Network Working Group S. Josefsson
Internet-Draft RSA Security
Expires: November 11, 2002 May 13, 2002
Domain Name System URI Scheme and MIME Media Types
draft-josefsson-dns-url-05
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This draft describes a URI scheme for DNS resources and MIME media
types for DNS data.
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Table of Contents
1. Introduction and Background . . . . . . . . . . . . . . . . . 3
2. DNS URI Registration . . . . . . . . . . . . . . . . . . . . . 4
3. MIME Type Registration of application/dns . . . . . . . . . . 6
4. MIME Type Registration of text/dns . . . . . . . . . . . . . . 7
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
Normative References . . . . . . . . . . . . . . . . . . . . . 10
Informative References . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 11
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 12
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1. Introduction and Background
DNS [1][2] is a widely deployed protocol used to, among other things,
translate host names into IP addresses. More recent work has added
support for storing certificates in DNS [8][9].
To be able to locate and retrieve certificates via a network, URIs
are often used. This document describes a URI scheme to locate DNS
information. The DNS URI scheme described here can be used to
reference any DNS data, not only certificates.
DNS information is often stored and served from text files, so called
"master files". The format is described in RFC 1035 [2]. This
document specify that the MIME type text/dns is used for master
files.
DNS data can also be stored in a format described in RFC 2540 [5].
The format intended to be used when archiving DNS data (it adds a
retrieval time stamp). This document specify that the MIME type
application/dns is used for the RFC 2540 format.
The rest of this document is outlined as follows. Section 2 contains
the URI Registration Template from [10]. Section 3 and 4 contains
the MIME registration template from [6] for application/dns and
text/dns respectively.
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 [7].
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2. DNS URI Registration
URL scheme name: "dns".
URL scheme syntax: A DNS URI designates a DNS resource record set,
referenced by domain name, type and class and optionally 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 SHOULD NOT be used when
a defined mnemonic for the corresponding value is known.
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 either is 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
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.
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Character encoding considerations: The characters are encoded as per
the "URI Generic Syntax" RFC [4].
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 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: E.g., CNRP.
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.
Security considerations: A DNS URI does not embed confidential
information. If it references domains in the Internet DNS
environment, even the information referenced by the URI is public
information. If a DNS URI is used within an "internal" DNS
environment, the same security considerations of the DNS environment
apply to the use and handling of DNS URIs themselves as well as the
data returned by looking up these URIs.
If security related information is referenced by DNS URIs (such as
certificates stored in DNS), care must be taken to prevent for man-
in-the-middle attacks that maliciously replace the certificate.
Techniques such as Secure DNS may be used.
This draft does not affect the security considerations related to DNS
itself.
Contact: sjosefsson@rsasecurity.com
Author/Change Controller: IESG
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3. MIME Type Registration of application/dns
To: ietf-types@iana.org
Subject: Registration of MIME media type application/dns
MIME media type name: application
MIME subtype name: dns
Required parameters: none
Optional parameters: none
Encoding considerations: 7bit, 8bit or binary
Security considerations: This definition identifies content as being
detached DNS information, as documented in RFC 2540 [5]. This data
may be security relevant according to RFC 2538 [9], or secured
information according to RFC 2535 [8].
Interoperability considerations: none
Published specification: The format of data that could be tagged with
this MIME type is documented in RFC 2540 [5].
Applications which use this media type: DNS related software.
Additional information:
Magic number(s): none
File extension(s): none
Macintosh File Type Code(s): unknown
Person & email address to contact for further information:
Simon Josefsson sjosefsson@rsasecurity.com
Intended usage: COMMON
Author/Change controller: IESG
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4. MIME Type Registration of text/dns
To: ietf-types@iana.org
Subject: Registration of MIME media type text/dns
MIME media type name: text
MIME subtype name: dns
Required parameters: none
Optional parameters: none
Encoding considerations: 7bit, 8bit or binary
Security considerations: This definition identifies content as being
DNS information in "master file" format, as documented in RFC 1035
[2]. The DNS data may be security relevant according to RFC 2538
[9], or secured information according to RFC 2535 [8].
Interoperability considerations: none
Published specification: The format of data that could be tagged with
this MIME type is documented in RFC 1035 [2].
Applications which use this media type: DNS related software.
Additional information:
Magic number(s): none
File extension(s): none
Macintosh File Type Code(s): unknown
Person & email address to contact for further information:
Simon Josefsson sjosefsson@rsasecurity.com
Intended usage: COMMON
Author/Change controller: IESG
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5. 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
The following illustrates data tagged with the text/plain MIME type:
$ORIGIN example.org
@ IN SOA ns-master dnsmaster 20 7200 600 3600000 60
IN NS ns1
IN NS ns2
IN MX 10 mail1
ns1 IN A 10.1.0.52
ns2 IN A 192.168.17.23
mail1 IN A 10.52.0.1
www IN A 192.168.17.23
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6. Security Considerations
A DNS URI does not embed confidential information. If it references
domains in the Internet DNS environment, even the information
referenced by the URI is public information. If a DNS URI is used
within an "internal" DNS environment, the same security
considerations of the DNS environment apply to the use and handling
of DNS URIs themselves as well as the data returned by looking up
these URIs.
If security related information is referenced by DNS URIs (such as
certificates stored in DNS), care must be taken to prevent for man-
in-the-middle attacks that maliciously replace the certificate.
Techniques such as Secure DNS may be used.
The application/dns definition identifies content as being detached
DNS information, as documented in RFC 2540 [5]. This data may be
security relevant according to RFC 2538 [9], or secured information
according to RFC 2535 [8].
The text/dns definition identifies content as being DNS information
in "master file" format, as documented in RFC 1035 [2]. The DNS data
may be security relevant according to RFC 2538 [9], or secured
information according to RFC 2535 [8].
This draft does not affect the security considerations related to DNS
itself.
7. IANA Considerations
The IANA is asked to register the DNS URI scheme, using the template
in section 2, in accordance with RFC 2717 [10].
The IANA is asked to register the MIME types application/dns and
text/dns using the templates in section 3 and 4 respectively, in
accordance with RFC 2048 [6].
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Acknowledgements
Thanks to Stuart Cheshire, Donald Eastlake, Pasi Eronen, Michael
Mealling, and Steve Mattson for comments and suggestions.
Normative References
[1] Mockapetris, P., "Domain Names - Concepts and Facilities", RFC
1034, November 1987.
[2] Mockapetris, P., "Domain Names - Implementation and
Specification", 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.
[5] Eastlake, D., "Detached Domain Name System (DNS) Information",
RFC 2540, March 1999.
Informative References
[6] Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures", RFC
2048, November 1996.
[7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[8] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[9] Eastlake, D. and O. Gudmundsson, "Storing Certificates in the
Domain Name System (DNS)", RFC 2538, March 1999.
[10] Petke, R. and I. King, "Registration Procedures for URL Scheme
Names", RFC 2717, November 1999.
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Author's Address
Simon Josefsson
RSA Security
Arenavgen 29
Stockholm 121 29
Sweden
Phone: +46 8 7250914
EMail: sjosefsson@rsasecurity.com
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