Registration Protocols Extensions (regext) G. Brown Internet-Draft A. Newton Intended status: Standards Track ICANN Expires: 27 July 2026 23 January 2026 Efficient RDAP Referrals draft-ietf-regext-rdap-referrals-02 Abstract This document describes an RDAP extension that allows RDAP clients to request to be referred to a related RDAP record for a resource. 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 27 July 2026. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Brown & Newton Expires 27 July 2026 [Page 1] Internet-Draft Efficient RDAP Referrals January 2026 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. RDAP Referral Request . . . . . . . . . . . . . . . . . . . . 3 3. RDAP Referral Response . . . . . . . . . . . . . . . . . . . 3 3.1. Selecting The Appropriate Link . . . . . . . . . . . . . 5 3.2. Caching by Intermediaries . . . . . . . . . . . . . . . . 5 3.3. Client Processing of Referral Responses . . . . . . . . . 5 4. RDAP Conformance . . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Changes from 01 to 02 . . . . . . . . . . . . . . . . . . 6 7.2. Changes from 00 to 01 . . . . . . . . . . . . . . . . . . 6 7.3. Changes from draft-brown-rdap-referrals-02 to draft-ietf-regext-rdap-referrals-00 . . . . . . . . . . . 6 7.4. Changes from 01 to 02 . . . . . . . . . . . . . . . . . . 6 7.5. Changes from 00 to 01 . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction Many Registration Data Access Protocol (RDAP, described in [RFC7480], [RFC7481], [RFC9082], [RFC9083] and others) resources contain links to related RDAP resources. For example, in the domain space, an RDAP record for a domain name received from the registry operator may include a link for the RDAP record for the same object provided by the sponsoring registrar (for example, see [gtld-rdap-profile]), while in the IP address space, an RDAP record for an address allocation may include links to enclosing or sibling prefixes. In both cases, RDAP service users are often equally if not more interested in these related RDAP resources than the resource provided by the TLD registry or RIR. While RDAP supports redirection of RDAP requests using HTTP redirections (which use a 3xx HTTP status and the "Location" header field, see Section 15.4 of [RFC9110]), it is not possible for RDAP servers to know _a priori_ whether a client requesting an RDAP record is doing so because it wants to retrieve a related RDAP record, or its own, so it can only respond by providing the full RDAP response. The client must then parse that response in order to extract the relevant URL from the "links" property of the object. Brown & Newton Expires 27 July 2026 [Page 2] Internet-Draft Efficient RDAP Referrals January 2026 This results in the wasteful expenditure of time, compute resources and bandwidth on the part of both the client and server. This document describes an extension to RDAP that allows clients to request that an RDAP server refer them to the URL of a related resource. 2. RDAP Referral Request To request a referral to a related resource, the client sends an HTTP GET request to the RDAP server with a path of the form: referrals0_ref/ The client replaces with the path component of the RDAP server's base URL (which, as per [RFC9224], has a trailing / character), with the lookup path of the object being sought, and with the desired relationship type. For example, the path of a referral query for the domain example.com sent to an RDAP server whose base path is / would be: /referrals0_ref/related/domain/example.com The referral query for the parent network of 192.0.2.42 would have the following full path: /referrals0_ref/rdap-up/ip/192.0.2.42 Lookup paths for domain names, IP networks, autonomous system numbers, nameservers, and entities are described in [RFC9082]. Lookups defined by RDAP extensions may also use this extension. Referral requests for searches, where more than one object is returned, and help queries, as described by [RFC9083], are not supported. Servers MUST return an HTTP 400 for these requests. 3. RDAP Referral Response If the object specified in the request exists, a single appropriate link exists, and the client is authorised to perform the request, the server response MUST: 1. have an HTTP status code of 301 (Moved Permanently), 302 (Found), 303 (See Other), or 307 (Temporary Redirect); and 2. include an HTTP Location header field, whose value contains the URL of the linked resource. Brown & Newton Expires 27 July 2026 [Page 3] Internet-Draft Efficient RDAP Referrals January 2026 If the server cannot find an appropriate link, the response MUST have an HTTP status of 404. If an RDAP server holds in its datastore more than one relationship type for an object, a scenario that is possible but not common, only one of the URLs, as determined by server policy, can be returned. The following examples use the HTTP/1.1 message exchange syntax as seen in [RFC9110]. An example of a referral request from a domain registry to a domain registrar: Client Request: GET /referrals0_ref/related/domain/example.com HTTP/1.1 Accept: application/rdap+json Server Response: HTTP/1.1 307 Temporary Redirect Location: https://registrar.example/domain/example.com An example of a referral request for a parent IPv4 network: Client Request: GET /referrals0_ref/rdap-up/ip/192.0.2.42 HTTP/1.1 Accept: application/rdap+json Server Response: HTTP/1.1 307 Temporary Redirect Location: https://rir.example/ip/192.0.2.0/24 An example of a referral request for a parent IPv6 network: Client Request: GET /referrals0_ref/rdap-up/ip/2001%3adb8%3a%3a1 HTTP/1.1 Accept: application/rdap+json" Server Response: HTTP/1.1 307 Temporary Redirect Location: https://rir.example/ip/2001%3adb8%3a%3a/32 Brown & Newton Expires 27 July 2026 [Page 4] Internet-Draft Efficient RDAP Referrals January 2026 3.1. Selecting The Appropriate Link When the server receives a referral request, it must select which of an object's links it should use to construct the response. The rel property of the selected link MUST match path segment of the request. The type and hreflang properties of the link, if present, MUST match the Accept and (if specified) Accept- Language header fields of the request. 3.2. Caching by Intermediaries To facilitate caching of RDAP resources by intermediary proxies, servers which provide a referral based on the value of the Accept header field in the request MUST include a Vary header field (See Section 12.5.5 of [RFC9110]) in the response. This field MUST include accept, and MAY include other header field names. Example: Vary: accept, accept-language 3.3. Client Processing of Referral Responses Note that as per Section 10.2.2 of [!@RFC9110], the URI-reference in location header fields MAY be relative. For relative references, RDAP clients MUST compute the full URI using the request URI. 4. RDAP Conformance Servers which implement this specification MUST include the string "referrals0" in the "rdapConformance" array in all RDAP responses. 5. IANA Considerations IANA is requested to register the following value in the RDAP Extensions Registry: *Extension identifier:* referrals0 *Registry operator:* any. *Published specification:* this document. *Contact:* the authors of this document. *Intended usage:* this extension allows clients to request to be referred to a related resource for an RDAP resource. Brown & Newton Expires 27 July 2026 [Page 5] Internet-Draft Efficient RDAP Referrals January 2026 6. Security Considerations A malicious HTTP redirect has the potential to create an infinite loop, which can exhaust resources on both client and server side. To prevent such loops, RDAP servers which receive referral requests for the self relation MUST respond with a 400 HTTP status. As described in Section 15.4 of [!@RFC9110], when processing server responses, RDAP clients SHOULD detect and intervene in cyclical redirections. 7. Change Log This section is to be removed before publishing as an RFC. 7.1. Changes from 01 to 02 * Add reference to [gtld-rdap-profile] which describes how gTLD RDAP servers link to registrar RDAP resoures. * Include in the path specification, and remove the / between and so that naive URL construction works. * Reuse the language from RFC 7480 on HTTP status codes used for redirection. * Fix HTTP status code in the examples. * Described the risk of redirection loops and things clients and servers have to do. 7.2. Changes from 00 to 01 * Switch to using a path segment and a 30x redirect. * Describe how the server behaves when multiple links exist. 7.3. Changes from draft-brown-rdap-referrals-02 to draft-ietf-regext- rdap-referrals-00 * Nothing apart from the name. 7.4. Changes from 01 to 02 * add this change log. Brown & Newton Expires 27 July 2026 [Page 6] Internet-Draft Efficient RDAP Referrals January 2026 7.5. Changes from 00 to 01 * change extension identifer from registrar_link_header to referrals0. 8. References 8.1. Normative References [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, . [RFC7481] Hollenbeck, S. and N. Kong, "Security Services for the Registration Data Access Protocol (RDAP)", STD 95, RFC 7481, DOI 10.17487/RFC7481, 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, . [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, . [RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, . 8.2. Informative References [RFC9224] Blanchet, M., "Finding the Authoritative Registration Data Access Protocol (RDAP) Service", STD 95, RFC 9224, DOI 10.17487/RFC9224, March 2022, . [gtld-rdap-profile] ICANN, "gTLD RDAP Profile", 2024, . Authors' Addresses Brown & Newton Expires 27 July 2026 [Page 7] Internet-Draft Efficient RDAP Referrals January 2026 Gavin Brown ICANN 12025 Waterfront Drive, Suite 300 Los Angeles, CA 90292 United States of America Email: gavin.brown@icann.org URI: https://icann.org Andy Newton ICANN 12025 Waterfront Drive, Suite 300 Los Angeles, CA 90292 United States of America Email: andy.newton@icann.org URI: https://icann.org Brown & Newton Expires 27 July 2026 [Page 8]