RFC 966 (rfc966) - Page 1 of 27

Host groups: A multicast extension to the Internet Protocol

Network Working Group                                      S. E. Deering
Request for Comments: 966                                 D. R. Cheriton
                                                     Stanford University
                                                           December 1985

                              Host Groups:
             A Multicast Extension to the Internet Protocol


1. Status of this Memo

   This RFC defines a model of service for Internet multicasting and
   proposes an extension to the Internet Protocol (IP) to support such a
   multicast service.  Discussion and suggestions for improvements are
   requested.  Distribution of this memo is unlimited.

2. Acknowledgements

   This memo was adapted from a paper [7] presented at the Ninth Data
   Communications Symposium.  This work was sponsored in part by the
   Defense Advanced Research Projects Agency under contract N00039-83-
   K-0431 and National Science Foundation Grant DCR-83-52048.

   The Internet task force on end-to-end protocols, headed by Bob
   Braden, has provided valuable input in the development of the host
   group model.

3. Introduction

   In this paper, we describe a model of multicast service we call host
   groups and propose this model as a way to support multicast in the
   DARPA Internet environment [14].  We argue that it is feasible to
   implement this facility as an extension of the existing "unicast" IP
   datagram model and mechanism.

   Multicast is the transmission of a datagram packet to a set of zero
   or more destination hosts in a network or internetwork, with a single
   address specifying the set of destination hosts.  For example, hosts
   A, B, C and D may be associated with multicast address X. On
   transmission, a packet with destination address X is delivered with
   datagram reliability to hosts A, B, C and D.

   Multicast has two primary uses, namely distributed binding and
   multi-destination delivery.  As a binding mechanism, multicast is a
   robust and often more efficient alternative to the use of name
   servers for finding a particular object or service when a particular
   host address is not known.  For example, in a distributed file
   system, all the file servers may be associated with one well-known
   multicast address.  To bind a file name to a particular server, a
   client sends a query packet containing the file name to the file
   server multicast address, for delivery to all the file servers.  The


Deering & Cheriton