[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]
Versions: (draft-crocker-dns-attrleaf) 00 01
02 03 04 05 06 07 08 09 10 11 12 13
14 15 16
dnsop D. Crocker
Internet-Draft Brandenburg InternetWorking
Intended status: Best Current Practice May 22, 2018
Expires: November 23, 2018
DNS Scoped Data Through '_Underscore' Naming of Attribute Leaves
draft-ietf-dnsop-attrleaf-08
Abstract
Formally, any DNS resource record may occur for any domain name.
However some services have defined an operational convention, which
applies to DNS leaf nodes that are under a DNS branch having one or
more reserved node names, each beginning with an underscore. The
underscore naming construct defines a semantic scope for DNS record
types that are associated with the parent domain, above the
underscored branch. This specification explores the nature of this
DNS usage and defines the "DNS Global Underscore Scoped Entry
Registry" with IANA. The purpose of the Underscore registry is to
avoid collisions resulting from the use of the same underscore-based
name, for different services.
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 November 23, 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
Crocker Expires November 23, 2018 [Page 1]
Internet-Draft DNS AttrLeaf May 2018
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
1.1. _Underscore Scoping . . . . . . . . . . . . . . . . . . . 2
1.2. Scaling Benefits . . . . . . . . . . . . . . . . . . . . 4
2. DNS Underscore Scoped Entry Registries Function . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
3.1. DNS Underscore Global Scoped Entry Registry . . . . . . . 6
3.2. DNS Underscore Global Scoped Entry Registry Definition . 6
3.3. Initial entries . . . . . . . . . . . . . . . . . . . . . 7
4. Guidance for Expert Review . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The core Domain Name System (DNS) technical specifications assign no
semantics to domain names or their parts, and no constraints upon
which resource record (RR) types are permitted to be stored under
particular names [RFC1035], [RFC2181]. Over time, some leaf node
names, such as "www" and "ftp" have come to imply support for
particular services, but this is a matter of operational convention,
rather than defined protocol semantics. This freedom in the basic
technology has permitted a wide range of administrative and semantic
policies to be used -- in parallel. DNS data semantics have been
limited to the specification of particular resource record types, on
the expectation that new ones would be added as needed.
Unfortunately, the addition of new resource record types has proven
extremely challenging, over the life of the DNS, with significant
adoption and use barriers.
1.1. _Underscore Scoping
As an alternative to defining a new RR type, some DNS service
enhancements call for using an existing resource record type, but
specify a restricted scope for its occurrence. Scope is meant as a
static property, not one dependent on the nature of the query. It is
Crocker Expires November 23, 2018 [Page 2]
Internet-Draft DNS AttrLeaf May 2018
an artifact of the DNS name. That scope is a leaf node, within which
the uses of specific resource record sets can be formally defined and
constrained. The leaf occurs in a branch having a distinguished
naming convention: At the top of the branch -- beneath the parent
domain name to which the scope applies -- one or more reserved DNS
node names begin with an underscore ("_"). Because the DNS rules for
a "host" (host name) are not allowed to use the underscore character,
this distinguishes the underscore name from all legal host names
[RFC952]. Effectively, this convention for leaf node naming creates
a space for the listing of 'attributes' -- in the form of resource
record types -- that are associated with the parent domain, above the
underscored sub-branch.
The scoping feature is particularly useful when generalized resource
record types are used -- notably "TXT", "SRV", and "URI" [RFC1035],
[RFC2782], [RFC6335], [RFC7553]. It provides efficient separation of
one use of them from others. Absent this separation, an
undifferentiated mass of these "RRsets" is returned to the DNS
client, which then must parse through the internals of the records in
the hope of finding ones that are relevant. Worse, in some cases the
results are ambiguous because a record type might not adequately
self-identify. With underscore-based scoping, only the relevant
"RRsets"s are returned.
A simple example is DKIM [RFC6376] , which uses "_domainkeys" for
defining a place to hold a "TXT" record containing signing
information for the parent domain.
This specification formally defines how underscore labels are used as
"attribute" enhancements for their parent domain names. For example,
domain name "_domainkey.example." acts as attribute of parent domain
name "example." To avoid collisions resulting from the use of the
same underscore-based labels for different applications using the
same resource record type, this document establishes DNS Underscore
Global Scoped Entry IANA Registry for the highest-level reserved
names that begin with _underscore; _underscore-based names that are
farther down the hierarchy are handled within the scope of the
highest-level _underscore name.
Discussion Venue: Discussion about this draft should be directed
to the dnsop@ietf.org [1] mailing list.
NOTE TO RFC EDITOR: Please remove "Discussion Venue" paragraph
prior to publication.
Crocker Expires November 23, 2018 [Page 3]
Internet-Draft DNS AttrLeaf May 2018
1.2. Scaling Benefits
Some resource record types are used in a fashion that can create
scaling problems, if an entire RRset associated with a domain name is
aggregated in the leaf node for that name. An increasingly-popular
approach, with excellent scaling properties, places the RRset under a
node having an underscore-based name, at a defined place in the DNS
tree under the 'parent' name. This constrains the use of particular
"RR" types associated with that parent name. A direct lookup to the
subordinate leaf node produces only the desired record types, at no
greater cost than a typical DNS lookup.
The definition of a underscore global registry, provided in this
specification, primarily attends to the top-most names used for
scoping an RR type; that is the _underscore "global" names.
2. DNS Underscore Scoped Entry Registries Function
A global registry for DNS nodes names that begin with an _underscore
is defined here. The purpose of the Underscore Global Registry is to
avoid collisions resulting from the use of the same _underscore-based
name, for different applications.
o If a public specification calls for use of an _underscore-prefixed
domain node name, the 'global' (right-most) _underscored name MUST
be entered into this registry.
The _underscore names define scope of use for specific resource
record types, which are associated with the domain name that is the
"parent" to the branch defined by the _underscore naming. A given
name defines a specific, constrained context for one or more RR
types, where use of such record types conforms to the defined
constraints.
o Within an _underscore scoped leaf, other RRsets that are not
specified as part of the scope MAY be used.
Structurally, the registry is defined as a single, flat table of RR
types, under node names beginning with _underscore. In some cases,
such as for use of an "SRV" record, the full scoping name might be
multi-part, as a sequence of underscore names. Semantically, that
sequence represents a hierarchical model and it is theoretically
reasonable to allow re-use of a subordinate underscore name in
different underscore context; that is, a subordinate name is
meaningful only within the scope of the right-most (top-level)
underscore name. Therefore they are ignored by this DNS Underscore
Global Scoped Entry Registry. This registry is for the definition of
highest-level -- ie, global -- underscore node name used.
Crocker Expires November 23, 2018 [Page 4]
Internet-Draft DNS AttrLeaf May 2018
+----------------------------+
| NAME |
+----------------------------+
| _service1 |
| ._protoB._service2 |
| _protoB._service3 |
| _protoC._service3 |
| _useX._protoD._service4 |
| _protoE._region._authority |
+----------------------------+
Example of Underscore Names
Only the right-most _underscore names are registered in the IANA
Underscore Global table.
The use of underscored node names is specific to each RRTYPE that
is being scoped. Each name defines a place, but does not define
the rules for what appears underneath that place, either as
additional underscored naming or as a leaf node with resource
records. Details for those rules are provided by specifications
for individual RRTYPEs. The sections below describe the way that
existing underscore labels are used with the RRTYPEs that they
name.
Definition and registration of the subordinate underscore node
names is the responsibility of the specification that creates the
highest-level (right-most) global registry entry.
That is, if a scheme using a global underscore node name also has
one or more subordinate levels of underscore node naming, the
namespaces from which names for those lower levels is chosen is
controlled by the parent underscore node name. Each globally-
registered underscore name owns a distinct, subordinate name
space.
3. IANA Considerations
Per [RFC8126], IANA is requested to establish the:
DNS Underscore Global Scoped Entry Registry
This section describes actions requested of IANA. The guidance in
[IANA] is used.
Crocker Expires November 23, 2018 [Page 5]
Internet-Draft DNS AttrLeaf May 2018
3.1. DNS Underscore Global Scoped Entry Registry
The DNS Global Underscore Scoped Entry Registry is for DNS node names
that begin with the underscore character (_) and are the right-most
occurrence of any underscored names in a domain name sequence having
that form; that is they are the "top" of a DNS branch, under a
"parent" domain name.
o This registry is to operate under the IANA rules for "Expert
Review" registration; see Section 4.
o The contents of each entry in the Global registry are defined in
Section 3.2.
o Each entry in the registry MUST contain values for all of the
fields specified in Section 3.2.
o Within the registry, the combination of RR Type and _Node Name
MUST be unique.
o The table is to be maintained with entries sorted by the first
column (RR Type) and within that the second column (_Node Name).
o The required Reference for an entry MUST have a stable resolution
to the organization controlling that registry entry
3.2. DNS Underscore Global Scoped Entry Registry Definition
A registry entry contains:
RR Type: Lists an RR type that is defined for use within this
scope.
_Node Name: Specifies a single _underscore name that defines a
reserved name; this name is the "global" entry name for the
scoped resource record types that are associated with that
name
References: Lists specification that defines a record type and its
use under this Name. The organization producing the
specification retains control over the registry entry for
the _Node Name.
Each RR type that is to be used MUST have a separate registry entry.
Crocker Expires November 23, 2018 [Page 6]
Internet-Draft DNS AttrLeaf May 2018
3.3. Initial entries
Initial entries in the registry are:
Crocker Expires November 23, 2018 [Page 7]
Internet-Draft DNS AttrLeaf May 2018
+------------+-----------------+------------+
| RR Type | _NODE NAME | REFERENCE |
+------------+-----------------+------------+
| OPENPGPKEY | _openpgpkey | [RFC7929] |
| SMIMEA | _smimecert | [RFC8162] |
| SRV | _dccp | [RFC2782] |
| SRV | _sctp | [RFC2782] |
| SRV | _tcp | [RFC2782] |
| SRV | _udp | [RFC2782] |
| TLSA | _sctp | [RFC6698] |
| TLSA | _tcp | [RFC6698] |
| TLSA | _udp | [RFC6698] |
| TXT | _mta-sts | [MTA-STS] |
| TXT | _acme-challenge | [ACME] |
| TXT | _dmarc | [RFC7489] |
| TXT | _domainkey | [RFC6376] |
| TXT | _spf | [RFC7208] |
| TXT | _vouch | [RFC5518] |
| URI | _iax | [RFC7553] |
| URI | _acct | [RFC7553] |
| URI | _dccp | [RFC7553] |
| URI | _email | [RFC7553] |
| URI | _ems | [RFC7553] |
| URI | _fax | [RFC7553] |
| URI | _ft | [RFC7553] |
| URI | _h323 | [RFC7553] |
| URI | _ical-sched | [RFC7553] |
| URI | _ical-access | [RFC7553] |
| URI | _ifax | [RFC7553] |
| URI | _im | [RFC7553] |
| URI | _mms | [RFC7553] |
| URI | _pres | [RFC7553] |
| URI | _pstn | [RFC7553] |
| URI | _sctp | [RFC7553] |
| URI | _sip | [RFC7553] |
| URI | _sms | [RFC7553] |
| URI | _tcp | [RFC7553] |
| URI | _udp | [RFC7553] |
| URI | _unifmsg | [RFC7553] |
| URI | _vcard | [RFC7553] |
| URI | _videomsg | [RFC7553] |
| URI | _voice | [RFC7553] |
| URI | _voicemsg | [RFC7553] |
| URI | _vpim | [RFC7553] |
| URI | _xmp | [RFC7553] |
+------------+-----------------+------------+
Table 1: Underscore Global Registry (initial entries)
Crocker Expires November 23, 2018 [Page 8]
Internet-Draft DNS AttrLeaf May 2018
4. Guidance for Expert Review
This section provides guidance for expert review of registration
requests in the of DNS Underscore Global Scoped Entry Registry.
This review is solely to determine adequacy of a requested entry
in this Registry, and does not include review of other aspects of
the document specifying that entry. For example such a document
might also contain a definition of the resource record type that
is referenced by the requested entry. Any required review of that
definition is separate from the expert review required here.
The review is for the purposes of ensuring that:
o The details for creating the registry entry are sufficiently
clear, precise and complete
o The combination of the _underscore name, under which the listed
resource record type is used, and the resource record type, is
unique in the table
For the purposes of this Expert Review, other matters of the
specification's technical quality, adequacy or the like are outside
of scope.
5. Security Considerations
This memo raises no security issues.
6. References
6.1. Normative References
[ACME] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", I-D draft-ietf-acme-acme-11, March 2018.
[IANA] M. Cotton, B. Leiba, and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", RFC 8126,
June 2017.
[MTA-STS] Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
and J. Jones, "SMTP MTA Strict Transport Security (MTA-
STS)", I-D draft-ietf-uta-mta-sts.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
Crocker Expires November 23, 2018 [Page 9]
Internet-Draft DNS AttrLeaf May 2018
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC5518] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
Reference", RFC 5518, April 2009.
[RFC6335] Cotton, M., Eggert, L., Tpuch, J., Westerlund, M., and S.
Cheshire, "nternet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", RFC 6335, Aug
2011.
[RFC6376] Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys
Identified Mail (DKIM) Signatures", RFC 6376, Sept 2011.
[RFC6698] Hoffman, J. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August .
[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for
Authorizing Use of Domains in E-Mail, Version 1",
RFC 7208, April 2014.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, March 2015.
[RFC7553] Falstrom, P. and O. Kolkman, "The Uniform Resource
Identifier (URI) DNS Resource Record", RFC 7553,
ISSN 2070-1721, June 2015.
[RFC7929] Wouters, P., , RFC 7929, August 2016.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", RFC 8126,
June 2017.
[RFC8162] Hoffman, P. and J. Schlyter, "Using Secure DNS to
Associate Certificates with Domain Names for S/MIME",
RFC 8162, May 2017.
[RFC952] Harrenstien, K., Stahl, M., and E. Feinler, "DOD Internet
Host Table Specification", RFC 952, October 1985.
Crocker Expires November 23, 2018 [Page 10]
Internet-Draft DNS AttrLeaf May 2018
6.2. URIs
[1] mailto:dnsop@ietf.org
Appendix A. Acknowledgements
Thanks go to Bill Fenner, Tony Hansen, Martin Hoffmann, Peter Koch,
Olaf Kolkman, and Andrew Sullivan for diligent review of the (much)
earlier drafts. For the later enhancements, thanks to: Stephane
Bortzmeyer, Bob Harold, Warren Kumari, John Levine, Joel Jaeggli,
Petr Špaček, Ondřej Surř, Paul Vixie, Tim
Wicinski, and Paul Wouters.
Special thanks to Ray Bellis for his persistent encouragement to
continue this effort, as well as the suggestion for an essential
simplification to the registration model.
Author's Address
Dave Crocker
Brandenburg InternetWorking
675 Spruce Dr.
Sunnyvale, CA 94086
USA
Phone: +1.408.246.8253
Email: dcrocker@bbiw.net
URI: http://bbiw.net/
Crocker Expires November 23, 2018 [Page 11]
Html markup produced by rfcmarkup 1.129b, available from
https://tools.ietf.org/tools/rfcmarkup/