All credit for the original creation of this list goes to Adam Gordon. Thank you Adam, for all you do!

I have amended this list with all the resources I use in my YouTube video “What ports do I need to know?”.

20, 21 - FTP

• What is File Transfer Protocol (FTP) meaning | Fortinet

22 - SSH

• What is SSH? | Secure Shell (SSH) protocol | Cloudflare

23 - Telnet

• Telnet Protocol - Definition & How it Works - ExtraHop

25 - SMTP

• What is the Simple Mail Transfer Protocol (SMTP)? | Cloudflare

49 - TACACS+

• Port 49