Chapter 1. Getting Started with Nmap

Nmap (“Network Mapper”) is a free and open source utility for network exploration and security auditing. Many systems and network administrators also find it useful for tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. It was designed to rapidly scan large networks, but works fine against single hosts. Nmap runs on all major computer operating systems, and both console and graphical versions are available.

This chapter uses fictional stories to provide a broad overview of Nmap and how it is typically used. An important legal section helps users avoid (or at least be aware of) controversial usage that could lead to ISP account cancellation or even civil and criminal charges. It also discusses the risks of crashing remote machines as well as miscellaneous issues such as the open source Nmap license (based on the GNU GPL), and copyright.