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Network World - Even if you have an enterprise-level Wi-Fi spectrum analyzer, like Wi-Spy or AirMagnet, free Wi-Fi tools can also come in handy. You might use them during the planning or installation stages of your wireless LAN, while troubleshooting, or when performing maintenance. They could even serve as your primarily tools in smaller and less-complex environments.
Here are several free programs you can use to do Wi-Fi stumbling and surveying on all the popular platforms—Windows, Mac OS X, and Linux. You'll be able see all the nearby wireless access points and their details, including channels, signal levels, and MAC address. (Watch a slideshow version of this story.)
NetStumbler is one of the oldest and most known Wi-Fi stumblers and runs on Windows and Windows CE/Mobile. It lists nearby access points and displays their basic details: SSID, channel, speed, MAC address, vendor, and encryption. Unlike most other stumblers, it also shows the signal, noise, and signal-to-noise ratio (SNR) levels. Additionally, it has GPS support to record access point locations when wardriving.
Keep in mind, NetStumbler hasn't been updated since 2004. It may not run well on Windows Vista or 7, or even 64-bit Windows XP. Additionally, it doesn't show the real encryption methods of access points. If an access point has encryption enabled it's always marked as WEP, regardless if it's WEP, WPA, or WPA2.
NetStumbler can be useful when doing basic signal reading or wardriving, but the limitations I mentioned prevent it from being a go-to tool for other situations, such as when doing a security audit to look for misconfigured or rogue access points.
Vistumbler is a newer open source stumbler first released in 2007 and updated as lately as 2010. It displays the basic access point details, including the exact authentication and encryption methods, and can even speak the SSID and RSSI of access points.
Similar to NetStumbler, you can view a list of all access points or drill down to those categorized by authentication, encryption, channel, network type, and SSID. You can also view graphs of the access point signals in addition to viewing text readouts. It's highly customizable and offers flexible configuration options. For example, you can define and save access point names to better distinguish them in the future. In addition to basic GPS support to record access point locations, it supports live tracking within the application using Google Earth.
However unlike NetStumbler, Vistumbler only gives you the signal levels and doesn't include the noise levels. Thus it doesn't report the signal-noise-ratio (SNR) values, which is usually more helpful than just the plain signal levels.
InSSIDer is a relatively new open source Wi-Fi stumbler developed by MetaGeek, the maker of the Wi-Spy spectrum analyzer. It shows the usual list of access point details, but doesn't show the exact authentication method. You can see the encryption method used but can't distinguish, for example, between WPA-PSK and WPA-Enterprise networks. Like most other stumblers, inSSIDer doesn't include the noise or signal-to-noise (SNR) values; just gives you the RSSI values.