There are 2 ways to setup external access for your Synology NAS, the first way is to setup Synology QuickConnect ID. The other method is to setup router port forwarding. If you are using QuickConnect ID definitely would be safer compare to router port forwarding method because you have to manage your router security better if you are doing it your way.
A standard port to access Synology NAS HTTP is port 5000. HTTP then required port 5001. To access photo station externally then you required a port 80. Surveillance Station required standard port 5000 or 5001.
Synology Network Ports
You can see the complete list of network port for Synology NAS, refer to here.
Although in the network port list, they mentioned required port 9000 or 9001 for Surveillance Station, but I noticed that exposing port 5000 and 5001 is sufficient enough.
Router Port Forwarding
Let’s say, for an example if your Synology NAS URL is, http://192.168.0.108:5000/webman/index.cgi
You can set your router port forwarding like below,
If your external IP address (router IP address) is like 18.104.22.168, you can access your Synology NAS using http://22.214.171.124:20000/ then you can see your Synology NAS login screen.
For cloud station, just access it with http://126.96.36.199:20001/ will do.
In order to test if your Synology NAS successfully exposed to external access, use Google Paping to double check with “paping 188.8.131.52 -p 20001”.
*Most importantly, setup your Synology NAS properly, please refer to here.*