Port is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system,
ex :
| Protocol | Port Number |
| FTP | 21 |
| SSH | 22 |
| Telnet | 23 |
| SMTP | 25 |
| DNS | 53 |
| DHCP | 66/67 |
| HTTP | 80 |
| POP | 110 |
| IMAP | 143 |
| SNMP | 161 |
| HTTPS | 443 |
| MYSQL | 3306 |
| RDP | 3389 |