Nmap: the network mapper for inventorying your own network

Nmap (about 14,000 stars on GitHub, with the canonical source at nmap.org) is the Network Mapper, first published by Gordon Lyon, known as Fyodor, in 1997 and developed continuously since. It is one of the oldest security tools still in daily use and is written in C and C++ with scripting in Lua. Lyon’s company Nmap Software LLC maintains it, with a group of long-term contributors. The GitHub repository is a mirror of the project’s own Subversion repository, which is why its star count understates how widely the tool is used.

What it does

Nmap sends packets to a range of addresses and ports and interprets the answers. From them it tells you which hosts are up, which TCP and UDP ports are open, closed or filtered, which services and versions are listening, and often which operating system is running. The Nmap Scripting Engine (NSE) adds several hundred Lua scripts for tasks such as reading TLS certificates, listing SMB shares, checking for default credentials or detecting a specific vulnerability. Companion tools in the same package include ncat (a network Swiss army knife), ndiff (compare two scans), nping (packet generation) and the Zenmap graphical front end.

Who it is for

• Administrators who need an inventory of what is actually reachable on their network, as opposed to what the documentation claims.
• Anyone who has just written a firewall rule and wants to confirm from the outside that a port really is closed.
• Developers checking which ports their own container or virtual machine exposes.
• Security professionals performing authorised assessments, where Nmap is usually the first tool run.

How to install and try it

sudo apt install nmap
nmap --version
nmap -sV 192.168.1.0/24

The third command scans every address in a home or lab network for common ports and tries to identify the services. Running as root enables faster SYN scans and OS detection. Packages exist for every major distribution, Homebrew and Windows installers are on the official site, and the reference guide explains scan types, timing and output formats such as XML and grepable text.

Use it responsibly

Scan only networks and hosts you own or are explicitly authorised to scan. Port scans are noisy, set off intrusion detection systems and, against addresses that are not yours, may violate your provider’s terms or the law. Inside your own network, prefer narrow ranges and the default timing so that embedded devices are not overwhelmed.

Credit

Nmap was created by Gordon Lyon and is maintained by Nmap Software LLC and its contributors. It is published under the Nmap Public Source License, a GPL-derived licence with additional terms; the official site explains the conditions and offers a commercial licence for products that embed Nmap.