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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 July 15, 2018 5 Expires: January 16, 2019 7 DNS Scoped Data Through 'underscore' Naming of Attribute Leaves 8 draft-ietf-dnsop-attrleaf-11 10 Abstract 12 Formally, any DNS resource record may occur under 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 underscored 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 January 16, 2019. 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 . . . . . . . . . . . . . . . . . . . 3 60 1.2. Scaling Benefits . . . . . . . . . . . . . . . . . . . . 4 61 1.3. 'Global' Underscored Node Names . . . . . . . . . . . . . 4 62 2. DNS Underscore Scoped Entry Registries Function . . . . . . . 4 63 3. RRset Use Registration Template . . . . . . . . . . . . . . . 6 64 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 65 4.1. DNS Underscore Global Scoped Entry Registry . . . . . . . 7 66 4.2. DNS Underscore Global Scoped Entry Registry Definition . 7 67 4.3. Initial entries . . . . . . . . . . . . . . . . . . . . . 8 68 5. Guidance for Expert Review . . . . . . . . . . . . . . . . . 10 69 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 70 6.1. Interaction with DNS wildcards . . . . . . . . . . . . . 10 71 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 72 7.1. Normative References . . . . . . . . . . . . . . . . . . 11 73 7.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 12 74 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 12 75 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12 77 1. Introduction 79 The core Domain Name System (DNS) technical specifications assign no 80 semantics to domain names or their parts, and no constraints upon 81 which resource record (RR) types are permitted to be stored under 82 particular names [RFC1035], [RFC2181]. Over time, some leaf node 83 names, such as "www" and "ftp" have come to imply support for 84 particular services, but this is a matter of operational convention, 85 rather than defined protocol semantics. This freedom in the basic 86 technology has permitted a wide range of administrative and semantic 87 policies to be used -- in parallel. DNS data semantics have been 88 limited to the specification of particular resource record types, on 89 the expectation that new ones would be added as needed. 90 Unfortunately, the addition of new resource record types has proven 91 extremely challenging, over the life of the DNS, with significant 92 adoption and use barriers. 94 1.1. Underscore Scoping 96 As an alternative to defining a new RR type, some DNS service 97 enhancements call for using an existing resource record type, but 98 specify a restricted scope for its occurrence. Scope is meant as a 99 static property, not one dependent on the nature of the query. It is 100 an artifact of the DNS name. That scope is a leaf node, within which 101 the uses of specific resource record sets can be formally defined and 102 constrained. The leaf occurs in a branch having a distinguished 103 naming convention: At the top of the branch -- beneath the parent 104 domain name to which the scope applies -- one or more reserved DNS 105 node names begin with an underscore ("_"). Because the DNS rules for 106 a "host" (host name) do not allow use of the underscore character, 107 this distinguishes the underscored name from all legal host names 108 [RFC952]. Effectively, this convention for leaf node naming creates 109 a space for the listing of 'attributes' -- in the form of resource 110 record types -- that are associated with the parent domain, above the 111 underscored sub-branch. 113 The scoping feature is particularly useful when generalized resource 114 record types are used -- notably "TXT", "SRV", and "URI" [RFC1035], 115 [RFC2782], [RFC6335], [RFC7553]. It provides efficient separation of 116 one use of them from others. Absent this separation, an 117 undifferentiated mass of these "RRsets" is returned to the DNS 118 client, which then must parse through the internals of the records in 119 the hope of finding ones that are relevant. Worse, in some cases the 120 results are ambiguous because a record type might not adequately 121 self-identify its specific purpose. With underscore-based scoping, 122 only the relevant "RRsets"s are returned. 124 A simple example is DKIM [RFC6376] , which uses "_domainkey" for 125 defining a place to hold a "TXT" record containing signing 126 information for the parent domain. 128 This specification formally defines how underscored labels are used 129 as "attribute" enhancements for their parent domain names. For 130 example, domain name "_domainkey.example." acts as an attribute of 131 the parent domain name "example." To avoid collisions resulting from 132 the use of the same underscore-based labels for different 133 applications using the same resource record type, this document 134 establishes the DNS Underscore Global Scoped Entry IANA Registry. 135 Use of such node names, which begin with underscore, are reserved 136 when they are the underscored name closest to the DNS root; they are 137 considered 'global'. Underscore-based names that are farther down 138 the hierarchy are handled within the scope of the global underscore 139 name. 141 Discussion Venue: Discussion about this draft should be directed 142 to the dnsop@ietf.org [1] mailing list. 144 NOTE TO RFC EDITOR: Please remove "Discussion Venue" paragraph 145 prior to publication. 147 1.2. Scaling Benefits 149 Some resource record types are used in a fashion that can create 150 scaling problems, if an entire RRset associated with a domain name is 151 aggregated in the leaf node for that name. An increasingly-popular 152 approach, with excellent scaling properties, places the RRset under a 153 specially named branch, which is in turn under the node name that 154 would otherwise contain the RRset. The rules for naming that branch 155 define the context for interpreting the RRset. That is, rather than: 157 domain-name.example 158 / 159 RRset 161 the arrangement is: 163 _branch.domain-name.example 164 / 165 RRset 167 A direct lookup to the subordinate leaf node produces only the 168 desired record types, at no greater cost than a typical DNS lookup. 170 1.3. 'Global' Underscored Node Names 172 As defined in [RFC1034] the DNS uses names organized in a tree- 173 structured, or hierarchical fashion. A domain name might have 174 multiple node names that begin with an _underscore. A 'global' 175 underscored node name is the one that is closest to the root of the 176 DNS hierarchy, also called the highest-level or top-most. In the 177 presentation convention described in Section 3.1 or [RFC1034] this is 178 the right-most name beginning with an underscore. In other 179 presentation environments it might be positioned differently. To 180 avoid concern for the presentation variations, the qualifier 'global' 181 is used here. 183 2. DNS Underscore Scoped Entry Registries Function 185 A registry for 'global' DNS nodes names that begin with an underscore 186 is defined here. The purpose of the Underscore Global Registry is to 187 avoid collisions resulting from the use of the same underscore-based 188 name, for different applications. 190 o If a public specification calls for use of an underscore-prefixed 191 domain node name, the 'global' underscored name -- the underscored 192 name that is closest to the DNS root -- MUST be entered into this 193 registry. 195 An underscored name define scope of use for specific resource record 196 types, which are associated with the domain name that is the "parent" 197 to the branch defined by the underscored name. A given name defines 198 a specific, constrained context for one or more RR types, where use 199 of such record types conforms to the defined constraints. 201 o Within an underscore scoped leaf, other RRsets that are not 202 specified as part of the scope MAY be used. 204 Structurally, the registry is defined as a single, flat table of RR 205 types, under node names beginning with underscore. In some cases, 206 such as for use of an "SRV" record, the full scoping name might be 207 multi-part, as a sequence of underscored names. Semantically, that 208 sequence represents a hierarchical model and it is theoretically 209 reasonable to allow re-use of a subordinate underscored name in a 210 different, global underscored context; that is, a subordinate name is 211 meaningful only within the scope of the global underscored name. 212 Therefore they are ignored by this DNS Underscore Global Scoped Entry 213 Registry. This registry is for the definition of highest-level -- 214 ie, global -- underscored node name used. 216 +----------------------------+ 217 | NAME | 218 +----------------------------+ 219 | _service1 | 220 | ._protoB._service2 | 221 | _protoB._service3 | 222 | _protoC._service3 | 223 | _useX._protoD._service4 | 224 | _protoE._region._authority | 225 +----------------------------+ 227 Example of Underscore Names 229 Only global underscored names are registered in the IANA Underscore 230 Global table. 232 o The use of underscored node names is specific to each RRTYPE that 233 is being scoped. Each name defines a place, but does not define 234 the rules for what appears underneath that place, either as 235 additional underscored naming or as a leaf node with resource 236 records. Details for those rules are provided by specifications 237 for individual RRTYPEs. The sections below describe the way that 238 existing underscore labels are used with the RRTYPEs that they 239 name. 241 o Definition and registration of subordinate, underscore node names 242 is the responsibility of the specification that creates the global 243 registry entry. 245 That is, if a scheme using a global underscore node name has one or 246 more subordinate levels of underscore node naming, the namespaces 247 from which names for those lower levels are chosen are controlled by 248 the parent underscore node name. Each globally-registered underscore 249 name owns a distinct, subordinate name space. 251 3. RRset Use Registration Template 253 This section provides a basic template that can be used to register 254 new entries in the IANA DNS Underscore Global Scoped Entry Registry, 255 if the global underscored name above the RRTYPE is not already 256 registered. The text can be added to specifications using 257 RRTYPE/_Node-name combinations that have not already been registered. 259 "Per {RFC Attrleaf} please add the following entry to the DNS 260 Underscore Global Scoped Entry Registry:" 262 Note to RFC Editor: Please replace the above "{RFC Attrleaf}" text 263 with a reference to this document's RFC number. /d 265 +----------+-------------------+------------------------------------+ 266 | RR Type | _NODE NAME | REFERENCE | 267 +----------+-------------------+------------------------------------+ 268 | {RRTYPE} | _{DNS global node | {citation for the document making | 269 | | name} | the addition.} | 270 +----------+-------------------+------------------------------------+ 272 Table 1: Underscore Global Registry Entry 274 4. IANA Considerations 276 Per [RFC8126], IANA is requested to establish the: 278 DNS Underscore Global Scoped Entry Registry 280 This section describes actions requested of IANA. The guidance in 281 [IANA] is used. 283 4.1. DNS Underscore Global Scoped Entry Registry 285 The DNS Global Underscore Scoped Entry Registry is any DNS node name 286 that begin with the underscore character (_) and is the underscored 287 node name closest to the root; that is it defines the highest-level 288 of a DNS branch, under a "parent" domain name. 290 o This registry is to operate under the IANA rules for "Expert 291 Review" registration; see Section 5. 293 o The contents of each entry in the Global registry are defined in 294 Section 4.2. 296 o Each entry in the registry MUST contain values for all of the 297 fields specified in Section 4.2. 299 o Within the registry, the combination of RR Type and _Node Name 300 MUST be unique. 302 o The table is to be maintained with entries sorted by the first 303 column (RR Type) and, within that, the second column (_Node Name). 305 o The required Reference for an entry MUST have a stable resolution 306 to the organization controlling that registry entry 308 4.2. DNS Underscore Global Scoped Entry Registry Definition 310 A registry entry contains: 312 RR Type: Lists an RR type that is defined for use within this 313 scope 315 _Node Name: Specifies a single, underscored name that defines a 316 reserved name; this name is the "global" entry name for the 317 scoped resource record types that are associated with that 318 name 320 References: Lists specification that defines a record type and its 321 use under this Name. The organization producing the 322 specification retains control over the registry entry for 323 the _Node Name 325 Each RR type that is to be used MUST have a separate registry entry. 327 4.3. Initial entries 329 Initial entries in the registry are: 331 +------------+-----------------+------------+ 332 | RR Type | _NODE NAME | REFERENCE | 333 +------------+-----------------+------------+ 334 | OPENPGPKEY | _openpgpkey | [RFC7929] | 335 | SMIMEA | _smimecert | [RFC8162] | 336 | SRV | _dccp | [RFC2782] | 337 | SRV | _sctp | [RFC2782] | 338 | SRV | _tcp | [RFC2782] | 339 | SRV | _udp | [RFC2782] | 340 | TLSA | _sctp | [RFC6698] | 341 | TLSA | _tcp | [RFC6698] | 342 | TLSA | _udp | [RFC6698] | 343 | TXT | _mta-sts | [MTA-STS] | 344 | TXT | _acme-challenge | [ACME] | 345 | TXT | _dmarc | [RFC7489] | 346 | TXT | _domainkey | [RFC6376] | 347 | TXT | _spf | [RFC7208] | 348 | TXT | _vouch | [RFC5518] | 349 | URI | _iax | [RFC7553] | 350 | URI | _acct | [RFC7553] | 351 | URI | _dccp | [RFC7553] | 352 | URI | _email | [RFC7553] | 353 | URI | _ems | [RFC7553] | 354 | URI | _fax | [RFC7553] | 355 | URI | _ft | [RFC7553] | 356 | URI | _h323 | [RFC7553] | 357 | URI | _ical-sched | [RFC7553] | 358 | URI | _ical-access | [RFC7553] | 359 | URI | _ifax | [RFC7553] | 360 | URI | _im | [RFC7553] | 361 | URI | _mms | [RFC7553] | 362 | URI | _pres | [RFC7553] | 363 | URI | _pstn | [RFC7553] | 364 | URI | _sctp | [RFC7553] | 365 | URI | _sip | [RFC7553] | 366 | URI | _sms | [RFC7553] | 367 | URI | _tcp | [RFC7553] | 368 | URI | _udp | [RFC7553] | 369 | URI | _unifmsg | [RFC7553] | 370 | URI | _vcard | [RFC7553] | 371 | URI | _videomsg | [RFC7553] | 372 | URI | _voice | [RFC7553] | 373 | URI | _voicemsg | [RFC7553] | 374 | URI | _vpim | [RFC7553] | 375 | URI | _xmp | [RFC7553] | 376 +------------+-----------------+------------+ 378 Table 2: Underscore Global Registry (initial entries) 380 5. Guidance for Expert Review 382 This section provides guidance for expert review of registration 383 requests in the of DNS Underscore Global Scoped Entry Registry. 385 This review is solely to determine adequacy of a requested entry 386 in this Registry, and does not include review of other aspects of 387 the document specifying that entry. For example such a document 388 might also contain a definition of the resource record type that 389 is referenced by the requested entry. Any required review of that 390 definition is separate from the expert review required here. 392 The review is for the purposes of ensuring that: 394 o The details for creating the registry entry are sufficiently 395 clear, precise and complete 397 o The combination of the underscored name, under which the listed 398 resource record type is used, and the resource record type, is 399 unique in the table 401 For the purposes of this Expert Review, other matters of the 402 specification's technical quality, adequacy or the like are outside 403 of scope. 405 6. Security Considerations 407 This memo raises no security issues. 409 6.1. Interaction with DNS wildcards 411 DNS wildcards interact poorly with underscored names in two ways. 412 Since wildcards only are interpreted as leaf names, one cannot create 413 the equivalent of a wildcard name for prefixed names. A name such 414 as_label.*.example.com is not a wildcard. 416 Conversely, a wildcard such as *.example.com can match any name 417 including an underscored name. So, a wildcard might match an 418 underscored name, returning a record that is the type controlled by 419 the underscored name but is not intended to be used in the 420 underscored context and does not conform to its rules. 422 7. References 423 7.1. Normative References 425 [ACME] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. 426 Kasten, "Automatic Certificate Management Environment 427 (ACME)", I-D draft-ietf-acme-acme-11, March 2018. 429 [IANA] M. Cotton, B. Leiba, and T. Narten, "Guidelines for 430 Writing an IANA Considerations Section in RFCs", RFC 8126, 431 June 2017. 433 [MTA-STS] Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A., 434 and J. Jones, "SMTP MTA Strict Transport Security (MTA- 435 STS)", I-D draft-ietf-uta-mta-sts. 437 [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", 438 STD 13, RFC 1034, November 1987. 440 [RFC1035] Mockapetris, P., "Domain Names - Implementation and 441 SSpecification", STD 13, RFC 1035, November 1987. 443 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 444 Specification", RFC 2181, July 1997. 446 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 447 specifying the location of services (DNS SRV)", RFC 2782, 448 February 2000. 450 [RFC5518] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By 451 Reference", RFC 5518, April 2009. 453 [RFC6335] Cotton, M., Eggert, L., Tpuch, J., Westerlund, M., and S. 454 Cheshire, "nternet Assigned Numbers Authority (IANA) 455 Procedures for the Management of the Service Name and 456 Transport Protocol Port Number Registry", RFC 6335, Aug 457 2011. 459 [RFC6376] Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys 460 Identified Mail (DKIM) Signatures", RFC 6376, Sept 2011. 462 [RFC6698] Hoffman, J. and J. Schlyter, "The DNS-Based Authentication 463 of Named Entities (DANE) Transport Layer Security (TLS) 464 Protocol: TLSA", RFC 6698, August . 466 [RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for 467 Authorizing Use of Domains in E-Mail, Version 1", 468 RFC 7208, April 2014. 470 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 471 Message Authentication, Reporting, and Conformance 472 (DMARC)", RFC 7489, March 2015. 474 [RFC7553] Falstrom, P. and O. Kolkman, "The Uniform Resource 475 Identifier (URI) DNS Resource Record", RFC 7553, 476 ISSN 2070-1721, June 2015. 478 [RFC7929] Wouters, P., , RFC 7929, August 2016. 480 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 481 Writing an IANA Considerations Section in RFCs", RFC 8126, 482 June 2017. 484 [RFC8162] Hoffman, P. and J. Schlyter, "Using Secure DNS to 485 Associate Certificates with Domain Names for S/MIME", 486 RFC 8162, May 2017. 488 [RFC952] Harrenstien, K., Stahl, M., and E. Feinler, "DOD Internet 489 Host Table Specification", RFC 952, October 1985. 491 7.2. URIs 493 [1] mailto:dnsop@ietf.org 495 Appendix A. Acknowledgements 497 Thanks go to Bill Fenner, Dick Franks, Tony Hansen, Martin Hoffmann, 498 Peter Koch, Olaf Kolkman, and Andrew Sullivan for diligent review of 499 the (much) earlier drafts. For the later enhancements, thanks to: 500 Stephane Bortzmeyer, Bob Harold, Warren Kumari, John Levine, Joel 501 Jaeggli, Petr Špaček, Ondřej Surř, Paul Vixie, 502 Tim Wicinski, and Paul Wouters. 504 Special thanks to Ray Bellis for his persistent encouragement to 505 continue this effort, as well as the suggestion for an essential 506 simplification to the registration model. 508 Author's Address 509 Dave Crocker 510 Brandenburg InternetWorking 511 675 Spruce Dr. 512 Sunnyvale, CA 94086 513 USA 515 Phone: +1.408.246.8253 516 Email: dcrocker@bbiw.net 517 URI: http://bbiw.net/