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.
The use of the 451 status code implies neither the existence nor nonexistence of the resource named in the request. That is to say, it is possible that if the legal demands were removed, a request for the resource still might not succeed. Note that in many cases clients can still access the denied resource by using technical countermeasures such as a VPN or the Tor network. A 451 response is cacheable by default, i.e., unless otherwise indicated by the method definition or explicit cache controls; see [RFC7234]. 4. Identifying Blocking Entities As noted above, when an attempt to access a resource fails with status 451, the entity blocking access might or might not be the origin server. There are a variety of entities in the resource- access path that could choose to deny access -- for example, ISPs, cache providers, and DNS servers. It is useful, when legal blockages occur, to be able to identify the entities actually implementing the blocking. When an entity blocks access to a resource and returns status 451, it SHOULD include a "Link" HTTP header field [RFC5988] whose value is a URI reference [RFC3986] identifying itself. When used for this purpose, the "Link" header field MUST have a "rel" parameter whose value is "blocked-by". The intent is that the header be used to identify the entity actually implementing blockage, not any other entity mandating it. A human- readable response body, as discussed above, is the appropriate location for discussion of administrative and policy issues. Bray Standards Track [Page 3] RFC 7725 HTTP-status-451 February 2016 5. Security Considerations Clients cannot rely upon the use of the 451 status code. It is possible that certain legal authorities might wish to avoid transparency, and not only demand the restriction of access to certain resources, but also avoid disclosing that the demand was made. 6. IANA Considerations The HTTP Status Codes Registry has been updated with the following entry: o Code: 451 o Description: Unavailable For Legal Reasons o Specification: RFC 7725 The Link Relation Type Registry has been updated with the following entry: o Relation Name: blocked-by o Description: Identifies the entity that blocks access to a resource following receipt of a legal demand. o Reference: RFC 7725 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . [RFC5988] Nottingham, M., "Web Linking", RFC 5988, DOI 10.17487/RFC5988, October 2010, . Bray Standards Track [Page 4] RFC 7725 HTTP-status-451 February 2016 [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", RFC 7234, DOI 10.17487/RFC7234, June 2014, . 7.2. Informative References [RFC4084] Klensin, J., "Terminology for Describing Internet Connectivity", BCP 104, RFC 4084, DOI 10.17487/RFC4084, May 2005, . [RFC4924] Aboba, B., Ed. and E. Davies, "Reflections on Internet Transparency", RFC 4924, DOI 10.17487/RFC4924, July 2007, . Acknowledgements Thanks to Terence Eden, who observed that the existing status code 403 was not really suitable for this situation, and suggested the creation of a new status code. Thanks also to Ray Bradbury. Author's Address Tim Bray Textuality Email: tbray@textuality.com URI: http://www.tbray.org/ongoing/ Bray Standards Track [Page 5]RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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