bpo-39128: Added algorithm description (GH-18624)
# [bpo-39128](https://bugs.python.org/issue39128): happy eyeballs description
# [3.9] 39128 - happy eyeballs description (GH-18624)
# [3.8] 39128 - happy eyeballs description (GH-18624)
https://bugs.python.org/issue39128
diff --git a/Doc/library/asyncio-eventloop.rst b/Doc/library/asyncio-eventloop.rst
index 3acd79d..d60a6ce 100644
--- a/Doc/library/asyncio-eventloop.rst
+++ b/Doc/library/asyncio-eventloop.rst
@@ -451,6 +451,17 @@
Added the *happy_eyeballs_delay* and *interleave* parameters.
+ Happy Eyeballs Algorithm: Success with Dual-Stack Hosts.
+ When a server's IPv4 path and protocol are working, but the server's
+ IPv6 path and protocol are not working, a dual-stack client
+ application experiences significant connection delay compared to an
+ IPv4-only client. This is undesirable because it causes the dual-
+ stack client to have a worse user experience. This document
+ specifies requirements for algorithms that reduce this user-visible
+ delay and provides an algorithm.
+
+ For more information: https://tools.ietf.org/html/rfc6555
+
.. versionadded:: 3.7
The *ssl_handshake_timeout* parameter.