IP multicast
IP multicast (RFC 1112) is a way of sending one packet to a group of interested receivers at once, instead of either broadcasting to every device on a network or sending a separate unicast copy to each recipient individually. A sender transmits to a reserved multicast address (224.0.0.0/4 for IPv4, or a ff00::/8 address for IPv6), and only devices that have joined that group, typically via IGMP for IPv4, actually receive and process the packet. On a local network, several zero-configuration discovery protocols build on this: mDNS and SSDP both send queries and announcements to a multicast address so other devices on the same segment can find them without a central server, which is convenient on a trusted home LAN but also means any other device on that same segment receives the same broadcasts by design.
By AdminKit team, Netbase JSC · Updated