On Fri, Jun 26, 2020 at 01:02:51AM +0000, Paul Vixie wrote: > On Thursday, 25 June 2020 18:29:03 UTC Paul Wouters wrote: > > On Thu, 25 Jun 2020, Mukund Sivaraman wrote: > > > For whoever is interested, this is a description of a pattern of queries > > > noticed at busy public resolvers that has led to issues in at least 4 > > > different sites in the last 2 months. > > > > > > The current revision is a work in progress. We are still developing some > > > mitigations for NIOS, and some more introductory text also has to be > > > added. > > > > I would add a more explicit section on using prefetching of frequently > > asked queries, which mitigates (eliminates) the period when an answer is not > > available in the cache. > > i'm sorry in advance for anybody who is now hearing this for the 100th time.
IIRC I read a message from the PowerDNS folks to dns-operations@
sometime ago that prefetch didn't help or show any observable effect in
practical deployment, as much as it is assumed to.
>
> please don't pre-fetch. feel free to pre-discard; TTL is a maximum, and if
> you
> want to randomly subtract from TTL upon every reuse, you'll remain compliant.
> if the data turns out to be important it'll return. but prospective pre-fetch
> means you may be creating network load for no purpose -- the data may not
> come
> back again, or if it does, it may have changed, in which case you don't want
> the stale stuff that pre-fetch would have brought you.
>
> this solves the thundering herd problem but without creating new problems.
> the
> goal is de-synchronization. random subtractions to TTL in cache accomplishes
> it.
>
> --
> Paul
>
>
Mukund
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