You'd do this on the router, or the unit providing NAT, which is probably not the Pi. Cf. Edgerouter: https://www.reddit.com/r/Ubiquiti/comments/6lndq4/questio

You'd do this on the router, or the unit providing NAT, which is probably not the Pi. Cf. Edgerouter: https://www.reddit.com/r/Ubiquiti/comments/6lndq4/question_redirect_port_53_to_internal_dns_server/ https://www.reddit.com/r/Ubiquiti/comments/6lndq4/question_r...