Multicast Basics

Multicasting relies on a series of reserved IP addresses in the upper end of the IP address space between addresses 224.0.0.0 and 239.255.255.255. When a packet is sent to one of these addresses, it is not routed in the normal way to a single machine, but instead is distributed through the network to all machines that have registered their interest in receiving transmissions on that address. These IP addresses are known in the multicasting world as "groups" because each address refers to a group of machines.

In effect, multicast groups act much like mailing lists. A process joins one or more groups, and the multicasting system makes sure that copies of the messages directed to the group are routed to each member of the group. ...

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