I have a room with only one Ethernet cable going there, but I would like to connect two devices on it. Is an Ethernet splitter suitable for that? I am talking about something like this:

image of splitter

In theory it should work like an Ethernet hub, which only amplifies the signal, but send it to all clients (like a splitter would). I've never used it, so I need confirmation that it work or not before I'll buy it.

  • 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
    Dec 27, 2015 at 0:20
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    There 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
    Dec 27, 2015 at 0:43
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    It 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? Dec 27, 2015 at 19:23
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    You 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
    Dec 28, 2015 at 7:00
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    Possible duplicate of Why does just splitting an Ethernet cable not work?
    – slebetman
    Dec 28, 2015 at 7:02

8 Answers 8


TL;DR. Buy a switch. Do not use Ethernet Splitters, EVER.

Midlan posted a link to this schematic:

Parallel Wired 'Ethernet splitter'

'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: https://www.eeweb.com/building-a-passive-ethernet-hub/


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.

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    I don't feel it can damage sensible ports. Ethernet ports are supposed to be exposed to static and typically have some protection. Also modern network cards may have TX/RX reversal detection, so there may be degraded connectivity to just network or just to the peer computer (but probably not to both).
    – Vi.
    Dec 27, 2015 at 12:05
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    Sure, but the idea of an Ethernet splitter is just bad. UTP Cat 5/5e/6 etc Base-T is supposed to wired in a certain way for it to work properly, and this idea of a splitter is breaking that in so many ways. Ethernet UTP Cat 5/5e/6 are supposed to wired as either T568A or T568B end-to-end, and you are not supposed to change the circuit, otherwise you change the expected voltages, impedance and attenuation.
    – David
    Dec 27, 2015 at 12:18
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    Parallel wireing... ewewewew. What's the point of those?
    – Journeyman Geek
    Dec 27, 2015 at 13:42
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    "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." — Old-timers who remember Ethernet as a shared medium would point out that the idea is not as ludicrous as it sounds. Dec 27, 2015 at 20:48
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    Op's splitter is meant to be the one you mentioned in the last paragraphs. Allowing two ethernet connections over a single cable via the typically unused pairs.
    – cde
    Dec 28, 2015 at 11:03

It's useful to understand what a splitter does. It turns one 8-strand ethernet cable into a what would be, essentially, a pair of sub-standard 4-strand cables that in theory should do Fast Ethernet (100BaseT/TX). Practically this might drop down to 10BaseT speeds, and you need to use a splitter on both ends for it to work. It will take up two ethernet ports on the far end. It will absolutely not work for Gigabit (1000Base) Ethernet, as that requires all 8 strands.

A hub and a switch are very different things.

A hub takes in data and retransmits it to all the ports (and I've never seen a fast Ethernet hub, let alone gigabit). A switch takes in data and switches packets only where they need to go (which is faster and more secure). This... well is a fairly dumb device that turns one cable into 'two'.

In theory it should work like an Ethernet hub, which only amplifies signal, but send it to all clients (like a splitter would). I've never used it, so I need confirmation that it work or not before I'll buy it.

Your theory is wrong, and what you REALLY need is a switch.

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    Heh, I've seen some built-in gigabit ports retch when faced with these. They used to be quite useful for 100Mbit equipped computers plus a VOIP phone. You have to set the link negotiation to manual 100Mbit Half Duplex and hope that Gigabit ports will deign to play at those speeds. Dec 27, 2015 at 0:53
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    Shouldn't. Did. I even scienced it.
    – Journeyman Geek
    Dec 28, 2015 at 10:35
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    Looked at the scienced post, I'd say the results had to do more with the cable being crappy then it did simply lacking the extra pairs. Maybe corroded connectors, or substandard copper wires. If you took a quality cable, removed or simply left the unneeded wires unconnected in the jack, would the results be the same? I've had issues where cheap and/or old connectors I used to build cables failed a fluke test.
    – cde
    Dec 28, 2015 at 11:00
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    Substandard copper wires is possible - that said, most reviews of these sort of units tend to suggest they are crappy and break easily. These cables were fresh out of packaging.
    – Journeyman Geek
    Dec 28, 2015 at 11:46
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    Not much. I'd assumed at the time of my answer hubs were limited to base 10 speeds. Switches are more common nowadays, and to me the right way to do it. If you can find a hub that meets your needs, sure. Just do not use a splitter without understanding what it does.
    – Journeyman Geek
    Dec 29, 2015 at 6:49

Some background:

A router or a switch connect to different devices. One device per cable. Ethernet cables usually have 8 wires in them and for 10 and 100mbit connections only 4 are used. 4 specific ones with well defined twist rates in the cable.


Best guess on that these do, depending on splitters I have seen in the past:

Ethernet cable has 8 wires. Sub-gigabit Ethernet only needs 4.

If we want to do ugly things then we can try to use one 8-wire cable as two 4-wire cables. This most likely will run your cable out of spec and the connection may be unreliable.

illustration of Ethernet splitter Note that these is no communication between the two NICs on the left side.

The only reason to do this is if you really need two different physical connections and only have one cable. It is an emergency kludge. At least one cable/connection is out of spec. It is not compatible with Gigabit. It is not guaranteed to work (though if you drop to 10Mbit it often will).

In almost all situations the right answer is to use a hub or a switch.

  • you write "A router of a switch " <-- a what? I've heard of devices that do both that are called routers, or a routers with a switch built in. But I haven't heard of them being called a switch with a router built in
    – barlop
    Dec 28, 2015 at 15:41
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    @barlop I'd assume it was a typo for "router or a switch"
    – Brian
    Dec 28, 2015 at 15:56
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    It was a typo. Two keys next to eachother on the keyboard and fat fingers.
    – Hennes
    Dec 28, 2015 at 22:16
  • What's an "Etthernet" (two 't's)? ;)
    – Cole Tobin
    Jan 1, 2016 at 1:14

Notice your image shows two splitters - that's because these adapters are used exclusively in pairs.

You will need two ports on your switching device, and two cables to this splitter (the combiner?) then one cable onwards through the walls. In your room you have one cable from the wall to the back of the splitter, then one cable to each device.

In contrast, if you put in a switch you would be neater and closer to best practice.

These splitters don't carry gigabit at all, and some of them can fail to negotiate 100 Mbit. Also, they won't negotiate POE either.

As an alternative, can you run more cable in the wall? Use the existing wire as a draw cord for several lengths? This is why overdoing cable runs is a good idea when the wall linings are open.


Depends upon what you are trying to do, If you are trying to connect two separate machines though Ethernet to the modem/router then you would need a switch(network), but a hub will just connect the two machines to each other and relay the same packets over and over, not achieving much.

Short and sweet: No, an Ethernet splitter will not work for your purpose, use a switch(they can be a little expensive)


An Ethernet splitter can be thought of a type of device that isn't a hub or a switch. It is a rather simple device that actually does nothing but connect two pairs of 2 Ethernet cables to a single Ethernet cable. If you don't trust Ethernet splitters then you can actually build a cable that does the exact same thing.

A splitter works by taking two physical Ethernet ports and sending both connections (which must be limited to using 100mbps speeds) though a single cable. A splitter doesn't connect both ports together in any way. It keeps both ports isolated unlike hubs and switches.

Here is a diagram to show you how a typical Ethernet splitter system works. Ethernet splitter wiring diagram

Basically, 100Mbps Ethernet only uses 2 out of the 4 pairs in a standard Ethernet cable unlike 1Gbps Ethernet which uses all 4 pairs. In 100Mbps Ethernet, 2 pairs simply get unused. In theory, if you were working with 100Mbps Ethernet, you could use the 2 unused pairs for almost anything. PoE is one way you can make use of the two unused pairs (PoE only works with 100Mbps connections for this very reason). Splitters are just another way of making use of the two unused pairs since you can fit entirely another 100Mbps connection since the connection requires only 2 pairs.

Unfortunately, there are several downsides with using splitters:

  • You'll be limited to 100Mbps speeds even if you connect it to hardware capable of 1Gbps speeds. Each connection lacks the necessary pairs to do 1Gbps speeds. Hardware that does 1Gbps speeds will see that 2 pairs are missing and auto-negotiate a speed of 100Mbps.

  • You still need 2 free ports on your existing switch/router. Switches/routers only provide one connection per port. Trying to use a splitter to turn one connection into two won't work since that's the job of switches/hubs which clearly, a splitter is not either of. If you attempt to use this two turn one connection into two, I see two possible scenarios: Only one device will receive a connection, or, the port on the switch/router will fail to work properly with both devices connected.

  • Any cable you connect to the splitter will count towards your total cable length. However, since a splitter has 2 physical connections, you have two cable lengths instead of just one. Theoretically, splitters don't amplify signals so your maximum cable length will not be extended.

Now to answer your question: It will work but only under certain conditions. If you need more than 100Mbps speeds then either run another cat 5e cable to your room or buy another switch. If this is not possible then you'll have to deal with 100Mbps speeds. Also, if you have only one spare port on your router/switch, this is not going to work for you.

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    No, Ethernet 10Base-T and 100Base-TX use pairs 2 and 3 (The green and yellow wires) to minimise crosstalk, RF and EM interference. The unused pairs, 1 and 4 (Blue and Brown), will suffer more from crosstalk and other RF/EM interference. Those pairs are sometimes used for analogue voice channels, but that is not really recommended. It is best to leave the wires properly wired as 568A or 568B. There is no such thing as an Ethernet Splitter. Remember that standard Ethernet cables are Unshielded Twisted Pair (UTP).
    – David
    Dec 27, 2015 at 13:43
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    Ethernet takes into account and requires the features cabling rated UTP Category 5 or better en.wikipedia.org/wiki/Category_5_cable . In other words, using the cabling in a non-standard way, you are going substantially mess up the frequency response, and cause yourself all sorts of problems.
    – David
    Dec 27, 2015 at 13:46

Speaking of the concept, more than just a connector...

Every ethernet network connects terminals via a splitter, so to speak. A splitter is just a parallel configuration of devices.

A daisy-chain configuration connects many devices in parallel to the one host.

A series configuration goes terminal to terminal, with each connected in parallel. Typically requires less overall cable length.

All ethernet devices on one network are connected together, in this simplest way. All terminals must be connected to the same network wire.

The ethernet philosophy is that each terminal listens before transmitting, and also listens during transmission, to detect collisions (two terminals transmitting at same time, interfering). If a collision occurs, each terminal backs off and waits a short random time (milliseconds), and then simply tries again, as often as necessary.

A switch could be used to remove other traffic from the terminal, and to improve bandwidth on that one wire, but it is not required to do so.

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    This does not really answer the question, which was "Will an Ethernet splitter work?". It also doesn't do a very good job of explaining how an Ethernet network and the devices used (routers, switches, hubs, and bridges) works. I'm left struggling trying to understand exactly what you are trying to tell us.
    – DavidPostill
    Dec 27, 2015 at 23:21
  • I thought it very clearly said "of course an ethernet splitter certainly will necessarily work". It is the way ethernet is designed, and the reason they call it a splitter. The question was not about routers, switches, hubs and bridges, but they can work too.
    – WayneF
    Dec 28, 2015 at 0:37
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    I'm sorry your answer is not clear, and certainly an 'Ethernet Splitter' will not work. A splitter is a very simple concept that parallel wires in 2 sockets onto pairs 2 and 3 running through a cable. Some are also calling what seems to be more like a cable multiplexer that maps pairs 1 and 4 over a length of cable, and you need this device at either either. For 568A wiring Pair 3 (green) is mapped to pins 1 and 2 and is the transmission (TX) wires, while Pair 2 (orange) is mapped to pins 3 and 6 are the reception (RX) wires. (For 568B wiring Pair 2 is on pins 1&2 and Pair 3 is on pins 3&6)
    – David
    Dec 28, 2015 at 12:36
  • Cross over cables are wired 568A at one end, and 568B at the other so then you wire 2 computers directly back-to-back, for example. Auto MDIX ports will automatically detect and switch their RX and TX pins.
    – David
    Dec 28, 2015 at 12:39
  • I posted a link to a simple Ethernet hub circuit in my response, and you can most certainly see that the ports are not 'just a parallel configuration of devices' in that there are at the very lest diodes and capacitors sitting between the ports. 10Base-T, 100Base-TX and 1000Base-T are most certainly a star topology with a 'concentrator device' at the centre.
    – David
    Dec 28, 2015 at 12:44

Cat.5e and even Cat.7 cables regularly come as UTP, and when these get bundled you will have individual pairs just a mm from each other, and splitters like these are seen (as devices or 4+4-Wire use of old cable plant at the patchbay) used in professional installations.

Downgrading to 100Mbit is expected behaviour (DO use a true 100Mbit switch in a permanent installation, you want something that auto-negotiates to 100FDX (100 Mb full duplex), a gigabit switch configured to 100Mbit usually will not, leaving other devices confused) - if it DOESN'T something is odd, either all devices on that cable support 1000BASE-TX -- which can work on two wires but needs even higher grade cable, and is uncommon in most equipment.

1000Base-T is what we commonly know as GBe, and it needs 4 pairs period; if a device claims it has a 1000Base-T link on 2 pairs it probably has mis-negotiated or not negotiated the link at all, and won't work. The PROBLEMS start when whoever designed that splitter made different assumptions than who made/installed your cables. Once you use wires from different physical pairs for one logical pair, all the electric "magic" of twisted pair cable is gone, and it will behave like rotten old baling wire instead of like a high spec rf cable.

  • 1
    Please use shorter sentences and paragraphs. It will make you answers more understandable. It seems to me that your answer really is more of a comment, does not answer the OP's question, or offer an alternative solution. BTW, the standard wiring specification for patch patch panels is T568A and T568B. professionally wired panels and wall plugs will adhere to those specs, as they match up the pairs properly. 10/100/1000Bast-T all will use Pair 2 and Pair 3. There won't be any assumptions made with professional installations, nor would any professionally managed system use Ethernet splitters.
    – David
    Dec 28, 2015 at 23:01
  • @David "professionally used" does not always mean "built or maintained to professional and/or modern standards"... Dec 28, 2015 at 23:16
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    I'm sorry, "professionally used" does mean "built or maintained to professional and/or modern standards." Any IT professional worth their salt would remove (or recommend) their removal as soon as possible. Anything less would be unprofessional. This sort of device can introduce all sorts of problems. I have seen old standard patch cables introduce weird and hard to diagnose problems. Ethernet splitters are worse than old, malfunctioning standard equipment; they are a non-standard component introduced into an environment where you expect certain, standard behaviour.
    – David
    Dec 28, 2015 at 23:49
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    It is simply unprofessional to recommend to a client or employer to use, or keep using devices such as this. Firstly you risk their ability to carry out their day-to-day business because you would have a host connecting through this device (or pair of), that would not be performing to spec, if at all. Secondly, since these devices are non-standard, they will not have been tested by UL therefore if a fire is caused by this device, then your client/employers fire insurance would be invalid. It is unprofessional any way you look at it, whether from a technical, operational, or risk perspective
    – David
    Dec 29, 2015 at 0:00

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