Re: [DNSOP] Fwd: New Version Notification for draft-muks-dnsop-dns-thundering-herd-00.txt

Mukund Sivaraman <muks@mukund.org> Fri, 26 June 2020 12:28 UTC

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Date: Fri, 26 Jun 2020 17:58:36 +0530
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From: Mukund Sivaraman <muks@mukund.org>
To: Paul Vixie <paul@redbarn.org>
Cc: dnsop@ietf.org, Cricket Liu <cricket@infobox.com>, Paul Wouters <paul@nohats.ca>
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Subject: Re: [DNSOP] Fwd: New Version Notification for draft-muks-dnsop-dns-thundering-herd-00.txt
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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