Issue with UDPClient.JoinMulticast group or UDPClient.BeginRecieve

[Karl Durrance]

Hi all,

I am having a weird issue with sending and receiving multicast messages
either using the UDPClient object or directly with sockets.

Normally, my application works perfectly, receiving all messages async
through the BeginRecieve() method of the UDPClient.

But in some circumstances, for instance while connected to a Cisco VPN, my
application just doesn¹t receive any multicast messages (the BeginRecieve()
method is never fired)

Now, to troubleshoot this I started Wireshark (Ethereal) to see if I could
see the packets, to my amazement while Wireshark is listening on the adapter
the application works perfectly on the VPN adapter, once I stop the trace,
the application no longer receives messages. I also elminated the UDPClient
object, and went back to raw sockets, with the exact same outcome.

There are no exceptions being thrown by the application at all, it Œseems¹
to be working, but it isn¹t.

Is there some sort of permission I need to set to allow my application to
send/receive messages? Does anyone have any ideas of what Wireshark may be
doing that would allow my app to function? This app works perfectly on
normal LANS/WLANS it is just this odd VPN issue?

Any advice or help would be appreciated.

Cheers,

Karl