In TCP, ports are the ends of logical connections that are used for carrying long term conversations. And, port scanning is the process of acquiring information on the open and closed ports on systems, mainly with the purpose of getting information on what services and software are running behind them.

Nmap is a commonly used software for port scanning. In this article, we will explain how to use Nmap for port scanning.

Numbering of Ports

Ports are specified by numbers ranging from 1 to 65535.

Out of these port numbers, the port numbers

• 0 – 1023 are used by various services of the Operating Systems.
• 1024 – 49151 are registered to be used by certain services.
• 49152 – 65535 are not registered and can be used for private use.

Installing Nmap

On a Linux system, Nmap can be easily installed following a few steps.

For example, in Ubuntu, it can be installed using :

#sudo apt-get install nmap

Nmap Test Server

Nmap reveals lots of information about a host. Many times, attackers use Nmap for malicious purposes. So, port scanning using Nmap should not be tested on other machines without properly getting approval from the owner of the machine.

Scanme.nmap.org is a test machine maintained by Nmap developers for learning purposes. If someone wants to test port scanning using Nmap for learning purposes, she can use this machine.

Port Scanning using Nmap

In this article, we will explain some of the most commonly used Nmap commands and their outputs.

1. To check the list of common ports

One can see the list of common ports used in a system using the following …