I agree. It was a nice discovery by @roberto . I forgot to mention that there is a third layer of communication between Unbound and DHCP service.
RFC 2136 is commonly referred to as Dynamic DNS Updates, and it provides a mechanism for automatically updating DNS records dynamically as soon as changes occur. In IPFire, when this is enabled in the DHCP settings, the DHCP server will automatically update the DNS records within Unbound whenever a DHCP lease is granted or renewed. This ensures that the hostname and IP address mappings are always up-to-date without requiring manual intervention.