CSA to DFS channel and ACS not compatible?

[Aditya Kumar Singh]

On 10/8/24 20:46, gluedig wrote:
> Hi,
> 
> I have 5GHz AP configured with (among other):
> ieee80211h=1
> acs_exclude_dfs=1
> channel=acs_survey
> 
> So ACS chooses non-DFS channel on startup (most commonly 36 or 40).
> 
> Now, I'm trying to switch channel to ex. 52 which is DFS (and not 
> cleared yet) in my regulatory domain (PL) by doing:
> hostapd_cli chan_switch 10 5260 bandwidth=20
> 
> And that results in AP interface going down and up with following prints:
> Tue Oct  8 17:04:49 2024 daemon.debug hostapd: DFS CAC required: (5250, 
> 5270): in range: yes
> Tue Oct  8 17:04:49 2024 daemon.debug hostapd: DFS/CAC to (channel=52, 
> freq=5260, sec_channel_offset=0, bw=20, center_freq1=0)
> Tue Oct  8 17:04:49 2024 daemon.debug hostapd: Restarting all 
> CSA-related BSSes
> Tue Oct  8 17:04:49 2024 daemon.notice hostapd: ath0: AP-DISABLED
> ...
> Tue Oct  8 17:04:50 2024 daemon.notice hostapd: ath0: interface state 
> DISABLED->COUNTRY_UPDATE
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: Previous country code PL, 
> new country code PL
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: Regulatory 
> information - country=PL (DFS-ETSI)
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: 2402-2482 @ 40 
> MHz 20 mBm
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: 5170-5250 @ 80 
> MHz 23 mBm (no outdoor)
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: 5250-5330 @ 80 
> MHz 23 mBm (no outdoor) (DFS)
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: 5490-5590 @ 80 
> MHz 30 mBm (DFS)
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: 5590-5650 @ 40 
> MHz 30 mBm (DFS)
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: 5650-5710 @ 40 
> MHz 30 mBm (DFS)
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: Mode IEEE 
> 802.11a: 5180 5200 5220 5240 5260[RADAR] 5280[RADAR] 5300[RADAR] 
> 5320[RADAR] 5500[RADAR] 5520[RADAR] 5540[RADAR] 5560[RADAR] 5580[RADAR] 
> 5600[RADAR] 5620[RADAR] 5640[RADAR] 5660[RADAR] 5680[RADAR] 5700[RADAR] 
> 5720[DISABLED][RADAR] 5745[DISABLED] 5765]
> Tue Oct  8 17:04:50 2024 daemon.notice hostapd: ACS: Automatic channel 
> selection started, this may take a bit
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: ACS: Scanning 1 / 5
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: ath0: nl80211: scan request
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: nl80211: Passive scan 
> requested
> Tue Oct  8 17:04:50 2024 daemon.debug hostapd: Scan requested (ret=0) - 
> scan timeout 10 seconds
> Tue Oct  8 17:04:50 2024 daemon.notice hostapd: ath0: interface state 
> COUNTRY_UPDATE->ACS
> Tue Oct  8 17:04:50 2024 daemon.notice hostapd: ath0: ACS-STARTED
> ...
> Tue Oct  8 17:04:53 2024 daemon.debug hostapd: ACS: Survey analysis for 
> selected bandwidth 20 MHz
> Tue Oct  8 17:04:53 2024 daemon.debug hostapd: ACS:  * channel 36: total 
> interference = 0.048
> Tue Oct  8 17:04:53 2024 daemon.debug hostapd: ACS:  * channel 40: total 
> interference = 0.0413333
> Tue Oct  8 17:04:53 2024 daemon.debug hostapd: ACS:  * channel 44: total 
> interference = 0.0666667
> Tue Oct  8 17:04:53 2024 daemon.debug hostapd: ACS:  * channel 48: total 
> interference = 0.0493333
> Tue Oct  8 17:04:53 2024 daemon.debug hostapd: ACS: Ideal channel is 40 
> (5200 MHz) with total interference factor of 0.0413333
> Tue Oct  8 17:04:53 2024 daemon.notice hostapd: ath0: ACS-COMPLETED 
> freq=5200 channel=40
> 
> After that it's back on same channel and according to logs CAC on 
> channel 52 is not done at all.
> 
> Is what I'm trying to do supported?
> Should manual channel switch to DFS channel when ACS is configured work ok?
> 
> For context - doing same thing when channel is set manually (even to 
> non-DFS one) works ok - CAC is triggered and new channel is used after 
> being cleared.
> 

Hi,

Are you using latest hostapd? I see the issue is fixed with commit -

36bd75dfd25e ("hostapd: Fix channel switch to a DFS channel")

Prior to this commit, the hostapd behavior is what you are seeing. So 
could you confirm if you have above changes?

> Best regards
> Piotr
> 
-- 
Aditya