Can't connect to 5GHz after radar is detected on WRT1900ACS

Installing and Using OpenWrt
1

Devices on my 5Ghz band have randomly disconnected. One interface is still visible to devices but attempting to connect just gives up after a couple of seconds without an error. My guest interface has disappeared completley. This has happened a few times before.

Im running OpenWrt 19.07.6 r11278-8055e38794 / LuCI openwrt-19.07 branch git-21.018.57536-6ba9740. Kernel version 4.14.215.

Looking at the log it appears a radar was detected and the router switched channels but I can't determine why devices now cannot connect to the network. My 2.4Ghz band is still working.

The 5Ghz channel is set to auto at 80Mhz width and I have set the location to United Kingdom.

Restarting the WIFI chipset gets everything back online but I'd like to solve the issue more permenantly.

I found a similar issue here: https://forum.openwrt.org/t/openwrt-18-06-2-on-linksys-wrt3200acm-5-ghz-band-drops/30554/9 .

Here is the log around the time my devices disconnected. My 5Ghz radio is wlan0. I've trimmed it down to focus on wlan0 but can post more if required.

Wed Feb  3 21:27:52 2021 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5260 ht_enabled=0 chan_offset=0 chan_width=3 cf1=5290 cf2=0
Wed Feb  3 21:27:52 2021 daemon.notice hostapd: wlan0: DFS-NEW-CHANNEL freq=5745 chan=149 sec_chan=1
Wed Feb  3 21:27:52 2021 kern.info kernel: [96850.197425] ieee80211 phy0: radar detected by firmware
Wed Feb  3 21:27:52 2021 daemon.info hostapd: wlan0: IEEE 802.11 driver starting channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
Wed Feb  3 21:27:52 2021 daemon.notice hostapd: wlan0: CTRL-EVENT-STARTED-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
Wed Feb  3 21:27:52 2021 daemon.info hostapd: wlan0-1: IEEE 802.11 driver starting channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
Wed Feb  3 21:27:52 2021 daemon.notice hostapd: wlan0-1: CTRL-EVENT-STARTED-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
Wed Feb  3 21:27:52 2021 kern.info kernel: [96850.728982] ieee80211 phy0: channel switch is done
Wed Feb  3 21:27:52 2021 kern.debug kernel: [96850.733858] ieee80211 phy0: change: 0x60
Wed Feb  3 21:27:52 2021 daemon.info hostapd: wlan0-1: IEEE 802.11 driver had channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
Wed Feb  3 21:27:52 2021 daemon.notice hostapd: wlan0-1: CTRL-EVENT-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
Wed Feb  3 21:27:52 2021 daemon.notice hostapd: wlan0-1: AP-CSA-FINISHED freq=5745 dfs=0
Wed Feb  3 21:27:52 2021 daemon.info hostapd: wlan0: IEEE 802.11 driver had channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
Wed Feb  3 21:27:52 2021 daemon.notice hostapd: wlan0: CTRL-EVENT-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
Wed Feb  3 21:27:52 2021 daemon.notice hostapd: wlan0: AP-CSA-FINISHED freq=5745 dfs=0

...

Wed Feb  3 21:58:27 2021 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5260 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5260 cf2=0
Wed Feb  3 21:58:27 2021 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5280 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5280 cf2=0
Wed Feb  3 21:58:27 2021 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5300 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5300 cf2=0
Wed Feb  3 21:58:27 2021 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5320 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5320 cf2=0
2

Try using a channel outside the DFS range.

1 Like
3

I would but there is only channel 42 (36) to pick from that isn't DFS and it has 3 neighbouring networks on it.

I have seen that band C in the 5Ghz range had been taken off the DFS list in the UK meaning channel 155 (149) should be OK to use. It was changed last year but how often does OpenWrt update that sort of thing?

I will give it a go but I do still want to fix the DFS issue ideally.

4

OpenWrt follows the regulatory repository with infrequent updates (to be fair, the regdb is also infrequently updated).

If a change has happened upstream that you want OpenWrt to follow and it hasn't yet, you can submit a patch to bring it up to date.

If upstream has not followed the ruling you're referring to yet, you need to contact the maintainer and submit proof of the changes.

The last change to the GB region was in November, and OpenWrt already has it. From a quick look at the changes, it doesn't sound like the one you're referring to.
https://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git/log/

1 Like
5

How would I go about doing this?

I've reaserched this a bit more and found an OfCom document specifying that DFS requirements have been removed from the 5.8Ghz band (5725-5850MHz - channel 144 to 165). It's specified on page 27 section 5.3.

Still as much as this would solve my problem I would like to get to the root cause. DFS should still work correctly.

6

Early on in the document it is stated that it is a decision paper, and the next steps are to amend the actual laws. I think you need evidence of that step having now occured (or is it still in progress).

Either way, that is a change that upstream doesn't have, so you aren't submitting a patch to OpenWrt. You need to mail the regulatory db maintainers and prove it needs changing.
https://wireless.wiki.kernel.org/en/developers/regulatory/wireless-regdb#sending_updates_to_the_regulatory_database

7

Glad you brought this up though, as Australia often follows the UK for this stuff. Now I've got something to poke the ACMA with.

8

Same issue again last night, woke up to no 5ghz band on my laptop, it still appears on my phone but will not connect.

I had been using the 155 (149) channel without issue until yesterday evening where, for my phone at least, it slowed to about 0.5MB/s down and 10MB/s up.

Taking a look at a WIFI monitor a new 20MHz wide device had sprung up right in the middle of my channel and double my signal strength. Rebooting my phone didnt work so I changed the channel to 128 (116) yesterday evening,

Does anyone have an ideas as to why after a DFS event my 5Ghz band dosen't recover?

Fri Feb  5 03:57:39 2021 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5640 ht_enabled=0 chan_offset=0 chan_width=3 cf1=5610 cf2=0
Fri Feb  5 03:57:39 2021 daemon.notice hostapd: wlan0: DFS-NEW-CHANNEL freq=5745 chan=149 sec_chan=1
Fri Feb  5 03:57:39 2021 kern.info kernel: [13270.609569] ieee80211 phy0: radar detected by firmware
Fri Feb  5 03:57:39 2021 daemon.info hostapd: wlan0: IEEE 802.11 driver starting channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
Fri Feb  5 03:57:39 2021 daemon.notice hostapd: wlan0: CTRL-EVENT-STARTED-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
Fri Feb  5 03:57:39 2021 daemon.info hostapd: wlan0-1: IEEE 802.11 driver starting channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
Fri Feb  5 03:57:39 2021 daemon.notice hostapd: wlan0-1: CTRL-EVENT-STARTED-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
Fri Feb  5 03:57:40 2021 kern.info kernel: [13271.159996] ieee80211 phy0: channel switch is done
Fri Feb  5 03:57:40 2021 kern.debug kernel: [13271.164858] ieee80211 phy0: change: 0x60
Fri Feb  5 03:57:40 2021 daemon.info hostapd: wlan0-1: IEEE 802.11 driver had channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
Fri Feb  5 03:57:40 2021 daemon.notice hostapd: wlan0-1: CTRL-EVENT-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
Fri Feb  5 03:57:40 2021 daemon.notice hostapd: wlan0-1: AP-CSA-FINISHED freq=5745 dfs=0
Fri Feb  5 03:57:40 2021 daemon.info hostapd: wlan0: IEEE 802.11 driver had channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
Fri Feb  5 03:57:40 2021 daemon.notice hostapd: wlan0: CTRL-EVENT-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
Fri Feb  5 03:57:40 2021 daemon.notice hostapd: wlan0: AP-CSA-FINISHED freq=5745 dfs=0
9

Your router is going to keep jumping to a different channel as soon as it detects a radar, you cannot change that. Then, why insist on using a channel, if you know the router is going to jump to another one?

1 Like
10

I have no preference for the channel that I use, I'm merely trying to quick fix the DFS problem by selecting a channel that has less radar interference or that dosen't have DFS restrictions.

The router can change channels five times a day for all I care, the problem is that when it does change channel I cannot connect to the router on 5GHz without rebooting the WIFI chipset which is the primary issue im trying to resolve.

11

Just found this post today, as I found similar events in my routers log about radar being detected and the channel being changed. I am also running on a WRT1900ACS (openwrt-19.07 branch (git-21.189.23240-7b931da)).

The symptoms OP describes are exactly what is happening to me as well. Every few hours or so, one of my SSID's (usually guest or smart) goes offline, and I am unable to rejoin the network on any of my devices (iOS/ Windows/ Android/ etc) until I reboot the router.

@joshkrz did you ever find a solution for this? I am going to set my channel to the highest possible to try to get out of the DFS range, and hope for the best...

12

Take a look at this list of 5 Ghz channels -

1 Like
13

Thank you for the reply. I was actually looking at this last night. I picked channel 161 which is not labeled as DFS in that chart, so hopefully I'm ok. So far so good.. :slight_smile: