11ac packet capture using Wireshark & QCA9880

Michal Kazior michal.kazior at tieto.com
Wed Nov 5 01:05:21 PST 2014

On 5 November 2014 09:35, Okhwan Lee <ohlee at 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.


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