Get a handle on Monitor mode
So what’s all the fuss about using an additional Wi-Fi card? In short, there are several modes that are potentially available on network cards. These modes include Monitor, Infrastructure, Mesh and Managed, as well as a few others. Most of the time users won’t have to understand or even make use of the modes. As a result the hardware manufacturers don’t spend much effort on making cards that work well with monitor mode.
While putting this article together, it took several attempts to find a USB card that works for Raspbian. It’s possible to find out which modes your network card works with using the command iwconfig info wlan0 (or other wireless interface). This will give various groups of information, including details on Supported modes. By default, Kismet configures the network card to use Monitor mode so it doesn’t have to be manually set.
It’s, however, possible to make the card manually switch into Monitor mode by using the following commands:
sudo ifdown wlan1 sudo iwconfig wlan1 mode Monitor sudo ifup wlan1
As previously noted, if you do this the network will stop responding if you use it on the network interface you’re connected through. It’s set to passively monitor and report all networks it sees. The wireless card used in this tutorial was a TP-LINK TL-WN727N purchased online for about £9. Do be sure to check its specs though – there are a lot of similar cards that don’t work.