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I've moved into a new house, and I'm experiencing some trouble with an ethernet socket in the wall. It's just a bit unstable; can lose internet if someone touches the cables. Also feels like it takes a while to get the network up and running when a connected machine boots up. Had trouble using a switch with this wall mount, it just won't receive any signal from the wall socket, so in the end I just connected it directly to a computer, which works alright, apart from the aforementioned problems.

I had a look at the wires, and discovered that it's a cat5-e cable that's been sliced open, four of the wires go to this socket, the remaining four go through the floor to a second socket downstairs. At the router's end, the cable splits into two separate RJ45 plugs, so it takes up two slots in the router, one for each wall socket.

I'm wondering whether it's this splitting of a single cable that's causing problems, or if perhaps it's just the wall socket itself that's slightly damaged. Intended use is to simply provide cabled internet to a htpc computer, and a smart tv.

Is it worth attempting to replace the socket, or is it definitely the splitting of the cable that's the issue?

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    splitting the cable could introduce some interference, but what you describe seems to be a physical issue "can lose internet if someone touches the cables". we once used a similar config, as we were limited with the amount of cables which we could put through walls, so we used one cable for a dual socket. in your case, I would definitively first check the socket.
    – Zina
    Dec 18, 2020 at 9:19

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For 10 and 100 Mbit/s Ethernet (10BASE-T and 100BASE-TX) only two of the four cable pairs are required. Sometimes a single cable is split to connect two sockets. If done properly that works fine. It's impossible to run Gigabit Ethernet (1000BASE-T) over that setup though.

can lose internet if someone touches the cables.

That clearly indicates the crimps/sockets are bad. If you don't want to live with that you'll have to check/redo the crimps and possibly replace the sockets. When redoing the termination you can also recombine the pairs to a full, gigabit-capable cable. Take care to keep the pairs matched, do not undo or overdo the twisting rate, and don't reverse the twist direction.

it takes a while to get the network up and running when a connected machine boots up.

That can be caused by bad cabling or by the missing pairs between two gigabit devices - those negotiate gigabit and fail to start the link. Some fall back to 100BASE-TX after some attempts, some don't (failing to link completely).

To get around that you'd have to configure the ports down to 100M - BEWARE: most gigabit devices don't support "auto 10/100" but only "100 full duplex", "100 half duplex" and so on. For full duplex you MUST configure both sides identically. Failing that, you can easily create a duplex mismatch which performs very poorly. As a workaround you can use "100 half-duplex" but that'll cost some performance (might not be an issue).

Had trouble using a switch with this wall mount

That might be caused by the split cable (failing gigabit negotiation) or by none of the link partners supporting Auto MDI-X - old-style switches use the reversed pinout of PCs/NICs and won't link with another such switch without a crossover cable.

I'd definitely undo the cable split to run stable gigabit. If you need more ports, just add a switch for fanout. After all, 1x 1000 Mbit/s is faster than 2x 100 Mbit/s.

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