UniFi: Unable To Access Synology On Local Network

Investing in a UniFi Dream Machine has been one of the wisest things I've done last year when it comes to relatively expensive purchases. It truly has been worth every penny for its reliability, security and rock-solid connection - something that is very much needed when working from home full-time.

The Dream Machine has been very low maintenance and I just leave it to do its thing apart from carrying out some minor configuration tweaks to aid my network. The only area that I did encounter problems was accessing the Synology Disk Station Manager (DSM) web interface. I could access Synology if I used the local IP address instead of the "myusername.synology.me" domain. Generally, this would be an ok solution, but not the right one for two reasons:

1. Using a local IP address would restrict connection to my Synology if I was working outside from another location. This was quite the deal-breaker as I do have a bunch of Synology apps installed on my Mac, such as Synology Drive that carries out backups and folder synchronisation.
2. I kept on getting a security warning in my browser when accessing DSM regarding the validity of my SSL certificate, which is to be expected as I force all connections to be carried out over SSL.

To my befuddlement, I had no issue accessing the data in my Synology by mapping them as network drives from my computer.

There was an issue with my local network as I was able to access the Synology DSM web interface externally. From perusing the UniFi community forum, there have been quite a few cases where users have reported the same thing and the common phrase that came popping up in all the posts was: Broken Hairpin NAT. What is a Hairpin NAT?

A Hairpin NAT allows you to run a server (in this case a NAS) inside your network but connect to it as if you were outside your network. For example via a web address, "myusername.synology.me" that will resolve to the internal IP of the server.

What I needed to do was to run an internal DNS server and a local entry for "myusername.synology.me" and point that to the internal IP address of the NAS. What was probably happening is that my computer/device was trying to make a connection past the firewall and then back in again to access the NAS. Not the most efficient way to make a connection for obvious reasons and in some cases may not work. A loopback would resolve this.

A clever user posted a solution to the issue on the UniFi forum that is very easy to follow and worked like a charm - Loopback/DNS Synology DiskStation.

I have also saved a screenshot of the solution for posterity.