Interpreting information elements from beacons and probe responses.

Adam Mikuta adammikuta at
Sat Feb 4 14:24:44 EST 2012

1. We have AP configured as open. wpa_supplicant is getting bss_info_handler:

bss[NL80211_BSS_CAPABILITY] - without WEP support flag
bss[NL80211_BSS_BEACON_IES] - without WPA Information Element
bss[NL80211_BSS_INFORMATION_ELEMENTS] - without WPA Information Element

Everything is clear.

2. Now AP is reconfigured to WPA and restarted.

Driver gets new beacon with WPA Information Element and WEP support
flag. wpa_supplicant gets bss_info_handler:

bss[NL80211_BSS_CAPABILITY] - with WEP support flag
bss[NL80211_BSS_BEACON_IES] - with WPA Information Element

Driver didn't get probe response yet, so IEs are not updated:

bss[NL80211_BSS_INFORMATION_ELEMENTS] - without WPA Information Element

3. Is this the correct behavior? Or maybe driver should wait for probe
response before sending message to supplicant?

4. If this behavior is correct... How supplicant should interpret
information which he got?

As I can see in wpa_supplicant_ctrl_iface_scan_result function it will
check if we have the WEP support flag (we have it). And also check
with wpa_bss_get_ie if we have WPA Information Element. The function
wpa_bss_get_ie checks only information elements from probe response.
So we don't have it. Network is recognized as WEP.

Best regards,

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