Is DNS Case-Sensitive? (There’s More To It Than Just Case Sensitivity)

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In the 1980s, when the internet was still evolving, computers could only communicate using numbers. During this time, IP addresses were used to identify websites. These IP addresses are strings of numbers assigned to devices connected to a computer network. Later, domain names were introduced to represent IP addresses in a more user-friendly form. The DNS, or domain name system, is a directory that translates a domain name to its corresponding IP address and directs a visitor to his destination on the internet. So, is DNS case-sensitive?

No, DNS is not case-sensitive. Capitalization doesn’t matter when typing the domain name. You will be directed to the same website regardless of whether you use uppercase or lowercase letters. However, the rest of the URL that comes after the domain name is case-sensitive.

So, if you type the part of the URL after the domain name incorrectly, you will receive an error message.

To understand how this works, let us explore how the DNS works in closer detail.

What Is DNS?

How do you visit a website?

You type its web address into the browser and click enter. This takes you to the requested page. The entire process is over in a few seconds. But, do you know that a lot of background activities occur from the time you key in the URL until you reach the website?

Now, this website is stored in a specific physical location, which is its IP address. For instance, is an IP address.

This format is not easy to remember. However, computers can easily read and understand it.

The domain name concept was introduced to bridge this gap. Paul Mockapetris introduced the idea in the 1980s to connect IP addresses to alphabetical names. It would make them more user-friendly. So, domain names are alphabetical representations of IP addresses, and they are connected through the DNS or domain name system.

Just like a phone book maps names to phone numbers, the DNS or domain name system also links website URLs to corresponding IP addresses. So, it essentially connects the user to the website page he wishes to visit by connecting it to its IP address.

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How Does DNS Work?

Let us revisit the process of reaching a website.

The first step is typing the URL into the browser. Every website’s domain name has a dedicated IP address assigned to it, which is the computer server that hosts the website. The DNS stores these details. With over 1.5 billion sites in the world, you can imagine how big and complex the domain network system is.

When you key in a URL, the DNS must quickly scan through massive amounts of information to find the single IP address that you wish to visit. This process involves several steps.

So, when you type the URL, the DNS gets to work. Here’s what happens behind the scenes during the lookup process.

  1. The query first reaches your computer’s local DNS cache. If you have recently visited the same webpage, a record will be available here. Your computer will use this information to locate the IP address and display the page. If it is unavailable, the query will next be addressed to your local ISP cache. If the domain is in the cache, the website is found and displayed.
  2. If there is no information in your computer or local ISP cache, the query now goes to the DNS recursor. The recursor receives multiple queries from different client machines, like web browsers. So, if the domain name is in the cache, it will be located, and the web page will be displayed. If not, the DNS recursor redirects it to the other DNS servers.
  3. The query is next addressed to the root servers. The root servers are indexes for more specific locations. So, if the query is for a .com web page, the DNS lookup will now focus only on web pages with this domain extension.
  4. Authoritative name servers store DNS records for their respective domain names. So, this is the last step in the DNS lookup. Once the query reaches the authoritative name server it is resolved because at this step, the request is directly sent to the IP address where the information is stored.
  5. Once the DNS receives the information, it will pass the corresponding IP address to your browser. It causes the website page to be displayed.

Although it is a detailed process involving several steps, the entire DNS lookup process takes mere seconds to complete. It is because each time a web page is accessed, its data is cached for easy access in the future. So, the overall performance improves with use.

Is DNS Case-Sensitive?

There are many things to consider when choosing a website name. One of them is case sensitivity for domain names and how this affects the DNS lookup.

Let me explain.

The URL that you type into the browser has different parts. Some of them are case-sensitive, and others are not.

The most important and identifiable part of the URL is the domain name. It is the unique name that identifies the website. For example, the domain name of this website is

The domain name is case-insensitive. So, when you type a website name into your browser and click ‘Enter’, the DNS pays attention to the domain name only. It interprets the domain name in a case-independent manner. So, you will be directed to the same IP address location, whether you use uppercase or lowercase letters.

For instance, let us take the example of a popular website: It doesn’t matter whether you type in or, the DNS will read it as in either case. So, it will display the same website.

This makes sense because if domain names were case-sensitive, there would be multiple websites with the same name. It would only confuse and cause visitors to land on random sites.

Now, here is the catch! While the domain name part of the URL is case-insensitive, the portion of the URL that comes after the DNS isn’t. It is because this part specifies the path to a requested resource on a specific computer. So, when you type a URL, you are trying to access a certain resource file.

Now, if the site was hosted on a Microsoft Windows system, case-sensitivity would not be an issue. However, if this resource file is on a Unix-based system, the underlying file name would be case-sensitive. So, if you type the wrong URL, the corresponding resource file will not be found. And so, you will get an error message in return.

Say, for example, you type: In this case, you are trying to access the specific file, wiki. If you instead type, you can end up with an error message.

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Concluding Thoughts…

The DNS system is case-insensitive. Regardless of whether you use the correct case or get it wrong when typing in the domain name, the DNS ensures that you reach the same website.

However, the rest of the URL is case-sensitive. If you use the wrong case in the part that follows the domain name, you may or may not receive an error. It again depends on whether the server on which the specific resource file is located is case-sensitive or not. So, you will still reach your destination if the site is hosted on a Windows system. However, if it is on a Unix system, you will receive an error.

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