dbndns is a fork

Fork (software development)

In software engineering, a project fork happens when developers take a legal copy of source code from one software package and start independent development on it, creating a distinct piece of software...

 of the djbdns

Djbdns

The djbdns software package is a DNS implementation created by Daniel J. Bernstein due to his frustrations with repeated BIND security holes. A $1000 prize for the first person to find a privilege escalation security hole in djbdns was awarded in March 2009 to Matthew Dempsky., djbdns's tinydns...

 software package, maintained by the Debian Project, made possible by the release of djbdns to the public domain.

Most notably, this now includes IPv6 support.

Previously, it was necessary to get a special 'djbdns-installer' package that downloaded the djbdns source from the authors' site and apply a patch, but the free software status means this is no longer necessary, and Debian can directly carry the source and patches, producing a redistributable binary deb package.

This package has filtered through into Ubuntu.

Reasons for fork

This fork was created, for reasons documented here:-

Public Domain Status

The public domain-status of the djbdns package was confirmed by the author as per authors' page:-