OpenWrt glitches on Linksys WRT1900ACS


I've been using OpenWrt 21.02.1 on Linksys WRT1900ACSV2 for a couple of weeks.

Two glitches regularly (but not always) happening:

  1. 5GHz wireless drops off (haven't tested 2.4GHz)
  2. After power down / power up with the ON/OFF button, the router reboots to the alternative partition (with the most recent firmware).

Linksys firmware, in turn, works like a charm (no rebooting to OpenWrt partition, no wireless drop-offs).

I spent quite a lot of time / effort to get this far with setting up OpenWrt, but the 2 glitches above really make me consider calling this a day on OpenWrt (on this router). This would be sad since one of the primary reasons to use WRT1900ACS with OpenWrt is for AdGuard Home, which also took effort/time to set up.

Does anyone know if the two glitches can be easily solved through any of the settings or these are to stay? 5GHz dropping off I can put up by hooking up WAP to the router (working only in a wired mode), but unexpected booting to alternative partition is a biggie.


Downgraded to 19.07.08 to see if this solves random restarting into alternative partition and wireless drop-offs.

Hmmm i used that build for sometime, i havent had any trouble. be sure you flash it whitout keep settings, because especialy this build setup DSA which might cause problems. I have had glitches that had my router reboot to alternative partition, but not lately.It can happen when it start up, it doesn't find connection because of improperly configured wan/dhcp/dns settings. When it happens it just reboot try to connect, failing that reboot a couple times, then it reboot to alternative, just like a sort of failsafe mechanism.
Be sure to configure wan dhcp and dns properly, for wifi just use the standard setup

Installed irqbalance. Change 'enabled' from '0' to '1' in 
'/etc/config/irqbalance'. Essential.
Enabled SQM. Significant improvement.
Disabled 802.11w (previously known to provide issues on mwlwifi). 
May not be necessary.
Patched firmware-88w8864 mwlwifi specific high latencies by disabling
tx_amsdu. Essential.
Add in luci > startup > local startup 
(nano /etc/rc.local) the following commands:
# Put your custom commands here that should be executed once
# the system init finished. By default this file does nothing.
#fix wifi bug
echo "0" >> /sys/kernel/debug/ieee80211/phy0/mwlwifi/tx_amsdu
echo "0" >> /sys/kernel/debug/ieee80211/phy1/mwlwifi/tx_amsdu
exit 0

I think you're right, this is eureka moment! I had enabled DNS forwarding to AdGuard Home. AGH was set to start after the rooter boots. Most likely attempts to resolve DNS on boot resulted in errors. This is also proved by the failure to update system clock on boot.

I have also implemented the hints suggested, let me see how stable 5GHz will be going forward.

Many thanks!

1 Like

Let me know if you need further assistance :smiley:

Thanks! Indeed, no rebooting to alternative partition without DNS forwarding. 2.5GHz wifi seems fine, but 5GHz wifi disconnects really frequently.

do you have this active on advanced configuration? because that does this ( btw this option is activated as default settings)
whit disconnects you mean the router loose wifi, or rather your devices( smartphone/pc/whatever) loose connection?

Took me some time to test the suggestions above for fixing the wireless. Now summing up (for future reference if anyone reads through this thread).

I did the following:

  1. Installed and enabled irqbalance
  2. Disabled 802.11w (through LuCI)
  3. Added to local startup in LuCI:
echo "0" >> /sys/kernel/debug/ieee80211/phy0/mwlwifi/tx_amsdu
echo "0" >> /sys/kernel/debug/ieee80211/phy1/mwlwifi/tx_amsdu
exit 0

On 19.07.08. this did not help improving stability of 5GHz, the connection was dropping almost every 5 minutes for devices connected to the router. 2.4GHz was stable, though.

Then I switched to 21.02.1. With all 3 changes above, 5GHz became more stable, connection dropping less frequently (once in an hour) for devices connected to the router.

Then I disabled "Disassociate On Low Acknowledgement" (still on 21.02.1). This was a game changer. 5GHz is now as stable as it can be, did not notice connection dropping for devices connected to the router.

Stiel, many thanks for your help!

PS Cannot mark both posts by Stiel simultaneously as Solution, but both are.

Try increasing the time for Station inactivity limit

It is empty by default. What is the reasonable value?

you should see them, the defaults value,

so default is 300 sec, you can put a value bigger than this, i never changed those value to be honest, just fix dtim interval to 2, then i put

Beacon interval 100 on the 5 ghz, and 150 on 2,5 ghz, to give priority to 5ghz for device when you have both active, device will connect to 5ghz unless you are far, than they will connect to 2,5 ghz.
but to do so, you need to input dtim interval 2 manually, on both instance, and input 100 to give priority 1, 150 priority 2= higher beacon interval less priority.

Thanks a lot, Stiel!

Interestingly, the next day I wrote here that

the router started misbehaving again. 5GHz started disappearing again (not as frequently as earlier, but still a couple of times per day), with no 5GHz wireless network available for the duration of 3-5 minutes (with 5GHz LED lights on the router front panel also going down).

Could it be that this is the [widely] discussed mwlwifi driver behind this?

Probably, maybe try a recent 21.02 snapshot build which includes the mac80211 fix for that issue.

Hmmm. I use the install with LuCI. Are you saying that 21.02. snapshot (without LuCI) has this mac80211 fix whereas install with LuCI has no such fix?

I think only master snapshots to not have LuCI, a quick look at the 21.02 snapshot manifest indicates things to be included.

Thank you. That seems to have done the trick.

A follow-up question re Fragmentation threshold and RTS/CTS Threshold. I can see that the defaults are empty for these fields. Why did you set them to 2346 and 2347? What do these settings control?

personal settings,you can google them and see what they do, its related to congestion anyway, you can use them or not, i use them and always been good.

@route66 btw, if you have problem, be sure you set a band for your wifi, 1-6-11 for 2,5ghz, and stick whit band 36 for 5g, you can try differents bands but its hard you need to. also if you use an high 5ghz band, that caused me problems and disconnects. so usually i stick to band 36, ofc dont leave them on auto.
ill give you screenshot on my settings, just in case.

1 Like

Thanks for interesting suggestion to try the recent snapshot!

I went from OpenWrt 21.02.1 r16325 to OpenWrt 21.02-SNAPSHOT r16392. Offtopic to this thread, but how can I know that this snapshot contains mac80211 fix?

Another off-topic question - the link above is part of this branch This branch seems hidden from the root; if I were to click down from the root to snapshots, I would reach another branch for snapshots Just out of curiosity - what is the difference between the two locations of snapshots?