<?xml version="1.0" encoding="US-ASCII"?>
<?rfc toc="yes"?>
<?rfc compact="yes"?>
<?rfc tocdepth="6"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
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<!DOCTYPE rfc SYSTEM "rfc2629.dtd">

<rfc category="info" docName="draft-palet-v6ops-rfc7084-bis-transition-00">
  <front>
    <title abbrev="IPv6 Transition CE Router Requirements">Transition Requirements for IPv6
    Customer Edge Routers</title>

    <author fullname="Jordi Palet Martinez" initials="J" surname="Palet Martinez">
      <organization>Consulintel, S.L.</organization>

      <address>
        <postal>
          <street>Molino de la Navata, 75</street>

          <city>La Navata - Galapagar</city>

          <region>Madrid</region>

          <code>28420</code>

          <country>Spain</country>
        </postal>

        <email>jordi.palet@consulintel.es</email>

        <uri>http://www.consulintel.es/</uri>
      </address>
    </author>


    <date year="2017"/>

    <workgroup>IPv6 Operations (v6ops)</workgroup>

    <keyword>IPv6 transition CE requirements</keyword>


    <abstract>
      <t>This document specifies the transition requirements for an IPv6 Customer Edge (CE)
      router. Specifically, this document extends the "Minimum Requirements for 
      IPv6-only Customer Edge Routers" (draft-palet-v6ops-rfc7084-bis2)
      in order to allow the provisioning of IPv6 transition services for the
      hosts attached to it and the support of HNCP (<xref target="RFC7788"/>) 
      for automated provisioning of downstream routers. 
      The document covers several transition technologies, either for delivering IPv6 in 
      IPv4-only access networks and specially for delivering IPv4 "as a service"
      as required in a world where IPv4 addresses are no longer available, so hosts 
      in the customer LANs with IPv4-only or IPv6-only applications or devices, requiring 
      to communicate with IPv4-only services at the Internet, are able to do so.</t>
    </abstract>
  </front>

  <middle>
    <section title="Introduction">
      <t>This document defines basic IPv6 transition features for a residential or 
      small-office router, referred to as an "IPv6 Transition CE router", in order to establish 
      an industry baseline for dual-stack and transition features to be implemented on 
      such a router.</t>
      
      <t>These routers are based on draft-palet-v6ops-rfc7084-bis2, so the scope of 
      this documents is to include also support IPv4, at least in the LAN side.</t>

      <t>This document covers the IP transition technologies required when ISPs have 
      already and IPv4-only access network that they can't turn to dual-stack or 
      IPv6-only, as well as the situation in a world 
      where IPv4 addresses are no longer available, so the service providers need to 
      provision IPv6-only WAN access, while at the same time ensuring that IPv4-only or
      IPv6-only devices or applications in the customer LANs can still reach IPv4-only
      devices or applications in Internet, which still don't have IPv6 support.</t>

      <t>This document specifies the transition mechanisms to be supported by an IPv6 
      transition CE router, relevant provisioning or configuration information differences 
      from draft-palet-v6ops-rfc7084-bis2. Automatic provisioning of more complex
      topology than a single router with multiple LAN interfaces may be handled by 
      means of HNCP (<xref target="RFC7788"/>). 
      In some cases, manual provisioning may be acceptable, 
      when intended for a small number of customers.</t>

      <section title="Requirements Language">
        <t>
           Take careful note: Unlike other IETF documents, the key words "MUST",
           "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
           "RECOMMENDED", "MAY", and "OPTIONAL" in this document are not used as
           described in <xref target="RFC2119">RFC 2119</xref>. This document uses 
           these keywords not
           strictly for the purpose of interoperability, but rather for the
           purpose of establishing industry-common baseline functionality.  As
           such, the document points to several other specifications (preferable
           in RFC or stable form) to provide additional guidance to implementers
           regarding any protocol implementation required to produce a
           successful IPv6 Transition CE router that interoperates successfully with a
           particular subset of currently deploying and planned common IPv6
           access networks.
         </t>

          
      </section>
    </section>

    <section title="Terminology">
      <t>This document uses the same terminology as in draft-palet-v6ops-rfc7084-bis2, 
      with two minor clarifications.</t>

      <t>The term "IPv6 transition Customer Edge Router" is defined 
      as an "IPv6 Customer Edge Router" that provides transition support to allow 
      IPv4-IPv6 coexistence either in the WAN, the LAN or both.</t>

      <t>The "WAN Interface" term used across this document, means that can also support 
      link technologies based in Internet-layer (or higher-layers) "tunnels", such as 
      tunnels over IPv4 or IPv6 itself.</t>
	</section>

    <section title="Usage Scenarios">
      <t>The IPv6 Transition CE router described in this document is expected to be used 
      typically, in any of the following scenarios:</t>
      
            <t><list style="numbers">
            <t>Residential/household users. Common usage is any kind of Internet access 
            (web, email, streaming, online gaming, etc.).</t>

            <t>Residential with Small Office/Home Office (SOHO). Same usage as for the 
            first scenario.</t>

            <t>Small Office/Home Office (SOHO). Same usage as for the first scenario.</t>

            <t>Small and Medium Enterprise (SME). Same usage as for the first scenario.</t>

            <t>Residential/household with advanced requirements. Same basic usage 
            as for the first scenario, however there may be requirements for exporting 
            services to the WAN (IP cameras, web, DNS, email, VPN, etc.).</t>

            <t>Small and Medium Enterprise (SME) with advanced requirements. Same 
            basic usage as for the first scenario, however there may be requirements for 
            exporting services to the WAN (IP cameras, web, DNS, email, VPN, etc.).</t>

          </list></t>

      <t>The above list is not intended to be comprehensive of all the possible usage 
      scenarios, just the main ones. In fact, combinations of the above usages are also 
      possible, for example a residential with SOHO and advanced requirements.</t>

      <t>The mechanisms for exporting IPv6 services are commonly "naturally" available 
      in any IPv6 router, as when using GUA, unless they are blocked by firewall rules, 
      which may require some manual configuration by means of a GUI and/or CLI.</t>
      
      <t>However, in the case of IPv4, because the usage of private addresses and NAT, it 
      typically requires some degree of manual configuration such as setting up a DMZ, 
      virtual servers, or port/protocol forwarding. In general, CE routers already 
      provide GUI and/or CLI to manually configure them, or the possibility to setup the 
      CE in bridge mode, so another CE behind it, takes care of that. It is out of the 
      scope of this document the definition of any requirements for that.</t>

      <t>The main difference for an IPv6 Transition CE router to support one or several of the above 
      indicated scenarios, is related to the packet processing capabilities, performance, 
      even other details such as the number of WAN/LAN interfaces, their maximum speed, 
      memory for keeping tables or tracking connections, etc. So, it is out of the scope 
      of this document to classify them.</t>
      
      <t>For example, an SME may have just 10 employees (micro-SME), which commonly will 
      be considered same as a SOHO, but a small SME can have up to 50 employees, or 250 
      for a medium one. Depending on the IPv6 Transition CE router capabilities or even how it is 
      being configured (for instance, using SLAAC or DHCPv6), it may support even a 
      higher number of employees if the traffic in the LANs is low, or switched by 
      another device(s), or the WAN bandwidth requirements are low, etc. The actual 
      bandwidth capabilities of access with technologies such as FTTH, cable and even 
      3GPP/LTE, allows the support of such usages, and indeed, is a very common situation that 
      access networks and the IPv6 Transition CE provided by the service provider are the same for SMEs 
      and residential users.</t>

      <t>There is also no difference in terms of who actually provides the IPv6 Transition CE 
      router. In most of the cases is the service provider, and in fact is responsible, 
      typically, of provisioning/managing at least the WAN side. However, commonly the 
      user has access to configure the LAN interfaces, firewall, DMZ, and many other 
      aspects. In fact, in many cases, the user must supply, or at least can replace the 
      IPv6 Transition CE router, which makes even more relevant that all the IPv6 Transition CE routers, 
      support the same requirements defined in this document.</t>
      
      <t>The IPv6 Transition CE router described in this document is not intended for usage in other 
      scenarios such as bigger Enterprises, Data Centers, Content Providers, etc. So, 
      even if the documented requirements meet their needs, may have additional 
      requirements, which are out of the scope of this document.</t>
      
    </section>

    <section title="Architecture">
      <section title="Current IPv4 End-User Network Architecture">
        <t>An end-user network will likely support both IPv4 and IPv6. It is
        not expected that an end user will change their existing network
        topology with the introduction of IPv6. There are some differences in
        how IPv6 works and is provisioned; these differences have implications
        for the network architecture. A typical IPv4 end-user network consists
        of a "plug and play" router with NAT functionality and a single link
        behind it, connected to the service provider network.</t>

        <t>A typical IPv4 NAT deployment by default blocks all incoming
        connections. Opening of ports is typically allowed using a Universal
        Plug and Play Internet Gateway Device (UPnP IGD) <xref
        target="UPnP-IGD"></xref> or some other firewall control protocol.</t>

        <t>Another consequence of using private address space in the end-user
        network is that it provides stable addressing; that is, it never changes
        even when you change service providers, and the addresses are always
        there even when the WAN interface is down or the customer edge router
        has not yet been provisioned.</t>

        <t>Many existing routers support dynamic routing (which learns routes 
           from other routers), and advanced end-users can build arbitrary, complex 
           networks using manual configuration of address prefixes combined with a 
           dynamic routing protocol.</t>
      </section>

      <section title="IPv6 End-User Network Architecture">
        <t>The end-user network architecture for IPv6 should provide
        equivalent or better capabilities and functionality than the current
        IPv4 architecture.</t>

        <t>The end-user network is a stub network, in the sense that is not providing 
        transit to other external networks. However HNCP (<xref target="RFC7788"/>) 
        allows support for automatic  provisioning of downstream routers. 
        Figure 1 illustrates the model topology for the end-user network.</t>

        <figure align="center" anchor="sp_architecture"
                title="An Example of a Typical End-User Network">
          <artwork align="left"><![CDATA[
                  +---------------+                      \
                  |   Service     |                       \
                  |   Provider    |                        | Service
                  |    Router     |                        | Provider
                  +-------+-------+                        | Network
                          |                               /
                          | Customer                     /
                          | Internet Connection         /
                          |                            
                   +------+--------+                    \
                   |     IPv6      |                     \
                   | Customer Edge |                      \
                   |    Router     |                      /
                   +---+-------+---+                     /
       Network A       |       |   Network B            | 
 ---+----------------+-+-    --+---+-------------+--    |
    |                |             |             |       \
+---+------+         |        +----+-----+ +-----+----+   \
|IPv6 Host |         |        | IPv4 Host| |IPv4/IPv6 |   /
|          |         |        |          | | Host     |  /
+----------+         |        +----------+ +----------+ /
                     |                                 |
              +------+--------+                        | End-User
              |     IPv6      |                        | Network(s)
              |    Router     |                         \
              +------+--------+                          \
       Network C     |                                    \
 ---+-------------+--+---                                  |
    |             |                                        |
+---+------+ +----+-----+                                  |
|IPv6 Host | |IPv6 Host |                                 /
|          | |          |                                /
+----------+ +----------+                               /
            ]]></artwork>
        </figure>

        <t>This architecture describes the:<list style="symbols">
            <t>Basic capabilities of an IPv6 Transition CE router</t>

            <t>Provisioning of the WAN interface connecting to the service
            provider</t>

            <t>Provisioning of the LAN interfaces</t>
          </list></t>

        <t>As indicated in draft-palet-v6ops-rfc7084-bis2, for IPv6 multicast traffic, 
        the IPv6 Transition CE router may act as a
        Multicast Listener Discovery (MLD) proxy <xref
        target="RFC4605"/> and may support a dynamic multicast routing
        protocol.</t>

        <t>The IPv6 Transition CE router may be manually configured in an arbitrary
        topology with a dynamic routing protocol or using HNCP (<xref target="RFC7788"/>). 
        Automatic provisioning and
        configuration is described for a single IPv6 Transition CE router only.</t>

        <section title="Local Communication">
          <t>Section 3.2.1 from draft-palet-v6ops-rfc7084-bis2 apply here without changes.</t>

          <t>Coexistence with IPv4 requires any IPv6 Transition CE router(s) on the LAN
          to conform to these recommendations, especially requirements ULA-5
          and L-4 from draft-palet-v6ops-rfc7084-bis2.</t>
        </section>
      </section>
    </section>

    <section title="Requirements">
      <section title="General Requirements">
        <t>The IPv6 Transition CE router must comply with the general requirements stated 
        in draft-palet-v6ops-rfc7084-bis2.</t>
      </section>

      <section title="WAN-Side Configuration">
        <t>The IPv6 Transition CE router must comply with WAN-Side Configuration as stated 
        in draft-palet-v6ops-rfc7084-bis2.</t>
        
      </section>

      <section title="LAN-Side Configuration">
        <t>The IPv6 Transition CE router must comply with LAN-Side Configuration as stated 
        in draft-palet-v6ops-rfc7084-bis2.</t>

        <t>In addition, a new LAN Requirement is:</t>
        
	 <t>L-16	The IPv6 CE router SHOULD provide HNCP (Home Networking Control Protocol) 
	 services, as specified in <xref target="RFC7788"/>.</t>
        
      </section>

    
      <section title="Transition Technologies Support">

		<t>Even if the main target of this document is the support of IPv6-only WAN 
		access, for some time, there will be a need to support IPv4-only devices 
		and applications in the customers LANs, in one side of the picture. 
		In the other side, some Service Providers willing to deploy IPv6, may not be 
		able to do so in the first stage, neither as IPv6-only or dual-stack in the WAN. 
		Consequently, transition technologies to resolve both issues should be taken 
		in consideration.</t>

        <section title="IPv4 Service Continuity in Customer LANs">

        <section title="464XLAT">
          <t>464XLAT <xref target="RFC6877"/> is a technique 
          to provide IPv4 access service to IPv6-only edge networks 
          without encapsulation.</t>

          <t>The IPv6 Transition CE router SHOULD support CLAT functionality. If 464XLAT is
          supported, it MUST be implemented according to <xref target="RFC6877"/>. 
          The following CE Requirements also apply:</t>

          <t>464XLAT requirements: <list style="format 464XLAT-%d:">
              <t>The IPv6 Transition CE router MUST perform IPv4 Network Address
              Translation (NAT) on IPv4 traffic translated using the CLAT, unless 
              a dedicated /64 prefix has been acquired using DHCPv6-PD 
              <xref target="RFC3633"/>.</t>

              <t>The IPv6 Transition CE router MUST implement <xref target="RFC7050"/> in order 
              to discover the PLAT-side translation IPv4 and IPv6 prefix(es)/suffix(es). 
              In environments with PCP support, the IPv6 Transition CE SHOULD follow 
              <xref target="RFC7225"/> to learn the PLAT-side translation 
              IPv4 and IPv6 prefix(es)/suffix(es) used by an upstream PCP-controlled 
              NAT64 device.</t>

              </list></t>
        </section>

        <section title="Dual-Stack Lite (DS-Lite)">
          <t>Dual-Stack Lite <xref target="RFC6333"/> enables both
          continued support for IPv4 services and incentives for the
          deployment of IPv6. It also de&nbhy;couples IPv6 deployment in the
          service provider network from the rest of the Internet, making
          incremental deployment easier. Dual-Stack Lite 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). It is expected that DS-Lite
          traffic is forwarded over the IPv6 Transition CE router's native IPv6 WAN interface,
          and not encapsulated in another tunnel.</t>

          <t>The IPv6 Transition CE router SHOULD implement DS-Lite functionality. If
          DS&nbhy;Lite is supported, it MUST be implemented according to <xref
          target="RFC6333"/>. This document takes no position on
          simultaneous operation of Dual-Stack Lite and native IPv4. The
          following IPv6 Transition CE router requirements also apply:</t>

          <t>DS-Lite requirements: <list style="format DSLITE-%d:">
              <t>The IPv6 Transition CE router MUST support configuration of DS-Lite via the 
                 DS-Lite DHCPv6 option <xref target="RFC6334"/>. 
                 The IPv6 Transition CE router MAY use other mechanisms to configure 
                 DS-Lite parameters. Such mechanisms are outside the scope 
                 of this document.</t>

              <t>The IPv6 Transition CE router MUST support the DHCPv6 S46 priority 
				 option described in <xref target="RFC8026"/>.</t>

              <t>The IPv6 Transition CE router MUST NOT perform IPv4 Network Address
              Translation (NAT) on IPv4 traffic encapsulated using
              DS-Lite.</t>

              <t>If the IPv6 Transition CE router is configured with an IPv4 address on
              its WAN interface, then the IPv6 Transition CE router SHOULD disable the
              DS-Lite Basic Bridging BroadBand (B4) element.</t>
            </list></t>
        </section>
 
         <section title="Lightweight 4over6 (lw4o6)">
          <t>Lw4o6 <xref target="RFC7596"/> specifies an extension to DS-Lite, 
          which moves the NAPT function from the DS-Lite tunnel concentrator to the 
          tunnel client located in the IPv6 Transition CE router, removing the requirement for a CGN 
          function in the tunnel concentrator and reducing the amount of centralized 
          state.</t>

          <t>The IPv6 Transition CE router SHOULD implement lw4o6 functionality. If DS-Lite is 
          implemented, lw4o6 MUST be supported as well. If lw4o6 is supported, it MUST 
          be implemented according to <xref target="RFC7596"/>. This document takes 
          no position on simultaneous operation of lw4o6 and native IPv4. The following 
          IPv6 Transition CE router Requirements also apply:</t>

          <t>Lw4o6 requirements: <list style="format LW4O6-%d:">
              <t>The IPv6 Transition CE router MUST support configuration of lw4o6 via the 
                 lw4o6 DHCPv6 options <xref target="RFC7598"/>. 
                 The IPv6 Transition CE router MAY use other mechanisms to configure 
                 lw4o6 parameters. Such mechanisms are outside the scope 
                 of this document.</t>

              <t>The IPv6 Transition CE router MUST support the DHCPv6 S46 priority 
				 option described in <xref target="RFC8026"/>.</t>

              <t>The IPv6 Transition CE router MUST support the DHCPv4-over-DHCPv6 (DHCP 4o6) transport
				 described in <xref target="RFC7341"/>.</t>

              <t>The IPv6 Transition CE router MAY support Dynamic Allocation of Shared IPv4 Addresses 
              as described in <xref target="RFC7618"/>.</t>
            </list></t>
        </section>

        <section title="MAP-E">
          <t>MAP-E <xref target="RFC7597"/> is a mechanism for transporting IPv4 
          packets across an IPv6 network using IP encapsulation, including a generic 
          mechanism for mapping between IPv6 addresses and IPv4 addresses as well as 
          transport-layer ports.</t>

          <t>The IPv6 Transition CE router SHOULD support MAP-E functionality. If MAP-E is
          supported, it MUST be implemented according to <xref target="RFC7597"/>. 
          The following CE Requirements also apply:</t>

          <t>MAP-E requirements: <list style="format MAPE-%d:">
              <t>The IPv6 Transition CE router MUST support configuration of MAP-E via the 
                 MAP-E DHCPv6 options <xref target="RFC7598"/>. 
                 The IPv6 Transition CE router MAY use other mechanisms to configure 
                 MAP-E parameters. Such mechanisms are outside the scope 
                 of this document.</t>

              <t>The IPv6 Transition CE router MUST support the DHCPv6 S46 priority 
				 option described in <xref target="RFC8026"/>.</t>

            </list></t>
        </section>

        <section title="MAP-T">
          <t>MAP-T <xref target="RFC7599"/> is a mechanism similar to MAP-E, 
          differing from it in that MAP-T uses IPv4-IPv6 translation, rather than 
          encapsulation, as the form of IPv6 domain transport.</t>

          <t>The IPv6 Transition CE router SHOULD support MAP-T functionality. If MAP-T is
          supported, it MUST be implemented according to <xref target="RFC7599"/>. 
          The following IPv6 Transition CE Requirements also apply:</t>

          <t>MAP-T requirements: <list style="format MAPT-%d:">
              <t>The CE router MUST support configuration of MAP-T via the 
                 MAP-E DHCPv6 options <xref target="RFC7598"/>. 
                 The IPv6 Transition CE router MAY use other mechanisms to configure 
                 MAP-E parameters. Such mechanisms are outside the scope 
                 of this document.</t>

              <t>The IPv6 Transition CE router MUST support the DHCPv6 S46 priority 
				 option described in <xref target="RFC8026"/>.</t>

            </list></t>
        </section>

        </section>

        <section title="Support of IPv6 in IPv4-only WAN access">
        <section title="6in4">
          <t>6in4 <xref target="RFC4213"/> specifies a tunneling mechanism 
          to allow end-users to manually configure IPv6 support
          via a service provider's IPv4 network infrastructure.</t>

          <t>The IPv6 Transition CE router MAY support 6in4 functionality.  
          6in4 used for a manually configured tunnel requires a subset of the 6rd 
          parameters (delegated prefix and remote IPv4 end-point). The on-wire and 
          forwarding plane is identical for both mechanisms, however 6in4 doesn't 
          support mesh traffic and requires manually provisioning. 
          Thus, if the device supports either 6rd or 6in4, it's commonly a minor 
          UI addition to support both. If 6in4 is supported, it MUST be implemented 
          according to <xref target="RFC4213"/>. The following CE Requirements 
          also apply:</t>

          <t>6in4 requirements: <list style="format 6IN4-%d:">
              <t>The IPv6 Transition CE router SHOULD support 6in4 automated configuration by means 
              of the 6rd DHCPv4 Option 212. If the IPv6 Transition CE router has obtained an IPv4
              network address through some other means such as PPP, it SHOULD
              use the DHCPINFORM request message <xref target="RFC2131"/> to 
              request the 6rd DHCPv4 Option. The IPv6 Transition CE router MAY use other mechanisms 
              to configure 6in4 parameters. Such mechanisms are outside the scope of 
              this document.</t>

              <t>If the IPv6 Transition CE router is capable of automated configuration
              of IPv4 through IPCP (i.e., over a PPP connection), it MUST
              support user-entered configuration of 6in4.</t>

              <t>If the IPv6 Transition CE router supports configuration mechanisms other than the 6rd 
              DHCPv4 Option 212 (user-entered, TR-069 <xref target="TR-069"/>, etc.), 
              the IPv6 Transition CE router MUST support 6in4 in "hub and spoke" mode. 6in4 in "hub and
              spoke" requires all IPv6 traffic to go to the 6rd Border Relay, which in 
              this case is the tunnel-end-point.
              In effect, this requirement removes the "direct connect to 6rd"
              route defined in Section 7.1.1 of <xref target="RFC5969"/>.</t>
              
              <t>The IPv6 Transition CE router MUST allow 6in4 and native IPv6 WAN interfaces 
                 to be active alone as well as simultaneously in order to support 
                 coexistence of the two technologies during an incremental transition 
                 period such as a transition from 6in4 to native IPv6.
              </t>

              <t>Each packet sent on a 6in4 or native WAN interface MUST be directed 
                 such that its source IP address is derived from the delegated prefix 
                 associated with the particular interface from which the packet 
                 is being sent (Section 4.3 of <xref target="RFC3704"/>).</t>
              
              <t>The IPv6 Transition CE router MUST allow different as well as identical delegated prefixes 
                 to be configured via each (6in4 or native) WAN interface.
              </t>

              <t>In the event that forwarding rules produce a tie between 6in4 and 
                 native IPv6, by default, the IPv6 Transition CE router MUST prefer native IPv6.
              </t>
              </list></t>
        </section>


        <section title="6rd">
          <t>6rd <xref target="RFC5969"/> specifies an automatic
          tunneling mechanism tailored to advance deployment of IPv6 to end users
          via a service provider's IPv4 network infrastructure. Key
          aspects include automatic IPv6 prefix delegation to sites, stateless
          operation, simple provisioning, and service that is equivalent to
          native IPv6 at the sites that are served by the mechanism. It is
          expected that such traffic is forwarded over the IPv6 Transition CE router's native
          IPv4 WAN interface and not encapsulated in another tunnel.</t>

          <t>The IPv6 Transition CE router MAY support 6rd functionality. If 6rd is
          supported, it MUST be implemented according to <xref
          target="RFC5969"/>. The following CE Requirements also
          apply:</t>

          <t>6rd requirements: <list style="format 6RD-%d:">
              <t>The IPv6 Transition CE router MUST support 6rd configuration via the 6rd
              DHCPv4 Option 212. If the IPv6 Transition CE router has obtained an IPv4
              network address through some other means such as PPP, it SHOULD
              use the DHCPINFORM request message <xref target="RFC2131"/> to 
              request the 6rd DHCPv4 Option. The IPv6 Transition CE router MAY use other mechanisms 
              to configure 6rd parameters. Such mechanisms are outside the scope of 
              this document.</t>

              <t>If the IPv6 Transition CE router is capable of automated configuration
              of IPv4 through IPCP (i.e., over a PPP connection), it MUST
              support user-entered configuration of 6rd.</t>

              <t>If the IPv6 Transition CE router supports configuration mechanisms other than the 6rd 
              DHCPv4 Option 212 (user-entered, TR-069 <xref target="TR-069"/>, etc.), 
              the IPv6 Transition CE router MUST support 6rd in "hub and spoke" mode. 6rd in "hub and
              spoke" requires all IPv6 traffic to go to the 6rd Border Relay.
              In effect, this requirement removes the "direct connect to 6rd"
              route defined in Section 7.1.1 of <xref target="RFC5969"/>.</t>

              <t>The IPv6 Transition CE router MUST allow 6rd and native IPv6 WAN interfaces 
                 to be active alone as well as simultaneously in order to support 
                 coexistence of the two technologies during an incremental transition 
                 period such as a transition from 6rd to native IPv6.
              </t>

              <t>Each packet sent on a 6rd or native WAN interface MUST be directed 
                 such that its source IP address is derived from the delegated prefix 
                 associated with the particular interface from which the packet 
                 is being sent (Section 4.3 of <xref target="RFC3704"/>).</t>
              
              <t>The IPv6 Transition CE router MUST allow different as well as identical delegated prefixes 
                 to be configured via each (6rd or native) WAN interface.
              </t>

              <t>In the event that forwarding rules produce a tie between 6rd and 
                 native IPv6, by default, the IPv6 Transition CE router MUST prefer native IPv6.
              </t>
            </list></t>
        </section>
        </section>
 
      </section>

      <section title="IPv4 Multicast Support">
        <t>Actual deployments support IPv4 multicast for services such as 
        IPTV. In the transition phase it is expected that multicast services 
        will still be provided using IPv4 to the customer LANs.</t>

        <t>In order to support the delivery of IPv4 multicast services to IPv4 
        clients over an IPv6 multicast network, the IPv6 Transition CE router SHOULD support 
        <xref target="RFC8114"/> and <xref target="RFC8115"/>.</t>
      </section>

      <section title="Security Considerations">
        <t>The IPv6 Transition CE router must comply with the Security Considerations as stated 
        in draft-palet-v6ops-rfc7084-bis2.</t>
      </section>


    <section anchor="Acknowledgements" title="Acknowledgements">
      <t>Thanks to James Woodyatt, Mohamed Boucadair, Masanobu Kawashima, 
      Mikael Abrahamsson, Barbara Stark, Ole Troan and Brian Carpenter for their review 
      and comments.</t>
    </section>

    <section title="ANNEX A: Code Considerations">
      <t>One of the apparent main issues for vendors to include new functionalities, 
      such as support for new transition mechanisms, is the lack of space in the flash 
      (or equivalent) memory. However, it has been confirmed from existing open source 
      implementations (OpenWRT/LEDE), that adding the support for the new transitions 
      mechanisms, requires around 10-12 Kbytes (because most of the code is shared 
      among several transition mechanisms), which typically means about 0,15% of the 
      existing code size in popular CEs in the market.</t>
      
      <t>It is also clear that the new requirements don't have extra cost in terms of 
      RAM memory, neither other hardware requirements such as more powerful CPUs.</t>      

      <t>The other issue seems to be the cost of developing the code for those new 
      functionalities. However at the time of writing this document, it has been 
      confirmed that there are several open source versions of the required code for 
      supporting the new transition mechanisms, so the development cost is negligent, 
      and only integration and testing cost may become a minor issue.</t>
    </section>
    
  </middle>

  <back>
  
    <references title="Normative References">
<?rfc include="reference.RFC.2119" ?>
<?rfc include="reference.RFC.2131" ?>
<?rfc include="reference.RFC.3633" ?>
<?rfc include="reference.RFC.3704" ?>
<?rfc include="reference.RFC.4213" ?>      
<?rfc include="reference.RFC.4605" ?>
<?rfc include="reference.RFC.5969" ?>
<?rfc include="reference.RFC.6333" ?>
<?rfc include="reference.RFC.6334" ?>
<?rfc include="reference.RFC.6877" ?>      
<?rfc include="reference.RFC.7050" ?>
<?rfc include="reference.RFC.7225" ?>
<?rfc include="reference.RFC.7341" ?>
<?rfc include="reference.RFC.7596" ?>      
<?rfc include="reference.RFC.7597" ?>      
<?rfc include="reference.RFC.7598" ?>
<?rfc include="reference.RFC.7599" ?>      
<?rfc include="reference.RFC.7618" ?>
<?rfc include="reference.RFC.7788" ?>
<?rfc include="reference.RFC.8026" ?>
<?rfc include="reference.RFC.8114" ?>
<?rfc include="reference.RFC.8115" ?>
    </references>

    <references title="Informative References">
       
<?rfc rfcedstyle="no" ?>
<reference anchor='TR-069' target="http://www.broadband-forum.org/technical/trlist.php">
<front>
<title>CPE WAN Management Protocol</title>

<author initials='' surname='' fullname=''>
    <organization> Broadband Forum</organization>
</author>

<date month='July' year='2011' />


</front>

<seriesInfo name='TR-069 Amendment' value='4' />
</reference>

      <reference anchor="UPnP-IGD" target="http://upnp.org/specs/gw/igd2/">
        <front>
          <title>InternetGatewayDevice:2 Device Template Version 1.01</title>

          <author fullname="UPnP Forum" surname="UPnP Forum">
            <organization></organization>
          </author>

          <date month="December" year="2010" />
        </front>
      </reference>
<?rfc rfcedstyle="yes"?>
    </references>
  </back>
</rfc>
