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POHow to set up a socket for UDP multicast with 2 network cards present?
 

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  1. POHow to set up a socket for UDP multicast with 2 network cards present?
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    <p>I'm trying to get udp multicast data using sockets and c++ (c). I have a server with 2 network cards so I need to bind socket to specific interface. Currently I'm testing on another server that has only one network card.</p> <p>When I use INADDR_ANY I can see the udp data, when I bind to specific interface I don't see any data. Function inet_addr is not failing (I removed checking for return value for now).</p> <p>Code is below. On a server with one network card, my IP address is 10.81.128.44. I receive data when I run as: ./client 225.0.0.37 12346</p> <p>This gives me no data: ./client 225.0.0.37 12346 10.81.128.44</p> <p>Any suggestions? (Hope the code compiles, I removed comments ...)</p> <pre><code> #include &lt;stdlib.h&gt; #include &lt;sys/types.h&gt; #include &lt;sys/socket.h&gt; #include &lt;netinet/in.h&gt; #include &lt;arpa/inet.h&gt; #include &lt;time.h&gt; #include &lt;string.h&gt; #include &lt;stdio.h&gt; #include &lt;iostream&gt; #include &lt;string&gt; using namespace std; #define HELLO_PORT 12345 #define HELLO_GROUP "225.0.0.37" #define MSGBUFSIZE 256 int main(int argc, char *argv[]) { string source_iface; string group(HELLO_GROUP); int port(HELLO_PORT); if (!(argc &lt; 2)) group = argv[1]; if (!(argc &lt; 3)) port = atoi(argv[2]); if (!(argc &lt; 4)) source_iface = argv[3]; cout &lt;&lt; "group: " &lt;&lt; group &lt;&lt; " port: " &lt;&lt; port &lt;&lt; " source_iface: " &lt;&lt; source_iface &lt;&lt; endl; int fd; if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) &lt; 0) { perror("socket"); exit(1); } u_int yes = 1; if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &amp;yes, sizeof(yes)) &lt; 0) { perror("Reusing ADDR failed"); exit(1); } struct sockaddr_in addr; memset(&amp;addr, 0, sizeof(addr)); addr.sin_family = AF_INET; addr.sin_port = htons(port); addr.sin_addr.s_addr = (source_iface.empty() ? htonl(INADDR_ANY) : inet_addr(source_iface.c_str())); if (bind(fd,(struct sockaddr *)&amp;addr, sizeof(addr)) &lt; 0) { perror("bind"); exit(1); } struct ip_mreq mreq; mreq.imr_multiaddr.s_addr = inet_addr(group.c_str()); mreq.imr_interface.s_addr = (source_iface.empty() ? htonl(INADDR_ANY) : inet_addr(source_iface.c_str())); if (setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &amp;mreq, sizeof(mreq)) &lt; 0) { perror("setsockopt"); exit(1); } socklen_t addrlen; int nbytes; char msgbuf[MSGBUFSIZE]; while (1) { memset(&amp;msgbuf, 0, MSGBUFSIZE); addrlen = sizeof(addr); if ((nbytes = recvfrom(fd, msgbuf, MSGBUFSIZE, 0, (struct sockaddr *)&amp;addr, &amp;addrlen)) &lt; 0) { perror("recvfrom"); exit(1); } cout.write(msgbuf, nbytes); cout.flush(); } return 0; } </code></pre> <p>Thanks in advance ...</p>
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