Network Working Group                                         D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Expires: December 27, 2006                                 June 25, 2006


                DNS Scoped Data Through Attribute Leaves
                     draft-crocker-dns-attrleaf-01

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Copyright Notice

   Copyright (C) The Internet Society (2006).

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 the name, within which the choice of
   valid RRs is limited to a defined set.  Hence the underscore
   construct defines a basic paradigm modification to the DNS.  This
   note explores the nature of this DNS usage and defines the procedures
   for registering new "underscore names" with IANA.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   5.  References -- Informative . . . . . . . . . . . . . . . . . . . 4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 7









































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1.  Introduction

   Historically, any DNS RR may occur for any domain name.  The DNS
   technical specification assigns no semantics to domain names and no
   constraints upon which resource records may be associated with a
   particular name.  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 semantics.
   This freedom in the basic technology has permitted a wide range of
   administrative and semantic policies to be used -- in parallel --
   with the DNS.  In the DNS data semantics have been limited to
   specifications for specific resource records, on the expectation that
   new ones would be added as needed.  Although there remains an
   expectation that this method of enhancement is preferred, alternative
   approaches have been explored.

   Recent additions have defined DNS leaves that contain a reserved leaf
   node name, beginning with an underscore.  The underscore construct is
   used to define a semantic scope for the name, within which the choice
   of valid RRs is limited to a defined set.  Hence the underscore
   construct defines a basic paradigm modification to the DNS.  Within
   the scope of a defined underscore leaf, the specific uses of specific
   resource records can be formally defined and constrained.  An
   established example is the SRV record,[RFC2782] which generalizes
   concepts long-used for email routing in the MX
   record.[RFC0974][RFC2821] The use of special DNS names has
   significant benefits and detriments.  Some of these are explored in
   [I-D.iab-dns-choices].

   One use that has perhaps not been noticed is that the underscore
   construct substantially changes possible concerns for scaling
   effects.  For example, different uses for the same RR, such as the
   free-form TXT record, become manageable when those are defined to be
   within different, scoped leaf nodes.

   This note disusses this enhancement, provides an explicit definition
   of it, and establishes an IANA registry for the reserved names
   beginning with underscore.


2.  Procedure

   NOTE:  This procedure is modeled after that specified in [RFC2489]

   The author of a new DHCP option will follow these steps to obtain
   approval for the option and publication of the specification of the
   option as an RFC:




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   1.  The author devises the new option.

   2.  The author documents the new option as an Internet Draft,
       choosing a node name that has not yet been registered.

   3.  The author submits the Internet Draft for publication as an RFC,
       either as an independent submission or as an IETF-approved
       document.

   4.  The specification of the new option is reviewed for publication
       by the appropriate bodies.

   5.  At the time of publication as an RFC, IANA formally lists the
       node name.


3.  Security Considerations

   This memo raises no security issues


4.  IANA Considerations

   IANA is requested to establish the DNS Underscore Name Registry, for
   DNS node names that begin with the underscore character and have been
   specified in any published RFC.

   Initial entries in the registry comprise:

                           NAME                RFC
                           ==============     ========
                           _<service>         rfc2782
                           _<proto>           rfc2782

   NOTE:  In the case of RFC2782, the set of <service> names is defined
      in terms of other IANA tables, namely any table with symbolic
      names.  Even more problematic is that the set of <proto> names is
      not explicitly defined, except in vague terms.  This makes it
      essentially impossible to guarantee that a new underscore name is
      unambiguous!


5.  References -- Informative

   [I-D.iab-dns-choices]
              Faltstrom, P., "Design Choices When Expanding DNS",
              draft-iab-dns-choices-03 (work in progress), April 2006.




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

   [RFC2489]  Droms, R., "Procedure for Defining New DHCP Options",
              BCP 29, RFC 2489, January 1999.

   [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.


Appendix A.  Acknowledgements

   Thanks go to Tony Hansen for diligent review.


































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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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