nl80211, wext, dhclient

Simon Kitching simon at
Fri Sep 4 14:47:32 EDT 2015

On 09/04/2015 06:26 PM, Dan Williams wrote:
> On Fri, 2015-09-04 at 15:25 +0200, Simon Kitching wrote:
>> Hi,
>> I've noticed some odd behaviour I hope someone here can explain.
>> I can get dhcpcd/dhclient to initialise an interface with wpa_supplicant
>> using "-Dwext" but not "-Dnl80211" (ie the default). Is that expected
>> behaviour?
>> System: Lenovo thinkpad with intel 7265 wireless. OS: debian8 or
>> linux-from-scratch (both show the same behaviour), systemd-based but all
>> network-related daemons disabled.
>> If I run
>>     wpa_supplicant -c.. -iwlp3s0
>> then the interface does not reach RUNNING state (according to ifconfig).
> Posting the debug logging from wpa_supplicant (pass '-dddt' to it to
> enable debug logging) and the config file network block would be
> necessary to figure out what's going on.  Also, what kernel version?
> Dan
>> Running "dhcpcd wlp3s0" afterwards reports "link not up" and eventually
>> exits. Running "dhclient wlp3s0" just hangs.
>> If I add "-Dwext" to the wpa_supplicant options, then the interface
>> reaches state RUNNING, and dhcpcd/dhclient allocate an address for it.

Ok, found the triggering factor. The nl80211 driver doesn't work with a 
hidden SSID. As soon as I switched my router to broadcast the id (and 
updated wpa_supplicant config to match), that driver works fine. Is that 

Attached is a targz file with the requested logging. There are traces 
for three cases:
* wext with hidden SSID (works)
* nl80211 with hidden SSID (doesn't work; just stops at "link not ready")
* nl80211 with public SSID (works)
and the wpa_supplicant.conf files are there too. Note that I've manually 
changed the SSID name in the files.

(and yes I know that hiding the SSID doesn't really add much security).

These traces are all from a system running kernel 3.19.

Thanks & Regards,
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