Multicast

Multicast lets one sender reach many receivers with a single stream. The sender addresses packets to a group address, and the network copies them only toward hosts that have asked to join that group, so the load on the sender and on links without group members stays low. It sits between unicast, one sender to one receiver, and broadcast, one sender to every host on the local segment. The ISC2 exam outline lists these, with anycast, under IP versions 4 and 6.

In IPv4, multicast uses the range 224.0.0.0 to 239.255.255.255, the former Class D, and hosts manage group membership with the Internet Group Management Protocol (IGMP). IPv6 has no broadcast at all and relies on multicast for jobs such as neighbour discovery, with membership handled by Multicast Listener Discovery. Common uses include streaming media, financial data feeds and routing protocol updates. Multicast usually rides on UDP, with no connection or delivery guarantee, and joining a group commonly needs no authentication, so anyone on a network that carries the stream may receive it. Confidentiality has to come from encrypting the content.

Exam relevance: questions in this area tend to set the four delivery types side by side. A scenario describing one-to-many delivery to subscribed receivers is likely to point to multicast rather than broadcast.