Problems running ath with bgscan enabled

Sam Leffler sam at
Sun Oct 21 06:35:09 PDT 2007

Kevin Oberman wrote:
> Ever since the update of the HAL and the new 802.11 code a few months
> ago (in current), I have been having problems, especially when I was in
> locations with multiple APs available. 
> The problem was periodic loss of association. If I was at home where I
> can usually only see a couple of APs, the problem would occur an
> average of about 10 times a day with re-association in about 10 seconds,
> sometimes less. This is annoying, but not very disruptive.
> When away from home and in an urban location where there are several
> APs, both the frequency of the loss of connectivity and the time to
> re-associate increase. Last week at the NANOG meeting there were 4
> conference b/g APs and 4 11a APS seen at all times along with the
> hotel's tmobile and a couple of random ones. Only the two conference
> SSIDs (nanog-arin and nanog-arin-a) were in my wpa_supplicant.conf
> file. 
> My bgscan interval was the default 300 and almost every 5 minutes I
> would lose connectivity, often for over a minute. When I made the
> association between the bgscan interval and the drop-outs, I did an
> "ifconfig ath0 -bgscan" and things stabilized immediately. No further
> problems. 
> ath_hal: (AR5210, AR5211, AR5212, RF5111, RF5112, RF2413, RF5413)
> ath0: <Atheros 5212> mem 0xb4000000-0xb400ffff irq 11 at device 2.0 on pci11
> ath0: mac 5.9 phy 4.3 radio 3.6
> This is really not acceptable for default behavior as it won't be clear
> to many how to fix it. Is it expected or is something wrong?
> Thanks!

There hasn't been a hal change in a long time.  bgscan works by telling
the ap your station is in power save mode, leaving the channel briefly,
and then returning.  I have not seen any issues with it w/ or w/o

Maybe you can provide some information to help diagnose this?  I see
nothing helpful like a log from wpa_supplicant or statistics.


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