Host Extensions for IP Multicasting

Authors: Steve Deering

Complete Citation

Deering, S. "Host Extensions for IP Multicasting", RFC 1112, Network Working Group, August 1989.
View the RFC

Abstract

IP multicasting is the transmission of an IP datagram to a "host group", a set of zero or more hosts identified by a single IP destination address. A multicast datagram is delivered to all members of its destination host group with the same "best-efforts" reliability as regular unicast IP datagrams, i.e., the datagram is not guaranteed to arrive intact at all members of the destination group or in the same order relative to other datagrams.

...

Internetwork forwarding of IP multicast datagrams is handled by "multicast routers" which may be co-resident with, or separate from, internet gateways. A host transmits an IP multicast datagram as a local network multicast which reaches all immediately-neighboring members of the destination host group. If the datagram has an IP time-to-live greater than 1, the multicast router(s) attached to the local network take responsibility for forwarding it towards all other networks that have members of the destination group. On those other member networks that are reachable within the IP time-to-live, an attached multicast router completes delivery by transmitting the datagram as a local multicast.

Annotations

This RFC is the original introduction of hardware, or "real", multicast on the Internet. While dated, it forms the basis of much multicasting work, and thus is formative and foundational to all subsequent work in the area.

The RFC describes 3 levels of compliance with multicast: noncompliance, forwarding compliance, and full interaction compliance. It outlines the mechanism employed for the joining, leaving, and use of multicast groups.

Key properties of multicast are introduced here. Routers must all run compliant code. Hosts must recognize and treat multicast packets differently. Applications must be aware of the multicast sublayer and utilize it properly. While this RFC itself has since been outdated, its concepts and foundation of multicast provide an excellent first look at multicast in the Internet.

I am currently looking for the exact RFC that is its successor, as that one too will be important to cite in my conference paper.

-- DavidMoore - 12 Dec 2007