Well-known ports: 0-1023
Registered ports: 1024-49,151
Dynamic ports: 49,152-65,535
Most common ports and services:
| Protocol name | TCP/UDP | Port number |
| File Transfer Protocol (FTP) | TCP | 20, 21 |
| Secure Shell (SSH) | TCP | 22 |
| Telnet | TCP | 23 |
| Simple Mail Transfer Protocol (SMTP) | TCP | 25 |
| Domain Name System (DNS) | TCP/UDP | 53 |
| Dynamic Host Configuration Protocol (DHCP) | UDP | 67, 68 |
| Trivial File Transfer Protocol (TFTP) | UDP | 69 |
| Hypertext Transfer Protocol (HTTP) | TCP | 80 |
| Post Office Protocol version 3 (POP3) | TCP | 110 |
| NetBIOS | TCP/UDP | 137, 138, 139 |
| Internet Message Access Protocol (IMAP) | TCP | 143 |
| Simple Network Management Protocol (SNMP) | UDP | 161, 162 |
| Lightweight Directory Access Protocol (LDAP) | TCP | 389 |
| Hypertext Transfer Protocol over SSL/TLS (HTTPS) | TCP | 443 |
| Lightweight Directory Access Protocol over TLS/SSL (LDAPS) | TCP | 636 |
| FTPS — FTP over... |