Nmap (Network Mapper) is a powerful open-source tool used for network discovery, security auditing, and vulnerability scanning. It is widely used by system administrators and security professionals to identify live hosts, open ports, and running services on a network. This guide provides an overview of Nmap’s usage, options, and practical examples.

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1. Installing Nmap

Before using Nmap, ensure it is installed on your system. To install Nmap on different Linux distributions, use:

# Debian/Ubuntu
sudo apt install nmap

# CentOS/RHEL
sudo yum install nmap

# Arch Linux
sudo pacman -S nmap

For Windows and macOS, you can download Nmap from the official website.

2. Basic Nmap Scan

To perform a simple scan on a target host, run:

nmap <target>

Example:

nmap 192.168.1.1

This command scans the specified IP address and lists the open ports and services.

3. Scan a Range of IPs

To scan multiple hosts or an entire subnet, use:

nmap 192.168.1.1-100

or

nmap 192.168.1.0/24

4. Scan Specific Ports

To scan a specific port, use:

nmap -p 80 192.168.1.1

To scan multiple ports:

nmap -p 22,80,443 192.168.1.1

To scan all 65535 ports:

nmap -p- 192.168.1.1

5. Detect Operating System and Services

To detect the operating system and running services on a target machine, use:

nmap -O 192.168.1.1

To get detailed service and version information:

nmap -sV 192.168.1.1

6. Perform a Stealth Scan

A stealth scan helps evade detection by firewalls and intrusion detection systems:

nmap -sS 192.168.1.1

7. Scan for Vulnerabilities

Nmap can integrate with the Nmap Scripting Engine (NSE) to check for vulnerabilities:

nmap --script vuln 192.168.1.1

8. Scan Multiple Targets from a File

If you have a list of IP addresses in a file, you can scan them all at once:

nmap -iL targets.txt

9. Save Scan Results to a File

To save the scan results for later analysis, use:

nmap -oN output.txt 192.168.1.1

For XML format:

nmap -oX output.xml 192.168.1.1

Conclusion

Nmap is a versatile and powerful tool for network scanning, security auditing, and penetration testing. Whether you’re identifying open ports, detecting running services, or checking for vulnerabilities, Nmap provides a comprehensive suite of features. Mastering Nmap is essential for any network administrator or cybersecurity professional.