What is DNS Filtering?

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Aditya Rayaprolu
Written by
Aditya Rayaprolu

Updated · Nov 17, 2023

Aditya Rayaprolu
Technology Architect | McKinsey & Company | Joined February 2023 | LinkedIn
Aditya Rayaprolu

Aditya is an Azure DevOps and Infrastructure Virtualization Architect with experience in automation,... | See full bio

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Edited by
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Girlie Defensor
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DNS filtering is the process of blocking access to certain websites for security reasons or to avoid distractions.

If DNS is like a phonebook of domain names and their respective IP addresses, then DNS filtering works like a caller ID blocker. 

To better understand why DNS filtering is vital in cybersecurity, it is crucial to know what it is and how it works. This article will cover just that, so read on. 

Key Takeaways

  • Security is enhanced through DNS filtering. It blocks access to specific websites, protecting users against phishing attacks and malware-hosting sites.
  • DNS filtering allows the blocking of entire domains, while URL filtering provides control over specific pages.
  • Implementation of DNS filtering can be done manually, automatically, or with managed services.
  • DNS filtering helps prevent cyberattack damage, reducing the risk of phishing scams, blocking malware, and saving resources for post-attack repairs.

DNS Filtering Definition

In 2022, 83% of business owners blamed phishing for most of the cyberattacks they experienced. 

A robust DNS filtering system can help avoid potential damage from phishing and other malicious attacks.

To understand what DNS filtering does, understanding how DNS resolution works is necessary:

DNS process

DNS filtering happens between steps 2 and 3. As an added step, the DNS filter will check if the queried domain name matches anything in its block list.

If it does, the query will not be resolved. Instead, it will return an error message informing the user that the website is blocked.

Sample error page for blocked website

DNS Filtering and Other Filtering Types

DNS filtering also holds the same goal as other filtering types like URL filtering and web filtering. They block a user’s access to a domain or content based on a set protocol. 

However, DNS filtering is different in some ways. Check out below to know what makes it distinct. 

DNS Filtering vs. Web Filtering

Web filtering is a broader concept than DNS filtering. It encompasses URL filtering, content filtering, keyword filtering, and DNS filtering itself. 

These terms are often used interchangeably because their purpose is the same.

DNS Filtering vs. URL Filtering

DNS filtering blocks whole domains, while URL filtering blocks specific URLs. It means that certain web pages within a domain can still load with URL filtering.

Businesses employ URL filtering to restrict access to some web pages on their company’s website. It does the same thing as DNS filtering but on a more granular level.

Below is a summary of the differences between DNS filtering and other types: 


DNS Filtering

Web Filtering

URL Filtering


Blocks websites based on DNS queries

Restricts website access broadly

Restricts access to specific URLs


Blocks entire domains

Covers various filtering methods

Targets specific URLs or pages


Enhances security against phishing and malware

Enforces internet policies and blocks malicious sites

Provides granular control over specific URLs

Approaches to DNS Filtering

There are three approaches to DNS filtering: manual, automatic, and managed. Take a closer look at each one below.

Manual DNS Filtering

This approach involves employing and training internal IT staff to set up a basic DNS-blocking system for certain sites. 

Open-source or free DNS filtering solutions usually require extensive IT expertise. However, employing an IT staff may also cost more than the available paid DNS filtering services on the market. 

Another downside of the manual approach is that it tends to be slower to adapt to evolving cyberattack tactics. 

Basic web domain filtering is vulnerable to more sophisticated phishing attacks that circumvent DNS blocks.

👤 Best for: Manual DNS filtering works for small-scale businesses or individuals. This approach provides the necessary filtering but with only a few web users to monitor.

Automated DNS Filtering

Automated DNS filtering relies more on paid services for better scalability.

This approach quickly adapts to the increasing sophistication of cyberattacks. It is also easier to scale as the business grows. 

The cost of automated DNS filtering varies depending on the DNS filtering software.

Managed DNS Filtering

Large-scale businesses employ this approach. It involves partnering with Managed Security Service Providers (MSSPs). 

This solution is costly but offers comprehensive support for any company’s web and data security needs. 

It means outsourcing all IT security duties to MSSPs—-from set up, maintenance, vulnerability testing, and emergency response to threats. 

🎉 Fun Fact: Some of today’s top MSSPs are AT&T, Cipher, and IBM. Providing top-tier cybersecurity, these companies cater to clients with varying requirements in different locations.

Importance and Benefits of DNS Filtering

DNS filtering provides several benefits to businesses of all sizes. To give you a clear picture, here are the primary benefits of DNS filtering for most companies:

Providing Protection Against Phishing Attacks

Phishing email sample

Phishing or scamming employees into giving their login credentials is one of the most common forms of cyberattack. 

Attackers target employees with phishing emails containing links to spoofed web pages, then ask them to sign in.

If a DNS filtering system is in place, access to these spoofed web pages will immediately be blocked, even if an employee happens to click on a suspicious link.

Blocking Malware-Hosting Sites

Red screen virus

As an added layer of security, DNS filtering makes sure that sites with various types of malware are immediately blocked. 

It is also on top of end-point device solutions like anti-malware or anti-viruses. 

DNS-level protection prevents the infection of malware and viruses before they even load on any company device.

Imposing Effective Internet Policies

Businesses see the need to restrict access to sites involving alcohol, gambling, illegal file sharing, and explicit content. 

Any site or content that is non-work-related and can harm the company’s software or image is blocked by DNS filtering. 

🎉 Fun Fact: Do you know people spend 2.5 hours on social media? This is why companies use filtering to increase productivity and avoid distractions during work hours. 


DNS filtering prevents access to certain websites at the domain level. This process is more than just blocking or allowing access to sites. 

It can significantly reduce the time and money spent repairing cyberattack damage.


Is a DNS filter better than a firewall?

None is better than the other, as they have different duties. Firewalls protect networks and devices at IP and port levels, while DNS filtering examines DNS requests to prevent access to blocked websites.

Can the Internet work without DNS?

Yes and no. Yes, because DNS was not present at the onset of the Internet. No, because as the Internet grew, it became indispensable to use DNS servers to translate millions of domain names into their corresponding IP addresses.

What happens if DNS is off?

If the DNS server is unavailable, the browser will not be able to get the IP address of the target domain. You will get an error if this happens.


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