Two computers connected to two networks?
August 7, 2006 8:06 AM   Subscribe

Can I cannect a computer to two networks and have them be invisible to one another? Pictures inside.

Here's my setup:

2 computers (desktop and laptop) with two nics each
1 router
1 switch
1 NAS (network attached storage) device

I'm on a network that does not allow routers (don't ask). Both computers should be able to access the internet and should be able to access the NAS. Currently I have:

ISP -> switch -> (desktop, laptop)

I can access the Internet with both computers. My question is, can I create a private network with the router that will let both computers access the internet as well as the NAS? The ISP _should not_ be aware that there's a private network. Googling brought up a bunch of pages about routing tables and metrics that I couldn't make sense of. Is there a simple way do do this? It is extremely important that this not "leak" addresses into the main network or interfere with it in any way. Here's a picture of the configuration I'm looking for:

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posted by null terminated to Technology (13 answers total)
You could probably emulate your computer's MAC address with the router, hook that directly to your DSL/Cable modem, and be done with it, depending on what router you have. Most support MAC spoofing nowadays.
posted by chrisfromthelc at 8:08 AM on August 7, 2006

Response by poster: Like I said, I can't use routers. I've tried spoofing the MAC address but they were still able to detect it somehow and now I have a "strike" against me. (This is on a campus network)
posted by null terminated at 8:18 AM on August 7, 2006

Response by poster: *can't use routers between my computer and the Web, I should say. Thanks for the suggestion though.
posted by null terminated at 8:26 AM on August 7, 2006

I'm not a network technician, but I believe you could connect to the modem with one computer, share the connection and then use that computer as a gateway for the other or the router. In theory it should work.

You would need one of the computer to have 2 nic cards. Basically what you would be doing is setting up a private network that would share the connection between the computers, but would only look as though one computer was accessing the network.
posted by gregschoen at 8:33 AM on August 7, 2006

Response by poster: gregschoen: This is what I had originally done but it was causing problems with the network (I was as surprised as you, as apparently they could tell I was accessing the net through multiple devices) so I was forced to stop doing this.
posted by null terminated at 8:35 AM on August 7, 2006

Make sure you set up the computer between the modem and the router to send out IPs with its own DHCP instead of trying to get its own unique IP, and make sure you use another netmask besides the one that the network you're on is giving. So something like 10.x.x.x instead of 192.168.x.x.

Otherwise, if you're using Windows, maybe something there was giving you away, maybe you could try running a cheap linux box to do the intermediary between the modem and the router.
posted by gregschoen at 8:39 AM on August 7, 2006

That configuration in the diagram should work without any fuss. For the NAS network, use a dumb hub/switch, set all three devices to use IPs in the same range (eg all 10.0.0.x) and it should just work.
posted by cillit bang at 8:39 AM on August 7, 2006

Also, make sure that the router is set to use your computer as a gateway. It could be that the router is somehow bypassing your computer to get certain information that is somehow tipping people off to what you're up to.
posted by gregschoen at 8:41 AM on August 7, 2006

Response by poster: Thanks for the advice. I'll give it a shot.
posted by null terminated at 8:44 AM on August 7, 2006

Otherwise, I'm not sure, but if you're just looking for the networking of having a router, you could try a tool like Hamachi.

It sets up a virtual private network over the internet, it's encrypted, and I believe you would be connecting to each other directly anyways, so it should work out of the box.

You may want to give it a try if you just want to share printers and/or files. I use a setup like this to print my parents Mapquest directions right to their printer. It might be overkill for what you're trying to do, but barring anything else, it might be what you're looking for.
posted by gregschoen at 8:46 AM on August 7, 2006

null terminated if the NAS doesn't need internet access, just do as above and get a cheap switch, plug the second network card of both computers and the NAS into that. Set the private interface of the two computers to (say), and set the NAS to have a static IP of Your NAS won't be able to access the internet, but your computers will be able to use it.

Don't use DHCP if you can avoid it. Plugging the wrong cable into the wrong hub is too easy to do and ITS will notice that.

Also, if your NAS is really an Infrant box like in your diagram it will default to in the absence of a DHCP server.
posted by Skorgu at 10:04 AM on August 7, 2006

Response by poster: Skorgu: That's exactly the setup I like.

When you say to set the "private interface", I assume that means the static ip address? What should be put in the "Subnet Mask", "Default Gateway" and "Preferred DNS server fields"?
posted by null terminated at 11:50 AM on August 7, 2006

Best answer: Sorry for the delay, VMWare was being a little bitch. If you're still reading this, here's a walkthrough. It sounds like you already know most of this but better to be thorough, right? :)

On each of the computers, leave one interface (the 'public' one that connects up to your resnet) alone. I suggest renaming one of them to something like Private or something so its easy to tell, but it doesn't make a differenece functionally. Take the private interface and go into its properties (via control panel -> network interfaces). Click TCP/IP and then Properties.

There should be two radio buttons, "Obtain an IP Address automatically" and "Use the following IP Address." Select the second one.

IP Address is whatever you're assigning to this machine. I suggest and .2 for the computers and maybe .10 for the NAS, easier to remember that way.

Subnet mask should be and gateway and DNS servers should be blank.

Same setup for the other computer, obviously with a different IP address. Your NAS will have its own procedure for setting a static IP, you'll have to follow that.

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posted by Skorgu at 9:05 AM on August 8, 2006 [1 favorite]

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