[PROPOSAL] Add hostapd.conf parameter to skip checkforneighboring BSS (prevent fallback in 150Mb mode)

Valeriy Kucherenko darkside_ua
Sun Apr 8 03:49:38 PDT 2012

> On Sun, Mar 04, 2012 at 09:00:29AM +0200, Alex Vorona wrote:
> > Scan for neighboring BSSes prior to enabling 40 MHz channel
> > [...]
> > 40 MHz affected channel range: [2422,2472] MHz
> > Neighboring BSS: cc:96:a0:f5:4a:00 freq=2422 pri=3 sec=7
> > 40 MHz pri/sec mismatch with BSS cc:96:a0:f5:4a:00 <2422,2442> (chan=3+) vs. <2457,2437>
> > 20/40 MHz operation not permitted on channel pri=10 sec=6 based on overlapping BSSes
> > 
> > I can change channel to any between 1 and 10 in hostapd.conf and got the same result.
> > using HT40- instead HT40+ did not help.
> Did you try using the same combination as the conflicting BSS, i.e.,
> channel 3 HT40+? The only rule that hostapd is currently using for 40
> MHz channels on 2.4 GHz band is to mandate that the same pri/sec
> channels are used with any other 40 MHz BSS in the affected frequency
> range.
> If there is more than one 40 MHz BSS on 2.4 GHz already running with
> conflicting channels, they should not really have started in the first
> place.. Is that the case here?

I guess that this is my case. Hostapd won't start in 40 mhz mode if any overlapping BSS is found on 13+9 channel,
but the main problem, as I write before, is that even if it starts in 40 mhz mode (clients shows 270-300 mbps connection), 
then from time to time it fallback in 20 mhz mode (clients shows 150 mbps connection). I can't understand why this happens,
but it happens. And after overriding scan results with oper40 = 1; this problem seems to go away.

Anyway, you wrote that hostapd check for overlapping BSSes only at startup. Let's assume that at the moment of start there was one
conflicting BSSes on our channels, so as result hostapd started in 20 mhz mode. Then, after some time this conflicting AP has 
gone away (this is an example from real life). In this case, I guess, hostapd will still work in 20 mhz mode and will not switch 
into 40 mhz mode because check for neighboring BSSes performed only at startup. Am I correct?

> -- 
> Jouni Malinen                                            PGP id EFC895FA
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