DNS leak
When name lookups travel to your ISP’s resolver instead of through the tunnel, exposing every domain you visit.
Glossary
IPv6 leak
When a tunnel carries only IPv4 while your connection also has IPv6, so IPv6-capable sites see your real address.
Why it matters
IPv6 deployment is now high enough that this is a live problem rather than a theoretical one, and it is invisible unless you specifically test for it.
What most explanations leave out
There are two acceptable answers: carry IPv6 inside the tunnel, or block it entirely at the interface. Both work. What does not work is ignoring it, which is what a client does when it configures only the IPv4 route and leaves IPv6 to the operating system.
Related terms
Kill switch
A control that blocks all internet traffic if the VPN tunnel drops, rather than letting it fall back to your normal connection.
Referenced from
Terms are defined here because they appear in our scoring rubric or in provider reviews, not to fill a glossary.