SMB, which operates on TCP port 445, is used for network file sharing. Blocking this port from external access is a common security practice to prevent exploitation from outside the network. Leaving this port open to the internet can lead to security breaches as attackers can potentially gain access to shared files or even execute remote code. Other listed ports serve different purposes; for example, TCP port 443 is used for secure web traffic (HTTPS), TCP port 3389 is for Remote Desktop Protocol (RDP), and TCP port 22 is for Secure Shell (SSH), none of which are the primary protocol for network file sharing.