802.11 monitor mode changes coming

Sam Leffler sam at errno.com
Mon May 18 18:16:57 UTC 2009

The patch here:


has significant changes to monitor mode operation.  Most importantly it 
replaces DLT_IEEE802_11 support in net80211 by DLT_IEEE802_11_RADIO and 
removes the latter from the underlying device.  The upshot is that you 
can no longer do:

tcpdump -i ath0

instead you will now need a wlanX ifnet; e.g.

ifconfig wlan create wlandev ath0 wlanmode monitor channel 6 up
tcpdump -i wlan0 -y IEEE802_11_RADIO

This addresses the longstanding issue that applications like kismet that 
want radiotap data needed to open two ifnets, one to receive data and 
one to do channel changes.  My main concern is whether losing 
DLT_IEEE802_11 support will affect any apps.  Those that depend on it 
should be easy to change; you just request a different DLT and strip the 
radiotap header from tap'd frames (or similar).

In sweeping the drivers to do these changes I've made radiotap support 
more consistent and improved some drivers.  Drivers not tested so far: 
malo, ipw, wpi, and upgt.  I tested iwi and it appears broken in that no 
frames are rx'd but I'm not sure I'll look at it before 8.0.

I plan to commit these changes by the end of the week.


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