Asus zenwifi XT8 not getting 1000mbit connection

[Philip Rohrhuber]

Problem:
I'm supposed to have a 1000 mbit connection. But for some reason, it's only doing 100 mbit.

It's not my ISPs issue. As we troubleshootet together and have just got a new fiberbox installed. All the way from my ISP through the fiberbox and to the first mesh node, it says 1000 mbit according to the ISP.

Despite a proper setup, my wifi and lan falls back to 100 mbit, limiting all device speeds (both wired PC and wireless iPad, iphones) to ~90 Mbps max.

Occasionally, the connection does negotiate 1 Gbit — e.g., right after a full restart or when I enable Dual WAN on the router settings— but it reverts to 100 mbit after some time.

My setup:

ISP: Fastspeed.dk 1 Gbit fiber
Router: Asus ZenWiFi XT8 (main node connected directly to fiber box)
Cables: Cat5e and Cat6 u/UTP (brand new)
3x XT8 mesh nodes and connected devices (PC, iPads, NAS) tested with the same results
QoS, AiProtection, and Traffic Analyzer are disabled
WAN is set to Automatic IP (DHCP)
Firmware is up to date
No switches in use — direct cabling only

What I’ve tried:
Tried new Ethernet cables (Cat6, short cables, etc.)
Checked Synology NAS link speed (shows 1 Gbit)
Enabled Dual WAN (helped briefly — forced 1 Gbit), but speed dropped back to 100 Mbps after some hours
Rebooting router sometimes helps, but the issue returns

Observations:
Asus router UI (Network Map) shows WAN/LAN ports in yellow (indicating 100 Mbps)

Whats the issue here, how do I get 1000mbit connection again??

Thanks in advance!

 

[GWTechTalk]

Use the SSH connection and post the response following this command:

ethtool eth0

I had two XT8's and their WAN ports were VERY temperamental with my ISP's fiber ONT. My ISP finally changed the ONT out for another model and the speeds were more stable but always had issues pulling a DHCP address from my ISP. I never figured out why I would just let the router and ONT boot then unplug and re-pluged the WAN cable.

Also post information showing your speed and the speed you pay for, I would like to rule out math errors. Use the internet router speed test to your local hub.