Nmap Basics Tutorial

INTRODUCTION:

Nmap ("Network Mapper") is a free and open source (license) utility for network discovery and security auditing. Many systems and network administrators also find it useful for tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. It was designed to rapidly scan large networks, but works fine against single hosts. Nmap runs on all major computer operating systems, and official binary packages are available for Linux, Windows, and Mac OS X. In addition to the classic command-line Nmap executable, the Nmap suite includes an advanced GUI and results viewer (Zenmap), a flexible data transfer, redirection, and debugging tool (Ncat), a utility for comparing scan results (Ndiff), and a packet generation and response analysis tool (Nping).(source: https://nmap.org/)

INSTALLING NMAP: 

Nmap is avaliable or both Linux based OS and Windows OS. 

Installing Nmap on Linux:

Open up a Terminal and type-

# apt-get install nmap 

Installing Nmap on Windows:

You can get the setup of latest version of  from this link https://nmap.org.

Beginning with Nmap:

To verify the installation open a Terminal (cmd prompt on windows) and type in-

# nmap 

 

As you can see there are a number of scan options available to use with nmap.

The most basic scan technique or command that we can use is

#nmap 192.168.129.132

 replace 192.168.129.132 with your target's ip address.

 

This will scan 1000 tcp ports and give us the list of open tcp ports and the services they are running, of the target. It will also show us the mac id of the target. Now before going any further we need to understand how nmap categorizes ports.
     Nmap divides ports into six different states: 

1. Open: An application is actively accepting TCP connections, UDP datagrams or SCTP associations on this port. Finding these is often the primary goal of port scanning.
2. Closed: A closed port is accessible (it receives and responds to Nmap probe packets), but there is no application listening on it. They can be helpful in showing that a host is up on an IP address (host discovery, or ping scanning), and as part of OS detection.
3. Filtered: Nmap cannot determine whether the port is open because packet filtering prevents its probes from reaching the port. The filtering could be from a dedicated firewall device, router rules, or host-based firewall software.
4. Unfiltered: The unfiltered state means that a port is accessible, but Nmap is unable to determine whether it is open or closed. Only the ACK scan, which is used to map firewall rulesets, classifies ports into this state. Scanning unfiltered ports with other scan types such as Window scan, SYN scan, or FIN scan, may help resolve whether the port is open. 
5. Open|Filtered: Nmap places ports in this state when it is unable to determine whether a port is open or filtered. This occurs for scan types in which open ports give no response. 
6. Closed|Filtered: This state is used when Nmap is unable to determine whether a port is closed or filtered. It is only used for the IP ID idle scan.

For more information, please refer to https://nmap.org/book/ 

In the next post we will cover some basic scan techniques.. Stay Tuned..