802.11 "monitor mode" issues

Adams, Kevin Kevin.Adams at compuware.com
Mon Feb 23 08:41:22 PST 2004


Thanks for your reply.

I tried it and did not see ANY debug info this time.  I think that's a good
thing.  But on the 'ifconfig' output, the 'status' field stated that it was
'associated'.  Just an observation.

Also, am I to assume that the 'monitor mode' itself, does not increment thru
the channels, it has to be done via the 'ifconfig' or ioctl in a program?



-----Original Message-----
From: Sam Leffler [mailto:sam at errno.com] 
Sent: Friday, February 20, 2004 5:46 PM
To: Adams, Kevin; 'freebsd-mobile at freebsd.org'
Subject: Re: 802.11 "monitor mode" issues

On Friday 20 February 2004 12:38 pm, Adams, Kevin wrote:
> In the man pages of "ifconfig" it states that "monitor"...
> "Put the interface in monitor mode. No packets are transmitted, and 
> received packets are discarded after bpf(4) processing."
> Now, using
>     ifconfig ath0 monitor up
> does not seem to be doing that.

The monitor thing is totally bogus; it should be removed.  You want to do

ifconfig ath0 mediaopt monitor <other stuff> up

(where other stuff might be commands to set the channel).  At that point you
can run programs like Ethereal and tcpdump w/o the driver trying to
associate with an AP.

If you get the latest ethereal from CVS it has radiotap support which lets
you look at frames "below the 802.11 layer".  The tcpdump port likewise has
radiotap support; you do

tcpdump -i ath0 -y IEEE802_11_RADIO

(I think, this is from memory).


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