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Saint-Andre 3 Internet-Draft Cisco Systems, Inc. 4 Obsoletes: 3406 (if approved) November 13, 2013 5 Intended status: BCP 6 Expires: May 17, 2014 8 Uniform Resource Name (URN) Namespace Definition Mechanisms 9 draft-ietf-urnbis-rfc3406bis-urn-ns-reg-07 11 Abstract 13 This document supplements the Uniform Resource Name (URN) syntax 14 specification by defining the concept of a URN namespace, as well as 15 mechanisms for defining and registering such namespaces. This 16 document obsoletes RFC 3406. 18 Status of this Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on May 17, 2014. 35 Copyright Notice 37 Copyright (c) 2013 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 3. What is a URN Namespace? . . . . . . . . . . . . . . . . . . . 4 55 4. URN Namespace Types . . . . . . . . . . . . . . . . . . . . . 5 56 4.1. Formal Namespaces . . . . . . . . . . . . . . . . . . . . 5 57 4.2. Informal Namespaces . . . . . . . . . . . . . . . . . . . 6 58 5. Defining a URN Namespace . . . . . . . . . . . . . . . . . . . 6 59 5.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 7 60 5.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 7 61 5.3. Assignment . . . . . . . . . . . . . . . . . . . . . . . . 8 62 5.4. Security . . . . . . . . . . . . . . . . . . . . . . . . . 9 63 5.5. Resolution . . . . . . . . . . . . . . . . . . . . . . . . 9 64 6. Registration Template . . . . . . . . . . . . . . . . . . . . 10 65 6.1. Namespace ID . . . . . . . . . . . . . . . . . . . . . . . 10 66 6.2. Version . . . . . . . . . . . . . . . . . . . . . . . . . 10 67 6.3. Date . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 68 6.4. Registrant . . . . . . . . . . . . . . . . . . . . . . . . 10 69 6.5. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 10 70 6.6. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 10 71 6.7. Assignment . . . . . . . . . . . . . . . . . . . . . . . . 10 72 6.8. Resolution . . . . . . . . . . . . . . . . . . . . . . . . 10 73 6.9. Documentation . . . . . . . . . . . . . . . . . . . . . . 10 74 7. Registering a URN Namespace . . . . . . . . . . . . . . . . . 11 75 7.1. Formal Namespaces . . . . . . . . . . . . . . . . . . . . 11 76 7.2. Informal Namespaces . . . . . . . . . . . . . . . . . . . 11 77 8. Guidelines for Designated Experts . . . . . . . . . . . . . . 11 78 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 79 10. Security Considerations . . . . . . . . . . . . . . . . . . . 12 80 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 81 11.1. Normative References . . . . . . . . . . . . . . . . . . . 12 82 11.2. Informative References . . . . . . . . . . . . . . . . . . 12 83 Appendix A. Changes from RFC 3406 . . . . . . . . . . . . . . . . 13 84 Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . 13 85 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 14 86 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 88 1. Introduction 90 A Uniform Resource Name (URN) [I-D.ietf-urnbis-rfc2141bis-urn] is a 91 Uniform Resource Identifier (URI) [RFC3986] that is intended to serve 92 as a persistent, location-independent resource identifier. This 93 document supplements the Uniform Resource Name (URN) syntax 94 specification [I-D.ietf-urnbis-rfc2141bis-urn] by defining: 96 o The concept of a URN namespace. 98 o A mechanism for defining a URN namespace and associating it with a 99 public identifier (called a Namespace ID or "NID"). 101 o Procedures for registering NIDs with the Internet Assigned Numbers 102 Authority (IANA). 104 Syntactically, the NID follows the 'urn' scheme name. For instance, 105 a URN in the 'example' namespace [RFC6963] might be of the form 106 "urn:example:foo". 108 This document rests on two key assumptions: 110 1. Assignment of a URN is a managed process. 112 A string that conforms to the URN syntax is not necessarily a 113 valid URN, because a URN needs to be assigned according to the 114 rules of a particular namespace (in terms of syntax, semantics, 115 and process). 117 2. The space of URN namespaces is itself managed. 119 A string in the namespace identifier slot of the URN syntax is 120 not necessarily a valid URN namespace identifier, because in 121 order to be valid a namespace needs to be defined and registered 122 in accordance with the rules of this document. 124 URN namespaces were originally defined in [RFC2611], which was 125 obsoleted by [RFC3406]. Based on experience with defining and 126 registering URN namespaces since that time, this document specifies 127 URN namespaces with the smallest reasonable set of changes from 128 [RFC3406], while at the same time simplifying the registration 129 process. This document obsoletes RFC 3406. 131 2. Terminology 133 Several important terms used in this document are defined in the URN 134 syntax specification [I-D.ietf-urnbis-rfc2141bis-urn]. 136 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 137 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 138 "OPTIONAL" in this document are to be interpreted as described in 139 [RFC2119]. 141 3. What is a URN Namespace? 143 A URN namespace is a collection of identifiers that are (1) unique, 144 (2) assigned in a consistent way, and (3) assigned according to a 145 common definition. 147 1. The "uniqueness" constraint means that an identifier within the 148 namespace is never assigned to more than one resource and never 149 reassigned to a different resource. 151 2. The "consistent assignment" constraint means that an identifier 152 within the namespace is assigned by an organization or minted in 153 accordance with a process or algorithm that is always followed. 155 3. The "common definition" constraint means that there are clear 156 definitions for the syntax of identifiers within the namespace 157 and the process of assigning or minting them. 159 A URN namespace is identified by a particular NID in order to ensure 160 the global uniqueness of URNs and, optionally, to provide a cue 161 regarding the structure of URNs assigned within a namespace. 163 With regard to global uniqueness, using different NIDs for different 164 collections of identifiers ensures that no two URNs will be the same 165 for different resources, since each collection is required to 166 uniquely assign each identifier. However, a single resource can have 167 more than one URN assigned to it for different purposes (e.g., some 168 numbers might be valid identifiers in two different identifier 169 systems, where the namespace identifier differentiates between the 170 resulting URNs). 172 With regard to the structure of URNs assigned within a namespace, the 173 development of an identifier structure (and thereby a collection of 174 identifiers) depends on the requirements of the community defining 175 the identifiers, how the identifiers will be assigned and used, etc. 176 These issues are beyond the scope of URN syntax and the general rules 177 for URN namespaces, because they are specific to the community 178 defining a namespace (e.g., the bibliographic and publishing 179 communities in the case of the 'ISBN' and 'ISSN' namespaces, or the 180 developers of extensions to the Extensible Messaging and Presence 181 Protocol in the case of the 'XMPP' namespace). 183 URN namespaces inherit certain rights and responsibilities, e.g.: 185 o They uphold the general principles of a well-managed URN namespace 186 by providing persistent identification of resources and unique 187 assignment of identifier strings. 188 o They can be registered in global registration services. 190 4. URN Namespace Types 192 There are two types of URN namespace: formal and informal. These are 193 distinguished by the expected level of service, the information 194 needed to define the namespace, and the procedures for registration. 195 Because the majority of the namespaces registered so far have been 196 formal, this document concentrates on formal namespaces. 198 Note: [RFC3406] defined a third type of "experimental namespaces", 199 denoted by prefixing the namespace identifier with the string "X-". 200 Consistent with [RFC6648], this specification removes the 201 experimental category. 203 4.1. Formal Namespaces 205 A formal namespace provides benefit to some subset of users on the 206 Internet (i.e., not limited to users in communities or networks not 207 connected to the Internet). For example, it would be inappropriate 208 for a NID to effectively force someone to use a proprietary network 209 or service not open to the general Internet user. The intent is 210 that, while the community of those who might actively use the names 211 assigned within that NID might be small, the potential use of 212 identifiers within that NID is open to any user on the Internet. 213 Formal NIDs might be appropriate when some aspects are not fully 214 open. For example, a namespace might make use of a fee-based, 215 privately managed, or proprietary registry for assignment of URNs in 216 the namespace. However, it might still benefit some Internet users 217 if the associated services have openly-published access protocols. 219 An organization that will assign URNs within a formal namespace ought 220 to meet the following criteria: 222 o Organizational stability and the ability to maintain the URN 223 namespace for a long time; absent such evidence, it ought to be 224 clear how the namespace can remain viable if the organization can 225 no longer maintain the namespace. 226 o Competency in name assignment. This will improve the likelihood 227 of persistence (e.g. to minimize the likelihood of conflicts). 229 o Commitment to not reassigning existing names and to allowing old 230 names to continue to be valid, even if the owners or assignees of 231 those names are no longer members or customers of that 232 organization. With regard to URN resolution [RFC2276], this does 233 not mean that there needs to be resolution of such names, only 234 that the names will not resolve to false or stale information. 236 A formal namespace establishes a particular NID, subject to the 237 following constraints (above and beyond the syntax rules specified in 238 [I-D.ietf-urnbis-rfc2141bis-urn]): 240 o It MUST NOT be an already-registered NID. 241 o It MUST NOT start with "urn-" (which is reserved for informal 242 namespaces). 243 o It MUST be more than two characters long. 244 o It MUST NOT start with "XY-", where "XY" is any combination of two 245 ASCII letters. 247 All two-letter combinations, and all two-letter combinations followed 248 by "-" and any sequence of valid NID characters, are reserved for 249 potential use as countrycode-based NIDs for eventual national 250 registrations of URN namespaces. The definition and scoping of rules 251 for allocation of responsibility for such countrycode-based 252 namespaces is beyond the scope of this document. 254 4.2. Informal Namespaces 256 Informal namespaces are full-fledged URN namespaces, with all the 257 associated rights and responsibilities. Informal namespaces differ 258 from formal namespaces in the process for assigning a NID: IANA will 259 assign an alphanumeric NID (e.g., "urn-7") to informal namespaces, 260 with the following syntax: 262 "urn-" 264 The only restrictions on are that it (1) consist strictly of 265 ASCII digits and (2) not cause the NID to exceed the length 266 limitations defined in the URN syntax specification 267 [I-D.ietf-urnbis-rfc2141bis-urn]. 269 5. Defining a URN Namespace 271 The definition of a formal namespace ought to pay particular 272 attention to: 274 o The purpose of the namespace. 275 o The syntax of URNs assigned within the namespace. 276 o The process for assigning URNs within the namespace. 277 o The security implications of assigning and using the assigned 278 URNs. 279 o Optionally, the process for resolving URNs issued within the 280 namepace. 282 The following sections explain these matters in greater detail. For 283 convenience, a template for defining and registering a URN namespace 284 is provided under Section 6. This information can be especially 285 helpful to entities that wish to request assignment of a URN in a 286 namespace and to entities that wish to provide URN resolution for a 287 namespace. 289 5.1. Purpose 291 The "Purpose" section of the template describes matters such as: 293 o The kinds of resources identified by URNs assigned within the 294 namespace. 296 o Why it is preferable to use URNs rather than some other technology 297 (e.g., URIs) and why existing URN namespace (if any) are not a 298 good fit. 300 o The kinds of software applications that can use or resolve the 301 assigned URNs (e.g., by differentiating among disparate 302 namespaces, identifying resources in a persistent fashion, or 303 meaningfully resolving and accessing services associated with the 304 namespace). 306 o The scope of the namespace (public vs. private, global vs. local 307 to a particular organization, nation, or industry). For example, 308 a namespace claiming to deal in "social security numbers" ought to 309 have a global scope and address all social security number 310 structures, whereas a URN scheme for a particular national system 311 would need to handle only that nation's social security numbers. 313 o How the intended community (and the Internet community at large) 314 will benefit from using or resolving the assigned URNs. 316 5.2. Syntax 318 The "Syntax" section of the template describes: 320 o A description of the structure of URNs within the namespace, in 321 conformance with the fundamental URN syntax 322 [I-D.ietf-urnbis-rfc2141bis-urn]. The structure might be 323 described in terms of a formal definition (e.g., using Augmented 324 BNF for Syntax Specifications (ABNF) as specified in [RFC5234]), 325 an algorithm for generating conformant URNs, a regular expression 326 for parsing the identifier into components, or by explaining that 327 the structure is opaque. 329 o Any special character encoding rules for assigned URNs (e.g., 330 which character ought to always be used for single-quotes). 332 o Rules for determining equivalence between two identifiers in the 333 namespace. Such rules ought to always have the effect of 334 eliminating false negatives that might otherwise result from 335 comparison. If it is appropriate and helpful, reference can be 336 made to the equivalence rules defined in the URI specification 337 [RFC3986]. Examples of equivalence rules include equivalence 338 between uppercase and lowercase characters in the Namespace 339 Specific String, between hyphenated and non-hyphenated groupings 340 in the identifier string, or between single-quotes and double- 341 quotes. (Note that these are not normative statements for any 342 kind of best practice related to handling of equivalences between 343 characters in general; they are statements limited to this 344 specific namespace only.) 346 o Any special considerations necessary for conforming with the URN 347 syntax. This is particularly applicable in the case of legacy 348 naming systems that are used in the context of URNs. For example, 349 if a namespace is used in contexts other than URNs, it might make 350 use of characters that are reserved in the URN syntax. This 351 section ought to note any such characters, and outline necessary 352 mappings to conform to URN syntax. Normally, this will be handled 353 by percent-encoding the character as specified in the URI 354 specification [RFC3986]. 356 5.3. Assignment 358 The "Assignment" section of the template describes matters such as: 360 o Mechanisms or authorities for assigning URNs to resources. It 361 ought to make clear whether assignment is completely open (e.g., 362 following a particular algorithm), completely closed (e.g., for a 363 private organization), or limited in various ways (e.g., delegated 364 to authorities recognized by a particular organization); if 365 limited, it ought to explain how to become an assigner of 366 identifiers or how to request assignemtn of identifers from 367 existing assignment authorities. 369 o Methods for ensuring that URNs within the namespace are unique. 370 For example, identifiers might be assigned sequentially or in 371 accordance with some well-defined process by a single authority, 372 assignment might be partitioned among delegated authorities that 373 are individually responsible for respecting uniqueness rules, or 374 URNs might be minted independently following an algorithm that 375 itself guarantees uniqueness. 377 o Methods for ensuring the longevity and maintainability of the 378 namespace and URNs assigned with the namespace. Although non- 379 reassignment of URNs ensures that a URN will persist in 380 identifying a particular resource even after the "lifetime of the 381 resource" or the assignment authority, some consideration ought to 382 be given to the persistence of the usability of the URN. This is 383 particularly important in the case of URN namespaces providing 384 global resolution. 386 5.4. Security 388 The "Security" section of the template describes any potential 389 security-related issues with regard to assignment, use, and 390 resolution of identifiers within the namespace. Examples of such 391 issues include the consequences of producing false negatives and 392 false positives during comparison for equivalence (see also 393 [RFC6943]), leakage of private information when identifiers are 394 communicated on the public Internet, the potential for directory 395 harvesting, and various issues discussed in the guidelines for 396 security considerations in RFCs [RFC3552]. 398 5.5. Resolution 400 The "Resolution" section specifies the rules for resolution of URNs 401 assigned within the namespace. If such URNs are intended to be 402 resolvable, the namespace needs to be registered in a Resolution 403 Discovery System (RDS, see [RFC2276]) such as DDDS. Resolution then 404 proceeds according to standard URI resolution processes, as well as 405 the mechanisms of the RDS. This section ought to lists the 406 requirements for becoming a recognized resolver of URNs in the 407 relevant namespace (and being so listed in the RDS registry). 408 Answers might include, but are not limited to: 410 o The namespace is not listed with an RDS; therefore this section is 411 not applicable. 412 o Resolution mirroring is completely open, with a mechanism for 413 updating an appropriate RDS. 414 o Resolution is controlled by entities to which assignment has been 415 delegated. 417 6. Registration Template 419 6.1. Namespace ID 421 Requested of IANA (formal) or assigned by IANA (informal). 423 6.2. Version 425 The version of the registration, starting with 1 and incrementing by 426 1 with each new version. 428 6.3. Date 430 The date when the registration is requested of IANA, using the format 431 YYYY-MM-DD. 433 6.4. Registrant 435 The person or organization that has registered the NID, including the 436 following information: 438 o The name and address of the registering organization. 439 o The name and contact information (email, phone number, and/or 440 postal address) of the designated contact person. 442 6.5. Purpose 444 Described under Section 5.1 of this document. 446 6.6. Syntax 448 Described under Section 5.2 of this document. 450 6.7. Assignment 452 Described under Section 5.3 of this document. 454 6.8. Resolution 456 Described under Section 5.5 of this document. 458 6.9. Documentation 460 Any Internet-Draft, RFC, specification, or other published document 461 that defines or explains the namespace. 463 7. Registering a URN Namespace 465 7.1. Formal Namespaces 467 The registration policy for formal namespaces is Expert Review as 468 defined in the "IANA Considerations" document [RFC5226]. The key 469 steps for registration of a formal namespace are: 471 1. Fill out the namespace registration template (see Section 6). 472 This can be done as part of an Internet-Draft or a specification 473 in another series, although that is not necessary. 474 2. Send the completed template to the urn-nid@ietf.org discussion 475 list for technical review. 476 3. If necessary to address comments received, repeat steps 1 and 2. 477 4. If the designated experts approve the request, the IANA will 478 register the requested NID. 480 A formal namespace registration can be revised by updating the 481 registration template, following the same steps outlined above for 482 new registrations. 484 7.2. Informal Namespaces 486 The registration policy for informal namespaces is First Come First 487 Served [RFC5226]. The key steps for registration of an informal 488 namespace are: 490 1. Write a completed namespace definition template (see Section 6). 491 2. Send it to the urn-nid@ietf.org discussion list for feedback. 492 3. Once the review period has expired, send the final template to 493 IANA (via the iana@iana.org email address). 495 An informal namespace registration can be revised by updating the 496 registration template, following the same steps outlined above for 497 new registrations. 499 8. Guidelines for Designated Experts 501 Experience to date with NID registration requests has shown that 502 registrants sometimes do not initially understand some of the 503 subtleties of URN namespaces, and that defining the namespace in the 504 form of a specification enables the registrants to clearly formulate 505 their "contract" with the intended user community. Therefore, 506 although the registration policy for formal namespaces is Expert 507 Review and a specification is not required, the designated experts 508 for NID registration requests are encouraged to prefer that a 509 specification exist documenting the namespace definition. 511 9. IANA Considerations 513 This document outlines the processes for registering URN namespaces, 514 and has implications for the IANA in terms of registries to be 515 maintained. In all cases, the IANA ought to assign the appropriate 516 NID (formal or informal) once the procedures outlined in this 517 document have been completed. 519 10. Security Considerations 521 This document largely focuses on providing mechanisms for the 522 declaration of public information. Nominally, these declarations 523 will be of relatively low security profile, however there is always 524 the danger of "spoofing" and providing misinformation. Information 525 in these declarations ought to be taken as advisory. 527 The definition of a URN namespace needs to account for potential 528 security issues related to assignment, use, and resolution of 529 identifiers within the namespace. 531 11. References 533 11.1. Normative References 535 [I-D.ietf-urnbis-rfc2141bis-urn] 536 Saint-Andre, P., "Uniform Resource Name (URN) Syntax", 537 draft-ietf-urnbis-rfc2141bis-urn-06 (work in progress), 538 August 2013. 540 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 541 Requirement Levels", BCP 14, RFC 2119, March 1997. 543 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 544 Resource Identifier (URI): Generic Syntax", STD 66, 545 RFC 3986, January 2005. 547 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 548 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 549 May 2008. 551 11.2. Informative References 553 [RFC2276] Sollins, K., "Architectural Principles of Uniform Resource 554 Name Resolution", RFC 2276, January 1998. 556 [RFC2611] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom, 557 "URN Namespace Definition Mechanisms", BCP 33, RFC 2611, 558 June 1999. 560 [RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom, 561 "Uniform Resource Names (URN) Namespace Definition 562 Mechanisms", BCP 66, RFC 3406, October 2002. 564 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC 565 Text on Security Considerations", BCP 72, RFC 3552, 566 July 2003. 568 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 569 Specifications: ABNF", STD 68, RFC 5234, January 2008. 571 [RFC6648] Saint-Andre, P., Crocker, D., and M. Nottingham, 572 "Deprecating the "X-" Prefix and Similar Constructs in 573 Application Protocols", BCP 178, RFC 6648, June 2012. 575 [RFC6943] Thaler, D., "Issues in Identifier Comparison for Security 576 Purposes", RFC 6943, May 2013. 578 [RFC6963] Saint-Andre, P., "A Uniform Resource Name (URN) Namespace 579 for Examples", BCP 183, RFC 6963, May 2013. 581 Appendix A. Changes from RFC 3406 583 This document makes the following substantive changes from [RFC3406]: 585 o Relaxes the registration policy for formal namespaces from "IETF 586 Review" to "Expert Review" [RFC5226]. 587 o Removes the category of experimental namespaces, consistent with 588 [RFC6648]. 589 o Simplifies the registration template. 591 In addition, some of the text has been updated to be consistent with 592 the definition of Uniform Resource Identifiers (URIs) [RFC3986] and 593 the processes for registering information with the IANA [RFC5226], as 594 well as more modern guidance with regard to security issues [RFC3552] 595 and identifier comparison [RFC6943]. 597 Appendix B. Contributors 599 RFC 3406, which provided the basis for this document, was authored by 600 Leslie Daigle, Dirk-Willem van Gulik, Renato Iannella, and Patrik 601 Faltstrom. Their work is gratefully acknowledged. 603 Appendix C. Acknowledgements 605 Thanks to Marc Blanchet, Juha Hakala, John Klensin, and Barry Leiba 606 for their input. 608 Author's Address 610 Peter Saint-Andre 611 Cisco Systems, Inc. 612 1899 Wynkoop Street, Suite 600 613 Denver, CO 80202 614 USA 616 Phone: +1-303-308-3282 617 Email: psaintan@cisco.com