Peter,

Thanks for the reply! The ping code is below. The key to the problem is that
this code is running in multiple threads, one for each machine. If a given
machine is up but has ICMP disabled, for example, the receive portion simply
grabs another machine/thread/socket's ICMP response. However, the other
socket also receives the response. My question is, is this expected
behavior? I can work around it by examining the ref endpoint to make sure
that the response is from the machine associated with the thread, but it's
important that I understand that this is not a defect in the framework, but
rather a side-effect of the nature of the ICMP protocol. Thanks,

Kevin

public void ping(int intTimeout)

{

   mPingStart = Environment.TickCount;

   mSocket.BeginSendTo(mPacket.serialize(), 0, mPacket.Size,
SocketFlags.None, mRemoteMachine, new AsyncCallback(SendCallback), null);

   //wait until signaled or the timeout period expires.

   mPaused.WaitOne(intTimeout, false);

   //did the call timeout?

   if (mPingTime == -1) //Yes

       mExceptionMessage = "Host Unreachable";

}

private void SendCallback(IAsyncResult ar)

{

   int bytesSent = 0;

   try

   {

       bytesSent = mSocket.EndSendTo(ar);

       //were any bytes sent?

       if (bytesSent == SOCKET_ERROR) //No

           mExceptionMessage = "Host Unreachable";

       else //Yes, bytes were sent

           mSocket.BeginReceiveFrom(mRecv_Buffer, 0, RECV_SIZE,
SocketFlags.None, ref mLocalMachine, new AsyncCallback(ReceiveCallback),
null);

   }

   catch (Exception e)

   {

       mExceptionMessage = e.Message;

   }

}

private void ReceiveCallback(IAsyncResult ar)

{

   int bytesReceived = 0;

   try

   {

       bytesReceived = mSocket.EndReceiveFrom(ar, ref mLocalMachine);

       //were any bytes received?

       if (bytesReceived > 0) //Yes

           mPingTime = Environment.TickCount - mPingStart;

   }

   catch (Exception e)

   {

       mExceptionMessage = e.Message;

   }

}