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RDAP Extensions

Document Type Active Internet-Draft (regext WG)
Authors Andy Newton , Jasdip Singh , Tom Harrison
Last updated 2024-03-04 (Latest revision 2024-02-27)
Replaces draft-newton-regext-rdap-extensions
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Registration Protocols Extensions (regext)                     A. Newton
Internet-Draft                                                     ICANN
Updates: 7480, 9082, 9083 (if approved)                         J. Singh
Intended status: Standards Track                                    ARIN
Expires: 30 August 2024                                      T. Harrison
                                                        27 February 2024

                            RDAP Extensions


   This document describes and clarifies the usage of extensions in

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 30 August 2024.

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   Copyright (c) 2024 IETF Trust and the persons identified as the
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The RDAP Extension Identifier . . . . . . . . . . . . . . . .   2
   3.  Usage in Queries  . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Usage in JSON . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Child JSON Values . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Bare Extension Identifiers  . . . . . . . . . . . . . . .   6
   5.  Camel Casing  . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Two Classes of Extensions . . . . . . . . . . . . . . . . . .   7
   7.  Profile and Marker Extensions . . . . . . . . . . . . . . . .   7
   8.  Extension Versioning  . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Backwards-Compatible Changes  . . . . . . . . . . . . . .   8
     8.2.  Backwards-Incompatible Changes  . . . . . . . . . . . . .   8
   9.  Extension Identifiers in a Response . . . . . . . . . . . . .   9
   10. Extension Definitions . . . . . . . . . . . . . . . . . . . .   9
   11. Existing Extension Registrations  . . . . . . . . . . . . . .  10
   12. Redirects . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   13. Referrals . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     15.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Background

   The Registration Data Access Protocol (RDAP) defines a uniform means
   to access data from Internet operations registries, specifically
   Domain Name Registries (DNRs) and Internet Number Registries (INRs).
   The queries for DNRs and INRs are defined in [RFC9082] and the
   responses for DNRs and INRs are defined in [RFC9083].

   RDAP contains a means to define extensions for queries not found in
   [RFC9082] and responses not found in [RFC9083].  RDAP extensions are
   also described in [RFC7480].  This document uniformly describes RDAP
   extensions, clarifies their usage, and defines additional semantics
   that were previously undefined.

2.  The RDAP Extension Identifier

   Section 6 of [RFC7480] describes the identifier used to signify RDAP
   extensions and the IANA registry into which RDAP extensions are to be

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   In brief, RDAP extensions identifiers start with an alphabetic
   character and may contain alphanumeric characters and "_"
   (underscore) characters.  This formulation was explicitly chosen to
   allow compatibility with variable names in programming languages and
   transliteration with XML.

   When in use in RDAP, extension identifiers are prepended to URL path
   segments, URL query parameters, and JSON object member names (herein
   further referred to as "JSON names").  In all cases, the extension
   identifier acts as a namespace preventing collisions between
   extension elements.

   Additionally, implementers and operators can use the extension
   identifiers to find an extensions definition (via the IANA registry).

   RDAP extension identifiers have no explicit structure and are opaque
   in that no inner-meaning can be "seen" in them.  This document
   restricts the syntax of RDAP extension identifiers from containing
   two consecutive "_" (underscore) characters and reserves their use
   for the future definition of structure (such as to define a
   versioning scheme).  That is, RDAP extensions MUST NOT define an
   identifier with two consecutive underscore characters ("__") unless
   explicitly adhering to an RFC describing such usage.

   RDAP extensions MUST NOT define an extension identifier that when
   prepended to an underscore character may collide with an existing
   extension identifier.  For example, if there were a pre-existing
   identifier of "foo_bar", another extension could not define the
   identifier "foo".  Likewise, if there were a pre-existing identifier
   of "foo_bar", another extension could not define the identifier
   "foo_bar_buzz".  However, an extension could define "foo" if "foobar"
   pre-existed and vice versa.

   For this reason, usage of an underscore character in RDAP extension
   identifiers is NOT RECOMMENDED.  Implementers should be aware that
   many existing extension identifiers do contain underscore characters.

3.  Usage in Queries

   Section 5 of [RFC9082] describes the use of extension identifiers in
   formulating URIs to query RDAP servers.  The extension identifiers
   are to be prepended to the path segments they use.  For example, if
   an extension uses the identifier foobar, then the path segments used
   in that extension are prepended with foobar_. If the foobar extension
   defines paths fizz and fazz, the URIs for this extension might take
   the following form:

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   Although [RFC9082] describes the use of URI query strings, it does
   not define their use with extensions.  [RFC7480] instructs servers to
   ignore unknown query parameters.  Therefore, the use of query
   parameters, prefixed or not with an extension identifier, is
   undefined as defined in [RFC9082] and [RFC7480].

   Despite this, there are several extensions that do specify query
   parameters.  This document updates [RFC9082] with regard to the use
   of RDAP extension identifiers in URL query parameters.

   When an RDAP extension defines query parameters to be used with a URL
   path that is not defined by that RDAP extension, those query
   parameter names SHOULD be constructed in the same manner as URL path
   segments (that is, extensions ID + '_' + parameter name).  See
   section Section 6 regarding when usage of an extension identifier is

   When an RDAP extension defines query parameters to be used with a URL
   path defined by that RDAP extension, prefixing of query parameters is
   not required.

   See Section 12 and Section 13 for other guidance on the use of query

4.  Usage in JSON

   Section 2 of [RFC9083] describes the use of extension identifiers in
   the JSON returned by RDAP servers.  Just as in URIs, the extension
   identifier is prepended to JSON names to create a namespace so that
   the JSON name from one extension will not collide with the JSON name
   of another extension.  And just as with URIs, clients are to ignore
   unknown JSON names.

   The example given in [RFC9083] is as follows:

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     "handle" : "ABC123",
     "lunarNIC_beforeOneSmallStep" : "TRUE THAT!",
     "remarks" :
         "description" :
           "She sells sea shells down by the sea shore.",
           "Originally written by Terry Sullivan."
     "lunarNIC_harshMistressNotes" :
       "In space,",
       "nobody can hear you scream."

   In this example, the extension identified by lunarNIC is prepended to
   the names of both a JSON string and a JSON array.

4.1.  Child JSON Values

   Prefixing of the extension identifier is not required of children of
   a prefixed JSON object defined by an RDAP extension.

   The following example shows this use with a JSON object.

     "handle" : "ABC123",
     "remarks" :
         "description" :
           "She sells sea shells down by the sea shore.",
           "Originally written by Terry Sullivan."
     "lunarNIC_author" :
       "firstInitial": "J",
       "lastName": "Heinlein"

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   Here the JSON name "lunarNic_author" will separate the JSON from
   other extensions that may have an "author" structure.  But the JSON
   contained within "lunarNIC_author" need not be prepended as the
   extension collision is avoided by "lunarNIC_author".

4.2.  Bare Extension Identifiers

   Some RDAP extensions define only one JSON value and do not prefix it
   with their RDAP extension identifier instead using the extension
   identifier as the JSON name for that JSON value.  That is, the
   extension identifier is used "bare" and not appended with an
   underscore character and subsequent names.

   Consider the example in Section 4.1.  Using the bare extension
   identifier pattern, that example could be written as:

     "handle" : "ABC123",
     "remarks" :
         "description" :
           "She sells sea shells down by the sea shore.",
           "Originally written by Terry Sullivan."
     "lunarNIC" :
       "firstInitial": "J",
       "lastName": "Heinlein"

   Usage of a bare extension identifier contravenes the guidance in
   [RFC9083].  This document updates [RFC9083] to explicitly allow this

5.  Camel Casing

   The styling convention used in [RFC9083] for JSON names is often
   called "camel casing", in reference to the hump of a camel.  In this
   style, the first letter of every word, except the first word,
   composing a name is capitalized.  This convention was adopted to
   visually separate the namespace from the name, with an underscore
   between them.

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   Though there is no explicit guidance to use camel case names,
   extensions would be wise to continue the style.

6.  Two Classes of Extensions

   Though all RDAP extensions are to be registered in the IANA RDAP
   extensions registry, there is an implicit two-class system of
   extensions that comes from the inherit ownership of the RDAP
   specifications by the IETF: extensions created by the IETF and
   extensions not created by the IETF.

   In the perspective of how extensions identifiers are used as
   namespace separators, extensions created by the IETF are not required
   to be prefixed with an extension identifier as the IETF can
   coordinate its own activities to avoid name collisions.  In practice,
   most extensions owned by the IETF do use extension identifiers.

   RDAP extensions not defined by the IETF MUST use the extension
   identifier as a prefix in accordance with this document, [RFC7480],
   [RFC9082], and [RFC9083].  And RDAP extensions defined by the IETF
   SHOULD use the extension identifier as a prefix or as a bare
   extension identifier (see Section 4.2) IETF defined RDAP extensions
   that do not follow this guidance MUST describe the necessity to do

7.  Profile and Marker Extensions

   Extensions are not required to extend the JSON or URL components of

   While the RDAP extension mechanism was created to extend RDAP queries
   and/or responses, extensions can also be used to signal server policy
   (for example, specifying the conditions of use for existing response
   structures).  Extensions that are primarily about signalling server
   policy are often called "profiles".

   Some extensions exist to denote the usage of values placed into an
   IANA registry, such as the IANA RDAP registries, or the usage of
   extensions to technologies used by RDAP such as extended vCard/jCard
   properties.  Such extensions exist to "mark" these usages and are
   often called "marker" extensions.

   Regardless of the category of these extensions, their usage may also
   leverage the appearance of their identifiers in the rdapConformance
   array.  Clients may use the /help query as defined in [RFC9082] to
   discover the extensions available.

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8.  Extension Versioning

   As stated in Section 2, RDAP extensions are opaque and they posses no
   explicit version despite the fact that some extension identifiers
   include trailing numbers.  That is, RDAP extensions without an
   explicitly defined versioning scheme are opaquely versioned.

   For example, fizzbuzz_1 may be the successor to fizzbuzz_0, but it
   may also be an extension for a completely separate purpose.  Only
   consultation of the definition of fizzbuzz_1 will determine its
   relationship with fizzbuzz_0.  Additionally, fizzbuzz_99 may be the
   predecessor of fizzbuzz_0.

   If a future RFC defines a versioning scheme (such as using the
   mechanims defined in section Section 2), an RDAP extension definition
   MUST explicitly denote this compliance.

8.1.  Backwards-Compatible Changes

   If an RDAP extension author wants to publish a new version of an
   extension that is backwards-compatible with the previous version,
   then one option is for the new version of the extension to define a
   new identifier, as well as requiring that both the previous
   identifier and the new identifier be included in the
   "rdapConformance" array of responses.  That way, clients relying on
   the previous version of the extension will continue to function as
   intended, while clients wanting to make use of the newer version of
   the extension can check for the new identifier in the response.

   This approach can be used for an arbitrary number of new backwards-
   compatible versions of a given extension.  For an extension with a
   large number of backwards-compatible successor versions, this may
   lead to a large number of identifiers being included in responses.
   An extension author may consider excluding older identifiers from the
   set required by new successor versions, based on data about client
   use/support or similar.

8.2.  Backwards-Incompatible Changes

   With the current extension model, an extension with a backwards-
   incompatible change is indistinguishable from a new, unrelated
   extension.  Implementors of such changes should consider the

   *  whether the new version of the extension can be provided alongside
      the old version of the extension, so that a service can simply
      support both during a transition period;

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   *  whether some sort of client signalling should be supported, so
      that clients can opt for the old or new version of the extension
      in responses that they receive (see
      [I-D.newton-regext-rdap-x-media-type] for an example of how this
      might work); and
   *  whether the extension itself should define how versioning is
      handled within the extension documentation.

9.  Extension Identifiers in a Response

   Extension specifications have customarily defined only one extension
   identifier.  However, there is no explicit limit on the number of
   extension identifiers that may be defined in a single extension
   specification.  One example is [I-D.ietf-regext-rdap-rir-search].

   Section 4.1 offers the following guidance on using the extension
   identifiers in RDAP responses:

A response to a "help" request will include identifiers for all of the specifications
supported by the server. A response to any other request will include only identifiers
for the specifications used in the construction of the response.

   A strict interpretation of this wording where "construction of the
   response" only refers to the JSON syntax would rule out the usage of
   Section 7 extension IDs which are in common use in RDAP.  This
   document updates the guidance.  For responses to queries other than
   "help", a response MUST include in the rdapConformance array only
   those extension identifiers necessary for a client to deserialize the
   JSON and understand the semantic meaning of the content within the
   JSON, and all extensions identifiers MUST be free from conflict in
   both their syntactic and semantic meaning.

   Note that this document does not update the guidance from Section 4.1
   regarding "help" responses and the rdapConformance array.

   When a server implementation supports multiple extensions, it is
   RECOMMENDED that the server also support and return versioning
   information as defined by [I-D.gould-regext-rdap-versioning].

10.  Extension Definitions

   Extensions must be documented in an RFC or in some other permanent
   and readily available reference, in sufficient detail that
   interoperability between independent implementations is possible.

   Though RDAP gives each extension its own namespace, the definition of
   an extension may re-use definitions found in the base RDAP
   specification or in any other properly registered extension.

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   [RFC9083] notes that the extension identifiers provide a "hint" to
   the client as to how to interpret the response.  This wording does
   not intentionally restrict the extension to defining only JSON values
   within the extensions namespace.  Therefore, an extension may define
   the use of its own JSON values together with the use of JSON values
   from other extensions or RDAP specifications.  As with the ICANN
   profile or NRO profile extensions, the extension may simply signal
   policy applied to already defined RDAP structures.

11.  Existing Extension Registrations

   The following extensions have been registered with IANA, but do not
   comply with the requirements set out in the base specifications, as
   clarified by this document:

   *  Extension identifier: fred

      -  RDAP conformance value: fred_version_0
      -  Field/path prefix: fred

   *  Extension identifier: artRecord

      -  RDAP conformance value: artRecord_level_0
      -  Field/path prefix: artRecord

   *  Extension identifier: platformNS

      -  RDAP conformance value: platformNS_level_0
      -  Field/path prefix: platformNS

   *  Extension identifier: regType

      -  RDAP conformance value: regType_level_0
      -  Field/path prefix: regType

   Client authors should be aware that responses that make use of these
   extensions may require special handling on the part of the client.
   Also, while these extensions will be retained in the registry, future
   extensions that are similarly noncompliant will not be registered.

   To avoid any confusion with the operation of the existing entries, an
   extension registration that attempts to use one of the RDAP
   conformance values given in this section as an extension identifier
   (and so as an RDAP conformance value also) will be rejected.

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12.  Redirects

   [RFC7480] describes the use of redirects in RDAP.  Redirects are
   prominent in the discovery of authoritative INR servers as the
   process outlined in [RFC9224], which uses IANA allocations, does not
   account for transfers of resources between INRs.  Section 4.3
   instructs servers to ignore unknown query parameters.  As it relates
   to issuing URLs for redirects, servers MUST NOT blindly copy query
   parameters from a request to a redirect URL as query parameters may
   contain sensitive information, such as security credentials, not
   relevant to the target server of the URL.  Following the advice in
   [RFC7480], servers SHOULD only place query parameters in redirect
   URLs when it is known by the origin server (the server issuing the
   redirect) that the target server (the server referenced by the
   redirect) can process the query parameter and the contents of the
   query parameter are appropriate to be received by the target.

   As it is unlikely that every server in a cross-authority, redirect
   scenario will be upgraded to process every new extension, extensions
   should not solely rely on query parameters to convey information
   about a resource as query parameters are not guaranteed to survive a

   This does not mean extensions are prohibited from using query
   parameters, but rather that the use of query parameters must be
   applied for the scenarios appropriate for the use of the extension.
   Therefore, extensions SHOULD NOT rely on query parameters when the
   extension is to be used in scenarios requiring clients to find
   authoritative servers, such as that described above, or other
   scenarios using redirects among servers of differing authorities.

   Extensions MAY use query parameters in scenarios where the client has
   an a priori knowledge of the authoritative server to which queries
   are to be sent.  Such scenarios are generally queries intended to
   yield multiple results, authentication or authorization, and other
   scenarios where the behavior of requests across multiple authorities
   is undefined.

   In general, extension authors should be mindful of situations
   requiring clients to directly handle redirects at the RDAP layer.
   Some clients may not be utilizing HTTP libraries that provide such an
   option, and many HTTP client libraries that do provide the option do
   not provide it as a default behavior.  Additionally, requiring
   clients to handle redirects at the RDAP layer adds complexity to the
   client in that additional logic must be implemented to handle
   redirect loops, parameter deconfliction, and URL encoding.  The
   guidance given in Section 5.2 exists to simplify clients, especially
   those constructed with shell scripts and HTTP command-line utilities.

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13.  Referrals

   It is common in the RDAP ecosystem to link from one RDAP resource to
   another, such as can be found in domain registrations in gTLD DNRs.
   These are typically conveyed in the link structure defined in
   Section 4.2 of [RFC9083] and use the "application/rdap+json" media

     "value" : "https://regy.example/domain/foo.example",
     "rel" : "related",
     "href" : "https://regr.example/domain/foo.example",
     "type" : "application/rdap+json"

   Extensions MUST explicitly define any required behavioral changes to
   the processing of referrals, otherwise clients MUST assume the
   information provided by referrals requires no additional processing
   or modification to use in the dereferencing of the referral.

14.  Acknowledgements

   The following individuals have provided feedback and contributions to
   the content and direction of this document: James Gould, Daniel
   Keathley, and Ties de Kock.

15.  References

15.1.  Normative References

              Gould, J., Keathley, D., and M. Loffredo, "Versioning in
              the Registration Data Access Protocol (RDAP)", Work in
              Progress, Internet-Draft, draft-gould-regext-rdap-
              versioning-02, 8 December 2023,

              Newton, A. and J. Singh, "An RDAP With Extensions Media
              Type", Work in Progress, Internet-Draft, draft-newton-
              regext-rdap-x-media-type-01, 29 August 2023,

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   [RFC7480]  Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
              Registration Data Access Protocol (RDAP)", STD 95,
              RFC 7480, DOI 10.17487/RFC7480, March 2015,

   [RFC9082]  Hollenbeck, S. and A. Newton, "Registration Data Access
              Protocol (RDAP) Query Format", STD 95, RFC 9082,
              DOI 10.17487/RFC9082, June 2021,

15.2.  Informative References

              Harrison, T. and J. Singh, "RDAP RIR Search", Work in
              Progress, Internet-Draft, draft-ietf-regext-rdap-rir-
              search-07, 30 January 2024,

   [RFC9083]  Hollenbeck, S. and A. Newton, "JSON Responses for the
              Registration Data Access Protocol (RDAP)", STD 95,
              RFC 9083, DOI 10.17487/RFC9083, June 2021,

   [RFC9224]  Blanchet, M., "Finding the Authoritative Registration Data
              Access Protocol (RDAP) Service", STD 95, RFC 9224,
              DOI 10.17487/RFC9224, March 2022,

Authors' Addresses

   Andy Newton

   Jasdip Singh

   Tom Harrison

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