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Versions: (draft-crocker-dns-attrleaf) 00 01 02

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


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

Abstract

   Formally, any DNS "RR" may occur for any domain name.  However some
   services have defined an operational convention that applies to DNS
   leaf nodes that have a reserved node name, beginning with an
   underscore.  The underscore construct is used to define a semantic
   scope for DNS records that are associated with the parent domain.
   This specification explores the nature of this DNS usage and defines
   the "DNS Global Underscore Scoped Entry Registry" registry with IANA.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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

Copyright Notice

   Copyright (c) 2017 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
   (http://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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Scaling Benefits and TXT and SRV Resource Records . . . . . .   3
   3.  DNS Global Underscore Scoped Entry Registry Function  . . . .   4
   4.  DNS Global Underscore Scoped Entry Registry Definition  . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Related and Updated Registries  . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  References -- Informative . . . . . . . . . . . . . . . .   9
     8.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The core 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.  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
   semantics have been limited to the specification of particular
   resource records, on the expectation that new ones would be added as
   needed.

   As an alternative to defining new RRs, some DNS service enhancements
   reuse an existing resource record, but have specified 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 a distinguished naming convention: It uses
   a reserved DNS node name that begins 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 that are associated
   with the parent domain, one level up.

   One example is the "SRV" record [RFC2782] which generalizes concepts
   long-used for email routing by the "MX" record [RFC0974][RFC5321].
   An equivalent usage to "SRV" is the "URI" "RR" [RFC7553].  Relying on



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   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".  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.  With underscore-based scoping, only the
   relevant "RR"s are returned.

   This specification discusses the underscore "attribute" enhancement,
   provides an explicit definition of it, and establishes an IANA
   registry for the highest-level reserved names that begin with
   _underscore; underscore-based names that are farther down the
   hierarchy is 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.  Scaling Benefits and TXT and SRV 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" and "SRV" records are notable examples.
   Used freely, some of these approaches 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 an underscore-based name, at a defined place
   in the DNS tree, so as to constrain to particular uses for 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 of "TXT" records, different uses have developed largely
   without coordination.  One side-effect is that there is no



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   consistently distinguishable internal syntax for the record; even the
   inefficiencies of internal inspection might not provide a reliable
   means of distinguishing among the different uses.  Underscore-based
   names therefore define 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 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 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, 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 to define scope of use for specific
   resource records.  A given name defines a specific, constrained
   context for the use of such records.  Within this scope, use of other
   resource records that are not specified is permitted.  The purpose of
   the Underscore registry is to avoid collisions resulting from the use
   of the same underscore-based name, for different applications.

   Structurally, the registry is defined as a single, flat table of
   names that begin with underscore.  In some cases, such as for "SRV",
   an underscore name might be multi-part, as a sequence of underscore
   names.  Semantically, that sequence represents a hierarchical model
   and it is theoretically reasonable to allow re-use of an underscore
   name in different underscore context; a subordinate name is
   meaningful only within the scope of the first (parent) underscore
   name.  As such, they can be ignored by this DNS Global Underscore
   Scoped Entry Registry.  That is, the registry is for the definition
   of highest-level underscore node name used.

                                   +---+







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                      +----------------------------+
                      |                       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
   table.  Definition and registration of the subordinate names is the
   responsibility of the specification that creates the highest-level
   (right-most) registry entry.

4.  DNS Global Underscore Scoped Entry Registry Definition

   A registry entry contains:



      Name:    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:    Specifies a single _underscore name that defines a
         name reservation; 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.

      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.







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5.  IANA Considerations

   Per [RFC5226], IANA is requested to establish a DNS Global Underscore
   Scoped Entry Registry, for DNS node names that begin with the
   underscore character (_) and have been specified in any published
   RFC, or are documented by a specification published by another
   standards organization.  The contents of each entry are defined in
   Section 4.

   Initial entries in the registry are:

      { Enhancement of this table to include all underscore name
      reservations in effect at the time this document is published is
      left as an exercise to the readers... /d }

   +------------+--------------+-------+-----------+-------------------+
   | NAME       | LABEL        | RR    | REFERENCE | PURPOSE           |
   +------------+--------------+-------+-----------+-------------------+
   | "SRV"      | _srv         | "SRV" | [RFC2782] | "SRV" template -- |
   |            |              |       |           | pro forma entry,  |
   |            |              |       |           | not directly      |
   |            |              |       |           | usable            |
   | "SRV" TCP  | _tcp         | "SRV" | [RFC2782] | Use of "SRV" for  |
   |            |              |       |           | a TCP-based       |
   |            |              |       |           | service           |
   | "SRV" UDP  | _udp         | "SRV" | [RFC2782] | Use of "SRV" for  |
   |            |              |       |           | a UDP-based       |
   |            |              |       |           | service           |
   | LDAP       | _ldap        | "SRV" | [RFC2782] | LDAP server       |
   | SIP        | _sip         | NAPTR | [RFC3263] | Locating SIP      |
   |            |              |       | [RFC6011] | Servers and UA    |
   |            |              |       |           | configuration     |
   | SPF        | _spf         | "TXT" | [RFC7372] | Authorized IP     |
   |            |              |       |           | addresses for     |
   |            |              |       |           | sending mail      |
   | DKIM       | _domainkey   | "TXT" | [RFC6376] | Public key for    |
   |            |              |       |           | verifying DKIM    |
   |            |              |       |           | signature.        |
   | PKI LDAP   | _PKIXREP     | "SRV" | [RFC4386] | PKI Repository    |
   | VBR        | _vouch       | "TXT" | [RFC5518] | Vouch-by-         |
   |            |              |       |           | refererence       |
   |            |              |       |           | domain assertion  |
   | DDDS       | --???!--     | "SRV" | [RFC3404] | Mapping DDDS      |
   |            |              |       |           | query to DNS      |
   |            |              |       |           | records           |
   | SOAP BEEP  | _soap-beep   | "SRV" | [RFC4227] | SOAP over BEEP    |
   |            |              |       |           | lookup, when no   |
   |            |              |       |           | port specified    |



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   | XMLRPC     | _xmlrpc-beep | "SRV" | [RFC3529] | Resolve url for   |
   | BEEP       |              |       |           | XML-RPC using     |
   |            |              |       |           | BEEP              |
   | Diameter   | _diameter    | "SRV" | [RFC6733] | Diameter          |
   |            |              |       |           | rendezvous        |
   | Tunnel     | _tunnel      | "SRV" | [RFC3620] | Finding the       |
   |            |              |       |           | appropriate       |
   |            |              |       |           | address for       |
   |            |              |       |           | tunneling into a  |
   |            |              |       |           | particular domain |
   | SLP        | _slpda       | "SRV" | [RFC3832] | Discovering       |
   |            |              |       |           | desired services  |
   |            |              |       |           | in given DNS      |
   |            |              |       |           | domains           |
   | Msg Track  | _mtqp        | "SRV" | [RFC3887] | Assist in         |
   |            |              |       |           | determining the   |
   |            |              |       |           | path that a       |
   |            |              |       |           | particular        |
   |            |              |       |           | message has taken |
   |            |              |       |           | through a         |
   |            |              |       |           | messaging system  |
   | XMPP       | _xmpp-client | "SRV" | [RFC6120] | XMPP client       |
   | Client     |              |       |           | lookup of server  |
   | XMPP       | _xmpp-server | "SRV" | [RFC6120] | XMPP server-      |
   | Server     |              |       |           | server lookup     |
   | DDDS "SRV" | _???         | "SRV" | [RFC3958] | Map domain name,  |
   |            |              | (and  |           | application       |
   |            |              | NAPTR |           | service name, and |
   |            |              | ?)    |           | application       |
   |            |              |       |           | protocol          |
   |            |              |       |           | dynamically to    |
   |            |              |       |           | target server and |
   |            |              |       |           | port              |
   | Kerberos   | _kerberos    | "SRV" | [RFC4120] | purpose           |
   | PKI        | _pkixrep     | "SRV" | [RFC4386] | Enables           |
   |            |              |       |           | certificate-using |
   |            |              |       |           | systems to locate |
   |            |              |       |           | PKI repositories  |
   | Certificat | _certificate | "SRV" | [RFC4387] | Obtain            |
   | es         | s            |       |           | certificates and  |
   |            |              |       |           | certificate       |
   |            |              |       |           | revocation lists  |
   |            |              |       |           | (CRLs) from PKI   |
   |            |              |       |           | repositories      |
   | PGP Key    | _pgpkeys     | "SRV" | [RFC4387] | Obtain            |
   | Store      |              |       |           | certificates and  |
   |            |              |       |           | certificate       |
   |            |              |       |           | revocation lists  |



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   |            |              |       |           | (CRLs) from PKI   |
   |            |              |       |           | repositories      |
   | MSRP Relay | _msrp        | "SRV" | [RFC4976] | purpose           |
   | Locator    |              |       |           |                   |
   | Mobile     | _mip6        | "SRV" | [RFC5026] | Bootstrap Mobile  |
   | IPv6       |              |       | [RFC5555] | IPv6 Home Agent   |
   | Bootstrap  |              |       |           | information from  |
   |            |              |       |           | non-topological   |
   |            |              |       |           | information       |
   | Digital    | _dvbservdsc  | "SRV" | [RFC5328] | Discover non-     |
   | Video Broa |              |       |           | default DVB entry |
   | dcasting   |              |       |           | points addresses  |
   | CAPWAP AC  | _capwap-     | rrs   | [RFC5415] | Discover the      |
   |            | control      |       |           | CAPWAP AC         |
   |            |              |       |           | address(es)       |
   | IEEE       | _mihis       | NAPTR | [RFC5679] | Discovering       |
   | 802.21     |              | ,     |           | servers that      |
   | Mobility   |              | "SRV" |           | provide IEEE      |
   |            |              |       |           | 802.21-defined    |
   |            |              |       |           | Mobility Services |
   | STUN Clien | _stun        | "SRV" | [RFC5389] | Find a STUN       |
   | t/Server   |              |       |           | server            |
   | TURN       | _turn        | "SRV" | [RFC5766] | Control the       |
   |            |              |       | [RFC5928] | operation of a    |
   |            |              |       |           | relay to bypass   |
   |            |              |       |           | NAT               |
   | STUN NAT   | _stun-       | "SRV" | [RFC5780] | Discover the      |
   | Behavior   | behavior     |       |           | presence and      |
   | Discovery  |              |       |           | current behavior  |
   |            |              |       |           | of NATs and       |
   |            |              |       |           | firewalls between |
   |            |              |       |           | the STUN client   |
   |            |              |       |           | and the STUN      |
   |            |              |       |           | server            |
   | Sieve      | _sieve       | "SRV" | [RFC5804] | Manage Sieve      |
   | Management |              |       |           | scripts on a      |
   |            |              |       |           | remote server     |
   | AFS VLDB   | _afs3-vlserv | "SRV" | [RFC5864] | Locate services   |
   |            | er           |       |           | for the AFS       |
   |            |              |       |           | distributed file  |
   |            |              |       |           | system            |
   | AFS PTS    | _afs3-prserv | "SRV" | [RFC5864] | Locate services   |
   |            | er           |       |           | for the AFS       |
   |            |              |       |           | distributed file  |
   |            |              |       |           | system            |
   | Mail MSA   | _submission  | "SRV" | [RFC6186] | Locate email      |
   | Submission |              |       |           | services          |
   | IMAP       | _imap        | "SRV" | [RFC6186] | Locate email      |



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   |            |              |       |           | services          |
   | POP        | _pop3        | "SRV" | [RFC6186] | Locate email      |
   |            |              |       |           | services          |
   | POP TLS    | _pop3s       | "SRV" | [RFC6186] | Locate email      |
   |            |              |       |           | services          |
   +------------+--------------+-------+-----------+-------------------+

    Table 1: DNS Global 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 Registry

7.  Security Considerations

   This memo raises no security issues.

8.  References

8.1.  Normative References

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226, May 2008.

8.2.  References -- Informative

   [RFC0974]  Partridge, C., "Mail routing and the domain system",
              RFC 974, January 1986.

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




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   [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, 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.



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   [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.




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

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

8.3.  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, Bob
   Harold, Joel Jaeggli, Ond&#345;ej Sury and Paul Wouters.  Special
   thanks to Ray Bellis for more than 10 years of persistent
   encouragement to continue this effort, as well as the suggestion for
   an essential simplification to the registration model.

Author's Address












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   Dave Crocker
   Brandenburg InternetWorking
   675 Spruce Dr.
   Sunnyvale, CA  94086
   USA

   Phone: +1.408.246.8253
   Email: dcrocker@bbiw.net
   URI:   http://bbiw.net/










































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