iwlwifi: 8265: unexpected LLC packets TX'ed in monitor mode

iwlwifi: 8265: unexpected LLC packets TX'ed in monitor mode

[Marco Fonseca]

Hello,

While in monitor mode, the 8265 will periodically transmit gratuitous
LLC packets.  In this mode, I would expect the wifi chipset to not
transmit any packets at all (unless packet injection is being used).

This behavior can be observed by a second wifi device in monitor mode.
A display filter on wireshark/tshark of 'llc' makes these easy to spot.

It seems these packets only get produced in presence of a few APs
and/or STAs but I'm not sure of the exact cause.  I don't see the LLC
packets on very quiet channels.

Other Details
-------------

wifi chipset:
  Intel(R) Dual Band Wireless AC 8265, REV=0x230

kernel:
  4.9.11 kernel

backports driver:
  iwlwifi-stack-public:release/core33:6653:327571a8

  I can use other backports versions if needed, but this was the
  version called out in:
  https://wireless.wiki.kernel.org/en/users/drivers/iwlwifi/core_release

Firmware:
36.952d9faa.0


Thank you,

Marco Fonseca

Re: iwlwifi: 8265: unexpected LLC packets TX'ed in monitor mode

[Johannes Berg]

On Wed, 2020-05-13 at 13:48 -0400, Marco Fonseca wrote:
> Hello,
> 
> While in monitor mode, the 8265 will periodically transmit gratuitous
> LLC packets.  In this mode, I would expect the wifi chipset to not
> transmit any packets at all (unless packet injection is being used).
> 
> This behavior can be observed by a second wifi device in monitor mode.
> A display filter on wireshark/tshark of 'llc' makes these easy to spot.
> 
> It seems these packets only get produced in presence of a few APs
> and/or STAs but I'm not sure of the exact cause.  I don't see the LLC
> packets on very quiet channels.

I think these are somehow related to calibrations in the device.

johannes

Re: iwlwifi: 8265: unexpected LLC packets TX'ed in monitor mode

[Marco]

On Mon May 25, 2020 at 7:23 AM EDT, Johannes Berg wrote:
> On Wed, 2020-05-13 at 13:48 -0400, Marco Fonseca wrote:
> > Hello,
> > 
> > While in monitor mode, the 8265 will periodically transmit gratuitous
> > LLC packets.  In this mode, I would expect the wifi chipset to not
> > transmit any packets at all (unless packet injection is being used).
> > 
> > This behavior can be observed by a second wifi device in monitor mode.
> > A display filter on wireshark/tshark of 'llc' makes these easy to spot.
> > 
> > It seems these packets only get produced in presence of a few APs
> > and/or STAs but I'm not sure of the exact cause.  I don't see the LLC
> > packets on very quiet channels.
>
> I think these are somehow related to calibrations in the device.
>
> johannes

Are you perhaps implying that I can alter calibration settings to fix
this problem?  If you have any pointers to this it would be
appreciative.

Regardless though, I would still expect the default behavior to not
emit packets when in monitor mode, unless the user directs it to;
similar to what I've seen from other wifi chipsets.

Marco

Re: iwlwifi: 8265: unexpected LLC packets TX'ed in monitor mode

[Johannes Berg]

On Thu, 2020-05-28 at 10:26 -0400, Marco wrote:
> 
> > I think these are somehow related to calibrations in the device.
> 
> Are you perhaps implying that I can alter calibration settings to fix
> this problem?  If you have any pointers to this it would be
> appreciative.

No, I don't know if this is possible. I'm just telling you what I think
the reason for them is.

> Regardless though, I would still expect the default behavior to not
> emit packets when in monitor mode, unless the user directs it to;
> similar to what I've seen from other wifi chipsets.

I have no idea precisely why (for what kind of calibration) these are
transmitted and if it could be changed, I guess you could try contacting
Intel's customer support?

johannes