One document matched: draft-josefsson-dns-url-07.txt

Differences from draft-josefsson-dns-url-06.txt

Network Working Group                                       S. Josefsson
Internet-Draft                                            April 20, 2003
Expires: October 19, 2003


            Domain Name System Uniform Resource Identifiers
                       draft-josefsson-dns-url-07

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on October 19, 2003.

Abstract

   This document define Uniform Resource Identifiers for Domain Name
   System resources.
















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Table of Contents

   1.  Introduction and Background  . . . . . . . . . . . . . . . . .  3
   1.1 Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.2 Changes since -06  . . . . . . . . . . . . . . . . . . . . . .  3
   2.  DNS URI Registration . . . . . . . . . . . . . . . . . . . . .  4
   3.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
       Normative References . . . . . . . . . . . . . . . . . . . . .  8
       Informative References . . . . . . . . . . . . . . . . . . . .  8
       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  8
       Intellectual Property and Copyright Statements . . . . . . . .  9






































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1. Introduction and Background

   The Domain Name System (DNS) [1][2] is a widely deployed protocol
   used to, among other things, translate host names into IP addresses.
   Recent work has added support for storing certificates in DNS [8].

   To be able to locate and retrieve certificates via a network, Uniform
   Resource Identifiers (URIs) are often used.  This document define a
   URI scheme for DNS information.  The DNS URI scheme defined here can,
   of course, be used to reference any DNS data, and is not limited to
   only certificates.

   The core part of this document is the URI Registration Template
   according to [9].

1.1 Terminology

   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 RFC 2119 [5].

1.2 Changes since -06

   Note to RFC editor: This section is to be removed on publication.

   The MIME registration templates for text/dns and application/dns was
   removed, and will be defined in separate documents.

   Improved discussion related to which mnemonics that must be
   supported.  The interoperability problem that provoked the
   clarification is also mentioned.

   Security consideration improvements.


















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2. DNS URI Registration

   URL scheme name: "dns".

   URL scheme syntax: A DNS URI designates a DNS resource record set
   that can be referenced by domain name, type, class and server.  The
   DNS URI follows the generic syntax from RFC 2396 [4], and is
   described using ABNF [3].  Strings are not case sensitive and free
   insertion of linear-white-space is not permitted.

   dnsurl          = "dns:" [ "//" hostport "/" ] dnsname ["?" dnsquery]
                                ; See RFC 2396 for "hostport"  definition

   dnsname         = *pchar
                                ; See RFC 2396 for "pchar" definition

   dnsquery        = dnsqueryelement [";" dnsquery]

   dnsqueryelement = ( "CLASS=" dnsclassval ) | ( "TYPE=" dnstypeval ) |
                     ( 1*alphanum "=" 1*alphanum )

   dnsclassval     = 1*digit / "IN" / "CH" / ...
                                ; Any standard DNS class expressed as
                                ; mnemonic or as decimal integer

   dnstypeval      = 1*digit / "A" / "NS" / "MD" / ...
                                ; Any standard DNS type expressed as
                                ; mnemonic or as decimal integer

   The digit representation of types and classes MAY be used when a
   mnemonic for the corresponding value is not well known (e.g., for
   newly introduced types or classes), but SHOULD NOT be used for the
   types or classes defined in the DNS specification [2].  All
   implementations of MUST recognize the mnemonics defined in [2].

   Unless specified in the URI, the server ("hostport") is assumed to be
   locally known, "dnsclassval" to be the Internet class ("IN"), and
   "dnstypeval" to be the Address (A) type.

   To resolve a DNS URI using the DNS protocol [2] a query is formed by
   using the dnsname, dnsclassval and dnstypeval from the URI string (or
   the previously mentioned default values if some value missing from
   the string).  If server ("hostport") is given in the URI string, this
   server should receive the DNS query, otherwise the default DNS server
   should receive it.

   A client MAY want to check that it understands the dnsclassval and
   dnstypeval before sending a query, so that it is able to correctly



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   parse the answer.  A typical example of a client that would not need
   to check dnsclassval and dnstypeval would be a proxy that just treat
   the answer as opaque data.

   Character encoding considerations: The characters are encoded as per
   the "URI Generic Syntax" RFC [4].  The DNS protocol do not consider
   character sets, it simply transports opaque data.

   To encode a "." that is part of a DNS label the "escaped" encoding
   MUST be used, and a label delimiter MUST be encoded as ".".  That is,
   the only way to encode a label delimiter is "." , and the only way to
   encode a "." as part of label is "%2e".  This approach was chosen to
   minimize the modifications users will have to do when manually
   translating a domain name string into the URI form.

   This URI specification allows all possible DNS names to be encoded
   (of course following the encoding rules of [4]), however certain
   applications may restrict the set of valid characters and care should
   be taken so that invalid characters in these contexts does not cause
   harm.  In particular, host names in DNS have certain restrictions.
   It is up to these application to limit this subset, this URI scheme
   places no restrictions.

   Intended usage: Broad usage.

   Applications and/or protocols which use this scheme: DNS related
   software.

   Interoperability considerations: The data referenced by this URI
   scheme might be transferred by protocols that are not URI aware (such
   as the DNS protocol).  This is not anticipated to have any serious
   interoperability impact though.

   Interoperability problems may occur if one entity understands a new
   DNS type or class mnemonic but another entity do not understand it.
   This is a interoperability problem for DNS software in general,
   although it is not a major practical problem as the DNS types and
   classes are fairly static.  To guarantee interoperability
   implementations could use integers for all mnemonics not defined in
   [2].

   Security considerations: See below.

   Contact: simon@josefsson.org

   Author/Change Controller: IESG





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3. Examples

   A DNS URI is of the following general form.  This is intended to
   illustrate, not define, the scheme.

   dns:[//server/]domain[?type=TYPE;class=CLASS]

   The following illustrate a DNS query for "www.example.org" for the
   Internet (IN) class and the Address (A) type:

   dns:www.example.org?class=IN;type=A

   The following illustrate a DNS query for "simon.example.org" for the
   CERT type in the Internet (IN) class:

   dns:simon.example.org?type=CERT

   The following illustrate a DNS query for "ftp.example.org" from the
   DNS server "internal-dns.example.org" server, in the Internet (IN)
   class and the address (A) type:

   dns://internal-dns.example.org/ftp.example.org?type=A

   The following illustrate a strange, albeit valid, DNS query.  Note
   the encoding of "." and 0x00:

   dns://internal-dns.example.org/*.%3f%20%00%2e%25+?type=TXT
























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4. Security Considerations

   If a DNS URI references domains in the Internet DNS environment, both
   the URI itself and the information referenced by the URI is public
   information.  If a DNS URI is used within an "internal" DNS
   environment, both the DNS URI and the data is referenced should be
   handled using the same considerations that apply to DNS data in the
   environment.

   If information referenced by DNS URIs are used to make security
   decisions (examples of such data include, but is not limited to,
   certificates stored in DNS), implementations may need to employ
   security techniques such as Secure DNS [7], or even CMS [10] or
   OpenPGP [6], to protect the data during transport.  How to implement
   this will depend on the usage scenario, and it is not up to this URI
   scheme to define how the data referenced by DNS URIs should be
   protected.

   If applications accept ill-formed DNS URIs and try to attach meaning
   to them (e.g., accepting the URI "dns:www.example.org?secret=value"),
   a covert channel used to "leak" information may be enabled.  The
   implications of covert channels should be understood by applications
   that accepts ill-formed DNS URIs.

   This draft does not modify the security considerations related to DNS
   itself.

5. IANA Considerations

   The IANA is asked to register the DNS URI scheme, using the template
   in section 2, in accordance with RFC 2717 [9].




















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Acknowledgements

   Thanks to Stuart Cheshire, Donald Eastlake, Pasi Eronen, Ted Hardie,
   Michael Mealling, and Steve Mattson for comments and suggestions.

Normative References

   [1]  Mockapetris, P., "Domain names - concepts and facilities", STD
        13, RFC 1034, November 1987.

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

   [3]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.

   [4]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
        Identifiers (URI): Generic Syntax", RFC 2396, August 1998.

Informative References

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

   [6]   Callas, J., Donnerhacke, L., Finney, H. and R. Thayer, "OpenPGP
         Message Format", RFC 2440, November 1998.

   [7]   Eastlake, D., "Domain Name System Security Extensions", RFC
         2535, March 1999.

   [8]   Eastlake, D. and O. Gudmundsson, "Storing Certificates in the
         Domain Name System (DNS)", RFC 2538, March 1999.

   [9]   Petke, R. and I. King, "Registration Procedures for URL Scheme
         Names", BCP 35, RFC 2717, November 1999.

   [10]  Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3369,
         August 2002.


Author's Address

   Simon Josefsson

   EMail: simon@josefsson.org






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Intellectual Property Statement

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Full Copyright Statement

   Copyright (C) Simon Josefsson (2003).  All Rights Reserved.

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.









































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