Port scanning is a technique used to determine which ports on a network are open and listening for data. It is a fundamental step in both network administration and security auditing.
How Port Scanning Works
Think of an IP address as a house and ports as the doors and windows. A port scan effectively knocks on every door to see which ones are unlocked (open). When a service (like a web server or email server) is running, it "listens" on a specific port.
Types of Scans
- TCP Connect Scan: The scanner attempts to complete a full TCP handshake with the target port. It's reliable but easily detected.
- SYN Scan (Stealth): The scanner sends a SYN packet (request to connect) and waits for a response, but never completes the connection. This is faster and stealthier.
- UDP Scan: Used to check for open UDP ports, which are often used by services like DNS and DHCP.
How to scan open ports easily
While command-line tools like Nmap are powerful, they require technical knowledge to use effectively. For quick checks, you can use our web-based tools.
Our Online Port Checker allows you to scan any public IP address or domain for common open ports directly from your browser.