IP Multicast

With IP Multicast, one packet sent to a multicast address can be received by many receivers.

Multicast is always available in some way within a single LAN.

But across IP routers, multicasting is more problematic. Simple IP routers often does not handle multicasting at all. And even if the routers does handle multicast, advanced configuration of the routers is needed for multicast to work.

Multicasting within a LAN

Dumb ethernet switches usually handle multicasts as broadcasts. So multicasted audio may use up some of the transmission capacity towards other units and PCs on the same LAN. But unwanted multicast traffic will usually be stopped in the network card, and not consume any computer resources. Worst case, simple network cards may forward the multicasts packets to the CPU, but then the OS will drop unwanted multicasts at a very low level.

More advanced ethernet switches may handle multicasts properly by only delivering traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group. These are usually Managed Switches. Look for IGMP snooping.