DNS Filtering: How can it help secure your business?

DNS filtering is a security technique that protects against malware by blocking access to malicious sites. It is a kind of automated access control that allows companies to protect against data theft and prevent harmful content from being downloaded to user devices.

What is DNS Filtering?

DNS filtering is the practice of blocking rogue websites and filtering out dangerous or unsuitable information using the Domain Name System. This maintains the security of company data and gives businesses control over what their workers may access on company-managed networks. DNS filtering is frequently used in conjunction with a wider access control scheme.

DNS filtering is the process of restricting access to specified websites for a specific reason, most often content screening. If a website or a group of websites has caught danger, then its IP address is banned by a DNS filter, and access to it is restricted. Adult, gambling, productivity drains, and sites considered to represent a major virus risk are all examples of sites that may be blacklisted.

dns filtering

How does it work?

It works simply. All DNS queries are routed through a Recursive DNS server (DNS resolver). DNS resolvers that have been specially configured can also act as filters by refusing to resolve queries for specific domains that are tracked in a blocklist, preventing users from accessing those domains. DNS filtering services can also employ an allowlist rather than a blocklist

Let’s say an employee for the organization receives a phishing email. It falls for the trick of clicking a link that takes them to The company’s DNS resolving service, which uses DNS filtering, receives a query from the employee’s computer before it loads the webpage. The DNS resolver will reject the request if the malicious website is listed on the company’s blocklist. This will stop from loading and stop the phishing attack.

DNS filtering can ban websites either by IP address or domain name:

  • By IP address: The DNS resolver tries to resolve every domain, but the resolver won’t send the result back if the querying device’s IP address is on the block list.
  • By domain: For some domains, the DNS resolver does not even attempt to resolve, or look up, the IP addresses.

Why should you filter DNS?

No matter how many cyber security measures you take and how much awareness training you give to employees, mistakes can happen, putting your company’s devices and network in danger. Effective filtering can strengthen a company’s default level of cyber security. Although there’s no way to ever completely eliminate the chances of a user connecting to a malicious site – bad actors are constantly creating new web pages that have yet to be reviewed and marked, meaning they have a better chance of slipping through – it is possible to block the vast majority of threats.

Another reason to use DNS filtering is to keep people from accessing certain categories of websites through the internet, whether for productivity or regulatory purposes. By creating an acceptable usage policy (AUP) and setting it up with your ISP, you can keep users from accessing everything from gaming and gambling sites to social media and adult content sites while on your network. In some cases, organizations must have filtering in place to comply with regulations – for instance, schools and libraries in the U.S. should have ways to prevent access to material that is objectionable or harmful to minors.

It can be possible to bypass DNS filtering controls. In some cases, this means admins can temporarily remove the block. However, it’s also possible a highly motivated employee could set up a proxy server or even change DNS settings at a local level to achieve access. That’s why it’s important to set up the service correctly and use tools designed for these contingencies.

dns filtering

How does it help block malware and phishing attacks?

DNS filtering can help keep malware, or malicious software, out of company networks and off of user devices. It can also help block some kinds of phishing attacks.

Blocking malicious websites

A website that hosts malware can either attempt to trick users into downloading a malicious program or execute a drive-by download: a download of a malicious piece of software that is automatically triggered when the webpage loads. A number of other attacks are possible as well. For instance, webpages run JavaScript code, and as a full programming language, JavaScript can be used in a range of ways to compromise user devices.

DNS filtering can prevent these kinds of attacks by blocking users from loading malicious web pages at all.

Blocking phishing websites

A phishing website is a fake website that is set up to steal login credentials in phishing attacks. The domain used could be a spoofed domain or just an official-looking domain that most users will not think to question. Regardless of the method, the goal is to fool the user into giving their account credentials to an attacker. These websites can be blocked using DNS filtering.

These capabilities are dependent upon the DNS filtering system knowing to identify the malicious IP addresses or domains as bad. While DNS filtering can block this malicious activity, attackers generate new domains very quickly and it is not possible to blocklist all of them.

How do you enable DNS filtering?

There are several ways to implement DNS filtering depending on the technology you choose to carry it out. You can block access on your:

  • Business VPN as part of access control.
  • Firewall.
  • Load balancer.
  • Subscription to a DNS filtering service.


DNS filtering is essential for organizations that want to keep their networks and users safe, whether working in a public Wi-Fi environment or within their corporate network. It provides granular customization options to tailor user access policies, block unwanted content, and enhance privacy. With the constant threat of DNS-based attacks on the rise, implementing a reliable DNS filtering service is the key to ensuring a secure connection for all users.


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