Connecting an XP box to two networks simultaneously

January 28, 2007 2:41 PM

I have two Windows XP boxes with their own separate DSL connections, and one wireless router. I'm having trouble connecting these two machines with a wireless connection.

Here's a crude diagram of the setup I've got. The two computers have internet access, and computer B can ping the wireless router over the wifi connection. However, it seems to be having trouble "joining" the local network that computer A is on.

I think it is because of some sort of conflict between IP addresses: the ISP to which it is connected (via DSL) has assigned it one IP address, but the wireless router needs to assign it a different IP address (the usual 192.168.1.xxx that Linksys routers default to). My knowledge of networking is admittedly limited, so I'm not sure how computer B can have two IP addresses simultaneously on two different networks, or if this is even possible.

posted by good in a vacuum to computers & internet (8 comments total)

Some important questions:

1) How is Computer B connected to the DSL modem? A wired connection?

2) Why do you have 2 computers within wireless range of each other and still have 2 DSL connections anyway? Is there a practical reason for this?

If Computer B can ping the wireless router, then it should be able to see Computer A, but how you're connected to DSL on Computer B could matter. I take it it's not a 192.168.1.* IP address on B?
posted by twiggy at 2:56 PM on January 28, 2007

Why do you need 2 DSL connections? Couldn't both computers have a wireless card in them and be done with it?
posted by k8t at 3:01 PM on January 28, 2007

Originally Computer B connected to the internet via wireless connection to the router/gateway. After at least a year of unreliable connection, the owner of Computer B, who depends on his internet connection for his job, got fed up and just purchased his own connection. However, I occasionally still need to transfer files and print things using the printer connected to Computer B, so I was hoping to still be able to connect to Computer B from time to time over wireless.

To answer your questions twiggy:

1) Computer B is connected to the DSL modem with an ethernet cable. In my crappy little diagram, all the green lines are wired connections.

2) Yeah, a single DSL connection sounded like the logical setup when I was putting this little network together, but the wifi connection to Computer B was/is horribly unreliable, possible due to the fact that Computer B is two floors below the router it is trying to connect to. After countless hours trying to improve it, I just gave up, and now there's two DSL connections.

3) No, Computer B does not have a 192.168.1.xxx IP address, but one assigned by its ISP.
posted by good in a vacuum at 3:22 PM on January 28, 2007

Since they can both reach the internet, you could create a virtual private network between the 2 using Hamachi.
posted by mattdini at 3:32 PM on January 28, 2007

Okay, so Computer B, then, has 2 network cards. One wired, one wireless, right?

This could cause some real confusion with Computer B's network connection. It's certainly possible to have multiple network cards, but the problem here is this:

Wired Card wants to talk to its "primary gateway" first all the time, which in this case is your DSL modem.

Wireless Card wants to talk to ITS primary gateway first all the time, which in this case should be your wireless router.

Because your wireless router is internet connected, if things are set up correctly, then computer B could get to a site on the internet via either its wired or wireless connection. This is a really bizarre setup.

I'd recommend disconnecting Computer B from its DSL connection temporarily and seeing if:

1) It still has internet access
2) Now it can see Computer A

Having multiple routes like that can work fine, or can work terribly depending upon the hardware and how it has been set up. First thing I'd do is debug this by trying one piece at a time.

Unfortunately, I'm not confident you'll ever get the setup you want to play nice, because you've got 2 network interfaces in one machine that's presumably running Windows, and I don't know if there's a good way to tell Windows "when I'm trying to go to XYZ IP addresses, use interface 2". You may just have to disconnect Computer B from the internet temporarily when you need to transfer files.
posted by twiggy at 4:41 PM on January 28, 2007

mattdini: Thanks for the recommendation of Hamachi, I will give it a try.

twiggy: Yes, Computer B has two network cards (well, one is built in to the motherboard and the other is a PCI wifi card, but yes, two network interfaces, one wired, one wireless). I was afraid that this might be a "bizarre setup," as you put it, since I was unable to find much information about such a setup through the usual Google and Usenet searches.

Next chance I get I'll give your advice a try, but my guess is that, with both network connections using DHCP, when Windows sees that the DSL connection to the internet is unavailable, it will revert to the wireless connection as its primary gateway, and take on the IP address that the wireless router assigns it via DHCP.

Thank you everyone for your responses. Even if such a setup proves impossible, at least I'll know that it is impossible rather than continuing to tear my hair out.
posted by good in a vacuum at 7:48 PM on January 28, 2007

Computer B certainly can have multiple addresses, its just a bit tricky to set up, since it needs to be set up on the gateways also, not just the computers. This is probably a case where DHCP isn't too helpful; set up each computer statically.
Have one connection gateway only configured for only 192.168.1.x addresses, and have the other configured for only 192.168.2.x addresses. On the computer B, have the wireless configured for 1 network (the .1.x one) , and the wired for another (.2.x). Insure that the wired interface is default for internet traffic.
If you still have problems routing to computer A, then you might use your "hosts" file to map a name to computer A's address.
Theres lots of moving parts, but once you understand how they work, you'll be able to hook it all up.
posted by TuffAustin at 8:24 PM on January 28, 2007

How'd I'd set this up

Routers IP 192.168.1.1/24
Computer A 192.168.1.2/24
Computer A's gateway 192.168.1.1

Computer B Wired IP: Whatever ISP gave you
Computer B's Wired Gateway: Whatever ISP gave you
Computer B's wireless IP 192.168.1.3
No gateway for B's wireless

The only real trick here is you must not give computer B's wifi connection a gateway (or router as folks call it). This means you won't be able to use DHCP on that interface. So manually assign the IP for the wireless connection. Leave the wireless gateway/router and DNS fields blank. The magic of routing should handle everything else.
posted by chairface at 9:57 PM on January 28, 2007