RFC 966 (rfc966) - Page 2 of 27

Host groups: A multicast extension to the Internet Protocol

RFC 966                                                    December 1985
Host Groups: A Multicast Extension to the Internet Protocol


   server that recognizes the file name then responds to the client,
   allowing subsequent interaction directly with that server host.  Even
   when name servers are employed, multicast can be used as the first
   step in the binding process, that is, finding a name server.

   Multi-destination delivery is useful to several applications,
   including:

      - distributed, replicated databases [6,9].

      - conferencing [11].

      - distributed parallel computation, including distributed
        gaming [2].

   Ideally, multicast transmission to a set of hosts is not more
   complicated or expensive for the sender than transmission to a single
   host.  Similarly, multicast transmission should not be more expensive
   for the networks and gateways than traversing the shortest path tree
   that connects the sending host to the hosts identified by the
   multicast address.

   Multicast, transmission to a set of hosts, is properly distinguished
   from broadcast, transmission to all hosts on a network or
   internetwork. Broadcast is not a generally useful facility since
   there are few reasons for communicating with all hosts.

   A variety of local network applications and systems make use of
   multicast.  For instance, the V distributed system [8] uses
   network-level multicast for implementing efficient operations on
   groups of processes spanning multiple machines.  Similar use is being
   made for replicated databases [6] and other distributed applications
   [4]. Providing multicast in the Internet environment would allow
   porting such local network distributed applications to the Internet,
   as well as making some existing Internet applications more robust and
   portable (by, for example, removing "wired-in" lists of addresses,
   such as gateway addresses).

   At present, an Internet application logically requiring multicast
   must send individually addressed packets to each recipient.  There
   are two problems with this approach.  Firstly, requiring the sending
   host to know the specific addresses of all the recipients defeats its
   use as a binding mechanism.  For example, a diskless workstation
   needs on boot to determine the network address of a disk server and
   it is undesirable to "wire in" specific network addresses.  With a
   multicast facility, the multicast address of the boot servers (or



Deering & Cheriton