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Versions: (draft-ietf-v6ops-ipv6-cpe-router-bis) 00 01 02 03 04 05 06 07 08 09 RFC 7084

Network Working Group                                           H. Singh
Internet-Draft                                                 W. Beebee
Updates: 6204 (if approved)                          Cisco Systems, Inc.
Intended status: Standards Track                               C. Donley
Expires: April 9, 2012                                         CableLabs
                                                                B. Stark
                                                                     ATT
                                                           O. Troan, Ed.
                                                     Cisco Systems, Inc.
                                                         October 7, 2011


           Basic Requirements for IPv6 Customer Edge Routers
                      draft-ietf-v6ops-6204bis-00

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.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 9, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Architecture . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Current IPv4 End-User Network Architecture . . . . . . . .  4
     3.2.  IPv6 End-User Network Architecture . . . . . . . . . . . .  5
       3.2.1.  Local Communication  . . . . . . . . . . . . . . . . .  6
   4.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.1.  General Requirements . . . . . . . . . . . . . . . . . . .  7
     4.2.  WAN-Side Configuration . . . . . . . . . . . . . . . . . .  7
     4.3.  LAN-Side Configuration . . . . . . . . . . . . . . . . . . 10
     4.4.  Transition Technologies Support  . . . . . . . . . . . . . 13
       4.4.1.  6rd  . . . . . . . . . . . . . . . . . . . . . . . . . 13
       4.4.2.  Dual-Stack(DS)-Lite  . . . . . . . . . . . . . . . . . 14
       4.4.3.  Transition Technologies Coexistence  . . . . . . . . . 15
     4.5.  Security Considerations  . . . . . . . . . . . . . . . . . 15
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   6.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19




















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1.  Introduction

   This document defines basic IPv6 features for a residential or small-
   office router, referred to as an IPv6 CE router.  Typically, these
   routers 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.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


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
                             Ethernets (simple or bridged), 802.11
                             wireless, or other LAN technologies.  An
                             IPv6 CE router may have one or more



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                             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 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 Ethernets (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.


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; i.e., 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.

   Rewriting addresses on the edge of the network also allows for some
   rudimentary multihoming, even though using NATs for multihoming does
   not preserve connections during a fail-over event [RFC4864].



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   Many existing routers support dynamic routing, 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.

   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



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   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.

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.

   A dual-stack host is multihomed to IPv4 and IPv6 networks.  The IPv4
   and IPv6 topologies may not be congruent, and different addresses may
   have different reachability, e.g., ULAs.  A host stack has to be able
   to quickly fail over and try a different source address and
   destination address pair if communication fails, as outlined in
   [HAPPY-EYEBALLS].

   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.

   In the event that more than one IPv6 CE router is present on the LAN,
   then coexistence with IPv4 requires all of them to conform to these
   recommendations, especially requirements ULA-5 and L-4 below.







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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.

   G-1:  An IPv6 CE router is an IPv6 node according to the IPv6 Node
         Requirements [RFC4294] specification.

   G-2:  The IPv6 CE router MUST implement ICMP 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 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) 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



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   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.

   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 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:  DHCPv6 address assignment (IA_NA) and DHCPv6 prefix delegation
         (IA_PD) SHOULD be done as a single DHCPv6 session.

   W-6:  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.

   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.

   Address assignment requirements:





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   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: IA_NA, Reconfigure Accept [RFC3315], and
           DNS_SERVERS [RFC3646].

   WAA-5:  The IPv6 CE router SHOULD support the DHCPv6 Simple Network
           Time Protocol (SNTP) option [RFC4075] and the Information
           Refresh Time option [RFC4242].

   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 is unable to assign address(es) through
           SLAAC, it MAY do DHCPv6 address assignment (request an IA_NA
           option) even if the M flag is set to 0.

   WAA-8:  If the IPv6 CE router does not acquire global IPv6
           address(es) from either SLAAC or DHCPv6, then it MUST create
           global IPv6 address(es) from its delegated prefix(es) and
           configure those on one of its internal virtual network
           interfaces.

   WAA-9:  As a router, the IPv6 CE router MUST follow the weak host
           (Weak ES) 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.

   Prefix delegation requirements:

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







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   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 MUST 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.

   WPD-4:  The IPv6 CE router MUST always initiate DHCPv6 prefix
           delegation, regardless of the M and O flags in a received
           Router Advertisement message.

   WPD-5:  If the IPv6 CE router initiates DHCPv6 before receiving a
           Router Advertisement, it MUST also request an IA_NA option in
           DHCPv6.

   WPD-6:  If the delegated prefix(es) are aggregate route(s) of
           multiple, more-specific routes, the IPv6 CE router MUST
           discard packets that match the aggregate route(s), but not
           any of the more-specific routes.  In other words, the next
           hop for the aggregate route(s) should be the null
           destination.  This is necessary to prevent forwarding loops
           when some addresses covered by the aggregate are not
           reachable [RFC4632].

           (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-7:  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.

   WPD-8:  By default, an IPv6 CE router MUST NOT initiate any dynamic
           routing protocol on its WAN interface.

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.



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   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].

   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 user-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.






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   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, the Prefix Information
          option's A and L flags MUST be set to 1 by default.

   L-7:   The A and L flags' 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.

   L-9:   Unless the IPv6 CE router is configured to support the DHCPv6
          IA_NA option, it SHOULD set the M flag to 0 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 SHOULD support providing DNS information in
          the Router Advertisement Recursive DNS Server (RDNSS) and DNS
          Search List (DNSSL) options as 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 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].




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   L-14:  The IPv6 CE router MUST send an ICMP 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 deprecated.

4.4.  Transition Technologies Support

4.4.1.  6rd

   The IPv6 CE Router can be used to offer IPv6 service to a LAN, even
   when the WAN access network only supports IPv4.  One technology that
   supports IPv6 service over an IPv4 network is IPv6 Rapid Deployment
   (6rd). 6rd encapsulates IPv6 traffic from the end user LAN inside
   IPv4 at the IPv6 CE Router and sends it to a Service Provider Border
   Relay (BR).  The IPv6 CE Router calculates a 6rd delegated IPv6
   prefix during 6rd configuration, and sub-delegates the 6rd delegated
   prefix to devices in the LAN.

   The IPv6 CE Router SHOULD implement 6rd functionality as specified in
   [RFC5969].

   6rd requirements:

   6RD-1:  If the IPv6 CE Router implements 6rd functionality, the CE
           Router WAN interface MUST support at least one 6rd Virtual
           Interface and 6rd CE functionality as specified in [RFC5969].

   6RD-2:  If the IPv6 CE Router implements 6rd CE functionality, it
           MUST support user-entered configuration and using the 6rd
           DHCPv4 Option (212) for 6rd configuration.  The IPv6 CE
           Router MAY use other mechanisms to configure 6rd parameters.
           Such mechanisms are outside the scope of this document.

   6RD-3:  If the CE router implements 6rd functionality, it MUST allow
           the user to specify whether all IPv6 traffic goes to the 6rd
           Border Relay, or whether other destinations within the same
           6rd domain are routed directly to those destinations.  The CE
           router MAY use other mechanisms to configure this.  Such
           mechanisms are outside the scope of this document.

   6RD-4:  If 6rd is operational on the IPv6 CE Router, multicast data
           MUST NOT be sent on any 6rd tunnel.

   6RD-5:  The CE Router MUST NOT forward 6RD traffic over a DS-Lite
           ([RFC6333]) tunnel.






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4.4.2.  Dual-Stack(DS)-Lite

   Even as users migrate from IPv4 to IPv6 addressing, a significant
   percentage of Internet resources and content will remain accessible
   only through IPv4.  Also, many end-user devices will only support
   IPv4.  As a consequence, Service Providers require mechanisms to
   allow customers to continue to access content and resources using
   IPv4 even after the last IPv4 allocations have been fully depleted.
   One technology that can be used for IPv4 address extension is DS-
   Lite.

   DS-Lite enables a Service Provider to share IPv4 addresses among
   multiple customers by combining two well-known technologies: IP in IP
   (IPv4-in-IPv6) tunneling and Carrier Grade NAT.  More specifically,
   Dual-Stack-Lite encapsulates IPv4 traffic inside an IPv6 tunnel at
   the IPv6 CE Router and sends it to a Service Provider Address Family
   Translation Router (AFTR).  Configuration of the IPv6 CE Router to
   support IPv4 LAN traffic is outside the scope of this document.

   The IPv6 CE Router SHOULD implement DS-Lite functionality as
   specified in [RFC6333].

   WAN requirements:

   DLW-1:  To facilitate IPv4 extension over an IPv6 network, if the CE
           Router supports DS-Lite functionality, the CE Router WAN
           interface MUST implement a B4 Interface as specified in
           [RFC6333].

   DLW-2:  If the IPv6 CE Router implements DS-Lite functionality, the
           CE Router MUST support using a DS-Lite DHCPv6 option
           [I-D.ietf-softwire-ds-lite-tunnel-option] to configure the
           DS-Lite tunnel.  The IPv6 CE Router MAY use other mechanisms
           to configure DS-Lite parameters.  Such mechanisms are outside
           the scope of this document.

   DLW-3:  IPv6 CE Router MUST NOT perform IPv4 Network Address
           Translation (NAT) on IPv4 traffic encapsulated using DS-Lite.

   DLW-4:  If the IPv6 CE Router is configured with a public IPv4
           address on its WAN interface, where public IPv4 address is
           defined as any address which is not in the private IP address
           space specified in [RFC1918] and also not in the reserved IP
           address space specified in [RFC6333], then the IPv6 CE Router
           MUST disable the DS-Lite B4 element.






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   DLW-5:  If DS-Lite is operational on the IPv6 CE Router, multicast
           data MUST NOT be sent on any DS-Lite tunnel.

   DLW-6:  The CE Router MUST NOT forward DS-Lite traffic over a 6RD
           tunnel.

4.4.3.  Transition Technologies Coexistence

   Run the following four in parallel to provision CPE router
   connectivity to the Service Provider:

   1.  Initiate IPv4 address acquisition.

   2.  Initiate IPv6 address acquisition as specified by [RFC6204].

   3.  If 6rd is provisioned, initiate 6rd.

   4.  If DS-Lite is provisioned, initiate DS-Lite.

   The default route for IPv6 through the native physical interface has
   preference over the 6rd tunnel interface.  The default route for IPv4
   through the native physical interface has preference over the DS-Lite
   tunnel interface.

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.

   S-2:  The IPv6 CE router MUST support ingress filtering in accordance
         with BCP 38 [RFC2827].






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5.  Acknowledgements

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

   Mikael Abrahamsson, Tore Anderson, Merete Asak, Scott Beuker, Mohamed
   Boucadair, Rex Bullinger, Brian Carpenter, Lorenzo Colitti, Remi
   Denis-Courmont, Gert Doering, Alain Durand, Katsunori Fukuoka, Tony
   Hain, Thomas Herbst, 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, Hiroki Sato, Teemu Savolainen, Matt
   Schmitt, David Thaler, Mark Townsley, Bernie Volz, Dan Wing, James
   Woodyatt, 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.


7.  References

7.1.  Normative References

   [I-D.ietf-softwire-ds-lite-tunnel-option]
              Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
              Protocol for IPv6 (DHCPv6) Option for Dual- Stack Lite",
              draft-ietf-softwire-ds-lite-tunnel-option-10 (work in
              progress), March 2011.

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

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and



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              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

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

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

   [RFC4075]  Kalusivalingam, V., "Simple Network Time Protocol (SNTP)
              Configuration Option for DHCPv6", RFC 4075, May 2005.

   [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.

   [RFC4294]  Loughney, J., "IPv6 Node Requirements", RFC 4294,
              April 2006.

   [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.




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   [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.

   [RFC4864]  Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
              E. Klein, "Local Network Protection for IPv6", RFC 4864,
              May 2007.

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

   [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.

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

   [RFC6204]  Singh, H., Beebee, W., Donley, C., Stark, B., and O.
              Troan, "Basic Requirements for IPv6 Customer Edge
              Routers", RFC 6204, April 2011.




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

7.2.  Informative References

   [HAPPY-EYEBALLS]
              Wing, D. and A. Yourtchenko, "Happy Eyeballs: Trending
              Towards Success with Dual-Stack Hosts", Work in Progress,
              March 2011.

   [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, March 2011.

   [UPnP-IGD]
              UPnP Forum, "Universal Plug and Play (UPnP) Internet
              Gateway Device (IGD)", November 2001,
              <http://www.upnp.org/>.

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/





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

   EMail: c.donley@cablelabs.com


   Barbara Stark
   ATT
   725 W Peachtree St.
   Atlanta, GA  30308
   USA

   EMail: barbara.stark@att.com


   Ole Troan (editor)
   Cisco Systems, Inc.
   Telemarksvingen 20
   N-0655 OSLO,
   Norway

   EMail: ot@cisco.com


























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