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HELP! Asus Ax11000 (Merlin 388.2)- Slow 5ghz Speeds when Enabling Guest 2.4ghz Wifi

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SocratesPrime

New Around Here
Hello guys,



I am very new to all this, so please be patient.



I got my first aftermarket router Asus Ax11000 just this very week, and it was simply awesome with the stock firmware. However, I faced some issues when adding pihole, and everything I read pointed me to using Merlin.


First off, Merlin is simply awesome. I downloaded the latest version for my router, which is version 388.2.

At first, I was surprised when I noticed it had two files, but I quickly realized that the primary distinction was the ROG skin. So I went with the ROG skin that was named "GT-AX11000_388.2_2_rog_ubi.w"



It was super easy to update the firmware, and I was able to set up my pihole perfectly. All good.



Now, the problem starts.



You see, for my wifi configuration, I have disabled Wifi-5ghz-2 and only use the 2.4ghz and Wifi-5ghz-1 . This works well for me, as my tv and phone uses the 5ghz and my IOT devices run on the 2.4ghz. Before installing Merlin, everything seemed to be running perfectly, I was getting excellent speeds on both 2.4ghz and 5ghz-1. For my testing, I run my speed test locally using LibreSpeed (a simple app that allows you to test lan speed from my Home Media Server). From my s23 ultra, I was able to get about 1400mbs-1500mbs up and down, which is insane since it's faster than my Gaming PC connected via gigabit ethernet. For internet, I get about 800mbs up and down on the phone. From the desktop, connected via ethernet, internet is 920mbs up and down. (My Internet Plan is 1gigabit fiber)



After I got Merlin, my speeds were not as good. The Lan speed from the phone was now 800mbs up and 1000mbs up. Desktop speeds remain the same. The funny thing is sometimes, it would randomly go to 1200mbs down on the lan test, but most times it was at 800mbs or less. For the internet test, I was now getting 500-600mbs down, much lower than the 700-800 I used to get from before. I only had the router on stock for a full day before deciding to go with Merlin, so who knows, maybe stock has the same issue, and I probably didn't notice.



I tried troubleshooting this myself.



I figured perhaps, it was something to do with my pihole, so I put everything on DNS back to default, but this didn't change anything.



Then I thought it was perhaps other devices on 5ghz wifi, so I restricted wifi access to only my phone and same same issue.



Finally, I decided I would restore back to factory, and test speeds, every single step of the way. I wiped everything using the checkbox in the admin page, and it booted with a clean version of Merlin. I first started with removing all ethernet connected devices, except my desktop, and disabled all Wifi except 5ghz1, and I tested multiple times over the hour. Since my server was not connected, my test was only over internet, and the speeds were consistently fast and stable. Then I proceeded to add my Server, and I managed to test the LAN speeds, and it was so freakingly fast just as day 1. 1400mbs-1500mbs, sometimes faster. So clearly, it was not the ethernet devices.


Now, I enabled my 2.4ghz wifi, and all of a sudden my speed on the 5ghz dropped significantly back to the problem speeds. I disabled the 2.4ghz, and then the speed was super fast again. Clearly, the issue was coming from the 2.4ghz, or at least something connected to it. So I changed the SSID for the 2.4ghz, so that no other device could connect to it, and that brought us back to the super fast speeds on the 5ghz wifi. So from here, I figured one of the IOT devices must have been messing up with the speeds. I have about 20 IOT devices, mainly lights, so you can imagine how tricky it would be to diagnose if a particular one was causing the issue. I decided it would be a great idea to create a GUEST network with the 2.4ghz SSID, and put all the IOT devices on there without the capability to communicate over lan. Yeah, that was a very dumb idea, because as soon as I created the GUEST wifi, my 5ghz speeds dropped down to less than half of what they used to be, lol. I was so shocked. Not a single device were even connected on the 2.4ghz, but the max speed I got for internet on 5ghz was 450mbs. I restarted the router multiple times, still same results. So I disabled the guest network, then back to the fast speeds. Is this a normal behavior for the router. Clearly, none of my IOT devices were connected so they could not have been culprit.


TLDR:

Enabling guest network for Wifi 2.4ghz is creating significantly slow speeds on Wifi 5ghz. Is this normal? Did I just find a bug? What can I do to fix this.



In the meantime, I'm going to troubleshoot each iot device, one at a time to see which one is culprit. It'd take a while, hopefully, I get some responses on here before then. Thank you.
 
Welcome to the forums @SocratesPrime.

Great sleuthing so far!

Just to be sure, after flashing the RMerlin firmware, did you do a full reset, and then minimally and manually configure the router? Without using a saved backup config file?

The following link may help to get your router/network to a good/known state.



A screenshot of how you have configured the Guest Network may be helpful. Along with screenshots of the main Wireless General and Professional settings too.
 
Hello,

Yes, after I flashed with Merlin, I did not use a saved backup. I did a full reset, and then minimally and manually configureed the router until i identified the cause of the issue. By the way, it took a while but I discovered the source of the original issue. It was one of my IOT devices connected to the 2.4Ghz Wifi, a cheap Govee LED strip lights that I have at home. I switched it off, and everything was working fine on the main WIfi. I have connected it again, after some time, and it has been a breeze for an entire day. Absolutely no issues on the main Wifi.

We are still left with the rather unusual behavior whenever the GUEST MODE is enabled. As soon as it is enabled, it would cause the wifi speeds for Wifi 5G-1 to slow down by half.

I have included some screenshots below for my config. You should see the config for the GUEST WIFI, General &Professional Config for the 2.4Ghz Wifi, and General and Professional Config for the 5Ghz - 1 Wifi.

I am going to find another phone, and use it to record the issue in action.

I wonder if I can upload a video on here.

Thanks in advance for helping with this



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1687564688384.png
 
Hello,

Yes, after I flashed with Merlin, I did not use a saved backup. I did a full reset, and then minimally and manually configureed the router until i identified the cause of the issue. By the way, it took a while but I discovered the source of the original issue. It was one of my IOT devices connected to the 2.4Ghz Wifi, a cheap Govee LED strip lights that I have at home. I switched it off, and everything was working fine on the main WIfi. I have connected it again, after some time, and it has been a breeze for an entire day. Absolutely no issues on the main Wifi.

We are still left with the rather unusual behavior whenever the GUEST MODE is enabled. As soon as it is enabled, it would cause the wifi speeds for Wifi 5G-1 to slow down by half.

I have included some screenshots below for my config. You should see the config for the GUEST WIFI, General &Professional Config for the 2.4Ghz Wifi, and General and Professional Config for the 5Ghz - 1 Wifi.

I am going to find another phone, and use it to record the issue in action.

I wonder if I can upload a video on here.

Thanks in advance for helping with this



View attachment 51264

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Technically it shouldn't be an issue, but your Guest SSIDs are long, with many spaces, dots, dashes, etc. I would try reducing that and simplifying. Personally I like no spaces or special characters (except dashes, never seen a problem with those).

Also disable universal beamforming on both bands. That is known to cause issues.
 

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