Slow speedtest results on router compare to LAN clients

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New Around Here
Hi There.

After several years with NetGear and DD-WRT, I am so glad to come back to the Asus Routers and Merlin.
I recently got the AX88U connected to a 1gb up/down fiber connection. Of course, as soon as I got the router I immediately
installed the Asuswrt-Merlin build and started tinkering with it.

One of the first things I did is speed test using the spdMerlin script. I immediately noticed that the speed is lower than usual:

Latency: 1.03 ms (0.89 ms jitter)
Download: 389.80 Mbps (data used: 382.9 MB)
Upload: 424.54 Mbps (data used: 396.0 MB)
Packet Loss: 0.0%

I thought it might have to do with QOS settings (probably not, because it is directly on the router), so turn on and off just for the sake of testing
but the same results.

I sshed to my ubuntu machine (connected to the router over ethernet cable) and tested the speed again using speedtest-cli:

Testing download speed................................................................................
Download: 619.04 Mbit/s
Testing upload speed......................................................................................................
Upload: 359.20 Mbit/s

I am going to ignore for now the fact that both are nowhere near the promised 1gb up/down speed (with the dd-wrt I used to get 750mbit/500mbit).

For a start, I was wondering if anyone has any idea why the client yields a much faster result than the router itself? could it be because of the hw specs
of the Linux server compare to the router?

Appreciate it if anyone has any ideas of how/where I should look into to get to the bottom of this issue.


Jack Yaz

Part of the Furniture
From the first post of spdMerlin:

spdMerlin uses SpeedTest CLI
If the speeds from this utility are significantly lower than those you see from the desktop app/browser test, the limiting factor will be your router's CPU. That being said, there is probably room for improvement/optimisation by the Ookla team in the CLI binary itself. Please direct feedback about speed issues to Ookla via the above link. There is nothing that I can do about them.

Running on the router itself also cannot fully leverage hardware acceleration for the test.

I'm very interested to see what Asus say/do for this with their speedtest in the 386 beta firmware...


Senior Member
Same issue on my site with RT AC88U. Max speed: D 341; U 369. From my clients on LAN, CAT 5e cable: D 924; U: 824.
I will direct feedback about speed issues to Ookla.

Thank you!


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Ronald Schwerer

Very Senior Member
I didn't notice this issue until I updated to 1Gb fiber. I'm getting similar slow speed reports on the router and expected (close enough) throughput on the clients. I previously had a 100Mb down and 10Mb up connection and always got the expected speeds (or better) on both router and client tests.
I had used the Ookla binaries in my own script to run the test on the 68U router every hour and post the results in the system log. I stopped testing on the router. It's a waste of CPU cycles generating meaningless statistics.


Regular Contributor
Min is the same, if I turn off QOS it is still slower but far better. QOS on with rates at 999/999 or 1000/1000 setup results in 100/100 in speed test or above


New Around Here
Yeah mine is REALLY odd though. I'm on an Internet link of 1000/50 and it will test as much.
If I put it on with spdMerlin doing its thing, it will only do 4Mbps/50Mbps
I can’t find else in-play to do it. Touch nothing and repeat without spdMerlin and we are back to 985/48Mbps
I'm stumped on this one. :(


New Around Here
Stumbled upon this thread while looking for potential reasons for the speed discrepancy between spdMerlin and regular web speedtesting (or even win64 speedtest CLI). Feared it might have something to do with hardware acceleration when I noticed the CPU usage when running spdMerlin.

Using a 500mbps/250mbps connection and I'm getting nowhere close the correct reported speed -web/win64 CLI reports a constant 480~/250, while spdMerlin reports... well... see below.


If I remember correctly, the built-in asus speedtest had similar issues.
Sad to see because the potential of this addon is great. Hopefully asus addresses this issue with one of their upcoming firmware updates.
For now I'll uninstall the addon to avoid wasting cpu cycles while I monitor this thread for further developments.

PS: using an RT-AC66U B1 running 384.19 (ARMv7/1ghz 2x cores/256mb ram)


Regular Contributor
In the recent Merlin beta threads people have reported that their router run speed tests were crippled by the TrendMicro AI Protection settings. Some folks found their speed tests dramatically improved once they forced a withdraw from the TrendMicro AI protection on the Administration > Privacy page. Couldn't hurt to disable AI protection and withdraw from it on the Privacy page as a troubleshooting step.


New Around Here
Well I'm definitely getting higher speed results after withdrawing from that privacy agreement (wasn't using any AI protection features at all though). Getting 270mbps~ downloads, still nowhere near my 490~mbps speeds but an improvement nonetheless.


Part of the Furniture
Did you reboot, wait for the router to settle afterward, and then retest?

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