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DNS Leak Test: What It Is, How to Check, and How to Fix It

DNS Leak Test: What It Is, How to Check, and How to Fix It

27. May 2026Category Privacy & Security2 min read
DNS Leak Test: What It Is, How to Check, and How to Fix It

What Is DNS?

Before understanding DNS leaks, you need to understand what DNS does. DNS stands for Domain Name System — it is the internet's address book. When you type "speediq.org" into your browser, your device sends a DNS query to a DNS server asking: "What is the IP address for this domain?" The DNS server responds with an IP address, and your browser connects to it. For the strategic overview of where DNS leaks fit alongside other privacy threats, see our complete privacy tools guide.

By default, your device uses the DNS servers provided by your Internet Service Provider (ISP). This means your ISP sees a log of every domain you query — which is effectively a record of every website you visit, even if the connection itself is encrypted with HTTPS.

What Is a DNS Leak?

A DNS leak occurs when your DNS queries are sent outside your VPN tunnel — typically to your ISP's DNS servers — even when you are connected to a VPN. The result: your ISP can see which websites you are visiting, defeating the core privacy purpose of your VPN.

DNS leaks are among the most common VPN privacy failures. They are easy to miss because everything appears to work normally: your IP address shows the VPN's IP, pages load, nothing seems wrong — but your browsing history is fully visible to your ISP.

What Causes DNS Leaks?

Operating System DNS Handling

Windows 10 and 11 have a feature called "Smart Multi-Homed Name Resolution" that sends DNS queries to all available network interfaces simultaneously. This feature causes DNS leaks even when a VPN is active.

IPv6 DNS Leaks

If your network uses IPv6 and your VPN only handles IPv4 traffic, IPv6 DNS queries will bypass the VPN entirely. See our IPv6 leak test guide for detection details.

How to Test for DNS Leaks

  • Disconnect from your VPN. Note which DNS servers appear.
  • Connect to your VPN. Run the DNS leak test again.
  • Analyze the results. If you see your ISP's DNS servers after connecting to your VPN, you have a DNS leak.

How to Fix DNS Leaks

Fix DNS Leaks on Windows

Press Win + R, type gpedit.msc, navigate to Computer Configuration → Administrative Templates → Network → DNS Client, and set "Turn off smart multi-homed name resolution" to "Enabled".

Enable DNS Leak Protection in Your VPN

Most reputable VPN clients have a built-in DNS leak protection setting. Enable this and also enable your VPN's kill switch.

Summary

DNS leaks silently expose your browsing activity to your ISP, even when your VPN appears to be working correctly. Test regularly with SpeedIQ's DNS leak test, enable DNS leak protection in your VPN client, and consider using encrypted DNS (DoH or DoT) as a fallback layer of protection.

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