



Network Working Group                                       P. Faltstrom
Internet-Draft                                                    Netnod
Intended status: Informational                                O. Kolkman
Expires: September 26, 2015                                         ISOC
                                                          March 25, 2015


       The Uniform Resource Identifier (URI) DNS Resource Record
                         draft-faltstrom-uri-14

Abstract

   This document describes the already registered DNS resource record
   type called the Uniform Resource Identifier (URI) RR, for publishing
   mappings from hostnames to URIs.

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
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   This Internet-Draft will expire on September 26, 2015.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Applicability Statement . . . . . . . . . . . . . . . . . . .   3
   3.  DNS considerations  . . . . . . . . . . . . . . . . . . . . .   3
   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
   5.  Usages  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Example: FTP server in the example.com domain . . . . . .   6
     5.2.  Relation to S-NAPTR . . . . . . . . . . . . . . . . . . .   6
     5.3.  Relation to U-NAPTR . . . . . . . . . . . . . . . . . . .   7
     5.4.  Relation to SRV . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Registration of the URI Resource Record Type  . . . . . .   7
     6.2.  Registration of services  . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Non-normative references  . . . . . . . . . . . . . . . .   9
   Appendix A.  The original RRTYPE Allocation Request . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   This document explains the use of the Domain Name System (DNS) for
   the storage of URIs [RFC3986], and how to resolve hostnames to such
   URIs that can be used by various applications using the URI Resource
   Record Type.  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.

   Historically, uses of the DNS to map a domain name to a URL have
   relied on the NAPTR RRTYPEs and then on the DDDS [RFC3401]
   application framework with the DNS as a database as specified in RFC
   3404 [RFC3404].  This has a number of implications such as the fact
   the RRSet returned will contain all URIs "connected" with the owner,
   and not only the ones related to a specific service.

   The URI resource record specified in this document enables the
   querying party to do the equivalence of selecting which ones of the
   NAPTR records one is interested in, and have only those returned.
   This because data in the service field of the NAPTR record is
   included in the owner part of the URI resource record type.  It is



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   also the case that as the URI resource record type include the target
   URI directly as part of the RDATA, it is very easy to extract the
   correct target URI, instead of applying rewrite rules as in NAPTR.

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

   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, an extra abstraction is needed in order to separate
   a domain name from a point of service (as addressed by the URI).  One
   example of such a situation is when an organisation has many domain
   names, but only one official web page.

   Applications MUST know the specific service to prepend the hostname
   with.  Using repetitive queries for URI records MUST NOT be a
   replacement for querying for NAPTR records according to the NAPTR
   (DDDS) or S-NAPTR algorithms.  NAPTR records serve the purpose to
   discover the various services and URIs for looking up access points
   for a given service.  Those are two very different kinds of needs.

3.  DNS considerations

   Using prefix labels, such as underscored service tags, for a specific
   owner name may cause a counter-intuitive effect when the owner name
   is a wildcard name.  For example, _s2._s1.*.example.net.  is not a
   wildcard name and cannot be used to return a synthesized answer for a
   query name of _s2._s1.a.example.net.  See Section 4.5 of RFC4592
   [RFC4592] for more details.  Besides, underscored service tags used
   for the URI RR (based on the Service Name and Transport Protocol Port
   Number Registry) 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




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   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 presentation format of the URI RR:


       Ownername TTL Class URI Priority Weight Target


   The URI RR does not cause any kind of Additional Section processing.

4.1.  Ownername, class and type

   The URI ownername is subject to special conventions.

   Just like the SRV RR [RFC2782] the URI RR has service information
   encoded in its ownername.  In order to encode the service for a
   specific owner name one uses service parameters.  Valid service
   parameters used are those registered by IANA in the Service Name and
   Transport Protocol Port Number Registry [RFC6335], or as Enumservice
   Registrations [RFC6117].  The Enumservice Registration parameters are
   reversed (subtype(s) before type), prepended with an underscore (_)
   and prepended to the owner name in separate labels.  The underscore
   is prepended to the service parameters to 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
   ENUM Service Parameter "A:B:C" for host example.com.  Then we would
   query for (QNAME,QTYPE)=("_C._B._A.example.com","URI")

   As another example, suppose we are looking for the URI for a service
   with Service Name "A" and Transport Protocol "B" for host
   example.com.  Then we would query for
   (QNAME,QTYPE)=("_A._B.example.com","URI")

   The type number for the URI record is 256.

   The URI resource record is class independent.

   The URI RR has no special TTL requirements.



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4.2.  Priority

   The priority of the target URI in this RR.  Its range is 0-65535.  A
   client MUST attempt to contact the URI with the lowest-numbered
   priority it can reach; URIs with the same priority SHOULD be selected
   according to propabilities defined by the weight field.

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.

4.4.  Target

   The URI of the target, enclosed in double-quote characters ('"'),
   where the URI is as specified in RFC 3986 [RFC3986].  Resolution of
   the URI is according to the definitions for the Scheme of the URI.

   Since the URI will not be encoded as a <character-string> (see
   RFC1035 section 3.3 [RFC1035]) there is no 255 character size
   limitation.

   The Target MUST NOT be an empty URI ("").

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.

   Priority and Weight are unsigned integers in network byte order.

   The remaining data in the RDATA contains the Target field.  The
   Target field contains the URI as a sequence of octets (without the
   enclosing double- quote characters used in the presentation format).

   The length of the target field MUST be greater than zero.













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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                            /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.  Usages

5.1.  Example: FTP server in the example.com domain

   An organisation has the domain names example.com and example.net, and
   their FTP archive is at ftp://ftp1.example.com/public.  Given the
   Service Name "ftp" and Transport Protocol "tcp" (from the IANA
   registry of Service Name and Transport Protocol Port Numbers), the
   following URI Resource Records could be made available in the
   respective zones (example.com and example.net):


   $ORIGIN example.com.
   _ftp._tcp    IN URI 10 1 "ftp://ftp1.example.com/public"

   $ORIGIN example.net.
   _ftp._tcp    IN URI 10 1 "ftp://ftp1.example.com/public"


5.2.  Relation to S-NAPTR

   The URI resource record type is not a replacement for the S-NAPTR.
   It is instead an extension and the second step of the S-NAPTR
   resolution can resolve a URI resource record instead of using SRV
   records and yet another algorithm for how to use SRV records for the
   specific protocol.


   $ORIGIN example.com.
   ;;       order pref flags
     IN NAPTR 100   10   "D"   "EM:ProtA"              ( ; service
                               ""                        ; regexp
                               _http._tcp.example.com.   ; replacement
   _http._tcp IN URI 10 1 "http://www.example.com/path"






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5.3.  Relation to U-NAPTR

   The URI Resource Record Type, together with S-NAPTR, can be viewed as
   a replacement for U-NAPTR [RFC4848].  The URI Resource Record Type is
   though only interesting when one know a base domain name, a protocol
   and service so that one can compose the record to look up.  NAPTR
   records of any kind are used to look up what services exists for a
   certain domain, which is one step before the URI resource record is
   used.

5.4.  Relation to SRV

   The URI Resource Record Type can be viewed as a replacement for the
   SRV record.  This because it like the SRV record can only be looked
   up if one know the base domain, the protocol and the service.  It has
   a similar functionality, and uses the same registry for Service
   Names, but instead of returning a hostname and port number, the URI
   record return a full URI.  As such, it can be viewed as a more
   powerful resource record than SRV.

6.  IANA Considerations

6.1.  Registration of the URI Resource Record Type

   After an expert review in February 2011 (see Appendix A) IANA has
   allocated RRTYPE 256 for the URI Resource Record Type in the registry
   named Resource Record (RR) TYPEs and QTYPEs as defined in BCP 42 (at
   the time RFC 6195 [RFC6195]), located at
   http://www.iana.org/assignments/dns-parameters.

   IANA is requested to update the reference with that registration to
   this RFC.

6.2.  Registration of services

   No new registry is needed for the registration of services as the
   Service Name, Transport Protocol Port Numbers, Enumservices and the
   DNS SRV Service Type registries are used also for the URI resource
   record type.

7.  Security Considerations

   Using the URI resource record together with security mechanisms that
   relies on verification of authentication of hostnames, like TLS,
   makes it important to choose the correct domain name when doing the
   comparison, and that the change in what hostname to use is secured by
   DNSSEC so that it can be trusted in a similar way as a redirect in
   HTTP using TLS.



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   If for example the URI resource record is not signed with the help of
   DNSSEC, and then validated successfully, trusting the non-signed URI
   will effectlyely lead to a downgrade attack.

   The basic mechanism for successful use of URI works as follows:

   1.   Announce the fact example.com is hosted at example.org (with
        some URL) in DNS

   2.   Secure the URI resource record with DNSSEC.  Best of course by
        doing validation in the application doing the lookup, but it
        could also be in the local recursive resolver or in the trusted
        recursive resolver also doing validation.  All according to the
        local trust policy.

   3.   Verify the TLS (for example) certificate for the connection to
        example.org matches, i.e.  use the hostname in the URI and not
        the hostname used originally when looking up the URI resource
        record.

   4.   If needed, do application layer authentication etc over the then
        encrypted connection.

   What also can happen is that the URI in the resource record type has
   errors in it.  Applications using the URI resource record type for
   resolution should behave similarly as if the user typed (or copy and
   pasted) the URI.  At least it must be clear to the user that the
   error is not due to any error from his side.

   One SHOULD NOT include userinfo (see User Information, Section 3.2.1,
   in RFC 3986 [RFC3986]) in a URI that is used in a URI resource record
   as DNS data must be viewed as publicly available information.

8.  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 Richard Barnes, Leslie
   Daigle, Victor Dukhovni, Olafur Gudmundsson, Philip Hallam-Baker, Ted
   Hardie, Sam Hartman, Evan Hunt, John klensin, Peter Koch, Eliot Lear,
   Andy Newton, Mark Nottingham, Penn Pfautz, Jinmei Tatuya, Willem
   Toorop, Nico Williams.

   Cisco is acknowledged as mr Faltstrom's employer at the time this
   document was developed.





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   The NLnet Labs is acknowledged as mr Kolkman's employer at the time
   this document was developed.

9.  References

9.1.  Normative References

   [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.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, August 2010.

   [RFC6117]  Hoeneisen, B., Mayrhofer, A., and J. Livingood, "IANA
              Registration of Enumservices: Guide, Template, and IANA
              Considerations", RFC 6117, March 2011.

   [RFC6195]  Eastlake, D., "Domain Name System (DNS) IANA
              Considerations", RFC 6195, March 2011.

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165, RFC
              6335, August 2011.

9.2.  Non-normative references

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

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



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   [RFC3403]  Mealling, M., "Dynamic Delegation Discovery System (DDDS)
              Part Three: The Domain Name System (DNS) Database", RFC
              3403, October 2002.

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

   [RFC3597]  Gustafsson, A., "Handling of Unknown DNS Resource Record
              (RR) Types", RFC 3597, September 2003.

   [RFC3833]  Atkins, D. and R. Austein, "Threat Analysis of the Domain
              Name System (DNS)", RFC 3833, August 2004.

   [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.

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

   [RFC4848]  Daigle, L., "Domain-Based Application Service Location
              Using URIs and the Dynamic Delegation Discovery Service
              (DDDS)", RFC 4848, April 2007.

   [RFC5507]  IAB, Faltstrom, P., Austein, R., and P. Koch, "Design
              Choices When Expanding the DNS", RFC 5507, April 2009.

Appendix A.  The original RRTYPE Allocation Request

   On February 22, 2011 IANA assigned RRTYPE 256 for the URI resource
   record based on a request that followed the procedure documented in
   RFC 6195 [RFC6195].  The DNS RRTYPE PARAMETER ALLOCATION form as
   submitted to IANA at thet time is replicated below for reference.

   A.   Submission Date:

        May 23, 2009



   B.   Submission Type:

        [X] New RRTYPE
        [ ] Modification to existing RRTYPE






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   C.   Contact Information for submitter:

        Name: Patrik Faltstrom
        Email Address: paf@cisco.com
        International telephone number: +46-8-6859131
        Other contact handles:
        (Note: This information will be publicly posted.)



   D.   Motivation for the new RRTYPE application?

        There is no easy way to get from a domain name to a URI (or
        IRI).  Some mechanisms exists via use of the NAPTR [RFC3403]
        resource record.  That implies quite complicated rules that are
        simplified via the S-NAPTR [RFC3958] specification.  But, the
        ability to directly look up a URI still exists.  This
        specification uses a prefix based naming mechanism originated in
        the definition of the SRV [RFC2782] resource record, and the
        RDATA is a URI, encoded as one text field.

        See also above (Section 1).



   E.   Description of the proposed RR type.

        The format of the URI resource record is as follows:


        Ownername TTL Class URI Priority Weight Target


        The URI RR has service information encoded in its ownername.  In
        order to encode the service for a specific owner name one uses
        service parameters.  Valid service parameters used are either
        Enumservice Registrations registered by IANA, or prefixes used
        for the SRV resource record.

        The wire format of the RDATA is as follows:











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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                            /
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




   F.   What existing RRTYPE or RRTYPEs come closest to filling that
        need and why are they unsatisfactory?

        The RRTYPE that come closest is the NAPTR resource record.  It
        is for example used in the DDDS and S-NAPTR algorithms.  The
        main problem with the NAPTR is that selection of what record (or
        records) one is interested in is based on data stored in the
        RDATA portion of the NAPTR resource record.  This, as explained
        in RFC 5507 [RFC5507], is not optimal for DNS lookups.  Further,
        most applications using NAPTR resource records uses regular
        expression based rewrite rules for creation of the URI, and that
        has shown be complicated to implement.

        The second closest RRTYPE is the SRV record that given a
        prefixed based naming just like is suggested for the URI
        resource record, one get back a port number and domain name.
        This can also be used for creation of a URI, but, only URIs
        without path components.



   G.   What mnemonic is requested for the new RRTYPE (optional)?

        URI



   H.   Does the requested RRTYPE make use of any existing IANA Registry
        or require the creation of a new IANA sub-registry in DNS
        Parameters?

        Yes, partially.






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        One of the mechanisms to select a service is to use the
        Enumservice Registry managed by IANA.  Another is to use
        services and protocols used for SRV records.



   I.   Does the proposal require/expect any changes in DNS servers/
        resolvers that prevent the new type from being processed as an
        unknown RRTYPE (see RFC 3597 [RFC3597])?

        No



   J.   Comments:

        None



Authors' Addresses

   Patrik Faltstrom
   Netnod

   Email: paf@netnod.se


   Olaf Kolkman
   Internet Society

   Email: kolkman@isoc.org



















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