I have a lan network which is used by my middle schooler so I use PiHole with OpenDNS family shield.
The VLAN is used by my daughter for her home office and I don't want any DNS filter blocking her from accessing work related stuff, so I have google DNS setup in the VLAN she connects.
Here's the setup;
LAN 192.168.4.0/24 Dhcp service DNS 192.168.4.2 (PiHole)
VLAN 10.0.8.0/24 Dhcp service DNS 8.8.8.8
System --> settings --> general --> DNS server "none"
What shoud be in /etc/resolv.config
nameserver 127.0.0.1
or
nameserver 8.8.8.8
or
nameserver 192.168.4.2
or wharever