IETF Logo Mail Archive

Re: [DNSOP] Mandated order of CNAME records in a CNAME chain?

Florian Weimer <fw@deneb.enyo.de> Sun, 09 October 2016 11:05 UTC

Return-Path: <fw@deneb.enyo.de>
X-Original-To: dnsop@ietfa.amsl.com
Delivered-To: dnsop@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id E5C1D129546 for <dnsop@ietfa.amsl.com>; Sun, 9 Oct 2016 04:05:29 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.896
X-Spam-Level:
X-Spam-Status: No, score=-4.896 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RP_MATCHES_RCVD=-2.996] 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 I1EjyZ0rwXD2 for <dnsop@ietfa.amsl.com>; Sun, 9 Oct 2016 04:04:42 -0700 (PDT)
Received: from albireo.enyo.de (albireo.enyo.de [5.158.152.32]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id F370E12962A for <dnsop@ietf.org>; Sun, 9 Oct 2016 04:03:39 -0700 (PDT)
Received: from [172.17.203.2] (helo=deneb.enyo.de) by albireo.enyo.de with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) id 1btBtE-00031g-8M; Sun, 09 Oct 2016 13:03:32 +0200
Received: from fw by deneb.enyo.de with local (Exim 4.84_2) (envelope-from <fw@deneb.enyo.de>) id 1btBtE-0000E8-4a; Sun, 09 Oct 2016 13:03:32 +0200
From: Florian Weimer <fw@deneb.enyo.de>
To: Mark Andrews <marka@isc.org>
References: <20160929123532.GD22645@laperouse.bortzmeyer.org> <20160929130333.qsrjntfgmrobj7i2@mycre.ws> <87bmz3p4lt.fsf@mid.deneb.enyo.de> <20161002221051.3642B5585DD3@rock.dv.isc.org>
Date: Sun, 09 Oct 2016 13:03:32 +0200
In-Reply-To: <20161002221051.3642B5585DD3@rock.dv.isc.org> (Mark Andrews's message of "Mon, 03 Oct 2016 09:10:51 +1100")
Message-ID: <871szpiy2j.fsf@mid.deneb.enyo.de>
MIME-Version: 1.0
Content-Type: text/plain
Archived-At: <https://mailarchive.ietf.org/arch/msg/dnsop/VwGRngAazrMFFBjJShuGziLdVXw>
Cc: Robert Edmonds <edmonds@mycre.ws>, dnsop@ietf.org
Subject: Re: [DNSOP] Mandated order of CNAME records in a CNAME chain?
X-BeenThere: dnsop@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: IETF DNSOP WG mailing list <dnsop.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/dnsop>, <mailto:dnsop-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/dnsop/>
List-Post: <mailto:dnsop@ietf.org>
List-Help: <mailto:dnsop-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/dnsop>, <mailto:dnsop-request@ietf.org?subject=subscribe>
X-List-Received-Date: Sun, 09 Oct 2016 11:05:30 -0000
X-List-Received-Date: Sun, 09 Oct 2016 11:05:30 -0000

* Mark Andrews:

> In message <87bmz3p4lt.fsf@mid.deneb.enyo.de>, Florian Weimer writes:
>> * Robert Edmonds:
>>
>> > I think there was already a thread on this topic recently on this list
>> > ("Order of CNAME and A in Authoritative Reply" from August 2015). There
>> > was some discussion over "adding" versus "appending" and it was pointed
>> > out that a lot of existing code (e.g., the BSD stub resolver) was
>> > written using the "add at the end" meaning.
>>
>> Are there stub resolvers which actually chase the CNAME chain?
>>
>> I assume it is quite common just to check the QNAME, and then extract
>> A/AAAA records from the answer section without matching their owner
>> names (but potentially recording their owner name as the canonical
>> name of the host, even though that's rarely useful these days).
>
> No.  libresolv has checked the owner names of the A (and AAAA)
> records for decades now skipping any records that don't match.

Okay.  Is it necessary to retain those checks and even fix them to
avoid the CNAME ordering assumption?

v2.23.0 | Report a Bug | By Email