In Internet Protocol version 6 (IPv6), an address that identifies a group of nodes, each of which can belong to multiple groups. A packet sent to a multicast group is delivered to every interface in the group. Multicast addresses begin with the prefix 11111111. In IPv4, a multicast address is any Class D address. See also broadcast, interface, IPv4, IPv4 address, IPv6, IPv6 address, node, and packet.