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.
33 Answers
It sounds as if you have a basic RJ45 splitter and not an Ethernet splitter, and that your splitter is connecting all four cable pairs to both terminals*.: You are likely to have at least two types of problem: reduced signal levels due to the additional loading (whether this is a problem will depend on how the equalisation is managed), and reflections of your transmitted data from the joint. There could be some double reflections, depending on how well the IOs of the terminals match the cable.
Even (basic) 1Gb/s Ethernet switches are really good value these days, but you probably only need 100-Mb/s, and there are reliable switches on the market at really low.
If you don't have enough local power sockets or don't want to clutter your floor you can use an Ethernet splitter, but a reliable splitter won't be any cheaper than a 100Mb/s switch. Ethernet splitters connect two of the four pairs in the cable to each terminal, which avoids both reflections and attenuation issues.
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 ...
1It 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.
