Multicast traffic lies between the extremes of unicast (one source, one destination) and broadcast (one source, all destinations). Multicast is a “one source, many destinations” method of traffic distribution, meaning that the destinations needing to receive the information from a particular source receive the traffic stream.
IP network destinations (clients) do not often communicate directly with sources (servers), so the routers between source and destination must be able to determine the topology of the network from the unicast or multicast perspective to avoid routing traffic haphazardly. The multicast router must find multicast sources on the network, send out copies of packets on several interfaces, prevent routing loops, connect interested destinations with the proper source, and keep the flow of unwanted packets to a minimum. Standard multicast routing protocols provide most of these capabilities.
This chapter contains the following topics. For more information about multicast, see the JUNOS Multicast Protocols Configuration Guide. For configuration instructions, see Configuring a Multicast Network.