





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/rfc5771.

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.






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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 [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
   of IPv4 multicast addresses.







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   This document is a revision of RFC 3171 [RFC3171], which it
   obsoletes.  It also obsoletes RFC 3138 [RFC3138] and updates
   [RFC2780].

   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 [RFC5226].

   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
   [RFC2119].

   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]:






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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) [RFC2328].

4.1.  Assignment Guidelines

   Pursuant to section 4.4.2 of [RFC2780], 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.






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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) [RFC4330]) and
   224.0.1.68 (mdhcpdiscover [RFC2730]).

5.1.  Assignment Guidelines

   Pursuant to section 4.4.2 of [RFC2780], 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 [RFC2780],
   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 [RFC2974] 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 [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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8.  Source-Specific Multicast Block (232/8)

   SSM [RFC4607] 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 [RFC3180].  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

   [RFC3138] 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
   [RFC1930].  This space was known as Extended GLOP (EGLOP).  RFC 3138
   should not have asked the RIRs to develop policies for the EGLOP
   space because [RFC2860] 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.






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   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 [RFC2606] 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 [RFC2365].

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 [RFC2365] are used to ensure that a service can
   be located independent of the extent of the enclosing scope (see
   [RFC3180] 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 [RFC2780], 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).





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   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 [RFC1819] 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.





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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

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

   [RFC5226] 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>.

   [RFC1819] Delgrossi, L., Ed., and L. Berger, Ed., "Internet Stream
             Protocol Version 2 (ST2) Protocol Specification - Version
             ST2+", RFC 1819, August 1995.

   [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation,
             selection, and registration of an Autonomous System (AS)",
             BCP 6, RFC 1930, March 1996.

   [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.



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   [RFC2606] Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS
             Names", BCP 32, RFC 2606, June 1999.

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

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

   [RFC2860] Carpenter, B., Baker, F., and M. Roberts, "Memorandum of
             Understanding Concerning the Technical Work of the Internet
             Assigned Numbers Authority", RFC 2860, June 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.

   [RFC3171] Albanna, Z., Almeroth, K., Meyer, D., and M. Schipper,
             "IANA Guidelines for IPv4 Multicast Address Assignments",
             BCP 51, RFC 3171, August 2001.

   [RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", BCP
             53, RFC 3180, September 2001.

   [RFC4330] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
             for IPv4, IPv6 and OSI", RFC 4330, January 2006.

   [RFC4607] 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/>.















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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
























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