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Re: [dnsoverhttp] Caching model

Ian Swett <ianswett@google.com> Mon, 30 October 2017 01:54 UTC

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From: Ian Swett <ianswett@google.com>
Date: Sun, 29 Oct 2017 21:53:56 -0400
Message-ID: <CAKcm_gOVJg954AGr93iwo0gO_hxOkn14gKREdE+_fMS5Mpd-9g@mail.gmail.com>
To: Martin Thomson <martin.thomson@gmail.com>
Cc: dnsoverhttp@ietf.org
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Subject: Re: [dnsoverhttp] Caching model
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I assumed HTTP caching would either be disabled or closely integrated with
the DNS resolver's TTL.  Both seem viable, but disabling HTTP caching seems
easier.

On Sun, Oct 29, 2017 at 9:36 PM, Martin Thomson <martin.thomson@gmail.com>
wrote:

> See https://github.com/paulehoffman/draft-ietf-doh-
> dns-over-https/issues/14
> and several others.
>
> My request is that we agree on what the model is, then we can talk
> about the properties we can extract from that.
>
> My understanding is that the DNS client would consult its local stack
> and that stack would use HTTP to talk to a DNS API server.  In that
> model, there are at least three caches in play: the local DNS resolver
> cache, the HTTP cache and the DNS API server cache.
>
> If those caches are ordered as I describe, and the two DNS caches are
> driven based on the TTL, I'm struggling to find a role for the HTTP
> cache.  There are things that HTTP can do with caching that would be
> nice, but I'm not seeing any way to really access HTTP caching
> features in that architecture.
>
> It's a little unfortunate, but in that architecture it would probably
> be better to disable HTTP caching entirely.  HTTP caching has a bunch
> of features that are more flexible, but if that caching is wedged
> between two relatively inflexible caches, it won't have any
> opportunity to add value.
>
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