Table of Contents

Simple Port Scanner

Core Functionality
Port State Detection
Security Relevance

Architecture
Quick Start

CLI Options

Project Structure
Build Requirements
Source Code

Simple Port Scanner

Concurrent TCP port scanner written in C++ with async I/O and banner grabbing.

Overview

A high-performance TCP port scanner using Boost.Asio for asynchronous I/O. Probes target hosts to identify open, closed, and filtered ports with concurrent scanning of hundreds of ports simultaneously. Includes service banner grabbing for fingerprinting.

Status: Complete | Difficulty: Beginner

Legal Disclaimer

This tool is for authorized security testing only. Only scan systems you own or have explicit written permission to test. Unauthorized port scanning may be illegal.

Tech Stack

Technology	Version	Purpose
C++	C++20	Core language
Boost.Asio	-	Async network I/O
Boost.Program_options	-	CLI argument parsing
CMake	3.31+	Build system

Features

Core Functionality

Concurrent TCP connect scanning
Configurable thread count (default 100)
Port range and list support (e.g., 1-1024 or 80,443,8080)
Three port state detection: OPEN, CLOSED, FILTERED
Service banner grabbing for fingerprinting
Configurable connection timeout

Port State Detection

State	Meaning	TCP Response
OPEN	Service listening	SYN-ACK received
CLOSED	Nothing listening, host responded	RST received
FILTERED	Firewall dropped packets silently	Timeout (no response)

Security Relevance

First step in penetration testing reconnaissance
Attack surface mapping for security audits
Detecting unauthorized services and backdoors
Understanding TCP handshake mechanics

Architecture

main.cpp (CLI parsing with boost::program_options)
    ↓
┌─────────────────────────────────────────────┐
│            PortScanner Class                 │
│                                              │
│  ┌─────────────────────────────────────┐    │
│  │         Boost.Asio io_context       │    │
│  │  Thread pool (configurable count)   │    │
│  └──────────────────┬──────────────────┘    │
│                     │                        │
│  ┌──────────────────▼──────────────────┐    │
│  │     Async TCP Connect per port      │    │
│  │  - Connect attempt with timeout     │    │
│  │  - State detection (open/closed/    │    │
│  │    filtered)                         │    │
│  │  - Banner grab on success           │    │
│  └──────────────────┬──────────────────┘    │
│                     │                        │
│  ┌──────────────────▼──────────────────┐    │
│  │         Results Collection           │    │
│  │  Port | State | Service | Banner    │    │
│  └─────────────────────────────────────┘    │
└─────────────────────────────────────────────┘

Quick Start

cd PROJECTS/beginner/simple-port-scanner

# Build
mkdir build && cd build
cmake ..
make

# Scan localhost ports 1-1024
./simplePortScanner -i 127.0.0.1 -p 1-1024

# Scan specific ports with custom settings
./simplePortScanner -i scanme.nmap.org -p 80,443,8080 -t 50 -e 3

CLI Options

Flag	Description	Default
`-i`	Target IP address	Required
`-p`	Port range or list	Required
`-t`	Thread count	100
`-e`	Timeout (seconds)	3

Project Structure

simple-port-scanner/
├── src/
│   ├── PortScanner.hpp    # Class definition and method signatures
│   └── PortScanner.cpp    # Scanning logic, async operations, banner grabbing
├── main.cpp               # Entry point, CLI argument parsing
└── CMakeLists.txt         # Build configuration (Boost dependencies)

Build Requirements

CMake 3.31+
C++20 compiler (GCC 10+, Clang 12+, or MSVC 2019+)
Boost libraries (apt install libboost-all-dev or brew install boost)

Source Code

View on GitHub

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