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!

  • Do cases #2 and #3 have the same connection speed? Who installed these cables? – sawdust Feb 16 '17 at 19:07
  • If you mean the wall sockets all three are the same kind. The cables were installed by the electrician in 2015 as our house was built. – András Vincze-Nagy Feb 16 '17 at 19:43
  • No, by "connection speed" I mean the actual connection properties as reported by the OS (and not the rating of the physical connector). All you are reporting are superficial the link "works" or "does not work". Try digging a bit deeper to determine the quality of the Ethernet connections, e.g. the link speed (assuming auto negotiation). – sawdust Feb 16 '17 at 19:49
  • Sorry. The network speed is the same in both cases. Writing 51 Mbps and reading 80 Mbps – András Vincze-Nagy Feb 16 '17 at 20:18

This might not solve your problem as I am unable to reason if there is some mechanism in play related to how Ethernet works. However, I had some years ago a similar problem with my Ethernet wall sockets.

Very brief: it was not crimped well. In my particular case I could connect, but was unable to get full duplex speed.

My solution was to open the wall sockets until I could reach the Ethernet connector itself (black box with golden contacts connected to the cable that went to the other room). With the backside of the point of a knife (the side that does not cut) I pushed very firmly on all contacts until I felt how some of them went a little deeper into the wires they were connected to. For this you may also use a small flat screwdriver.

I mounted everything back together and then I made sure that the contacts inside the connector (the ones that touch the cable that goes to my PC) were not bent upwards. These are like springs, and might make a bad contact with the cable if bent a little upwards. I pulled at them with a needle whose tip I had bent into a hook.

This solved my problem. No weird Ethernet voodoo nor problems with my switch. It was a simple bad electrical connection. Its been working now for several years flawlessly. Keep us posted if you solve it :)

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