Hot Off the Wire

Using a Windows XP Workstation as the Base Station for a Home Wireless Network

By John Wagner

Okay, so you have a nice Windows XP desktop machine in your house, connected to a modem or cable modem, and you're sitting pretty. Internet access, lots of file space on your multiple disks, a backup strategy; life is good. But one day, after succumbing to temptation at the computer store, you come home with a new addition--a laptop (or laptops). Worse, your spouse comes home with a laptop that has an Apple logo on the lid. Agonizing questions begin to fly: What now? Who gets to monopolize the phone line (or cable-modem ethernet cable)? How do you transfer files among the machines? What good is a laptop if I have to go down to the basement and plug in the network connection to get Internet access? What's the meaning of life?

Contrary to the pronouncements of Bill Gates and Steve Jobs, no software vendor has yet come up with the answer to the last question. But for the others, a wireless home network may be just what you need. Here's an introduction to how you can do it.

To begin with, this article assumes that your home desktop machine is running Windows XP. That's not because it can only be done with XP; the functionality I'm describing can be managed with an OS X Mac or Linux box. And in fact, if you're willing to spend the money, you can even buy dedicated hardware for this purpose (Apple, just to name one, will happily sell you a dedicated device called an "AirPort Base Station"). But Windows is undeniably the dominant home computing platform (for better or worse), so that's the angle from which I'll be approaching.

Likewise, the wireless hub shown in my examples is a Linksys WAP54G (Figure 1).

Figure 1

At the time of my test installations, this was the least-expensive (about $129) 802.11g wireless hub available, and it's proven reliable and stable since then. But the process I'm outlining can certainly be implemented with other vendors' products--read the fine print before you buy.

The first question you need to ask is: does my laptop (or laptops) even have wireless network capability? Most of the newer ones have it built-in, and almost all older PCs will easily accept wireless networking cards that plug in to the PCMCIA slot on the side. New Mac laptops usually have built-in wireless capability by default; if you have an older laptop Mac without wireless, you'll have to see if it can be upgraded or not.

The second thing you need to know is that not all networks are created equal. There's an old joke that the nice thing about standards is that there are so many to choose from, and wireless networking is no exception. For practical purposes, we'll limit our choices to the two most common current wireless standards, 802.11b and the newer 802.11g. The "B" standard has a theoretical maximum data rate of 11mb/sec, while "G" has a theoretical maximum of 54mb/sec. The two standards have other differences besides speed, but that's about all that we need to be concerned with for most home network planning. My own advice would be to go with 802.11g equipment as long as it's not radically more expensive, but that's your call.

The first hardware you'll need is a wireless hub (also called an access point; the Linksys unit shown in Figure 1 is a wireless hub/access point). For those unaccustomed to networking terminology, a "hub" is a place where network data arrives from one or more sources and gets forwarded out in some other direction. In our case, network traffic from your wireless laptop client machines is going to be channeled through the access point to the XP workstation, which will route it to the wider internet when necessary.

The wireless access point itself connects to the workstation with a crossover cable, which is just a length of standard ethernet cable with an RJ45 connector on each end. However, the strands within the cable are "crossed over" so that their order is the same on each end. You can buy these from Radio Shack for about $10, or, if you know what you're doing and have a crimping tool, make your own. This cable connects from the access point's RJ45 port to the ethernet port on your XP workstation. It should look something like this (Figure 2):

Figure 2

"But wait," the impatient will begin to whine, "I can't get to the Internet yet!" Well, Sparky, actually you can't get to anything, yet. All we've done so far is the hardware setup. Before you can start networking, some configuration is required, both on your laptop(s) and your XP desktop machine.

First, the desktop machine will have to be configured as either an Internet Gateway (if you connect to the Net via a dialup modem) or a Network Bridge (if you connect to the Net via a cable modem or direct ethernet).

If you're using a cable modem (or ethernet connection):

If that arrow labeled "To the Net" in Figure 2 is a cable modem (which has an ethernet cable coming out of it) or a direct ethernet connection, you're going to need a second ethernet port in your desktop machine. That's right, even if your desktop came with built-in ethernet, you'll still need another one. That's because your machine will be bridging network traffic between your external network connection and the wireless hub, so your laptops can use the external connection. Fortunately, the price of a PCI 10/100 ethernet card has dropped to around $10, so the cost isn't going to bankrupt you.

Once you've installed the second network card in your desktop machine, you've got two ethernet ports. Connect your wireless hub to one of them (with the crossover cable, remember), and connect the other to your cable modem or wall ethernet jack. Whichever network interface is connected to the net will have to be correctly set up from the Windows Control Panel, of course (you'd have to do that anyway).

Now you'll have to Bridge the two connections, by entering Control Panel/Network Connections and selecting both ethernet devices (CTRL/click), then right-clicking. The result will be a context menu allowing you to choose the Bridge Connections option (Figure 3).

Figure 3

Having done this, the result will be a virtual device called a Network Bridge (Figure 4). The bridge is the link between your wireless hub and the ethernet connection to the outside world.

Figure 4

If You're Using a Dialup Modem

The same principle is involved in using a dialup modem--you must span the wireless hub to the connection to the outside world. The only conceptual difference is that the external connection takes place through a phone-line modem instead of an ethernet cable. You'll only need one ethernet connection in this case, and the crossover cable attached to your wireless hub goes into it. The "To the Net" arrow in Figure 2 in this case would be a modem connection, either serial-port, USB, or built in to your computer.

To enable Internet Connection Sharing, you must open Control Panel/Network Connections, and select the dialup connection you'll be sharing (note that only one can be designated as shared at one time). Click the "Advanced" tab, and you'll see the Properties box (Figure 5). Click the "Allow network users to connect..." checkbox, and you're in business. And while you're here, it's also an excellent idea to check the Internet Connection Firewall box as well, to protect both the host machine and the clients that will be using its shared dialup connection through the wireless hub. In fact, checking this box is a good idea on general principle.

Figure 5

Configuring the Wireless Access Point

It's hard to be very specific about configuring the wireless hub, because the setup interfaces and utilities vary so widely from brand to brand. But there are a couple of important parameters that are (or should be) common across the board, and can easily be confusing at first:

1: WEP encryption. WEP stands for "Wired Equivalent Privacy," and is a method of encrypting the packets passing between wireless clients and the access point so that potential spies will have a hard time looking at what's in your network traffic. Note that I said "have a hard time," and not "can't." WEP encryption can be broken (though it's by no means a trivial task). For the average home user, it's pretty unlikely that anyone would bother investing the considerable time and effort required to eavesdrop on you, but you should be aware that even the best current wireless encryption isn't 100% spy-proof.

There are two commonly-used types of WEP encryption, 64-bit and 128-bit. These refer to the lengths of the encryption key supplied by the user. (As a side note, you will also see references to "40-bit" keys. They are functionally identical to 64-bit keys, since the wireless hub itself supplies the extra 24 bits—which are called the initialization vector. Likewise, "128-bit" keys are actually 104 bits plus 24 bits of initialization vector. Aren't you glad you know that?)

You can think of these encryption keys as passwords (though they're actually quite a lot more than that) that you'll have to enter from your client machine each time you connect to the access point.

Creating these keys is often a baffling and frustrating process for the novice. Some access point setup utilities let you enter them as ordinary ASCII characters, while others want to see hex characters--requiring you to have a hex-to-ASCII conversion table (easily available with a quick web search) handy.

In either case, the number of characters is important. A 40/64-bit key is five ASCII characters. An example would be "R011$". A 128-bit key is thirteen ASCII characters, for example "MyC0mputerB0x". Obviously, the longer key is the harder one to crack.

So how come a 40/64-bit key is 5 characters and a 104/128-bit key is 13? Because each ASCII character takes up 8 bits, so 8X5=40 and 8X13=104. Simple, though not especially obvious, and not all wireless-hub makers deign to explain it to the hapless user.

On the client side, when connecting, you will enter the easy-for-humans-to-remember ASCII version of the key. But when setting up the hub, you may have to enter the keys in their hex form--which, for the examples given above, would be "52 30 31 31 24" and "4D 79 43 30 6D 70 75 74 65 72 42 30 78" respectively. If your access point requires this, find and download a hex/ASCII conversion chart.

2: SSID broadcast. The SSID (Service Set IDentifier) is a name by which the wireless access point can be identified on the network, just as your computer name identifies your computer. It can't be more than 32 characters long, but otherwise you can make it whatever you want. If this SSID is allowed to be broadcast, other wireless users within its range can see it and attempt to connect to it. Bad idea. So if your wireless hub allows it (most do), you should disable SSID broadcast.

The Clients

Once you've gotten the server end of your wireless network properly set up and working, it's time to get your client machines ready to go. Neither XP nor OS X are very hard to configure for wireless use.

Windows XP:

Figure 6

Under Control Panel/Network Connections, double-click your Wireless Network Connection, then click Properties and the Wireless Networks tab. This will show you the wireless networks in range, and hopefully the one you've just finished setting up will be in the list (Figure 6). Now click "Configure".

Figure 7

(Figure 7) Choose WEP for your data encryption method, and enter your access point's key (as ASCII characters).

If your client machine has been assigned an IP address, you must configure it in the TCP/IP section of Network Connection Properties. Otherwise, set your machine to "Obtain an IP address automatically."

Figure 8

It's even easier. Go to System Preferences /Network /AirPort (wireless networking is all "AirPort" to a Mac). Set up your TCP/IP parameters for either DHCP or a fixed IP address (see above; this will usually be DHCP).

Figure 9

Now you're ready to connect. Go to the wireless icon in the menu bar, pull it down and choose the wireless network. Note that if you've turned off SSID broadcasting, you won't see the access point's name here--when connecting, you'll have to choose "Other" and manually fill in the name (Figure 9).

Figure 10

You'll be presented with a box asking you to fill in the WEP encryption key you specified when you set up your access point. Click OK and you're connected (Figure 10).

And now...

Ideally, you should now be able to start reaping the benefits of your new wireless network by roaming around your house (or even outside of it) with your laptop(s), using your modem connection or cable modem, free of the constraints of wires, surfing the web, accessing files on your desktop workstation and even printing. Simple, wasn't it?

Well, no, of course it wasn't simple, and it's a rare neophyte who gets it all right the first time. This introduction is very broad, very general, and very condensed to fit in a constrained space (the ITS Newsletter doesn't have unlimited storage capacity). Some experimentation--maybe a lot of it--is still going to be required to get your wireless network configured and running correctly. But hopefully we've exposed some of the obscure points that vendors don't bother to tell you about, introduced you to a few wireless concepts, and given you an overview of just how the whole thing works. And it does work once you pull all the pieces together. This article was created on an OS X Mac iBook and a Dell D600 XP laptop, accessing the two wireless networks in my office and one at home. Why, if everything wasn't working flawlessly at all times, I'd have been cut off while typing, probably right in the middle of a sen--