Python Port Scanning Tutorial: Build Your Own Scanner

🛠️ Python Port Scanning Tutorial: Build Your Own Scanner

📌 Table of Contents

1. Introduction
2. Prerequisites
3. Building a Basic Port Scanner
4. Enhancing the Scanner with Threading
5. Advanced Features
6. Best Practices
7. Common Use Cases
8. Troubleshooting
9. Additional Resources
10. 🔗 Friendly Links

🧭 Introduction

Port scanning is a critical technique in network diagnostics and cybersecurity. It helps identify which ports are open on a host and what services may be running. By building your own scanner in Python, you’ll learn more about:

• TCP connections
• Networking protocols
• Threading for performance

📋 Prerequisites

Before starting, ensure you have:

• Python 3.x installed
• Familiarity with:
  • Basic Python syntax
  • Sockets and the TCP/IP model
• A terminal or IDE to run your code
• Authorization to scan your chosen target IP (scanning external networks without permission is illegal)

🔧 Building a Basic Port Scanner

Let’s create a simple scanner that checks for open TCP ports from 1 to 1024.

✅ Step 1: Import Required Libraries

python import socket
from datetime import datetime

✅ Step 2: Define the Target

python


target = input("Enter the host to be scanned: ")

✅ Step 3: Port Scanning Loop

python print(f"Scanning target {target}")
start_time = datetime.now()

for port in range(1, 1025):
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    socket.setdefaulttimeout(1)
    result = s.connect_ex((target, port))
    if result == 0:
        print(f"Port {port}: Open")
    s.close()

end_time = datetime.now()
print(f"Scanning completed in: {end_time - start_time}")

🧪 Test it locally using 127.0.0.1 or localhost.

⚡ Enhancing the Scanner with Threading

Speed up the scan using Python’s threading module.

✅ Step 1: Add Threading

python


import threading

✅ Step 2: Define a Threaded Scan Function

python def scan_port(port):
    try:
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        socket.setdefaulttimeout(1)
        result = s.connect_ex((target, port))
        if result == 0:
            print(f"Port {port}: Open")
        s.close()
    except:
        pass

✅ Step 3: Launch Multiple Threads

python for port in range(1, 1025):
    thread = threading.Thread(target=scan_port, args=(port,))
    thread.start()

🧠 You can also use concurrent.futures.ThreadPoolExecutor for even more control.

🚀 Advanced Features

📡 1. Banner Grabbing

pythondef grab_banner(port):
    try:
        s = socket.socket()
        s.settimeout(2)
        s.connect((target, port))
        banner = s.recv(1024)
        print(f"Port {port} Banner: {banner.decode().strip()}")
        s.close()
    except:
        pass

🛎 2. Service Detection

python common_ports = {
    21: 'FTP',
    22: 'SSH',
    23: 'Telnet',
    25: 'SMTP',
    53: 'DNS',
    80: 'HTTP',
    110: 'POP3',
    443: 'HTTPS',
}

Use this mapping for user-friendly output.

💾 3. Save Results to File

python with open('scan_results.txt', 'a') as file:
    file.write(f"Port {port}: Open\n")

✅ Best Practices

• ✅ Only scan with permission
• ⏱ Use reasonable timeouts (0.5–2 seconds)
• 🔁 Log results to avoid losing data
• 🧯 Handle exceptions to prevent crashes

🔍 Common Use Cases

• 🔐 Security auditing & vulnerability scanning
• 🖥 System monitoring by administrators
• 🎓 Educational learning in networking or cybersecurity courses

🧰 Troubleshooting

📚 Additional Resources

• 🎥 YouTube - Python Port Scanner Tutorial Build a Basic Port Scanner in Python (Tech With Tim)
• 📘 GeeksforGeeks Guide Threaded Port Scanner
• 🔗 ThePythonCode.com Advanced Port Scanner in Python
• 🧵 AsyncIO Version Fast Python Port Scanner Using AsyncIO

🔗 Friendly Links

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• 🎥 Tech With Tim’s Python Tutorial — Great YouTube channel for Python learners.
• 🔐 Nmap - Network Scanner Tool — A professional-grade open-source scanner you should also explore.