wpa_supplicant roaming question

Janusz Dziedzic janusz.dziedzic at gmail.com
Wed Aug 31 04:21:34 EDT 2011

2011/8/30 Matt Causey <matt.causey at gmail.com>:
> Hello,
> I have a question about how scans are meant to be triggered with
> wpa_supplicant, mac80211, and family.  At my site, we have a fleet of
> small devices that run the Atheros ar928x wireless cards.  We use
> EAP-TLS on Motorolla WLAN infrastructure.  We're running linux
> 2.6.38-2 with no vendor patches.  Our wpa_supplicant version is 0.7.3.
> In our situation, we'll have a client adjacent to 2 or 3 BSSIDs
> broadcasting the same ESSID, and the client moves about from time to
> time.  What I am seeing is that the client will sit on a -70 access
> point, without roaming, for hours even in the presence of another
> access point that registers as -50.  However, if I do something to
> manually trigger a scan, the device will suddenly roam to the more
> favorable access point.
> For example, I can do 'iwlist scan', or HUP the supplicant.  iwlist I
> am sure causes the driver to generate a new set of scan results -
> which the supplicant picks up and uses.  HUP of the supplicant causes
> the supplicant to call wpa_supplicant_req_scan(), and then roam as a
> result of the new scan data.  This leaves me thinking that the roaming
> algorithm is working great, it's just that the background scanning is
> not working as I would expect...
> So I read about bgscan here:
> http://hostap.epitest.fi/gitweb/gitweb.cgi?p=hostap-07.git;a=commit;h=e2f74005f548d90014cdf080802d455382e37cb9
> It looks like what I want - to configure the supplicant to scan
> periodically.  However I have it enabled and I don't ever see it kick
> in.  Any ideas why?
> Here is our supplicant config:
> network={
>        ssid="wpa2"
>        bgscan="simple:30:-45:300"
>        freq_list=<a list of the frequencies that we use>
>        identity="<client-id>"
>        key_mgmt=WPA-EAP
>        proto=WPA2
>        pairwise=CCMP
>        group=CCMP
>        eap=TLS
>        ca_cert="/etc/cert/root.pem"
>        client_cert="/etc/cert/user_cert.pem"
>        private_key="/etc/cert/user_key.pem"
>        private_key_passwd="<noober mic nooberson>"
> }
> If there is other info I can provide please let me know!

Did you enable this CONFIG_BGSCAN_SIMPLE=y in wpa_supplicant/.config
file before compilation?

We are using bgscan simple and learn and don't have such problems.
If still an issue:
Run wpa_supplicant with -ddd option. After that you should get debug
messages connected with bgscan_simple.


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