Nmap, short for network map, is a program that is used to discover hosts and services on a computer network. Hence, it creates a map of the network. It is often used for network security audits, but it is also useful for routine administrative tasks. When you run Nmap, you receive a list of scanned targets as an output. The output depends upon which options are used, but you will always get a list of interesting ports, what services are running on those ports, and the state of the port (open, filtered, closed, or unfiltered). These states can be defined as follows:
- Open: If a port is listed as open, then an application is listening on this port; in other words, it is waiting for connections.
- Filtered: The port is blocked by a firewall. ...
