Subject: Re: mac80211 / iwl3945 + dynamic wep (again)
From: Johannes Berg <johannes@sipsolutions.net>
To: Dan Williams <dcbw@redhat.com>
Cc: drago01 <drago01@gmail.com>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Jouni Malinen <j@w1.fi>,
	ipw3945-devel <ipw3945-devel@lists.sourceforge.net>,
	Zhu Yi <yi.zhu@intel.com>
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Date: Mon, 26 Nov 2007 17:14:23 +0100
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> Because in the case of hidden SSIDs, wpa_supplicant pretty much says to
> use ap_scan=3D2.
>=20
> There are a few problems here:
>=20
> 1) Historically, some drivers worked better with ap_scan=3D1 (madwifi),
> others worked better with ap_scan=3D2 (many fullmac drivers)
>=20
> 2) scan_ssid=3D1 hasn't worked consistently on all drivers because it's
> pretty new and many drivers don't support it yet.  This is supposed to
> make the driver/firmware send out probe request for the SSID in
> question.
>=20
> So basically, we're up shit creek without a paddle.  You have to use
> ap_scan=3D2 on some cards because they don't support specific-ssid
> scanning (with scan_ssid=3D1) to find the BSS you want to connect to, but
> some cards can handle ap_scan=3D1+scan_ssid=3D1 OK.

Fun. I'm pretty sure mac80211 handles ap_scan=3D1/scan_ssid=3D1 fine,
sending probe requests for that specific SSID.

> NM has logic to cache the BSSIDs of APs you've connected to before, and
> to match those up with an SSID when it sees them in the scan list if the
> AP isn't broadcasting the SSID.  Unfortunately, that information isn't
> available to wpa_supplicant because wpa_supplicant doesn't have an
> interface to handle that sort of thing.  Therefore, when faced with an a
> request to connect to a hidden network, wpa_supplicant must rely
> _entirely_ on the driver Doing The Right Thing with scan_ssid=3D1 or
> ap_scan=3D2, and that almost never works due to inconsistency in driver
> implementation.

Who invented hidden SSIDs anyway? Well, I guess I can actually test this
now that I finally have a second mac80211-based wireless card, although
iwl4965 is special wrt. scanning. I guess the trick will be to make
ap_scan=3D2 work although ap_scan=3D1/scan_ssid=3D1 works much better :(

We can fix that in nl80211 by making sure that scan_ssid is implemented
right away and whoever has nl80211 support needs to support that so that
we can rely on it...

johannes

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