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Obsoleted by:8141 BEST CURRENT PRACTICE
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Network Working Group                                          L. DaigleRequest for Comments: 3406                      Thinking Cat EnterprisesBCP: 66                                                   D.W. van GulikObsoletes:2611                                               WebWeavingCategory: Best Current Practice                              R. Iannella                                                             IPR Systems                                                            P. Faltstrom                                                                   Cisco                                                            October 2002Uniform Resource Names (URN) Namespace Definition MechanismsStatus of this Memo   This document specifies an Internet Best Current Practices for the   Internet Community, and requests discussion and suggestions for   improvements.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2002).  All Rights Reserved.Abstract   This document lays out general definitions of and mechanisms for   establishing Uniform Resource Names (URN) "namespaces".  The URN WG   has defined a syntax for URNs inRFC 2141, as well as some proposed   mechanisms for their resolution and use in Internet applications inRFC 3401 andRFC 3405.  The whole rests on the concept of individual   "namespaces" within the URN structure.  Apart from proof-of-concept   namespaces, the use of existing identifiers in URNs has been   discussed inRFC 2288.Table of Contents1.0 Introduction .................................................22.0 What is a URN Namespace? .....................................33.0 URN Namespace (Registration) Types ...........................33.1 Experimental Namespaces .....................................43.2 Informal Namespaces .........................................43.3 Formal Namespaces ...........................................4   4.0 URN Namespace Registration, Update, and NID Assignment       Process .....................................................64.1 Experimental ................................................64.2 Informal ....................................................64.3 Formal ......................................................75.0 Security Considerations .....................................9Daigle, et. al.          Best Current Practice                  [Page 1]

RFC 3406          URN Namespace Definition Mechanisms       October 20026.0 IANA Considerations .........................................97.0 References ..................................................9Appendix A -- URN Namespace Definition Template .................11Appendix B -- Illustration ......................................15B.1 Example Template ............................................15B.2 Registration steps in practice ..............................17Appendix C -- Changes fromRFC 2611 .............................18C.1 Detailed Document Changes ...................................19   Authors' Addresses ..............................................21   Full Copyright Statement ........................................221.0 Introduction   Uniform Resource Names (URNs) are resource identifiers with the   specific requirements for enabling location independent   identification of a resource, as well as longevity of reference.   URNs are part of the larger Uniform Resource Identifier (URI) family   [RFC3305] with the specific goal of providing persistent naming of   resources.   There are 2 assumptions that are key to this document:   Assumption #1:      Assignment of a URN is a managed process.      I.e., not all strings that conform to URN syntax are necessarily      valid URNs.  A URN is assigned according to the rules of a      particular namespace (in terms of syntax, semantics, and process).   Assumption #2:      The space of URN namespaces is managed.      I.e., not all syntactically correct URN namespaces (per the URN      syntax definition) are valid URN namespaces.  A URN namespace must      have a recognized definition in order to be valid.   The purpose of this document is to outline a mechanism and provide a   template for explicit namespace definition, as well as provide the   mechanism for associating an identifier (called a "Namespace ID", or   NID) which is registered with the Internet Assigned Numbers Authority   (IANA).   Note that this document restricts itself to the description of   processes for the creation of URN namespaces.  If "resolution" of any   so-created URN identifiers is desired, a separate process of   registration in a global NID directory, such as that provided by theDaigle, et. al.          Best Current Practice                  [Page 2]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   DDDS system [RFC3401], is necessary.  See [RFC3405] for information   on obtaining registration in the DDDS global NID directory.2.0 What is a URN Namespace?   For the purposes of URNs, a "namespace" is a collection of uniquely-   assigned identifiers.  That is, the identifiers are not ever assigned   to more than 1 resource, nor are they ever re-assigned to a different   resource.  A single resource, however, may have more than one URN   assigned to it for different purposes.  A URN namespace itself has an   identifier in order to:      -  ensure global uniqueness of URNs      -  (where desired) provide a cue for the structure of the         identifier   For example, many identifier systems may use strings of numbers as   identifiers (e.g., ISBN, ISSN, phone numbers).  It is conceivable   that there might be some numbers that are valid identifiers in two   different established identifier systems.  Using different   designators for the two collections ensures that no two URNs will be   the same for different resources (since each collection is required   to uniquely assign each identifier).   The development of an identifier structure, and thereby a collection   of identifiers, is a process that is inherently dependent on the   requirements of the community defining the identifier, how they will   be assigned, and the uses to which they will be put.  All of these   issues are specific to the individual community seeking to define a   namespace (e.g., publishing community, association of booksellers,   protocol developers, etc); they are beyond the scope of the IETF URN   work.   This document outlines the processes by which a collection of   identifiers satisfying certain constraints (uniqueness of assignment,   etc) can become a bona fide URN namespace by obtaining a NID.  In a   nutshell, a template for the definition of the namespace is completed   for deposit with IANA, and a NID is assigned.  The details of the   process and possibilities for NID strings are outlined below.3.0 URN Namespace (Registration) Types   There are three categories of URN namespaces defined here,   distinguished by expected level of service and required procedures   for registration.  Registration processes for each of these namespace   types are given inSection 4.0.Daigle, et. al.          Best Current Practice                  [Page 3]

RFC 3406          URN Namespace Definition Mechanisms       October 20023.1  Experimental Namespaces   These are not explicitly registered with IANA.  They take the form:      X-<NID>   No provision is made for avoiding collision of experimental NIDs;   they are intended for use within internal or limited experimental   contexts.3.2 Informal Namespaces   These are fully fledged URN namespaces, with all the rights and   requirements associated thereto.  Informal namespaces can be   registered in global registration services.  They are required to   uphold the general principles of a well-managed URN namespace --   providing persistent identification of resources, and unique   assignment of identifier strings.  Informal and formal namespaces   (described below) differ in the NID assignment.  IANA will assign an   alphanumeric NID to registered informal namespaces, per the process   outlined inSection 4.0.3.3 Formal Namespaces   A formal namespace may be requested, and IETF review sought, in cases   where the publication of the NID proposal and the underlying   namespace will provide benefit to some subset of users on the   Internet.  That is, a formal NID proposal, if accepted, must be   functional on and with the global Internet, not limited to users in   communities or networks not connected to the Internet.  For example,   a NID that is meant for naming of physics research is requested.  If   that NID request required that the user use a proprietary network or   service that was not at all open to the general Internet user, then   it would make a poor request for a formal NID.  The intent is that,   while the community of those who may actively use the names assigned   within that NID may be small (but no less important), the potential   use of names within that NID is open to any user on the Internet.   It is expected that Formal NIDs may be applied to namespaces where   some aspects are not fully open.  For example, a namespace may make   use of a fee-based, privately managed, or proprietary registry for   assignment of URNs in the namespace, but it may still provide benefit   to some Internet users if the services associated have openly-   published access protocols.Daigle, et. al.          Best Current Practice                  [Page 4]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   In addition to the basic registration information defined in the   registration template (inAppendix A), a formal namespace request   must be accompanied by documented considerations of the need for a   new namespace and of the community benefit from formally establishing   the proposed URN namespace.   Additionally, since the goal of URNs is to provide persistent   identification, some consideration as to the longevity and   maintainability of the namespace must be given.  The URN WG discussed   at length the issue of finding objective measures for predicting (a   priori) the continued success of a namespace.  No conclusion was   reached -- much depends on factors that are completely beyond the   technical scope of the namespace.  However, the collective experience   of the IETF community does contain a wealth of information on   technical factors that will prevent longevity of identification.  The   IESG may elect not to publish a proposed namespace RFC if the IETF   community consensus is that it contains technical flaws that will   prevent (or seriously impair the possibility of) persistent   identification.   The kinds of things the URN WG discussed included:      -  the organization maintaining the URN namespace should         demonstrate stability and the ability to maintain the URN         namespace for a long time, and/or it should be clear how the         namespace can continue to be usable/useful if the organization         ceases to be able to foster it;      - it should demonstrate ability and competency in name assignment.         This should improve the likelihood of persistence (e.g. to         minimize the likelihood of conflicts);      -  it should commit to not re-assigning existing names and         allowing old names to continue to be valid, even if the owners         or assignees of those names are no longer members or customers         of that organization.  This does not mean that there must be         resolution of such names, but that they must not resolve the         name to false or stale information, and that they must not be         reassigned.   These aspects, though hard to quantify objectively, should be   considered by organizations/people considering the development of a   Formal URN namespace, and they will be kept in mind when evaluating   the technical merits of any proposed Formal namespace.Daigle, et. al.          Best Current Practice                  [Page 5]

RFC 3406          URN Namespace Definition Mechanisms       October 20024.0 URN Namespace Registration, Update, and NID Assignment Process   Different levels of disclosure are expected/defined for namespaces.   According to the level of open-forum discussion surrounding the   disclosure, a URN namespace may be assigned or may request a   particular identifier.  The  "IANA Considerations" document [RFC2434]   suggests the need to specify update mechanisms for registrations --   who is given the authority to do so, from time to time, and what are   the processes.  Since URNs are meant to be persistently useful, few   (if any) changes should be made to the structural interpretation of   URN strings (e.g., adding or removing rules for lexical equivalence   that might affect the interpretation of URN IDs already assigned).   However, it may be important to introduce clarifications, expand the   list of authorized URN assigners, etc, over the natural course of a   namespace's lifetime.  Specific processes are outlined below.   The official list of registered URN namespaces is maintained by IANA.   URN namespace registrations are currently being posted in the   anonymous FTP directory:http://www.iana.org/assignments/urn-namespaces   See [RFC3232] for the current location of IANA registry.   The registration and maintenance procedures vary slightly from one   namespace type (as defined inSection 3.0) to another.4.1 Experimental   These are not explicitly registered with IANA.  They take the form:      X-<NID>   No provision is made for avoiding collision of experimental NIDs;   they are intended for use within internal or limited experimental   contexts.   As there is no registration, no registration maintenance procedures   are needed.4.2 Informal   These are registered with IANA and are assigned a number sequence as   an identifier, in the format:      "urn-" <number>Daigle, et. al.          Best Current Practice                  [Page 6]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   where <number> is chosen by the IANA on a First Come First Served   basis (see [RFC2434]).   Registrants should send a copy of the registration template (seeAppendix A), duly completed, to:      urn-nid@apps.ietf.org   and allow for a 2 week discussion period for clarifying the   expression of the registration information and suggestions for   technical improvements to the namespace proposal.   After suggestions for clarification of the registration information   have been incorporated, the template may be submitted for assignment   of a NID to:      iana@iana.org   The only restrictions on <number> are that it consist strictly of   digits and that it not cause the NID to exceed length limitations   outlined in the URN syntax ([RFC2141]).   Registrations may be updated by the original registrant, or an entity   designated by the registrant, by updating the registration template,   submitting it to the discussion list for a further 2 week discussion   period, and finally resubmitting it to IANA, as described above.4.3 Formal   Formal NIDs are assigned via IETF Consensus, as defined in [RFC2434]:      "IETF Consensus - New values are assigned through the IETF      consensus process.  Specifically, new assignments are made via      RFCs approved by the IESG.  Typically, the IESG will seek input on      prospective assignments from appropriate persons (e.g., a relevant      Working Group if one exists)."   Thus, the Formal NID application is made via publication of an RFC   through standard IETF processes.  The RFC need not be standards-   track, but it will be subject to IESG review and acceptance pursuant   to the guidelines written here (as well as standard RFC publication   guidelines).  The template defined inAppendix A may be included as   part of an RFC defining some other aspect of the namespace, or it may   be put forward as an RFC in its own right.  The proposed template   should be sent to the:      urn-nid@apps.ietf.orgDaigle, et. al.          Best Current Practice                  [Page 7]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   mailing list to allow for a two week discussion period for clarifying   the expression of the registration information, before the IESG   reviews the document.   The RFC must include a "Namespace Considerations" section, which   outlines the perceived need for a new namespace (i.e., where existing   namespaces fall short of the proposer's requirements).   Considerations might include:      -  URN assignment procedures      -  URN resolution/delegation      -  type of resources to be identified      -  type of services to be supported   NOTE: It is expected that more than one namespace may serve the same   "functional" purpose; the intent of the "Namespace Considerations"   section is to provide a record of the proposer's "due diligence" in   exploring existing possibilities, for the IESG's consideration.   The RFC must also include a "Community Considerations" section, which   indicates the dimensions upon which the proposer expects its   community to be able to benefit by publication of this namespace as   well as how a general Internet user will be able to use the space if   they care to do so.  Potential considerations include:      -  open assignment and use of identifiers within the namespace      -  open operation of resolution servers for the namespace (server)      -  creation of software that can meaningfully resolve and access         services for the namespace (client)   The RFC must include an "IANA Considerations" section, indicating   that the document includes a URN NID registration that is to be   entered into the IANA registry of URN NIDs.   A particular NID string is requested, and is assigned by IETF   consensus (as defined in [RFC2434]), with the additional constraints   that the NID string must:      -  not be an already-registered NID      -  not start with "x-" (see Type I above)      -  not start with "urn-" (see Type II above)      -  not start with "XY-", where XY is any combination of 2 ASCII         letters  (see NOTE, below)      -  be more than 2 letters longDaigle, et. al.          Best Current Practice                  [Page 8]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   NOTE: ALL two-letter combinations, and two-letter combinations   followed by "-" and any sequence of valid NID characters are reserved   for potential use as countrycode-based NIDs for eventual national   registrations of URN namespaces.  The definition and scoping of rules   for allocation of responsibility for such namespaces is beyond the   scope of this document.   Registrations may be revised by updating the RFC through standard   IETF RFC update processes (see [RFC2606] for a discussion of IETF   process).  In any case, a revised document, in the form of a new   Internet-Draft, must be published, and the proposed updated template   must be circulated on the urn-nid discussion list, allowing for a 2   week review period before pursuing publication of the new RFC   document.5.0 Security Considerations   This document largely focuses on providing mechanisms for the   declaration of public information.  Nominally, these declarations   should be of relatively low security profile, however there is always   the danger of "spoofing" and providing mis-information.  Information   in these declarations should be taken as advisory.6.0 IANA Considerations   This document outlines the processes for registering URN namespaces,   and has implications for the IANA in terms of registries to be   maintained.  In all cases, the IANA should assign the appropriate NID   (informal or formal), as described above, once an IESG-designated   expert has confirmed that the requisite registration process steps   have been completed.  This document defines processes to replace   those outlined in [RFC2611].7.0 References   [ISO8601] ISO 8601 : 1988 (E), "Data elements and interchange formats             - Information interchange - Representation of dates and             times"   [RFC1737] Sollins, K. and L. Masinter, "Functional Requirements for             Uniform Resource Names",RFC 1737, December 1994.   [RFC2026] Bradner, S., "The Internet Standards Process -- Revision             3",BCP 9,RFC 2026, October 1996.   [RFC2141] Moats, R., "URN Syntax",RFC 2141, May 1997.Daigle, et. al.          Best Current Practice                  [Page 9]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   [RFC2276] Sollins, K., "Architectural Principles of Uniform Resource             Name Resolution",RFC 2276, January 1998.   [RFC2288] Lynch, C., Preston, C. and R. Daniel, "Using Existing             Bibliographic Identifiers as Uniform Resource Names",RFC2288, February 1998.   [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an             IANA Considerations Section in RFCs",BCP 26,RFC 2434,             October 1998.   [RFC2611] Daigle, L., van Gulik, D., Iannella, R. and P. Faltstrom,             "URN Namespace Definition Mechanisms",RFC 2611, June 1999.   [RFC3232] Reynolds, J, Editor, "Assigned Numbers:RFC 1700 is             Replaced by an On-line Database",RFC 3232, January 2002.   [RFC3305] Mealling, M. (Ed.) and R. Denenberg (Ed.), "Report from the             Joint W3C/IETF URI Planning Interest Group:  Uniform             Resource Identifiers (URIs), URLs, and Uniform Resource             Names (URNs):  Clarifications and Recommendations",RFC3305, August 2002.   [RFC3401] Mealling, M., "Dynamic Delegation Discovery System (DDDS)             Part One: The Comprehensive DDDS",RFC 3401, October 2002.   [RFC3405] Mealling, M., "Dynamic Delegation Discovery System (DDDS)             Part Five: URI.ARPA Assignment Procedures",RFC 3405,             October 2002.Daigle, et. al.          Best Current Practice                 [Page 10]

RFC 3406          URN Namespace Definition Mechanisms       October 2002Appendix A -- URN Namespace Definition Template   Definition of a URN namespace is accomplished by completing the   following information template.  Apart from providing a mechanism for   disclosing structure of the URN namespace, this information is   designed to be useful for      -  entities seeking to have a URN assigned in a namespace (if         applicable)      -  entities seeking to provide URN resolvers for a namespace (if         applicable)   This is particularly important for communities evaluating the   possibility of using a portion of an existing URN namespace rather   than creating their own.   Applications for Formal URN namespaces must also document "Namespace   Considerations", "Community Considerations" and "IANA   Considerations", as described inSection 4.3.   Information in the template is as follows:   Namespace ID:      Assigned by IANA.  In the case of a Formal NID registration, a      particular NID string may be requested.   Registration Information:      This is information to identify the particular version of      registration information:      -  registration version number: starting with 1, incrementing by 1         with each new version      -  registration date: date submitted to the IANA, using the format         outlined in [ISO8601]:            YYYY-MM-DD   Declared registrant of the namespace:      This includes:         Registering organization            Name            Address         Designated contact person            Name            Coordinates (at least one of: e-mail, phone, postal address)Daigle, et. al.          Best Current Practice                 [Page 11]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   Declaration of syntactic structure:      This section should outline any structural features of identifiers      in this namespace.  At the very least, this description may be      used to introduce terminology used in other sections.  This      structure may also be used for determining realistic      caching/shortcuts approaches; suitable caveats should be provided.      If there are any specific character encoding rules (e.g., which      character should always be used for single-quotes), these should      be listed here.      Answers might include, but are not limited to:      -  the structure is opaque (no exposition)      -  a regular expression for parsing the identifier into         components, including naming authorities   Relevant ancillary documentation:      This section should list any RFCs, standards, or other published      documentation that defines or explains all or part of the      namespace structure.      Answers might include, but are not limited to:      -  RFCs outlining syntax of the namespace      -  Other of the defining community's (e.g., ISO) documents         outlining syntax of the identifiers in the namespace      -  Explanatory material introducing the namespace   Identifier uniqueness considerations:      This section should address the requirement that URN identifiers      be assigned uniquely -- they are assigned to at most one resource,      and are not reassigned.      (Note that the definition of "resource" is fairly broad; for      example, information on "Today's Weather" might be considered a      single resource, although the content is dynamic.)      Possible answers include, but are not limited to:      -  exposition of the structure of the identifiers, and         partitioning of the space of identifiers amongst assignment         authorities which are individually responsible for respecting         uniqueness rules      -  identifiers are assigned sequentially      -  information is withheld; the namespace is opaqueDaigle, et. al.          Best Current Practice                 [Page 12]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   Identifier persistence considerations:      Although non-reassignment of URN identifiers ensures that a URN      will persist in identifying a particular resource even after the      "lifetime of the resource", some consideration should be given to      the persistence of the usability of the URN.  This is particularly      important in the case of URN namespaces providing global      resolution.      Possible answers include, but are not limited to:      -  quality of service considerations   Process of identifier assignment:      This section should detail the mechanisms and/or authorities for      assigning URNs to resources.  It should make clear whether      assignment is completely open, or if limited, how to become an      assigner of identifiers, and/or get one assigned by existing      assignment authorities.      Answers could include, but are not limited to:      -  assignment is completely open, following a particular algorithm      -  assignment is delegated to authorities recognized by a         particular organization (e.g., the Digital Object Identifier         Foundation controls the DOI assignment space and its         delegation)      -  assignment is completely closed (e.g., for a private         organization)   Process for identifier resolution:      If a namespace is intended to be accessible for global resolution,      it must be registered in an RDS (Resolution Discovery System, see      [RFC2276]) such as DDDS.  Resolution then proceeds according to      standard URI resolution processes, and the mechanisms of the RDS.      What this section should outline is the requirements for becoming      a recognized resolver of URNs in this namespace (and being so-      listed in the RDS registry).      Answers may include, but are not limited to:      -  the namespace is not listed with an RDS; this is not relevant      -  resolution mirroring is completely open, with a mechanism for         updating an appropriate RDS      -  resolution is controlled by entities to which assignment has         been delegatedDaigle, et. al.          Best Current Practice                 [Page 13]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   Rules for Lexical Equivalence:      If there are particular algorithms for determining equivalence      between two identifiers in the underlying namespace (hence, in the      URN string itself), rules can be provided here.      Some examples include:      -  equivalence between hyphenated and non-hyphenated groupings in         the identifier string      -  equivalence between single-quotes and double-quotes      -  Namespace-defined equivalences between specific characters,         such as "character X with or without diacritic marks".      Note that these are not normative statements for any kind of best      practice for handling equivalences between characters; they are      statements limited to reflecting the namespace's own rules.   Conformance with URN Syntax:      This section should outline any special considerations required      for conforming with the URN syntax.  This is particularly      applicable in the case of legacy naming systems that are used in      the context of URNs.      For example, if a namespace is used in contexts other than URNs,      it may make use of characters that are reserved in the URN syntax.      This section should flag any such characters, and outline      necessary mappings to conform to URN syntax.  Normally, this will      be handled by hex encoding the symbol.      For example, see the section on SICIs in [RFC2288].   Validation mechanism:      Apart from attempting resolution of a URN, a URN namespace may      provide mechanisms for "validating" a URN -- i.e., determining      whether a given string is currently a validly-assigned URN.  There      are 2 issues here: 1) users should not "guess" URNs in a      namespace; 2) when the URN namespace is based on an existing      identifier system, it may not be the case that all the existing      identifiers are assigned on Day 0.  The reasonable expectation is      that the resource associated with each resulting URN is somehow      related to the thing identified by the original identifier system,      but those resources may not exist for each original identifier.      For example, even if a telephone number-based URN namespace was      created, it is not clear that all telephone numbers wouldDaigle, et. al.          Best Current Practice                 [Page 14]

RFC 3406          URN Namespace Definition Mechanisms       October 2002      immediately become "valid" URNs, that could be resolved using      whatever mechanisms are described as part of the namespace      registration.      Validation mechanisms might be:      -  a syntax grammar      -  an on-line service      -  an off-line service   Scope:      This section should outline the scope of the use of the      identifiers in this namespace.  Apart from considerations of      private vs. public namespaces, this section is critical in      evaluating the applicability of a requested NID.  For example, a      namespace claiming to deal in "social security numbers" should      have a global scope and address all social security number      structures (unlikely).  On the other hand, at a national level, it      is reasonable to propose a URN namespace for "this nation's social      security numbers".Appendix B -- IllustrationB.1 Example Template   The following example is provided for the purposes of illustrating   the URN NID template described inAppendix A.  Although it is based   on a hypothetical "generic Internet namespace" that has been   discussed informally within the URN WG, there are still technical and   infrastructural issues that would have to be resolved before such a   namespace could be properly and completely described.   Namespace ID:      To be assigned   Registration Information:      Version 1      Date: <when submitted>Daigle, et. al.          Best Current Practice                 [Page 15]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   Declared registrant of the namespace:      Name:           Thinking Cat Enterprises      Address:        1 ThinkingCat Way                      Trupville, NewCountry      Contact:           L. Daigle                      E-mail: leslie@thinkingcat.com   Declaration of structure:      The identifier structure is as follows:      URN:<assigned number>:<FQDN>:<assigned string>      where FQDN is a fully-qualified domain name, and the assigned      string is conformant to URN syntax requirements.   Relevant ancillary documentation:      Definition of domain names, found in:      P. Mockapetris, "DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION",RFC 1035, November 1987.   Identifier uniqueness considerations:      Uniqueness is guaranteed as long as the assigned string is never      reassigned for a given FQDN, and that the FQDN is never      reassigned.      N.B.:  operationally, there is nothing that prevents a domain name      from being reassigned;  indeed, it is not an uncommon occurrence.      This is one of the reasons that this example makes a poor URN      namespace in practice, and is therefore not seriously being      proposed as it stands.   Identifier persistence considerations:      Persistence of identifiers is dependent upon suitable delegation      of resolution at the level of "FQDN"s, and persistence of FQDN      assignment.      Same note as above.Daigle, et. al.          Best Current Practice                 [Page 16]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   Process of identifier assignment:      Assignment of these URNs is delegated to individual domain name      holders (for FQDNs).  The holder of the FQDN registration is      required to maintain an entry (or delegate it) in the DDDS.      Within each of these delegated name partitions, the string may be      assigned per local requirements.      e.g., urn:<assigned number>:thinkingcat.com:001203   Process for identifier resolution:      Domain name holders are responsible for operating or delegating      resolution servers for the FQDN in which they have assigned URNs.   Rules for Lexical Equivalence:      FQDNs are case-insensitive.  Thus, the portion of the URN                  urn:<assigned number>:<FQDN>:      is case-insensitive for matches.  The remainder of the identifier      must be considered case-sensitive.   Conformance with URN Syntax:      No special considerations.   Validation mechanism:      None specified.   Scope:      Global.B.2 Registration steps in practice   The key steps for registration of informal or formal namespaces   typically play out as follows:   Informal NID:      1. Complete the registration template.  This may be done as part         of an Internet-Draft.Daigle, et. al.          Best Current Practice                 [Page 17]

RFC 3406          URN Namespace Definition Mechanisms       October 2002      2. Communicate the registration template to urn-nid@apps.ietf.org         for technical review -- as a published I-D, or text e-mail         message containing the template.      3. Update the registration template as necessary from comments,         and repeat steps 2 and 3 as necessary.      4. Once comments have been addressed (and the review period has         expired), send a request to IANA with the revised registration         template.   Formal NID:      1. Write an Internet-Draft describing the namespace and include         the registration template, duly completed.  Be sure to include         "Namespace Considerations", "Community Considerations" and         "IANA Considerations" sections, as described inSection 4.3.      2. Send the Internet-Draft to the I-D editor, and send a copy to         urn-nid@apps.ietf.org for technical review.      3. Update the Internet-Draft as necessary from comments, and         repeat steps 2 and 3 as needed.      4. Send a request to the IESG to publish the I-D as an RFC.  The         IESG may request further changes (published as I-D revisions)         and/or direct discussion to designated working groups, area         experts, etc.      5. If the IESG approves the document for publication as an RFC,         send a request to IANA to register the requested NID.Appendix C -- Changes fromRFC 2611   This revision of [RFC2611] adds more detail describing the process of   registering a URN namespace identifier (in terms of mechanical   steps).   This version of the document also separates the process (mechanics)   from the discussion of the requirements for namespaces, attempting to   make the latter as objective as possible.   Throughout the document, references have been updated to the current   versions of the DDDS and related documentation (which collectively   obsolete [RFC2168] and related drafts).Daigle, et. al.          Best Current Practice                 [Page 18]

RFC 3406          URN Namespace Definition Mechanisms       October 2002C.1 Detailed Document Changes   Added table of contentsSection 2   Clarified the definition of a URN namespace, the uniqueness of   assignment, and that a single resource may have more than one   identifier associated with it.   Clarified the "number example" -- that the same string may appear in   2 different namespaces, and be applied to different resources.   Originally used ISBN/ISSN example, but structurally this is not   possible.Section 3 (new)   This section explicitly defines the 3 categories of namespace --   Experimental, Informal and Formal.  This section provides a   description of the intended use of the different namespace types, as   well as some acceptability guidelines for Formal namespaces (which   require IETF review).Section 4.0   Spelled out the name ofRFC 2434 ("IANA Considerations").   Provided a pointer to the IANA URN namespace registry.   Sections4.1-4.3   New subsection divisions of the existing discussion of individual   namespace types.Section 4.2   Corrected reference to URN Syntax document (RFC 2141, notRFC 2168).Section 4.3   Added clarifying text as to the intended nature of Formal namespaces   and processes for registering them.   Added text to describe the requirement for a "Namespace   Considerations" section in RFCs defining Formal namespaces.  Defined   the required content of that section.Daigle, et. al.          Best Current Practice                 [Page 19]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   Added text to describe the new requirement for a "Community   Considerations" section in RFCs defining Formal namespaces.  Defined   the required content of that section.   Added text to explicitly call out the need for an "IANA   Considerations" section in such RFCs, in order to alert IANA to   required action.   Added text to further clarify the (IETF) process for revising Formal   namespace registrations through the RFC and IETF review process.Section 6   New section -- added text to describe the IANA considerations for   this document.Section 7 -- References   Added references to revised NAPTR documentation ([RFC3401]), and the   previous version of this document ([RFC2611]).Appendix A   Section created by moving the "URN Namespace Definition Template"   (RFC2611'sSection 3) to an appendix.   Added references to the new requirements for "Namespace   Considerations", "Community Considerations", and "IANA   Considerations" sections for Formal namespace registrations.   Clarified the "Declared registrant of the namespace" template   element.   Added text to describe the purpose and scope of the "Validating   Mechanism".Appendix B   Section B.1 is the "example template" that was "Section 5" inRFC2611.   Update the sample "declared registrant" data per the changes to the   template description.   Removed the reference to "US-ASCII" in the "namespace specific   string" of the example namespace.Daigle, et. al.          Best Current Practice                 [Page 20]

RFC 3406          URN Namespace Definition Mechanisms       October 2002   Section B.2 (new)   This added section is a step-by-step walkthrough of the process for   registering Informal namespaces and Formal namespaces.Authors' Addresses   Leslie L. Daigle   Thinking Cat Enterprises   EMail: leslie@thinkingcat.com   Dirk-Willem van Gulik   WebWeaving Internet Engineering   Nieuwsteeg 37A   2311 RZ Leiden   The Netherlands   URL:http://www.webweaving.org/   Email:  dirkx@webweaving.org   Renato Iannella   IPR Systems Pty Ltd.   EMail: renato@iprsystems.com   Patrik Faltstrom   Cisco Systems Inc   170 W Tasman Drive SJ-13/2   San Jose CA 95134   USA   EMail: paf@cisco.comDaigle, et. al.          Best Current Practice                 [Page 21]

RFC 3406          URN Namespace Definition Mechanisms       October 2002Full Copyright Statement   Copyright (C) The Internet Society (2002).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Daigle, et. al.          Best Current Practice                 [Page 22]

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