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Re: [v6ops] An Update to Happy Eyeballs

Lorenzo Colitti <lorenzo@google.com> Wed, 22 March 2017 15:15 UTC

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From: Lorenzo Colitti <lorenzo@google.com>
Date: Thu, 23 Mar 2017 00:15:16 +0900
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To: Fred Baker <fredbaker.ietf@gmail.com>
Cc: Mark Andrews <marka@isc.org>, IPv6 Operations <v6ops@ietf.org>
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Subject: Re: [v6ops] An Update to Happy Eyeballs
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On Thu, Mar 23, 2017 at 12:04 AM, Fred Baker <fredbaker.ietf@gmail.com>
wrote:

> > I think it's extremely hard to argue that waiting for an A query when
> you have an AAAA in cache (or vice versa) is going to reduce latency or
> improve user experience. You can use getaddrinfo if you want, but you're
> going to pay the price in terms of latency. I wouldn't call that a best
> practice.
>
> I must be missing something. If you already know the AAAA, fine. If you're
> using the resolver's cache, what API gets you an IPv6 address other than
> getaddrinfo?
>

You don't have to use getaddrinfo to do AAAA lookups. You can use your own
code, or even pass binary blobs to res_send if you want.

getaddrinfo is not very smart. It keeps trying until it has answers for
everything you asked it to do, and then it returns everything. That means
that if the A query is in cache and the AAAA query is not, then you have to
wait for the AAAA query to succeed.

I think the key point here is that integrating the DNS resolver retry loops
with the connection attempts provide latency savings.

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