[systemd-devel] udev breaks hostap linkage of raw/user interfaces, causing wpa_supplicant problems

Thomas Richter thor at math.tu-berlin.de
Sun Mar 15 05:40:28 PDT 2015

Hi folks,

udev seems to create a problem here with the hostap (prism2) kernel 
driver. Unlike many wifi devices, the hostap device driver always 
creates paired interfaces, a raw interface (wifiX) and a network 
interface (wlanX) that represents the configured network.

Unfortunately, udev (or hostap?) does not seem to be aware of this 
linkage, and hence, if you have two wifi radios in your system, may 
rename the second (wlanX) without the first (wifiX), and hence causing a 
name mismatch between the two.

In general, this is not a problem, however, wpa_supplicant seems to 
depend on the linkage of the names. Hence, if wifiX does not match 
wlanX, wpa_supplicant will be unable to provide a WPA2 connection over a 
hostap driven wifi connection.

Even worse, the complete procedure is completely untransparent to the 
user, i.e. neither wpa_supplicant (nor network-manager, depending on 
wpa_supplicant) nor network-manager provide a useful error message.

Any chance of fixing this problem? Is this "only" a configuration issue? 
Is this an issue of hostap? Is this an issue of wpa_supplicant?

Either way, it took me several hours of figuring out what was wrong....


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