Detecting the Device
There are a couple of ways of detecting rogue APs. One of the more popular and cost-effective techniques is to have a technician perform manual checks with a laptop or PDA running NetStumbler. NetStumbler is a tool for detecting all wireless networks within a broadcast area. There are actually two different versions of NetStumbler, and both are downloadable for free at the company's Web site.
One version is designed for use with laptops, while the other version (Mini Stumbler) is for use with a Pocket PC. Both versions also support GPS cards. This lets NetStumbler create a map showing the locations of all the wireless APs within a specified area.
The simplest way to hunt down a rogue AP is to take a laptop that's running NetStumbler and walk in the direction that produces the greatest signal strength from the questionable access point. You'll soon know if the signal is coming from within your building or from somewhere else. If the signal is coming from your building, you can use the signal strength to narrow down your search to a single room. After that, you'll just have to hunt around the room until you find the access point.
One thing to keep in mind when using NetStumbler: if you are using an 802.11b Wi-Fi card in your laptop, you can expect to find 802.11b and 802.11g access points. However, if you are a running 802.11a network, then an 802.11b card will not detect it. That's because 802.11b uses a 2.4GHz signal, while 802.11a operates in the 5GHz range
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