Re: [Doh] meta qtypes

Miek Gieben <miek@miek.nl> Sun, 18 March 2018 19:08 UTC

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Date: Sun, 18 Mar 2018 19:08:04 +0000
From: Miek Gieben <miek@miek.nl>
To: Patrick McManus <pmcmanus@mozilla.com>
Cc: DoH WG <doh@ietf.org>
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Subject: Re: [Doh] meta qtypes
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[ Quoting <pmcmanus@mozilla.com>; in "Re: [Doh] meta qtypes..." ]
>Hi - DoH itself doesn't require axfr/etc anywhere that DNS would not (I'm
>not aware of whether it does or not) - the text is just meant to give the
>HTTP considerations when it does carry larger DNS responses such as that.
>
>WRT HTTP caching - section 4 of DoH talks about how HTTP freshness
>lifetimes should be set for DoH responses. Is there something different
>here?

This HTTP caching opens up a pretty big can of worms on what to set the cache
TTL to.

If we consider HTTP/2 *just* the transport than it should not be concerned with
caching (i.e. TCP doesn't cache).

If we do want to cache on this layer a server implementing DoH needs to inspect 
the DNS packet, it should (among other things), look for a SOA record to get a 
TTL or MINTTL, or get the minimum TTL of all the records in the message, or look 
for RRSIG expiration times and distill a minimum TTL from those.

I think this draft should say "MUST not cache these responses".

/Miek

--
Miek Gieben