Re: [Doh] [Ext] DNS Camel thoughts: TC and message size

Robert Edmonds <edmonds@mycre.ws> Fri, 08 June 2018 02:45 UTC

Return-Path: <edmonds@mycre.ws>
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 E0AD2130E13 for <doh@ietfa.amsl.com>; Thu, 7 Jun 2018 19:45:19 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.901
X-Spam-Level:
X-Spam-Status: No, score=-1.901 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, SPF_PASS=-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 PwpW8jfMrqG8 for <doh@ietfa.amsl.com>; Thu, 7 Jun 2018 19:45:17 -0700 (PDT)
Received: from mycre.ws (mycre.ws [45.33.102.105]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id F32BB130E15 for <doh@ietf.org>; Thu, 7 Jun 2018 19:45:16 -0700 (PDT)
Received: by chase.mycre.ws (Postfix, from userid 1000) id C620512C1D14; Thu, 7 Jun 2018 22:45:15 -0400 (EDT)
Date: Thu, 7 Jun 2018 22:45:15 -0400
From: Robert Edmonds <edmonds@mycre.ws>
To: Dave Lawrence <tale@dd.org>
Cc: DoH WG <doh@ietf.org>
Message-ID: <20180608024515.jkimytwch7lstkxi@mycre.ws>
References: <20180606093212.GA23880@server.ds9a.nl> <alpine.DEB.2.11.1806061501340.10764@grey.csi.cam.ac.uk> <F5774061-35B9-477F-ADDA-8BB3472F30EF@icann.org> <alpine.DEB.2.11.1806071121350.1809@grey.csi.cam.ac.uk> <5B71AC15-80F4-427B-BABA-1BE3C514145F@icann.org> <23321.25400.502754.584769@gro.dd.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <23321.25400.502754.584769@gro.dd.org>
Archived-At: <https://mailarchive.ietf.org/arch/msg/doh/0lXIa-r4rM4B0kowP20unqaHQHA>
Subject: Re: [Doh] [Ext] DNS Camel thoughts: TC and message size
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: Fri, 08 Jun 2018 02:45:20 -0000

Dave Lawrence wrote:
> Paul Hoffman writes:
> > Tony is completely correct here. DNS messages have well-defined
> > length limits: 512-or-more-depending if carried over UDP, and 65535
> > if carried over TCP. 
> 
> Right.  And completely undefined over any other transport.  There is
> no intrinsic limit to the limit of a DNS message, compression pointers
> notwithstanding.

No, there is an intrinsic limit to the size of a DNS message. If I'm not
mistaken:

12 octets header

1 question resource record:
    255 octets QNAME
    2 octets QTYPE
    2 octets QCLASS

3 response sections:
    65535 RR's per section:
        255 octets NAME
        2 octets TYPE
        2 octets CLASS
        4 octets TTL
        2 octets RDLENGTH
        65535 octets RDATA

12 + 1*(255+2+2) + 3*65535*(255+2+2+4+2+65535) = 12936609271 octets, or,
about 13 gigs.

-- 
Robert Edmonds