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Network Working Group                                       M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Informational                                  J. Touch
Expires: March 5, 2012                                           USC/ISI
                                                                P. Levis
                                                          France Telecom
                                                                R. Penno
                                                        Juniper Networks
                                                       September 2, 2011


 Analysis of Solution Candidates to Reveal a Host Identifier in Shared
                          Address Deployments
             draft-boucadair-intarea-nat-reveal-analysis-04

Abstract

   This document analyzes a set of solution candidates which have been
   proposed to mitigate some of the issues encountered when address
   sharing is used.  In particular, this document focuses on means to
   reveal a host identifier when a Carrier Grade NAT (CGN) or
   application proxies are involved in the path.  This host identifier
   must be unique to each host under the same shared IP address.

   The ultimate goal is to assess the viability of proposed solutions
   and hopefully to make a recommendation on the more suitable
   solution(s).

Requirements Language

   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 RFC 2119 [RFC2119].

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."



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   This Internet-Draft will expire on March 5, 2012.

Copyright Notice

   Copyright (c) 2011 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.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Problem to Be Solved . . . . . . . . . . . . . . . . . . .  4
     1.2.  HOST_ID and Privacy  . . . . . . . . . . . . . . . . . . .  5
     1.3.  IPv6 May Also Be Concerned . . . . . . . . . . . . . . . .  6
     1.4.  Purpose and Scope  . . . . . . . . . . . . . . . . . . . .  6
   2.  Recommendations  . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Solutions Analysis . . . . . . . . . . . . . . . . . . . . . .  8
     3.1.  Define an IP Option  . . . . . . . . . . . . . . . . . . .  8
       3.1.1.  Description  . . . . . . . . . . . . . . . . . . . . .  8
       3.1.2.  Analysis . . . . . . . . . . . . . . . . . . . . . . .  9
     3.2.  Define a TCP Option  . . . . . . . . . . . . . . . . . . .  9
       3.2.1.  Description  . . . . . . . . . . . . . . . . . . . . .  9
       3.2.2.  Analysis . . . . . . . . . . . . . . . . . . . . . . .  9
     3.3.  Use the Identification Field of IP Header (IP-ID)  . . . . 10
       3.3.1.  Description  . . . . . . . . . . . . . . . . . . . . . 10
       3.3.2.  Analysis . . . . . . . . . . . . . . . . . . . . . . . 11
     3.4.  Inject Application Headers . . . . . . . . . . . . . . . . 11
       3.4.1.  Description  . . . . . . . . . . . . . . . . . . . . . 11
       3.4.2.  Analysis . . . . . . . . . . . . . . . . . . . . . . . 11
     3.5.  PROXY Protocol . . . . . . . . . . . . . . . . . . . . . . 12
       3.5.1.  Description  . . . . . . . . . . . . . . . . . . . . . 12
       3.5.2.  Analysis . . . . . . . . . . . . . . . . . . . . . . . 12
     3.6.  Enforce a Source-based Selection Algorithm at the
           Server Side (Port Set) . . . . . . . . . . . . . . . . . . 12
       3.6.1.  Description  . . . . . . . . . . . . . . . . . . . . . 12
       3.6.2.  Analysis . . . . . . . . . . . . . . . . . . . . . . . 13
     3.7.  Host Identity Protocol (HIP) . . . . . . . . . . . . . . . 13
       3.7.1.  Description  . . . . . . . . . . . . . . . . . . . . . 13
       3.7.2.  Analysis . . . . . . . . . . . . . . . . . . . . . . . 13
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16













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1.  Introduction

   As reported in [RFC6269], several issues are encountered when an IP
   address is shared among several subscribers.  Examples of such issues
   are listed below:

   o  Implicit identification (Section 13.2 of [RFC6269])
   o  SPAM (Section 13.3 of [RFC6269])
   o  Blacklisting a mis-behaving user (Section 13.1 of [RFC6269])
   o  Redirect users with infected machines to a dedicated portal
      (Section 5.1 of [RFC6269])

   The sole use of the IPv4 address is not sufficient to uniquely
   distinguish a host.  As a mitigation, it is tempting to investigate
   means which would help in disclosing an information to be used by the
   remote server as a means to uniquely disambiguate packets of hosts
   using the same IPv4 address.

   The risk of not mitigating these issues are: OPEX increase for IP
   connectivity service providers (costs induced by calls to a hotline),
   revenue loss for content providers (loss of users audience),
   customers unsatisfaction (low quality of experience, service
   segregation, etc.).

1.1.  Problem to Be Solved

   Observation:  Today, servers use the source IPv4 address as an
             identifier to treat some incoming connections differently.
             Tomorrow, due to the introduction of CGNs (e.g., NAT44
             [I-D.ietf-behave-lsn-requirements], NAT64 [RFC6146]), that
             address will be shared.  In particular, when a server
             receives packets from the same source address.  Because
             this address is shared, the server does not know which host
             is the sending host.
   Objective:  The server should be able to sort out the packets by
             sending host.
   Requirement:  The server must have extra information than the source
             IP address to differentiate the sending host.  We call
             HOST_ID this information.

   For all solutions analyzed, we provide answers to the following
   questions:

   What is the HOST_ID?  It must be unique to each host under the same
        IP address.  It does not need to be globally unique.  Of course,
        the combination of the (public) IPv4 source address and the
        identifier (i.e., HOST_ID) ends up being relatively unique.  As
        unique as today's 32-bit IPv4 addresses which, today, can change



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        when a host re-connects.

   Where is the HOST_ID? (which protocol, which field):  If the HOST_ID
        is put at the IP level, all packets will have to bear the
        identifier.  If it is put at a higher connection-oriented level,
        the identifier is only needed once in the session establishment
        phase (for instance TCP three-way-handshake), then, all packets
        received in this session will be attributed to the HOST_ID
        designated during the session opening.

   Who puts the HOST_ID?  For almost all the analyzed solutions, the
        address sharing function injects the HOST_ID.  When there are
        several address sharing functions in the data path, we describe
        to what extent the proposed solution is efficient.  Another
        option to avoid potential performance degradation is to let the
        host inject its HOST_ID but the address sharing function will
        check its content (just like an IP anti-spoofing function).

   What are the security considerations?  Security considerations are
        common to all analyzed solutions (see Section 5).  Privacy-
        related aspect are discussed in Section 1.2.

1.2.  HOST_ID and Privacy

   HOST_ID provides an additional information to uniquely disambiguate a
   host among those sharing the same IP address.  Unlike URIs, HOST_ID
   does not leak user's identity information.

   The HOST_ID does not reveal more privacy information than what the
   source IP address does in a non-shared address environment (see
   [I-D.morris-privacy-considerations]).

   The volatility of the HOST_ID information is similar to the source IP
   address: a distinct HOST_ID may be used by the address sharing
   function when the host reboots or gets a new internal IP address.  If
   the HOST_ID is persistent it may be used to track a host (similar to
   persistent IP addresses).

   The trust on the information conveyed in the HOST_ID is likely to be
   the same as for current practices with the source IP address.  In
   that sense, a HOST_ID can be spoofed as this is also the case for
   spoofing an IP address.

   It is the responsibility of the remote server to rely or not on the
   content of the HOST_ID to enforce its policies and to log or not the
   content conveyed in the HOST_ID.

   Enabling explicit identification means and adequate security suite is



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   more robust than relying on source IP address or HOST_ID.  But
   tension may appear between strong privacy and usability (see Section
   4.2 of [I-D.iab-privacy-workshop]).

1.3.  IPv6 May Also Be Concerned

   Issues similar to the ones described in Section 1.1 may be
   encountered also in an IPv6 environment (e.g., when the same /64 is
   used among several hosts).

1.4.  Purpose and Scope

   The purpose of this document is to analyze the solutions that have
   been proposed so far and to assess to what extent they solve the
   problem (see Section 1.1).

   The purpose of this document is not to argue in favor of mandating
   the use of a HOST_ID but to document encountered issues, proposed
   solutions and their limitations.

   Only IPv4-based solutions are analyzed in the following sections:

   o  define a new IP option (Section 3.1)
   o  define a new TCP option (Section 3.2)
   o  use the Identification field of IP header (denoted as IP-ID,
      Section 3.3)
   o  inject application headers (Section 3.4)
   o  enable Proxy Protocol ( (Section 3.5))
   o  use of port set (Section 3.6)
   o  activate HIP (Section 3.7).


2.  Recommendations

   The following Table 1 summarizes the approaches analyzed in this
   document.

   o  "Success ratio" indicates the ratio of successful communications
      when the option is used.  Provided figures are inspired from the
      results documented in [Options].
   o  "Deployable today" indicates if the solution can be generalized
      without any constraint on current architectures and practices.
   o  "Possible Perf Impact" indicates the level of expected performance
      degradation.  The rationale behind the indicated potential
      performance degradation is whether the injection requires some
      treatment at the IP level or not.





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   o  "OS TCP/IP Modif" indicates whether a modification of the OS
      TCP/IP stack is required at the server side.

              +-------+-------+-------+--------+----------+------+-----+
              | IP    | TCP   | IP-ID | HTTP   | Proxy    | Port | HIP |
              | Option| Option|       | Header | Protocol | Set  |     |
              |       |       |       | (XFF)  |          |      |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    UDP       | Yes   | No    | Yes   | No     | No       | Yes  |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    TCP       | Yes   | Yes   | Yes   | No     | Yes      | Yes  |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    HTTP      | Yes   | Yes   | Yes   | Yes    | Yes      | Yes  |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    Encrypted | Yes   | Yes   | Yes   | No     | Yes      | Yes  |     |
    Traffic   |       |       |       |        |          |      |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    Success   | 30%   | 99%   | 100%  | 100%   | Low      | 100% |Low  |
    Ratio     |       |       |       |        |          |      |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    Possible  | High  | Med   |  Low  |  Med   | High     | No   | N/A |
    Perf      |       |  to   |   to  |   to   |          |      |     |
    Impact    |       | High  |  Med  |  High  |          |      |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    OS TCP/IP | Yes   | Yes   | Yes   | No     | No       | No   |     |
    Modif     |       |       |       |        |          |      |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    Deployable| Yes   | Yes   | Yes   | Yes    | No       | Yes  | No  |
    Today     |       |       |       |        |          |      |     |
    ----------+-------+-------+-------+--------+----------+------+-----+
    Notes     |       |       |  (1)  |  (2)   |          | (1)  | (4) |
              |       |       |       |        |          | (3)  | (5) |
    ----------+-------+-------+-------+--------+----------+------+-----+

                  Table 1: Summary of analyzed solutions.

   Notes for the above table:
   (1)  Requires mechanism to advertise NAT is participating in this
        scheme (e.g., DNS PTR record)
   (2)  This solution is widely deployed
   (3)  When the port set is not advertised, the solution is less
        efficient for third-party services.
   (4)  Requires the client and the server to be HIP-compliant and HIP
        infrastructure to be deployed.







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   (5)  If the client and the server are HIP-enabled, the address
        sharing function does not need to insert a host-hint.  If the
        client is not HIP-enabled, designing the device that performs
        address sharing to act as a UDP/TCP-HIP relay is not viable.

   According to the above table and the analysis elaborated in
   Section 3:

   o  IP Option, IP-ID and Proxy Protocol proposals are broken;

   o  HIP is not largely deployed;

   o  The use of Port Set may contradict the port randomization
      [RFC6056] requirement identified in [RFC6269].  This solution can
      be used by a service provider for the delivery of its own service
      offerings relying on implicit identification.

   o  XFF is de facto standard deployed and supported in operational
      networks (e.g., HTTP Severs, Load-Balancers, etc.).

   o  From an application standpoint, the TCP Option is superior to XFF
      since it is not restricted to HTTP.  Nevertheless XFF is
      compatible with the presence of address sharing and load-balancers
      in the communication path.  To provide a similar functionality,
      the TCP Option may be extended to allow conveying a list of IP
      addresses to not loose the source IP address in the presence of
      load-balancers.  Note that TCP Option requires the modification of
      the OS TCP/IP stack of remote servers; which can be seen as a
      blocking point.

   As a conclusion of this analysis, the following recommendation is
   made:

      [Hopefully to be completed]


3.  Solutions Analysis

3.1.  Define an IP Option

3.1.1.  Description

   This proposal aims to define an IP option [RFC0791] to convey a "host
   identifier".  This identifier can be inserted by the address sharing
   function to uniquely distinguish a host among those sharing the same
   IP address.  The option can convey an IPv4 address, the prefix part
   of an IPv6 address, etc.




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   Another way for using IP option has been described in Section 4.6 of
   [RFC3022].

3.1.2.  Analysis

   Unlike the solution presented in Section 3.2, this proposal can apply
   for any transport protocol.  Nevertheless, it is widely known that
   routers (and other middle boxes) filter IP options.  IP packets with
   IP options can be dropped by some IP nodes.  Previous studies
   demonstrated that "IP Options are not an option" (Refer to
   [Not_An_Option], [Options]).

   As a conclusion, using an IP option to convey a host-hint is not
   viable.

3.2.  Define a TCP Option

3.2.1.  Description

   This proposal [I-D.wing-nat-reveal-option] defines a new TCP option
   called USER_HINT.  This option encloses the TCP client's identifier
   (e.g., the lower 16 bits of their IPv4 address, their VLAN ID, VRF
   ID, subscriber ID).  The address sharing device inserts this TCP
   option to the TCP SYN packet.

3.2.2.  Analysis

   The risk related to handling a new TCP option is low as measured in
   [Options].

   [I-D.wing-nat-reveal-option] discusses the interference with other
   TCP options.

   Using a new TCP option to convey the host-hint does not require any
   modification to the applications but it is applicable only for TCP-
   based applications.  Applications relying on other transport
   protocols are therefore left unsolved.

   Some downsides have been raised against defining a TCP option to
   reveal a host identity:

   o  Conveying an IP address in a TCP option may be seen as a violation
      of OSI layers but since IP addresses are already used for the
      checksum computation, this is not seen as a blocking point.
      Moreover, Updated version of [I-D.wing-nat-reveal-option] does not
      allow anymore to convey an IP address (the HOST_ID is encoded in
      16bits).




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   o  TCP option space is limited, and might be consumed by the TCP
      client.  Earlier versions of [I-D.wing-nat-reveal-option] discuss
      two approaches to sending the HOST_ID: sending the HOST_ID in the
      TCP SYN (which consumes more bytes in the TCP header of the TCP
      SYN) and sending the HOST_ID in a TCP ACK (which consumes only two
      bytes in the TCP SYN).  Content providers may find it more
      desirable to receive the HOST_ID in the TCP SYN, as that more
      closely preserves the host hint received in the source IP address
      as per current practices.  It is more complicated to implement
      sending the HOST_ID in a TCP ACK, as it can introduce MTU issues
      if the ACK packet also contains TCP data, or a TCP segment is
      lost.  The latest specification of the HOST_ID TCP Option,
      documented at [I-D.wing-nat-reveal-option], allows only to enclose
      the HOST_ID in the TCP SYN packet.

   o  When there are several NATs in the path, the original HOST_ID may
      be lost.  In such case, the procedure may not be efficient.

   o  Interference with current usages such as X-Forwarded-For (see
      Section 3.4) should be elaborated to specify the behavior of
      servers when both options are used; in particular specify which
      information to use: the content of the TCP option or what is
      conveyed in the application headers.

   o  When load-balancers or proxies are in the path, this option does
      not allow to preserve the original source IP address and source.
      Preserving such information is required for logging purposes for
      instance.

3.3.  Use the Identification Field of IP Header (IP-ID)

3.3.1.  Description

   IP-ID (Identification field of IP header) can be used to insert an
   information which uniquely distinguishes a host among those sharing
   the same IPv4 address.  An address sharing function can re-write the
   IP-ID field to insert a value unique to the host (16 bits are
   sufficient to uniquely disambiguate hosts sharing the same IP
   address).  Note that this field is not altered by some NATs; hence
   some side effects such as counting hosts behind a NAT as reported in
   [Count].

   A variant of this approach relies upon the format of certain packets,
   such as TCP SYN, where the IP-ID can be modified to contain a 16 bit
   host-hint.  Address sharing devices performing this function would
   require to indicate they are performing this function out of band,
   possibly using a special DNS record.




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3.3.2.  Analysis

   This usage is not compliant with what is recommended in
   [I-D.ietf-intarea-ipv4-id-update].

3.4.  Inject Application Headers

3.4.1.  Description

   Another option is to not require any change at the transport nor the
   IP levels but to convey at the application payload the required
   information which will be used to disambiguate hosts.  This format
   and the related semantics depend on its application (e.g., HTTP, SIP,
   SMTP, etc.).

   For HTTP, the X-Forwarded-For (XFF) header can be used to display the
   original IP address when an address sharing device is involved.
   Service Providers operating address sharing devices can enable the
   feature of injecting the XFF header which will enclose the original
   IPv4 address or the IPv6 prefix part.  The address sharing device has
   to strip all included XFF headers before injecting their own.
   Servers may rely on the contents of this field to enforce some
   policies such as blacklisting misbehaving users.  Note that XFF can
   also be logged by some servers (this is for instance supported by
   Apache).

3.4.2.  Analysis

   Not all applications impacted by the address sharing can support the
   ability to disclose the original IP address.  Only a subset of
   protocols (e.g., HTTP) can rely on this solution.

   For the HTTP case, to prevent users injecting invalid host-hints, an
   initiative has been launched to maintain a list of trusted ISPs using
   XFF: See for example the list available at: [Trusted_ISPs] of trusted
   ISPs as maintained by Wikipedia.  If an address sharing device is on
   the trusted XFF ISPs list, users editing Wikipedia located behind the
   address sharing device will appear to be editing from their
   "original" IP address and not from the NATed IP address.  If an
   offending activity is detected, individual hosts can be blacklisted
   instead of all hosts sharing the same IP address.

   XFF header injection is a common practice of load balancers.  When a
   load balancer is in the path, the original content of any included
   XFF header should not be stripped.  Otherwise the information about
   the "origin" IP address will be lost.

   When several address sharing devices are crossed, XFF header can



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   convey the list of IP addresses.  The origin HOST_ID can be exposed
   to the target server.

   XFF also introduces some implementation complexity if the HTTP packet
   is at or close to the MTU size.

   It has been reported that some "poor" implementation may encounter
   some parsing issues when injecting XFF header.

   For encrypted HTTP traffic, injecting XFF header may be broken.

3.5.  PROXY Protocol

3.5.1.  Description

   The solution, referred to as Proxy Protocol [Proxy], does not require
   any application-specific knowledge.  The rationale behind this
   solution is to prepend each connection with a line reporting the
   characteristics of the other side's connection as shown in the
   example below (excerpt from [Proxy]):

       PROXY TCP4 198.51.100.1 198.51.100.11 56324 443\r\n

   Upon receipt of a message conveying this line, the server removes the
   line.  The line is parsed to retrieve the transported protocol.  The
   content of this line is recorded in logs and used to enforce
   policies.

3.5.2.  Analysis

   This solution can be deployed in a controlled environment but it can
   not be deployed to all access services available in the Internet.  If
   the remote server does not support the Proxy Protocol, the session
   will fail.  Other complications will raise due to the presence of
   firewalls for instance.

   As a consequence, this solution is broken and can not be recommended.

3.6.  Enforce a Source-based Selection Algorithm at the Server Side
      (Port Set)

3.6.1.  Description

   This solution proposal does not require any action from the address
   sharing function to disclose a host identifier.  Instead of assuming
   all the ports are associated with the same host, a random-based
   algorithm (or any port selection method) is run to generate the set
   of ports (including the source port of the received packet).  The



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   length of the ports set to be generated by the server may be
   configurable (e.g., 8, 32, 64, 512, 1024, etc.).  Instead of a
   random-based scheme, the server can use contiguous port ranges to
   form the port sets.

   The server may reduce (or enlarge) the width of the ports set of the
   misbehaving action is (not) mitigated.

   A variant of this proposal is to announce by off-line means the port
   set assignment policy of an operator.  This announcement is not
   required for the delivery of internal services (i.e., offered by the
   service provider deploying the address sharing function) relying on
   implicit identification.

3.6.2.  Analysis

   In nominal mode, no coordination is required between the address
   sharing function and the server side but the efficiency of the method
   depends on the port set selection algorithm.

   The method is more efficient if the provider that operates the
   address sharing device advertises its port assignment policy but this
   may contradicts the port randomization as identified in [RFC6269].

   The method is deterministic for the delivery of services offered by
   the service provider offering also the IP connectivity service.

3.7.  Host Identity Protocol (HIP)

3.7.1.  Description

   [RFC5201] specifies an architecture which introduces a new namespace
   to convey an identity information.

3.7.2.  Analysis

   This solution requires both the client and the server to support HIP
   [RFC5201].  Additional architectural considerations are to be taken
   into account such as the key exchanges, etc.

   If the address sharing function is required to act as a UDP/TCP-HIP
   relay, this is not a viable option.


4.  IANA Considerations

   This document does not require any action from IANA.




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5.  Security Considerations

   The same security concerns apply for the injection of an IP option,
   TCP option and application-related content (e.g., XFF) by the address
   sharing device.  If the server trusts the content of the HOST_ID
   field, a third party user can be impacted by a misbehaving user to
   reveal a "faked" original IP address.


6.  Acknowledgments

   Many thanks to D. Wing and C. Jacquenet for their review, comments
   and inputs.

   Thanks also to P. McCann, T. Tsou, Z. Dong, B. Briscoe, T. Taylor, M.
   Blanchet, D. Wing and A. Yourtchenko for the discussions in Prague.

   Some of the issues related to defining a new TCP option have been
   raised by L. Eggert.


7.  References

7.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

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

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              January 2001.

   [RFC6056]  Larsen, M. and F. Gont, "Recommendations for Transport-
              Protocol Port Randomization", BCP 156, RFC 6056,
              January 2011.

7.2.  Informative References

   [Count]    "A technique for counting NATted hosts",
              <http://www.cs.columbia.edu/~smb/papers/fnat.pdf>.

   [I-D.iab-privacy-workshop]
              Cooper, A., "Report from the Internet Privacy Workshop",
              draft-iab-privacy-workshop-00 (work in progress),
              June 2011.



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   [I-D.ietf-behave-lsn-requirements]
              Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common requirements for Carrier Grade NAT
              (CGN)", draft-ietf-behave-lsn-requirements-03 (work in
              progress), August 2011.

   [I-D.ietf-intarea-ipv4-id-update]
              Touch, J., "Updated Specification of the IPv4 ID Field",
              draft-ietf-intarea-ipv4-id-update-02 (work in progress),
              March 2011.

   [I-D.morris-privacy-considerations]
              Aboba, B., Morris, J., Peterson, J., and H. Tschofenig,
              "Privacy Considerations for Internet Protocols",
              draft-morris-privacy-considerations-03 (work in progress),
              March 2011.

   [I-D.wing-nat-reveal-option]
              Yourtchenko, A. and D. Wing, "Revealing hosts sharing an
              IP address using TCP option",
              draft-wing-nat-reveal-option-02 (work in progress),
              June 2011.

   [Not_An_Option]
              R. Fonseca, G. Porter, R. Katz, S. Shenker, and I.
              Stoica,, "IP options are not an option", 2005, <http://
              www.eecs.berkeley.edu/Pubs/TechRpts/2005/
              EECS-2005-24.html>.

   [Options]  Alberto Medina, Mark Allman, Sally Floyd, "Measuring
              Interactions Between Transport Protocols and Middleboxes",
              2005, <http://conferences.sigcomm.org/imc/2004/papers/
              p336-medina.pdf>.

   [Proxy]    Tarreau, W., "The PROXY protocol", November 2010, <http://
              haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt>.

   [RFC5201]  Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
              "Host Identity Protocol", RFC 5201, April 2008.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

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




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   [Trusted_ISPs]
              "Trusted XFF list", <http://meta.wikimedia.org/wiki/
              XFF_project#Trusted_XFF_list>.


Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes,   35000
   France

   Email: mohamed.boucadair@orange-ftgroup.com


   Joe Touch
   USC/ISI


   Email: touch@isi.edu


   Pierre Levis
   France Telecom
   Caen,   14000
   France

   Email: pierre.levis@orange-ftgroup.com


   Reinaldo Penno
   Juniper Networks
   1194 N Mathilda Avenue
   Sunnyvale, California  94089
   USA

   Email: rpenno@juniper.net














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