@DownUnder Usually every devices who use DNS and allow to use more then 1, use them as backup. Mean that if your DNS server available, then it will be used, and if not, the backup DNS will replace...

@Kevin_Z What need to be here ?

@Kevin_Z Hi Kevin, The router is 192.168.0.1, then DHCP is from 192.168.0.100-255 The Pi-Hole is 192.168.0.120

@Kevin_Z Then it will be out of the segmant and I cannot access it.

The main problem here isn't the firewall, is only to get easy using hosts (call an ip by name). I need only to configure that in the router, what is the IP that my raspberry pi need to get ?

I Have router from ISP that I'm using in bridge mode (like modem) The Archer C2 - Internet port connected to 'modem' and my 1- my pc, 2- my rapsberrypi2 (The DNS I want to use), 3- other pc