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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT Andreas Gustafsson 3 draft-ietf-dnsext-unknown-rrs-04.txt Nominum Inc. 4 September 2002 6 Handling of Unknown DNS RR Types 8 Status of this Memo 10 This document is an Internet-Draft and is in full conformance with 11 all provisions of Section 10 of RFC2026. 13 Internet-Drafts are working documents of the Internet Engineering 14 Task Force (IETF), its areas, and its working groups. Note that 15 other groups may also distribute working documents as Internet- 16 Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as "work in progress." 23 The list of current Internet-Drafts can be accessed at 24 http://www.ietf.org/ietf/1id-abstracts.txt 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 Abstract 31 Extending the Domain Name System with new Resource Record types 32 currently requires changes to name server software. This document 33 specifies the changes necessary to allow future DNS implementations 34 to handle new RR types transparently. 36 1. Introduction 38 The DNS is designed to be extensible to support new services through 39 the introduction of new resource record (RR) types. In practice, 40 deploying a new RR type currently requires changes to the name server 41 software not only at the authoritative DNS server that is providing 42 the new information and the client making use of it, but also at all 43 slave servers for the zone containing it, and in some cases also at 44 caching name servers and forwarders used by the client. 46 Because the deployment of new server software is slow and expensive, 47 the potential of the DNS in supporting new services has never been 48 fully realized. This memo proposes changes to name servers and to 49 procedures for defining new RR types aimed at simplifying the future 50 deployment of new RR types. 52 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 53 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 54 document are to be interpreted as described in [RFC 2119]. 56 2. Definition 58 An "RR of unknown type" is an RR whose RDATA format is not known to 59 the DNS implementation at hand, such that it cannot be converted to a 60 type-specific text format, compressed, or otherwise handled in a 61 type-specific way, and whose type is not an assigned QTYPE or Meta- 62 TYPE in RFC2929 section 3.1 nor within the range reserved in that 63 section for assignment only to QTYPEs and Meta-TYPEs. 65 In the case of a type whose RDATA format is class specific, an RR is 66 considered to be of unknown type when the RDATA format for that 67 combination of type and class is not known. 69 3. Transparency 71 To enable new RR types to be deployed without server changes, name 72 servers and resolvers MUST handle RRs of unknown type transparently. 73 That is, they must treat the RDATA section of such RRs as 74 unstructured binary data, storing and transmitting it without change 75 [RFC1123]. 77 To ensure the correct operation of equality comparison (section 6) 78 and of the DNSSEC canonical form (section 7) when an RR type is known 79 to some but not all of the servers involved, servers MUST also 80 exactly preserve the RDATA of RRs of known type, except for changes 81 due to compression or decompression where allowed by section 4 of 82 this memo. In particular, the character case of domain names that 83 are not subject to compression MUST be preserved. 85 4. Domain Name Compression 87 RRs containing compression pointers in the RDATA part cannot be 88 treated transparently, as the compression pointers are only 89 meaningful within the context of a DNS message. Transparently 90 copying the RDATA into a new DNS message would cause the compression 91 pointers to point at the corresponding location in the new message, 92 which now contains unrelated data. This would cause the compressed 93 name to be corrupted. 95 To avoid such corruption, servers MUST NOT compress domain names 96 embedded in the RDATA of types that are class-specific or not well- 97 known. This requirement was stated in RFC1123 without defining the 98 term "well-known"; it is hereby specified that only the RR types 99 defined in RFC1035 are to be considered "well-known". 101 Receiving servers MUST decompress domain names in RRs of well-known 102 type, and SHOULD also decompress RRs of type RP, AFSDB, RT, SIG, PX, 103 NXT, NAPTR, and SRV (although the current specification of the SRV RR 104 in RFC2782 prohibits compression, RFC2052 mandated it, and some 105 servers following that earlier specification are still in use). 107 Future specifications for new RR types that contain domain names 108 within their RDATA MUST NOT allow the use of name compression for 109 those names, and SHOULD explicitly state that the embedded domain 110 names MUST NOT be compressed. 112 As noted in RFC1123, the owner name of an RR is always eligible for 113 compression. 115 5. Text Representation 117 In the "type" field of a master file line, an unknown RR type is 118 represented by the word "TYPE" immediately followed by the decimal RR 119 type number, with no intervening whitespace. In the "class" field, 120 an unknown class is similarly represented as the word "CLASS" 121 immediately followed by the decimal class number. 123 This convention allows types and classes to be distinguished from 124 each other and from TTL values, allowing the "[] [] 125 " and "[] [] " forms of 126 RFC1035 to both be unambiguously parsed. 128 The RDATA section of an RR of unknown type is represented as a 129 sequence of white space separated words as follows: 131 The special token \# (a backslash immediately 132 followed by a hash sign), which identifies the 133 RDATA as having the generic encoding defined 134 herein rather than a traditional type-specific 135 encoding. 137 An unsigned decimal integer specifying the 138 RDATA length in octets. 140 Zero or more words of hexadecimal data encoding 141 the actual RDATA field, each containing an even 142 number of hexadecimal digits. 144 If the RDATA is of zero length, the text representation contains only 145 the \# token and the single zero representing the length. 147 An implementation MAY also choose to represent some RRs of known type 148 using the above generic representations for the type, class and/or 149 RDATA, which carries the benefit of making the resulting master file 150 portable to servers where these types are unknown. Using the generic 151 representation for the RDATA of an RR of known type can also be 152 useful in the case of an RR type where the text format varies 153 depending on a version, protocol, or similar field (or several) 154 embedded in the RDATA when such a field has a value for which no text 155 format is known, e.g., a LOC RR [RFC1876] with a VERSION other than 156 0. 158 Even though an RR of known type represented in the \# format is 159 effectively treated as an unknown type for the purpose of parsing the 160 RDATA text representation, all further processing by the server MUST 161 treat it as a known type and take into account any applicable type- 162 specific rules regarding compression, canonicalization, etc. 164 The following are examples of RRs represented in this manner, 165 illustrating various combinations of generic and type-specific 166 encodings for the different fields of the master file format: 168 a.example. CLASS32 TYPE731 \# 6 abcd ( 169 ef 01 23 45 ) 170 b.example. HS TYPE62347 \# 0 171 e.example. IN A \# 4 0A000001 172 e.example. CLASS1 TYPE1 10.0.0.2 174 6. Equality Comparison 176 Certain DNS protocols, notably Dynamic Update [RFC2136], require RRs 177 to be compared for equality. Two RRs of the same unknown type are 178 considered equal when their RDATA is bitwise equal. To ensure that 179 the outcome of the comparison is identical whether the RR is known to 180 the server or not, specifications for new RR types MUST NOT specify 181 type-specific comparison rules. 183 This implies that embedded domain names, being included in the 184 overall bitwise comparison, are compared in a case-sensitive manner. 185 As a result, when a new RR type contains one or more embedded domain 186 names, it is possible to have multiple RRs owned by the same name 187 that differ only in the character case of the embedded domain 188 name(s). This is similar to the existing possibility of multiple TXT 189 records differing only in character case, and not expected to cause 190 any problems in practice. 192 7. DNSSEC Canonical Form and Ordering 194 DNSSEC [RFC2535] defines a canonical form and ordering for RRs. In 195 the canonical form, domain names embedded in the RDATA are converted 196 to lower case. 198 To ensure backwards compatibility, this canonical form remains 199 unchanged for any RR types defined in RFC2931 or earlier. That is, 200 the domain names embedded in RRs of type NS, MD, MF, CNAME, SOA, MB, 201 MG, MR, PTR, HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, 202 NAPTR, KX, SRV, DNAME, and A6 are converted to lower case according 203 to the DNS rules for character comparisons. 205 For all other RR types, the canonical form is hereby changed such 206 that no downcasing of embedded domain names takes place. The owner 207 name is always set to lower case according to the DNS rules for 208 character comparisons, regardless of the RR type. 210 The canonical ordering is as specified in RFC2535 section 8.3, where 211 the octet sequence is the canonical form as revised by this 212 specification. 214 8. Additional Section Processing 216 Unknown RR types cause no additional section processing. Future RR 217 type specifications MAY specify type-specific additional section 218 processing rules, but any such processing MUST be optional as it can 219 only be performed by servers for which the RR type in case is known. 221 9. IANA Considerations 223 The IANA is hereby requested to verify that specifications for new RR 224 types requesting an RR type number comply with this specification. 225 In particular, the IANA MUST NOT assign numbers to new RR types whose 226 specification allows embedded domain names to be compressed. 228 10. Security Considerations 230 This specification is not believed to cause any new security 231 problems, nor to solve any existing ones. 233 References 235 [RFC1034] - Domain Names - Concepts and Facilities, P. Mockapetris, 236 November 1987. 238 [RFC1035] - Domain Names - Implementation and Specifications, P. 239 Mockapetris, November 1987. 241 [RFC1123] - Requirements for Internet Hosts -- Application and 242 Support, R. Braden, Editor, October 1989. 244 [RFC1876] - A Means for Expressing Location Information in the Domain 245 Name System, C. Davis, P. Vixie, T. Goodwin, I. Dickinson, January 246 1996. 248 [RFC2052] - A DNS RR for specifying the location of services (DNS 249 SRV), A. Gulbrandsen, P. Vixie, October 1996. Obsoleted by RFC2782. 251 [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate 252 Requirement Levels", BCP 14, RFC 2119, March 1997. 254 [RFC2136] - Dynamic Updates in the Domain Name System (DNS UPDATE). 255 P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997. 257 [RFC2535] - Domain Name System Security Extensions. D. Eastlake, 258 March 1999. 260 [RFC2782] - A DNS RR for specifying the location of services (DNS 261 SRV). A. Gulbrandsen, P. Vixie, L. Esibov, February 2000. 263 [RFC2929] - Domain Name System (DNS) IANA Considerations. D. 264 Eastlake, E. Brunner-Williams, B. Manning, September 2000. 266 Author's Address 268 Andreas Gustafsson 269 Nominum Inc. 270 2385 Bay Rd 271 Redwood City, CA 94063 272 USA 274 Phone: +1 650 381 6004 276 Email: gson@nominum.com 278 Full Copyright Statement 280 Copyright (C) The Internet Society (2001 - 2002). All Rights Reserved. 282 This document and translations of it may be copied and furnished to 283 others, and derivative works that comment on or otherwise explain it 284 or assist in its implmentation may be prepared, copied, published and 285 distributed, in whole or in part, without restriction of any kind, 286 provided that the above copyright notice and this paragraph are 287 included on all such copies and derivative works. However, this 288 document itself may not be modified in any way, such as by removing 289 the copyright notice or references to the Internet Society or other 290 Internet organizations, except as needed for the purpose of 291 developing Internet standards in which case the procedures for 292 copyrights defined in the Internet Standards process must be 293 followed, or as required to translate it into languages other than 294 English. 296 The limited permissions granted above are perpetual and will not be 297 revoked by the Internet Society or its successors or assigns. 299 This document and the information contained herein is provided on an 300 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 301 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 302 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 303 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 304 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."