An application that uses a Happy Eyeballs algorithm checks both IPv4 and IPv6 connectivity (with a preference for IPv6) and uses the first connection that connects successfully.

While the Happy Eyeballs algorithm and suggested configuration parameters are not adjusted to the iterative resolution process of a resolver, we are still interested to see if and how resolvers …

Below you will see counters of how often IPv6 is used, IPv4 is used, or both fail. Note that if you move this tab to the background it will run for up to just 3 hours. Bringing it to the foreground …

Charter for Working Group RFC 8305 defined “Happy Eyeballs Version 2”, a client algorithm for resolving and connecting to a server with different server IP address options, aiming to …

RFC 6555 Happy Eyeballs Dual Stack April 2012 1. Introduction In order to use applications over IPv6, it is necessary that users enjoy nearly identical performance as compared to IPv4. A …

Most dual-stack clients don’t “pick IPv6 or IPv4” once and for all—they race them. The idea, nicknamed Happy Eyeballs, is simple: start with a bias toward IPv6, introduce small delays so …

Happy Eyeballs (HE) started out by describing a mechanism that prefers IPv6 connections while ensuring a fast fallback to IPv4 when IPv6 fails. The IETF is currently working on the third …

Oct 7, 2025 · The first version of Happy Eyeballs (HE) was standardized by the IETF in 2012 as RFC 6555 by the v6ops Working Group. It describes a mechanism to prefer IPv6 for dual …

Jun 2, 2025 · Happy Eyeballs, formally described in RFC 6555 and refined in RFC 8305, is a connection management algorithm designed to reduce the wait time users might experience …

The Happy Eyeballs RFC proposes establishing a TCP connection to both IPv6 and IPv4 addresses concurrently. If the IPv6 path is broken, the communication continues with IPv4, …