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DNSEXT                                                           J. Reid
Internet-Draft                                                Telnic Ltd
Intended status: Standards Track                            July 4, 2008
Expires: January 5, 2009

                The Zone Status (ZS) DNS Resource Record

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   A Domain Name System (DNS) resource record which provides status
   information about a zone is described in this document.

Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Rationale  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Justification For New RRtype . . . . . . . . . . . . . . . . .  6
   5.  ZS Resource Record . . . . . . . . . . . . . . . . . . . . . .  7
   6.  End User Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 12
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 15

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1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14, RFC2119

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2.  Introduction

   The DNS protocol is defined in RFC1034 [refs.RFC1034], RFC1035
   [refs.RFC1035] and clarified in RFC2181 [refs.RFC2181].  The DNS does
   not currently provide a well defined mechanism for obtaining
   information about the status of a zone: what it is being used for,
   the significance of the zone's contents, when the zone was last
   updated and so on.  This means a variety of ad-hoc techniques are
   deployed whenever zone administrators choose to make this information
   available.  Typical strategies include descriptive TXT records in the
   zone or embedding meta-information in the values of existing RRtypes
   or subtypes such as the SOA record's serial number and RNAME.  These
   are confusing and impractical since an arbitrary DNS client needs a
   priori knowledge of which of these schemes, if any, has been used by
   a zone administrator.

   This document advocates the introduction of a new resource record
   specifically to provide this type of information.

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3.  Rationale

   Common examples where indicating the status of a zone would be useful
   include: whenever the domain is in the process of a substantial
   update; a domain undergoing a long-term migration; and changes to the
   authoritative name servers for a zone. eg "Use of example.net was
   deprecated on April 1st.  Please visit example.com instead."  It
   would be convenient to store this type of meta information within the
   zone in a way that makes it easily retrieved.  This kind of status
   information would be particularly helpful for systems such as ENUM
   [refs.RFC3761] which can be used for publishing real-time contact
   data for zone owners.

   These sorts of details are generally associated with the
   administration of the zone rather than being tied to the rest of the
   zone content.  Clarifying this separation between information that
   reflects the status of a zone from any text that a domain holder may
   choose to publish via DNS is useful.  It also avoids the current
   subtyping issues that would affect processing of a TXT RRset if the
   status information was embedded there.  TXT records are too general
   and would require imprecise RDATA parsing in order to extract any
   relevant items of interest to a particular client.

   The proposed RRtype will be of particular use for zones where contact
   data are published in the DNS as NAPTR records [refs.RFC3403].  For
   instance a set of tel: and sip: URIs [refs.RFC3986] could be
   associated with the proposed zone status RRtype.  That could indicate
   these URIs are the ones published by the zone owner when they are at
   work, or while travelling or when at home.  Client software could
   lookup the zone's ZS records and display a meaningful message to the
   end user about the NAPTR records that had been retrieved from an
   earlier lookup.  A description of which contact data the zone owner
   has published would offer additional information to what might be
   inferred from the actual NAPTR RRset or other zone data itself.  The
   ZS RRtype could express concepts like "the zone owner is asleep, so
   don't bother trying voice-based communication" or "the zone owner is
   at work but in a meeting".

   Publishing and obtaining this information will become more
   significant because of emerging applications and services which make
   innovative use of the DNS such as the real-time manipulation of zone
   content data.  For example, updating NAPTR records (ie the zone
   owner's contact data) whenever the zone owner switches between the
   NAPTR RRset they publish while at work, at home, commuting or while

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4.  Justification For New RRtype

   TXT records are unsuitable for providing this sort of zone status
   information because the semantics of TXT record RDATA are
   unstructured.  TXT records can and are used for all sorts of
   purposes: version control strings, comments or reminders to zone
   administrators, anti-spam information, references to ticketing
   systems, contact details of the zone administrator and so on.  It
   would be impractical for an application to interpret the contents of
   a response to a TXT query and guess which, if any, of the returned
   TXT records contained meaningful data about the status of the zone.

   One approach would be to adopt a convention that a "magic string" in
   the RDATA for some TXT record identified zone status information.
   This is not viable for two reasons.  First, it may break backwards
   compatibility with the installed base which might already be using
   this "magic string" in TXT records.  The second reason is this
   proposal would introduce yet another example of subtyping which is
   generally accepted as poor protocol design.

   Likewise, it is not sensible to insert TXT records in some part of
   the name space to be dedicated for this specific purpose.  That would
   be another instance of bad protocol design because a fundamental but
   unstated principle of the Domain Name System is any RRtype can be
   used in any zone irrespective of the name of the zone.

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5.  ZS Resource Record

   Apart from its type code, the wire and text formats for the proposed
   ZS RRtype are identical to the definitions of the TXT record given in

   ZS RDATA format

               /                   ZS-DATA                    /

   where: ZS-DATA One or more character-strings.

   The ZS RRtype will hold descriptive text intended to contain
   information reflecting the status of the zone in which it is held.

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6.  End User Considerations

   Users publishing ZS records SHOULD pay attention to the needs of
   potential readers of these resource records, especially with respect
   to character sets and language.  Although arbitrary text can be
   stored in character-strings, publishers of ZS records SHOULD
   carefully consider the capabilities of the devices and end users who
   query for ZS records.  For example, a mobile phone or other hand-held
   device may not have the font information or suitable rendering
   capabilities to display (say) Chinese or Arabic characters.
   Similarly, publishers of ZS records should try to avoid displaying
   information in multiple languages or assume that all readers of these
   records understand the same language or languages they have chosen to
   use.  In these circumstances it would be inadvisable to publish a
   string in a ZS record that is unlikely to be intelligible to those
   who lookup ZS records.

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7.  Security Considerations

   Although this document does not appear to introduce any extra
   security issues beyond those listed in the thorough analysis of the
   threats to DNS in RFC3833 [refs.RFC3833], there are some additional
   considerations.  These are described below.

   It is unrealistic to assume that zone owners who publish ZS records
   can be relied upon to ensure any ZS records contain accurate, timely
   information.  Similarly it cannot be assumed that ZS records contain
   text that will be understandable by an arbitrary reader that looks
   them up in the DNS.  Therefore any data contained in a ZS record is
   solely for informational purposes.  The information contained in a ZS
   record MUST NOT be relied upon for any location-based services.  In
   particular, emergency services MUST NOT not treat the contents of a
   ZS record as definitive information about the location or disposition
   of the domain name owner.

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8.  IANA Considerations

   IANA is requested to issue a new type code and mnemonic for the
   proposed resource record.  No other IANA services are required by
   this document.

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9.  Acknowledgements

   The author would like to thank Ben Timms, John Cundall, John Tidmuss
   and Lawrence Conroy for their constructive suggestions to this
   document and for helping to identify potential uses for the proposed
   record type.

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10.  References

10.1.  Normative References

              Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES",
              RFC 1034, November 1987.

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

              Braden, R., "Requirements for Internet Hosts --
              Application and Support", RFC 1123, October 1989.

              Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, July 1997.

              Mealling, M., "Dynamic Delegation Discovery System (DDDS)
              Part Three: The Domain Name System (DNS) Database",
              RFC 3403, October 2002.

              Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

10.2.  Informative References

              Bradner, S., "The Internet Standards Process -- Revision
              3", RFC 2026, BCP 9, October 1996.

              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, BCP 14, March 1997.

              Faltstrom, P. and M. Mealling, "The E.164 to Uniform
              Resource Identifiers (URI) Dynamic Delegation  Discovery
              System (DDDS) Application (ENUM)", RFC 3761, April 2004.

              Atkins, D. and R. Austein, "Threat Analysis of the Domain
              Name System (DNS)", RFC 3833, August 2004.

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              Bradner, S., "IETF Rights in Contributions", BCP 78,
              RFC 3978, March 2005.

              Bradner, S., "Intellectual Property Rights in IETF
              Technology", BCP 79, RFC 3979, March 2005.

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Author's Address

   Jim Reid
   Telnic Ltd
   Telnic Ltd.
   6 Langside Court
   Bothwell, SCOTLAND
   United Kingdom

   Phone: +44 20 7467 6400
   Email: jim@telnic.org

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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an

Intellectual Property

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   Copies of IPR disclosures made to the IETF Secretariat and any
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   The IETF invites any interested party to bring to its attention any
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