RFC 5771

IANA Guidelines for IPv4 Multicast Address Assignments

📅 published March 2010, from ietf

Internet Engineering Task Force (IETF) 💖 RFC 5771: IANA Guidelines for IPv4 Multicast Address Assignments ✨

okay bestie, let's get into it 🎀 This is a Best Current Practice (BCP 51) from March 2010, written by M. Cotton, L. Vegoda (ICANN), and D. Meyer 🦋. It's part of the IETF's whole vibe, and it's basically the rulebook for how IANA hands out IPv4 multicast addresses 💅. It obsoletes RFC 3171 and RFC 3138, and it updates RFC 2780 🌸. The ISSN is 2070-1721 in case you're collecting numbers 🔥.

Abstract

This doc gives IANA guidance on 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 doc is a product of the Internet Engineering Task Force (IETF) 👑. It represents the consensus of the IETF community, it got public review, and the Internet Engineering Steering Group (IESG) approved it for publication ✨. More info on BCPs is in Section 2 of RFC 5741 💅.

Info about the current status of this doc, any errata, and how to give feedback can be found at http://www.rfc-editor.org/info/rfc5771 🦋.

Copyright Notice

This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stood on the publication date 📜. Please actually read these, bestie, because they explain your rights and restrictions 🙈. Code Components pulled from this document must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Simplified BSD License 🫶.

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 🌸

okay so the Internet Assigned Numbers Authority (IANA) (www.iana.org) is in charge of handing out parameter values for fields in protocols that the Internet Engineering Task Force (IETF) designed, created, or maintains 💅. RFC 2780 [RFC2780] gives IANA its guidance for assigning parameters to fields in newly developed protocols 🦋. This memo builds on section 4.4.2 of RFC 2780 and tries to write down how IANA already handles IPv4 multicast addresses 🧚.

This doc is a revision of RFC 3171 [RFC3171], so it obsoletes that one 💜. 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 mean the processes described in [RFC5226] 🎀.

Here's the main idea: the IPv4 multicast address space is pretty small, so giving out more of it should only happen in limited situations 🙈. Basically, IANA should only assign addresses when:

the dynamic selection Session Description Protocol/Session Announcement Protocol (SDP/SAP) can't be used;
GLOP (not an acronym) can't be used;
Source-Specific Multicast (SSM) can't be used; or
Administratively Scoped address spaces can't be used.

The guidelines below show up in [IANA-protocols] 📜. Network operators should also know that IPv6 multicast addresses exist and should think about using them where it's doable 🌈.

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 read as described in BCP 14, RFC 2119 [RFC2119] 🫶.

The word "allocation" means a block of addresses that a registry manages for making assignments and allocations 🦋. The word "assignment" means a block of addresses, or one 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 go out to Regional Internet Registries (RIRs), IPv4 multicast addresses are assigned directly by IANA 👑. The current registration groups look like this [IANA] 🎀:

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

IANA usually assigns addresses from the Local Network Control, Internetwork Control, and AD-HOC blocks 🌈. The assignment guidelines for each of those, plus 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 for protocol control traffic that does not get forwarded off link 🙈. An example is OSPFIGP All Routers (224.0.0.5) [RFC2328] 💅.

4.1. Assignment Guidelines 💖

Following section 4.4.2 of [RFC2780], assignments from the Local Network Control Block go through an Expert Review, IESG Approval, or Standards Action process 📜. See IANA [IANA] for the current set of assignments 🔥.

5. Internetwork Control Block (224.0.1/24) 🌸

Addresses in the Internetwork Control Block are 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 🎀

Following section 4.4.2 of [RFC2780], assignments from the Internetwork Control Block go through 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 to applications that don't fit in either the Local or Internetwork Control blocks 💅. These addresses MAY be globally routed, and they're typically used by applications that need small blocks of addressing (e.g., less than a /24 ) 🫶. Future assignments of blocks that don't 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 🔥. Following section 4.4.2 of [RFC2780], assignments from the AD-HOC blocks go through 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 get addresses through the Session Announcement Protocol [RFC2974], for use via apps 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 even though 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 🚨.

8. Source-Specific Multicast Block (232/8) 👑

SSM [RFC4607] is an extension of IP Multicast where traffic gets forwarded to receivers only from the multicast sources the receivers have explicitly expressed interest in, and it's mainly aimed at one-to-many (broadcast) applications 🌸. Note that this block was originally assigned to the Versatile Message Transaction Protocol (VMTP) transient groups [IANA] 🎀.

8.1. Assignment Guidelines 🌈

Because the SSM model basically makes the entire multicast address space local to the host, no IANA assignment policy is required 💜. Note, though, that even though 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 the domain's autonomous system number, written in octets as X.Y, into the middle two octets of the GLOP Block, which gives an assignment of 233.X.Y.0/24 🧚. The mapping and assignment are 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 🫶.

Part 2 is coming, so stay tuned, bestie 💕🌈

9.2. AD-HOC Block III 💖

okay so [RFC3138] handed the GLOP sub-block 233.252.0.0 - 233.255.255.255 to the RIRs to assign ✨. That sub-block is the space mapped by the private Autonomous System (AS) space 64512-65534 plus the IANA reserved ASN 65535 [RFC1930]. People called it Extended GLOP (EGLOP) 🌸. Honestly, RFC 3138 should not have asked the RIRs to write policies for EGLOP, because [RFC2860] reserves that job for the IETF 🙈. Network operators really need this space, so it's lowkey important to make it usable. That's why this document obsoletes RFC 3138 and marks this range as available for AD-HOC assignment, following the guidelines in section 6 👑.

The first /24 in this range, 233.252.0.0/24, is assigned as "MCAST-TEST-NET" for documentation and example code 🧚. 233.252.0.0/24 SHOULD be used alongside 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. That test net stays off the public Internet, bestie 🙈🚫

10. Administratively Scoped Block (239/8) 🎀

The Administratively Scoped Block is all about local vibes. These addresses are for use inside a domain, and the full tea is in [RFC2365] 🦋.

10.1. Assignment Guidelines

Because these addresses stay local to a domain, no IANA assignment policy is required ✨.

10.1.1. Relative Offsets

Relative offsets from [RFC2365] exist so a service can be found no matter how big the enclosing scope is (see [RFC3180] for details) 🧚. There are only 256 of these offsets, so the IANA should only hand one out to a protocol that provides an infrastructure supporting service 🥹. Examples include the Session Announcement Protocol [RFC2974].

Per section 4.4.2 of [RFC2780], assignments of relative offsets follow an Expert Review, IESG Approval, or Standards Action process 💜. Check [IANA] for the current list of assignments.

11. Application Form 📝

You can submit requests for multicast address assignments through the application form on the IANA web site at [IANA-registration] 🌈. It's really important to include enough detail so the IESG designated expert can review your application. If the details in the request aren't clear, or more info is needed, the IESG designated expert may ask for additional information before assigning an address 🫶.

11.1. Size of Assignments of IPv4 Multicast Addresses

Sometimes more than one multicast address is needed. In these cases, multiple addresses are available in AD-HOC Block III 🍓. If there's 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 been decided yet, so these will be documented in a future version of this document 🔮.

12. Annual Review 🗓️

Multicast over IPv4 is super dynamic, and so is the infrastructure around it. The previous IPv4 multicast address assignment guidelines weren't documented, either. So 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. It should reclaim the addresses that are not in use on the global Internet, meaning those applications that can use SSM, GLOP, or Administratively Scoped addressing, or that are not globally routed 🔥.

12.2. Positive Renewal

Sometimes it's appropriate to make temporary assignments that can be renewed as needed 🦋. When that happens, the registrant needs to positively request an extension to the temporary assignment or the addresses assigned. If the IANA hasn't 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 ✨.

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. This is the part where we don't mess with the security game, periodt 💀🔐.

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.

[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/>.

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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