The default MTU of 9072 octets was chosen because the theoretical maximum of 60480 octets is impractical due to its worst-case transmission time of several seconds over ARCnet. The MTU can be negotiated via Router Advertisement MTU options within the 60480 limit.

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A node with an EUI-64 already in use on another interface attached to a different link MAY reuse that EUI-64 for the ARCnet interface as well, allowing flexible address assignment in multi-interface nodes.

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All IPv6 multicast addresses MUST be mapped to the single ARCnet multicast address 00 hexadecimal, as ARCnet provides only one multicast address.

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An IPv6 address prefix used for stateless auto-configuration of an ARCnet interface MUST have a length of 64 bits.

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If a node has an EUI-64 not used for another interface, it SHOULD use that EUI-64 to form the Interface Identifier for its ARCnet interface, with the U/L bit complemented.

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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, the MTU option MUST be ignored (though it may be logged).

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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.

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Implementations MAY accept arriving IPv6 datagrams larger than their configured MTU and are not required to discard them. If they cannot handle larger datagrams, they MAY log the event but MUST otherwise silently discard them.

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The default MTU for IPv6 packets on an ARCnet network is 9072 octets. All ARCnet implementations on a given network should agree on this or a smaller value, as the theoretical maximum of 60480 octets has an impractical worst-case transmission time.

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When a node has no EUI-64 available, it MUST form the Interface Identifier by appending the 8-bit ARCnet address to 56 zero bits, as specified in RFC 2373 Appendix A for links with non-global identifiers.

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IPv6 packets are transmitted over ARCnet using link-layer fragmentation and reassembly according to the PHDS (ARCnet Packet Header Definition Standard). The protocol ID (System Code) assigned to IPv6 on ARCnet is C4 hexadecimal.

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The IPv6 link-local address for an ARCnet interface is formed by appending the 64-bit Interface Identifier to the prefix FE80::/64, yielding a 128-bit address with 10 bits of prefix (1111111010), 54 zero bits, and the Interface Identifier.

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The method of deriving Interface Identifiers from ARCnet addresses is intended to preserve local uniqueness when possible, but there is no protection from duplication through accident or forgery.

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The Interface Identifier for an ARCnet interface is formed from the EUI-64 by complementing the U/L bit (next-to-lowest order bit of the first octet). When no EUI-64 is available, the 8-bit ARCnet address is appended to 56 zero bits, resulting in a 64-bit identifier with the U/L bit set to 0 (local scope).

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The Source/Target Link-layer Address option for ARCnet is 16 bits (Length=1, in units of 8 octets): 1 byte Type, 1 byte Length, 1 byte ARCnet address in canonical bit order, followed by 5 bytes of padding.

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