Before connecting to a site, a program turns its name into an address. If that lookup goes out over your own connection, your internet provider sees the name, and a site that checks may notice the lookup came from a different country than the visit.
An HTTP proxy resolves names on the proxy side by itself. With SOCKS5 it depends on the program: in curl, socks5h:// resolves through the proxy and socks5:// does not. Browsers have their own setting for it.
A leak does not stop the proxy working, which is why it goes unnoticed. The page still loads through the proxy; only the lookup took another route. It matters when the lookup itself must not be seen, or when a site compares where the lookup came from with where the visit came from.
Questions about DNS leak
How do I test for a DNS leak?
Open a DNS leak test page through the proxy. If it lists your own internet provider's servers, lookups are going around the proxy.
Does an HTTP proxy leak DNS?
Not for requests sent through it: your program gives the proxy the site's name and the proxy looks it up. Browsers can still look names up early to save time, which a browser setting turns off.
Related terms
- SOCKS5 proxy
- A SOCKS5 proxy passes any kind of network connection, not only web pages, and can sign you in with a username and password.
- WebRTC leak
- A WebRTC leak is when a browser's video-call feature reveals your real IP address to a website even though you are using a proxy.
- HTTP proxy
- An HTTP proxy is a proxy that speaks the web's own protocol. Almost every program supports it, and it carries both http and https sites.
Read next: HTTP vs SOCKS5 proxies