Setup BIND9 DNS Server on Debian 10 in an internal network

When running different systems on your internal network (e.g. as services on your homelab) it would be nice not to have to memorize the IP addresses of all the server.

You can achieve this by either using the given DNS functionality of your router (e.g. on a tomato router firmware) or by setting up an internal DNS server yourself using the BIND9 DNS server.