INTERNET-DRAFT Donald E. Eastlake 3rd Obsoletes RFC 2929, Updates RFC 1183 Motorola Laboratories Expires: December 2005 June 2005 Domain Name System (DNS) IANA Considerations ------ ---- ------ ----- ---- -------------- <draft-eastlake-dnsext-2929bis-01.txt> Status of This Document By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Distribution of this draft, which is intended to become a Best Current Practice, is unlimited. Comments should be sent to the DNS Working Group mailing list <namedroppers@ops.ietf.org> or to the author. 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 a "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 Abstract Internet Assigned Number Authority (IANA) parameter assignment considerations are given for the allocation of Domain Name System (DNS) classes, RR types, operation codes, error codes, RR header bits, and AFSDB subtypes. D. Eastlake 3rd [Page 1]
INTERNET-DRAFT DNS IANA Considerations June 2005 Table of Contents Status of This Document....................................1 Abstract...................................................1 Table of Contents..........................................2 1. Introduction............................................3 1.1 The DNS Special Allocation Policy......................3 2. DNS Query/Response Headers..............................4 2.1 One Spare Bit?.........................................4 2.2 Opcode Assignment......................................5 2.3 RCODE Assignment.......................................5 3. DNS Resource Records....................................6 3.1 RR TYPE IANA Considerations............................8 3.1.1 Special Note on the OPT RR...........................9 3.1.2 The AFSDB RR Subtype Field...........................9 3.2 RR CLASS IANA Considerations...........................9 3.3 RR NAME Considerations................................11 4. Security Considerations................................11 Appendix: Changes from RFC 2929...........................11 Copyright and Disclaimer..................................13 Normative References......................................13 Informative References....................................14 Authors Addresses.........................................16 Expiration and File Name..................................16 D. Eastlake 3rd [Page 2]
INTERNET-DRAFT DNS IANA Considerations June 2005 1. Introduction The Domain Name System (DNS) provides replicated distributed secure hierarchical databases which hierarchically store "resource records" (RRs) under domain names. This data is structured into CLASSes and zones which can be independently maintained. See [RFC 1034, 1035, 2136, 2181, 4033] familiarity with which is assumed. This document provides, either directly or by reference, general IANA parameter assignment considerations applying across DNS query and response headers and all RRs. There may be additional IANA considerations that apply to only a particular RR type or query/response opcode. See the specific RFC defining that RR type or query/response opcode for such considerations if they have been defined except for AFSDB considerations [RFC 1183] which are included herein. This RFC replaces [RFC 2929]. IANA currently maintains a web page of DNS parameters. See <http://www.iana.org/numbers.htm>. "IETF Standards Action", "IETF Consensus", "Specification Required", and "Private Use" are as defined in [RFC 2434]. 1.1 The DNS Special Allocation Policy Many DNS parameters are allocated by IANA based on the DNS special policy. This policy authorizes IANA allocation base on meeting any of the following three criteria: 1. An IETF Standards Action. 2. Approval as an Experimental Protocol. 3. As provided in [RFC 4020] for Early Allocation except that all the criteria in Section 2 of [RFC 4020] are replaced by the following: 3.a: The format, semantics, processing, and other rules related to handling the protocol entities defined by the code points (the "specifications") are adequately described in an Internet draft that is intended to become Standards Track or Experimental. 3.b: There is sufficient interest in early (pre-RFC) implementation and deployment in the community as determined by working group consensus. D. Eastlake 3rd [Page 3]
INTERNET-DRAFT DNS IANA Considerations June 2005 2. DNS Query/Response Headers The header for DNS queries and responses contains field/bits in the following diagram taken from [RFC 2136, 2929]: 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA| Z|AD|CD| RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | QDCOUNT/ZOCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ANCOUNT/PRCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NSCOUNT/UPCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ARCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ The ID field identifies the query and is echoed in the response so they can be matched. The QR bit indicates whether the header is for a query or a response. The AA, TC, RD, RA, AD, and CD bits are each theoretically meaningful only in queries or only in responses, depending on the bit. However, many DNS implementations copy the query header as the initial value of the response header without clearing bits. Thus any attempt to use a "query" bit with a different meaning in a response or to define a query meaning for a "response" bit is dangerous given existing implementation. Such meanings may only be assigned by an IETF Standards Action. The unsigned fields query count (QDCOUNT), answer count (ANCOUNT), authority count (NSCOUNT), and additional information count (ARCOUNT) express the number of records in each section for all opcodes except Update. These fields have the same structure and data type for Update but are instead the counts for the zone (ZOCOUNT), prerequisite (PRCOUNT), update (UPCOUNT), and additional information (ARCOUNT) sections. 2.1 One Spare Bit? There have been ancient DNS implementations for which the Z bit being on in a query meant that only a response from the primary server for a zone is acceptable. It is believed that current DNS D. Eastlake 3rd [Page 4]
INTERNET-DRAFT DNS IANA Considerations June 2005 implementations ignore this bit. Assigning a meaning to the Z bit requires an IETF Standards Action. 2.2 Opcode Assignment Currently DNS OpCodes are assigned as follows: OpCode Name Reference 0 Query [RFC 1035] 1 IQuery (Inverse Query, Obsolete) [RFC 3425] 2 Status [RFC 1035] 3 available for assignment 4 Notify [RFC 1996] 5 Update [RFC 2136] 6-15 available for assignment New OpCode assignments require an IETF Standards Action modified by [RFC 4020]. 2.3 RCODE Assignment It would appear from the DNS header above that only four bits of RCODE, or response/error code are available. However, RCODEs can appear not only at the top level of a DNS response but also inside OPT RRs [RFC 2671], TSIG RRs [RFC 2845], and TKEY RRs [RFC 2930]. The OPT RR provides an eight bit extension resulting in a 12 bit RCODE field and the TSIG and TKEY RRs have a 16 bit RCODE field. Error codes appearing in the DNS header and in these three RR types all refer to the same error code space with the single exception of error code 16 which has a different meaning in the OPT RR from its meaning in other contexts. See table below. D. Eastlake 3rd [Page 5]
INTERNET-DRAFT DNS IANA Considerations June 2005 RCODE Name Description Reference Decimal Hexadecimal 0 NoError No Error [RFC 1035] 1 FormErr Format Error [RFC 1035] 2 ServFail Server Failure [RFC 1035] 3 NXDomain Non-Existent Domain [RFC 1035] 4 NotImp Not Implemented [RFC 1035] 5 Refused Query Refused [RFC 1035] 6 YXDomain Name Exists when it should not [RFC 2136] 7 YXRRSet RR Set Exists when it should not [RFC 2136] 8 NXRRSet RR Set that should exist does not [RFC 2136] 9 NotAuth Server Not Authoritative for zone [RFC 2136] 10 NotZone Name not contained in zone [RFC 2136] 11 - 15 Available for assignment 16 BADVERS Bad OPT Version [RFC 2671] 16 BADSIG TSIG Signature Failure [RFC 2845] 17 BADKEY Key not recognized [RFC 2845] 18 BADTIME Signature out of time window [RFC 2845] 19 BADMODE Bad TKEY Mode [RPC 2930] 20 BADNAME Duplicate key name [RPF 2930] 21 BADALG Algorithm not supported [RPF 2930] 22 - 3,840 Available for assignment 0x0016 - 0x0F00 3,841 - 4,095 Private Use 0x0F01 - 0x0FFF 4,096 - 5,7343 Available for assignment 0x1000 - 0xDFFF 57,344 - 65,534 Specification Required 0xE000 - 0xFFFE 65,535 Reserved 0xFFFF Assignment of new RCODE listed above as "Available for assignment" requires an IETF Standards Action modified by [RFC 4020]. Assignment of RCODE 65,535 requires an IETF Standards Action. 3. DNS Resource Records All RRs have the same top level format shown in the figure below taken from [RFC 1035]: D. Eastlake 3rd [Page 6]
INTERNET-DRAFT DNS IANA Considerations June 2005 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | / / / NAME / | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | TYPE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | CLASS | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | TTL | | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | RDLENGTH | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--| / RDATA / / / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ NAME is an owner name, i.e., the name of the node to which this resource record pertains. NAMEs are specific to a CLASS as described in section 3.2. NAMEs consist of an ordered sequence of one or more labels each of which has a label type [RFC 1035, 2671]. TYPE is a two octet unsigned integer containing one of the RR TYPE codes. See section 3.1. CLASS is a two octet unsigned integer containing one of the RR CLASS codes. See section 3.2. TTL is a four octet (32 bit) bit unsigned integer that specifies the number of seconds that the resource record may be cached before the source of the information should again be consulted. Zero is interpreted to mean that the RR can only be used for the transaction in progress. RDLENGTH is an unsigned 16 bit integer that specifies the length in octets of the RDATA field. RDATA is a variable length string of octets that constitutes the resource. The format of this information varies according to the TYPE and in some cases the CLASS of the resource record. D. Eastlake 3rd [Page 7]
INTERNET-DRAFT DNS IANA Considerations June 2005 3.1 RR TYPE IANA Considerations There are three subcategories of RR TYPE numbers: data TYPEs, QTYPEs, and MetaTYPEs. Data TYPEs are the primary means of storing data. QTYPES can only be used in queries. Meta-TYPEs designate transient data associated with an particular DNS message and in some cases can also be used in queries. Thus far, data TYPEs have been assigned from 1 upwards plus the block from 100 through 103 while Q and Meta Types have been assigned from 255 downwards (except for the OPT Meta-RR which is assigned TYPE 41). There have been DNS implementations which made caching decisions based on the top bit of the bottom byte of the RR TYPE. There are currently three Meta-TYPEs assigned: OPT [RFC 2671], TSIG [RFC 2845], and TKEY [RFC 2930]. There are currently five QTYPEs assigned: * (all), MAILA, MAILB, AXFR, and IXFR. Considerations for the allocation of new RR TYPEs are as follows: Decimal Hexadecimal 0 0x0000 - TYPE zero is used as a special indicator for the SIG RR [RFC 2535] and in other circumstances and must never be allocated for ordinary use. 1 - 127 0x0001 - 0x007F - remaining TYPEs in this range are assigned for data TYPEs by the DNS Special Allocation Policy. 128 - 255 0x0080 - 0x00FF - remaining TYPEs in this rage are assigned for Q and Meta TYPEs by the DNS Special Allocation Policy. 256 - 32,767 0x0100 - 0x7FFF - assigned for data, Q, or Meta TYPE use by the DNS Special Allocation Policy. 32,768 - 65,279 0x8000 - 0xFEFF - Specification Required as defined in [RFC 2434]. 65280 - 65534 0xFF00 - 0xFFFE - Private Use. D. Eastlake 3rd [Page 8]
INTERNET-DRAFT DNS IANA Considerations June 2005 65,535 0xFFFF - can only be assigned by an IETF Standards Action. 3.1.1 Special Note on the OPT RR The OPT (OPTion) RR, number 41, is specified in [RFC 2671]. Its primary purpose is to extend the effective field size of various DNS fields including RCODE, label type, OpCode, flag bits, and RDATA size. In particular, for resolvers and servers that recognize it, it extends the RCODE field from 4 to 12 bits. 3.1.2 The AFSDB RR Subtype Field The AFSDB RR [RFC 1183] is a CLASS insensitive RR that has the same RDATA field structure as the MX RR but the 16 bit unsigned integer field at the beginning of the RDATA is interpreted as a subtype as follows: Decimal Hexadecimal 0 0x0000 - Allocation requires IETF Standards Action. 1 0x0001 - Andrews File Service v3.0 Location Service [RFC 1183]. 2 0x0002 - DCE/NCA root cell directory node [RFC 1183]. 3 - 65,534 0x0003 - 0xFFFE - Allocation by the DNS Special Allocation Policy. 65,535 0xFFFF - Allocation requires IETF Standards Action. 3.2 RR CLASS IANA Considerations DNS CLASSes have been little used but constitute another dimension of the DNS distributed database. In particular, there is no necessary relationship between the name space or root servers for one CLASS and those for another CLASS. The same name can have completely different meanings in different CLASSes although the label types are the same and the null label is usable only as root in every CLASS. However, D. Eastlake 3rd [Page 9]
INTERNET-DRAFT DNS IANA Considerations June 2005 as global networking and DNS have evolved, the IN, or Internet, CLASS has dominated DNS use. There are two subcategories of DNS CLASSes: normal data containing classes and QCLASSes that are only meaningful in queries or updates. The current CLASS assignments and considerations for future assignments are as follows: Decimal Hexadecimal 0 0x0000 - assignment requires an IETF Standards Action. 1 0x0001 - Internet (IN). 2 0x0002 - available for assignment by the DNS Special Allocation Policy as a data CLASS. 3 0x0003 - Chaos (CH) [Moon 1981]. 4 0x0004 - Hesiod (HS) [Dyer 1987]. 5 - 127 0x0005 - 0x007F - available for assignment by the DNS Special Allocation Policy for data CLASSes only. 128 - 253 0x0080 - 0x00FD - available for assignment by the DNS Special Allocation Policy for QCLASSes only. 254 0x00FE - QCLASS None [RFC 2136]. 255 0x00FF - QCLASS Any [RFC 1035]. 256 - 32767 0x0100 - 0x7FFF - assigned by the DNS Special Allocation Policy. 32768 - 65280 0x8000 - 0xFEFF - assigned based on Specification Required as defined in [RFC 2434]. D. Eastlake 3rd [Page 10]
INTERNET-DRAFT DNS IANA Considerations June 2005 65280 - 65534 0xFF00 - 0xFFFE - Private Use. 65535 0xFFFF - can only be assigned by an IETF Standards Action. 3.3 RR NAME Considerations DNS NAMEs are sequences of labels [RFC 1035]. The last label in each NAME is "ROOT" which is the zero length label. By definition, the null or ROOT label can not be used for any other NAME purpose. At the present time, there are two categories of label types, data labels and compression labels. Compression labels are pointers to data labels elsewhere within an RR or DNS message and are intended to shorten the wire encoding of NAMEs. The two existing data label types are sometimes referred to as Text and Binary. Text labels can, in fact, include any octet value including zero value octets but most current uses involve only [US-ASCII]. For retrieval, Text labels are defined to treat ASCII upper and lower case letter codes as matching [insensitive]. Binary labels are bit sequences [RFC 2673]. The Binary label type is Experimental [RFC 3363]. IANA considerations for label types are given in [RFC 2671]. NAMEs are local to a CLASS. The Hesiod [Dyer 1987] and Chaos [Moon 1981] CLASSes are essentially for local use. The IN or Internet CLASS is thus the only DNS CLASS in global use on the Internet at this time. A somewhat out-of-date description of name allocation in the IN Class is given in [RFC 1591]. Some information on reserved top level domain names is in Best Current Practice 32 [RFC 2606]. 4. Security Considerations This document addresses IANA considerations in the allocation of general DNS parameters, not security. See [RFC 4033, 4034, 4035] for secure DNS considerations. Appendix: Changes from RFC 2929 RFC Editor: This section should be deleted for publication. D. Eastlake 3rd [Page 11]
INTERNET-DRAFT DNS IANA Considerations June 2005 Changes from RFC 2929 to this draft: 1. Changed many "IETF Consensus" and some "IETF Standards Action" allocation requirements changed to be "DNS Special Allocation Policy" and add the specification of that policy. Change most remaining "IETF Standards Action" allocation requirements to say "as modified by [RFC 4020]". 2. Updated various RFC references. 3. Mentioned that the Binary label type is now Experimental and IQuery is Obsolete.. 4. Changed allocation status of RR Type 0xFFFF and RCODE 0xFFFF to be IETF Standards Action required. 5. Change allocation status of the upper one eighth of the current RCODE space (except 0xFFFF) to be Specification Required. 6. Add allocation policy for the AFSDB RR Subtype field. 7. Addition of reference to case insensitive draft. D. Eastlake 3rd [Page 12]
INTERNET-DRAFT DNS IANA Considerations June 2005 Copyright and Disclaimer Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Normative References [RFC 1034] - Mockapetris, P., "Domain Names - Concepts and Facilities", STD 13, RFC 1034, November 1987. [RFC 1035] - Mockapetris, P., "Domain Names - Implementation and Specifications", STD 13, RFC 1035, November 1987. [RFC 1183] - Everhart, C., Mamakos, L., Ullmann, R., and P. Mockapetris, "New DNS RR Definitions", RFC 1183, October 1990. [RFC 1996] - Vixie, P., "A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)", RFC 1996, August 1996. [RFC 2136] - Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. [RFC 2181] - Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, July 1997. [RFC 2434] - Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC 2671] - Vixie, P., "Extension mechanisms for DNS (EDNS0)", RFC 2671, August 1999. [RFC 2673] - Crawford, M., "Binary Labels in the Domain Name System", RFC 2673, August 1999. [RFC 2845] - Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington, "Secret Key Transaction Authentication for DNS (TSIG)", RFC 2845, May 2000. D. Eastlake 3rd [Page 13]
INTERNET-DRAFT DNS IANA Considerations June 2005 [RFC 2930] - Eastlake, D., "Secret Key Establishment for DNS (TKEY RR)", September 2000. [RFC 3363] - Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T. Hain, "Representing Internet Protocol version 6 (IPv6) Addresses in the Domain Name System (DNS)", RFC 3363, August 2002. [RFC 3425] - Lawrence, D., "Obsoleting IQUERY", RFC 3425, November 2002. [RFC 4020] - Kompella, K. and A. Zinin, "Early IANA Allocation of Standards Track Code Points", BCP 100, RFC 4020, February 2005. [RFC 4033] - Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005. [RFC 4034] - Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, March 2005. [RFC 4044] - Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, March 2005. [US-ASCII] - ANSI, "USA Standard Code for Information Interchange", X3.4, American National Standards Institute: New York, 1968. Informative References [Dyer 1987] - Dyer, S., and F. Hsu, "Hesiod", Project Athena Technical Plan - Name Service, April 1987, [Moon 1981] - D. Moon, "Chaosnet", A.I. Memo 628, Massachusetts Institute of Technology Artificial Intelligence Laboratory, June 1981. [RFC 1591] - Postel, J., "Domain Name System Structure and Delegation", RFC 1591, March 1994. [RFC 2929] - Eastlake 3rd, D., Brunner-Williams, E., and B. Manning, "Domain Name System (DNS) IANA Considerations", BCP 42, RFC 2929, September 2000. [RFC 2606] - Eastlake, D. and A. Panitz, "Reserved Top Level DNS Names", RFC 2606, June 1999. [insensitive] - Eastlake, D., "Domain Name System (DNS) Case D. Eastlake 3rd [Page 14]
INTERNET-DRAFT DNS IANA Considerations June 2005 Insensitivity Clarification", draft-ietf-dnsext-insensitive-*.txt, work in progress. D. Eastlake 3rd [Page 15]
INTERNET-DRAFT DNS IANA Considerations June 2005 Authors Addresses Donald E. Eastlake 3rd Motorola Laboratories 155 Beaver Street Milford, MA 01757 USA Telephone: +1-508-786-7554 (w) email: Donald.Eastlake@motorola.com Expiration and File Name This draft expires December 2005. Its file name is draft-eastlake-dnsext-2929bis-01.txt. D. Eastlake 3rd [Page 16]