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Network Working Group                                        M. CrawfordRequest for Comments: 2464                                      FermilabObsoletes:1972                                            December 1998Category: Standards TrackTransmission of IPv6 Packets over Ethernet 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 Ethernet 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 Ethernet.   This document replacesRFC 1972, "A Method for the Transmission of   IPv6 Packets over Ethernet Networks", 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   The default MTU size for IPv6 [IPV6] packets on an Ethernet is 1500   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 each node.  If a Router Advertisement received on an   Ethernet interface has an MTU option specifying an MTU larger than   1500, or larger than a manually configured value, that MTU option may   be logged to system management but must be otherwise ignored.Crawford                    Standards Track                     [Page 1]

RFC 2464               IPv6 Packets over Ethernet          December 1998   For purposes of this document, information received from DHCP is   considered "manually configured" and the term Ethernet includes   CSMA/CD and full-duplex subnetworks based on ISO/IEC 8802-3, with   various data rates.3.  Frame Format   IPv6 packets are transmitted in standard Ethernet frames.  The   Ethernet header contains the Destination and Source Ethernet   addresses and the Ethernet type code, which must contain the value   86DD hexadecimal.  The data field contains the IPv6 header followed   immediately by the payload, and possibly padding octets to meet the   minimum frame size for the Ethernet link.                     0                   1                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                    |          Destination          |                    +-                             -+                    |            Ethernet           |                    +-                             -+                    |            Address            |                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                    |             Source            |                    +-                             -+                    |            Ethernet           |                    +-                             -+                    |            Address            |                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                    |1 0 0 0 0 1 1 0 1 1 0 1 1 1 0 1|                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                    |             IPv6              |                    +-                             -+                    |            header             |                    +-                             -+                    |             and               |                    +-                             -+                    /            payload ...        /                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                    (Each tic mark represents one bit.)Crawford                    Standards Track                     [Page 2]

RFC 2464               IPv6 Packets over Ethernet          December 19984.  Stateless Autoconfiguration   The Interface Identifier [AARCH] for an Ethernet 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.)   The OUI of the Ethernet 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 Ethernet 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.  Complementing   this bit will generally change a 0 value to a 1, since an interface's   built-in address is expected to be from a universally administered   address space and hence have a globally unique value.  A universally   administered IEEE 802 address or an EUI-64 is signified by a 0 in the   U/L bit position, while a globally unique IPv6 Interface Identifier   is signified by a 1 in the corresponding position.  For further   discussion on this point, see [AARCH].   For example, the Interface Identifier for an Ethernet 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 Ethernet interface must have a length of 64 bits.Crawford                    Standards Track                     [Page 3]

RFC 2464               IPv6 Packets over Ethernet          December 19985.  Link-Local Addresses   The IPv6 link-local address [AARCH] for an Ethernet 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    |     +----------+-----------------------+----------------------------+6.  Address Mapping -- Unicast   The procedure for mapping IPv6 unicast addresses into Ethernet link-   layer addresses is described in [DISC].  The Source/Target Link-layer   Address option has the following form when the link layer is   Ethernet.                    0                   1                    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                   |     Type      |    Length     |                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                   |                               |                   +-          Ethernet           -+                   |                               |                   +-           Address           -+                   |                               |                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Option fields:   Type        1 for Source Link-layer address.               2 for Target Link-layer address.   Length      1 (in units of 8 octets).   Ethernet Address               The 48 bit Ethernet 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.Crawford                    Standards Track                     [Page 4]

RFC 2464               IPv6 Packets over Ethernet          December 19987.  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   Ethernet 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]     |                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+8.  Differences FromRFC 1972   The following are the functional differences between this   specification andRFC 1972.       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.9.  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.10.  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.   [DISC]  Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery           for IP Version 6 (IPv6)",RFC 2461, December 1998.Crawford                    Standards Track                     [Page 5]

RFC 2464               IPv6 Packets over Ethernet          December 1998   [EUI64] "Guidelines For 64-bit Global Identifier (EUI-64)",http://standards.ieee.org/db/oui/tutorials/EUI64.html   [IPV6]  Deering, S. and R. Hinden, "Internet Protocol, Version 6           (IPv6) Specification",RFC 2460, December 1998.   [RFC 2119]  Bradner, S., "Key words for use in RFCs to Indicate           Requirement Levels",BCP 14,RFC 2119, March 1997.11.  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 6]

RFC 2464               IPv6 Packets over Ethernet          December 199812.  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 7]