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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",
 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 1998

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,
 would be
 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 1998

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
                  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 1998

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
                |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.

Crawford Standards Track [Page 5] RFC 2464 IPv6 Packets over Ethernet December 1998

 [EUI64] "Guidelines For 64-bit Global Identifier (EUI-64)",
 [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
 Phone: +1 630 840-3461

Crawford Standards Track [Page 6] RFC 2464 IPv6 Packets over Ethernet December 1998

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
 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

Crawford Standards Track [Page 7]

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