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Network Working Group                                        M. CrawfordRequest for Comments: 1972                                      FermilabCategory: Standards Track                                    August 1996A Method for the Transmission 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.Introduction   This memo specifies the frame format for transmission of IPv6 [IPV6]   packets and the method of forming IPv6 link-local addresses on   Ethernet networks.  It also specifies 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 Ethernet.Maximum Transmission Unit   The default MTU size for 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 is received   with an MTU option specifying an MTU larger than 1500, or larger than   a manually configured value less than 1500, that MTU option must be   ignored.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 Ethernet.Crawford                    Standards Track                     [Page 1]

RFC 1972       Transmission of IPv6 Packets Over Ethernet    August 1996       +-------+-------+-------+-------+-------+-------+       ^       |          Destination Ethernet address         |       |       +-------+-------+-------+-------+-------+-------+    ethernet       |            Source Ethernet address            |     header       +-------+-------+-------+-------+-------+-------+       |       |  86      DD   |                                       v       +-------+-------+-------+-------+-------+------+------+       |            IPv6 header and payload ...              /       +-------+-------+-------+-------+-------+------+------+Stateless Autoconfiguration and Link-Local Addresses   The address token [CONF] for an Ethernet interface is the interface's   built-in 48-bit IEEE 802 address, in canonical bit order and with the   octets in the same order in which they would appear in the header of   an ethernet frame.  (The individual/group bit is in the first octet   and the OUI is in the first three octets.) A different MAC address   set manually or by software should not be used as the address token.   An IPv6 address prefix used for stateless autoconfiguration of an   ethernet interface must be 80 bits in length.   The IPv6 Link-local address [AARCH] for an Ethernet interface is   formed by appending the interface's IEEE 802 address to the 80-bit   prefix FE80::.      +-------+-------+-------+-------+-------+-------+------+------+      |  FE      80      00      00      00      00      00     00  |      +-------+-------+-------+-------+-------+-------+------+------+      |  00      00   |               Ethernet Address              |      +-------+-------+-------+-------+-------+-------+------+------+Address Mapping -- Unicast   The procedure for mapping IPv6 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.     +-------+-------+-------+-------+-------+-------+-------+-------+     | Type  |Length |               Ethernet Address                |     +-------+-------+-------+-------+-------+-------+-------+-------+Crawford                    Standards Track                     [Page 2]

RFC 1972       Transmission of IPv6 Packets Over Ethernet    August 1996Option 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 as            the address token.Address Mapping -- Multicast   An IPv6 packet with a multicast destination address DST 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, ordered from more to least significant.             +-------+-------+-------+-------+-------+-------+             |   33  |   33  | DST13 | DST14 | DST15 | DST16 |             +-------+-------+-------+-------+-------+-------+Security Considerations   Security issues are not discussed in this memo.References   [AARCH] Hinden, R., and S. Deering, "IP Version 6 Addressing           Architecture",RFC 1884, December 1995.   [CONF] Thomson, S., and T. Narten, "IPv6 Stateless Address          Autoconfiguration",RFC 1971, August 1996.   [DISC] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery          for IP Version 6 (IPv6)",RFC 1970, August 1996.   [IPV6] Deering, S., and R. Hinden, "Internet Protocol, Version 6          (IPv6) Specification",RFC 1883, December 1995.Crawford                    Standards Track                     [Page 3]

RFC 1972       Transmission of IPv6 Packets Over Ethernet    August 1996Author's Address   Matt Crawford   Fermilab MS 368   PO Box 500   Batavia, IL 60510   USA   Phone: +1 708 840-3461   EMail: crawdad@fnal.govCrawford                    Standards Track                     [Page 4]