Security stumbles

If you haven't got Network Stumbler for Windows - NetStumbler to its friends - you should. This utility can be found at NetStumbler is an all-purpose software tool that, among other things, lets you detect unauthorised "rogue" access points in your workplace, or other networks that may be causing interference on your network. It's other use is for war driving (hunting around looking for open wireless access points), which isn't illegal in itself, though accessing someone else's network without permission definitely is.

It's also very useful for analysing your broadcast coverage - it can find locations with poor coverage in your wireless network and help you position your access point's antenna to improve the reach of your wireless network.

NetStumbler includes a most useful field strength and signal-to-noise ratio display - see Figure 1. By wandering about with a notebook running NetStumbler, you can easily detect weak and dead spots in your access point's (AP) coverage, as well as determine the edge of an AP's useful range.

NetStumbler is also useful in testing the relative effectiveness of Wi-Fi antennas, by placing a laptop running NetStumbler in a fixed position and then aiming antennas at it from some distance away. If the antennas are all at the same distance from the PC, NetStumbler's readings will accurately reflect how well they work with respect to one another. Highly recommended if you have reception problems.

If you don't have or want to get NetStumbler there's always good old Ping (packet Internet groper), the humble command-line TCP/IP diagnostics tool. While most Wi-Fi devices provide a rough indication of signal strength you might find it helpful to use Ping to measure the response time or latency across your wireless link and orientate your access point's antenna to achieve the smallest time on average. To do this, open command prompt, click Start-All Programs-Accessories and then click Command Prompt.

At the C: prompt enter the following command to run Ping indefinitely:
ping -t
then hit <Enter> - see Figure 2.

Here is the IP address of my access point - yours may be different, so run ipconfig at a command prompt, if you don't know the IP address you're aiming for - normally the AP will be the same as the gateway. You will then see ping responses on the screen. Look across to the time field and adjust your access point's antenna (or indeed the whole AP, cable lengths permitting) to achieve the smallest time in milliseconds (ms). Enter a <Ctrl>-C to terminate the ping.

If your AP doesn't reach those parts of your building you'd like it too, consider fitting a higher gain antenna. The standard antenna that comes with an access point usually has a low gain (around 2dB). If the access point has a removable antenna, then replacing the default antenna with a higher gain omni-directional antenna boosts range significantly, typically adding 6dB to the system, or about a four-fold increase in signal power.

For about $80 I've fitted a large 6dB antenna (made by Linksys) to my trusty Netgear DG834G to boost its reach by about 25 per cent. We should all by now know that Wi-Fi is by default inherently insecure - it's tantamount to dangling a network cable out of your window with a prominent "Help Yourself" label attached to it. Unfortunately, the earliest attempt at Wi-Fi security, WEP (Wired Equivalent Protocol), proved deeply flawed and very easy to hack. WPA (Wireless Protected Access) and in particular WPA2 (which features near-unbreakable AES encryption) has gone a long way to rectifying this glaring defect. Even so, many wireless networks remain unprotected.

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Roger Gann

PC Advisor (UK)
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