How to make a switch handle/bridge a divided ethernet cable?

I currently have a set up where my router is terribly placed for wifi performance (basically surrounded by thick structural concrete walls). I thought about possible solutions, and came to this one:

The router is placed there because the ethernet signal arrives there, and all LAN cables go to the rest of the house from there as well. Because of this, I bought a switch (TL-SG105E) to redistribute the signal to the LAN, and decided to put the router in another room, this requires one wire to take the signal from the modem to the router, and another to bring it back to the switch. The problem is I only have one wire going to any of the rooms with ethernet access, and it is impossible to pass another one because of lack of space on the conduits. To solve this I divided the wire in two to use the same wire to get the signal from the modem and then send it back to the switch. That is where another problem arose, and it is what I need help with.

The divided wire comes from the router in the other room, but it can't be divided before arriving at the switch, because my father doesn't want me to mess with the cables that are coming directly from the wall. What I tried then, was make the cable with both signals enter the switch coming from the wall, and come out from the switch using another port (both in a VLAN), to only then get divided again to go to the modem and back to the switch to enter the other VLAN and go to the rest of the house. I know this is confusing, I hope this drawing helps:

Both wires entering the VLAN1 ports carry two signals (8 wires being used). The wires entering the modem, router, and the left port of VLAN2 carry only one signal (4wires being used).

This sounded fine, but the switch doesn't seem to work with two signals using the same port (4 wires for each connection). The only part that works is the one using the 4 wires used for fast ethernet, the other 4 that are usually used only for gigabit doesn't seem to work to get the signal across.

Is there a way to do this with the switch (one port with two independent signals or a bridge)? I thought about using two female RJ45 to get the signal from the wall to another cable, to divide it before entering the switch, which should work, but I wanted to know if I can do this only with the switch.

Of course if you have a better idea for the setup as a whole, I'd be happy to hear it, even though I think this is the only possible setup to get the router to another room.

Ivan Lerner

Posted 2018-06-11T07:08:42.290

Reputation: 152

1This can't be done. If you combine the cable before entering the wall, you need to split it back to two cables again once exitting the room. Also, do note, that if you split the cable, and only use 4 wires instead of 8, the maximum speed will be 100 mbit. Good for internet, slow for networking. So don't think about using a NAS server to store files with this. It'll be very slow. – LPChip – 2018-06-11T07:14:10.997

1This may be doable - but it depends on the router. What make and model is the router (or do you know if it works with DD-WRT). If it does you can reconfigure the router and a switch port to have incoming and outgoing data share just 2 pairs by using different VLAN tags. – davidgo – 2018-06-11T07:18:17.937

Additional relevant questions - what speed is your internet connection, have you considered ethernet over power, what model modem do you have and why do you need a router ? (Why not reconfigure the router as an AP and let the modem act as the router?) – davidgo – 2018-06-11T07:19:49.383

Also, do you have a budget for additional/replacement equipment? – davidgo – 2018-06-11T07:20:38.547

Thanks for the comments. @LPChip yes, the splited cable will only be used to connect the internet, the gigabit switch will connect everything together, maintaining LAN speed. – Ivan Lerner – 2018-06-11T07:37:23.083

@davidgo Last time I checked it was still in development, but the whole point of this is to move the router, not use it as a switch. My speed is 60mbit, I do use ethernet over power, but only for places that don't have cables, using it to take the signal back to the switch degraded performance for the cable connections. – Ivan Lerner – 2018-06-11T07:37:26.557

@LPChip But why can't this be done? Is it just not a feature of the switch or some other limitation? – Ivan Lerner – 2018-06-11T07:43:17.487

1Unless the switch supports it (custom firmware such as DD-WRT might), by default its not supported. – LPChip – 2018-06-11T07:44:40.190

But WHY do you need/want a router in addition to the modem? (I get the i.pression from your post that networking does not work quite like you think it does) – davidgo – 2018-06-11T07:54:27.057

1Because the modems provided by my service providers are terrible routers, I use it only as a modem and leave the routing to my dedicated router. This also has the benefit that if the provider needs to change the modem for any reason, this changes nothing on my network. – Ivan Lerner – 2018-06-11T07:57:59.643

Answers

Don't split the cable, you'll never make this work properly, and you'll needlessly degrade performance. Instead, use VLAN on the single cable.

So configure your router to accept "WAN" with VLAN (say, id=1) on the same port as "LAN" with VLAN (say, id=2). If you have not rooted your router, install some router firmware where you can configure this, e.g. OpenWRT.

Configure your switch to split off both WAN and LAN from the router with the same ids, and the connect up the split ports properly.

Problem solved.

dirkt

Posted 2018-06-11T07:08:42.290

Reputation: 11 627

The degraded performance is fine, since my internet connection is only 60mbit, the switch takes care of the LAN speed. I don't think I get it, are you saying I can configure 1 port with two VLANs, WAN for input, LAN for output, all on the same port? – Ivan Lerner – 2018-06-11T07:48:09.773

1Yes, you can configure two (or more) VLANs on the same port. They just happen to correspond to WAN and LAN on the router, but nothing prevents you from doing even more complex things. Your switch should allow you to do this in the UI. As I wrote, you may need custom firmware on your router. If you are unsure about this, maybe first try to set up several VLANs on a single port connected to a PC? E.g. on Linux, it's easy to add VLANs. Just give them different IPs and play around with ping to see if it works. – dirkt – 2018-06-11T07:59:43.457

Cool, very interesting. I'll try that and get back to you. – Ivan Lerner – 2018-06-11T08:06:40.770

Sorry for taking so long, in the end my router still didn't have an alternative firmware with VLAN features, maybe it does today, I'll check it out. I'll accept this answer since it was the first that mentions VLANs, which even though I can't use seems like the most appropriate solution. In the meantime I have split the cables and you were right that it was a pain to set it up, I had to redo the connections multiple times before it finally worked. It has been working fine for months though. – Ivan Lerner – 2018-12-07T05:18:19.227

Which brand and model of router exactly do you have (unless I overlooked it, you only mentioned the switch)? You can look up e.g. on the OpenWRT supported devices page if the hardware supports VLANs.

– dirkt – 2018-12-07T06:32:47.337

It's a TP-LINK Archer C25 V1. In the link it says the availability of OpenWRT is discontinued, do you think it would work? – Ivan Lerner – 2018-12-07T18:55:12.510

Where does it say the Archer C25 is discontinued? The device page actually says "Ethernet w/ vlan support", and the linked issue thread seems to indicate it's working in principle, though there are 5 GHz issues. Simplest way is to try; you can flash the original firmware again if it doesn't work.

– dirkt – 2018-12-10T06:44:05.687

You have received multiple answers, but no one mentioned what i think may be the easiest solution.

You can use VLANs to make use of the existing cable, which would need VLAN aware switches and a VLAN aware router to logically divide the network. (this solution can be expensive, you are no longer in the home user realm).

I think a better solution may just be to look into Siamese CAT-5E cabling. its built for situations with limited conduit spacing. There are a few types of cabling that i know of that may help here.

Side by Side:

Cat-5e-4c-j:

Flattened types:

This last type can fit in the tightest conduit situations, you can tape two together every three feet or so, and it is still half the size of a regular cable. depending on how tight the conduit is, you may need some lubricant to pull it through.

Tim_Stewart

Posted 2018-06-11T07:08:42.290

Reputation: 3 983

Something I'm currently using are Ethernet extenders. It can send the Ethernet signal over your power line within the house. You can plug them in an outlet wherever you like. With this, you don't need any complicated setup.

They aren't that cheap though, and the more you need, the more expensive it will get.

marijnr

Posted 2018-06-11T07:08:42.290

Reputation: 171

I do use this exact model for other purposes in my house, but using it to bring the signal back to the switch degrades performance for the whole network, including the cable connections. – Ivan Lerner – 2018-06-11T07:38:26.127

-1

You can google for split ethernet cable and you will get the pinouts. As stated in the comments you have to split both ends of the cable and connect the router LAN port to the switch, the WAN port to the modem. Although your router link is limited to 100mbit/s, your switch (if it is Gbit) will still allow all other connected devices to have higher speed to each other.

Winnie Tigger

Posted 2018-06-11T07:08:42.290

Reputation: 144