Artificially create a connection timeout error

Connect to a non-routable IP address, such as 10.255.255.1.

Connect to an existing host but to a port that is blocked by the firewall that simply drops TCP SYN packets. For example, www.google.com:81.

Plenty of good answers but the cleanest solution seems to be this service

https://httpstat.us/504?sleep=60000

You can configure the timeout duration (up to 230 seconds) and eventual return code.

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.

You might install Microsoft Loopback driver that will create a separate interface for you. Then you can connect on it to some service of yours (your own host). Then in Network Connections you can disable/enable such interface...

Despite it isn't completely clear which one the OP wants to test: there's a difference between attempting a connection to a non-existent host/port and a timeout of an already established connection. I would go with Rob and wait until the connection is working and then pull the cable. Or - for convenience - have a virtual machine working as the test server (with bridged networking) and just deactivating the virtual network interface once the connection is established.

The technique I use frequently to simulate a random connection timeout is to use ssh local port forwarding.

ssh -L 12345:realserver.com:80 localhost

This will forward traffic on localhost:12345 to realserver.com:80 You can loop this around in your own local machine as well, if you want:

ssh -L 12345:localhost:8080 localhost

So you can point your application at your localhost and custom port, and the traffic will get routed to the target host:port. Then you can exit out of this shell (you may also need to ctrl+c the shell after you exit) and it will kill the forwarding which causes your app to see a connection loss.

There are a couple of tactics I've used in the past to simulate networking issues;

1. Pull out the network cable
2. Switch off the switch (ideally with the switch that the computer is plugged into still being powered so the machine maintains it's "network connection") between your machine and the "target" machine
3. Run firewall software on the target machine that silently drops received data

One of these ideas might give you some means of artifically generating the scenario you need

Depending on what firewall software you have installed/available, you should be able to block the outgoing port and depending on how your firewall is setup it should just drop the connection request packet. No connection request, no connection, timeout ensues. This would probably work better if it was implemented at a router level (they tend to drop packets instead of sending resets, or whatever the equivalent is for the situation) but there's bound to be a software package that'd do the trick too.

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.

-- EDIT -- 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.

The easiest thing would be to drop your connection using CurrPorts.

However, in order to unit test your exception handling code, perhaps you should consider abstracting your network connection code, and write a stub, mock or decorator which throws exceptions on demand. You will then be able to test the application error-handling logic without having to actually use the network.

You can try to connect to one of well-known Web sites on a port that may not be available from outside - 200 for example. Most of firewalls work in DROP mode and it will simulate a timeout for you.

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