Internet Engineering Task Force (IETF)
Request for Comments: 7480
Category: Standards Track
ISSN: 2070-1721
A. Newton
B. Ellacott
N. Kong
March 2015

HTTP Usage in the Registration Data Access Protocol (RDAP)


This document is one of a collection that together describes the Registration Data Access Protocol (RDAP). It describes how RDAP is transported using the Hypertext Transfer Protocol (HTTP). RDAP is a successor protocol to the very old WHOIS protocol. The purpose of this document is to clarify the use of standard HTTP mechanisms for this application.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at

Copyright Notice

Copyright © 2015 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 ( 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Design Intents  . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Queries . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  HTTP Methods  . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Accept Header . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Query Parameters  . . . . . . . . . . . . . . . . . . . .   6
   5.  Types of HTTP Response  . . . . . . . . . . . . . . . . . . .   6
     5.1.  Positive Answers  . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Redirects . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.3.  Negative Answers  . . . . . . . . . . . . . . . . . . . .   7
     5.4.  Malformed Queries . . . . . . . . . . . . . . . . . . . .   7
     5.5.  Rate Limits . . . . . . . . . . . . . . . . . . . . . . .   7
     5.6.  Cross-Origin Resource Sharing (CORS)  . . . . . . . . . .   8
   6.  Extensibility . . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  RDAP Extensions Registry  . . . . . . . . . . . . . . . .   9
   9.  Internationalization Considerations . . . . . . . . . . . . .  10
     9.1.  URIs and IRIs . . . . . . . . . . . . . . . . . . . . . .  10
     9.2.  Language Identifiers in Queries and Responses . . . . . .  10
     9.3.  Language Identifiers in HTTP Headers  . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Protocol Example . . . . . . . . . . . . . . . . . .  13
   Appendix B.  Cache Busting  . . . . . . . . . . . . . . . . . . .  13
   Appendix C.  Bootstrapping and Redirection  . . . . . . . . . . .  14
   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1. Introduction

This document describes the usage of the Hypertext Transfer Protocol (HTTP) [RFC7230] for the Registration Data Access Protocol (RDAP). The goal of this document is to tie together usage patterns of HTTP into a common profile applicable to the various types of directory services serving registration data using practices informed by the Representational State Transfer (REST) [REST] architectural style. By giving the various directory services common behavior, a single client is better able to retrieve data from directory services adhering to this behavior.

Registration data expected to be presented by this service is Internet resource registration data -- registration of domain names and Internet number resources. This data is typically provided by WHOIS [RFC3912] services, but the WHOIS protocol is insufficient to modern registration data service requirements. A replacement protocol is expected to retain the simple transactional nature of WHOIS, while providing a specification for queries and responses, redirection to authoritative sources, support for Internationalized Domain Names (IDNs) [RFC5890], and support for localized registration data such as addresses and organization or person names.

In designing these common usage patterns, this document introduces considerations for a simple use of HTTP. Where complexity may reside, it is the goal of this document to place it upon the server and to keep the client as simple as possible. A client implementation should be possible using common operating system scripting tools (e.g., bash and wget).

This is the basic usage pattern for this protocol:

  1. A client determines an appropriate server to query along with the appropriate base Uniform Resource Locator (URL) to use in such queries. [RFC7484] describes one method to determine the server and the base URL. See Appendix C for more information.
  1. A client issues an HTTP (or HTTPS) query using GET [RFC7231]. As an example, a query URL for the network registration might be

[RFC7482] details the various queries used in RDAP.

  1. If the receiving server has the information for the query, it examines the Accept header field of the query and returns a 200 response with a response entity appropriate for the requested format. [RFC7483] details a response in JavaScript Object Notation (JSON).
  1. If the receiving server does not have the information for the query but does have knowledge of where the information can be found, it will return a redirection response (3xx) with the Location header field containing an HTTP(S) URL pointing to the information or another server known to have knowledge of the location of the information. The client is expected to requery using that HTTP URL.
  1. If the receiving server does not have the information being requested and does not have knowledge of where the information can be found, it returns a 404 response.
  1. If the receiving server will not answer a request for policy reasons, it will return an error response (4xx) indicating the reason for giving no answer.

It is not the intent of this document to redefine the meaning and semantics of HTTP. The purpose of this document is to clarify the use of standard HTTP mechanisms for this application.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

As is noted in "Security and Stability Advisory Committee (SSAC) Report on WHOIS Terminology and Structure" [SAC-051], the term "WHOIS" is overloaded, often referring to a protocol, a service, and data. In accordance with [SAC-051], this document describes the base behavior for an RDAP. [SAC-051] describes a protocol profile of RDAP for Domain Name Registries (DNRs), the Domain Name Registration Data Access Protocol (DNRD-AP).

In this document, an RDAP client is an HTTP user agent performing an RDAP query, and an RDAP server is an HTTP server providing an RDAP response. RDAP query and response formats are described in [RFC7482] and [RFC7483], while this document describes how RDAP clients and servers use HTTP to exchange queries and responses. [RFC7481] describes security considerations for RDAP.

3. Design Intents

There are a few design criteria this document attempts to meet.

First, each query is meant to require only one path of execution to obtain an answer. A response may contain an answer, no answer, or a redirect, and clients are not expected to fork multiple paths of execution to make a query.

Second, the semantics of the request/response allow for future and/or non-standard response formats. In this document, only a JSON [RFC7159] response media type is noted, with the response contents to be described separately (see [RFC7483]). This document only describes how RDAP is transported using HTTP with this format.

Third, this protocol is intended to be able to make use of the range of mechanisms available for use with HTTP. HTTP offers a number of mechanisms not described further in this document. Operators are able to make use of these mechanisms according to their local policy, including cache control, authorization, compression, and redirection. HTTP also benefits from widespread investment in scalability, reliability, and performance, as well as widespread programmer understanding of client behaviors for web services styled after REST [REST], reducing the cost to deploy Registration Data Directory Services and clients. This protocol is forward compatible with HTTP 2.0.

4. Queries

4.1. HTTP Methods

Clients use the GET method to retrieve a response body and use the HEAD method to determine existence of data on the server. Clients SHOULD use either the HTTP GET or HEAD methods (see [RFC7231]). Servers are under no obligation to support other HTTP methods; therefore, clients using other methods will likely not interoperate properly.

Clients and servers MUST support HTTPS to support security services.

4.2. Accept Header

To indicate to servers that an RDAP response is desired, clients include an Accept header field with an RDAP-specific JSON media type, the generic JSON media type, or both. Servers receiving an RDAP request return an entity with a Content-Type header containing the RDAP-specific JSON media type.

This specification does not define the responses a server returns to a request with any other media types in the Accept header field, or with no Accept header field. One possibility would be to return a response in a media type suitable for rendering in a web browser.

4.3. Query Parameters

Servers MUST ignore unknown query parameters. Use of unknown query parameters for cache busting is described in Appendix B.

5. Types of HTTP Response

This section describes the various types of responses a server may send to a client. While no standard HTTP response code is forbidden in usage, this section defines the minimal set of response codes in common use by servers that a client will need to understand. While some clients may be constructed with simple tooling that does not account for all of these response codes, a more robust client accounting for these codes will likely provide a better user experience. It is expected that usage of response codes and types for this application not defined here will be described in subsequent documents.

5.1. Positive Answers

If a server has the information requested by the client and wishes to respond to the client with the information according to its policies, it returns that answer in the body of a 200 (OK) response (see [RFC7231]).

5.2. Redirects

If a server wishes to inform a client that the answer to a given query can be found elsewhere, it returns either a 301 (Moved Permanently) response code to indicate a permanent move or a 302 (Found), 303 (See Other), or 307 (Temporary Redirect) response code to indicate a non-permanent redirection, and it includes an HTTP(S) URL in the Location header field (see [RFC7231]). The client is expected to issue a subsequent request to satisfy the original query using the given URL without any processing of the URL. In other words, the server is to hand back a complete URL, and the client should not have to transform the URL to follow it. Servers are under no obligation to return a URL conformant to [RFC7482].

For this application, such an example of a permanent move might be a Top-Level Domain (TLD) operator informing a client the information being sought can be found with another TLD operator (i.e., a query for the domain bar in foo.example is found at http://foo.example/domain/bar).

For example, if the client uses

the server redirecting to

would set the Location: field to the value

5.3. Negative Answers

If a server wishes to respond that it has an empty result set (that is, no data appropriately satisfying the query), it returns a 404 (Not Found) response code. Optionally, it MAY include additional information regarding the negative answer in the HTTP entity body.

If a server wishes to inform the client that information about the query is available, but cannot include the information in the response to the client for policy reasons, the server MUST respond with an appropriate response code out of HTTP's 4xx range. A client MAY retry the query if that is appropriate for the respective response code.

5.4. Malformed Queries

If a server receives a query that it cannot interpret as an RDAP query, it returns a 400 (Bad Request) response code. Optionally, it MAY include additional information regarding this negative answer in the HTTP entity body.

5.5. Rate Limits

Some servers apply rate limits to deter address scraping and other abuses. When a server declines to answer a query due to rate limits, it returns a 429 (Too Many Requests) response code as described in [RFC6585]. A client that receives a 429 response SHOULD decrease its query rate and honor the Retry-After header field if one is present. Servers may place stricter limits upon clients that do not honor the Retry-After header. Optionally, the server MAY include additional information regarding the rate limiting in the HTTP entity body.

Note that this is not a defense against denial-of-service (DoS) attacks, since a malicious client could ignore the code and continue to send queries at a high rate. A server might use another response code if it did not wish to reveal to a client that rate limiting is the reason for the denial of a reply.

5.6. Cross-Origin Resource Sharing (CORS)

When responding to queries, it is RECOMMENDED that servers use the Access-Control-Allow-Origin header field, as specified by [W3C.REC-cors-20140116]. A value of "*" is suitable when RDAP is used for public resources.

This header (often called the CORS header) helps in-browser web applications by lifting the "same-origin" restriction (i.e., a browser may load RDAP client code from one web server but query others for RDAP data).

By default, browsers do not send cookies when cross origin requests are allowed. Setting the Access-Control-Allow-Credentials header field to "true" will send cookies. Use of the Access-Control-Allow-Credentials header field is NOT RECOMMENDED.

6. Extensibility

For extensibility purposes, this document defines an IANA registry for prefixes used in JSON [RFC7159] data serialization and URI path segments (see Section 8).

Prefixes and identifiers SHOULD only consist of the alphabetic US- ASCII characters A through Z in both uppercase and lowercase, the numerical digits 0 through 9, and the underscore character, and they SHOULD NOT begin with an underscore character, numerical digit, or the characters "xml". The following describes the production of JSON names in ABNF [RFC5234].

name = ALPHA *( ALPHA / DIGIT / "_" )

Figure 1: ABNF for JSON Names

This restriction is a union of the Ruby programming language identifier syntax and the XML element name syntax and has two purposes. First, client implementers using modern programming languages such as Ruby or Java can use libraries that automatically promote JSON names to first-order object attributes or members. Second, a clean mapping between JSON and XML is easy to accomplish using these rules.

7. Security Considerations

This document does not pose strong security requirements to the RDAP protocol. However, it does not restrict against the use of security mechanisms offered by the HTTP protocol. It does require that RDAP clients and servers MUST support HTTPS.

This document makes recommendations for server implementations against DoS (Section 5.5) and interoperability with existing security mechanisms in HTTP clients (Section 5.6).

Additional security considerations to the RDAP protocol are covered in [RFC7481].

8. IANA Considerations

8.1. RDAP Extensions Registry

IANA has created a new category in the protocol registries labeled "Registration Data Access Protocol (RDAP)", and within that category, has established a URL-referenceable, stand-alone registry labeled "RDAP Extensions". The purpose of this registry is to ensure uniqueness of extension identifiers. The extension identifier is used as a prefix in JSON names and as a prefix of path segments in RDAP URLs.

The production rule for these identifiers is specified in Section 6.

In accordance with [RFC5226], the IANA policy for assigning new values, shall be Specification Required: values and their meanings 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.

The following is a template for an RDAP extension registration:

Extension identifier: the identifier of the extension

Registry operator: the name of the registry operator

Published specification: RFC number, bibliographical reference, or URL to a permanent and readily available specification

Person & email address to contact for further information: The names and email addresses of individuals to contact regarding this registry entry

Intended usage: brief reasons for this registry entry (as defined by [RFC5226]).

The following is an example of a registration in the RDAP extension registry:

      Extension identifier: lunarNic

Registry operator: The Registry of the Moon, LLC

      Published specification: http://www.example/moon_apis/rdap

Person & email address to contact for further information: Professor Bernardo de la Paz <berny@moon.example>

      Intended usage: COMMON

9. Internationalization Considerations

9.1. URIs and IRIs

Clients can use Internationalized Resource Identifiers (IRIs) [RFC3987] for internal use as they see fit but MUST transform them to URIs [RFC3986] for interaction with RDAP servers. RDAP servers MUST use URIs in all responses, and again clients can transform these URIs to IRIs for internal use as they see fit.

9.2. Language Identifiers in Queries and Responses

Under most scenarios, clients requesting data will not signal that the data be returned in a particular language or script. On the other hand, when servers return data and have knowledge that the data is in a language or script, the data SHOULD be annotated with language identifiers whenever they are available, thus allowing clients to process and display the data accordingly.

[RFC7483] provides such a mechanism.

9.3. Language Identifiers in HTTP Headers

Given the description of the use of language identifiers in Section 9.2, unless otherwise specified, servers SHOULD ignore the HTTP [RFC7231] Accept-Language header field when formulating HTTP entity responses, so that clients do not conflate the Accept-Language header with the 'lang' values in the entity body.

However, servers MAY return language identifiers in the Content- Language header field so as to inform clients of the intended language of HTTP layer messages.

10. References

10.1. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005,
   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005,
   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008, <>.
   [RFC6585]  Nottingham, M. and R. Fielding, "Additional HTTP Status
              Codes", RFC 6585, April 2012,
   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing", RFC
              7230, June 2014, <>.
   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              June 2014, <>.
   [RFC7481]  Hollenbeck, S. and N. Kong, "Security Services for the
              Registration Data Access Protocol (RDAP)", RFC 7481,
              February 2015, <>.
   [RFC7482]  Newton, A. and S. Hollenbeck, "Registration Data Access
              Protocol (RDAP) Query Format", RFC 7482, February 2015,
   [RFC7483]  Newton, A. and S. Hollenbeck, "JSON Responses for the
              Registration Data Access Protocol (RDAP)", RFC 7483,
              February 2015, <>.
   [RFC7484]  Blanchet, M., "Finding the Authoritative Registration Data
              (RDAP) Service", RFC 7484, February 2015,


Kesteren, A., "Cross-Origin Resource Sharing", W3C

Recommendation, REC-cors-20140116, January 2014,


10.2. Informative References

   [REST]     Fielding, R. and R. Taylor, "Principled Design of the
              Modern Web Architecture", ACM Transactions on Internet
              Technology, Vol. 2, No. 2, May 2002.
   [RFC3912]  Daigle, L., "WHOIS Protocol Specification", RFC 3912,
              September 2004, <>.
   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008,
   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, August 2010,
   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014,
   [SAC-051]  Piscitello, D., Ed., "SSAC Report on Domain Name WHOIS
              Terminology and Structure", A report from the ICANN
              Security and Stability Advisory Committee (SSAC),
              September 2011.


              LACNIC, "Joint Whois", December 2005,

Appendix A. Protocol Example

To demonstrate typical behavior of an RDAP client and server, the following is an example of an exchange, including a redirect. The data in the response has been elided for brevity, as the data format is not described in this document. The media type used here is described in [RFC7483].

An example of an RDAP client and server exchange:


         <TCP connect to port 80>
         GET /rdap/ip/ HTTP/1.1
         Accept: application/rdap+json

         HTTP/1.1 301 Moved Permanently
         Content-Length: 0
         Content-Type: application/rdap+json
         <TCP disconnect>


         <TCP connect to port 80>
         GET /rdap/ip/ HTTP/1.1
         Accept: application/rdap+json

         HTTP/1.1 200 OK
         Content-Type: application/rdap+json
         Content-Length: 9001
         { ... }
         <TCP disconnect>

Appendix B. Cache Busting

Some HTTP [RFC7230] cache infrastructures do not adhere to caching standards adequately and could cache responses longer than is intended by the server. To overcome these issues, clients can use an ad hoc and improbably used query parameter with a random value of their choosing. As Section 4.3 instructs servers to ignore unknown parameters, this is compatible with the RDAP definition.

An example of using an unknown query parameter to bust caches:

Use of an unknown parameter to overcome misbehaving caches is not part of any specification and is offered here for informational purposes.

Appendix C. Bootstrapping and Redirection

The traditional deployment model of WHOIS [RFC3912] does not provide a mechanism for determining the authoritative source for information.

Some approaches have been implemented in the past, most notably the Joint WHOIS [lacnic-joint-whois] initiative. However, among other shortcomings, Joint WHOIS is implemented using proxies and server- side referrals.

These issues are solved in RDAP using HTTP redirects and bootstrapping. Bootstrapping is discussed in [RFC7484]. In constrained environments, the processes outlined in [RFC7484] may not be viable, and there may be the need for servers acting as a "redirector".

Redirector servers issue HTTP redirects to clients using a redirection table informed by [RFC7484]. Figure 2 diagrams a client using a redirector for bootstrapping.

                                      REDIRECTOR       ARIN
                                      RDAP             RDAP
                                        .               .
                                        |               |
        Q: -----------------> |               |
                                        |               |
           <---------- HTTP 301 --------|               |
                  ('Try ARIN RDAP')     |               |
                                        |               |
          Q: -------------------------------> |
             <---------- HTTP 200 --------------------- |
                    (JSON response is returned)         |

Figure 2: Querying RDAP Data for

In some cases, particularly sub-delegations made between Regional Internet Registries (RIRs) known as "ERX space" and transfers of networks, multiple HTTP redirects will be issued. Figure 3 shows such a scenario.

                          REDIRECTOR  LACNIC           ARIN
                          RDAP        RDAP             RDAP
                            .           .               .
        Q: ---->  |           |               |
                            |           |               |
          <-- HTTP 301 ---  |           |               |
         ('Try LACNIC')     |           |               |
                            |           |               |
                            |           |               |
        Q: -----------------> |               |
                                        |               |
           <---------- HTTP 301 --------|               |
                  ('Try ARIN RDAP')     |               |
                                        |               |
          Q: -------------------------------> |
             <---------- HTTP 200 --------------------- |
                    (JSON response is returned)         |

Figure 3: Querying RDAP Data for Data That Has Been Transferred


John Levine provided text to tighten up the Accept header field usage and the text for the section on 429 responses.

Marc Blanchet provided some clarifying text regarding the use of URLs with redirects, as well as very useful feedback during Working Group Last Call (WGLC).

Normative language reviews were provided by Murray S. Kucherawy, Andrew Sullivan, Tom Harrison, Ed Lewis, and Alexander Mayrhofer.

Jean-Phillipe Dionne provided text for the Security Considerations section.

The concept of the redirector server informatively discussed in Appendix C was documented by Carlos M. Martinez and Gerardo Rada of

LACNIC and Linlin Zhou of CNNIC and subsequently incorporated into this document.

This document is the work product of the IETF's WEIRDS working group, of which Olaf Kolkman and Murray Kucherawy were chairs.

Authors' Addresses

   Andrew Lee Newton
   American Registry for Internet Numbers
   3635 Concorde Parkway
   Chantilly, VA  20151
   United States
   Byron J. Ellacott
   Asia Pacific Network Information Centre
   6 Cordelia Street
   South Brisbane  QLD 4101
   Ning Kong
   China Internet Network Information Center
   4 South 4th Street, Zhongguancun, Haidian District
   Beijing  100190
   Phone: +86 10 5881 3147