multicasting

Multicasting is a method of delivering network data to a group of interested recipients with a single stream. Unlike unicast, where each receiver gets a separate copy, or broadcast, which reaches all devices on a network segment, multicasting targets only members of a specific group. In IPv4, multicast addresses range from 224.0.0.0 to 239.255.255.255; in IPv6, the scope is FF00::/8. Recipients join groups via protocols such as IGMP for IPv4 or MLD for IPv6. Routers use multicast routing protocols to build distribution trees that deliver data only to networks with interested receivers.

Multicast relies on routing protocols to minimize duplication and to scale. Common schemes include DVMRP and PIM, which support different forwarding tree models and determine how a source is reached by subscribers. Routers and, on local networks, switches build these trees so that data is copied only to destinations with listeners.

Common uses include live video and audio distribution, IPTV, and large-scale streams on local networks. The main advantage is bandwidth efficiency, as a single stream can serve many receivers. Limitations include reliance on multicast-capable infrastructure, limited deployment over the public Internet, and potential unreliability of UDP-based streams as well as access control concerns. Alternatives include unicast streaming and content delivery networks.

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