In the simplest form, the DDNS is not actually looking for the 192.168.xxx.xxx at all. It is
looking for your current Public IP address and whatever will answer at that
address. The target computer needs an open firewall port and an application that is listening on that port that
will answer, hopefully with a strong password, AND the router needs that port opened to that computer (here is where the local, private IP address
gets involved). There are also security considerations for the target
computer regarding file and printer sharing (make sure it is off at all drives,
printers, etc) because more than just your app can answer!
From the Internet outside towards target computer...
The addressing goes like this: (Public) IP:port (or in the case of DDNS, https://yoursite.com:port)
Here are a few hypothetical samples.... (random Public IP shown)
(Sample computer #1 is at 192.168.1.1 Port 81 open, Router Port 81 open for both TCP and UDP) to this local IP address)
22.214.171.124:81 (because in this sample port 81 is open) This computer can respond.
More computers/devices can connect via DDNS too...
(Sample computer #2 is at 192.168.1.2 Port 82 open, Router Port 82 open for both TCP and UDP) to this local IP address)
126.96.36.199:82 (because in this sample port 82 is open) This computer can respond.
Camera #1 is at 192.168.1.22 and it uses port 8000 (access your security camera if address, router port, and camera port is set up correctly). You would enter 188.8.131.52:8000 to access it. Some cameras require more than one port so check camera documentation to see which ports are needed and type (UDP or TCP or both).
You can open multiple router ports to an internal IP address, however, a specific router port can be opened to only ONE local IP address.
Any computer accessed by DDNS must have a local static IP address.
It is advisable to purchase a good Internet security gateway since you are connecting computers to a DDNS. Look HERE
There are restricted ports you cannot use.... Go HERE to see them
Maybe this helps