dnsop                                                         D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Intended status: Best Current Practice                    March 29, 2017 19, 2018
Expires: September 30, 2017 20, 2018

    DNS Scoped Data Through Global '_Underscore' Naming of Attribute Leaves
                      draft-ietf-dnsop-attrleaf-02
                      draft-ietf-dnsop-attrleaf-03

Abstract

   Formally, any DNS "RR" resource record may occur for any domain name.
   However some services have defined an operational convention that
   applies to DNS leaf nodes that have are under a DNS branch that has one or
   more reserved node name, beginning names that begin with an underscore.  The
   underscore naming construct is used to define defines a semantic scope for DNS records
   that are associated with the parent domain. domain, above the underscored
   branch.  This specification explores the nature of this DNS usage and
   defines the "DNS Global Underscore Scoped Entry Registry" 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.

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   This Internet-Draft will expire on September 30, 2017. 20, 2018.

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   Copyright (c) 2017 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Scaling Benefits and TXT and SRV Resource Records
     1.1.  _Underscore Scoping . . . . . . . . . . . . . . . . . . .   3
   3.
     1.2.  Scaling Benefits for TXT, SRV, and URI Resource Records .   4
   2.  DNS Global Underscore Scoped Entry Registry Registries Function . . . . . . .   4
   4.
     2.1.  DNS Underscore Global Scoped Entry Registry Definition  .   5
     2.2.  DNS Common Second-Level Underscore Scoped Entry Registry
           Definition  . . .   5
   5. . . . . . . . . . . . . . . . . . . . .   6
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Related and Updated Registries   7
     3.1.  DNS Underscore Global Scoped Entry Registry . . . . . . .   7
     3.2.  DNS Common Second-Level Underscore Scoped Entry
           Registry  . . . . . . . . . . . . . . . .   9
   7. . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  11
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  11
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  11
     5.2.  References -- Informative . . . . . . . . . . . . . . . .   9
     8.3.  11
     5.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  12  14
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  12  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12  14

1.  Introduction

   The core DNS Domain Name System (DNS) technical specifications assign no
   semantics to domain names or their parts, and no constraints upon
   which resource records (RRs) are permitted to be associated with
   particular names. names.[RFC1035] 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.  Data  DNS data semantics have been limited to the
   specification of particular resource records, on the expectation that
   new ones would be added as needed.  Unfortunately, the addition of
   new resource records has proved extremely challenging, over the life
   of the DNS, with significant adoption and use barriers.

1.1.  _Underscore Scoping

   As an alternative to defining new RRs, some DNS service enhancements
   reuse
   call for using an existing resource record, but have specified specify a restricted
   scope for its occurrence.  That scope is a leaf node, within which
   the uses of specific resource records can be formally defined and
   constrained.  The leaf has occurs in a branch having a distinguished
   naming convention: It uses
   a At the top of the branch -- beneath the parent
   domain name to which the scope applies -- one or more reserved DNS
   node name that begins 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
   [RFC1035].  Effectively, this convention for leaf node naming creates
   a space for attributes the listing of 'attributes' -- in the form of resource
   records -- that are associated with the parent domain, one level up.

   One example is above the "SRV" record [RFC2782] which generalizes concepts
   long-used for email routing by the "MX" record [RFC0974][RFC5321].
   An equivalent usage to "SRV"
   underscore sub-branch.

   The scoping feature is the particularly useful when generalized resource
   records are used -- notably "TXT", "SRV", and "URI" "RR" [RFC7553].  Relying on
   special DNS names has significant benefits and detriments.  Some of
   these are explored in [RFC5507].

   [Comment]:    The terms "resolution context" and "scoping rules" have
      been suggested, in place of "semantic scope".  In order to avoid
      concern for matters of semantics, this specification uses the term
      "scoping rules", to create a focus on the mechanics being defined,
      rather than nuances of interpretation for the mechanism.

   The scoping feature is particularly useful when generalized resource
   records are used -- notably "TXT", "SRV" and "URI".
   [RFC1035],[RFC2782],[RFC7553].  It provides efficient separation of
   one use of them from others.  Absent this separation, an
   undifferentiated mass of these "RR"s 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 the records do not adequately self-identify. self-
   identify.  With underscore-based scoping, only the relevant "RR"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 discusses the formally defines how underscore labels are used as
   "attribute" enhancement,
   provides an explicit definition enhancements for their parent domain names.  For example,
   domain name "_domainkey.example." acts as attribute of it, and parent domain
   name "example."  To avoid collisions resulting from the use of the
   same underscore-based labels for different applications, this
   document establishes an DNS Underscore Global Scoped Entry IANA
   registry Registry
   for the highest-level reserved names that begin with _underscore; underscore-based
   _underscore-based names that are farther down the hierarchy is are
   handled within the scope of the highest-level _underscore name.  It updates the many existing specifications that
   have defined underscore names, in order to aggregate the references
   to a single IANA table.

   Discussion Venue:    Discussion about this draft should be directed
      to the dnsop@ietf.org [1] mailing list.

2.

      NOTE TO RFC EDITOR:    Please remove "Discussion Venue" paragraph
         prior to publication.

1.2.  Scaling Benefits for TXT, SRV, and TXT and SRV URI Resource Records

   Some resource records are generic and support a variety of uses.
   Each additional use defines its own rules and, possibly, its own
   internal syntax and node-naming conventions to distinguish among
   particular types.  The "TXT" "TXT", "SRV", and "SRV" "URI" records are notable
   examples.
   Used freely, some of these approaches  Their use can scale poorly, particularly when the same
   "RR" can be present in the same leaf node, but with different uses.

   An increasingly-popular approach, with excellent scaling properties, uses
   place the RR undr a node wit an underscore-based name, at a defined
   place in the DNS tree, so as to constrain to particular uses for the use of particular
   "RR"s farther down the branch using that name.  This means that a
   direct lookup produces only the desired records, at no greater cost
   than a typical DNS lookup.

   In the case

   The definition of "TXT" records, different uses have developed largely
   without coordination.  One side-effect is a underscore global registry, provided in this
   specification, primarily attends to the "upper-level" names used for
   RRs; that there is no
   consistently distinguishable internal syntax for the record; even the
   inefficiencies of internal inspection might not provide _underscore "global" names.  For efficiency, a reliable
   means
   single, subordinate _underscore second-level table also is defined,
   for use with a common set of distinguishing among the different uses.  Underscore-based applications.

2.  DNS Underscore Scoped Entry Registries Function

   A global registry for DNS nodes names therefore define that begin with an administrative way of separating "TXT"
   records that might have different uses, but otherwise would have no
   syntactic markers for distinguishing among them.

   In the case of the "SRV" "RR" and "URI" "RR", distinguishing among
   different types _underscore
   is defined here.  The names are used to define scope of use was part of the design [RFC2782], [RFC7553].
   The "SRV" and "URI" specifications serve as templates, defining "RR"s
   that might only be used for
   specific applications when there is an
   additional specification.  The template definition includes reference
   to two levels of tables of names from which underscore-names should
   be drawn.  The lower-level (local scope) set of <"_service"> names is
   defined in terms of other IANA tables, namely any table resource records, associated with symbolic
   names.  The upper-level (global scope) "SRV" naming field is
   <"_proto">, although its pool of names is not explicitly defined.

   The current definition of a global underscore registry attends only
   to the "upper-level" names used for these RRs, domain name that is
   the "_proto"
   names.

3.  DNS Global Underscore Scoped Entry Registry Function

   This specification creates a registry for DNS nodes names that begin
   with an underscore and are used "parent" to define scope of use for specific
   resource records. the branch defined by the _underscore naming.

      A given name defines a specific, constrained context for the one or
      more RR records, in which use of such records. records MUST conform to the
      defined constraints.  Within this scope, use of other resource records
      that are not specified is permitted. MAY be used.

   The purpose of the Underscore registry Global Registry is to avoid collisions
   resulting from the use of the same underscore-based _underscore-based name, for
   different applications.

   Structurally, the registry is defined as a single, flat table of
   names that begin with underscore. _underscore.  In some cases, such as for "SRV", use of
   an underscore "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 re-
   use of an a subordinate underscore name in different underscore context;
   that is, a subordinate name is meaningful only within the scope of
   the first (parent) (top-level) underscore name.  As such,  Therefore they can be are ignored by
   this DNS Global Underscore Global Scoped Entry Registry.  That is, the  This registry is
   for the definition of highest-level -- ie, global -- underscore node
   name used.

                                   +---+

                      +----------------------------+
                      |                       NAME |
                      +----------------------------+
                      |                  _service1 |
                      |         ._protoB._service2 |
                      |          _protoB._service3 |
                      |          _protoC._service3 |
                      |    _useX._protoD._service4 |
                      | _protoE._region._authority |
                      +----------------------------+

                        Example of Underscore Names

   Only the right-most names are registered in the IANA Underscore
   Global table.  Definition and registration of the subordinate names
   is the responsibility of the specification that creates the highest-level highest-
   level (right-most) registry entry.

4.

   For convenience, an Underscore Common Second-Level Names table is
   also defined, to cover some popular cases involving the subordinate
   name used with two-level _underscore naming.  In particular, this
   table covers uses of second-level names that scope SRV RRs use.

2.1.  DNS Global Underscore Global Scoped Entry Registry Definition

      Additions/Removals/Changes:    Please post to the list or send the
         author direct email, that indicates the exact details of
         changes needed to this table.  If a reference needs to be added
         or changed, the xml for this would be ideal.  Thanks. /d .

         NOTE TO RFC EDITOR:    Please remove "Additions/Removals/
            Changes" paragraph prior to publication.

   A registry entry contains:

      Name:

      ID:    Specifies a textual name for a scoped portion of the DNS.
         The name will usually be taken from the specification cited in
         the "Purpose" column and is intended for use in discussions
         about the entry.

      DNS Label:

      _Node Name:    Specifies a single _underscore name that defines a
         name reservation;
         reserved name; this name is the "global" entry name for the
         scoped resource records that are associated with that name.

      Constraints:    Specifies any restrictions on use of the name. DNS
         Label.

      RR(s):    Lists the RRs that are defined for use within this
         scope.

      References  Lists specifications that define the records and their
         use under this Name.

      Purpose:    Specifies the particular purpose/use for specific
         "RR"(s), defined for use within the scope of the registered
         underscore name.

5.

2.2.  DNS Common Second-Level Underscore Scoped Entry Registry
      Definition

   A registry entry contains:

      ID:    Specifies a textual name for a scoped portion of the DNS,
         occurring under a 'global' -- right-most -- _underscore node
         name.  The name will usually be taken from the specification
         cited in the "Purpose" column and is intended for use in
         discussions about the entry.

      _Node Name:    Specifies a single _underscore name that defines a
         reserved name; this name is the "second-level" entry name for
         the scoped resource records that are associated with that name.

      Constraints:    Specifies any restrictions on use of the name.

      RR(s):    Lists the RRs that are defined for use within this
         scope.

      References  Lists specifications that define the records and their
         use under this Name.

      Purpose:    Specifies the particular purpose/use for specific
         "RR"(s), defined for use within the scope of the registered
         underscore name.

3.  IANA Considerations

   Per [RFC5226], [RFC8126], IANA is requested to establish a two registries:

   1.  DNS Underscore Global Scoped Entry Registry

   2.  DNS Underscore Common Second-Level Scoped Entry Registry

   This section describes actions requested of IANA.  The guidance in
   [IANA] is used.

3.1.  DNS Underscore Global Scoped Entry Registry

   The DNS Global Underscore Scoped Entry Registry, Registry is for DNS node names
   that begin with the underscore character (_) and have been specified in any published
   RFC, or occur at the "top"
   of a DNS branch -- ie, are documented by right-most -- under a specification published by another
   standards organization. "parent" domain
   name.

      This registry is to operate under the IANA rules for "First Come
      First Served" registration.

   The contents of each entry in the Global registry are defined in
   Section 4.

   Initial entries in 2.1.

      Additions/Removals/Changes:    Please post to the registry are:

      { Enhancement list or send the
         author direct email, that indicates the exact details of
         changes needed to this table table.  If a reference needs to include all underscore name
      reservations in effect at be added
         or changed, the time xml for this document is published is
      left as an exercise would be ideal.  Thanks. /d .

         NOTE TO RFC EDITOR:    Please remove "Additions/Removals/
            Changes" paragraph prior to publication.

   Initial entries in the readers... /d }

   +------------+--------------+-------+-----------+-------------------+ registry are:

   +-------+------------+-----+------------+---------------------------+
   | NAME ID    | LABEL _NODE NAME | RR  | REFERENCE  | PURPOSE                   |
   +------------+--------------+-------+-----------+-------------------+
   | "SRV"      | _srv         | "SRV" | [RFC2782] | "SRV" template -- |
   |            |              |       |           | pro forma entry,  |
   |            |              |       |           | not directly      |
   |            |              |
   +-------+------------+-----+------------+---------------------------+
   |           | usable            |
   | "SRV" TCP SRV   | _tcp       | "SRV" SRV | [RFC2782]  | Use of "SRV" SRV for  |
   |            |              |       |           | a TCP-based TCP-     |
   | TCP   |            |     |            | based service             |
   | "SRV" UDP SRV   | _udp       | "SRV" SRV | [RFC2782]  | Use of "SRV" SRV for a UDP-     |
   | UDP   |            |     |            | a UDP-based based service             |
   | SPF   | _spf       | TXT | [RFC7208]  | service Authorized IP addresses   |
   | LDAP       | _ldap            | "SRV"     | [RFC2782]            | LDAP server for sending mail          |
   | SIP DKIM  | _sip _domainkey | NAPTR TXT | [RFC3263] [RFC6376]  | Locating SIP Public key for verifying  |
   |       |            |     | [RFC6011]            | Servers and UA DKIM signature.           |
   | VBR   | _vouch     | TXT | [RFC5518]  | configuration Vouch-by-refererence      |
   | SPF       | _spf            | "TXT"     | [RFC7372]            | Authorized IP domain assertion          |
   +-------+------------+-----+------------+---------------------------+

           Table 1: Underscore Global Registry (initial entries)

3.2.  DNS Common Second-Level Underscore Scoped Entry Registry

   A DNS Common Second-Level Underscore Scoped Entry Registry is for DNS
   node names that begin with the underscore character (_) and occur
   immediately below a Global ("top-level") node name beginning with an
   _underscore.

      This registry is to operate under the IANA rules for "First Come
      First Served" registration.

   The contents of each entry in the Common, Second-Level registry are
   defined in Section 2.2.

   Initial entries in the registry are:

   +-------------+--------------+---------+----------+-----------------+
   | ID          | _NODE NAME   | RR      | REFERENC | addresses for PURPOSE         |
   |             |              |         | E        | sending mail                 |
   +-------------+--------------+---------+----------+-----------------+
   | DKIM LDAP        | _domainkey _ldap        | "TXT" SRV     | [RFC6376] [RFC2782 | Public key for LDAP server     |
   |             |              |         | ]        | verifying DKIM                 |
   | SIP         | _sip         | NAPTR   | [RFC3263 | signature. Locating SIP    |
   | PKI LDAP             | _PKIXREP              | "SRV"         | [RFC4386] ] [RFC60 | PKI Repository Servers and UA  |
   | VBR             | _vouch              | "TXT"         | [RFC5518] 11]      | Vouch-by- configuration   |
   | PKI LDAP    | _PKIXREP     | SRV     | [RFC4386 | refererence PKI Repository  |
   |             |              |         | ]        | domain assertion                 |
   | DDDS        | --???!--     | "SRV" SRV     | [RFC3404] [RFC3404 | Mapping DDDS    |
   |             |              |         | ]        | query to DNS    |
   |             |              |         |          | records         |
   | SOAP BEEP   | _soap-beep   | "SRV" SRV     | [RFC4227] [RFC4227 | SOAP over BEEP  |
   |             |              |         | ]        | lookup, when no |
   |             |              |         |          | port specified  |
   | XMLRPC BEEP | _xmlrpc-beep | "SRV" SRV     | [RFC3529] [RFC3529 | Resolve url for |
   | BEEP             |              |         | ]        | XML-RPC using   |
   |             |              |         |          | BEEP            |
   | Diameter    | _diameter    | "SRV" SRV     | [RFC6733] [RFC6733 | Diameter        |
   |             |              |         | ]        | rendezvous      |
   | Tunnel      | _tunnel      | "SRV" SRV     | [RFC3620] [RFC3620 | Finding the     |
   |             |              |         | ]        | appropriate     |
   |             |              |         |          | address for     |
   |             |              |         |          | tunneling into a  |
   |             |              |         |          | a particular    |
   |             |              |         |          | domain          |
   | SLP         | _slpda       | "SRV" SRV     | [RFC3832] [RFC3832 | Discovering     |
   |             |              |         | ]        | desired services         |
   |             |              |         |          | services in     |
   |             |              |         |          | given DNS       |
   |             |              |         |          | domains         |
   | Msg Track   | _mtqp        | "SRV" SRV     | [RFC3887] [RFC3887 | Assist in       |
   |             |              |         | ]        | determining the |
   |             |              |         |          | path that a     |
   |             |              |         |          | particular      |
   |             |              |         |          | message has taken     |
   |             |              |         |          | taken through a |
   |             |              |         |          | messaging       |
   |             |              |         |          | system          |
   | XMPP Client | _xmpp-client | "SRV" SRV     | [RFC6120] [RFC6120 | XMPP client     |
   | Client             |              |         | ]        | lookup of       |
   |             |              |         |          | server          |
   | XMPP Server | _xmpp-server | "SRV" SRV     | [RFC6120] [RFC6120 | XMPP server-    |
   | Server             |              |         | ]        | server lookup   |
   | DDDS "SRV" SRV    | _???         | "SRV" SRV     | [RFC3958] [RFC3958 | Map domain name,      |
   |             |              | (and    | ]        | name,           |
   |             |              | NAPTR?) |          | application     |
   |             |              | NAPTR         |          | service name, and   |
   |             |              | ?)         |          | and application |
   |             |              |         |          | protocol        |
   |             |              |         |          | dynamically to  |
   |             |              |         |          | target server and   |
   |             |              |         |          | and port        |
   | Kerberos    | _kerberos    | "SRV" SRV     | [RFC4120] [RFC4120 | purpose         |
   |             |              |         | ]        |                 |
   | PKI         | _pkixrep     | "SRV" SRV     | [RFC4386] [RFC4386 | Enables         |
   |             |              |         | ]        | certificate-    |
   |             | certificate-using              |         |          | using systems   |
   |             |              |         |          | systems to locate PKI   |
   |             |              |         |          | PKI repositories    |
   | Certificat Certificate | _certificate | "SRV" SRV     | [RFC4387] [RFC4387 | Obtain          |
   | es s           | s            |         | ]        | certificates and    |
   |             |              |         |          | and certificate |
   |             |              |         |          | revocation lists      |
   |             |              |         |          | lists (CRLs)    |
   |             |              |         |          | from PKI        |
   |             |              |         |          | repositories    |
   | PGP Key     | _pgpkeys     | "SRV" SRV     | [RFC4387] [RFC4387 | Obtain          |
   | Store       |              |         | ]        | certificates and    |
   |             |              |         |          | and certificate |
   |             |              |         |          | revocation lists      |
   |             |              |         |          | lists (CRLs)    |
   |             |              |         |          | from PKI        |
   |             |              |         |          | repositories    |
   | MSRP Relay  | _msrp        | "SRV" SRV     | [RFC4976] [RFC4976 | purpose         |
   | Locator     |              |         | ]        |                 |
   | Mobile IPv6 | _mip6        | "SRV" SRV     | [RFC5026] [RFC5026 | Bootstrap Mobile       |
   | IPv6 Bootstrap   |              |         | [RFC5555] ] [RFC55 | Mobile IPv6     |
   |             |              |         | 55]      | Home Agent      |
   | Bootstrap             |              |         |          | information     |
   |             |              |         |          | from non-       |
   |             |              |         |          | non-topological topological     |
   |             |              |         |          | information     |
   | Digital     | _dvbservdsc  | "SRV" SRV     | [RFC5328] [RFC5328 | Discover non-   |
   | Video Broa Broad |              |         | ]        | default DVB entry     |
   | dcasting casting     |              |         |          | entry points    |
   |             |              |         |          | addresses       |
   | CAPWAP AC   | _capwap-     | rrs     | [RFC5415] [RFC5415 | Discover the    |
   |             | control      |         | ]        | CAPWAP AC       |
   |             |              |         |          | address(es)     |
   | IEEE 802.21 | _mihis       | NAPTR NAPTR,  | [RFC5679] [RFC5679 | Discovering     |
   | 802.21 Mobility    |              | , SRV     | ]        | servers that    |
   | Mobility             |              | "SRV"         |          | provide IEEE    |
   |             |              |         |          | 802.21-defined  |
   |             |              |         |          | Mobility        |
   |             |              |         |          | Services        |
   | STUN Clien Client | _stun        | "SRV" SRV     | [RFC5389] [RFC5389 | Find a STUN     |
   | t/Server /Server     |              |         | ]        | server          |
   | TURN        | _turn        | "SRV" SRV     | [RFC5766] [RFC5766 | Control the     |
   |             |              |         | [RFC5928] ] [RFC59 | operation of a  |
   |             |              |         | 28]      | relay to bypass |
   |             |              |         |          | NAT             |
   | STUN NAT    | _stun-       | "SRV" SRV     | [RFC5780] [RFC5780 | Discover the    |
   | Behavior    | behavior     |         | ]        | presence and    |
   | Discovery   |              |         |          | current behavior         |
   |             |              |         |          | behavior of     |
   |             |              |         |          | NATs and        |
   |             |              |         |          | firewalls between       |
   |             |              |         |          | between the STUN client     |
   |             |              |         |          | and the STUN client and |
   |             |              |         |          | the STUN server |
   | Sieve       | _sieve       | "SRV" SRV     | [RFC5804] [RFC5804 | Manage Sieve    |
   | Management  |              |         | ]        | scripts on a    |
   |             |              |         |          | remote server   |
   | AFS VLDB    | _afs3-vlserv | "SRV" SRV     | [RFC5864] [RFC5864 | Locate services |
   |             | er           |         | ]        | for the AFS     |
   |             |              |         |          | distributed file     |
   |             |              |         |          | file system     |
   | AFS PTS     | _afs3-prserv | "SRV" SRV     | [RFC5864] [RFC5864 | Locate services |
   |             | er           |         | ]        | for the AFS     |
   |             |              |         |          | distributed file     |
   |             |              |         |          | file system     |
   | Mail MSA    | _submission  | "SRV" SRV     | [RFC6186] [RFC6186 | Locate email    |
   | Submission  |              |         | ]        | services        |
   | IMAP        | _imap        | "SRV" SRV     | [RFC6186] [RFC6186 | Locate email    |
   |             |              |         | ]        | services        |
   | POP         | _pop3        | "SRV" SRV     | [RFC6186] [RFC6186 | Locate email    |
   |             |              |         | ]        | services        |
   | POP TLS     | _pop3s       | "SRV" SRV     | [RFC6186] [RFC6186 | Locate email    |
   |             |              |         | ]        | services        |
   +------------+--------------+-------+-----------+-------------------+
   +-------------+--------------+---------+----------+-----------------+

          Table 1: DNS Global 2: Underscore Scoped Entry Registry (with initial
                                  values)

6.  Related and Updated Registries

      This section needs to contained details specification of the
      updates to existing underscore "registries", in order to have
      those specifications point to this new registry.

   Numerous specifications have defined their own, independent
   registries for use of underscore names.  It is likely that adoption
   of the proposed, integrated registry should render these piecemeal
   registries obsolete

   Registries that are candidates for replacement include:

      Instant Messaging "SRV" Protocol Label Registry

      Public Key Infrastructure using X.509 (PKIX) Parameters

      Presence "SRV" Protocol Label 2d-Level Registry

7. (initial entries)

4.  Security Considerations

   This memo raises no security issues.

8.

5.  References

8.1.

5.1.  Normative References

   [RFC5226]  Narten, T.

   [RFC8126]  Cotton, M., Leiba, B., and H. Alvestrand, T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", RFC 5226, May 2008.

8.2. 8126,
              June 2017.

5.2.  References -- Informative

   [RFC0974]  Partridge, C., "Mail routing

   [IANA]     M. Cotton, B. Leiba, and the domain system",
              RFC 974, January 1986. T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", I-D
              draft-leiba-cotton-iana-5226bis-11, 2017.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [RFC3263]  Rosenberg, J. and H. Schulzrinne, "Session Initiation
              Protocol (SIP): Locating SIP Servers", RFC 3263, June
              2002.

   [RFC3404]  MMealling,  Mealling, M., "Dynamic Delegation Discovery System (DDDS)
              Part Four: The Uniform Resource Identifiers (URI)
              Resolution Application", RFC 3404, October 2002.

   [RFC3529]  Harold, W., "Using Extensible Markup Language-Remote
              Procedure Calling (XML-RPC) in Blocks Extensible Exchange
              Protocol (BEEP)", RFC 3529, April 2003.

   [RFC3620]  New, D., "The TUNNEL Profile", RFC 3620, October 2003.

   [RFC3832]  Columbia University, Columbia University, Sun
              Microsystems, IBM, and IBM, "Remote Service Discovery in
              the Service Location Protocol (SLP) via DNS SRV",
              RFC 3832, July 2004.

   [RFC3887]  "Message Tracking Query Protocol", RFC 3887, September
              2007.

   [RFC3958]  Daigle, L. and A. Newton, "Domain-Based Application
              Service Location Using SRV RRs and the Dynamic Delegation
              Discovery Service (DDDS)", RFC 3958, January 2005.

   [RFC4120]  USC-ISI, MIT, MIT, and MIT, "The Kerberos Network
              Authentication Service (V5)", RFC 4120, July 2005.

   [RFC4227]  O'Tuathail, E. and M. Rose, "Using the Simple Object
              Access Protocol (SOAP) in Blocks Extensible Exchange
              Protocol (BEEP)", RFC 4227, January 2006.

   [RFC4386]  Boeyen, S. and P. Hallam-Baker, "Internet X.509 Public Key
              Infrastructure: Repository Locator Service", RFC 4386,
              February 2006.

   [RFC4387]  Gutmann, P., Ed., "Internet X.509 Public Key
              Infrastructure Operational Protocols: Certificate Store
              Access via HTTP", RFC 4387, February 2006.

   [RFC4976]  Jennings, C., Mahy, R., and Roach, "Relay Extensions for
              the Message Session Relay Protocol (MSRP)", RFC 4976,
              September 2007.

   [RFC5026]  Giaretta, G., Ed., Kempf, J., and V. Devarapalli, Ed.,
              "Mobile IPv6 Bootstrapping in Split Scenario", RFC 5026,
              October 2007.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              Oct 2008.

   [RFC5328]  Adolf, A. and P. MacAvock, "A Uniform Resource Name (URN)
              Namespace for the Digital Video Broadcasting Project
              (DVB)", RFC 5328, September 2008.

   [RFC5389]  Rosenberg, , Mahy, , Matthews, , and Wing, "Session Traversal
              Utilities for NAT (STUN)", RFC 5389, October 2008.

   [RFC5415]  Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
              Ed., "Control And Provisioning of Wireless Access Points
              (CAPWAP) Protocol Specification", RFC 5415, March 2009.

   [RFC5507]  Faltstrom, P., Ed. and R. Austein, Ed., "Design Choices
              When Expanding the DNS", RFC 5507, April 2009.

   [RFC5518]  Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
              Reference", RFC 5518, April 2009.

   [RFC5555]  Soliman, H., Ed., "Mobile IPv6 Support for Dual Stack
              Hosts and Routers", RFC 5555, June 2009.

   [RFC5679]  Bajko, G., "Locating IEEE 802.21 Mobility Services Using
              DNS", RFC 5679, December 2009.

   [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, April 2010.

   [RFC5780]  MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
              Using Session Traversal Utilities for NAT (STUN)",
              RFC 5780, May 2010.

   [RFC5804]  Melnikov, A., Ed. and T. Martin, "A Protocol for Remotely
              Managing Sieve Scripts", RFC 5804, July 2010.

   [RFC5864]  Allbery, R., "NS SRV Resource Records for AFS", RFC 5864,
              April 2010.

   [RFC5928]  Petit-Huguenin, M., "Traversal Using Relays around NAT
              (TURN) Resolution Mechanism", RFC 5928, August 2010.

   [RFC6011]  Lawrence, S., Ed. and J. Elwell, "Session Initiation
              Protocol (SIP) User Agent Configuration", RFC 6011,
              October 2010.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, March 2011.

   [RFC6186]  Daboo, C., "Use of SRV Records for Locating Email
              Submission/Access Services", RFC 6186, March 2011.

   [RFC6376]  Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys
              Identified Mail (DKIM) Signatures", RFC 6376, Sept 2011.

   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", RFC 6733, October 2012.

   [RFC7372]

   [RFC7208]  Kitterman, S., "Sender Policy Framework (SPF) for
              Authorizing Use of Domains in E-Mail, Version 1",
              RFC 7372, 7208, April 2014.

   [RFC7553]  Falstrom, P. and O. Kolkman, "The Uniform Resource
              Identifier (URI) DNS Resource Record", RFC RFC7553, 7553,
              ISSN 2070-1721, June 2015.

8.3.

5.3.  URIs

   [1] mailto:dnsop@ietf.org

Appendix A.  Acknowledgements

   Thanks go to Bill Fenner, Tony Hansen, Peter Koch, Olaf Kolkman, and
   Andrew Sullivan for diligent review of the (much) earlier drafts.
   For the later enhancements, thanks to: Tim Wicinski, John Levine, Stephane Bortzmeyer, Bob
   Harold, John Levine, Joel Jaeggli, Petr &#352;pa&#269;ek, Ond&#345;ej Sury
   Sur&#345;, Tim Wicinski, and Paul Wouters.

   Special thanks to Ray Bellis for more than 10 12 years of 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/