mac80211 + hostapd: EAPOL frames rate selection

Helmut Schaa helmut.schaa at googlemail.com
Fri Jul 29 13:55:04 EDT 2011


On Fri, Jul 29, 2011 at 7:37 PM, Jouni Malinen <j at w1.fi> wrote:
> On Fri, Jul 29, 2011 at 11:14:20AM +0200, Helmut Schaa wrote:
>> I just noticed that EAPOL frames generated by hostapd during the 4-way
>> handshake are sent out by mac80211 using a rate as selected by the rc
>> algorithm for data frames. In my case minstrel_ht selects a MCS rate for
>> 11n clients which sometimes results in a 4-way handshake timeout under
>> low signal conditions.
>
> That sounds like an issue that should be fixed in the rate control
> algorithm if it is indeed using unsuitable rate immediately after
> association. Dropping data frames completely is not really a good thing
> regardless of whether they are EAPOL packets or not..

True. Nevertheless other drivers like madwifi or the ralink legacy drivers also
force EAPOL frames to a low rate. That's why I had the idea in the first place.

> Some EAPOL frames can be quite large (e.g., EAP-TLS). Forcing those to
> go out at 1 Mbps on a congested 2.4 GHz band channel sounds like a bad
> idea in general if the stations would be able to use HT rates at the
> time..

Good point.

Helmut


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