Multicast is a network delivery method where one sender transmits packets to a group address, and any device subscribed to that group can receive the traffic. Unlike unicast, which targets one host, multicast is meant to efficiently reach many receivers on the same local segment without sending a separate copy to each one.
In cyber security, multicast matters because it can create large bursts of traffic with relatively little effort. Services that listen on multicast groups may process many packets at once, which can expose weak rate limiting, memory pressure, or parsing bugs. Attackers can abuse this to cause denial of service by flooding a segment with multicast packets, while defenders use segmentation, filtering, and adapter binding controls to reduce exposure. In industrial and virtualized environments, multicast is especially important because lab tools and simulators may become reachable on a real network if they are bridged incorrectly or allowed to accept traffic they do not need.