Possible issue with mac80211 and certain access points

Possible issue with mac80211 and certain access points

[Chad Koehler]

Recently purchased a Palm Pre and immediately found some issues with
connecting to the Wifi Hotspot.  Connecting to other access points
would work flawlessly.

Using the Palm Pre hotspot, I can get connected, but the connection
will drop after a very short period of time.  There are messages in
the system log whenever the connection drops:

No probe response from AP <address> after 500ms, disconnecting.

An internet search turned up several results for people with the same
issue, different wireless drivers and different access point types.

I traced this message down to mac80211/mlme.c, to the
ieee80211_sta_work() function, and was able to determine that for some
reason this particular AP was not responding to probe requests.  This
let me further on to the function ieee80211_mgd_probe_ap_send(), which
sends a direct probe request to the AP -- this probe request was being
sent and never responded to.

If I change this function to send a probe request to the broadcast
address, in a similar manner to what is done in
ieee80211_direct_probe(), then the access point responds and works
without issue.

Due to the volume of issues on the internet that I see with the same
underlying symptoms, I wonder if there are some small amount of access
points that will not respond to a direct packet probe request even
when associated.

I admittedly know very little about wireless networking internals, so
I am hesitant to state that this fix is necessary or appropriate, but
it does solve the issue for me and I am able to remain connected to
the Palm Pre hotspot, as well as other access points that I have
tried.

Please let me know if I can provide further information in this space.


Thank You,
Chad

Re: Possible issue with mac80211 and certain access points

[Marcel Holtmann]

Hi Chad,

> Recently purchased a Palm Pre and immediately found some issues with
> connecting to the Wifi Hotspot.  Connecting to other access points
> would work flawlessly.
> 
> Using the Palm Pre hotspot, I can get connected, but the connection
> will drop after a very short period of time.  There are messages in
> the system log whenever the connection drops:
> 
> No probe response from AP <address> after 500ms, disconnecting.
> 
> An internet search turned up several results for people with the same
> issue, different wireless drivers and different access point types.
> 
> I traced this message down to mac80211/mlme.c, to the
> ieee80211_sta_work() function, and was able to determine that for some
> reason this particular AP was not responding to probe requests.  This
> let me further on to the function ieee80211_mgd_probe_ap_send(), which
> sends a direct probe request to the AP -- this probe request was being
> sent and never responded to.
> 
> If I change this function to send a probe request to the broadcast
> address, in a similar manner to what is done in
> ieee80211_direct_probe(), then the access point responds and works
> without issue.
> 
> Due to the volume of issues on the internet that I see with the same
> underlying symptoms, I wonder if there are some small amount of access
> points that will not respond to a direct packet probe request even
> when associated.
> 
> I admittedly know very little about wireless networking internals, so
> I am hesitant to state that this fix is necessary or appropriate, but
> it does solve the issue for me and I am able to remain connected to
> the Palm Pre hotspot, as well as other access points that I have
> tried.
> 
> Please let me know if I can provide further information in this space.

actually I ran into the same issue two days ago and was going to post
it. So what I am seeing with the Palm Pre is that when we actually scan
while connected to the Palm Pre, a second later we end up disconnected.

Regards

Marcel

Re: Possible issue with mac80211 and certain access points

[Johannes Berg]

On Fri, 2010-05-14 at 00:07 +0200, Marcel Holtmann wrote:

> > Using the Palm Pre hotspot, I can get connected, but the connection
> > will drop after a very short period of time.  There are messages in
> > the system log whenever the connection drops:

> actually I ran into the same issue two days ago and was going to post
> it. So what I am seeing with the Palm Pre is that when we actually scan
> while connected to the Palm Pre, a second later we end up disconnected.

So the Palm is acting as an AP? A beer for each of you says their AP
implementation is buggy.

johannes