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Versions: 00 01 02 03 04 05 draft-ietf-pcp-dslite

PCP Working Group                                              F. Dupont
Internet-Draft                               Internet Systems Consortium
Intended status: Standards Track                                 T. Tsou
Expires: October 25, 2013                            Huawei Technologies
                                                                  J. Qin
                                                         ZTE Corporation
                                                            M. Wasserman
                                                       Painless Security
                                                                D. Zhang
                                                          April 23, 2013

       The Port Control Protocol in Dual-Stack Lite environments


   This document specifies the so-called "plain mode" for the use of the
   Port Control Protocol (PCP) in Dual-Stack Lite (DS-Lite)

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 October 25, 2013.

Copyright Notice

   Copyright (c) 2013 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.

1.  Introduction

   Dual-Stack Lite (DS-Lite, [RFC6333]) is a technology which enables a
   broadband service provider to share IPv4 addresses among customers by
   combining two well-known technologies: IP in IP (IPv4-in-IPv6) and
   Network Address Translation (NAT).

   Typically, the home gateway embeds a Basic Bridging BroadBand (B4)
   capability that encapsulates IPv4 traffic into a IPv6 tunnel to the
   carrier-grade NAT, named the Address Family Transition Router (AFTR).
   AFTRs are run by service providers.

   The Port Control Protocol (PCP, [I-D.ietf-pcp-base] allows customer
   applications to create mappings in a NAT for new inbound
   communications destined to machines located behind a NAT.  In a DS-
   Lite environment, PCP servers control AFTR devices.

   Two different modes of operations have been proposed: the plain and
   the encapsulation modes.  This document recommends use of the plain

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Plain Mode

   In the plain mode the B4, the customer end-point of the DS-Lite IPv6
   tunnel, implements a PCP proxy ([I-D.ietf-pcp-proxy]) function and
   uses UDP over IPv6 with the AFTR to send PCP requests and receive PCP

   The B4 MUST source PCP requests with the IPv6 address of its DS-Lite
   tunnel end-point and MUST use a THIRD PARTY option either empty or
   carrying the IPv4 internal address of the mappings.

   In the plain mode the PCP discovery ([I-D.ietf-pcp-base] section 7.1
   "General PCP Client: Generating a Request") is changed into:

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   1.  if a PCP server is configured (e.g., in a configuration file or
       via DHCPv6), that single configuration source is used as the list
       of PCP Server(s), else;
   2.  use the IPv6 address of the AFTR.
   To summarize, the first rule remains the same with the precision that
   DHCP is DHCPv6, in the second rule the default router list is
   replaced by the AFTR.

3.  IANA Considerations

   This document makes no request of IANA.

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

4.  Security Considerations

   A DS-Lite PCP deployment could be secure under the Simple Threat
   Model described in the Security Considerations of the base PCP
   specification, even though the B4 device makes PCP mapping requests
   on behalf of internal clients using the THIRD_PARTY option.

   To meet the requirements of the Simple Threat Model the DS-Lite PCP
   server MUST be configured to only allow the B4 device to make
   THIRD_PARTY requests, and only on behalf of other Internal Hosts
   sharing the same DS-Lite IPv6 tunnel.  The B4 must ensure that the
   internal IP address in the THIRD_PARTY option corresponds to the IP
   source address in the IP Header of the PCP request (or proxied UPnP
   request) that triggered the THIRD_PARTY request.  The B4 device MUST
   guard against spoofed packets being injected into the IPv6 tunnel
   using the B4 device's IPv4 source address, so the DS-Lite PCP Server
   can trust that packets received over the DS-Lite IPv6 tunnel with the
   B4 device's source IPv4 address do in fact originate from the B4
   device.  The B4 device is in a position to enforce this requirement,
   because it is the DS-Lite IPv6 tunnel endpoint.

   Allowing the B4 device to use the THIRD_PARTY option to create
   mappings for hosts reached via the IPv6 tunnel terminated by the B4
   device is acceptable, because the B4 device is capable of creating
   these mappings implicitly and can prevent others from spoofing these

   If the conditions described above cannot be ensured, a PCP
   Authentication mechanism must be implemented to meet the requirements
   of the Advanced Security Model, as discussed in the PCP

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   The plain mode provides a control point inside the home network where
   any policy on PCP requests can be applied, e.g.:
   o  restrict the use of THIRD PARTY options to the B4
   o  apply an access-list on internal addresses and/or ports
   Therefore, use of the PCP Simple Security model will generally be
   acceptable within plain mode implementations.

   On the other hand, the encapsulation mode Appendix A defaults to
   being fully transparent for the B4: PCP requests are blindly
   encapsulated as any other IPv4 packets to the Internet.  This makes
   it more difficult to apply policy to PCP requests, and will generally
   require implementation of a PCP authentication protocol to meet the
   Security Considerations of the base PCP specification.

5.  Acknowledgments

   Reinaldo Penno who checks the validity of the argument about the
   relative complexity of the encapsulation mode at the AFTR side.

   Christian Jacquenet and Mohammed Boucadair who proposed improvements
   to the document, including the PCP server discovery by Mohammed.

   Sam Hartman for his help with the Security Considerations text.

6.  References

6.1.  Normative References

              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-29 (work in progress), November 2012.

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

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

6.2.  Informative References

              Boucadair, M., Penno, R., and D. Wing, "Port Control
              Protocol (PCP) Proxy Function", draft-ietf-pcp-proxy-02
              (work in progress), February 2013.

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              Boucadair, M., Penno, R., and D. Wing, "Universal Plug and
              Play (UPnP) Internet Gateway Device (IGD)-Port Control
              Protocol (PCP) Interworking Function",
              draft-ietf-pcp-upnp-igd-interworking-08 (work in
              progress), April 2013.

Appendix A.  Encapsulation Mode

   The encapsulation mode deals at the B4 side with PCP traffic as any
   IPv4 traffic: it is encapsulated to and decapsulated from the AFTR
   over the DS-Lite IPv4 over IPv6 tunnel.

   At the AFTR side things are a bit more complex because the PCP server
   needs the context, here the source IPv6 address, for both to manage
   mappings and to send back response.  So the AFTR MUST tag PCP
   requests with the source IPv6 address after decapsulation and before
   forwarding them to the PCP server, and use the same tag to
   encapsulate PCP responses to correct B4s. (the term "tag" is used to
   describe the private convention between the AFTR and the PCP server).

Appendix B.  Justification

   We believe most customers will run a PCP proxy on the B4 because:
   o  they want a control point where to apply security (Section 4)
   o  they run an InterWorking Function (IWF) for other protocols
      ([I-D.ietf-pcp-upnp-igd-interworking]) on the B4 so the proxy is
      just part of a bigger system
   BTW when the home network has only one node (dual-stack capable with
   embedded B4 element) attached, it is the PCP client.

   For a PCP proxy to use IPv4 (encapsulation mode) or IPv6 (plain mode)
   does not make a sensible difference, so from an implementation point
   of view the real difference is on the PCP server / AFTR side: the
   encapsulation mode require an Application Level Gateway (ALG) to tag
   PCP request with the corresponding customer after decapsulation, when
   the plain mode is fully transparent.

Authors' Addresses

   Francis Dupont
   Internet Systems Consortium

   Email: fdupont@isc.org

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   Tina Tsou
   Huawei Technologies
   2330 Central Expressway
   Santa Clara

   Phone: +1-408-330-4424
   Email: tina.tsou.zouting@huawei.com

   Jacni Qin
   ZTE Corporation

   Email: jacni@jacni.com

   Margaret Wasserman
   Painless Security
   356 Abbott Street
   North Andover, MA  01845

   Phone: +1 781 405 7464
   Email: mrw@painless-security.com
   URI:   http://www.painless-security.com

   Dacheng Zhang

   Email: zhangdacheng@huawei.com

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