Network cable splitter not working

-1

I'm working on a home set-up where I can split my network cable to use two computers on one side, and two ports on my modem on the other side (so a 2-1-2 config). I have the following set-up:

1 (longer) gigabit network cable between the 2 computers and my modem.
2 ISDN RJ45 splitters
cat 5 cables between my two computers and one splitter, and two cat 5 cables between the other splitter and two ports on the modem.

However, whenever I have both cables connected on my modem and just one cable (to one PC) to the splitter, my PC cannot get a connection (it just shows unplugged). Whenever I take out one of the cables on the modem side, it starts working again.

I've understood this should work as long as I also have it connected to two ports on the modem, but I can't get it to work. Do I need different cables? Or is this a method that just doesn't work anymore?

I understand this is also not a preferred method (and something like a switch would be better), but I am trying to run this cheaply for a short period of time, and running two long cables is not an option unfortunately.

Deniz Zoeteman

Posted 2018-01-15T20:55:43.540

Reputation: 1 001

I believe you need a minimum of a hub and better a switch - which you've said you don't want. A switch is better than a hub. Also, the modem must be able to assign more than one IP address which means it'll need router functions or you'll need to talk to your ISP to get an extra IP. – headkase – 2018-01-15T21:12:41.333

And if you have a cheap router lying around just run one cable from the modem and use the router to split it and also assign IPs. That would be a good method if you do have one kicking around. – headkase – 2018-01-15T21:15:38.223

@headkase Sorry, I should have specified, it's a router/modem combo from my ISP. – Deniz Zoeteman – 2018-01-15T21:27:00.460

Answers

As far as I know, the ISDN RJ45 splitters are not made for two ethernet LAN cables, but for one LAN cable and one ISDN cable. So I'd expect one port to have the wrong pin connections.

But it depends on what splitters you have. Do they have the connections documented somewhere? Compare with the T568A/B pinout.

If the connections are right, it should simulate a 10MB/100MB connection, as 10BASE-T and 100BASE-TX only require two pairs (pins 1–2, 3–6) to operate.

But looking up prices on Amazon, there are simple switches for 10 EUR, and the splitters also for 10 EUR, so I don't really see how you save money with the splitters ...

dirkt

Posted 2018-01-15T20:55:43.540

Reputation: 11 627

The splitter seems to have the same connections on both ports, and I can connect my PC to either port, and it works fine. All info I can find on the splitter is that it's RJ45 female on all ports, and labelled as "8p8c" on the one side and 2x "8p4c" on the other side (my networking knowhow isn't great, so I don't know what that means, but maybe you know more). I know a switch isn't super expensive, but it's also another device I have to keep powered and have around, while I won't have this set-up for long. The splitters were only 2 EUR each ;) – Deniz Zoeteman – 2018-01-15T21:34:10.707

It sounds like you are using the wrong sort of splitter.

It sounds like what you have is a splitter that just connects all pins on the two sockets to the same pins on the plug. Such a splitter might be used in phone or ISDN applications to connect two phones to the same line.

To run two Ethernet lines down the same cable you need splitters specifically designed for the purpose that route two pairs of the cable to each Ethernet port.

plugwash

Posted 2018-01-15T20:55:43.540

Reputation: 4 587