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Versions: (draft-penno-behave-64-analysis) 00 01 02 03 04 05 06 07 RFC 6889

Behavior Engineering for Hindrance                              R. Penno
Avoidance                                               Juniper Networks
Internet-Draft                                                 T. Saxena
Intended status: Informational                             Cisco Systems
Expires: June 25, 2012                                      M. Boucadair
                                                          France Telecom
                                                            S. Sivakumar
                                                           Cisco Systems
                                                       December 23, 2011


                  Analysis of Stateful 64 Translation
                    draft-ietf-behave-64-analysis-05

Abstract

   Due to specific problems, NAT-PT was deprecated by the IETF as a
   mechanism to perform IPv6-IPv4 translation.  Since then, new efforts
   have been undertaken within IETF to standardize alternative
   mechanisms to perform IPv6-IPv4 translation.  This document evaluates
   how the new stateful translation mechanisms avoid the problems that
   caused the IETF to deprecate NAT-PT.

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."

   This Internet-Draft will expire on June 25, 2012.

Copyright Notice




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   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Definition . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Context  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.3.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Analysis of 64 Translation Against Concerns of RFC4966 . . . .  4
     2.1.  Problems Impossible to Solve . . . . . . . . . . . . . . .  5
     2.2.  Problems Which Can be Solved . . . . . . . . . . . . . . .  5
     2.3.  Problems Solved  . . . . . . . . . . . . . . . . . . . . .  7
   3.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14



















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1.  Introduction

1.1.  Definition

   This document uses stateful 64 (or 64 for short) to refer to the
   mechanisms defined in the following documents:

   o  IP/ICMP Translation Algorithm [RFC6145]

   o  Stateful NAT64: Network Address and Protocol Translation from IPv6
      Clients to IPv4 Servers [RFC6146]

   o  DNS64: DNS extensions for Network Address Translation from IPv6
      Clients to IPv4 Servers [RFC6147]

   o  IPv6 Addressing of IPv4/IPv6 Translators [RFC6052]

   o  Framework for IPv4/IPv6 Translation [RFC6144]

1.2.  Context

   Stateful 64 is widely seen as a major interconnection technique
   designed to enable communications between IPv6-only and IPv4-only
   networks.  One of the building blocks of the stateful 64 is
   decoupling the DNS functionality from the protocol translation
   itself.

   This approach is pragmatic in the sense that there is no dependency
   on DNS implementation for the successful NAT handling.  As long as
   there is a function (e.g., DNS64 [RFC6147] or other means) that can
   construct an IPv6-embedded IPv4 address with a pre-configured IPv6
   prefix, an IPv4 address and a suffix (refer to [RFC6052]), NAT64 will
   work just fine.

   The focus of the stateful 64 is on the deployment and not the
   implementation details.  As long as a NAT64 implementation conforms
   to the expected behavior, as desired in the deployment scenario, the
   details are not very important as mentioned in this excerpt from
   [RFC6146]:

      "A NAT64 MAY perform the steps in a different order, or MAY
      perform different steps, but the externally visible outcome MUST
      be the same as the one described in this document."








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1.3.  Scope

   This document provides an analysis of how the proposed set of
   documents that specify stateful IPv6-only to IPv4-only translation
   and replace NAT-PT [RFC2766] address the issues raised in [RFC4966].

   As a reminder, it is worth mentioning the analysis is limited in the
   sense that hosts from IPv6 networks can initiate a communication to
   IPv4 network/Internet, but not vice-versa.  This corresponds to
   Scenario 1 and Scenario 5 described in [RFC6144].  Hence, the
   scenario of servers moving to IPv6 while clients remaining IPv4
   remains unaddressed.  Of course, IPv6 to IPv4 communications can also
   be supported if static or explicit bindings (e.g.,
   [I-D.ietf-pcp-base]) are configured on the stateful NAT64.

   Stateful 64, just like any other technique under development, has
   some positives and some drawbacks.  The ups and downs of the proposal
   must be clearly understood while going forward with its future
   development.

   The scope of this document does not include stateless translation.


2.  Analysis of 64 Translation Against Concerns of RFC4966

   Of the set of problems pointed out in [RFC4966], the stateful 64
   addresses some of them, whereas leaves others unaddressed.

   Some issues mentioned in [RFC4966] were solved by [RFC4787],
   [RFC5382] and [RFC5508].  At the time when NAT-PT was published these
   recommendations were not in place but they are orthogonal to the
   translation algorithm per se, therefore they could be implemented
   with NAT-PT.  On the other hand, NAT64 [RFC6146] explicitly mentions
   that these recommendations need to be followed and thus should be
   seen as a complete specification.

   It is also worth pointing out that the scope of the stateful 64 is
   reduced when compared to NAT-PT.  Following is a point by point
   analysis of the problems.  Issues listed in [RFC4966] are classified
   into three categories:

   1.  Problems impossible to solve;

   2.  Problems which can be solved.

   3.  Problems solved.





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2.1.  Problems Impossible to Solve

   Problems discussed in [RFC4966], which are impossible to solve:

   1.  Inability to redirect traffic for protocols that lack de-
       multiplexing capabilities or are not built on top of specific
       transport-layer protocols for transport address translations
       (Section 2.2 of [RFC4966]).

          Analysis: This issue is not specific to 64 but to all NAT-
          based solutions.

   2.  Loss of information due to incompatible semantics between IPv4
       and IPv6 versions of headers and protocols (Section 2.4 of
       [RFC4966]).

          Analysis: This issue is not specific to 64 but due to the
          design of IPv4 and IPv6.

   3.  Need for the NAT64-capable device to act as proxy for
       correspondent node when IPv6 node is mobile, with consequent
       restrictions on mobility (Section 2.7 of [RFC4966]).

          Analysis: This is not specific to NAT64 but to all NAT
          flavors.  Refer to [I-D.haddad-mext-nat64-mobility-harmful]
          for an early analysis on mobility complications encountered
          when NAT64 is involved.

2.2.  Problems Which Can be Solved

   Problems discussed in [RFC4966], which can be solved:

   1.  Disruption of all protocols that embed IP addresses (and/or
       ports) in packet payloads or apply integrity mechanisms using IP
       addresses (and ports) (Section 2.1 of [RFC4966]).

          Analysis: In the case of FTP [RFC0959] this problem can be
          mitigated in several ways (e.g., use a FTP64 ALG [RFC6384] or
          in the FTP client (e.g., [I-D.ietf-ftpext2-ftp64])).

          In the case of SIP [RFC3261], no specific issue is induced by
          64; the same techniques for NAT traversal can be used when a
          NAT64 is involved in the path (e.g., ICE [RFC5245], maintain
          SIP-related NAT bindings as per Section 3.4 of [RFC5853],
          media latching [I-D.ietf-mmusic-media-path-middleboxes],
          embedded SIP ALGs, etc.).  [RFC6157] provides more discussion
          on how to establish SIP sessions between IPv4 and IPv6 SIP
          user agents.



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          The functioning of other protocols is left for future study.
          Note that the traversal of NAT64 by application embedding IP
          address literal is not specific to NAT64 but generic to all
          NAT-based solutions.

   2.  Interaction with SCTP [RFC4960] and multihoming (Section 2.6 of
       [RFC4966]).

          Analysis: Only TCP and UDP transport protocols are within the
          scope of NAT64 [RFC6146].  SCTP is out of scope of this
          document.

   3.  Inability to handle multicast traffic (Section 2.8 of [RFC4966]).

          Analysis: This problem is not addressed by the current 64
          specifications.

   4.  Scalability concerns together with introduction of a single point
       of failure and a security attack nexus (Section 3.2 of
       [RFC4966]).

          Analysis: This is not specific to NAT64 but to all stateful
          NAT flavors.  The presence of single point of failures is
          deployment-specific.

   5.  Restricted validity of translated DNS records: a translated
       record may be forwarded to an application that cannot use it
       (Section 4.2 of [RFC4966]).

          Analysis: If a node on the IPv4 side forwards the address of
          the other endpoint to a node which cannot reach the NAT box or
          is not covered under the endpoint-independent constraint of
          NAT, then the new node will not be able to initiate a
          successful session.

          Actually, this is not a limitation of 64 (or even NAT-PT) but
          a deployment context where shared IPv4 addresses managed by
          the NAT64 are not globally reachable.  The same limitation can
          be encountered when referrals (even without any NAT in the
          path) include reachability information with limited
          reachability scope (See [I-D.carpenter-behave-referral-object]
          for more discussion about issues related to reachability
          scope).

   6.  Unless UDP encapsulation is used for IPsec [RFC3948], traffic
       using IPsec AH (Authentication Header), in transport and tunnel
       mode, and IPsec ESP (Encapsulating Security Payload), in
       transport mode, is unable to be carried through NAT-PT without



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       terminating the security associations on the NAT-PT, due to their
       usage of cryptographic integrity protection (Section 4.5 of
       [RFC4966]).

          Analysis: This is not specific to NAT64 but to all NAT
          flavors.

   7.  Address selection issues when either the internal or external
       hosts implement both IPv4 and IPv6 (Section 4.1 of [RFC4966]).

          Analysis: This is out of scope of 64 since Scenarios 1 and 5
          of [RFC6144] assume IPv6-only hosts.

          Therefore this issue is not resolved and mitigation techniques
          outside the 64 need to be used (e.g.,
          [I-D.ietf-6man-addr-select-opt]).  These techniques may allow
          to offload NAT64 resources and prefer native communications
          which do not involve address family translation.  Avoiding NAT
          devices in the path is encouraged for mobile nodes in order to
          save power consumption due to keepalive messages which are
          required to maintain NAT states ("always-on" services).  An
          in-depth discussion can be found in
          [I-D.wing-behave-dns64-config].

2.3.  Problems Solved

   Problems, identified in [RFC4966], which are solved:

   1.  Constraints on network topology (as it relates to DNS-ALG; see
       Section 3.1 of [RFC4966]).

          Analysis: This issue has mitigated severity as the DNS is
          separated from the NAT functionality.  Nevertheless, a minimal
          coordination may be required to ensure that the NAT64 to be
          crossed (the one to which the IPv4-Converted IPv6 address
          returned to a requesting host) must be in the path and has
          also sufficient resources to handle received traffic.

   2.  Need for additional state and/or packet reconstruction in dealing
       with packet fragmentation.  Otherwise, implement no support for
       fragments.  (Section 2.5 of [RFC4966])

          Analysis: This issue is not specific to 64 but to all NAT-
          based solutions.  [RFC6146] specifies how to handle
          fragmentation; appropriate recommendations to avoid
          fragmentation-related DoS attacks are proposed (e.g., limit
          resources to be dedicated to out of order fragments).




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   3.  Inappropriate translation of responses to A queries from IPv6
       nodes (Section 4.3 of [RFC4966]).

          Analysis: DNS64 [RFC6147] does not alter A queries.

   4.  Address selection issues and resource consumption in a DNS-ALG
       with multi-addressed nodes (Section 4.4 of [RFC4966]).

          Analysis: Since no DNS-ALG is required to be co-located with
          NAT64, there is no need to maintain temporary states in
          anticipation of connections.  Note that explicit bindings (See
          Section 3 of [I-D.ietf-pcp-base]) are required to allow for
          communications initiated from an IPv4-only client to an IPv6-
          only server.

   5.  Limitations on DNS security capabilities when using a DNS-ALG
       (Section 2.5 of [RFC4966]).

          Analysis: A DNSSEC validating stub resolver behind a DNS64 in
          server mode is not supported.  Therefore if a host wants to do
          its own DNSSEC validation, and it wants to use a NAT64, the
          host has to also perform its own DNS64 synthesis.  Refer to
          Section 3 of[RFC6147] for more details.

   6.  Creation of a DoS (Denial of Service) threat relating to
       exhaustion of memory and address/port pool resources on the
       translator (Section 3.4 of [RFC4966]).

          Analysis: This specific DoS concern on Page 6 of [RFC4966] is
          under a DNS-ALG heading in that document, and refers to NAT-
          PT's creation of NAT mapping state when a DNS query occurred.
          With the new IPv6-IPv4 translation mechanisms, DNS queries do
          not create any mapping state in the NAT64.

          To mitigate the exhaustion of port pool issue (Section 3.4 of
          [RFC4966]), 64 must enforce a port limit similar to the one
          defined in [I-D.ietf-behave-lsn-requirements].

          Thus, this concern can be fully eliminated in 64.

   7.  Requirement for applications to use keepalive mechanisms to
       workaround connectivity issues caused by premature timeout for
       session table and BIB entries (Section 2.3 of [RFC4966]).

          Analysis: Since NAT64 follows some of the [RFC4787], [RFC5382]
          and [RFC5508] requirements, there is a high lower bound for
          the lifetime of sessions.  In NAT-PT this was unknown and
          applications needed to assume the worst case.  For instance,



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          in NAT64, the lifetime for a TCP session is approximately 2
          hours, so not much keep-alive signaling overhead is needed.

          Application clients (e.g., VPN clients) are not aware of the
          timer configured in the NAT device.  For unmanaged services, a
          conservative approach would be adopted by applications which
          issue frequent keepalive messages to be sure that an active
          mapping is still be maintained by any involved NAT64 device
          even if the NAT64 complies with TCP/UDP/ICMP BEHAVE WG
          specifications.

          Note that keepalive messages may be issued by applications to
          ensure that an active entry is maintained by a firewall, with
          or without a NAT in the path, which is located in the
          boundaries of a local domain.

   8.  Lack of address mapping persistence: Some applications require
       address retention between sessions.  The user traffic will be
       disrupted if a different mapping is used.  The use of the DNS-ALG
       to create address mappings with limited lifetimes means that
       applications must start using the address shortly after the
       mapping is created, as well as keep it alive once they start
       using it.  (Section 3.3 of [RFC4966])

          Analysis: In the following, address persistence is used to
          refer to the support of "IP address pooling" behavior of
          "Paired" [RFC4787].

          In the context of 64, the external IPv4 address (representing
          the IPv6 host in the IPv4 network) is assigned by the NAT64
          machinery and not the DNS64 function.  Address persistence can
          be therefore easily ensured by the NAT64 function (which
          complies with BEHAVE NAT recommendations [RFC4787][RFC5382]).
          Address persistence should be guaranteed for both dynamic and
          static bindings.

          In the IPv6 side of the NAT64, the same IPv6 address is used
          to represent an IPv4 host; no issue about address persistence
          is raised in IPv6 network.


3.  Conclusions

   The above analysis of the solutions provided by the stateful 64 shows
   that the majority of the problems that are not directly related to
   the decoupling of NAT and DNS remain unaddressed.  Some of these
   problems are not specific to 64 but are generic to all NAT-based
   solutions.



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   This points to several shortcomings of stateful 64 which must be
   addressed if the future network deployments have to move reliably
   towards 64 as a solution to IPv6-IPv4 interconnection.

   Some of the issues, as pointed out in [RFC4966], have possible
   solutions.  However these solutions will require significant updates
   to the stateful 64, increasing its complexity.

   The following table summarizes the conclusions based on the analysis
   of stateful 64.

   +---------------+----------+---------+----------+---------+---------+
   |     Issue     |  NAT-PT  |  Exists |  DNS ALG | Generic |  Can be |
   |               | Specific |    in   | Specific |   NAT   | solved? |
   |               |          |  NAT64  |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |   Protocols   |    No    |   Yes   |    No    |   Yes   |   Yes   |
   |   embedding   |          |         |          |         |         |
   |   addresses   |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |   Protocols   |    No    |   Yes   |    No    |   Yes   |    No   |
   | without demux |          |         |          |         |         |
   |   capability  |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   | Binding state |    No    |   Yes   |    No    |   Yes   |   Yes   |
   |     decay     |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |    Loss of    |    No    |   Yes   |    No    |    No   |    No   |
   |  information  |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   | Fragmentation |    No    |    No   |    No    |   Yes   |   Yes   |
   +---------------+----------+---------+----------+---------+---------+
   |    SCTP and   |    No    |   Yes   |    No    |   Yes   |   Yes   |
   |  Multihoming  |          |         |          |         |         |
   |  interaction  |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |     Proxy     |    No    |   Yes   |    No    |    No   |    No   |
   | correspondent |          |         |          |         |         |
   |    node for   |          |         |          |         |         |
   |     MIPv6     |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |   Multicast   |    No    |   Yes   |    No    |   Yes   |   Yes   |
   +---------------+----------+---------+----------+---------+---------+
   |    Topology   |    Yes   |    No   |    Yes   |    No   |   Yes   |
   |  constraints  |          |         |          |         |         |
   |  with DNS-ALG |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+




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   +---------------+----------+---------+----------+---------+---------+
   |   Scale and   |    No    |   Yes   |    No    |   Yes   |   Yes   |
   |  Single point |          |         |          |         |         |
   |   of failure  |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |    Lack of    |    No    |   Yes   |    No    |   Yes   |   Yes   |
   |    address    |          |         |          |         |         |
   |  persistence  |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |  DoS attacks  |    No    |   Yes   |    No    |   Yes   |   Yes   |
   +---------------+----------+---------+----------+---------+---------+
   |    Address    |    Yes   |    No   |    Yes   |    No   |   Yes   |
   |   selection   |          |         |          |         |         |
   |  issues with  |          |         |          |         |         |
   |   Dual stack  |          |         |          |         |         |
   |     hosts     |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |   Non-global  |    Yes   |    No   |    Yes   |    No   |   Yes   |
   |  validity of  |          |         |          |         |         |
   | Translated RR |          |         |          |         |         |
   |    records    |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |   Incorrect   |    Yes   |    No   |    Yes   |    No   |   Yes   |
   |  translation  |          |         |          |         |         |
   |      of A     |          |         |          |         |         |
   |   responses   |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |  DNS-ALG and  |    No    |   Yes   |    No    |   Yes   |   Yes   |
   |     Multi-    |          |         |          |         |         |
   |   addressed   |          |         |          |         |         |
   |     nodes     |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+
   |     DNSSEC    |    No    |   Yes   |    No    |   Yes   |   Yes   |
   |  limitations  |          |         |          |         |         |
   +---------------+----------+---------+----------+---------+---------+

                    Table 1: Summary of NAT64 analysis


4.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.






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5.  Security Considerations

   This document does not specify any new protocol or architecture.  It
   only analyzes how BEHAVE WG 64 documents mitigate concerns raised in
   [RFC4966] and which ones are still unaddressed.


6.  Acknowledgements

   Many thanks to M. Bagnulo, D. Wing, X. Li and D. Anipko for their
   review and comments.


7.  References

7.1.  Normative References

   [RFC0959]  Postel, J. and J. Reynolds, "File Transfer Protocol",
              STD 9, RFC 959, October 1985.

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

   [RFC2766]  Tsirtsis, G. and P. Srisuresh, "Network Address
              Translation - Protocol Translation (NAT-PT)", RFC 2766,
              February 2000.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3948]  Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets",
              RFC 3948, January 2005.

   [RFC4787]  Audet, F. and C. Jennings, "Network Address Translation
              (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
              RFC 4787, January 2007.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [RFC4966]  Aoun, C. and E. Davies, "Reasons to Move the Network
              Address Translator - Protocol Translator (NAT-PT) to
              Historic Status", RFC 4966, July 2007.

   [RFC5382]  Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.



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              Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
              RFC 5382, October 2008.

   [RFC5508]  Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
              Behavioral Requirements for ICMP", BCP 148, RFC 5508,
              April 2009.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC6144]  Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation", RFC 6144, April 2011.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.

   [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.

   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              April 2011.

7.2.  Informative References

   [I-D.carpenter-behave-referral-object]
              Carpenter, B., Boucadair, M., Halpern, J., Jiang, S., and
              K. Moore, "A Generic Referral Object for Internet
              Entities", draft-carpenter-behave-referral-object-01 (work
              in progress), October 2009.

   [I-D.haddad-mext-nat64-mobility-harmful]
              Haddad, W. and C. Perkins, "A Note on NAT64 Interaction
              with Mobile IPv6",
              draft-haddad-mext-nat64-mobility-harmful-02 (work in
              progress), March 2011.

   [I-D.ietf-6man-addr-select-opt]
              Matsumoto, A., Fujisaki, T., Kato, J., and T. Chown,
              "Distributing Address Selection Policy using DHCPv6",
              draft-ietf-6man-addr-select-opt-01 (work in progress),
              June 2011.

   [I-D.ietf-behave-lsn-requirements]
              Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,



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              and H. Ashida, "Common requirements for Carrier Grade NATs
              (CGNs)", draft-ietf-behave-lsn-requirements-05 (work in
              progress), November 2011.

   [I-D.ietf-ftpext2-ftp64]
              Liu, D., Beijnum, I., and Z. Cao, "FTP extension for IPv4/
              IPv6 transition", draft-ietf-ftpext2-ftp64-01 (work in
              progress), July 2011.

   [I-D.ietf-mmusic-media-path-middleboxes]
              Stucker, B. and H. Tschofenig, "Analysis of Middlebox
              Interactions for Signaling Protocol Communication along
              the Media Path",
              draft-ietf-mmusic-media-path-middleboxes-03 (work in
              progress), July 2010.

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-19 (work in progress), December 2011.

   [I-D.wing-behave-dns64-config]
              Wing, D., "IPv6-only and Dual Stack Hosts on the Same
              Network with DNS64", draft-wing-behave-dns64-config-03
              (work in progress), February 2011.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              April 2010.

   [RFC5853]  Hautakorpi, J., Camarillo, G., Penfield, R., Hawrylyshen,
              A., and M. Bhatia, "Requirements from Session Initiation
              Protocol (SIP) Session Border Control (SBC) Deployments",
              RFC 5853, April 2010.

   [RFC6157]  Camarillo, G., El Malki, K., and V. Gurbani, "IPv6
              Transition in the Session Initiation Protocol (SIP)",
              RFC 6157, April 2011.

   [RFC6384]  van Beijnum, I., "An FTP Application Layer Gateway (ALG)
              for IPv6-to-IPv4 Translation", RFC 6384, October 2011.









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Authors' Addresses

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

   Email: rpenno@juniper.net


   Tarun Saxena
   Cisco Systems


   Email: tasaxena@cisco.com


   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Senthil Sivakumar
   Cisco Systems
   7100-8 Kit Creek Road
   Research Triangle Park, North Carolina  27709
   USA

   Email: ssenthil@cisco.com


















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