Subject: Re: How does DNS Queries handle for IPv6 dual stack

Re: How does DNS Queries handle for IPv6 dual stack

From: Paul Marks <pmarks_at_google.com>
Date: Wed, 10 Feb 2016 14:43:03 -0800

On Tue, Feb 9, 2016 at 9:09 AM, kritesh tripathi
<tripathi.kritesh_at_gmail.com> wrote:
> Hi All,
>
> Is anybody have idea about DNS Query handling by ares lib in IPv6 dual stack
> scenario.
>
> For Example -
>
> If Preferred Network-IPv6 in Dual stack and Primary DNS Server-Ipv6
> ,Secondary DNS Server=Ipv4 then
>
> 1- Is DNS quad A query send first and if it is unsuccessful then Standard A
> query send
> or
> 2- DNS Quad A Query and Standard A query send in parallel which is resolved
> first .. will use accordingly .
>

Sending the AAAA/A requests in parallel is a good idea for efficiency,
but "resolved first" is a poor way to connect, as the bias towards
IPv4/IPv6 becomes unpredictable.

Once both DNS requests have completed, you should sort the results
(ideally using the RFC6724 algorithm), and then either connect to each
address in sequence, or use Happy Eyeballs if the client needs to
tolerate single-family blackholes in the network.
Received on 2016-02-10