Recently I had to setup DDNS for my parents DS212+ DiskStation from Synology.
I have an all-inkl.com hosting package including a dynamic DNS feature (DDNS under tools):

The problem was to get the right settings for the Synology box.

Solution for the DDNS problem

I found the solution in this blog article:
http://www.pflipsen.net/2015/12/21/all-inkl-com-ddns-auf-der-synology-diskstation-einrichten/

I saved the article as PDF as well:
all-inkl