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What is DNS Firewall? A beginner’s guide

September 14, 2018

With the ever increasing demands on IT, security and networking teams, tools that reduce workloads, which don’t cost the earth, are always welcome.  One such tool is DNS Firewall. For those not familiar with how DNS Firewall works, and the benefits it provides, read on…

An introduction to DNS Firewall

At its most basic level, similar to traditional firewalls, DNS Firewall blocks/redirects end-users from accessing malicious sites.  The main difference between the two is that DNS Firewall is applied at a different layer and phase, namely threat intelligence data feeds are applied to the domain name system (DNS).  This circumvents the loss of visibility that is making traditional firewalls less effective due to the significant increases in end to end encrypted traffic.

But why should you use it?

In addition to protecting your users against identity theft, installation of malware and data exfiltration, there are other reasons to use this type of firewall as part of your multi-layered security, including:

Educating your end users: Following an attempt to connect to a bad domain you can enlighten your end-user as to the danger they have just avoided e.g. potentially connecting to a phishing site.  This can either be done via a landing page which they are redirected to, or by reaching out to them directly; turning a bad decision into a positive teaching opportunity.

Freeing up your busy team: Utilizing this kind of firewall automatically mitigates some of the serious issues that may arise on your network as a result of it being compromised.  This provides your teams with additional time to focus on resolving other pressing network and security issues.

Gaining insight to be proactive: It provides you with more visibility into compromised users or clients on your network.  This enables you to take immediate action without the time lag of either being notified by a third party, or discovering the issue at a later date, be that days, weeks or months after the attack.

It’s easy to apply & simple to maintain: Once this firewall has been applied to the DNS all the clients on your network, including IoT devices, are protected from accessing malicious sites.  This minimizes deployment resources.  Meanwhile the data feeds, against which potential connections are checked, are continuously update.  This removes the need for upgrades and updates.

Brand protection: For ‘trusted’ brands online security breaches can have a huge impact on business.  One only has to look to British Airways in the UK and their significant data breach to understand the consequences.  It is vital to have multiple layers of security to keep company networks and users ‘safe’.

Lower cyber risk insurance costs:  Insurance (and its associated costs) probably don’t fall under your department’s responsibilities or budget.  However, it’s highly likely that someone in your organization will be pleased to discover that implementing DNS Firewall can reduce your cyber risk insurance costs.

How can DNS Firewall be implemented?

There are three ways to implement DNS Firewall. It is worth noting that all three use ‘threat intelligence data feeds’ to identify bad domains, however there are differing ways in how you can access/utilize these feeds:

Data and synchronisingOn-premises open source software:  Threat intelligence data feeds are transferred via AXFR/IXFR to your DNS resolver as ‘zone’ files. Originally, DNS Firewall was designed to be an open and translatable standard, with it’s initial home being BIND.  Now other DNS servers such as PowerDNS, Knot, and Unbound also provide support for using DNS Firewall threat feeds.

On-premises appliance: An internal solution/application, located within your network, working as a management system for your DNS’s security infrastructure which utilizes threat intelligence data feeds. Depending on the supplier you may, or may not, have the flexibility to choose your preferred data feed supplier.

Cloud with data flowing in and outCloud: Service providers with their own DNS resolvers which are protected by DNS Firewall with threat intelligence data feeds, and are accessed, like a managed service, by customers.

How DNS Firewall works

Picture of how DNS firewall work

Let’s take a deeper dive into how DNS Firewall works:

Standard DNS Resolvers: When an end-user attempts to go to a website/domain, the resolver will query a root server, then a top-level domain server, and finally the server of the site, which will complete the resolution of the request by the end-user.  The client’s request to access the site will take place regardless of whether the site is malicious or not.

DNS Resolver with DNS Firewall: During the resolution process “zones”, which consist of sets of threat intelligence data, are queried.  The requested domain is analyzed for potential security risks against the data sets, and if a match is returned the request is blocked or redirected.

Take a look at the examples below to see what end-users may potentially see if they tried to connect to a phishing site in each of the following situations:

No DNS Firewall: phishing site accessed

 

text saying "This site can't be reached".

DNS Firewall enabled: phishing site blocked

 

advisory notice that user attempted to access a phishing site

DNS Firewall enabled: phishing site blocked and advice provided for user

Where the DNS Firewall is enabled the end-user who has attempted to access the phishing site has been prevented from doing so, and consequently protected from the potential harm that could lead to.  Moreover, because the mitigation has occurred at the DNS level there has been no need for the end-user to install an additional program or update software on their workstation.

What next?

DNS Firewall has the potential to free up teams to accomplish other tasks and build a secure proactive, not reactive, network experience for everyone within your organization.

Now you know how DNS Firewall works it’s time to look at what considerations you need to be making when implementing it.

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