VPN-Kill-Switch
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Definition
Eine VPN-Funktion, die automatisch den gesamten Internetverkehr blockiert, wenn die VPN-Verbindung unerwartet abbricht, um zu verhindern, dass die echte IP-Adresse des Benutzers und unverschlüsselte Daten dem ISP oder Netzwerk offengelegt werden.
Why a Kill Switch Is Essential
A VPNVirtual Private Network. A technology that creates an encrypted tunnel between a device and a remote server, protecting data in transit and masking the user's real IP address. Used for privacy, security, and accessing restricted networks. kill switch blocks all internet traffic the moment the VPN tunnel drops — preventing your real Public IP AddressA globally unique IP address assigned by an ISP that is routable on the public internet. Every device directly accessible from the internet must have a public IP address. from being exposed during reconnection. Without it, a brief tunnel interruption (server overload, network change, ISP hiccup) leaks your true IP to every server you're communicating with, defeating the VPN's anonymity entirely. This is especially critical for Double VPNA privacy technique that routes traffic through two separate VPN servers in succession, applying two layers of encryption. Provides additional anonymity at the cost of increased latency and reduced speed. configurations where two simultaneous tunnels must both stay active.
Implementation Approaches
Kill switches operate at two levels:
| Level | Mechanism | Scope |
|---|---|---|
| Application-level | VPN client monitors tunnel interface | Only client-managed apps |
| OS/firewall-level | iptables / Windows Firewall rules |
All system traffic |
OS-level kill switches are more robust. On Linux, iptables rules mark the VPN interface as the only allowed outbound path; if the interface goes down, packets are dropped with no fallback. On Windows, the VPN client typically configures Windows Filtering Platform rules.
Testing and Verification
After enabling a kill switch, verify it with WebRTC Leak Test — WebRTC can bypass VPN tunnels and expose the real IP even when the kill switch appears active. Run a DNS Leak Test separately to confirm DNS queries also stay inside the tunnel. A reliable kill switch also blocks traffic when the system boots before the VPN connects — often called an "always-on" kill switch.