CG-NAT Blocks my OpenVPN and restricks the NAT type
Credit to a customer named Roger Wentland.
After buying the TP-Link router to used in my house, I can get the internet on my device without an issue. However, there are two devices in my network that can’t work properly - my camera and a switch.
To view the camera from the outside network, I need to connect the OpenVPN to my router. And another strange thing is that my switch network couldn't play online games with others. When checking internet connectivity on the switch, the NAT setting is “D”. The information on the network tells me that I need to set port forwarding or DMZ, but neither works in my case.
So I contacted TP-Link Support, and they checked my OpenVPN configuration file(Use the txt/notepad+ to open the OpenVPN configure file) and told me that my router's WAN IP is a private network IP.
Then I contacted my ISP-Comporium. I did an online chat with Comporium and the tech gave me a link that shows my public IP address and CG-NAT IP address. The tech confirmed that CG-NAT will block the OpenVPN connection, or it blocks some ports automatically for my network. The Comporium also offers a Static IP address access to solve the issue, but I need to pay a small fee.
(Related data of Comporium: https://www.comporium.com/help/cgnat-transition-faq/)
Although I would like to find other ways to solve this problem, buying a static IP is undoubtedly the most convenient one. With a static public network IP, I can normally use my OpenVPN and forward the local resources to the outside.
Except Comporium, my ISP, I also know that DirectLink, who provides a radio service, is one of another CG-NAT ISPs in my country. BTW, I'm based in the United States.
(Wiki: CGN or CG-NAT is a type of NAT for use in IPv4 network design. It permits the sharing of small pools of public addresses among many end sites. This shifts the NAT function and configuration thereof from the customer premises to the Internet service provider network. So there's a layer of NAT processing in front of the router.)