Monitor mode on FreeBSD for Cisco/Aironet cards
On FreeBSD, for Cisco/Aironet cards, you can only see 802.11 headers in monitor mode; they are always supplied in monitor mode. To capture in monitor mode, you should put the card into monitor mode with the command ancontrol -i interface -M flag, where flag should be the sum of:
1, to turn monitor mode on;
2, if you want to capture traffic from any service set rather than just the service set with which the card is associated;
4, if you want to see beacon packets (capturing beacon packets increases the CPU requirements of capturing).
Don't add 8 in to flag; Wireshark currently doesn't support the full Aironet header.
When the capture completes, turn off monitor mode with the command ancontrol -i interface -M 0.