Unicast-Prefix-Based IPv4 Multicast Addresses
RFC 6034

Internet Engineering Task Force (IETF)                         D. Thaler
Request for Comments: 6034                                     Microsoft
Category: Standards Track                                   October 2010
ISSN: 2070-1721

             Unicast-Prefix-Based IPv4 Multicast Addresses

Abstract

   This specification defines an extension to the multicast addressing
   architecture of the IP Version 4 protocol.  The extension presented
   in this document allows for unicast-prefix-based assignment of
   multicast addresses.  By delegating multicast addresses at the same
   time as unicast prefixes, network operators will be able to identify
   their multicast addresses without needing to run an inter-domain
   allocation protocol.

Status of This Memo

   This is an Internet Standards Track document.

   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
   Internet Standards 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/rfc6034.

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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Thaler                       Standards Track                    [Page 1]
RFC 6034             Uni-Prefix-Based IPv4 Multicast        October 2010

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 5

1.  Introduction

   RFC 3180 [RFC3180] defines an allocation mechanism (called "GLOP") in
   233/8 whereby an Autonomous System (AS) number is embedded in the
   middle 16 bits of an IPv4 multicast address, resulting in 256
   multicast addresses per AS.  Advantages of this mechanism include the
   ability to get multicast address space without an inter-domain
   multicast address allocation protocol, and the ease of determining
   the AS that was assigned the address for debugging and auditing
   purposes.

   Some disadvantages of GLOP include:

   o  RFC 4893 [RFC4893] expands the size of an AS number to 4 bytes,
      and GLOP cannot work with 4-byte AS numbers.

   o  When an AS covers multiple sites or organizations, administration
      of the multicast address space within an AS must be handled by
      other mechanisms, such as manual administrative effort or the
      Multicast Address Dynamic Client Allocation Protocol (MADCAP)
      [RFC2730].

   o  During debugging, identifying the AS does not immediately identify
      the correct organization when an AS covers multiple organizations.

   o  Only 256 addresses are automatically available per AS, and
      obtaining any more requires administrative effort.

   More recently, a mechanism [RFC3306] has been developed for IPv6 that
   provides a multicast range to every IPv6 subnet, which is at a much
   finer granularity than an AS.  As a result, the first three
   disadvantages above are avoided (and the last disadvantage does not
   apply to IPv6 due to the extended size of the address space).

Thaler                       Standards Track                    [Page 2]
RFC 6034             Uni-Prefix-Based IPv4 Multicast        October 2010

   Another advantage of providing multicast space to a subnet, rather
   than just to an entire AS, is that multicast address assignments