Re: [Doh] a tad confused on response sizes

Tony Finch <dot@dotat.at> Tue, 05 June 2018 14:14 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 3C8A1131084 for <doh@ietfa.amsl.com>; Tue, 5 Jun 2018 07:14:02 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.199
X-Spam-Level:
X-Spam-Status: No, score=-4.199 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, 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 21hsEUbo_mk2 for <doh@ietfa.amsl.com>; Tue, 5 Jun 2018 07:13:58 -0700 (PDT)
Received: from ppsw-31.csi.cam.ac.uk (ppsw-31.csi.cam.ac.uk [131.111.8.131]) (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 9B0CA13107D for <doh@ietf.org>; Tue, 5 Jun 2018 07:13:58 -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]:55214) by ppsw-31.csi.cam.ac.uk (ppsw.cam.ac.uk [131.111.8.137]:25) with esmtps (TLSv1:ECDHE-RSA-AES256-SHA:256) id 1fQCii-000pem-M8 (Exim 4.91) (return-path <dot@dotat.at>); Tue, 05 Jun 2018 15:13:56 +0100
Date: Tue, 05 Jun 2018 15:13:56 +0100
From: Tony Finch <dot@dotat.at>
To: bert hubert <bert.hubert@powerdns.com>
cc: doh@ietf.org
In-Reply-To: <20180605120510.GA29047@server.ds9a.nl>
Message-ID: <alpine.DEB.2.11.1806051507360.1809@grey.csi.cam.ac.uk>
References: <20180605120510.GA29047@server.ds9a.nl>
User-Agent: Alpine 2.11 (DEB 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset="US-ASCII"
Archived-At: <https://mailarchive.ietf.org/arch/msg/doh/BouChOPp6GvkW-n-q6mtQEI28Rg>
Subject: Re: [Doh] a tad confused on response sizes
X-BeenThere: doh@ietf.org
X-Mailman-Version: 2.1.26
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: Tue, 05 Jun 2018 14:14:03 -0000

bert hubert <bert.hubert@powerdns.com> wrote:
>
> This seems says sending a TC response is some kind of error, which implies
> a DNS API server should be willing to send 65 kilobyte answers.

Yes.

> I think for the new usecases, this would be a fine default. However, there
> might be UDP-to-DOH bridges which would then need to put explicit EDNS
> buffersize of 512 in there if they get non-EDNS adorned UDP queries.

If a UDP-to-DoH proxy gets an oversized answer it will have to do
its own truncation.

My trivial DoH code makes upstream queries over TCP, so the EDNS buffer
size is ignored. I don't think a DoH server should have to truncate
answers.

Tony.
-- 
f.anthony.n.finch  <dot@dotat.at>  http://dotat.at/
Tyne, Dogger: North 5 or 6, becoming cyclonic 3 or 4, occasionally 2 later.
Moderate. Occasional drizzle later. Good, occasionally poor later.