[dns-operations] Surprising behaviour by certain authoritative name servers

[Tony Finch]

Niall O'Reilly <niall.oreilly at ucd.ie> wrote:
>
> What's surprising is that an authoritative name server
> shows both a decremented TTL value (as if it were answering
> from cache) and the AA flag.
>
> I'm not sure which of the following labels is the best fit
> for this behaviour:
>
> - normal and expected (but so far outside my experience),
> - strange but harmless,
> - downright wrong.

I would argue somewhere between the last two :-)

During the IETF dnsop ANAME work I did some thinking about the TTL
implications, and I realised that decrementing the TTL on an authoritative
server would cause a thundering herd effect due to caches timing out at
the same time. But I don't have any measurements that would indicate how
much of a problem this is in practice...

https://tools.ietf.org/html/draft-ietf-dnsop-aname-04#appendix-C

Tony.
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