rfc3171.txt

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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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RFC 3171             IANA IPv4 Multicast Guidelines          August 2001


   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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RFC 3171             IANA IPv4 Multicast Guidelines          August 2001


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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RFC 3171             IANA IPv4 Multicast Guidelines          August 2001


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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