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Network Working Group                                       I. SouvatzisRequest for Comments: 2497                            The NetBSD ProjectSee Also: 1201                                              January 1999Category: Standards TrackTransmission of IPv6 Packets over ARCnet NetworksStatus 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 inRFC 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 19993. 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 19997. 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 199911. Author's Address   Ignatios Souvatzis   The NetBSD Project   Stationenweg 29   D-53332 Bornheim   Germany   Phone (work): +49 (228) 734316   EMail: is@netbsd.orgSouvatzis                   Standards Track                     [Page 5]

RFC 2497                IPv6 Datagrams on ARCnet            January 199912.  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]