@Kossie The whole idea is to have ISP modem/router in its default gateway mode (not bridge mode) and have Deco mesh connect to it in Access Point mode.

Kossie wrote @Alexandre. I'll try that. Just wondering: Might a replacement of the deco router with a 'real' gigabit wifi router - and changing all decos to access points - be a better solution?...

@Kossie Connect laptop to second Ethernet port of Main Deco and run same speed test on it. You should be getting close to gigabit speeds, same as when laptop is connected to modem.

@EvilDoctorK Yes, that gets confusing. Bring back Zyxel switch to its original place, unplug everything from it but the link to TL-SG1008D. Also, unplug every device from patch panel connected to...

@Kossie I used to have Deco M9 Plus. I have gigabit Internet. On desktop PC wired to second Ethernet port of Main Deco I had 950Mbps. On smartphone wirelessly connected to Main Deco I have seen...

@Marcos_K You can connect Deco X1500 through TP-Link powerline adapters (their Ethernet port). I suggest to check wired speed over powerline link: if you are getting less than 200Mbps over powerline...