curl/docs/cmdline-opts/happy-eyeballs-timeout-ms.md
Daniel Stenberg 2494b8dd51
docs/cmdline: change to .md for cmdline docs
- switch all invidual files documenting command line options into .md,
   as the documentation is now markdown-looking.

 - made the parser treat 4-space indents as quotes

 - switch to building the curl.1 manpage using the "mainpage.idx" file,
   which lists the files to include to generate it, instead of using the
   previous page-footer/headers. Also, those files are now also .md
   ones, using the same format. I gave them underscore prefixes to make
   them sort separately:
   _NAME.md, _SYNOPSIS.md, _DESCRIPTION.md, _URL.md, _GLOBBING.md,
   _VARIABLES.md, _OUTPUT.md, _PROTOCOLS.md, _PROGRESS.md, _VERSION.md,
   _OPTIONS.md, _FILES.md, _ENVIRONMENT.md, _PROXYPREFIX.md,
   _EXITCODES.md, _BUGS.md, _AUTHORS.md, _WWW.md, _SEEALSO.md

 - updated test cases accordingly

Closes #12751
2024-01-23 14:30:15 +01:00

1015 B

c SPDX-License-Identifier Long Arg Help Added Category Multi See-also Example
Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. curl happy-eyeballs-timeout-ms <milliseconds> Time for IPv6 before trying IPv4 7.59.0 connection single
max-time
connect-timeout
--happy-eyeballs-timeout-ms 500 $URL

--happy-eyeballs-timeout-ms

Happy Eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6 addresses for dual-stack hosts, giving IPv6 a head-start of the specified number of milliseconds. If the IPv6 address cannot be connected to within that time, then a connection attempt is made to the IPv4 address in parallel. The first connection to be established is the one that is used.

The range of suggested useful values is limited. Happy Eyeballs RFC 6555 says "It is RECOMMENDED that connection attempts be paced 150-250 ms apart to balance human factors against network load." libcurl currently defaults to 200 ms. Firefox and Chrome currently default to 300 ms.