Happy Eyeballs makes a simultaneous connection over IPv4 and IPv6 to an HTTP server, and uses the first connection that gets a server acknowledgement. This is u

Happy Eyeballs makes a simultaneous connection over IPv4 and IPv6 to an HTTP server, and uses the first connection that gets a server acknowledgement. This is useful because many networks have noticeably different response times for IPv4 and IPv6, and many have one of them configured but not working properly (usually IPv6). Without Happy Eyeballs web browsers can be slow fetching some web pages, for some users, waiting for a request timeout on IP addresses that don't work before trying one that works, or working but with the slower IP. It's called Happy Eyeballs because it improves the visible page load time in web browsers for many users. https://en.m.wikipedia.org/wiki/Happy_Eyeballs https://en.m.wikipedia.org/wiki/Happy_Eyeballs