Examples: Sending and receiving a multicast datagram

IP multicasting provides the capability for an application to send a single IP datagram that a group of hosts in a network can receive. The hosts that are in the group may reside on a single subnet or may be on different subnets that connect multicast-capable routers. Hosts may join and leave groups at any time. There are no restrictions on the location or number of members in a host group. A class D Internet address in the range 224.0.0.1 to 239.255.255.255 identifies a host group.

An application program can send or receive multicast datagrams by using the socket() API and connectionless SOCK_DGRAM type sockets. Multicasting is a one-to-many transmission method. You cannot use connection-oriented sockets of type SOCK_STREAM for multicasting. When a socket of type SOCK_DGRAM is created, an application can use the setsockopt() function to control the multicast characteristics associated with that socket. The setsockopt() function accepts the following IPPROTO_IP level flags:

• IP_ADD_MEMBERSHIP: Joins the multicast group specified.
• IP_DROP_MEMBERSHIP: Leaves the multicast group specified.
• IP_MULTICAST_IF: Sets the interface over which outgoing multicast datagrams are sent.
• IP_MULTICAST_TTL: Sets the Time To Live (TTL) in the IP header for outgoing multicast datagrams.
• IP_MULTICAST_LOOP: Specifies whether or not a copy of an outgoing multicast datagram is delivered to the sending host as long as it is a member of the multicast group.

The following examples enable a socket to send and receive multicast datagrams. The steps needed to differ from the steps needed to .