First of all, please excuse my english, I might make some mistakes.
So I have this problem for a year now, I can't find a solution.
I have ROOM A, there is my main router. ROOM B is my study room. And there is ROOM C which is empty right now.
So I have a wall socket in every room, with 2 connectors. So every room has direct Cat 6A connection to both other rooms. It is like a triangle.
I want to connect my Desktop PC from ROOM B to my router in ROOM A.
CASE 1: The Ethernet cable from the rooter is connected to the wall socket in ROOM A. In ROOM B the PC is connected via ethernet cable to the wall socket. In this case the PC doesn't observe the cable, like there is absolutely no cable connected (red X on the Network icon).
CASE 2: ROOM A is like above. In ROOM B the cable from the wall socket is connected to a simple LAN-Switch which is powered through an AC-adapter. With another Ethernet cable I connect the switch to the PC. In this case everything seems to work fine.
CASE 3: The Ethernet cable from the router is connected to the wall socket which goes to ROOM C. In ROOM C I connect the socket from ROOM A to the socket from ROOM B with a short Ethernet Cable. In ROOM B the cable goes from the wall socket in the PC. In this case everything connects fine.
So my thought was that the connection between ROOM A and ROOM B is the problem. The connection works only through the AC-powered switch. I am not an expert on Networking, but it's strange that only the extra electricity is missing. With this extra electricity from the Switch the connection is working. Let me clear that I also tried other devices instead of my Desktop PC, with my laptop it's the same.
So yesterday I went to buy an Ethernet connection tester. This is a pair of devices which have LEDs on them. If the connection is OK the 8 LEDs light up from 1 to 8. Everything works fine! The connection is good. All 8 LEDs light up and in the same order on both devices. Only the LED G (shield) won't light up, so the connection is non-shielded. I wanted to test if that could be the problem so I went to test the connection between ROOM A and ROOM C (which I knew that it works perfectly). The LEDs light up the same way, no LED G, it is also non-shielded. So there is apparently no difference between the perfectly working connection from A to C and the faulty connection from A to B.
Anybody has an idea? If all the connections from 1 to 8 are working (or at least the same like in the other room) what could cause the problem?
Thank you in advance!