2

The Wi-Fi experience where I am right now is usable, but not ideal. The Wi-Fi drops out or reconnects surprisingly often. This is despite 2 to 3 bars out of 3 for signal strength (Wi-Fi icon in gnome-shell).

I am sure there is a problem within the local network, not an internet access problem. I ping the IP address of the local router, and I keep on seeing ping stop and eventually show "Host unreachable".

Question

I am curious about something I noticed, when looking at iw dev wlp2s0 link and iw event -t. I was surprised at how often the channel changed. (I do not know whether this is causing a problem or not).

Some channel switching could be due to DFS. I asked a separate question as to whether I can monitor DFS specifically: Monitor "Dynamic Frequency Selection" (DFS)?

However, I captured logs (below) which show switching between six different 2.4Ghz channels in about six minutes. These channels should not be subject to DFS.

I think I have mostly answered my own question by now. I guess it has to be due to the Wi-Fi access point. I.e. it has been configured to choose a channel automatically. It is just changing... more frequently than I expected.

From what I can see, there is no reason for the AP to be channel-switching here. All I can think is the AP is a bit mad. That is not very interesting because I do not know enough about either the AP, or this particular madness.

So, is there anything obvious I missed here? I.e., is there some other angle I could pursue to investigate or troubleshoot the frequent channel-switching, that is not already shown in this question? (Or is there a well-known problem, or some further information, that might be relevant?)

Context

I do not control the Wi-Fi access point(s) here (nor all the other Wi-FI clients). I cannot look at the Wi-Fi access point(s). The access points and my PC are in fixed locations.

I can see with sudo nmap -sn, that there are only a few Wi-Fi clients connected at a time. It was a quiet period when I captured the logs below; there was only one or two other devices connected.

iw dev wlp2s0 scan finds two different possible connections for the same Wi-Fi network (SSID), and currently one other SSID.

Looking at the nmap results, I think there are at most two Wi-Fi access points. But most likely there is one dual-band Wi-Fi access point, and one wired-only modem/router. (nmap showed IP addresses .2 and .1 with MAC addresses belonging to Ruckus Wireless and Technicolor. The next lowest IP address that nmap found was .13).

The Wi-Fi network requires authentication through Sky's "The Cloud" brand, which uses a captive portal. Maybe this system brings its own issues :-).

BSS e0:10:7f:1f:d0:58(on wlp2s0) -- associated
    freq: 2452
    capability: ESS ShortPreamble ShortSlotTime (0x0421)
    signal: -46.00 dBm
    last seen: 1163 ms ago
    Information elements from Probe Response frame:
    SSID: _The Cloud
    DS Parameter set: channel 9
    ...
BSS e0:10:7f:5f:d0:58(on wlp2s0)
    last seen: 2285.242s [boottime]
    TSF: 3507100069 usec (0d, 00:58:27)
    freq: 2452
    beacon interval: 100 TUs
    capability: ESS Privacy ShortPreamble ShortSlotTime (0x0431)
    signal: -45.00 dBm
    last seen: 1160 ms ago
    Information elements from Probe Response frame:
    SSID: 
    Supported rates: 1.0* 2.0* 5.5* 11.0* 
    DS Parameter set: channel 9
    ...
BSS e0:10:7f:1f:d0:5c(on wlp2s0)
    freq: 5680
    beacon interval: 100 TUs
    capability: ESS ShortSlotTime (0x0401)
    signal: -57.00 dBm
    last seen: 155 ms ago
    Information elements from Probe Response frame:
    SSID: _The Cloud
    DS Parameter set: channel 136
    ...
BSS e0:10:7f:5f:d0:5c(on wlp2s0)
    last seen: 2263.535s [boottime]
    TSF: 2970025 usec (0d, 00:00:02)
    freq: 5680
    beacon interval: 100 TUs
    capability: ESS Privacy SpectrumMgmt ShortSlotTime (0x0511)
    signal: -48.00 dBm
    last seen: 22867 ms ago
    Information elements from Probe Response frame:
    SSID: 
    Supported rates: 6.0* 9.0 12.0* 18.0 24.0* 36.0 48.0 54.0 
    DS Parameter set: channel 136
    ...

BSS b0:c5:54:bd:ea:4f(on wlp2s0)
    last seen: 2276.958s [boottime]
    TSF: 167990579532 usec (1d, 22:39:50)
    freq: 2412
    beacon interval: 100 TUs
    capability: ESS Privacy ShortSlotTime (0x0411)
    signal: -97.00 dBm
    last seen: 9444 ms ago
    Information elements from Probe Response frame:
    SSID: TALKTALK-BDEA4F
    Supported rates: 1.0* 2.0* 5.5* 11.0* 9.0 18.0 36.0 54.0 
    DS Parameter set: channel 1
    ...

Channel-switching logs

$ while true; do date; iw dev wlp2s0 link; read; done

[this output has been edited to only include the channel information]

Thu  4 Apr 14:46:16 BST 2019
Connected to e0:10:7f:1f:d0:58 (on wlp2s0)
    SSID: _The Cloud
    freq: 2452

Thu  4 Apr 14:47:16 BST 2019
Not connected.

Thu  4 Apr 14:48:16 BST 2019
Connected to e0:10:7f:1f:d0:58 (on wlp2s0)
    SSID: _The Cloud
    freq: 2432

Thu  4 Apr 14:49:16 BST 2019
Connected to e0:10:7f:1f:d0:58 (on wlp2s0)
    SSID: _The Cloud
    freq: 2447

Thu  4 Apr 14:50:16 BST 2019
Connected to e0:10:7f:1f:d0:58 (on wlp2s0)
    SSID: _The Cloud
    freq: 2462

Thu  4 Apr 14:51:16 BST 2019
Connected to e0:10:7f:1f:d0:58 (on wlp2s0)
    SSID: _The Cloud
    freq: 2422

Thu  4 Apr 14:51:34 BST 2019
Connected to e0:10:7f:1f:d0:58 (on wlp2s0)
    SSID: _The Cloud
    freq: 2417

Thu  4 Apr 14:52:34 BST 2019
Connected to e0:10:7f:1f:d0:58 (on wlp2s0)
    SSID: _The Cloud
    freq: 2432

iw event -t | grep -v scan is also very busy:

1554385601.404654: wlp2s0 (phy #0): CQM event: beacon loss
1554385601.507239: wlp2s0 (phy #0): CQM event: beacon loss
1554385601.609473: wlp2s0 (phy #0): CQM event: beacon loss
1554385601.711916: wlp2s0 (phy #0): CQM event: beacon loss
1554385601.814282: wlp2s0 (phy #0): CQM event: beacon loss
1554385601.940671: wlp2s0: del station e0:10:7f:1f:d0:58
1554385601.946807: wlp2s0 (phy #0): deauth 10:02:b5:4d:e4:0f -> e0:10:7f:1f:d0:58 reason 4: Disassociated due to inactivity
1554385601.947040: wlp2s0 (phy #0): disconnected (local request) reason: 4: Disassociated due to inactivity
1554385602.069937: wlp2s0: new station e0:10:7f:1f:d0:5c
1554385602.213051: wlp2s0: del station e0:10:7f:1f:d0:5c
1554385602.217220: wlp2s0 (phy #0): auth: timed out
1554385603.733933: wlp2s0: new station e0:10:7f:1f:d0:58
1554385603.953117: wlp2s0: del station e0:10:7f:1f:d0:58
1554385603.957185: wlp2s0 (phy #0): auth: timed out
1554385638.448036: wlp2s0: new station e0:10:7f:1f:d0:58
1554385638.559597: wlp2s0 (phy #0): auth e0:10:7f:1f:d0:58 -> 10:02:b5:4d:e4:0f status: 0: Successful
1554385638.566516: wlp2s0 (phy #0): assoc e0:10:7f:1f:d0:58 -> 10:02:b5:4d:e4:0f status: 0: Successful
1554385638.566669: wlp2s0 (phy #0): connected to e0:10:7f:1f:d0:58
1554385638.568375: wlp2s0 (phy #0): CQM event: RSSI went above threshold
1554385661.697961: wlp2s0: unknown event 110 (ch_switch_started_notify)
1554385664.081713: wlp2s0: del station e0:10:7f:1f:d0:58
1554385664.086119: wlp2s0 (phy #0): deauth 10:02:b5:4d:e4:0f -> e0:10:7f:1f:d0:58 reason 4: Disassociated due to inactivity
1554385664.086235: wlp2s0 (phy #0): disconnected (local request) reason: 4: Disassociated due to inactivity
1554385667.703118: wlp2s0: new station e0:10:7f:1f:d0:58
1554385667.707214: wlp2s0 (phy #0): auth e0:10:7f:1f:d0:58 -> 10:02:b5:4d:e4:0f status: 0: Successful
1554385667.724730: wlp2s0 (phy #0): assoc e0:10:7f:1f:d0:58 -> 10:02:b5:4d:e4:0f status: 0: Successful
1554385667.724853: wlp2s0 (phy #0): connected to e0:10:7f:1f:d0:58
1554385667.728126: wlp2s0 (phy #0): CQM event: RSSI went above threshold
1554385677.672865: wlp2s0: unknown event 110 (ch_switch_started_notify)
1554385679.618562: wlp2s0: unknown event 88 (ch_switch_notify)
1554385693.740384: wlp2s0: unknown event 110 (ch_switch_started_notify)
1554385695.890181: wlp2s0: unknown event 88 (ch_switch_notify)
1554385710.831624: wlp2s0: unknown event 110 (ch_switch_started_notify)
1554385711.855320: wlp2s0: unknown event 88 (ch_switch_notify)
... continuing similarly ...
1554386103.006501: wlp2s0: unknown event 110 (ch_switch_started_notify)
1554386105.155613: wlp2s0: unknown event 88 (ch_switch_notify)
1554386284.050009: wlp2s0: unknown event 110 (ch_switch_started_notify)
1554386286.199094: wlp2s0: unknown event 88 (ch_switch_notify)
1554386300.117247: wlp2s0: unknown event 110 (ch_switch_started_notify)
1554386302.266779: wlp2s0: unknown event 88 (ch_switch_notify)

Software & hardware used

  • Linux 5.0.4-200.fc29.x86_64
  • NetworkManager 1.12.6-5.fc29.x86_64
  • wpa_supplicant 2.7-1.fc29.x86_64
  • Intel Corporation Wireless 7265 (rev 59)
  • iwlwifi
    • iwlwifi 0000:02:00.0: enabling device (0000 -> 0002)
    • iwlwifi 0000:02:00.0: loaded firmware version 29.1044073957.0 op_mode iwlmvm
    • iwlwifi 0000:02:00.0: Detected Intel(R) Dual Band Wireless AC 7265, REV=0x210
    • ieee80211 phy0: Selected rate control algorithm 'iwl-mvm-rs'
  • Got a smartphone? Get an app to search for the access points and monitor what frequency they're on. – K7AAY Apr 4 at 20:47
3

Given that the BSSID differs only in one bit (0x5c vs 0x58), it's almost certainly a single dual-band AP.

There don't seem to be any sources of interference. Thus I think what you're seeing is just the automatic channel selection algoritm in the AP gone completely insane. I'd guess the algorithm is not very smart and when all of the channels seem more or less equally good (noise-wise), it always picks the current "best" one, even though the differences between the channels are minuscule and random.

Anyway, the bad news is that there's not much you can do with it from a client perspective. If the AP wants to switch channels all the time, all clients have to play along.

If you're feeling adventurous, you could create your own WLAN with your machine as the AP just to occupy some of the channels and hopefully steer the real AP towards a single channel. It depends on your WLAN card if it can do AP and client mode at the same time, but perhaps you can use your phone as the "noise generator". Note that running your own Wi-Fi network might not be allowed wherever you are.

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