Internet Engineering Task Force (IETF) S. Hollenbeck

Internet Engineering Task Force (IETF) S. Hollenbeck
Request for Comments: 9082 Verisign Labs
STD: 95 A. Newton
Obsoletes: 7482 AWS
Category: Standards Track June 2021
ISSN: 2070-1721

Registration Data Access Protocol (RDAP) Query Format

Abstract

This document describes uniform patterns to construct HTTP URLs that
may be used to retrieve registration information from registries
(including both Regional Internet Registries (RIRs) and Domain Name
Registries (DNRs)) using "RESTful" web access patterns. These
uniform patterns define the query syntax for the Registration Data
Access Protocol (RDAP). This document obsoletes RFC 7482.

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 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9082.

Copyright Notice

Copyright (c) 2021 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 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. Conventions Used in This Document
2.1. Acronyms and Abbreviations
3. Path Segment Specification
3.1. Lookup Path Segment Specification
3.1.1. IP Network Path Segment Specification
3.1.2. Autonomous System Path Segment Specification
3.1.3. Domain Path Segment Specification
3.1.4. Nameserver Path Segment Specification
3.1.5. Entity Path Segment Specification
3.1.6. Help Path Segment Specification
3.2. Search Path Segment Specification
3.2.1. Domain Search
3.2.2. Nameserver Search
3.2.3. Entity Search
4. Query Processing
4.1. Partial String Searching
4.2. Associated Records
5. Extensibility
6. Internationalization Considerations
6.1. Character Encoding Considerations
7. IANA Considerations
8. Security Considerations
9. References
9.1. Normative References
9.2. Informative References
Appendix A. Changes from RFC 7482
Acknowledgments
Authors' Addresses

1. Introduction

This document describes a specification for querying registration
data using a RESTful web service and uniform query patterns. The
service is implemented using the Hypertext Transfer Protocol (HTTP)
[RFC7230] and the conventions described in [RFC7480]. These uniform
patterns define the query syntax for the Registration Data Access
Protocol (RDAP). This document obsoletes RFC 7482.

The protocol described in this specification is intended to address
deficiencies with the WHOIS protocol [RFC3912] that have been
identified over time, including:

* lack of standardized command structures;

* lack of standardized output and error structures;

* lack of support for internationalization and localization; and

* lack of support for user identification, authentication, and
access control.

The patterns described in this document purposefully do not encompass
all of the methods employed in the WHOIS and other RESTful web
services used by the RIRs and DNRs. The intent of the patterns
described here is to enable queries of:

* networks by IP address;

* Autonomous System (AS) numbers by number;

* reverse DNS metadata by domain;

* nameservers by name; and

* entities (such as registrars and contacts) by identifier.

Server implementations are free to support only a subset of these
features depending on local requirements. Servers MUST return an
HTTP 501 (Not Implemented) [RFC7231] response to inform clients of
unsupported query types. It is also envisioned that each registry
will continue to maintain WHOIS and/or other RESTful web services
specific to their needs and those of their constituencies, and the
information retrieved through the patterns described here may
reference such services.

Likewise, future IETF specifications may add additional patterns for
additional query types. A simple pattern namespacing scheme is
described in Section 5 to accommodate custom extensions that will not
interfere with the patterns defined in this document or patterns
defined in future IETF specifications.

WHOIS services, in general, are read-only services. Accordingly, URL
[RFC3986] patterns specified in this document are only applicable to
the HTTP [RFC7231] GET and HEAD methods.

This document does not describe the results or entities returned from
issuing the described URLs with an HTTP GET. The specification of
these entities is described in [RFC9083].

Additionally, resource management, provisioning, and update functions
are out of scope for this document. Registries have various and
divergent methods covering these functions, and it is unlikely a
uniform approach is needed for interoperability.

HTTP contains mechanisms for servers to authenticate clients and for
clients to authenticate servers (from which authorization schemes may
be built), so such mechanisms are not described in this document.
Policy, provisioning, and processing of authentication and
authorization are out of scope for this document as deployments will
have to make choices based on local criteria. Supported
authentication mechanisms are described in [RFC7481].

2. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

2.1. Acronyms and Abbreviations

IDN: Internationalized Domain Name, a fully-qualified domain name
containing one or more labels that are intended to include one or
more Unicode code points outside the ASCII range (cf. "domain
name", "fully-qualified domain name", and "internationalized
domain name" in RFC 8499 [RFC8499]).

IDNA: Internationalized Domain Names in Applications, a protocol for
the handling of IDNs. In this document, "IDNA" refers
specifically to the version of those specifications known as
"IDNA2008" [RFC5890].

DNR: Domain Name Registry or Domain Name Registrar

NFC: Unicode Normalization Form C [Unicode-UAX15]

NFKC: Unicode Normalization Form KC [Unicode-UAX15]

RDAP: Registration Data Access Protocol

REST: Representational State Transfer. The term was first described
in a doctoral dissertation [REST].

RESTful: An adjective that describes a service using HTTP and the
principles of REST.

RIR: Regional Internet Registry

3. Path Segment Specification

The base URLs used to construct RDAP queries are maintained in an
IANA registry (the "bootstrap registry") described in [RFC7484].
Queries are formed by retrieving an appropriate base URL from the
registry and appending a path segment specified in either Sections
3.1 or 3.2. Generally, a registry or other service provider will
provide a base URL that identifies the protocol, host, and port, and
this will be used as a base URL that the complete URL is resolved
against, as per Section 5 of RFC 3986 [RFC3986]. For example, if the
base URL is "https://example.com/rdap/", all RDAP query URLs will
begin with "https://example.com/rdap/".

The bootstrap registry does not contain information for query objects
that are not part of a global namespace, including entities and help.
A base URL for an associated object is required to construct a
complete query. This limitation can be overcome for entities by
using the practice described in RFC 8521 [RFC8521].

For entities, a base URL is retrieved for the service (domain,
address, etc.) associated with a given entity. The query URL is
constructed by concatenating the base URL with the entity path
segment specified in either Sections 3.1.5 or 3.2.3.

For help, a base URL is retrieved for any service (domain, address,
etc.) for which additional information is required. The query URL is
constructed by concatenating the base URL with the help path segment
specified in Section 3.1.6.

3.1. Lookup Path Segment Specification

A simple lookup to determine if an object exists (or not) without
returning RDAP-encoded results can be performed using the HTTP HEAD
method as described in Section 4.1 of [RFC7480].

The resource type path segments for exact match lookup are:

'ip': Used to identify IP networks and associated data referenced
using either an IPv4 or IPv6 address.

'autnum': Used to identify Autonomous System number registrations
and associated data referenced using an asplain Autonomous System
number.

'domain': Used to identify reverse DNS (RIR) or domain name (DNR)
information and associated data referenced using a fully qualified
domain name.

'nameserver': Used to identify a nameserver information query using
a host name.

'entity': Used to identify an entity information query using a
string identifier.

3.1.1. IP Network Path Segment Specification

Syntax: ip/<IP address> or ip/<CIDR prefix>/<CIDR length>

Queries for information about IP networks are of the form /ip/XXX or
/ip/XXX/YY where the path segment following 'ip' is either an IPv4
dotted decimal or IPv6 [RFC5952] address (i.e., XXX) or an IPv4 or
IPv6 Classless Inter-domain Routing (CIDR) [RFC4632] notation address
block (i.e., XXX/YY). Semantically, the simpler form using the
address can be thought of as a CIDR block with a prefix length of 32
for IPv4 and a prefix length of 128 for IPv6. A given specific
address or CIDR may fall within multiple IP networks in a hierarchy
of networks; therefore, this query targets the "most-specific" or
smallest IP network that completely encompasses it in a hierarchy of
IP networks.

The IPv4 and IPv6 address formats supported in this query are
described in Section 3.2.2 of RFC 3986 [RFC3986] as IPv4address and
IPv6address ABNF definitions. Any valid IPv6 text address format
[RFC4291] can be used. This includes IPv6 addresses written using
with or without compressed zeros and IPv6 addresses containing
embedded IPv4 addresses. The rules to write a text representation of
an IPv6 address [RFC5952] are RECOMMENDED. However, the zone_id
[RFC4007] is not appropriate in this context; therefore, the
corresponding syntax extension in RFC 6874 [RFC6874] MUST NOT be
used, and servers SHOULD ignore it.

For example, the following URL would be used to find information for
the most specific network containing 192.0.2.0:

https://example.com/rdap/ip/192.0.2.0

The following URL would be used to find information for the most
specific network containing 192.0.2.0/24:

https://example.com/rdap/ip/192.0.2.0/24

The following URL would be used to find information for the most
specific network containing 2001:db8::

https://example.com/rdap/ip/2001:db8::

3.1.2. Autonomous System Path Segment Specification

Syntax: autnum/<autonomous system number>

Queries for information regarding Autonomous System number
registrations are of the form /autnum/XXX where XXX is an asplain
Autonomous System number [RFC5396]. In some registries, registration
of Autonomous System numbers is done on an individual number basis,
while other registries may register blocks of Autonomous System
numbers. The semantics of this query are such that if a number falls
within a range of registered blocks, the target of the query is the
block registration and that individual number registrations are
considered a block of numbers with a size of 1.

For example, the following URL would be used to find information
describing Autonomous System number 12 (a number within a range of
registered blocks):

https://example.com/rdap/autnum/12

The following URL would be used to find information describing 4-byte
Autonomous System number 65538:

https://example.com/rdap/autnum/65538

3.1.3. Domain Path Segment Specification

Syntax: domain/<domain name>

Queries for domain information are of the form /domain/XXXX, where
XXXX is a fully qualified (relative to the root) domain name (as
specified in [RFC0952] and [RFC1123]) in either the in-addr.arpa or
ip6.arpa zones (for RIRs) or a fully qualified domain name in a zone
administered by the server operator (for DNRs). Internationalized
Domain Names (IDNs) represented in either A-label or U-label format
[RFC5890] are also valid domain names. See Section 6.1 for
information on character encoding for the U-label format.

IDNs SHOULD NOT be represented as a mixture of A-labels and U-labels;
that is, internationalized labels in an IDN SHOULD be either all
A-labels or all U-labels. It is possible for an RDAP client to
assemble a query string from multiple independent data sources. Such
a client might not be able to perform conversions between A-labels
and U-labels. An RDAP server that receives a query string with a
mixture of A-labels and U-labels MAY convert all the U-labels to
A-labels, perform IDNA processing, and proceed with exact-match
lookup. In such cases, the response to be returned to the query
source may not match the input from the query source. Alternatively,
the server MAY refuse to process the query.

The server MAY perform the match using either the A-label or U-label
form. Using one consistent form for matching every label is likely
to be more reliable.

The following URL would be used to find information describing the
zone serving the network 192.0.2/24:

https://example.com/rdap/domain/2.0.192.in-addr.arpa

The following URL would be used to find information describing the
zone serving the network 2001:db8:1::/48:

https://example.com/rdap/domain/1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa

The following URL would be used to find information for the
blah.example.com domain name:

https://example.com/rdap/domain/blah.example.com

The following URL would be used to find information for the
xn--fo-5ja.example IDN:

https://example.com/rdap/domain/xn--fo-5ja.example

3.1.4. Nameserver Path Segment Specification

Syntax: nameserver/<nameserver name>

The <nameserver name> parameter represents a fully qualified host
name as specified in [RFC0952] and [RFC1123]. Internationalized
names represented in either A-label or U-label format [RFC5890] are
also valid nameserver names. IDN processing for nameserver names
uses the domain name processing instructions specified in
Section 3.1.3. See Section 6.1 for information on character encoding
for the U-label format.

The following URL would be used to find information for the
ns1.example.com nameserver:

https://example.com/rdap/nameserver/ns1.example.com

The following URL would be used to find information for the
ns1.xn--fo-5ja.example nameserver:

https://example.com/rdap/nameserver/ns1.xn--fo-5ja.example

3.1.5. Entity Path Segment Specification

Syntax: entity/<handle>

The <handle> parameter represents an entity (such as a contact,
registrant, or registrar) identifier whose syntax is specific to the
registration provider. For example, for some DNRs, contact
identifiers are specified in [RFC5730] and [RFC5733].

The following URL would be used to find information for the entity
associated with handle XXXX:

https://example.com/rdap/entity/XXXX

3.1.6. Help Path Segment Specification

Syntax: help

The help path segment can be used to request helpful information
(command syntax, terms of service, privacy policy, rate-limiting
policy, supported authentication methods, supported extensions,
technical support contact, etc.) from an RDAP server. The response
to "help" should provide basic information that a client needs to
successfully use the service. The following URL would be used to
return "help" information:

https://example.com/rdap/help

3.2. Search Path Segment Specification

Pattern matching semantics are described in Section 4.1. The
resource type path segments for search are:

'domains': Used to identify a domain name information search using a
pattern to match a fully qualified domain name.

'nameservers': Used to identify a nameserver information search
using a pattern to match a host name.

'entities': Used to identify an entity information search using a
pattern to match a string identifier.

RDAP search path segments are formed using a concatenation of the
plural form of the object being searched for and an HTTP query
string. The HTTP query string is formed using a concatenation of the
question mark character ('?', US-ASCII value 0x003F), a noun
representing the JSON object property associated with the object
being searched for, the equal sign character ('=', US-ASCII value
0x003D), and the search pattern (this is in contrast to the more
generic HTTP query string that allows multiple simultaneous
parameters). Search pattern query processing is described more fully
in Section 4. For the domain, nameserver, and entity objects
described in this document, the plural object forms are "domains",
"nameservers", and "entities".

Detailed results can be retrieved using the HTTP GET method and the
path segments specified here.

3.2.1. Domain Search

Syntax: domains?name=<domain search pattern>

Syntax: domains?nsLdhName=<nameserver search pattern>

Syntax: domains?nsIp=<nameserver IP address>

Searches for domain information by name are specified using this
form:

domains?name=XXXX

XXXX is a search pattern representing a domain name in "letters,
digits, hyphen" (LDH) format [RFC5890]. The following URL would be
used to find DNR information for domain names matching the
"example*.com" pattern:

https://example.com/rdap/domains?name=example*.com

IDNs in U-label format [RFC5890] can also be used as search patterns
(see Section 4). Searches for these names are of the form
/domains?name=XXXX, where XXXX is a search pattern representing a
domain name in U-label format [RFC5890]. See Section 6.1 for
information on character encoding for the U-label format.

Searches for domain information by nameserver name are specified
using this form:

domains?nsLdhName=YYYY

YYYY is a search pattern representing a host name in "letters,
digits, hyphen" format [RFC5890]. The following URL would be used to
search for domains delegated to nameservers matching the
"ns1.example*.com" pattern:

https://example.com/rdap/domains?nsLdhName=ns1.example*.com

Searches for domain information by nameserver IP address are
specified using this form:

domains?nsIp=ZZZZ

ZZZZ is an IPv4 [RFC1166] or IPv6 [RFC5952] address. The following
URL would be used to search for domains that have been delegated to
nameservers that resolve to the "192.0.2.0" address:

https://example.com/rdap/domains?nsIp=192.0.2.0

3.2.2. Nameserver Search

Syntax: nameservers?name=<nameserver search pattern>

Syntax: nameservers?ip=<nameserver IP address>

Searches for nameserver information by nameserver name are specified
using this form:

nameservers?name=XXXX

XXXX is a search pattern representing a host name in "letters,
digits, hyphen" format [RFC5890]. The following URL would be used to
find information for nameserver names matching the "ns1.example*.com"
pattern:

https://example.com/rdap/nameservers?name=ns1.example*.com

Internationalized nameserver names in U-label format [RFC5890] can
also be used as search patterns (see Section 4). Searches for these
names are of the form /nameservers?name=XXXX, where XXXX is a search
pattern representing a nameserver name in U-label format [RFC5890].
See Section 6.1 for information on character encoding for the U-label
format.

Searches for nameserver information by nameserver IP address are
specified using this form:

nameservers?ip=YYYY

YYYY is an IPv4 [RFC1166] or IPv6 [RFC5952] address. The following
URL would be used to search for nameserver names that resolve to the
"192.0.2.0" address:

https://example.com/rdap/nameservers?ip=192.0.2.0

3.2.3. Entity Search

Syntax: entities?fn=<entity name search pattern>

Syntax: entities?handle=<entity handle search pattern>

Searches for entity information by name are specified using this
form:

entities?fn=XXXX

XXXX is a search pattern representing the "fn" property of an entity
(such as a contact, registrant, or registrar) name as described in
Section 5.1 of [RFC9083]. The following URL would be used to find
information for entity names matching the "Bobby Joe*" pattern:

https://example.com/rdap/entities?fn=Bobby%20Joe*

Searches for entity information by handle are specified using this
form:

entities?handle=XXXX

XXXX is a search pattern representing an entity (such as a contact,
registrant, or registrar) identifier whose syntax is specific to the
registration provider. The following URL would be used to find
information for entity handles matching the "CID-40*" pattern:

https://example.com/rdap/entities?handle=CID-40*

URLs MUST be properly encoded according to the rules of [RFC3986].
In the example above, "Bobby Joe*" is encoded to "Bobby%20Joe*".

4. Query Processing

Servers indicate the success or failure of query processing by
returning an appropriate HTTP response code to the client. Response
codes not specifically identified in this document are described in
[RFC7480].

4.1. Partial String Searching

Partial string searching uses the asterisk ('*', US-ASCII value 0x2A)
character to match zero or more trailing characters. A character
string representing a domain label suffix MAY be concatenated to the
end of the search pattern to limit the scope of the search. For
example, the search pattern "exam*" will match "example.com" and
"example.net". The search pattern "exam*.com" will match
"example.com". If an asterisk appears in a search string, any label
that contains the non-asterisk characters in sequence plus zero or
more characters in sequence in place of the asterisk would match. A
partial string search MUST NOT include more than one asterisk.
Additional pattern matching processing is beyond the scope of this
specification.

If a server receives a search request but cannot process the request
because it does not support a particular style of partial match
searching, it SHOULD return an HTTP 422 (Unprocessable Entity)
[RFC4918] response (unless another response code is more appropriate
based on a server's policy settings) to note that search
functionality is supported, but this particular query cannot be
processed. When returning a 422 error, the server MAY also return an
error response body as specified in Section 6 of [RFC9083] if the
requested media type is one that is specified in [RFC7480].

Partial matching is not feasible across combinations of Unicode
characters because Unicode characters can be combined with each
other. Servers SHOULD NOT partially match combinations of Unicode
characters where a legal combination is possible. It should be
noted, though, that it may not always be possible to detect cases
where a character could have been combined with another character,
but was not, because characters can be combined in many different
ways.

Clients SHOULD NOT submit a partial match search of Unicode
characters where a Unicode character may be legally combined with
another Unicode character or characters. Partial match searches with
incomplete combinations of characters where a character must be
combined with another character or characters are invalid. Partial
match searches with characters that may be combined with another
character or characters are to be considered non-combined characters
(that is, if character x may be combined with character y but
character y is not submitted in the search string, then character x
is a complete character and no combinations of character x are to be
searched).

4.2. Associated Records

Conceptually, any query-matching record in a server's database might
be a member of a set of related records, related in some fashion as
defined by the server -- for example, variants of an IDN. The entire
set ought to be considered as candidates for inclusion when
constructing the response. However, the construction of the final
response needs to be mindful of privacy and other data-releasing
policies when assembling the RDAP response set.

Note too that due to the nature of searching, there may be a list of
query-matching records. Each one of those is subject to being a
member of a set as described in the previous paragraph. What is
ultimately returned in a response will be the union of all the sets
that has been filtered by whatever policies are in place.

Note that this model includes arrangements for associated names,
including those that are linked by policy mechanisms and names bound
together for some other purposes. Note also that returning
information that was not explicitly selected by an exact-match
lookup, including additional names that match a relatively fuzzy
search as well as lists of names that are linked together, may cause
privacy issues.

Note that there might not be a single, static information return
policy that applies to all clients equally. Client identity and
associated authorizations can be a relevant factor in determining how
broad the response set will be for any particular query.

5. Extensibility

This document describes path segment specifications for a limited
number of objects commonly registered in both RIRs and DNRs. It does
not attempt to describe path segments for all of the objects
registered in all registries. Custom path segments can be created
for objects not specified here using the process described in
Section 6 of "HTTP Usage in the Registration Data Access Protocol
(RDAP)" [RFC7480].

Custom path segments can be created by prefixing the segment with a
unique identifier followed by an underscore character (0x5F). For
example, a custom entity path segment could be created by prefixing
"entity" with "custom_", producing "custom_entity". Servers MUST
return an appropriate failure status code for a request with an
unrecognized path segment.

6. Internationalization Considerations

There is value in supporting the ability to submit either a U-label
(Unicode form of an IDN label) or an A-label (US-ASCII form of an IDN
label) as a query argument to an RDAP service. Clients capable of
processing non-US-ASCII characters may prefer a U-label since this is
more visually recognizable and familiar than A-label strings, but
clients using programmatic interfaces might find it easier to submit
and display A-labels if they are unable to input U-labels with their
keyboard configuration. Both query forms are acceptable.

Internationalized domain and nameserver names can contain character
variants and variant labels as described in [RFC4290]. Clients that
support queries for internationalized domain and nameserver names
MUST accept service provider responses that describe variants as
specified in "JSON Responses for the Registration Data Access
Protocol (RDAP)" [RFC9083].

6.1. Character Encoding Considerations

Servers can expect to receive search patterns from clients that
contain character strings encoded in different forms supported by
HTTP. It is entirely possible to apply filters and normalization
rules to search patterns prior to making character comparisons, but
this type of processing is more typically needed to determine the
validity of registered strings than to match patterns.

An RDAP client submitting a query string containing non-US-ASCII
characters converts such strings into Unicode in UTF-8 encoding. It
then performs any local case mapping deemed necessary. Strings are
normalized using Normalization Form C (NFC) [Unicode-UAX15]; note
that clients might not be able to do this reliably. UTF-8 encoded
strings are then appropriately percent-encoded [RFC3986] in the query
URL.

After parsing any percent-encoding, an RDAP server treats each query
string as Unicode in UTF-8 encoding. If a string is not valid UTF-8,
the server can immediately stop processing the query and return an
HTTP 400 (Bad Request) response.

When processing queries, there is a difference in handling DNS names,
including those with putative U-labels, and everything else. DNS
names are treated according to the DNS matching rules as described in
Section 3.1 of RFC 1035 [RFC1035] for Non-Reserved LDH (NR-LDH)
labels and the matching rules described in Section 5.4 of RFC 5891
[RFC5891] for U-labels. Matching of DNS names proceeds one label at
a time because it is possible for a combination of U-labels and NR-
LDH labels to be found in a single domain or host name. The
determination of whether a label is a U-label or an NR-LDH label is
based on whether the label contains any characters outside of the US-
ASCII letters, digits, or hyphen (the so-called LDH rule).

For everything else, servers map fullwidth and halfwidth characters
to their decomposition equivalents. Servers convert strings to the
same coded character set of the target data that is to be looked up
or searched, and each string is normalized using the same
normalization that was used on the target data. In general, storage
of strings as Unicode is RECOMMENDED. For the purposes of
comparison, Normalization Form KC (NFKC) [Unicode-UAX15] with case
folding is used to maximize predictability and the number of matches.
Note the use of case-folded NFKC as opposed to NFC in this case.

7. IANA Considerations

This document has no IANA actions.

8. Security Considerations

Security services for the operations specified in this document are
described in "Security Services for the Registration Data Access
Protocol (RDAP)" [RFC7481].

Search functionality typically requires more server resources (such
as memory, CPU cycles, and network bandwidth) when compared to basic
lookup functionality. This increases the risk of server resource
exhaustion and subsequent denial of service due to abuse. This risk
can be mitigated by developing and implementing controls to restrict
search functionality to identified and authorized clients. If those
clients behave badly, their search privileges can be suspended or
revoked. Rate limiting as described in Section 5.5 of "HTTP Usage in
the Registration Data Access Protocol (RDAP)" [RFC7480] can also be
used to control the rate of received search requests. Server
operators can also reduce their risk by restricting the amount of
information returned in response to a search request.

Search functionality also increases the privacy risk of disclosing
object relationships that might not otherwise be obvious. For
example, a search that returns IDN variants [RFC6927] that do not
explicitly match a client-provided search pattern can disclose
information about registered domain names that might not be otherwise
available. Implementers need to consider the policy and privacy
implications of returning information that was not explicitly
requested.

Note that there might not be a single, static information return
policy that applies to all clients equally. Client identity and
associated authorizations can be a relevant factor in determining how
broad the response set will be for any particular query.

9. References

9.1. Normative References

[RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
host table specification", RFC 952, DOI 10.17487/RFC0952,
October 1985, <https://www.rfc-editor.org/info/rfc952>.

[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.

[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/info/rfc1123>.

[RFC1166] Kirkpatrick, S., Stahl, M., and M. Recker, "Internet
numbers", RFC 1166, DOI 10.17487/RFC1166, July 1990,
<https://www.rfc-editor.org/info/rfc1166>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.

[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
2006, <https://www.rfc-editor.org/info/rfc4632>.

[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918,
DOI 10.17487/RFC4918, June 2007,
<https://www.rfc-editor.org/info/rfc4918>.

[RFC5396] Huston, G. and G. Michaelson, "Textual Representation of
Autonomous System (AS) Numbers", RFC 5396,
DOI 10.17487/RFC5396, December 2008,
<https://www.rfc-editor.org/info/rfc5396>.

[RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
<https://www.rfc-editor.org/info/rfc5730>.

[RFC5733] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
Contact Mapping", STD 69, RFC 5733, DOI 10.17487/RFC5733,
August 2009, <https://www.rfc-editor.org/info/rfc5733>.

[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/info/rfc5890>.

[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010,
<https://www.rfc-editor.org/info/rfc5891>.

[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/info/rfc5952>.

[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.

[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.

[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,
<https://www.rfc-editor.org/info/rfc7480>.

[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,
<https://www.rfc-editor.org/info/rfc7481>.

[RFC7484] Blanchet, M., "Finding the Authoritative Registration Data
(RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March
2015, <https://www.rfc-editor.org/info/rfc7484>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.

[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,
<https://www.rfc-editor.org/info/rfc9083>.

[Unicode-UAX15]
The Unicode Consortium, "Unicode Standard Annex #15:
Unicode Normalization Forms", September 2013,
<https://www.unicode.org/reports/tr15/>.

9.2. Informative References

[REST] Fielding, R., "Architectural Styles and the Design of
Network-based Software Architectures", Ph.D.
Dissertation, University of California, Irvine, 2000,
<https://www.ics.uci.edu/~fielding/pubs/dissertation/
fielding_dissertation.pdf>.

[RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912,
DOI 10.17487/RFC3912, September 2004,
<https://www.rfc-editor.org/info/rfc3912>.

[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.

[RFC4290] Klensin, J., "Suggested Practices for Registration of
Internationalized Domain Names (IDN)", RFC 4290,
DOI 10.17487/RFC4290, December 2005,
<https://www.rfc-editor.org/info/rfc4290>.

[RFC6874] Carpenter, B., Cheshire, S., and R. Hinden, "Representing
IPv6 Zone Identifiers in Address Literals and Uniform
Resource Identifiers", RFC 6874, DOI 10.17487/RFC6874,
February 2013, <https://www.rfc-editor.org/info/rfc6874>.

[RFC6927] Levine, J. and P. Hoffman, "Variants in Second-Level Names
Registered in Top-Level Domains", RFC 6927,
DOI 10.17487/RFC6927, May 2013,
<https://www.rfc-editor.org/info/rfc6927>.

[RFC8521] Hollenbeck, S. and A. Newton, "Registration Data Access
Protocol (RDAP) Object Tagging", BCP 221, RFC 8521,
DOI 10.17487/RFC8521, November 2018,
<https://www.rfc-editor.org/info/rfc8521>.

Appendix A. Changes from RFC 7482

* Addressed known errata.

* Addressed other reported clarifications and corrections: IDN,
IDNA, and DNR definitions. Noted that registrars are entities.
Added a reference to RFC 8521 to address the bootstrap registry
limitation. Removed extraneous "...". Clarified HTTP query
string, search pattern, name server search, domain label suffix,
and asterisk search.

* Addressed "The HTTP query string" clarification.

* Modified coauthor address.

* Updated references to RFC 7483 to RFC 9083.

* Added an IANA Considerations section. Changed references to use
HTTPS for targets.

* Changed "XXXX is a search pattern representing the "FN" property
of an entity (such as a contact, registrant, or registrar) name as
specified in Section 5.1" to "Changed "XXXX is a search pattern
representing the "fn" property of an entity (such as a contact,
registrant, or registrar) name as described in Section 5.1".

* Added acknowledgments.

* Changed "The intent of the patterns described here are to enable
queries" to "The intent of the patterns described here is to
enable queries".

* Changed "the corresponding syntax extension in RFC 6874 [RFC6874]
MUST NOT be used, and servers are to ignore it if possible" to
"the corresponding syntax extension in RFC 6874 [RFC6874] MUST NOT
be used, and servers SHOULD ignore it".

* Changed "Only a single asterisk is allowed for a partial string
search" to "A partial string search MUST NOT include more than one
asterisk".

* Changed "Clients should avoid submitting a partial match search of
Unicode characters where a Unicode character may be legally
combined with another Unicode character or characters" to "Clients
SHOULD NOT submit a partial match search of Unicode characters
where a Unicode character may be legally combined with another
Unicode character or characters".

* Changed description of nameserver IP address "search pattern" in
Sections 3.2.1 and 3.2.2.

* IESG review feedback: Added "obsoletes 7482" to the headers,
Abstract, and Introduction. Changed "IETF standards" to "IETF
specifications" and "Therefore" to "Accordingly" in Section 1.
Updated the BCP 14 boilerplate. Added definition of "bootstrap
registry" and changed "concatenating ... to" to "concatenating ...
with" in Section 3. Changed "bitmask length" to "prefix length"
and "2001:db8::0" to "2001:db8::" in Section 3.1.1. Added "in
contrast to the more generic HTTP query string that admits
multiple simultaneous parameters" in Section 3.2. Changed
"0x002A" to "0x2A" in Section 4.1. Clarified use of HTTP 422
SHOULD in Section 4.1.

Acknowledgments

This document is derived from original work on RIR query formats
developed by Byron J. Ellacott of APNIC, Arturo L. Servin of LACNIC,
Kaveh Ranjbar of the RIPE NCC, and Andrew L. Newton of ARIN.
Additionally, this document incorporates DNR query formats originally
described by Francisco Arias and Steve Sheng of ICANN and Scott
Hollenbeck of Verisign Labs.

The authors would like to acknowledge the following individuals for
their contributions to this document: Francisco Arias, Marc Blanchet,
Ernie Dainow, Jean-Philippe Dionne, Byron J. Ellacott, Behnam
Esfahbod, John Klensin, John Levine, Edward Lewis, Mario Loffredo,
Patrick Mevzek, Mark Nottingham, Kaveh Ranjbar, Arturo L. Servin,
Steve Sheng, Jasdip Singh, and Andrew Sullivan.

Authors' Addresses

Scott Hollenbeck
Verisign Labs
12061 Bluemont Way
Reston, VA 20190
United States of America

Email: [email protected]
URI: https://www.verisignlabs.com/

Andy Newton
Amazon Web Services, Inc.
13200 Woodland Park Road
Herndon, VA 20171
United States of America

Email: [email protected]