DNS Overview

 

Background on DNS and the Internet

The Domain Name System (DNS) was developed because of the need to provide a name-to-address mapping service for computers on the Internet. Before DNS was introduced in 1987, the practice of mapping friendly computer names to IP addresses was done mainly through the use of a shared static file, known as a Hosts file.

Originally, the Internet was small enough to use one centrally administered file that was published and downloaded using FTP for Internet-connected sites. Periodically, each Internet site would update its copy of the Hosts file, and updated versions of the Hosts file were posted to reflect network changes.

As the number of computers on the Internet grew, it became unworkable to have one centralized authority managing a single Hosts file for all Internet hosts. The file became increasingly larger, which made it harder to maintain and distribute to all sites in a current and updated form.

The DNS standard was developed to provide an alternative to Hosts files. RFCs 1034 and 1035 specify most of the core protocols and have been added to and updated by additional RFCs submitted to the Internet Engineering Task Force (IETF). The IETF reviews and approves new drafts continuously, so the standards for DNS evolve and change as needed.

 

DNS defined
 

DNS is an abbreviation for Domain Name System, a system for naming computers and network services that is organized into a hierarchy of domains. DNS naming is used in TCP/IP networks, such as the Internet, to locate computers and services through user-friendly names. When a user enters a DNS name in an application, DNS services can resolve the name to other information associated with the name, such as an IP address.

For example, most users prefer a friendly name such as example.microsoft.com to locate a computer such as a mail or Web server on a network. A friendly name can be easier to learn and remember. However, computers communicate over a network by using numeric addresses. To make use of network resources easier, name services such as DNS provide a way to map the user-friendly name for a computer or service to its numeric address. If you have ever used a Web browser, you have used DNS.

The following graphic shows a basic use of DNS, which is finding the IP address of a computer based on its name.

In this example, a client computer queries a server, asking for the IP address of a computer configured to use host-a.example.microsoft.com as its DNS domain name. Because the server is able to answer the query based on its local database, it replies with an answer containing the requested information, which is a host (A) resource record that contains the IP address information for host-a.example.microsoft.com.

The example shows a simple DNS query between a single client and server. In practice, DNS queries can be more involved than this.

 

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