@felixk If that's the case, then reporting the issue, definitely would help TP-Link folks to further trace what causing it.

@felixk Kevin's idea was to setup DMZ to the host in question, try to establish a VPN connection and see if it works (without trying to open the 1701 port). What I wanted to point out is the...

@RFP Did you try to ping C6 from a device connected to C80 ? That's rather strange behaviour - everything works, but no access to the extended router. I would suggest that you have changed the web...

@RFP " Can't find it either in Network Map (Archer C80 main router's management page) or DHCP Client List. " If the C6 is with static IP address I believe this is normal. Why don't you access the C6...

@Bshara If you want to go further and avoid the double NAT in your LAN (from introducing the VR400 as a second router), you can follow this guide and use the VR400 as an AP. The cabling in that case...

The device is under warranty, why don't you contact the retailer or if he can't assist you, approach your local support for a resolution.