nl80211, wext, dhclient

Arend van Spriel arend at
Fri Sep 4 14:54:26 EDT 2015

On 09/04/2015 08:47 PM, Simon Kitching wrote:
> 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
> expected?
> 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).

In the supplicant config you have 'ap_scan=2'. What happens when you 
comment out that line or change 2 into 1.


> These traces are all from a system running kernel 3.19.
> Thanks & Regards,
> Simon
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