    Internet Engineering Task Force (IETF)                          H. Singh
    Request for Comments: 7084                                     W. Beebee
    Obsoletes: 6204                                      Cisco Systems, Inc.
    Category: Informational                                        C. Donley
    ISSN: 2070-1721                                                CableLabs
                                                                    B. Stark
                                                                        AT&T
                                                               November 2013

               Basic Requirements for IPv6 Customer Edge Routers

    Abstract

       This document specifies requirements for an IPv6 Customer Edge (CE)
       router.  Specifically, the current version of this document focuses
       on the basic provisioning of an IPv6 CE router and the provisioning
       of IPv6 hosts attached to it.  The document also covers IP transition
       technologies.  Two transition technologies in RFC 5969's IPv6 Rapid
       Deployment on IPv4 Infrastructures (6rd) and RFC 6333's Dual-Stack
       Lite (DS-Lite) are covered in the document.  The document obsoletes
       RFC 6204.

    Status of This Memo

       This document is not an Internet Standards Track specification; it is
       published for informational purposes.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Not all documents
       approved by the IESG are a candidate for any level of Internet
       Standard; see Section 2 of RFC 5741.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       http://www.rfc-editor.org/info/rfc7084.

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    RFC 7084               IPv6 CE Router Requirements         November 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
       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. Requirements Language ......................................3
       2. Terminology .....................................................4
       3. Architecture ....................................................5
          3.1. Current IPv4 End-User Network Architecture .................5
          3.2. IPv6 End-User Network Architecture .........................5
               3.2.1. Local Communication .................................7
       4. Requirements ....................................................7
          4.1. General Requirements .......................................7
          4.2. WAN-Side Configuration .....................................8
          4.3. LAN-Side Configuration ....................................12
          4.4. Transition Technologies Support ...........................14
               4.4.1. 6rd ................................................14
               4.4.2. Dual-Stack Lite (DS-Lite) ..........................15
          4.5. Security Considerations ...................................16
       5. Acknowledgements ...............................................17
       6. Contributors ...................................................17
       7. References .....................................................18
          7.1. Normative References ......................................18
          7.2. Informative References ....................................20

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    RFC 7084               IPv6 CE Router Requirements         November 2013

    1.  Introduction

       This document defines basic IPv6 features for a residential or small-
       office router, referred to as an "IPv6 CE router", in order to
       establish an industry baseline for features to be implemented on such
       a router.

       These routers typically also support IPv4.

       Mixed environments of dual-stack hosts and IPv6-only hosts (behind
       the CE router) can be more complex if the IPv6-only devices are using
       a translator to access IPv4 servers [RFC6144].  Support for such
       mixed environments is not in scope of this document.

       This document specifies how an IPv6 CE router automatically
       provisions its WAN interface, acquires address space for provisioning
       of its LAN interfaces, and fetches other configuration information
       from the service provider network.  Automatic provisioning of more
       complex topology than a single router with multiple LAN interfaces is
       out of scope for this document.

       See [RFC4779] for a discussion of options available for deploying
       IPv6 in service provider access networks.

       The document also covers the IP transition technologies that were
       available at the time this document was written.  Two transition
       technologies in 6rd [RFC5969] and DS-Lite [RFC6333] are covered in
       the document.

    1.1.  Requirements Language

       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 RFC 2119 [RFC2119].  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 CE router that interoperates successfully with a
       particular subset of currently deploying and planned common IPv6
       access networks.

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    2.  Terminology

       End-User Network          one or more links attached to the IPv6 CE
                                 router that connect IPv6 hosts.

       IPv6 Customer Edge Router a node intended for home or small-office
                                 use that forwards IPv6 packets not
                                 explicitly addressed to itself.  The IPv6
                                 CE router connects the end-user network to
                                 a service provider network.

       IPv6 Host                 any device implementing an IPv6 stack
                                 receiving IPv6 connectivity through the
                                 IPv6 CE router.

       LAN Interface             an IPv6 CE router's attachment to a link in
                                 the end-user network.  Examples are
                                 Ethernet (simple or bridged), 802.11
                                 wireless, or other LAN technologies.  An
                                 IPv6 CE router may have one or more
                                 network-layer LAN interfaces.

       Service Provider          an entity that provides access to the
                                 Internet.  In this document, a service
                                 provider specifically offers Internet
                                 access using IPv6, and it may also offer
                                 IPv4 Internet access.  The service provider
                                 can provide such access over a variety of
                                 different transport methods such as DSL,
                                 cable, wireless, and others.

       WAN Interface             an IPv6 CE router's attachment to a link
                                 used to provide connectivity to the service
                                 provider network; example link technologies
                                 include Ethernet (simple or bridged), PPP
                                 links, Frame Relay, or ATM networks, as
                                 well as Internet-layer (or higher-layer)
                                 "tunnels", such as tunnels over IPv4 or
                                 IPv6 itself.

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    3.  Architecture

    3.1.  Current IPv4 End-User Network Architecture

       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.

       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) [UPnP-IGD] or some
       other firewall control protocol.

       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.

       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.

    3.2.  IPv6 End-User Network Architecture

       The end-user network architecture for IPv6 should provide equivalent
       or better capabilities and functionality than the current IPv4
       architecture.

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       The end-user network is a stub network.  Figure 1 illustrates the
       model topology for the end-user network.

                       +-------+-------+                      \
                       |   Service     |                       \
                       |   Provider    |                        | Service
                       |    Router     |                        | Provider
                       +-------+-------+                        | Network
                               |                               /
                               | Customer                     /
                               | Internet Connection         /
                               |
                        +------+--------+                    \
                        |     IPv6      |                     \
                        | Customer Edge |                      \
                        |    Router     |                      /
                        +---+-------+-+-+                     /
            Network A       |       |   Network B            | End-User
      ---+-------------+----+-    --+--+-------------+---    | Network(s)
         |             |               |             |        \
     +----+-----+ +-----+----+     +----+-----+ +-----+----+   \
     |IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |   /
     |          | |          |     |          | |          |  /
     +----------+ +-----+----+     +----------+ +----------+ /

                Figure 1: An Example of a Typical End-User Network

       This architecture describes the:

       o  Basic capabilities of an IPv6 CE router

       o  Provisioning of the WAN interface connecting to the service
          provider

       o  Provisioning of the LAN interfaces

       For IPv6 multicast traffic, the IPv6 CE router may act as a Multicast
       Listener Discovery (MLD) proxy [RFC4605] and may support a dynamic
       multicast routing protocol.

       The IPv6 CE router may be manually configured in an arbitrary
       topology with a dynamic routing protocol.  Automatic provisioning and
       configuration are described for a single IPv6 CE router only.

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    3.2.1.  Local Communication

       Link-local IPv6 addresses are used by hosts communicating on a single
       link.  Unique Local IPv6 Unicast Addresses (ULAs) [RFC4193] are used
       by hosts communicating within the end-user network across multiple
       links, but without requiring the application to use a globally
       routable address.  The IPv6 CE router defaults to acting as the
       demarcation point between two networks by providing a ULA boundary, a
       multicast zone boundary, and ingress and egress traffic filters.

       At the time of this writing, several host implementations do not
       handle the case where they have an IPv6 address configured and no
       IPv6 connectivity, either because the address itself has a limited
       topological reachability (e.g., ULA) or because the IPv6 CE router is
       not connected to the IPv6 network on its WAN interface.  To support
       host implementations that do not handle multihoming in a multi-prefix
       environment [MULTIHOMING-WITHOUT-NAT], the IPv6 CE router should not,
       as detailed in the requirements below, advertise itself as a default
       router on the LAN interface(s) when it does not have IPv6
       connectivity on the WAN interface or when it is not provisioned with
       IPv6 addresses.  For local IPv6 communication, the mechanisms
       specified in [RFC4191] are used.

       ULA addressing is useful where the IPv6 CE router has multiple LAN
       interfaces with hosts that need to communicate with each other.  If
       the IPv6 CE router has only a single LAN interface (IPv6 link), then
       link-local addressing can be used instead.

       Coexistence with IPv4 requires any IPv6 CE router(s) on the LAN to
       conform to these recommendations, especially requirements ULA-5 and
       L-4 below.

    4.  Requirements

    4.1.  General Requirements

       The IPv6 CE router is responsible for implementing IPv6 routing; that
       is, the IPv6 CE router must look up the IPv6 destination address in
       its routing table to decide to which interface it should send the
       packet.

       In this role, the IPv6 CE router is responsible for ensuring that
       traffic using its ULA addressing does not go out the WAN interface
       and does not originate from the WAN interface.

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       G-1:  An IPv6 CE router is an IPv6 node according to the IPv6 Node
             Requirements specification [RFC6434].

       G-2:  The IPv6 CE router MUST implement ICMPv6 according to
             [RFC4443].  In particular, point-to-point links MUST be handled
             as described in Section 3.1 of [RFC4443].

       G-3:  The IPv6 CE router MUST NOT forward any IPv6 traffic between
             its LAN interface(s) and its WAN interface until the router has
             successfully completed the IPv6 address and the delegated
             prefix acquisition process.

       G-4:  By default, an IPv6 CE router that has no default router(s) on
             its WAN interface MUST NOT advertise itself as an IPv6 default
             router on its LAN interfaces.  That is, the "Router Lifetime"
             field is set to zero in all Router Advertisement messages it
             originates [RFC4861].

       G-5:  By default, if the IPv6 CE router is an advertising router and
             loses its IPv6 default router(s) and/or detects loss of
             connectivity on the WAN interface, it MUST explicitly
             invalidate itself as an IPv6 default router on each of its
             advertising interfaces by immediately transmitting one or more
             Router Advertisement messages with the "Router Lifetime" field
             set to zero [RFC4861].

    4.2.  WAN-Side Configuration

       The IPv6 CE router will need to support connectivity to one or more
       access network architectures.  This document describes an IPv6 CE
       router that is not specific to any particular architecture or service
       provider and that supports all commonly used architectures.

       IPv6 Neighbor Discovery and DHCPv6 protocols operate over any type of
       IPv6-supported link layer, and there is no need for a link-layer-
       specific configuration protocol for IPv6 network-layer configuration
       options as in, e.g., PPP IP Control Protocol (IPCP) for IPv4.  This
       section makes the assumption that the same mechanism will work for
       any link layer, be it Ethernet, the Data Over Cable Service Interface
       Specification (DOCSIS), PPP, or others.

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       WAN-side requirements:

       W-1:  When the router is attached to the WAN interface link, it MUST
             act as an IPv6 host for the purposes of stateless [RFC4862] or
             stateful [RFC3315] interface address assignment.

       W-2:  The IPv6 CE router MUST generate a link-local address and
             finish Duplicate Address Detection according to [RFC4862] prior
             to sending any Router Solicitations on the interface.  The
             source address used in the subsequent Router Solicitation MUST
             be the link-local address on the WAN interface.

       W-3:  Absent other routing information, the IPv6 CE router MUST use
             Router Discovery as specified in [RFC4861] to discover a
             default router(s) and install a default route(s) in its routing
             table with the discovered router's address as the next hop.

       W-4:  The router MUST act as a requesting router for the purposes of
             DHCPv6 prefix delegation ([RFC3633]).

       W-5:  The IPv6 CE router MUST use a persistent DHCP Unique Identifier
             (DUID) for DHCPv6 messages.  The DUID MUST NOT change between
             network-interface resets or IPv6 CE router reboots.

       W-6:  The WAN interface of the CE router SHOULD support a Port
             Control Protocol (PCP) client as specified in [RFC6887] for use
             by applications on the CE router.  The PCP client SHOULD follow
             the procedure specified in Section 8.1 of [RFC6887] to discover
             its PCP server.  This document takes no position on whether
             such functionality is enabled by default or mechanisms by which
             users would configure the functionality.  Handling PCP requests
             from PCP clients in the LAN side of the CE router is out of
             scope.

       Link-layer requirements:

       WLL-1:  If the WAN interface supports Ethernet encapsulation, then
               the IPv6 CE router MUST support IPv6 over Ethernet [RFC2464].

       WLL-2:  If the WAN interface supports PPP encapsulation, the IPv6 CE
               router MUST support IPv6 over PPP [RFC5072].

       WLL-3:  If the WAN interface supports PPP encapsulation, in a dual-
               stack environment with IPCP and IPV6CP running over one PPP
               logical channel, the Network Control Protocols (NCPs) MUST be
               treated as independent of each other and start and terminate
               independently.

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       Address assignment requirements:

       WAA-1:   The IPv6 CE router MUST support Stateless Address
                Autoconfiguration (SLAAC) [RFC4862].

       WAA-2:   The IPv6 CE router MUST follow the recommendations in
                Section 4 of [RFC5942], and in particular the handling of
                the L flag in the Router Advertisement Prefix Information
                option.

       WAA-3:   The IPv6 CE router MUST support DHCPv6 [RFC3315] client
                behavior.

       WAA-4:   The IPv6 CE router MUST be able to support the following
                DHCPv6 options: Identity Association for Non-temporary
                Address (IA_NA), Reconfigure Accept [RFC3315], and
                DNS_SERVERS [RFC3646].  The IPv6 CE router SHOULD be able to
                support the DNS Search List (DNSSL) option as specified in
                [RFC3646].

       WAA-5:   The IPv6 CE router SHOULD implement the Network Time
                Protocol (NTP) as specified in [RFC5905] to provide a time
                reference common to the service provider for other
                protocols, such as DHCPv6, to use.  If the CE router
                implements NTP, it requests the NTP Server DHCPv6 option
                [RFC5908] and uses the received list of servers as primary
                time reference, unless explicitly configured otherwise.  LAN
                side support of NTP is out of scope for this document.

       WAA-6:   If the IPv6 CE router receives a Router Advertisement
                message (described in [RFC4861]) with the M flag set to 1,
                the IPv6 CE router MUST do DHCPv6 address assignment
                (request an IA_NA option).

       WAA-7:   If the IPv6 CE router does not acquire a global IPv6
                address(es) from either SLAAC or DHCPv6, then it MUST create
                a global IPv6 address(es) from its delegated prefix(es) and
                configure those on one of its internal virtual network
                interfaces, unless configured to require a global IPv6
                address on the WAN interface.

       WAA-8:   The CE router MUST support the SOL_MAX_RT option [RFC7083]
                and request the SOL_MAX_RT option in an Option Request
                Option (ORO).

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       WAA-9:   As a router, the IPv6 CE router MUST follow the weak host
                (Weak End System) model [RFC1122].  When originating packets
                from an interface, it will use a source address from another
                one of its interfaces if the outgoing interface does not
                have an address of suitable scope.

       WAA-10:  The IPv6 CE router SHOULD implement the Information Refresh
                Time option and associated client behavior as specified in
                [RFC4242].

       Prefix delegation requirements:

       WPD-1:  The IPv6 CE router MUST support DHCPv6 prefix delegation
               requesting router behavior as specified in [RFC3633]
               (Identity Association for Prefix Delegation (IA_PD) option).

       WPD-2:  The IPv6 CE router MAY indicate as a hint to the delegating
               router the size of the prefix it requires.  If so, it MUST
               ask for a prefix large enough to assign one /64 for each of
               its interfaces, rounded up to the nearest nibble, and SHOULD
               be configurable to ask for more.

       WPD-3:  The IPv6 CE router MUST be prepared to accept a delegated
               prefix size different from what is given in the hint.  If the
               delegated prefix is too small to address all of its
               interfaces, the IPv6 CE router SHOULD log a system management
               error.  [RFC6177] covers the recommendations for service
               providers for prefix allocation sizes.

       WPD-4:  By default, the IPv6 CE router MUST initiate DHCPv6 prefix
               delegation when either the M or O flags are set to 1 in a
               received Router Advertisement (RA) message.  Behavior of the
               CE router to use DHCPv6 prefix delegation when the CE router
               has not received any RA or received an RA with the M and the
               O bits set to zero is out of scope for this document.

       WPD-5:  Any packet received by the CE router with a destination
               address in the prefix(es) delegated to the CE router but not
               in the set of prefixes assigned by the CE router to the LAN
               must be dropped.  In other words, the next hop for the
               prefix(es) delegated to the CE router should be the null
               destination.  This is necessary to prevent forwarding loops
               when some addresses covered by the aggregate are not
               reachable [RFC4632].

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          (a)  The IPv6 CE router SHOULD send an ICMPv6 Destination
               Unreachable message in accordance with Section 3.1 of
               [RFC4443] back to the source of the packet, if the packet is
               to be dropped due to this rule.

       WPD-6:  If the IPv6 CE router requests both an IA_NA and an IA_PD
               option in DHCPv6, it MUST accept an IA_PD option in DHCPv6
               Advertise/Reply messages, even if the message does not
               contain any addresses, unless configured to only obtain its
               WAN IPv6 address via DHCPv6; see [DHCPv6-STATEFUL-ISSUES].

       WPD-7:  By default, an IPv6 CE router MUST NOT initiate any dynamic
               routing protocol on its WAN interface.

       WPD-8:  The IPv6 CE router SHOULD support the [RFC6603] Prefix
               Exclude option.

    4.3.  LAN-Side Configuration

       The IPv6 CE router distributes configuration information obtained
       during WAN interface provisioning to IPv6 hosts and assists IPv6
       hosts in obtaining IPv6 addresses.  It also supports connectivity of
       these devices in the absence of any working WAN interface.

       An IPv6 CE router is expected to support an IPv6 end-user network and
       IPv6 hosts that exhibit the following characteristics:

       1.  Link-local addresses may be insufficient for allowing IPv6
           applications to communicate with each other in the end-user
           network.  The IPv6 CE router will need to enable this
           communication by providing globally scoped unicast addresses or
           ULAs [RFC4193], whether or not WAN connectivity exists.

       2.  IPv6 hosts should be capable of using SLAAC and may be capable of
           using DHCPv6 for acquiring their addresses.

       3.  IPv6 hosts may use DHCPv6 for other configuration information,
           such as the DNS_SERVERS option for acquiring DNS information.

       Unless otherwise specified, the following requirements apply to the
       IPv6 CE router's LAN interfaces only.

       ULA requirements:

       ULA-1:  The IPv6 CE router SHOULD be capable of generating a ULA
               prefix [RFC4193].

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       ULA-2:  An IPv6 CE router with a ULA prefix MUST maintain this prefix
               consistently across reboots.

       ULA-3:  The value of the ULA prefix SHOULD be configurable.

       ULA-4:  By default, the IPv6 CE router MUST act as a site border
               router according to Section 4.3 of [RFC4193] and filter
               packets with local IPv6 source or destination addresses
               accordingly.

       ULA-5:  An IPv6 CE router MUST NOT advertise itself as a default
               router with a Router Lifetime greater than zero whenever all
               of its configured and delegated prefixes are ULA prefixes.

       LAN requirements:

       L-1:   The IPv6 CE router MUST support router behavior according to
              Neighbor Discovery for IPv6 [RFC4861].

       L-2:   The IPv6 CE router MUST assign a separate /64 from its
              delegated prefix(es) (and ULA prefix if configured to provide
              ULA addressing) for each of its LAN interfaces.

       L-3:   An IPv6 CE router MUST advertise itself as a router for the
              delegated prefix(es) (and ULA prefix if configured to provide
              ULA addressing) using the "Route Information Option" specified
              in Section 2.3 of [RFC4191].  This advertisement is
              independent of having or not having IPv6 connectivity on the
              WAN interface.

       L-4:   An IPv6 CE router MUST NOT advertise itself as a default
              router with a Router Lifetime [RFC4861] greater than zero if
              it has no prefixes configured or delegated to it.

       L-5:   The IPv6 CE router MUST make each LAN interface an advertising
              interface according to [RFC4861].

       L-6:   In Router Advertisement messages ([RFC4861]), the Prefix
              Information option's A and L flags MUST be set to 1 by
              default.

       L-7:   The A and L flags' ([RFC4861]) settings SHOULD be user
              configurable.

       L-8:   The IPv6 CE router MUST support a DHCPv6 server capable of
              IPv6 address assignment according to [RFC3315] OR a stateless
              DHCPv6 server according to [RFC3736] on its LAN interfaces.

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       L-9:   Unless the IPv6 CE router is configured to support the DHCPv6
              IA_NA option, it SHOULD set the M flag to zero and the O flag
              to 1 in its Router Advertisement messages [RFC4861].

       L-10:  The IPv6 CE router MUST support providing DNS information in
              the DHCPv6 DNS_SERVERS and DOMAIN_LIST options [RFC3646].

       L-11:  The IPv6 CE router MUST support providing DNS information in
              the Router Advertisement Recursive DNS Server (RDNSS) and DNS
              Search List options.  Both options are specified in [RFC6106].

       L-12:  The IPv6 CE router SHOULD make available a subset of DHCPv6
              options (as listed in Section 5.3 of [RFC3736]) received from
              the DHCPv6 client on its WAN interface to its LAN-side DHCPv6
              server.

       L-13:  If the delegated prefix changes, i.e., the current prefix is
              replaced with a new prefix without any overlapping time
              period, then the IPv6 CE router MUST immediately advertise the
              old prefix with a Preferred Lifetime of zero and a Valid
              Lifetime of either a) zero or b) the lower of the current
              Valid Lifetime and two hours (which must be decremented in
              real time) in a Router Advertisement message as described in
              Section 5.5.3, (e) of [RFC4862].

       L-14:  The IPv6 CE router MUST send an ICMPv6 Destination Unreachable
              message, code 5 (Source address failed ingress/egress policy)
              for packets forwarded to it that use an address from a prefix
              that has been invalidated.

    4.4.  Transition Technologies Support

    4.4.1.  6rd

       6rd [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 CE router's native IPv4 WAN interface and not
       encapsulated in another tunnel.

       The CE router SHOULD support 6rd functionality.  If 6rd is supported,
       it MUST be implemented according to [RFC5969].  The following CE
       Requirements also apply:

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       6rd requirements:

       6RD-1:  The IPv6 CE router MUST support 6rd configuration via the 6rd
               DHCPv4 Option 212.  If the CE router has obtained an IPv4
               network address through some other means such as PPP, it
               SHOULD use the DHCPINFORM request message [RFC2131] to
               request the 6rd DHCPv4 Option.  The IPv6 CE router MAY use
               other mechanisms to configure 6rd parameters.  Such
               mechanisms are outside the scope of this document.

       6RD-2:  If the IPv6 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.

       6RD-3:  If the CE router supports configuration mechanisms other than
               the 6rd DHCPv4 Option 212 (user-entered, TR-069 [TR-069],
               etc.), the 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
               [RFC5969].

       6RD-4:  A 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
               migration period such as a migration from 6rd to native IPv6.

       6RD-5:  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
               [RFC3704]).

       6RD-6:  The CE router MUST allow different as well as identical
               delegated prefixes to be configured via each (6rd or native)
               WAN interface.

       6RD-7:  In the event that forwarding rules produce a tie between 6rd
               and native IPv6, by default, the IPv6 CE router MUST prefer
               native IPv6.

    4.4.2.  Dual-Stack Lite (DS-Lite)

       Dual-Stack Lite [RFC6333] enables both continued support for IPv4
       services and incentives for the deployment of IPv6.  It also
       de-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

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       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 CE router's
       native IPv6 WAN interface, and not encapsulated in another tunnel.

       The IPv6 CE router SHOULD implement DS-Lite functionality.  If
       DS-Lite is supported, it MUST be implemented according to [RFC6333].
       This document takes no position on simultaneous operation of Dual-
       Stack Lite and native IPv4.  The following CE router requirements
       also apply:

       WAN requirements:

       DLW-1:  The CE router MUST support configuration of DS-Lite via the
               DS-Lite DHCPv6 option [RFC6334].  The IPv6 CE router MAY use
               other mechanisms to configure DS-Lite parameters.  Such
               mechanisms are outside the scope of this document.

       DLW-2:  The IPv6 CE router MUST NOT perform IPv4 Network Address
               Translation (NAT) on IPv4 traffic encapsulated using DS-Lite.

       DLW-3:  If the IPv6 CE router is configured with an IPv4 address on
               its WAN interface, then the IPv6 CE router SHOULD disable the
               DS-Lite Basic Bridging BroadBand (B4) element.

    4.5.  Security Considerations

       It is considered a best practice to filter obviously malicious
       traffic (e.g., spoofed packets, "Martian" addresses, etc.).  Thus,
       the IPv6 CE router ought to support basic stateless egress and
       ingress filters.  The CE router is also expected to offer mechanisms
       to filter traffic entering the customer network; however, the method
       by which vendors implement configurable packet filtering is beyond
       the scope of this document.

       Security requirements:

       S-1:  The IPv6 CE router SHOULD support [RFC6092].  In particular,
             the IPv6 CE router SHOULD support functionality sufficient for
             implementing the set of recommendations in [RFC6092],
             Section 4.  This document takes no position on whether such
             functionality is enabled by default or mechanisms by which
             users would configure it.

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    RFC 7084               IPv6 CE Router Requirements         November 2013

       S-2:  The IPv6 CE router SHOULD support ingress filtering in
             accordance with BCP 38 [RFC2827].  Note that this requirement
             was downgraded from a MUST from RFC 6204 due to the difficulty
             of implementation in the CE router and the feature's redundancy
             with upstream router ingress filtering.

       S-3:  If the IPv6 CE router firewall is configured to filter incoming
             tunneled data, the firewall SHOULD provide the capability to
             filter decapsulated packets from a tunnel.

    5.  Acknowledgements

       Thanks to the following people (in alphabetical order) for their
       guidance and feedback:

       Mikael Abrahamsson, Tore Anderson, Merete Asak, Rajiv Asati, Scott
       Beuker, Mohamed Boucadair, Rex Bullinger, Brian Carpenter, Tassos
       Chatzithomaoglou, Lorenzo Colitti, Remi Denis-Courmont, Gert Doering,
       Alain Durand, Katsunori Fukuoka, Brian Haberman, Tony Hain, Thomas
       Herbst, Ray Hunter, Joel Jaeggli, Kevin Johns, Erik Kline, Stephen
       Kramer, Victor Kuarsingh, Francois-Xavier Le Bail, Arifumi Matsumoto,
       David Miles, Shin Miyakawa, Jean-Francois Mule, Michael Newbery,
       Carlos Pignataro, John Pomeroy, Antonio Querubin, Daniel Roesen,
       Hiroki Sato, Teemu Savolainen, Matt Schmitt, David Thaler, Mark
       Townsley, Sean Turner, Bernie Volz, Dan Wing, Timothy Winters, James
       Woodyatt, Carl Wuyts, and Cor Zwart.

       This document is based in part on CableLabs' eRouter specification.
       The authors wish to acknowledge the additional contributors from the
       eRouter team:

       Ben Bekele, Amol Bhagwat, Ralph Brown, Eduardo Cardona, Margo Dolas,
       Toerless Eckert, Doc Evans, Roger Fish, Michelle Kuska, Diego
       Mazzola, John McQueen, Harsh Parandekar, Michael Patrick, Saifur
       Rahman, Lakshmi Raman, Ryan Ross, Ron da Silva, Madhu Sudan, Dan
       Torbet, and Greg White.

    6.  Contributors

       The following people have participated as co-authors or provided
       substantial contributions to this document: Ralph Droms, Kirk
       Erichsen, Fred Baker, Jason Weil, Lee Howard, Jean-Francois Tremblay,
       Yiu Lee, John Jason Brzozowski, and Heather Kirksey.  Thanks to Ole
       Troan for editorship in the original RFC 6204 document.

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    RFC 7084               IPv6 CE Router Requirements         November 2013

    7.  References

    7.1.  Normative References

       [RFC1122]  Braden, R., "Requirements for Internet Hosts -
                  Communication Layers", STD 3, RFC 1122, October 1989.

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

       [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol", RFC
                  2131, March 1997.

       [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
                  Networks", RFC 2464, December 1998.

       [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
                  Defeating Denial of Service Attacks which employ IP Source
                  Address Spoofing", BCP 38, RFC 2827, May 2000.

       [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
                  and M. Carney, "Dynamic Host Configuration Protocol for
                  IPv6 (DHCPv6)", RFC 3315, July 2003.

       [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
                  Host Configuration Protocol (DHCP) version 6", RFC 3633,
                  December 2003.

       [RFC3646]  Droms, R., "DNS Configuration options for Dynamic Host
                  Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
                  December 2003.

       [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
                  Networks", BCP 84, RFC 3704, March 2004.

       [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
                  (DHCP) Service for IPv6", RFC 3736, April 2004.

       [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
                  More-Specific Routes", RFC 4191, November 2005.

       [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
                  Addresses", RFC 4193, October 2005.

       [RFC4242]  Venaas, S., Chown, T., and B. Volz, "Information Refresh
                  Time Option for Dynamic Host Configuration Protocol for
                  IPv6 (DHCPv6)", RFC 4242, November 2005.

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    RFC 7084               IPv6 CE Router Requirements         November 2013

       [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
                  Message Protocol (ICMPv6) for the Internet Protocol
                  Version 6 (IPv6) Specification", RFC 4443, March 2006.

       [RFC4605]  Fenner, B., He, H., Haberman, B., and H. Sandick,
                  "Internet Group Management Protocol (IGMP) / Multicast
                  Listener Discovery (MLD)-Based Multicast Forwarding
                  ("IGMP/MLD Proxying")", RFC 4605, August 2006.

       [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
                  (CIDR): The Internet Address Assignment and Aggregation
                  Plan", BCP 122, RFC 4632, August 2006.

       [RFC4779]  Asadullah, S., Ahmed, A., Popoviciu, C., Savola, P., and
                  J. Palet, "ISP IPv6 Deployment Scenarios in Broadband
                  Access Networks", RFC 4779, January 2007.

       [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
                  "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
                  September 2007.

       [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
                  Address Autoconfiguration", RFC 4862, September 2007.

       [RFC5072]  Varada, S., Haskins, D., and E. Allen, "IP Version 6 over
                  PPP", RFC 5072, September 2007.

       [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
                  Time Protocol Version 4: Protocol and Algorithms
                  Specification", RFC 5905, June 2010.

       [RFC5908]  Gayraud, R. and B. Lourdelet, "Network Time Protocol (NTP)
                  Server Option for DHCPv6", RFC 5908, June 2010.

       [RFC5942]  Singh, H., Beebee, W., and E. Nordmark, "IPv6 Subnet
                  Model: The Relationship between Links and Subnet
                  Prefixes", RFC 5942, July 2010.

       [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
                  Infrastructures (6rd) -- Protocol Specification", RFC
                  5969, August 2010.

       [RFC6092]  Woodyatt, J., "Recommended Simple Security Capabilities in
                  Customer Premises Equipment (CPE) for Providing
                  Residential IPv6 Internet Service", RFC 6092, January
                  2011.

    Singh, et al.                 Informational                    [Page 19]

    RFC 7084               IPv6 CE Router Requirements         November 2013

       [RFC6106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
                  "IPv6 Router Advertisement Options for DNS Configuration",
                  RFC 6106, November 2010.

       [RFC6177]  Narten, T., Huston, G., and L. Roberts, "IPv6 Address
                  Assignment to End Sites", BCP 157, RFC 6177, March 2011.

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

       [RFC6334]  Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
                  Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
                  RFC 6334, August 2011.

       [RFC6434]  Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
                  Requirements", RFC 6434, December 2011.

       [RFC6603]  Korhonen, J., Savolainen, T., Krishnan, S., and O. Troan,
                  "Prefix Exclude Option for DHCPv6-based Prefix
                  Delegation", RFC 6603, May 2012.

       [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
                  Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
                  2013.

       [RFC7083]  Droms, R., "Modification to Default Values of SOL_MAX_RT
                  and INF_MAX_RT", RFC 7083, November 2013.

    7.2.  Informative References

       [DHCPv6-STATEFUL-ISSUES]
                  Troan, O. and B. Volz, "Issues with multiple stateful
                  DHCPv6 options", Work in Progress, May 2013.

       [MULTIHOMING-WITHOUT-NAT]
                  Troan, O., Ed., Miles, D., Matsushima, S., Okimoto, T.,
                  and D. Wing, "IPv6 Multihoming without Network Address
                  Translation", Work in Progress, December 2010.

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

       [TR-069]   Broadband Forum, "CPE WAN Management Protocol", TR-069
                  Amendment 4, July 2011,
                  <http://www.broadband-forum.org/technical/trlist.php>.

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    RFC 7084               IPv6 CE Router Requirements         November 2013

       [UPnP-IGD] UPnP Forum, , "InternetGatewayDevice:2 Device Template
                  Version 1.01", December 2010,
                  <http://upnp.org/specs/gw/igd2/>.

    Authors' Addresses

       Hemant Singh
       Cisco Systems, Inc.
       1414 Massachusetts Ave.
       Boxborough, MA  01719
       USA

       Phone: +1 978 936 1622
       EMail: shemant@cisco.com
       URI:   http://www.cisco.com/

       Wes Beebee
       Cisco Systems, Inc.
       1414 Massachusetts Ave.
       Boxborough, MA  01719
       USA

       Phone: +1 978 936 2030
       EMail: wbeebee@cisco.com
       URI:   http://www.cisco.com/

       Chris Donley
       CableLabs
       858 Coal Creek Circle
       Louisville, CO  80027
       USA

       EMail: c.donley@cablelabs.com

       Barbara Stark
       AT&T
       1057 Lenox Park Blvd. NE
       Atlanta, GA  30319
       USA

       EMail: barbara.stark@att.com

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