---
title: "What is Nmap? | Daniel Christensen"
canonical_url: "https://danielchristensen.no/en/glossary/nmap"
last_updated: "2026-09-02T13:55:00.038Z"
locale: en
meta:
  description: "The network scanner that maps which machines and services exist on a network. Often the first step of a pentest."
  "og:description": "The network scanner that maps which machines and services exist on a network. Often the first step of a pentest."
  "og:title": "What is Nmap?"
---

[← All terms](https://danielchristensen.no/en/glossary)Glossary

# Nmap

The network scanner that maps which machines and services exist on a network. Often the first step of a pentest.

Nmap (Network Mapper) scans networks and tells you which machines respond, which ports are open and which services run behind them. It’s usually among the first things run in a pentest, because you can neither secure nor test what you don’t know exists.

The tool is over 25 years old, still actively developed, and iconic enough to have appeared in Hollywood movies. For companies the point is simple: run Nmap against your own systems before someone else does.

What Nmap most often uncovers isn’t advanced holes, it’s things nobody knew were there. A test server set up two years ago and never switched off. An admin interface that was supposed to sit behind the firewall. A database answering the whole internet because a default setting was never changed. Networks of any size nearly always have some of this.

Scanning your own systems is both legal and sensible, and should happen regularly rather than once a year. Scanning someone else’s is a different matter, even if you’re “just looking”. It tends to be read as an attempted attack, it lands in their logs, and at worst it’s illegal. Stick to what you own or have written permission to test.

Next step

## Want this explained live?

My talks take the terms from this list and show what they mean in practice, with real examples and demos the room remembers.

[See the talks →](https://danielchristensen.no/en/talks) [Try the password generator](https://danielchristensen.no/en/tools/password-generator)