Nmap (“Network Mapper”) is an open source tool for network exploration and
security auditing. It was designed to rapidly scan large networks, although it
works fine against single hosts. 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. While Nmap is commonly used for security
audits, many systems and network administrators find it useful for routine
tasks such as network inventory, managing service upgrade schedules, and
monitoring host or service uptime.