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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 dnsop D. Crocker 3 Internet-Draft Brandenburg InternetWorking 4 Intended status: Best Current Practice March 25, 2018 5 Expires: September 26, 2018 7 DNS Scoped Data Through '_Underscore' Naming of Attribute Leaves 8 draft-ietf-dnsop-attrleaf-05 10 Abstract 12 Formally, any DNS resource record may occur for any domain name. 13 However some services have defined an operational convention, which 14 applies to DNS leaf nodes that are under a DNS branch having one or 15 more reserved node names, each beginning with an underscore. The 16 underscore naming construct defines a semantic scope for DNS records 17 that are associated with the parent domain, above the underscored 18 branch. This specification explores the nature of this DNS usage and 19 defines the "DNS Global Underscore Scoped Entry Registry" with IANA. 20 The purpose of the Underscore registry is to avoid collisions 21 resulting from the use of the same underscore-based name, for 22 different services. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on September 26, 2018. 41 Copyright Notice 43 Copyright (c) 2018 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 1.1. _Underscore Scoping . . . . . . . . . . . . . . . . . . . 2 60 1.2. Scaling Benefits for TXT, SRV, and URI Resource Records . 3 61 2. DNS Underscore Scoped Entry Registries Function . . . . . . . 4 62 2.1. DNS Underscore Global Scoped Entry Registry Definition . 5 63 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 64 3.1. DNS Underscore Global ScopedEntry Registry . . . . . . . 6 65 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 66 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 5.1. Normative References . . . . . . . . . . . . . . . . . . 6 68 5.2. References -- Informative . . . . . . . . . . . . . . . . 7 69 5.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7 70 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7 71 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 73 1. Introduction 75 The core Domain Name System (DNS) technical specifications assign no 76 semantics to domain names or their parts, and no constraints upon 77 which resource records (RRs) are permitted to be associated with 78 particular names.[RFC1035] Over time, some leaf node names, such as 79 "www" and "ftp" have come to imply support for particular services, 80 but this is a matter of operational convention, rather than defined 81 protocol semantics. This freedom in the basic technology has 82 permitted a wide range of administrative and semantic policies to be 83 used -- in parallel. DNS data semantics have been limited to the 84 specification of particular resource records, on the expectation that 85 new ones would be added as needed. Unfortunately, the addition of 86 new resource records has proved extremely challenging, over the life 87 of the DNS, with significant adoption and use barriers. 89 1.1. _Underscore Scoping 91 As an alternative to defining new RRs, some DNS service enhancements 92 call for using an existing resource record, but specify a restricted 93 scope for its occurrence. That scope is a leaf node, within which 94 the uses of specific resource records can be formally defined and 95 constrained. The leaf occurs in a branch having a distinguished 96 naming convention: At the top of the branch -- beneath the parent 97 domain name to which the scope applies -- one or more reserved DNS 98 node names begin with an underscore ("_"). Because the DNS rules for 99 a "host" (host name) are not allowed to use the underscore character, 100 this distinguishes the underscore name from all legal host names 101 [RFC1035]. Effectively, this convention for leaf node naming creates 102 a space for the listing of 'attributes' -- in the form of resource 103 records -- that are associated with the parent domain, above the 104 underscore sub-branch. 106 The scoping feature is particularly useful when generalized resource 107 records are used -- notably "TXT", "SRV", and "URI" 108 [RFC1035],[RFC2782],[RFC6335], [RFC7553]. It provides efficient 109 separation of one use of them from others. Absent this separation, 110 an undifferentiated mass of these "RR"s is returned to the DNS 111 client, which then must parse through the internals of the records in 112 the hope of finding ones that are relevant. Worse, in some cases the 113 results are ambiguous because the records do not adequately self- 114 identify. With underscore-based scoping, only the relevant "RR"s are 115 returned. 117 A simple example is DKIM [RFC6376] , which uses "_domainkeys" for 118 defining a place to hold a "TXT" record containing signing 119 information for the parent domain. 121 This specification formally defines how underscore labels are used as 122 "attribute" enhancements for their parent domain names. For example, 123 domain name "_domainkey.example." acts as attribute of parent domain 124 name "example." To avoid collisions resulting from the use of the 125 same underscore-based labels for different applications, this 126 document establishes DNS Underscore Global Scoped Entry IANA Registry 127 for the highest-level reserved names that begin with _underscore; 128 _underscore-based names that are farther down the hierarchy are 129 handled within the scope of the highest-level _underscore name. 131 Discussion Venue: Discussion about this draft should be directed 132 to the dnsop@ietf.org [1] mailing list. 134 NOTE TO RFC EDITOR: Please remove "Discussion Venue" paragraph 135 prior to publication. 137 1.2. Scaling Benefits for TXT, SRV, and URI Resource Records 139 Some resource records are generic and support a variety of uses. 140 Each additional use defines its own rules and, possibly, its own 141 internal syntax and node-naming conventions to distinguish among 142 particular types. The "TXT", "SRV", and "URI" records are notable 143 examples. Their use can scale poorly, particularly when the same 144 "RR" can be present in the same leaf node, but with different uses. 146 An increasingly-popular approach, with excellent scaling properties, 147 place the RR under a node with an underscore-based name, at a defined 148 place in the DNS tree, so as to constrain the use of particular "RR"s 149 farther down the branch with that name. This means that a direct 150 lookup produces only the desired records, at no greater cost than a 151 typical DNS lookup. 153 The definition of a underscore global registry, provided in this 154 specification, primarily attends to the top-most names used for RRs; 155 that is the _underscore "global" names. 157 2. DNS Underscore Scoped Entry Registries Function 159 A global registry for DNS nodes names that begin with an _underscore 160 is defined here. 162 The 'global' (right-most) node name that uses an _underscore 163 prefix MUST be entered into this registry. 165 The names define scope of use for specific resource records, which 166 are associated with the domain name that is the "parent" to the 167 branch defined by the _underscore naming. 169 A given name defines a specific, constrained context for one or 170 more RR records, in which use of such records MUST conform to the 171 defined constraints. Within this scope, other resource records 172 that are not specified MAY be used. 174 The purpose of the Underscore Global Registry is to avoid collisions 175 resulting from the use of the same _underscore-based name, for 176 different applications. 178 Structurally, the registry is defined as a single, flat table of 179 names that begin with _underscore. In some cases, such as for use of 180 an "SRV" record, the full scoping name might be multi-part, as a 181 sequence of underscore names. Semantically, that sequence represents 182 a hierarchical model and it is theoretically reasonable to allow re- 183 use of a subordinate underscore name in different underscore context; 184 that is, a subordinate name is meaningful only within the scope of 185 the first (top-level) underscore name. Therefore they are ignored by 186 this DNS Underscore Global Scoped Entry Registry. This registry is 187 for the definition of highest-level -- ie, global -- underscore node 188 name used. 190 +----------------------------+ 191 | NAME | 192 +----------------------------+ 193 | _service1 | 194 | ._protoB._service2 | 195 | _protoB._service3 | 196 | _protoC._service3 | 197 | _useX._protoD._service4 | 198 | _protoE._region._authority | 199 +----------------------------+ 201 Example of Underscore Names 203 Only the right-most _underscore names are registered in the IANA 204 Underscore Global table. 206 Definition and registration of the subordinate underscore node 207 names is the responsibility of the specification that creates the 208 highest-level (right-most) global registry entry. 210 That is, if a scheme using a global underscore node name also has 211 one or more subordinate levels of underscore node naming, the 212 namespaces from which names for those lower levels is chosen is 213 controlled by the parent underscore node name. Each globally- 214 registered underscore name owns a distinct, subordinate name 215 space. 217 2.1. DNS Underscore Global Scoped Entry Registry Definition 219 A registry entry contains: 221 _Node Name: Specifies a single _underscore name that defines a 222 reserved name; this name is the "global" entry name for the 223 scoped resource records that are associated with that name. 225 RR(s): Lists the RRs that are defined for use within this scope. 227 References Lists specification that define the records and their use 228 under this Name. The organization producing the 229 specification retains control over the registry entry for 230 the _Node Name. 232 3. IANA Considerations 234 Per [RFC8126], IANA is requested to establish the: 236 DNS Underscore Global Scoped Entry Registry 238 This section describes actions requested of IANA. The guidance in 239 [IANA] is used. 241 3.1. DNS Underscore Global ScopedEntry Registry 243 The DNS Global Underscore Scoped Entry Registry is for DNS node names 244 that begin with the underscore character (_) and are the first 245 occurrence of any names in a domain name sequence having that form; 246 that is they are the "top" of a DNS branch and are shown as the 247 right-most _underscore name -- under a "parent" domain name. 249 o This registry is to operate under the IANA rules for "First Come 250 First Served" registration. 252 o The contents of each entry in the Global registry are defined in 253 Section 2.1. 255 o The required Reference for an entry MUST have a stable resolution 256 to the organization controlling that registry entry 258 Initial entries in the registry are: 260 +-------------+-----+------------+ 261 | _NODE NAME | RR | REFERENCE | 262 +-------------+-----+------------+ 263 | _tcp | SRV | [RFC2782] | 264 | _udp | SRV | [RFC2782] | 265 | _sctp | SRV | [RFC2782] | 266 | _dccp | SRV | [RFC2782] | 267 | _domainkey | TXT | [RFC6376] | 268 | _spf | TXT | [RFC7208] | 269 | _dmarc | TXT | [RFC7489] | 270 | _vouch | TXT | [RFC5518] | 271 +-------------+-----+------------+ 273 Table 1: Underscore Global Registry (initial entries) 275 4. Security Considerations 277 This memo raises no security issues. 279 5. References 281 5.1. Normative References 283 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 284 Writing an IANA Considerations Section in RFCs", RFC 8126, 285 June 2017. 287 5.2. References -- Informative 289 [IANA] M. Cotton, B. Leiba, and T. Narten, "Guidelines for 290 Writing an IANA Considerations Section in RFCs", I-D 291 draft-leiba-cotton-iana-5226bis-11, 2017. 293 [RFC1035] Mockapetris, P., "Domain names - implementation and 294 specification", STD 13, RFC 1035, November 1987. 296 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 297 specifying the location of services (DNS SRV)", RFC 2782, 298 February 2000. 300 [RFC5518] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By 301 Reference", RFC 5518, April 2009. 303 [RFC6335] Cotton, M., Eggert, L., Tpuch, J., Westerlund, M., and S. 304 Cheshire, "nternet Assigned Numbers Authority (IANA) 305 Procedures for the Management of the Service Name and 306 Transport Protocol Port Number Registry", RFC 6335, Aug 307 2011. 309 [RFC6376] Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys 310 Identified Mail (DKIM) Signatures", RFC 6376, Sept 2011. 312 [RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for 313 Authorizing Use of Domains in E-Mail, Version 1", 314 RFC 7208, April 2014. 316 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 317 Message Authentication, Reporting, and Conformance 318 (DMARC)", RFC 7489, March 2015. 320 [RFC7553] Falstrom, P. and O. Kolkman, "The Uniform Resource 321 Identifier (URI) DNS Resource Record", RFC 7553, 322 ISSN 2070-1721, June 2015. 324 5.3. URIs 326 [1] mailto:dnsop@ietf.org 328 Appendix A. Acknowledgements 330 Thanks go to Bill Fenner, Tony Hansen, Peter Koch, Olaf Kolkman, and 331 Andrew Sullivan for diligent review of the (much) earlier drafts. 332 For the later enhancements, thanks to: Stephane Bortzmeyer, Bob 333 Harold, John Levine, Joel Jaeggli, Petr Špaček, Ondřej 334 Surř, Tim Wicinski, and Paul Wouters. 336 Special thanks to Ray Bellis for more than 12 years of persistent 337 encouragement to continue this effort, as well as the suggestion for 338 an essential simplification to the registration model. 340 Author's Address 342 Dave Crocker 343 Brandenburg InternetWorking 344 675 Spruce Dr. 345 Sunnyvale, CA 94086 346 USA 348 Phone: +1.408.246.8253 349 Email: dcrocker@bbiw.net 350 URI: http://bbiw.net/