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Versions: (draft-petersson-forwarded-for) 00 01 02 03 04 05 06 07 08 09 10 RFC 7239

Network Working Group                                       A. Petersson
Internet-Draft                                                M. Nilsson
Intended status: Standards Track                          Opera Software
Expires: December 20, 2012                                 June 18, 2012


                        Forwarded HTTP Extension
                  draft-ietf-appsawg-http-forwarded-04

Abstract

   This document standardizes an HTTP extension header field that allows
   proxy components to disclose information lost in the proxying
   process, e.g., the originating IP address of a request or IP number
   of the proxy on the user-agent-facing interface.  Given a trusted
   path of proxying components, this makes it possible to arrange so
   that each subsequent component will have access to e.g., 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 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 http://datatracker.ietf.org/drafts/current/.

   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 December 20, 2012.

Copyright Notice

   Copyright (c) 2012 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



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   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 . . . . . . . . . . . . . . . . . . . .  3
   3.  Syntax Notations . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Forwarded HTTP header field  . . . . . . . . . . . . . . . . .  3
   5.  Parameters . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     5.1.  Forwarded by . . . . . . . . . . . . . . . . . . . . . . .  5
     5.2.  Forwarded for  . . . . . . . . . . . . . . . . . . . . . .  5
     5.3.  Forwarded host . . . . . . . . . . . . . . . . . . . . . .  6
     5.4.  Forwarded proto  . . . . . . . . . . . . . . . . . . . . .  6
     5.5.  Extensions . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Node identifiers . . . . . . . . . . . . . . . . . . . . . . .  6
     6.1.  IPv4 and IPv6 identifiers  . . . . . . . . . . . . . . . .  7
     6.2.  The "unknown" identifier . . . . . . . . . . . . . . . . .  7
     6.3.  Obfuscated identifier  . . . . . . . . . . . . . . . . . .  7
   7.  Implementation considerations  . . . . . . . . . . . . . . . .  8
     7.1.  HTTP lists . . . . . . . . . . . . . . . . . . . . . . . .  8
     7.2.  Header field preservation  . . . . . . . . . . . . . . . .  8
     7.3.  Relation to Via  . . . . . . . . . . . . . . . . . . . . .  9
     7.4.  Transition . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.5.  Example usage  . . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security considerations  . . . . . . . . . . . . . . . . . . . 10
     8.1.  Header validity and integrity  . . . . . . . . . . . . . . 10
     8.2.  Information leak . . . . . . . . . . . . . . . . . . . . . 10
     8.3.  Privacy considerations . . . . . . . . . . . . . . . . . . 10
   9.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 11
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1. Normative references . . . . . . . . . . . . . . . . . . . 12
     10.2. Informative references . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . . 13
     A.1.  Since draft-petersson-forwarded-for-00 . . . . . . . . . . 13
     A.2.  Since draft-petersson-forwarded-for-01 . . . . . . . . . . 13
     A.3.  Since draft-petersson-forwarded-for-02 . . . . . . . . . . 13
     A.4.  Since draft-ietf-appsawg-http-forwarded-00 . . . . . . . . 13
     A.5.  Since draft-ietf-appsawg-http-forwarded-01 . . . . . . . . 14
     A.6.  Since draft-ietf-appsawg-http-forwarded-02 . . . . . . . . 14
     A.7.  Since draft-ietf-appsawg-http-forwarded-03 . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14




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1.  Introduction

   In today's HTTP landscape, there are a multitude of different
   applications acting as a proxy for the user agent and effectively
   anonymizing the requests to look as if they originated from the proxy
   IP address or in other ways changing the information in the original
   request.  Examples of such applications include caching, content
   filtering, content compression, crypto offload, and load balancing.
   As most of the time this loss of information is not the primary
   purpose, or even a desired effect, a way of disclosing the original
   information at HTTP level instead of depending on the TCP/IP
   connection remote IP address and transport port number is needed.

   In addition to the above mentioned problems, there may also be issues
   due to the use of NAT.  This is further discussed in [RFC6269].

   A common way to disclose this information is by using the de facto
   standard header fields such as X-Forwarded-For, X-Forwarded-By, and
   X-Forwarded-Proto.  This document intends to standardize syntax and
   semantics for disclosing such information.  The header field also
   combines all information within one single header field, making it
   possible to correlate the header fields to each other.  With the
   header field format described in this document, it is possible to
   know what information belongs together, given that the proxies are
   trusted.  Such conclusions are not possible to make with the
   X-Forwarded class of header fields.  This new header field also
   extends the de facto standard of, e.g., X-Forwarded-For with features
   for which real life deployments have shown a need.


2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


3.  Syntax Notations

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234] with the list rule extension defined in Section
   3.2.5 of [I-D.ietf-httpbis-p1-messaging].


4.  Forwarded HTTP header field

   The Forwarded HTTP header field is an OPTIONAL header field that,
   when used, contains a list of parameter-identifier pairs that



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   disclose information that is altered or lost when a proxy is involved
   in the path of the request.  This applies to forwarding proxies, as
   well as reverse proxies.  Information passed in this header can be,
   e.g., the source IP address of the request, the IP address of the
   incoming interface on the proxy, or whether HTTP or HTTPS was used.
   If the request is passing through several proxies, each proxy MAY add
   a set of parameters; it MAY also remove earlier added Forwarded-
   header fields.

   The top-level list is represented as a list of HTTP header field-
   value's as defined in Section 3.2 of [I-D.ietf-httpbis-p1-messaging].
   The first element in this list holds information added by the first
   proxy, followed by information added by any subsequent proxy.  Each
   field-value is a semicolon-separated list; this sub-list consists of
   parameter-identifier pairs.  Parameter-identifier pairs are grouped
   together by an equals sign.  The parameter names are case-
   insensitive.  The header field can be defined in augmented BNF syntax
   as:

       Forwarded   = "Forwarded" ":" LWS Forwarded-v
       Forwarded-v = 1#forwarded-element

       forwarded-element =
               [ forwarded-pair ] *( ";" [ forwarded-pair ] )

       forwarded-pair = token "=" value
       value          = token / quoted-string

   Examples:

       Forwarded: For="[2001:db8:cafe::17]:4711"
       Forwarded: for=192.0.2.60;proto=http;by=203.0.113.43
       Forwarded: for=192.0.2.43, for=198.51.100.17

   Note that as ":" and "[]" are not valid characters in token, IPv6
   addresses are written as quoted-string.

   Given that a proxy wishes to add a Forwarded header field to the
   outgoing request, if the incoming request has no such header field,
   the proxy simply adds the header field with the list of parameters
   desired.  If, on the other hand, the incoming request has such a
   header field, the proxy can either add a comma and the list of
   parameters, or add a new instance of the header field.  A proxy MAY
   remove all Forwarded header fields from a request.  It MUST, however,
   ensure that the correct header field is updated in case of multiple
   Forwarded header fields.





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5.  Parameters

   This document specifies a number of parameters and valid values for
   each of them.  Each parameter MUST NOT occur more than once per
   "forwarded-element" as defined in ABNF in Section 4.

   o  "by" identifies the user-agent facing interface of the proxy.

   o  "for" identifies the node making the request to the proxy.

   o  "host" is the host request header-field as received by the proxy.

   o  "proto" indicates what protocol was used to make the request.

5.1.  Forwarded by

   The "by" parameter is used to disclose the interface where the
   request came in to the proxy server.  Typically, the value of this
   parameter is an IP address and optionally a port number; however, it
   can also be some other kind of identifier.

   The syntax of a "by" value, after potential quoted-string unescaping,
   MUST conform to the "node" ABNF described in Section 6.

   This is primarily added by reverse proxies that wish to forward this
   information to the backend server.  It can also be interesting in a
   multi-homed environment to signal to backend servers where the
   request came from.

5.2.  Forwarded for

   The "for" parameter is used to disclose information about the client
   that initiated the request and following proxies in a chain of
   proxies.  Typically, the value of this parameter is an IP address,
   but it can also be some other kind of identifier.

   The syntax of a "for" value, after potential quoted-string
   unescaping, MUST conform to the "node" ABNF described in Section 6.

   In a chain of proxy servers where this is fully utilized, the first
   for-parameter will disclose the user agent where the request was
   first made, followed by any subsequent proxy identifiers.  The last
   proxy in the chain is not part of the list of for-parameters.  The
   last proxy's IP address, and optionally a port number, are, however,
   readily available as the remote IP address of the TCP/IP connection.
   It can, however, be more relevant to read information about the last
   proxy from preceding Forwarded header field's by-parameter, if
   present.



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5.3.  Forwarded host

   The "host" parameter is used to forward the original value of the
   "Host" header field.  This can be used, for example, by the origin
   server if a reverse proxy is rewriting the "Host" header field to
   some internal host name.

   The syntax for a "host" value, after potential quoted-string
   unescaping, MUST conform to the Host ABNF described in Section 5.4 of
   [I-D.ietf-httpbis-p1-messaging].

5.4.  Forwarded proto

   The "proto" parameter has the value of the used protocol type.  The
   syntax of a "proto" value, after potential quoted-string unescaping,
   MUST conform to the URI scheme name as defined in Section 3.1 in
   [RFC3986] and registered to IANA according to [RFC4395].  Typical
   values are "http" or "https".

   For example, in an environment where a reverse proxy is also used as
   a crypto offloader, this allows the origin server to rewrite URLs in
   a document to match the type of connection as the user agent
   requested, even though all connections to the origin server are
   unencrypted HTTP.

5.5.  Extensions

   Private extensions allow for adding own parameters and values.  This
   can be particularly useful in a reverse proxy environment.  If these
   extensions are to be widely spread, it is RECOMMENDED that they are
   standardized.  It is possible to register additional parameters to
   the register HTTP Forwarded Parameters.  This is further discussed in
   Section 9.


6.  Node identifiers

   The node identifiers are the IP address, and, optionally port number,
   of the network node, a predefined token hiding the real identity, but
   signaling that such a component exists in the network path, or a
   generated token allowing for tracing and debugging without revealing
   network internals.

       nodename = IPv4address / "[" IPv6address "]" /
                   "unknown" / obfnode

   All of the identifiers may optionally have the port identifier, for
   example, allowing the identification of the end point in a NATted



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   environment.

       node            = nodename [ ":" node-port ]

   The node-port can be identified either by its TCP port number or by a
   generated token obfuscating the real port number.

       node-port       = port / obfport
       port            = 1*5DIGIT
       obfport         = "_" 1*(ALPHA / DIGIT / "." / "_" / "-")

   Note that this also allows port numbers to be appended to the the
   "unknown" identifier.  Interpretation of such notation is, however,
   left to the possessor of a proxy adding such a value to the header
   field.  To distinguish an obfport from a port, obfport MUST have a
   leading underscore.  Further, it MUST also consist of only US-ASCII
   letters, US-ASCII digits and the characters ".", "_" and "-".

   It is important to note that an IPv6 address and any nodename with
   node-port specified MUST be quoted, since ":" is not an allowed
   character in token.

   Examples:

             "192.0.2.43:47011"
             "[2001:db8:cafe::17]:47011"

6.1.  IPv4 and IPv6 identifiers

   The ABNF rules for "IPv6address" and "IPv4address" are defined in
   [RFC3986] The IPv6address SHOULD comply with textual representation
   recommendations [RFC5952] (e.g., lowercase, compression of zeroes).

   Note that the IP address may be one from the internal nets, as
   defined in [RFC1918] and [RFC4193].  Also, note that an IPv6 address
   is always enclosed in square brackets.

6.2.  The "unknown" identifier

   The "unknown" identifier is used when the identity of the preceding
   entity is not known.  One example would be a proxy server process
   generating an outgoing request without direct access to the incoming
   request TCP socket.

6.3.  Obfuscated identifier

   A generated identifier may be used where there is a wish to keep the
   internal IP addresses secret, while still allowing the Forwarded



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   header field to be used for tracing.  This can also be useful if the
   proxy uses some sort of interface labels and it is desired to pass
   them rather than an IP address.  The identifiers can be randomly
   generated for each request and do not need to be statically assigned
   to resources.  To distinguish the obfuscated identifier from other
   identifiers, it MUST have a leading underscore "_".  Further, it MUST
   also consist of only US-ASCII letters, US-ASCII digits and the
   characters ".", "_" and "-".

       obfnode         = "_" 1*( ALPHA / DIGIT / "." / "_" / "-")

   Example:

       Forwarded: for=_hidden, for=_SEVKISEK


7.  Implementation considerations

7.1.  HTTP lists

   Note that an HTTP list allows white spaces to occur between the
   identifiers, and the list may be split over multiple header fields.
   As an example, the header field

       Forwarded: for=192.0.2.43,for="[2001:db8:cafe::17]",for=unknown

   is equivalent to the header field

       Forwarded: for=192.0.2.43, for="[2001:db8:cafe::17]", for=unknown

   which is equivalent to the header fields

       Forwarded: for=192.0.2.43
       Forwarded: for="[2001:db8:cafe::17]", for=unknown

7.2.  Header field preservation

   There are some cases when this header field should be kept and some
   cases where it should not be kept.  A directly forwarded request
   should preserve and possibly extend it.  If a single incoming request
   causes the proxy to make multiple outbound requests, special care
   must be taken to decide whether the header field should be preserved
   or not.  In many cases the header field should be preserved, but if
   the outbound request is not a direct consequence of the incoming
   request, the header field should not be preserved.  Consider also the
   case when a proxy has detected a content mismatch in a 304 response
   and is following the instructions in
   [I-D.ietf-httpbis-p4-conditional] Section 4.1 to repeat the request



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   unconditionally, in which case the new request is still basically a
   direct consequence of the origin request, and the header should
   probably be kept.

7.3.  Relation to Via

   Note that it is not possible to combine information from this header
   field with the information from the Via header field.  Some proxies
   will not update the Forwarded header field, some proxies will not
   update the Via header field, and some proxies will update both.

7.4.  Transition

   If a proxy gets incoming requests with X-Forwarded-* header fields
   present, it is encouraged to convert these into the header field
   described in this document, if it can be done in a sensible way.  If
   the request only contains one type, ex.  X-Forwarded-For, this can be
   translated to Forwarded, by prepending each element with "for=".
   Note that IPv6-addresses may not be quoted in X-Forwarded-For, but
   they are quoted in Forwarded.

       X-Forwarded-For: 192.0.2.43, [2001:db8:cafe::17]

   becomes:

       Forwarded: for=192.0.2.43, for="[2001:db8:cafe::17]"

   Special care must, however, be taken if, for example, both
   X-Forwarded-For and X-Forwarded-By exists.  In such cases, it may not
   be possible to do a conversion, since it is not possible to know in
   what order the already existing fields were added.  Also, note that
   removing the X-Forwarded-For header field may cause issues for
   parties that have not yet implemented support for this new header
   field.

7.5.  Example usage

   A request from a client with IP address 192.0.2.43 passes through a
   proxy with IP address 198.51.100.17, then through another proxy with
   IP address 203.0.113.60 before reaching a origin server.  This could,
   for example, be an office client behind a corporate malware filter
   talking to a origin server through a reverse proxy.

   o  The HTTP request between the client and the first proxy has no
      Forwarded header field.

   o  The HTTP request between the first and second proxy has a
      "Forwarded: for=192.0.2.43" header field.



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   o  The HTTP request between the second proxy and the origin server
      has a "Forwarded: for=192.0.2.43,
      for=198.51.100.17;by=203.0.113.60;proto=http;host=example.com"
      header field.

   Note that, at some points in a connection chain, the information
   might not be updated in the Forwarded header field, either because of
   lack of support of this HTTP extension or because of a policy
   decision not to disclose information about this network component.


8.  Security considerations

8.1.  Header validity and integrity

   The Forwarded HTTP header field cannot be relied upon to be correct,
   as it may be modified, whether mistakenly or for malicious reasons,
   by every node on the way to the server, including the client making
   the request.

   One approach is to verify the correctness of proxies and to whitelist
   them as trusted.  This approach has at least two weaknesses.  First,
   the chain of IP addresses listed before the request came to the proxy
   cannot be trusted.  Second, unless the communication between proxies
   and the end point is secured, the data can be modified by an attacker
   with access to the network.

8.2.  Information leak

   The Forwarded HTTP header field can reveal internal structures of the
   network setup behind the NAT or proxy setup, which may be undesired.
   This can be addressed either by using obfuscated elements, preventing
   the internal nodes from updating the HTTP header field, or by having
   an egress proxy removing entries that reveals internal network
   information.

   This header field should never be copied into response messages by
   origin servers or intermediaries, as it can reveal the whole proxy
   chain to the client.  As a side effect, special care must be taken in
   hosting environments not to allow the TRACE request where the
   Forwarded field is used, as it would appear in the body of the
   response message.

8.3.  Privacy considerations

   From an end-user perspective, intermediate proxies in the request
   path are either known or unknown.  Hidden proxies using this
   extension will preserve the information of a direct connection, and



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   thus it has no end-user privacy impact.

   Proxies that are known to the end user, such as explicitly configured
   proxies, using this extension will not anonymize the end-user IP
   address.  This extension, however, only standardizes the format for
   forwarding client connection information.  There are already deployed
   proxies supporting this feature, so there is no new privacy risk in
   that proxies are thought to be anonymizing, but in reality are not.

   A proxy that is intended to anonymize the request should be very
   careful to use this header field at all.


9.  IANA considerations

   This document specifies the HTTP header listed below, which should be
   added to the permanent HTTP header registry defined in [RFC3864].

   Header field: Forwarded
   Applicable protocol: http/https
   Status: standard
   Author/Change controller:
       IETF (iesg@ietf.org)
       Internet Engineering Task Force
   Specification document(s): this specification (Section 4)
   Related information: None

   The Forwarded header field contains parameters for which IANA is to
   create and maintain a new registry entiteled "HTTP Forwarded
   parameters".  Initial registrations are given below; for future
   assignments, RFC is required [RFC5226].  The author should consider
   security- and privacy aspects and, if there are any, include such
   sections in the RFC.  New parameters and their values MUST conform
   the forwarded-pair as defined in ABNF in Section 4.  Further, a short
   description should be provided in the registration.

   +-------------+---------------------------------------+-------------+
   | Parameter   | Description                           | Definition  |
   | name        |                                       |             |
   +-------------+---------------------------------------+-------------+
   | by          | IP-address of incoming interface of a | Section 5.1 |
   |             | proxy                                 |             |
   | for         | IP-address of client making a request | Section 5.2 |
   |             | through a proxy                       |             |
   | host        | Host header field of the incoming     | Section 5.3 |
   |             | request                               |             |





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   | proto       | Application protocol used for         | Section 5.4 |
   |             | incoming request                      |             |
   +-------------+---------------------------------------+-------------+

                       Table 1: Initial assignments


10.  References

10.1.  Normative references

   [I-D.ietf-httpbis-p1-messaging]
              Fielding, R., Lafon, Y., and J. Reschke, "HTTP/1.1, part
              1: URIs, Connections, and Message Parsing",
              draft-ietf-httpbis-p1-messaging-19 (work in progress),
              March 2012.

   [I-D.ietf-httpbis-p4-conditional]
              Fielding, R., Lafon, Y., and J. Reschke, "HTTP/1.1, part
              4: Conditional Requests",
              draft-ietf-httpbis-p4-conditional-19 (work in progress),
              March 2012.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 35,
              RFC 4395, February 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.



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   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 2010.

10.2.  Informative references

   [RFC6269]  Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
              Roberts, "Issues with IP Address Sharing", RFC 6269,
              June 2011.


Appendix A.  Change Log (to be removed by RFC Editor before publication)

A.1.  Since draft-petersson-forwarded-for-00

   Added IANA considerations.

   Expanded scope and add parameterized list.

A.2.  Since draft-petersson-forwarded-for-01

   Removed "x-" from private extensions.

   Allow for any protocol name.

   Rename kv-v to forwarded-element and kv to forwarded-value.

   Add informative reference RFC6269.

A.3.  Since draft-petersson-forwarded-for-02

   Name change to draft-ietf-appsawg-http-forwarded-00.

   Updated proto in list under section 5 Parameters.

   Remove "hidden" but mention _hidden as an example in 6.3 Obfuscated
   identifier.

   Clarify that IPv6-addresses must be enclosed by square brackets.

   Restrict ext-value: do not allow "," or ";".

A.4.  Since draft-ietf-appsawg-http-forwarded-00

   Write IP address instead of IP number.




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   Remove BNF for IP addresses.

A.5.  Since draft-ietf-appsawg-http-forwarded-01

   Refer to httpbis instead of RFC2616.  Thereby also change to RFC5234
   ABNF.

   Split up ABNF to be more general on top level.

   Add some comments on draft-ietf-httpbis-p2-semantics-19#section-3.1
   to "Implementation Considerations"

   Removal of ABNF appendix.

   Merging of the sections "Private extensions" and "Future extensions".

A.6.  Since draft-ietf-appsawg-http-forwarded-02

   Require obfport to start with an underscore.

   Include "._-" as valid characters in obfnode.

   Remove MAY-references from section 5.

   Add a section about the relation to the via-header field.

   Add some privacy considerations.

   Encourage proxies to convert X-Forwarded-* to this format, when
   possible.

   Mention and demonstrate that IPv6-addresses must be quoted.

   Add motivation for the obfnode.

   Add some notes on when this header field should be preserved or not.

   Fix some typos and make some clarifications.

A.7.  Since draft-ietf-appsawg-http-forwarded-03

   Require that each parameter only occur once per instance.

   Request for a new registry at IANA.







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Authors' Addresses

   Andreas Petersson
   Opera Software
   S:t Larsgatan 12
   Linkoping  SE-582 24

   Email: pettson@opera.com


   Martin Nilsson
   Opera Software
   S:t Larsgatan 12
   Linkoping  SE-582 24

   Email: nilsson@opera.com



































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