Linux Hint published a tutorial about checking open ports in Debian 10.

Debian 10 Check Open Ports

The endpoints of communication are called ports. They are required when two or more parties communicate with each other via a network. Usually, while communicating, their respective ports should stay open. However, when a communication terminates, the ports could still stay open, which can enhance various security concerns. In this article, different methods are explained to check the open ports in Debian 10.

Debian 10 Check Open Ports – Linux Hint