HELP! No internet after Router reboot

[ABSCrazy]

Hello everyone,
after months of troubleshooting, i gave up and i m here to ask support to the community.
I have an Asus Router AX88U Pro, with merlin Firmware (3004.388.6_2).
The asus is between my LAN and the Fritzbox router that i received from the Internet Provider.

Inside my LAN (so behind the asus), i have a raspberry pi4 with Homeassistant. The Homeassistant provide also a DNS Filtering services (ADGuard Home).
In order to force all the devices/client/server in my LAN to use the ADGuard DNS Filtering services, i configured the DNS Redirector on the Asus Router to perform the redirect to the Raspberry's IP.

With this configuration ADGuard is correctly working, it filters the requests that receive from the devices, and also the requests redirected from the router BUT when the router goes OFF (Blackout or reboot), i cannot reach the internet... I can ping 8.8.8.8 but the DNS resolution of internet website stopped working. To fix this problem, i have to disable the DNS Redirector on the asus (so reach the internet with other DNS) and then re-turn on the DNS Redirector. With this workaround everything keep working (until the next asus's reboot or blackout).

Attached the network diagram, with more info about the configurations.

 

[Morris]

In your DNS Director setup, do you have a client entry for your 192.168.50.2 (DNS Server)? If not, have it point to router. Without this, you are blocking it from going to route DNS servers to load it's cache.

 

[Tech9]

RPi on 192.168.50.2 has to be excluded, No Redirection.

There is also no point setting filtered and unfiltered upstream DNS servers in AdGuard Home.

 

[ABSCrazy]

@Tech9 I think that the problem could be this!! Thank you, i will try that configuration asap, and let u know!

Meanwhile... Why there is no point setting filtered and unfiltered upstream DNS servers in AdGuard Home? Can you explain me it?
Sorry for getting newbie

 

[Tech9]

Why there is no point setting filtered and unfiltered upstream DNS servers

Because whatever is one DNS server filtering is resolved by the other DNS server.

There are some other unclear details around your configuration. You say the ISP provided FRITZ!Box is a router. This means your Asus router is getting private WAN IP. This means your IPv6 configuration must be Passthrough mode. This means your FRITZ!Box is actually driving your IPv6 connectivity. This means it's using completely different DNS server perhaps bypassing your entire setup. If all of the above is true - you have to rethink your configuration.

Sorry for getting newbie

This is not an issue.