RFC 966 (rfc966) - Page 2 of 27
Host groups: A multicast extension to the Internet Protocol
Alternative Format: Original Text Document
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
