Multicast Extensions to Windows Sockets Internet Protocol multicasting is currently supported only on AF_INET sockets of type SOCK_DGRAM and SOCK_RAW. By default, IP multicast datagrams are sent with a Time to Live (TTL) of 1. Applications can use the setsockopt function to specify a TTL. By convention, multicast routers use TTL thresholds to determine how far to forward datagrams. These TTL thresholds are defined as follows: Multicast datagrams with initial TTL 0 are restricted to the same host. Multicast datagrams with initial TTL 1 are restricted to the same subnet. Multicast datagrams with initial TTL 32 are restricted to the same site. Multicast datagrams with initial TTL 64 are restricted to the same region. Multicast datagrams with initial TTL 128 are restricted to the same continent. Multicast datagrams with initial TTL 255 are unrestricted in scope.
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