DNS resolver reaction to non-reachable authoritative DNS server

[dougb at dougbarton.us (Doug Barton)]

On 03/13/2014 12:35 AM, Anurag Bhatia wrote:
> Hello there!
>
>
> I am trying to troubleshoot a case of DNS failure issue with one of Indian
> Govt's domain (nic.in). I can see that 1 out of 4 authoritative DNS server
> is IPv6 only. We have quite a few users running IPv4 only setup and hence
> 1/4 of these DNS servers are non-reachable from the recursor hosted by our
> clients.
>
>
> How is DNS query expected to respond in such case? Will it give SRVFAIL and
> terminate immediately (causing DNS resolution failure) OR it will just see
> one of the auth DNS as non-reachable and next will proceed with either of
> other three thus slowing down but with no failure?

Basically the latter.

If your customers are using BIND there is a flag you can supply to named 
to cause it to operate only in IPv4. That would avoid this problem 
altogether.

hope this helps,

Doug