One document matched: draft-ietf-ipngwg-fddi-ntwrks-00.txt

Internet Engineering Task Force                            Matt Crawford
INTERNET-DRAFT                                                  Fermilab
<draft-ietf-ipngwg-fddi-ntwrks-00.txt>                   August 15, 1995


    A Method for the Transmission of IPv6 Packets over FDDI Networks



Status of this Memo

   This document is an Internet Draft.  Internet Drafts are working
   documents of the Internet Engineering Task Force (IETF), its Areas,
   and its Working Groups.  Note that other groups may also distribute
   working documents as Internet Drafts.

   Internet Drafts are draft documents valid for a maximum of six
   months.  Internet Drafts may be updated, replaced, or obsoleted by
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   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt'' listing contained in the Internet Drafts Shadow
   Directories on ds.internic.net (US East Coast), nic.nordu.net
   (Europe), ftp.isi.edu (US  West  Coast), or munnari.oz.au (Pacific
   Rim).

   Distribution of this memo is unlimited.


Introduction

   This memo specifies the frame format for transmission of IPv6 [IPV6]
   packets and the method of forming IPv6 link-local addresses on FDDI
   networks.  It also specifies the content of the Source/Target Link-
   layer Address option used the the Router Solicitation, Router
   Advertisement, Neighbor Solicitation, and Neighbor Advertisement
   messages described in [DISC], when those messages are transmitted on
   an FDDI network.


Maximum Transmission Unit

   Although FDDI permits a frame length of 4500 octets (9000 symbols),
   including Data Link encapsulation, it is desirable to allow for
   future extensions to the MAC header and frame status fields.  The
   default MTU size for IPv6 packets on an FDDI network is therefore



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   4352 octets.  This size may be reduced by a Router Advertisement
   [DISC] containing an MTU option which specifies a smaller MTU, or by
   manual configuration of each node.  If a Router Advertisement is
   received with an MTU option specifying an MTU larger than 4352, or
   larger than a manually configured value less than 4352, that MTU
   option must be ignored.



Frame Format

   FDDI provides both synchronous and asynchronous transmission, with
   the latter class further subdivided by the use of restricted and
   unrestricted tokens.  Only asynchronous transmission with
   unrestricted tokens is required for FDDI interoperability.
   Accordingly, IPv6 packets shall be sent in asynchronous frames using
   unrestricted tokens.  The robustness principle dictates that nodes
   should be able to receive synchronous frames and asynchronous frames
   sent using restricted tokens.

   IPv6 packets are transmitted in LLC/SNAP frames, using long-format
   (48 bit) addresses.  The data field contains the IPv6 header and
   payload and is followed by the FDDI Frame Check Sequence, Ending
   Delimiter, and Frame Status symbols.


       +-------+                                               ^
       |  FC   |                                               |
       +-------+-------+-------+-------+-------+-------+       |
       |            Destination FDDI address           |       |
       +-------+-------+-------+-------+-------+-------+      FDDI
       |              Source FDDI address              |     header
       +-------+-------+-------+-------+-------+-------+       |
       | DSAP  | SSAP  |  CTL  |          OUI          |       |
       +-------+-------+-------+-------+-------+-------+       |
       |   Ethertype   |                                       v
       +-------+-------+-------+-------+-------+------+------+
       |            IPv6 header and payload ...              /
       +-------+-------+-------+-------+-------+------+------+



FDDI Header Fields:


FC          The Frame Code shall be in the range 50 to 57 hexadecimal,
            inclusive, with the three low order bits indicating the
            frame priority.  Transmission by hosts and routers of frames



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            with priority zero (FC =3D 50 hex) is discouraged in order to=

            aid implementors who wish to distinguish on-ring nodes from
            off-ring nodes.


DSAP, SSAP  Both the DSAP and SSAP fields shall contain the value AA
            hexadecimal, indictating SNAP encapsulation.


CTL         The Control field shall be set to 03 hexadecimal, indicating
            Unnumbered Information.


OUI         The Organizationally Unique Identifier shall be set to
            000000 hexadecimal.


Ethertype   The ethernet protocol type ("ethertype") shall be set to the
            value 86DD hexadecimal.


Stateless Autoconfiguration and Link-Local Addresses

   The address token [CONF] for an FDDI interface is the interface's
   built-in 48-bit IEEE 802 address, in canonical bit order.  A
   different MAC address set manually or by software should not be used
   as the address token.

   An IPv6 address prefix used for stateless autoconfiguration of an
   FDDI interface must be 80 bits in length.

   The IPv6 Link-local address [AARCH] for an FDDI interface is formed
   by appending the interface's IEEE 802 address to the 80-bit prefix
   FE80::.


      +-------+-------+-------+-------+-------+-------+------+------+
      |  FE      80      00      00      00      00      00     00  |
      +-------+-------+-------+-------+-------+-------+------+------+
      |  00      00   |                  FDDI Address               |
      +-------+-------+-------+-------+-------+-------+------+------+



Address Mapping -- Unicast

   The procedure for mapping IPv6 addresses into FDDI link-layer
   addresses is described in [DISC].  The Source/Target Link-layer



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   Address option has the following form when the link layer is FDDI.


      +-------+-------+-------+-------+-------+-------+------+------+
      | Type  |Length |                 FDDI Address                |
      +-------+-------+-------+-------+-------+-------+------+------+



Option fields:


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


Length      1 (in units of 8 octets).


FDDI Address
            The 48 bit FDDI IEEE 802 address, in canonical bit order.


Address Mapping -- Multicast

   An IPv6 packet with a multicast destination address DST is
   transmitted to the FDDI multicast address whose first two octets are
   the value 3333 hexadecimal and whose last four octets are the last
   four octets of DST, ordered from more to least significant.


             +-------+-------+-------+-------+-------+-------+
             |  33   |  33   | DST13 | DST14 | DST15 | DST16 |
             +-------+-------+-------+-------+-------+-------+



Open Issues

   What about subnets bridged together with different MTU?  For example,
   Ethernet and FDDI.  This will be addressed in a separate document.


Security Considerations

   Security considerations are not addressed in this memo.





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References


[AARCH] R. Hinden, S. Deering, IP Version 6 Addressing Architecture.
        Currently draft-ietf-ipngwg-addr-arch-03.txt.


[CONF]  S. Thomson, IPv6 Stateless Address Autoconfiguration.  Currently
        draft-ietf-addrconf-ipv6-03.txt.


[DISC]  T. Narten, E. Nordmark, W. A. Simpson, Neighbor Discovery for IP
        Version 6 (IPv6).  Currently draft-ietf-ipngwg-discovery-01.txt.


[IPV6]  S. Deering, R. Hinden, Internet Protocol, Version 6 (IPv6)
        Specification.  Currently draft-ietf-ipngwg-ipv6-spec-02.txt.


Author's Address

   Matt Crawford
   Fermilab MS 368
   PO Box 500
   Batavia, IL 60510
   USA

   Phone: +1 708 840-3461

   EMail: crawdad@fnal.gov





















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