Network Scanning with Nmap

Today each of us operates, consciously or not, a computer network. Whether it's small home LAN consisting of one or two computers, whether we speak of large corporate LAN, it is important to be aware of what it means to expose a machine on the Net

Almost always it requires, as a first step, to become familiar with the suite of TCP / IP and, secondly, to verify operation with a scanning their network. Approaching this second stage is unlikely we shall hear no talk of Nmap.

Nmap - N etwork map for - is one of the most known and used security scanner in the world, the first version, developed by Gordon - Fyodor - Lyon, was published on September 1, 1997 Phrack.org, the well known hackers of the underground magazine.
Released under the GPL for all major platforms, has undergone several rewrites over time evolved up to be a true reference in the field of IT security.

Nmap the discovery of hosts and services, present on a computer network, by sending TCP / UDP packets handled in a timely manner: the ability not only allows, as we shall see, merely a recognition of open ports on different hosts, but to enable a number of features such as recognition of the OS of the target system, the name and version of his active services, the presence of intervening security mechanisms (such as IDS and firewalls).

Before continuing, we should remember that scan hosts without permission of the owner, regardless of the purpose "teaching" activity, behavior is generally frowned upon by network administrators and, depending on the law in force in various states, punishable operation of crime.

Who should read this article

Although this is an article aimed at newcomers to the network scanning, the understanding of this article requires a good knowledge of the suite of TCP / IP concepts such as IP packet or TCP / UDP port will be given for granted, and if you were not Please read the first few basic guide .

For the same reasons, this text does not purport to cover all complex software such as Nmap in all its facets, but to illustrate the main features, leaving most willing to further study.

Get Nmap

As briefly mentioned, though born as a software for GNU / Linux, Nmap is now available for all major platforms including Microsoft Windows (in all its incarnations), Mac OSX, BSD, Solaris, and many more, whatever the system, since stress now that most of the functionality of Nmap require administrative privileges.

Get a copy of Nmap is very simple, as well as through the official website , almost every GNU / Linux distribution includes a copy in its repository. As in all reality the GPL, savvy users can also fill out and / or modify the software source code, optimizing it for prorie needs.

In this article, we will reference the version 5.21, pre-compiled for Debian GNU / Linux 64-bit, unless otherwise indicated, it is understood that any recommendation is independent from this particular setup. To simplify its use is recommended, if not automatically avenisse, Append to the directory containing the executable of Nmap to $ PATH system variable (or equivalent).

The first scan

Temporarily suspend the theory and relax your brain a bit approaching the practice. The first scan, we will examine in detail, has traditionally been a target standard scanme.nmap.org. Far from betraying the initiatory rite, we open a console or a command prompt and execute:

 



 nmap-T5-sS-v-A-oA first_scan scanme.nmap.org

 

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