Nmap

Network discovery and security auditing utility — the Network Mapper.

Nmap (Network Mapper) is the definitive open-source utility for network discovery and security auditing. It uses raw IP packets to determine what hosts are available on the network, what services those hosts are offering, what operating systems they are running, what type of packet filters and firewalls are in use, and dozens of other characteristics. Nmap supports a wide array of scanning techniques including TCP SYN, TCP connect, UDP, SCTP, and idle scans, along with advanced features like OS detection via TCP/IP fingerprinting, version detection for identifying service software, and scriptable interaction via the Nmap Scripting Engine (NSE). With a command-line interface and the Zenmap graphical frontend, Nmap is used by system administrators for network inventory and by security professionals for vulnerability assessment and penetration testing.