In this guide i will show you how to assign a fixed host and domain name to a dynamic Internet IP address, using your TerraMaster NAS.
We'll use the free DDNS service provider Duck DNS available at https://www.duckdns.org/
If you already have a Duck DNS domain available, skip to Step 3
Open your web browser and navigate to https://www.duckdns.org.
Sign in using one of the 4 available method (Persona, Twitter, GitHub or Google)

Once you're loged in, type your desired domain name (myddnsdomain in this guide) and press on add domain button.

You will get a message that the new domain myddnsdomain.duckdns.org was added to your account.
We also see that is was linked to your WAN IP address (hidden in this guide). Whenever you want to access your external IP, you can just type myddnsdomain.duckdns.org.

If your internet service provider has given you a dynamic IP address, after every renewal, your WAN IP will not be linked anymore to your domain.
To keep this linked, we"ll use the function from TOS6 to keep the WAN IP and your domain synced.
Access your TOS6 and go to Control Panel > Remote Access

Now choose DDNS and press on the + icon

Leave the default Use and existing service provider and press on Next

On the DDNS service provider select duckdns

For token, you need the token available in your duckdns account.
Go back to your duckdns account and copy the toeken

Paste this into the token attribute on TOS
On the Dynamic domain, type your domain
Select the Update intervam from 5 to 30 minutes
Press on Apply

The service is created now and initially will show as Disconnected

Refresh the page and it will show as Connected if your setup is OK.
From now on, whenever you Internet IP will change, it will be synced every x minutes to your domain myddnsdomain.duckdns.org
