Kill Switch Explained (And How to Test It)

What Is a Kill Switch?

A VPN kill switch (also called "network lock" or "internet kill switch") is a security feature that automatically blocks all internet traffic if your VPN connection drops unexpectedly.

Why You Need a Kill Switch

VPN connections can drop for many reasons:

• Network instability: Wi-Fi drops, ISP issues, network switching
• Server problems: VPN server overload or maintenance
• Software issues: VPN app crashes, updates, conflicts
• Firewall interference: Security software blocking VPN
• Sleep/wake cycles: Device waking from sleep may not reconnect

Even a brief exposure can be problematic:

• Torrenting: Your real IP logged by peers in the swarm
• Streaming: Service detects your real location
• Privacy: Websites log your actual IP
• Censorship: Authorities detect VPN bypass attempts

Types of Kill Switches

App-Level Kill Switch

• Implemented within the VPN application
• Only works while VPN app is running
• May fail if VPN app crashes
• Easier to implement, less reliable

System-Level Kill Switch

• Modifies OS firewall rules
• Works even if VPN app crashes
• Blocks traffic at the network stack level
• More reliable, recommended

OS-Native Kill Switch

• Android: "Block connections without VPN" in system settings
• Windows: Some VPNs use Windows Filtering Platform (WFP)
• Linux: iptables/nftables rules

How to Test Your Kill Switch

Don't assume your kill switch works-test it yourself:

Basic Test Method

1. Connect to VPN and verify your IP has changed
2. Open a webpage that shows your IP (keep it open)
3. Force disconnect the VPN (don't use the app's disconnect button)
4. Quickly refresh the IP check page
5. Check the result: If you see your real IP, the kill switch failed

Advanced Test Method

1. Connect to VPN
2. Start a continuous ping to a public server
3. Kill the VPN process (Task Manager/Activity Monitor)
4. Watch the ping results
5. If pings continue after VPN dies, kill switch failed

Test Scripts & Commands

Windows (PowerShell)

# Continuous ping test
ping -t 8.8.8.8

# Or with timestamp
ping -t 8.8.8.8 | ForEach-Object { "{0} - {1}" -f (Get-Date), $_ }

# Kill VPN process (replace with your VPN's process name)
# taskkill /IM "vpnclient.exe" /F

macOS/Linux (Terminal)

# Continuous ping with timestamp
ping 8.8.8.8 | while read line; do echo "$(date): $line"; done

# Find VPN process
ps aux | grep -i vpn

# Kill VPN process (replace PID)
# kill -9 [PID]

Automated Test Script (Bash)

#!/bin/bash
# Kill switch test script

echo "Starting kill switch test..."
echo "Current IP:"
curl -s ifconfig.me
echo ""

echo "Starting continuous connectivity check..."
echo "Kill your VPN process now and watch for changes"
echo "Press Ctrl+C to stop"
echo ""

while true; do
    IP=$(curl -s --max-time 2 ifconfig.me 2>/dev/null)
    if [ -n "$IP" ]; then
        echo "$(date '+%H:%M:%S') - CONNECTED - IP: $IP"
    else
        echo "$(date '+%H:%M:%S') - BLOCKED (kill switch working)"
    fi
    sleep 1
done

Troubleshooting Failed Kill Switches

Kill Switch Not Activating

• Check it's enabled: Many VPNs have kill switch disabled by default
• Verify permissions: VPN may need admin/root access for firewall rules
• Check firewall conflicts: Other security software may interfere
• Update VPN app: Older versions may have bugs

Traffic Leaking Despite Kill Switch

• IPv6 leaks: Kill switch may only block IPv4
• DNS leaks: DNS queries may bypass the kill switch
• App-level limitation: If VPN app crashes, app-level kill switch fails
• Split tunneling conflict: Excluded apps bypass kill switch

Solutions

• Use Android's native "Block connections without VPN"
• Disable IPv6 on your device
• Use a VPN with system-level kill switch
• Configure firewall rules manually as backup

Platform-Specific Notes

Windows

Best kill switch support. Look for VPNs using Windows Filtering Platform (WFP) for system-level blocking. TAP adapter-based kill switches are less reliable.

macOS

Kill switch reliability varies. Network Extensions (modern) are better than kernel extensions (legacy). Some VPNs use packet filter (pf) rules.

Android

Use the native "Always-on VPN" with "Block connections without VPN" in Settings → Network → VPN. This is more reliable than app-based kill switches.

iOS

iOS kill switches are limited due to Apple restrictions. The VPN can disconnect without the kill switch activating during network transitions. iOS 14+ has improved but still not perfect.

Linux

Most reliable with proper iptables/nftables configuration. Many VPNs provide scripts or have built-in firewall rule management.

Frequently Asked Questions