Receiving multiple multicast feeds on the same port – C, Linux

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After some years facing this linux strange behaviour, and using the bind workaround describe in previous answers, I realize that the ip(7) manpage describe a possible solution :

IP_MULTICAST_ALL (since Linux 2.6.31)
This option can be used to modify the delivery policy of
multicast messages to sockets bound to the wildcard INADDR_ANY
address. The argument is a boolean integer (defaults to 1).
If set to 1, the socket will receive messages from all the
groups that have been joined globally on the whole system.
Otherwise, it will deliver messages only from the groups that
have been explicitly joined (for example via the
IP_ADD_MEMBERSHIP option) on this particular socket.

Then you can activate the filter to receive messages of joined groups using :

int mc_all = 0;
if ((setsockopt(sock, IPPROTO_IP, IP_MULTICAST_ALL, (void*) &mc_all, sizeof(mc_all))) < 0) {
    perror("setsockopt() failed");
}

This problem and the way to solve it enabling IP_MULTICAST_ALL is discussed in Redhat Bug 231899, this discussion contains test programs to reproduce the problem and to solve it.

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