IANA Guidelines for IPv4 Multicast Address Assignments
RFC 3171

Network Working Group                                         Z. Albanna
Request for Comments: 3171                              Juniper Networks
BCP: 51                                                      K. Almeroth
Category: Best Current Practice                                     UCSB
                                                                D. Meyer
                                                                  Sprint
                                                             M. Schipper
                                                                    IANA
                                                             August 2001

         IANA Guidelines for IPv4 Multicast Address Assignments

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This memo provides guidance for the Internet Assigned Numbers
   Authority (IANA) in assigning IPv4 multicast addresses.

1. Introduction

   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.

   The terms "Specification Required", "Expert Review", "IESG Approval",
   "IETF Consensus", and "Standards Action", are used in this memo to
   refer to the processes described in [RFC2434].  The keywords MUST,
   MUST NOT, MAY, OPTIONAL, REQUIRED, RECOMMENDED, SHALL, SHALL NOT,
   SHOULD, SHOULD NOT are to be interpreted as defined in RFC 2119
   [RFC2119].

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   In general, due to the relatively small size of the IPv4 multicast
   addresses 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 http://www.iana.org/numbers.html.

2. Definition of Current Assignment Practice

   Unlike IPv4 unicast address assignment, where blocks of addresses are
   delegated to regional registries, IPv4 multicast addresses are
   assigned directly by the IANA.  Current assignments appear as follows
   [IANA]:

   224.0.0.0   - 224.0.0.255     (224.0.0/24)  Local Network Control Block
   224.0.1.0   - 224.0.1.255     (224.0.1/24)  Internetwork Control Block
   224.0.2.0   - 224.0.255.0                   AD-HOC Block
   224.1.0.0   - 224.1.255.255   (224.1/16)    ST Multicast Groups
   224.2.0.0   - 224.2.255.255   (224.2/16)    SDP/SAP Block
   224.252.0.0 - 224.255.255.255               DIS Transient Block
   225.0.0.0   - 231.255.255.255               RESERVED
   232.0.0.0   - 232.255.255.255 (232/8)       Source Specific Multicast
                                               Block
   233.0.0.0   - 233.255.255.255 (233/8)       GLOP Block
   234.0.0.0   - 238.255.255.255               RESERVED
   239.0.0.0   - 239.255.255.255 (239/8)       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.

3. 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) [RFC2328].

3.1. Assignment Guidelines

   Pursuant to section 4.4.2 of RFC 2780 [RFC2780], 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.

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4. Internetwork Control Block (224.0.1/24)

   Addresses in the Internetwork Control block are used for protocol
   control that must be forwarded through the Internet.  Examples
   include 224.0.1.1 (NTP [RFC2030]) and 224.0.1.68 (mdhcpdiscover
   [RFC2730]).

4.1. Assignment Guidelines

   Pursuant to section 4.4.2 of RFC 2780 [RFC2780], assignments from the
   Internetwork Control block follow an Expert Review, IESG Approval or
   Standards Action process.  See [IANA] for the current set of
   assignments.

5. AD-HOC Block (224.0.2.0/24 - 224.0.255.0/24)

   Addresses in the AD-HOC block have traditionally been assigned for
   those applications that don't fit in either the Local or Internetwork
   Control blocks.  These addresses are globally routed and are
   typically used by applications that require small blocks of
   addressing (e.g., less than a /24).

5.1. Assignment Guidelines

   In general, the IANA SHOULD NOT assign addressing in the AD-HOC
   Block.  However, the IANA may under special special circumstances,
   assign addressing from this block.  Pursuant to section 4.4.2 of RFC
   2780 [RFC2780], assignments from the AD-HOC block follow an Expert
   Review, IESG Approval or Standards Action process.  See [IANA] for
   the current set of assignments.

6. SDP/SAP Block (224.2/16)

   Addresses in the SDP/SAP block are used by applications that receive
   addresses through the Session Announcement Protocol [RFC2974] for use
   via applications like the session directory tool (such as SDR [SDR]).

6.1. Assignment Guidelines

   Since addresses in the SDP/SAP block are chosen randomly from the
   range of addresses not already in use [RFC2974], 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.

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7. Source Specific Multicast Block (232/8)

   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 as initially assigned to the VMTP transient
   groups [IANA].

7.1. 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 SSM block are explicitly for use by SSM and MUST NOT
   be used for other purposes.

8. GLOP Block (233/8)

   Addresses in the GLOP block are globally scoped statically assigned
   addresses.  The assignment is made by mapping a domain's autonomous
   system number into the middle two octets of 233.X.Y.0/24.  The
   mapping and assignment is defined in [RFC2770].

8.1. Assignment Guidelines

   Because addresses in the GLOP block are algorithmically pre-assigned,
   no IANA assignment policy is required.  In addition, RFC 3138
   [RFC3138] delegates assignment of the GLOP sub-block mapped by the
   RFC 1930 [RFC1930] private AS space (233.252.0.0 - 233.255.255.255)
   to the Internet Routing Registries.  Note that while no additional
   IANA assignment is required, addresses in the GLOP  block are
   assigned for use as defined in RFC 2770 and MUST NOT be used for
   other purposes.

9. Administratively Scoped Address Block (239/8)

   Addresses in the Administratively Scoped Address block are for local
   use within a domain and are described in [RFC2365].

9.1. Assignment Guidelines

   Since addresses in this block are local to a domain, no IANA
   assignment policy is required.

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9.1.1. Relative Offsets

   The relative offsets [RFC2365] are used to ensure that a service can
   be located independent of the extent of the enclosing scope (see RFC
   2770 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 [RFC2974].  Pursuant to section
   4.4.2 of RFC 2780 [RFC2780], assignments of Relative Offsets follow
   an Expert Review, IESG Approval or Standards Action process.  See
   [IANA] for the current set of assignments.

10. Annual Review

   Given the dynamic nature of IPv4 multicast and its associated infra-
   structure, and the previously undocumented IPv4 multicast address
   assignment guidelines, the IANA should conduct an annual review of
   currently assigned addresses.

10.1. 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 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).

11. Use of IANA Reserved Addresses

   Applications MUST NOT use addressing in the IANA reserved blocks.

12. 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.

13. Acknowledgments

   The authors would like to thank Joe St. Sauver, John Meylor, Randy
   Bush, and Thomas Narten for their constructive feedback and comments.

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14. Authors' Addresses

   Zaid Albanna
   1149 N. Mathilda Ave
   Sunnyvale, CA. 94089

   EMail: zaid@juniper.net

   Kevin Almeroth
   UC Santa Barbara
   Santa Barbara, CA.

   EMail: almeroth@cs.ucsb.edu

   David Meyer
   Sprint E|Solutions

   EMail: dmm@sprint.net

   Michelle Schipper
   IANA Administrator
   Internet Assigned Numbers Authority
   4676 Admiralty Way, Suite 330
   Marina del Rey, CA 90292

   EMail: iana@iana.org

15. References

   [IANA]    http://www.iana.org/numbers.html

   [RFC1190] Topolcic, C., "Experimental Internet Stream Protocol,
             Version 2 (ST-II)", RFC 1190, October 1990.

   [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation,
             selection, and registration of an Autonomous System (AS)",
             RFC 1930, March 1996.

   [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
             3", BCP 9, RFC 2026, October 1996.

   [RFC2030] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
             for IPv4, IPv6 and OSI", RFC 2030, October 1996.

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   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
             RFC 2365, July 1998.

   [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", BCP 26, RFC 2434,
             October 1998.

   [RFC2730] Hanna, S., Patel, B. and M. Shah, "Multicast Address
             Dynamic Client Allocation Protocol (MADCAP), RFC 2730,
             December 1999.

   [RFC2770] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", RFC
             2770, February 2000.

   [RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
             Values In the Internet Protocol and Related Headers", BCP
             37, RFC 2780, March 2000.

   [RFC2908] Thaler, D., Handley, M. and D.Estrin, "The Internet
             Multicast Address Allocation Architecture", RFC 2908,
             September 2000.

   [RFC2909] Thaler, D., Handley, M. and D. Estrin, "The Multicast
             Address-Set Claim (MASC) Protocol", RFC 2909, September
             2000.

   [RFC2974] Handley, M., Perkins, C. and E. Whelan, "Session
             Announcement Protocol", RFC 2974, October 2000.

   [RFC3138] Meyer, D., "Extended Assignments in 233/8", RFC 3138, June
             2001.

   [SDR]     http://www-mice.cs.ucl.ac.uk/multimedia/software/

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16. Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
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   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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