2 TM-AC1900, connecting AP to main router causes download speed to drop?

[pierop]

I have 3 Asus TM-1900 routers in my network config,
My current set up consist of a Modem plugged in to WAN port of Main Router (R1),
R1 and Router 2 (R2) in AP Mode are connected LAN to LAN port.
R1 and Router 3 (R3) in AP Mode are connected LAN to LAN port.

With the above I was paying for 300/300, and I was getting 300/300 but now since I upgraded to 500/500.
I noticed that my speeds are roughly 300/500.

At first I thought It was my ISP so I can called them and we tried connecting (Modem --> Router --> DesktopPC) and I do get 500/500.

As a test I unplugged everything except R1 and R2 and my desktop,
I have my desktop connected to the main router, I run a speedtest and get 500/500,
then I make a connection between one of the LAN ports on the AP to one of the LAN ports on the main router, and after a minute or two, the speeds become 300/500.
Since I have 2 routers in AP mode, I redid this test with R1 and R3, and I got the same results.

I also tried plugging in a gigabit network switch between my modem and router (I think I saw it suggested in a similar thread) but no luck.

It seems my download speed is being throttled by my secondary router (AP).

Network information:
Router 1 is 192.168.29.1
subnetmask: 255.255.255.0
default gateway: 192.168.29.1
DHCP enabled
IP Pool start: 192.168.29.100
IP Pool end: 192.168.29.254

Router 2 (AP Mode) is 192.168.29.2
subnetmask: 255.255.255.0
default gateway: 192.168.29.1

QoS is disabled.

I'm starting to think these T-Mobile routers have some sort of special patch in their firmware that might be causing this.
Anyone have any idea whats going on?

P.S. These routers are not flashed, as far as I know, and they are all firmware 3.0.0.4.376_3199 if that matters.

 

[ColinTaylor]

I have my desktop connected to the main router, I run a speedtest and get 500/500,
then I make a connection between one of the LAN ports on the AP to one of the LAN ports on the main router, and after a minute or two, the speeds become 300/500.

So you're saying that when you first plugged your desktop into the AP's LAN port you got the full 500/500? And it was only after a couple of minutes that the speed dropped. When the speed had dropped did you try plugging the desktop back into the main router and seeing if that did the same?

 

[pierop]

So you're saying that when you first plugged your desktop into the AP's LAN port you got the full 500/500? And it was only after a couple of minutes that the speed dropped. When the speed had dropped did you try plugging the desktop back into the main router and seeing if that did the same?

I have the PC connected to the Main Router (the one that has the modem connected to its WAN port), this way I get 500/500.
BUT, if I plug in the second router in AP mode, to one of the LAN ports on the Main router, THEN after a few minutes, the dl speed drops to 300.
Rebooting the router between connecting cables also did not help.

 

[ColinTaylor]

I have the PC connected to the Main Router (the one that has the modem connected to its WAN port), this way I get 500/500.
BUT, if I plug in the second router in AP mode, to one of the LAN ports on the Main router, THEN after a few minutes, the dl speed drops to 300.

So after the speed has dropped on the AP what speeds do you get if you unplug the desktop from the AP and re-plug it into the main router (without rebooting or any other changes)? Do the speeds go back to 500/500, are they now also 300/500, or does the same thing happen (starts at 500/500 and then drops to 300/500)?

Or are you saying that your PC is always connected to the main router and the speed drop occurs merely by plugging in the AP?

 

[pierop]

Or are you saying that your PC is always connected to the main router and the speed drop occurs merely by plugging in the AP?

Exactly this.

 

[ColinTaylor]

Does your desktop PC also have wifi?

Maybe try connecting the AP by it's WAN port rather than its LAN port. They should function in exactly the same way in AP mode so in theory it should make no difference.

Try turning off Spanning-Tree Protocol and Jumbo frames under LAN - Switch Control. Again, in theory it shouldn't make any difference.

 

[pierop]

Does your desktop PC also have wifi?

Maybe try connecting the AP by it's WAN port rather than its LAN port. They should function in exactly the same way in AP mode so in theory it should make no difference.

Try turning off Spanning-Tree Protocol and Jumbo frames under LAN - Switch Control. Again, in theory it shouldn't make any difference.

pc doesn't have wifi.
Jumbo frames was already off, not sure where to find Spanning-Tree Protocol,

 

[L&LD]

This won't help with the speed issues, but why are you running 376.xx level firmware at the end of 2020?

 

[pierop]

This won't help with the speed issues, but why are you running 376.xx level firmware at the end of 2020?

tbh, I never had anything go wrong with the routers before this, so I never looked into upgrading.
Can these t-mobile routers even be upgraded?

 

[ColinTaylor]

not sure where to find Spanning-Tree Protocol,

That's fine. Not all models have that option.

This won't help with the speed issues, but why are you running 376.xx level firmware at the end of 2020?

Because that's the last version available for that router.

 

[L&LD]

For all you know, your network is not your own today.

Regardless of the performance, the new firmware provides you with the latest security updates too. Not to mention updates to the Wi-Fi stack at the same time.

 

[ColinTaylor]

the new firmware provides you with the latest security updates too.

Re-read the thread title or the first post.

 

[L&LD]

I have. Still no reason to be using this old firmware today.

 

[ColinTaylor]

@pierop Is it possible that when you connect the AP there are wireless devices that are now connected to your network that start consuming your download bandwidth? Try changing the SSID(s) on the AP to something that's never been used and also disable any guest networks, then test again. Also disable access to the main router's WiFi in the same manner.

 

[pierop]

@CollinTaylor no there's no device that is downloading while I am testing the speed.
I change my wifi ssid to something random on both routers, I disabled the guest network on the main router. there are no guest networks on the AP.
Rebooted both routers.

Its been 3 mins, looks like I'm getting around 500/500 at both the router and AP.
However, I've had this happen before, it was at 500/500 then it went back to 300/500 after some time, I think the only difference is now there are literally no wifi devices connected on the network.

 

[ColinTaylor]

Its been 3 mins, looks like I'm getting around 500/500 at both the router and AP.

Maybe it's nothing to do with your setup and it's just intermittent congestion on your ISP's network.

 

[pierop]

Maybe it's nothing to do with your setup and it's just intermittent congestion on your ISP's network.

I doubt that, I've had this issue for 4 days now, and I've did multiple speedtests every day, always got 300/500.

Looks like the speed is stable for now though.
I'm going to start plugging stuff back in and turn on wifi and see what happens.

 

[ColinTaylor]

I thought you were testing downloads from the internet. Your screenshot shows a LAN speed test.

 

[pierop]

I thought you were testing downloads from the internet. Your screenshot shows a LAN speed test.

No yeah, earlier I was using Fast.com to test my speed, its still 500/500.
I guess I don't know what Iperf3 does exactly, my mistake.

anyway, I tested the speed again on Fast.com, its still 500/500, this is with all my other wired devices plugged in.
I'll try turning on WIFI without connecting any clients and update.

 

[pierop]

Ok, I've tried the following:
turned on WIFI only on AP, put the SSID back to what it was before, rebooted both routers.
I did the above step twice to confirm, it seems the turning on the WIFI and having clients connected to it throttles my download speed on my desktop.
I find this weird because I constantly get 500/500 when I'm connected wired, even though I have an NVR with 7 4k IP cameras plugged in at the same time.
On WIFI I have 4 smartphones, 4 smart switches, 2 smart thermostats and 3 chromecasts, and they are all off or on standby.


Then ran a few tests on the PC plugged in to the main router,
I'm getting DL speed of:
420
370
420
350
390