TCP/UDP Port Lookup

TCP/UDP Port Numbers Reference

A network port is a numeric identifier (0–65535) in the TCP/UDP header that allows the OS to route traffic to the correct application. Ports 0–1023 are well-known ports reserved by IANA.

Key ports to know

• 22 SSH — secure remote access;
• 80/443 HTTP/HTTPS — web traffic;
• 3306/5432 MySQL/PostgreSQL — databases;
• 6379 Redis, 27017 MongoDB — NoSQL databases.

Frequently Asked Questions

• How do I find out which port a program on my computer is using?

  Open a command prompt (Windows) or terminal (Linux/macOS) and run netstat -an | grep LISTEN on Linux, or netstat -ano on Windows. You will see a list of active listening ports along with process IDs. Cross-reference the port number with the 101ip.ru port reference to identify the application using it.

• Why can the same port be listed for both TCP and UDP?

  Many services historically use both protocols for different purposes. For example, DNS (port 53) operates over UDP for standard queries but falls back to TCP for large responses such as zone transfers. Web servers (port 80) use only TCP, while games and VoIP often use UDP for lower latency. When both protocols are listed, the service supports either depending on the situation.

• Which ports do attackers most commonly scan, and how can I protect myself?

  Attackers typically probe well-known ports: 21 (FTP), 22 (SSH), 23 (Telnet), 3389 (RDP), and 3306 (MySQL). To protect yourself, close unused ports in the firewall, move critical services to non-standard port numbers (for example, SSH to 2222), and regularly audit open ports using the Port Scanner tool at 101ip.ru.