Re: [Doh] Clarification for a newbie DoH implementor

Tony Finch <dot@dotat.at> Wed, 19 June 2019 16:05 UTC

Return-Path: <dot@dotat.at>
X-Original-To: doh@ietfa.amsl.com
Delivered-To: doh@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 22D4B12017C for <doh@ietfa.amsl.com>; Wed, 19 Jun 2019 09:05:07 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.198
X-Spam-Level:
X-Spam-Status: No, score=-4.198 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_NONE=0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Ih1JZjuJsU3R for <doh@ietfa.amsl.com>; Wed, 19 Jun 2019 09:05:05 -0700 (PDT)
Received: from ppsw-30.csi.cam.ac.uk (ppsw-30.csi.cam.ac.uk [131.111.8.130]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 3F358120140 for <doh@ietf.org>; Wed, 19 Jun 2019 09:05:05 -0700 (PDT)
X-Cam-AntiVirus: no malware found
X-Cam-ScannerInfo: http://help.uis.cam.ac.uk/email-scanner-virus
Received: from grey.csi.cam.ac.uk ([131.111.57.57]:37796) by ppsw-30.csi.cam.ac.uk (ppsw.cam.ac.uk [131.111.8.136]:25) with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) id 1hdd54-001H3A-ct (Exim 4.92) (return-path <dot@dotat.at>); Wed, 19 Jun 2019 17:05:02 +0100
Date: Wed, 19 Jun 2019 17:05:01 +0100
From: Tony Finch <dot@dotat.at>
To: Mark Delany <d5e@xray.emu.st>
cc: doh@ietf.org
In-Reply-To: <20190609083724.23965.qmail@f3-external.bushwire.net>
Message-ID: <alpine.DEB.2.20.1906191658540.9430@grey.csi.cam.ac.uk>
References: <20190418071238.68406.qmail@f3-external.bushwire.net> <20190518233815.44249.qmail@f3-external.bushwire.net> <CAHbrMsCMWtzHXZvpodak59RtAkSQC_ZM03oekKj00WqzNkDaaA@mail.gmail.com> <20190519055255.45717.qmail@f3-external.bushwire.net> <CAHbrMsC-1OQnoaYFE5BO8UzDsebo7jhJBfc9F4J-zgeA2FZm7Q@mail.gmail.com> <20190609083724.23965.qmail@f3-external.bushwire.net>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Archived-At: <https://mailarchive.ietf.org/arch/msg/doh/Wyh_dLRp0iYFJCN8JB7z354eFT0>
Subject: Re: [Doh] Clarification for a newbie DoH implementor
X-BeenThere: doh@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: DNS Over HTTPS <doh.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/doh>, <mailto:doh-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/doh/>
List-Post: <mailto:doh@ietf.org>
List-Help: <mailto:doh-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/doh>, <mailto:doh-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 19 Jun 2019 16:05:07 -0000

Mark Delany <d5e@xray.emu.st> wrote:
>
> As we've discussed previously, it's pointless returning TC=1 to the stub as it
> will simply re-issue an identical query as far as the DoH server is concerned.

TC=1 implies that the client should retry using a different transport
that can handle larger messages. If your transport is not UDP, there
aren't any alternatives that can handle larger messages :-)

You *can* get TC=1 on TCP etc, because it is possible to create an RRset
that is larger than 65536 octets.

Tony.
-- 
f.anthony.n.finch  <dot@dotat.at>  http://dotat.at/
the widest possible distribution of wealth