Internet Draft IPng Working Group Matt Crawford Internet Draft Fermilab July 3, 1997 Transmission of IPv6 Packets over Ethernet Networks <draft-ietf-ipngwg-trans-ethernet-01.txt> Status of this Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). Distribution of this memo is unlimited. 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 [KWORD]. Expires January 3, 1998 Crawford [Page 1] =0C Internet Draft IPv6 Over Ethernet July 3, 1997 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 MTU, if any, that MTU option must be ignored. 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 Ethernet. 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.) Expires January 3, 1998 Crawford [Page 2] =0C Internet Draft IPv6 Over Ethernet July 3, 1997 4. Stateless Autoconfiguration The interface token [CONF] 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 token 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 token is signified by a 1 in the corresponding position. For example, the interface token 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 token. 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 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 token, as defined above, to the prefix FE80::/64. Expires January 3, 1998 Crawford [Page 3] =0C Internet Draft IPv6 Over Ethernet July 3, 1997 10 bits 54 bits 64 bits +----------+-----------------------+----------------------------+ |1111111010| (zeros) | Interface Token | +----------+-----------------------+----------------------------+ 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 token. 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 Expires January 3, 1998 Crawford [Page 4] =0C Internet Draft IPv6 Over Ethernet July 3, 1997 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] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Security Considerations The method of derivation of interface tokens from MAC addresses is intended to preserve global uniqueness when possible. However, there is no protection from duplication through accident or forgery. 8. References [AARCH] R. Hinden, S. Deering "IP Version 6 Addressing Architecture", RFC 1884. [CONF] S. Thomson, T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 1971. [DISC] T. Narten, E. Nordmark, W. A. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 1970. [EUI64] "64-Bit Global Identifier Format Tutorial", http://standards.ieee.org/db/oui/tutorials/EUI64.html. [IPV6] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 1883. [KWORD] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels," RFC 2119. Expires January 3, 1998 Crawford [Page 5] =0C Internet Draft IPv6 Over Ethernet July 3, 1997 9. Author's Address Matt Crawford Fermilab MS 368 PO Box 500 Batavia, IL 60510 USA Phone: +1 630 840-3461 EMail: crawdad@fnal.gov Expires January 3, 1998 Crawford [Page 6]