Artificially create a connection timeout error

You can use the Python REPL to simulate a timeout while receiving data (i.e. after a connection has been established successfully). Nothing but a standard Python installation is needed.

Python 2.7.4 (default, Apr  6 2013, 19:54:46) [MSC v.1500 32 bit (Intel)] on win32
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>>> import socket
>>> s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)        
>>> s.bind(('localhost', 9000))
>>> s.listen(0)
>>> (clientsocket, address) = s.accept()

Now it waits for an incoming connection. Connect whatever you want to test to localhost:9000. When you do, Python will accept the connection and accept() will return it. Unless you send any data through the clientsocket, the caller's socket should time out during the next recv().

How about a software solution:

Install SSH server on the application server. Then, use socket tunnel to create a link between your local port and the remote port on the application server. You can use ssh client tools to do so. Have your client application connect to your mapped local port instead. Then, you can break the socket tunnel at will to simulate the connection timeout.

I had issues along the same lines you do. In order to test the software behavior, I just unplugged the network cable at the appropriate time. I had to set a break-point right before I wanted to unplug the cable.

If I were doing it again, I'd put a switch (a normally closed momentary push button one) in a network cable.

If the physical disconnect causes a different behavior, you could connect your computer to a cheap hub and put the switch I mentioned above between your hub and the main network.

In many cases you'll need the network connection working until you get to a certain point in your program, THEN you'll want to disconnect using one of the many suggestions offered.

Plug in your network cable into a switch which has no other connection/cables. That should work imho.