Hi, Just set up a Linksys WRT1900 ACS and am trying to use the same channel as my old router(Channel 104, 5520). It appears that LEDE detects a Radar in that frequency:
hostapd: wlan0: DFS-RADAR-DETECTED freq=5520 ht_enabled=0 chan_offset=0 chan_width=3 cf1=5530 cf2=0
I found this strange as my old router never complained. So, I moved down the channels and used channel 60, no RADAR detected but at some point the channel will change back to 36 and I've not found anything in the logs. Any suggestions?
It just did it while I was monitoring, quick check of the log gives me this information:
Fri Apr 20 14:19:59 2018 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5300 chan=60 sec_chan=1, width=1, seg0=58, seg1=0, cac_time=60s
Fri Apr 20 14:20:59 2018 daemon.notice hostapd: wlan0: DFS-CAC-COMPLETED success=1 freq=5300 ht_enabled=0 chan_offset=0 chan_width=3 cf1=5290 cf2=0
Fri Apr 20 14:20:59 2018 daemon.err hostapd: Using interface wlan0 with hwaddr 5a:ef:68:a5:fb:bc and ssid "Test"
Fri Apr 20 14:21:00 2018 kern.info kernel: [57574.269696] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
Fri Apr 20 14:21:00 2018 kern.info kernel: [57574.276150] br-lan: port 2(wlan0) entered forwarding state
Fri Apr 20 14:21:00 2018 kern.info kernel: [57574.281688] br-lan: port 2(wlan0) entered forwarding state
Fri Apr 20 14:21:00 2018 daemon.notice hostapd: wlan0: interface state DFS->ENABLED
Fri Apr 20 14:21:00 2018 daemon.notice hostapd: wlan0: AP-ENABLED
Fri Apr 20 14:21:00 2018 daemon.notice netifd: Network device 'wlan0' link is up
Fri Apr 20 14:21:02 2018 kern.info kernel: [57576.281628] br-lan: port 2(wlan0) entered forwarding state
Fri Apr 20 14:24:58 2018 kern.info kernel: [57812.577050] ieee80211 phy0: radar detected by firmware
Fri Apr 20 14:24:58 2018 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5300 ht_enabled=0 chan_offset=0 chan_width=3 cf1=5290 cf2=0
Fri Apr 20 14:24:58 2018 daemon.notice hostapd: wlan0: DFS-NEW-CHANNEL freq=5180 chan=36 sec_chan=1
Fri Apr 20 14:24:58 2018 kern.info kernel: [57813.178423] ieee80211 phy0: channel switch is done
Fri Apr 20 14:24:58 2018 kern.debug kernel: [57813.183246] ieee80211 phy0: change: 0x40
Fri Apr 20 14:24:59 2018 daemon.info hostapd: wlan0: IEEE 802.11 driver had channel switch: freq=5180, ht=1, offset=1, width=3 (80 MHz), cf1=5210, cf2=0
Fri Apr 20 14:24:59 2018 daemon.notice hostapd: wlan0: AP-CSA-FINISHED freq=5180 dfs=0
Fri Apr 20 14:25:03 2018 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5500 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5500 cf2=0
Fri Apr 20 14:25:03 2018 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5520 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5520 cf2=0
Fri Apr 20 14:25:03 2018 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5540 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5540 cf2=0
Fri Apr 20 14:25:03 2018 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5560 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5560 cf2=0
I assume this means that although it initially decides it can use Channel 60, it changes its mind?
It certainly looks like it began to operate on channel 60, and within five minutes detected radar and, as required by regulation, changed channels. Looks like it also may have ruled out channels 100-112 (5500-5560 MHz).
At least as I understand it, and perhaps only for North America, channels 52-64 and 100-144 are subject to DFS restrictions (there is a gap between those two ranges for wireless use). While weather radar is typically in the channels in the 120s, this doesn't mean that there isn't other radar or services operating or that triggers DFS. As an example, maritime / navigation radar also can operate in these bands.
If the channel number is important to you (point-to-point links, as an example), then I'd chose from the 36-48 or 149-161 ranges.
For some interesting, or exceptionally boring information on DFS, depending on your perspective; http://www.ieee802.org/18/Meeting_documents/2007_Nov/WFA-DFS-Best%20Practices.pdf
Thanks for the reply.
I'm attempting to not use the channels from 36-48(In the UK 144 upwards are not allowed) as there heavily congested in my area. I think there is about 20 of them. I suppose this could be that they are all detecting RADAR and moving down and my old router was not functioning correctly.
Out of interest how large/small would a RADAR need to be and what distance do they travel? It seems that all DFS channels are unusable in my location.
Given that the radars often have power output in the 10-100 kW range and have very narrow-beam antennas, "a long way"
https://www.metcheck.com/WEATHER/radar.asp shows current weather-radar plots coverage. Pick a rainy day -- looks pretty clear there this afternoon! Looking at the current San Francisco report suggests a 100-150 km radius for the "short range" image, and two or four times that for the "long range" image.
A quick check of UK weather RADARS shows the nearest 120KM away, so possible. Although the massive USAF base within 10KM might be more of a problem.
Would one RADAR really take out all DSF channels? Although I imagine the USAF has many RADARS not just the one.
The other possibility is false positives on the radar detection, I'm guessing manufacturers are understandably going to err on the side of "hey there's some weird crap on this channel, must be radar"
That seems likely. The operating frequencies and pulse patterns of military radar are generally not revealed in any detail to the public.
For the 5GHz channel, you want the highest possible channel to be utilized, and Auto should never be used.
As a follow up, whatever DSF frequency I choose it eventually falls back to channel 36. USAF you is bad! Dont tell them I said that.