Lost EAPOL packets while connection

Jouni Malinen j at w1.fi
Fri Jan 13 02:21:03 PST 2017

On Mon, Jan 09, 2017 at 02:10:51PM +0100, Thomas Graf wrote:
> I tracked down the issue to lost EAPOL packets. I'm using the ath9k driver
> which is repeating packets 10 times. The problem is when they are lost.

Are you saying that you have an environment where 10 retries of a single
EAPOL frame is not sufficient to get it through in significant number of
cases? That sounds quite extreme environment..

Would you be able to share a wireless sniffer capture showing that type
of case with connection failing?

> On a previous proprietary platform the usual way was to flag EAPOL packets
> for more retries and the wpa-supplicant was notified of unsuccessful
> transmission.

The IEEE 802.1X Authenticator on the AP is expected to retry EAPOL
frames that do not get a response. Are you seeing that happening? And
the same issue with following 10 retries from the station are all lost
again? That would sound like a really horrible radio environment to the
point of being useless in practice. Or there is something else causing
connection issues..

> On linux with wpa_supplicant I only see long timeouts after lost EAPOL
> frames. I suppose in mac80211 there should be some extended handling for
> EAPOL frames.
> Always waiting for the timeout and then restarting from the beginning is not
> a good solution.

So is this a completely failure to connect or just something that takes
a long time because of the Authenticator retries being after couple of

> On a channel on 2.4Ghz I see a typical channel usage of 50% or more. That
> causes the authentication to fail of lost packets of about 10% in my
> environment.

10% frame (MPDU) loss is fine and common, but that should not cause loss
of the actual Data frame due to link layer retries and adjusted TX rate,
if needed, when not in sufficient range of the AP to be able to use a
higher rate that might have been tried first.

Jouni Malinen                                            PGP id EFC895FA

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