IANA Guidelines for IPv4 Multicast Address Assignments
Internet Corporation for Assigned Names and Numbers
4676 Admiralty Way, Suite 33090292Marina del ReyUnited States+310-823-9358michelle.cotton@icann.org
http://www.iana.org/
Internet Corporation for Assigned Names and Numbers
4676 Admiralty Way, Suite 33090292Marina del ReyUnited States+310-823-9358leo.vegoda@icann.org
http://www.iana.org/
dmm@1-4-5.netipv4multicastguidelines
This document provides guidance for the Internet Assigned Numbers
Authority (IANA) in assigning IPv4 multicast addresses. It obsoletes RFC 3171 and RFC 3138.
The Internet Assigned Numbers Authority (IANA) (www.iana.org) is
charged with allocating parameter values for fields in protocols
which have been designed, created or are maintained by the Internet
Engineering Task Force (IETF). RFC 2780 [RFC2780] provides the IANA
guidance in the assignment of parameters for fields in newly
developed protocols. This memo expands on section 4.4.2 of RFC 2780
and attempts to codify existing IANA practice used in the assignment
IPv4 multicast addresses.
This document is a revision of RFC 3171 , which it
obsoletes. It also obsoletes RFC 3138 .
The terms "Specification Required", "Expert Review", "IESG Approval",
"IETF Review", and "Standards Action", are used in this memo to
refer to the processes described in .
In general, due to the relatively small size of the IPv4 multicast
address space, further assignment of IPv4 multicast address space
is recommended only in limited circumstances. Specifically, the IANA
should only assign addresses in those cases where the dynamic
selection (SDP/SAP), GLOP, SSM or Administratively Scoped address
spaces cannot be used. The guidelines described below are reflected
in . Network operators
should also be aware of the availability of IPv6 multicast addresses and
consider using them where feasible.
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 BCP 14, RFC 2119 .
The word "allocation" designates a block of addresses managed by
a registry for the purpose of making assignments and allocations.
The word "assignment" designates a block of addresses, or a single
address, registered to an end-user for use on a specific network,
or set of networks.
Unlike IPv4 unicast address assignment, where blocks of addresses are
delegated to Regional Internet Registries (RIRs), IPv4 multicast addresses
are assigned directly by the IANA. Current registration groups appear as
follows :
The IANA generally assigns addresses from the Local Network Control,
Internetwork Control and AD-HOC blocks. Assignment guidelines for
each of these blocks, as well as for the Source Specific Multicast,
GLOP and Administratively Scoped Blocks, are described below.
Addresses in the Local Network Control block are used for protocol
control traffic that is not forwarded off link. Examples of this
type of use include OSPFIGP All Routers (224.0.0.5) .
Pursuant to section 4.4.2 of , assignments from the
Local Network Control block follow an Expert Review, IESG Approval or
Standards Action process. See IANA for the current set of
assignments.
Addresses in the Internetwork Control block are used for protocol
control traffic that MAY be forwarded through the Internet. Examples
include 224.0.1.1 (NTP ) and 224.0.1.68 (mdhcpdiscover
).
Pursuant to section 4.4.2 of , assignments from the
Internetwork Control block follow an Expert Review, IESG Approval or
Standards Action process. See IANA for the current set of
assignments.
Addresses in the AD-HOC blocks were traditionally used for assignments for
those applications that don't fit in either the Local or Internetwork
Control blocks. These addresses MAY be globally routed and are
typically used by applications that require small blocks of
addressing (e.g., less than a /24 ). Future assignments of blocks of addresses that do not
fit in the Local or Internetwork block will be made in the Ad-Hoc Block III.
In general, the IANA SHOULD NOT assign addressing in the AD-HOC
Blocks. However, the IANA MAY under special circumstances,
assign addresses from these blocks. Pursuant to section 4.4.2 of
, assignments from the AD-HOC blocks follow an Expert
Review, IESG Approval or Standards Action process. See for
the current set of assignments.
Addresses in the SDP/SAP block are used by applications that receive
addresses through the Session Announcement Protocol for use
via applications like the session directory tool (such as SDR [SDR]).
Since addresses in the SDP/SAP block are chosen randomly from the
range of addresses not already in use , no IANA assignment
policy is required. Note that while no additional IANA assignment is
required, addresses in the SDP/SAP block are explicitly for use by
SDP/SAP and MUST NOT be used for other purposes.
The Source Specific Multicast (SSM) is an extension of IP Multicast
in which traffic is forwarded to receivers from only those multicast
sources for which the receivers have explicitly expressed interest,
and is primarily targeted at one-to-many (broadcast) applications.
Note that this block was initially assigned to the VMTP transient
groups .
Because the SSM model essentially makes the entire multicast address
space local to the host, no IANA assignment policy is required.
Note, however, that while no additional IANA assignment is required,
addresses in the SSM block are explicitly for use by SSM and MUST NOT
be used for other purposes.
Addresses in the GLOP block are globally scoped statically assigned
addresses. The assignment is made, for a domain with 16 bit
Autonomous System Number (ASN), by mapping a domain's autonomous
system number, expressed in octets as X.Y, into the middle two
octets of the GLOP block, yielding an assignment of 233.X.Y.0/24.
The mapping and assignment is defined in . Domains
with 32 bit ASN should apply for space in AD-HOC Block III, or
consider using IPv6 multicast addresses.
Because addresses in the GLOP block are algorithmically pre-assigned,
no IANA assignment policy is required.
delegated to the RIRs the assignment of the GLOP sub-block (233.252.0.0 - 233.255.255.255)
mapped by the private AS space (64512-65534) and the IANA reserved ASN 65535
. This space was known as eGLOP. RFC 3138 should not have
asked the RIRs to develop policies for the EGLOP space because reserves that
to the IETF. It is important to make this space available for use by network operators
and it is therefore appropriate to obsolete RFC 3138 and classify this address range
as available for AD-HOC assignment as per the guidelines in section 6.
The first /24 in this range, 233.252.0.0/24, is assigned as
"MCAST-TEST-NET" for use in documentation and example code.
233.252.0.0/24 SHOULD be used in conjunction with the domain names
example.com or example.net in vendor and protocol documentation. Addresses
within 233.252.0.0/24 MUST NOT appear on the public Internet.
Addresses in the Administratively Scoped Address block are for local
use within a domain and are described in .
Since addresses in this block are local to a domain, no IANA
assignment policy is required.
The relative offsets are used to ensure that a service can
be located independent of the extent of the enclosing scope (see
for details). Since there are only 256 such offsets, the IANA
should only assign a relative offset to a protocol that provides an
infrastructure supporting service. Examples of such services include
the Session Announcement Protocol . Pursuant to section
4.4.2 of , assignments of Relative Offsets follow
an Expert Review, IESG Approval or Standards Action process. See
for the current set of assignments.
Requests for multicast address assignments can be submitted through the
application form on the IANA web site at:
It is important to submit sufficient detail to allow the IESG designated
expert to review the application. If the details given in the request are not
clear, or further information is needed, the IESG designated expert may
request additional information before assigning an address.
Occasionally more than one multicast address is required. In these cases
multiple addresses are available in AD-HOC Block III. Where there is a
requirement for a very large number of addresses, the assignment will be
staged. The additional stages will only be made after the complete use of
the initial assignment(s).
A separate document describing the policy governing assignment of addresses
in the AD-HOC blocks I, II and III will be developed and published.
The format, location and content has not yet been decided and so these will
be documented in a future version of this document.
Given the dynamic nature of IPv4 multicast and its associated
infrastructure, and the previously undocumented IPv4 multicast address
assignment guidelines, the IANA should conduct an annual review of
currently assigned addresses.
During the review described above, addresses that were mis-assigned
should, where possible, be reclaimed or reassigned.
The IANA should also review assignments in the AD-HOC, "DIS Transient
Groups", and ST Multicast Groups blocks and reclaim those addresses
that are not in use on the global Internet (i.e, those applications
which can use SSM, GLOP, or Administratively Scoped addressing, or
are not globally routed).
It is occasionally appropriate to make temporary assignments that can be
renewed as necessary. In cases where this happens the registrant needs to
positively request an extension to the temporary assignment or the addresses
assigned. When the IANA has not received a request to renew the registration
of a temporary assignment within 30 days of the expiry of the assignment it
MUST be removed from the multicast registry.
Addresses returned to the IANA when a temporary assignment ends MUST NOT be
assigned to anyone other than the last registrant for at least one calendar year.
Applications MUST NOT use addressing in the IANA reserved blocks.
IANA is requested to update its IPv4 multicast request and
assignment procedures to reflect this document.
The assignment guidelines described in this document do not alter the
security properties of either the Any Source or Source Specific
multicast service models.
The authors would like to thank Joe St. Sauver, John Meylor, Randy
Bush, Thomas Narten, Marshall Eubanks, Zaid Albanna (co-author of RFC3171),
Kevin Almeroth (co-author of RFC3171) Pekka Savola and Alfred Hoenes for their
constructive feedback and comments.
IANA Matrix for Protocol Parameter Assignment/Registration ProceduresIANA