Network Working Group S. Josefsson Internet-Draft Extundo Expires: April 25, 2003 October 25, 2002 Domain Name System URI Scheme and MIME Media Types draft-josefsson-dns-url-06 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 April 25, 2003. 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. Josefsson Expires April 25, 2003 [Page 1] Internet-Draft DNS URI and MIME types October 2002 Table of Contents 1. Introduction and Background . . . . . . . . . . . . . . . . . 3 1.1 Changes since -05 . . . . . . . . . . . . . . . . . . . . . . 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 Josefsson Expires April 25, 2003 [Page 2] Internet-Draft DNS URI and MIME types October 2002 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, and is not limited to 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 the application/dns MIME media type and the text/dns MIME media type 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]. 1.1 Changes since -05 Note to RFC editor: This section is to be removed on publication. Updated author address, made two cosmetic changes and added STD/BCP status to references. Josefsson Expires April 25, 2003 [Page 3] Internet-Draft DNS URI and MIME types October 2002 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. Josefsson Expires April 25, 2003 [Page 4] Internet-Draft DNS URI and MIME types October 2002 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: simon@josefsson.org Author/Change Controller: IESG Josefsson Expires April 25, 2003 [Page 5] Internet-Draft DNS URI and MIME types October 2002 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 simon@josefsson.org Intended usage: COMMON Author/Change controller: IESG Josefsson Expires April 25, 2003 [Page 6] Internet-Draft DNS URI and MIME types October 2002 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 simon@josefsson.org Intended usage: COMMON Author/Change controller: IESG Josefsson Expires April 25, 2003 [Page 7] Internet-Draft DNS URI and MIME types October 2002 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 Josefsson Expires April 25, 2003 [Page 8] Internet-Draft DNS URI and MIME types October 2002 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]. Josefsson Expires April 25, 2003 [Page 9] Internet-Draft DNS URI and MIME types October 2002 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", 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. [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", BCP 13, RFC 2048, November 1996. [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, 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", BCP 35, RFC 2717, November 1999. Josefsson Expires April 25, 2003 [Page 10] Internet-Draft DNS URI and MIME types October 2002 Author's Address Simon Josefsson Extundo Drottningholmsv. 70 Stockholm 112 42 Sweden EMail: simon@josefsson.org Josefsson Expires April 25, 2003 [Page 11] Internet-Draft DNS URI and MIME types October 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. 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