RFC 2908 (rfc2908) - Page 2 of 13

The Internet Multicast Address Allocation Architecture

RFC 2908                  MALLOC Architecture             September 2000


1.  Introduction

   This document proposes a multicast address allocation architecture
   (MALLOC) for the Internet, and is intended to be generic enough to
   apply to both IPv4 and IPv6 environments.

   As with unicast addresses, the usage of any given multicast address
   is limited in two dimensions:

   Lifetime:
      An address has a start time and a (possibly infinite) end time,
      between which it is valid.

   Scope:
      An address is valid over a specific area of the network.  For
      example, it may be globally valid and unique, or it may be a
      private address which is valid only within a local area.

   This architecture assumes that the primary scoping mechanism in use
   is administrative scoping, as described in RFC 2365 [1].  While
   solutions that work for TTL scoping are possible, they introduce
   significant additional complication for address allocation [2].
   Moreover, TTL scoping is a poor solution for multicast scope control,
   and our assumption is that usage of TTL scoping will decline before
   this architecture is widely used.

2.  Requirements

   From a design point of view, the important properties of multicast
   allocation mechanisms are robustness, timeliness, low probability of
   clashing allocations, and good address space utilization in
   situations where space is scare.  Where this interacts with multicast
   routing, it is desirable for multicast addresses to be allocated in a
   manner that aids aggregation of routing state.

   o  Robustness/Availability

      The robustness requirement is that an application requiring the
      allocation of an address should always be able to obtain one, even
      in the presence of other network failures.

   o  Timeliness

      From a timeliness point of view, a short delay of up to a few
      seconds is probably acceptable before the client is given an
      address with reasonable confidence in its uniqueness.  If the
      session is defined in advance, the address should be allocated as
      soon as possible, and should not wait until just before the



Thaler, et al.               Informational