# WebRTC leaks and timezone mismatches
> What a browser leak test can and cannot prove about a VPN.
WebRTC is how browsers do voice and video calls. While setting up a call it gathers “ICE candidates”: possible network paths, including local addresses. A VPN is supposed to be the only public address a site sees. A leak is a second public address, gathered by the browser, that is not the VPN address.

## What the test on this site does

It runs only after you click. It opens a peer connection, asks a public STUN server for candidates, and compares them with the IP this site already saw. A 10.x, 192.168.x, or 100.64.x address is your own network or CGNAT, not a leak by itself. An mDNS name such as `abc.local` means the browser hid the local address, which is what current browsers try to do.

## Timezone

The browser timezone comes from the operating system. The IP timezone comes from a geolocation database. They differ when you travel, when the database is wrong, and when a VPN exits in another region. A mismatch is a reason to look, not proof of a VPN. Pair it with the [location checker](https://ipinfo.fyi/tools/location) and the ASN on the [privacy check](https://ipinfo.fyi/tools/privacy).

Canonical: https://ipinfo.fyi/guides/webrtc-leaks