There are 2 networks in my lab environment. 1 test network and 1 general IT network connection. Test network is used for communication between test server, PQIUHC and UUT - for all the testing purpose. Test network is an isolated network. On the other hand, general IT network is used to connect to all other networks such as Internet, other lab or factory network. Test server has 2 NIC (1 connect to test network and 1 connect to general IT network)

My customer reported he failed to connect to test server from his UUT. Network failed intermittently. The simple way to test network connection is using command prompt to test it. Key in ‘ping -t testserver‘ (replace testserver with your IP) in command prompt. In normal condition, you will get ‘Reply from testserver: bytes=32 time=1ms TTL=125‘. Else you will get ‘Request timed out‘ if the server network is totally out of service. However, sometime you get reply from it and sometime don’t. This is what we call intermittent network issue.

There are many factor that can cause this issue to happen. Hardware might the one that causing the problem but very less percentage unless your hardware is very old. Another one is caused by software. Finally, human’s mistake. Most of the time, it is caused by ourselves.

For this case, it is caused by human error. Somehow, there is cable from general IT switch link go to test network switch. Therefore, whenever PQIUHC or UUT want to talk to test server. They will face problem to connect to test server due to there are 2 routes (test network and general IT network). So intermittent network issue will happen. Only 1 route is allowed in this case. All we need to do is unplug the cable between these 2 switches and everything back to normal again…