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Commenting below ...<br>
<br>
<div class="moz-cite-prefix">On 1/19/22 2:51 PM, Dmitry Karpov via
c-ares wrote:<br>
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cite="mid:BYAPR01MB56064059B8D6F5670AD3A01FC3599@BYAPR01MB5606.prod.exchangelabs.com">
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> Infact, happyeyeballs itself doesn't always do parallel
connection attempts, its an implementation-defined delay
before also attempting the next address in the list.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">In case of Happy Eyeballs, a delay between
IPv4 and IPv6 connections is constant and typically relatively
short – 200-300ms.<br>
But non-functional IPv6 name servers in the server list may
create dynamic delays in connection establishment which can be
very large.<br>
<br>
<o:p></o:p></p>
<p class="MsoNormal">By default, c-ares uses 5s timeout per name
server, so it may take 5s and more (if several IPv6 name
servers are in the list) to get to the connection Happy
Eyeballs thus taking much more than expected 200-300ms.</p>
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<br>
It would be assumed as part of this patch set, this timer would be
reduced.<br>
<br>
<br>
<blockquote type="cite"
cite="mid:BYAPR01MB56064059B8D6F5670AD3A01FC3599@BYAPR01MB5606.prod.exchangelabs.com">
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<p class="MsoNormal"><o:p></o:p></p>
<p class="MsoNormal"><br>
> It would be much easier to stay closer to happy eyeballs
and just sort the dns server list using prior result
success/fail (even upfront sorting using some algorithm to
interleave ipv6/ipv4 in a pattern would help,
<o:p></o:p></p>
<p class="MsoNormal">> maybe with using logic such as from
RFC6724 sec 2.1 like we do in ares_getaddrinfo for returned
addresses, but instead of the nameservers themselves).
<br>
<br>
Yes, of course, it is possible that c-ares client can
implement some kind of name server sorting/filtering logic
outside of c-ares and just pass a list of “good” name servers
to c-ares, but in this case it has to be more involved into
the name resolution business than it would be desired.<br>
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<br>
I wasn't suggesting this be outside of c-ares, I was talking about
implementing this inside of c-ares as a simpler alternative to your
proposal.<br>
<br>
-Brad<br>
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