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 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 15, 2001. Distribution of this document is unlimited. Comments and suggestions on this document are encouraged. 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. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved. Abstract This draft describe a URL scheme to locate DNS resources. Josefsson Expires December 15, 2001 [Page 1] Internet-Draft DNS URL scheme June 2001 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 Josefsson Expires December 15, 2001 [Page 2] Internet-Draft DNS URL scheme June 2001 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 Josefsson Expires December 15, 2001 [Page 3] Internet-Draft DNS URL scheme June 2001 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 Josefsson Expires December 15, 2001 [Page 4] Internet-Draft DNS URL scheme June 2001 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. Josefsson Expires December 15, 2001 [Page 5] Internet-Draft DNS URL scheme June 2001 [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 Arenav„gen 29 Stockholm 121 29 Sweden Phone: +46 8 7250914 EMail: sjosefsson@rsasecurity.com Josefsson Expires December 15, 2001 [Page 6] Internet-Draft DNS URL scheme June 2001 Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. 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