DNS could be a problem.
OK, so no one actually asked me this; it happened to me. But I’m sure others have had the same problem so I thought it worth posting.
If you have a Synology NAS and you’re finding that it can’t see any packages available and Dynamic DNS is not syncing, then it could be a problem with your DNS settings.
These are both services that rely on connecting to online sources, namely the Synology servers and your dynamic DNS host. So if you can’t connect to either then it stands to reason that your NAS can’t see the external servers.
In my case the problem was that I had set a static IP on my NAS and my router wasn’t supplying DNS information as a result.
This is an easy fix; all you’ll need is a valid DNS server.
You should be able to find this information by checking the settings on your router, or you could use an alternative such as Google’s free DNS servers: 8.8.8.8 and 8.8.4.4
To add them to your Synology settings, login to DSM and go to:
Control Panel --> Network --> Manually Configure DNS Server
And then enter your DNS settings, Simple!