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rfc:rfc2467

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

Crawford Standards Track [Page 1] RFC 2467 IPv6 over FDDI December 1998

 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.

Crawford Standards Track [Page 2] RFC 2467 IPv6 over FDDI December 1998

                    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.

Crawford Standards Track [Page 3] RFC 2467 IPv6 over FDDI December 1998

 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].

Crawford Standards Track [Page 4] RFC 2467 IPv6 over FDDI December 1998

 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           -+
              |                               |
              +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Crawford Standards Track [Page 5] RFC 2467 IPv6 over FDDI December 1998

 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.

Crawford Standards Track [Page 6] RFC 2467 IPv6 over FDDI December 1998

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.

Crawford Standards Track [Page 7] RFC 2467 IPv6 over FDDI December 1998

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

Crawford Standards Track [Page 8] RFC 2467 IPv6 over FDDI December 1998

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.

Crawford Standards Track [Page 9]

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