linux multicast join doesn't, why? - linux

Question

I need to receive multicast data from two sources on one ethernet connection, 224.0.31.132 port 14384 and 224.0.31.130 port 14382.
First I tried to bind with port 14384 and then join both ip addresses, but I only get the data from 224.0.31.132.
If I bind with 14382 and join both, I only get the data from 224.0.31.130.
So then I tried to create two sockets, bind the first to 14384 and join 224.0.31.132, then bind the second to 14382 and join 224.0.31.130.
When I do that, I get the data from 224.0.31.130, but not from 224.0.31.132, and ip maddr show shows that the join to 224.0.31.132 has apparently been deleted by the setting up of the second socket.
What do I do to receive data from these two sources on the single eth port?
Here is code for first approach:
/* Create a datagram socket on which to receive. */
int sd = socket(AF_INET, SOCK_DGRAM, 0);
if(sd < 0)
{
perror("Opening datagram socket error");
exit(1);
}
else
cout<<"Opening datagram socket....OK."<<endl;
/* Enable SO_REUSEADDR to allow other */
/* applications to receive copies of the multicast datagrams. */
{
int reuse = 1;
if(setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse)) < 0)
{
perror("Setting SO_REUSEADDR error");
close(sd);
exit(1);
}
else
cout<<"Setting SO_REUSEADDR...OK."<<endl;
}
/* Enable SO_REUSEPORT to allow multiple uses of receive port */
{
int reuse = 1;
if(setsockopt(sd, SOL_SOCKET, SO_REUSEPORT, (char *)&reuse, sizeof(reuse)) < 0)
{
perror("Setting SO_REUSEPORT error");
close(sd);
exit(1);
}
else
cout<<"Setting SO_REUSEPORT...OK."<<endl;
}
/* Bind to the proper port number with the IP address */
/* specified as INADDR_ANY. */
struct sockaddr_in localSock;
memset((char *) &localSock, 0, sizeof(localSock));
localSock.sin_family = AF_INET;
localSock.sin_port = htons(14384);
localSock.sin_addr.s_addr = INADDR_ANY;
if(bind(sd, (struct sockaddr*)&localSock, sizeof(localSock)))
{
perror("Binding datagram socket error");
close(sd);
exit(1);
}
else
cout<<"Binding datagram socket...OK."<<endl;
/* Join the multicast groups on the local nic interface. */
struct ip_mreq group;
group.imr_interface.s_addr = inet_addr("0.0.0.0");
int ipcount = stoi(getSetup("mcstcount"));
while(ipcount>0)
{
string which = "listenip" + to_string(ipcount);
cout<<"listen to "<<getSetup(which.c_str())<<endl;
group.imr_multiaddr.s_addr = inet_addr(getSetup(which.c_str()).c_str());
ipcount--;
if(setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&group, sizeof(group)) < 0)
{
perror("Adding multicast group error");
close(sd);
exit(1);
}
else
cout<<"Adding multicast group...OK."<<endl;
}
// process Mdp feed
while( !stop_cond )
{
/* Read from the socket. */
const int DBUFSZ = 5000;
uint8_t databuf[DBUFSZ];
int datalen;
datalen=read(sd, databuf, DBUFSZ);
if(datalen < 0)
{
perror("Reading datagram message error");
close(sd);
exit(1);
}
//process data
}
Here is resulting output:
Opening datagram socket....OK.
Setting SO_REUSEADDR...OK.
Setting SO_REUSEPORT...OK.
Binding datagram socket...OK.
listen to 224.0.33.80
Adding multicast group...OK.
listen to 224.0.31.130
Adding multicast group...OK.
listen to 224.0.31.132
Adding multicast group...OK.
But data only comes in from 224.0.31.132.

Answer 1

Concluded one cannot use a single socket as there are multiple ports to receive from. Went back to approach two, using multiple sockets. Got it working, not sure what was wrong the first time.