Pi-Hole cannot resolve any request

[jfb]

@fythic

I set a secondary DNS Server to make sure that if the primary ever goes down for whatever reason, the second will (hopefully) take over.

This is not the way it works. The primary isn't strictly a primary, and the secondary isn't strictly a secondary. Given multiple DNS options, clients will use any of them.

Why should Pi-hole be my only DNS server?

Reduced Ad Blocking Capability The main reason you should Pi-hole as your only DNS server is that you will see increased performance in the blocking of ads. If you have two DNS servers (Pi-hole and something else), your network clients may not always query Pi-hole for name resolution. If a query happens to be answered from a non-Pi-hole DNS server, your block lists will not apply (since that DNS server doesn't know about them). All Queries Need To Go Through Pi-hole First Since other DNS serv…

@fythic

When I set the Primary DNS server to 8.8.8.8 (google) on my router, I believe the pi-hole gets an internet connection back

This seems odd. The internet connection for the Pi should be independent of the DNS server in use. For example, on the Pi if you ping -c5 8.8.8.8 , no DNS resolution is required and the ping should go directly to the IP. It is only when you ping -c5 dns.google that the DNS resolver gets involved to provide the IP 8.8.8.8.

You will need to do some more work with your router to get the Pi back online.

Edit - one more thought. What is the nameserver in use by the Pi:

cat /etc/resolv.conf