Port Checker

How It Works

Network ports are virtual endpoints for communication in computer networking. Every network connection between two devices uses a combination of an IP address and a port number to identify the specific service or application communicating.

Port numbers range from 0 to 65535 and are divided into three ranges:

• Well-Known Ports (0 – 1023): Reserved for common system services and protocols. These are assigned by IANA (Internet Assigned Numbers Authority) and typically require elevated privileges to bind to. Examples include HTTP (80), HTTPS (443), and SSH (22).
• Registered Ports (1024 – 49151): Available for user processes and applications. Organizations can register specific ports with IANA for their services. Examples include MySQL (3306), PostgreSQL (5432), and Redis (6379).
• Dynamic/Private Ports (49152 – 65535): Used for temporary (ephemeral) connections. When your computer connects to a web server, it typically uses a random port from this range as the source port for the connection.

TCP vs UDP

Ports operate over two main transport protocols:

• TCP (Transmission Control Protocol): Connection-oriented protocol that ensures reliable, ordered delivery of data. Used by HTTP, HTTPS, SSH, FTP, SMTP, and most web services.
• UDP (User Datagram Protocol): Connectionless protocol that prioritizes speed over reliability. Used by DNS, DHCP, VoIP, video streaming, and online gaming.

Port Security

Understanding which ports are open on a system is essential for network security. Open ports represent potential entry points for attackers. Best practices include:

• Close all ports that are not actively needed
• Use firewalls to restrict access to necessary ports
• Regularly audit open ports with tools like netstat, ss, or nmap
• Keep services behind open ports updated and patched