This topic

ASUS Router with BT Fiber not getting full speed

Col8 — Tue, 21 Dec 2021 18:13:46 GMT

I have an ASUS RT-AX88U running ASUSWRT-Merlin 386.3_2.

I have just had BT Full Fiber 1GB installed.

Using the supplied BT hub I get 850mb/s

Using my ASUS router im getting 650mb/s.

(Both tests via ethernet connection to lap top).

Could someone advise me of settings I need to change to optimise the speed.

Currently I set WAN Connection type to PPPoE, both MTU and MRU set to 1492 (default), Enable VPN + DHCP Connection set to yes.

The ASUS router network map summary shows WAN as 1 Gbps

Any thoughts on how I can get my lost 200mb/s back?

Re: ASUS Router with BT Fiber not getting full speed

Tnr-mx — Thu, 23 Dec 2021 03:07:22 GMT

Near enough exactly the same here. Just had fttp/500 installed and it’s rock solid on the BT router.
The only downside is the BT router is so incredibly limited on features / configuration - hence the AX88 purchase.

After taking my time flashing the AX88 with Merlin 386.3_2 and setting the router up from scratch, I’m finding I get no more than 200mb down 😔 It’s also very erratic - BT router is a constant 500, whereas the AX88 is slow to ramp up and then jumps around.

I’ve intentionally been very light on the config side of things, additional “features” are off with the only things configured being the DHCP address scope and WiFi config.

All tests performed via enet cat6.

The only thing that I can see being worth trying is adjusting the MTU, although something tells me this will be pointless as the 1492 would (to me anyway) be the most appropriate size.

Re: ASUS Router with BT Fiber not getting full speed

Checked2013 — Thu, 23 Dec 2021 08:42:12 GMT

I use the AX88 and two AX92U's for AiMesh nodes using the firmware supplied by ASUS and not seen any slowdowns at all. Is it possible the firmware you are using is causing the slowdowns?

Re: ASUS Router with BT Fiber not getting full speed

TimCurtis — Thu, 23 Dec 2021 10:10:40 GMT

@Col8

@Tnr-mx

I'd go along with @Checked2013 thoughts and try the standard Asus firmware to rule out the Merlin firmware being the issue.

Re: ASUS Router with BT Fiber not getting full speed

Col8 — Thu, 23 Dec 2021 10:22:14 GMT

I've tried the stock firmware and it's the same issue.

Re: ASUS Router with BT Fiber not getting full speed

stevebrass — Thu, 23 Dec 2021 11:39:33 GMT

Have you tried without VPN enabled?

Re: ASUS Router with BT Fiber not getting full speed

Col8 — Thu, 23 Dec 2021 13:41:39 GMT

Do you mean the Vpn and dchp setting at the bottom of the WAN internet settings page?

Re: ASUS Router with BT Fiber not getting full speed

Les-Gibson — Thu, 23 Dec 2021 13:48:27 GMT

Have you tried using ping to determine to determine the correct MRU/MTU, I normally go for 1488 but that's not going to make the difference that you're experiencing

Re: ASUS Router with BT Fiber not getting full speed

Tnr-mx — Thu, 23 Dec 2021 14:10:11 GMT

@Col8 Have you performed a speed test directly from the router yet?
(Log in to the Router > Adaptive QOS > Internet Speed)

I've spent the morning troubleshooting this again and have just discovered that I am getting the full 500mb into the router, but only getting ridiculously erratic speeds on the LAN side.

Any device on LAN side (wired):

Speed test direct from the router:

I would say it's a bug in the Merlin firmware but I'm getting the same results on the stock Asus version.

**EDIT: The issue only appears to be on devices that are WIRED! Using 5Ghz WiFi I'm managing to get approx. 470 - 480mb download and the full 70mb upload.

Any wired laptop or desktop gets a ridiculously unstable connection but this is only occurring when using the ASUS router. If I connect up the BT Hub everything is as expected / full speed.

All devices are showing as connected @1gb so not entirely sure why I'm encountering this bottleneck. **

The mystery continues...

Re: ASUS Router with BT Fiber not getting full speed

willinliv — Sat, 10 Jun 2023 18:50:11 GMT

Did you get to the bottom of this? Only recently got fibre so maybe things are settling down, however I am seeing same behaviour on router vs wired

Re: ASUS Router with BT Fiber not getting full speed

Crimliar — Sat, 10 Jun 2023 21:27:11 GMT

For the original OP, you've never lost those 200Mbps! The way the Ookla Speedtest is implemented in the Asus WEB-UI is CPU intensive, and all but the latest top-end Asus routers don't have a powerful enough CPU to generate an accurate result. You can see multiple discussions on this on https://snbforums.com

Re: ASUS Router with BT Fiber not getting full speed

Dal2 — Sat, 10 Jun 2023 22:06:47 GMT

Use ping to determine the correct MTU size to get the optimal speed for your own router. i.e

ping -l 1200 -f 8.8.4.4

Change the -l buffer size until you get the message "Packet needs to be fragmented but DF set."

The highest -l value where you receive a "Reply from 8.8.4.4:....." message is you correct MTU to use. You will need to add 28 (header) to the value.

Re: ASUS Router with BT Fiber not getting full speed

Col8 — Sun, 11 Jun 2023 08:49:20 GMT

I changed my settings and it really helped.

https://youtu.be/PBqJRb0rbqo

Re: ASUS Router with BT Fiber not getting full speed

willinliv — Sun, 11 Jun 2023 09:39:22 GMT

Thanks guys for the suggestions re setting the MTU. The default on my router (RT-AC86U) is 1492 (stock firmware). I went through a few ping tests and determined I could get 1464 ok (1465 gave losses). Adding 28 took me back up to 1492 so did not need to change. However the internet on my PC with the longest ethernet cable is now reporting speeds of about 550Mbps that match the Asus's Ookla test. So fingers crossed this is just some teething to get things right. Thanks again, Will

Re: ASUS Router with BT Fiber not getting full speed

Col8 — Sun, 11 Jun 2023 12:05:30 GMT

What speed did you buy from buy from BT

Re: ASUS Router with BT Fiber not getting full speed

willinliv — Sun, 11 Jun 2023 14:52:56 GMT

500

Re: ASUS Router with BT Fiber not getting full speed

flycop2000 — Sun, 11 Jun 2023 18:52:53 GMT

I am currently using the RT-AX88U-Pro and previously used the RT-AX88U. I have used both the Asus and Merlin firmware on both routers and there was difference in download/upload speeds.

I'm on a 500Mbps package and get:

473Mbps down

93Mbps up

There was no settling down period, I got these speeds from day 1.