Question

I’m using at struct sockaddr_in to receive multicast data sent out from another machine. When I print out the source address using inet_ntop it gives me the source address of the PC that sent the data.

I would like to know if there is a way of getting the multicast address that the data was ‘sent to’?

Answer 1

Use setsockopt(2) to set the IP_PKTINFO option (see ip(7)) on your receiving socket. Then use recvmsg(2) to collect incoming datagrams, with the msg_control and msg_controllen fields of its msg argument referring to a buffer where the datagram’s destination address can be captured.

Systems other than Linux might provide this capability through the BSD IP_RECVDSTADDR option instead.