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rfc:rfc2497

Network Working Group I. Souvatzis Request for Comments: 2497 The NetBSD Project See Also: 1201 January 1999 Category: Standards Track

         Transmission of IPv6 Packets over ARCnet 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 (1999).  All Rights Reserved.

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

 IPv6 packets are link layer fragmented and reassembled according to
 [PHDS]. A brief but sufficient discussion of this fragmentation
 method can be found in [ARCIPV4].
 The protocol ID (System Code in ARCnet terminology) assigned to IPv6
 is C4 hexadecimal.

Souvatzis Standards Track [Page 1] RFC 2497 IPv6 Datagrams on ARCnet January 1999

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.
 The default MTU for IPv6 [IPV6] packets on an ARCnet is 9072 octets.
 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-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:

Souvatzis Standards Track [Page 2] RFC 2497 IPv6 Datagrams on ARCnet January 1999

 |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 ARCnet 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 |               |
          +---------------+              -+
          |                               |
          +-    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.

Souvatzis Standards Track [Page 3] RFC 2497 IPv6 Datagrams on ARCnet January 1999

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 memo are either based on
 [ETHIPV6] or on Matt Crawford's review of an earlier version.

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.
 [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)", RFC 2461, December
           1998.
 [ETHIPV6] Crawford, M., "Transmission of IPv6 Packets over Ethernet
           Networks", RFC 2464, December 1998.
 [EUI64]   "64-Bit Global Identifier Format Tutorial", http://stan­
           dards.ieee.org/db/oui/tutorials/EUI64.html.
 [IPV6]    Deering, S. and R. Hinden, "Internet Protocol, Version 6
           (IPv6) Specification", RFC 2460, December 1998.
 [KWORD]   Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997.
 [PHDS]    Novell, Inc., "ARCNET Packet Header Definition Standard",
           Novell Part Number 100-00721-001, November 1989.

Souvatzis Standards Track [Page 4] RFC 2497 IPv6 Datagrams on ARCnet January 1999

11. Author's Address

 Ignatios Souvatzis
 The NetBSD Project
 Stationenweg 29
 D-53332 Bornheim
 Germany
 Phone (work): +49 (228) 734316
 EMail: is@netbsd.org

Souvatzis Standards Track [Page 5] RFC 2497 IPv6 Datagrams on ARCnet January 1999

12. Full Copyright Statement

 Copyright (C) The Internet Society (1999).  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.

Souvatzis Standards Track [Page 6]

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