Re: mac80211 and broadcast frames

[Valentin Manea <linux-wireless@mrs.ro>]

Hi,

   I've tracked this problem down and to my shame the problem was on the 
sending side, it seems that when sending broadcast/multicast frames the 
sending side chooses the lowest bit rate possible. Is this how it is 
supposed to behave?

Best Regards,
Valentin

On 07/01/2009 08:33 PM, Luis R. Rodriguez wrote:
> 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