In what situations is it necessary to open TCP ports on a server?

TCP ports on the server need to be opened when the server must accept incoming connections for specific protocols and services. For example:

• Web server (HTTP) usually listens on port 80 or 443.
• SSH server — port 22 for remote management.
• Databases — their own ports (e.g., 3306 for MySQL).

Opening a port means the server is ready to accept connections on that port. If the port is closed (filtered by a firewall or not listened to by an application), external clients will not be able to connect.

It is important to open only the necessary ports for security and risk minimization.