Restrict use of static / manual DNS to connect internet?

[zackytravis]

is it possible to restrict the clients from using custom DNS to pass through the router's specified DNS ?
i have installed pi-hole on a linux server to block some queries, but it is useless if the clients is using custom DNS

my router's ip is 192.168.0.1 and my linux server is 192.168.0.2

[frollic]

Catch all outgoing traffic on port 53 UDP and TCP in your FW and redirect it to your pihole.

[trendy]

Block and Redirect DNS to PiHole

You are right! I tried the masquerade rules (initially I thought you were saying about the wan postrouting masquerade) and now replies back to clients seem to come from the legitimate nameserver. Regarding IPv6 why are you trying to masquerade on the wan? Any host contacting some other host on the internet should use the GUA, not the LUA. I also fixed the reply from unexpected source for ipv6 just with this: ip6tables -t nat -A POSTROUTING -d fd00:bbbb::2 -p udp -m udp --dport 53 -m comment --…