TPLink C7 - SSIDs vanish and re-appear in WIFI scans

michib · March 31, 2022, 7:03am

Hello,

I've got two new TP Link Archer C7 v5 to use them as APs with OpenWRT. Since setting them up for the first time (either stock FW or OpenWRT), I notice the following when scanning vor WIFI SSIDs with my mobile devices:

The SSIDs advertised by the TP Links are periodically vanishing and re-appearing in the lists, period is about 10-20s. Often it takes a while before they appear for the first time. In Wifi Analyzer for Android, for instance, the according curve showing channel vs. signal strength falls and rises periodically. This is independent of signal strength, even if I stand directly near the TP Link device.

However, all SSIDs of my other AP/router devices (Zyxel, Linksys, Asus) are continously shown without interruption.

Is this normal? A hint for further trouble (connection losses?)? A thing that can be parameterized?

Thanks for any answers on this.

Best
Michael

golialive · March 31, 2022, 7:09am

Hey there.

Check syslog for whatever seems odd.
My belly tells me this could be related to radar detection (DFS), but my brain tells me this can't be because DFS would (if I remember correctly) just turn of a colliding device, not just drop for a couple of seconds.

Regards,
Stephan.

eduperez · March 31, 2022, 7:59am

Did you configure a specific channel, or did you set it as "auto"?

michib · March 31, 2022, 10:38am

Thanks for your answers!

syslog seems to be ok, mostly WPA handshaking etc.
I manually set the channels, but it also appears when on auto.

It is not exactly periodically, but still short term.
What I didn't mention: I am running two SSIDs on 2.4GHz. Here, sometimes both are shown, or none, or either of them. The second SSIDs seems to vanish more often.

Now having one device on stock FW (only 1 SSID) and one on OpenWRT (2 SSIDs), the one with stock FW seems to be more stable in this sense.

However, once connected, the connection is stable.
A Zyxel NWA1123-AC with 2 SSIDs is constantly shown in Wifi Analyzer with comparible signal strength.

Could this be some kind of advertising interval that is configured here?

walterav · March 31, 2022, 1:12pm

Maybe related:

Also only on 2,4GHz not on 5GHz?

michib · March 31, 2022, 8:11pm

I would say, yes, it is 2.4GHz only.

In Wifi Analyzer, also other SSIDs from neighbor APs disappear and reappear. Here, I would assume it is related to low signal strength.

I would also say, that with only one SSID per channel, it is more stable.

anon89577378 · March 31, 2022, 8:34pm

SSH in to the router and run -

cat /etc/config/wireless

Redact the passwords in the "option key" sections.

Post the results in preformatted text, by using the icon highlighted in red...

walterav · April 1, 2022, 7:37am

Since 21.02.2 also running multiple SSID's on 2,4GHz but the main/first SSID mostly dissapears. The other SSID's on the 2,4GHz do show up and dissapear as well but not all at the same time.

anon89577378 · April 1, 2022, 7:49am

I haven't seen it on my C7 V2 running 21.02.n...which also uses ath9k/ath10k.

May be model/version specific.

I'd like to see the OP's wireless configs.

michib · April 1, 2022, 10:26am

So here is my wireless config

config wifi-device 'radio0'
        option type 'mac80211'
        option path 'pci0000:00/0000:00:00.0'
        option band '5g'
        option htmode 'VHT80'
        option cell_density '0'
        option txpower '20'
        option channel '44'

config wifi-iface 'default_radio0'
        option device 'radio0'
        option network 'lan'
        option mode 'ap'
        option key '...'
        option ieee80211r '1'
        option mobility_domain '1000'
        option ft_over_ds '1'
        option ft_psk_generate_local '1'
        option encryption 'psk2'
        option ssid 'bagaNet5'

config wifi-device 'radio1'
        option type 'mac80211'
        option path 'platform/ahb/18100000.wmac'
        option band '2g'
        option htmode 'HT20'
        option cell_density '0'
        option txpower '20'
        option channel '1'

config wifi-iface 'default_radio1'
        option device 'radio1'
        option network 'lan'
        option mode 'ap'
        option key '...'
        option ieee80211r '1'
        option mobility_domain '1000'
        option ft_over_ds '1'
        option ft_psk_generate_local '1'
        option encryption 'psk2'
        option ssid 'bagaNet'

config wifi-iface 'wifinet2'
        option device 'radio1'
        option mode 'ap'
        option ssid 'fibaNet'
        option encryption 'psk-mixed'
        option key '...'
        option network 'FiBaNet'
        option disabled '1'

config wifi-iface 'wifinet3'
        option device 'radio0'
        option mode 'ap'
        option ssid 'bagaNet5_WZ'
        option encryption 'psk2'
        option key '...'
        option ieee80211r '1'
        option mobility_domain '1000'
        option ft_over_ds '1'
        option ft_psk_generate_local '1'
        option network 'lan'

config wifi-iface 'wifinet4'
        option device 'radio1'
        option mode 'ap'
        option ssid 'bagaNet_WZ'
        option encryption 'psk-mixed'
        option wmm '0'
        option key '...'
        option ieee80211r '1'
        option mobility_domain '1000'
        option ft_over_ds '1'
        option ft_psk_generate_local '1'
        option network 'lan'

thedukesd · April 1, 2022, 4:26pm

Does the signal value for the other APs changes when particular APs don't show up in WiFi Analyzer?

With Android 10 and 11 you need to disable "WiFi scan throttling" to make WiFi Analyzer work properly. Not sure if you have to do it for other versions of Android.

With my Samsung smartphone after like 15s WiFi Analyzer plain stop scanning, with WiFi scan throttlin disable it works fine (it does show some dramatic signal changes... signal changes that I'm only seeing with Android devices while with anything else it's nowhere that dramatical).

Did you checked with something else except WiFi Analyzer? Something like wavemon in Linux and with a wifi card that has proper antennas (not usb dongle without external antennas)?

L.E.: To be honest you need to check the link stability with a client connected to the AP(s) that vanish. If the hardware is problematic you might not always get something in the logs (some bad caps, bad soldered caps (that well might fall off if touched) might cause something like this).
Obvious problems will be visible with mtr on an ip and at some moments you will see all nodes losing packets; but this is an obvious problem...

anon89577378 · April 1, 2022, 8:35pm

Try WPA2-PSK encryption with AES.

Turn WMM on.

michib · April 2, 2022, 11:45am

Thanks for your hints!

I use Android 8, not aware of a WIFI throttle there.

WMM was off accidentially, but only on one SSID. Does not change it. PSK-mixed is due to some backward compatibility...

When connected, the connection appears to be stable. However, I experienced lost network connectivity from time to time although the wifi signal was shown with full strength. This occured with stock FW and OpenWRT.

I will return the devices.

walterav · April 2, 2022, 1:21pm

Hopefully ontopic enough as a Ath9k user...

Is WMM needed in 20MHz bandwidth mode, from what I read for HT 40/80/160 mode it is mandated. Its something available since the 802.11g era but I haven't seen a OpenWrt device where it is on be default?

As for security in my situation it was already WPA2-PSK CCMP only, I guess this would not have an effect on 'OP' his config. Besides for legacy he has a mixed situation.

@michib Could you make a seperate SSID for the WPA2-TKIP need?

However on the 5GHz in my situation only WPA3-SAE is used and is always visible... will revert to WPA2-CCMP in a couple of weeks and see if these SSID will also start dis/re-appearing.

slh · April 2, 2022, 10:15pm

WMM is a requirement for 802.11n and up, disabling locks you to sub-54-MBit/s (802.11g); it's unrelated to the channel bandwidth.

walterav · April 7, 2022, 7:34am

WMM is indeed enabled as a checkbox on most off my device in webinterface luci, however the option is not explicitly mentioned as enabled in /etc/config/wireless?

anon89577378 · April 7, 2022, 7:43am

Correct...it isn't.

walterav · April 30, 2022, 3:43pm

@michib
Have you already tried 21.02.3, it seems that 2,4GHz SSID gets detected & connected a lot faster for the Unifi AP PRO compared to 21.02.1/2?

Cannot say its fixed yet.

walterav · May 8, 2022, 11:34am

Almost 3 weeks later it seems fixed for me on 21.02.3.

michib · May 8, 2022, 11:47am

Sounds good!

I got rid of the TP-Link devices and had very bad experiences with a mesh built with fritz!box and fritz!repeater devices.

Now I am changing to Unifi devices with original FW/SW, hope that improves.