Network Working Group                                         D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Intended status: BCP                                    October 14, 2011
Expires: April 16, 2012


                DNS Scoped Data Through Attribute Leaves
                     draft-crocker-dns-attrleaf-06

Abstract

   Historically, any DNS RR may occur for any domain name.  Recent
   additions have defined DNS leaf nodes that contain a reserved node
   name, beginning with an underscore.  The underscore construct is used
   to define a semantic scope for DNS records associated with the parent
   domain.  This note explores the nature of this DNS usage and defines
   the "underscore names" 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 April 16, 2012.

Copyright Notice

   Copyright (c) 2011 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
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Scaling Benefits and TXT and SRV Resource Records  . . . . . .  4
   3.  Underscore DNS          Registry Function  . . . . . . . . . .  4
   4.  DNS Underscore Registry Definition . . . . . . . . . . . . . .  5
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   6.  Related Registries . . . . . . . . . . . . . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     8.2.  References -- Informative  . . . . . . . . . . . . . . . . 13
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 16
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16


































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1.  Introduction

   The core DNS technical specifications assign no semantics to domain
   names or their parts, and no constraints upon which resource records
   (RRs) may 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.

   Some recent service enhancements have defined a restricted scope for
   the occurrence of particular resource records.  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 host names are not allowed to use the
   underscore character, this distinguishes the name from all legal host
   name.  Effectively, this convention creates a space for attributes
   that are associated with the parent domain, one level up.

   An established example is the SRV record [RFC2782] which generalizes
   concepts long-used for email routing by the MX record
   [RFC0974][RFC2821].  The use of 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 and SRV.  It provides efficient
   separation of one use of them from another.  Absent this separation,
   an undifferentiated mass of these RRs are returned to the client
   which then must parse through the internals of the records in the
   hope of finding ones that are relevant.  With underscore-based
   scoping, only the relevant RRs are returns.

   This specification discusses the underscore "attribute" enhancement,
   provides an explicit definition of it, and establishes an IANA
   registry for the reserved names that begin with underscore.






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   Discussion Venue:   Discussion about this draft is directed to the
      dnsop@lists.uoregon.edu [1] mailing list of the IETF DNSOP Working
      Group [2].


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 the 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 to a define place in the
   DNS that is constrained to particular uses for particular RRs.  This
   means that a direct lookup produces only the desired records, at no
   greater cost than a typical lookup.

   In the case of TXT records, different uses have developed largely
   without coordination.  One side-effect is that there is no
   consistently distinguishable internal syntax for the record; even
   internal inspection might not be a reliable means of distinguishing
   among the different uses.  Underscore-based names therefore provide
   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 distinguishing among different types of use
   was part of the design.  [RFC2782] The SRV specification serves as a
   template, defining an RR that may only be used for specific
   applications when there is an additional specification.  The template
   definition includes reference to tables of names from which
   underscore-names should be drawn.  The set of <service> names is
   defined in terms of other IANA tables, namely any table with symbolic
   names.  The other SRV naming field is <proto>, although its pool of
   names is not explicitly defined.


3.  Underscore DNS          Registry Function

   This specification defines a registry for DNS nodes names, used to
   define scope of use for specific resource records (RR).  A given name
   defines a specific, constrained context for the use of such records.
   This does not constrain the use of other resource records that are
   not specified.  The purpose of the registry is to avoid collisions
   resulting from the use of the same underscore name, for different
   applications.



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   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 names.
   Semantically, this is a hierarchical model, thereby making a flat
   registry unexpected.

   The registry requires such hierarchies to be registered as a
   combinatorial case analysis set, with each entry being a full
   sequence of underscore names.  Given a scheme that is actually
   structured, this flat design is inelegant.  However it has the
   benefit of being extremely simple, with the added advantage of being
   easier for readers to understand, as long as these cases are small
   and few.

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

                        Example of Underscore Names

   The flat registry design:

   o  provides significantly simpler administration than is needed for
      hierarchical tables, simples, and

   o  is significantly simpler for readers to understand and is likely
      to produce fewer programming or administration errors.


4.  DNS Underscore Registry Definition

   A registry entry MUST contain:



      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.





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      DNS Label(s):   Specifies a sequence of one or more underscore
         names that define a single name reservation.

      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.


5.  IANA Considerations

   Per [RFC2434], IANA is requested to establish a DNS Underscore Name
   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.

   +----------+--------------+--------+------+---------+---------------+
   | NAME     | DNS LABEL    | CONSTR | RR(s | REFEREN | PURPOSE       |
   |          |              | AINTS  | )    | CES     |               |
   +----------+--------------+--------+------+---------+---------------+
   | SRV TCP  | _srv._tcp    |        | SRV  | [RFC278 | SRV template  |
   |          |              |        |      | 2]      |               |
   | SRV UDP  | _srv._udp    |        | SRV  | [RFC278 | SRV template  |
   |          |              |        |      | 2]      |               |
   | LDAP SRV | _ldap._tcp   |        | SRV  | [RFC278 | LDAP server   |
   |          |              |        |      | 2]      |               |
   | SIP TCP  | _sip._tcp    |        | NAPT | [RFC326 | Locating SIP  |
   |          |              |        | R    | 3],     | Servers and   |
   |          |              |        |      |  [RFC60 | UA            |
   |          |              |        |      | 11]     | configuration |
   | SIPS TCP | _sips._tcp   |        | NAPT | [RFC326 | Locating SIP  |
   |          |              |        | R    | 3],     | Servers and   |
   |          |              |        |      |  [RFC60 | UA            |
   |          |              |        |      | 11]     | configuration |
   | SIP UDP  | _sip._udp    |        | SRV  | [RFC326 | Locating SIP  |
   |          |              |        |      | 3],     | servers and   |
   |          |              |        |      |  [RFC60 | UA            |
   |          |              |        |      | 11]     | configuration |
   | SPF      | _spf         |        | TXT  | [RFC440 | Authorized IP |
   |          |              |        |      | 8]      | addresses for |
   |          |              |        |      |         | sending mail  |



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   | DKIM     | _domainkey   |        | TXT  | [RFC487 | Public key    |
   |          |              |        |      | 1]      | for verifying |
   |          |              |        |      |         | DKIM          |
   |          |              |        |      |         | signature.    |
   | ADSP     | _adsp._domai |        | TXT  | [RFC561 | Published     |
   |          | nkey         |        |      | 7]      | DKIM usage    |
   |          |              |        |      |         | practices     |
   | PKI LDAP | _PKIXREP._ld |        | SRV  | [RFC438 | LDAP PKI      |
   |          | ap           |        |      | 6]      | Repository    |
   | PKI HTTP | _PKIXREP._ht |        | SRV  | [RFC438 | HTTP PKI      |
   |          | tp           |        |      | 6]      | Repository    |
   | PKI OCSP | _PKIXREP._oc |        | SRV  | [RFC438 | OCSP PKI      |
   |          | sp           |        |      | 6]      | Repository    |
   | VBR      | _vouch       |        | TXT  | [RFC551 | Vouch-by-refe |
   |          |              |        |      | 8]      | rerence domai |
   |          |              |        |      |         | nassertion    |
   | DDDS     | --unknown!-- |        | SRV  | [RFC340 | Mapping DDDS  |
   |          |              |        |      | 4]      | query to DNS  |
   |          |              |        |      |         | records       |
   | SOAP     | _soap-beep._ |        | SRV  | [RFC422 | SOAP over     |
   | BEEP     | tcp          |        |      | 7]      | BEEP lookup,  |
   |          |              |        |      |         | when no port  |
   |          |              |        |      |         | specified     |
   | XMLRPC   | _xmlrpc-beep |        | SRV  | [RFC352 | Resolve url   |
   | BEEP     | ._tcp        |        |      | 9]      | for XML-RPC   |
   |          |              |        |      |         | using BEEP    |
   | Diameter | _diameter._s |        | SRV  | [RFC358 | Diameter      |
   | SCTP     | ctp          |        |      | 8]      | rendezvous    |
   |          |              |        |      |         | over SCTP     |
   | Diameter | _diameter._t |        | SRV  | [RFC358 | Diameter      |
   | TCP      | cp           |        |      | 8]      | rendezvous    |
   |          |              |        |      |         | over TCP      |
   | Tunnel   | _tunnel._tcp |        | SRV  | [RFC362 | Finding the   |
   |          |              |        |      | 0]      | appropriate   |
   |          |              |        |      |         | address for   |
   |          |              |        |      |         | tunneling     |
   |          |              |        |      |         | into a        |
   |          |              |        |      |         | particular    |
   |          |              |        |      |         | domain        |
   | SLP TCP  | _slpda._tcp  |        | SRV  | [RFC383 | Discovering   |
   |          |              |        |      | 2]      | desired       |
   |          |              |        |      |         | services in   |
   |          |              |        |      |         | given DNS     |
   |          |              |        |      |         | domains       |







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   | SLP UDP  | _slpda._udp  |        | SRV  | [RFC383 | Discovering   |
   |          |              |        |      | 2]      | desired       |
   |          |              |        |      |         | services in   |
   |          |              |        |      |         | given DNS     |
   |          |              |        |      |         | domains       |
   | IM       | _im          |        | SRV  | [RFC386 | Instant       |
   |          |              |        |      | 1]      | Messaging     |
   |          |              |        |      |         | address       |
   |          |              |        |      |         | resolution    |
   | Pres     | _pres        |        | SRV  | [RFC386 | Presence      |
   |          |              |        |      | 1]      | address       |
   |          |              |        |      |         | resolution    |
   | Msg      | _mtqp._tcp   |        | SRV  | [RFC388 | Assist in     |
   | Track    |              |        |      | 7]      | determining   |
   |          |              |        |      |         | the path that |
   |          |              |        |      |         | a particular  |
   |          |              |        |      |         | message has   |
   |          |              |        |      |         | taken through |
   |          |              |        |      |         | a messaging   |
   |          |              |        |      |         | system        |
   | XMPP     | _xmpp-client |        | SRV  | [RFC612 | XMPP client   |
   | Client   | ._tcp        |        |      | 0]      | lookup of     |
   |          |              |        |      |         | server        |
   | XMPP     | _xmpp-server |        | SRV  | [RFC612 | XMPP          |
   | Server   | ._tcp        |        |      | 0]      | server-server |
   |          |              |        |      |         | lookup        |
   | DDDS SRV | _???         | (unabl | SRV  | [RFC395 | Map domain    |
   |          |              | eto    | (and | 8]      | name,         |
   |          |              |  disce | NAPT |         | application   |
   |          |              | rn     | R?)  |         | service name, |
   |          |              |   deta |      |         | and           |
   |          |              | ils.   |      |         | application   |
   |          |              |    /dc |      |         | protocol      |
   |          |              | rocker |      |         | dynamically   |
   |          |              | )      |      |         | to target     |
   |          |              |        |      |         | server and    |
   |          |              |        |      |         | port          |
   | Kerberos | _kerberos._t |        | SRV  | [RFC412 | purpose       |
   | TCP      | cp           |        |      | 0]      |               |
   | Kerberos | _kerberos._u |        | SRV  | [RFC412 | purpose       |
   | UDP      | dp           |        |      | 0]      |               |
   | PKI LDAP | _pkixrep._ld |        | SRV  | [RFC438 | Enables       |
   |          | ap           |        |      | 6]      | certificate-u |
   |          |              |        |      |         | sing systems  |
   |          |              |        |      |         |  to locate PK |
   |          |              |        |      |         | Irepositories |





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   | PKI HTTP | _pkixrep._ht |        | SRV  | [RFC438 | Enables       |
   |          | tp           |        |      | 6]      | certificate-u |
   |          |              |        |      |         | sing systems  |
   |          |              |        |      |         |  to locate PK |
   |          |              |        |      |         | Irepositories |
   | PKI OCSP | _pkixrep._oc |        | SRV  | [RFC438 | Enables       |
   |          | sp           |        |      | 6]      | certificate-u |
   |          |              |        |      |         | sing systems  |
   |          |              |        |      |         |  to locate PK |
   |          |              |        |      |         | Irepositories |
   | Cert     | _certificate |        | SRV  | [RFC438 | Obtain        |
   | Store    | s._tcp       |        |      | 7]      | certificates  |
   |          |              |        |      |         | and           |
   |          |              |        |      |         | certificate   |
   |          |              |        |      |         | revocation    |
   |          |              |        |      |         | lists (CRLs)  |
   |          |              |        |      |         | from PKI      |
   |          |              |        |      |         | repositories  |
   | Cert     | _crls._tcp   |        | SRV  | [RFC438 | Obtain        |
   | Revocati |              |        |      | 7]      | certificates  |
   | on Store |              |        |      |         | and           |
   |          |              |        |      |         | certificate   |
   |          |              |        |      |         | revocation    |
   |          |              |        |      |         | lists (CRLs)  |
   |          |              |        |      |         | from PKI      |
   |          |              |        |      |         | repositories  |
   | PGP Key  | pgpkeys._tcp |        | SRV  | [RFC438 | Obtain        |
   | Store    |              |        |      | 7]      | certificates  |
   |          |              |        |      |         | and           |
   |          |              |        |      |         | certificate   |
   |          |              |        |      |         | revocation    |
   |          |              |        |      |         | lists (CRLs)  |
   |          |              |        |      |         | from PKI      |
   |          |              |        |      |         | repositories  |
   | MSRP     | _msrp._tcp   |        | SRV  | [RFC497 | purpose       |
   | Relay    |              |        |      | 6]      |               |
   | Locator  |              |        |      |         |               |
   | Mobile   | _mip6._ipv6  |        | SRV  | [RFC502 | Bootstrap     |
   | IPv6     |              |        |      | 6],     | Mobile IPv6   |
   | Bootstra |              |        |      |  [RFC55 | Home Agent    |
   | p        |              |        |      | 55]     | information   |
   |          |              |        |      |         | from          |
   |          |              |        |      |         | non-topologic |
   |          |              |        |      |         | al informatio |
   |          |              |        |      |         | n             |






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   | Digital  | _dvbservdsc. |        | SRV  | [RFC532 | Discover      |
   | Video    | _tcp         |        |      | 8]      | non-default   |
   | Broadcas |              |        |      |         | DVB entry     |
   | ting TCP |              |        |      |         | points        |
   |          |              |        |      |         | addresses     |
   | Digital  | _dvbservdsc. |        | SRV  | [RFC532 | Discover      |
   | Video    | _udp         |        |      | 8]      | non-default   |
   | Broadcas |              |        |      |         | DVB entry     |
   | ting UDP |              |        |      |         | points        |
   |          |              |        |      |         | addresses     |
   | CAPWAP   | _capwap-cont |        | rrs  | [RFC541 | Discover the  |
   | AC       | rol._udp     |        |      | 5]      | CAPWAP AC     |
   |          |              |        |      |         | address(es)   |
   | IM SIP   | _im._sip     |        | SRV  | [RFC550 | For resolving |
   |          |              |        |      | 9]      | Instant       |
   |          |              |        |      |         | Messaging and |
   |          |              |        |      |         | Presence      |
   |          |              |        |      |         | services with |
   |          |              |        |      |         | SIP           |
   | Pres SIP | _pres._sip   |        | SRV  | [RFC550 | For resolving |
   |          |              |        |      | 9]      | Instant       |
   |          |              |        |      |         | Messaging and |
   |          |              |        |      |         | Presence      |
   |          |              |        |      |         | services with |
   |          |              |        |      |         | SIP           |
   | IEEE     | _mihis._tcp  |        | NAPT | [RFC567 | Discovering   |
   | 802.21   |              |        | R,   | 9]      | servers that  |
   | Mobility |              |        |  SRV |         | provide IEEE  |
   | TCP      |              |        |      |         | 802.21-define |
   |          |              |        |      |         | dMobility     |
   |          |              |        |      |         |  Services     |
   | IEEE     | _mihis._udp  |        | NAPT | [RFC567 | Discovering   |
   | 802.21   |              |        | R,   | 9]      | servers that  |
   | Mobility |              |        |  SRV |         | provide IEEE  |
   | UDP      |              |        |      |         | 802.21-define |
   |          |              |        |      |         | dMobility     |
   |          |              |        |      |         |  Services     |
   | STUN     | _stun._.tcp  |        | SRV  | [RFC538 | Find a STUN   |
   | Client/S |              |        |      | 9]      | server        |
   | erver TC |              |        |      |         |               |
   | P        |              |        |      |         |               |
   | STUN     | _stun._.udp  |        | SRV  | [RFC538 | Find a STUN   |
   | Client/S |              |        |      | 9]      | server        |
   | erver UD |              |        |      |         |               |
   | P        |              |        |      |         |               |






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   | STUN     | _stuns._.tcp |        | SRV  | [RFC538 | Find a STUN   |
   | Client/S |              |        |      | 9]      | server        |
   | erver TL |              |        |      |         |               |
   | S        |              |        |      |         |               |
   | TURN TCP | _turn._tcp   |        | SRV  | [RFC576 | Control the   |
   |          |              |        |      | 6],     | operation of  |
   |          |              |        |      |  [RFC59 | a relay to    |
   |          |              |        |      | 28]     | bypass NAT    |
   | TURN UDP | _turn._udp   |        | SRV  | [RFC576 | Control the   |
   |          |              |        |      | 6],     | operation of  |
   |          |              |        |      |  [RFC59 | a relay to    |
   |          |              |        |      | 28]     | bypass NAT    |
   | TURN TLS | _turns._tcp  |        | SRV  | [RFC576 | Control the   |
   |          |              |        |      | 6],     | operation of  |
   |          |              |        |      |  [RFC59 | a relay to    |
   |          |              |        |      | 28]     | bypass NAT    |
   | STUN NAT | _stun-behavi |        | SRV  | [RFC578 | Discover the  |
   | Behavior | or._tcp      |        |      | 0]      | presence and  |
   | Discover |              |        |      |         | current       |
   | yTCP     |              |        |      |         | behavior of   |
   |          |              |        |      |         | NATs and      |
   |          |              |        |      |         | firewalls     |
   |          |              |        |      |         | between the   |
   |          |              |        |      |         | STUN client   |
   |          |              |        |      |         | and the STUN  |
   |          |              |        |      |         | server        |
   | STUN NAT | _stun-behavi |        | SRV  | [RFC578 | Discover the  |
   | Behavior | or._udp      |        |      | 0]      | presence and  |
   | Discover |              |        |      |         | current       |
   | yUDP     |              |        |      |         | behavior of   |
   |          |              |        |      |         | NATs and      |
   |          |              |        |      |         | firewalls     |
   |          |              |        |      |         | between the   |
   |          |              |        |      |         | STUN client   |
   |          |              |        |      |         | and the STUN  |
   |          |              |        |      |         | server        |
   | STUN NAT | _stun-behavi |        | SRV  | [RFC578 | Discover the  |
   | Behavior | ors._tcp     |        |      | 0]      | presence and  |
   | Discover |              |        |      |         | current       |
   | yTLS     |              |        |      |         | behavior of   |
   |          |              |        |      |         | NATs and      |
   |          |              |        |      |         | firewalls     |
   |          |              |        |      |         | between the   |
   |          |              |        |      |         | STUN client   |
   |          |              |        |      |         | and the STUN  |
   |          |              |        |      |         | server        |





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   | Sieve    | _sieve._tcp  |        | SRV  | [RFC580 | Manage Sieve  |
   | Manageme |              |        |      | 4]      | scripts on a  |
   | nt       |              |        |      |         | remote server |
   | AFS VLDB | _afs3-vlserv |        | SRV  | [RFC586 | Locate        |
   |          | er._udp      |        |      | 4]      | services for  |
   |          |              |        |      |         | the AFS       |
   |          |              |        |      |         | distributed   |
   |          |              |        |      |         | file system   |
   | AFS PTS  | _afs3-prserv |        | SRV  | [RFC586 | Locate        |
   |          | er._udp      |        |      | 4]      | services for  |
   |          |              |        |      |         | the AFS       |
   |          |              |        |      |         | distributed   |
   |          |              |        |      |         | file system   |
   | Mail MSA | _submission. |        | SRV  | [RFC618 | Locate email  |
   | Submissi | _tcp         |        |      | 6]      | services      |
   | on       |              |        |      |         |               |
   | IMAP     | _imap._tcp   |        | SRV  | [RFC618 | Locate email  |
   |          |              |        |      | 6]      | services      |
   | IMAP TLS | _imaps._tcp  |        | SRV  | [RFC618 | Locate email  |
   |          |              |        |      | 6]      | services      |
   | POP      | _pop3._tcp   |        | SRV  | [RFC618 | Locate email  |
   |          |              |        |      | 6]      | services      |
   | POP TLS  | _pop3s._tcp  |        | SRV  | [RFC618 | Locate email  |
   |          |              |        |      | 6]      | services      |
   +----------+--------------+--------+------+---------+---------------+

     Table 1: DNS Underscore SCOPE Name Registry                 (with
                              initial values)


6.  Related Registries

   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







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7.  Security Considerations

   This memo raises no security issues.


8.  References

8.1.  Normative References

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 2434,
              October 1998.

8.2.  References -- Informative

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

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

   [RFC2821]  Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
              April 2001.

   [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.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", September 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",
              July 2004.

   [RFC3861]  Peterson, J., "Address Resolution for Instant Messaging



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              and Presence", RFC 3861, August 2004.

   [RFC3887]  "Message Tracking Query Protocol", 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",
              February 2006.

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

   [RFC4408]  Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
              for Authorizing Use of Domains in E-Mail, Version 1",
              RFC 4408, April 2006.

   [RFC4871]  Allman, E., Callas, J., Delany, M., Libbey, M., Fenton,
              J., and M. Thomas, "DomainKeys Identified Mail (DKIM)
              Signatures", RFC 4871, May 2007.

   [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.

   [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



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              (CAPWAP) Protocol Specification", RFC 5415, March 2009.

   [RFC5507]  Faltstrom, P., Ed. and R. Austein, Ed., "", RFC 5507,
              April 2009.

   [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,
              April 2009.

   [RFC5518]  Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
              Reference", RFC5 5518, April 2009.

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

   [RFC5617]  Sendmail, Inc., Cisco Systems, Inc., Yahoo! Inc., and
              Taughannock Networks, "DomainKeys Identified Mail (DKIM)
              Author Domain Signing Practices (ADSP)", August 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



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              Submission/Access Services", RFC 6186, March 2011.

URIs

   [1]  <mailto:dnsop@lists.uoregon.edu>

   [2]  <http://ietf.org/html.charters/dnsop-charter.html>


Appendix A.  Acknowledgements

   Thanks go to Bill Fenner, Tony Hansen, Peter Koch, Olaf Kolkman, and
   Andrew Sullivan for diligent review of the earlier drafts.


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/

























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