nmap (Network Mapper) is a security scanner, originally written by Gordon Lyon.

Nmap features include:
Host discovery – Identifying hosts on a network. For example, listing the hosts that respond to TCP and/or ICMP requests or have a particular port open.

Port scanning – Enumerating the open ports on target hosts.

Version detection – Interrogating network services on remote devices to determine application name and version number.[7]

OS detection – Determining the operating system and hardware characteristics of network devices.

Scriptable interaction with the target – using Nmap Scripting Engine[8] (NSE) and Lua programming language.

If you want to check whether a port on remote host is open:

sudo nmap -v -p 80 google.com

In response it shows that the port is open/closed/filtered:

Not shown: 987 filtered ports
 20/tcp   closed ftp-data
 80/tcp   open   http

In case you want to scan all port using nmap:

sudo nmap -v your_target_victim.com

It lists all the gathered information about open ports.

#nmap #security #port #open #open_port #port_scanner