IPv6 Multicast Address Scopes

RFC 4291 defines "scop is a 4-bit multicast scope value used to limit the scope of the multicast group." scop 3 is defined as "reserved" in RFC 4291. The multicast protocol specification in draft-ietf-roll-trickle-mcast desires to use multicast scop 3 for transport of multicast traffic scoped to a network of nodes connected in a mesh. The use of this scop value is to accommodate a multicast scope that is greater than Link-Local but is also automatically determined by the network architecture.

The following table updates the definitions in RFC 4291:

The following change is applied to section 2.7 of RFC 4291:

The definition of any Realm-Local scope for a particular network technology should be published in an RFC. For example, such a scope definition would be appropriate for publication in an "IPv6-over-foo" RFC. Any RFCs that include the definition of a Realm-Local scope will be added to the IANA 'IPv6 Multicast Address Scopes' registry under the Realm-Local scope entry, and those specifications must include such a request in their IANA Considerations. of this document gives the definition of scop 3 for IEEE 802.15.4 networks.

Section 5 of RFC 4007 and section 2.7 of RFC 4291 disagree about the way in which multicast scope 3 is configured. To resolve that disagreement, change the last bullet in the list in section 5 of RFC 4007 as follows:

When used in an IP-over-IEEE802.15.4 network, "scop 3" is defined to include all interfaces sharing a PAN ID.

IANA is requested to establish a sub-registry titled "IPv6 Multicast Address Scopes" in the existing "Internet Protocol version 6 (IPv6) Multicast Address Allocations" registry. The new registry is to be populated with the scope values given in . New definitions for scop values will be made with "IETF Review" policy. IANA is requested to add a reference to the Realm-Local scope entry (scop 3) in the "IPv6 Multicast Address Scopes" registry for each future RFC that defines a Realm-Local scope for new network technologies. Such RFCs are expected to make an explicit request to IANA for inclusion in the registry. IANA is requested to include a note to the top of the "IPv6 Multicast Address Scopes" registry:

Robert Cragie, Kerry Lynn, Jinmei Tatuya, Dave Thaler and Stig Venaas all contributed text and/or review to ensure that the updates to RFC 4007 and RFC 4291 are correct.

This document has no security considerations beyond those in RFC 4007 and RFC 4291.