The easiest way to see what channels your wireless card can use comes from the iwlist command.
iwlist $DEV channel
Where $DEV is your wireless device (wlan0 for me). If you’re card can only do 802.11b, you will most likely just see channels 1-11. The last entry is the current channel that your card is on, if it is on one.
On a wired ethernet interface, placing the interface into promiscuos mode enables it to view all traffic that is being sent across it’s wire as opposed to only traffic directed to it. Promiscuous mode is an essential troubleshooting tool in many situations. Wireless networks have an equivalent mode called Monitor mode that some wireless cards can enter into. Since wifi cards can only bind to one channel at once, you may need to setup a channel hopper to step through the wireless frequencies if you aren’t interested in listening to just one. Note that not all wireless cards support this. I’m using an Intel PRO/Wireless 3945ABG on a Thinkpad X61T with great success. Run the following as root
iwconfig $DEV mode Monitor
iwconfig $DEV channel $CHANNEL
Where $DEV is your wireless device (wlan0 for me) and $CHANNEL is your wireless channel that you would like to listen on. Depending on your card and what you want to see, this could be anything from 1 to 216.
