wpa_supplicant can't find hidden SSID

Dan Williams dcbw
Thu Mar 19 09:36:04 PDT 2009

On Thu, 2009-03-19 at 16:31 +0000, planetf1 wrote:
> On 19/03/09 15:25, Dan Williams wrote:
> > Try turning off hardware scanning with "disable_hw_scan=1" when loading
> > the 3945 driver in modprobe.conf.  We've found Intel hardware scanning
> > still somewhat flaky in quite a few cases.
> Thanks. I've just tried this again, using
> options iwl3945 debug=0x0000bc88 disable_hw_scan=1
> to be really sure the module had reloaded after rmmod/modprobe, and get 
> the same behaviour of "SSID mismatch".

So since your SSID is hidden, you're going to have problems.  Cisco
itself doesn't recommend hiding SSIDs:


Q. If I disable SSID broadcast, can I achieve enhanced security on a
WLAN network?

A. When you disable SSID broadcast, SSID is not sent in Beacon messages.
However, other frames such as, Probe Requests and Probe Responses still
have the SSID in clear text. So you do not achieve enhanced Wireless
security if you disable the SSID. The SSID is not designed, nor intended
for use, as a security mechanism. In addition, if you disable SSID
broadcasts, you can encounter problems with Wi-Fi interoperability for
mixed-client deployments. Therefore, Cisco does not recommend that you
use the SSID as a mode of security. 

The key phrase being "In addition, if you disable SSID broadcasts, you
can encounter problems with Wi-Fi interoperability for mixed-client

And in essence, that is exactly what your AP is doing :)  But of course
if you don't have any control over the AP that doesn't help you.

To see if the driver can help here at all, try the following:

1) Stop both NetworkManager and wpa_supplicant
1.5) rmmod iwl3945, modprobe it again
2) run "iwlist wlan0 scan" and see if the SSID of your AP shows up in
the list
3) if it *doesn't*, that's what we want for the moment; if it does show
up in the list, rmmod the module and modprobe it again
4) run "iwlist wlan0 scan essid <your essid>" a few times, waiting a few
seconds each time
5) check if your AP's SSID is now shown in the list, and tell me whether
it is or not

The Intel cards do some odd stuff for scanning, which can result in
Probe Requests for specific SSIDs getting dropped on the floor.  It
could also be that your AP sucks and isn't responding to probe requests
with the right SSID.  But it should.


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