Re: [DNSOP] Fwd: New Version Notification for draft-ietf-dnsop-dns-wireformat-http-02.txt

Paul Vixie <paul@redbarn.org> Thu, 22 March 2018 17:11 UTC

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Date: Thu, 22 Mar 2018 10:11:19 -0700
From: Paul Vixie <paul@redbarn.org>
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To: Bob Harold <rharolde@umich.edu>
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Subject: Re: [DNSOP] Fwd: New Version Notification for draft-ietf-dnsop-dns-wireformat-http-02.txt
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Bob Harold wrote:
>
> ...
>
> Unfortunately, the resolver needs to make decisions based on the
> original transport, for example if the transport is TCP, it can send any
> size response.  But if UDP, it needs to fit in a smaller size, and it
> often sends less info in the response.  Likewise, session signalling,
> anti-spoofing decisions, etc depend on the transport.

except that i don't find it unfortunately but simply factual, i agree.

>
> That brings up another question.  Would it also need to know the MTU of
> the original connection, or any other info?  (Assuming EDNS is not
> used)  In that case, a different media type is not enough, and we need
> to change the format to add some 'header" info.

not in my opinion. if the far end has a larger MTU outbound than the 
near end had inbound, then truncation damage will occur -- and the 
original initiator will retry with TCP. we just need to be transparent 
so that the original initiator can drive its own transport selections.

-- 
P Vixie