Python for Network Scanning: Building Your Own Port Scanner

Network scanning is a crucial skill in cybersecurity and network administration. It helps identify open ports, services, and potential vulnerabilities on a network. In this blog post, we’ll explore how to create a basic port scanner using Python’s socket library. This tool will allow you to scan for open ports on a target system.

What is a Port Scanner?

A port scanner is a tool that checks the status of ports on a target system (e.g., open, closed, or filtered). It’s commonly used by network administrators and security professionals to:

• Identify open ports and services.
• Detect potential vulnerabilities.
• Monitor network security.

Building a Port Scanner in Python

Python’s socket library provides low-level networking interfaces, making it ideal for building a port scanner. Below is a step-by-step guide to creating a basic port scanner.

Step 1: Import the Required Library

We’ll use the socket library to create the port scanner. Here’s how to import it:

        import socket
    

Step 2: Define the Target and Port Range

To scan a target, you need to specify the target IP address and the range of ports to scan. For example:

        target = "192.168.1.1"  # Replace with your target IP
        start_port = 1
        end_port = 1024  # Scan ports from 1 to 1024
    

Step 3: Writing the Port Scanner

Here’s the Python code for a basic port scanner:

        import socket

        target = "192.168.1.1"  # Replace with your target IP
        start_port = 1
        end_port = 1024

        def scan_port(ip, port):
            try:
                # Create a socket object
                sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                sock.settimeout(0.5)  # Set a timeout for the connection

                # Attempt to connect to the port
                result = sock.connect_ex((ip, port))
                if result == 0:
                    print(f"Port {port} is open")
                sock.close()
            except Exception as e:
                print(f"Error scanning port {port}: {e}")

        # Scan the specified range of ports
        for port in range(start_port, end_port + 1):
            scan_port(target, port)
    

Step 4: Running the Port Scanner

Save the script as port_scanner.py and run it. The program will scan the specified range of ports on the target IP address and print which ports are open.

Enhancing the Port Scanner

You can enhance the port scanner by adding features like:

• Scanning multiple IP addresses.
• Adding support for UDP ports.
• Exporting results to a file.

Here’s an example of scanning multiple IP addresses:

        import socket

        targets = ["192.168.1.1", "192.168.1.2"]  # List of target IPs
        start_port = 1
        end_port = 1024

        def scan_port(ip, port):
            try:
                sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                sock.settimeout(0.5)
                result = sock.connect_ex((ip, port))
                if result == 0:
                    print(f"Port {port} is open on {ip}")
                sock.close()
            except Exception as e:
                print(f"Error scanning port {port} on {ip}: {e}")

        for target in targets:
            for port in range(start_port, end_port + 1):
                scan_port(target, port)
    

Ethical Considerations

When using a port scanner, it’s important to:

• Obtain permission before scanning any network or system.
• Use the tool responsibly and ethically.
• Comply with local laws and regulations.

Conclusion

Building a port scanner in Python is a great way to learn about network scanning and cybersecurity. With just a few lines of code, you can create a tool that identifies open ports on a target system. Remember to use this knowledge responsibly and always obtain permission before scanning any network.

Have you tried building a port scanner or any other network tool in Python? Share your experiences in the comments below!

Disclaimer: This blog post is for educational purposes only. The author does not condone or encourage the misuse of port scanners or any other tools for malicious purposes.