- 20 – FTP (File Transfer Protocol – Data Transfer)
- 21 – FTP (File Transfer Protocol – Command Control)
- 22 – SSH (Secure Shell)
- 23 – Telnet
- 25 – SMTP (Simple Mail Transfer Protocol
- 53 – DNS (Domain Name System Service)
- 80 – HTTP (Hypertext Transfer Protocol)
- 110 – POP3 (Post Office Protocol)
- 119 – NNTP (Network News Transfer Protocol)
- 123 – NTP (Network Time Protocol)
- 143 – IMAP (Internet Message Access Protocol)
- 161 – SNMP (Simple Network Management Protocol)
- 194 – IRC (Internet Relay Chat)
- 443 – HTTPS (Hyptertext Transfer Protocol Secure)
- 3389 – RDP (Remote Desktop Protocol)
While the above are some of the more common ports used you can fine a more complete list here: https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
