WAN speed on AVM FRITZ!Box 4040


I run openwrt behind a cable modem. My provider provides me with a 500Mbit download / 25Mbit upload connection. With openwrt the speed is only 120-230Mbit.
After a restart of the openwrt router the speed of the connection increases for about 10 seconds to 500Mbit only to break in again.
I have the same behaviour when I reset all settings to factory defaults and update all packages.

I'm using OpenWrt 19.07.2 and wonder what other possibilities of diagnosis you would suggest or if you have any solutions for me.

Do you get similar results running the speed test with your computer directly connected to the cable modem?

My pc is connected with ethernet to the openwrt router. In between there is a 5port switch.
Because my openwrt router is located right next to my cabel modem, I connected the switch with the PC directly to the cabel modem. With this configuration the download speed is constant at 502Mbit over a large time periode ( >10 minutes )
This was to avoid that the ethernet port on the pc, the ethernet cable or the switch is the limiting factor.

I have a similar issue with the FB4040 (400/20 MBit down/up provided), did some tests:
Cable Modem (Connect Box) in bridged mode,
FB4040 with Openwrt 19.07.2 : U/D = 150/20

Cable Modem as router, (FB4040 not involved): U/D = 400/20

Cable Modem back to bridged mode,
Openwrt 18.06.8: U/D = (almost 400)/20

So, I decided to stay at Openwrt 18.06.8, waiting for the next 19.07.x release.
I will give the next release a try, but have no great hope for things getting better (faster)


Thanks for the feedback Thomas.
Currently playing with the idea to go back to stock firmware.
It's good to know that the described behaviour does not occur at Openwrt 18.06.8 :slight_smile:

I'll do a rollback to 18.06.08 and if that doesn't help there is still the option with the stock firmware

After a rollback to the stock firmware my WAN<->LAN Speed is at it should be. Let's see if future versions fix the problem.

Same here, FB4040 slow WAN-speed with openwrt 18.06.4, 19.07.3 and daily from yesterday.
Connection capable of 400/200: with PC direct or fb4040 stock-FW 7.14 ~ 400/200 fine, with openwrt 200/80 with some peaks up to 280/100. Tested with wget files from speedtest.belwue.net and iperf3 to various servers. No difference if "Software/Hardware flow offloading" checked or not.

Same speed problem here with the latest 19.07.3. Going back to stock firmware.

I've got the same problem with 19.07.3
Direct connection to the cable modem or the fb 4040 with stock firmware are fine.

I've done an speedtest via iperf3 directly on the FritzBox via SSH and got nearly full internet speed. The same speedtest via an wired connected notebook (1 Gbit/s full duplex) droped my internet speed to 1/5. I think it must have something to do with NAT-performance.

Update: Also the same problem with the latest development snapshot from 6th of July.

Good morning here from Germany!
I think I've resolved the problem. It has to do with the cpu governor scaling setting. It's set to "ondemand" which is good for high performance cpus respectively in laptops or desktops. I achieved nearly gigabit speed with the following settings:

  1. Enable "Software flow offloading" in Network -> Firewall -> Routing/NAT Offloading
  2. Add the following line to System -> Startup -> Local Startup before 'exit 0'
    echo performance > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
  3. Disable SQM QoS if you are using it!
  4. Install the irqbalance package. System -> Software -> Filter irqbalance -> Install
  5. Reboot your FritzBox.

Now test your internet speed.

Kind Regards

Update: Install irqbalance package.


The above steps from citydweller solved the problem. Now i get nearly gigabit (around 850Mbit) speed. Awesome work!
Thanks for that.

Best Regards

I have tried it and it has been removed again because it gives me that I have mini connection cuts.
I will try again and I will be attentive to the comments here, but I had the sensation of instability

Another FB4040 victim here ...
Software or Hardware flow offloading ?
(screenshot is from 18.06.8)


Hardware flowoffloading is so far restricted to mt7621, which is the only SOC to provide the necessary driver support (that might change in the future, but not anytime soon).

1 Like

Now i'm using 19.07.3 and with those settings it's doing fine, even faster than stock avm-7.14 before - 500/200 mbps in average now. Thanks for the hint.


I've just bought a Fritz!Box 4040 and installed OpenWrt 19.07.3 r11063-85e04e9f46 / LuCI openwrt-19.07 branch git-20.136.49537-fb2f363.
And I have a fiber connection, 100/100. The problem is that the Wifi connection is really slow on both 2.4 GHz and 5 GHz.
When standing three feet (1m) from the router I get a download speed of about 50 Mbit/s on the 2.4 GHz freq and about 60 Mbit/s on the 5 GHz freq. Is this normal?

Thanks in advance for the help.