Internet Engineering Task Force (IETF) R. Droms
Request for Comments: 7346 Cisco
Updates: 4007, 4291 August 2014
Category: Standards Track
IPv6 Multicast Address Scopes
This document updates the definitions of IPv6 multicast scopes and
therefore updates RFCs 4007 and 4291.
Status of This Memo
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RFC 4291 [RFC4291] defines "scop" as "a 4-bit multicast scope value
used to limit the scope of the multicast group" and defines "scop 3"
as "reserved". The multicast protocol specification in [MPL] desires
to use multicast scop 3 to transport multicast traffic scoped to a
network of nodes connected in a mesh. This scop value is used to
accommodate a multicast scope that is greater than Link-Local but is
also automatically determined by the network architecture.
2. Definition of IPv6 Multicast Address Scopes (Updates RFC 4291)
The following table updates the definitions in [RFC4291]:
| scop | NAME | REFERENCE |
| 0 | Reserved | [RFC4291], RFC 7346 |
| 1 | Interface-Local scope | [RFC4291], RFC 7346 |
| 2 | Link-Local scope | [RFC4291], RFC 7346 |
| 3 | Realm-Local scope | [RFC4291], RFC 7346 |
| 4 | Admin-Local scope | [RFC4291], RFC 7346 |
| 5 | Site-Local scope | [RFC4291], RFC 7346 |
| 6 | Unassigned | |
| 7 | Unassigned | |
| 8 | Organization-Local scope | [RFC4291], RFC 7346 |
| 9 | Unassigned | |
| A | Unassigned | |
| B | Unassigned | |
| C | Unassigned | |
| D | Unassigned | |
| E | Global scope | [RFC4291], RFC 7346 |
| F | Reserved | [RFC4291], RFC 7346 |
The following change is applied to Section 2.7 of [RFC4291].
Admin-Local scope is the smallest scope that must be
administratively configured, i.e., not automatically derived from
physical connectivity or other, non-multicast-related
Interface-Local, Link-Local, and Realm-Local scope boundaries are
automatically derived from physical connectivity or other non-
multicast-related configurations. Global scope has no boundary.
The boundaries of all other non-reserved scopes of Admin-Local or
larger are administratively configured. For reserved scopes, the
way of configuring their boundaries will be defined when the
semantics of the scope are defined.
According to RFC 4007 [RFC4007], the zone of a Realm-Local scope
must fall within zones of larger scope. Because the zone of a
Realm-Local scope is configured automatically while the zones of
larger scopes are configured manually, care must be taken in the
definition of those larger scopes to ensure that the inclusion
constraint is met.
Realm-Local scopes created by different network technologies are
considered to be independent and will have different zone indices
(see Section 6 of [RFC4007]). A router with interfaces on links
using different network technologies does not forward traffic
between the Realm-Local multicast scopes defined by those
3. Definition of Realm-Local Scopes
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"
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.
Section 5 of this document gives the definition of scop 3 for IEEE
802.15.4 [IEEE802.15.4] networks.
4. Definition of Automatic and Administratively Configured Scopes
(Updates RFC 4007)
Section 5 of RFC 4007 [RFC4007] and Section 2.7 of RFC 4291 [RFC4291]
disagree on the way in which multicast scop 3 is configured. To
resolve that disagreement, the last bullet in the list in Section 5
of [RFC4007] is updated as follows:
o The boundaries of zones of a scope other than interface-local,
link-local, and global must be defined and configured by network
o The boundaries of zones of a scope are defined by the IPv6
addressing architecture [RFC4291] and updated by RFC 7346.
5. Definition of Realm-Local Scope for IEEE 802.15.4
When used in an IP-over-IEEE802.15.4 network, scop 3 is defined to
include all interfaces sharing a Personal Area Network Identifier
6. IANA Considerations
IANA has established a sub-registry titled "IPv6 Multicast Address
Scopes" in the existing "IPv6 Multicast Address Space Registry". The
new registry has been populated with the scop values given in
Section 2. New definitions for scop values will be made following
the "IETF Review" policy [RFC5226].
For each future RFC that defines a Realm-Local scope for new network
technologies (scop 3), IANA will add a reference to the defining
document in the "IPv6 Multicast Address Scopes" registry. Such RFCs
are expected to make an explicit request to IANA for inclusion in the
IANA has included a note on the top of the "IPv6 Multicast Address
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-
Any RFCs that define a Realm-Local scope will be listed in this
registry as an additional reference in the Realm-Local scope
entry. Such RFCs are expected to make an explicit request to IANA
for inclusion in this 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.
8. Security Considerations
This document has no security considerations beyond those in RFC 4007
[RFC4007] and RFC 4291 [RFC4291].