atheros madwifi - Monitor Mode

wlanconfig ath0 destroy
wlanconfig ath0 create wlandev wifi0 wlanmode monitor
ifconfig ath0 up


By default, monitor mode receives packets with prism2 headers prepended on them. To change this, you must run one of the following:

Only 802.11 headers:
echo '801' > /proc/sys/net/ath0/dev_type

Prism2 headers:
echo '802' > /proc/sys/net/ath0/dev_type

Radiotap headers:
echo '803' > /proc/sys/net/ath0/dev_type

Atheros Descriptors:
echo '804' > /proc/sys/net/ath0/dev_type


from
http://madwifi.org/wiki/UserDocs/MonitorModeInterface