IETF Logo Mail Archive

Re: [dmarc-ietf] Tree Walk + CNAME

Tim Wicinski <tjw.ietf@gmail.com> Wed, 30 March 2022 13:29 UTC

Return-Path: <tjw.ietf@gmail.com>
X-Original-To: dmarc@ietfa.amsl.com
Delivered-To: dmarc@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 8C57A3A181F for <dmarc@ietfa.amsl.com>; Wed, 30 Mar 2022 06:29:00 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.107
X-Spam-Level:
X-Spam-Status: No, score=-2.107 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
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 CUjwzfolNFB4 for <dmarc@ietfa.amsl.com>; Wed, 30 Mar 2022 06:28:56 -0700 (PDT)
Received: from mail-lf1-x135.google.com (mail-lf1-x135.google.com [IPv6:2a00:1450:4864:20::135]) (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 9F7B33A181E for <dmarc@ietf.org>; Wed, 30 Mar 2022 06:28:55 -0700 (PDT)
Received: by mail-lf1-x135.google.com with SMTP id t25so35808351lfg.7 for <dmarc@ietf.org>; Wed, 30 Mar 2022 06:28:55 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=eoeD+arOZh/jLo8Ed57TjCmiWAt86kiJIWl6DUpxofY=; b=KVHjMhavqKkLp3LF07sVHxlDLyEJtktgQb0GcAG/j5q6wOBtRUD38YqcwpLz1+/35r qBxrYXG64OtXzy3xxwcid4OFfigZdTndO6Fk03NAPPUfP0uaGxEiXuY0cnTTZNhcrhph yKUp2MxBJS5DZU8IIu0F7U4oFqhhuz6ibud9pZDz19xCV/eTUim8qkYs8cikyYP6/6Jb iukcGBg6tQYDyPzKt/FICnZC5lY0XGqbKopJJAbkWfbQ/8ce9meOrE/geiwtq/w2/xQn TtzAojyiq725t1QcAt/++oSop5I20cGOQI0DQwes7wF49J4mmFcFPnlGsbCUGQ68nefh afhA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=eoeD+arOZh/jLo8Ed57TjCmiWAt86kiJIWl6DUpxofY=; b=Kb30lihdeLg7o7a/Rf4RP61/tJofaO70YLZiKs5M1MR5MWNDNdxdAhiOG3t6n/GIZn R30obT/vDMy5Izxj2rrbH1+gBKYbwigqGwi3b9hauLKAMtq5lLmOuVA2l7ps4W97YHPa GK7pvSwc/hnaxVkE27eSZlGC7Sy/7hbGfbPSUJL88HPTLr3UggwOt/Ze6oebzMSjEyIE xg+eig8QNwP/p8v14y4RQExFWhWPxSaAXLfthvDcd0LPYzbHFoaFPsOvBNzm6yjvOe3T HcDoPVxJn+U5aJaWKLIPnrebCrVKWhI+uaWh5pc92JR+ffIeVBtTFEjBZGfD0/Bwnz0F U4vw==
X-Gm-Message-State: AOAM531pV+k3js0FiNeA9ZNJfrAI/rIX+sKr75c395H+vppGGxRMqu8J WxuhhWt83EKuA3O56WJWW8BOIDMPD1KlZPIwuyq4j5fn
X-Google-Smtp-Source: ABdhPJxVqrFkbMCLjuRLJWV3SJKU5BFozLT4c8rcopBB3Qfh/VoS4HkI7RD6OSo31QCBRqYo8Mzpio132dTYxrMUyc0=
X-Received: by 2002:a05:6512:22d5:b0:44a:a939:cf33 with SMTP id g21-20020a05651222d500b0044aa939cf33mr6708107lfu.230.1648646933615; Wed, 30 Mar 2022 06:28:53 -0700 (PDT)
MIME-Version: 1.0
References: <CH2PR11MB4342CCC64C5B6D6F9F7DB01DF71F9@CH2PR11MB4342.namprd11.prod.outlook.com>
In-Reply-To: <CH2PR11MB4342CCC64C5B6D6F9F7DB01DF71F9@CH2PR11MB4342.namprd11.prod.outlook.com>
From: Tim Wicinski <tjw.ietf@gmail.com>
Date: Wed, 30 Mar 2022 09:28:42 -0400
Message-ID: <CADyWQ+Gdd1=3wmFH8+Jiyu25M8ARw_0qfYV1TuRRqtuvrk-ihA@mail.gmail.com>
To: "Brotman, Alex" <Alex_Brotman=40comcast.com@dmarc.ietf.org>
Cc: "dmarc@ietf.org" <dmarc@ietf.org>
Content-Type: multipart/alternative; boundary="000000000000d695c005db6f868c"
Archived-At: <https://mailarchive.ietf.org/arch/msg/dmarc/p8JefBnK-EQzuxbOeIih8ubg9fM>
Subject: Re: [dmarc-ietf] Tree Walk + CNAME
X-BeenThere: dmarc@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Domain-based Message Authentication, Reporting, and Compliance \(DMARC\)" <dmarc.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/dmarc>, <mailto:dmarc-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/dmarc/>
List-Post: <mailto:dmarc@ietf.org>
List-Help: <mailto:dmarc-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/dmarc>, <mailto:dmarc-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 30 Mar 2022 13:29:01 -0000

On Wed, Mar 30, 2022 at 8:50 AM Brotman, Alex <Alex_Brotman=
40comcast.com@dmarc.ietf.org> wrote:

> >From section 4.6:
>
> To illustrate, for a message with the arbitrary RFC5322.From domain
>    of "a.b.c.d.e.mail.example.com", a full DNS Tree Walk would require
>    the following five queries, in order to locate the policy or
>    Organizational Domain:
>
>    *  _dmarc.a.b.c.d.e.mail.example.com
>
>    *  _dmarc.e.mail.example.com
>
>    *  _dmarc.mail.example.com
>
>    *  _dmarc.example.com
>
>    *  _dmarc.com
>
>
> What should the evaluator do if one of these results in a CNAME that
> either:
>
>         a) points outside of the tree
>

I would say "Follow the CNAME" - consider LargeCo which points many DMARC
records
of domains in their portfolio to a record in their main domain.  Or
outsourced DMARC
to third party.

        b) results in a loop pointing at a previously evaluated record
>

CNAME loops are usually detected in resolvers, but loops should return no
record found

tim



>
> --
> Alex Brotman
> Sr. Engineer, Anti-Abuse & Messaging Policy
> Comcast
>
> _______________________________________________
> dmarc mailing list
> dmarc@ietf.org
> https://www.ietf.org/mailman/listinfo/dmarc
>

v2.8.7 | Report a Bug | By Email