$nmap -p- portsdb.org
Every TCP & UDP port, explained.
Look up any port: what service runs on it, why it matters, how it's attacked, and how to lock it down — with a ready-to-run nmap snippet.
Most-attacked ports
CharGEN (Character Generator Protocol)
Character Generator — a legacy debugging service that emits a stream of characters in response to any input.
FTP (File Transfer Protocol) data channel
FTP active-mode data channel that carries file contents and directory listings.
FTP (File Transfer Protocol) control channel
FTP command and authentication channel for browsing and transferring files.
SSH (Secure Shell)
Secure Shell — encrypted remote login, command execution, and tunneling.
Telnet
Unencrypted remote terminal protocol for interactive login and device management.
SMTP (Simple Mail Transfer Protocol)
Server-to-server email transfer protocol used to relay and deliver mail between MTAs.
DNS (Domain Name System)
Domain Name System — resolves hostnames to IP addresses and serves zone data.
DHCP (Dynamic Host Configuration Protocol) server
DHCP server port — assigns IP addresses and network configuration to clients.