One document matched: draft-dupont-pcp-dslite-05.xml

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<rfc category="std" docName="draft-dupont-pcp-dslite-05" ipr="trust200902">
  <front>
    <title abbrev="PCP DS-Lite">
      The Port Control Protocol in Dual-Stack Lite environments
    </title>

    <author fullname="Francis Dupont" initials="F." surname="Dupont">
      <organization>Internet Systems Consortium</organization>
      <address>
        <email>fdupont@isc.org</email>
      </address>
    </author>
    <author fullname="Tina Tsou" initials="T." surname="Tsou">
      <organization>Huawei Technologies</organization>
      <address>
        <postal>
          <street>2330 Central Expressway</street>
          <city>Santa Clara</city>
          <country>USA</country>
        </postal>
        <phone>+1-408-330-4424</phone>
        <email>tina.tsou.zouting@huawei.com</email>
      </address>
    </author>
    <author fullname="Jacni Qin" initials="J." surname="Qin">
      <organization>ZTE Corporation</organization>
      <address>
	<postal>
	  <street/>
	  <city>Shanghai</city>
	  <country>P.R.China</country>
	</postal>
	<email>jacni@jacni.com</email>
      </address>
    </author>
    <author initials="M." surname="Wasserman" fullname="Margaret Wasserman">
      <organization>Painless Security</organization>
      <address>
        <postal>
          <street>356 Abbott Street</street>
          <city>North Andover</city> <region>MA</region>
          <code>01845</code>
          <country>USA</country>
        </postal>
        <phone>+1 781 405 7464</phone>
        <email>mrw@painless-security.com</email>
        <uri>http://www.painless-security.com</uri>
      </address>
    </author>
    <author fullname="Dacheng Zhang" initials="D." surname="Zhang">
      <organization>Huawei</organization>
      <address>
        <postal>
          <street></street>
          <city>Beijing</city>
          <region></region>
          <code></code>
          <country>China</country>
        </postal>
        <phone></phone>
        <facsimile></facsimile>
        <email>zhangdacheng@huawei.com</email>
        <uri></uri>
      </address>
    </author>

    <date day="23" month="April" year="2013" />

    <workgroup>PCP Working Group</workgroup>

    <keyword>PCP, DS-Lite</keyword>

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

  <middle>
    <section title="Introduction">
      <t>Dual-Stack Lite (DS-Lite, <xref target="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).</t>

      <t>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.</t>

      <t>The Port Control Protocol (PCP, <xref
      target="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.</t>

      <t>
	Two different modes of operations have been proposed: the
	plain and the encapsulation modes. This document recommends
	use of the plain mode.
      </t>

      <t>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 <xref target="RFC2119">RFC 2119</xref>.</t>
    </section>

    <section title="Plain Mode">
      <t>In the plain mode the B4, the customer end-point of
      the DS-Lite IPv6 tunnel, implements a PCP proxy
      (<xref target="I-D.ietf-pcp-proxy"/>) function
      and uses UDP over IPv6 with the AFTR to send PCP requests
      and receive PCP responses.</t>

      <t>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.</t>

      <t>In the plain mode the PCP discovery (<xref
      target="I-D.ietf-pcp-base"/> section 7.1 "General PCP Client:
      Generating a Request") is changed into:
      <list style="numbers">
	<t>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;</t>
        <t>use the IPv6 address of the AFTR.</t>
      </list>
      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.</t>
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <t>This document makes no request of IANA.</t>

      <t>Note to RFC Editor: this section may be removed on
      publication as an RFC.</t>
    </section>

    <section anchor="Security" title="Security Considerations">
      <t>
	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.
      </t>
      <t>
	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.
      </t>
      <t>
	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 mappings.
      </t>
      <t>
	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 specification.
      </t>
      
      <t>The plain mode provides a control point inside the home
      network where any policy on PCP requests can be applied, e.g.:
      <list style="symbols">
        <t>restrict the use of THIRD PARTY options to the B4</t>
        <t>apply an access-list on internal addresses and/or ports</t>
      </list>
      Therefore, use of the PCP Simple Security model will generally
      be acceptable within plain mode implementations.</t>

      <t>On the other hand, the encapsulation mode
      <xref target="encap"/> 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.
      </t>
    </section>

    <section title="Acknowledgments">
      <t>Reinaldo Penno who checks the validity of the argument
	about the relative complexity of the encapsulation mode
	at the AFTR side.</t>
      <t>Christian Jacquenet and Mohammed Boucadair who proposed
	improvements to the document, including the PCP server
	discovery by Mohammed.</t>
      <t>Sam Hartman for his help with the Security Considerations
	text.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include="reference.RFC.6333"?>
      <?rfc include="reference.I-D.ietf-pcp-base"?>
      <?rfc include="reference.RFC.2119"?>
    </references>

    <references title="Informative References">
      <?rfc include="reference.I-D.ietf-pcp-proxy"?>
      <?rfc include="reference.I-D.ietf-pcp-upnp-igd-interworking"?>
    </references>

    <section anchor="encap" title="Encapsulation Mode">
      <t>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.</t>

      <t>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).</t>
    </section>

    <section title="Justification">
      <t>We believe most customers will run a PCP proxy on the B4
      because:
      <list style="symbols">
        <t>they want a control point where to apply security
        (<xref target="Security"/>)</t>
        <t>they run an InterWorking Function (IWF) for other
        protocols (<xref target="I-D.ietf-pcp-upnp-igd-interworking"/>)
        on the B4 so the proxy is just part of a bigger system</t>
      </list>
     BTW when the home network has only one node (dual-stack capable
     with embedded B4 element) attached, it is the PCP client.</t>

     <t>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.</t>
    </section>
   </back>
</rfc>