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- c: Copyright (C) 1998 - 2022, Daniel Stenberg, <[email protected]>, et al.
- SPDX-License-Identifier: curl
- Long: happy-eyeballs-timeout-ms
- Arg: <milliseconds>
- Help: Time for IPv6 before trying IPv4
- Added: 7.59.0
- Category: connection
- Example: --happy-eyeballs-timeout-ms 500 $URL
- See-also: max-time connect-timeout
- ---
- 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.
- If this option is used several times, the last one will be used.
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