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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 7553

Network Working Group                                       P. Faltstrom
Internet-Draft                                                     Cisco
Intended status: Standards Track                              O. Kolkman
Expires: August 21, 2008                                           NLNet
                                                       February 18, 2008


       The Uniform Resource Identifier (URI) DNS Resource Record
                       draft-faltstrom-uri-00.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This document defines a new DNS resource record, called the Uniform
   Resource Identifier (URI) RR, for publishing mappings from hostnames
   to URIs.







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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Applicability Statement . . . . . . . . . . . . . . . . . . . . 3
   3.  DNS considerations  . . . . . . . . . . . . . . . . . . . . . . 4
   4.  The format of the URI RR  . . . . . . . . . . . . . . . . . . . 4
     4.1.  Ownername, class and type . . . . . . . . . . . . . . . . . 4
     4.2.  Priority  . . . . . . . . . . . . . . . . . . . . . . . . . 5
     4.3.  Weight  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     4.4.  Target  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     4.5.  URI RDATA Wire Format . . . . . . . . . . . . . . . . . . . 5
     4.6.  The URI RR Presentation Format  . . . . . . . . . . . . . . 6
   5.  Definition of the flag 'D' for NAPTR records  . . . . . . . . . 6
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Homepage at one domain, but two domains in use  . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     10.1. Normative References  . . . . . . . . . . . . . . . . . . . 7
     10.2. Non-normative references  . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9




























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1.  Introduction

   This document explains the use of the Domain Name System (DNS) for
   storage of URIs, and how to resolve hostnames to such URIs that can
   be used by various applications.  For resolution the application need
   to know both the hostname and the protocol that the URI is to be used
   for.  The protocol is registered by IANA.

   Currently, looking up URIs given a hostname uses the DDDS [RFC3401]
   application framework with the DNS as a database as specified in RFC
   3404 [RFC3404].  This have a number of implications as described in
   draft-iab-dns-choices [I-D.iab-dns-choices] such as the inability to
   select what NAPTR records that match the query is interesting.  The
   RRSet returned will always consist of all URIs "connected" with the
   domain in question.

   The URI resource record specified in this document create an ability
   for the querying party to select which ones of the NAPTR records one
   is interested in.  This because data in the service field of the
   NAPTR record is included in the owner part of the URI resource record
   type.

   Querying for the URI resource record type is not replacing querying
   for the NAPTR (or S-NAPTR [RFC3958]) resource record type.  Instead
   it is a complementary mechanism to use when one know already what
   service field is interesting.  One can with the URI resource record
   type directly query for the specific subset of the otherwise possibly
   large RRSet given back when querying for NAPTR resource records.

   This document updates RFC 3958 and RFC 3404 by adding the flag "D" to
   the list of defined terminal flags in section 2.2.3 of RFC 3958 and
   4.3 of RFC 3404.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119].


2.  Applicability Statement

   In general, it is expected that URI records will be used by clients
   for applications where the relevant protocol to be used is known, but
   for example extra abstraction given by separating a hostname from a
   point of service (as address by the URI) is needed.  Example of such
   a situation is when an organisation have many domain names, but only
   one official web page.




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   Applications MUST know the specific service fields to prepend the
   hostname with.  Using repetitive queries for URI records MUST NOT be
   a replacement for querying for NAPTR or S-NAPTR records.  NAPTR and
   S-NAPTR records are for discovery of the various services and URI for
   looking up access point for a given service.  Those are two very
   different kinds of needs.


3.  DNS considerations

   Using prefix labels, such as underscored service tags, prevents the
   use of wildcards [I-D.iab-dns-choices], as constructs as
   _s2._s1.*.example.net. are not possible in the DNS, see RFC 4592
   [RFC4592].  Besides, underscored service tags used for the URI RR
   (based on the NAPTR service descriptions) may have slightly different
   semantics than service tags used for underscored prefix labels that
   are used in combination with other (yet unspecified) RR types.  This
   may cause subtle management problems when delegation structure that
   has developed within the context of URI RRs is also to be used for
   other RR types.  Since the service labels might be overloaded
   applications should carefully check that the application level
   protocol is indeed the protocol they expect.

   Subtle management issues may also arise when the delegations from
   service to sub service label involves several parties and different
   stake holders.


4.  The format of the URI RR

   This is the format of the URI RR, whose DNS type code is NNNN (to be
   assigned by IANA).


   Ownername TTL Class URI Priority Weight Target


4.1.  Ownername, class and type

   The URI ownername is subject to special conventions.

   Just like the SRV RR [ref] the URI RR has service information encoded
   in its ownername.  In order to encode the service for a specific
   owner name one use service parameters.  Valid service parameters used
   are those as registered by IANA for NAPTR Records of any kind [ref to
   IANA registry name].  The service parameters are reversed, prepended
   with an underscore (_) and prepended to the owner name in separate
   labels.  The underscore is prepended to the service parameters to



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   avoid collisions with DNS labels that occur in nature, and the order
   is reversed to make it possible to do delegations, if needed, to
   different zones (and therefore providers of DNS).

   For example, suppose we are looking for the URI for a service with
   Service Parameter "A:B:C" for host example.com..  Then we would query
   for (QNAME,QTYPE)=("_C._B._A.example.com","URI")

   The type number for the URI record is NNNN (to be assigned by IANA).

   The URI resource record is class independent.

   The URI RR has no special TTL requirements.

4.2.  Priority

   The priority of this target URI.  A client MUST attempt to contact
   the URI with the lowest-numbered priority it can reach; URIs with the
   same priority SHOULD be tried in an order defined by the weight
   field.  The range is 0-65535.  This is a 16 bit unsigned integer in
   network byte order.

4.3.  Weight

   A server selection mechanism.  The weight field specifies a relative
   weight for entries with the same priority.  Larger weights SHOULD be
   given a proportionately higher probability of being selected.  The
   range of this number is 0-65535.  This is a 16 bit unsigned integer
   in network byte order.

4.4.  Target

   The URI of the target.  Resolution of the URI is according to the
   definitions for the URI Scheme the URI consists of.

   The URI is encoded as one or more <character-string> RFC1035 section 
   3.3 [RFC1035].

4.5.  URI RDATA Wire Format

   The RDATA for a URI RR consists of a 2 octet Priority field, a two
   octet Weight field, and a variable length target field.









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                        1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Priority             |          Weight               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               /
   /                             Target                            /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.6.  The URI RR Presentation Format

   The presentation format of the RDATA portion is as follows:

   Priority field MUST be represented as an unsigned decimal integer.

   The Weight Type field MUST be represented as an unsigned decimal
   integer.

   The target URI is enclosed in double-quotes (").  If the total length
   of the URI exceeds 255 characters the URI will be encoded in multiple
   <character-strings>.


5.  Definition of the flag 'D' for NAPTR records

   This document specifies the flag "D" for use as a flag in NAPTR
   records.  The flag indicate a terminal NAPTR record because it
   denotes the end of the DDDS/NAPTR processing rules.  In the case of a
   "D" flag, the Replacement field in the NAPTR record is used as the
   Owner of a DNS query for URI records, and normal URI processing as
   defined in this document is applied.

   The Regexp field in the NAPTR record MUST be empty when the 'D' flag
   is in use.


6.  Examples

6.1.  Homepage at one domain, but two domains in use

   An organisation have the domain names example.com and example.net,
   but the official URI http://www.example.com/.  Given the Service Tag
   "web" for the imagined "homepage" application service, the following
   URI Resource Records could be made available in the respective zones
   (example.com and example.net):




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   $ORIGIN example.com.
     IN NAPTR 1 1 "D" "http"               ( ; service
                      ""                     ; regexp
                      _http                ) ; replacement
   _http    IN URI 10 1 "http://www.example.com/"

   $ORIGIN example.net.
   IN NAPTR 1 1 "D" "http"               ( ; service
                    ""                     ; regexp
                    _http                ) ; replacement
   _http    IN URI 10 1 "http://www.example.com/"




7.  IANA Considerations


8.  Security Considerations


9.  Acknowledgements

   Ideas on how to split the two different kind of queries "What
   services exists for this domain name" and "What is the URI for this
   service" came from Scott Bradner and Lawrence Conroy.  Other people
   that have contributed to this document include Olafur Gudmundsson,
   Maria Hall, Peter Koch and Penn Pfautz.


10.  References

10.1.  Normative References

   [E164]     ITU-T, "The International Public Telecommunication Number
              Plan", Recommendation E.164, May 1997.

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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC3958]  Daigle, L. and A. Newton, "Domain-Based Application



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              Service Location Using SRV RRs and the Dynamic Delegation
              Discovery Service (DDDS)", RFC 3958, January 2005.

10.2.  Non-normative references

   [I-D.iab-dns-choices]
              Faltstrom, P., "Design Choices When Expanding DNS",
              draft-iab-dns-choices-04 (work in progress), October 2006.

   [RFC3401]  Mealling, M., "Dynamic Delegation Discovery System (DDDS)
              Part One: The Comprehensive DDDS", RFC 3401, October 2002.

   [RFC4592]  Lewis, E., "The Role of Wildcards in the Domain Name
              System", RFC 4592, July 2006.


Authors' Addresses

   Patrik Faltstrom
   Cisco Systems

   Email: paf@cisco.com


   Olaf Kolkman
   NLnet Labs

   Email: olaf@NLnetLabs.nl























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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
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