Asus AC68

[deHakkelaar]

And read this bit bout Asus routers:

Pi-Hole not blocking ads

Sounds like the Asus router is pushing two DNS servers to the clients via DHCP: If want to know for sure, install nmap on Pi-hole: sudo apt install nmap And do a DHCP discovery targeting the "<ASUS_ROUTER_IP_ADDRESS>": sudo nmap -sU -p67 --script dhcp-discover <ASUS_ROUTER_IP_ADDRESS>