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dimich

Member

From: Kharkiv, Ukraine

Registered: 2009-11-03

Posts: 607

[SOLVED] iwlwifi: expected VHT, found HT in beacon, disconnect

In the last few days I encountered wireless connection issues and weird NetworkManager behavior ten times: WiFi disconnected, nm-applet asks for PSK to authenticate, despite PSK is stored in corresponding /etc/NetworkManager/system-connections/<ID>.nmconnection.
However, why NetworkManager won't pick up PSK after disconnect is a topic for another post in another subforum. Now I'm trying to investigate the root cause of disconnections. It's made worse by many parameters and vague conditions.

Wireless network I use is provided by ASUS ZenWiFi AC Mini router (50:eb:f6:6a:b0:62) with one satellite (50:eb:f6:6a:d1:0e) connected via ethernet-backhaul.

That's how disconnect looks in dmesg:

[ 4858.410420] wlan0: authenticate with 50:eb:f6:6a:b0:62 (local address=08:d2:3e:08:6d:17)
[ 4858.411403] wlan0: send auth to 50:eb:f6:6a:b0:62 (try 1/3)
[ 4858.452064] wlan0: authenticated
[ 4858.452440] wlan0: associating to AP 50:eb:f6:6a:b0:62 with corrupt beacon
[ 4858.452860] wlan0: associate with 50:eb:f6:6a:b0:62 (try 1/3)
[ 4858.465475] wlan0: RX ReassocResp from 50:eb:f6:6a:b0:62 (capab=0x1511 status=0 aid=3)
[ 4858.468743] wlan0: associated
[ 4858.546042] wlan0: AP 50:eb:f6:6a:b0:62 appears to change mode (expected VHT, found HT) in beacon, disconnect
[ 4858.722779] wlan0: authenticate with 50:eb:f6:6a:d1:0e (local address=08:d2:3e:08:6d:17)
[ 4858.723736] wlan0: send auth to 50:eb:f6:6a:d1:0e (try 1/3)
[ 4858.871002] wlan0: send auth to 50:eb:f6:6a:d1:0e (try 2/3)
[ 4858.872403] wlan0: authenticated
[ 4858.872887] wlan0: associate with 50:eb:f6:6a:d1:0e (try 1/3)
[ 4858.885651] wlan0: RX AssocResp from 50:eb:f6:6a:d1:0e (capab=0x1511 status=0 aid=1)
[ 4858.889094] wlan0: associated
[ 4858.933088] wlan0: Limiting TX power to 24 (27 - 3) dBm as advertised by 50:eb:f6:6a:d1:0e
[ 5160.658685] wlan0: disconnect from AP 50:eb:f6:6a:d1:0e for new auth to 50:eb:f6:6a:b0:62
[ 5160.701054] wlan0: authenticate with 50:eb:f6:6a:b0:62 (local address=08:d2:3e:08:6d:17)
[ 5160.701974] wlan0: send auth to 50:eb:f6:6a:b0:62 (try 1/3)
[ 5160.742078] wlan0: authenticated
[ 5160.742497] wlan0: associating to AP 50:eb:f6:6a:b0:62 with corrupt beacon
[ 5160.742932] wlan0: associate with 50:eb:f6:6a:b0:62 (try 1/3)
[ 5160.755602] wlan0: RX ReassocResp from 50:eb:f6:6a:b0:62 (capab=0x1511 status=0 aid=3)
[ 5160.759925] wlan0: associated
[ 5160.840202] wlan0: AP 50:eb:f6:6a:b0:62 appears to change mode (expected VHT, found HT) in beacon, disconnect

At this time laptop is closer to the router than the satellite. So it connects to the router, disconnects due to "AP appears to change mode (expected VHT, found HT) in beacon", connects to satellite and works some time.
After 5 minutes it tries to switch back to the router (I suppose because of stronger signal) and disconnects again.

I would blame the router, but its configuration hasn't been changed last two or three years. Also no issues on two other laptops with windows, nor on android devices.

Digged into journal and found that "AP appears to change mode" and "associating to AP with corrupt beacon" started to appear on May 01, just after kernel upgraded from 7.0.2.arch1-1 to 7.0.3.arch1-1.
/* Also found ten the same messages on Sep 03 last year. No kernel upgrades were around that day, like the issue appeared and disappeared at the same day with no reason */

Machine: Dell Latitude 5400, Intel(R) Wireless-AC 9560

[   13.808554] iwlwifi 0000:00:14.3: enabling device (0000 -> 0002)
[   13.814370] iwlwifi 0000:00:14.3: Detected crf-id 0x2816, cnv-id 0x1000100 wfpm id 0x80000000
[   13.815077] iwlwifi 0000:00:14.3: PCI dev 9df0/4030, rev=0x312, rfid=0x105110
[   13.815081] iwlwifi 0000:00:14.3: Detected Intel(R) Wireless-AC 9560 160MHz
[   13.827755] iwlwifi 0000:00:14.3: WRT: Overriding region id 0
...
[   13.827787] iwlwifi 0000:00:14.3: WRT: Overriding region id 28
[   13.828121] iwlwifi 0000:00:14.3: loaded firmware version 46.7e3e4b69.0 9000-pu-b0-jf-b0-46.ucode op_mode iwlmvm

Already tried:
* options mac80211 minstrel_vht_only=0
* options iwlwifi power_save=0
* options iwlmvm power_scheme=1
in different combinations. With no effect.

Also going to try linux-lts. However, since the issue is vague, it's unclear how long to test it before conclusion that the issue is not reproduced.

I see that iwlwifi is under active development, and Linux Wireless Mail List would be better place to report the issue. However, I want to collect more information to formulate report more precisely.
Maybe someone encountered the same issue? Also will appreciate for suggestions how to fix it.

Upd1: the same with linux-6.18.26-2-lts. The same with linux-firmware-intel downgraded to 20260309-1.

Upd2: plugged another USB WiFi dongle, captured 802.11 frames. Indeed, "main" AP broadcasted malformed beacon frames (Malformed Packet: IEEE 802.11: length of contained item exceeds length of containing item), 1-byte bigger than satellite beacon frames.
Rebooting the router fixed the issue (at least temporarily). Router already has weekly reboot configured due to known memory leak issues, but this one is something new.

Last edited by dimich (2026-05-04 02:05:54)