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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Crocker 3 Internet-Draft Brandenburg InternetWorking 4 Intended status: Best Current Practice March 14, 2016 5 Expires: September 15, 2016 7 DNS Scoped Data Through '_Underscore' Attribute Leaves 8 draft-ietf-dnsop-attrleaf-00 10 Abstract 12 Historically, any DNS RR may occur for any domain name. Recent 13 additions have defined DNS leaf nodes that contain a reserved node 14 name, beginning with an underscore. The underscore construct is used 15 to define a semantic scope for DNS records that are associated with 16 the parent domain. This specification explores the nature of this 17 DNS usage and defines the "underscore names" registry with IANA. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on September 15, 2016. 36 Copyright Notice 38 Copyright (c) 2016 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. Scaling Benefits and TXT and SRV Resource Records . . . . . . 3 55 3. Underscore DNS Registry Function . . . . . . . . . . . . . . 4 56 4. DNS Underscore Registry Definition . . . . . . . . . . . . . 5 57 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 58 6. Related and Updated Registries . . . . . . . . . . . . . . . 9 59 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 60 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 61 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 62 8.2. References -- Informative . . . . . . . . . . . . . . . . 9 63 8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 12 64 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 12 65 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12 67 1. Introduction 69 The core DNS technical specifications assign no semantics to domain 70 names or their parts, and no constraints upon which resource records 71 (RRs) are permitted to be associated with particular names. Over 72 time, some leaf node names, such as "www" and "ftp" have come to 73 imply support for particular services, but this is a matter of 74 operational convention, rather than defined protocol semantics . 75 This freedom in the basic technology has permitted a wide range of 76 administrative and semantic policies to be used -- in parallel. Data 77 semantics have been limited to the specification of particular 78 resource records, on the expectation that new ones would be added as 79 needed. 81 As an alternative to defining new RRs, some DNS service enhancements 82 have specified a restricted scope for the occurrence of particular 83 resource records. That scope is a leaf node, within which the uses 84 of specific resource records can be formally defined and constrained. 85 The leaf has a distinguished naming convention: It uses a reserved 86 DNS node name that begins with an underscore ("_"). Because a "host" 87 domain name is not allowed to use the underscore character, this 88 distinguishes the name from all legal host names.[RFC1035] 89 Effectively, this convention creates a space for attributes that are 90 associated with the parent domain, one level up. 92 An established example is the SRV record [RFC2782] which generalizes 93 concepts long-used for email routing by the MX record 94 [RFC0974][RFC2821]. The use of special DNS names has significant 95 benefits and detriments. Some of these are explored in [RFC5507]. 97 [Comment]: The terms "resolution context" and "scoping rules" have 98 been suggested, in place of "semantic scope". In order to avoid 99 concern for matters of semantics, this specification uses the term 100 "scoping rules", to create a focus on the mechanics being defined, 101 rather than nuances of interpretation for the mechanism. 103 The scoping feature is particularly useful when generalized resource 104 records are used -- notably TXT and SRV. It provides efficient 105 separation of one use of them from another. Absent this separation, 106 an undifferentiated mass of these RRs is returned to the DNS client, 107 which then must parse through the internals of the records in the 108 hope of finding ones that are relevant; in some cases the results are 109 ambiguous, because the records do not adequately self-identify. With 110 underscore-based scoping, only the relevant RRs are returned. 112 This specification discusses the underscore "attribute" enhancement, 113 provides an explicit definition of it, and establishes an IANA 114 registry for the reserved names that begin with underscore. It 115 updates the many existing specifications that have defined underscore 116 names, in order to aggregate the references to a single IANA table. 118 Discussion Venue: Discussion about this draft is directed to the 119 apps-discuss@ietf.org [1] mailing list. 121 2. Scaling Benefits and TXT and SRV Resource Records 123 Some resource records are generic and support a variety of uses. 124 Each additional use defines its own rules and, possibly, its own 125 internal syntax and node-naming conventions to distinguish among 126 particular types. The TXT and SRV records are the notable examples. 127 Used freely, some of these approaches scale poorly, particularly when 128 the same RR can be present in the same leaf node, but with different 129 uses. An increasingly-popular approach, with excellent scaling 130 properties, uses an underscore-based name, at a defined place in the 131 DNS tree, so as to constrain to particular uses for particular RRs 132 farther down the branch using that name. This means that a direct 133 lookup produces only the desired records, at no greater cost than a 134 typical DNS lookup. 136 In the case of TXT records, different uses have developed largely 137 without coordination. One side-effect is that there is no 138 consistently distinguishable internal syntax for the record; even the 139 inefficiencies of internal inspection might not provide a reliable 140 means of distinguishing among the different uses. Underscore-based 141 names therefore define an administrative way of separating TXT 142 records that might have different uses, but otherwise would have no 143 syntactic markers for distinguishing among them. 145 In the case of the SRV RR distinguishing among different types of use 146 was part of the design. [RFC2782] The SRV specification serves as a 147 template, defining an RR that might only be used for specific 148 applications when there is an additional specification. The template 149 definition includes reference to tables of names from which 150 underscore-names should be drawn. The set of names is 151 defined in terms of other IANA tables, namely any table with symbolic 152 names. The other SRV naming field is , although its pool of 153 names is not explicitly defined. 155 3. Underscore DNS Registry Function 157 This specification creates a registry for DNS nodes names that begin 158 with an underscore and are used to define scope of use for specific 159 resource records (RR). A given name defines a specific, constrained 160 context for the use of such records. Within this scope, use of other 161 resource records that are not specified is permitted. The purpose of 162 the Underscore registry is to avoid collisions resulting from the use 163 of the same underscore-based name, for different applications. 165 Structurally, the registry is defined as a single, flat table of 166 names that begin with underscore. In some cases, such as for SRV, an 167 underscore name might be multi-part, as a sequence of underscore 168 names. Semantically, this is a hierarchical model and it is 169 theoretically reasonable to allow re-use of an underscore name in 170 different underscore contexts. That is, a subordinate name is 171 meaningful only within the scope of the first (parent) underscore 172 name. As such, they can be ignored by this global Underscore 173 registry. That is, the registry is for the definition of highest- 174 level underscore node name used. 176 +----------------------------+ 177 | NAME | 178 +----------------------------+ 179 | _service1 | 180 | ._protoB._service2 | 181 | _protoB._service3 | 182 | _protoC._service3 | 183 | _useX._protoD._service4 | 184 | _protoE._region._authority | 185 +----------------------------+ 187 Example of Underscore Names 189 Only the right-most names are registered in the IANA table. 190 Definition and registration of the subordinate names is the 191 responsibility of the specification that creates the highest-level 192 (right-most) registry entry. 194 4. DNS Underscore Registry Definition 196 A registry entry contains: 198 Name: Specifies a textual name for a scoped portion of the DNS. 199 The name will usually be taken from the specification cited in 200 the "Purpose" column and is intended for use in discussions 201 about the entry. 203 DNS Label: Specifies a single underscore name that defines a 204 name reservation; this name is the "global" entry name for the 205 scoped resource records that are associated with that name. 207 Constraints: Specifies any restrictions on use of the name. 209 RR(s): Lists the RRs that are defined for use within this 210 scope. 212 References Lists specifications that define the records and their 213 use under this Name. 215 Purpose: Specifies the particular purpose/use for specific 216 RR(s), defined for use within the scope of the registered 217 underscore name. 219 5. IANA Considerations 221 Per [RFC2434], IANA is requested to establish a DNS Underscore Name 222 Registry, for DNS node names that begin with the underscore character 223 (_) and have been specified in any published RFC, or are documented 224 by a specification published by another standards organization. The 225 contents of each entry are defined in Section 4. 227 Initial entriess in the registry are: 229 { Enhancement of this table to include all underscore name 230 reservations in effect at the time this document is published is 231 left as an exercise to the readers... /d } 233 +------------+--------------+-------+-----------+-------------------+ 234 | NAME | LABEL | RR | REFERENCE | PURPOSE | 235 +------------+--------------+-------+-----------+-------------------+ 236 | SRV | _srv | SRV | [RFC2782] | SRV template -- | 237 | | | | | pro forma entry, | 238 | | | | | not directly | 239 | | | | | usable | 240 | SRV TCP | _tcp | SRV | [RFC2782] | Use of SRV for a | 241 | | | | | TCP service | 242 | SRV UDP | _udp | SRV | [RFC2782] | Use of SRV for a | 243 | | | | | UDB service | 244 | LDAP | _ldap | SRV | [RFC2782] | LDAP server | 245 | SIP | _sip | NAPTR | [RFC3263] | Locating SIP | 246 | | | | [RFC6011] | Servers and UA | 247 | | | | | configuration | 248 | SPF | _spf | TXT | [RFC4408] | Authorized IP | 249 | | | | | addresses for | 250 | | | | | sending mail | 251 | DKIM | _domainkey | TXT | [RFC4871] | Public key for | 252 | | | | | verifying DKIM | 253 | | | | | signature. | 254 | PKI LDAP | _PKIXREP | SRV | [RFC4386] | PKI Repository | 255 | VBR | _vouch | TXT | [RFC5518] | Vouch-by- | 256 | | | | | refererence | 257 | | | | | domain assertion | 258 | DDDS | --???!-- | SRV | [RFC3404] | Mapping DDDS | 259 | | | | | query to DNS | 260 | | | | | records | 261 | SOAP BEEP | _soap-beep | SRV | [RFC4227] | SOAP over BEEP | 262 | | | | | lookup, when no | 263 | | | | | port specified | 264 | XMLRPC | _xmlrpc-beep | SRV | [RFC3529] | Resolve url for | 265 | BEEP | | | | XML-RPC using | 266 | | | | | BEEP | 267 | Diameter | _diameter | SRV | [RFC3588] | Diameter | 268 | | | | | rendezvous | 269 | Tunnel | _tunnel | SRV | [RFC3620] | Finding the | 270 | | | | | appropriate | 271 | | | | | address for | 272 | | | | | tunneling into a | 273 | | | | | particular domain | 274 | SLP | _slpda | SRV | [RFC3832] | Discovering | 275 | | | | | desired services | 276 | | | | | in given DNS | 277 | | | | | domains | 278 | IM | _im | SRV | [RFC3861] | Instant Messaging | 279 | | | | | address | 280 | | | | | resolution | 281 | Pres | _pres | SRV | [RFC3861] | Presence address | 282 | | | | | resolution | 283 | Msg Track | _mtqp | SRV | [RFC3887] | Assist in | 284 | | | | | determining the | 285 | | | | | path that a | 286 | | | | | particular | 287 | | | | | message has taken | 288 | | | | | through a | 289 | | | | | messaging system | 290 | XMPP | _xmpp-client | SRV | [RFC6120] | XMPP client | 291 | Client | | | | lookup of server | 292 | XMPP | _xmpp-server | SRV | [RFC6120] | XMPP server- | 293 | Server | | | | server lookup | 294 | DDDS SRV | _??? | SRV | [RFC3958] | Map domain name, | 295 | | | (and | | application | 296 | | | NAPTR | | service name, and | 297 | | | ?) | | application | 298 | | | | | protocol | 299 | | | | | dynamically to | 300 | | | | | target server and | 301 | | | | | port | 302 | Kerberos | _kerberos | SRV | [RFC4120] | purpose | 303 | PKI | _pkixrep | SRV | [RFC4386] | Enables | 304 | | | | | certificate-using | 305 | | | | | systems to locate | 306 | | | | | PKI repositories | 307 | Certificat | _certificate | SRV | [RFC4387] | Obtain | 308 | es | s | | | certificates and | 309 | | | | | certificate | 310 | | | | | revocation lists | 311 | | | | | (CRLs) from PKI | 312 | | | | | repositories | 313 | PGP Key | pgpkeys | SRV | [RFC4387] | Obtain | 314 | Store | | | | certificates and | 315 | | | | | certificate | 316 | | | | | revocation lists | 317 | | | | | (CRLs) from PKI | 318 | | | | | repositories | 319 | MSRP Relay | _msrp | SRV | [RFC4976] | purpose | 320 | Locator | | | | | 321 | Mobile | _mip6 | SRV | [RFC5026] | Bootstrap Mobile | 322 | IPv6 | | | [RFC5555] | IPv6 Home Agent | 323 | Bootstrap | | | | information from | 324 | | | | | non-topological | 325 | | | | | information | 326 | Digital | _dvbservdsc | SRV | [RFC5328] | Discover non- | 327 | Video Broa | | | | default DVB entry | 328 | dcasting | | | | points addresses | 329 | CAPWAP AC | _capwap- | rrs | [RFC5415] | Discover the | 330 | | control | | | CAPWAP AC | 331 | | | | | address(es) | 332 | IM | _im | SRV | [RFC5509] | For resolving | 333 | | | | | Instant Messaging | 334 | | | | | and Presence | 335 | | | | | services with SIP | 336 | Presence | _pres | SRV | [RFC5509] | For resolving | 337 | | | | | Instant Messaging | 338 | | | | | and Presence | 339 | | | | | services with SIP | 340 | IEEE | _mihis | NAPTR | [RFC5679] | Discovering | 341 | 802.21 | | , SRV | | servers that | 342 | Mobility | | | | provide IEEE | 343 | | | | | 802.21-defined | 344 | | | | | Mobility Services | 345 | STUN Clien | _stun | SRV | [RFC5389] | Find a STUN | 346 | t/Server | | | | server | 347 | TURN | _turn | SRV | [RFC5766] | Control the | 348 | | | | [RFC5928] | operation of a | 349 | | | | | relay to bypass | 350 | | | | | NAT | 351 | STUN NAT | _stun- | SRV | [RFC5780] | Discover the | 352 | Behavior | behavior | | | presence and | 353 | Discovery | | | | current behavior | 354 | | | | | of NATs and | 355 | | | | | firewalls between | 356 | | | | | the STUN client | 357 | | | | | and the STUN | 358 | | | | | server | 359 | Sieve | _sieve | SRV | [RFC5804] | Manage Sieve | 360 | Management | | | | scripts on a | 361 | | | | | remote server | 362 | AFS VLDB | _afs3-vlserv | SRV | [RFC5864] | Locate services | 363 | | er | | | for the AFS | 364 | | | | | distributed file | 365 | | | | | system | 366 | AFS PTS | _afs3-prserv | SRV | [RFC5864] | Locate services | 367 | | er | | | for the AFS | 368 | | | | | distributed file | 369 | | | | | system | 370 | Mail MSA | _submission | SRV | [RFC6186] | Locate email | 371 | Submission | | | | services | 372 | IMAP | _imap | SRV | [RFC6186] | Locate email | 373 | | | | | services | 374 | POP | _pop3 | SRV | [RFC6186] | Locate email | 375 | | | | | services | 376 | POP TLS | _pop3s | SRV | [RFC6186] | Locate email | 377 | | | | | services | 378 +------------+--------------+-------+-----------+-------------------+ 380 Table 1: DNS Underscore SCOPE Name Registry (with initial values) 382 6. Related and Updated Registries 384 This section needs to contained details specification of the 385 updates to existing underscore "registries", in order to have 386 those specifcations point to this new registry. 388 Numerous specifications have defined their own, independent 389 registries for use of underscore names. It is likely that adoption 390 of the proposed, integrated registry should render these piecemeal 391 registries obsolete 393 Registries that are candidates for replacement include: 395 Instant Messaging SRV Protocol Label Registry 397 Public Key Infrastructure using X.509 (PKIX) Parameters 399 Presence SRV Protocol Label Registry 401 7. Security Considerations 403 This memo raises no security issues. 405 8. References 407 8.1. Normative References 409 [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an 410 IANA Considerations Section in RFCs", RFC 2434, October 411 1998. 413 8.2. References -- Informative 415 [RFC0974] Partridge, C., "Mail routing and the domain system", 416 RFC 974, January 1986. 418 [RFC1035] Mockapetris, P., "Domain names - implementation and 419 specification", STD 13, RFC 1035, November 1987. 421 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 422 specifying the location of services (DNS SRV)", RFC 2782, 423 February 2000. 425 [RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, 426 April 2001. 428 [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation 429 Protocol (SIP): Locating SIP Servers", RFC 3263, June 430 2002. 432 [RFC3404] MMealling, M., "Dynamic Delegation Discovery System (DDDS) 433 Part Four: The Uniform Resource Identifiers (URI) 434 Resolution Application", RFC 3404, October 2002. 436 [RFC3529] Harold, W., "Using Extensible Markup Language-Remote 437 Procedure Calling (XML-RPC) in Blocks Extensible Exchange 438 Protocol (BEEP)", RFC 3529, April 2003. 440 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 441 Arkko, "Diameter Base Protocol", September 2003. 443 [RFC3620] New, D., "The TUNNEL Profile", RFC 3620, October 2003. 445 [RFC3832] Columbia University, Columbia University, Sun 446 Microsystems, IBM, and IBM, "Remote Service Discovery in 447 the Service Location Protocol (SLP) via DNS SRV", July 448 2004. 450 [RFC3861] Peterson, J., "Address Resolution for Instant Messaging 451 and Presence", RFC 3861, August 2004. 453 [RFC3887] "Message Tracking Query Protocol", September 2007. 455 [RFC3958] Daigle, L. and A. Newton, "Domain-Based Application 456 Service Location Using SRV RRs and the Dynamic Delegation 457 Discovery Service (DDDS)", RFC 3958, January 2005. 459 [RFC4120] USC-ISI, MIT, MIT, and MIT, "The Kerberos Network 460 Authentication Service (V5)", RFC 4120, July 2005. 462 [RFC4227] O'Tuathail, E. and M. Rose, "Using the Simple Object 463 Access Protocol (SOAP) in Blocks Extensible Exchange 464 Protocol (BEEP)", RFC 4227, January 2006. 466 [RFC4386] Boeyen, S. and P. Hallam-Baker, "Internet X.509 Public Key 467 Infrastructure: Repository Locator Service", February 468 2006. 470 [RFC4387] Gutmann, P., Ed., "Internet X.509 Public Key 471 Infrastructure Operational Protocols: Certificate Store 472 Access via HTTP", RFC 4387, February 2006. 474 [RFC4408] Wong, M. and W. Schlitt, "Sender Policy Framework (SPF) 475 for Authorizing Use of Domains in E-Mail, Version 1", 476 RFC 4408, April 2006. 478 [RFC4871] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton, 479 J., and M. Thomas, "DomainKeys Identified Mail (DKIM) 480 Signatures", RFC 4871, May 2007. 482 [RFC4976] Jennings, C., Mahy, R., and Roach, "Relay Extensions for 483 the Message Session Relay Protocol (MSRP)", RFC 4976, 484 September 2007. 486 [RFC5026] Giaretta, G., Ed., Kempf, J., and V. Devarapalli, Ed., 487 "Mobile IPv6 Bootstrapping in Split Scenario", RFC 5026, 488 October 2007. 490 [RFC5328] Adolf, A. and P. MacAvock, "A Uniform Resource Name (URN) 491 Namespace for the Digital Video Broadcasting Project 492 (DVB)", RFC 5328, September 2008. 494 [RFC5389] Rosenberg, , Mahy, , Matthews, , and Wing, "Session 495 Traversal Utilities for NAT (STUN)", RFC 5389, October 496 2008. 498 [RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley, 499 Ed., "Control And Provisioning of Wireless Access Points 500 (CAPWAP) Protocol Specification", RFC 5415, March 2009. 502 [RFC5507] Faltstrom, P., Ed. and R. Austein, Ed., , RFC 5507, April 503 2009. 505 [RFC5509] Loreto, S., "Internet Assigned Numbers Authority (IANA) 506 Registration of Instant Messaging and Presence DNS SRV RRs 507 for the Session Initiation Protocol (SIP)", RFC 5509, 508 April 2009. 510 [RFC5518] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By 511 Reference", RFC5 5518, April 2009. 513 [RFC5555] Soliman, H., Ed., "Mobile IPv6 Support for Dual Stack 514 Hosts and Routers", RFC 5555, June 2009. 516 [RFC5679] Bajko, G., "Locating IEEE 802.21 Mobility Services Using 517 DNS", RFC 5679, December 2009. 519 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 520 Relays around NAT (TURN): Relay Extensions to Session 521 Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. 523 [RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery 524 Using Session Traversal Utilities for NAT (STUN)", 525 RFC 5780, May 2010. 527 [RFC5804] Melnikov, A., Ed. and T. Martin, "A Protocol for Remotely 528 Managing Sieve Scripts", RFC 5804, July 2010. 530 [RFC5864] Allbery, R., "NS SRV Resource Records for AFS", RFC 5864, 531 April 2010. 533 [RFC5928] Petit-Huguenin, M., "Traversal Using Relays around NAT 534 (TURN) Resolution Mechanism", RFC 5928, August 2010. 536 [RFC6011] Lawrence, S., Ed. and J. Elwell, "Session Initiation 537 Protocol (SIP) User Agent Configuration", RFC 6011, 538 October 2010. 540 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 541 Protocol (XMPP): Core", RFC 6120, March 2011. 543 [RFC6186] Daboo, C., "Use of SRV Records for Locating Email 544 Submission/Access Services", RFC 6186, March 2011. 546 8.3. URIs 548 [1] mailto:we-need-a-list 550 Appendix A. Acknowledgements 552 Thanks go to Bill Fenner, Tony Hansen, Peter Koch, Olaf Kolkman, and 553 Andrew Sullivan for diligent review of the earlier drafts. Special 554 thanks to Ray Bellis for nearly 10 years of persistent encouragement 555 to pursue this document. 557 Author's Address 559 Dave Crocker 560 Brandenburg InternetWorking 561 675 Spruce Dr. 562 Sunnyvale, CA 94086 563 USA 565 Phone: +1.408.246.8253 566 Email: dcrocker@bbiw.net 567 URI: http://bbiw.net/