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IETF RFC 5771
IANA Guidelines for IPv4 Multicast Address Assignments
Last modified on Monday, March 15th, 2010
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Internet Engineering Task Force (IETF) M. Cotton
Request for Comments: 5771 L. Vegoda
BCP: 51 ICANN
Updates: 2780 D. Meyer
Obsoletes: 3138, 3171 March 2010
Category: Best Current Practice
ISSN: 2070-1721
IANA Guidelines for IPv4 Multicast Address Assignments
 Abstract
This document provides guidance for the Internet Assigned Numbers
Authority (IANA) in assigning IPv4 multicast addresses. It obsoletes
RFC 3171 and RFC 3138 and updates RFC 2780.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 5771.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Cotton, et al. Best Current Practice PAGE 1 
RFC 5771 IPv4 Multicast Guidelines March 2010
Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................3
3. Definition of Current Assignment Practice .......................3
4. Local Network Control Block (224.0.0/24) ........................4
4.1. Assignment Guidelines ......................................4
5. Internetwork Control Block (224.0.1/24) .........................5
5.1. Assignment Guidelines ......................................5
6. AD-HOC Blocks (I, II, and III) ..................................5
6.1. Assignment Guidelines ......................................5
7. SDP/SAP Block (224.2/16) ........................................5
7.1. Assignment Guidelines ......................................5
8. Source-Specific Multicast Block (232/8) .........................6
8.1. Assignment Guidelines ......................................6
9. GLOP Block (233/8) ..............................................6
9.1. Assignment Guidelines ......................................6
9.2. AD-HOC Block III ...........................................6
10. Administratively Scoped Block (239/8) ..........................7
10.1. Assignment Guidelines .....................................7
10.1.1. Relative Offsets ...................................7
11. Application Form ...............................................7
11.1. Size of Assignments of IPv4 Multicast Addresses ...........7
12. Annual Review ..................................................8
12.1. Address Reclamation .......................................8
12.2. Positive Renewal ..........................................8
13. Use of IANA Reserved Addresses .................................8
14. IANA Considerations ............................................8
15. Security Considerations ........................................9
16. Acknowledgments ................................................9
17. References .....................................................9
17.1. Normative References ......................................9
17.2. Informative References ....................................9
1. Introduction
The Internet Assigned Numbers Authority (IANA) (www.iana.org) is
charged with allocating parameter values for fields in protocols that
have been designed, created, or are maintained by the Internet
Engineering Task Force (IETF). RFC 2780 [RFC 2780] 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
of IPv4 multicast addresses.
Cotton, et al. Best Current Practice PAGE 2
RFC 5771 IPv4 Multicast Guidelines March 2010
This document is a revision of RFC 3171 [RFC 3171], which it
obsoletes. It also obsoletes RFC 3138 [RFC 3138] and updates
[RFC 2780].
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 [RFC 5226].
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 Session Description Protocol/Session
Announcement Protocol (SDP/SAP);
- GLOP (not an acronym);
- Source-Specific Multicast (SSM); or
- Administratively Scoped address spaces cannot be used.
The guidelines described below are reflected in [IANA-protocols].
Network operators should also be aware of the availability of IPv6
multicast addresses and consider using them where feasible.
2. Terminology
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
[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.
3. Definition of Current Assignment Practice
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 [IANA]:
Cotton, et al. Best Current Practice PAGE 3
RFC 5771 IPv4 Multicast Guidelines March 2010
Address Range Size Designation
------------- ---- -----------
224.0.0.0 - 224.0.0.255 (/24) Local Network Control Block
224.0.1.0 - 224.0.1.255 (/24) Internetwork Control Block
224.0.2.0 - 224.0.255.255 (65024) AD-HOC Block I
224.1.0.0 - 224.1.255.255 (/16) RESERVED
224.2.0.0 - 224.2.255.255 (/16) SDP/SAP Block
224.3.0.0 - 224.4.255.255 (2 /16s) AD-HOC Block II
224.5.0.0 - 224.255.255.255 (251 /16s) RESERVED
225.0.0.0 - 231.255.255.255 (7 /8s) RESERVED
232.0.0.0 - 232.255.255.255 (/8) Source-Specific Multicast Block
233.0.0.0 - 233.251.255.255 (16515072) GLOP Block
233.252.0.0 - 233.255.255.255 (/14) AD-HOC Block III
234.0.0.0 - 238.255.255.255 (5 /8s) RESERVED
239.0.0.0 - 239.255.255.255 (/8) Administratively Scoped Block
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.
4. Local Network Control Block (224.0.0/24)
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) [RFC 2328].
4.1. Assignment Guidelines
Pursuant to section 4.4.2 of [RFC 2780], assignments from the Local
Network Control Block follow an Expert Review, IESG Approval, or
Standards Action process. See IANA [IANA] for the current set of
assignments.
Cotton, et al. Best Current Practice PAGE 4
RFC 5771 IPv4 Multicast Guidelines March 2010
5. Internetwork Control Block (224.0.1/24)
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 (Network Time Protocol (NTP) [RFC 4330]) and
224.0.1.68 (mdhcpdiscover [RFC 2730]).
5.1. Assignment Guidelines
Pursuant to section 4.4.2 of [RFC 2780], assignments from the
Internetwork Control Block follow an Expert Review, IESG Approval, or
Standards Action process. See IANA [IANA] for the current set of
assignments.
6. AD-HOC Blocks (I, II, and III)
Addresses in the AD-HOC blocks (including 224.0.2.0 - 224.0.255.255,
224.3.0.0 - 224.4.255.255, and 233.252.0.0 - 233.255.255.255) 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 Network or Internetwork Control blocks will be made in
AD-HOC Block III.
6.1. Assignment Guidelines
In general, the IANA SHOULD NOT assign addresses in the AD-HOC
blocks. However, the IANA MAY, under special circumstances, assign
addresses from these blocks. Pursuant to section 4.4.2 of [RFC 2780],
assignments from the AD-HOC blocks follow an Expert Review, IESG
Approval, or Standards Action process. See [IANA] for the current
set of assignments.
7. SDP/SAP Block (224.2/16)
Addresses in the SDP/SAP Block are used by applications that receive
addresses through the Session Announcement Protocol [RFC 2974] for use
via applications like the session directory tool (such as [SDR]).
7.1. Assignment Guidelines
Since addresses in the SDP/SAP Block are chosen randomly from the
range of addresses not already in use [RFC 2974], 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.
Cotton, et al. Best Current Practice PAGE 5
RFC 5771 IPv4 Multicast Guidelines March 2010
8. Source-Specific Multicast Block (232/8)
SSM [RFC 4607] 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 Versatile Message Transaction
Protocol (VMTP) transient groups [IANA].
8.1. Assignment Guidelines
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 Source-Specific Multicast Block are explicitly for
use by SSM and MUST NOT be used for other purposes.
9. GLOP Block (233/8)
Addresses in the GLOP Block are globally-scoped, statically-assigned
addresses. The assignment is made, for a domain with a 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 [RFC 3180]. Domains with a
32-bit ASN MAY apply for space in AD-HOC Block III, or consider using
IPv6 multicast addresses.
9.1. Assignment Guidelines
Because addresses in the GLOP Block are algorithmically pre-assigned,
no IANA assignment policy is required.
9.2. AD-HOC Block III
[RFC 3138] delegated to the RIRs the assignment of the GLOP sub-block
(233.252.0.0 - 233.255.255.255) mapped by the private Autonomous
System (AS) space (64512-65534) and the IANA reserved ASN 65535
[RFC 1930]. This space was known as Extended GLOP (EGLOP). RFC 3138
should not have asked the RIRs to develop policies for the EGLOP
space because [RFC 2860] 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.
Cotton, et al. Best Current Practice PAGE 6
RFC 5771 IPv4 Multicast Guidelines March 2010
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 [RFC 2606] 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.
10. Administratively Scoped Block (239/8)
Addresses in the Administratively Scoped Block are for local use
within a domain and are described in [RFC 2365].
10.1. Assignment Guidelines
Since addresses in this block are local to a domain, no IANA
assignment policy is required.
10.1.1. Relative Offsets
The relative offsets [RFC 2365] are used to ensure that a service can
be located independent of the extent of the enclosing scope (see
[RFC 3180] 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 [RFC 2974]. Pursuant to
section 4.4.2 of [RFC 2780], assignments of relative offsets follow an
Expert Review, IESG Approval, or Standards Action process. See
[IANA] for the current set of assignments.
11. Application Form
Requests for multicast address assignments can be submitted through
the application form on the IANA web site at [IANA-registration]. 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.
11.1. Size of Assignments of IPv4 Multicast Addresses
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).
Cotton, et al. Best Current Practice PAGE 7
RFC 5771 IPv4 Multicast Guidelines March 2010
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.
12. Annual Review
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.
12.1. Address Reclamation
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 [RFC 1819] blocks and reclaim those
addresses that are not in use on the global Internet (i.e., those
applications that can use SSM, GLOP, or Administratively Scoped
addressing, or are not globally routed).
12.2. Positive Renewal
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.
13. Use of IANA Reserved Addresses
Applications MUST NOT use addressing in the IANA reserved blocks.
14. IANA Considerations
IANA has updated its IPv4 multicast request and assignment procedures
to reflect this document.
Cotton, et al. Best Current Practice PAGE 8
RFC 5771 IPv4 Multicast Guidelines March 2010
15. Security Considerations
The assignment guidelines described in this document do not alter the
security properties of either the Any Source or Source-Specific
Multicast service models.
16. Acknowledgments
The authors would like to thank Joe St. Sauver, John Meylor, Randy
Bush, Thomas Narten, Marshall Eubanks, Zaid Albanna (co-author of RFC
3171), Kevin Almeroth (co-author of RFC 3171), Pekka Savola, and
Alfred Hoenes for their constructive feedback and comments.
17. References
17.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, May
2008.
17.2. Informative References
[IANA] IANA, "IANA Protocol Registries", <http://www.iana.org/>.
[IANA-protocols]
IANA, "IANA Protocol Registries",
<http://www.iana.org/protocols>.
[IANA-registration]
IANA, "IANA Protocol Registration Forms",
<http://www.iana.org/protocols/apply>.
[RFC 1819] Delgrossi, L., Ed., and L. Berger, Ed., "Internet Stream
Protocol Version 2 (ST2) Protocol Specification - Version
ST2+", RFC 1819, August 1995.
[RFC 1930] Hawkinson, J. and T. Bates, "Guidelines for creation,
selection, and registration of an Autonomous System (AS)",
BCP 6, RFC 1930, March 1996.
[RFC 2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC 2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, July 1998.
Cotton, et al. Best Current Practice PAGE 9
RFC 5771 IPv4 Multicast Guidelines March 2010
[RFC 2606] Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, June 1999.
[RFC 2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address
Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
December 1999.
[RFC 2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", BCP
37, RFC 2780, March 2000.
[RFC 2860] Carpenter, B., Baker, F., and M. Roberts, "Memorandum of
Understanding Concerning the Technical Work of the Internet
Assigned Numbers Authority", RFC 2860, June 2000.
[RFC 2974] Handley, M., Perkins, C., and E. Whelan, "Session
Announcement Protocol", RFC 2974, October 2000.
[RFC 3138] Meyer, D., "Extended Assignments in 233/8", RFC 3138, June
2001.
[RFC 3171] Albanna, Z., Almeroth, K., Meyer, D., and M. Schipper,
"IANA Guidelines for IPv4 Multicast Address Assignments",
BCP 51, RFC 3171, August 2001.
[RFC 3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", BCP
53, RFC 3180, September 2001.
[RFC 4330] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
for IPv4, IPv6 and OSI", RFC 4330, January 2006.
[RFC 4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
[SDR] University College London / ISI, "Session Directory Tool",
<http://www-mice.cs.ucl.ac.uk/multimedia/software/sdr/>.
Cotton, et al. Best Current Practice PAGE 10
RFC 5771 IPv4 Multicast Guidelines March 2010
Authors' Addresses
Michelle Cotton
Internet Corporation for Assigned Names and Numbers
4676 Admiralty Way, Suite 330
Marina del Rey, CA 90292
United States of America
Phone: +310-823-9358
EMail: michelle.cotton@icann.org
URI: http://www.iana.org/
Leo Vegoda
Internet Corporation for Assigned Names and Numbers
4676 Admiralty Way, Suite 330
Marina del Rey, CA 90292
United States of America
Phone: +310-823-9358
EMail: leo.vegoda@icann.org
URI: http://www.iana.org/
David Meyer
EMail: dmm@1-4-5.net
Cotton, et al. Best Current Practice PAGE 11
IANA Guidelines for IPv4 Multicast Address Assignments
RFC TOTAL SIZE: 22239 bytes
PUBLICATION DATE: Monday, March 15th, 2010
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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