-1 fixed channel on mon0 in aircrack

Question

I installed recently aircrack 1.1 and when I enable my wlan card into monitor mode by airmon-ng start wlan0 6 I always get fixed channel -1. Anybody knows how to fix it?

My wifi card is Ethernet controller: Atheros Communications Inc. AR5007G Wireless Network Adapter (rev 01). And linux ver 2.6.38-12-generic.

Any ideas?

Answer 1

This is a compatibility issue between mac80211 kernel subsystem and aircrack-ng. It landed in mainline linux kernel 2.6.35 and appears to have been there ever since (writing this on kernel 3.1).

There's two workarounds. You can either patch aircrack-ng or wifi drivers. I prefer the latter since it's very simple and, as a side-effect, gives you most recent drivers.

Here's the recipe:

# we need kernel headers and a toolchain to build wifi drivers 
sudo apt-get install build-essentials linux-headers-2.6.38-12-generic

# download current wireless driver source tree
wget http://linuxwireless.org/download/compat-wireless-2.6/compat-wireless-2.6.tar.bz2

# uncompress
tar xjf compat-wireless-2.6.tar.bz2

# download patch that fixes the problem
wget http://patches.aircrack-ng.org/channel-negative-one-maxim.patch

# apply patch
cd compat-wireless-20*
patch -p1 < ../channel-negative-one-maxim.patch

# compile and install
make
sudo make install

# follow simple instructions to reload the drivers without reboot. Eg:
sudo make unload
sudo modprobe ath5k

For some background see here: http://trac.aircrack-ng.org/ticket/742