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Transmission of IPv6 Packets Over FDDI

The information below is for an old version of the document that is already published as an RFC.
Document Type This is an older version of an Internet-Draft that was ultimately published as an RFC.
Author Dr. Matt Crawford
Last updated 2013-03-02 (Latest revision 1996-03-14)
Stream Internet Engineering Task Force (IETF)
Stream WG state (None)
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IESG IESG state RFC 2019 (Proposed Standard)
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Internet Engineering Task Force                            Matt Crawford
INTERNET-DRAFT                                                  Fermilab
<draft-ietf-ipngwg-fddi-ntwrks-03.txt>                 February 26, 1996

    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
   other documents at any time.  It is not appropriate to use Internet
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   draft" or "work in progress."

   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt'' listing contained in the Internet Drafts Shadow
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   Distribution of this memo is unlimited.


   This memo specifies the MTU and frame format for transmission of IPv6
   [IPV6] packets on FDDI networks, including a method for MTU
   determination in the presence of 802.1d bridges to other media.  It
   also specifies the method of forming IPv6 link-local addresses on
   FDDI networks and 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

   FDDI permits a frame length of 4500 octets (9000 symbols), including
   at least 22 octets (44 symbols) of Data Link encapsulation when
   long-format addresses are used.  Subtracting 8 octets of LLC/SNAP

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   header, this would, in principle, allow the IPv6 packet in the
   Information field to be up to 4470 octets.  However, it is desirable
   to allow for the variable sizes and possible future extensions to the
   MAC header and frame status fields.  The default MTU size for IPv6
   packets on an FDDI network is therefore 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 a
   smaller value on each node.  If a Router Advertisement is received
   with an MTU option specifying an MTU larger than the default or the
   manually configured value, that MTU option may be logged to system
   management but must be otherwise ignored.

   For purposes of this document, information received from DHCP is
   considered ``manually configured''.

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 ...              /

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FDDI Header Fields:

FC          The Frame Code must be in the range 50 to 57 hexadecimal,
            inclusive, with the three low order bits indicating the
            frame priority.  The Frame Code should be in the range 51 to
            57 hexadecimal, inclusive, for reasons given in the next

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.

Interaction with Bridges

   For correct operation when mixed media are bridged together, the
   smallest MTU of all the media must be manually configured in each
   node or advertised by routers in an MTU option.  Nodes transmitting
   IPv6 on FDDI should implement the following simple mechanism for
   ``FDDI adjacency detection''.

   If a node N1 receives, in an FDDI frame with a non-zero LLC priority,
   a valid Router Advertisement, Neighbor Advertisement, or Neighbor
   Solicitation from a node N2, then N1 may send unicast IPv6 packets to
   N2 with sizes up to the default IPv6 FDDI MTU (4352 octets),
   regardless of any smaller MTU configured manually or received in a
   Router Advertisement MTU option.  N2 may be the IPv6 destination or
   the next hop router to the destination.

   Nodes implementing FDDI adjacency detection must provide a
   configuration option to disable the mechanism.  This option may be
   used when a smaller MTU is desired for reasons other than mixed-media
   bridging.  By default, FDDI adjacency detection should be enabled.

   The only contemplated use of the LLC priority field of the FC octet
   is to aid in per-destination MTU determination.  It would be
   sufficient for that purpose to require only that Router
   Advertisements, Neighbor Advertisements, and Neighbor Solicitations
   sent on FDDI always have non-zero priority.  However, it may be
   simpler or more useful to transmit all IPv6 packets on FDDI with

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   non-zero priority.

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 and with the
   octet in the same order in which they would appear in the header of
   an ethernet frame.  (The individual/group bit is in the first octet
   and the OUI is in the first three octets.) 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

      |  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
   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.
            This is the address the interface currently responds to, and
            may be different from the built-in address used as the

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            address token.

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 |

Security Considerations

   Security considerations are not addressed in this memo.


   Erik Nordmark contributed to the method for interaction with bridges.


[AARCH] R. Hinden, S. Deering, IP Version 6 Addressing Architecture.

[CONF]  S. Thomson, IPv6 Stateless Address Autoconfiguration.  Currently

[DISC]  T. Narten, E. Nordmark, W. A. Simpson, Neighbor Discovery for IP
        Version 6 (IPv6).  Currently draft-ietf-ipngwg-discovery-05.txt.

[IPV6]  S. Deering, R. Hinden, Internet Protocol, Version 6 (IPv6)
        Specification.  RFC1883.

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Author's Address

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

   Phone: +1 708 840-3461


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