@TP-Link Hi, I found the problem. One was from the LAN speed limitation on the box setting (100Mbps to 1000Mbps) and second one was the Ethernet cable between DECO and box thank you for your help....

I plugged my deco x20 into one of the LAN sockets of my fiber box. It works correctly but the internet speed test is now 90 mbps while on the box directly it was 300mbps. Why is the speed through the...