11ac packet capture using Wireshark & QCA9880

11ac packet capture using Wireshark & QCA9880

[Okhwan Lee]

Hi all, 

We install a station to capture 11ac packets using wireshark. 
The station equips with QCA 9880 and operates  Ubuntu (Kernel version 3.16.1)
We also install backport (3.16.1) to use the emerging ath10k device driver and 10.1.467.2-1 firmware. 

In our testbed, there is three nodes, AP (ASUS AC66), client (QCA9880) and the monitor station (QCA9880). 
The monitor station can capture the packets transmitted by AP but not capture the packets transmitted by the client. 
We use the same parameter settings (MCS~0, 1 streams, 20 MHz bandwidth, BCC, long preamble) on both AP and client, so there may be no packet error or loss. 
We also confirm that the packets transmitted by AP contain VHT information. 
In other word,  the monitor station can capture 11ac packets (VHT-PPDU). 

Is there any reason why QCA 9880 can not capture only packets transmitted by the client equipped with QCA9880?

-- 
Okhwan Lee
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Re: 11ac packet capture using Wireshark & QCA9880

[Michal Kazior]

On 5 November 2014 09:35, Okhwan Lee <ohlee@mwnl.snu.ac.kr> wrote:
> Hi all,
>
> We install a station to capture 11ac packets using wireshark.
> The station equips with QCA 9880 and operates  Ubuntu (Kernel version 3.16.1)
> We also install backport (3.16.1) to use the emerging ath10k device driver and 10.1.467.2-1 firmware.
>
> In our testbed, there is three nodes, AP (ASUS AC66), client (QCA9880) and the monitor station (QCA9880).
> The monitor station can capture the packets transmitted by AP but not capture the packets transmitted by the client.
> We use the same parameter settings (MCS~0, 1 streams, 20 MHz bandwidth, BCC, long preamble) on both AP and client, so there may be no packet error or loss.
> We also confirm that the packets transmitted by AP contain VHT information.
> In other word,  the monitor station can capture 11ac packets (VHT-PPDU).
>
> Is there any reason why QCA 9880 can not capture only packets transmitted by the client equipped with QCA9880?

Hmm.. This may be related to A-MSDU. ath10k's msdu chaining code
doesn't handle all possible cases.

ath10k's firmware does A-MSDU for sure. I'm guessing AC66 doesn't do
it (or does it less often) - this would explain why sniffing AP -> STA
traffic works while STA -> AP does not.

Do you use encryption? Can you try setting the AP without encryption
and see if you can sniff STA -> AP traffic?

Another thing to try is to override amsdu aggregation setup on the STA:
 mount -t debugfs debug /sys/kernel/debug
 echo 1 64 > /sys/kernel/debug/ieee80211/phy*/ath10k/htt_max_amsdu_ampdu

This should effectively disable A-MSDU Tx on the ath10k STA so it
should check if this is related to msdu chaining at all.

I'm aware neither of this is a solution. It's more of a confirmation
if my reasoning is correct.


Michał

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