int getInterfaceInfo(const char *ifc, uint32_t *ipaddr, uint8_t *mac)
{
# define MAX_IFC_SETS 16

  printf("get InterfaceInfo ifc: <%s>, len: %i\n", ifc,strlen(ifc));

  struct ifconf ifr_conf;
  struct ifreq set[MAX_IFC_SETS];
  int s;
  unsigned i;
  struct sockaddr_in *addr;

  if ((s = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
    printf("Error Socket!\n");
    return -1;
  }

  ifr_conf.ifc_len = sizeof(struct ifreq) * MAX_IFC_SETS;
  ifr_conf.ifc_req = set;

  if (ioctl(s, SIOCGIFCONF, & ifr_conf) < 0) {
    printf("Error SIOCGICONF!\n");
    return -1;
  }

  for (i = 0; i < ifr_conf.ifc_len / sizeof(struct ifreq); i++){
    if ((!ifc[0] && strncmp(ifr_conf.ifc_req[i].ifr_name, "eth0", IFNAMSIZ) == 0) || 
        (ifc[0] && strncmp(ifr_conf.ifc_req[i].ifr_name, ifc, IFNAMSIZ) == 0)) {
       addr = (struct sockaddr_in *) & ifr_conf.ifc_req[i].ifr_addr;
       *ipaddr =  addr->sin_addr.s_addr;
       // return interface index
       printf("Our Interface: index: %i, name: %s, ip: %s\n",i,ifr_conf.ifc_req[i].ifr_name,inet_ntoa(addr->sin_addr));

       // get also mac
       if (ioctl(s, SIOCGIFHWADDR, &ifr_conf.ifc_req[i])  < 0) 
         return -1;
       memcpy(mac, ifr_conf.ifc_req[i].ifr_hwaddr.sa_data, 6);
       close(s);
       return i;
    }
  }
  close(s);

  return -1;
}

MCPort::MCPort(const PortAddress_t mcaddr, const uint16_t port, const char *laddr) {

  struct sockaddr_in ssock;
  struct ip_mreq mreq;
  int one = 1;
  int zero = 0;
  int ttl = 64;

  m_port = port;
  uint8_t mac[6];
  // initialize 
  memset(&ssock, 0, sizeof(ssock));
  ssock.sin_family = AF_INET;
  ssock.sin_addr.s_addr = INADDR_ANY;

  // create datagram socket
  if ((m_sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
    return;
  
  setsockopt(m_sock, SOL_SOCKET, SO_REUSEADDR, (char *)&one, sizeof(one));

  // bind to port
  ssock.sin_port = htons(port);
  if (bind(m_sock, (struct sockaddr *)&ssock, 
           sizeof(struct sockaddr_in)) < 0){
    m_sock = -1;
    return;
  }

  // to be able to receive multicast packets
  memcpy(&mreq.imr_multiaddr.s_addr,&mcaddr.addr,sizeof(mreq.imr_multiaddr.s_addr));
  uint32_t ipaddr;
  int index = getInterfaceInfo(laddr, &ipaddr, mac);
  mreq.imr_interface.s_addr = ipaddr; 
  if (setsockopt(m_sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&mreq, sizeof(mreq)) < 0) {
    m_sock = -3;
    return;
  }
  // prevent from receiving own multicast packet
  if (setsockopt(m_sock, IPPROTO_IP, IP_MULTICAST_LOOP, (char *)&zero, sizeof(zero)) < 0) {
    m_sock = -4;
    return;
  }

  // to be able to send multicast packets from the right interface
  struct in_addr localInterface;
  localInterface.s_addr = ipaddr;
  printf("sockopt ip: %s\n",inet_ntoa(localInterface));
  if (setsockopt(m_sock, IPPROTO_IP, IP_MULTICAST_IF, (char*)&localInterface, sizeof(localInterface)) < 0)
  {
     printf("Error %i: %s\n",errno,strerror(errno));
     m_sock = -6;
     return;
  }
}

[root@localhost ~]# ifconfig
eth0      Link encap:Ethernet  HWaddr 08:00:27:78:EC:49
          inet addr:192.168.102.166  Bcast:192.168.103.255  Mask:255.255.254.0
          inet6 addr: fe80::a00:27ff:fe78:ec49/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:827107 errors:0 dropped:0 overruns:0 frame:0
          TX packets:678985 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:419623378 (400.1 MiB)  TX bytes:547112945 (521.7 MiB)

eth0.57   Link encap:Ethernet  HWaddr 08:00:27:78:EC:49
          inet addr:11.0.0.66  Bcast:11.255.255.255  Mask:255.0.0.0
          inet6 addr: fe80::a00:27ff:fe78:ec49/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:33 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:4177 (4.0 KiB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

[root@localhost ~]# uname -a
Linux LiveLinVM 2.6.32-220.el6.i686 #1 SMP Tue Dec 6 16:15:40 GMT 2011 i686 i686 i386 GNU/Linux

Linux localhost 2.6.32-220.el6.x86_64 #1 SMP Tue Dec 6 19:48:22 GMT 2011 x86_64 x86_64 x86_64 GNU/Linux