Asus RT-AX88U internet speed slows down after a few days

[scandalous]

Hi,

For the last few weeks I've been having an issue with my AX88U where me internet connection slows down considerably. My gigabit speeds go down about half (or lower) and only a reboot fixes the issue. I check this via internal speedtest tool but also directly via the speedtest.net website.
The problem presents itself via Wi-Fi and my wired devices (exact same speed, regardless of device). I've currently set up a reboot scheduler in the night to negate the issue, but I don't think this is a permanent solution and would like to know where the issue stems from.
The speed itself is a bit inconsistent, where it can be a little higher or lower but never reaches the full gigabit speeds until a reboot.

Some setup information and history.

- I have a gigabit connection that I've had for 2 years from the same provider. My WAN IP has not changed in all that time.
- My AX88U is connected to an ONT via a cat7 (all my cables are cat7 for future upgrades) and acts as my modem/router. It's been running Merlin since I bought it and is currently on "RT-AX88U_3004_388.9_0". I've dirty upgraded ever since I got the router a couple of years ago, without issues.
- I have the following devices connected via cable to the router:
1. Synology NAS
2. ASUS ZenWIFI XD6, which is setup as a NODE elsewhere in my home. Connected to this node are a desktop PC and a PS5 via cable as well. The XD6 runs the latest firmware.

I haven't done anything that interesting in terms of configuration. Up until a month ago this was my setup:
- For the WAN I configured the PPPoE for the internet connection. DNS is currently set to Cloudfare with Google as a secondary.
- Regular (separated) Wi-Fi setup for 5Ghz and 2.4GHz bands.
- For the LAN I've set up MAC reservations for every device in my home and limited the IP pool to what I currently need.
- Have a Wireguard VPN server running for when I'm abroad so I can connect to home.

A month ago I made the following small changes:
- I enabled guest-Wi-Fi #3 for the 2.4ghz band (#1 acted weird for some reason) to disallow access to intranet.
- I configured a Wireguard VPN client with a Proton VPN config. I have two devices in the network that go out this way.

What I've tried and checked:
- Note; every change I made was followed by a reboot because no config change actually (not even temporarily) solved the problem. I waited to make sure the issue presented itself again and then tried something else.
I don't have an exact timeline on how long it takes before the issue presents itself. But it's somewhere in the span of 24-48 hours.

1. I assumed the issue might lie with my configuration changes. So I reverted everything as it had been running for the last 2 years, prior to my changes. Meaning disabling the guest network and disabling the VPN client. No luck, the issue still persisted.
2. I rolled back to the previous firmware ( "RT-AX88U_3004_388.8_4"), first with the changes enabled and then without.
3. I did a full factory reset for both the router and the node, configured everything manually, without the VPN client and guest Wi-Fi, but no luck still. I tried this on both the previous and latest firmware.
4. I re-did step 3, but now with all my devices disconnected and only my desktop connected via cable. I also repeated this step but only with my laptop connected via cable and then again with my phone via Wi-Fi. I wanted to ensure that it wasn't some device or negotiation issue. Everything also presented as 1gbit if connected via cable.
5. I re-did step 3 and now with no configuration changes except for the PPPoE setup and still have the same issue.
6. I tried a different ONT with no luck.
7. I googled around to see if I could find people with the same issues. While they weren't exactly the same, I tried changing some of the things suggested like different DNS, making sure QOS was disabled, DDNS was off, AI protection was off, hw-acceleration was enabled. But most of these things are set like that by default. I also left the router off for a couple of hours.
8. The temp of the router is aprox. 60 degrees Celsius. The RAM also doesn't fill up and is below 50% usage, even when the issue occurs. There's no traffic (very low KB/s) to be seen unless I'm doing something, so nothing is clogging up my connection. CPU usage is near near 0% if I'm not doing anything. During a speedtest, core 1 shoots up to 100%. The rest doesn't do anything.
9. EDIT: I forgot to add that I also tried different LAN ports on the router just in case. Didn't make a difference and it seemed unlikely to be the issue since the problem also presents itself on Wi-Fi. I also swapped out the cable between the router and ONT.

I considered it to be a throttling issue, but my provider has confirmed that not to be the case. Like I mentioned before, a reboot solves it and it works for a day or maybe 2, which makes me wonder if it's an actual configuration issue. I also don't see anyone posting about it on the forum, which makes it unlikely to be a bug in the firmware.

I hope someone could help me further into solving this as I'm not quite sure on what to do next.

 

[northumberland]

Wish I could add something you could try here, same router and running similar setup, though with a LOT of devices/servers here.

One thing I can add is that when ISPs 'confirm' things, it can often be taken with a pinch of salt.

I had an issue some 10 years ago, whereby internet would slow to a crawl after several hours, and especially when I absolutely needed it. Mines was down into the kbps/s speeds if I left it. A reboot would fix the issue. It turned out it was a cable, don't think I was even using it, but an old cable none the less. Removing this fixed everything! Perhaps unplug any unused wiring, and try each device off in order. Awkward troubleshooting as it takes hours or days sometimes before you know it's definitely fixed.

Good luck

 

[Makaveli]

Hi,

For the last few weeks I've been having an issue with my AX88U where me internet connection slows down considerably. My gigabit speeds go down about half (or lower) and only a reboot fixes the issue. I check this via internal speedtest tool but also directly via the speedtest.net website.
The problem presents itself via Wi-Fi and my wired devices (exact same speed, regardless of device). I've currently set up a reboot scheduler in the night to negate the issue, but I don't think this is a permanent solution and would like to know where the issue stems from.
The speed itself is a bit inconsistent, where it can be a little higher or lower but never reaches the full gigabit speeds until a reboot.

Some setup information and history.

- I have a gigabit connection that I've had for 2 years from the same provider. My WAN IP has not changed in all that time.
- My AX88U is connected to an ONT via a cat7 (all my cables are cat7 for future upgrades) and acts as my modem/router. It's been running Merlin since I bought it and is currently on "RT-AX88U_3004_388.9_0". I've dirty upgraded ever since I got the router a couple of years ago, without issues.
- I have the following devices connected via cable to the router:
1. Synology NAS
2. ASUS ZenWIFI XD6, which is setup as a NODE elsewhere in my home. Connected to this node are a desktop PC and a PS5 via cable as well. The XD6 runs the latest firmware.

I haven't done anything that interesting in terms of configuration. Up until a month ago this was my setup:
- For the WAN I configured the PPPoE for the internet connection. DNS is currently set to Cloudfare with Google as a secondary.
- Regular (separated) Wi-Fi setup for 5Ghz and 2.4GHz bands.
- For the LAN I've set up MAC reservations for every device in my home and limited the IP pool to what I currently need.
- Have a Wireguard VPN server running for when I'm abroad so I can connect to home.

A month ago I made the following small changes:
- I enabled guest-Wi-Fi #3 for the 2.4ghz band (#1 acted weird for some reason) to disallow access to intranet.
- I configured a Wireguard VPN client with a Proton VPN config. I have two devices in the network that go out this way.

What I've tried and checked:
- Note; every change I made was followed by a reboot because no config change actually (not even temporarily) solved the problem. I waited to make sure the issue presented itself again and then tried something else.
I don't have an exact timeline on how long it takes before the issue presents itself. But it's somewhere in the span of 24-48 hours.

1. I assumed the issue might lie with my configuration changes. So I reverted everything as it had been running for the last 2 years, prior to my changes. Meaning disabling the guest network and disabling the VPN client. No luck, the issue still persisted.
2. I rolled back to the previous firmware ( "RT-AX88U_3004_388.8_4"), first with the changes enabled and then without.
3. I did a full factory reset for both the router and the node, configured everything manually, without the VPN client and guest Wi-Fi, but no luck still. I tried this on both the previous and latest firmware.
4. I re-did step 3, but now with all my devices disconnected and only my desktop connected via cable. I also repeated this step but only with my laptop connected via cable and then again with my phone via Wi-Fi. I wanted to ensure that it wasn't some device or negotiation issue. Everything also presented as 1gbit if connected via cable.
5. I re-did step 3 and now with no configuration changes except for the PPPoE setup and still have the same issue.
6. I tried a different ONT with no luck.
7. I googled around to see if I could find people with the same issues. While they weren't exactly the same, I tried changing some of the things suggested like different DNS, making sure QOS was disabled, DDNS was off, AI protection was off, hw-acceleration was enabled. But most of these things are set like that by default. I also left the router off for a couple of hours.
8. The temp of the router is aprox. 60 degrees Celsius. The RAM also doesn't fill up and is below 50% usage, even when the issue occurs. There's no traffic (very low KB/s) to be seen unless I'm doing something, so nothing is clogging up my connection. CPU usage is near near 0% if I'm not doing anything. During a speedtest, core 1 shoots up to 100%. The rest doesn't do anything.
9. EDIT: I forgot to add that I also tried different LAN ports on the router just in case. Didn't make a difference and it seemed unlikely to be the issue since the problem also presents itself on Wi-Fi. I also swapped out the cable between the router and ONT.

I considered it to be a throttling issue, but my provider has confirmed that not to be the case. Like I mentioned before, a reboot solves it and it works for a day or maybe 2, which makes me wonder if it's an actual configuration issue. I also don't see anyone posting about it on the forum, which makes it unlikely to be a bug in the firmware.

I hope someone could help me further into solving this as I'm not quite sure on what to do next.

did your ISP provide you with their own modem/router to connect to the ONT and you just replaced with the asus router?

 

[Equinox]

I had the exact same issue with my AX86U on a 1-gigabit cable internet connection. A technician came and replaced the cable, but it didn’t solve the problem. The issue was in the firmware. After upgrading to a new version of the firmware, the issue went away.

 

[scandalous]

Wish I could add something you could try here, same router and running similar setup, though with a LOT of devices/servers here.

One thing I can add is that when ISPs 'confirm' things, it can often be taken with a pinch of salt.

I had an issue some 10 years ago, whereby internet would slow to a crawl after several hours, and especially when I absolutely needed it. Mines was down into the kbps/s speeds if I left it. A reboot would fix the issue. It turned out it was a cable, don't think I was even using it, but an old cable none the less. Removing this fixed everything! Perhaps unplug any unused wiring, and try each device off in order. Awkward troubleshooting as it takes hours or days sometimes before you know it's definitely fixed.

Good luck

did your ISP provide you with their own modem/router to connect to the ONT and you just replaced with the asus router?

Thanks for the replies guys! The provider installed the ONT when the connection was first setup years ago. I had a spare ONT that came in the box that they left behind at the time, hence I was able to swap them out and test it. I forgot to add the information to my opening post, but they also provided me with their own modem at the time and the problem doesn't present itself when I have that running. At least it doesn't happen within the same 24-48 hour window. This further confirms that the issue lies with ASUS router rather than my connection. I'd also find it strange for it to be anything else since a reboot of the router immediately resolves the problem. It works perfectly fine for a couple of days which also doesn't make me think it's a hardware issue. But I have no idea where to look next.

 

[Makaveli]

Thanks for the replies guys! The provider installed the ONT when the connection was first setup years ago. I had a spare ONT that came in the box that they left behind at the time, hence I was able to swap them out and test it. I forgot to add the information to my opening post, but they also provided me with their own modem at the time and the problem doesn't present itself when I have that running. At least it doesn't happen within the same 24-48 hour window. This further confirms that the issue lies with ASUS router rather than my connection. I'd also find it strange for it to be anything else since a reboot of the router immediately resolves the problem. It works perfectly fine for a couple of days which also doesn't make me think it's a hardware issue. But I have no idea where to look next.

this is what I wanted to know so with their modem it doesn't happen so you can isolate the issue to the other device.

 

[scandalous]

I had the exact same issue with my AX86U on a 1-gigabit cable internet connection. A technician came and replaced the cable, but it didn’t solve the problem. The issue was in the firmware. After upgrading to a new version of the firmware, the issue went away.

Do you have any idea if there was a specific commit in the firmware release that resolved it? I've tried a firmware that was perfectly fine since the latter half of last year and the issue still presents itself.

 

[degrub]

Did you hard factory reset the router and manually config the router after changing firmware ? loading an existing saved config file will corrupt the testing and carry over issues not to mention the saved config may not exactly match the different firmware.

 

[Equinox]

Do you have any idea if there was a specific commit in the firmware release that resolved it? I've tried a firmware that was perfectly fine since the latter half of last year and the issue still presents itself.

I don't remember the release number; it happened three or four years ago.

 

[scandalous]

this is what I wanted to know so with their modem it doesn't happen so you can isolate the issue to the other device.

Yeah, it's one of the first things I tried to make sure it really wasn't the connection and I was just chasing ghosts.

Did you hard factory reset the router and manually config the router after changing firmware ? loading an existing saved config file will corrupt the testing and carry over issues not to mention the saved config may not exactly match the different firmware.

Point 3 in my opening posts refers to that. I did in fact factory reset and configured the router manually. At no point during the process did I ever use a configuration file. I figured the same thing, that if it's a configuration issue then I'd just be loading the problem back onto the router.

Also note in point 5 that I factory reset the router and did not change anything in terms of configuration, except the required PPPoE for the internet connection.
So I've tried to eliminate it being a configuration issue and I've (thus far) eliminated it being a ISP connection issue with the original modem. Which leaves me with either hardware issue or firmware bug.

The problem is that I've tried 2 different Merlin firmware, one that ran completely fine for 6+ months, which also tells me that it might not be the firmware. On the other hand the router runs fine for 2 days if I don't reboot it. So it's left me wondering how it could be a hardware issue but still run fine for that long.

 

[degrub]

Anything in the system logs about the time the speed drops ?
And just curious, are you running the same firmware versions on the Node and the main router ?

 

[scandalous]

Anything in the system logs about the time the speed drops ?
And just curious, are you running the same firmware versions on the Node and the main router ?

The node is not supported by Merlin as far as I know and is running on the latest stock ASUS firmware.

I haven't looked at the logs as of yet, I'm not even sure what I'm supposed to be looking for. I also don't know exactly when the issue starts since I'm not constantly monitoring. There's a chance on any given day I'd have to go through +24 hours of logs. Any tips on what I might be looking for or how to optimize looking for whatever it might be?

 

[degrub]

Just for giggles, if you have a CAT 6 cable handy, try that between the ONT and the Asus router. CAT7 is more sensitive to imperfections in the termination and receptacle.

If you want to run speed tests, they should be run from lan client device and not the router. Generally, not reasonably accurate when run on the router due to the CPU load.

 

[bbunge]

Have you tried the Asus firmware?
This is a long shot but what is your MTU setting? Does your ISP give you a value for the MTU with PPPoE? Try lowering the MTU.
Also, use one DNS provider. Not a great practice to use Cloudflare and Google. Try a filtering DNS like Quad9, Cloudflare Security, CleanBrowsing or Control D.

 

[scandalous]

Just for giggles, if you have a CAT 6 cable handy, try that between the ONT and the Asus router. CAT7 is more sensitive to imperfections in the termination and receptacle.

If you want to run speed tests, they should be run from lan client device and not the router. Generally, not reasonably accurate when run on the router due to the CPU load.

I didn't know that, I'll have to source one and test this. I'll get back to you later next week! The tests are always run on multiple client devices. I only ran the "in-router" test to confirm it wasn't something in the network itself. Speeds are the same when the issue presents itself though.

Have you tried the Asus firmware?
This is a long shot but what is your MTU setting? Does your ISP give you a value for the MTU with PPPoE? Try lowering the MTU.
Also, use one DNS provider. Not a great practice to use Cloudflare and Google. Try a filtering DNS like Quad9, Cloudflare Security, CleanBrowsing or Control D.

I have....not tried the stock firmware. I'll give that a shot as well!

I'll try the cat6 cable recommended above first and then yours. I tried a single DNS as well and that didn't make any changes. I've tried Cloudfare, Google, Q9, ahadns and adguard. I do think a DNS (from how I understand they work) would be a weird culprit to affect my bandwith though. But as of yet, they've made no difference in solving the issue.

The recommended MTU value from my provider was 1500 if I'm not mistaken. I have (not intentional) tried a lower MTU already. After a factory reset, I believe the MTU is set in the 1487? range in the Merlin firmware and I ran it on that to test.