[dns-operations] The Use of TTL for IPv4 and IPv6 RRs...

Bob Harold rharolde at umich.edu
Tue May 3 16:04:23 UTC 2016

On Tue, May 3, 2016 at 11:42 AM, Mark Jeftovic <markjr at easydns.com> wrote:

> RFC4472 talks about this situation:
> example.com.        300    IN    MX     foo.example.com.
>       foo.example.com.    300    IN    A
>       foo.example.com.    100    IN    AAAA   2001:db8::1
> and what can happen.
> My first reaction was "so keep the TTLs the same then", but that doesn't
> guarantee that the A and AAAA RRs will get queried and cached by the
> resolver at the same time time, does it?
> So even if you do that, you can still run into the situations described
> in 4.4.1 and 4.4.2
> Right?
> - mark
> --
> Mark Jeftovic, Founder & CEO, easyDNS Technologies Inc.
> Company Website: http://easydns.com
> Read my blog: http://markable.com
> +1-416-535-8672 ext 225
> _______________________________________________

It seems to me that according to 4.4.2, the data can only be received with
the NS query, so it would always be received at the same time, and thus
expire at the same time if the TTL's are the same between A and AAAA.   But
you can query the child, and if the TTL's at the child do not match the
parent, or between A and AAAA, then I can see it being an issue.

4.4.1 would still be an issue.

Bob Harold
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