🚪 What are Port Numbers?

A port number is a 16-bit number (from 0 to 65535) that identifies a specific application or process on a device. While an IP address gets network traffic to the right computer, the port number gets that traffic to the right application on that computer.

Analogy: If an IP address is the street address of an apartment building, the port number is the specific apartment number. It ensures the delivery goes to the correct resident (application).

📚 Categories of Port Numbers

Ports are divided into three main ranges:

1. Well-Known Ports (0 - 1023) These are reserved for standard, system-level services. Common examples include:

   • Port 80: HTTP (Standard web traffic)
   • Port 443: HTTPS (Secure web traffic)
   • Port 53: DNS
   • Port 22: SSH (Secure Shell)
   • Port 25: SMTP (Email sending)

2. Registered Ports (1024 - 49151) These are registered for specific user applications (e.g., many database services use these).

3. Dynamic or Ephemeral Ports (49152 - 65535) These are used for temporary, outbound connections. When your web browser connects to a website, it uses a random port from this range as its source port.

🤝 How Ports are Used in a Connection

A network connection is defined by a pair of sockets. A socket is the combination of an IP address and a port number.

For example, when you visit google.com:

• Your Device (Client): Source IP:Source Port (e.g., 192.168.1.10:51234)
• Google’s Server: Destination IP:Destination Port (e.g., 142.250.196.110:443)

The router uses this full address information to shuttle traffic between your browser and Google’s web server.

🔬 Sub-Topic: Inspecting Port Numbers with Wireshark

🤔 What is Wireshark?

Wireshark is a free and powerful network protocol analyzer. It captures and displays the data packets traveling on your network, allowing you to see what’s happening in real-time.

🔍 Finding Port Numbers in Wireshark

1. Start Capture: Open Wireshark, select your active network interface (e.g., “Wi-Fi”), and start the capture by clicking the shark fin icon.
2. Generate Traffic: Open a web browser and visit a website.
3. Stop Capture: Return to Wireshark and click the red square to stop the capture.
4. Analyze the Packet List: The main window shows all captured packets. Look for traffic involving your computer’s IP address.
5. Inspect Packet Details:
   • Click on a packet in the list.
   • In the “Packet Details” pane below, expand the Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) section.
   • Inside, you will clearly see the Source Port and Destination Port for that specific packet of data.