Nmap: Scanning Networks and Understanding Results

Nmap is the standard tool for network discovery and security audits. It finds devices, open ports and running services.

Basic commands

nmap -sn 192.168.1.0/24      # host discovery (ping scan)
nmap 192.168.1.10            # default port scan
nmap -p 1-1000 192.168.1.10   # port range
nmap -sV 192.168.1.10        # service detection
nmap -sS 192.168.1.10        # SYN scan (half-open, needs root)

Understanding output

22/tcp open ssh means port 22 is reachable and detected as SSH. filtered means a firewall blocks or drops packets.

NSE scripts

nmap --script vuln 192.168.1.10        # vulnerability check
nmap --script http-headers example.com

Legal

Scanning without permission can be illegal. Only scan your own systems or systems with written authorization.

See also: Networking.