See Also
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4/8/2010
Internet Protocol multicasting is currently supported only on AF_INET sockets of type SOCK_DGRAM. Windows Embedded CE also supports SOCK_RAW for IPv4. By default, IP multicast datagrams are sent with a time-to-live (TTL) value of 1, meaning they are restricted to the same subnet. Applications can use the setsockoptfunction 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.