Authoritative and recursive DNS servers. Authoritative listens on 5300 (with a router NATing it for public access), and recursive listens on 53.

The DNS zone is generated automatically by Nix, here. If you don't want to use Nix, you should create/reuse a placeholder host and add services there to add it to the DNS zone. See here for an example, or add a custom record to the zone here

Managed declaratively through Nix.