





Network Working Group                                        M. Crawford
Request for Comments: 2467                                      Fermilab
Obsoletes: 2019                                            December 1998
Category: Standards Track


            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.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

1.  Introduction

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

   This document replaces RFC 2019, "Transmission of IPv6 Packets Over
   FDDI", which will become historic.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC 2119].

2.  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 [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 of 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



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   which specifies a smaller MTU, or by manual configuration of each
   node.  If a Router Advertisement received on an FDDI interface has an
   MTU option specifying an MTU larger than 4352, or larger than a
   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" and the term FDDI includes CDDI.

3.  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.



























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                      0                   1
                      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                                     +-+-+-+-+-+-+-+-+
                                     |      FC       |
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |          Destination          |
                     +-                             -+
                     |             FDDI              |
                     +-                             -+
                     |            Address            |
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |            Source             |
                     +-                             -+
                     |             FDDI              |
                     +-                             -+
                     |            Address            |
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |     DSAP      |     SSAP      |
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |      CTL      |      OUI ...  |
                     +-+-+-+-+-+-+-+-+               +
                     |          ... OUI              |
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |           Ethertype           |
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |             IPv6              |
                     +-                             -+
                     |            header             |
                     +-                             -+
                     |             and               |
                     +-                             -+
                     /            payload ...        /
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    (Each tic mark represents one bit.)

   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.

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

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




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   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.

4.  Interaction with Bridges

   802.1d MAC bridges which connect different media, for example
   Ethernet and FDDI, have become very widespread.  Some of them do IPv4
   packet fragmentation and/or support IPv4 Path MTU discovery [RFC
   1981], many others do not, or do so incorrectly.  Use of IPv6 in a
   bridged mixed-media environment must not depend on support from MAC
   bridges, unless those bridges are known to correctly implement IPv6
   Path MTU Discovery [RFC 1981, ICMPV6].

   For correct operation when mixed media are bridged together by
   bridges which do not support IPv6 Path MTU Discovery, the smallest
   MTU of all the media must be advertised by routers in an MTU option.
   If there are no routers present, this MTU must be manually configured
   in each node which is connected to a medium with a default MTU larger
   than the smallest MTU.

5.  Stateless Autoconfiguration

   The Interface Identifier [AARCH] for an FDDI interface is based on
   the EUI-64 identifier [EUI64] derived from the interface's built-in
   48-bit IEEE 802 address.  The EUI-64 is formed as follows.
   (Canonical bit order is assumed throughout.  See [CANON] for a
   caution on bit-order effects in LAN interfaces.)

   The OUI of the FDDI MAC address (the first three octets) becomes the
   company_id of the EUI-64 (the first three octets).  The fourth and
   fifth octets of the EUI are set to the fixed value FFFE hexadecimal.
   The last three octets of the FDDI MAC address become the last three
   octets of the EUI-64.

   The Interface Identifier is then formed from the EUI-64 by
   complementing the "Universal/Local" (U/L) bit, which is the next-to-
   lowest order bit of the first octet of the EUI-64.  For further
   discussion on this point, see [ETHER] and [AARCH].










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   For example, the Interface Identifier for an FDDI interface whose
   built-in address is, in hexadecimal,

                             34-56-78-9A-BC-DE

   would be

                         36-56-78-FF-FE-9A-BC-DE.

   A different MAC address set manually or by software should not be
   used to derive the Interface Identifier.  If such a MAC address must
   be used, its global uniqueness property should be reflected in the
   value of the U/L bit.

   An IPv6 address prefix used for stateless autoconfiguration [ACONF]
   of an FDDI interface must have a length of 64 bits.

6.  Link-Local Addresses

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

     10 bits            54 bits                  64 bits
   +----------+-----------------------+----------------------------+
   |1111111010|         (zeros)       |    Interface Identifier    |
   +----------+-----------------------+----------------------------+

7.  Address Mapping -- Unicast

   The procedure for mapping IPv6 unicast 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.

                 0                   1
                 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                |     Type      |    Length     |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                |                               |
                +-            FDDI             -+
                |                               |
                +-           Address           -+
                |                               |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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   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 to
               derive the Interface Identifier.

8.  Address Mapping -- Multicast

   An IPv6 packet with a multicast destination address DST, consisting
   of the sixteen octets DST[1] through DST[16], 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.

                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |0 0 1 1 0 0 1 1|0 0 1 1 0 0 1 1|
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |   DST[13]     |   DST[14]     |
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 |   DST[15]     |   DST[16]     |
                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

9.  Differences From RFC 2019

   The following are the functional differences between this
   specification and RFC 2019.

       "FDDI adjacency detection" has been removed, due to recent work
       in IEEE 802.1p.

       The Address Token, which was a node's 48-bit MAC address, is
       replaced with the Interface Identifier, which is 64 bits in
       length and based on the EUI-64 format [EUI64].  An IEEE-defined
       mapping exists from 48-bit MAC addresses to EUI-64 form.

       A prefix used for stateless autoconfiguration must now be 64 bits
       long rather than 80.  The link-local prefix is also shortened to
       64 bits.






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10.  Security Considerations

   The method of derivation of Interface Identifiers from MAC addresses
   is intended to preserve global uniqueness when possible.  However,
   there is no protection from duplication through accident or forgery.

11.  References

   [AARCH] Hinden, R. and S. Deering "IP Version 6 Addressing
           Architecture", RFC 2373, July 1998.

   [ACONF] Thomson, S. and T. Narten, "IPv6 Stateless Address
           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.

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

   [ETHER] Crawford, M., "Transmission of IPv6 Packets over Ethernet
           Networks", RFC 2464, December 1998.

   [EUI64] "Guidelines For 64-bit Global Identifier (EUI-64)",
           http://standards.ieee.org/db/oui/tutorials/EUI64.html.

   [ICMPV6]  Conta, A. and S. Deering, "Internet Control Message
             Protocol (ICMPv6) for the Internet Protocol Version 6
             (IPv6) Specification", RFC 2463, December 1998.

   [IPV6]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
           (IPv6) Specification", RFC 2460, December 1998.

   [RFC 1981]  McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery
               for IP version 6", RFC 1981, August 1996.

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













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12.  Author's Address

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

   Phone: +1 630 840-3461
   EMail: crawdad@fnal.gov









































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13.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  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.
























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