Forcing all DNS traffic from the LAN to the firewall

Let me refine, NTP, DHCP, DNS are all separate servers located in the green zone. Not running on the ipfire box itself. DHCP because it easier to configure and maintained with the custom forefront/scripts already created. NTP because it a Stratum-1 server. With fail-over servers, etc… Servers which are working, upgraded and maintained for at least a decade. That I can’t migrate to the ipfire box without breaking things and undercut functionality. NTP for example is stratum 1, etc…

So how do I redirect all the traffic for DNS and NTP request instead as explained above to those servers instead of the ipfire box itself.