When using a VPN to protect your online privacy, you expect all your internet traffic to be routed through an encrypted tunnel, hiding your real IP address from websites, ISPs, and potential eavesdroppers. However, many VPN users unknowingly expose their real IPv6 address even while connected to their VPN—a critical security vulnerability known as an IPv6 leak. This comprehensive guide explains what IPv6 VPN leaks are, why they occur, how to detect them, and most importantly, how to prevent them.
An IPv6 leak occurs when your IPv4 connection is correctly routed through the VPN tunnel, but your IPv6 connection bypasses the VPN entirely and connects directly through your Internet Service Provider (ISP). In this scenario:
This dual-state creates a false sense of security. While websites that only check IPv4 addresses will see your VPN's IP, any website or service that supports IPv6 can see your real IPv6 address, effectively bypassing your VPN protection entirely.
IPv6 leaks are surprisingly common because:
According to industry studies, over 30% of VPN connections are vulnerable to IPv6 leaks, with users completely unaware that their actual location and identity are being exposed.
The fundamental issue is simple: most VPN services only establish IPv4 tunnels. When your device attempts to connect to an IPv6-enabled website:
Dual-Stack Networking Complexity
Modern systems run both IPv4 and IPv6 simultaneously (dual-stack configuration). This creates two parallel networking stacks, each requiring separate routing rules, tunnels, and security policies. VPN software must handle both protocols—but many don't.
Routing Table Priority
Operating systems maintain separate routing tables for IPv4 and IPv6. When a VPN establishes a tunnel, it modifies the IPv4 routing table to redirect all traffic through the VPN interface. However, if the VPN doesn't modify the IPv6 routing table, IPv6 traffic continues using the default route directly to your ISP.
DNS Resolution Challenges
Even if your VPN tunnels IPv6 traffic, DNS leaks can expose you. If your DNS resolver supports IPv6 and returns AAAA records before A records, your browser will attempt IPv6 connections first. If these DNS queries leak outside the VPN tunnel, your browsing activity becomes visible to your ISP.
IPv6 addresses are globally unique and directly identify your location, ISP, and often your specific device. Unlike IPv4 private addresses behind NAT, many ISPs assign public IPv6 addresses directly to customer devices. When your IPv6 address leaks:
If you're using a VPN to access region-restricted content, IPv6 leaks can reveal your actual location:
For users in regions with internet surveillance or censorship:
In jurisdictions where VPN usage for certain activities may be legally questionable, IPv6 leaks can:
The fastest way to check for IPv6 leaks is using specialized online testing tools. These services attempt to detect your IPv6 address and compare it to your IPv4 address.
Testing Process:
test-ipv6.run provides comprehensive IPv6 leak testing by:
Other Testing Tools:
Complete VPN Leak Test Protocol:
Baseline Test (VPN Disconnected)
1. Ensure VPN is completely disconnected
2. Visit test-ipv6.run and record:
- Your real IPv4 address
- Your real IPv6 address (if any)
- Your ISP name
- Your geographic location
VPN Connected Test
1. Connect to your VPN service
2. Wait 10-15 seconds for connection to stabilize
3. Visit test-ipv6.run again
4. Check that:
- IPv4 address has changed to VPN server location
- IPv6 address is NOT shown (or shows VPN server's IPv6)
- ISP name reflects VPN provider, not your actual ISP
- Geographic location shows VPN server location
Dual-Stack Website Test
While connected to VPN, visit major IPv6-enabled sites:
- Google (ipv6.google.com)
- Facebook
- YouTube
Check test-ipv6.run results after visiting each site to verify
your IPv6 address wasn't exposed during the connection.
DNS Leak Test
Visit dnsleaktest.com or ipleak.net while connected to VPN
Verify all DNS requests are routed through VPN servers, not your ISP
Scenario 1: No IPv6 Leak (Secure)
Scenario 2: IPv6 Leak Detected (Vulnerable)
Scenario 3: Broken IPv6 (Connectivity Issues)
For advanced users, you can detect IPv6 leaks using built-in system commands:
Linux/macOS:
# Check your IPv6 address before VPN connection
ip -6 addr show | grep inet6
# or
ifconfig | grep inet6
# Connect to VPN, then check again
# If the same IPv6 address appears, you have a leak
# Test IPv6 connectivity through VPN
curl -6 https://api6.ipify.org
# Check routing table
ip -6 route show
# Look for default route - it should point to VPN interface (tun0/tap0)
Windows:
# Check IPv6 configuration
ipconfig
# Test IPv6 connectivity
curl -6 https://api6.ipify.org
# Check routing table
netsh interface ipv6 show route
What to Look For:
The most comprehensive solution is choosing a VPN provider that fully supports IPv6 by routing it through the encrypted tunnel.
What to Look For:
VPN Providers with IPv6 Support (as of 2025):
Verification After Connection: Test at test-ipv6.run to confirm both your IPv4 and IPv6 addresses show the VPN server's location, not your real location.
Most VPN services that don't support IPv6 routing offer IPv6 blocking as a leak prevention mechanism. The VPN client disables IPv6 on your device while connected, preventing any IPv6 traffic from leaving your system.
How It Works:
Advantages:
Disadvantages:
Major VPNs with IPv6 Blocking:
If your VPN doesn't provide IPv6 protection, you can manually disable IPv6 at the operating system level.
Windows 10/11:
1. Open "Network and Sharing Center"
2. Click "Change adapter settings"
3. Right-click your active network connection
4. Select "Properties"
5. Uncheck "Internet Protocol Version 6 (TCP/IPv6)"
6. Click OK
Alternative Windows Method (Command Line):
# Run PowerShell as Administrator
netsh interface ipv6 set teredo disabled
netsh interface ipv6 set 6to4 disabled
netsh interface ipv6 set isatap disabled
# Disable IPv6 on all interfaces
netsh interface ipv6 set interface "Ethernet" disabled
netsh interface ipv6 set interface "Wi-Fi" disabled
macOS:
# Disable IPv6 on Wi-Fi
networksetup -setv6off Wi-Fi
# Disable IPv6 on Ethernet
networksetup -setv6off Ethernet
# To re-enable later
networksetup -setv6automatic Wi-Fi
Linux:
# Temporary disable (until reboot)
sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1
sudo sysctl -w net.ipv6.conf.default.disable_ipv6=1
# Permanent disable (add to /etc/sysctl.conf)
echo "net.ipv6.conf.all.disable_ipv6 = 1" | sudo tee -a /etc/sysctl.conf
echo "net.ipv6.conf.default.disable_ipv6 = 1" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p
iOS/iPadOS:
Unfortunately, iOS does not provide a built-in option to disable IPv6.
You must rely on your VPN app to block IPv6 or use a VPN with IPv6 support.
Android:
Android does not offer a standard way to disable IPv6 system-wide.
Some custom ROMs or rooted devices can disable it, but for most users,
choosing a VPN with IPv6 leak protection is the only viable option.
Considerations:
A VPN kill switch monitors your VPN connection and blocks all internet traffic if the VPN disconnects unexpectedly. Most modern VPN clients include kill switch functionality for both IPv4 and IPv6.
How It Works:
Firewall-Based Kill Switch (Linux/macOS):
Linux (using iptables):
#!/bin/bash
# Replace tun0 with your VPN interface name
# Block all IPv6 traffic
sudo ip6tables -P INPUT DROP
sudo ip6tables -P OUTPUT DROP
sudo ip6tables -P FORWARD DROP
# Allow IPv4 only through VPN interface
sudo iptables -A OUTPUT -o tun0 -j ACCEPT
sudo iptables -A OUTPUT -o lo -j ACCEPT
sudo iptables -A OUTPUT -j DROP
macOS (using pf firewall):
# Create /etc/pf.anchors/vpn_killswitch
block all
pass on lo0
pass on utun2 # Replace with your VPN interface
# Load the rule
sudo pfctl -e -f /etc/pf.anchors/vpn_killswitch
Advanced users can manually configure IPv6 routing to ensure all IPv6 traffic goes through the VPN interface.
Linux:
# After connecting to VPN (replace tun0 with your VPN interface)
sudo ip -6 route add default dev tun0
# Remove the default IPv6 route through your ISP
sudo ip -6 route del default via fe80::1 dev eth0
Verification:
# Check that default IPv6 route points to VPN
ip -6 route show
# Should show: default dev tun0
When evaluating VPN services for IPv6 leak protection, consider these categories:
Providers: Mullvad, IVPN, ProtonVPN, Perfect Privacy
Providers: NordVPN, ExpressVPN, Surfshark, CyberGhost, Private Internet Access
Providers: Various smaller/budget VPN services
Check Your VPN's Documentation:
Test Your Current VPN:
After implementing any of the above solutions, verify your protection is working:
Verification Checklist:
Initial Test
Protected Test
Stress Test
Reconnection Test
Browser Test
False. IPv6 leaks affect anyone using a VPN. Residential ISPs worldwide are rapidly deploying IPv6, and consumer devices enable it by default.
False. Price doesn't correlate with IPv6 protection. Even premium VPN services may lack IPv6 support or leak protection.
False. Studies show over 30% of VPN connections are vulnerable to IPv6 leaks. It's a widespread problem.
False. The vast majority of internet services remain accessible via IPv4. Only a tiny fraction of websites are IPv6-only.
False. If your IPv6 traffic bypasses the VPN entirely, it's completely unencrypted and directly exposed, regardless of your VPN's encryption strength.
IPv6 leaks represent a critical vulnerability that undermines the core purpose of using a VPN—protecting your privacy and security online. The prevalence of IPv6 adoption combined with IPv4-only VPN implementations creates a widespread problem affecting millions of users who believe they're protected when they're actually exposed.
Key Takeaways:
The good news is that IPv6 leaks are entirely preventable with the right approach. Whether you choose a VPN with native IPv6 support, one that blocks IPv6, or manually disable IPv6 on your system, the important step is taking action to close this security gap.
Don't assume your VPN protects you. Test it, verify it, and ensure your entire internet connection—both IPv4 and IPv6—is actually private.
Recommended Action Plan:
References: