Internet Draft

IPng Working Group                                      A. Conta
INTERNET-DRAFT                                          M. Mueller
                                                        (Lucent)
                                                        July 1997


             Transmission of IPv6 Packets over Frame Relay.

                             Specification

                    draft-conta-ipv6-trans-fr-00.txt


Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working 
doc uments of the Internet Engineering Task Force (IETF), its Areas,  
and its  Working Groups. Note that other groups may also distribute 
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   Distribution of this memo is unlimited.


Abstract

   This memo describes the  transmission  of  IPv6  packets  over  
Frame Relay,  the  IPv6  Frame  Relay interface token, the IPv6 Frame 
Relay link local addresses, the IPv6 Frame  Relay  link  layer  
Information formatting for Neighbor Discovery.


1. Introduction


   This  document  specifies  the  frame format for transmission of 
IPv6
   packets and the method of forming IPv6 link-local addresses on  
Frame
   Relay  links.   It  also  specifies  the content of the 
Source/Target



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   Link-layer Address option used in  Neighbor Discovery [ND] or 
Inverse
   Neighbor Discovery [IND] messages when those messages are 
transmitted
   over a Frame Relay link.

   The information in this document applies to Frame Relay devices 
which
   serve  as end stations (DTEs) on a public or private Frame Relay 
net-
   work (for example, provided by a common carrier or PTT.)

   In a Frame Relay network, a number of virtual circuits form the  
con-
   nections  between the attached stations.  The resulting set of 
inter-
   connected devices forms a private Frame  Relay  group  which  may  
be
   either  fully  interconnected  with a complete "mesh" of virtual 
cir-
   cuits, or only partially interconnected.  In either case,  each  
vir-
   tual  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.

   A Frame Relay virtual circuit acts like a virtual-link, with its  
own
   link  parameters,  distinct from the parameters of other virtual 
cir-
   cuits 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,    
incom-
   ing/outgoing burst size, incoming/outgoing frame rate.

   A  DLCI  can  be  of  10,  17, or 24 bits in length, spanning a 2, 
3,
   respectively 4 octet Frame Relay header.

   This document is intended to apply to  both  switched  and  
permanent
   Frame Relay virtual circuits.

   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  minimum  frame size for a Frame Relay link is 5, 6, or 7 
octets,
   depending on the size of the DLCI (10, 17, or 24 bits). A Frame 
Relay
   network  must  support  at  least  a maximum size of 262 octets. 
IPv6
   requires a minimum MTU size of 576 octets.

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

   A smaller than default MTU  can  be  configured  but  of  course  
not
   smaller than the minimum MTU of 576 octets.



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   An  adequate larger than default MTU can be configured to avoid 
frag-
   mentation.  The maximum MTU 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 MTU 
size
   to approximately 4080 bytes.  A larger desired MTU 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.

   Implementations may allow, if upper  layers  provide  adequate  
error
   protection/detection  mechanisms, configuring a Frame Relay link 
with
   a larger than 4080  octets  MTU  but  with  a  lesser  error  
protec-
   tion/detection mechanism at link layer.

   Although a Frame Relay circuit allows the definition of distinct 
max-
   imum 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 limit the setting of the Frame Relay  
to
   the  link  level,  which  is  enforced on all of the VCs that use 
the
   link, i.e. MTU can NOT be set for each VC using a link.


3. Frame format

   IPv6 packets are transmitted in standard [ENCAPS] SNAP frame 
encapsu-
   lation format:

            0                       1                          (Octets)
           +-----------------------+-----------------------+
(Octets)0  |                 Q.922 Address                 |
           +-----------------------+-----------------------+
        2  | Control (UI)  0x03    |     pad     0x00      |
           +-----------------------+-----------------------+
        4  |   NLPID 0x80 (SNAP)   |                       |  SNAP 
Header
           +-----------------------+  OUI =3D 0x00-00-00     +  
Indicating
        6  |                                               |  IPv6
           +-----------------------+-----------------------+
        8  |              IPv6 PID   0x86DD                |
           +-----------------------+-----------------------+
       10  |                  IPv6 packet                  |
           |                       .                       |
           |                       .                       |
           +-----------------------+-----------------------+

   The  IPv6  does  not have an NLPID defined at this time, therefore 
at
   this point only the SNAP encapsulation is used.



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4. Stateless Autoconfiguration

   The interface token [CONF] for an IPv6 Frame Relay interface must  
be
   unique  on the virtual link represented  by the virtual circuit 
i.e.,
   the circuit's end-point nodes must have  distinct  interface  
tokens.
   This  applies  regardless  the  virtual  circuit is a 
point-to-point,
   point-to-multipoint, or multipoint-to-multipoint circuit, and 
regard-
   less the timing of the node joining a multi-point ended circuit.

   The  interface  token is locally generated by the Frame Relay 
device,
   and it can have as seed any combination of 64 bits, as  long  as  
the
   result is a unique token on the link.

   A method to construct the Frame Relay Interface Token is as follows:

             0     1     2     3     4     5     6     7      (Bits)
            +-----+-----+-----+-----+-----+-----+-----+-----+
(Ootets) 0  |                                   |    MBZ    |
            +                    Any value      +-----+-----+
         1  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+
         2  |          Frame Relay Node Identifier          |
            +-----+-----+-----+-----+-----+-----+-----+-----+
         3  |                                               |
            +-         Frame Relay Link Identifier         -+
         4  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+
         5  |                                               |
            +-                                             -+
         6  |              Frame Relay DLCI                 |
            +-                                             -+
         7  |                                               |
            +-----+-----+-----+-----+-----+-----+-----+-----+

   The  EUI-64  "universal/local" bit is set to zero to reflect that 
the
   64 bit interface identifier value has local significance. The  
"indi-
   vidual/group"  bit is set to 0 to reflect the unicast address. 
There-
   fore bits 6, and 7 of the first octet Must Be Zero (MBZ).

   The rest of the first two octets can be any combination of  bit  
val-
   ues.

   The  Frame Relay Node Identifier is a user administered value used 
to
   Locally identify this Frame Relay Switching Node.

   The Frame Relay link identifier is a numerical representation of  
the
   link over which the Frame Relay VC is configured.




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   The DLCI value is normalized to a 24 bit representation. This 
handles
   all combinations of 10, 17, and 24 bit DLCIs.

   Note that other mechanisms to generate the  interface  token  can  
be
   used,  such  as  random  number generators, etc... In either case, 
in
   conformance to {AARCH] the bit 6 and 7  MUST  be  0  to  reflect  
the
   EUI-64  local  significance,  respectively the unicast address. 
Addi-
   tionally, octet 5, 6, and 7, MUST be  the  normalized  value  of  
the
   DLCI.  This  ensures  that the Frame Relay  "solicited-node 
multicast
   address" derived from the IPv6  address  built  with  this  
interface
   token  contains  the  DLCI.  It  also  allows  building  a valid 
IPv6
   "solicited-node multicast" address knowing a DLCI of an interface.

              0     1     2     3     4     5     6     7     (Bits)
           +-----+-----+-----+-----+-----+-----+-----+-----+
        0  |                                   |    MBZ    |
           +                                   +-----+-----+
        1  |                                               |
           +-                                             -+
        2  |          Random Generated Number              |
           +-                                             -+
        3  |                                               |
           +-                                             -+
        4  |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
        5  |                                               |
           +-                                             -+
        6  |              Frame Relay DLCI                 |
           +-                                             -+
        7  |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+

      The Duplicate  Address  Detection  specified  in  [CONF]  is  
used
      repeatedly  during the interface token and local-link address 
gen-
      eration process, until the  generated  token  and  the  
link-local
      address on the link is unique.

      Since  DLCI values are local to a Frame Relay node, it is 
possible
      to have Frame Relay nodes within a Frame Relay  network  with  
the
      same  interface  token  and link-local address on distinct 
virtual
      circuits (links).

5. Link-Local Addresses

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




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


6. Address Mapping - Unicast

   The procedure for mapping IPv6 addresses to  Frame  Relay  
link-layer
   addresses is described in [ND] and [IND].

   The  Source/Target Link-layer Address option used in Neighbor 
Discov-
   ery and Inverse Neighbor Discovery messages has the following  
format
   for a Frame Relay link:

                  0    1    2    3    4    5    6    7
                 +----+----+----+----+----+----+----+----+
              0  |                 Type                  |
                 +----+----+----+----+----+----+----+----+
              1  |                 Length                |
                 +----+----+----+----+----+----+----+----+

   with the following option values:

                 +----+----+----+----+----+----+----+----+
              2  |EA=3D0| C/R|      DLCI(high order)       |
                 +----+----+----+----+----+----+----+----+
              3  |EA=3D1| DE |BECN|FECN|  DLCI(low order)  |
                 +----+----+----+----+----+----+----+----+
              4  |                                       |
                 +                                       +
              5  |                                       |
                 +               Padding                 +
              6  |               (zeros)                 |
                 +                                       +
              7  |                                       |
                 +----+----+----+----+----+----+----+----+














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                  0    1    2    3    4    5    6    7
                 +----+----+----+----+----+----+----+----+
              2  |EA=3D0| C/R|     DLCI (high order)       |
                 +----+----+----+----+----+----+----+----+
              3  |EA=3D0|              DLCI                |
                 +----+----+----+----+----+----+----+----+
              4  |EA=3D1| DE |BECN|FECN|  DLCI(low order)  |
                 +----+----+----+----+----+----+----+----+
              5  |                                       |
                 +                                       +
              6  |               Padding                 |
                 +                                       +
              7  |                                       |
                 +----+----+----+----+----+----+----+----+

                  0    1    2    3    4    5    6    7
                 +----+----+----+----+----+----+----+----+
              2  |EA=3D0| C/R|     DLCI (high order)       |
                 +----+----+----+----+----+----+----+----+
              3  |EA=3D0|             DLCI                 |
                 +----+----+----+----+----+----+----+----+
              4  |EA=3D0|             DLCI                 |
                 +----+----+----+----+----+----+----+----+
              5  |EA=3D1| DE |BECN|FECN|  DLCI(low order)  |
                 +----+----+----+----+----+----+----+----+
              6  |                                       |
                 +               Padding                 +
              7  |                                       |
                 +----+----+----+----+----+----+----+----+

       Option fields:

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

       Length      1 (in units of 8 octets) for a 10, 17, or 24 bit 
DLCI

       DLCI        The 10, 17, or 24 bit DLCI. The C/R, DE, BECN, FECN 
bits
                   have no addressing significance. The EA bit signals 
the
                   end of a DLCI.


6. Address Mapping - Solicited-Node Multicast Address

   A Frame Relay interface token contains the 24 bit normalized value 
of
   the DLCI.  An IPv6 packet with an IPv6 Solicited-Node Multicast  
des-
   tination  address  consisting  of  the  sixteen octets DST[1] 
through
   DST[16], is transmitted to the Frame Relay DLCI derived from 
DST[14],



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   DST[15],  and  DST[16]  -  24  bit  normalized 10, 17, or 24 bit 
DLCI
   value.

   Conversely, an IPv6 "solicited-node multicast" address built based 
on
   an  interface's  known  DLCI  is  a  valid multicast address for 
that
   interface.

                  0    1    2    3    4    5    6    7
                 +----+----+----+----+----+----+----+----+
              0  |EA=3D0| C/R|      DLCI(high order)       |
                 +----+----+----+----+----+----+----+----+
              1  |EA=3D1| DE |BECN|FECN|  DLCI(low order)  |
                 +----+----+----+----+----+----+----+----+

                  0    1    2    3    4    5    6    7
                 +----+----+----+----+----+----+----+----+
              0  |EA=3D0| C/R|     DLCI (high order)       |
                 +----+----+----+----+----+----+----+----+
              1  |EA=3D0|              DLCI                |
                 +----+----+----+----+----+----+----+----+
              2  |EA=3D1| DE |BECN|FECN|  DLCI(low order)  |
                 +----+----+----+----+----+----+----+----+

                  0    1    2    3    4    5    6    7
                 +----+----+----+----+----+----+----+----+
              0  |EA=3D0| C/R|     DLCI (high order)       |
                 +----+----+----+----+----+----+----+----+
              1  |EA=3D0|             DLCI                 |
                 +----+----+----+----+----+----+----+----+
              2  |EA=3D0|             DLCI                 |
                 +----+----+----+----+----+----+----+----+
              3  |EA=3D1| DE |BECN|FECN|  DLCI(low order)  |
                 +----+----+----+----+----+----+----+----+


7. Security Considerations

   The mechanisms defined in this document  for  generating  IPv6  
Frame
   Relay  address  tokens are intended to provide local link 
uniqueness.
   There is no security protection from duplication through  forgery  
or
   accident.


8. Acknowledgments

   Thanks to Dan Harrington and Milan Merhar for reviewing this 
document
   and providing useful suggestions.




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9. References

   [RFC-1883] S. Deering, R. Hinden, "Internet Protocol Version 6 
Speci-
   fication"


   [AARCH]R. Hinden, S. Deering "IPv6 Addressing Architecture"


   [ND]  RFC 1970, T. Narten, E. Nordmark, W.Simpson "Neighbor 
Discovery
   for IP Version 6 (IPv6)"


   [CONF] RFC 1971, S. Thomson, T. Narten "IPv6 Stateless 
Autoconfigura-
   tion"


   [ENCAPS]RFC  1490,  T.  Bradley,  C.  Brown, A. Malis, 
"Multiprotocol
   Interconnect
    over Frame Relay".


   [IND] A. Conta "IPv6 ND Extensions for Inverse Neighbor Discovery".


   Authors' Addresses

   Alex Conta
   Lucent Technologies Inc.
   300 Baker Ave, Suite 100
   Concord, MA 01742
   +1-508-287-2842
   email: aconta@lucent.com

   Martin Mueller
   Lucent Technologies Inc.
   300 Baker Ave, Suite 100
   Concord, MA 01742
   +1-508-287-2833
   email:  memueller@lucent.com











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