5Ghz networks takes longer to connect

Installing and Using OpenWrt
1

I am running Openwrt 22.03 on Archer C7 v2 and everything seems to be fine. I have two SSID, one is running ac standard with 80 Mhz band, the other n standard at 40 mhz band. When I scan my surroundings, I am the only one isung 5Ghz at the channels I set, there are few other stations on 2,4 ghz but nothing too major.

Now, when I start my laptop, it tends to connect to teh 2,4Ghz network because it sees it way sooner (on the order of 30 seconds). I set the priority of the conenction in Network Manager (I am on Kubuntu 22.04) but it just takes quite a long time after a reboot to notice the 5Ghz network.

When I run scannig with linssid, ti sees the 5Ghz network immediately, but it just is not available for selecting in KDE's network manager applet (the strenth of the signal reported by linssid is lower than for 2,4 Ghz bands, but theconnection works fine once estabilished).

Any idea why this might be? I am not usre if OpenWRT or Kubuntu is to blame.

2

If you picked a DFS channel, it will take a minute (literally) to come up, by design. It needs to scan for active radars.

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3

The one minute DFS scanning time mentioned by @Borromini can be seen in the system log (at least if you have enabled a bit debug logging for hostapd/wpad).
From DFS-CAC-START to DFS-CAC-COMPLETED:

Thu Sep 15 22:25:45 2022 daemon.notice hostapd: wlan0: interface state UNINITIALIZED->COUNTRY_UPDATE
Thu Sep 15 22:25:45 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Thu Sep 15 22:25:46 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DFS
Thu Sep 15 22:25:46 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=1, seg0=106, seg1=0, cac_time=60s
Thu Sep 15 22:25:47 2022 daemon.notice netifd: Wireless device 'radio0' is now up
Thu Sep 15 22:26:49 2022 daemon.notice hostapd: wlan0: DFS-CAC-COMPLETED success=1 freq=5500 ht_enabled=0 chan_offset=0 chan_width=3 cf1=5530 cf2=0
Thu Sep 15 22:26:49 2022 daemon.notice netifd: Network device 'wlan0' link is up
Thu Sep 15 22:26:49 2022 daemon.notice hostapd: wlan0: interface state DFS->ENABLED
Thu Sep 15 22:26:49 2022 daemon.notice hostapd: wlan0: AP-ENABLED
4

I see, thanks for pointing that out.. I was indeed using channel 132. When I se it to 36, 5Ghz comes up way more quickly (but still like 5 or ten seconds after 2,4Ghz).

Is there another downside to using the DFS channels apart from this one minute delay ( I assume I would get hit by it just when rebooting OpenWRT, not my computer, right?)

This https://en.wikipedia.org/wiki/List_of_WLAN_channels is a bit puzzling to me. They say that one can use either Power control or DFS, does that mean that if I limited transmit control, I would get rid of the delay?

5

Downside is that the radio will always/regularly monitor for weather radars, and if it detects/misdetects radar, it might shut down the radio if there is no list of fallback alternative channels defined.

See

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