Hidden SSID/BSSID cache

Simon Barber simon at barber.net
Fri Nov 11 14:35:25 EST 2011


The problem with active scan for that SSID is that this slows down the 
case of finding other, non hidden SSIDs (e.g. my home AP). The 
persistent cache allows both non hidden, and hidden (after 1st use) APs 
to be found quickly - all in 1 step. Only first use hidden SSIDs would 
pay the time penalty - an uncommon case. I can do some sniffing to find 
out what the driver is actually doing right now.

Simon

On 11/09/2011 05:58 AM, Jouni Malinen wrote:
> On Mon, Nov 07, 2011 at 05:19:37PM -0800, Simon Barber wrote:
>> I use a Ubuntu laptop at work, and the corporate WLAN uses a hidden
>> SSID. Every day I connect at the same place, and wpa_supplicant seems to
>> do an initial scan, then try to scan for the hidden SSID. This takes
>> some extra time. Since I regularly use the same APs would it be possible
>> to extend wpa_supplicant to persistently cache the BSSID->hidden SSID
>> relationships it learns (in a file). This way the next day I open my
>> laptop the initial scan will find the BSSID of the AP I normally use,
>> and learn from the cache that it can immediately attempt to associate
>> with that BSSID, skipping the second scan, and resulting in a faster
>> connection.
>
> I don't see any particular reason for doing this; more generic approach
> would be to just make the initial scan use active scan for the specific
> SSID (or set of SSIDs if you happen to have multiple such networks
> configured).
>
> This should actually already work with nl80211 since it allows multiple
> SSIDs to be included in the scan request.. Have you tried that?
>


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