Unstable network

Today, I go to company to check the PC which can't connect to Internet.

I turn on the PC and the system show LAN cable unplug. I use the cable tester to the LAN cable and it is normal. I write down the LAN socket number on my note then I go to Server room. I check the router ports and the LAN port and one of them is no signal in the router. I unplug the LAN cable and plug it to other ports. I leave the Server room and check the PC again. The system show the Network is unstable. I return to the Server room. I check those network devices again and then plug the LAN cable to other router’s port. I leave the Server room again and check the PC. The PC can connect to Internet.

I leave the company at 14:15.