoconfiguration..................................5
      4.1 Generating the MID field.................................7
   5. Link-Local Address...........................................9
   6. Address Mapping -- Unicast, Multicast........................9
   7. Sending Neighbor Discovery Messages.........................14
   8. Receiving Neighbor Discovery Messages.......................15
   9. Security Considerations.....................................15
   10. Acknowledgments............................................16
   11. References.................................................16
   12. Authors' Addresses.........................................18
   13. Full Copyright Statement...................................19






Conta, et al.               Standards Track                     [Page 1]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


1. Introduction

   This document specifies the frame format for transmission of IPv6
   packets over Frame Relay networks, the method of forming IPv6 link-
   local addresses on Frame Relay links, and the mapping of the IPv6
   addresses to Frame Relay addresses.  It also specifies the content of
   the Source/Target link-layer address option used in Neighbor
   Discovery [ND] and Inverse Neighbor Discovery [IND] messages when
   those messages are transmitted over a Frame Relay link.  It is part
   of a set of specifications that define such IPv6 mechanisms for Non
   Broadcast Multi Access (NBMA) media [IPv6-NBMA], [IPv6-ATM], and a
   larger set that defines such mechanisms for specific link layers
   [IPv6-ETH], [IPv6-FDDI], [IPv6-PPP], [IPv6-ATM], etc...

   The information in this document applies to Frame Relay devices which
   serve as end stations (DTEs) on a public or private Frame Relay
   network (for example, provided by a common carrier or PTT.) Frame
   Relay end stations can be IPv6 hosts or routers. In this document
   they are referred to as nodes.

   In a Frame Relay network, a number of virtual circuits form the
   connections between the attached stations (nodes). 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
   (card) by a Data Link Connection Identifier (DLCI).  In most
   circumstances, DLCIs have strictly local significance at each Frame
   Relay interface.

   A Frame Relay virtual circuit acts like a virtual-link (also referred
   to as logical-link), with its own link parameters, distinct from the
   parameters of other virtual circuits established on the same wire or
   fiber. Such parameters are the input/output maximum frame size,
   incoming/outgoing requested/agreed throughput, incoming/outgoing
   acceptable throughput, incoming/outgoing burst size,
   incoming/outgoing frame rate.

   By default a DLCI is 10 bits in length. Frame Relay specifications
   define also 16, 17, or 23 bit DLCIs. The former is not used, while
   the latter two are suggested for use with SVCs.

   Frame Relay virtual circuits can be created administratively as
   Permanent Virtual Circuits -- PVCs -- or dynamically as Switched
   Virtual Circuits -- SVCs.  The mechanisms defined in this document
   are intended to apply to both permanent and switched Frame Relay
   virtual circuits, whether they are point to point or point to multi-
   point.



Conta, et al.               Standards Track                     [Page 2]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


   The keywords MUST, MUST NOT, MAY, OPTIONAL, REQUIRED, RECOMMENDED,
   SHALL, SHALL NOT, SHOULD, SHOULD NOT are to be interpreted as defined
   in [RFC 2119].

2. Maximum Transmission Unit

   The IPv6 minimum MTU is defined in [IPv6].

   In general, Frame Relay devices are configured to have a maximum
   frame size of at least 1600 octets. Therefore, the default IPv6 MTU
   size for a Frame Relay interface is considered to be 1592.

   A smaller than default frame size can be configured but of course not
   smaller than the minimum IPv6 MTU.

   An adequate larger than default IPv6 MTU and Frame Relay frame size
   can be configured to avoid fragmentation. The maximum frame size is
   controlled by the CRC generation mechanisms employed at the HDLC
   level. CRC16 will protect frames up to 4096 bytes in length, which
   reduces the effective maximum frame size to approximately 4088 bytes.
   A larger desired frame size (such as that used by FDDI or Token
   Ring), would require the CRC32 mechanism, which is not yet widely
   used and is not mandatory for frame relay systems conforming to Frame
   Relay Forum and ITU-T standards.

   In general, if upper layers provide adequate error
   protection/detection mechanisms, implementations may allow
   configuring a Frame Relay link with a larger than 4080 octets frame
   size but with a lesser error protection/detection mechanism at link
   layer. However, because IPv6 relies on the upper and lower layer
   error detection, configuring the IPv6 MTU to a value larger than 4080
   is strongly discouraged.

   Although a Frame Relay circuit allows the definition of distinct
   maximum frame sizes for input and output, for simplification
   purposes, this specification assumes symmetry, i.e. the same MTU for
   both input and output.

   Furthermore, implementations may limit the setting of the Frame Relay
   maximum frame size to the interface (link, or card) level, which then
   is enforced on all of the PVCs or SVCs on that interface (on that
   link, or card). For an SVC, the maximum frame size parameter
   negotiated during circuit setup will not exceed the configured
   maximum frame size.







Conta, et al.               Standards Track                     [Page 3]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


3. IPv6 Frame Format

   The IPv6 frame encapsulation for Frame Relay (for both PVCs and SVCs)
   follows [ENCAPS], which allows a VC to carry IPv6 packets along with
   other protocol packets. The NLPID frame format is used, in which the
   IPv6 NLPID has a value of 0x8E:

            0                       1                       (Octets)
           +-----------------------+-----------------------+
(Octets)0  |                                               |
           /                 Q.922 Address                 /
           /            (length 'n' equals 2 or 4)         /
           |                                               |
           +-----------------------+-----------------------+
        n  | Control (UI)  0x03    |      NLPID  0x8E      |  NLPID
           +-----------------------+-----------------------+  indicating
      n+2  |                       .                       |  IPv6
           /                       .                       /
           /                  IPv6 packet                  /
           |                       .                       |
           +-----------------------+-----------------------+
           |                                               |
           +                      FCS                      +
           |                                               |
           +-----------------------+-----------------------+

      "n" is the length of the Q.922 address which can be 2 or 4 octets.

      The Q.922 representation of a DLCI (in canonical order - the first
      bit is stored in the least significant, i.e., the right-most bit
      of a byte in memory) [CANON] is the following:

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

              10 bits DLCI











Conta, et al.               Standards Track                     [Page 4]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


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

              17 bits DLCI

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

              23 bits DLCI

   The encapsulation of data or control messages exchanged by various
   protocols that use SNAP encapsulation (with their own PIDs) is not
   affected. The encoding of the IPv6 protocol identifier in such
   messages MUST be done according to the specifications of those
   protocols, and [ASSNUM].

4. Stateless Autoconfiguration

   An interface identifier [AARCH] for an IPv6 Frame Relay interface
   must be unique on a Frame Relay link [AARCH], and must be unique on
   each of the virtual links represented by the VCs terminated on the
   interface.

   The interface identifier for the Frame Relay interface is locally
   generated by the IPv6 module.

   Each virtual circuit in a Frame Relay network is uniquely identified
   on a Frame Relay interface by a DLCI. Furthermore, a DLCI can be seen
   as an identification of the end point of a virtual circuit on a Frame
   Relay interface. Since each Frame Relay VC is configured or
   established separately, and acts like an independent virtual-link
   from other VCs in the network, or on the interface, link, wire or



Conta, et al.               Standards Track                     [Page 5]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


   fiber, it seems beneficial to view each VC's termination point on the
   Frame Relay interface as a "pseudo-interface" or "logical-interface"
   overlaid on the Frame Relay interface. Furthermore, it seems
   beneficial to be able to generate and associate an IPv6
   autoconfigured address (including an IPv6 link local address) to each
   "pseudo-interface", i.e. end-point of a VC, i.e. to each DLCI on a
   Frame Relay interface.

   In order to achieve the benefits described above, the mechanisms
   specified in this document suggest constructing the Frame Relay
   interface identifier from 3 distinct fields (Fig.1):

   (a)  The "EUI bits" field. Bits 6 and 7 of the first octet,
        representing the EUI-64 "universal/local" and respectively
        "individual/group" bits converted to IPv6 use. The former is set
        to zero to reflect that the 64 bit interface identifier value
        has local significance [AARCH]. The latter is set to 0 to
        reflect the unicast address [AARCH].

   (b)  The "Mid" field. A 38 bit field which is generated with the
        purpose of adding uniqueness to the interface identifier.

   (c)  The "DLCI" field. A 24 bit field that MAY hold a 10, 17, or 23
        bit DLCI value which MUST be extended with 0's to 24 bits. A
        DLCI based interface identifier -- which contains a valid DLCI
        -- SHOULD be generated as a result of successfully establishing
        a VC -- PVC or SVC.

        If a DLCI is not known, the field MUST be set to the
        "unspecified DLCI" value which consists of setting each of the
        24 bits to 1.

   Since DLCIs are local to a Frame Relay node, it is possible to have
   Frame Relay distinct virtual circuits within a Frame Relay network
   identified with the same DLCI values.
















Conta, et al.               Standards Track                     [Page 6]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


             7     6     5     4     3     2     1     0   (bit order)
            +-----+-----+-----+-----+-----+-----+-----+-----+
(Octets) 0  |                                   |"EUI bits" |
            +                                   +-----+-----+
         1  |                                               |
            +                                               +
         2  |                   "Mid"                       |
            +                                               +
         3  |                                               |
            +                                               +
         4  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+
         5  |                                               |
            +                                               +
         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).







Conta, et al.               Standards Track                     [Page 7]

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.









Conta, et al.               Standards Track                     [Page 8]

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:




Conta, et al.               Standards Track                     [Page 9]

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                    |
             +-----+-----+-----+-----+-----+-----+-----+-----+








Conta, et al.               Standards Track                    [Page 10]

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
















Conta, et al.               Standards Track                    [Page 11]

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.








Conta, et al.               Standards Track                    [Page 12]

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:

        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 octet.
                    It may have the value:

                     2 -- for E.164, or X.121 numbers or NSAP
                          addresses not longer than 11 octets
                          [E164], [X25], [NSAP].

                     3 -- for NSAP addresses longer than 11 but
                          not longer than 19 octets.




Conta, et al.               Standards Track                    [Page 13]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


                     4 -- for NSAP addresses longer than 19 octets
                          (not longer than the maximum NSAP address
                          length) [NSAP].

        Link-Layer Address       The E.164, X.121, number encoded in
                                 Binary Coded Decimal (BCD), or the NSAP
                                 address.

   Description

     The "Frame Relay Address" option value has three components:

     (a)  Address Type -- encoded in the first two bits of the first
          octet.  The first bit is set to 0, the second bit is set to 1.

     (b)  Size -- encoded in the last (high order) 6 bits of the first
          octet. The maximum value of the field is the maximum size of
          the E.164, X.121, or NSAP addresses.

     (c)  Address Family Number -- the number assigned for the E.164,
          X.121, or NSAP address family [ASSNUM].

     (d)  E.164, X.121, number -- encoded in BCD (two digits per octet).
          If the E.164, or X.121 has an even number of digits the
          encoding will fill all encoding octets -- half the number of
          digits. If the E.164, or X.121 number has an odd number of
          digits, the lowest order digit fills only half of an octet --
          it is placed in the first 4 bits of the last octet of the
          E.164, or X.121 BCD encoding. The rest of the field up to the
          last octet of the 11 octets available is padded with zeros.

          NSAP address -- the NSAP address. It is padded with zeros if
          the NSAP address does not fit in a number of octets that makes
          the length of the option an even number of 8 octets.

7. Sending Neighbor Discovery Messages

   Frame Relay networks do not provide link-layer native multicasting
   mechanisms. For the correct functioning of the Neighbor Discovery
   mechanisms, link-layer multicasting must be emulated.

   To emulate multicasting for Neighbor Discovery (ND) the node MUST
   send frames carrying ND multicast packets to all VCs on a Frame Relay
   interface. This applies to ND messages addressed to both all-node and
   solicited-node multicast addresses. This method works well with PVCs.
   A mesh of PVCs MAY be configured and dedicated to multicast traffic
   only.  An alternative to a mesh of PVCs is a set of point-to-
   multipoint PVCs.



Conta, et al.               Standards Track                    [Page 14]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


8. Receiving Neighbor Discovery Messages

   If a Neighbor Discovery Solicitation message received by a node
   contains the Source  link-layer  address option with a DLCI, the
   message MUST undergo Frame Relay specific preprocessing required for
   the correct interpretation of the field during the ND protocol engine
   processing. This processing is done before the Neighbor Discovery
   message is processed by the Neighbor Discovery (ND) protocol engine.

   The motivation for this processing is the local significance of the
   DLCI fields in the Neighbor Discovery message: the DLCI significance
   at the sender node is different than the DLCI significance at the
   receiver node. In other words, the DLCI that identifies the Frame
   Relay virtual circuit at the sender may be different than the DLCI
   that identifies the virtual circuit at the receiver node.
   Furthermore, the sender node may not be aware of the DLCI value at
   the receiver. Therefore, the Frame Relay specific preprocessing
   consists in modifying the Neighbor Discovery Solicitation message
   received, by storing into the Source link-layer address option the
   DLCI value of the virtual circuit on which the frame was received, as
   known to the receiver node. The DLCI value being stored must be
   encoded in the appropriate format (see previous sections). The
   passing of the DLCI value from the Frame Relay module to the Neighbor
   Discovery preprocessing module is an implementation choice.

9. Security Considerations

   The mechanisms defined in this document for generating an IPv6 Frame
   Relay interface identifier are intended to provide uniqueness at link
   level -- virtual circuit.  The protection against duplication is
   achieved by way of IPv6 Stateless Autoconfiguration Duplicate Address
   Detection mechanisms. Security protection against forgery or accident
   at the level of the mechanisms described here is provided by the IPv6
   security mechanisms [IPSEC], [IPSEC-Auth], [IPSEC-ESP] applied to
   Neighbor Discovery [IPv6-ND] or Inverse Neighbor Discovery [IND]
   messages.

   To avoid an IPsec Authentication verification failure, the Frame
   Relay specific preprocessing of a Neighbor Discovery Solicitation
   message that contains a DLCI format Source link-layer address option,
   MUST be done by the receiver node after it completed IP Security
   processing.









Conta, et al.               Standards Track                    [Page 15]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


10. Acknowledgments

   Thanks to D. Harrington, and M. Merhar for reviewing  this document
   and providing useful suggestions. Also thanks to G. Armitage for his
   reviewing and suggestions. Many thanks also to Thomas Narten for
   suggestions on improving the document.

11. References

   [AARCH]      Hinden, R. and S. Deering, "IPv6 Addressing
                Architecture", RFC 2373, July 1998.

   [ASSNUM]     Reynolds, J. and J. Postel, "Assigned Numbers", STD 2,
                RFC 1700, October 1994.  See also:
                http://www.iana.org/numbers.html

   [AUTOCONF]   Thomson, S. and T. Narten, "IPv6 Stateless
                Autoconfiguration", RFC 2462, December 1998.

   [CANON]      Narten, T. and C. Burton, "A Caution on the Canonical
                Ordering of Link-Layer Addresses", RFC 2469, December
                1998.

   [ENCAPS]     Brown, C. and A. Malis, "Multiprotocol Interconnect over
                Frame Relay", STD 55, RFC 2427, November 1998.

   [IND]        Conta, A., "Extensions to IPv6 Neighbor Discovery for
                Inverse Discovery", Work in Progress, December 1998.

   [IPv6]       Deering, S. and R. Hinden, "Internet Protocol Version 6
                Specification", RFC 2460, December 1998.

   [IPv6-ATM]   Armitage, G., Schulter, P. and M. Jork, "IPv6 over ATM
                Networks", RFC 2492, January 1999.

   [IPv6-ETH]   Crawford, M., "Transmission of IPv6 packets over
                Ethernet Networks", RFC 2464, December 1998.

   [IPv6-FDDI]  Crawford, M., "Transmission of IPv6 packets over FDDI
                Networks", RFC 2467, December 1998.

   [IPv6-NBMA]  Armitage, G., Schulter, P., Jork, M. and G. Harter,
                "IPv6 over Non-Broadcast Multiple Access (NBMA)
                networks", RFC 2491, January 1999.

   [IPv6-ND]    Narten, T., Nordmark, E. and W. Simpson, "Neighbor
                Discovery for IP Version 6 (IPv6)", RFC 2461, December
                1998.



Conta, et al.               Standards Track                    [Page 16]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


   [IPv6-PPP]   Haskin, D. and E. Allen, "IP Version 6 over PPP", RFC
                2472, December 1998.

   [IPv6-TR]    Narten, T.,  Crawford, M. and M. Thomas, "Transmission
                of IPv6 packets over Token Ring Networks", RFC 2470,
                December 1998.

   [IPSEC]      Atkinson, R. and S. Kent, "Security Architecture for the
                Internet Protocol", RFC 2401, November 1998.

   [IPSEC-Auth] Atkinson, R. and S. Kent, "IP Authentication Header",
                RFC 2402, December 1998.

   [IPSEC-ESP]  Atkinson, R. and S. Kent, "IP Encapsulating Security
                Protocol (ESP)", RFC 2406, November 1998.

   [RFC2119]    Bradner, S., "Key words for use in RFCs to indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.

   [E164]       International Telecommunication Union - "Telephone
                Network and ISDN Operation, Numbering, Routing, amd
                Mobile Service", ITU-T Recommendation E.164, 1991.

   [NSAP]       ISO/IEC, "Information Processing Systems -- Data
                Communications -- Network Service Definition Addendum 2:
                Network Layer Addressing". International Standard
                8348/Addendum 2, ISO/IEC JTC 1, Switzerland 1988.

   [X25]        "Information Technology -- Data Communications -- X.25
                Packet Layer Protocol for Data Terminal Equipment",
                International Standard 8208, March 1988.




















Conta, et al.               Standards Track                    [Page 17]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


12. Authors' Addresses

   Alex Conta
   Lucent Technologies Inc.
   300 Baker Ave, Suite 100
   Concord, MA 01742

   Phone: +1-978-287-2842
   EMail: aconta@lucent.com


   Andrew Malis
   Ascend Communications
   1 Robbins Rd
   Westford, MA 01886

   Phone: +1-978-952-7414
   EMail: malis@ascend.com


   Martin Mueller
   Lucent Technologies Inc.
   300 Baker Ave, Suite 100
   Concord, MA 01742

   PHone: +1-978-287-2833
   EMail:  memueller@lucent.com
























Conta, et al.               Standards Track                    [Page 18]

RFC 2590             IPv6 over Frame Relay Networks             May 1999


13.  Full Copyright Statement

   Copyright (C) The Internet Society (1999).  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
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















Conta, et al.               Standards Track                    [Page 19]

