DNS leaks
When you connect to a VPN, your DNS queries should also go through the encrypted tunnel. A DNS leak happens when those queries are sent directly to your ISP’s resolver instead, revealing which sites you visit. The fix is usually a VPN setting called “DNS leak protection” or the use of a private resolver inside the tunnel.
IPv6 leaks
If your device has a working IPv6 connection but the VPN only tunnels IPv4, some of your traffic can leave the tunnel over IPv6. Check whether you see an IPv6 address and whether the VPN routes it. Many privacy-focused VPNs disable or route IPv6 explicitly.
WebRTC leaks
WebRTC (used by video calls and some chat apps) can reveal your real IP address even behind a VPN, because it discovers your local network addresses through the browser. Test with a WebRTC leak tool, and use browser settings or extensions to block WebRTC if needed.
How to test
Connect to your VPN, then visit a “what is my IP” page. The IP shown should be the VPN server’s IP. Repeat for DNS and WebRTC using dedicated leak test sites. If you see your ISP or real IP anywhere, the VPN is leaking.