The router is set after optical terminal on fiberoptics line. Internet is through PPPoE.
I'm running a raspberry pi with pi hole as a DNS server. if I use Raspberry IP (192.168.1.225) as DNS in the DHCP server setting of the router it has no effect, it seems that the provider DNS servers are used in practice.
if I override the ISP provider's DNS servers from internet connection settings and use 192.168.1.225 the router crashes as it cannot manage having a DHCP client as DNS. During this also the default changes to 192.168.0.1.
How can I use raspberry pi as the only DNS server??