RFC1972 - A Method for the Transmission of IPv6 Packets over Ethernet Networks

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　　Network Working Group M. Crawford
Request for Comments: 1972 Fermilab
Category: Standards Track August 1996

A Method for the Transmission of IPv6 Packets over Ethernet 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.

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.

+-------+-------+-------+-------+-------+-------+ ^
| 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 |
+-------+-------+-------+-------+-------+-------+-------+-------+

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 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", RFC1884, December 1995.

[CONF] Thomson, S., and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC1971, August 1996.

[DISC] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC1970, August 1996.

[IPV6] Deering, S., and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC1883, December 1995.

Author's Address

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

Phone: +1 708 840-3461
EMail: crawdad@fnal.gov

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