Port Numbers to Know for the A+, Network+, and Security+ Exams
Port numbers are one of the few things on a CompTIA exam that reward flat memorization. There is no reasoning your way to the fact that LDAP is 389. You either know it or you lose the point — and ports show up on the A+, Network+, and Security+ exams, sometimes several times each. The good news is that the list is short and there is a structure hiding inside it. Learn the insecure and secure pairs together. Most of the list is one protocol appearing twice — once in the clear, once wrapped in TLS. The Ports You Must Know Port Protocol TCP/UDP What it does 20, 21 FTP TCP File transfer — 20 is data, 21 is control. Unencrypted. 22 SSH, SCP, SFTP TCP Encrypted remote administration and file transfer. 23 Telnet TCP Remote administration in cleartext. Legacy; know it as the insecure counterpart to SSH. 25 SMTP TCP Sending mail between servers. 49 TACACS+ TCP AAA service, Cisco-oriented. Encrypts the entire payload. 53 DNS UDP and TCP Name resolution. UDP for queries, TCP for zo...