OpenWrt/LEDE Project

  • Status Unconfirmed
  • Percent Complete
  • Task Type Bug Report
  • Category Kernel
  • Assigned To No-one
  • Operating System All
  • Severity High
  • Priority Very Low
  • Reported Version Trunk
  • Due in Version Undecided
  • Due Date Undecided
  • Private
Attached to Project: OpenWrt/LEDE Project
Opened by Konrad Kosmatka - 28.12.2019

FS#2707 - mt7621/ath9k: unreliable AP with hardware encryption

Board: MikroTik Routerboard RBM33G (ramips/mt7621)
Interface: MikroTik R11e-2HPnD (ath9k/ar9582)
Tested versions: 18.06.5, snapshot

Some background: I’ve been using RB433AH & UBNT XR2 (ath5k) as home AP for many years. It was extremely reliable with OpenWRT, LEDE and OpenWRT once again. However, the 802.11g is not sufficient nowadays, so I decided to upgrade. I’ve acquired a RBM33G board and R11e-2HPnD module, but this setup is very unreliable for me.

The bug: At some point, the AP cannot receive (decrypt?) packets from a station, but the connection is still established.


  • It can happen on any active station connected to AP, but only one stalls at a given time (not all of them).
  • AP actually receives data from STA, as the RX byte counter increases, but the RX packet count is typically stuck at the same value. For example, several subsequent calls to `iw wlan0 station dump` show: rx bytes: 12121338 / 12127266 / 12141740, rx packets: 1282 / 1282 / 1282.
  • Driver discards the packets, as the replay counter greatly increases when this bug occurs. (e.g. /sys/kernel/debug/ieee80211/phy0/keys/3/replays: 484947)
  • There is nothing relevant in `dmesg` or `logread`.


  • It happens after several hours of a typical traffic.
  • I can trigger it manually much faster by passing high data throughput between clients (e.g. using iperf).


config wifi-device 'radio0'
        option type 'mac80211'
        option channel '11'
        option hwmode '11g'
        option path 'pci0000:00/0000:00:00.0/0000:01:00.0'
        option htmode 'NOHT'
        option txpower '16'
        option disabled '0'

config wifi-iface 'default_radio0'
        option device 'radio0'
        option network 'lan'
        option mode 'ap'
        option ssid '<SSID>'
        option encryption 'psk2+ccmp'
        option key '<KEY>'

Stations tested:

  • Dell Latitude E7440 with Intel Wireless 7260 (iwlwifi), running linux 5.4.6
  • Dell Latitude E7270 with Intel Wireless 8260 (iwlwifi), running linux 4.19.91
  • RB411U with DBII F20-PRO (ath5k, AR5414), running LEDE 17.01.4 (in WDS link)

What does NOT help:

  • Changing the basic configuration (SSID, key).
  • Disabling 802.11n.
  • Disabling WDS (both AP & STA).
  • Disabling SMP (nosmp kernel cmdline option).
  • Using another version of hostapd, i.e. wpad-mesh.
  • Changing miniPCIe slot on the RBM33G board.
  • Disabling CPU powersave in MikroTik bootloader.


  • Disable the encryption at all, but that’s obviously not an option.
  • Disable hardware encryption with ath9k’s nohwcrypt=1 parameter.

This bug does not occur with software encryption, at least in 802.11g mode. In 802.11n mode, the throughput is limited to a little over 30 Mbps and there are frequent disconnects. Apparently, the CPU is not the limiting factor, as `top` reports usage of approximately 10%.

Unfortunately, this bug renders the AP unusable for me, because I need the best reliability.

I also tested this setup with different board and (so far) I cannot reproduce this bug on RW2458N (ar71xx) & R11e-2HPnD with OpenWRT 18.06.5.

Paul Fertser commented on 29.12.2019 12:18 likely related.
hostapd doesn't seem to be honouring NL80211_EXT_FEATURE_CAN_REPLACE_PTK0 at all, as well as NL80211_EXT_FEATURE_EXT_KEY_ID.


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