Transmission of IPv6 Packets Over FDDI
RFC 2019

Document Type RFC - Proposed Standard (October 1996; No errata)
Obsoleted by RFC 2467
Last updated 2013-03-02
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Network Working Group                                        M. Crawford
Request for Comments: 2019                                      Fermilab
Category: Standards Track                                   October 1996

    A Method for the Transmission of IPv6 Packets over FDDI Networks

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.


   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
   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".

Crawford                    Standards Track                     [Page 1]
RFC 2019         Transmission of IPv6 Packets Over FDDI     October 1996

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 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.

Crawford                    Standards Track                     [Page 2]
RFC 2019         Transmission of IPv6 Packets Over FDDI     October 1996
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