< draft-ietf-dnsext-unknown-rrs-05.txt		draft-ietf-dnsext-unknown-rrs-06.txt >
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	INTERNET-DRAFT Andreas Gustafsson		RFC 3597
	draft-ietf-dnsext-unknown-rrs-05.txt Nominum Inc.
	March 2003
	Updates: RFC 1034, RFC 2163, RFC 2535
	Handling of Unknown DNS Resource Record Types
	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.
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	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."
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	Abstract
	Extending the Domain Name System with new Resource Record (RR) types
	currently requires changes to name server software. This document
	specifies the changes necessary to allow future DNS implementations
	to handle new RR types transparently.
	1. Introduction
	The DNS is designed to be extensible to support new services through
	the introduction of new resource record (RR) types. In practice,
	deploying a new RR type currently requires changes to the name server
	software not only at the authoritative DNS server that is 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 server software is slow and expensive,
	the potential of the DNS in supporting new services has never been
	fully realized. This memo proposes changes to name servers and to
	procedures for defining new RR types aimed at simplifying the future
	deployment of new RR types.
	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].
	2. Definition
	An "RR of unknown type" is an RR whose RDATA format is not known to
	the DNS implementation at hand, such that it cannot be converted to a
	type-specific text format, compressed, or otherwise handled in a
	type-specific way, and whose type is not an assigned QTYPE or Meta-
	TYPE in RFC2929 section 3.1 nor within the range reserved in that
	section for assignment only to QTYPEs and Meta-TYPEs.
	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].
	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 memo. 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".
	The specifications of a few existing RR types have explicitly allowed
	compression contrary to this specification: RFC2163 specified that
	compression applies to the PX RR, and RFC2535 allowed compression in
	SIG RRs and NXT RRs records. Since this specification disallows
	compression in these cases, it is an update to RFC2163 (section 4)
	and RFC2535 (sections 4.1.7 and 5.2).
	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 (although the current specification of the SRV RR
	in RFC2782 prohibits compression, RFC2052 mandated it, and some
	servers following that earlier specification are still in use).
	Future 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
	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.
	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 0A000001
	e.example. CLASS1 TYPE1 10.0.0.2
	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.
	7. DNSSEC Canonical Form and Ordering
	DNSSEC defines a canonical form and ordering for RRs [RFC2535,
	section 8.1]. In that canonical form, domain names embedded in the
	RDATA are converted to lower case.
	The downcasing is necessary to ensure the correctness of DNSSEC
	signatures when case distinctions in domain names are lost due to
	compression, but since it requires knowledge of the presence and
	position of embedded domain names, it cannot be applied to unknown
	types.
	To ensure continued consistency of the canonical form of RR types
	where compression is allowed, and for continued interoperability with
	existing implementations that already implement the RFC2535 canonical
	form and apply it to their known RR types, the canonical form remains
	unchanged for all RR types whose whose initial publication as an RFC
	was prior to the initial publication of this specification as an RFC
	(RFC TBD).
	As a courtesy to implementors, it is hereby noted that the complete
	set of such previously published RR types that contain embedded
	domain names, and whose DNSSEC canonical form therefore involves
	downcasing according to the DNS rules for character comparisons,
	consists of the RR types NS, MD, MF, CNAME, SOA, MB, MG, MR, PTR,
	HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, NAPTR, KX, SRV,
	DNAME, and A6.
	This document specifies that for all other RR types (whether treated
	as unknown types or treated as known types according to an RR type
	definition RFC more recent than than RFC TBD), the canonical form is
	such that no downcasing of embedded domain names takes place, and
	otherwise identical to the canonical form specified in RFC2535
	section 8.1.
	Note that the owner name is always set to lower case according to the
	DNS rules for character comparisons, regardless of the RR type.
	The DNSSEC canonical RR ordering is as specified in RFC2535 section
	8.3, where the octet sequence is the canonical form as revised by
	this specification.
	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
	The IANA is hereby requested to verify that specifications for new RR
	types requesting an RR type number comply with this specification.
	In particular, the IANA MUST NOT assign numbers to new RR types whose
	specification allows embedded domain names to be compressed.
	10. Security Considerations
	This specification is not believed to cause any new security
	problems, nor to solve any existing ones.
	Normative References
	[RFC1034] - Domain Names - Concepts and Facilities, P. Mockapetris,
	November 1987.
	[RFC1035] - Domain Names - Implementation and Specifications, P.
	Mockapetris, November 1987.
	[RFC1123] - Requirements for Internet Hosts -- Application and
	Support, R. Braden, Editor, October 1989.
	[RFC2119] - Key words for use in RFCs to Indicate Requirement Levels,
	S. Bradner, BCP 14, March 1997.
	[RFC2535] - Domain Name System Security Extensions. D. Eastlake,
	March 1999.
	[RFC2613] - Using the Internet DNS to Distribute MIXER Conformant
	Global Address Mapping (MCGAM), C. Allocchio, January 1998.
	[RFC2929] - Domain Name System (DNS) IANA Considerations, D.
	Eastlake, E. Brunner-Williams, B. Manning, September 2000.
	Non-normative References
	[RFC1876] - A Means for Expressing Location Information in the Domain
	Name System, C. Davis, P. Vixie, T. Goodwin, I. Dickinson, January
	1996.
	[RFC2052] - A DNS RR for specifying the location of services (DNS
	SRV), A. Gulbrandsen, P. Vixie, October 1996. Obsoleted by RFC2782.
	[RFC2136] - Dynamic Updates in the Domain Name System (DNS UPDATE),
	P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997.
	[RFC2782] - A DNS RR for specifying the location of services (DNS
	SRV), A. Gulbrandsen, P. Vixie, L. Esibov, February 2000.
	Author's Address		Title: Handling of Unknown DNS Resource Record (RR) Types
			Author(s): A. Gustafsson
			Status: Standards Track
			Date: September 2003
			Mailbox: gson@nominum.com
			Pages: 8
			Characters: 17559
			Updates/Obsoletes/SeeAlso: None
	Andreas Gustafsson		I-D Tag: draft-ietf-dnsext-unknown-rrs-06.txt
	Nominum Inc.
	2385 Bay Rd
	Redwood City, CA 94063
	USA
	Phone: +1 650 381 6004		URL: ftp://ftp.rfc-editor.org/in-notes/rfc3597.txt
	Email: gson@nominum.com		Extending the Domain Name System (DNS) with new Resource Record (RR)
			types currently requires changes to name server software. This
			document specifies the changes necessary to allow future DNS
			implementations to handle new RR types transparently.
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