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+INTERNET-DRAFT A. Gustafsson
+ Araneus Information Systems Oy
+ September 23, 2009
+
+Intended status: Draft Standard
+Obsoletes: RFC3597
+
+ Handling of Unknown DNS Resource Record (RR) Types
+ draft-ietf-dnsext-rfc3597-bis-00.txt
+
+Status of this Memo
+
+ This Internet-Draft is submitted to IETF in full conformance with the
+ provisions of BCP 78 and BCP 79.
+
+ 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/1id-abstracts.html
+
+ The list of Internet-Draft Shadow Directories can be accessed at
+ http://www.ietf.org/shadow.html
+
+Copyright Notice
+
+ Copyright (c) 2009 IETF Trust and the persons identified as the
+ document authors. All rights reserved.
+
+ This document is subject to BCP 78 and the IETF Trust's Legal
+ Provisions Relating to IETF Documents in effect on the date of
+ publication of this document (http://trustee.ietf.org/license-info).
+ Please review these documents carefully, as they describe your rights
+ and restrictions with respect to this document.
+
+Abstract
+
+ Extending the Domain Name System (DNS) with new Resource Record (RR)
+ types should not requires changes to name server software. This
+ document specifies how new RR types are transparently handled by DNS
+ software.
+
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+1. Introduction
+
+ The DNS [RFC1034] is designed to be extensible to support new
+ services through the introduction of new resource record (RR) types.
+ Nevertheless, DNS implementations have historically required software
+ changes to support new RR types, not only at the authoritative DNS
+ server providing the new information and the client making use of it,
+ but also at all slave servers for the zone containing it, and in some
+ cases also at caching name servers and forwarders used by the client.
+ Because the deployment of new DNS software is slow and expensive,
+ this has been a significant impediment to supporting new services in
+ the DNS.
+
+ [RFC3597] defined DNS implementation behavior and procedures for
+ defining new RR types aimed at simplifying the deployment of new RR
+ types by allowing them to be treated transparently by existing
+ implementations. Thanks to the widespread adoption of that
+ specification, much of the DNS is now capable of handling new record
+ types without software changes.
+
+ This document is a self-contained revised specification supplanting
+ and obsoleting [RFC3597].
+
+2. Definitions
+
+ 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 [RFC2119].
+
+ An "RR of unknown type" is an RR whose RDATA format is not known to
+ the DNS implementation at hand, and whose type is not an assigned
+ QTYPE or Meta-TYPE as specified in [RFC5395] (section 3.1) nor within
+ the range reserved in that section for assignment only to QTYPEs and
+ Meta-TYPEs. Such an RR cannot be converted to a type-specific text
+ format, compressed, or otherwise handled in a type-specific way.
+
+ In the case of a type whose RDATA format is class specific, an RR is
+ considered to be of unknown type when the RDATA format for that
+ combination of type and class is not known.
+
+3. Transparency
+
+ To enable new RR types to be deployed without server changes, name
+ servers and resolvers MUST handle RRs of unknown type transparently.
+ That is, they must treat the RDATA section of such RRs as
+ unstructured binary data, storing and transmitting it without change
+ [RFC1123].
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+ To ensure the correct operation of equality comparison (section 6)
+ and of the DNSSEC canonical form (section 7) when an RR type is known
+ to some but not all of the servers involved, servers MUST also
+ exactly preserve the RDATA of RRs of known type, except for changes
+ due to compression or decompression where allowed by section 4 of
+ this document. In particular, the character case of domain names
+ that are not subject to compression MUST be preserved.
+
+4. Domain Name Compression
+
+ RRs containing compression pointers in the RDATA part cannot be
+ treated transparently, as the compression pointers are only
+ meaningful within the context of a DNS message. Transparently
+ copying the RDATA into a new DNS message would cause the compression
+ pointers to point at the corresponding location in the new message,
+ which now contains unrelated data. This would cause the compressed
+ name to be corrupted.
+
+ To avoid such corruption, servers MUST NOT compress domain names
+ embedded in the RDATA of types that are class-specific or not well-
+ known. This requirement was stated in [RFC1123] without defining the
+ term "well-known"; it is hereby specified that only the RR types
+ defined in [RFC1035] are to be considered "well-known".
+
+ Receiving servers MUST decompress domain names in RRs of well-known
+ type, and SHOULD also decompress RRs of type RP, AFSDB, RT, SIG, PX,
+ NXT, NAPTR, and SRV to ensure interoperability with implementations
+ predating [RFC3597].
+
+ Specifications for new RR types that contain domain names within
+ their RDATA MUST NOT allow the use of name compression for those
+ names, and SHOULD explicitly state that the embedded domain names
+ MUST NOT be compressed.
+
+ As noted in [RFC1123], the owner name of an RR is always eligible for
+ compression.
+
+5. Text Representation
+
+ In the "type" field of a master file line, an unknown RR type is
+ represented by the word "TYPE" immediately followed by the decimal RR
+ type number, with no intervening whitespace. In the "class" field,
+ an unknown class is similarly represented as the word "CLASS"
+ immediately followed by the decimal class number.
+
+ This convention allows types and classes to be distinguished from
+ each other and from TTL values, allowing the "[<TTL>] [<class>]
+ <type> <RDATA>" and "[<class>] [<TTL>] <type> <RDATA>" forms of
+
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+ [RFC1035] to both be unambiguously parsed.
+
+ The RDATA section of an RR of unknown type is represented as a
+ sequence of white space separated words as follows:
+
+ The special token \# (a backslash immediately followed by a hash
+ sign), which identifies the RDATA as having the generic encoding
+ defined herein rather than a traditional type-specific encoding.
+
+ An unsigned decimal integer specifying the RDATA length in octets.
+
+ Zero or more words of hexadecimal data encoding the actual RDATA
+ field, each containing an even number of hexadecimal digits.
+
+ If the RDATA is of zero length, the text representation contains only
+ the \# token and the single zero representing the length.
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+ An implementation MAY also choose to represent some RRs of known type
+ using the above generic representations for the type, class and/or
+ RDATA, which carries the benefit of making the resulting master file
+ portable to servers where these types are unknown. Using the generic
+ representation for the RDATA of an RR of known type can also be
+ useful in the case of an RR type where the text format varies
+ depending on a version, protocol, or similar field (or several)
+ embedded in the RDATA when such a field has a value for which no text
+ format is known, e.g., a LOC RR [RFC1876] with a VERSION other than
+ 0.
+
+ Even though an RR of known type represented in the \# format is
+ effectively treated as an unknown type for the purpose of parsing the
+ RDATA text representation, all further processing by the server MUST
+ treat it as a known type and take into account any applicable type-
+ specific rules regarding compression, canonicalization, etc.
+
+ The following are examples of RRs represented in this manner,
+ illustrating various combinations of generic and type-specific
+ encodings for the different fields of the master file format:
+
+ a.example. CLASS32 TYPE731 \# 6 abcd (
+ ef 01 23 45 )
+ b.example. HS TYPE62347 \# 0
+ e.example. IN A \# 4 C0000201
+ e.example. CLASS1 TYPE1 192.0.2.1
+
+6. Equality Comparison
+
+ Certain DNS protocols, notably Dynamic Update [RFC2136], require RRs
+ to be compared for equality. Two RRs of the same unknown type are
+ considered equal when their RDATA is bitwise equal. To ensure that
+ the outcome of the comparison is identical whether the RR is known to
+ the server or not, specifications for new RR types MUST NOT specify
+ type-specific comparison rules.
+
+ This implies that embedded domain names, being included in the
+ overall bitwise comparison, are compared in a case-sensitive manner.
+
+ As a result, when a new RR type contains one or more embedded domain
+ names, it is possible to have multiple RRs owned by the same name
+ that differ only in the character case of the embedded domain
+ name(s). This is similar to the existing possibility of multiple TXT
+ records differing only in character case, and not expected to cause
+ any problems in practice.
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+7. DNSSEC Considerations
+
+ The rules for the DNSSEC canonical form and ordering were updated to
+ support transparent treatment of unknown types in [RFC3597]. Those
+ updates have subsequently been integrated into the base DNSSEC
+ specification, such that the DNSSEC canonical form and ordering are
+ now specified in [RFC4034] or its successors rather than in this
+ document.
+
+8. Additional Section Processing
+
+ Unknown RR types cause no additional section processing. Future RR
+ type specifications MAY specify type-specific additional section
+ processing rules, but any such processing MUST be optional as it can
+ only be performed by servers for which the RR type in case is known.
+
+9. IANA Considerations
+
+ This document does not require any IANA actions.
+
+10. Security Considerations
+
+ This specification is not believed to cause any new security
+ problems, nor to solve any existing ones.
+
+11. Normative References
+
+ [RFC1034] Mockapetris, P., "Domain Names - Concepts and
+ Facilities", STD 13, RFC 1034, November 1987.
+
+ [RFC1035] Mockapetris, P., "Domain Names - Implementation and
+ Specifications", STD 13, RFC 1035, November 1987.
+
+ [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts --
+ Application and Support", STD 3, RFC 1123, October 1989.
+
+ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [RFC5395] Eastlake, D., "Domain Name System (DNS) IANA
+ Considerations", BCP 42, RFC 5395, November 2008.
+
+12. Informative References
+
+ [RFC1876] Davis, C., Vixie, P., Goodwin, T. and I. Dickinson, "A
+ Means for Expressing Location Information in the Domain
+ Name System", RFC 1876, January 1996.
+
+
+
+
+Expires March 2010 Standards Track [Page 6]
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+ [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y. and J. Bound,
+ "Dynamic Updates in the Domain Name System (DNS UPDATE)",
+ RFC 2136, April 1997.
+
+ [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
+ (RR) Types", RFC 3597, September 2003.
+
+ [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
+ Rose, "Resource Records for the DNS Security Extensions",
+ RFC 4034, March 2005.
+
+14. Author's Address
+
+ Andreas Gustafsson
+ Araneus Information Systems Oy
+ PL 110
+ 02321 Espoo
+ Finland
+
+ Phone: +358 40 547 2099
+ EMail: gson@araneus.fi
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projects / thirdparty / bind9.git / commitdiff
