Port scanning

A port scanner is a software application designed to probe a server or host for open ports. This is often used by administrators to verify security policies of their network and by attackers to identify running services on a host with the view to compromise it.

A port scan or portscan can be defined as a process that sends client requests to a range of server port addresses on a host, with the goal of finding an active port. While not a nefarious process in and of itself, it is one used by hackers to probe target machine services with the aim of exploiting a known vulnerability of that service. However the majority of uses of a port scan are not attacks and are simple probes to determine services available on a remote machine.

To portsweep is to scan multiple hosts for a specific listening port. The latter is typically used to search for a specific service, for example, an SQL-based computer worm may portsweep looking for hosts listening on TCP port. 

Types of port scanning:- 

- TCP scanning 

-SYN scanning 

-UDP scanning

-ACK scanning

-Window scanning