The Port Control Protocol in Dual-Stack Lite environments
draft-dupont-pcp-dslite-03

PCP Working Group                                              F. Dupont
Internet-Draft                               Internet Systems Consortium
Intended status: Standards Track                                 T. Tsou
Expires: April 25, 2013                              Huawei Technologies
                                                                  J. Qin
                                                         ZTE Corporation
                                                        October 22, 2012

       The Port Control Protocol in Dual-Stack Lite environments
                       draft-dupont-pcp-dslite-03

Abstract

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

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 25, 2013.

Copyright Notice

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

1.  Disclaimer

   This is a temporary version to avoid unwanted expire.

2.  Introduction

   The 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 were proposed: the plain and the
   encapsulation modes.  This document selects the plain mode as the one
   to use.

   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].

3.  Plain Mode

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

   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 summary: 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.

4.  IANA Considerations

   This document makes no request of IANA.

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

5.  Security Considerations

   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

   At the opposite the encapsulation mode Appendix A by default is fully
   transparent for the B4: PCP requests are blindly encapsulated as any
   other IPv4 packets to the Internet.  So to apply a policy on them
   requires heavier and far less flexible tools.

6.  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.

7.  References

7.1.  Normative References

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-28 (work in progress), October 2012.

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   [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.

7.2.  Informative References

   [I-D.bpw-pcp-proxy]
              Boucadair, M., Penno, R., Wing, D., and F. Dupont, "Port
              Control Protocol (PCP) Proxy Function",
              draft-bpw-pcp-proxy-02 (work in progress), September 2011.

   [I-D.bpw-pcp-upnp-igd-interworking]
              Boucadair, M., Penno, R., Wing, D., and F. Dupont,
              "Universal Plug and Play (UPnP) Internet Gateway Device
              (IGD)-Port Control Protocol (PCP) Interworking Function",
              draft-bpw-pcp-upnp-igd-interworking-02 (work in progress),
              February 2011.

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 5)
   o  they run an InterWorking Function (IWF) for other protocols
      ([I-D.bpw-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)

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   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

   Tina Tsou
   Huawei Technologies
   2330 Central Expressway
   Santa Clara
   USA

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

   Jacni Qin
   ZTE Corporation
   Shanghai
   P.R.China

   Email: jacni@jacni.com

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