Commit 18cf953f authored by Mark Andrews's avatar Mark Andrews

new draft

parent cdb6532e
DNS Extensions Working Group J. Schlyter, Ed.
Internet-Draft November 26, 2003
Updates: RFC 2535, RFC TCR (if approved)
Expires: May 26, 2004
DNSSEC NSEC RDATA Format
draft-ietf-dnsext-nsec-rdata-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document defines updates the NSEC resource record RDATA format
to cover all type codes.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The NSEC Resource Record . . . . . . . . . . . . . . . . . . 3
2.1 NSEC RDATA Wire Format . . . . . . . . . . . . . . . . . . . 4
2.1.1 The Next Domain Name Field . . . . . . . . . . . . . . . . . 4
2.1.2 The List of Type Bit Map(s) Field . . . . . . . . . . . . . 4
2.1.3 Inclusion of Wildcard Names in NSEC RDATA . . . . . . . . . 5
2.2 The NSEC RR Presentation Format . . . . . . . . . . . . . . 5
2.3 NSEC RR Example . . . . . . . . . . . . . . . . . . . . . . 5
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . 6
Normative References . . . . . . . . . . . . . . . . . . . . 6
Informational References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . 6
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . 8
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1. Introduction
The NSEC [3] Resource Record (RR) is used for authenticated proof of
the non-existence of DNS owner names and types. The RDATA format for
the NSEC RR, as described in RFC 2535 [2], had a limitation in that,
without using a yet undefined extension mechanism, the the RDATA
could only carry information about the existence of the first 127
types.
To prevent the introduction of an extension mechanism into a deployed
base of DNSSEC aware servers and resolvers, once the first 127 type
codes are allocated, this document redefines the wire format of the
"Type Bit Map" field in the NSEC RDATA to cover the full RR type
space.
This document introduces a new format for the type bit map. The
properties of the type bit map format are that it can cover the full
possible range of typecodes; that it is relatively economic in the
amount of space it uses for the common case of a few types with an
owner name; that it can represent owner names with all possible type
present in packets of approximately 8.5 kilobytes; that the
representation is simple to implement. Efficient searching of the
type bitmap for the presence of certain types is not a requirement.
For convenience and completeness this document presents the syntax
and semantics for the NSEC RR based on the specification in RFC 2535
[2] and as updated by RFC TCR [3], thereby not introducing changes
except for the syntax of the type bit map.
[Editors note: this is the text that is to be copied into
draft-ietf-dnssec-dnssec-records]
This document updates RFC 2535 [2] and RFC TCR [3].
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 [1].
2. The NSEC Resource Record
The NSEC resource record lists two separate things: the owner name of
the next authoritative RRset in the canonical ordering of the zone,
and the set of RR types present at the NSEC RR's owner name. The
complete set of NSEC RRs in a zone both indicate which authoritative
RRsets exist in a zone and also form a chain of authoritative owner
names in the zone. This information is used to provide authenticated
denial of existence for DNS data, as described in RFC 2535 [2].
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The type value for the NSEC RR is 47.
The NSEC RR is class independent.
The NSEC RR has no special TTL requirements.
2.1 NSEC RDATA Wire Format
The RDATA of the NSEC RR is as shown below:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Next Domain Name /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ List of Type Bit Map(s) /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.1.1 The Next Domain Name Field
The Next Domain Name field contains the owner name of the next
authoritative RRset in the canonical ordering of the zone. The value
of the Next Domain Name field in the last NSEC record in the zone is
the name of the zone apex (the owner name of the zone's SOA RR).
A sender MUST NOT use DNS name compression on the Next Domain Name
field when transmitting an NSEC RR. A receiver which receives an
NSEC RR containing a compressed Next Domain Name field SHOULD
decompress the field value.
Owner names of RRsets not authoritative for the given zone (such as
glue records) MUST NOT be listed in the Next Domain Name unless at
least one authoritative RRset exists at the same owner name.
2.1.2 The List of Type Bit Map(s) Field
The List of Type Bit Map(s) Field identifies the RRset types which
exist at the NSEC RR's owner name and uses a simple windowed bitmap
encoding. It is a logical extension to the encoding used by NXT [2]
and is designed to be both efficient and easy to implement without
errors.
The type space is split into into 256 window blocks. Each block that
has at least one active type is encoded using a window octet (from 0
to 255), a bitmap length octet (from 1 to 32) and a bitmap (covering
up to 256 type codes) in network bit order (similar to NXT). Blocks
with no types present MUST NOT be included. Trailing zero octets in
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the bitmap MUST be removed. Blocks is presented in increasing
numerical order.
"|" denotes concatenation
NSEC RDATA = ( Window Block # | Bitmap Length | Bitmap ) +
A zone MUST NOT generate an NSEC RR for any domain name that only
holds glue records.
Bits representing pseudo-RR types MUST be set to 0, since they do not
appear in zone data. If encountered, they must be ignored upon
reading.
2.1.3 Inclusion of Wildcard Names in NSEC RDATA
If a wildcard owner name appears in a zone, the wildcard label ("*")
is treated as a literal symbol and is treated the same as any other
owner name for purposes of generating NSEC RRs. Wildcard owner names
appear in the Next Domain Name field without any wildcard expansion.
RFC 2535 [2] describes the impact of wildcards on authenticated
denial of existence.
2.2 The NSEC RR Presentation Format
The presentation format of the RDATA portion is as follows:
The Next Domain Name field is represented as a domain name.
The Type Bit Map field is represented either as a sequence of RR type
mnemonics or as a sequence of unsigned decimal integers denoting the
RR type codes.
2.3 NSEC RR Example
The following NSEC RR identifies the RRsets associated with
alfa.example.com. and identifies the next authoritative name after
alfa.example.com.
alfa.example.com. 86400 IN NSEC host.example.com. A MX RRSIG NSEC
The first four text fields specify the name, TTL, Class, and RR type
(NSEC). The entry host.example.com. is the next authoritative name
after alfa.example.com. in canonical order. The A, MX, RRSIG and NSEC
mnemonics indicate there are A, MX, RRSIG and NSEC RRsets associated
with the name alfa.example.com.
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Assuming that the resolver can authenticate this NSEC record, it
could be used to prove that beta.example.com does not exist, or could
be used to prove there is no AAAA record associated with
alfa.example.com. Authenticated denial of existence is discussed in
RFC 2535 [2].
3. IANA Considerations
This document introduces no new IANA considerations, because all of
the protocol parameters used in this document have already been
assigned by RFC TCR [3].
4. Security Considerations
The change introducted here does not affect security, since it only
updates the RDATA format and encoding.
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[3] Weiler, S., "Legacy Resolver Compatibility for Delegation
Signer", draft-ietf-dnsext-dnssec-2535typecode-change-05 (work
in progress), October 2003.
Informational References
[4] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.
[5] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
Author's Address
Jakob Schlyter (editor)
Karl Gustavsgatan 15
Goteborg SE-411 25
Sweden
EMail: jakob@schlyter.se
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Appendix A. Acknowledgements
The encoding described in this document was initially proposed by
Mark Andrews. Other encodings where proposed by David Blacka and
Michael Graff.
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Schlyter Expires May 26, 2004 [Page 9]
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