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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-00.txt Nominum Inc. 3 November 2000 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 type whose RDATA format is not known 61 to the DNS implementation at hand, and which therefore cannot be 62 converted to a type-specific text format, compressed, or otherwise 63 handled in any type-specific way. This includes the case where the 64 RR's type is recognized but its RDATA format is class specific and 65 the RR is of a class for which the format is not known. 67 3. Transparency 69 To enable new RR types to be deployed without server changes, name 70 servers and resolvers MUST handle RRs of unknown type transparently. 71 That is, they must treat the RDATA section of such RRs as 72 unstructured binary data, storing and transmitting it without change. 74 4. Domain Name Compression 76 RRs containing compression pointers in the RDATA part cannot be 77 treated transparently, as the compression pointers are only 78 meaningful within the context of a DNS message. Transparently 79 copying the RDATA into a new DNS message would cause the compression 80 pointers to point at the corresponding location in the new message, 81 which now contains unrelated data. This would cause the compressed 82 name to be corrupted. 84 To avoid such corruption, servers MUST NOT compress domain names 85 embedded in the RDATA of types that are not well known. 87 Receiving servers MUST decompress domain names in RRs of well-known 88 type, and SHOULD also decompress RRs of type RP, AFSDB, RT, SIG, PX, 89 NXT, NAPTR, and SRV (although the SRV RR is clearly defined to not 90 allow compression of the target field, some existing name servers 91 compress it anyway). 93 Future specifications for new RR types that contain domain names 94 within their RDATA MUST NOT allow the use of name compression for 95 those names, and SHOULD explicitly state that the embedded domain 96 names MUST NOT be compressed. 98 5. Text Representation 100 In the "type" field of a master file line, an unknown RR type is 101 represented by the word "TYPE" immediately followed by the decimal RR 102 type number, with no intervening whitespace. In the "class" field, 103 an unknown class is similarly represented as the word "CLASS" 104 immediately followed by the decimal class number. 106 This convention allows types and classes to be distinguished from 107 each other and from TTL values, allowing the "[] [] 108 " and "[] [] " forms of 109 RFC1035 to both be unambiguously parsed. 111 The RDATA section of an RR of unknown type is represented as a 112 sequence of white space separated words as follows: 114 The special token \# (a backslash immediately 115 followed by a hash sign), which identifies the 116 RDATA as having the generic encoding defined 117 herein rather than a traditional type-specific 118 encoding. 120 An unsigned decimal integer specifying the 121 RDATA length in octets. 123 Zero or more words of hexadecimal data encoding 124 the actual RDATA field, each containing an even 125 number of hexadecimal digits. 127 If the RDATA is of zero length, the text representation contains only 128 the \# token and the single zero representing the length. 130 An implementation MAY also choose to represent some RRs of known type 131 using the above generic representations for the type, class and/or 132 RDATA, which carries the benefit of making the resulting master file 133 portable to servers where these types are unknown. 135 Even though an RR of known type represented in the \# format is 136 effectively treated as an unknown type for the purpose of parsing the 137 RDATA text representation, all further processing by the server MUST 138 treat it as a known type and take into account any applicable type- 139 specific rules regarding compression, canonicalization, etc. 141 The following are examples of RRs represented in this manner, 142 illustrating various combinations of generic and type-specific 143 encodings for the different fields of the master file format: 145 a.example. CLASS32 TYPE731 \# 6 abcd ( 146 ef 01 23 45 ) 147 b.example. HS TYPE62347 \# 0 148 e.example. IN A \# 4 0A000001 149 e.example. CLASS1 TYPE1 10.0.0.2 151 6. Equality Comparison 153 Certain DNS protocols, notably Dynamic Update [RFC2136], require RRs 154 to be compared for equality. Two RRs of the same unknown type are 155 considered equal when their RDATA is bitwise equal. To ensure that 156 the outcome of the comparison is identical whether the RR is known to 157 the server or not, specifications for new RR types MUST NOT specify 158 type-specific comparison rules. 160 This implies that embedded domain names, being included in the 161 overall bitwise comparison, are compared in a case-sensitive manner. 162 As a result, when a new RR type contains one or more embedded domain 163 names, it is possible to have multiple RRs owned by the same name 164 that differ only in the character case of the embedded domain 165 name(s). This is similar to the existing possibility of multiple TXT 166 records differing only in character case, and not expected to cause 167 any problems in practice. 169 7. DNSSEC Canonical Form and Ordering 171 DNSSEC [RFC2535] defines a canonical form and ordering for RRs. In 172 the canonical form, domain names embedded in the RDATA are converted 173 to lower case. 175 To ensure backwards compatilbility, this canonical form remains 176 unchanged for any RR types defined in RFC2931 or earlier. That is, 177 the domain names embedded in RRs of type NS, MD, MF, CNAME, SOA, MB, 178 MG, MR, PTR, HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, 179 NAPTR, KX, SRV, DNAME, and A6 are converted to lower case. For all 180 other RR types, the canonical form is hereby changed such that no 181 downcasing of embedded domain names takes place. The owner name is 182 still set to lower case. 184 The canonical ordering is as specified in RFC2535 section 8.3, where 185 the octet sequence is the canonical form as revised by this 186 specification. 188 8. Additional Section Processing 190 Unknown RR types cause no additional section processing. Future RR 191 type specifications MAY specify type-specific additional section 192 processing rules, but any such processing MUST be optional as it can 193 only be performed by servers for which the RR type in case is known. 195 9. IANA Considerations 197 The IANA is hereby requested to verify that specifications for new RR 198 types requesting an RR type number comply with this specification. 199 In particular, the IANA MUST NOT assign numbers to RR types whose 200 specification allows embedded domain names to be compressed. 202 10. Security Considerations 204 This specification is not believed to cause any new security 205 problems, nor to solve any existing ones. 207 References 209 [RFC1034] - Domain Names - Concepts and Facilities, P. Mockapetris, 210 November 1987. 212 [RFC1035] - Domain Names - Implementation and Specifications, P. 213 Mockapetris, November 1987. 215 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 216 Requirement Levels", BCP 14, RFC 2119, March 1997. 218 [RFC2136] Dynamic Updates in the Domain Name System (DNS UPDATE). P. 219 Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound. April 1997. 221 [RFC2535] Domain Name System Security Extensions. D. Eastlake. March 222 1999. 224 Author's Address 226 Andreas Gustafsson 227 Nominum Inc. 228 950 Charter Street 229 Redwood City, CA 94063 230 USA 232 Phone: +1 650 779 6004 234 Email: Andreas.Gustafsson@nominum.com 236 Full Copyright Statement 237 Copyright (C) The Internet Society (2000). All Rights Reserved. 239 This document and translations of it may be copied and furnished to 240 others, and derivative works that comment on or otherwise explain it 241 or assist in its implmentation may be prepared, copied, published and 242 distributed, in whole or in part, without restriction of any kind, 243 provided that the above copyright notice and this paragraph are 244 included on all such copies and derivative works. However, this 245 document itself may not be modified in any way, such as by removing 246 the copyright notice or references to the Internet Society or other 247 Internet organizations, except as needed for the purpose of 248 developing Internet standards in which case the procedures for 249 copyrights defined in the Internet Standards process must be 250 followed, or as required to translate it into languages other than 251 English. 253 The limited permissions granted above are perpetual and will not be 254 revoked by the Internet Society or its successors or assigns. 256 This document and the information contained herein is provided on an 257 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 258 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 259 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 260 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 261 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."