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Network Working Group S. Kitterman
Internet-Draft fTLD Registry Services
Updates: 7489 (if approved) October 13, 2018
Intended status: Informational
Expires: April 16, 2019
DMARC (Domain-based Message Authentication, Reporting, and Conformance)
Extension For PSDs (Public Suffix Domains)
draft-kitterman-dmarc-psd-00
Abstract
DMARC (Domain-based Message Authentication, Reporting, and
Conformance) is a scalable mechanism by which a mail-originating
organization can express domain-level policies and preferences for
message validation, disposition, and reporting, that a mail-receiving
organization can use to improve mail handling. DMARC policies can be
applied at the individual domain level or for a set of domains at the
organizational level. The design of DMARC precludes grouping
policies for a set of domains above the organizational level, such as
TLDs (Top Level Domains). These types of domains (which are not all
at the top level of the DNS tree) can be collectively referred to as
Public Suffix Domains (PSDs). For the subset of PSDs that require
DMARC usage, it is appropriate to provide PSD level DMARC capability
to provide policy and collect feedback for a set of domains. This
memo describes an extension to DMARC to enable a subset of DMARC
functionality for such domains.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 16, 2019.
Kitterman Expires April 16, 2019 [Page 1]
Internet-Draft PSD DMARC October 2018
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Definitions . . . . . . . . . . . . . . . . . 4
2.1. Conventions Used in This Document . . . . . . . . . . . . 4
2.2. Public Suffix Domain (PSD) . . . . . . . . . . . . . . . 4
2.3. Longest PSD . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Public Suffix Operator (PSO) . . . . . . . . . . . . . . 4
2.5. PSO Controlled Domain Names . . . . . . . . . . . . . . . 5
2.6. Non-existent Domains . . . . . . . . . . . . . . . . . . 5
3. PSD DMARC Updates to DMARC Requirements . . . . . . . . . . . 5
3.1. General Updates . . . . . . . . . . . . . . . . . . . . . 5
3.2. Section 6.1 DMARC Policy Record . . . . . . . . . . . . . 5
3.3. Section 6.5. Domain Owner Actions . . . . . . . . . . . 5
3.4. Section 6.6.3. Policy Discovery . . . . . . . . . . . . 5
3.5. Section 7. DMARC Feedback . . . . . . . . . . . . . . . 6
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6
4.1. Feedback leakage . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. DMARC Public Suffix Domain (PSD) Registry 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
DMARC [RFC7489] provides email sending organizational policy
information to email receivers. DMARC [RFC7489] allows policy to be
specified for both individual domains and sets of domains within a
single organization. For domains above the organizational level in
Kitterman Expires April 16, 2019 [Page 2]
Internet-Draft PSD DMARC October 2018
the DNS tree, they are currently limited to expressing policy for the
exact domain. There is no method available to such domains to
express lower level policy or receive feedback reporting for sets of
domains. This prevents policy declarations for non-existent domains
and identification of domain abuse in email, which can be important
for brand and consumer protection.
As an example, imagine a country code TLD (ccTLD) which has
subdomains for government and commercial use (.gov.example and
.com.example). Within the .gov.example public suffix, use of DMARC
[RFC7489] has been mandated and .gov.example has published its own
DMARC [RFC7489] record:
"v=DMARC1;p=reject;rua=mailto:[email protected]"
at
_dmarc.gov.example.
This would provide policy and feedback for mail sent from
@gov.example, but not @tax.gov.example and there is no way to publish
an organizational level policy that would do so. While, in theory,
receivers could reject mail from non-existent domains, in practice
there are operational issues with doing so that make it impractical.
Non-existence of the sending domain is often a factor in a mail
delivery decision, but not generally treated as definitive on its
own.
This memo provides a simple extension to DMARC [RFC7489] to allow
operators of Public Suffix Domains (PSDs) to express policy for
groups of subdomains, extends the DMARC [RFC7489] policy query
functionality to detect and process such a policy, describes receiver
feedback for such policies, and provides controls to mitigate
potential privacy considerations associated with this extension.
There are two types of Public Suffix Operators (PSOs) for which this
extension would be useful and appropriate:
o Branded PSDs (e.g., ".google"): These domains are effectively
organizational domains as discussed in DMARC [RFC7489]. They
control all subdomains of the tree. The ".gov.example" used above
is an example of this class.
o Multi-organization PSDs that require DMARC usage (e.g., ".bank"):
Because existing organizational domains using this PSD have their
own DMARC policy, the applicability of this extension is for non-
existent domains. The extension allows the brand protection
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Internet-Draft PSD DMARC October 2018
benefits of DMARC [RFC7489] to extend to the entire PSD, including
cousin domains of registere organizations.
Due to the design of DMARC [RFC7489] and the nature of the Internet
email architecture [RFC5598], there are interoperability issues
associated with DMARC [RFC7489] deployment. These are discussed in
Interoperability Issues between DMARC and Indirect Email Flows
[RFC7960]. These issues are not applicable to PSDs, since they do
not send mail.
DMARC [RFC7489], by design, does not support requirements of PSD
operators. For PSDs that require use of DMARC [RFC7489], a subset of
DMARC reporting and enforcement capability is needed for PSD
operators to effectively manage and monitor implementation of PSD
requirements.
2. Terminology and Definitions
This section defines terms used in the rest of the document.
2.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Public Suffix Domain (PSD)
The global Internet Domain Name System (DNS) is documented in
numerous Requests for Comment (RFC). It defines a tree of names
starting with root, ".", immediately below which are Top Level Domain
names such as ".com" and ".us". They are not available for private
registration. In many cases the public portion of the DNS tree is
more than one level deep. PSD DMARC includes all public domains
above the organizational level in the tree, e.g., ".gov.uk".
2.3. Longest PSD
Organizational Domain with one label removed.
2.4. Public Suffix Operator (PSO)
A Public Suffix Operator manages operations within their PSD.
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2.5. PSO Controlled Domain Names
PSO Controlled Domain Names are names in the DNS that are managed by
a PSO and are not available for use as Organizational Domains (the
term organizational domains is defined in DMARC [RFC7489]).
Depending on PSD policy, these will have one (e.g., ".com") or more
(e.g., ".co.uk") name components.
2.6. Non-existent Domains
For DMARC [RFC7489] purposes, a non-existent domain is a domain name
that publishes none of A, AAAA, or MX records. This is a broader
definition than that in NXDOMAIN [RFC8020].
3. PSD DMARC Updates to DMARC Requirements
This document updates DMARC [RFC7489] as follows:
3.1. General Updates
References to "Domain Owners" also apply to PSOs.
3.2. Section 6.1 DMARC Policy Record
PSD DMARC records are published as a subdomain of the PSD. For the
PSD ".example", the PSO would post DMARC preferences in a TXT record
at "_dmarc.example".
3.3. Section 6.5. Domain Owner Actions
In addition to the DMARC [RFC7489] domain owner actions, PSOs will
need to update the "DMARC Public Suffix Domain (PSD) Registry". This
registry is defined in Section 6.1.
3.4. Section 6.6.3. Policy Discovery
A new step between step 3 and 4 is added:
3A. If the set is now empty and the longest PSD (Section 2.3) of the
Organizational Domain is listed in the DMARC PSD Registry (defined
in Section 6.1), the Mail Receiver MUST query the DNS for a DMARC
TXT record at the DNS domain matching the longest PSD
(Section 2.3) in place of the RFC5322.From domain in the message
(if different). A possibly empty set of records is returned.
As an example, for a message with the Organizational Domain of
"example.compute.cloudcompany.com.cctld", the query for PSD DMARC
would use "compute.cloudcompany.com.cctld" as the longest PSD
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(Section 2.3). The receiver would check to see if that PSD is listed
in the DMARC PSD Registry, and if so, perform the policy lookup at
"_dmarc.compute.cloudcompany.com.cctld".
Note: Because the PSD policy query comes after the Organizational
Domain policy query, PSD policy is not used for Organizational
domains that have published a DMARC [RFC7489] policy. Specifically,
this is not a mechanism to provide feedback addresses (RUA/RUF) when
an Organizational Domain has declined to do so.
3.5. Section 7. DMARC Feedback
Operational note for PSD DMARC: For PSOs, feedback for non-existent
domains is desired and useful. Because of the constraints on PSD
DMARC scope, there are not significant privacy considerations
associated with this reporting (See Section 4).
4. Privacy Considerations
This document does not significantly change the Privacy
Considerations of [RFC7489].
4.1. Feedback leakage
Providing feedback reporting to PSOs can, in some cases, create
leakage of information outside of an organization to the PSO. There
are roughly three cases to consider:
o Branded PSDs (e.g., ".google"), RUA and RUF reports based on PSD
DMARC have the potential to contain information about emails
related to entities managed by the organization. Since both the
PSO and the Organizational Domain owners are common, there is no
privacy risk for either normal or Non-existent Domain reporting.
o Multi-organization PSDs that require DMARC usage (e.g., ".bank"):
PSD DMARC based reports will only be generated for domains that do
not publish a DMARC policy at the organizational level. For
domains that do publish the required DMARC policy records, the
feedback reporting addresses (RUA and RUF) of the organization
will be used. Since PSD DMARC is limited to PSDs that mandate
organizational domains publish DMARC policy for existing domains,
the risk of this issue is limited to organizational domains that
are out of compliance with PSD policy.
o Multi-organization PSDs (e.g., ".com") that do not mandate DMARC
usage. Privacy risks for organizational domains within such PSDs
would be significant. This is mitigated by the limitation to only
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include PSDs listed in the public IANA DMARC PSD Registry
described in Section 6.1.
PSOs will receive feedback on non-existent domains, which may be
similar to existing organizational domains. Feedback related to such
cousin domains have a small risk of carrying information related to
an actual organizational domain. To minimize this potential concern,
PSD DMARC feedback is best limited to Aggregate Reports. Feedback
Reports carry more detailed information and present a greater risk.
5. Security Considerations
This document does not change the Security Considerations of
[RFC7489].
6. IANA Considerations
This section describes actions requested to be completed by IANA.
6.1. DMARC Public Suffix Domain (PSD) Registry
IANA is requested to create a new DMARC Public Suffix Domain (PSD)
Registry within the Domain-based Message Authentication, Reporting,
and Conformance (DMARC) Parameters Registry.
Names of PSDs participating in PSD DMARC must be registered with IANA
in this new sub-registry. New entries are assigned only for PSDs
that require use of DMARC. The requirement has to be documented in a
manner that satisfies the terms of Expert Review, per [RFC5226]. The
Designated Expert needs to confirm that provided documentation
adequately describes PSD policy to require domain owners to use DMARC
or that all domain owners are part of a single organization with the
PSO.
The initial set of entries in this registry is as follows:
+-------------+----------------+---------------+
| PSD | Reference | Status |
+-------------+----------------+---------------+
| .bank | this document | current |
+-------------+----------------+---------------+
| .insurance | this document | current |
+-------------+----------------+---------------+
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598,
DOI 10.17487/RFC5598, July 2009,
<https://www.rfc-editor.org/info/rfc5598>.
[RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky,
E., Ed., and K. Andersen, Ed., "Interoperability Issues
between Domain-based Message Authentication, Reporting,
and Conformance (DMARC) and Indirect Email Flows",
RFC 7960, DOI 10.17487/RFC7960, September 2016,
<https://www.rfc-editor.org/info/rfc7960>.
[RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is
Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020,
November 2016, <https://www.rfc-editor.org/info/rfc8020>.
Acknowledgements
TBS
Kitterman Expires April 16, 2019 [Page 8]
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Author's Address
Scott Kitterman
fTLD Registry Services
600 13th Street, NW, Suite 400
Washington, DC 20005
United States of America
Phone: +1 301 325-5475
Email: [email protected]
Kitterman Expires April 16, 2019 [Page 9]