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Internet Basics #5: Demystifying DNS

Mathijs Baas
  • 12 months ago
  • 4 min read

As the internet has grown and evolved, so has the way in which we navigate it, too. When you type a website address into your browser, how does your computer know where to find it? That’s where DNS comes in.

DNS, or Domain Name System, is an essential part of how the internet works, but it can be a confusing concept for many people. In this post, we’ll break down the basics of DNS,  explain how it works, the different types of DNS records, and why all of it is so important.

How does DNS work?

In simple terms, DNS is like a phone book for the internet. When you type a website address into your browser (e.g., www.dataprovider.com), your computer sends a request to a DNS server to find the IP address (e.g., 172.217.88.207) associated with that domain. Once the DNS server has found the correct IP address, it sends it back to your computer, which can then connect to the correct web server and load the website. This process is known as a DNS lookup. 

DNS servers are distributed around the world, and they work together to ensure that every website can be found. Without DNS, users would have to manually type in the IP address associated with a website, which would be incredibly tedious and inefficient. Once you hit enter after typing a domain name into your web browser, your device sends a DNS query to a DNS resolver. The resolver first checks its cache to see if it has the IP address for the requested domain name. If not, it sends a query to a root server which directs the resolver to the appropriate Top Level Domain (TLD) server. The TLD server then responds with the address of the authoritative nameserver for the domain name, and lastly the resolver queries this server for the correct IP address. Once it has the IP address, the resolver caches it and returns it to your device, which then uses it to communicate with the server hosting the requested website (see Figure 1).

Figure 1: Schematic representation of a DNS lookup
Figure 1: Schematic representation of a DNS lookup

This process can take a significant amount of time, especially if the authoritative nameserver is slow to respond or if there are network issues. To speed up the process, DNS resolvers often use a technique called recursive DNS resolution. In recursive DNS resolution, the DNS resolver sends queries to other DNS resolvers in a chain until it finds an authoritative nameserver that can provide the IP address for the domain name.

Query types

There are several types of DNS queries that a device can send to a DNS resolver:

  • Recursive query: The device asks the DNS resolver to find the IP address for a domain name, and the resolver returns the answer, even if it has to query other resolvers to find it.
  • Iterative query: The device asks the DNS resolver to find the IP address for a domain name, but the resolver only returns the address of another DNS server that might know the answer. The device then queries that server, and the process continues until the answer is found.
  • Reverse query: The device asks the DNS resolver to find the domain name associated with an IP address. 
  • Zone transfer query: This is a specialized type of query used by DNS servers to replicate their databases with other servers. It's not used by devices to resolve domain names.

Each type of query has its own characteristics and use cases, but the most common query type is the recursive query.

DNS records

DNS records are the key to how DNS works. Every domain has a set of DNS records that contain information about the domain, such as the IP address of the web server, the email server, and other important information. These records are stored on DNS servers and are used to direct traffic to the correct location.

There are several different types of DNS records, each with its own specific purpose. Some of the most common DNS records include:

  • A record: This is the most important DNS record, as it maps a domain name to an IP address. Every domain needs an A record to function correctly.
  • AAAA record: In contrast to A record, AAAA records (or quad A) maps domain names specifically to IPv6 addresses.
  • MX record: This record specifies the email server for a domain. When someone sends an email to a domain, the MX record tells their email server where to deliver the message.
  • CNAME record: This record allows a domain to be mapped to another domain. For example, you could set up a CNAME record to map blog.example.com to www.example.com.
  • TXT record: This record is used to store any text-based information about a domain. It’s commonly used to store Sender Policy Framework (SPF) records, which help prevent email spoofing.

Understanding DNS is important because it is a crucial part of how the internet works. It helps to simplify website access for users and ensures that websites are always reachable. Having a basic understanding of DNS records and how DNS queries work can help you manage and troubleshoot issues with your website and make informed decisions about your website's hosting and domain name.

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