Nmap – Network Discovery and Security Auditing Tool

What is Nmap?

Nmap (Network Mapper) is a free and open-source utility for network discovery and security auditing. Created by Gordon Lyon (Fyodor) in 1997, Nmap has evolved into one of the most trusted and widely used security tools, employed by network administrators and security professionals worldwide.

Originally designed for rapidly scanning large networks, Nmap uses raw IP packets to determine available hosts, services, operating systems, firewall configurations, and numerous other characteristics that make it indispensable for security assessments.

Key Features

• Host discovery: Identify live hosts on a network using various probing techniques
• Port scanning: Enumerate open ports on target hosts with multiple scan types
• Service detection: Determine application names and versions running on open ports
• OS detection: Identify operating systems and hardware characteristics
• Scriptable interaction: Nmap Scripting Engine (NSE) for advanced tasks
• Output formats: Normal, XML, grepable, and script kiddie output
• IPv6 support: Full support for IPv6 network scanning
• Cross-platform: Runs on Linux, Windows, macOS, and BSD

Legal Considerations

Important: Only scan networks and systems you own or have explicit written permission to test. Unauthorized scanning may violate computer crime laws in many jurisdictions.

System Requirements

• Any modern operating system (Linux, Windows, macOS, BSD)
• Root/administrator privileges for some scan types
• libpcap (Linux/macOS) or Npcap (Windows)
• Minimal RAM and CPU requirements

Installation Guide

debian">Ubuntu/Debian

sudo apt update
sudo apt install nmap

rhel-fedora">CentOS/RHEL/Fedora

sudo dnf install nmap

Arch Linux

sudo pacman -S nmap

macOS (Homebrew)

brew install nmap

From Source

wget https://nmap.org/dist/nmap-7.94.tar.bz2
tar xvf nmap-7.94.tar.bz2
cd nmap-7.94
./configure
make
sudo make install

Basic Scan Types

Host Discovery

# Ping scan - discover live hosts
nmap -sn 192.168.1.0/24

# ARP scan for local network
nmap -PR 192.168.1.0/24

# Skip host discovery, scan all targets
nmap -Pn 192.168.1.1

Port Scanning

# TCP SYN scan (default, requires root)
sudo nmap -sS 192.168.1.1

# TCP connect scan
nmap -sT 192.168.1.1

# UDP scan
sudo nmap -sU 192.168.1.1

# Scan specific ports
nmap -p 22,80,443 192.168.1.1

# Scan all 65535 ports
nmap -p- 192.168.1.1

# Scan top 1000 ports (default)
nmap --top-ports 1000 192.168.1.1

Service and Version Detection

# Detect service versions
nmap -sV 192.168.1.1

# Aggressive version detection
nmap -sV --version-intensity 5 192.168.1.1

# OS detection
sudo nmap -O 192.168.1.1

# Comprehensive scan
sudo nmap -A 192.168.1.1

Nmap Scripting Engine (NSE)

# Run default scripts
nmap -sC 192.168.1.1

# Run specific script category
nmap --script vuln 192.168.1.1

# Run specific script
nmap --script http-title 192.168.1.1

# List available scripts
ls /usr/share/nmap/scripts/

# Script categories available:
# auth, broadcast, brute, default, discovery,
# dos, exploit, external, fuzzer, intrusive,
# malware, safe, version, vuln

Output Options

# Save in all formats
nmap -oA scan_results 192.168.1.1

# Normal output
nmap -oN output.txt 192.168.1.1

# XML output
nmap -oX output.xml 192.168.1.1

# Grepable output
nmap -oG output.gnmap 192.168.1.1

Common Use Cases

• Network inventory: Discover all devices on your network
• Security auditing: Find open ports and potential vulnerabilities
• Firewall testing: Verify firewall rules are working correctly
• Compliance checking: Ensure systems meet security requirements
• Troubleshooting: Diagnose network connectivity issues

Timing and Performance

# Timing templates (T0-T5)
nmap -T4 192.168.1.1  # Aggressive timing

# T0: Paranoid (very slow)
# T1: Sneaky
# T2: Polite
# T3: Normal (default)
# T4: Aggressive
# T5: Insane (may miss results)

Zenmap – GUI for Nmap

Zenmap is the official graphical user interface for Nmap, providing an easier way to run scans and visualize results with network topology maps.

Download

Nmap is released under a custom open-source license. Download the latest version:

Download Nmap

Latest Version: 7.94
License: Nmap Public Source License
Developer: Gordon Lyon (Fyodor)