In a corporate environment, where you have several IT- security related regulations, it is critical to know what kind of wireless networks are in range of your facilities to avoid the bypassing of corporate security infrastructure (such as proxies, firewalls…)

This is where Kismet comes into play and assists you in finding rogue wireless LANs, using the monitor mode of your WLAN card.

You can get the software here: http://www.kismetwireless.net/
Kismet is open-source and also included in several security related linux distros.

The usage is quite simple. Just press “h” while the program runs to display a list of available keyboard shortcuts.

Featues
(taken from kismetwireless.net)

• Ethereal/Tcpdump compatible data logging
• Airsnort compatible weak-iv packet logging
• Network IP range detection
• Built-in channel hopping and multicard split channel hopping
• Hidden network SSID decloaking
• …

Here are some screenshots of Kismet in action

Hint (as fas as I know while using it under Ubuntu 8.10):
After closing the program, you might have to get your WLAN card back to managed mode.

• ifconfig ethXX down
• iwconfig ethXX mode managed
• ifconfig ethXX up