Can you send two different networks down one CAT5e cable and then split it at the other end?

Question

We have an office with two DSL lines coming in for different VPN's setup on each and we can't change this.  However, when the office was cabled only one cable goes from the router to each smaller office which then has a 8 port switch to allow multiply computers to connect.  Now with the new DSL line i need to also have the other network sent to each smaller office for peoples 2nd pc.  We dont have the budget to re-cable so is there anyway to send both routers signals down the CAT5 and then split them at the other end? thanks

So DSL router A & DSL Router B go down cable X which then gets split and goes to switcher C and switcher D each with its own network?

Tracy L · Accepted Answer

I will tell you that cat 5 only uses 2 pair (4 wires) of the 8 that are in the cable. So using a single cable and running two different networks is possible.  (Just check wiring diagrams for the used pairs.)

This isn't the best idea because NOISE between the two systems can cause major interference if the cable is too long or if there is any weak or noisy ethernet cards or switches anywhere!

Here is a diagram of the wiring needed to make the cable work
http://www.pcman.net/pages/misc/cat5.htm
and
http://www.zytrax.com/tech/layer_1/cables/tech_lan.htm
These both assume 100baseTX or 10baseT - no gigabit allowed. Also no power over ethernet allowed!

Notice - only four wires are used.  If you are careful you can use the other four for the second network. BUT I WOULDN'T!  Cable is cheap and the issues caused by taking a really cheap route (not running another cable) will be very costly.

This is one of those, pay now or pay forever situations.

Ian G · Answer

I believe that this is possible, but you may need to upgrade your networking devices to achieve it.  A router in the main office could take traffic from 2 networks and sent it down one cable, but you would also need a router in the small office to split them again.

Another option would be to have manageable switches at each end and set up each network with its own vlan, and then the link between the switches would need to be set up as a trucking link.

The cost of the switches or routes would probably be more than the cost of running another cable.

Ivan · Answer

If your switches are capable of supporting VLANs and VLAN Trunking (also referred to as 802.1Q or dot1q) then yes, there is a way.
You could put a switch in where your routers are and connect both into different VLANs and share the physical connection back to the offices by making it a Trunk which will carry multiple VLANs. 
If your kit can do this it sounds as if the best set up would be to configure 4 ports of each switch to one of the VLANs and then you can plug PCs into whichever connection you want.

Taba · Answer

It would be easier if you setup each network seperatly and then purchase a network bridge to place in-between your switches.

digitalgadget · Answer

As far as I know you need all the wires for an ethernet connection.  You might consider using PowerLine ethernet or something.

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Can you send two different networks down one CAT5e cable and then split it at the other end?

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