A multicast address is designed to enable the delivery of datagrams to a set of hosts that have been configured as members of a multicast group across various subnetworks. This pattern shows in Fig. 2. For those applications which involve a single node sending to many recipients, a multicast facility is clearly a more natural programming paradigm than unicast. For each outgoing IP packet from this multicast source, a multicast group destination address is specified. This is mapped into an Ethernet broadcast address.
All hosts receive each packet.
H1, H2 and H5 are listening on the specified multicast address. IP delivers the packet to their applications. H4 is not listening. IP receives the packet, and quietly discards it. H1, H20 and H2000 are listening.