Package(/NAS application) "DNS Server" needs PORT 53 to run, so it can run while installing Package, "Synology Directory Server" But Port 53 is taken - I never deal with ports, is this
Synology - Početna stranica | Facebook
Synology Routers
How to Change Synology DSM ports 5000 and 5001 – Marius Hosting
How to gain Remote Access to a Synology File Server - Network Antics