Question

Two subnets on one wire

Asked by: lenkne

For reasons not worth going into, I have a building that has only one CAT5 cable to it.  The problem is I need to get two seperate subnets to it because:

Need one subnet for several computer that is part of the office network
Need one subnet for a SonicPoint WAP

The SonicPoint is managed by a Sonicwall 3060 and is on a subnet with seven other SonicPoints.  The Sonicwall updates and controls the security of the SonicPoints, and does not allow any other devices to attach to the subnet.  This is great as it keeps the wireless network completely seperate from the office network.  However, I also need to get a handful of computer connected to our office network using the same wire.  The simple solution is to run another cable to the building, but the cost is $1,100, more than I can justify for the need.

Any ideas for a solution costing less than running another cable?

Thanks

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Asked On
2006-08-08 at 06:08:08ID21946875
Tags

two

Topic

Miscellaneous Networking

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Answers

 

by: ScooterAndersonPosted on 2006-08-08 at 06:43:26ID: 17271180

It's probably not a recommended solution, but in the days of 10bT, you could split your cable to fully utilize the four sets of twisted pair and have two connections over the same wire.  This comes about as 10/100 only uses two pairs of wires for communication.  This setup should work with a 10/100 connection, but is definately _not_ approved for Gigabit.  You'll also need to test out the wires for crosstalk, but as long as you stay within specs and keep the wires twisted up to the RJ, you should be OK...   If nothing else 15 minutes, 4 new RJ's and a crimper could save you more than 15% on your wiring costs (sorry, can't help with your car insurance here though... :)

On one end (assuming 568-B)                                                        and on the other

Pin1/RJ1 -------------------------- 1-orange/w  --------------------------  Pin1/RJ1
Pin2/RJ1 -------------------------- 2-orange     --------------------------  Pin2/RJ1
Pin3/RJ1 -------------------------- 3-green/w    -------------------------  Pin3/RJ1
    Pin1/RJ2 ----------------------- 4-blue         ------------------------------  Pin1/RJ2
    Pin2/RJ2 ----------------------- 5-blue/w     ------------------------------  Pin2/RJ2
Pin6/RJ1 -------------------------- 6-green       --------------------------  Pin6/RJ1
    Pin3/RJ2 ----------------------- 7-brown/w  ------------------------------  Pin3/RJ2
    Pin6/RJ2 ----------------------- 8-brown      ------------------------------  Pin6/RJ2

Scooter

 

by: RobWillPosted on 2006-08-08 at 07:02:10ID: 17271355

You can run two subnets over the same wire using the same switches, without a problem. Unless there is a router configured to allow packets to be routed between the two subnets, they will be isolated.
If your switches will allow you could also create VLANs (Virtual LANS) but someone else would have to explain the configuration for you.

As for splitting the wire, it's a definite no-no. As Scooter suggested in "the old days" you could get away with it, but the excessive "cross talk" can bring a 100mbps connection to it's knees.  If you try it and have someone run a test with a cable certification meter such as a Fluke you will see it will fail miserably.

 

by: Scotty_ciscoPosted on 2006-08-08 at 07:56:01ID: 17271862

The other thing to keep in mind if you are running two segments on the same wire is that any savy person can see the other segments traffic so if there is a security concern I would split the wire pair.  If not then hey run them down the same wire you can usually secondary interface many devices and make them listen to both segments as well.

Thanks
Scott

 

by: jabiiiPosted on 2006-08-08 at 08:33:14ID: 17272202

Using VLAN's you will be okay. But if that's not an option, the traffic will flow over the wire even if there is only a hub on the distant end and no vlan. Albeit not very well..

 

by: SunBowPosted on 2006-08-08 at 09:40:24ID: 17272796

Q: Title: Two subnets on one wire

A: Yes, been there/done that, having run four subnets on same wire

The wire itself is not subnetted, it addresses using MAC. IP is for routing. Your problem would only be to secure one from the other, and OS authentications should be able to address that.
 

 

by: lenknePosted on 2006-08-08 at 11:47:48ID: 17273712

Okay, I need some help figuring out how a VLAN solution would work.  In the main building, there are two seperate subnets:

172.17.0.0 - Main office network

192.168.1.0 - SonicPoint subnet routed through a Sonicwall.  The Sonicwall provides DHCP to the Sonicpoints and in fact, will only let Sonicpoints get an IP address.

On the remote side, we will need to have the same seperate subnets.

With the two subnets seperated in the main building, how do use a VLAN to get them together and then the VLAN directed to the proper ports on the remote side?  we are using managable Linksys switches.

Thanks.

 

by: mohawk1Posted on 2006-08-09 at 09:24:43ID: 17280668

Hi,

You won't be able to use separate layer 3 subnets without a layer 3 switch or a router.  The main office has two subnets and you wish to extend these to the other building, right?  You need to define the layer 3 vlans on the router or L3 switch and connect the other building using your cable.  That port should be defined at a dot1q trunk.  On the switch the other end, simply configure which vlan they need to connect to.  If you let me know the models of your switches and/or routers, I may be able to help out a little more?

Cheers
Mohawk1

 

by: lenknePosted on 2006-08-09 at 11:13:43ID: 17281563

Mohawk1

Yes, what you stated is what we are trying to do.  You mentioned defining the port on the main office side a trunk.  Does this mean that port would be able to carry both subnets?  

I think that is where I am getting stuck, the fact that a one particular port could be configured to participate in multiple VLANs.  If that works, then on the remote side, the cable coming from the main office would also go into a trunk port?  Then individual ports on the remote side switch would be put into the proper VLAN?

The switches in the main office are Linksys SRW2048.  There is just a swall unmanaged switch currently on the remote side, but I would purchase another Linksys (8 port) for it to make it work.

Having not worked with VLAN before, I am not sure about some of the terminology used.  It looks like we need to create a VLAN and then tell if ports are static, forbidden, or excluded.  The next option is whether they are untaggeg, tagged, or none.  Some quick help on this would be great.

Thanks

20120131-EE-VQP-002

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