Port 3389 — RDP

TCP registered

What runs on port 3389

Windows Remote Desktop.

Security considerations

A primary ransomware entry vector. Put it behind a VPN, require network level authentication, and never expose it directly.

Checking whether something is listening

# Linux / macOS — what is bound to the port
sudo lsof -i :3389
sudo ss -lntp | grep :3389

# Windows
netstat -ano | findstr :3389
Get-NetTCPConnection -LocalPort 3389

# is it reachable from outside?
nc -zv example.com 3389
curl -v telnet://example.com:3389

Freeing the port

# find the process, then stop it
sudo lsof -ti :3389 | xargs kill        # Linux / macOS
netstat -ano | findstr :3389            # note the PID, then:
taskkill /PID <pid> /F                    # Windows

Other common ports

• Port 20 — FTP data
• Port 21 — FTP control
• Port 22 — SSH / SFTP
• Port 23 — Telnet
• Port 25 — SMTP
• Port 53 — DNS
• Port 67 — DHCP server
• Port 68 — DHCP client
• Port 69 — TFTP
• Port 80 — HTTP
• Port 110 — POP3
• Port 123 — NTP
• Port 143 — IMAP
• Port 161 — SNMP
• Port 389 — LDAP
• Port 443 — HTTPS
• Port 445 — SMB
• Port 465 — SMTPS

All port numbers