What Is DNS Filtering?

You might have heard about DNS filtering but are still confused about it and how it works. Don’t worry; we are here to explain it to you and take your worries away.

DNS filtering is a technique used to block access to domains on the internet. The most common use of this technology is in schools and businesses, but governments can also use it. In some cases, DNS filtering will prevent computers from accessing the internet entirely, while in other cases, users will simply not be able to visit specific websites. This is a passive censorship and surveillance measure, which means it is done invisibly without any notification.

How Does a Firewall Protect a Compu...
How Does a Firewall Protect a Computer?

How Does DNS Filtering Work?

DNS filtering works by changing the Domain Name System (DNS) settings on your computer or mobile device. This is usually done using an app that runs silently in the background almost always, even when you are not using the internet. DNS filtering works by changing the Domain Name System (DNS) settings on your computer or mobile device. This is usually done using an app that runs silently in the background almost always, even when you are not using the internet.

It operates most commonly by allowing a remote local network administrator access to your DNS settings, usually controlled by your Internet Service Provider (ISP). When the filter is activated, your ISP will instead replace your DNS server with its own so that they can monitor every site you visit. This filtering method is particularly common in schools where most computers connect to a single filtered internet connection for the whole school.

Governments worldwide have also started using this technology on ISPs and at internet exchange points (IXPs). Activating filters allows them to filter traffic across an entire country rather than just on individual networks. It means that everyone connecting to the internet through an IXP or ISP that implements DNS blocking will be subject to website blocks without their knowledge or consent.

Where Is DNS Filtering Used?

Right now, the primary users of this technology are schools and businesses. Blocking certain websites on the school internet prevents students from visiting time-wasting websites during lesson time. Companies use them to block access to sites that have been declared inappropriate for work or where employees spend too much time surfing when they should be working. In both cases, the filtering is usually done by administrators on a network level so that it applies across all devices connected to the network. You may not even notice when this happens as part of your daily routine because it will always ask you for permission before redirecting your internet connection.

This method is also in extensive use in many countries worldwide, especially those with a history of censorship and surveillance. Middle Eastern countries such as the United Arab Emirates, Qatar, Oman, Kuwait, Iran, and Saudi Arabia are the worst offenders. Several large ISPs actively block access to websites or internet services without warning. Brazil became one of the first countries in the world to require all mobile operators to offer DNS filtering earlier this month after years of fighting against child pornography. China is also known for using DNS filtering on its Great Firewall, which blocks many sites, including Google Search and Facebook.

What Are The Problems With DNS Filtering?

There are many problems with DNS filtering on a technical level. Firstly, there is no way of knowing when this happens because it silently changes your DNS settings in the background without any notification. Even rebooting your computer will not undo the change, and you may have no idea that anything has happened until you suddenly can’t visit your favorite website anymore.

The second problem is that while most filters run on a network-wide basis, some mobile apps execute the filter at an application level instead. This means they can affect all internet access from a specific application such as Skype or Facebook, whether you are on 3G or 4G data connections. There’s also been controversy recently about how many apps implement their ad-blocking features using this technology, resulting in websites you visit taking much longer to load than usual.

Another problem with DNS filtering is that it can easily be abused by network administrators looking for an easy way to block employees from visiting time-wasting websites during office hours or stopping children from accessing pornography at home. The technology is also open to abuse by governments who can easily use it to block access to websites they don’t like or even make it impossible for their citizens to access any news that contradicts the official line.


We must remain vigilant about this method of website filtering and continue to raise awareness of its existence so that more people understand how it works and what the potential risks are. Your ISP may appear trustworthy, but you should assume nothing about your internet connection and always be on the lookout for unusual behavior, which could indicate DNS filtering has taken place without your knowledge or consent.

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