When VPNs Fail
Real-World Leak Scenarios.
You flip the switch, the app turns green, and you think you are invisible. But what if the tunnel collapses? When a VPN fails, it usually happens silently. One second you are protected behind a VPN exit point in London; the next, your real IP address may be visible to websites, apps, or your ISP. Let's look at exactly how this happens and how to reduce the risk.
The Anatomy of a Leak
Silent Failures
A VPN leak happens when the encrypted tunnel stops protecting part of your traffic, while your internet connection still carries on. That can expose your real IP address, your DNS requests, or browser-level connection details without a dramatic warning screen.
There are three common leak types to watch for: DNS leaks, where your ISP or another resolver can still see the domains you request; IP leaks, where sites can see your real IP and approximate location; and WebRTC leaks, where your browser may expose local or public IP details outside the tunnel.
Real-World Scenarios
You might think a disconnection is obvious. In reality, it is often invisible. Here are three common ways users get exposed:
Scenario 1: The "Micro-Drop" (Torrenting)
You are downloading a large file. Your VPN connection drops for just 2 seconds because of packet loss or a server reset, then reconnects almost immediately. It looks like a harmless blip.
The Consequence: In those 2 seconds, your torrent client may continue announcing your presence to the swarm. Your home IP address can be logged by peers or monitoring firms, even though the VPN appears to be back online.
Scenario 2: The "Wi-Fi Wanderer" (Mobile)
You are in a coffee shop on Wi-Fi. You walk outside to catch a bus, the Wi-Fi signal drops, and your phone switches to 4G or 5G mobile data.
The Consequence: During that handover, the VPN tunnel may need a moment to rebuild. For a few seconds, background traffic from email, social apps, or your browser can leave over your normal mobile connection rather than through the VPN tunnel, unless you have a kill switch or a block-connections setting in place.
Scenario 3: The "IPv6 Ghost"
You set up your VPN correctly, but your router and ISP now support IPv6. Your VPN app only protects IPv4 traffic, or it mishandles IPv6.
The Consequence: A website requests your address. Your VPN masks your IPv4 traffic, but your device still sends IPv6 traffic outside the tunnel. That reveals your real IPv6 address, and the VPN app may not display any obvious error because the main tunnel still looks active.
The Kill Switch: Your Best Defence
How It Protects You
The most reliable defence against a sudden VPN failure is a kill switch. This feature monitors the tunnel status and blocks internet traffic the moment the protected connection drops.
Without a kill switch, your device may quietly reconnect over your normal network path, whether that is home broadband, public Wi-Fi, or mobile data. On Android, an app-level VPN plus Always-on VPN and Block connections without VPN can offer similar protection.
Types of Leaks Compared
| Leak Type | What Is Exposed? | Who Sees It? | Severity |
|---|---|---|---|
| IP Leak | Real IP and approximate location | Websites and apps | Critical |
| DNS Leak | DNS requests and visited domains | Your ISP or another DNS resolver | High |
| WebRTC Leak | Local or public IP details | Websites via your browser | Moderate |
How to Test for Leaks in 3 Minutes
Run a Quick Leak Check Before You Trust Any VPN
A VPN that connects is not automatically a VPN that protects you. The fastest way to catch problems is to test it on the exact device and browser you actually use.
- Connect to your VPN and note the country or city shown in the app.
- Visit an IP and DNS leak checker such as dnsleaktest.com and confirm the visible IP and DNS servers match the VPN, not your ISP.
- Check a WebRTC test page such as browserleaks.com/webrtc and make sure it does not reveal your real IP details.
- Repeat the test while switching from Wi-Fi to mobile data, or after reconnecting the VPN, because that is where many brief leaks appear.
Warning: Free VPNs
This is one of the biggest trade-offs when choosing a free provider. Building and maintaining a dependable kill switch across Windows, macOS, Android, and iOS takes serious engineering work.
The Risk: Many free VPNs either lack a full system-level kill switch or implement a weaker version. If they disconnect, overload, or mishandle IPv6 or DNS, you may not realise you are exposed until afterwards.
FAQs
What is a VPN Kill Switch?
A kill switch is a security feature that instantly blocks your device's internet traffic if the VPN tunnel drops. Its job is to stop your real IP address and DNS requests from escaping outside the tunnel.
What is a DNS Leak?
A DNS leak happens when your DNS requests bypass the VPN and go directly to your ISP or another resolver. Even if your visible IP looks correct, those DNS requests can still reveal the domains you visit.
Is Always-on VPN the same as a kill switch?
Not always. On Android, Always-on VPN helps keep the VPN active, but the setting that stops normal traffic when the VPN is unavailable is Block connections without VPN. Some VPN apps also include their own app-level or system-level kill switch.
How do I test for leaks?
Connect to your VPN, then test your IP, DNS, and WebRTC results on sites such as dnsleaktest.com and browserleaks.com/webrtc. If you ever see your actual ISP, home region, or home IP details, your setup is leaking.
