@Ketankumar_G About your question 3: I suggest configuring the wifi of the Deco with the same name and password as the wifi on the AT&T modem. Then disabling the wifi of the AT&T modem, or assigning...

@socoolone It is clearly marketed as a household appliance, I am surprised you expect it to be a "professional unit".

@schneids Did you try after removing the secondary DNS address?

@Raydar I do not believe the Deco provides that information.

@socoolone By "I am using this system as my main firewall.", do you mean that you require the Deco to have an isolated LAN IPv4 subnet, hence you require the Router mode of the Deco?

I run the Deco in Router mode. In the Deco settings of the DHCP Server, I did not specify primary and secondary DNS. I observe that Deco distributes, via DHCP, as address for the secondary DNS...