computer network protocol
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This article is about a method for checking information about ownership of a domain name. For an IRC command called WHOIS, see List of Internet Relay Chat commands § WHOIS.

WHOIS (pronounced as the phrase who is) is a query and response protocol that is widely used for querying databases that store the registered users or assignees of an Internet resource, such as a domain name, an IP address block, or an autonomous system, but is also used for a wider range of other information. The protocol stores and delivers database content in a human-readable format.[1] The WHOIS protocol is documented in RFC 3912.



When the Internet was emerging out of the ARPANET, there was only one organization that handled all domain registrations, which was DARPA itself. The process of registration was established in {{IETF RFC|920}}. WHOIS was standardized in the early 1980s to look up domains, people and other resources related to domain and number registrations. As all registration was done by one organization at that time, one centralized server was used for WHOIS queries. This made looking up such information very easy.

Responsibility of domain registration remained with DARPA as the ARPANET became the Internet during the 1980s. UUNET began offering domain registration service; however they simply handled the paperwork which they forwarded to the DARPA Network Information Center (NIC). Then the National Science Foundation directed that management of Internet domain registration would be handled by commercial, third-party entities. InterNIC was formed in 1993 under contract with the NSF, consisting of Network Solutions, Inc., General Atomics and AT&T. The General Atomics contract was canceled after several years due to performance issues.

20th century WHOIS servers were highly permissive and would allow wild-card searches. A WHOIS query of a person's last name would yield all individuals with that name. A query with a given keyword returned all registered domains containing that keyword. A query for a given administrative contact returned all domains the administrator was associated with. Since the advent of the commercialized Internet, multiple registrars and unethical spammers, such permissive searching is no longer available.

On December 1, 1999, management of the top-level domains (TLDs) com, net, and org was assigned to ICANN. At the time, these TLDs were converted to a thin WHOIS model. Existing WHOIS clients stopped working at that time. A month later, it had self-detecting Common Gateway Interface support so that the same program could operate a web-based WHOIS lookup, and an external TLD table to support multiple WHOIS servers based on the TLD of the request. This eventually became the model of the modern WHOIS client.

By 2005, there were many more generic top-level domains than there had been in the early 1980s. There are also many more country-code top-level domains. This has led to a complex network of domain name registrars and registrar associations, especially as the management of Internet infrastructure has become more internationalized. As such, performing a WHOIS query on a domain requires knowing the correct, authoritative WHOIS server to use. Tools to do WHOIS proxy searches have become common.


In 2003, an IETF committee was formed to create a new standard for looking up information on domain names and network numbers: Cross Registry Information Service Protocol (CRISP).[2] Between January 2005 and July 2006, the working name for this proposed new standard was Internet Registry Information Service (IRIS) [3][4] The initial IETF Proposed Standards RFCs for IRIS are:

The status of RFCs this group worked on can be found on the IETF Tools site.[5]

As of March 2009, the CRISP IETF Working Group concluded,[6] after a final RFC 5144 was published by the group [7] Newton, Andrew; Sanz, Marcos (February 2008). A Domain Availability Check (DCHK) Registry Type for the Internet Registry Information Service (IRIS). IETF. RFC 5144. https://tools.ietf.org/html/rfc5144. Retrieved 1 June 2015. .

Note: The IETF CRISP working group is not to be confused with the Number Resource Organization's (NRO) Team of the same name "Consolidated RIR IANA Stewardship Proposal Team" (CRISP Team).[8]


In 2013, the IETF acknowledged that IRIS had not been a successful replacement for WHOIS. The primary technical reason for that appeared to be the complexity of IRIS. Further, non-technical reasons were deemed to lie in areas upon which the IETF does not pass judgment. Meanwhile, ARIN and RIPE NCC managed to serve WHOIS data via RESTful web services. The charter (drafted in February 2012) provided for separate specifications, for number registries first and for name registries to follow.[9] The working group produced five proposed standard documents:

and an informational document:


The WHOIS protocol had its origin in the ARPANET NICNAME protocol and was based on the NAME/FINGER Protocol, described in {{IETF RFC|742}} (1977). The NICNAME/WHOIS protocol was first described in {{IETF RFC|812}} in 1982 by Ken Harrenstien and Vic White of the Network Information Center at SRI International.

WHOIS was originally implemented on the Network Control Program (NCP) but found its major use when the TCP/IP suite was standardized across the ARPANET and later the Internet.

The protocol specification is the following (original quote):[10]

Connect to the service host
   TCP: service port 43 decimal
   NCP: ICP to socket 43 decimal, establishing two 8-bit connections
Send a single "command line", ending with <CRLF>.
Receive information in response to the command line.  The
server closes its connections as soon as the output is

The command line server query is normally a single name specification. i.e. the name of a resource. However, servers accept a query, consisting of only the question mark (?) to return a description of acceptable command line formats. Substitution or wild-card formats also exist, e.g., appending a full-stop (period) to the query name returns all entries beginning with the query name.

On the modern Internet, WHOIS services are typically communicated using the Transmission Control Protocol (TCP). Servers listen to requests on the well-known port number 43. Clients are simple applications that establish a communications channel to the server, transmit a text record with the name of the resource to be queried and await the response in form of a sequence of text records found in the database. This simplicity of the protocol also permits an application, and a command line interface user, to query a WHOIS server using the Telnet protocol.


WHOIS lookups were traditionally performed with a command line interface application, but now many alternative web-based tools exist. WHOIS has a sister protocol called Referral Whois (RWhois).

A WHOIS database consists of a set of text records for each resource. These text records consists of various items of information about the resource itself, and any associated information of assignees, registrants, administrative information, such as creation and expiration dates.

Two data models exist for storing resource information in a WHOIS database, the thick and the thin model.

Thin and thick lookupsEdit

WHOIS information can be stored and looked up according to either a thick or a thin data model:

A Thick WHOIS server stores the complete WHOIS information from all the registrars for the particular set of data (so that one WHOIS server can respond with WHOIS information on all .org domains, for example).
A Thin WHOIS server stores only the name of the WHOIS server of the registrar of a domain, which in turn has the full details on the data being looked up (such as the .com WHOIS servers, which refer the WHOIS query to the registrar where the domain was registered).

The thick model usually ensures consistent data and slightly faster queries, since only one WHOIS server needs to be contacted. If a registrar goes out of business, a thick registry contains all important information (if the registrant entered correct data, and privacy features were not used to obscure the data) and registration information can be retained. But with a thin registry, the contact information might not be available, and it could be difficult for the rightful registrant to retain control of the domain.[11]

If a WHOIS client did not understand how to deal with this situation, it would display the full information from the registrar. Unfortunately, the WHOIS protocol has no standard for determining how to distinguish the thin model from the thick model.

Specific details of which records are stored vary among domain name registries. Some top-level domains, including com and net, operate a thin WHOIS, requiring domain registrars to maintain their own customers' data. The other global top-level registries, including org, operate a thick model.[12] Each country-code top-level registry has its own national rules.


The first applications written for the WHOIS information system were command line interface tools for Unix and Unix-like operating systems (i.e. Solaris, Linux etc.). WHOIS client and server software is distributed as free open-source software and binary distributions are included with all Unix-like systems. Various commercial Unix implementations may use a proprietary implementation (for example, Solaris 7).

A WHOIS command line client passes a phrase given as an argument directly to the WHOIS server. Various free open source examples can still be found on sites such as sourceforge.net. However, most modern WHOIS tools implement command line flags or options, such as the -h option to access a specific server host, but default servers are preconfigured. Additional options may allow control of the port number to connect on, displaying additional debugging data, or changing recursion/referral behavior.

Like most TCP/IP client-server applications, a WHOIS client takes the user input and then opens an Internet socket to its destination server. The WHOIS protocol manages the transmission of the query and reception of results.


With the advent of the World Wide Web and especially the loosening up of the Network Solutions monopoly, looking up WHOIS information via the web has become quite common. At present, popular web-based WHOIS-queries may be conducted from ARIN,[13] RIPE[14] and APNIC.[15] Most early web-based WHOIS clients were merely front-ends to a command-line client, where the resulting output just gets displayed on a web page with little, if any, clean-up or formatting.

Currently, web based WHOIS clients usually perform the WHOIS queries directly and then format the results for display. Many such clients are proprietary, authored by domain name registrars.

The need for web-based clients came from the fact that command-line WHOIS clients largely existed only in the Unix and large computing worlds. Microsoft Windows and Macintosh computers had no WHOIS clients installed by default, so registrars had to find a way to provide access to WHOIS data for potential customers. Many end-users still rely on such clients, even though command line and graphical clients exist now for most home PC platforms. Microsoft provides the Sysinternals Suite that includes a whois client at no cost.

There are also many sites not owned by registrars or Internet-related companies. These support most of main TLD and remain free. But most of web-based whois sites are incomplete and do not support all TLD nor IP search.[16]

Some work from a built-in WHOIS server list and some other try to retrieve the one which fits the TLD you ask for from a live Domain Information Groper query (command line clients do this query in background first).

CPAN has several Perl modules available that work with WHOIS servers. Many of them are not current and do not fully function with the current (2005) WHOIS server infrastructure. However, there is still much useful functionality to derive including looking up AS numbers and registrant contacts.[citation needed]


Regional Internet registriesEdit

Regional Internet Registries

WHOIS servers operated by Regional Internet Registries (RIR) can be queried directly to determine the Internet Service Provider responsible for a particular resource.

The records of each of these registries are cross-referenced, so that a query to ARIN for a record which belongs to RIPE will return a place-holder pointing to the RIPE WHOIS server. This lets the WHOIS user making the query know that the detailed information resides on the RIPE server. In addition to the RIRs servers, commercial services exist, such as the Routing Assets Database used by some large networks (e.g., large Internet providers that acquired other ISPs in several RIR areas).

Server discoveryEdit

There is currently no standard for determining the responsible WHOIS server for a DNS domain, though a number of methods are in common use for top-level domains (TLDs). Some WHOIS lookups require searching the procuring domain registrar to display domain owner details.

Query exampleEdit

Normally the contact information of the resources assignee is returned. However, some registrars offer private registration, in which case the contact information of the registrar is shown instead.

Some registry operators are wholesalers, meaning that they typically provide domain name services to a large number of retail registrars, who in turn offer them to consumers. For private registration, only the identity of the wholesale registrar may be returned. In this case, the identity of the individual as well as the retail registrar may be hidden.

Below is an example of WHOIS data returned for an individual resource holder. This is the result of a WHOIS query of example.com:

whois example.com
[Querying whois.verisign-grs.com]
[Redirected to whois.iana.org]
[Querying whois.iana.org]
% IANA WHOIS server
% for more information on IANA, visit http://www.iana.org
% This query returned 1 object
domain:       EXAMPLE.COM
organisation: Internet Assigned Numbers Authority
created:      1992-01-01
source:       IANA

Referral WhoisEdit

Referral Whois (RWhois) is an extension of the original Whois protocol and service. RWhois extends the concepts of Whois in a scalable, hierarchical fashion, potentially creating a system with a tree-like architecture. Queries are deterministically routed to servers based on hierarchical labels, reducing a query to the primary repository of information.[17]

Lookups of IP address allocations are often limited to the larger Classless Inter-Domain Routing (CIDR) blocks (e.g., /24, /22, /16), because usually only the regional Internet registries (RIRs) and domain registrars run RWhois or Whois servers, although RWhois is intended to be run by even smaller local Internet registries, to provide more granular information about IP address assignment.

RWhois is intended to replace Whois, providing an organized hierarchy of referral services where one could connect to any RWhois server, request a look-up and be automatically re-directed to the correct server(s). However, while the technical functionality is in place, adoption of the RWhois standard has been weak.

RWhois services are typically communicated using the Transmission Control Protocol (TCP). Servers listen to requests on the well-known port number 4321.

Rwhois was first specified in {{IETF RFC|1714}} in 1994 by Network Solutions,[17] but the specification was superseded in 1997 by RFC 2167.[18]

The referral features of RWhois are different than the feature of a Whois server to refer responses to another server, which RWhois also implements.


One criticism of WHOIS is the lack of full access to the data.[19][20] Few parties have realtime access to the complete databases. Others cite the competing goal of domain privacy as a criticism although this problem is strongly mitigated by domain privacy services. Currently the Internet Corporation for Assigned Names and Numbers (ICANN) broadly requires that the mailing address, phone number and e-mail address of those owning or administrating a domain name to be made publicly available through the "WHOIS" directories. The registrant's (domain owner's) contact details, such as address and telephone number, are easily accessible to anyone who queries a WHOIS server. However, that policy enables spammers, direct marketers, identity thieves, or other attackers to loot the directory for personal information about these people. Although ICANN has been exploring changing WHOIS to enable greater privacy, there is a lack of consensus among major stakeholders as to what type of change should be made.[21] Some domain registrars offer private registrations (also known as domain privacy), by which the contact information of the registrar is shown instead of the customer's. With the offer of private registration from many registrars, some of the risk has been mitigated.

Studies have shown that spammers can and do harvest plain-text email addresses from WHOIS servers.[22] For this reason, some WHOIS servers and websites offering WHOIS queries have implemented rate-limiting systems, such as web-based CAPTCHA and limited amounts of search queries per user IP address.

The WHOIS protocol was not written with an international audience in mind. A WHOIS server and/or client cannot determine the text encoding in effect for the query or the database content. Many servers were originally using US-ASCII and Internationalization concerns weren't taken into consideration until much later.[23] This might impact the usability or usefulness of the WHOIS protocol in countries outside the USA.[1] In the case of internationalized domain names it is the responsibility of the client application to perform the translation of the domain name between its native language script and the DNS name in punycode.

Accuracy of informationEdit

In cases where the registrant's (Domain Owner) identity is public, anyone can easily confirm the status of a domain via WHOIS.

In the case of private registrations, ascertaining registration information may be more difficult. If a registrant, who acquired a domain name, wants to verify the registrar has completed the registration process, three steps may be required:

  1. Perform a WHOIS and confirm that the resource is at least registered with ICANN,
  2. Determine the name of the wholesale registrar, and
  3. Contact the wholesaler and obtain the name of the retail registrar.

This provides some confidence that the retailer actually registered the name. But if the registrar goes out of business, such as the failure of RegisterFly in 2007, the rightful domain holder with privacy-protected registrations may have difficulty regaining back the administration of his/her domain name.[11] Registrants using "private registration" can attempt to protect themselves by using a registrar that places customer data in escrow with a third party.

ICANN requires that each registrant of domain name be given the opportunity to correct any inaccurate contact data associated with his/her domain. For this reason, registrars are required to periodically send the holder the contact information on record for verification, but they do not provide any guarantee about the accuracy of information if the registrant provided inaccurate information.

Law and policyEdit

WHOIS has generated policy issues in the United States federal government. As noted above, WHOIS creates a privacy issue which is also tied to free speech and anonymity. However, WHOIS is an important tool for law enforcement officers investigating violations like spam and phishing to track down the holders of domain names. As a result, law enforcement agencies have sought to make WHOIS records both open and verified:[24]

  • The Federal Trade Commission has testified about how inaccurate WHOIS records thwart their investigations.[25]
  • Congressional hearings have been conducted about the importance of WHOIS in 2001, 2002 and 2006.[26]
  • The Fraudulent Online Identity Sanctions Act[27] "make it a violation of trademark and copyright law if a person knowingly provided, or caused to be provided, materially false contact information in making, maintaining, or renewing the registration of a domain name used in connection with the violation,"[28] where the latter "violation" refers to a prior violation of trademark or copyright law. The act does not make the submission of false WHOIS data illegal in itself, only if used to shield oneself from prosecution for crimes committed using that domain name.

ICANN proposal to abolish WHOISEdit

The Expert Working Group (EWG) of the Internet Corporation for Assigned Names and Numbers (ICANN) recommended on 24 June 2013 that WHOIS should be scrapped. It recommends that WHOIS be replaced with a system that keeps information secret from most Internet users, and only discloses information for "permissible purposes."[29] ICANN's list of permissible purposes includes domain-name research, domain-name sale and purchase, regulatory enforcement, personal data protection, legal actions, and abuse mitigation.[30] Although WHOIS has been a key tool of journalists in determining who was disseminating certain information on the Internet,[31] the use of WHOIS by the free press is not included in ICANN’s proposed list of permissible purposes.

The EWG collected public input on the initial report until 13 September 2013. Its final report was issued on 6 June 2014, without meaningful changes to the recommendations.[32] ICANN is now in the "process of re-inventing WHOIS," working on "ICANN WHOIS Beta."[33][34]

Standards documentsEdit

  • RFC 812 – NICNAME/WHOIS (1982, obsolete)
  • RFC 954 – NICNAME/WHOIS (1985, obsolete)
  • RFC 3912 – WHOIS protocol specification (2004, current)

See alsoEdit


  1. ^ a b RFC 3912, WHOIS Protocol Specification, L. Daigle (September 2004)
  2. ^ Murphy, Cathy (2 October 2003). "CRISP (Cross-Registry Information Service Protocol) Working Group Meeting Minutes". Internet Engineering Task Force. Minneapolis, Minnesota USA: IETF. Archived from the original on 1 June 2015. Retrieved 1 June 2015. The CRISP (Cross-Registry Information Service Protocol) WG will define a standard mechanism that can be used for finding authoritative information associated with a label, a protocol to transport queries and responses for accessing that information, and a first profile (schema & queries) to support commonly-required queries for domain registration information. 
  3. ^ Newton, Andrew (July 2006). "Replacing the Whois Protocol: IRIS and the IETF's CRISP Working Group". IEEE Internet Computing. 10 (4): 79–84. doi:10.1109/MIC.2006.86. Retrieved 1 June 2015. The Nicname/Whois protocol has served well, but it remains unchanged since it was first published in the early 1980s, despite great change in the infrastructure and administration of the Internet. There is now more diversity with domain names and IP networks and associated contacts, as well as among the users submitting queries via Whois. The protocol is now so fragmented in terms of information flow and output that queries yield inconsistent results under current conditions. To address the needs of today's Internet, the IETF Cross Registry Internet Service Protocol (CRISP) working group is developing a new protocol, the Internet Registry Information Service (IRIS), to replace Whois. 
  4. ^ Sanz, Marcos; Newton, Andrew; Daigle, Leslie (12 January 2005). "The Internet Registry Information Service (IRIS) Protocol" (PDF). gnso.icann.org. Internet Corporation for Assigned Names and Numbers (ICANN). Archived from the original (PDF) on 1 June 2015. Retrieved 1 June 2015. CRISP - Cross-Registry Internet Service Protocol: The CRISP Working Group was tasked with finding a solution to the problems that currently infest the Nicname/Whois protocol. The CRISP Working Group created a list of functional requirements. Proposals meeting these requirements were evaluated. IRIS was selected as the protocol to publish as a standard. Now an IETF Proposed Standard: RFCs: 3981, 3982, 3983 
  5. ^ "Crisp Status Pages". IETF Tools: CRISP WG Status Pages. IETF. Archived from the original on 1 June 2015. Retrieved 2 June 2015. 
  6. ^ IESG Secretary (26 March 2009). "WG Action: Conclusion of Cross Registry Information Service Protocol (crisp)". IETF CRISP WG: Mail Archive. Archived from the original on 2 June 2015. Retrieved 2 June 2015. The Cross Registry Information Service Protocol (crisp) working group in the Applications Area has concluded. 
  7. ^ Mevzek, Patrick (21 January 2009). "[CRISP] [[Request for Comments|RFC]] [https://tools.ietf.org/html/rfc5144 5144] up and running". IETF CRISP WG: Mail Archive. Archived from the original on 2 June 2015. Retrieved 2 June 2015.  External link in |title= (help); URL–wikilink conflict (help)
  8. ^ Nimpuno, Nurani. "Consolidated RIR IANA Stewardship Proposal Team (CRISP Team)". nro.net. Number Resource Organization (NRO). Retrieved 1 June 2015. 
  9. ^ "Web Extensible Internet Registration Data Service (weirds) Working Group". IETF-88 Proceedings. IETF. Retrieved 8 July 2015. 
  10. ^ RFC 812: NICNAME/WHOIS, K.Harrenstien, V.White (1982)
  11. ^ a b Circleid.com
  12. ^ Sarah Stoll (30 May 2009). "Thick vs. Thin Whois for New gTLDs" (PDF). memorandum. ICANN. Retrieved 17 September 2011. Current gTLD registry agreements vary between thin and thick Whois outputs: com, net and jobs are thin; all other gTLD agreements – aero, asia, biz, cat, coop, info, mobi, museum, name, org, pro, tel, travel – are thick. 
  13. ^ ARIN WHOIS
  14. ^ RIPE WHOIS
  16. ^ IP WHOIS
  17. ^ a b RFC 1714, Referral Whois Protocol (RWhois), S. Williamson, M. Kosters (November 1994)
  18. ^ RFC 2167, Referral Whois (RWhois) V1.5, S. Williamson, M. Kosters, D. Blacka, J. Singh, K. Zeilstra (June 1997)
  19. ^ "Battle Begins Over IP Address Whois Data". Internet Governance Project. Retrieved 4 April 2015. 
  20. ^ "WHOIS Privacy Plan Draws Fire". KerbsonSecurity. Retrieved 4 April 2015. 
  21. ^ "The Privacy Conundrum in Domain Registration". Act Now Domains. Retrieved 26 March 2013. 
  22. ^ "SAC 023: Is the WHOIS Service a Source for email Addresses for Spammers?", ICANN Security and Stability Advisory Committee, October 2007
  23. ^ "WHOIS Internalization Issues", November 2012
  24. ^ FTC Calls for Openness, Accessibility in Whois Database System, FTC 7/18/2006
  25. ^ FTC Testimony on WHOIS, FTC 5/22/02
  26. ^ Bowman, Lisa (11 July 2001). "Whois at heart of congressional hearings". CNET. Archived from the original on 27 August 2005. 
  27. ^ THOMAS
  28. ^ Fraudulent Online Identity Sanctions Act
  29. ^ "Initial Report from the Expert Working Group on gTLD Directory Services: A Next Generation Registration Directory Service" (PDF). whois.icann.org. ICANN. 24 June 2013. Retrieved 24 March 2015. 
  30. ^ http://newlegalreview.cpaglobal.com/icann-earmarks-domains-record-whois-scrapheap/
  31. ^ http://jour.sc.edu/news/csj/CSJNov04.html
  32. ^ "Final Report from the Expert Working Group on gTLD Directory Services: A Next-Generation Registration Directory Service (RDS)" (PDF). https://whois.icann.org. ICANN. 6 June 2014. Retrieved 24 March 2015.  External link in |website= (help)
  33. ^ "About WHOIS". https://whois.icann.org/. ICANN. Retrieved 24 March 2015.  External link in |website= (help)
  34. ^ "What's on the Horizon?". https://whois.icann.org. ICANN. Retrieved 24 March 2015.  External link in |website= (help)

External linksEdit