1. Introduction

The Internet Assigned Numbers Authority (IANA) (www.iana.org) is charged with allocating parameter values for fields in protocols that 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 of IPv4 multicast addresses.

This document is a revision of RFC 3171 [RFC3171], which it obsoletes. 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 refer to the processes described in [RFC5226].

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 Session Description Protocol/Session Announcement Protocol (SDP/SAP);

• GLOP (not an acronym);

• Source-Specific Multicast (SSM); or

• Administratively Scoped address spaces cannot be used.

The guidelines described below are reflected in [IANA-protocols]. Network operators should also be aware of the availability of IPv6 multicast addresses and consider using them where feasible.