Nmap

What it is

Nmap is a free network discovery and security-auditing scanner, maintained by the Nmap Project (Insecure.Com LLC / Fyodor and contributors), that maps live hosts, open ports, services and operating systems on IP networks. The suite also ships Zenmap (GUI), Ncat, Ndiff and Nping, plus the Nmap Scripting Engine (NSE) for scripted checks.

What it helps with

- Discover which hosts respond on a network and which ports are open, closed or filtered.
- Identify service names and versions, and fingerprint likely operating systems.
- Probe firewall and filter behaviour with multiple TCP, UDP and other scan techniques.
- Extend scans with NSE scripts for enumeration and authorised vulnerability checks.
- Compare scan results over time with Ndiff and generate packets with Nping.
- Inventory networks for administration as well as authorised security assessments.

Who it's for

Penetration testers, red and purple teams, network and system administrators, and defenders who need a reliable inventory of reachable services.

Worth knowing

Use Nmap only on networks and systems you are authorised to test. Official binaries cover Linux, Windows and macOS; many Unix-like systems are also supported. Source and redistributable use fall under the Nmap Public Source License (NPSL), which adds terms beyond GPLv2 and is not OSI-certified; commercial embedding requires Nmap OEM. Attribution: licence posture from nmap.org/npsl/; platforms and suite components from nmap.org.