Some operators o WISP companies use what is called CG-NAT or shared connection.
The router is the NAT of the public IP which is in the hands of the operator. Therefore, forget about asking them to “open ports in this PC, to enable you to use an application”. Also, you will not be able to change the public IP address, only the operator will be able to do this.
If you have in your home a web server FTP, SSH or VPN…For example if you have Nextcloud to synchronize your files where ever you are, or if you play games online which need to open ports, you weren´t be able to do so. It will be impossible to host servers. You will have a private IP and not a public IP address. Therefore, you will not have point to point internet, it will all pass through CGN.
Another issue that you may have, will be with your neighbours that you share this public IP address with.
If they decide to download on a site that is limited by an IP, you will also be affected. In the case that, for example, you go into a forum and your neighbours IP is banned, you will also be unable to enter, as you use the same IP address.
Or even worse, if they commit some illegality, credit card fraud, share paedophile material….it is possible that the police will also knock on your door. If the ISP doesn’t save all records of the movements of the NAT, so the ISP will only have one public IP address shared with multiple customers.
Also, saving this record clashes head-on with the data protection law. This is due to the fact that the operator has a record of our operations on the network. This doesn’t occur when you use a public IP address. In this case, the cyber police only require information of who had the public IP address at the time that the crime was committed. With no private information register of the operations made on the network by the client.
Is it beneficial to have a CGN connexion? In our opinion, no. Unless your usage of internet is very basic (you don´t use host servers, you don´t play online, IPTV, steaming services, etc).