Port Basics
A Port is a logical assignment number used in conjunction with an IP address to identify a specific process (program) or service running on a computer.
If an IP address is the building address to find a computer, the Port number is the room number (or recipient) inside that building.
1. Role and Range of Ports
① Role
When a data packet arrives at a computer via the network, the operating system checks the destination port number of the packet and delivers the data to the specific program (web browser, email client, game, etc.) listening on that port.
② Range (0 ~ 65535)
Port numbers are 16-bit integers, allowing for 65,536 possible ports, divided into three ranges:
- Well-Known Ports (0 ~ 1023): Reserved for standard protocols. (e.g., HTTP, FTP)
- Registered Ports (1024 ~ 49151): Used by specific vendors or applications. (e.g., MySQL, Minecraft)
- Dynamic/Private Ports (49152 ~ 65535): Temporarily assigned to client programs on user PCs.
2. List of Representative Port Numbers
These are essential ports commonly encountered in network management and development.
| Port No. | Protocol | Service | Description |
|---|---|---|---|
| 20, 21 | TCP | FTP | File Transfer Protocol (20: Data, 21: Control) |
| 22 | TCP | SSH | Secure Shell (Essential for remote Linux management) |
| 23 | TCP | Telnet | Unencrypted text communications (Legacy, insecure) |
| 25 | TCP | SMTP | Email Sending (Transfer between mail servers) |
| 53 | UDP/TCP | DNS | Domain Name System (Name resolution) |
| 80 | TCP | HTTP | Web traffic (Unencrypted) |
| 110 | TCP | POP3 | Email Receiving (Download and delete) |
| 143 | TCP | IMAP | Email Receiving (Server synchronization) |
| 443 | TCP | HTTPS | Secure Web traffic (SSL/TLS encrypted) |
| 3306 | TCP | MySQL | MySQL Database connection |
| 3389 | TCP | RDP | Windows Remote Desktop Protocol |
| 8080 | TCP | HTTP Proxy | Commonly used as an alternative web server port |