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Network Working Group                                        M. CrawfordRequest for Comments: 2467                                      FermilabObsoletes:2019                                            December 1998Category: Standards TrackTransmission of IPv6 Packets over FDDI NetworksStatus 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 replacesRFC 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 optionCrawford                    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 FromRFC 2019   The following are the functional differences between this   specification andRFC 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 199810.  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 199812.  Author's Address   Matt Crawford   Fermilab MS 368   PO Box 500   Batavia, IL 60510   USA   Phone: +1 630 840-3461   EMail: crawdad@fnal.govCrawford                    Standards Track                     [Page 8]

RFC 2467                     IPv6 over FDDI                December 199813.  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]