Guide to understand DNS Filtering


DNS (Domain Name System) filtering is a mechanism to filter and block certain websites. It provides an easier way to access websites by using domain names rather than IP addresses. This method allows you to remember websites more easily since remembering IP addresses is tricky.

The system works in such a way that it tracks IP addresses for domain names for access. This is because every domain has a unique IP address. So whenever a domain is bought, it is assigned a specific IP address. So when it is being accessed, the system is fetching the IP address for the domain. As soon as the system finds the IP address, it will link with it and open the desired website.

The process

DNS Filtering works in such a way; whenever a website is accessed, it checks if the website has malicious content. If the website does have malicious content, it goes on to block the website. The filter will trace any previous record of the website from known malicious websites. While the website does contain such content, it will redirect the user to a local IP address. That page will explain why the website cannot be accessed.

The DNS filtering service provider maintains a list of known malicious websites through which the access of certain websites is blocked based on policy.

The filter can also be used to prevent access to certain websites which are not desirable. Such websites can include pornographic websites, adult-rated, data sharing, and gambling websites. In addition, businesses may block out any website that does not cater to their employee’s jobs.

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This method is called AUD (Acceptable Usage Policy), which sets up a list of websites that can be accessed. Hence, employee access will not be blocked to the selected websites which are deemed safe.

Malicious websites

Though a DNS filter is useful against malicious websites, it cannot block all the websites. Moreover, the process can take a while because the website first has to be checked for any malicious data and if deemed malicious, then it will be blocked. So DNS filtering might not stop all malicious websites, but it will block most. BCA IT in Miami is a managed IT service company that can assist with cybersecurity.

Phishing websites

These websites are fake websites created to steal sensitive information such as login details and back details. The websites are designed to look as convincing as possible so that users do not question them. Unfortunately, many people fall for these, and they cannot tell whether it is fake or real.

And since the user believes that the website is genuine, they will enter their credentials and get tricked. DNS filtering systems maintain an updated list of such websites. This can block access to such websites and prevent any attack on the user.

DNS bypass

With the use of proxy servers, DNS filtering can be easily bypassed. The DNS filter, although it will block how many proxy servers but not all. So if a particular proxy server is used which is not listed, the filter will be bypassed. This way, employees and users can access prohibited websites even with the filtering system.

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Manually changing DNS settings is also another way of bypassing the system. If the settings are locked, it will prevent most users from gaining access and changing the settings. Although a determined user might be able to access websites, most will fail.

If there is a valid reason to suspend DNS filtering for access temporarily, administrators can do that. Administrators have the power to change filtering settings, but no one else does. So instead, specific keys are used to alter filtering settings and bypass the filtering system for a period.

Secure DNS servers

Such a server blocks and prevents access to prohibited websites and is also a part of DNS filtering. Few secure DNS servers block malicious websites far more efficiently, such as Cloudflare. It uses a protocol that clears all the logs after 24 hours.

DNS filtering is only one way of making your connection safe. Another way of making your connection more secure is verifying data that an attacker has not compromised. In addition, specific protocols encrypt DNS queries from an attacker.

DNS filtering and web filtering

Web filtering is a broader term to explain web security protocols. For example, DNS filtering also comes under web filtering along with URL filtering and keyword filtering.


The blocklist is a way for the cybersecurity community to maintain an updated list of malicious websites. This list is used by DNS filtering to check whether a certain website is on the list or not. Many DNS filters automatically evaluate websites and hence add them to the list.

The same method is used to block any website which hosts undesirable content. Many companies do not allow their employees to access certain websites or use company servers for personal use. For this purpose, they only allow their employees to access certain websites which are related to work.

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DNS filtering is a great way to block out any harmful websites to prevent any malware. It is also a great way to protect your child from any harmful content on the internet. Therefore, this method is an essential part of the cybersecurity system.

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