VPN Leaks Explained: DNS, WebRTC, IPv6 and the Kill Switch

A VPN leak happens when some of your traffic or identifying details travel outside the encrypted tunnel, exposing your real IP address or the sites you look up. The main causes are DNS requests that bypass the VPN, browser WebRTC features, IPv6 traffic the VPN does not handle and the connection dropping without a kill switch. All are testable and usually fixable.

Why leaks happen

A VPN works by changing how your device routes traffic. If any component ignores that routing, it can use your normal connection instead. Operating systems, browsers and apps all make their own network decisions, so a VPN client has to override many of them. When it does so imperfectly, a leak appears.

The main types of leak

• DNS leak: your device sends domain lookups to your ISP’s resolver instead of through the tunnel. Your ISP can then see which sites you visit even though the traffic itself is encrypted.
• WebRTC leak: WebRTC is a browser technology for real-time features like video calls. In some browsers it can reveal your real local or public IP address to a website, even with a VPN on.
• IPv6 leak: if your network supports IPv6 but the VPN handles only IPv4, requests over IPv6 may skip the tunnel entirely.
• Disconnect leak: if the VPN connection drops, apps carry on using your normal connection, exposing your real IP until you notice.
• Split-tunnel or app leaks: apps excluded from the VPN, or those that use their own network paths, send traffic outside the tunnel.

How to test for leaks

1. Note your real public IP address with the VPN off, using a reputable IP-check page.

2. Connect to the VPN and recheck. The IP address and location should now show the VPN server.

3. Run a DNS leak test and confirm that the resolvers listed belong to the VPN or the resolver you chose, not your ISP.

4. Run a WebRTC test in your browser and make sure no real IP appears.

5. Check for IPv6: a test page should show either the VPN’s IPv6 address or no IPv6 at all.

6. Test the kill switch by connecting, then disabling your network adapter or switching Wi-Fi off and on while watching whether any traffic gets out.

How to fix leaks

• Enable the kill switch in the VPN app, and choose the stricter option that blocks all traffic outside the tunnel if offered.
• Turn on DNS leak protection or set the provider’s DNS in the app.
• Disable IPv6 at the system level if the VPN does not support it, or choose a VPN that does.
• Limit WebRTC with browser settings, or use a browser with built-in protection, and be careful with extensions you install for this purpose.
• Update the VPN client and reboot after changing network settings.
• Review split-tunnelling rules and exclude only apps you really want outside the VPN.
• If leaks persist, try a different protocol or contact the provider’s support.

Why this matters for your choice of VPN

A provider that documents its leak protection, offers a working kill switch on every platform and lets you test it is giving you meaningful evidence of quality. A tool that cannot pass a basic leak test provides little privacy, however polished its marketing.

Keeping a routine

Run the test suite when you first set up a VPN, when you move to a new network type, such as from Wi-Fi to mobile data, and after operating system upgrades. It takes a few minutes and tells you whether the protection you depend on is actually working.

Mobile and router considerations

On phones, enable the always-on VPN and block-connections-without-VPN options if your operating system offers them, so a drop in the signal does not expose you. If you configure a VPN on a router, every device is covered, but you lose per-device control and must check for leaks from the router itself. Test on cellular data as well as Wi-Fi, because mobile networks often use IPv6 by default.

What a leak does and does not expose

A DNS leak shows your ISP the domains you ask for. An IP leak shows a website your real address. Neither gives attackers access to your device, and neither reveals the contents of an encrypted page. Understanding the actual risk helps you decide how much effort the fix deserves for your situation.

Troubleshooting a failed test

If a leak test shows your real IP, first confirm that the VPN is actually connected and that no browser extension or proxy is overriding it. Switch protocol or server, restart the app and then the device, and disable IPv6. If a particular browser leaks while others do not, update it or adjust its WebRTC setting. When nothing works, collect the test results and ask the provider’s support to investigate; a good provider will take such a report seriously.

Frequently asked questions

What is a kill switch?

A kill switch blocks internet access if the VPN connection drops, so your real IP and traffic are never sent over the unprotected connection.

Can a browser leak my IP while using a VPN?

Yes. WebRTC in some browsers can reveal your real IP. Test for it and change browser settings if needed.

How often should I test for leaks?

When you set up the VPN, on new networks and after major updates. Occasional spot checks help confirm that nothing has changed.

Key takeaways

• Leaks expose your real IP or lookups outside the VPN tunnel.
• Test DNS, WebRTC, IPv6 and kill-switch behaviour.
• Enable the kill switch and DNS leak protection, and disable unsupported IPv6.
• Retest after updates and on new networks.