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.
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].
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.
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.
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:
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.
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.
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.
Copyright (C) The Internet Society (1999). All Rights Reserved.
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