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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-01.txt Nominum Inc. 3 July 2001 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. Definitions 57 In this document, a "well known" RR type means one defined in 58 RFC1035. 60 An "RR of unknown type" is an RR whose RDATA format is not known to 61 the DNS implementation at hand, such that it cannot be converted to a 62 type-specific text format, compressed, or otherwise handled in a 63 type-specific way, and whose type is not an assigned QTYPE or Meta- 64 TYPE in RFC2929 section 3.1 nor within the range reserved in that 65 section for assignment only to QTYPEs and Meta-TYPEs. 67 In the case of a type whose RDATA format is class specific, an RR is 68 considered to be of unknown type when the RDATA format for that 69 combination of type and class is not known. 71 3. Transparency 73 To enable new RR types to be deployed without server changes, name 74 servers and resolvers MUST handle RRs of unknown type transparently. 75 That is, they must treat the RDATA section of such RRs as 76 unstructured binary data, storing and transmitting it without change. 78 4. Domain Name Compression 80 RRs containing compression pointers in the RDATA part cannot be 81 treated transparently, as the compression pointers are only 82 meaningful within the context of a DNS message. Transparently 83 copying the RDATA into a new DNS message would cause the compression 84 pointers to point at the corresponding location in the new message, 85 which now contains unrelated data. This would cause the compressed 86 name to be corrupted. 88 To avoid such corruption, servers MUST NOT compress domain names 89 embedded in the RDATA of types that are not well known. 91 Receiving servers MUST decompress domain names in RRs of well-known 92 type, and SHOULD also decompress RRs of type RP, AFSDB, RT, SIG, PX, 93 NXT, NAPTR, and SRV (although the SRV RR is clearly defined to not 94 allow compression of the target field, some existing name servers 95 compress it anyway). 97 Future specifications for new RR types that contain domain names 98 within their RDATA MUST NOT allow the use of name compression for 99 those names, and SHOULD explicitly state that the embedded domain 100 names MUST NOT be compressed. 102 5. Text Representation 104 In the "type" field of a master file line, an unknown RR type is 105 represented by the word "TYPE" immediately followed by the decimal RR 106 type number, with no intervening whitespace. In the "class" field, 107 an unknown class is similarly represented as the word "CLASS" 108 immediately followed by the decimal class number. 110 This convention allows types and classes to be distinguished from 111 each other and from TTL values, allowing the "[] [] 112 " and "[] [] " forms of 113 RFC1035 to both be unambiguously parsed. 115 The RDATA section of an RR of unknown type is represented as a 116 sequence of white space separated words as follows: 118 The special token \# (a backslash immediately 119 followed by a hash sign), which identifies the 120 RDATA as having the generic encoding defined 121 herein rather than a traditional type-specific 122 encoding. 124 An unsigned decimal integer specifying the 125 RDATA length in octets. 127 Zero or more words of hexadecimal data encoding 128 the actual RDATA field, each containing an even 129 number of hexadecimal digits. 131 If the RDATA is of zero length, the text representation contains only 132 the \# token and the single zero representing the length. 134 An implementation MAY also choose to represent some RRs of known type 135 using the above generic representations for the type, class and/or 136 RDATA, which carries the benefit of making the resulting master file 137 portable to servers where these types are unknown. 139 Even though an RR of known type represented in the \# format is 140 effectively treated as an unknown type for the purpose of parsing the 141 RDATA text representation, all further processing by the server MUST 142 treat it as a known type and take into account any applicable type- 143 specific rules regarding compression, canonicalization, etc. 145 The following are examples of RRs represented in this manner, 146 illustrating various combinations of generic and type-specific 147 encodings for the different fields of the master file format: 149 a.example. CLASS32 TYPE731 \# 6 abcd ( 150 ef 01 23 45 ) 151 b.example. HS TYPE62347 \# 0 152 e.example. IN A \# 4 0A000001 153 e.example. CLASS1 TYPE1 10.0.0.2 155 6. Equality Comparison 157 Certain DNS protocols, notably Dynamic Update [RFC2136], require RRs 158 to be compared for equality. Two RRs of the same unknown type are 159 considered equal when their RDATA is bitwise equal. To ensure that 160 the outcome of the comparison is identical whether the RR is known to 161 the server or not, specifications for new RR types MUST NOT specify 162 type-specific comparison rules. 164 This implies that embedded domain names, being included in the 165 overall bitwise comparison, are compared in a case-sensitive manner. 166 As a result, when a new RR type contains one or more embedded domain 167 names, it is possible to have multiple RRs owned by the same name 168 that differ only in the character case of the embedded domain 169 name(s). This is similar to the existing possibility of multiple TXT 170 records differing only in character case, and not expected to cause 171 any problems in practice. 173 7. DNSSEC Canonical Form and Ordering 175 DNSSEC [RFC2535] defines a canonical form and ordering for RRs. In 176 the canonical form, domain names embedded in the RDATA are converted 177 to lower case. 179 To ensure backwards compatibility, this canonical form remains 180 unchanged for any RR types defined in RFC2931 or earlier. That is, 181 the domain names embedded in RRs of type NS, MD, MF, CNAME, SOA, MB, 182 MG, MR, PTR, HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, 183 NAPTR, KX, SRV, DNAME, and A6 are converted to lower case. For all 184 other RR types, the canonical form is hereby changed such that no 185 downcasing of embedded domain names takes place. The owner name is 186 still set to lower case. 188 The canonical ordering is as specified in RFC2535 section 8.3, where 189 the octet sequence is the canonical form as revised by this 190 specification. 192 8. Additional Section Processing 194 Unknown RR types cause no additional section processing. Future RR 195 type specifications MAY specify type-specific additional section 196 processing rules, but any such processing MUST be optional as it can 197 only be performed by servers for which the RR type in case is known. 199 9. IANA Considerations 201 The IANA is hereby requested to verify that specifications for new RR 202 types requesting an RR type number comply with this specification. 203 In particular, the IANA MUST NOT assign numbers to new RR types whose 204 specification allows embedded domain names to be compressed. 206 10. Security Considerations 208 This specification is not believed to cause any new security 209 problems, nor to solve any existing ones. 211 References 213 [RFC1034] - Domain Names - Concepts and Facilities, P. Mockapetris, 214 November 1987. 216 [RFC1035] - Domain Names - Implementation and Specifications, P. 217 Mockapetris, November 1987. 219 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 220 Requirement Levels", BCP 14, RFC 2119, March 1997. 222 [RFC2136] Dynamic Updates in the Domain Name System (DNS UPDATE). P. 223 Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997. 225 [RFC2535] Domain Name System Security Extensions. D. Eastlake, March 226 1999. 228 [RFC2929] Domain Name System (DNS) IANA Considerations. D. Eastlake, 229 E. Brunner-Williams, B. Manning, September 2000. 231 Author's Address 233 Andreas Gustafsson 234 Nominum Inc. 235 950 Charter Street 236 Redwood City, CA 94063 237 USA 239 Phone: +1 650 381 6004 240 Email: Andreas.Gustafsson@nominum.com 242 Full Copyright Statement 244 Copyright (C) The Internet Society (2001). All Rights Reserved. 246 This document and translations of it may be copied and furnished to 247 others, and derivative works that comment on or otherwise explain it 248 or assist in its implmentation may be prepared, copied, published and 249 distributed, in whole or in part, without restriction of any kind, 250 provided that the above copyright notice and this paragraph are 251 included on all such copies and derivative works. However, this 252 document itself may not be modified in any way, such as by removing 253 the copyright notice or references to the Internet Society or other 254 Internet organizations, except as needed for the purpose of 255 developing Internet standards in which case the procedures for 256 copyrights defined in the Internet Standards process must be 257 followed, or as required to translate it into languages other than 258 English. 260 The limited permissions granted above are perpetual and will not be 261 revoked by the Internet Society or its successors or assigns. 263 This document and the information contained herein is provided on an 264 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 265 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 266 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 267 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 268 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."