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Summary: 4 errors (**), 0 flaws (~~), 12 warnings (==), 5 comments (--). 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-05.txt Nominum Inc. 3 March 2003 5 Updates: RFC 1034, RFC 2163, RFC 2535 7 Handling of Unknown DNS Resource Record Types 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as Internet- 17 Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at 25 http://www.ietf.org/ietf/1id-abstracts.txt 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 Abstract 32 Extending the Domain Name System with new Resource Record (RR) types 33 currently requires changes to name server software. This document 34 specifies the changes necessary to allow future DNS implementations 35 to handle new RR types transparently. 37 1. Introduction 39 The DNS is designed to be extensible to support new services through 40 the introduction of new resource record (RR) types. In practice, 41 deploying a new RR type currently requires changes to the name server 42 software not only at the authoritative DNS server that is providing 43 the new information and the client making use of it, but also at all 44 slave servers for the zone containing it, and in some cases also at 45 caching name servers and forwarders used by the client. 47 Because the deployment of new server software is slow and expensive, 48 the potential of the DNS in supporting new services has never been 49 fully realized. This memo proposes changes to name servers and to 50 procedures for defining new RR types aimed at simplifying the future 51 deployment of new RR types. 53 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 54 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 55 document are to be interpreted as described in [RFC 2119]. 57 2. Definition 59 An "RR of unknown type" is an RR whose RDATA format is not known to 60 the DNS implementation at hand, such that it cannot be converted to a 61 type-specific text format, compressed, or otherwise handled in a 62 type-specific way, and whose type is not an assigned QTYPE or Meta- 63 TYPE in RFC2929 section 3.1 nor within the range reserved in that 64 section for assignment only to QTYPEs and Meta-TYPEs. 66 In the case of a type whose RDATA format is class specific, an RR is 67 considered to be of unknown type when the RDATA format for that 68 combination of type and class is not known. 70 3. Transparency 72 To enable new RR types to be deployed without server changes, name 73 servers and resolvers MUST handle RRs of unknown type transparently. 74 That is, they must treat the RDATA section of such RRs as 75 unstructured binary data, storing and transmitting it without change 76 [RFC1123]. 78 To ensure the correct operation of equality comparison (section 6) 79 and of the DNSSEC canonical form (section 7) when an RR type is known 80 to some but not all of the servers involved, servers MUST also 81 exactly preserve the RDATA of RRs of known type, except for changes 82 due to compression or decompression where allowed by section 4 of 83 this memo. In particular, the character case of domain names that 84 are not subject to compression MUST be preserved. 86 4. Domain Name Compression 88 RRs containing compression pointers in the RDATA part cannot be 89 treated transparently, as the compression pointers are only 90 meaningful within the context of a DNS message. Transparently 91 copying the RDATA into a new DNS message would cause the compression 92 pointers to point at the corresponding location in the new message, 93 which now contains unrelated data. This would cause the compressed 94 name to be corrupted. 96 To avoid such corruption, servers MUST NOT compress domain names 97 embedded in the RDATA of types that are class-specific or not well- 98 known. This requirement was stated in RFC1123 without defining the 99 term "well-known"; it is hereby specified that only the RR types 100 defined in RFC1035 are to be considered "well-known". 102 The specifications of a few existing RR types have explicitly allowed 103 compression contrary to this specification: RFC2163 specified that 104 compression applies to the PX RR, and RFC2535 allowed compression in 105 SIG RRs and NXT RRs records. Since this specification disallows 106 compression in these cases, it is an update to RFC2163 (section 4) 107 and RFC2535 (sections 4.1.7 and 5.2). 109 Receiving servers MUST decompress domain names in RRs of well-known 110 type, and SHOULD also decompress RRs of type RP, AFSDB, RT, SIG, PX, 111 NXT, NAPTR, and SRV (although the current specification of the SRV RR 112 in RFC2782 prohibits compression, RFC2052 mandated it, and some 113 servers following that earlier specification are still in use). 115 Future specifications for new RR types that contain domain names 116 within their RDATA MUST NOT allow the use of name compression for 117 those names, and SHOULD explicitly state that the embedded domain 118 names MUST NOT be compressed. 120 As noted in RFC1123, the owner name of an RR is always eligible for 121 compression. 123 5. Text Representation 125 In the "type" field of a master file line, an unknown RR type is 126 represented by the word "TYPE" immediately followed by the decimal RR 127 type number, with no intervening whitespace. In the "class" field, 128 an unknown class is similarly represented as the word "CLASS" 129 immediately followed by the decimal class number. 131 This convention allows types and classes to be distinguished from 132 each other and from TTL values, allowing the "[] [] 133 " and "[] [] " forms of 134 RFC1035 to both be unambiguously parsed. 136 The RDATA section of an RR of unknown type is represented as a 137 sequence of white space separated words as follows: 139 The special token \# (a backslash immediately 140 followed by a hash sign), which identifies the 141 RDATA as having the generic encoding defined 142 herein rather than a traditional type-specific 143 encoding. 145 An unsigned decimal integer specifying the 146 RDATA length in octets. 148 Zero or more words of hexadecimal data encoding 149 the actual RDATA field, each containing an even 150 number of hexadecimal digits. 152 If the RDATA is of zero length, the text representation contains only 153 the \# token and the single zero representing the length. 155 An implementation MAY also choose to represent some RRs of known type 156 using the above generic representations for the type, class and/or 157 RDATA, which carries the benefit of making the resulting master file 158 portable to servers where these types are unknown. Using the generic 159 representation for the RDATA of an RR of known type can also be 160 useful in the case of an RR type where the text format varies 161 depending on a version, protocol, or similar field (or several) 162 embedded in the RDATA when such a field has a value for which no text 163 format is known, e.g., a LOC RR [RFC1876] with a VERSION other than 164 0. 166 Even though an RR of known type represented in the \# format is 167 effectively treated as an unknown type for the purpose of parsing the 168 RDATA text representation, all further processing by the server MUST 169 treat it as a known type and take into account any applicable type- 170 specific rules regarding compression, canonicalization, etc. 172 The following are examples of RRs represented in this manner, 173 illustrating various combinations of generic and type-specific 174 encodings for the different fields of the master file format: 176 a.example. CLASS32 TYPE731 \# 6 abcd ( 177 ef 01 23 45 ) 178 b.example. HS TYPE62347 \# 0 179 e.example. IN A \# 4 0A000001 180 e.example. CLASS1 TYPE1 10.0.0.2 182 6. Equality Comparison 184 Certain DNS protocols, notably Dynamic Update [RFC2136], require RRs 185 to be compared for equality. Two RRs of the same unknown type are 186 considered equal when their RDATA is bitwise equal. To ensure that 187 the outcome of the comparison is identical whether the RR is known to 188 the server or not, specifications for new RR types MUST NOT specify 189 type-specific comparison rules. 191 This implies that embedded domain names, being included in the 192 overall bitwise comparison, are compared in a case-sensitive manner. 194 As a result, when a new RR type contains one or more embedded domain 195 names, it is possible to have multiple RRs owned by the same name 196 that differ only in the character case of the embedded domain 197 name(s). This is similar to the existing possibility of multiple TXT 198 records differing only in character case, and not expected to cause 199 any problems in practice. 201 7. DNSSEC Canonical Form and Ordering 203 DNSSEC defines a canonical form and ordering for RRs [RFC2535, 204 section 8.1]. In that canonical form, domain names embedded in the 205 RDATA are converted to lower case. 207 The downcasing is necessary to ensure the correctness of DNSSEC 208 signatures when case distinctions in domain names are lost due to 209 compression, but since it requires knowledge of the presence and 210 position of embedded domain names, it cannot be applied to unknown 211 types. 213 To ensure continued consistency of the canonical form of RR types 214 where compression is allowed, and for continued interoperability with 215 existing implementations that already implement the RFC2535 canonical 216 form and apply it to their known RR types, the canonical form remains 217 unchanged for all RR types whose whose initial publication as an RFC 218 was prior to the initial publication of this specification as an RFC 219 (RFC TBD). 221 As a courtesy to implementors, it is hereby noted that the complete 222 set of such previously published RR types that contain embedded 223 domain names, and whose DNSSEC canonical form therefore involves 224 downcasing according to the DNS rules for character comparisons, 225 consists of the RR types NS, MD, MF, CNAME, SOA, MB, MG, MR, PTR, 226 HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, NAPTR, KX, SRV, 227 DNAME, and A6. 229 This document specifies that for all other RR types (whether treated 230 as unknown types or treated as known types according to an RR type 231 definition RFC more recent than than RFC TBD), the canonical form is 232 such that no downcasing of embedded domain names takes place, and 233 otherwise identical to the canonical form specified in RFC2535 234 section 8.1. 236 Note that the owner name is always set to lower case according to the 237 DNS rules for character comparisons, regardless of the RR type. 239 The DNSSEC canonical RR ordering is as specified in RFC2535 section 240 8.3, where the octet sequence is the canonical form as revised by 241 this specification. 243 8. Additional Section Processing 245 Unknown RR types cause no additional section processing. Future RR 246 type specifications MAY specify type-specific additional section 247 processing rules, but any such processing MUST be optional as it can 248 only be performed by servers for which the RR type in case is known. 250 9. IANA Considerations 252 The IANA is hereby requested to verify that specifications for new RR 253 types requesting an RR type number comply with this specification. 254 In particular, the IANA MUST NOT assign numbers to new RR types whose 255 specification allows embedded domain names to be compressed. 257 10. Security Considerations 259 This specification is not believed to cause any new security 260 problems, nor to solve any existing ones. 262 Normative References 264 [RFC1034] - Domain Names - Concepts and Facilities, P. Mockapetris, 265 November 1987. 267 [RFC1035] - Domain Names - Implementation and Specifications, P. 268 Mockapetris, November 1987. 270 [RFC1123] - Requirements for Internet Hosts -- Application and 271 Support, R. Braden, Editor, October 1989. 273 [RFC2119] - Key words for use in RFCs to Indicate Requirement Levels, 274 S. Bradner, BCP 14, March 1997. 276 [RFC2535] - Domain Name System Security Extensions. D. Eastlake, 277 March 1999. 279 [RFC2613] - Using the Internet DNS to Distribute MIXER Conformant 280 Global Address Mapping (MCGAM), C. Allocchio, January 1998. 282 [RFC2929] - Domain Name System (DNS) IANA Considerations, D. 283 Eastlake, E. Brunner-Williams, B. Manning, September 2000. 285 Non-normative References 287 [RFC1876] - A Means for Expressing Location Information in the Domain 288 Name System, C. Davis, P. Vixie, T. Goodwin, I. Dickinson, January 289 1996. 291 [RFC2052] - A DNS RR for specifying the location of services (DNS 292 SRV), A. Gulbrandsen, P. Vixie, October 1996. Obsoleted by RFC2782. 294 [RFC2136] - Dynamic Updates in the Domain Name System (DNS UPDATE), 295 P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997. 297 [RFC2782] - A DNS RR for specifying the location of services (DNS 298 SRV), A. Gulbrandsen, P. Vixie, L. Esibov, February 2000. 300 Author's Address 302 Andreas Gustafsson 303 Nominum Inc. 304 2385 Bay Rd 305 Redwood City, CA 94063 306 USA 308 Phone: +1 650 381 6004 310 Email: gson@nominum.com 312 Full Copyright Statement 314 Copyright (C) The Internet Society (2001 - 2002). All Rights Reserved. 316 This document and translations of it may be copied and furnished to 317 others, and derivative works that comment on or otherwise explain it 318 or assist in its implmentation may be prepared, copied, published and 319 distributed, in whole or in part, without restriction of any kind, 320 provided that the above copyright notice and this paragraph are 321 included on all such copies and derivative works. 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