I just recently set up a Pi-hole sinkhole and got everything working nicely. I configured Pi-hole as the primary DNS server in the router settings. However, from the web interface I noticed that query logs seemed to always end to previous day at 11 PM with PTR type requests to 8.8.4.4 and 8.8.8.8. At first I didn't think too much about it, but as this happened everyday I started looking into it. So, it seems that my router for some reason overrides the set Pi-hole IP with my ISP's own DNS server IPs everytime the global IP of the router expires. The router changes back to Pi-hole as DNS server when I reboot the router.
Any suggestion how to fix this? The settings of the router are a bit vague.
My router is Sagemcom F@ST 3686 with ISP customized firmware.
I would recommend setting the PiHole as your DHCP server, my router wouldn't even use the DNS I provided so that's what I ended up having to do. ( I have SagecomF@ST 5260 ) I'd recommend this over diagnosing weird router behavior but it's up to you
To do that you have to:
Make sure your PiHole has a static IP configured in /etc/dhcpcd.conf
Enable DHCP in the Pihole settings -> DHCP tab
Disable your routers DHCP server ( likely under the DHCP tab there )
( if you turned your Raspberry PIs firewall on you might have to open some ports )
That did it! I didn't realize Pi-hole can handle the local DHCP service itself and doesn't need to be configured into the router other than turning its' own DHCP service off. Many thanks!