Domain Name Servers (or service,or system) (DNS) are the Internet's equivalent of a phone book. They maintain a directory of domain names and translate them to Internet Protocol (IP) addresses. This is necessary because, although domain names are easy for people to remember, computers or machines, access websites based on IP addresses. Information from all the domain name servers across the Internet are gathered together and housed at the Central Registry. Host companies and Internet Service Providers interact with the Central Registry on a regular schedule to get updated DNS information.  After you register a new domain name or when you update the DNS servers on your domain name, it usually takes about 12-36 hours for the domain name servers world-wide to be updated and able to access the information. This 36-hour period is referred to as propagation.


 


Without DNS servers, the Internet would shut down very quickly. But how does your computer know what DNS server to use? Typically, when you connect to your home network,  internet service provider (ISP) or WiFi network, the modem or router that assigns your computer's network address also sends some important network configuration information to your computer or mobile device. That configuration includes one or more DNS servers that the device should use when translating DNS names to IP address. When you enter a URL into your Web browser, your DNS server uses its resources to resolve the name into the IP address for the appropriate Web server.



DNS servers are an excellent target for hackers and penetration testers. They usually contain information that is considered highly valuable to attackers. DNS is a core component of both our local networks and the Internet. Among other things, DNS is responsible for the process of translating domain names to IP addresses. As humans, it is much easier for us to remember "google.com" rather than http://74.125.95.105. However, machines prefer the reverse. DNS serves as the middle man to perform this translation process. As penetration testers, it is important to focus on the DNS servers that belong to our target. The reason is simple. In order for DNS to function properly, it needs to be aware of both the IP address and the corresponding domain name of each computer on its network. In terms of reconnaissance, gaining full access to a company's DNS server is like finding a pot of gold a the end of a rainbow. Or maybe more accurately,it is like a blueprint to the organization. But in this case,the blueprint contains a full listing of internal IP address and host name thats belongs to our target.