IPv6 over Ethernet: Transmission of IPv6 Packets over Ethernet Networks
How IPv6 packets ride inside Ethernet frames, and how an Ethernet card gets its IPv6 addresses.
Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, <https://www.rfc-editor.org/info/rfc2464>.
@misc{rfc2464,
series = {Request for Comments},
number = 2464,
howpublished = {RFC 2464},
publisher = {RFC Editor},
doi = {10.17487/RFC2464},
url = {https://www.rfc-editor.org/info/rfc2464},
author = {M. Crawford},
title = {{Transmission of IPv6 Packets over Ethernet Networks}},
pagetotal = 7,
year = 1998,
month = dec,
} RFC text
Contents
Network Working Group M. Crawford
Request for Comments: 2464 Fermilab
Obsoletes: 1972 December 1998
Category: Standards Track
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.
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 replaces RFC 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.
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.)
4. 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.
5. 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.
7. 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 From RFC 1972
The following are the functional differences between this
specification and RFC 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.
[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.gov
12. 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.
AI ELI5
On this page
§1What This RFC Covers
RFC 2464 specifies three things for IPv6 on Ethernet: the frame format, the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses, and the content of the Source/Target Link-layer Address option.
That option is used in Router Solicitation, Router Advertisement, Neighbor Solicitation, Neighbor Advertisement and Redirect messages when they are sent on an Ethernet. The document replaces RFC 1972, which the text says will become historic.
For this document, the term Ethernet includes CSMA/CD and full-duplex subnetworks based on ISO/IEC 8802-3, with various data rates.
It is a short instruction sheet for using IPv6 on ordinary network cables: how to pack the data, how to name your device, and how to find your neighbors.
§2Maximum Transmission Unit
The default MTU for IPv6 packets on an Ethernet is 1500 octets. That size may be reduced by a Router Advertisement carrying an MTU option with a smaller value, or by manual configuration of each node.
If a Router Advertisement on an Ethernet interface carries an MTU option larger than 1500, or larger than a manually configured value, the option may be logged to system management but must otherwise be ignored. Information received from DHCP counts as manually configured.
A truck can only carry so much at once. The default load is 1500 bytes, and a router can ask you to carry less, but never more.
§3The Ethernet Frame
IPv6 packets are sent in standard Ethernet frames. The Ethernet header holds the destination and source Ethernet addresses and the Ethernet type code, which must contain the value 86DD hexadecimal.
The data field holds the IPv6 header followed immediately by the payload, and possibly padding octets to reach the minimum frame size for the Ethernet link.
The frame is an envelope with the receiver's address, your address, and a stamp that says 'IPv6 inside'. The letter goes in the middle.
§4Interface Identifiers and Link-Local Addresses
The Interface Identifier of an Ethernet interface is based on the EUI-64 identifier derived from the interface's built-in 48-bit IEEE 802 address. The first three octets (the OUI) become the company_id of the EUI-64, the fourth and fifth octets are set to FFFE hexadecimal, and the last three octets of the Ethernet address become the last three octets of the EUI-64.
The Interface Identifier is then made by complementing the Universal/Local bit, the next-to-lowest order bit of the first octet. For the built-in address 34-56-78-9A-BC-DE the result is 36-56-78-FF-FE-9A-BC-DE.
A different MAC address set manually or by software should not be used for this. An IPv6 address prefix used for stateless autoconfiguration of an Ethernet interface must be 64 bits long. The link-local address is formed by appending the Interface Identifier to the prefix FE80::/64.
Your device builds its name from the serial number printed on its network card, with a little flip of one switch. Then it adds a standard 'this street only' start to make an address for talking to neighbors.
§6Mapping IPv6 Addresses to Ethernet Addresses
For unicast addresses, the mapping procedure is described in the Neighbor Discovery specification. This RFC defines the Source/Target Link-layer Address option for Ethernet: a Type field (1 for a Source Link-layer address, 2 for a Target Link-layer address), a Length of 1 in units of 8 octets, and the 48-bit Ethernet address in canonical bit order.
That address is the one the interface currently responds to, which may differ from the built-in address used to derive the Interface Identifier.
For multicast, a packet with destination address DST (octets DST[1] to DST[16]) is sent to the Ethernet multicast address whose first two octets are 3333 hexadecimal and whose last four octets are DST[13] through DST[16].
To mail a neighbor you need their street number on the cable. For group messages, the last part of the group address is copied behind a fixed beginning, like writing a group name on a shared mailbox.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 1 byte | 1 for Source Link-layer address, 2 for Target Link-layer address. | |
LENGTH | Length | 1 byte | 1 | 1, in units of 8 octets. |
ETH-ADDR | Ethernet Address | 6 bytes | The 48-bit IEEE 802 address, in canonical bit order. |
§8Differences From RFC 1972
The Address Token, which was a node's 48-bit MAC address, is replaced by the Interface Identifier, which is 64 bits long and based on the EUI-64 format. 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, and the link-local prefix is also shortened to 64 bits.
The old rule used a shorter name tag and a longer street. The new rule uses a longer name tag and a shorter street, so the two always add up the same.
| Item | RFC 1972 | RFC 2464 |
|---|---|---|
| Node identifier | Address Token: 48-bit MAC address | Interface Identifier: 64 bits, based on EUI-64 |
| Autoconfiguration prefix length THIS RFC | 80 bits | 64 bits |
§9Security Considerations
The way Interface Identifiers are derived from MAC addresses is meant to preserve global uniqueness when possible. The RFC adds that there is no protection from duplication through accident or forgery.
Your name tag comes from a serial number that should be one of a kind. But nobody stops two devices from wearing the same tag by mistake or on purpose.