You need to configure DDNS if you want to access your Synology NAS DS713+ on the internet without remembering your IP address.
You can afterwards map your own domain name to your DDNS name to access your synology with it and if you do that, you will be able to secure your synology with a Lets encrypt certificate (Https connections).
Ok, let’s get started:
Configure DNNS
It is very simple and can be explained in a few simple steps:
1. Click on “main menu” 
and then “Control Panel” 
2. On “Network services” click on DDNS:
The rest of the steps are the same.
3. Click on “Add”:
4. Click on “Enable DDNS” , select Synology or any other provider of your choice and “Register Now”:
5. Click on “Create a Synology account”, add your email and the password you want for this account, click on the terms of services and ok:
6. Click on “Test Connection” and you will see Normal in green text at the bottom, click ok:
7. If everything was done correctly you will see your DDNS account in the list:
And you can now proceed with the next steps on how to access your Synology on the internet.
Map your synology with your own domain name and secure it with SSL certificate
You can afterwards map your own domain name to your DDNS name to access your synology with it and if you do that, you will be able to secure your synology with a Lets encrypt certificate (Https connections).
Isn’t it easier just to use domain forwarding? On Google Domains it’s as simple as adding the DDNS address you want your domain to forward to. Example, http://domain.net forwards to http://ds218.synology.me.
I have a domain solely for accessing the DiskStation DSM so its easier to remember and type, and domain forwarding is super simple.
Sure, this way is free 🙂
/Ruth
Nice writeup. Do you know the added settings in order to manage not one but TWO DSM from the same network (i.e. they both have to share the same single dynamic external IP address that the ISP assigns at random). Thank you!
Never tried I am afraid…
/Ruth
Ruth
Nice write up – I have created a guide for creating multiple entries for the same service provider here: https://ten20four.co.uk/synology-add-multiple-ddns-entries/ not quite what @Alejandro was looking for but close.