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                                                      
                                                                            
 .  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].                   
                                                                            
 .  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                                        
                                                                            
 .  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*".        
                                                                            
 .  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.                
                                                                            
 .  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.                                              
                                                                            
 .  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.        
                                                                            
 .  IANA Considerations                                                    
                                                                            
    This document has no IANA actions.                                      
                                                                            
 .  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.                
                                                                            
 .  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: shollenbeck@verisign.com                                         
    URI:   https://www.verisignlabs.com/                                    
                                                                            
                                                                            
    Andy Newton                                                             
    Amazon Web Services, Inc.                                               
    13200 Woodland Park Road                                                
    Herndon, VA 20171                                                       
    United States of America                                                
                                                                            
    Email: andy@hxr.us