TL;DR. Buy a switch. Do not use Ethernet Splitters, EVER.
Midlan posted a link to this schematic:
![Parallel Wired 'Ethernet splitter'](../../I/static/images/0b4b6063daea1d8ecc26037f874b4634a1a17cf1f5c49c5faeafa14dcf20c6eb.gif)
'Parallel wired' means that if you use a device like that at best you will get a load of packet collisions because you have wired the two computers (Jacks 1&2) TX pins (Pair 3, Pins 1&2) together, and the RX (Pair 2, Pins 3&6) pins together.Ethernet Wiring
Twisted pair Ethernet, 10base-T, 100base-TX, 1000bast-T, etc. all need to be connected end-to-end. At each there is a transmission (TX) pair, and reception (RX) pair. This is how a cross-over cable works.
Indeed the simplest Ethernet network using twisted pair media is using a crossover cable between two computers:
-----------------------------------------
| Computer-A |
| 568A |
| Pair 3 - Pin 1 - TX+ Green on White +-------\
| Pair 3 - Pin 2 - TX- Green +=======|==\
| Pair 2 - Pin 3 - RX+ Orange on White +-\ | |
| Pair 1 - Pin 4 - B+ Blue + | | |
| Pair 1 - Pin 5 - B- Blue on White + | | |
| Pair 2 - Pin 6 - RX- Orange +=|==\ | |
| Pair 4 - Pin 7 - B+ Brown on White + | | | |
| Pair 4 - Pin 8 - B- Brown + | | | |
| | | | | |
----------------------------------------- | | | |
| | | |
----------------------------------------- | | | |
| Computer-B | | | | |
| 568B | | | | |
| Pair 2 - Pin 1 - TX+ Orange on White +-/ | | |
| Pair 2 - Pin 2 - TX- Orange +----/ | |
| Pair 3 - Pin 3 - RX+ Green on White +-------/ |
| Pair 1 - Pin 4 - B+ Blue + |
| Pair 1 - Pin 5 - B- Blue on White + |
| Pair 3 - Pin 6 - RX- Green +==========/
| Pair 4 - Pin 7 - B+ Brown on White +
| Pair 4 - Pin 8 - B- Brown +
| |
-----------------------------------------
As you can see, the TX pins on Computer-A are wired to the RX pins on Computer-B, and similarly, the RX pins on Computer-A are wired to the TX pins on Computer-B. (For simplicity's sake, I have not wired up pins 4,5,7 & 8, but for completeness they should be wired straight through pin 4 to 4, 5 to 5, etc.)
What your Ethernet Splitter
is doing is just adding in a Computer-C
beside Computer-B
, so that Computer B&C's pins are wired together, pin 1 to pin 1, 2 to 2, 3 to 3 etc. At best, your devices will not work, at worst you will damage your Ethernet ports.
Computer-A could infact be a hub or a switch, but you still have the problem of Computer-B
's and Computer-C
's TX and RX ports being wired together.
Here is a wiring diagram for a simple (passive/unpowered) Ethernet hub
:
http://www.eeweb.com/blog/circuit_projects/building-a-passive-ethernet-hub
https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair
Ethernet is a digital signal, and it is not like an analogue telephone signal where you can use a splitter to add in another extension. Each little wave pattern is a packet of information that is transmitted from a TX port that is intended to go a RX port. Wiring TX ports together is going to cause all sorts of weirdness.
Instead of a splitter, your best option is to add a mini-switch, but you need to be careful with your wiring topology if you already have multiple other switches in your network.
There were other search results which mapped the two unused pairs (1&4) on 100 Base-TX to pins on 1 2 3 and 6 on the second port, so you would have to use these device on each end. However, the Ethernet wire protocol has been designed to use twisted pairs in such a way that cross-talk
is eliminated between the wires. Start doing non-standard, non-compliant things, and you will end up getting non-standard, non-compliant, unexpected results.
2
@Moab but why? If the network with hub works, why it shouldn't work with that splitter? I've found image of internal connection of splitter which I'am talking about: link
– midlan – 2015-12-27T00:20:06.24323There is no such thing as an ethernet spittler. By using a true splitter (a phone splitter usually isn't a true splitter), you have suddenly introduced a break in the required twists, and a couple of impedance mismatches, and electrical problems. Ethernet signalling is nothing like telephone. You can get a cheap 4-port switch. – Ron Maupin – 2015-12-27T00:43:03.717
1If you have one Ethernet connection with no real router or switch behind it, this thing won’t work. Meaning both connections would get the same IP address which is not a good thing. These kinds of splitters are mainly useful for low-speed splitting of an 8-strand Ethernet connection into two, slower 4-strand connections when that connection is on a device that can properly manage handing out multiple IPs. Also a cheap switch costs maybe $19.99 to $29.99. This costs maybe $5. The price difference might seem steep but this is like a long term purchase so $19.99 to $29.99 is actually reasonable. – JakeGould – 2015-12-27T00:44:02.523
1One big downside to this device, is it would map the talking wires of both endpoints together, such that the two devices could never talk to Each Other, only another device upstream. using CrossPatch cabling would not resolve the issue. – Frank Thomas – 2015-12-27T07:01:57.667
1It doesn’t work like that, even “in theory”. This is a completely passive device that’s nothing like a hub or switch. Hubs and switches are active units. This thing here only ever works when both ends of a cable have it attached. Otherwise, it’s unlikely even one device could successfully establish a connection. What’s on the (single) cable is non-standard. – Daniel B – 2015-12-27T18:09:16.777
20It is problematic that some people are supplying answers in comments and those answers contain wrong information. Comments are to clarify the question. An example: Are you running 10Mb, 100Mb, or 1Gb Ethernet through this device? Do you intend for the two devices past the splitter to be able to talk to each other? Does the upstream device limit the number of IPs on the port the other end of the cable will be plugged into? Do you believe half of these commenters actually understand either hub-wired or radio CSMA/CD? – Eric Towers – 2015-12-27T19:23:46.390
1... oh, and are the two devices past the splitter going to be streaming > 30% each of the aggregate bandwidth of the link? – Eric Towers – 2015-12-27T19:27:53.227
2You have a big misunderstanding of what a 10-base-T Ethernet hub is. A 10-base-T hub is basically the same as a switch except that it doesn't keep an ARP table in RAM (most don't even have RAM). That's the difference. A hub sends all incoming packets to all ports except the originating port. A switch remembers the MAC addresses (there can be more than one) connected to each port and only send packets to the appropriate destination port. Either way, both a hub and a switch needs to execute some sort of logic (usually using a CPU). – slebetman – 2015-12-28T07:00:31.387
5
Possible duplicate of Why does just splitting an Ethernet cable not work?
– slebetman – 2015-12-28T07:02:56.7002These devices ARE NOT SPLITTERS. They are MULTIPLEXERs completely different things. – Aron – 2015-12-28T09:51:52.880
If you are in Europe or USA you could get one for free (google for the SamKnows initiative) – beppe9000 – 2015-12-28T13:17:12.697
@Aron, amusingly enough, a muxer is exactly the same as a splitter, but with the signal flowing the opposite direction. – Frank Thomas – 2015-12-28T13:20:34.713
2@EricTowers A lot of times for—frankly—bad questions the best way to handle is to provide advice/answers in the comments. The reality is if someone has a question and seeks an answer, the text in a comment is as valuable as a full answer. But posting a full answer—while more desirable—will open up a can of worms in the first 24 hours where the risk of “Me too!” and generally crud comments/answers can be posted without the ability to quickly protect the question. I’m all for answers, but I am not for just posting one for a question like this and the assumption it presents. – JakeGould – 2015-12-28T15:34:37.580
@midlan The schematic you posted is not for an Ethernet splitter, multiplexer, or anything of the sort. It would just make a mess. If you read the spec sheet for this device, it never mentions Ethernet.
– David Schwartz – 2015-12-28T15:38:17.497