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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT Andreas Gustafsson 2 draft-ietf-dnsext-unknown-rrs-03.txt Nominum Inc. 3 June 2002 5 Handling of Unknown DNS RR Types 7 Status of this Memo 9 This document is an Internet-Draft and is in full conformance with 10 all provisions of Section 10 of RFC2026. 12 Internet-Drafts are working documents of the Internet Engineering 13 Task Force (IETF), its areas, and its working groups. Note that 14 other groups may also distribute working documents as Internet- 15 Drafts. 17 Internet-Drafts are draft documents valid for a maximum of six months 18 and may be updated, replaced, or obsoleted by other documents at any 19 time. It is inappropriate to use Internet-Drafts as reference 20 material or to cite them other than as "work in progress." 22 The list of current Internet-Drafts can be accessed at 23 http://www.ietf.org/ietf/1id-abstracts.txt 25 The list of Internet-Draft Shadow Directories can be accessed at 26 http://www.ietf.org/shadow.html. 28 Abstract 30 Extending the Domain Name System with new Resource Record types 31 currently requires changes to name server software. This document 32 specifies the changes necessary to allow future DNS implementations 33 to handle new RR types transparently. 35 1. Introduction 37 The DNS is designed to be extensible to support new services through 38 the introduction of new resource record (RR) types. In practice, 39 deploying a new RR type currently requires changes to the name server 40 software not only at the authoritative DNS server that is providing 41 the new information and the client making use of it, but also at all 42 slave servers for the zone containing it, and in some cases also at 43 caching name servers and forwarders used by the client. 45 Because the deployment of new server software is slow and expensive, 46 the potential of the DNS in supporting new services has never been 47 fully realized. This memo proposes changes to name servers and to 48 procedures for defining new RR types aimed at simplifying the future 49 deployment of new RR types. 51 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 52 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 53 document are to be interpreted as described in [RFC 2119]. 55 2. Definition 57 An "RR of unknown type" is an RR whose RDATA format is not known to 58 the DNS implementation at hand, such that it cannot be converted to a 59 type-specific text format, compressed, or otherwise handled in a 60 type-specific way, and whose type is not an assigned QTYPE or Meta- 61 TYPE in RFC2929 section 3.1 nor within the range reserved in that 62 section for assignment only to QTYPEs and Meta-TYPEs. 64 In the case of a type whose RDATA format is class specific, an RR is 65 considered to be of unknown type when the RDATA format for that 66 combination of type and class is not known. 68 3. Transparency 70 To enable new RR types to be deployed without server changes, name 71 servers and resolvers MUST handle RRs of unknown type transparently. 72 That is, they must treat the RDATA section of such RRs as 73 unstructured binary data, storing and transmitting it without change 74 [RFC1123]. 76 4. Domain Name Compression 78 RRs containing compression pointers in the RDATA part cannot be 79 treated transparently, as the compression pointers are only 80 meaningful within the context of a DNS message. Transparently 81 copying the RDATA into a new DNS message would cause the compression 82 pointers to point at the corresponding location in the new message, 83 which now contains unrelated data. This would cause the compressed 84 name to be corrupted. 86 To avoid such corruption, servers MUST NOT compress domain names 87 embedded in the RDATA of types that are class-specific or not well- 88 known. This requirement was stated in RFC1123 without defining the 89 term "well-known"; it is hereby specified that only the RR types 90 defined in RFC1035 are to be considered "well-known". 92 Receiving servers MUST decompress domain names in RRs of well-known 93 type, and SHOULD also decompress RRs of type RP, AFSDB, RT, SIG, PX, 94 NXT, NAPTR, and SRV (although the current specification of the SRV RR 95 in RFC2782 prohibits compression, RFC2052 mandated it, and some 96 servers following that earlier specification are still in use). 98 Future specifications for new RR types that contain domain names 99 within their RDATA MUST NOT allow the use of name compression for 100 those names, and SHOULD explicitly state that the embedded domain 101 names MUST NOT be compressed. 103 As noted in RFC1123, the owner name of an RR is always eligible for 104 compression. 106 5. Text Representation 108 In the "type" field of a master file line, an unknown RR type is 109 represented by the word "TYPE" immediately followed by the decimal RR 110 type number, with no intervening whitespace. In the "class" field, 111 an unknown class is similarly represented as the word "CLASS" 112 immediately followed by the decimal class number. 114 This convention allows types and classes to be distinguished from 115 each other and from TTL values, allowing the "[] [] 116 " and "[] [] " forms of 117 RFC1035 to both be unambiguously parsed. 119 The RDATA section of an RR of unknown type is represented as a 120 sequence of white space separated words as follows: 122 The special token \# (a backslash immediately 123 followed by a hash sign), which identifies the 124 RDATA as having the generic encoding defined 125 herein rather than a traditional type-specific 126 encoding. 128 An unsigned decimal integer specifying the 129 RDATA length in octets. 131 Zero or more words of hexadecimal data encoding 132 the actual RDATA field, each containing an even 133 number of hexadecimal digits. 135 If the RDATA is of zero length, the text representation contains only 136 the \# token and the single zero representing the length. 138 An implementation MAY also choose to represent some RRs of known type 139 using the above generic representations for the type, class and/or 140 RDATA, which carries the benefit of making the resulting master file 141 portable to servers where these types are unknown. Using the generic 142 representation for the RDATA of an RR of known type can also be 143 useful in the case of an RR type where the text format varies 144 depending on a version, protocol, or similar field (or several) 145 embedded in the RDATA when such a field has a value for which no text 146 format is known, e.g., a LOC RR [RFC1876] with a VERSION other than 147 0. 149 Even though an RR of known type represented in the \# format is 150 effectively treated as an unknown type for the purpose of parsing the 151 RDATA text representation, all further processing by the server MUST 152 treat it as a known type and take into account any applicable type- 153 specific rules regarding compression, canonicalization, etc. 155 The following are examples of RRs represented in this manner, 156 illustrating various combinations of generic and type-specific 157 encodings for the different fields of the master file format: 159 a.example. CLASS32 TYPE731 \# 6 abcd ( 160 ef 01 23 45 ) 161 b.example. HS TYPE62347 \# 0 162 e.example. IN A \# 4 0A000001 163 e.example. CLASS1 TYPE1 10.0.0.2 165 6. Equality Comparison 167 Certain DNS protocols, notably Dynamic Update [RFC2136], require RRs 168 to be compared for equality. Two RRs of the same unknown type are 169 considered equal when their RDATA is bitwise equal. To ensure that 170 the outcome of the comparison is identical whether the RR is known to 171 the server or not, specifications for new RR types MUST NOT specify 172 type-specific comparison rules. 174 This implies that embedded domain names, being included in the 175 overall bitwise comparison, are compared in a case-sensitive manner. 176 As a result, when a new RR type contains one or more embedded domain 177 names, it is possible to have multiple RRs owned by the same name 178 that differ only in the character case of the embedded domain 179 name(s). This is similar to the existing possibility of multiple TXT 180 records differing only in character case, and not expected to cause 181 any problems in practice. 183 7. DNSSEC Canonical Form and Ordering 185 DNSSEC [RFC2535] defines a canonical form and ordering for RRs. In 186 the canonical form, domain names embedded in the RDATA are converted 187 to lower case. 189 To ensure backwards compatibility, this canonical form remains 190 unchanged for any RR types defined in RFC2931 or earlier. That is, 191 the domain names embedded in RRs of type NS, MD, MF, CNAME, SOA, MB, 192 MG, MR, PTR, HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, 193 NAPTR, KX, SRV, DNAME, and A6 are converted to lower case. For all 194 other RR types, the canonical form is hereby changed such that no 195 downcasing of embedded domain names takes place. The owner name is 196 still set to lower case. 198 The canonical ordering is as specified in RFC2535 section 8.3, where 199 the octet sequence is the canonical form as revised by this 200 specification. 202 8. Additional Section Processing 204 Unknown RR types cause no additional section processing. Future RR 205 type specifications MAY specify type-specific additional section 206 processing rules, but any such processing MUST be optional as it can 207 only be performed by servers for which the RR type in case is known. 209 9. IANA Considerations 211 The IANA is hereby requested to verify that specifications for new RR 212 types requesting an RR type number comply with this specification. 213 In particular, the IANA MUST NOT assign numbers to new RR types whose 214 specification allows embedded domain names to be compressed. 216 10. Security Considerations 218 This specification is not believed to cause any new security 219 problems, nor to solve any existing ones. 221 References 223 [RFC1034] - Domain Names - Concepts and Facilities, P. Mockapetris, 224 November 1987. 226 [RFC1035] - Domain Names - Implementation and Specifications, P. 227 Mockapetris, November 1987. 229 [RFC1123] - Requirements for Internet Hosts -- Application and 230 Support, R. Braden, Editor, October 1989. 232 [RFC1876] - A Means for Expressing Location Information in the Domain 233 Name System, C. Davis, P. Vixie, T. Goodwin, I. Dickinson, January 234 1996. 236 [RFC2052] - A DNS RR for specifying the location of services (DNS 237 SRV), A. Gulbrandsen, P. Vixie, October 1996. Obsoleted by RFC2782. 239 [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate 240 Requirement Levels", BCP 14, RFC 2119, March 1997. 242 [RFC2136] - Dynamic Updates in the Domain Name System (DNS UPDATE). 243 P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997. 245 [RFC2535] - Domain Name System Security Extensions. D. Eastlake, 246 March 1999. 248 [RFC2782] - A DNS RR for specifying the location of services (DNS 249 SRV). A. Gulbrandsen, P. Vixie, L. Esibov, February 2000. 251 [RFC2929] - Domain Name System (DNS) IANA Considerations. D. 252 Eastlake, E. Brunner-Williams, B. Manning, September 2000. 254 Author's Address 256 Andreas Gustafsson 257 Nominum Inc. 258 2385 Bay Rd 259 Redwood City, CA 94063 260 USA 262 Phone: +1 650 381 6004 264 Email: gson@nominum.com 266 Full Copyright Statement 268 Copyright (C) The Internet Society (2001 - 2002). All Rights Reserved. 270 This document and translations of it may be copied and furnished to 271 others, and derivative works that comment on or otherwise explain it 272 or assist in its implmentation may be prepared, copied, published and 273 distributed, in whole or in part, without restriction of any kind, 274 provided that the above copyright notice and this paragraph are 275 included on all such copies and derivative works. However, this 276 document itself may not be modified in any way, such as by removing 277 the copyright notice or references to the Internet Society or other 278 Internet organizations, except as needed for the purpose of 279 developing Internet standards in which case the procedures for 280 copyrights defined in the Internet Standards process must be 281 followed, or as required to translate it into languages other than 282 English. 284 The limited permissions granted above are perpetual and will not be 285 revoked by the Internet Society or its successors or assigns. 287 This document and the information contained herein is provided on an 288 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 289 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 290 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 291 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 292 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."