What Is a DNS Leak? How to Test for and Prevent One

Direct Answer

A DNS leak happens when your device's domain lookups go to your own internet provider's resolver instead of through your proxy. Even with the proxy active, those lookups can reveal your real network and location. You prevent it by making DNS resolve at the proxy — for example with socks5h or by routing the whole device over OpenVPN.

Why DNS Can Leak

Every time you open a site, your device first asks a DNS resolver to turn the domain into an IP address. The problem: a basic proxy may forward your web traffic while your device still sends those DNS questions to your normal provider's resolver. The page loads through the proxy, but the lookup that found it didn't — and that lookup carries signals about your real network.

This is the same family of issue as a WebRTC leak: your traffic looks routed, but a side channel quietly uses your real connection. None of this is about hiding wrongdoing — it is basic hygiene so your data collection runs from the IP you actually intend.

How to Test for a DNS Leak

Connect through your German mobile proxy as you normally would.
Open a DNS-leak test page (search "DNS leak test") in the same context that uses the proxy.
Check the resolver(s) it reports. If they belong to your own internet provider, DNS is leaking. If they match your proxy's network, you're clean.
Cross-check your visible IP with our traffic check — or our how to verify your setup walkthrough — so you confirm both the IP and the DNS path.

How to Prevent a DNS Leak

Use socks5h instead of socks5. The extra h tells your client to resolve DNS at the proxy, not locally. In Python requests, for example, that single character moves the lookup to the mobile endpoint — see the Python guide.
Route the whole device over OpenVPN. Device-level routing sends DNS through the tunnel too, which closes the leak across every app — see OpenVPN on Windows, Android or iPhone. On Windows this only holds if the .ovpn sets block-outside-dns (Windows 10+ enforces it via the Windows Filtering Platform) or pushes DNS through the tunnel; a config we supply already does, but verify with the test above.
Verify after every change. Re-run the test above whenever you switch tools or networks; a config that was clean yesterday can leak after an update.

Where DNS Leaks Bite

For legitimate data work, a DNS leak quietly undermines the point of the proxy. A price-monitoring or ad-verification run that looks German by IP but resolves through a foreign provider can produce mixed signals and inconsistent results. Closing the leak keeps the whole request path consistent — IP, DNS and content all coming from the same German mobile vantage point.

FAQ

Does a mobile proxy stop DNS leaks automatically?

Not on its own. Whether DNS leaks depends on how your client resolves names. Use socks5h, or route the device over OpenVPN, then test to confirm.

Is a DNS leak the same as a WebRTC leak?

They're cousins. Both expose your real connection through a side channel while the proxy looks active. A DNS leak is about name lookups; a WebRTC leak is about the browser's real-time features. Test for both.

How often should I test?

After any change to your tool, proxy settings, or network — and periodically during long-running jobs. Pair it with an IP check so you verify both paths at once.

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