[PATCH] AP: Do not reply to probe request with DS IE mismatch

Jouni Malinen j at w1.fi
Sun Feb 8 06:22:46 EST 2015


On Sun, Feb 08, 2015 at 10:49:40AM +0000, Peer, Ilan wrote:
> > Strictly speaking, this seems to be non-compliant with IEEE Std 802.11-2012.
> > The AP shall do this if dot11RadioMeasurementActivated is true (so yes, for
> > that case, this change is indeed required), but the standard language seems
> > to imply that the AP shall reply to the Probe Request that matches all the
> > described rules and in case of dot11RadioMeasurementActivated false, that
> > would include the case of DSS Parameter Set element value not matching the
> > current channel..
> 
> Yep. Somehow the spec. does read very complete around this. It states that adding the DSSS IE is optional if
> dot11RadioMeasurementActivated is not set, but does not describe the behavior in such a case.

The standard does describe the behavior: "An AP shall respond to all
probe requests meeting the above criteria". This means that an AP with
dot11RadioMeasurementActivated set to false shall reply regardless of
DSSS Parameter Set matching while an AP with
dot11RadioMeasurementActivated set to true shall reply if the channel
matches or DSSS Parameter Set is not present in the Probe Request frame.

Sure, you may not agree with that being a good behavior, but anyway, the
standard seems to be unambiguous on this. It could be useful to change
the standard to match the desired behavior here, though.. I'll try to
remember to add a comment on the P802.11-REVmc sponsor ballot for this.

> This is the main motivation here. I guess that whoever want to add the scan optimization would need to handle
> this later.

I'm tempting to apply this patch (or well, with some cleanup and
comments pointing out the conflict with the standard). Though, I had
thought about doing this same change when adding the DSSS Parameter Set
element into Probe Request frame. For some reason, I did not at this
on the AP side.. I just can't remember why,

-- 
Jouni Malinen                                            PGP id EFC895FA


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