Association often fails first time when roaming with 802.11r.

Ben Greear greearb
Tue Nov 12 12:36:51 PST 2013

On 11/12/2013 12:10 PM, Johannes Berg wrote:
> On Tue, 2013-11-12 at 12:05 -0800, Ben Greear wrote:
>> A more correct roam also takes about 150ms, but at least not because of the
>> error in my previous email.  Seems it takes it 100+ms to go if-up after
>> the assoc-request is sent.  I'll go dig into that further.
> The interface is already up (has to be to authenticate), the event you
> get at that point (just after the ~110ms delay) is for LOWER_UP really -
> which means carrier_on() in the kernel I believe. At that point you'd
> need kernel level tracing or messages to investigate.
> Maybe something is waiting for a beacon there?

At least in the case I just looked at, it seems there were lots and lots
of retries of the re-assoc request from station to AP, and AP finally answers
after ~100ms.  We had the cisco's configured for OTA, so possibly that was
part of the issue.

On a second test, with cisco configured for non-OTA, it seems the response
comes back within 3ms, and there are no retransmits.

Looking at sniffer trace makes everything look nice at first, but if I compare the
actual packet timestamps with supplicant log time-stamps, it seems that it took
109ms from the time that supplicant sent the packet until the sniffer saw it.
I didn't see any other retransmits, and ACKs seem to show up normally in
the sniff.

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