you’re getting a private (i.e. not routable) IP address
from your provider. That’s not gonna work. Your provider
has to assign you a public IP - if you get a dynamic one
then you need DDNS indeed. If you get a static public
IP you don’t even need a DDNS service.
And (I think) you’d better use port forwarding instead of
SNAT.
Regards,
Timelapse Admin (running 60+ routers with various port forwards and public IPs)