Re: [Doh] [Ext] a tad confused on response sizes

Tony Finch <dot@dotat.at> Tue, 05 June 2018 16:17 UTC

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Date: Tue, 5 Jun 2018 17:17:00 +0100
From: Tony Finch <dot@dotat.at>
To: Stephane Bortzmeyer <bortzmeyer@nic.fr>
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Subject: Re: [Doh] [Ext] a tad confused on response sizes
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Stephane Bortzmeyer <bortzmeyer@nic.fr>; wrote:
>
> TC is supposed to be hop-to-hop but DoH makes things more complicated,
> the HTTPS link having different semantics. For DoH, it means (I quote
> the -10 draft) "I was not able to retrieve a full answer for the query
> but I give you the best answer I could get"

That is not consistent with RFC 1035:

        TC      TrunCation - specifies that this message was truncated
                due to length greater than that permitted on the
                transmission channel.

Since https's permitted length is longer than a DNS message,
it is invalid for a DoH server to truncate.

> PS : what happens when a DNS-over-TCP client receives a truncated
> answer over TCP?

RFC 1035 doesn't allow TC for TCP messages.

Tony.
-- 
f.anthony.n.finch  <dot@dotat.at>;  http://dotat.at/
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