DNS Sinkhole: Where Digital Threats Go to Disappear

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DNS Sinkhole is a simple technique to intercept DNS requests for malicious traffic and re-route them to a safe IP address, effectively blocking and monitoring the request simultaneously.

Your ISP might already be using the mechanism to keep its customers safe. However, you can always set up a DNS Sinkhole on your personal machine or as a system administrator for a network of computers.

While it is a straightforward concept, it has a couple of use cases in cybersecurity.

Here, let me highlight all the essentials you need to know about DNS Sinkhole.

DNS Sinkhole: Its Purpose


In cybersecurity, every type of concept is important. Why? Because everything helps and counts to enhance and improve the security strategy.

Similarly, the DNS Sinkhole is a nice thing to have.

It has a critical role in monitoring network traffic and preventing users from unintentionally connecting to malicious websites. So, what exactly does it do?

First, it detects DNS requests trying to connect to domains known for malicious activities and blocks them. Occasionally, it can be a completely harmless interaction of a user clicking on a link from an email, which could be a part of a phishing campaign.

Additionally, regular detection of malicious DNS requests can also mean that any of the systems are infected with malware or spyware.

All the detected requests are re-routed to a specified IP address, which shows a warning or notice to the user.

The same mechanism of DNS Sinkhole can also be applied to block unauthorized domains, like social media or entertainment websites, for instance, on a workplace network.

Ultimately, whether it is about trying to access unauthorized websites or malicious portals, the process of intercepting the requests also allows you to log suspicious activity, helping you monitor the network overall.

In other words, DNS Sinkhole is a black hole of sorts where all the malicious network traffic ends up.

How Does a DNS Sinkhole Work?


The DNS Sinkhole sits at the DNS server, where DNS requests reach from a system (or a network of computers).

The DNS server is responsible for guiding you to the destination on the web.

As a quick refresher: the DNS server does this by translating domain names to their respective IP addresses, which loads up as the resource we need. You might want to learn how DNS works if you are hearing about it for the first time.

So, the DNS Sinkhole is configured within the DNS server to intercept the requests and re-route the malicious traffic to an assigned IP address, keeping things secure. The DNS Sinkhole always has a list of websites and IP addresses that are known to be unsafe. Sometimes, the list is created manually; sometimes, third-party security services provide it for enhanced protection.

For example, xyz.com is a website that attempts to connect to an IP address 192.158.1.XX. However, the IP address is known for malicious activities. So, when the request is intercepted, you are re-routed to connect to an assigned IP address (or the sinkhole), which displays a warning and blocks your connection.

If the DNS server does not have a sinkhole configured, the user will access the malicious webpage, which could infect the computer and put the network at risk.

So, a DNS Sinkhole protects the user and keeps other connected networks safe from any threats.

How to Set Up a DNS Sinkhole?

DNS. Domain Name System. Network Web Communication 2023

You can set up a DNS sinkhole on your personal computer, work computer, or a firewall environment.

The process of configuring a DNS sinkhole with a firewall could depend on what service you utilize.

For instance, if you use Palo Alto Networks firewall, you will have to refer to its official instructions to add an IP address to set the sinkhole. Not to forget, you need to first make sure that the firewall you use supports adding a DNS sinkhole.

If you are trying to set up a DNS Sinkhole on your computer, these are the steps you will have to follow:

  1. Note the sinkhole IP address from your hosted DNS provider, or choose to create your DNS sinkhole by running a DNS server as the redirect server from a separate Linux machine.
  2. If you are creating a sinkhole server from scratch, you can refer to an open-source or commercial list of known malicious domains and add it to the blocklist.
  3. Once you have the IP address (sinkhole), add it to your DNS server configuration and test it by accessing a known malicious website.

The nitty-gritty details for the process of setting up a DNS sinkhole will depend on the type of DNS Sinkhole you pick.

Let me highlight the types of DNS Sinkhole you can pick from.

Types of DNS Sinkhole

There are three types of DNS Sinkholes that you can opt for:

  • Creating your own from scratch by dedicating an entire computer to act as a redirecting server.
  • Enabling DNS Sinkhole capability from an application firewall.
  • Utilizing a cloud-hosted DNS service supporting DNS Sinkhole

The first type of DNS Sinkhole, i.e., creating from scratch, requires technical know-how and a lot of effort for the setup.

While it lets you customize and control it however you want, it may be cumbersome to maintain. You do not get any support for it, and the list of blocked domains has to be regularly updated as part of running things.

You should only go for it if you have the expertise and the time.

The second type of DNS Sinkhole can be easily configured by accessing the options in your firewall. Of course, there are a bunch of firewalls available to protect your network; choose one and check if it includes DNS Sinkhole support.

Once you are certain that the firewall supports it, you just need to head to the option and set it up as per its official instructions.

The last type of DNS Sinkhole is the easiest and most convenient option. The entire DNS sinkhole server is managed by the DNS provider; you just have to follow their instruction to integrate it into your network.

You do not have to configure anything else in your network with hosted services.

One of the examples includes Amazon Route 53, which is one of the key offerings of AWS.

Best Practices for DNS Sinkhole Deployment

As a system administrator or network admin, you should deploy the DNS Sinkhole, making sure it is the most effective. Some tips include:

  • Use a dynamically updating list of malicious domains
  • Ensure that all the malicious traffic is redirected to the sinkhole address
  • It is essential to use a log analyzer to check the blocked network activities to further identify issues in the network
  • The sinkhole should be deployed isolated from the network (and secure) so any attacker cannot take control of it or detect it.

Benefits of Using DNS Sinkhole

There are numerous advantages of using a DNS Sinkhole, such as:

  • Enhancing network monitoring by detecting suspicious connections and analyzing them further
  • Gain insights about what systems or users fall for malicious traffic
  • Can block access to unauthorized websites like a DNS filtering service
  • Reduce the chances of being infected by malware through a download or web service

Wrapping Up

A DNS Sinkhole is a tiny implementation with big benefits. It can be integrated in numerous ways, and both personal and business users can deploy it.

While it blocks malicious traffic, it cannot remove the malware from your computer. Furthermore, it is essential to note that a DNS Sinkhole can only block some known malicious requests and is not a replacement for a cloud firewall.

As per your business size and requirements, you should combine the use of firewalls, end-point security, and things like DNS Sinkhole to have the best security protection.