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What is the Domain Name System (DNS)?

The Internet is the world’s largest computer network, with more than 250 million registered domains. From the perspective of a user, each system or resource on the Internet is identified by a unique fully qualified domain name.

Understanding the basics of DNS

There are many types of Intern resources. Some common examples of these resources are:

  • Web servers that enable access to a content on a website.
  • Mail servers that are used to send and deliver email.
  • Application servers that enable software and connect to databases.

Network equipment (e.g., routers) route communication packets across the Internet. However, the unique resource identifier is the Internet Protocol (IPv4 or IPv6) address, represented as a series of four numbers separated by dots (e.g., To access Internet resources by user-friendly domain names rather than these IP addresses, users need a system that translates these domain names to IP addresses and back. This translation is the core task by the system called the Domain Name System (DNS).

What is name resolution?

Users access an Internet resource (e.g., a Web server) through the corresponding client or user program (e.g., a Web browser) by typing the domain name. To contact the Web server and retrieve the appropriate Web page, the browser needs the corresponding IP address from an DNS A record. It uses DNS to provide this information. This function of mapping domain names to IP addresses is called name resolution. The protocol that DNS uses to perform the name resolution function is called the DNS protocol.

The building blocks of DNS

First, DNS servers have a data repository to store the domain names and their associated IP addresses. Because the number of domain names is large, scalability and performance considerations dictate that DNS should be distributed. The domain name repositories (zones) are usually replicated to provide fault tolerance.

Second, there is software that manages this repository and provides the name resolution function. These two functions (managing the domain names repository and providing name resolution service) are provided by the primary DNS component, the name server.

Types of DNS servers

There are many categories of name servers, distinguished by type of data served and functions performed. To access the services provided by a DNS name server on behalf of user programs, there is another component of DNS called the resolver.

There are two primary categories of resolvers. There are caching, recursive and resolving name servers and stub resolvers, distinguished by functionality. The DNS communication protocol; the various DNS components; the policies governing the configuration of these components; and procedures for creation, storage, and usage of domain names constitute the worldwide DNS infrastructure. Learn more about the common DNS acronyms used in DNS security.

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