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Reid 3 Internet-Draft Telnic Ltd 4 Intended status: Standards Track July 4, 2008 5 Expires: January 5, 2009 7 The Zone Status (ZS) DNS Resource Record 8 10 Status of this Memo 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware 14 have been or will be disclosed, and any of which he or she becomes 15 aware will be disclosed, in accordance with Section 6 of BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on January 5, 2009. 35 Abstract 37 A Domain Name System (DNS) resource record which provides status 38 information about a zone is described in this document. 40 Table of Contents 42 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 43 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 44 3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 5 45 4. Justification For New RRtype . . . . . . . . . . . . . . . . . 6 46 5. ZS Resource Record . . . . . . . . . . . . . . . . . . . . . . 7 47 6. End User Considerations . . . . . . . . . . . . . . . . . . . 8 48 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 49 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 50 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 51 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 52 10.1. Normative References . . . . . . . . . . . . . . . . . . 12 53 10.2. Informative References . . . . . . . . . . . . . . . . . 12 54 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 55 Intellectual Property and Copyright Statements . . . . . . . . . . 15 57 1. Terminology 59 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 60 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 61 document are to be interpreted as described in BCP 14, RFC2119 62 [refs.RFC2119]. 64 2. Introduction 66 The DNS protocol is defined in RFC1034 [refs.RFC1034], RFC1035 67 [refs.RFC1035] and clarified in RFC2181 [refs.RFC2181]. The DNS does 68 not currently provide a well defined mechanism for obtaining 69 information about the status of a zone: what it is being used for, 70 the significance of the zone's contents, when the zone was last 71 updated and so on. This means a variety of ad-hoc techniques are 72 deployed whenever zone administrators choose to make this information 73 available. Typical strategies include descriptive TXT records in the 74 zone or embedding meta-information in the values of existing RRtypes 75 or subtypes such as the SOA record's serial number and RNAME. These 76 are confusing and impractical since an arbitrary DNS client needs a 77 priori knowledge of which of these schemes, if any, has been used by 78 a zone administrator. 80 This document advocates the introduction of a new resource record 81 specifically to provide this type of information. 83 3. Rationale 85 Common examples where indicating the status of a zone would be useful 86 include: whenever the domain is in the process of a substantial 87 update; a domain undergoing a long-term migration; and changes to the 88 authoritative name servers for a zone. eg "Use of example.net was 89 deprecated on April 1st. Please visit example.com instead." It 90 would be convenient to store this type of meta information within the 91 zone in a way that makes it easily retrieved. This kind of status 92 information would be particularly helpful for systems such as ENUM 93 [refs.RFC3761] which can be used for publishing real-time contact 94 data for zone owners. 96 These sorts of details are generally associated with the 97 administration of the zone rather than being tied to the rest of the 98 zone content. Clarifying this separation between information that 99 reflects the status of a zone from any text that a domain holder may 100 choose to publish via DNS is useful. It also avoids the current 101 subtyping issues that would affect processing of a TXT RRset if the 102 status information was embedded there. TXT records are too general 103 and would require imprecise RDATA parsing in order to extract any 104 relevant items of interest to a particular client. 106 The proposed RRtype will be of particular use for zones where contact 107 data are published in the DNS as NAPTR records [refs.RFC3403]. For 108 instance a set of tel: and sip: URIs [refs.RFC3986] could be 109 associated with the proposed zone status RRtype. That could indicate 110 these URIs are the ones published by the zone owner when they are at 111 work, or while travelling or when at home. Client software could 112 lookup the zone's ZS records and display a meaningful message to the 113 end user about the NAPTR records that had been retrieved from an 114 earlier lookup. A description of which contact data the zone owner 115 has published would offer additional information to what might be 116 inferred from the actual NAPTR RRset or other zone data itself. The 117 ZS RRtype could express concepts like "the zone owner is asleep, so 118 don't bother trying voice-based communication" or "the zone owner is 119 at work but in a meeting". 121 Publishing and obtaining this information will become more 122 significant because of emerging applications and services which make 123 innovative use of the DNS such as the real-time manipulation of zone 124 content data. For example, updating NAPTR records (ie the zone 125 owner's contact data) whenever the zone owner switches between the 126 NAPTR RRset they publish while at work, at home, commuting or while 127 sleeping. 129 4. Justification For New RRtype 131 TXT records are unsuitable for providing this sort of zone status 132 information because the semantics of TXT record RDATA are 133 unstructured. TXT records can and are used for all sorts of 134 purposes: version control strings, comments or reminders to zone 135 administrators, anti-spam information, references to ticketing 136 systems, contact details of the zone administrator and so on. It 137 would be impractical for an application to interpret the contents of 138 a response to a TXT query and guess which, if any, of the returned 139 TXT records contained meaningful data about the status of the zone. 141 One approach would be to adopt a convention that a "magic string" in 142 the RDATA for some TXT record identified zone status information. 143 This is not viable for two reasons. First, it may break backwards 144 compatibility with the installed base which might already be using 145 this "magic string" in TXT records. The second reason is this 146 proposal would introduce yet another example of subtyping which is 147 generally accepted as poor protocol design. 149 Likewise, it is not sensible to insert TXT records in some part of 150 the name space to be dedicated for this specific purpose. That would 151 be another instance of bad protocol design because a fundamental but 152 unstated principle of the Domain Name System is any RRtype can be 153 used in any zone irrespective of the name of the zone. 155 5. ZS Resource Record 157 Apart from its type code, the wire and text formats for the proposed 158 ZS RRtype are identical to the definitions of the TXT record given in 159 RFC1035: 161 ZS RDATA format 163 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 164 / ZS-DATA / 165 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 167 where: ZS-DATA One or more character-strings. 169 The ZS RRtype will hold descriptive text intended to contain 170 information reflecting the status of the zone in which it is held. 172 6. End User Considerations 174 Users publishing ZS records SHOULD pay attention to the needs of 175 potential readers of these resource records, especially with respect 176 to character sets and language. Although arbitrary text can be 177 stored in character-strings, publishers of ZS records SHOULD 178 carefully consider the capabilities of the devices and end users who 179 query for ZS records. For example, a mobile phone or other hand-held 180 device may not have the font information or suitable rendering 181 capabilities to display (say) Chinese or Arabic characters. 182 Similarly, publishers of ZS records should try to avoid displaying 183 information in multiple languages or assume that all readers of these 184 records understand the same language or languages they have chosen to 185 use. In these circumstances it would be inadvisable to publish a 186 string in a ZS record that is unlikely to be intelligible to those 187 who lookup ZS records. 189 7. Security Considerations 191 Although this document does not appear to introduce any extra 192 security issues beyond those listed in the thorough analysis of the 193 threats to DNS in RFC3833 [refs.RFC3833], there are some additional 194 considerations. These are described below. 196 It is unrealistic to assume that zone owners who publish ZS records 197 can be relied upon to ensure any ZS records contain accurate, timely 198 information. Similarly it cannot be assumed that ZS records contain 199 text that will be understandable by an arbitrary reader that looks 200 them up in the DNS. Therefore any data contained in a ZS record is 201 solely for informational purposes. The information contained in a ZS 202 record MUST NOT be relied upon for any location-based services. In 203 particular, emergency services MUST NOT not treat the contents of a 204 ZS record as definitive information about the location or disposition 205 of the domain name owner. 207 8. IANA Considerations 209 IANA is requested to issue a new type code and mnemonic for the 210 proposed resource record. No other IANA services are required by 211 this document. 213 9. Acknowledgements 215 The author would like to thank Ben Timms, John Cundall, John Tidmuss 216 and Lawrence Conroy for their constructive suggestions to this 217 document and for helping to identify potential uses for the proposed 218 record type. 220 10. References 222 10.1. Normative References 224 [refs.RFC1034] 225 Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES", 226 RFC 1034, November 1987. 228 [refs.RFC1035] 229 Mockapetris, P., "Domain names - implementation and 230 specification", STD 13, RFC 1035, November 1987. 232 [refs.RFC1123] 233 Braden, R., "Requirements for Internet Hosts -- 234 Application and Support", RFC 1123, October 1989. 236 [refs.RFC2181] 237 Elz, R. and R. Bush, "Clarifications to the DNS 238 Specification", RFC 2181, July 1997. 240 [refs.RFC3403] 241 Mealling, M., "Dynamic Delegation Discovery System (DDDS) 242 Part Three: The Domain Name System (DNS) Database", 243 RFC 3403, October 2002. 245 [refs.RFC3986] 246 Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 247 Resource Identifier (URI): Generic Syntax", STD 66, 248 RFC 3986, January 2005. 250 10.2. Informative References 252 [refs.RFC2026] 253 Bradner, S., "The Internet Standards Process -- Revision 254 3", RFC 2026, BCP 9, October 1996. 256 [refs.RFC2119] 257 Bradner, S., "Key words for use in RFCs to Indicate 258 Requirement Levels", RFC 2119, BCP 14, March 1997. 260 [refs.RFC3761] 261 Faltstrom, P. and M. Mealling, "The E.164 to Uniform 262 Resource Identifiers (URI) Dynamic Delegation Discovery 263 System (DDDS) Application (ENUM)", RFC 3761, April 2004. 265 [refs.RFC3833] 266 Atkins, D. and R. Austein, "Threat Analysis of the Domain 267 Name System (DNS)", RFC 3833, August 2004. 269 [refs.RFC3978] 270 Bradner, S., "IETF Rights in Contributions", BCP 78, 271 RFC 3978, March 2005. 273 [refs.RFC3979] 274 Bradner, S., "Intellectual Property Rights in IETF 275 Technology", BCP 79, RFC 3979, March 2005. 277 Author's Address 279 Jim Reid 280 Telnic Ltd 281 Telnic Ltd. 282 6 Langside Court 283 Bothwell, SCOTLAND 284 United Kingdom 286 Phone: +44 20 7467 6400 287 Email: jim@telnic.org 289 Full Copyright Statement 291 Copyright (C) The IETF Trust (2008). 293 This document is subject to the rights, licenses and restrictions 294 contained in BCP 78, and except as set forth therein, the authors 295 retain all their rights. 297 This document and the information contained herein are provided on an 298 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 299 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 300 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 301 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 302 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 303 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 305 Intellectual Property 307 The IETF takes no position regarding the validity or scope of any 308 Intellectual Property Rights or other rights that might be claimed to 309 pertain to the implementation or use of the technology described in 310 this document or the extent to which any license under such rights 311 might or might not be available; nor does it represent that it has 312 made any independent effort to identify any such rights. Information 313 on the procedures with respect to rights in RFC documents can be 314 found in BCP 78 and BCP 79. 316 Copies of IPR disclosures made to the IETF Secretariat and any 317 assurances of licenses to be made available, or the result of an 318 attempt made to obtain a general license or permission for the use of 319 such proprietary rights by implementers or users of this 320 specification can be obtained from the IETF on-line IPR repository at 321 http://www.ietf.org/ipr. 323 The IETF invites any interested party to bring to its attention any 324 copyrights, patents or patent applications, or other proprietary 325 rights that may cover technology that may be required to implement 326 this standard. Please address the information to the IETF at 327 ietf-ipr@ietf.org.