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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: Standards Track November 3, 2018 5 Expires: May 7, 2019 7 DNS Scoped Data Through "Underscore" Naming of Attribute Leaves 8 draft-ietf-dnsop-attrleaf-15 10 Abstract 12 Formally, any DNS resource record may occur under any domain name. 13 However some services use an operational convention for defining 14 specific interpretations of an RRset, by locating the records in a 15 DNS branch, under the parent domain to which the RRset actually 16 applies. The top of this subordinate branch is defined by a naming 17 convention that uses a reserved node name, which begins with an 18 _underscore. The underscored naming construct defines a semantic 19 scope for DNS record types that are associated with the parent 20 domain, above the underscored branch. This specification explores 21 the nature of this DNS usage and defines the "DNS Global Underscore 22 Scoped Entry Registry" with IANA. The purpose of the Underscore 23 registry is to avoid collisions resulting from the use of the same 24 underscore-based name, for different services. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on May 7, 2019. 43 Copyright Notice 45 Copyright (c) 2018 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (https://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 1.1. Underscore Scoping . . . . . . . . . . . . . . . . . . . 3 62 1.2. Scaling Benefits . . . . . . . . . . . . . . . . . . . . 4 63 1.3. "Global" Underscored Node Names . . . . . . . . . . . . . 4 64 1.4. Interaction with DNS wildcards . . . . . . . . . . . . . 5 65 1.5. History . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 2. DNS Underscore Scoped Entry Registries Function . . . . . . . 5 67 3. RRset Use Registration Template . . . . . . . . . . . . . . . 7 68 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 69 4.1. DNS Underscore Global Scoped Entry Registry . . . . . . . 8 70 4.2. DNS Underscore Global Scoped Entry Registry Definition . 8 71 4.3. Initial entries . . . . . . . . . . . . . . . . . . . . . 9 72 4.4. Enumservices Registrations Registry . . . . . . . . . . . 10 73 5. Guidance for Expert Review . . . . . . . . . . . . . . . . . 10 74 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 75 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 76 7.1. Normative References . . . . . . . . . . . . . . . . . . 11 77 7.2. References -\- Informative . . . . . . . . . . . . . . . 13 78 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 14 79 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 14 80 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14 82 1. Introduction 84 The core Domain Name System (DNS) technical specifications assign no 85 semantics to domain names or their parts, and no constraints upon 86 which resource record (RR) types are permitted to be stored under 87 particular names [RFC1035], [RFC2181]. Over time, some leaf node 88 names, such as "www" and "ftp" have come to imply support for 89 particular services, but this is a matter of operational convention, 90 rather than defined protocol semantics. This freedom in the basic 91 technology has permitted a wide range of administrative and semantic 92 policies to be used -- in parallel. DNS data semantics have been 93 limited to the specification of particular resource record types, on 94 the expectation that new resource record types would be added as 95 needed. Unfortunately, the addition of new resource record types has 96 proven extremely challenging, over the life of the DNS, with 97 significant adoption and use barriers. 99 1.1. Underscore Scoping 101 As an alternative to defining a new RR type, some DNS service 102 enhancements call for using an existing resource record type, but 103 specify a restricted scope for its occurrence. Scope is meant as a 104 static property, not one dependent on the nature of the query. It is 105 an artifact of the DNS name. That scope is a leaf node, within which 106 the uses of specific resource record sets can be formally defined and 107 constrained. The leaf occurs in a branch having a distinguished 108 naming convention: At the top of the branch -- beneath the parent 109 domain name to which the scope applies -- one or more reserved DNS 110 node names begin with an underscore ("_"). Because the DNS rules for 111 a "host" (host name) do not allow use of the underscore character, 112 this distinguishes the underscored name from all legal host names 113 [RFC952]. Effectively, this convention for leaf node naming creates 114 a space for the listing of "attributes" -- in the form of resource 115 record types -- that are associated with the parent domain, above the 116 underscored sub-branch. 118 The scoping feature is particularly useful when generalized resource 119 record types are used -- notably "TXT", "SRV", and "URI" [RFC1035], 120 [RFC2782], [RFC6335], [RFC7553]. It provides efficient separation of 121 one use of them from others. Absent this separation, an 122 undifferentiated mass of these "RRsets" is returned to the DNS 123 client, which then must parse through the internals of the records in 124 the hope of finding ones that are relevant. Worse, in some cases the 125 results are ambiguous because a record type might not adequately 126 self-identify its specific purpose. With underscore-based scoping, 127 only the relevant "RRsets"s are returned. 129 A simple example is DKIM [RFC6376] , which uses "_domainkey" for 130 defining a place to hold a "TXT" record containing signing 131 information for the parent domain. 133 This specification formally defines how underscored labels are used 134 as "attribute" enhancements for their parent domain names. For 135 example, domain name "_domainkey.example." acts as an attribute of 136 the parent domain name "example." To avoid collisions resulting from 137 the use of the same underscore-based labels for different 138 applications using the same resource record type, this document 139 establishes the DNS Underscore Global Scoped Entry IANA Registry. 140 Use of such node names, which begin with underscore, are reserved 141 when they are the underscored name closest to the DNS root; they are 142 considered "global". Underscore-based names that are farther down 143 the hierarchy are handled within the scope of the global underscore 144 name. 146 Discussion Venue: Discussion about this draft should be directed 147 to the dnsop@ietf.org [1] mailing list. 149 NOTE TO RFC EDITOR: Please remove "Discussion Venue" paragraph 150 prior to publication. 152 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 153 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 154 "OPTIONAL" in this document are to be interpreted as described in 155 BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all 156 capitals, as shown here. 158 1.2. Scaling Benefits 160 Some resource record types are used in a fashion that can create 161 scaling problems, if an entire RRset associated with a domain name is 162 aggregated in the leaf node for that name. An increasingly-popular 163 approach, with excellent scaling properties, places the RRset under a 164 specially named branch, which is in turn under the node name that 165 would otherwise contain the RRset. The rules for naming that branch 166 define the context for interpreting the RRset. That is, rather than: 168 domain-name.example 169 / 170 RRset 172 the arrangement is: 174 _branch.domain-name.example 175 / 176 RRset 178 A direct lookup to the subordinate leaf node produces only the 179 desired record types, at no greater cost than a typical DNS lookup. 181 1.3. "Global" Underscored Node Names 183 As defined in [RFC1034] the DNS uses names organized in a tree- 184 structured, or hierarchical fashion. A domain name might have 185 multiple node names that begin with an _underscore. A "global" 186 underscored node name is the one that is closest to the root of the 187 DNS hierarchy, also called the highest-level or top-most. In the 188 presentation convention described in Section 3.1 of [RFC1034] this is 189 the right-most name beginning with an underscore. In other 190 presentation environments it might be positioned differently. To 191 avoid concern for the presentation variations, the qualifier "global" 192 is used here. 194 1.4. Interaction with DNS wildcards 196 DNS wildcards interact poorly with underscored names in two ways. 197 Since wildcards only are interpreted as leaf names, one cannot create 198 the equivalent of a wildcard name for prefixed names. A name such as 199 label.*.example.com is not a wildcard. 201 Conversely, a wildcard such as *.example.com can match any name 202 including an underscored name. So, a wildcard might match an 203 underscored name, returning a record that is the type controlled by 204 the underscored name but is not intended to be used in the 205 underscored context and does not conform to its rules. 207 1.5. History 209 Originally different uses of underscore-based node names developed 210 largely without coordination. For "TXT" records, there is no 211 consistent, internal syntax that to permits distinguishing among the 212 different uses. In the case of the "SRV" "RR" and "URI" "RR", 213 distinguishing among different types of use was part of the design 214 [RFC2782], [RFC7553]. The "SRV" and "URI" specifications serve as 215 templates, defining "RR"s that might only be used for specific 216 applications when there is an additional specification. The template 217 definition included reference to two levels of tables of names from 218 which underscore-names should be drawn. The lower-level (local 219 scope) set of <"_service"> names is defined in terms of other IANA 220 tables, namely any table with symbolic names. The upper-level 221 (global scope) "SRV" naming field is <"_proto">, although its pool of 222 names is not explicitly defined. 224 The aggregate effect of these independent efforts was a long list of 225 underscore-based names that were reserved without coordination, which 226 invites an eventual name-assignment collision. The remedy is this 227 base document, which defines a registry for these names, and attempts 228 to register all those already in use, with a companion document 229 [attrleaf-fix] developed to direct changes to the pre-registry 230 specifications that used underscore-based (global) node names. 232 2. DNS Underscore Scoped Entry Registries Function 234 A registry for "global" DNS node names that begin with an underscore 235 is defined here. The purpose of the Underscore Global Registry is to 236 avoid collisions resulting from the use of the same underscore-based 237 name, for different applications. 239 o If a public specification calls for use of an underscore-prefixed 240 domain node name, the "global" underscored name -- the underscored 241 name that is closest to the DNS root -- MUST be entered into this 242 registry. 244 An underscored name defines the scope of use for specific resource 245 record types, which are associated with the domain name that is the 246 "parent" to the branch defined by the underscored name. A given name 247 defines a specific, constrained context for one or more RR types, 248 where use of such record types conforms to the defined constraints. 250 o Within an underscore scoped leaf, other RRsets that are not 251 specified as part of the scope MAY be used. 253 Structurally, the registry is defined as a single, flat table of RR 254 types, under node names beginning with underscore. In some cases, 255 such as for use of an "SRV" record, the full scoping name might be 256 multi-part, as a sequence of underscored names. Semantically, that 257 sequence represents a hierarchical model and it is theoretically 258 reasonable to allow re-use of a subordinate underscored name in a 259 different, global underscored context; that is, a subordinate name is 260 meaningful only within the scope of the global underscored name. 261 Therefore they are ignored by this DNS Underscore Global Scoped Entry 262 Registry. This registry is for the definition of highest-level -- 263 ie, global -- underscored node name used. 265 +----------------------------+ 266 | NAME | 267 +----------------------------+ 268 | _service1 | 269 | _protoB._service2 | 270 | _protoB._service3 | 271 | _protoC._service3 | 272 | _useX._protoD._service4 | 273 | _protoE._region._authority | 274 +----------------------------+ 276 Table 1: Examples of Underscored Names 278 Only global underscored names are registered in the IANA Underscore 279 Only the global underscored names "_service1", "_service2", Global 280 table. (From the example, that would mean registering "_service3", 281 "_service4", and "_authority" are registered in the IANA _service1, 282 _service2, _service3, _service 4, and _authority.) 284 o The use of underscored node names is specific to each RRTYPE that 285 is being scoped. Each name defines a place, but does not define 286 the rules for what appears underneath that place, either as 287 additional underscored naming or as a leaf node with resource 288 records. Details for those rules are provided by specifications 289 for individual RRTYPEs. The sections below describe the way that 290 existing underscore labels are used with the RRTYPEs that they 291 name. 293 o Definition and registration of subordinate, underscore node names 294 is the responsibility of the specification that creates the global 295 registry entry. 297 That is, if a scheme using a global underscore node name has one or 298 more subordinate levels of underscore node naming, the namespaces 299 from which names for those lower levels are chosen are controlled by 300 the parent underscore node name. Each globally-registered underscore 301 name owns a distinct, subordinate name space. 303 3. RRset Use Registration Template 305 This section provides a basic template that can be used to register 306 new entries in the IANA DNS Underscore Global Scoped Entry Registry, 307 if the global underscored name above the RRTYPE is not already 308 registered. The text can be added to specifications using 309 RRTYPE/_Node-name combinations that have not already been registered. 311 "Per {RFC Attrleaf} please add the following entry to the DNS 312 Underscore Global Scoped Entry Registry:" 314 Note to RFC Editor: Please replace the above "{RFC Attrleaf}" text 315 with a reference to this document's RFC number. /d 317 +----------+-------------------+------------------------------------+ 318 | RR Type | _NODE NAME | REFERENCE | 319 +----------+-------------------+------------------------------------+ 320 | {RRTYPE} | _{DNS global node | {citation for the document making | 321 | | name} | the addition.} | 322 +----------+-------------------+------------------------------------+ 324 Table 2: Underscore Global Registry Entry Template 326 4. IANA Considerations 328 Per [RFC8126] IANA is requested to establish the: 330 "DNS Underscore Global Scoped Entry Registry" 332 This section describes actions requested of IANA. The guidance in 333 [IANA] is used. 335 4.1. DNS Underscore Global Scoped Entry Registry 337 The DNS Global Underscore Scoped Entry Registry is any DNS node name 338 that begin with the underscore character ("_", ASCII 0x5F) and is the 339 underscored node name closest to the root; that is it defines the 340 highest-level of a DNS branch, under a "parent" domain name. 342 o This registry is to operate under the IANA rules for "Expert 343 Review" registration; see Section 5. 345 o The contents of each entry in the Global registry are defined in 346 Section 4.2. 348 o Each entry in the registry MUST contain values for all of the 349 fields specified in Section 4.2. 351 o Within the registry, the combination of RR Type and _Node Name 352 MUST be unique. 354 o The table is to be maintained with entries sorted by the first 355 column (RR Type) and, within that, the second column (_Node Name). 357 o The required Reference for an entry MUST have a stable resolution 358 to the organization controlling that registry entry. 360 4.2. DNS Underscore Global Scoped Entry Registry Definition 362 A registry entry contains: 364 RR Type: Lists an RR type that is defined for use within this 365 scope. 367 _Node Name: Specifies a single, underscored name that defines a 368 reserved name; this name is the "global" entry name for 369 the scoped resource record types that are associated 370 with that name; for characters in the name that have an 371 upper-case form and a lower-case form, the character 372 MUST be recorded as lower-case, to simplify name 373 comparisons. 375 References: Lists the specification that defines a record type 376 and its use under this _Node Name. The organization 377 producing the specification retains control over the 378 registry entry for the _Node Name. 380 Each RR type that is to be used with a _Node Name MUST have a 381 separate registry entry. 383 4.3. Initial entries 385 Initial entries in the registry are: 387 +------------+------------------+------------+ 388 | RR Type | _NODE NAME | REFERENCE | 389 +------------+------------------+------------+ 390 | NULL | _ta-* {see note} | [RFC8145] | 391 | OPENPGPKEY | _openpgpkey | [RFC7929] | 392 | SMIMEA | _smimecert | [RFC8162] | 393 | SRV | _dccp | [RFC2782] | 394 | SRV | _http | [RFC4386] | 395 | SRV | _ipv6 | [RFC5026] | 396 | SRV | _ldap | [RFC4386] | 397 | SRV | _ocsp | [RFC4386] | 398 | SRV | _sctp | [RFC2782] | 399 | SRV | _sip | [RFC5509] | 400 | SRV | _tcp | [RFC2782] | 401 | SRV | _udp | [RFC2782] | 402 | SRV | _xmpp | [RFC3921] | 403 | TLSA | _dane | [RFC7671] | 404 | TLSA | _sctp | [RFC6698] | 405 | TLSA | _tcp | [RFC6698] | 406 | TLSA | _udp | [RFC6698] | 407 | TXT | _acme-challenge | [ACME] | 408 | TXT | _dmarc | [RFC7489] | 409 | TXT | _domainkey | [RFC6376] | 410 | TXT | _mta-sts | [MTA-STS] | 411 | TXT | _spf | [RFC7208] | 412 | TXT | _tcp | [RFC6763] | 413 | TXT | _udp | [RFC6763] | 414 | TXT | _vouch | [RFC5518] | 415 | URI | _acct | [RFC6118] | 416 | URI | _dccp | [RFC7566] | 417 | URI | _email | [RFC6118] | 418 | URI | _ems | [RFC6118] | 419 | URI | _fax | [RFC6118] | 420 | URI | _ft | [RFC6118] | 421 | URI | _h323 | [RFC6118] | 422 | URI | _iax | [RFC6118] | 423 | URI | _ical-access | [RFC6118] | 424 | URI | _ical-sched | [RFC6118] | 425 | URI | _ifax | [RFC6118] | 426 | URI | _im | [RFC6118] | 427 | URI | _mms | [RFC6118] | 428 | URI | _pres | [RFC6118] | 429 | URI | _pstn | [RFC6118] | 430 | URI | _sctp | [RFC6118] | 431 | URI | _sip | [RFC6118] | 432 | URI | _sms | [RFC6118] | 433 | URI | _tcp | [RFC6118] | 434 | URI | _udp | [RFC6118] | 435 | URI | _unifmsg | [RFC6118] | 436 | URI | _vcard | [RFC6118] | 437 | URI | _videomsg | [RFC6118] | 438 | URI | _voice | [RFC6118] | 439 | URI | _voicemsg | [RFC6118] | 440 | URI | _vpim | [RFC6118] | 441 | URI | _web | [RFC6118] | 442 | URI | _xmpp | [RFC6118] | 443 +------------+------------------+------------+ 445 Table 3: Underscore Global Registry (initial entries) 447 NOTE: Under the NULL RR, the entry ""_ta-*"" denotes all node 448 names beginning with the string ""_ta-*"". It does NOT refer to a 449 DNS wildcard specification. 451 4.4. Enumservices Registrations Registry 453 Please add a note to the Enumservice Registrations registry with the 454 following -- or similar -- language: 456 "When adding an entry to this registry, strong consideration 457 should be given to also adding an entry to the 'DNS Underscore 458 Global Scoped Entry Registry'." 460 5. Guidance for Expert Review 462 This section provides guidance for expert review of registration 463 requests in the DNS Underscore Global Scoped Entry Registry. 465 This review is solely to determine adequacy of a requested entry 466 in this Registry, and does not include review of other aspects of 467 the document specifying that entry. For example such a document 468 might also contain a definition of the resource record type that 469 is referenced by the requested entry. Any required review of that 470 definition is separate from the expert review required here. 472 The review is for the purposes of ensuring that: 474 o The details for creating the registry entry are sufficiently 475 clear, precise and complete 477 o The combination of the underscored name, under which the listed 478 resource record type is used, and the resource record type, is 479 unique in the table 481 For the purposes of this Expert Review, other matters of the 482 specification's technical quality, adequacy or the like are outside 483 of scope. 485 6. Security Considerations 487 This memo raises no security issues. 489 7. References 491 7.1. Normative References 493 [ACME] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. 494 Kasten, "Automatic Certificate Management Environment 495 (ACME)", I-D draft-ietf-acme-acme-11, March 2018. 497 [IANA] M. Cotton, B. Leiba, and T. Narten, "Guidelines for 498 Writing an IANA Considerations Section in RFCs", RFC 8126, 499 June 2017. 501 [MTA-STS] Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A., 502 and J. Jones, "SMTP MTA Strict Transport Security (MTA- 503 STS)", I-D draft-ietf-uta-mta-sts. 505 [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", 506 STD 13, RFC 1034, November 1987. 508 [RFC1035] Mockapetris, P., "Domain Names - Implementation and 509 Specification", STD 13, RFC 1035, November 1987. 511 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 512 Requirement Levels", BCP 14, RFC 2119, March 1997. 514 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 515 Specification", RFC 2181, July 1997. 517 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 518 specifying the location of services (DNS SRV)", RFC 2782, 519 February 2000. 521 [RFC3921] Saint-Andre, P., Ed., "Extensible Messaging and Presence 522 Protocol (XMPP): Instant Messaging and Presence", 523 RFC 3921, DOI 10.17487/RFC3921, October 2004, 524 . 526 [RFC4386] Boeyen, S. and P. Hallam-Baker, "Internet X.509 Public Key 527 Infrastructure Repository Locator Service", RFC 4386, 528 DOI 10.17487/RFC4386, February 2006, 529 . 531 [RFC5026] Giaretta, G., Ed., Kempf, J., and V. Devarapalli, Ed., 532 "Mobile IPv6 Bootstrapping in Split Scenario", RFC 5026, 533 DOI 10.17487/RFC5026, October 2007, 534 . 536 [RFC5509] Loreto, S., "Internet Assigned Numbers Authority (IANA) 537 Registration of Instant Messaging and Presence DNS SRV RRs 538 for the Session Initiation Protocol (SIP)", RFC 5509, 539 DOI 10.17487/RFC5509, April 2009, 540 . 542 [RFC5518] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By 543 Reference", RFC 5518, April 2009. 545 [RFC6118] Hoeneisen, B. and A. Mayrhofer, "Update of Legacy IANA 546 Registrations of Enumservices", RFC 6118, 547 DOI 10.17487/RFC6118, March 2011, 548 . 550 [RFC6335] Cotton, M., Eggert, L., Tpuch, J., Westerlund, M., and S. 551 Cheshire, "nternet Assigned Numbers Authority (IANA) 552 Procedures for the Management of the Service Name and 553 Transport Protocol Port Number Registry", RFC 6335, Aug 554 2011. 556 [RFC6376] Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys 557 Identified Mail (DKIM) Signatures", RFC 6376, Sept 2011. 559 [RFC6698] Hoffman, J. and J. Schlyter, "The DNS-Based Authentication 560 of Named Entities (DANE) Transport Layer Security (TLS) 561 Protocol: TLSA", RFC 6698, August . 563 [RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn, 564 Ed., "Diameter Base Protocol", RFC 6733, 565 DOI 10.17487/RFC6733, October 2012, 566 . 568 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 569 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 570 . 572 [RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for 573 Authorizing Use of Domains in E-Mail, Version 1", 574 RFC 7208, April 2014. 576 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 577 Message Authentication, Reporting, and Conformance 578 (DMARC)", RFC 7489, March 2015. 580 [RFC7553] Falstrom, P. and O. Kolkman, "The Uniform Resource 581 Identifier (URI) DNS Resource Record", RFC 7553, 582 ISSN 2070-1721, June 2015. 584 [RFC7566] Goix, L. and K. Li, "Enumservice Registration for 'acct' 585 URI", RFC 7566, DOI 10.17487/RFC7566, June 2015, 586 . 588 [RFC7671] Dukhovni, V. and W. Hardaker, "The DNS-Based 589 Authentication of Named Entities (DANE) Protocol: Updates 590 and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671, 591 October 2015, . 593 [RFC7929] Wouters, P., , RFC 7929, August 2016. 595 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 596 Writing an IANA Considerations Section in RFCs", RFC 8126, 597 June 2017. 599 [RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust 600 Anchor Knowledge in DNS Security Extensions (DNSSEC)", 601 RFC 8145, April 2017. 603 [RFC8162] Hoffman, P. and J. Schlyter, "Using Secure DNS to 604 Associate Certificates with Domain Names for S/MIME", 605 RFC 8162, May 2017. 607 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 608 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 609 May 2017, . 611 [RFC952] Harrenstien, K., Stahl, M., and E. Feinler, "DOD Internet 612 Host Table Specification", RFC 952, October 1985. 614 7.2. References -\- Informative 616 [attrleaf-fix] 617 Crocker, D., "Changes to Rationalize Underscore DNS Node 618 Names", I-D draft-crocker-attrleaf-simplification-00, 619 2017. 621 7.3. URIs 623 [1] mailto:dnsop@ietf.org 625 Appendix A. Acknowledgements 627 Thanks go to Bill Fenner, Dick Franks, Tony Hansen, Martin Hoffmann, 628 Paul Hoffman, Peter Koch, Olaf Kolkman, Murray Kucherawy, John 629 Levine, Benno Overeinder, and Andrew Sullivan for diligent review of 630 the (much) earlier drafts. For the later enhancements, thanks to: 631 Stephane Bortzmeyer, Alissa Cooper, Bob Harold, Benjamin Kaduk, Mirja 632 Kuehlewind, Warren Kumari, John Levine, Joel Jaeggli, Benno 633 Overeinder, Eric Rescorla, Adam Roach, Petr Špaček, 634 Ondřej Sury, Paul Vixie, Tim Wicinski, and Paul Wouters. 636 Special thanks to Ray Bellis for his persistent encouragement to 637 continue this effort, as well as the suggestion for an essential 638 simplification to the registration model. 640 Author's Address 642 Dave Crocker 643 Brandenburg InternetWorking 644 675 Spruce Dr. 645 Sunnyvale, CA 94086 646 USA 648 Phone: +1.408.246.8253 649 Email: dcrocker@bbiw.net 650 URI: http://bbiw.net/