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Common TCP and UDP ports: a cheat sheet
A scannable reference of common TCP and UDP ports grouped by purpose — web, mail, file transfer, remote access, databases, and infrastructure.
How to scan ports with Nmap: a practical guide
Learn how to scan TCP and UDP ports with Nmap: install, port selection, SYN vs connect scans, version detection, NSE scripts, and output formats.
The most commonly attacked ports (and how to secure them)
The internet-facing ports attackers hit first — RDP, SSH, SMB, databases — and the single most important hardening step for each.
Which ports should you block at the firewall?
A practical guide to ports you should never expose to the internet — SMB, RDP, Telnet, databases and more — with the risk and a safer alternative for each.
TCP vs UDP: what's the difference?
A clear comparison of TCP and UDP: handshakes, reliability, headers, real-world use cases, and why UDP fuels amplification DDoS attacks.
Well-known, registered, and dynamic ports explained
Understand the IANA port ranges: well-known (0-1023), registered (1024-49151), and dynamic (49152-65535), plus how the 16-bit port space and ephemeral ports work.