Network Working Group S. Josefsson
Internet-Draft RSA Security
Expires: December 15, 2001 June 16, 2001
DNS URL scheme
draft-josefsson-dns-url-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This draft describe a URL scheme to locate DNS resources.
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Table of Contents
1. Introduction and Background . . . . . . . . . . . . . . . . . 3
2. URL Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. URL 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
References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 7
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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, URLs are often used. This document describe a URL
scheme to locate DNS information. The DNS URL scheme described here
can be used to reference any DNS data, not only certificates. The
format of data located is described in [8].
This following sections are modelled after the URL Registration
Template in [9].
2. URL Scheme
The name of the URL scheme defined in this document is "dns".
A DNS URL designates a DNS resource record; by domain name, type and
class and optionally server. The DNS URL follows the generic syntax
from RFC 2396 [5], and is described using ABNF [4] in section 3.
A DNS URL is of the following general form. This is intended to
illustrate, not define, the scheme.
dns:[//server/]domain[?type=TYPE;class=CLASS]
3. URL Scheme Syntax
Strings are not case sensitive and free insertion of
linear-white-space is not permitted.
dnsurl = "dns:" [ "//" hostport "/" ] hostname ["?" query]
; See RFC 2396 for "hostport" and
; "hostname" definitions
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.
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.
4. Character Encoding Considerations
Since 8-bit characters are not permitted in URLs, they must be
encoded as per the "URI Generic Syntax" RFC. DNS domains has been
historically restricted to a subset of the US ASCII alphabet, but
recent work within the IETF IDN working group is likely to change
this restriction. Since this specification re-uses the "hostport"
definition from the URI specification [5], a possible future update
of the "hostport" definition within the URL specifications might be
sufficient to adapt DNS URLs to IDNs.
5. Intended Usage
Broad usage. The application/dns or text/dns MIME types are
associated with this URL scheme [10].
6. Applications and/or Protocols Using This Scheme
E.g. CNRP.
7. Interoperability Considerations
The data referenced by this URL scheme might be transfered by
protocols that aren't MIME aware (such as the DNS protocol). This is
not anticipated to have any serious interoperability impact though.
8. Security Considerations
A DNS URL does not embed confidential information. If it references
domains in the Internet DNS environment, even the information
references by the URL is public information. If a DNS URL is used
within a "internal" DNS environment, the same security
considerations of the DNS environment apply to the use and handling
of DNS URLs themselves as well as the data returned by looking up
these URLs.
If security related information is referenced by DNS URLs (such as
certificates stored in DNS), care must be taken to prevent for
man-in-the-middle attacks that malicously replace the certificate.
Techniques such as Secure DNS may be used.
This draft does not affect the security considerations related to
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DNS itself.
9. IANA Considerations
The IANA is asked to register the DNS URL scheme using this document
as the template in accordance with RFC 2717 [9].
10. Examples
This 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
This illustrate a DNS query for "simon.example.org" for the CERT
type in the Internet (IN) class:
dns:simon.example.org;type=CERT
This illustrate a DNS query for "ftp.example.org" from the DNS
server "internal-dns.example.org" server, and the address type:
dns://internal-dns.example.org/ftp.example.org;type=A
Acknowledgement
Thanks to Michael Mealling for comments on an early version of this
draft.
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] 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.
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[7] Eastlake, D. and O. Gudmundsson, "Storing Certificates in the
Domain Name System (DNS)", RFC 2538, March 1999.
[8] Eastlake, D., "Detached Domain Name System (DNS) Information",
RFC 2540, March 1999.
[9] Petke, R. and I. King, "Registration Procedures for URL Scheme
Names", RFC 2717, November 1999.
[10] Josefsson, S., "DNS Information MIME Media Type
Registrations", I-D draft-josefsson-mime-dns-01, January 2001.
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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