What Is the Domain Name System?

The domain name system (DNS) is a database that holds all of the internet's IP addresses. When you go to a certain website, you put in the domain name, like www.cousera.org. However, your web browser needs the internet protocol (IP) address of that domain to function. While domain names are easy for humans to remember, browsers need an IP address made up of numbers. So, the domain name system converts the domain you enter into an IP address for your web browser and computer to read. The DNS works in the background anytime you use the internet, and it's considered a fundamental part of the online world. 

What is the DNS resolution process? 

When you enter a domain name into a web browser, the DNS goes through a process called the DNS resolution process or DNS lookup. Every time you type in a domain name, your computer will do an initial search of its cache and host files to see if it already stores that IP address. If it's not there, your computer sends a request to the DNS. When the DNS receives that request, it takes it through its four servers to find the IP address of the website you want to visit.   

What are the four DNS servers? 

When the DNS searches for the IP address of the website you want to visit, it goes through four servers: the recursive DNS server, the root name server, the top-level domain server, and the authoritative nameserver.  

The recursive DNS server, also called the DNS resolver, is the first stop, and it serves as a middle point between the computer and the other servers. Basically, it searches its own cache for the IP address. If it finds it, your request is complete. If not, it sends the request to the next server. 

The root name server intercepts the request and points the recursive DNS server in the right direction to a top-level domain server, similiar to a grocery store employee telling you  which aisle you'll find the rice. You'll find top-level domain servers stored all over the world, and they're usually broken down by the last section of a domain name, like .com, .org, .gov, or .edu. So, if you're searching for www.coursera.org, your request would go to a .org server. 

The top-level domain server then points the request toward the correct authoritative nameserver that stores the IP address you want. Once it arrives, your website loads, or if it's not found, you'll receive an error message. 

Read more: Information Technology (IT) Terms: A to Z Glossary

Related terms 

• Address resolution protocol

• Physical security

• Command line interface

• Unified threat management 

• IT infrastructure 

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