Problem receiving multicast packets

I've got a strange problem receiving multicast packets in a C# application. What's strange is that it works *sometimes* but not always.

I create a socket, call bind(), set the multicast socket option and then fire off a thread that calls "receiveFrom()" in a loop. This works sometimes, but other times it'll get into a funk where the "receiveFrom()" call doesn't return even though a packet trace capture (Ethereal) shows that the multicast packet was received.

Here's where I'm creating the socket and setting up the thread:

private void createListener()
{
	createListenerSocket();

	_listenerThread = new Thread(new ThreadStart(listenerProc));
	_listenerThread.Name = "Multicast Listener";
        _listenerThread.IsBackground = true;
	_fRunning = true;
	_listenerThread.Start();
}

private void createListenerSocket()
{
IPEndPoint iep = new IPEndPoint(IPAddress.Any, _nGroupPort);
int nTTL = AppSettings.Instance.LAN.MulticastTTL;
_socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
_socket.Bind(iep);
_socket.SetSocketOption(SocketOptionLevel.IP,
SocketOptionName.AddMembership,
new MulticastOption(_groupAddress));
_socket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastTimeToLive, nTTL);
}


And here's the loop where I'm receiving and processing the packets.

private void listenerProc()
{
	IPEndPoint iep = new IPEndPoint(IPAddress.Any, 0);
	EndPoint ep = iep;
	byte[] recvBuff = new byte[8192];
	int nBytes;
	while (_fRunning)
	{
		nBytes = _socket.ReceiveFrom(recvBuff, ref ep);
							
		if (isFromMyself((IPEndPoint)ep))
		{
			logMessage("Packet was sent by me.  Ignoring.", TraceLevel.Verbose);
			continue;
		}

logMessage("listenerProc - Received " + nBytes + " bytes from " + ep.ToString(), TraceLevel.Verbose);
IPEndPoint iepRemote = (IPEndPoint)ep;
processPacket(getMessageBytes(recvBuff, nBytes), iepRemote);
}
}

So, to reiterate, I've verified that the packet is being recieved by my NIC and is being sent to the proper multicast address. In my case the address is "230.2.1.75" with a TTL of 2. But, most of the time, the "_socket.ReceiveFrom()" never returns. Sometimes this works just fine.

Does anyone see what I'm doing wrong?  (I'm hoping Rich Blum sees this :-)

Thanks,
Terry
.

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