[dns-operations] Opinions sought .... have I come to the right place?

Jelte Jansen jelte.jansen at sidn.nl
Thu Nov 7 15:24:52 UTC 2013

On 11/07/2013 03:52 PM, Edward Lewis wrote:
> In experimenting with some recursive servers (and by no means an
> exhaustive set), some code bases did adhere to the "rules" and some code
> bases seem to ignore the "rules."  I say this to the extent that the
> collective set of deployed tools out there pretty much are eating into
> the "longer TTLs will reduce queries" part of the above trade-off.

...which would give you only the drawbacks and not the upside...

Not answering your question what a good value is (...it depends, but
apparently what it depends on may be something different than we
thought), but I do have one immediate question: Did you see specific
points at which TTLs are no longer adhered to? (e.h. do resolvers out
there cap TTL values and if so, do they set it to said cap or reduce it
to a fixed value, or does it appear completely random)?

TBH I don't think it's very important to the pre-fetch discussion
itself; some tools will play nice and use the sane pre-fetch values
(like pre-fetch only if queries in the last few seconds of a TTL), and
some tools will be tools and not play nice no matter what. I don't think
it adds a lot of extra uncertainty, as long as prefetchers don't go into
the area of 'always fetch at 50% of TTL'. OTOH if all bets are off
anyway, adding some more unpredictability wouldn't hurt ;)


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