What Is a DNS Leak?

What Is DNS?

DNS, short for “Domain Name System,” is a distributed database that provides translation services between hostnames and IP addresses. On the internet, every computer has a unique IP address, just as every person has a unique ID number. However, an IP address consists of a string of numbers, such as 192.168.1.1, which is not easy for humans to remember. Therefore, a method is needed to convert these numbers into names that are easier to remember, and this is exactly the primary function of DNS.



For example, when you enter www.google.com in your browser, your computer first sends a request to a DNS server, asking what IP address corresponds to this website. The DNS server replies that the IP address of www.google.com is 64.233.170.113. Then, your computer sends a request to this IP address to retrieve the webpage content. In short, DNS servers are like the internet’s “phone book,” helping us find the “phone number” (that is, the IP address) of each website.



How Does DNS Work When Changing IP Addresses?

When you use a VPN or proxy server, in theory, all of your internet traffic—including DNS requests (that is, the names of the websites you visit)—should be transmitted through the VPN or proxy server. This process usually includes the following four steps:

1. Your computer tells the VPN or proxy server that you want to visit google.com.
   
   
   
2. The VPN or proxy server sends a request to its own DNS server: give me the IP address of a Google server.
   
   
   
3. The DNS server returns the IP address of a Google server.
   
   
   
4. The VPN or proxy server accesses Google based on the returned IP address.
   
   
   
   Suppose a user located in Singapore uses a VPN or proxy server with a U.S. IP address to access a website. If their VPN or software is configured correctly, the detection result should be: the IP address of the DNS server should also be located in the United States, consistent with the IP region of the VPN or proxy server. If the DNS server is not in the United States, for example in Canada or another region, there is no need to worry—at least the user’s real location (Singapore) has not been leaked.
   
   
   
   What Is a “DNS Leak”?
   
   Even if your internet traffic is transmitted through a VPN or proxy server, your device may still continue to use the DNS servers of your internet service provider (ISP), rather than the DNS servers provided by the VPN or proxy service. As a result, your IP address and DNS requests (that is, the names of the websites you visit) may be exposed to your ISP. This is what is known as a “DNS leak.”
   
   
   
   For example, a Singapore user uses a U.S. proxy IP to access Google, but due to incorrect VPN or software configuration, their device requests Google’s IP address from a local DNS server in Singapore. At this point, the user’s ISP knows that they are accessing Google. When the user checks whether there is a DNS leak, they will find that the IP region of the DNS server matches the region of the user’s real IP (both are in Singapore), which means a DNS leak has occurred!
   
   
   
   Risks of DNS Leaks
   
   If a DNS leak occurs, your DNS requests will be sent to your ISP’s DNS servers instead of the VPN’s DNS servers. This means:
   
   
   
   Real location exposure: Your ISP can learn your IP address, thereby exposing your actual geographic location.
   
   
   
   Personal privacy leakage: Your ISP may record the websites you visit and use this information for targeted advertising or sell it to third parties.
   
   
   
   Increased security risks: Some malware or cyberattacks may tamper with your DNS settings, causing your DNS requests to be sent to unsafe DNS servers. Unsafe DNS servers may redirect your requests to malicious websites, a tactic known as DNS hijacking. For example, you may want to visit your bank’s website but be redirected to a fake banking website. This fake website may look exactly like the real bank’s website, but it is actually set up by cybercriminals to steal your username and password.
   
   
   
   How to Prevent DNS Leaks
   
   Use a reliable VPN/proxy service
   
   Some VPN or proxy service providers offer features to prevent DNS leaks. These VPNs or proxies ensure that all of your DNS requests are transmitted through their servers rather than through your ISP’s servers. When choosing a VPN or proxy service, you should check whether they provide DNS leak protection.
   
   
   
   Use secure public DNS servers
   
   You can manually change the DNS servers in your device’s network settings to secure public DNS servers, such as Google Public DNS (8.8.8.8 and 8.8.4.4) or Cloudflare DNS (1.1.1.1). This way, even if your VPN connection is interrupted, your DNS requests will not be sent to your ISP’s servers.
   
   
   
   Use DNS leak detection tools
   
   Before using a VPN or proxy server to access websites, you can use a DNS leak detection tool to check whether a DNS leak exists. Regular testing is a good habit for ensuring privacy and security.
   
   
   
   Summary: DNS leaks are a common security risk when using VPNs or proxies, and they may lead to real IP exposure and privacy leakage. By choosing a reliable VPN service, configuring secure public DNS servers, and regularly performing leak tests, you can effectively prevent this risk and protect your network security and personal privacy.