DNS Leak

To understand what a DNS leak is, imagine a postman. You ask him to deliver the letter, but instead of going to the address directly, he loudly asks the whole neighborhood: “Who knows where Ivanov lives?” — and every passerby now knows where your letter is going. This is how a DNS query works: even if your Internet traffic is encrypted by a VPN or proxy, sometimes the DNS queries themselves (that is, the questions “what IP does this site have?”) go past the secure tunnel. This is DNS leak — DNS leak.

Why is this important? Because DNS queries reveal the list of sites you visit, even if the pages themselves are encrypted. For privacy, it’s like wearing a mask, but loudly announcing to the whole hall exactly where you’re going.

Where the leak is most common:

• when working through an unreliable VPN;
• in public Wi-Fi networks where the PROVIDER imposes its DNS servers;
• in operating systems that send requests bypassing the tunnel.

How DNS Normally Works

DNS is like an Internet phone book. Instead of remembering long numbers (IP addresses), we type in convenient names — google.com , wikipedia.org , netflix.com The DNS server translates these names into numeric addresses.

How it works step by step:

1. You enter the website in the browser.
2. The browser asks the system: “What is the IP of this domain?”
3. The system sends a request to the DNS server (most often the provider’s server).
4. The DNS server returns the IP address, and the browser connects to the site.

Here, the provider plays a key role: it is his servers that usually serve your DNS queries, which means that he sees the list of sites that you visit. Even if the traffic is encrypted with HTTPS or VPN, the information about where you went remains with the provider.

Historical Background: From DNS to DNS Leak Awareness

The history of DNS began back in the 1980s. Back then, the Internet was just developing, and there was a need for a system that would translate domain names into IP addresses. DNS has become such a system — simple and convenient, like a telephone directory.

For a long time, no one thought about the “DNS leak”. DNS leakage was not considered a problem because Internet privacy was a secondary concern: the main thing was to make everything work.

The situation changed in the 2010s, when massive VPN services and privacy protection technologies appeared. Users expected their traffic to be fully protected, but suddenly it turned out that the VPN encrypts the data, and DNS requests continue to go directly to the provider. This is how the concept of “DNS leak” arose.

The first public tests (for example, dnsleaktest.com They became an eye-opener for thousands of users: they thought their traffic was private, but in fact the provider continued to see everything. This prompted VPN services to add DNS leak protection, which is the forced routing of DNS requests through a secure tunnel.

What Causes a DNS Leak

There are many reasons for DNS leaks, and most often they are related to the fact that some part of the system “plays by its own rules”:

• Incorrect VPN settings. If the VPN does not redirect DNS requests to its tunnel, they will go directly to the ISP.
• Public Wi-Fi without encryption. Many access points impose their DNS servers, and requests are easily intercepted.
• Errors in the proxy and firewall configuration. Sometimes, even with a VPN, some of the traffic passes by due to incorrectly configured routing rules.
• OS and application features. Windows and some mobile systems can send individual DNS queries directly, ignoring the VPN tunnel. This is done “to speed up”, but in fact it breaks privacy.

With the availability of the information and your personal data it is very important to know the potential risks and things that can be done with your IP.

In fact, DNS leak occurs when your “questions” in the Internet directory do not end up in a secure VPN box, but directly to the provider or a third party.

Types of DNS Leaks

DNS leaks are different, and each has its own mechanisms:

• Leaks through the ISP. Even if you have a VPN enabled, the system may continue to use your ISP’s DNS servers. As a result, he sees all your requests, and therefore the list of sites that you visit.
• Leaks via WebRTC. WebRTC is a technology for video calls and streaming data exchange in the browser. She sometimes sends DNS queries directly, bypassing the VPN. The result is that your real IP and DNS servers are revealed to the sites.
• Split-tunneling and VPN bypass. In some VPN settings, some traffic goes through an encrypted tunnel, and some goes directly. DNS queries can fall into the “unprotected” part, which causes a leak.
• Local leaks within the network. This is when DNS requests are intercepted inside a corporate or home network. For example, a router or a system service can force them to go to their DNS servers, ignoring the VPN settings.

Risks and Consequences of a DNS Leak

DNS leak is not just a technical error, but a serious risk to privacy:

• Loss of anonymity. Even if your traffic is encrypted with VPN or HTTPS, the list of visited sites remains visible to the provider and third parties.
• The ability to track activity. Using DNS queries, you can restore the picture: which sites you read, which services you use, and what time you connect to the network.
• Censorship and blocking. In countries with Internet filtering, providers often use DNS queries to block them. If they go directly, you get censored, even with a VPN.
• Reputational and legal risks. For businesses, DNS leak can mean leakage of corporate activity, which is fraught with loss of customers and even legal problems.

How to Detect and Prevent a DNS Leak

Fortunately, DNS leaks can be checked and prevented.

• Online verification services. Sites like dnsleaktest.com or browserleaks.com they show which DNS servers are actually processing your requests. If the ISP’s IP is on there, it means you have a DNS leak.
• Checking through commands. You can use nslookup on Windows, and dig on Linux and macOS. These utilities allow you to see exactly where DNS queries go.
• VPN with DNS leak protection. Modern VPN services offer built-in protection: they redirect all DNS requests to an encrypted tunnel and use their own DNS servers.
• DoH/DoT and firewall. Switching to DNS over HTTPS (DoH) or DNS over TLS (DoT) protocols makes requests encrypted. And a properly configured firewall can prohibit any DNS bypass requests outside the tunnel.