Forwarded HTTP Extension
RFC 7239

Internet Engineering Task Force (IETF)                      A. Petersson
Request for Comments: 7239                                    M. Nilsson
Category: Standards Track                                 Opera Software
ISSN: 2070-1721                                                June 2014

                        Forwarded HTTP Extension

Abstract

   This document defines an HTTP extension header field that allows
   proxy components to disclose information lost in the proxying
   process, for example, the originating IP address of a request or IP
   address of the proxy on the user-agent-facing interface.  In a path
   of proxying components, this makes it possible to arrange it so that
   each subsequent component will have access to, for example, all IP
   addresses used in the chain of proxied HTTP requests.

   This document also specifies guidelines for a proxy administrator to
   anonymize the origin of a request.

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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7239.

Petersson & Nilsson          Standards Track                    [Page 1]
RFC 7239                Forwarded HTTP Extension               June 2014

Copyright Notice

   Copyright (c) 2014 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
   (http://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 ....................................................3
   2. Notational Conventions ..........................................4
   3. Syntax Notations ................................................4
   4. Forwarded HTTP Header Field .....................................4
   5. Parameters ......................................................6
      5.1. Forwarded By ...............................................6
      5.2. Forwarded For ..............................................6
      5.3. Forwarded Host .............................................7
      5.4. Forwarded Proto ............................................7
      5.5. Extensions .................................................7
   6. Node Identifiers ................................................8
      6.1. IPv4 and IPv6 Identifiers ..................................9
      6.2. The "unknown" Identifier ...................................9
      6.3. Obfuscated Identifier ......................................9
   7. Implementation Considerations ..................................10
      7.1. HTTP Lists ................................................10
      7.2. Header Field Preservation .................................10
      7.3. Relation to Via ...........................................10
      7.4. Transition ................................................11
      7.5. Example Usage .............................................11
   8. Security Considerations ........................................12
      8.1. Header Validity and Integrity .............................12
      8.2. Information Leak ..........................................12
      8.3. Privacy Considerations ....................................12
   9. IANA Considerations ............................................14
   10. References ....................................................14
      10.1. Normative References .....................................14
      10.2. Informative References ...................................15
   Appendix A. Acknowledgments .......................................16

Petersson & Nilsson          Standards Track                    [Page 2]
RFC 7239                Forwarded HTTP Extension               June 2014

1.  Introduction

   In today's HTTP landscape, there are a multitude of different
   applications that act as proxies for the user agents.  In many cases,