Ports
Category: Networking Basics
Key Takeaway
Ports are virtual communication endpoints used by devices to send and receive data over a network.
What Are Ports?
A port is a virtual endpoint that allows a computer or device to send and receive data over a network. Think of your computer as a building, and ports are doors: different doors are used for different services (like web, email, or file transfers).
Why Ports Matter
| Benefit | Description |
|---|---|
| Multiple Services | A single device can run many services at the same time, each using a different port. |
| Traffic Direction | Helps the system know which service should handle incoming data. |
| Security Controls | Firewalls and ACLs can allow or block traffic based on port numbers. |
| Troubleshooting | Identifying open/closed ports helps diagnose network and application issues. |
Common Port Types
TCP vs UDP
- TCP (Transmission Control Protocol): Reliable, connection-oriented.
- UDP (User Datagram Protocol): Faster, connectionless, no guaranteed delivery.
Common Ports (0–1023)
| Port | Protocol | Common Use |
|---|---|---|
| 20/21 | TCP | FTP (File Transfer) |
| 22 | TCP | SSH (Secure Shell) |
| 23 | TCP | Telnet (Unsecure remote login) |
| 25 | TCP | SMTP (Email sending) |
| 53 | TCP/UDP | DNS (Domain Name System) |
| 80 | TCP | HTTP (Web traffic) |
| 110 | TCP | POP3 (Email retrieval) |
| 143 | TCP | IMAP (Email retrieval) |
| 443 | TCP | HTTPS (Secure web traffic) |
| 3389 | TCP | RDP (Remote Desktop Protocol) |
How Ports Work
- Your computer sends a packet to a server IP address and specifies a port number.
- The server looks at the port number to determine which service should handle the data.
- Response traffic comes back to the same source port on your computer.
Analogy: Ports are like mail slots in an apartment building—each slot directs mail to the correct apartment (service).
Quick Quiz
-
Q: What is the main purpose of network ports?
Show Answer
To direct network traffic to the correct service or application on a device.
-
Q: Which port is commonly used for secure web traffic?
Show Answer
Port 443 for HTTPS.