orr:/root# ifconfig wi0 mediaopt monitor channel 6 up
orr:/root# tcpdump -i wi0 -L
Data link types (use option -y to set):
IEEE802_11_RADIO (802.11 plus BSD radio information
orr:/root# tcpdump -n -i wi0 -y IEEE802_11
One of the students asked if Tcpdump supported hopping across channels to monitor multiple networks simultaneously. I did not know of a way to do this, because the channel to monitor must be specified as shown above. An alternative requires running multiple wireless NICs.
I just learned of Microsoft's VirtualWiFi research project. This is continuation of Ranveer Chandra's work on MultiNet. If VirtualWiFi supports putting a wireless NIC into monitor mode on Windows, it is possible to virtualize the NIC for as many channels as one wishes to monitor. Separate WinDump instances could sniff each virtual NIC. If anyone wishes to try this, please share your results in a comment.