INTERNET-DRAFT I. Souvatzis Expires 1 April 1999 The NetBSD Project 1 October 1998 A Method for the Transmission of IPv6 Packets over ARCnet Networks. 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 and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``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 ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this memo is unlimited. Please send comments to the author. 1. Introduction This memo specifies a frame format for transmission of IPv6 [IPV6] packets and the method of forming IPv6 link-local and statelessly autoconfigured addresses on ARCnet networks. It also specifies the content of the Source/Target Link-layer Address option used by the Router Solicitation, Router Advertisement, Neighbor Solicitation, Neighbor Advertisement and Redirect messages described in [DISC], when those messages are transmitted on an ARCnet. 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 [KWORD]. 2. Frame Format Souvatzis Expires 1 April 1999 [Page 1] INTERNET-DRAFT IPv6 Datagrams on ARCnet 1 October 1998 IPv6 packets are link layer fragmented and reassembled according to [PHDS]. A brief but sufficient discussion of this fragmentation method can be found in [ARCIP4]. The protocol id used is D4 hexadecimal, the same as for IPv4. IPv6 packets are recognized by looking at the version number in the high half of the first octet of the data, which is 4 for IPv4 and 6 for IPv6. This method of distinguishing IPv6 packets was chosen because there are only 256 values of ARCnet protocol ids available. 3. Maximum Transmission Unit The maximum IPv6 packet length possible using this encapsulation method is 60480 octets. Since this length is impractical because of its worst case transmission time of several seconds, all ARCnet implementations on a given ARCnet network should agree on a smaller value. Implementations SHOULD support an MTU of 9072 octets and MUST support the minimum MTU required by [IPV6]. In the presence of a router, this size MAY be changed by a Router Advertisement [DISC] containing an MTU option. If a Router Advertisement is received with an MTU option specifying an MTU larger than 60480, or larger than a manually configured value less than 60480, that MTU option may be logged to system management but MUST be otherwise ignored. If no router is available, the local MTU MUST be left at 9072 or MUST be manually configured to the same different value on all connected stations. Implementations MAY accept arriving IPv6 datagrams which are larger than their configured maximum transmission unit. They are not required to discard such datagrams. If they can not handle larger datagrams, they MAY log the event to the system administration, but MUST otherwise silently discard them. 4. Stateless Auto-configuration If a node has an EUI-64 which is not used to form the Interface Identifier for any other interface, it SHOULD use that EUI-64 to form the Interface Identifier for its ARCnet interface. If that EUI-64 is in use for another interface attached to a different link, it MAY be used for the ARCnet interface as well. The Interface Identifier is then formed from the EUI-64 by complementing the "Universal/Local" (U/L) bit, which is the next- to- Souvatzis Expires 1 April 1999 [Page 2] INTERNET-DRAFT IPv6 Datagrams on ARCnet 1 October 1998 lowest order bit of the first octet of the EUI-64. When a node has no EUI-64 available for forming its ARCnet Interface Identifer, it MUST form that identifier as specified in [AARCH], Appendix A, section "Links with Non-Global Identifier". That is, the 8 bit manually configured ARCnet address is appended to the 56 zero bits. For example, for an ARCnet interface with the configured address of 49 hexadecimal this results in the following identifier: |0 1|1 3|3 4|4 6| |0 5|6 1|2 7|8 3| +----------------+----------------+----------------+----------------+ |0000000000000000|0000000000000000|0000000000000000|0000000001001001| +----------------+----------------+----------------+----------------+ Note that this results in the universal/local bit set to "0" to indicate local scope. An IPv6 address prefix used for stateless auto-configuration [ACONF] of an ARCnet 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 addresses into ARCnet link-layer addresses is described in [DISC]. The Source/Target link layer Address option has the following form when the link layer is ARCnet. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |ARCnet address | | +---------------+ -+ Souvatzis Expires 1 April 1999 [Page 3] INTERNET-DRAFT IPv6 Datagrams on ARCnet 1 October 1998 | | +- 5 octets of padding -+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option fields: Type 1 for Source Link-layer address. 2 for Target Link-layer address. Length 1 (in units of 8 octets). ARCnet address The 8 bit ARCnet address, in canonical bit order. 7. Address Mapping -- Multicast As ARCnet only provides 1 multicast address (00 hexadecimal), all IPv6 multicast addresses must be mapped to this address. 8. Security Considerations The method of derivation of Interface Identifiers from ARCnet addresses is intended to preserve local uniqueness when possible. However, there is no protection from duplication through accident or forgery. 9. Acknowledgements Big parts of the new version of this draft are either based on [ETHIPV6] or on Matt Crawfords review of an earlier version. 10. References [AARCH] Hinden, R., and S. Deering, "IP Version 6 Addressing Architec­ ture", RFC 2373. [ACONF] S. Thomson, T. Narten, "IPv6 Stateless Address Autoconfigura­ tion", currently draft-ietf-ipngwg-addrconf-v2-02.txt. [ARCIPV4] Provan, D., "Transmitting IP Traffic over ARCNET Networks", RFC1201, Novell, Inc., February 1991. [DISC] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", currently draft-ietf-ipngwg-discov­ ery-v2-03.txt. Souvatzis Expires 1 April 1999 [Page 4] INTERNET-DRAFT IPv6 Datagrams on ARCnet 1 October 1998 [ETHIPV6] M. Crawford, "Transmission of IPv6 Packets over Ethernet Net­ works", currently draft-ietf-ipngwg-trans-ethernet-04.txt [EUI64] "64-Bit Global Identifier Format Tutorial", http://stan­ dards.ieee.org/db/oui/tutorials/EUI64.html. [IPV6] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", currently draft-ietf-ipngwg-ipv6-spec- v2-02.txt. [KWORD] S.Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119. [PHDS] Novell, Inc., "ARCNET Packet Header Definition Standard", November 1989. Souvatzis Expires 1 April 1999 [Page 5] INTERNET-DRAFT IPv6 Datagrams on ARCnet 1 October 1998 10. Author's Address Ignatios Souvatzis The NetBSD Project Stationenweg 29 D-53332 Bornheim Germany Phone (work): +49 (228) 734316 EMail: is@netbsd.org Souvatzis Expires 1 April 1999 [Page 6]