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What Is a DNS Leak and How Can You Check It?

You might have your traffic encrypted with a VPN, but DNS leaks can still expose your browsing activity. A DNS leak is one of the most common and overlooked privacy vulnerabilities. This guide explains what DNS leaks are, why they happen, and how to protect yourself.

By IP Tester Editorial Team · Updated September 9, 2026

Understanding DNS

The Domain Name System (DNS) translates human-readable domain names (like example.com) into IP addresses (like 93.184.216.34) that computers use. Every time you visit a website, your device sends a DNS query to find the correct IP address. Normally, your ISP handles these DNS queries. This means your ISP has a complete log of every website you've visited — every domain name request goes through their servers.

What Is a DNS Leak?

A DNS leak occurs when DNS queries are sent to your ISP's DNS servers instead of through your VPN's encrypted tunnel. This can happen even when you think your traffic is fully protected by a VPN. The leak happens because DNS resolution is a separate process from regular internet traffic. If the operating system or VPN client doesn't properly route all DNS queries through the encrypted tunnel, some requests may fall through to the default DNS servers — which belong to your ISP.

Why Do DNS Leaks Happen?

Common causes include:

  • VPN misconfiguration — the VPN isn't set to handle DNS queries
  • 操作系统设置 — your OS may override VPN DNS settings
  • IPv6 traffic — some VPNs don't properly tunnel IPv6 DNS requests
  • Smart DNS or split tunneling — features that intentionally route some traffic outside the VPN
  • Browser extensions — some DNS-related extensions can bypass VPN DNS settings

How to Test for DNS Leaks

Testing for DNS leaks is straightforward. Visit our DNS Leak Test page to check which DNS servers are handling your queries. For the most thorough test, use multiple testing services and compare results. If you see DNS servers from your ISP when you're connected to a VPN, you likely have a DNS leak.

How to Prevent DNS Leaks

Steps to prevent DNS leaks:

  • Choose a VPN provider with built-in DNS leak protection
  • Manually configure your DNS servers to use encrypted DNS (DoH or DoT)
  • Disable IPv6 if your VPN doesn't properly support it
  • Use DNS-over-HTTPS (DoH) or DNS-over-TLS (DoT) for encrypted DNS queries
  • Consider using a firewall that blocks all DNS traffic except through your VPN
  • Test regularly after software or system updates

Frequently Asked Questions

Yes. This guide is written by the IP Tester editorial team and reviewed for accuracy. However, technology evolves, so details may change over time. Always check the publication date for currency.
Check our other guides for more in-depth articles on networking and privacy topics.

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Written by IP Tester Editorial Team | Last updated: September 9, 2026