How to Detect VPN Leaks: A Complete Guide for Privacy-Focused Users

You've set up your VPN, connected to a server, and feel secure. But are you really protected? VPN leaks can expose your real IP address, DNS queries, and browsing activity—completely defeating the purpose of using a VPN. This guide will teach you how to detect and fix every type of VPN leak.

What Are VPN Leaks?

A VPN leak occurs when some of your internet traffic bypasses the VPN tunnel, exposing information to your ISP, network administrators, or websites you visit. Even with an active VPN connection, leaks can reveal:

• Your real IP address
• Your DNS queries (what websites you're visiting)
• Your physical location
• Your ISP information

Types of VPN Leaks

1. IP Address Leaks

The most serious type of leak—your actual IP address is exposed to websites, defeating the primary purpose of a VPN.

How to Test:

1. Connect to your VPN
2. Visit multiple IP checking sites:
   • ipleak.net
   • browserleaks.com/ip
   • whatismyipaddress.com
3. Compare the shown IP with your VPN server's IP
4. Repeat with different browsers and in incognito mode

Common Causes:

• VPN connection drops without kill switch
• Misconfigured split tunneling
• Browser extensions bypassing VPN
• Dual-stack (IPv4/IPv6) misconfigurations

2. DNS Leaks

Even if your IP is hidden, DNS leaks reveal what websites you're visiting to your ISP's DNS servers.

How to Test:

1. Connect to your VPN
2. Visit these DNS leak test sites:
   • dnsleaktest.com (run extended test)
   • ipleak.net (check DNS section)
   • browserleaks.com/dns
3. Check if any DNS servers belong to your ISP

What You Should See:

All DNS servers should belong to your VPN provider or be anonymous/third-party servers (like Cloudflare or Google). If you see your ISP's DNS servers, you have a leak.

How to Fix DNS Leaks:

# On Windows, flush DNS cache and set VPN DNS
ipconfig /flushdns

# On Linux/Mac
sudo systemd-resolve --flush-caches
# or
sudo dscacheutil -flushcache

Most VPN apps should handle DNS automatically. If you have leaks:

• Enable "DNS leak protection" in your VPN settings
• Disable "Smart Multi-homed Name Resolution" in Windows
• Manually set DNS to your VPN's DNS servers

3. WebRTC Leaks

WebRTC (Web Real-Time Communication) is a browser feature for video calls and P2P communication. It can leak your real IP address even through a VPN.

How to Test:

1. Connect to your VPN
2. Visit browserleaks.com/webrtc
3. Check if your real IP appears under "Local IP Address" or "Public IP Address"

How to Fix WebRTC Leaks:

Firefox:

1. Type about:config in the address bar
2. Search for media.peerconnection.enabled
3. Set it to false

Chrome:

• Install "WebRTC Leak Prevent" extension
• Or use "uBlock Origin" which can block WebRTC

Brave:

1. Go to Settings → Privacy and security
2. Under "WebRTC IP Handling Policy"
3. Select "Disable non-proxied UDP"

4. IPv6 Leaks

Many VPNs only tunnel IPv4 traffic. If your connection supports IPv6 and it's not properly handled, IPv6 traffic can bypass the VPN.

How to Test:

1. Connect to your VPN
2. Visit test-ipv6.com
3. Check if your IPv6 address is your real one
4. Also check ipleak.net for IPv6 information

How to Fix IPv6 Leaks:

Option 1: Disable IPv6 on your system

Windows:

1. Open Network Connections
2. Right-click your adapter → Properties
3. Uncheck "Internet Protocol Version 6 (TCP/IPv6)"

Linux:

sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1
sudo sysctl -w net.ipv6.conf.default.disable_ipv6=1

macOS:

sudo networksetup -setv6off Wi-Fi
sudo networksetup -setv6off Ethernet

Option 2: Use a VPN that properly handles IPv6 (tunnels it or blocks it)

5. Kill Switch Failures

A kill switch should block all internet traffic if the VPN disconnects. If it fails, you're exposed.

How to Test:

1. Connect to your VPN
2. Start a continuous ping: ping google.com
3. Disconnect your VPN (simulate a drop)
4. Check if pings continue—they shouldn't
5. Also monitor your IP on ipleak.net during this test

Manual Kill Switch (Linux):

# Allow only VPN traffic with iptables
sudo iptables -A OUTPUT -o tun0 -j ACCEPT
sudo iptables -A OUTPUT -d YOUR_VPN_SERVER_IP -j ACCEPT  
sudo iptables -A OUTPUT -j DROP

Comprehensive Leak Testing Procedure

Follow this checklist every time you set up a new VPN or change settings:

Step 1: Baseline Check (Without VPN)

1. Disconnect from VPN
2. Note your real IP address at whatismyipaddress.com
3. Note your ISP name
4. Note any IPv6 address

Step 2: Connect and Initial Test

1. Connect to your VPN
2. Wait 30 seconds for connection to stabilize
3. Visit ipleak.net
4. Verify IP matches VPN server location

Step 3: Extended DNS Test

1. Go to dnsleaktest.com
2. Run the "Extended test"
3. Verify no ISP DNS servers appear

Step 4: WebRTC Test

1. Visit browserleaks.com/webrtc
2. Check both local and public IP sections
3. Your real IP should not appear

Step 5: IPv6 Test

1. Visit test-ipv6.com
2. Verify IPv6 is either tunneled through VPN or disabled

Step 6: Torrent IP Test (If Applicable)

1. Visit ipleak.net/torrent.html
2. Download the magnet link
3. Check the IP your torrent client reports

Step 7: Kill Switch Test

1. Keep ipleak.net open and refreshing
2. Disconnect VPN suddenly
3. Verify internet is blocked or IP doesn't change

Tools for Continuous Monitoring

Browser Extensions:

• uBlock Origin - Can block WebRTC and provide some leak protection
• WebRTC Control - Specifically manages WebRTC
• Privacy Badger - General privacy protection

Command Line Tools:

# Monitor DNS queries in real-time
sudo tcpdump -i any port 53

# Check current DNS servers
cat /etc/resolv.conf  # Linux
scutil --dns  # macOS
ipconfig /all  # Windows

VPN Provider Leak Protection Features

Quality VPN providers include these protections. Verify your provider offers:

• ✅ Kill switch (system-wide, not just app-level)
• ✅ DNS leak protection
• ✅ IPv6 leak protection (or IPv6 support)
• ✅ WebRTC leak protection (in browser extensions)
• ✅ Split tunneling (if needed, properly configured)

What to Do If You Find Leaks

Immediate Steps:

1. Disconnect from the internet entirely
2. Clear browser cache and cookies
3. Flush DNS cache
4. Restart your device

Long-term Fixes:

1. Update your VPN application
2. Enable all leak protection features
3. Consider switching VPN providers if leaks persist
4. Use a VPN-configured router for network-wide protection
5. Consider Whonix or Tails for maximum security

Beyond Basic Leak Testing

For advanced users concerned about sophisticated tracking:

Browser Fingerprinting

Even without IP leaks, websites can identify you through browser fingerprinting. Test at:

• coveryourtracks.eff.org
• browserleaks.com (various tests)
• amiunique.org

Canvas Fingerprinting

Your browser's rendering can be unique. Mitigate with:

• Tor Browser
• Canvas Blocker extension
• Brave's built-in fingerprint protection

Conclusion

VPN leaks can completely undermine your privacy efforts. Regular testing is essential—don't assume your VPN is working correctly just because you're connected. Make leak testing part of your routine, especially after updates or configuration changes.

Remember: A VPN is just one layer of privacy protection. For sensitive activities, combine your VPN with good operational security practices, a privacy-focused browser, and awareness of the limitations of the tools you use.