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pe1chl
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DFS and scan list + auto frequency

Thu Nov 05, 2020 5:55 pm

In another attempt to get DFS working on a newly installed wAP ac (before I throw in the towel and disable DFS, as it usually goes...) I tried this setup:
set [ find default-name=wlan2 ] band=5ghz-a/n/ac \
    channel-width=20/40mhz-Ce country=netherlands disabled=no distance=\
    indoors frequency=auto installation=indoor mode=ap-bridge scan-list=DFS
where the scan-list DFS contains:
add band=5ghz-a/n/ac extension-channel=Ce frequency=5540 list=DFS name=ch108 \
    width=20
add band=5ghz-a/n/ac extension-channel=Ce frequency=5500 list=DFS name=ch100 \
    width=20
add band=5ghz-a/n/ac extension-channel=Ce frequency=5660 list=DFS name=ch132 \
    width=20
I would have hoped that it would automatically pick a channel from the list (100,108,132) and
check if radar is on the frequency, and of so it would search again and land on another channel.

However, it always selects 5540 and after:
wlan2: radar detected on 5540000
it just disables the interface for some time (detecting radar) and after it finds nothing it continues
to operate on 5540. It never switches to one of the other channels.

Is my understanding of the DFS process wrong? When I use a scanlist on 2 GHz (I normally make
one with channels 1-6-11 and select auto) it finds a random channel from these 3. Of course there
is no DFS on that band, but it appears that the auto frequency on 5 GHz does not even try to
find a suitable channel but always selects the first one from the list. When I open the status tab
of a 2 GHz interface and then disable/enable it I see it quickly look at the 3 frequencies and then
stick on one. At 5 GHz I do not see this happen, it always selects the first one and never moves.

Is this a bug or is it intended functionality? I run 6.47.7 on it.
 
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bpwl
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Re: DFS and scan list + auto frequency

Thu Nov 05, 2020 6:49 pm

This works for me on SXTsq ac (not set to "auto", just had set the frequency 5540). By radar detect the DFS list is used top down. It's not 100% clear if the list continues or not, with the second radar detection later on. (It's too long ago to reconstruct. Reboot and any modification restarts everything. I removed the source of false posities (wAP ac on 5220) in my setup, so no recent incidents available)

Differences are: ROS 6.45.6, SXTsq, frequency set to 5540, installation = any
The 5540 will not be checked as possible solution on radar detect, but another from the list. (next? can't tell for sure)
Is "auto" just checking every freq in the channel list, and your first one (5540) passes the radar test ?????
In my list 5500 is the first , 5660 is the next after 5540. List is 5500,5540, 5660, 5580
Feb/20/2020 22:18:31 dude,event syslog: 192.168.20.5: wireless,info wlan1: radar detected on 5540000
Feb/20/2020 22:18:31 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:7B@wlan1: disconnected, disabling
Feb/20/2020 22:18:31 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:A5@wlan1: disconnected, disabling
Feb/20/2020 22:18:31 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:B3@wlan1: disconnected, disabling
Feb/20/2020 22:18:33 dude,event syslog: 192.168.20.5: wireless,debug wlan1: must select channel
Feb/20/2020 22:18:33 dude,event syslog: 192.168.20.5: wireless,debug wlan1: radar reported on 5540000
Feb/20/2020 22:18:33 dude,event syslog: 192.168.20.5: wireless,debug wlan1: selected channel 5660000
Feb/20/2020 22:18:33 dude,event syslog: 192.168.20.5: wireless,debug wlan1: search for radars on 5660000
Feb/20/2020 22:19:33 dude,event syslog: 192.168.20.5: wireless,debug wlan1: no radar detetected, start network
...
Feb/12/2020 18:42:55 dude,event 
Feb/12/2020 20:11:54 dude,event syslog: 192.168.20.5: wireless,info wlan1: radar detected on 5540000
Feb/12/2020 20:11:54 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:7B@wlan1: disconnected, disabling
Feb/12/2020 20:11:54 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:A5@wlan1: disconnected, disabling
Feb/12/2020 20:11:54 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:B3@wlan1: disconnected, disabling
Feb/12/2020 20:11:56 dude,event syslog: 192.168.20.5: wireless,debug wlan1: must select channel
Feb/12/2020 20:11:56 dude,event syslog: 192.168.20.5: wireless,debug wlan1: radar reported on 5540000
Feb/12/2020 20:11:56 dude,event syslog: 192.168.20.5: wireless,debug wlan1: selected channel 5660000
Feb/12/2020 20:11:56 dude,event syslog: 192.168.20.5: wireless,debug wlan1: search for radars on 5660000
Feb/12/2020 20:12:56 dude,event syslog: 192.168.20.5: wireless,debug wlan1: no radar detetected, start network
...
but I also have this
...
Jun/19/2020 13:24:28 dude,event syslog: 192.168.20.5: wireless,info wlan1: radar detected on 5540000
Jun/19/2020 13:24:28 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:7B@wlan1: disconnected, disabling
Jun/19/2020 13:24:28 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:A5@wlan1: disconnected, disabling
Jun/19/2020 13:24:28 dude,event syslog: 192.168.20.5: wireless,info xx:xx:xx:A7:EB:B3@wlan1: disconnected, disabling
Jun/19/2020 13:24:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: must select channel
Jun/19/2020 13:24:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: radar reported on 5540000
Jun/19/2020 13:24:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: selected channel 5500000
Jun/19/2020 13:24:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: search for radars on 5500000
Jun/19/2020 13:25:22 dude,event syslog: 192.168.20.5: wireless,info wlan1: radar detected on 5500000
Jun/19/2020 13:25:25 dude,event syslog: 192.168.20.5: wireless,debug wlan1: must select channel
Jun/19/2020 13:25:25 dude,event syslog: 192.168.20.5: wireless,debug wlan1: radar reported on 5540000
Jun/19/2020 13:25:25 dude,event syslog: 192.168.20.5: wireless,debug wlan1: selected channel 5500000
Jun/19/2020 13:25:25 dude,event syslog: 192.168.20.5: wireless,debug wlan1: search for radars on 5500000
Jun/19/2020 13:25:27 dude,event syslog: 192.168.20.5: wireless,info wlan1: radar detected on 5500000
Jun/19/2020 13:25:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: must select channel
Jun/19/2020 13:25:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: radar reported on 5540000
Jun/19/2020 13:25:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: selected channel 5500000
Jun/19/2020 13:25:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: search for radars on 5500000
Jun/19/2020 13:26:30 dude,event syslog: 192.168.20.5: wireless,debug wlan1: no radar detetected, start network
...
other device, different list
...
Jun/28/2020 19:09:05 dude,event syslog: 192.168.20.12: wireless,info debug: wlan1: radar detected on 5540000
Jun/28/2020 19:09:05 dude,event syslog: 192.168.20.12: wireless,info debug: xx:xx:xx:A7:EB:73@wlan1: disconnected, disabling
Jun/28/2020 19:09:09 dude,event syslog: 192.168.20.12: wireless,debug debug: wlan1: must select channel
Jun/28/2020 19:09:09 dude,event syslog: 192.168.20.12: wireless,debug debug: wlan1: radar reported on 5540000
Jun/28/2020 19:09:09 dude,event syslog: 192.168.20.12: wireless,debug debug: wlan1: selected channel 5580000
Jun/28/2020 19:09:09 dude,event syslog: 192.168.20.12: wireless,debug debug: wlan1: search for radars on 5580000
Jun/28/2020 19:10:09 dude,event syslog: 192.168.20.12: wireless,debug debug: wlan1: no radar detetected, start network
 
pe1chl
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Re: DFS and scan list + auto frequency

Thu Nov 05, 2020 7:15 pm

Ok thanks for info. It is a different chip and a different RouterOS version, maybe that has some influence as well.
I am sure that those channels I put in the list (100,108,132) do not have radar, but there occasionally is misdetection due to nearby phones transmitting on 3G/4G.
Best solution is probably to disable DFS. As it is now, it just isn't a workable system (not only for MikroTik, other manufacturers have similar misdetection issues)...
 
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bpwl
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Re: DFS and scan list + auto frequency

Thu Nov 05, 2020 8:01 pm

Well outdoor you have no choice in Europe (ETSI). There are no U-NII-3 ( 5.8GHz) channels allowed. And channels 36-48 (+DFS 52-64) are indoor-only.

First device was SXT sa5 ac, second SXTsq ac.
 
pe1chl
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Re: DFS and scan list + auto frequency

Fri Nov 06, 2020 12:37 pm

Of course we all want a DFS system that does what it is supposed to do: detect the presence of other band users (weather radar) and switch to another frequency when they are detected.
But it seems the manufacturers are unable to make it. What we get is a system that makes false detections (affected by nearby mobile phones transmitting on 2G/3G/4G) and even worse: when it makes such a false detection it does not exhibit reasonable behavior. e.g. in my case I want it to try only those 3 channels, not leave it free to choose another channel and then select ch116 or ch124 where the weather radar is actually present, so it will get a DFS hit AGAIN and waste more time. But the combination of auto frequency selection, a scan list, and DFS enabled does not seem to work correctly.

Faced with that situation, and without any help from the manufacturer, the only recourse is to disable DFS and operate it on the channels where there is no radar.
It is not that the users are not willing to operate with DFS, it just is that the manufacturers do not provide a working DFS solution.
 
johnmoore
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Joined: Fri Sep 12, 2014 3:08 pm

Re: DFS and scan list + auto frequency

Tue Dec 01, 2020 6:25 pm

How can one completly disable the DFS feature? I was under the impression that one can not!

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