Python Port Scanner

Custom Network Reconnaissance Tool

Project Overview

I developed this tool to understand the TCP Three-Way Handshake and how network sockets function at the OS level. It scans a target IP for common open ports (21, 22, 80, 443, etc.) and reports back on service availability.

Technical Stack

Language: Python 3.x
Library: socket module
Focus: Error handling & timeout management
Speed: Synchronous scanning logic

How it works

The script attempts to create a connection to a specific port. If the connect_ex() method returns 0, the port is open. If it returns an error code, the port is closed or filtered. I implemented a timeout feature to ensure the scanner doesn't hang on unresponsive IPs.

Source Concept

scanner.py

import socket

target = "127.0.0.1" 
ports = [21, 22, 80, 443, 3389]

print(f"Scanning {target}...")

for port in ports:
    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} is OPEN")
    s.close()