I wrote this HOWTO, using LDAP on Synology so I could try out the Synology Directory Server. This is how I managed to get Linux machines to authenticate against it. At the time of writing, Synology was on DSM 6.2-23739 Update 2. I will be using Ubuntu 18.04 as the Linux clients
The Synology documentation for Directory Server is appalling only stating the blindingly obvious. That is all assuming the page has been updated, most having missing options or features.
I am constantly installing Ubuntu with various configurations. I find having a local Ubuntu 16.04 Mirror on a Synology Diskstation speeds up the installation and updates, making the time spent setting it up well worth while.
Backup your diskstation before doing anything else, just in case.
Synology documentation sucks big time! It usually only states the blindingly obvious missing off any useful or helpful information.
This post will run through the harder parts of setting up DNS and DHCP on Synology NAS. It is a little tricky the first time you do this especially if you have not come across bind or bind9 before. It seems a little over the top or just plain weird. You will only really need this if you have some local servers, computers or other devices that need to be accessed.
Updated for DSM 6.0, because Synology buggered about with stuff! This may not work on earlier versions.
To setup a Synology NAS as a secondary DNS to provide a fall back if/when the primary DNS is off line. To setup a DNS and DHCP serve see my post for DNS with bind9 and DHCP on Ubuntu 14.04.