Hostapd to Wpa_supplicant 4 way Handshake Problem

Damon Southworth damon
Wed Aug 27 05:14:08 PDT 2008


A couple of weeks ago I posted a number of messages regarding problems I
was experiencing with unreliability of the 4-way handshake re-key. The
initial 4-way is successful to establish the link but subsequent re-keys
can be unreliable due to transmission delays and non guranantee of the
ordering between transmitting the handshake and installing the key.

I would like to ask a few more questions in relation to this problem.

This problem still exists and we are still unclear as to the best way to
solve it. I did monitor the key exchange using a sniffer and managed to
see that the problem was that the 4/4 message did not get through to the
AP in time. Two 3/4 retries were seen 100ms apart before the final
disconnect packet was sent from the AP after a further 100ms.

In this case the AP was a Cisco 1200 series and the EAPOL messages
containing the key exchange were sent with a QoS header highest priority
7 (management) and were very precise in their transmssion times and
retries. Packets from the station didn't have a QoS header and timings
varied with the amount of traffic. Has any thought or work been done to
allow wpa_supplicant to use the 802.11 QoS extensions and improve the
delivery of the key exchange. I can see there is support in the Madwifi
driver for QoS but I am unclear as to the correct kernel interface to
utilise these extensions. Does information on this exist?



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