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 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 May 26, 2004. 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. Schlyter Expires May 26, 2004 [Page 1] Internet-Draft DNSSEC NSEC RDATA Format November 2003 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 Schlyter Expires May 26, 2004 [Page 2] Internet-Draft DNSSEC NSEC RDATA Format November 2003 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]. Schlyter Expires May 26, 2004 [Page 3] Internet-Draft DNSSEC NSEC RDATA Format November 2003 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 Schlyter Expires May 26, 2004 [Page 4] Internet-Draft DNSSEC NSEC RDATA Format November 2003 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. Schlyter Expires May 26, 2004 [Page 5] Internet-Draft DNSSEC NSEC RDATA Format November 2003 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 Schlyter Expires May 26, 2004 [Page 6] Internet-Draft DNSSEC NSEC RDATA Format November 2003 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. Schlyter Expires May 26, 2004 [Page 7] Internet-Draft DNSSEC NSEC RDATA Format November 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION Schlyter Expires May 26, 2004 [Page 8] Internet-Draft DNSSEC NSEC RDATA Format November 2003 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Schlyter Expires May 26, 2004 [Page 9]