kern/163318: [ath] ath(4) stops working

Kevin Oberman kob6558 at gmail.com
Sun Dec 18 18:20:46 UTC 2011


On Sun, Dec 18, 2011 at 8:40 AM, Joel Dahl <joel at freebsd.org> wrote:
> The following reply was made to PR kern/163318; it has been noted by GNATS.
>
> From: Joel Dahl <joel at freebsd.org>
> To: bug-followup at freebsd.org
> Cc:
> Subject: Re: kern/163318: [ath] ath(4) stops working
> Date: Sun, 18 Dec 2011 17:35:18 +0100
>
>  Disabling bgscan with
>
>   ifconfig wlan0 -bgscan
>
>  fixes the problem. The machine has been running for 9 hours now without any
>  problems.

I have been recommending that people having problems with wireless
cards suddenly losing connectivity turn off bgscan for some time. It
certainly fixed my problems with my old ath card, thought I am not
sure that it is ath specific.

I first reported this several years ago when Sam was still doing the
ath work and received a prompt reply that I was wrong and bgscan was
completely non-intrusive. I sent Sam details on exactly what I was
seeing with the failures always occuring on the 5 minute intervals
when background scans are done (though not at nearly every scan) and
the conditions that triggered the problem and got a prompt response
that what I was reporting was not possible and that whatever was
causing the problems I was seeing was not bgscan.

I have suggested turning off bgscan to many others reporting similar
problems and gotten several responses that it worked. I am still
convinced that something is not right about bgscan on FreeBSD, though
I don't know if it is ath specific or more generally a wlan issue. I
can say that it shows up most often when there are several APs with a
common SSID showing up. I had particular problems when I was attending
a large conference, such as NANOG, where there were several APs for a
large room.

I have no expertise on 802.11, so I can't tell much more, but I am
convinced that something is wrong with bgscan on FreeBSD, at least
with ath. I'd love to see someone get to the bottom of this. It has
been showing up for at least 4 years and pre-dates the wlan split
going back the the very early days of ath support.
-- 
R. Kevin Oberman, Network Engineer
E-mail: kob6558 at gmail.com


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