Issue with UDPClient.JoinMulticast group or UDPClient.BeginRecieve

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  • Karl Durrance

    Issue with UDPClient.JoinMulticast group or UDPClient.BeginRecieve

    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

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