Common ports and protocols, explained one by one
The 22 port numbers CompTIA lists in the Network+ and A+ objectives, each on its own page: what the port is used for, TCP or UDP, the secure alternative, what it is confused with and a practice question.
The port list
| Port | Protocol | TCP or UDP | Listed in |
|---|---|---|---|
| 20 and 21 | FTP | TCP | Network+ · A+ |
| 22 | SSH | TCP | Network+ · A+ |
| 23 | Telnet | TCP | Network+ · A+ |
| 25 | SMTP | TCP | Network+ · A+ |
| 53 | DNS | UDP and TCP | Network+ · A+ |
| 67 and 68 | DHCP | UDP | Network+ · A+ |
| 69 | TFTP | UDP | Network+ |
| 80 | HTTP | TCP | Network+ · A+ |
| 110 | POP3 | TCP | A+ |
| 123 | NTP | UDP | Network+ |
| 137-139 | NetBIOS | UDP and TCP | A+ |
| 143 | IMAP | TCP | A+ |
| 161 and 162 | SNMP | UDP | Network+ |
| 389 | LDAP | TCP | Network+ · A+ |
| 443 | HTTPS | TCP and UDP | Network+ · A+ |
| 445 | SMB | TCP | Network+ · A+ |
| 514 | Syslog | UDP | Network+ |
| 587 | SMTP submission | TCP | Network+ |
| 636 | LDAPS | TCP | Network+ |
| 1433 | SQL Server | TCP | Network+ |
| 3389 | RDP | TCP and UDP | Network+ · A+ |
| 5060 and 5061 | SIP | UDP and TCP | Network+ |
Network+ N10-009 lists its ports under objective 1.4 (Networking Concepts); A+ Core 1 220-1201 under objective 2.1 (Networking). Numbers checked against the IANA registry.
What are well-known ports?
Port numbers run from 0 to 65535 and IANA divides them into three ranges. System ports, also called well-known ports, are 0 to 1023 and are assigned to core services such as SSH (22), DNS (53) and HTTPS (443). User ports, also called registered ports, are 1024 to 49151, for example SQL Server (1433) and RDP (3389). Dynamic or private ports, 49152 to 65535, are never assigned: any application may use them, typically as temporary source ports for outgoing connections.