Description:

Nmap is a utility for network exploration or security auditing. It
supports ping scanning (determine which hosts are up), many port
scanning techniques (determine what services the hosts are offering),
and TCP/IP fingerprinting (remote host operating system
identification). Nmap also offers flexible target and port
specification, decoy scanning, determination of TCP sequence
predictability characteristics, sunRPC scanning, reverse-identd
scanning, and more.

nmap supports a large number of scanning techniques such as: UDP, TCP
connect(), TCP SYN (half open), ftp proxy (bounce attack),
Reverse-ident, ICMP (ping sweep), FIN, ACK sweep, Xmas Tree, SYN
sweep, and Null scan.