Many VPNs tunnel IPv4 only. If your network has IPv6 connectivity, traffic may route outside the VPN and reveal your identity. Test whether IPv6 is reachable and what address is visible.
When IPv6 is enabled on your router but the VPN does not assign an IPv6 address, browsers may prefer IPv6 for dual-stack sites, bypassing the encrypted tunnel entirely.
Disable IPv6 on the OS or router, or use a VPN that provides IPv6 support and blocks native IPv6 when disconnected.
If your VPN does not support IPv6, disabling it on your system prevents accidental bypass leaks.
Common on home networks with ISP-provided IPv6 and VPN clients that only handle IPv4.