TCP vs UDP and common ports: FTP 20/21, SSH 22, Telnet 23, SMTP 25, DNS 53, DHCP 67/68, HTTP 80, POP3 110, IMAP 143, SNMP 161/162, LDAP 389, HTTPS 443, SMB 445, RDP 3389

Every network conversation needs two things beyond an IP address: a transport protocol and a port number. The IP address gets a packet to the right computer, and the port number gets it to the right service on that computer, such as a web server or mail server. The two main transport protocols are TCP and UDP. The A+ exam expects you to know how they differ and to recall the standard port for each common service, because firewalls, router rules and troubleshooting all depend on them.