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rfc:bcp:bcp222

[Note that this file is a concatenation of more than one RFC.]

Internet Engineering Task Force (IETF) D. Crocker Request for Comments: 8552 Brandenburg InternetWorking BCP: 222 March 2019 Category: Best Current Practice ISSN: 2070-1721

       Scoped Interpretation of DNS Resource Records through
              "Underscored" Naming of Attribute Leaves

Abstract

 Formally, any DNS Resource Record (RR) may occur under any domain
 name.  However, some services use an operational convention for
 defining specific interpretations of an RRset by locating the records
 in a DNS branch under the parent domain to which the RRset actually
 applies.  The top of this subordinate branch is defined by a naming
 convention that uses a reserved node name, which begins with the
 underscore character (e.g., "_name").  The underscored 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
 "Underscored and Globally Scoped DNS Node Names" registry with IANA.
 The purpose of this registry is to avoid collisions resulting from
 the use of the same underscored name for different services.

Status of This Memo

 This memo documents an Internet Best Current Practice.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 BCPs is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8552.

Crocker Best Current Practice [Page 1] RFC 8552 DNS AttrLeaf March 2019

Copyright Notice

 Copyright (c) 2019 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
   1.1.  Underscore-Based Scoping  . . . . . . . . . . . . . . . .   3
   1.2.  Scaling Benefits  . . . . . . . . . . . . . . . . . . . .   4
   1.3.  Global Underscored Node Names . . . . . . . . . . . . . .   4
   1.4.  Interaction with DNS Wildcards  . . . . . . . . . . . . .   5
   1.5.  History . . . . . . . . . . . . . . . . . . . . . . . . .   5
 2.  "Underscored and Globally Scoped DNS Node Names" Registry . .   6
 3.  Guidance for Registering RRset Use  . . . . . . . . . . . . .   7
 4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   4.1.  "Underscored and Globally Scoped DNS Node Names" Registry   8
   4.2.  Enumservices Registrations Registry . . . . . . . . . . .  11
 5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
 6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   6.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
   6.2.  Informative References  . . . . . . . . . . . . . . . . .  15
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  15
 Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

1. Introduction

 The core Domain Name System (DNS) technical specifications ([RFC1035]
 and [RFC2181]) 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 resource record

Crocker Best Current Practice [Page 2] RFC 8552 DNS AttrLeaf March 2019

 types would be added as needed.  Unfortunately, the addition of new
 resource record types has proven extremely challenging, with
 significant adoption and use barriers occurring over the life of the
 DNS.

1.1. Underscore-Based Scoping

 As an alternative to defining a new RR TYPE, some DNS service
 enhancements call for using an existing resource record type but
 specifying a restricted scope for its occurrence.  Scope is meant as
 a static property, not one dependent on the nature of the query.  It
 is an artifact of the DNS name.  That scope is a leaf node containing
 the specific resource record sets that are formally defined and
 constrained.  Specifically:
    The leaf occurs in a branch having a distinguished naming
    convention: there is a parent domain name to which the scoped data
    applies.  The branch is under this name.  The sub-branch is
    indicated by a sequence of one or more reserved DNS node names; at
    least the first (highest) of these names begins with an underscore
    (e.g., "_name").
 Because the DNS rules for a "host" (host name) do not allow use of
 the underscore character, the underscored name is distinguishable
 from all legal host names [RFC0952].  Effectively, this convention
 for naming leaf nodes 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 its specific purpose.  With underscore-based scoping,
 only the relevant RRsets are returned.
 A simple example is DomainKeys Identified Mail (DKIM) [RFC6376],
 which uses "_domainkey" to define a place to hold a TXT record
 containing signing information for the parent domain.
 This specification formally defines how underscored names are used as
 "attribute" enhancements for their parent domain names.  For example,
 the domain name "_domainkey.example." acts as an attribute of the
 parent domain name "example.".  To avoid collisions resulting from

Crocker Best Current Practice [Page 3] RFC 8552 DNS AttrLeaf March 2019

 the use of the same underscored names for different applications
 using the same resource record type, this document establishes the
 "Underscored and Globally Scoped DNS Node Names" registry with IANA.
 Use of such node names, which begin with an underscore character, is
 reserved when they are the underscored name closest to the DNS root;
 as in that case, they are considered "global".  Underscored names
 that are farther down the hierarchy are handled within the scope of
 the global underscored node name.
 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.

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
 specially named branch, which is in turn under the node name that
 would otherwise contain the RRset.  The rules for naming that branch
 define the context for interpreting the RRset.  That is, rather than:
                          domain-name.example
                            /
                           RRset
 the arrangement is:
                      _branch.domain-name.example
                        /
                       RRset
 A direct lookup to the subordinate leaf node produces only the
 desired record types, at no greater cost than a typical DNS lookup.

1.3. Global Underscored Node Names

 As defined in [RFC1034], the DNS uses names organized in a tree-
 structured or hierarchical fashion.  A domain name might have
 multiple node names that begin with the underscore character (e.g.,
 "_name").  A global underscored node name is the one that is closest
 to the root of the DNS hierarchy, also called the highest level or
 topmost.  In the presentation convention described in Section 3.1 of
 [RFC1034], this is the rightmost name beginning with an underscore.

Crocker Best Current Practice [Page 4] RFC 8552 DNS AttrLeaf March 2019

 In other presentation environments, it might be positioned
 differently.  To avoid concern for the presentation variations, the
 qualifier "global" is used here.

1.4. Interaction with DNS Wildcards

 DNS wildcards interact poorly with underscored names in two ways:
 Since wildcards are only interpreted as leaf names, one cannot create
 the equivalent of a wildcard name for prefixed names.  A name such as
 label.*.example.com is not a wildcard.
 Conversely, a wildcard such as *.example.com can match any name
 including an underscored name.  So, a wildcard might match an
 underscored name, returning a record that is the type controlled by
 the underscored name but is not intended to be used in the
 underscored context and does not conform to its rules.

1.5. History

 Originally, different uses of underscored node names developed
 largely without coordination.  For TXT records, there is no
 consistent, internal syntax that permits distinguishing among the
 different uses.  In the case of the SRV RR and URI RR, distinguishing
 among different types of use was part of the design (see [RFC2782]
 and [RFC7553]).  The SRV and URI specifications serve as templates,
 defining RRs that might only be used for specific applications when
 there is an additional specification.  The template definition
 included reference to two levels of tables of names from which
 underscored names should be drawn.  The lower-level (local scope) set
 of "_service" names is defined in terms of other IANA tables, namely
 any table with symbolic names.  The upper-level (global scope) SRV
 naming field is "_proto", although its pool of names is not
 explicitly defined.
 The aggregate effect of these independent efforts was a long list of
 underscored names that were reserved without coordination, which
 invites an eventual name-assignment collision.  The remedy is this
 base document and a companion document ([RFC8553]), which define a
 registry for these names and attempt to register all those already in
 use as well as to direct changes to the pre-registry specifications
 that used global underscored node names.

Crocker Best Current Practice [Page 5] RFC 8552 DNS AttrLeaf March 2019

2. "Underscored and Globally Scoped DNS Node Names" Registry

 A registry for global DNS node names that begin with an underscore is
 defined here.  The purpose of the "Underscored and Globally Scoped
 DNS Node Names" registry is to avoid collisions resulting from the
 use of the same underscored name for different applications.
    If a public specification calls for use of an underscored node
    name, the global underscored node name -- the underscored name
    that is closest to the DNS root -- MUST be entered into this
    registry.
 An underscored name defines the 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 underscored name.  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 a leaf that is underscore scoped, 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 underscored names.  Semantically, that
 sequence represents a hierarchical model, and it is theoretically
 reasonable to allow reuse of a subordinate underscored name in a
 different, global underscored context; that is, a subordinate name is
 meaningful only within the scope of the global underscored node name.
 Therefore, they are ignored by this "Underscored and Globally Scoped
 DNS Node Names" registry.  This registry is for the definition of
 highest-level -- that is, global -- underscored node name used.
                    +----------------------------+
                    |                       NAME |
                    +----------------------------+
                    |                  _service1 |
                    |          _protoB._service2 |
                    |          _protoB._service3 |
                    |          _protoC._service3 |
                    |    _useX._protoD._service4 |
                    | _protoE._region._authority |
                    +----------------------------+
                Table 1: Examples of Underscored Names

Crocker Best Current Practice [Page 6] RFC 8552 DNS AttrLeaf March 2019

 Only global underscored node names are registered in the "Underscored
 and Globally Scoped DNS Node Names" registry.  From the example
 above, that would mean _service1, _service2, _service3, _service 4,
 and _authority would be listed in the IANA registry.
 o  The use of underscored node names is specific to each RR TYPE 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 RR TYPEs.  The sections below describe the way that
    existing underscored names are used with the RR TYPEs that they
    name.
 o  Definition and registration of subordinate underscored node names
    are the responsibility of the specification that creates the
    global underscored node name registry entry.
 That is, if a scheme using a global underscored node name has one or
 more subordinate levels of underscored node naming, the namespaces
 from which names for those lower levels are chosen are controlled by
 the parent underscored node name.  Each registered global underscored
 node name owns a distinct, subordinate namespace.

3. Guidance for Registering RRset Use

 This section provides guidance for specification writers, with a
 basic template they can use, to register new entries in the
 "Underscored and Globally Scoped DNS Node Names" registry.  The text
 can be added to specifications using RR TYPE / _NODE NAME
 combinations that have not already been registered:
    Per RFC 8552, please add the following entry to the "Underscored
    and Globally Scoped DNS Node Names" registry:
 +---------+-------------------+-------------------------------------+
 | RR Type | _NODE NAME        | Reference                           |
 +---------+-------------------+-------------------------------------+
 | {RR     | _{DNS global node | {citation for the document making   |
 | TYPE}   | name}             | the addition.}                      |
 +---------+-------------------+-------------------------------------+
                 Table 2: Template for Entries in the
       "Underscored and Globally Scoped DNS Node Names" Registry

Crocker Best Current Practice [Page 7] RFC 8552 DNS AttrLeaf March 2019

4. IANA Considerations

 IANA has established the "Underscored and Globally Scoped DNS Node
 Names" registry.  This section describes the registry, the
 definitions, the initial entries, the use of_ta and _example, and the
 use of [RFC8126] as guidance for expert review.  IANA has also
 updated the "Enumservices Registrations" registry with a pointer to
 this document.

4.1. "Underscored and Globally Scoped DNS Node Names" Registry

 The "Underscored and Globally Scoped DNS Node Names" registry
 includes any DNS node name that begins with the underscore character
 ("_", ASCII 0x5F) and is the underscored node name closest to the
 root; that is, it defines the highest level of a DNS branch under a
 "parent" domain name.
 o  This registry operates under the IANA rules for "Expert Review"
    registration; see Section 4.1.5.
 o  The contents of each entry in the registry are defined in
    Section 4.1.1.
 o  Each entry in the registry MUST contain values for all of the
    fields specified in Section 4.1.1.
 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.

Crocker Best Current Practice [Page 8] RFC 8552 DNS AttrLeaf March 2019

4.1.1. Contents of an Entry in the "Underscored and Globally Scoped DNS

      Node Names" Registry
 A registry entry contains:
    RR Type:    Lists an RR TYPE that is defined for use within this
                scope.
    _NODE NAME: Specifies a single, underscored 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.  For characters in the name that have
                an uppercase form and a lowercase form, the character
                MUST be recorded as lowercase to simplify name
                comparisons.
    Reference:  Lists the specification that defines a record type and
                its use under this _Node Name.  The organization
                producing the specification retains control over the
                registry entry for the _Node Name.
 Each RR TYPE that is to be used with a _Node Name MUST have a
 separate registry entry.

4.1.2. Initial Node Names

 The initial entries in the registry are as follows:
        +------------+-----------------------+---------------+
        | RR Type    | _NODE NAME            | Reference     |
        +------------+-----------------------+---------------+
        | *          | _example              | Section 4.1.4 |
        | NULL       | _ta-* {Section 4.1.3} | [RFC8145]     |
        | OPENPGPKEY | _openpgpkey           | [RFC7929]     |
        | SMIMEA     | _smimecert            | [RFC8162]     |
        | SRV        | _dccp                 | [RFC2782]     |
        | SRV        | _http                 | [RFC4386]     |
        | SRV        | _ipv6                 | [RFC5026]     |
        | SRV        | _ldap                 | [RFC4386]     |
        | SRV        | _ocsp                 | [RFC4386]     |
        | SRV        | _sctp                 | [RFC2782]     |
        | SRV        | _sip                  | [RFC5509]     |
        | SRV        | _tcp                  | [RFC2782]     |
        | SRV        | _udp                  | [RFC2782]     |
        | SRV        | _xmpp                 | [RFC3921]     |
        | TLSA       | _dane                 | [RFC7671]     |
        | TLSA       | _sctp                 | [RFC6698]     |
        | TLSA       | _tcp                  | [RFC6698]     |

Crocker Best Current Practice [Page 9] RFC 8552 DNS AttrLeaf March 2019

        | TLSA       | _udp                  | [RFC6698]     |
        | TXT        | _acme-challenge       | [RFC8555]     |
        | TXT        | _dmarc                | [RFC7489]     |
        | TXT        | _domainkey            | [RFC6376]     |
        | TXT        | _mta-sts              | [RFC8461]     |
        | TXT        | _spf                  | [RFC7208]     |
        | TXT        | _sztp                 | [ZEROTOUCH]   |
        | TXT        | _tcp                  | [RFC6763]     |
        | TXT        | _udp                  | [RFC6763]     |
        | TXT        | _vouch                | [RFC5518]     |
        | URI        | _acct                 | [RFC6118]     |
        | URI        | _dccp                 | [RFC7566]     |
        | URI        | _email                | [RFC6118]     |
        | URI        | _ems                  | [RFC6118]     |
        | URI        | _fax                  | [RFC6118]     |
        | URI        | _ft                   | [RFC6118]     |
        | URI        | _h323                 | [RFC6118]     |
        | URI        | _iax                  | [RFC6118]     |
        | URI        | _ical-access          | [RFC6118]     |
        | URI        | _ical-sched           | [RFC6118]     |
        | URI        | _ifax                 | [RFC6118]     |
        | URI        | _im                   | [RFC6118]     |
        | URI        | _mms                  | [RFC6118]     |
        | URI        | _pres                 | [RFC6118]     |
        | URI        | _pstn                 | [RFC6118]     |
        | URI        | _sctp                 | [RFC6118]     |
        | URI        | _sip                  | [RFC6118]     |
        | URI        | _sms                  | [RFC6118]     |
        | URI        | _tcp                  | [RFC6118]     |
        | URI        | _udp                  | [RFC6118]     |
        | URI        | _unifmsg              | [RFC6118]     |
        | URI        | _vcard                | [RFC6118]     |
        | URI        | _videomsg             | [RFC6118]     |
        | URI        | _voice                | [RFC6118]     |
        | URI        | _voicemsg             | [RFC6118]     |
        | URI        | _vpim                 | [RFC6118]     |
        | URI        | _web                  | [RFC6118]     |
        | URI        | _xmpp                 | [RFC6118]     |
        +------------+-----------------------+---------------+
                   Table 3: Initial Contents of the
       "Underscored and Globally Scoped DNS Node Names" Registry

4.1.3. _ta

 Under the NULL RR Type, the entry "_ta-*" denotes all node names
 beginning with the string "_ta-*".  It does NOT refer to a DNS
 wildcard specification.

Crocker Best Current Practice [Page 10] RFC 8552 DNS AttrLeaf March 2019

4.1.4. _example

 The node name "_example" is reserved across all RRsets.

4.1.5. Guidance for Expert Review

 This section provides guidance for expert review of registration
 requests in the "Underscored and Globally Scoped DNS Node Names"
 registry.
    This review is solely to determine adequacy of a requested entry
    in this registry, and it 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 underscored 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.

4.2. Enumservices Registrations Registry

 The following note has been added to the "Enumservice Registrations"
 registry:
    When adding an entry to this registry, strong consideration should
    be given to also adding an entry to the "Underscored and Globally
    Scoped DNS Node Names" registry.

5. Security Considerations

 This memo raises no security issues.

Crocker Best Current Practice [Page 11] RFC 8552 DNS AttrLeaf March 2019

6. References

6.1. Normative References

 [RFC0952]  Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
            host table specification", RFC 952, DOI 10.17487/RFC0952,
            October 1985, <https://www.rfc-editor.org/info/rfc952>.
 [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
            STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
            <https://www.rfc-editor.org/info/rfc1034>.
 [RFC1035]  Mockapetris, P., "Domain names - implementation and
            specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
            November 1987, <https://www.rfc-editor.org/info/rfc1035>.
 [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>.
 [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
            Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
            <https://www.rfc-editor.org/info/rfc2181>.
 [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
            specifying the location of services (DNS SRV)", RFC 2782,
            DOI 10.17487/RFC2782, February 2000,
            <https://www.rfc-editor.org/info/rfc2782>.
 [RFC3921]  Saint-Andre, P., Ed., "Extensible Messaging and Presence
            Protocol (XMPP): Instant Messaging and Presence",
            RFC 3921, DOI 10.17487/RFC3921, October 2004,
            <https://www.rfc-editor.org/info/rfc3921>.
 [RFC4386]  Boeyen, S. and P. Hallam-Baker, "Internet X.509 Public Key
            Infrastructure Repository Locator Service", RFC 4386,
            DOI 10.17487/RFC4386, February 2006,
            <https://www.rfc-editor.org/info/rfc4386>.
 [RFC5026]  Giaretta, G., Ed., Kempf, J., and V. Devarapalli, Ed.,
            "Mobile IPv6 Bootstrapping in Split Scenario", RFC 5026,
            DOI 10.17487/RFC5026, October 2007,
            <https://www.rfc-editor.org/info/rfc5026>.

Crocker Best Current Practice [Page 12] RFC 8552 DNS AttrLeaf March 2019

 [RFC5509]  Loreto, S., "Internet Assigned Numbers Authority (IANA)
            Registration of Instant Messaging and Presence DNS SRV RRs
            for the Session Initiation Protocol (SIP)", RFC 5509,
            DOI 10.17487/RFC5509, April 2009,
            <https://www.rfc-editor.org/info/rfc5509>.
 [RFC5518]  Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
            Reference", RFC 5518, DOI 10.17487/RFC5518, April 2009,
            <https://www.rfc-editor.org/info/rfc5518>.
 [RFC6118]  Hoeneisen, B. and A. Mayrhofer, "Update of Legacy IANA
            Registrations of Enumservices", RFC 6118,
            DOI 10.17487/RFC6118, March 2011,
            <https://www.rfc-editor.org/info/rfc6118>.
 [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
            Cheshire, "Internet Assigned Numbers Authority (IANA)
            Procedures for the Management of the Service Name and
            Transport Protocol Port Number Registry", BCP 165,
            RFC 6335, DOI 10.17487/RFC6335, August 2011,
            <https://www.rfc-editor.org/info/rfc6335>.
 [RFC6376]  Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
            "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
            RFC 6376, DOI 10.17487/RFC6376, September 2011,
            <https://www.rfc-editor.org/info/rfc6376>.
 [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
            of Named Entities (DANE) Transport Layer Security (TLS)
            Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
            2012, <https://www.rfc-editor.org/info/rfc6698>.
 [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
            Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
            <https://www.rfc-editor.org/info/rfc6763>.
 [RFC7208]  Kitterman, S., "Sender Policy Framework (SPF) for
            Authorizing Use of Domains in Email, Version 1", RFC 7208,
            DOI 10.17487/RFC7208, April 2014,
            <https://www.rfc-editor.org/info/rfc7208>.
 [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>.

Crocker Best Current Practice [Page 13] RFC 8552 DNS AttrLeaf March 2019

 [RFC7553]  Faltstrom, P. and O. Kolkman, "The Uniform Resource
            Identifier (URI) DNS Resource Record", RFC 7553,
            DOI 10.17487/RFC7553, June 2015,
            <https://www.rfc-editor.org/info/rfc7553>.
 [RFC7566]  Goix, L. and K. Li, "Enumservice Registration for 'acct'
            URI", RFC 7566, DOI 10.17487/RFC7566, June 2015,
            <https://www.rfc-editor.org/info/rfc7566>.
 [RFC7671]  Dukhovni, V. and W. Hardaker, "The DNS-Based
            Authentication of Named Entities (DANE) Protocol: Updates
            and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
            October 2015, <https://www.rfc-editor.org/info/rfc7671>.
 [RFC7929]  Wouters, P., "DNS-Based Authentication of Named Entities
            (DANE) Bindings for OpenPGP", RFC 7929,
            DOI 10.17487/RFC7929, August 2016,
            <https://www.rfc-editor.org/info/rfc7929>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <https://www.rfc-editor.org/info/rfc8126>.
 [RFC8145]  Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust
            Anchor Knowledge in DNS Security Extensions (DNSSEC)",
            RFC 8145, DOI 10.17487/RFC8145, April 2017,
            <https://www.rfc-editor.org/info/rfc8145>.
 [RFC8162]  Hoffman, P. and J. Schlyter, "Using Secure DNS to
            Associate Certificates with Domain Names for S/MIME",
            RFC 8162, DOI 10.17487/RFC8162, May 2017,
            <https://www.rfc-editor.org/info/rfc8162>.
 [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>.
 [RFC8461]  Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
            and J. Jones, "SMTP MTA Strict Transport Security (MTA-
            STS)", RFC 8461, DOI 10.17487/RFC8461, September 2018,
            <https://www.rfc-editor.org/info/rfc8461>.
 [RFC8555]  Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
            Kasten, "Automatic Certificate Management Environment
            (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
            <https://www.rfc-editor.org/info/rfc8555>.

Crocker Best Current Practice [Page 14] RFC 8552 DNS AttrLeaf March 2019

6.2. Informative References

 [RFC8553]  Crocker, D., "DNS Attrleaf Changes: Fixing Specifications
            That Use Underscored Node Names", RFC 8553,
            DOI 10.17487/RFC8553, March 2019,
            <https://www.rfc-editor.org/info/rfc8553>.
 [ZEROTOUCH]
            Watsen, K., Abrahamsson, M., and I. Farrer, "Secure Zero
            Touch Provisioning (SZTP)", Work in Progress, draft-ietf-
            netconf-zerotouch-29, January 2019.

Acknowledgements

 Thanks go to Bill Fenner, Dick Franks, Tony Hansen, Martin Hoffmann,
 Paul Hoffman, Peter Koch, Olaf Kolkman, Murray Kucherawy, John
 Levine, Benno Overeinder, and Andrew Sullivan for diligent review of
 the (much) earlier draft versions.  For the later enhancements,
 thanks to Stephane Bortzmeyer, Alissa Cooper, Bob Harold, Joel
 Jaeggli, Benjamin Kaduk, Mirja Kuehlewind, Warren Kumari, John
 Levine, Benno Overeinder, Eric Rescorla, Adam Roach, Petr Spacek,
 Ondrej Sury, 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
 United States of America
 Phone: +1.408.246.8253
 Email: dcrocker@bbiw.net
 URI:   http://bbiw.net/

Crocker Best Current Practice [Page 15]

Internet Engineering Task Force (IETF) D. Crocker Request for Comments: 8553 Brandenburg InternetWorking BCP: 222 March 2019 Updates: 2782, 3263, 3529, 3620, 3832,

       3887, 3958, 4120, 4227, 4386,
       4387, 4976, 5026, 5328, 5389,
       5415, 5518, 5555, 5617, 5679,
       5766, 5780, 5804, 5864, 5928,
       6120, 6186, 6376, 6733, 6763,
       7208, 7489, 8145

Category: Best Current Practice ISSN: 2070-1721

                       DNS AttrLeaf Changes:
       Fixing Specifications That Use Underscored Node Names

Abstract

 Using an underscore for a prefix creates a space for constrained
 interoperation of resource records.  Original uses of an underscore
 character as a domain node name prefix were specified without the
 benefit of an IANA registry.  This produced an entirely uncoordinated
 set of name-creation activities, all drawing from the same namespace.
 A registry for these names has now been defined by RFC 8552.
 However, the existing specifications that use underscored naming need
 to be modified in order to be in line with the new registry.  This
 document specifies those changes.  The changes preserve existing
 software and operational practice, while adapting the specifications
 for those practices to the newer underscore registry model.

Status of This Memo

 This memo documents an Internet Best Current Practice.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 BCPs is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8553.

Crocker Best Current Practice [Page 1] RFC 8553 DNS AttrLeaf Fix March 2019

Copyright Notice

 Copyright (c) 2019 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.  Underscored RRset Use in Specifications . . . . . . . . . . .   3
   2.1.  TXT RRset . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.2.  SRV RRset . . . . . . . . . . . . . . . . . . . . . . . .   5
   2.3.  URI RRset . . . . . . . . . . . . . . . . . . . . . . . .   6
 3.  Underscored Template Specifications . . . . . . . . . . . . .   7
   3.1.  SRV Specification Changes . . . . . . . . . . . . . . . .   7
   3.2.  URI Specification Changes . . . . . . . . . . . . . . . .   8
   3.3.  DNSSEC Signaling Specification Changes  . . . . . . . . .  10
 4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
 5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
 6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
   6.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
   6.2.  Informative References  . . . . . . . . . . . . . . . . .  12
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  15
 Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

1. Introduction

 Original uses of an underscore character as a domain node name
 [RFC1035] prefix, which creates a space for constrained
 interpretation of resource records, were specified without the
 benefit of an IANA registry [IANA-reg].  This produced an entirely
 uncoordinated set of name-creation activities, all drawing from the
 same namespace.  A registry has now been defined (see Section 4 of
 [RFC8552]); the RFC that defined it discusses the background for the
 use of underscored domain names [RFC8552].

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 The basic model for underscored name registration, as specified in
 [RFC8552], is to have each registry entry be unique in terms of the
 combination of a resource record type and a "global" (highest-level)
 underscored node name; that is, the node name beginning with an
 underscore that is the closest to the DNS root.
 The specifications describing the existing uses of underscored naming
 do not reflect the existence of this integrated registry.  For the
 new reader or the new editor of one of those documents, there is
 currently nothing signaling that the underscored name(s) defined in
 the document are now processed through an IANA registry.  This
 document remedies that, by marking such a published document with an
 update that indicates the nature of the change.
 Further, the documents that define the SRV [RFC2782] and URI
 [RFC7553] DNS resource records provide a meta-template for
 underscored name assignments, partially based on separate registries
 [RFC6335].  For the portion that selects the global (highest-level)
 underscored node name, this perpetuates uncoordinated assignment
 activities by separate technical specifications, out of the same
 namespace.  This document remedies that by providing detail for
 revisions to the SRV and URI specifications to bring their use in
 line with the single, integrated "Underscored and Globally Scoped DNS
 Node Names" registry.
 The result of these changes preserves existing software and
 operations practices while adapting the technical specifications to
 the newer underscore registry model.
 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. Underscored RRset Use in Specifications

 The use of underscored node names is specific to each RR TYPE 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 RR
 TYPEs.  The sections below describe the way that existing underscored
 names are used with the RR TYPEs that they name.

Crocker Best Current Practice [Page 3] RFC 8553 DNS AttrLeaf Fix March 2019

2.1. TXT RRset

    NOTE -  Documents falling into this category include: [RFC5518],
       [RFC5617], [RFC6120], [RFC6376], [RFC6763], [RFC7208], and
       [RFC7489].
 This section provides a generic approach for changes to existing
 specifications that define straightforward use of underscored node
 names when scoping the use of a TXT RRset.  The approach provides the
 information needed for adapting such specifications to the use of the
 IANA "Underscored and Globally Scoped DNS Node Names" registry
 [RFC8552].  Hence, the approach is meant both as an update to these
 existing specifications and as guidance for changes when those
 documents are revised.
 For any document that specifies the use of a TXT RRset under one or
 more underscored names, the global node name is expected to be
 registered in the IANA "Underscored and Globally Scoped DNS Node
 Names" registry [RFC8552].  An effort has been made to locate
 existing documents that do this, to register the global underscored
 node names, and to list them in the initial set of names added to the
 registry.
 If a public specification defines use of a TXT RRset and calls for
 the use of an underscored node name, here is a template of suggested
 text for registering the global underscored node name -- the one
 closest to the root -- that can be used through the IANA
 Considerations section of the specification:
    "Per [RFC8552], please add the following entry to the "Underscored
    and Globally Scoped DNS Node Names" registry:"
 +--------+----------------+-----------------------------------------+
 | RR     | _NODE NAME     | Reference                               |
 | Type   |                |                                         |
 +--------+----------------+-----------------------------------------+
 | TXT    | _{DNS node     | {citation for the document making the   |
 |        | name}          | addition}                               |
 +--------+----------------+-----------------------------------------+
      Table 1: Entry for the "Underscored and Globally Scoped DNS
                  Node Names" Registry for TXT RR Use

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2.2. SRV RRset

    NOTE -  Documents falling into this category include:
       [RFC3263], [RFC3529], [RFC3620], [RFC3832], [RFC3887],
       [RFC3958], [RFC4120], [RFC4227], [RFC4386], [RFC4387],
       [RFC4976], [RFC5026], [RFC5328], [RFC5389], [RFC5415],
       [RFC5555], [RFC5679], [RFC5766], [RFC5780], [RFC5804],
       [RFC5864], [RFC5928], and [RFC6186].
 Specification of the SRV resource record [RFC2782] provides a
 template for use of underscored node names.  The global node name is
 characterized as referencing the 'protocol' that is associated with
 SRV RRset usage.
 This section provides a generic approach for changes to existing
 specifications that define the use of an SRV RRset.  The approach
 provides the information needed for adapting such specifications to
 the use of the IANA "Underscored and Globally Scoped DNS Node Names"
 registry [RFC8552].  Hence, the approach is meant both as an update
 to these existing specifications and as guidance for changes when
 those documents are revised.
 For any document that specifies the use of an SRV RRset, the global
 ('protocol') underscored node name is expected to be registered in
 the IANA "Underscored and Globally Scoped DNS Node Names" registry
 [RFC8552].  An effort has been made to locate existing documents that
 do this, to register the global underscored node names, and to list
 them in the initial set of names added to the registry.
 If a public specification defines use of an SRV RRset and calls for
 the use of an underscored node name, here is a template of suggested
 text for registering the global underscored node name -- the one
 closest to the root -- that can be used through the IANA
 Considerations section of the specification:

Crocker Best Current Practice [Page 5] RFC 8553 DNS AttrLeaf Fix March 2019

    "Per [RFC8552], please add the following entry to the "Underscored
    and Globally Scoped DNS Node Names" registry:
 +--------+----------------------+-----------------------------------+
 | RR     | _NODE NAME           | Reference                         |
 | Type   |                      |                                   |
 +--------+----------------------+-----------------------------------+
 | SRV    | _{DNS 'protocol'     | {citation for the document making |
 |        | node name}           | the addition}                     |
 +--------+----------------------+-----------------------------------+
   Table 2: Entry for the "Underscored and Globally Scoped DNS Node
                    Names" Registry for SRV RR Use

2.3. URI RRset

 Specification of the URI resource record [RFC7553] provides a
 template for use of underscored node names.  The global node name is
 characterized as naming the 'protocol' that is associated with URI RR
 usage or by reversing an Enumservice sequence [RFC6117].
 This section provides a generic approach for changes to existing
 specifications that define use of a URI RRset.  The approach provides
 the information needed for adapting such specifications to the use of
 the IANA "Underscored and Globally Scoped DNS Node Names" registry
 [RFC8552].  Hence, the approach is meant both as an update to these
 existing specifications and as guidance for changes when those
 documents are revised.
 For any document that specifies the use of a URI RRset, the global
 ('protocol' or highest-level Enumservice) underscored node name is
 expected to be registered in the IANA "Underscored and Globally
 Scoped DNS Node Names" registry [RFC8552].  An effort has been made
 to locate existing documents that do this, to register the global
 underscored node names, and to list them in the initial set of names
 added to the registry.
 If a public specification defines use of a URI RRset and calls for
 the use of an underscored node name, here is a template of suggested
 text for registering the global underscored node name -- the one
 closest to the root -- that can be used through the IANA
 Considerations section of the specification:

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    "Per [RFC8552], please add the following entry to the "Underscored
    and Globally Scoped DNS Node Names" registry:
 +-------+----------------------------+------------------------------+
 | RR    | _NODE NAME                 | Reference                    |
 | Type  |                            |                              |
 +-------+----------------------------+------------------------------+
 | URI   | _{DNS 'protocol' or        | {citation for the document   |
 |       | Enumservice node name}     | making the addition}         |
 +-------+----------------------------+------------------------------+
   Table 3: Entry for the "Underscored and Globally Scoped DNS Node
                    Names" Registry for URI RR Use

3. Underscored Template Specifications

3.1. SRV Specification Changes

 The specification for a domain name, under which an SRV resource
 record [RFC2782] appears, provides a template for use of underscored
 node names.  The global underscored node name is characterized as
 indicating the 'protocol' that is associated with SRV RR usage.
 The text of [RFC2782] is changed as described below.  In addition,
 note that a normative reference to RFC 8552 is added to the
 References section of RFC 2782.
    OLD:
 The format of the SRV RR
  Here is the format of the SRV RR, whose DNS type code is 33:
        _Service._Proto.Name TTL Class SRV Priority Weight Port Target
  ...
  Proto
       The symbolic name of the desired protocol, with an underscore
       (_) prepended to prevent collisions with DNS labels that occur
       in nature.  _TCP and _UDP are at present the most useful values
       for this field, though any name defined by Assigned Numbers or
       locally may be used (as for Service).  The Proto is case
       insensitive.

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    NEW:
       The format of the SRV RR
       Here is the format of the SRV RR, whose DNS type code is 33:
          "_Service._Proto.Name TTL Class SRV Priority Weight Port
          Target"
          _..._
       Proto
          The symbolic name of the desired protocol with an underscore
          (e.g., "_name") prepended to prevent collisions with DNS
          labels that occur in nature. _TCP and _UDP are at present
          the most useful values for this field.  The Proto is case
          insensitive.
          The SRV RRset 'protocol' (global) underscored node name
          SHOULD be registered in the IANA "Underscored and Globally
          Scoped DNS Node Names" registry [RFC8552].

3.2. URI Specification Changes

 Specification for the domain name (under which a URI resource record
 [RFC7553] occurs) is similar to that for the SRV resource record
 [RFC2782], although the text refers only to 'service' name, rather
 than distinguishing 'service' from 'protocol'.  Further, the URI RR
 specification permits alternative underscored naming schemes:
    One matches what is used for SRV, with the global underscored node
    name called 'protocol'.
    The other is based on a reversing of an Enumservice [RFC6117]
    sequence.
 Text of [RFC7553] is changed as described below.  In addition, a
 normative reference to RFC 8552 is added to the References section of
 RFC 7553.

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    OLD:
 4.1.  Owner Name, Class, and Type
 The URI owner name is subject to special conventions.
 Just like the SRV RR [RFC2782], the URI RR has service information
 encoded in its owner name.  In order to encode the service for a
 specific owner name, one uses service parameters.  Valid service
 parameters are those registered by IANA in the "Service Name and
 Transport Protocol Port Number Registry" [RFC6335] or as "Enumservice
 ---
 Registrations [RFC6117].  The Enumservice Registration parameters are
 reversed (i.e., subtype(s) before type), prepended with an underscore
 (_), and prepended to the owner name in separate labels.  The
 underscore is prepended to the service parameters to avoid collisions
 with DNS labels that occur in nature, and the order is reversed to
 make it possible to do delegations, if needed, to different zones
 (and therefore providers of DNS).
 For example, suppose we are looking for the URI for a service with
 ENUM Service Parameter "A:B:C" for host example.com.  Then we would
 query for (QNAME,QTYPE)=("_C._B._A.example.com","URI").
 As another example, suppose we are looking for the URI for a service
 with Service Name "A" and Transport Protocol "B" for host
 example.com.  Then we would query for
 (QNAME,QTYPE)=("_A._B.example.com","URI").
    NEW:
       4.1.  Owner Name, Class, and Type
       The URI owner name is subject to special conventions.
       As for the SRV RRset [RFC2782], the URI RRset global (highest-
       level) underscored node name SHOULD be registered in the IANA
       "Underscored and Globally Scoped DNS Node Names" registry
       [RFC8552].
       Just like the SRV RRset, the URI RRset has service information
       encoded in its owner name.  In order to encode the service for
       a specific owner name, one uses service parameters.  Valid
       service parameters are:
       +  Those registered by IANA in the "Service Name and Transport
          Protocol Port Number Registry" [RFC6335].  The underscore is
          prepended to the service parameters to avoid collisions with

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          DNS labels that occur in nature, and the order is reversed
          to make it possible to do delegations, if needed, to
          different zones (and therefore providers of DNS).
       +  Those listed in "Enumservice Registrations" [RFC6117].  The
          Enumservice Registration parameters are reversed (i.e.,
          subtype(s) before type), prepended with an underscore (e.g.,
          "_name"), and prepended to the owner name in separate
          labels.  The highest-level (global) underscored Enumservice
          name becomes the global name per RFC 8552 to register.
       For example, suppose we are looking for the URI for a service
       with ENUM Service Parameter "A:B:C" for host example.com.  Then
       we would query for
       (QNAME,QTYPE)=("_C._B._A.example.com","URI").
       As another example, suppose we are looking for the URI for a
       service with Service Name "A" and Transport Protocol "B" for
       host example.com.  Then we would query for
       (QNAME,QTYPE)=("_A._B.example.com","URI").

3.3. DNSSEC Signaling Specification Changes

 "Signaling Trust Anchor Knowledge in DNS Security Extensions
 (DNSSEC)" [RFC8145] defines a use of DNS node names that effectively
 consumes all names beginning with the string "_ta-" when using the
 NULL RR in the query.
 Text of Section 5.1, "Query Format", of RFC 8145 is changed as
 described below.  In addition, a normative reference to RFC 8552 is
 added to the References section of RFC 8145.
    OLD:
 For example, a validating DNS resolver ...
                            QNAME=_ta-4444.
    NEW:
       For example, a validating DNS resolver ...  "QNAME=_ta-4444".
       Under the NULL RR, an entry is registered in the IANA
       "Underscored and Globally Scoped DNS Node Names" registry
       [RFC8552] for all node names beginning with "_ta-".

Crocker Best Current Practice [Page 10] RFC 8553 DNS AttrLeaf Fix March 2019

4. IANA Considerations

 Although this document makes reference to IANA registries, it
 introduces no new IANA registries or procedures.

5. Security Considerations

 This memo raises no security issues.

6. References

6.1. 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>.
 [RFC6117]  Hoeneisen, B., Mayrhofer, A., and J. Livingood, "IANA
            Registration of Enumservices: Guide, Template, and IANA
            Considerations", RFC 6117, DOI 10.17487/RFC6117, March
            2011, <https://www.rfc-editor.org/info/rfc6117>.
 [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
            Cheshire, "Internet Assigned Numbers Authority (IANA)
            Procedures for the Management of the Service Name and
            Transport Protocol Port Number Registry", BCP 165,
            RFC 6335, DOI 10.17487/RFC6335, August 2011,
            <https://www.rfc-editor.org/info/rfc6335>.
 [RFC7553]  Faltstrom, P. and O. Kolkman, "The Uniform Resource
            Identifier (URI) DNS Resource Record", RFC 7553,
            DOI 10.17487/RFC7553, June 2015,
            <https://www.rfc-editor.org/info/rfc7553>.
 [RFC8145]  Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust
            Anchor Knowledge in DNS Security Extensions (DNSSEC)",
            RFC 8145, DOI 10.17487/RFC8145, April 2017,
            <https://www.rfc-editor.org/info/rfc8145>.
 [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>.
 [RFC8552]  Crocker, D., "Scoped Interpretation of DNS Resource
            Records through "Underscored" Naming of Attribute Leaves",
            RFC 8552, DOI 10.17487/RFC8552, March 2019,
            <https://www.rfc-editor.org/info/rfc8552>.

Crocker Best Current Practice [Page 11] RFC 8553 DNS AttrLeaf Fix March 2019

6.2. Informative References

 [IANA-reg]
            IANA, "Protocol Registries",
            <https://www.iana.org/protocols>.
 [RFC1035]  Mockapetris, P., "Domain names - implementation and
            specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
            November 1987, <https://www.rfc-editor.org/info/rfc1035>.
 [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
            specifying the location of services (DNS SRV)", RFC 2782,
            DOI 10.17487/RFC2782, February 2000,
            <https://www.rfc-editor.org/info/rfc2782>.
 [RFC3263]  Rosenberg, J. and H. Schulzrinne, "Session Initiation
            Protocol (SIP): Locating SIP Servers", RFC 3263,
            DOI 10.17487/RFC3263, June 2002,
            <https://www.rfc-editor.org/info/rfc3263>.
 [RFC3529]  Harold, W., "Using Extensible Markup Language-Remote
            Procedure Calling (XML-RPC) in Blocks Extensible Exchange
            Protocol (BEEP)", RFC 3529, DOI 10.17487/RFC3529, April
            2003, <https://www.rfc-editor.org/info/rfc3529>.
 [RFC3620]  New, D., "The TUNNEL Profile", RFC 3620,
            DOI 10.17487/RFC3620, October 2003,
            <https://www.rfc-editor.org/info/rfc3620>.
 [RFC3832]  Zhao, W., Schulzrinne, H., Guttman, E., Bisdikian, C., and
            W. Jerome, "Remote Service Discovery in the Service
            Location Protocol (SLP) via DNS SRV", RFC 3832,
            DOI 10.17487/RFC3832, July 2004,
            <https://www.rfc-editor.org/info/rfc3832>.
 [RFC3887]  Hansen, T., "Message Tracking Query Protocol", RFC 3887,
            DOI 10.17487/RFC3887, September 2004,
            <https://www.rfc-editor.org/info/rfc3887>.
 [RFC3958]  Daigle, L. and A. Newton, "Domain-Based Application
            Service Location Using SRV RRs and the Dynamic Delegation
            Discovery Service (DDDS)", RFC 3958, DOI 10.17487/RFC3958,
            January 2005, <https://www.rfc-editor.org/info/rfc3958>.
 [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
            Kerberos Network Authentication Service (V5)", RFC 4120,
            DOI 10.17487/RFC4120, July 2005,
            <https://www.rfc-editor.org/info/rfc4120>.

Crocker Best Current Practice [Page 12] RFC 8553 DNS AttrLeaf Fix March 2019

 [RFC4227]  O'Tuathail, E. and M. Rose, "Using the Simple Object
            Access Protocol (SOAP) in Blocks Extensible Exchange
            Protocol (BEEP)", RFC 4227, DOI 10.17487/RFC4227, January
            2006, <https://www.rfc-editor.org/info/rfc4227>.
 [RFC4386]  Boeyen, S. and P. Hallam-Baker, "Internet X.509 Public Key
            Infrastructure Repository Locator Service", RFC 4386,
            DOI 10.17487/RFC4386, February 2006,
            <https://www.rfc-editor.org/info/rfc4386>.
 [RFC4387]  Gutmann, P., Ed., "Internet X.509 Public Key
            Infrastructure Operational Protocols: Certificate Store
            Access via HTTP", RFC 4387, DOI 10.17487/RFC4387, February
            2006, <https://www.rfc-editor.org/info/rfc4387>.
 [RFC4976]  Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
            for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
            DOI 10.17487/RFC4976, September 2007,
            <https://www.rfc-editor.org/info/rfc4976>.
 [RFC5026]  Giaretta, G., Ed., Kempf, J., and V. Devarapalli, Ed.,
            "Mobile IPv6 Bootstrapping in Split Scenario", RFC 5026,
            DOI 10.17487/RFC5026, October 2007,
            <https://www.rfc-editor.org/info/rfc5026>.
 [RFC5328]  Adolf, A. and P. MacAvock, "A Uniform Resource Name (URN)
            Namespace for the Digital Video Broadcasting Project
            (DVB)", RFC 5328, DOI 10.17487/RFC5328, September 2008,
            <https://www.rfc-editor.org/info/rfc5328>.
 [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
            "Session Traversal Utilities for NAT (STUN)", RFC 5389,
            DOI 10.17487/RFC5389, October 2008,
            <https://www.rfc-editor.org/info/rfc5389>.
 [RFC5415]  Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
            Ed., "Control And Provisioning of Wireless Access Points
            (CAPWAP) Protocol Specification", RFC 5415,
            DOI 10.17487/RFC5415, March 2009,
            <https://www.rfc-editor.org/info/rfc5415>.
 [RFC5518]  Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
            Reference", RFC 5518, DOI 10.17487/RFC5518, April 2009,
            <https://www.rfc-editor.org/info/rfc5518>.
 [RFC5555]  Soliman, H., Ed., "Mobile IPv6 Support for Dual Stack
            Hosts and Routers", RFC 5555, DOI 10.17487/RFC5555, June
            2009, <https://www.rfc-editor.org/info/rfc5555>.

Crocker Best Current Practice [Page 13] RFC 8553 DNS AttrLeaf Fix March 2019

 [RFC5617]  Allman, E., Fenton, J., Delany, M., and J. Levine,
            "DomainKeys Identified Mail (DKIM) Author Domain Signing
            Practices (ADSP)", RFC 5617, DOI 10.17487/RFC5617, August
            2009, <https://www.rfc-editor.org/info/rfc5617>.
 [RFC5679]  Bajko, G., "Locating IEEE 802.21 Mobility Services Using
            DNS", RFC 5679, DOI 10.17487/RFC5679, December 2009,
            <https://www.rfc-editor.org/info/rfc5679>.
 [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
            Relays around NAT (TURN): Relay Extensions to Session
            Traversal Utilities for NAT (STUN)", RFC 5766,
            DOI 10.17487/RFC5766, April 2010,
            <https://www.rfc-editor.org/info/rfc5766>.
 [RFC5780]  MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
            Using Session Traversal Utilities for NAT (STUN)",
            RFC 5780, DOI 10.17487/RFC5780, May 2010,
            <https://www.rfc-editor.org/info/rfc5780>.
 [RFC5804]  Melnikov, A., Ed. and T. Martin, "A Protocol for Remotely
            Managing Sieve Scripts", RFC 5804, DOI 10.17487/RFC5804,
            July 2010, <https://www.rfc-editor.org/info/rfc5804>.
 [RFC5864]  Allbery, R., "DNS SRV Resource Records for AFS", RFC 5864,
            DOI 10.17487/RFC5864, April 2010,
            <https://www.rfc-editor.org/info/rfc5864>.
 [RFC5928]  Petit-Huguenin, M., "Traversal Using Relays around NAT
            (TURN) Resolution Mechanism", RFC 5928,
            DOI 10.17487/RFC5928, August 2010,
            <https://www.rfc-editor.org/info/rfc5928>.
 [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
            Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
            March 2011, <https://www.rfc-editor.org/info/rfc6120>.
 [RFC6186]  Daboo, C., "Use of SRV Records for Locating Email
            Submission/Access Services", RFC 6186,
            DOI 10.17487/RFC6186, March 2011,
            <https://www.rfc-editor.org/info/rfc6186>.
 [RFC6376]  Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
            "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
            RFC 6376, DOI 10.17487/RFC6376, September 2011,
            <https://www.rfc-editor.org/info/rfc6376>.

Crocker Best Current Practice [Page 14] RFC 8553 DNS AttrLeaf Fix March 2019

 [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
            Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
            <https://www.rfc-editor.org/info/rfc6763>.
 [RFC7208]  Kitterman, S., "Sender Policy Framework (SPF) for
            Authorizing Use of Domains in Email, Version 1", RFC 7208,
            DOI 10.17487/RFC7208, April 2014,
            <https://www.rfc-editor.org/info/rfc7208>.
 [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>.

Acknowledgements

 Thanks go to Bill Fenner, Dick Franks, Tony Hansen, Peter Koch, Olaf
 Kolkman, and Andrew Sullivan for diligent review of the (much)
 earlier draft versions.  For the later enhancements, thanks to Tim
 Wicinski, John Levine, Bob Harold, Joel Jaeggli, Ondrej Sury, 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
 United States of America
 Phone: +1.408.246.8253
 Email: dcrocker@bbiw.net
 URI:   http://bbiw.net/

Crocker Best Current Practice [Page 15]

/data/webs/external/dokuwiki/data/pages/rfc/bcp/bcp222.txt · Last modified: 2019/03/20 23:38 (external edit)