computer network A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...

ing, 451 Unavailable For Legal Reasons is an

HTTP status code Hypertext Transfer Protocol (HTTP) response status codes are issued by a server in response to a client's request made to the server. It includes codes from IETF Request for Comments (RFCs), other specifications, and some additional codes use ...

used when the user requests a resource which cannot be served for legal reasons, such as a web page censored by a government. The number 451 is a reference to

Ray Bradbury Ray Douglas Bradbury ( ; August 22, 1920June 5, 2012) was an American author and screenwriter. One of the most celebrated 20th-century American writers, he worked in a variety of genres, including fantasy, science fiction, Horror fiction, horr ...

's 1953

dystopia A dystopia (lit. "bad place") is an imagined world or society in which people lead wretched, dehumanized, fearful lives. It is an imagined place (possibly state) in which everything is unpleasant or bad, typically a totalitarian or environmen ...

n novel ''

Fahrenheit 451 ''Fahrenheit 451'' is a 1953 Dystopian fiction, dystopian novel by American writer Ray Bradbury. It presents a future American society where books have been outlawed and "firemen" Book burning, burn any that are found. The novel follows in the ...

'', in which books are outlawed. 451 provides more information than

HTTP 403 HTTP 403 is an HTTP status code meaning access to the requested resource is forbidden. The server understood the request, but will not fulfill it, if it was correct. Specifications HTTP 403 provides a distinct error case from HTTP 401; whil ...

, which is often used for the same purpose. This status code is currently a proposed standard in , which updated the IANA HTTP Status Codes Registry to include 451. Examples of situations where an HTTP 451 error code could be displayed include web pages deemed a danger to national security, or web pages deemed to violate copyright, privacy,

blasphemy law A blasphemy law is a law prohibiting blasphemy, which is the act of insulting or showing contempt or lack of Reverence (attitude), reverence to a deity, or sacred objects, or toward something considered sacred or inviolable. According to Pew Re ...

s, or any other law or court order. After introduction of the

GDPR The General Data Protection Regulation (Regulation (EU) 2016/679), abbreviated GDPR, is a European Union regulation on information privacy in the European Union (EU) and the European Economic Area (EEA). The GDPR is an important component of ...

in the EEA it became common practice for websites located outside the EEA to serve HTTP 451 errors to EEA visitors instead of trying to comply with this new privacy law. For instance, many regional U.S. news sites no longer serve web browsers from the EU. The RFC is specific that a 451 response does not indicate whether the resource exists but requests for it have been blocked, if the resource has been removed for legal reasons and no longer exists, or even if the resource has never existed, but any discussion of its topic has been legally forbidden (see

injunction An injunction is an equitable remedy in the form of a special court order compelling a party to do or refrain from doing certain acts. It was developed by the English courts of equity but its origins go back to Roman law and the equitable rem ...

). Some sites have previously returned

HTTP 404 In computer network communications, the HTTP 404, 404 not found, 404, 404 error, page not found, or file not found error message is a hypertext transfer protocol (HTTP) standard response code, to indicate that the browser was able to comm ...

(missing) or similar if they are not legally permitted to disclose that the resource has been removed. It is used in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

by some

Internet service provider An Internet service provider (ISP) is an organization that provides a myriad of services related to accessing, using, managing, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, no ...

s utilising the

Internet Watch Foundation The Internet Watch Foundation (IWF) is a registered charity based in Cambridge, England. It states that its remit is "to minimise the availability of online sexual abuse content, specifically child sexual abuse images and videos hosted anywhe ...

blacklist, returning a 404 message or another error message instead of showing a message indicating the site is blocked. The status code was formally proposed in 2013 by

Tim Bray Timothy William Bray (born June 21, 1955) is a Canadian software developer, environmentalist, political activist and one of the co-authors of the original XML specification. He worked for Amazon Web Services from December 2014 until May 2020 w ...

, following earlier informal proposals by Chris Applegate in 2008 and

Terence Eden Terence Eden is a technologist specialising in open standards, open data, open source software, and privacy matters. Career Education Eden graduated in 2002 from the University of East Anglia with a Bachelor of Science in Applied Computing ...

in 2012. It was approved by the

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet standard, Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster ...

on 18 December 2015. It was published as in the Proposed Standard in February 2016. HTTP 451 was mentioned by the BBC's ''

From Our Own Correspondent ''From Our Own Correspondent'' is a weekly BBC radio programme in which BBC foreign correspondents deliver a sequence of short talks reflecting on current events and topical themes in the countries outside the UK in which they are based. The prog ...

'' programme, as an indication of the effects of sanctions on

Sudan Sudan, officially the Republic of the Sudan, is a country in Northeast Africa. It borders the Central African Republic to the southwest, Chad to the west, Libya to the northwest, Egypt to the north, the Red Sea to the east, Eritrea and Ethiopi ...

and the inability to access

Airbnb Airbnb, Inc. ( , an abbreviation of its original name, "Air Bed and Breakfast") is an American company operating an online marketplace for short-and-long-term homestays, experiences and services in various countries and regions. It acts as a ...

, the

App Store An app store, also called an app marketplace or app catalog, is a type of digital distribution platform for computer software called applications, often in a mobile context. Apps provide a specific set of functions which, by definition, do not i ...

, or other Western web services.

Usage

When an entity intercepts the request and returns status 451, it should include a "Link" HTTP header field whose value is a URI reference identifying itself. The "Link" header field must then have a "rel" parameter whose value is "blocked-by". This is intended to identify the entity implementing the blocking (an ISP, DNS provider, caching system, etc.), not the legal authority mandating the block. At an IETF hackathon, participants used a web crawler to discover that several implementations misunderstood this header and gave the legal authority instead.

Additional uses

The meaning of "a resource which cannot be served for legal reasons" has been interpreted to extend beyond government censorship: * When content cannot be shown in the user's country, due to contractual or licensing restrictions with the content owner, for example, a TV program may not be available to users in some countries. * When a publisher refuses to serve content to a user, because the user's country adds regulatory requirements that the publisher refuses to comply with, e.g. websites based outside of the EU may refuse to serve users in the EU because they do not want to comply with the

Example

HTTP/1.1 451 Unavailable For Legal Reasons Link: ; rel="blocked-by" Content-Type: text/html Unavailable For Legal Reasons

Unavailable For Legal Reasons

This request may not be serviced in the Roman Province of Judea due to the Lex Julia Majestatis, which disallows access to resources hosted on servers deemed to be operated by the People's Front of Judea.

References

External links