Network Working Group S. Josefsson
Internet-Draft RSA Security
Expires: March 29, 2002 September 28, 2001
DNS URI scheme
draft-josefsson-dns-url
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be interpreted as described in RFC 2119 [3].
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This draft describes a URI scheme to locate DNS resources.
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Table of Contents
1. Introduction and Background . . . . . . . . . . . . . . . . . 3
2. URI Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. URI Scheme Syntax . . . . . . . . . . . . . . . . . . . . . . 3
4. Character Encoding Considerations . . . . . . . . . . . . . . 4
5. Intended Usage . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Applications and/or Protocols Using This Scheme . . . . . . . 4
7. Interoperability Considerations . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . 4
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6
References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
A. IANA URI Registration Template . . . . . . . . . . . . . . . . 6
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 8
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1. Introduction and Background
DNS [1][2] is a widely deployed protocol used to, among other
things, translate domain names into IP addresses. More recent work
has added support for storing cryptographic keys and certificates in
DNS [6][7]. To be able to locate, for example, certificates via a
network resource, 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.
The following sections are modelled after the Registration Template
in [8]. The template can be found in Appendix A.
2. URI Scheme
The name of the URI scheme defined in this document is "dns".
A DNS URI designates a DNS resource record: By domain name, type and
class and optionally server. The DNS URI follows the generic syntax
from RFC 2396 [5], and is described using ABNF [4] in section 3.
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]
3. URI Scheme Syntax
Strings are not case sensitive and free insertion of
linear-white-space is not permitted.
dnsurl = "dns:" [ "//" hostport "/" ] dnsname ["?" query]
; See RFC 2396 for "hostport" definition
domainname = uric
; See RFC 2396 for "uric" definition
query = queryelement [";" query]
queryelement = ( "CLASS=" classval ) | ( "TYPE=" typeval ) |
( 1*alphanum "=" 1*alphanum )
classval = 1*digit / "IN" / "CH" / ...
; Any standard DNS class expressed as
; mnemonic or as decimal integer
typeval = 1*digit / "A" / "NS" / "MD" / ...
; Any standard DNS type expressed as
; mnemonic or as decimal integer
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The digit representation of types and classes SHOULD NOT be used
when a defined mnemonic for the corresponding value is known.
Of the "reserved" characters in the "dnsname" element, the "?"
character MUST be escaped, the rest MAY be escaped. Otherwise, it
would be impossible to separate a domain name containing "?" from
the "query" delimiter.
Unless specified, the "server" is assumed to be locally
(pre-)configured, and "class" to be the Internet class ("IN"), and
"type" to be the Address (A) type.
To resolve a DNS URI using the DNS protocol [2] a query is formed by
using the domainname, classval and typeval from the URI string (or
the previously mentioned default values if either classval or
typeval is missing from the string). If hostport is given in the
URI string, this server should receive the DNS query, otherwise the
default DNS server should receive it.
4. Character Encoding Considerations
The characters in the URI, in particular the "dnsname", MUST be
encoded as per the "URI Generic Syntax" RFC [5].
This URI specification allows all possible DNS names to be encoded
(of course following the encoding rules of [5]), 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, hostnames in DNS often have certain
restrictions. It is up to these application to limit this subset,
this URI scheme places no restrictions.
5. Intended Usage
Broad usage.
6. Applications and/or Protocols Using This Scheme
E.g. CNRP.
7. Interoperability Considerations
The data referenced by this URI scheme might be transferred by
protocols that aren't URI aware (such as the DNS protocol). This is
not anticipated to have any serious interoperability impact though.
8. Security Considerations
A DNS URI does not embed confidential information. If it references
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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.
9. IANA Considerations
The IANA is asked to register the DNS URI scheme using this document
as the template in accordance with RFC 2717 [8].
10. Examples
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:
dns://internal-dns.example.org/*.%3f%20 %00%25+?type=TXT
Acknowledgement
Thanks to Michael Mealling, Steve Mattson and Stuart Cheshire for
comments.
References
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[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] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[4] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[5] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[6] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[7] Eastlake, D. and O. Gudmundsson, "Storing Certificates in the
Domain Name System (DNS)", RFC 2538, March 1999.
[8] Petke, R. and I. King, "Registration Procedures for URL Scheme
Names", RFC 2717, November 1999.
Author's Address
Simon Josefsson
RSA Security
Arenav�gen 29
Stockholm 121 29
Sweden
Phone: +46 8 7250914
EMail: [email protected]
Appendix A. IANA URI Registration Template
URL scheme name: dns
URL scheme syntax: Section 3
Character encoding considerations: Section 4
Intended usage: Section 5
Applications and/or protocols which use this scheme: Section 5.
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Interoperability considerations: Section 7.
Security considerations: Section 8
Contact: [email protected]
Author/Change Controller: IESG
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