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NMAP
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DESCRIPTION

Nmap is designed to allow system administrators and curious individuals to scan large networks to determine which hosts are up and what services they are offering. 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. See the Scan Types section for more details. nmap also offers a number of advanced features such as remote OS detection via TCP/IP fingerprinting, stealth scanning, dynamic delay and retransmission calculations, parallel scanning, detection of down hosts via parallel pings, decoy scanning, port filtering detection, direct (non-portmapper) RPC scanning, fragmentation scanning, and flexible target and port specification. Significant effort has been put into decent nmap performance for non-root users. Unfortunately, many critical kernel interfaces (such as raw sockets) require root privileges. nmap should be run as root whenever possible. The result of running nmap is usually a list of interesting ports on the machine(s) being scanned (if any). Nmap always gives the port’s "well known" service name (if any), number, state, and protocol. The state is either ’open’, ´filtered´, or ´unfiltered´. Open means that the target machine will accept() connections on that port. Filtered means that a firewall, filter, or other network obstacle is covering the port and preventing nmap from determining whether the port is open. Unfiltered means that the port is known by nmap to be closed and no firewall/filter seems to be interfering with nmap’s attempts to determine this. Unfiltered ports are the common case and are only shown when most of the scanned ports are in the filtered state. Depending on options used, nmap may also report the following characteristics of the remote host: OS in use, TCP sequencability, usernames running the programs which have bound to each port, the DNS name, whether the host is a smurf address, and a few others.