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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 June 5, 2018 5 Expires: December 7, 2018 7 DNS Scoped Data Through '_Underscore' Naming of Attribute Leaves 8 draft-ietf-dnsop-attrleaf-10 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 record 17 types that are associated with the parent domain, above the 18 underscored branch. This specification explores the nature of this 19 DNS usage and defines the "DNS Global Underscore Scoped Entry 20 Registry" with IANA. The purpose of the Underscore registry is to 21 avoid collisions resulting from the use of the same underscore-based 22 name, for 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 December 7, 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 . . . . . . . . . . . . . . . . . . . . 4 61 2. DNS Underscore Scoped Entry Registries Function . . . . . . . 4 62 3. RRset Use Registration Template . . . . . . . . . . . . . . . 6 63 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 64 4.1. DNS Underscore Global Scoped Entry Registry . . . . . . . 6 65 4.2. DNS Underscore Global Scoped Entry Registry Definition . 7 66 4.3. Initial entries . . . . . . . . . . . . . . . . . . . . . 7 67 5. Guidance for Expert Review . . . . . . . . . . . . . . . . . 9 68 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 69 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 70 7.1. Normative References . . . . . . . . . . . . . . . . . . 9 71 7.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 11 72 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 11 73 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 75 1. Introduction 77 The core Domain Name System (DNS) technical specifications assign no 78 semantics to domain names or their parts, and no constraints upon 79 which resource record (RR) types are permitted to be stored under 80 particular names [RFC1035], [RFC2181]. Over time, some leaf node 81 names, such as "www" and "ftp" have come to imply support for 82 particular services, but this is a matter of operational convention, 83 rather than defined protocol semantics. This freedom in the basic 84 technology has permitted a wide range of administrative and semantic 85 policies to be used -- in parallel. DNS data semantics have been 86 limited to the specification of particular resource record types, on 87 the expectation that new ones would be added as needed. 88 Unfortunately, the addition of new resource record types has proven 89 extremely challenging, over the life of the DNS, with significant 90 adoption and use barriers. 92 1.1. _Underscore Scoping 94 As an alternative to defining a new RR type, some DNS service 95 enhancements call for using an existing resource record type, but 96 specify a restricted scope for its occurrence. Scope is meant as a 97 static property, not one dependent on the nature of the query. It is 98 an artifact of the DNS name. That scope is a leaf node, within which 99 the uses of specific resource record sets can be formally defined and 100 constrained. The leaf occurs in a branch having a distinguished 101 naming convention: At the top of the branch -- beneath the parent 102 domain name to which the scope applies -- one or more reserved DNS 103 node names begin with an underscore ("_"). Because the DNS rules for 104 a "host" (host name) are not allowed to use the underscore character, 105 this distinguishes the underscore name from all legal host names 106 [RFC952]. Effectively, this convention for leaf node naming creates 107 a space for the listing of 'attributes' -- in the form of resource 108 record types -- that are associated with the parent domain, above the 109 underscored sub-branch. 111 The scoping feature is particularly useful when generalized resource 112 record types are used -- notably "TXT", "SRV", and "URI" [RFC1035], 113 [RFC2782], [RFC6335], [RFC7553]. It provides efficient separation of 114 one use of them from others. Absent this separation, an 115 undifferentiated mass of these "RRsets" is returned to the DNS 116 client, which then must parse through the internals of the records in 117 the hope of finding ones that are relevant. Worse, in some cases the 118 results are ambiguous because a record type might not adequately 119 self-identify. With underscore-based scoping, only the relevant 120 "RRsets"s are returned. 122 A simple example is DKIM [RFC6376] , which uses "_domainkeys" for 123 defining a place to hold a "TXT" record containing signing 124 information for the parent domain. 126 This specification formally defines how underscore labels are used as 127 "attribute" enhancements for their parent domain names. For example, 128 domain name "_domainkey.example." acts as attribute of parent domain 129 name "example." To avoid collisions resulting from the use of the 130 same underscore-based labels for different applications using the 131 same resource record type, this document establishes DNS Underscore 132 Global Scoped Entry IANA Registry for the highest-level reserved 133 names that begin with _underscore; _underscore-based names that are 134 farther down the hierarchy are handled within the scope of the 135 highest-level _underscore name. 137 Discussion Venue: Discussion about this draft should be directed 138 to the dnsop@ietf.org [1] mailing list. 140 NOTE TO RFC EDITOR: Please remove "Discussion Venue" paragraph 141 prior to publication. 143 1.2. Scaling Benefits 145 Some resource record types are used in a fashion that can create 146 scaling problems, if an entire RRset associated with a domain name is 147 aggregated in the leaf node for that name. An increasingly-popular 148 approach, with excellent scaling properties, places the RRset under a 149 specially named branch, which is in turn under the node name that 150 would otherwise contain the RRset. The rules for naming that branch 151 define the context for interpreting the RRset. That is, rather than: 153 domain-name.example 154 / 155 RRset 157 the arrangement is: 159 _branch.domain-name.example 160 / 161 RRset 163 A direct lookup to the subordinate leaf node produces only the 164 desired record types, at no greater cost than a typical DNS lookup. 166 The definition of an underscore global registry, provided in this 167 specification, primarily attends to the top-most names used for 168 scoping an RR type; that is the _underscore "global" names. 170 2. DNS Underscore Scoped Entry Registries Function 172 A global registry for DNS nodes names that begin with an _underscore 173 is defined here. The purpose of the Underscore Global Registry is to 174 avoid collisions resulting from the use of the same _underscore-based 175 name, for different applications. 177 o If a public specification calls for use of an _underscore-prefixed 178 domain node name, the 'global' (right-most) _underscored name MUST 179 be entered into this registry. 181 The _underscore names define scope of use for specific resource 182 record types, which are associated with the domain name that is the 183 "parent" to the branch defined by the _underscore naming. A given 184 name defines a specific, constrained context for one or more RR 185 types, where use of such record types conforms to the defined 186 constraints. 188 o Within an _underscore scoped leaf, other RRsets that are not 189 specified as part of the scope MAY be used. 191 Structurally, the registry is defined as a single, flat table of RR 192 types, under node names beginning with _underscore. In some cases, 193 such as for use of an "SRV" record, the full scoping name might be 194 multi-part, as a sequence of underscore names. Semantically, that 195 sequence represents a hierarchical model and it is theoretically 196 reasonable to allow re-use of a subordinate underscore name in 197 different underscore context; that is, a subordinate name is 198 meaningful only within the scope of the right-most (top-level) 199 underscore name. Therefore they are ignored by this DNS Underscore 200 Global Scoped Entry Registry. This registry is for the definition of 201 highest-level -- ie, global -- underscore node name used. 203 +----------------------------+ 204 | NAME | 205 +----------------------------+ 206 | _service1 | 207 | ._protoB._service2 | 208 | _protoB._service3 | 209 | _protoC._service3 | 210 | _useX._protoD._service4 | 211 | _protoE._region._authority | 212 +----------------------------+ 214 Example of Underscore Names 216 Only the right-most _underscore names are registered in the IANA 217 Underscore Global table. 219 The use of underscored node names is specific to each RRTYPE that 220 is being scoped. Each name defines a place, but does not define 221 the rules for what appears underneath that place, either as 222 additional underscored naming or as a leaf node with resource 223 records. Details for those rules are provided by specifications 224 for individual RRTYPEs. The sections below describe the way that 225 existing underscore labels are used with the RRTYPEs that they 226 name. 228 Definition and registration of the subordinate underscore node 229 names is the responsibility of the specification that creates the 230 highest-level (right-most) global registry entry. 232 That is, if a scheme using a global underscore node name also has 233 one or more subordinate levels of underscore node naming, the 234 namespaces from which names for those lower levels is chosen is 235 controlled by the parent underscore node name. Each globally- 236 registered underscore name owns a distinct, subordinate name 237 space. 239 3. RRset Use Registration Template 241 This section provides a basic template that can be used to register 242 new entries in the IANA DNS Underscore Global Scoped Entry Registry, 243 if the right-most underscored name above the RRTYPE is not already 244 registered. The text can be added to specifications using 245 RRTYPE/_Node-name combinations that have not already been registered. 247 "Per {RFC Attrleaf} please add the following entry to the DNS 248 Underscore Global Scoped Entry Registry:" 250 Note to RFC Editor: Please replace the above "{RFC Attrleaf}" text 251 with a reference to this document's RFC number. /d 253 +----------+-------------------+------------------------------------+ 254 | RR Type | _NODE NAME | REFERENCE | 255 +----------+-------------------+------------------------------------+ 256 | {RRTYPE} | _{DNS global node | {citation for the document making | 257 | | name} | the addition.} | 258 +----------+-------------------+------------------------------------+ 260 Table 1: Underscore Global Registry Entry 262 4. IANA Considerations 264 Per [RFC8126], IANA is requested to establish the: 266 DNS Underscore Global Scoped Entry Registry 268 This section describes actions requested of IANA. The guidance in 269 [IANA] is used. 271 4.1. DNS Underscore Global Scoped Entry Registry 273 The DNS Global Underscore Scoped Entry Registry is for DNS node names 274 that begin with the underscore character (_) and are the right-most 275 occurrence of any underscored names in a domain name sequence having 276 that form; that is they are the "top" of a DNS branch, under a 277 "parent" domain name. 279 o This registry is to operate under the IANA rules for "Expert 280 Review" registration; see Section 5. 282 o The contents of each entry in the Global registry are defined in 283 Section 4.2. 285 o Each entry in the registry MUST contain values for all of the 286 fields specified in Section 4.2. 288 o Within the registry, the combination of RR Type and _Node Name 289 MUST be unique. 291 o The table is to be maintained with entries sorted by the first 292 column (RR Type) and within that the second column (_Node Name). 294 o The required Reference for an entry MUST have a stable resolution 295 to the organization controlling that registry entry 297 4.2. DNS Underscore Global Scoped Entry Registry Definition 299 A registry entry contains: 301 RR Type: Lists an RR type that is defined for use within this 302 scope. 304 _Node Name: Specifies a single _underscore name that defines a 305 reserved name; this name is the "global" entry name for the 306 scoped resource record types that are associated with that 307 name 309 References: Lists specification that defines a record type and its 310 use under this Name. The organization producing the 311 specification retains control over the registry entry for 312 the _Node Name. 314 Each RR type that is to be used MUST have a separate registry entry. 316 4.3. Initial entries 318 Initial entries in the registry are: 320 +------------+-----------------+------------+ 321 | RR Type | _NODE NAME | REFERENCE | 322 +------------+-----------------+------------+ 323 | OPENPGPKEY | _openpgpkey | [RFC7929] | 324 | SMIMEA | _smimecert | [RFC8162] | 325 | SRV | _dccp | [RFC2782] | 326 | SRV | _sctp | [RFC2782] | 327 | SRV | _tcp | [RFC2782] | 328 | SRV | _udp | [RFC2782] | 329 | TLSA | _sctp | [RFC6698] | 330 | TLSA | _tcp | [RFC6698] | 331 | TLSA | _udp | [RFC6698] | 332 | TXT | _mta-sts | [MTA-STS] | 333 | TXT | _acme-challenge | [ACME] | 334 | TXT | _dmarc | [RFC7489] | 335 | TXT | _domainkey | [RFC6376] | 336 | TXT | _spf | [RFC7208] | 337 | TXT | _vouch | [RFC5518] | 338 | URI | _iax | [RFC7553] | 339 | URI | _acct | [RFC7553] | 340 | URI | _dccp | [RFC7553] | 341 | URI | _email | [RFC7553] | 342 | URI | _ems | [RFC7553] | 343 | URI | _fax | [RFC7553] | 344 | URI | _ft | [RFC7553] | 345 | URI | _h323 | [RFC7553] | 346 | URI | _ical-sched | [RFC7553] | 347 | URI | _ical-access | [RFC7553] | 348 | URI | _ifax | [RFC7553] | 349 | URI | _im | [RFC7553] | 350 | URI | _mms | [RFC7553] | 351 | URI | _pres | [RFC7553] | 352 | URI | _pstn | [RFC7553] | 353 | URI | _sctp | [RFC7553] | 354 | URI | _sip | [RFC7553] | 355 | URI | _sms | [RFC7553] | 356 | URI | _tcp | [RFC7553] | 357 | URI | _udp | [RFC7553] | 358 | URI | _unifmsg | [RFC7553] | 359 | URI | _vcard | [RFC7553] | 360 | URI | _videomsg | [RFC7553] | 361 | URI | _voice | [RFC7553] | 362 | URI | _voicemsg | [RFC7553] | 363 | URI | _vpim | [RFC7553] | 364 | URI | _xmp | [RFC7553] | 365 +------------+-----------------+------------+ 367 Table 2: Underscore Global Registry (initial entries) 369 5. Guidance for Expert Review 371 This section provides guidance for expert review of registration 372 requests in the of DNS Underscore Global Scoped Entry Registry. 374 This review is solely to determine adequacy of a requested entry 375 in this Registry, and does not include review of other aspects of 376 the document specifying that entry. For example such a document 377 might also contain a definition of the resource record type that 378 is referenced by the requested entry. Any required review of that 379 definition is separate from the expert review required here. 381 The review is for the purposes of ensuring that: 383 o The details for creating the registry entry are sufficiently 384 clear, precise and complete 386 o The combination of the _underscore name, under which the listed 387 resource record type is used, and the resource record type, is 388 unique in the table 390 For the purposes of this Expert Review, other matters of the 391 specification's technical quality, adequacy or the like are outside 392 of scope. 394 6. Security Considerations 396 This memo raises no security issues. 398 7. References 400 7.1. Normative References 402 [ACME] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. 403 Kasten, "Automatic Certificate Management Environment 404 (ACME)", I-D draft-ietf-acme-acme-11, March 2018. 406 [IANA] M. Cotton, B. Leiba, and T. Narten, "Guidelines for 407 Writing an IANA Considerations Section in RFCs", RFC 8126, 408 June 2017. 410 [MTA-STS] Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A., 411 and J. Jones, "SMTP MTA Strict Transport Security (MTA- 412 STS)", I-D draft-ietf-uta-mta-sts. 414 [RFC1035] Mockapetris, P., "Domain names - implementation and 415 specification", STD 13, RFC 1035, November 1987. 417 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 418 Specification", RFC 2181, July 1997. 420 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 421 specifying the location of services (DNS SRV)", RFC 2782, 422 February 2000. 424 [RFC5518] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By 425 Reference", RFC 5518, April 2009. 427 [RFC6335] Cotton, M., Eggert, L., Tpuch, J., Westerlund, M., and S. 428 Cheshire, "nternet Assigned Numbers Authority (IANA) 429 Procedures for the Management of the Service Name and 430 Transport Protocol Port Number Registry", RFC 6335, Aug 431 2011. 433 [RFC6376] Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys 434 Identified Mail (DKIM) Signatures", RFC 6376, Sept 2011. 436 [RFC6698] Hoffman, J. and J. Schlyter, "The DNS-Based Authentication 437 of Named Entities (DANE) Transport Layer Security (TLS) 438 Protocol: TLSA", RFC 6698, August . 440 [RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for 441 Authorizing Use of Domains in E-Mail, Version 1", 442 RFC 7208, April 2014. 444 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 445 Message Authentication, Reporting, and Conformance 446 (DMARC)", RFC 7489, March 2015. 448 [RFC7553] Falstrom, P. and O. Kolkman, "The Uniform Resource 449 Identifier (URI) DNS Resource Record", RFC 7553, 450 ISSN 2070-1721, June 2015. 452 [RFC7929] Wouters, P., , RFC 7929, August 2016. 454 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 455 Writing an IANA Considerations Section in RFCs", RFC 8126, 456 June 2017. 458 [RFC8162] Hoffman, P. and J. Schlyter, "Using Secure DNS to 459 Associate Certificates with Domain Names for S/MIME", 460 RFC 8162, May 2017. 462 [RFC952] Harrenstien, K., Stahl, M., and E. Feinler, "DOD Internet 463 Host Table Specification", RFC 952, October 1985. 465 7.2. URIs 467 [1] mailto:dnsop@ietf.org 469 Appendix A. Acknowledgements 471 Thanks go to Bill Fenner, Tony Hansen, Martin Hoffmann, Peter Koch, 472 Olaf Kolkman, and Andrew Sullivan for diligent review of the (much) 473 earlier drafts. For the later enhancements, thanks to: Stephane 474 Bortzmeyer, Bob Harold, Warren Kumari, John Levine, Joel Jaeggli, 475 Petr Špaček, Ondřej Surř, Paul Vixie, Tim 476 Wicinski, and Paul Wouters. 478 Special thanks to Ray Bellis for his persistent encouragement to 479 continue this effort, as well as the suggestion for an essential 480 simplification to the registration model. 482 Author's Address 484 Dave Crocker 485 Brandenburg InternetWorking 486 675 Spruce Dr. 487 Sunnyvale, CA 94086 488 USA 490 Phone: +1.408.246.8253 491 Email: dcrocker@bbiw.net 492 URI: http://bbiw.net/