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From: "Luis R. Rodriguez" <mcgrof@gmail.com>
Date: Wed, 1 Jul 2009 10:33:00 -0700
Message-ID: <43e72e890907011033r52c4256dtecf603f56213a825@mail.gmail.com>
Subject: Re: mac80211 and broadcast frames
To: Valentin Manea <linux-wireless@mrs.ro>
Cc: linux-wireless@vger.kernel.org
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Sender: linux-wireless-owner@vger.kernel.org

On Tue, Jun 30, 2009 at 11:42 PM, Valentin Manea<linux-wireless@mrs.ro> wrote:
>
>
> On 06/30/2009 07:20 PM, Luis R. Rodriguez wrote:
>>
>> On Tue, Jun 30, 2009 at 3:53 AM, Valentin Manea<linux-wireless@mrs.ro>
>>  wrote:
>>>
>>> Hi,
>>>
>>>   I've been working on a small project that basically sends broadcast UDP
>>> frames from an Wireless AP to multiple clients. While I can send UDP
>>> frames
>>> just fine from the AP to the client the only a few broadcast frames reach
>>> my
>>> client. What is really puzzling is that on the client machine using
>>> tcpdump
>>> I can see all the broadcast frames arriving, my application sees only a
>>> small fraction of them.
>>
>> Keep in mind when you use tcpdump it will modify the RX filters of the
>> device you use but if you say you see them on tcpdump and at the same
>> time do not see them on the application that seems fishy and non
>> driver related.
>>
>>   Luis
>
> tcpdump doesn't affect the results at all, with or without it running it's
> the same.

Well it would if you had had other nodes sending data on the same BSS,
it would mean more RX'd frames that are passed up on your host. This
would just be specific to your BSS as you would be using promiscuous
mode and not a real monitor mode, so just wanted to point that out.

> I have tried tracing the packets, I thought that maybe there is a problem in
> the 80211 stack and for some reason they would be dropped but as far as I
> can tell every packet is routed to the ip stack with the correct protocol
> and pkt_type.

OK  then the issue is further down and not related to the driver or
wireless stack it seems.

> One more strange thing, if I'm looking at netstat -s everything seems to be
> normal, InBcastPkts is fine, also the number of incomming UDP packets.

More confirmation things are peachy on the linux-wireless front and
that this is a userspace issue somewhere.

> Any ideas where I could look? it just gets stranger and stranger.

If you see the frames do get to the host then definitely not on the
drivers / stack.

  Luis