Key ports: HTTP 80, HTTPS 443, SSH 22, SMTP 25, DNS 53, DHCP 67/68, RDP 3389, SMB 445, LDAP 389, LDAPS 636, SNMP 161/162, FTP 20/21, Telnet 23, IMAP 143, POP3 110.
Memorize the key ports — they appear frequently on Security+ AND Network+ exams. Encrypted alternatives: SSH (22) replaces Telnet (23), SFTP replaces FTP (21), LDAPS (636) replaces LDAP (389), HTTPS (443) replaces HTTP (80).