Strange problem with ath9k and ASUS N66U AP.

Ben Greear greearb at candelatech.com
Wed Apr 25 02:23:55 EDT 2012


On 04/24/2012 11:08 PM, Jouni Malinen wrote:
> On Tue, Apr 24, 2012 at 05:26:07PM -0700, Ben Greear wrote:
>> On 04/24/2012 03:50 PM, Ben Greear wrote:
>>> I am trying some ath9k virtual clients against an ASUS N66U.
>
>>> Here is part of the N66U wifi log showing that it
>>> thinks sta11 is not authorized:
>>>
>>> 00:95:95:00:00:0C  associated
>>> 00:95:95:00:00:0D  associated authorized
>
>> Here's a better log.  Makes me think supplicant might be at fault???
>
> Looks more like an AP bug to me..
>
>> sta8 failed, sta9 works fine.  The difference appears to be the extra
>> RX EAPOL packet that sta8 receives...
>
>> 1335313181.999422: sta8: WPA: RX message 3 of 4-Way Handshake from c8:60:00:e8:88:b0 (ver=2)
>> 1335313181.999465: sta8: WPA: Sending EAPOL-Key 4/4
>
>> 1335313182.063695: sta8: WPA: RX message 3 of 4-Way Handshake from c8:60:00:e8:88:b0 (ver=2)
>> 1335313182.063745: sta8: WPA: Sending EAPOL-Key 4/4
>
> Either the AP did not receive the first EAPOL-Key 4/4 or processed it
> only after retransmitting 3/4. Supplicant side will need to to reply to
> retransmitted 3/4 to complete the 4-way handshake. If the AP received
> either of these 4/4 messages, it should be fine with the result. If it
> didn't receive either, it should disconnect the station. It does not
> look like either of those happened.

Ok, it seems strange they would have such a lame
bug, but maybe they never tried associating several stations at once.
(I see around 30% failure rate when using just 15 stations).

We have several off-the-shelf APs and home-grown ones (using ath9k) that work fine,
even when associating 100+ stations, so at the least the N66U is weird...

That said, I'll probably need to attempt a work-around for this.  The only
obvious thing I see is the extra RX EAPOL (in all error cases I looked at, and none
where it associated properly), and the fact that DHCP just fails to acquire a lease.

I'll try adding a hack to detect the duplicate RX EAPOL and bounce the connection
if that hits, and see if that helps any...

Thanks,
Ben



-- 
Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


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