Multicast on a specific NIC

[yalakvar]

Hi all,

I am trying to setup a socket that listens and send on a specific NIC. This socket also joins a multicast group. For some reason it doesn't work. Here is a sample code of what I do:


#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define MY_IP "20.1.1.1"
#define MY_PORT 52101
#define MY_MC "230.0.0.8"

int main()
{
int sock = socket (AF_INET, SOCK_DGRAM, 0);
if (sock <= 0)
return -1;

sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr (MY_IP);
addr.sin_port = htons (MY_PORT);

int ret = bind (sock, (sockaddr*)&addr, sizeof (addr));
if (ret != 0)
return -1;

ip_mreq mreq;
mreq.imr_multiaddr.s_addr = inet_addr (MY_MC);
mreq.imr_interface.s_addr = inet_addr (MY_IP);

ret = setsockopt (sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof (mreq));
if (ret != 0)
return -1;

char buff[1500];
ret = recv (sock, buff, sizeof (buff), 0);
if (ret <= 0)
{
printf ("Error in recv!\n");
return -1;
}

printf ("Received packet from MC!!");
return 0;
}

In this sample the recv function never returns. If I change MY_IP to be INADDR_ANY the function recv returns. In my application I want to get only packets from a specific interface and not from all of them.

Thx in advance for help.

[chaosless]

instead of:

mreq.imr_interface.s_addr = inet_addr (MY_IP);


i think you want:

mreq.imr_interface.s_addr=htonl(INADDR_ANY);


if that's not the issue then i can look more closely...

[yalakvar]

Hi,

Thank you for answering.
What I meant was that if I replace the line:

addr.sin_addr.s_addr = inet_addr (MY_IP);

with

addr.sin_addr.s_addr = htonl (INADDR_ANY);

then it works fine and my socket receives multicast packets. The problem is that in this case I also receive non-multicast packets with destination port=MY_PORT which arrived on other interfaces.