DNS Explained in Simple Terms

By John King, CISSP, PMP, CISM •  Updated: 01/03/23 •  4 min read

The Domain Name System (DNS) is a required component of the modern internet. It is essentially a directory of all the website names and addresses on the internet and acts as a kind of “phone book” for the internet. When someone types a website address into their internet browser, the computer sends a request to a DNS server to translate the domain name into an IP address. The IP address is a series of numbers that uniquely identifies a device on the internet, and it is used to locate the website’s server and retrieve the content you requested.


DNS has been around since the early days of the internet, and it has evolved significantly over the years. In the beginning, the internet was relatively small, and the DNS was simply a text file that listed all the domain names and their corresponding IP addresses. This file was maintained by a central authority and distributed to all the computers on the internet. As the internet grew, this approach became impractical, and a decentralized system was needed.


Today, DNS is a hierarchical system of servers that work together to translate domain names into IP addresses. At the top of the hierarchy are the root servers, a group of 13 servers responsible for maintaining the root zone file. The root zone file is a database that contains all the top-level domains (TLDs) such as .com, .org, and .net, as well as country-code TLDs like .uk and .au.
When a computer sends a request for a domain name, it first contacts one of the root servers to find out which TLD the domain belongs to. The root server responds with the IP address of a TLD server for the appropriate TLD. The computer then sends a request to the TLD server, which responds with the IP address of a domain name server (DNS) for the specific domain. Finally, the computer sends a request to the domain name server, which responds with the IP address of the website’s server.


There are several types of DNS servers, each with a different role in the hierarchy. In addition to the root servers and TLD servers, there are also authoritative name servers, recursive resolvers, and caching name servers.


Authoritative name servers are the servers that are responsible for storing the DNS records for a specific domain. They contain the IP addresses and other information about the domain’s resources, such as email servers and web servers. When a computer sends a request for a domain name, it is the authoritative name server that responds with the IP address of the website’s server.


Recursive resolvers are servers responsible for resolving domain names on behalf of clients. When a computer sends a request for a domain name, it sends it to a recursive resolver, which is responsible for finding the IP address of the website’s server. If the recursive resolver does not have the IP address in its cache, it will send a request to a root server and follow the hierarchy until it finds the IP address.


Caching name servers are servers that store DNS records in a cache for a certain period. When a computer sends a request for a domain name, the caching name server will check its cache to see if it has the IP address. If it does, it will respond with the IP address from the cache. If it does not, it will send a request to a recursive resolver to find the IP address.


There are several benefits to using DNS. One of the main benefits is that it allows users to access websites using easy-to-remember domain names rather than having to remember the IP addresses of each website. This makes it much easier for users to navigate the internet and find the websites they are looking for.

John King, CISSP, PMP, CISM

John King currently works in the greater Los Angeles area as a ISSO (Information Systems Security Officer). John has a passion for learning and developing his cyber security skills through education, hands on work, and studying for IT certifications.