@FrustratedXuser Make sure that C6 is in 'router mode' and use this guide for configuring the WDS feature (i.e. wireless repeater).

@Rajit Go through this thread to learn for some considerations when daisy-chaining range extenders. You can go through this FAQ - Part 3 - Q3.6/A as well.

@Kranthi-Swaroop If your WR840N is HW v5 use these FW releases. If you use a wrong HW version / FW region file you'll receive this kind of error. HW version and FW region is printed on the bottom...

@waggy75 Set VR400 LAN IP address to be in your Deco subnet and disable VR400 DHCP server: Disable VR400 Wi-Fi radio (both bands): Now you can use VR400 like a plain switch (ports from LAN1 to LAN4).

@Zebop917 Here's a guide on how to configure port forwarding on VR400.

@WMC When using the WDS feature both routers' LAN IP address should be on the same subnet i.e. 192.168.1.0/24. Follow the WDS configurations guide then test if everything's OK.