2018-01-30 19:33:51 -05:00
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Long: happy-eyeballs-timeout-ms
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Arg: <milliseconds>
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2020-05-12 03:13:43 -04:00
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Help: Time for IPv6 before trying IPv4
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2018-01-30 19:33:51 -05:00
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Added: 7.59.0
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2020-07-13 08:15:04 -04:00
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Category: connection
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2018-01-30 19:33:51 -05:00
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---
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Happy eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6
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addresses for dual-stack hosts, preferring IPv6 first for the number of
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milliseconds. If the IPv6 address cannot be connected to within that time then
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a connection attempt is made to the IPv4 address in parallel. The first
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connection to be established is the one that is used.
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The range of suggested useful values is limited. Happy Eyeballs RFC 6555 says
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"It is RECOMMENDED that connection attempts be paced 150-250 ms apart to
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balance human factors against network load." libcurl currently defaults to
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200 ms. Firefox and Chrome currently default to 300 ms.
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If this option is used several times, the last one will be used.
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