Important note on WLAN sniffing and injection

WLANs typically operate within three different frequency ranges—2.4 GHz, 3.6 GHz, and 4.9/5.0 GHz. Not all Wi-Fi cards support all these ranges and associated bands. For instance, older Alfa cards only support IEEE 802.11b/g. This would mean that these cards cannot operate in 802.11a/n. The key here is to sniff or inject packets in a particular band; your Wi-Fi card will need to support it.

Another interesting aspect of Wi-Fi is that, in each of these bands, there are multiple channels. It is important to note that your Wi-Fi card can only be on one channel at any given moment. It is not possible to tune into multiple channels at the same time. The best analogy I can give you is your car radio. You can tune it to only one of the available channels at any given time. If you want to hear something else, you will have to change the channel. The same principle applies to WLAN sniffing. This brings us to an important conclusion—we cannot sniff all channels at the same time; we will need to select the channel that is of interest to us. What this means is that, if our access point of interest is on channel 1, we will need to set our card on channel 1.

Though we have addressed WLAN sniffing in the preceding paragraphs, the same applies to injection as well. To inject packets on a specific channel, we will need to put the card radio on that channel.

Let's now do some exercises on setting our card to specific channels, channel hopping, setting regulatory domains, power levels, and many more.