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Versions: 00 01 02 03 04 05 rfc2497                                     
INTERNET-DRAFT                                              I. Souvatzis
Expires 1 February 1998                               The NetBSD Project
                                                           1 August 1997

  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
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   ftp.isi.edu (US West Coast).

   Distribution of this memo is unlimited. Please send comments to the

1. Introduction

   This memo specifies a frame format for transmission of IPv6 [IPV6]
   packets and the method of forming IPv6 link-local 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, and Neighbor Advertisement
   messages described in [DISC], when those messages are transmitted on
   an ARCnet.

2. Frame Format

   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 hexadecimal 0xD4, the same as for IPv4. IPv6
   packets are recognized by looking at the version number in the high

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   half of the first octet of the data, which is 4 for IPv4 and 6 for

3. Maximum Transmission Unit

   The maximum IPv6 packet length possible using this encapsulation
   method is 60,480 octets. Since this length is impractical, all ARCnet
   implementations on a given ARCnet network will need to agree on a
   smaller value. In the presence of a router, this size should be
   reduced by a Router Advertisement [DISC] containing an MTU option, or
   by manual configuration of each node. 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 must be ignored.

   In any case, implementations must be able to send and receive IPv6
   datagrams up to 576 octets in length, and are strongly encouraged to
   handle IPv6 datagrams up to 1500 octets in length.

   Implementations may accept arriving IPv6 datagrams which are larger
   than their configured maximum transmission unit.  They are not
   required to discard such datagrams.

4. Stateless Auto-configuration

   The Interface Identifier [AARCH] for an ARCnet interface is based on
   the EUI-64 identifier [EUI64] derived from the interface's configured
   8-bit address. The EUI-64 is formed by taking the 8 bit configured
   interface address and zero filling it to the left.

   For example, for an ARCnet interface with the configured hexidecimal
   address of 0x49 this results in the following identifier:

   |0              1|1              3|3              4|4              6|
   |0              5|6              1|2              7|8              3|

   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 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

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   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 |               |
                    +---------------+              -+
                    |                               |
                    +-    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 (hex 0x00), all IPv6
   multicast packets 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

9. References

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   [AARCH]   Hinden, R., and S. Deering, "IP Version 6 Addressing Archi-
             tecture", Currently draft-ietf-ipngwg-addr-arch-v2-02.txt.

   [ARCIPV4] Provan, D., "Transmitting IP Traffic over ARCNET Networks",
             RFC1201, Novell, Inc., February 1991.

   [CONF]    Thomson, S., and T. Narten, "IPv6 Stateless Address Auto-
             configuration", RFC 1971, August 1996.

   [DISC]    Narten, T., Nordmark, E., and W. Simpson, "Neighbor
             Discovery for IP Version 6 (IPv6)", RFC 1970, August 1996.

   [EUI64]   "64-Bit Global Identifier Format Tutorial",

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

   [PHDS]    Novell, Inc., "ARCNET Packet Header Definition Standard",
             Novell, Inc., November 1989.

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10. Author's Address

             Ignatios Souvatzis
             The NetBSD Project
             Stationenweg 29
             D-53332 Bornheim

             Phone (work): +49 (228) 734316

             EMail: is@netbsd.org

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