pfSense

The text below the "DNS servers" fields on the DHCP server configuration reads "Leave blank to use the system default DNS servers: this interface's IP if DNS Forwarder or Resolver is enabled, otherwise the servers configured on the System / General Setup page.".

This is limiting, when using an alternative DNS service (such as the BIND package), especially for IPv6 where IPs are likely not to be static. There should be a way to access the later part of this functionality, advertising the interface IP as the DNS server, even without the DNS forwarder or resolver packages enabled.

The request is for a checkbox to tell the DHCP server to advertise an interface's IP address as the DNS server rather than defaulting to the servers configured on the System / General Setup page, as the servers used by the router for DNS resolution may well not be what you want to advertise to clients. This does not require any knowledge of the fact that a DNS server is or is not running on the interface; if one isn't, then DNS resolution will simply be broken for DHCP clients until the admin fixes the misconfiguration.