Choose what you need
* Make DNS relay
Rules > IP rules
SAT lan/lannet core/lan_ip dns-all, SAT: new destination = yourdnsserver
NAT lan/lannet core/lan_ip dns-all
* Pass DNS traffic only to specified DNS server
Make this rules before lan_to_wan rules
NAT lan/lannet wan/yourdnsserver dns-all
Drop lan/lannet wan/all-nets dns-all