A DNS firewall is a network security solution that blocks users and systems from accessing malicious websites. As part of the DNS system, it checks every accessed IP address to determine whether it has been classified as dangerous. Depending on the check results, the webpage is either displayed or not.

How does the DNS firewall work?

A DNS firewall filters the traffic that moves through DNS endpoint services. Each DNS request is screened against a denylist, including various dangerous IP addresses, hosts, or websites. The web request is denied if an address or host is found on the denylist.

Scheme how DNS firewall works

DNS firewalls need to be continuously updated with the latest DNS threat data for this solution to be effective. As malicious domains are constantly taken down and set up, a DNS firewall must keep up with the changes by updating threat intelligence.

Some DNS firewalls are expanded with AI capabilities capable of learning and recognizing malicious websites in real time. The bottom line is that a DNS firewall is as secure as an up-to-date or smart denylist is.

Benefits of DNS firewall

Traditional firewalls use complex and proprietary technologies yet can fail at detecting various DNS-based threats. Which is why DNS firewalls are an important subset of DNS security. Here are the principal benefits that they're bringing to organizations.

Highly customizable

Malicious URL redirects can serve as educational materials by informing users what they have just avoided. Additionally, not only malicious websites can be blocked with DNS firewalls - this applies to all websites. Social media or streaming media websites can also be blocked. This makes it a much more versatile tool for controlling user traffic flows within DNS infrastructure.

Low maintenance

Applying DNS firewall capabilities to DNS resolver instantly covers all users. This means a much easier deployment and simpler maintenance. The updates can be instantly pushed by updating the DNS firewall so that network administrators can focus solely on the denylist and security policies.

Fluid integration

DNS firewalls can protect against a wide range of threats, especially when integrated with other solutions. For instance, DDI — a shorthand for DNS, DHCP, and IP address management encompasses all network services communications over IP-based networks. This allows the creation of a much more complex system to filter out unwanted traffic, ensuring business continuity and security.

Prevents malicious traffic

DNS firewall provides automatic protection from most malicious traffic sources, blocks phishing links and malware downloads within the DNS level. Intercepted DNS queries don't get resolved, which means that threats never even reach endpoints, which helps maintain the network and device security.

Recursive DNS firewall

Recursive DNS lookup is when one DNS server communicates with several other DNS servers when the needed IP address isn't found within its cache. This system can be expanded by introducing a DNS firewall.

In this case, when using a recursive server with enabled DNS protection, each DNS query is checked for denylists before returning to the client. If an IP address is from flagged malicious domains, this disrupts the chain of exchanges, denying entry into the website. However, if no security threats are detected, the query is resolved as usual, and the user is taken to its intended destination like using an ordinary DNS server.

Types of threats blocked by DNS firewall

DNS firewall filters domain names and doesn't resolve queries requesting denylisted IP addresses. Additionally, the DNS firewall filters DNS/UDP traffic but doesn't filter threats using other application layer protocols like HTTPS, SSH, TLS, etc. Still, a DNS firewall can protect users from multiple threats.

Data exfiltration

Data exfiltration refers to unauthorized data movement from a device. What's particularly challenging is that while it's often done by the hackers that obtain access to internal resources, it isn't always the case. Users often help hackers by making unauthorized copies and transmitting them to hackers.

DNS firewalls can prevent data exfiltration cases by blocking connections to unidentified servers. That way a DNS firewall could act as a barrier to stopping a data breach.

Phishing attacks

A phishing attack is a threat spreading through email and text messages, tricking the recipient into revealing sensitive information. Various imitations of genuine websites are often set up, and when users type in their genuine credentials, they are sent to hackers. Then, hackers can use real credentials to hijack real accounts.

DNS firewalls can put a stop to this by blocking access to sketchy websites in cases when users do inadvertently click on links. The hacker's plan falls apart when the websites can't be opened.


Ransomware is a type of malware that keeps data hostage. It asks for payment in cryptocurrencies and displays a timer, which, after it runs out, the data is wiped. This is one of the most dangerous types of malware affecting businesses, as some organizations managed to retrieve the data by paying the ransom.

Various forms of web filtering, including DNS firewalls, have contributed to limiting ransomware attacks. Unknown hosts can be denied access, which also stops ransomware from being downloaded on the user's endpoint.


Malware is an umbrella term for software that intends to steal or inflict damage on devices and networks. As it's usually spread via various infected hosts, network traffic filtering is the primary weapon against malware. Keeping up with various latest trends and updates also helps to make sure that the DNS firewall can detect even the most recent types of viruses, trojans, and spyware.

Do you need a DNS firewall?

Not only do DNS firewalls help to block threats like malware and phishing, they also provide other benefits. DNS firewalls can save bandwidth, secure servers from downtime, and increase service availability. An organization using a DNS firewall can avoid pitfalls and ensure business continuity.

That said, if your organization is already relying on a much more advanced solution like a next-generation firewall (NGFW), a DNS firewall could be a downgrade. When considering various technological solutions for your organization, it's always important to properly evaluate what risks, i.e. DNS attacks, DDoS attacks, or other threats, are the main focus.