Howto: DNS Enumeration

A penetration testing is a method of evaluating the security of a computer system or network by simulating an attack from a malicious source. The process involves an active analysis of the system for any potential vulnerabilities that may result from poor or improper system configuration, known and/or unknown hardware or software flaws, or operational weaknesses in process or technical countermeasures.

The first step of penetration testing or more accurately called information security testing is information gathering. Information gathering is part of the preparatory pre-attack phase and involves accumulating data regarding a target's environment and architecture, usually for the purpose of finding ways to intrude into that environment. Information gathering can reveal system vulnerabilities and identify the ease with which they can be exploited. This is the easiest way for attacker to gather information about computer systems and the companies they belong to. The purpose of this phase is to learn as much as you can about a system, its remote access capabilities, its ports and services, and any specific aspects of its security.

Using a combination of tools and techniques, attackers can take an unknown entity and reduce it to a specific range of domain names, network blocks, subnets, routers, and individual IP addresses of systems directly connected to the Internet, as well as many other details pertaining to its security posture. Although there are many types of information gathering techniques, they are primarily aimed at discovering information related to the following environments: Internet, intranet, remote access, and extranet.

To read more details, you can download my article here:

http://www.exploit-db.com/download_pdf/12389

http://www.packetstormsecurity.org/filedesc/dns-enumeration.pdf.html