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This document obsoletes RFC 3171. It provides guidance for the Internet Assigned Numbers Authority (IANA) in assigning IPv4 multicast addresses.
1.
Introduction
2.
Terminology
3.
Definition of Current Assignment Practice
4.
Local Network Control Block (224.0.0/24)
4.1.
Assignment Guidelines
5.
Internetwork Control Block (224.0.1/24)
5.1.
Assignment Guidelines
6.
AD-HOC Blocks (including 224.0.2.0/24 - 224.0.255.0/24)
6.1.
Assignment Guidelines
7.
SDP/SAP Block (224.2/16)
7.1.
Assignment Guidelines
8.
Source Specific Multicast Block (232/8)
8.1.
Assignment Guidelines
9.
GLOP Block (233/8)
9.1.
Assignment Guidelines
9.2.
Extended AD-HOC
10.
Administratively Scoped Address Block (239/8)
10.1.
Assignment Guidelines
11.
Application Form
11.1.
Size of assignments of IPv4 Multicast Addresses
12.
Annual Review
12.1.
Address Reclamation
12.2.
Positive renewal
13.
Use of IANA Reserved Addresses
14.
IANA Considerations
15.
Security Considerations
16.
Acknowledgments
17.
References
17.1.
Normative References
17.2.
Informative References
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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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 [RFC3171] (Albanna, Z., Almeroth, K., Meyer, D., and M. Schipper, “IANA Guidelines for IPv4 Multicast Address Assignments,” August 2001.), which it obsoletes. It should retain RFC 3171's status as BCP 51. It also obsoletes RFC 3138 [RFC3138] (Meyer, D., “Extended Assignments in 233/8,” June 2001.)."
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] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” October 1998.). The keywords MUST, MUST NOT, MAY, OPTIONAL, REQUIRED, RECOMMENDED, SHALL, SHALL NOT, SHOULD, SHOULD NOT are to be interpreted as defined in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).
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 http://www.iana.org/numbers.html. Network operators should also be aware of the availability of IPv6 multicast addresses and consider using them where feasible.
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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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).
The word "allocation" is defined as a block of addresses managed by a registry for the purpose of making assignments and allocations. The word "assignment" is defined a block of addresses, or a single address, registered to an end-user for use on a specific network, or set of networks.
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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] (IANA, “IANA Matrix for Protocol Parameter Assignment/Registration Procedures,” .):
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 64769 AD-HOC Block (1) 224.1.0.0 - 224.1.255.255 224.1/16 RESERVED 224.2.0.0 - 224.2.255.255 224.2/16 SDP/SAP Block 224.252.0.0 - 224.255.255.255 224.252/14 RESERVED 225.0.0.0 - 231.255.255.255 7 /8s RESERVED 232.0.0.0 - 232.255.255.255 232/8 Source Specific Multicast Block 233.0.0.0 - 233.251.255.255 16515072 GLOP Block 233.252.0.0 - 233.255.255.255 233.252/14 AD-HOC Block (2) 234.0.0.0 - 238.255.255.255 5 /8s 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.
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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] (Moy, J., “OSPF Version 2,” April 1998.).
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Pursuant to section 4.4.2 of [RFC2780] (Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000.), assignments from the Local Network Control block follow an Expert Review, IESG Approval or Standards Action process. See IANA (IANA, “IANA Matrix for Protocol Parameter Assignment/Registration Procedures,” .) [IANA] for the current set of assignments.
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Addresses in the Internetwork Control block are used for protocol control that MAY be forwarded through the Internet. Examples include 224.0.1.1 (NTP [RFC2030] (Mills, D., “Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI,” October 1996.)) and 224.0.1.68 (mdhcpdiscover [RFC2730] (Hanna, S., Patel, B., and M. Shah, “Multicast Address Dynamic Client Allocation Protocol (MADCAP),” December 1999.)).
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Pursuant to section 4.4.2 of [RFC2780] (Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000.), assignments from the Internetwork Control block follow an Expert Review, IESG Approval or Standards Action process. See IANA (IANA, “IANA Matrix for Protocol Parameter Assignment/Registration Procedures,” .) [IANA] for the current set of assignments.
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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 are 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 Extended block.
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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 [RFC2780] (Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000.), assignments from the AD-HOC blocks follow an Expert Review, IESG Approval or Standards Action process. See IANA (IANA, “IANA Matrix for Protocol Parameter Assignment/Registration Procedures,” .) [IANA] for the current set of assignments.
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Addresses in the SDP/SAP block are used by applications that receive addresses through the Session Announcement Protocol [RFC2974] (Handley, M., Perkins, C., and E. Whelan, “Session Announcement Protocol,” October 2000.) for use via applications like the session directory tool (such as SDR [SDR]).
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Since addresses in the SDP/SAP block are chosen randomly from the range of addresses not already in use [RFC2974] (Handley, M., Perkins, C., and E. Whelan, “Session Announcement Protocol,” October 2000.), 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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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 (IANA, “IANA Matrix for Protocol Parameter Assignment/Registration Procedures,” .) [IANA].
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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.
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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 of the GLOP block, yielding an assignment of 233.X.Y.0/24. The mapping and assignment is defined in [RFC3180] (Meyer, D. and P. Lothberg, “GLOP Addressing in 233/8,” September 2001.). Domains with 32 bit ASN should apply for space in the Extended AD-HOC block, or consider using IPv6 multicast addresses.
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Because addresses in the GLOP block are algorithmically pre-assigned, no IANA assignment policy is required.
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[RFC3138] (Meyer, D., “Extended Assignments in 233/8,” June 2001.) delegated assignment of the GLOP sub-block mapped by the [RFC1930] (Hawkinson, J. and T. Bates, “Guidelines for creation, selection, and registration of an Autonomous System (AS),” March 1996.) private AS space (233.252.0.0 - 233.255.255.255) to the RIRs. This space was known as eGLOP. RFC 3138 should not have asked the RIRs to develop policies for the EGLOP space because [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” June 2000.) 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. It SHOULD be used in conjunction with the [RFC2606] (Eastlake, D. and A. Panitz, “Reserved Top Level DNS Names,” June 1999.) domain names example.com or example.net in vendor and protocol documentation. Addresses within this block MUST NOT appear on the public Internet.
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Addresses in the Administratively Scoped Address block are for local use within a domain and are described in [RFC2365] (Meyer, D., “Administratively Scoped IP Multicast,” July 1998.).
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Since addresses in this block are local to a domain, no IANA assignment policy is required.
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The relative offsets [RFC2365] (Meyer, D., “Administratively Scoped IP Multicast,” July 1998.) are used to ensure that a service can be located independent of the extent of the enclosing scope (see [RFC3180] (Meyer, D. and P. Lothberg, “GLOP Addressing in 233/8,” September 2001.) 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] (Handley, M., Perkins, C., and E. Whelan, “Session Announcement Protocol,” October 2000.). Pursuant to section 4.4.2 of [RFC2780] (Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000.), assignments of Relative Offsets follow an Expert Review, IESG Approval or Standards Action process. See IANA (IANA, “IANA Matrix for Protocol Parameter Assignment/Registration Procedures,” .) [IANA] for the current set of assignments.
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Requests for multicast address assignments can be submitted through the application form on the IANA web site at:
http://www.iana.org/cgi-bin/multicast.pl
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.
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Occasionally, more than one multicast address is required. In these cases multiple addresses are available in the Extended AD-HOC block. Where a very large number of addresses is required, the assignment will be staged, with additional stages only being made after the complete use of the initial assignment(s).
A separate document describing the policy governing assignment of addresses in the AD-HOC and Extended AD-HOC blocks 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.
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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.
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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 [RFC1190] (Casner, S., Lynn, C., Park, P., Schroder, K., and C. Topolcic, “Experimental Internet Stream Protocol: Version 2 (ST-II),” October 1990.) 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).
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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 for at least one calendar year.
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Applications MUST NOT use addressing in the IANA reserved blocks.
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This document is all about IANA Considerations.
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The assignment guidelines described in this document do not alter the security properties of either the Any Source or Source Specific multicast service models.
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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) and Leo Vegoda for their constructive feedback and comments.
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| [RFC2119] | Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). |
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| Michelle Cotton | |
| Internet Corporation for Assigned Names and Numbers | |
| 4676 Admiralty Way, Suite 330 | |
| Marina del Rey 90292 | |
| United States | |
| Phone: | +310-823-9358 |
| Email: | michelle.cotton@icann.org |
| URI: | http://www.iana.org/ |
| David Meyer | |
| Email: | dmm@1-4-5.net |
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