UDP Multicast HELP!

[Martin v. Loewis]

"Larry" <ld @ nospam.com> writes:

> s1.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, '234.5.6.7')

The problem here is that IP_ADD_MEMBERSHIP requires a struct ip_mreq,
which is typically defined as

struct ip_mreq
  {
    struct in_addr imr_multiaddr;       /* IP multicast address of group */
    struct in_addr imr_interface;       /* local IP address of interface */
  };

So this is an 8-byte value. For imr_interface, you usually specify
INADDR_ANY, which is '\0\0\0\0', so you really need to use

group = socket.inet_aton('234.5.6.7') + '\0\0\0\0'
s1.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, group)

[Strictly speaking, you should use struct.pack to build the struct,
 but the code above is just as portable, I assume]

HTH,
Martin