Skip to main content

An HTTP Status Code to Report Legal Obstacles

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7725.
Author Tim Bray
Last updated 2017-11-14 (Latest revision 2015-11-10)
Replaces draft-tbray-http-legally-restricted-status
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Mark Nottingham
Shepherd write-up Show Last changed 2015-11-20
IESG IESG state Became RFC 7725 (Proposed Standard)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Barry Leiba
Send notices to (None)
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
HTTP Working Group                                               T. Bray
Internet-Draft                                                Textuality
Intended status: Standards Track                       November 10, 2015
Expires: May 13, 2016

             An HTTP Status Code to Report Legal Obstacles


   This document specifies a Hypertext Transfer Protocol (HTTP) status
   code for use when resource access is denied as a consequence of legal

Editorial Note (To be removed by RFC Editor before publication)

   Discussion of this draft takes place on the HTTPBIS working group
   mailing list (, which is archived at [1].

   Working Group information can be found at [2] and [3]; source code
   and issues list for this draft can be found at [4].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 13, 2016.

Copyright Notice

   Copyright (c) 2015 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
   ( in effect on the date of

Bray                      Expires May 13, 2016                  [Page 1]
Internet-Draft               HTTP-status-451               November 2015

   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
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  451 Unavailable For Legal Reasons . . . . . . . . . . . . . .   3
   4.  Identifying Blocking Entities . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   This document specifies a Hypertext Transfer Protocol (HTTP) status
   code for use when a server operator has received a legal demand to
   deny access to a resource or to a set of resources which includes the
   requested resource.

   This status code can be used to provide transparency in circumstances
   where issues of law or public policy affect server operations.  This
   transparency may be beneficial both to these operators and to end

   [RFC4924] discusses the forces working against transparent operation
   of the Internet; these clearly include legal interventions to
   restrict access to content.  As that document notes, and as Section 4
   of [RFC4084] states, such restrictions should be made explicit.

   Feedback should occur on the mailing list.

2.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

Bray                      Expires May 13, 2016                  [Page 2]
Internet-Draft               HTTP-status-451               November 2015

3.  451 Unavailable For Legal Reasons

   This status code indicates that the server is denying access to the
   resource as a consequence of a legal demand.

   The server in question might not be an origin server.  This type of
   legal demand typically most directly affects the operations of ISPs
   and search engines.

   Responses using this status code SHOULD include an explanation, in
   the response body, of the details of the legal demand: the party
   making it, the applicable legislation or regulation, and what classes
   of person and resource it applies to.  For example:

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

    <head><title>Unavailable For Legal Reasons</title></head>
     <h1>Unavailable For Legal Reasons</h1>
     <p>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.</p>

   The use of the 451 status code implies neither the existence nor non-
   existence 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

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-

Bray                      Expires May 13, 2016                  [Page 3]
Internet-Draft               HTTP-status-451               November 2015

   access path which 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.

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

6.  IANA Considerations

   The HTTP Status Codes Registry should be updated with the following

   o  Code: 451

   o  Description: Unavailable for Legal Reasons

   o  Specification: [ this document ]

   The Link Relation Type Registry should updated with the following

   o  Relation Name: blocked-by

   o  Description: Identifies the entity blocking access to a resource
      folllowing on receipt of a legal demand.

   o  Reference: This document

Bray                      Expires May 13, 2016                  [Page 4]
Internet-Draft               HTTP-status-451               November 2015

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,

   [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,

Appendix A.  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


Bray                      Expires May 13, 2016                  [Page 5]