Requirements for IPv6 Customer Edge Routers to Support IPv4 Connectivity as-a-Service
draft-ietf-v6ops-transition-ipv4aas-11

IPv6 Operations (v6ops)                                J. Palet Martinez
Internet-Draft                                          The IPv6 Company
Intended status: Informational                              H. M.-H. Liu
Expires: June 3, 2019                               D-Link Systems, Inc.
                                                            M. Kawashima
                                                     NEC Platforms, Ltd.
                                                       November 30, 2018

Requirements for IPv6 Customer Edge Routers to Support IPv4 Connectivity
                              as-a-Service
                 draft-ietf-v6ops-transition-ipv4aas-11

Abstract

   This document specifies the IPv4 service continuity requirements for
   an IPv6 Customer Edge (CE) router, either provided by the service
   provider or through the retail market.

   Specifically, this document extends the "Basic Requirements for IPv6
   Customer Edge Routers" in order to allow the provisioning of IPv6
   transition services for the support of "IPv4 as-a-Service" (IPv4aaS)
   by means of new transition mechanisms.  The document only covers
   transition technologies for delivering IPv4 in IPv6-only access
   networks, commonly called "IPv4 as-a-Service" (IPv4aaS).  This is
   necessary because there aren't sufficient IPv4 addresses available
   for every possible customer/device.  However, devices or applications
   in the customer LANs may be IPv4-only or IPv6-only and still need to
   communicate with IPv4-only services at the Internet.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on June 3, 2019.

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Copyright Notice

   Copyright (c) 2018 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
   (https://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
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   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 - Special Note  . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  LAN-Side Configuration  . . . . . . . . . . . . . . . . .   5
     3.2.  Transition Technologies Support for IPv4 Service
           Continuity        (IPv4 as-a-Service - IPv4aaS) . . . . .   5
       3.2.1.  464XLAT . . . . . . . . . . . . . . . . . . . . . . .   6
       3.2.2.  Dual-Stack Lite (DS-Lite) . . . . . . . . . . . . . .   7
       3.2.3.  Lightweight 4over6 (lw4o6)  . . . . . . . . . . . . .   8
       3.2.4.  MAP-E . . . . . . . . . . . . . . . . . . . . . . . .   9
       3.2.5.  MAP-T . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  IPv4 Multicast Support  . . . . . . . . . . . . . . . . . . .  10
   5.  UPnP Support  . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Comparison to RFC7084 . . . . . . . . . . . . . . . . . . . .  11
   7.  Code Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   11. Annex A: Usage Scenarios  . . . . . . . . . . . . . . . . . .  12
   12. Annex B: End-User Network Architecture  . . . . . . . . . . .  14
   13. ANNEX C: Changes from -00 . . . . . . . . . . . . . . . . . .  16
   14. ANNEX D: Changes from -01 . . . . . . . . . . . . . . . . . .  16
   15. ANNEX E: Changes from -02 . . . . . . . . . . . . . . . . . .  16
   16. ANNEX F: Changes from -03 . . . . . . . . . . . . . . . . . .  17
   17. ANNEX G: Changes from -04 . . . . . . . . . . . . . . . . . .  17
   18. ANNEX H: Changes from -05 . . . . . . . . . . . . . . . . . .  17
   19. ANNEX I: Changes from -06 . . . . . . . . . . . . . . . . . .  17
   20. ANNEX J: Changes from -07 . . . . . . . . . . . . . . . . . .  17
   21. ANNEX K: Changes from -08, -09 and -10  . . . . . . . . . . .  18
   22. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18

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     22.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     22.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   This document defines IPv4 service continuity features over an
   IPv6-only network, for a residential or small-office router, referred
   to as an "IPv6 Transition CE Router", in order to establish an
   industry baseline for transition features to be implemented on such a
   router.

   These routers rely upon "Basic Requirements for IPv6 Customer Edge
   Routers" ([RFC7084]), so the scope of this document is to ensure the
   IPv4 "service continuity" support, in the LAN side and the access to
   IPv4-only Internet services from an IPv6-only access WAN even from
   IPv6-only applications or devices in the LAN side.

   This document covers a set of IP transition techniques required when
   ISPs have, or want to have, an IPv6-only access network.  This is a
   common situation in when sufficient IPv4 addresses are no longer
   available for every possible customer and device, causing IPv4
   addresses to become prohibitive expense.  This, in turn, may result
   in service providers provisioning IPv6-only WAN access.  At the same
   time, they need to ensure that both IPv4-only and IPv6-only devices
   or applications in the customer networks can still reach IPv4-only
   devices and applications in the Internet.

   This document specifies the IPv4 service continuity mechanisms to be
   supported by an IPv6 Transition CE Router, and relevant provisioning
   or configuration information differences from [RFC7084].

   This document is not a recommendation for service providers to use
   any specific transition mechanism.

   Automatic provisioning of more complex topology than a single router
   with multiple LAN interfaces may be handled by means of HNCP
   ([RFC7788]), which is out of the scope of this document.

   Service providers who specify feature sets for IPv6 Transition CE
   Router may specify a different set of features than those included in
   this document.  Since it is impossible to know prior to sale which
   transition mechanism a device will need over the lifetime of the
   device, IPv6 Transition CE Router intended for the retail market MUST
   support all the IPv4aaS transition mechanism supported by this
   document.

   A complete description of "Usage Scenarios" and "End-User Network

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   Architecture" is provided in Annexes A and B, respectively.

1.1.  Requirements Language - Special Note

   The keywords "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 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-only access networks.

   Additionally, the keyword "DEFAULT" is to be interpreted in this
   document as pertaining to a configuration as applied by a vendor,
   prior to the administrator changing it for its initial activation.

2.  Terminology

   This document uses the same terms as in [RFC7084], with minor
   clarifications.

   "IPv4aaS" stands for "IPv4 as-a-Service", meaning transition
   technologies for delivering IPv4 in IPv6-only connectivity.

   The term "IPv6 transition Customer Edge Router with IPv4aaS"
   (shortened as "IPv6 Transition CE Router") is defined as an "IPv6
   Customer Edge Router" that provides features for the delivery of IPv4
   services over an IPv6-only WAN network, including IPv6-IPv4
   communications.

   The "WAN Interface" term used across this document, defines an IPv6
   Transition CE Router attachment to an IPv6-only link used to provide
   connectivity to a service provider network, including link Internet-
   layer (or higher layers) "tunnels", such as IPv4-in-IPv6 tunnels.

3.  Requirements

   The IPv6 Transition CE Router MUST comply with [RFC7084] (Basic
   Requirements for IPv6 Customer Edge Routers) and this document adds
   new requirements, as described in the following sub-sections.

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3.1.  LAN-Side Configuration

   A new LAN requirement is added, which in fact is common in regular
   IPv6 Transition CE Router, and it is required by most of the
   transition mechanisms:

   L-1:  The IPv6 Transition CE Router MUST implement a DNS proxy as
         described in [RFC5625] (DNS Proxy Implementation Guidelines).

3.2.  Transition Technologies Support for IPv4 Service Continuity (IPv4
      as-a-Service - IPv4aaS)

   The main target of this document is the support of IPv6-only WAN
   access.  To enable legacy IPv4 functionality, this document also
   includes the support of IPv4-only devices and applications in the
   customers LANs, as well as IPv4-only services on the Internet.  Thus,
   both IPv4-only and the IPv6-only devices in the customer-side LANs of
   the IPv6 Transition CE Router are able to reach the IPv4-only
   services.

   This document takes no position on simultaneous operation of one or
   several transition mechanisms and/or native IPv4.

   In order to seamlessly provide the IPv4 Service Continuity in
   Customer LANs, allowing an automated IPv6 transition mechanism
   provisioning, general transition requirements are defined.

   General transition requirements:

   TRANS-1:  The IPv6 Transition CE Router MUST support the DHCPv6 S46
             priority options described in [RFC8026] (Unified IPv4-in-
             IPv6 Softwire Customer Premises Equipment (CPE): A
             DHCPv6-Based Prioritization Mechanism).

   TRANS-2:  The IPv6 Transition CE Router MUST have a GUI, CLI and/or
             API option to manually enable/disable each of the supported
             transition mechanisms.

   TRANS-3:  If an IPv6 Transition CE Router supports more than one LAN
             subnet, the IPv6 Transition CE Router MUST allow
             appropriate subnetting and configuring the address space
             (which may depend on each transition mechanism) among the
             several interfaces.  In some transition mechanisms, this
             may require differentiating mappings/translations per
             interfaces.

   In order to allow the service provider to disable all the transition
   mechanisms and/or choose the most convenient one, the IPv6 Transition

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   CE Router MUST follow the following configuration steps:

   CONFIG-1:  Request the relevant configuration options for each
              supported transition mechanisms, which MUST remain
              disabled at this step.

   CONFIG-2:  Following Section 1.4 of [RFC8026], MUST check for a valid
              match in OPTION_S46_PRIORITY, which allows enabling/
              disabling a transition mechanism.

   CONFIG-3:  Keep disabled all the transition mechanisms if no match is
              found between the priority list and the candidate list.

   The following sections describe the requirements for supporting each
   one of the transition mechanisms.  An IPv6 Transition CE Router
   intended for the retail market MUST support all of them.

3.2.1.  464XLAT

   464XLAT [RFC6877] is a technique to provide IPv4 service over an
   IPv6-only access network without encapsulation.  This architecture
   assumes a NAT64 [RFC6146] (Stateful NAT64: Network Address and
   Protocol Translation from IPv6 Clients to IPv4 Servers) function
   deployed at the service provider or a third-party network.

   The IPv6 Transition CE Router SHOULD support CLAT functionality.  If
   464XLAT is supported, it MUST be implemented according to [RFC6877].
   The following IPv6 Transition CE Router requirements also apply:

   464XLAT requirements:

   464XLAT-1:  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, either using DHCPv6-PD [RFC3633] (IPv6 Prefix
               Options for DHCPv6) or by alternative means.

   464XLAT-2:  The IPv6 Transition CE Router SHOULD support IGD-PCP IWF
               [RFC6970] (UPnP Internet Gateway Device - Port Control
               Protocol Interworking Function).

   464XLAT-3:  If PCP ([RFC6887]) is implemented, the IPv6 Transition CE
               Router MUST also implement [RFC7291] (DHCP Options for
               the PCP).  Following ([RFC6887]), if no PCP server is
               configured, the IPv6 Transition CE Router MAY verify if
               the default gateway, or the NAT64 is the PCP server.
               Plain IPv6 mode (i.e., no IPv4-in-IPv6 encapsulation is
               used) MUST be used to send PCP requests to the server.

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   464XLAT-4:  The IPv6 Transition CE Router MUST implement [RFC7050]
               (Discovery of the IPv6 Prefix Used for IPv6 Address
               Synthesis) in order to discover the PLAT-side translation
               IPv4 and IPv6 prefix(es)/suffix(es).

   464XLAT-5:  If PCP is implemented, the IPv6 Transition CE Router MUST
               follow [RFC7225] (Discovering NAT64 IPv6 Prefixes Using
               the PCP), in order to learn the PLAT-side translation
               IPv4 and IPv6 prefix(es)/suffix(es) used by an upstream
               PCP-controlled NAT64 device.

   464XLAT-6:  [RFC8115] MUST be implemented and a DHCPv6 Option
               "OPTION_V6_PREFIX64" ([RFC8115]), with zeroed
               ASM_mPrefix64 and SSM_mPrefix64, MUST also be considered
               as a valid NAT64 prefix (uPrefix64).

   464XLAT-7:  The priority for the NAT64 prefix, in case the network
               provides several choices, MUST be: 1) [RFC7225], 2)
               [RFC8115], and 3) [RFC7050].

   464XLAT-8:  If a DHCPv6 Option "OPTION_V6_PREFIX64" ([RFC8115]), with
               zeroed ASM_mPrefix64 and SSM_mPrefix64 provides a NAT64
               prefix, or one or more NAT64 prefixes are learnt by means
               of either [RFC7050] or [RFC7225], then 464XLAT MUST be
               included in the candidate list of possible S46 mechanism
               (Section 1.4.1 of [RFC8026]).

   The NAT64 prefix could be discovered by means of [RFC7050] only in
   the case the service provider uses DNS64 ([RFC6147]).  If DNS64
   ([RFC6147]) is not used, or not trusted, as the DNS configuration at
   the CE (or hosts behind the CE) may be modified by the customer, then
   the service provider may opt to configure the NAT64 prefix either by
   means of [RFC7225] or [RFC8115], which also can be used if the
   service provider uses DNS64 ([RFC6147]).

3.2.2.  Dual-Stack Lite (DS-Lite)

   Dual-Stack Lite [RFC6333] enables continued support for IPv4
   services.  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.

   The IPv6 Transition CE Router SHOULD implement DS-Lite B4
   functionality [RFC6333].  If DS-Lite is supported, it MUST be
   implemented according to [RFC6333].  The following IPv6 Transition CE

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   Router requirements also apply:

   DS-Lite requirements:

   DSLITE-1:  The IPv6 Transition CE Router MUST support configuration
              of DS-Lite via the DS-Lite DHCPv6 option [RFC6334] (DHCPv6
              Option for Dual-Stack Lite).  The IPv6 Transition CE
              Router MAY use other mechanisms to configure DS-Lite
              parameters.  Such mechanisms are outside the scope of this
              document.

   DSLITE-2:  The IPv6 Transition CE Router SHOULD support IGD-PCP IWF
              [RFC6970] (UPnP Internet Gateway Device - Port Control
              Protocol Interworking Function).

   DSLITE-3:  If PCP ([RFC6887]) is implemented, the IPv6 Transition CE
              Router SHOULD implement [RFC7291] (DHCP Options for the
              PCP).  If PCP ([RFC6887]) is implemented and a PCP server
              is not configured, the IPv6 Transition CE Router MUST
              assume, by DEFAULT, that the AFTR is the PCP server.
              Plain IPv6 mode (i.e., no IPv4-in-IPv6 encapsulation is
              used) MUST be used to send PCP requests to the server.

   DSLITE-4:  The IPv6 Transition CE Router MUST NOT perform IPv4
              Network Address Translation (NAT) on IPv4 traffic
              encapsulated using DS-Lite ([RFC6333]).

3.2.3.  Lightweight 4over6 (lw4o6)

   lw4o6 [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.

   The IPv6 Transition CE Router SHOULD implement lwB4 functionality
   [RFC7596].  If DS-Lite is implemented, lw4o6 SHOULD be implemented as
   well.  If lw4o6 is supported, it MUST be implemented according to
   [RFC7596].  The following IPv6 Transition CE Router requirements also
   apply:

   lw4o6 requirements:

   LW4O6-1:  The IPv6 Transition CE Router MUST support configuration of
             lw4o6 via the lw4o6 DHCPv6 options [RFC7598] (DHCPv6
             Options for Configuration of Softwire Address and Port-
             Mapped Clients).  The IPv6 Transition CE Router MAY use
             other mechanisms to configure lw4o6 parameters.  Such

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             mechanisms are outside the scope of this document.

   LW4O6-2:  The IPv6 Transition CE Router MUST support the DHCPv4-over-
             DHCPv6 (DHCP 4o6) transport described in [RFC7341] (DHCPv4-
             over-DHCPv6 Transport).

   LW4O6-3:  The IPv6 Transition CE Router MAY support Dynamic
             Allocation of Shared IPv4 Addresses as described in
             [RFC7618] (Dynamic Allocation of Shared IPv4 Addresses).

3.2.4.  MAP-E

   MAP-E [RFC7597] is a mechanism for transporting IPv4 packets across
   an IPv6 network using IP encapsulation, including an algorithmic
   mechanism for mapping between IPv6 and IPv4 addresses.

   The IPv6 Transition CE Router SHOULD support MAP-E CE functionality
   [RFC7597].  If MAP-E is supported, it MUST be implemented according
   to [RFC7597].  The following IPv6 Transition CE Router requirements
   also apply:

   MAP-E requirements:

   MAPE-1:  The IPv6 Transition CE Router MUST support configuration of
            MAP-E via the MAP-E DHCPv6 options [RFC7598] (DHCPv6 Options
            for Configuration of Softwire Address and Port-Mapped
            Clients).  The IPv6 Transition CE Router MAY use other
            mechanisms to configure MAP-E parameters.  Such mechanisms
            are outside the scope of this document.

   MAPE-2:  The IPv6 Transition CE Router MAY support Dynamic Allocation
            of Shared IPv4 Addresses as described in [RFC7618] (Dynamic
            Allocation of Shared IPv4 Addresses).

3.2.5.  MAP-T

   MAP-T [RFC7599] is a mechanism similar to MAP-E, differing from it in
   that MAP-T uses IPv4-IPv6 translation, instead of encapsulation, as
   the form of IPv6 domain transport.

   The IPv6 Transition CE Router SHOULD support MAP-T CE functionality
   [RFC7599].  If MAP-T is supported, it MUST be implemented according
   to [RFC7599].  The following IPv6 Transition CE Router requirements
   also apply:

   MAP-T requirements:

   MAPT-1:  The IPv6 Transition CE Router MUST support configuration of

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            MAP-T via the MAP-T DHCPv6 options [RFC7598] (DHCPv6 Options
            for Configuration of Softwire Address and Port-Mapped
            Clients).  The IPv6 Transition CE Router MAY use other
            mechanisms to configure MAP-T parameters.  Such mechanisms
            are outside the scope of this document.

   MAPT-2:  The IPv6 Transition CE Router MAY support Dynamic Allocation
            of Shared IPv4 Addresses as described in [RFC7618] (Dynamic
            Allocation of Shared IPv4 Addresses).

4.  IPv4 Multicast Support

   Existing IPv4 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.

   If the IPv6 Transition CE Router supports delivery of IPv4 multicast
   services, then it MUST support [RFC8114] (Delivery of IPv4 Multicast
   Services to IPv4 Clients over an IPv6 Multicast Network) and
   [RFC8115] (DHCPv6 Option for IPv4-Embedded Multicast and Unicast IPv6
   Prefixes).

5.  UPnP Support

   If the UPnP WANIPConnection:2 service [UPnP-WANIPC] is enabled on a
   CE router, but cannot be associated with an IPv4 interface
   established by an IPv4aaS mechanism or cannot determine which ports
   are available, an AddPortMapping() or AddAnyPortMapping() action MUST
   be rejected with error code 729 "ConflictWithOtherMechanisms".  Port
   availability could be determined through PCP or access to a
   configured port set (if the IPv4aaS mechanism limits the available
   ports).

   An AddPortMapping() request for a port that is not available MUST
   result in "ConflictInMappingEntry".

   An AddAnyPortMapping() request for a port that is not available
   SHOULD result in a successful mapping with an alternative
   "NewReservedPort" value from within the configured port set range, or
   as assigned by PCP as per [RFC6970], Section 5.6.1.

   Note that IGD:1 and its WANIPConnection:1 service have been
   deprecated by OCF.

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6.  Comparison to RFC7084

   This document doesn't include support for 6rd ([RFC5969]), because as
   in an IPv6-in-IPv4 tunneling.

   Regarding DS-LITE [RFC6333], this document includes slightly
   different requirements, because the PCP ([RFC6887]) support and the
   prioritization of the transition mechanisms, including dual-stack.

7.  Code Considerations

   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, Linux, others), that adding the support for the new
   transitions mechanisms, requires around 10-12 Kbytes (because most of
   the code base is shared among several transition mechanisms already
   supported by [RFC7084]), as a single data plane is common to all
   them, which typically means about 0,15% of the existing code size in
   popular CEs already in the market [OpenWRT].

   In general, the new requirements don't have extra cost in terms of
   RAM memory, neither other hardware requirements such as more powerful
   CPUs, if compared to the cost of NAT44 code so, existing hardware
   supports them with minimal impact.

   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 all the new transition mechanisms,
   and several vendors already have implementations and provide it to
   ISPs, so the development cost is negligible, and only integration and
   testing cost may become a minor issue.

8.  Security Considerations

   The IPv6 Transition CE Router must comply with the Security
   Considerations as stated in [RFC7084], as well as those stated by
   each transition mechanism implemented by the IPv6 Transition CE
   Router.

9.  IANA Considerations

   IANA is requested, by means of this document, to update the "Option
   Codes permitted in the S46 Priority Option" registry available at
   https://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-
   parameters.xhtml#option-codes-s46-priority-option, with the following

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   entry.

             +-------------+--------------------+-----------+
             | Option Code |   S46 Mechanism    | Reference |
             +-------------+--------------------+-----------+
             |     113     |      464XLAT       | [thisdoc] |
             +-------------+--------------------+-----------+

                  Table 1: DHCPv6 Option Code for 464XLAT

10.  Acknowledgements

   Thanks to Mikael Abrahamsson, Fred Baker, Mohamed Boucadair, Brian
   Carpenter, Ian Farrer, Lee Howard, Richard Patterson, Barbara Stark,
   Ole Troan, James Woodyatt, Lorenzo Colitti and Alejandro D'Egidio,
   for their review and comments in this and/or previous versions of
   this document.

11.  Annex A: Usage Scenarios

   The situation previously described, where there is ongoing IPv6
   deployment and lack of IPv4 addresses, is not happening at the same
   pace in every country, and even within every country, every ISP.  For
   different technical, financial, commercial/marketing and socio-
   economic reasons, each network is transitioning at their own pace;
   the global transition timings cannot be estimated.

   Different studies (for example [IPv6Survey]) also show that the IPv6
   deployment is a changing situation.  In a single country, not all
   operators will necessarily provide IPv6 support.  Consumers may also
   switch ISPs, and use the same IPv6 Transition CE Router with either
   an ISP that provides IPv4-only or an ISP that provides IPv6 with
   IPv4aaS.

   So, to cover all those evolving situations, an IPv6 Transition CE
   Router is required, at least from the perspective of the transition
   support.

   Moreover, because some services will remain IPv4-only for an
   undetermined time, and some service providers will remain IPv4-only
   for an undetermined period of time, IPv4 will be needed for an
   undetermined period of time.  There will be a need for CEs with
   support "IPv4 as-a-Service" for an undetermined period of time.

   This document, based on those premises, ensures that the IPv6
   Transition CE Router allows the continued transition from networks
   that today may provide access with dual-stack or IPv6-in-IPv4, as
   described in [RFC7084], and as an "extension" to it, evolve to an

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   IPv6-only access with IPv4-as-a-Service.

   Considering that situation and different possible usage cases, the
   IPv6 Transition CE Router described in this document is expected to
   be used typically, in residential/household, Small Office/Home Office
   (SOHO) and Small/Medium Enterprise (SME).  Common usage is any kind
   of Internet access (web, email, streaming, online gaming, etc.) and
   even more advanced requirements including inbound connections (IP
   cameras, web, DNS, email, VPN, etc.).

   The above is not intended to be comprehensive list of all the
   possible usage cases, just an overall view.  In fact, combinations of
   the above usages are also possible, as well as situations where the
   same CE is used at different times in different scenarios or even
   different services providers that may use a different transition
   mechanism.

   The mechanisms for allowing inbound connections are "naturally"
   available in any IPv6 router, when using GUA (IPv6 Global Unicast
   Addresses), unless they are blocked by firewall rules, which may
   require some manual configuration by means of a GUI, CLI and/or API.

   However, in the case of IPv4aaS, because the usage of private
   addresses and NAT and even depending on the specific transition
   mechanism, inbound connections typically require some degree of more
   complex manual configuration such as setting up a DMZ, virtual
   servers, or port/protocol forwarding.  In general, IPv4 CE Routers
   already provide a GUI and/or a CLI to manually configure them, or the
   possibility to setup the CE in bridge mode, so another CE behind it,
   takes care of that.  The requirements for that support are out of the
   scope of this document.

   It is not relevant who 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 features.  However, in many
   cases, the user must supply or may replace the IPv6 Transition CE
   Router.  This underscores the importance of the IPv6 Transition CE
   Routers supporting the same requirements defined in this document.

   The IPv6 Transition CE Router described in this document is not
   intended for usage in other scenarios such as large Enterprises, Data
   Centers, Content Providers, etc.  So even if the documented
   requirements meet their needs, they may have additional requirements,
   which are out of the scope of this document.

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12.  Annex B: End-User Network Architecture

   According to the descriptions in the preceding sections, 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 upstream, connected to the
   service provider network.

   From the perspective of an "IPv4 user" behind an IPv6 transition
   Customer Edge Router with IPv4aaS, this doesn't change.

   However, while a typical IPv4 NAT deployment by default blocks all
   incoming connections and may allow opening of ports using a Universal
   Plug and Play Internet Gateway Device (UPnP IGD) [UPnP-IGD] or some
   other firewall control protocol, in the case of an IPv6-only access
   and IPv4aaS, that may not be feasible depending on specific
   transition mechanism details.  PCP (Port Control Protocol, [RFC6887])
   may be an alternative solution.

   Another consequence of using IPv4 private address space in the end-
   user network is that it provides stable addressing; that is, it
   doesn't change, even when you change service providers, and the
   addresses are always usable even when the WAN interface is down or
   the customer edge router has not yet been provisioned.  In the case
   of an IPv6-only access, private IPv4 addresses are also available if
   the IPv4aaS transition mechanism keeps running the NAT interface
   towards the LAN side when the WAN interface is down.

   More advanced 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.  Once again, this is true
   for both, IPv4 and IPv6.

   In general, 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, in the sense that is not
   providing transit to other external networks.  However, HNCP
   ([RFC7788]) allows support for automatic provisioning of downstream
   routers.  Figure 1 illustrates the model topology for the end-user
   network.

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                     +---------------+                      \
                     |   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 |                                 /
   |          | |          |                                /
   +----------+ +----------+                               /

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

   This architecture describes the:

   o  Basic capabilities of the IPv6 Transition CE Router

   o  Provisioning of the WAN interface connecting to the service
      provider

   o  Provisioning of the LAN interfaces

   The IPv6 Transition CE Router may be manually configured in an
   arbitrary topology with a dynamic routing protocol or using HNCP
   ([RFC7788]).  Automatic provisioning and configuration is described

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   for a single IPv6 Transition CE Router only.

13.  ANNEX C: Changes from -00

   Section to be removed for WGLC.  Significant updates are:

   1.  ID-Nits: IANA section.

   2.  ID-Nits: RFC7084 reference removed from Abstract.

   3.  This document no longer updates RFC7084.

   4.  UPnP section reworded.

   5.  "CE Router" changed to "IPv6 Transition CE Router".

   6.  Reduced text in Annex A.

14.  ANNEX D: Changes from -01

   Section to be removed for WGLC.  Significant updates are:

   1.  TRANS requirements reworked in order to increase operator control
       and allow gradual transitioning from dual-stack to IPv6-only on
       specific customers.

   2.  New TRANS requirement so all the supported transition mechanisms
       are disabled by default, in order to facilitate the operator
       management.

   3.  New TRANS requirement in order to allow turning on/off each
       transition mechanism by the user.

   4.  Clarification on how to obtain multiple /64 for 464XLAT.

   5.  S46 priority update to RFC8026 for including 464XLAT and related
       changes in several sections.

15.  ANNEX E: Changes from -02

   Section to be removed for WGLC.  Significant updates are:

   1.  RFC8026 update removed, not needed with new approach.

   2.  TRANS and 464XLAT requirements reworded in order to match new
       approach to allow operator control on each/all the transition
       mechanisms.

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   3.  Added text in 464XLAT to clarify the usage.

16.  ANNEX F: Changes from -03

   Section to be removed for WGLC.  Significant updates are:

   1.  Several editorial changes across the document, specially TRANS
       requirements.

   2.  DNS proxy MUST instead of SHOULD.

17.  ANNEX G: Changes from -04

   Section to be removed for WGLC.  Significant updates are:

   1.  Removed G-1.

   2.  Added support for draft-pref64folks-6man-ra-pref64.

   3.  General text clarifications.

18.  ANNEX H: Changes from -05

   Section to be removed for WGLC.  Significant updates are:

   1.  Reworded and shorter UPnP section and new informative reference.

   2.  New general transition requirement in case multiple public IPv4
       prefixes are provided, so to run multiple instances according to
       each specific transition mechanism.

   3.  General text clarifications.

19.  ANNEX I: Changes from -06

   Section to be removed for WGLC.  Significant updates are:

   1.  Removed reference and text related to pref64folks-6man-ra-pref64.

   2.  General text clarifications.

20.  ANNEX J: Changes from -07

   Section to be removed for WGLC.  Significant updates are:

   1.  Added text to UPnP section.

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21.  ANNEX K: Changes from -08, -09 and -10

   Section to be removed for WGLC.  Significant updates are:

   1.  Editorial edits.

22.  References

22.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              DOI 10.17487/RFC3633, December 2003,
              <https://www.rfc-editor.org/info/rfc3633>.

   [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines",
              BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
              <https://www.rfc-editor.org/info/rfc5625>.

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification",
              RFC 5969, DOI 10.17487/RFC5969, August 2010,
              <https://www.rfc-editor.org/info/rfc5969>.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <https://www.rfc-editor.org/info/rfc6146>.

   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              DOI 10.17487/RFC6147, April 2011,
              <https://www.rfc-editor.org/info/rfc6147>.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
              <https://www.rfc-editor.org/info/rfc6333>.

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   [RFC6334]  Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
              Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
              RFC 6334, DOI 10.17487/RFC6334, August 2011,
              <https://www.rfc-editor.org/info/rfc6334>.

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,
              <https://www.rfc-editor.org/info/rfc6877>.

   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,
              <https://www.rfc-editor.org/info/rfc6887>.

   [RFC6970]  Boucadair, M., Penno, R., and D. Wing, "Universal Plug and
              Play (UPnP) Internet Gateway Device - Port Control
              Protocol Interworking Function (IGD-PCP IWF)", RFC 6970,
              DOI 10.17487/RFC6970, July 2013,
              <https://www.rfc-editor.org/info/rfc6970>.

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis",
              RFC 7050, DOI 10.17487/RFC7050, November 2013,
              <https://www.rfc-editor.org/info/rfc7050>.

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              DOI 10.17487/RFC7084, November 2013,
              <https://www.rfc-editor.org/info/rfc7084>.

   [RFC7225]  Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the
              Port Control Protocol (PCP)", RFC 7225,
              DOI 10.17487/RFC7225, May 2014,
              <https://www.rfc-editor.org/info/rfc7225>.

   [RFC7291]  Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
              the Port Control Protocol (PCP)", RFC 7291,
              DOI 10.17487/RFC7291, July 2014,
              <https://www.rfc-editor.org/info/rfc7291>.

   [RFC7341]  Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
              Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport",
              RFC 7341, DOI 10.17487/RFC7341, August 2014,
              <https://www.rfc-editor.org/info/rfc7341>.

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   [RFC7596]  Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
              Farrer, "Lightweight 4over6: An Extension to the Dual-
              Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596,
              July 2015, <https://www.rfc-editor.org/info/rfc7596>.

   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
              Port with Encapsulation (MAP-E)", RFC 7597,
              DOI 10.17487/RFC7597, July 2015,
              <https://www.rfc-editor.org/info/rfc7597>.

   [RFC7598]  Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
              W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for
              Configuration of Softwire Address and Port-Mapped
              Clients", RFC 7598, DOI 10.17487/RFC7598, July 2015,
              <https://www.rfc-editor.org/info/rfc7598>.

   [RFC7599]  Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S.,
              and T. Murakami, "Mapping of Address and Port using
              Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599, July
              2015, <https://www.rfc-editor.org/info/rfc7599>.

   [RFC7618]  Cui, Y., Sun, Q., Farrer, I., Lee, Y., Sun, Q., and M.
              Boucadair, "Dynamic Allocation of Shared IPv4 Addresses",
              RFC 7618, DOI 10.17487/RFC7618, August 2015,
              <https://www.rfc-editor.org/info/rfc7618>.

   [RFC8026]  Boucadair, M. and I. Farrer, "Unified IPv4-in-IPv6
              Softwire Customer Premises Equipment (CPE): A DHCPv6-Based
              Prioritization Mechanism", RFC 8026, DOI 10.17487/RFC8026,
              November 2016, <https://www.rfc-editor.org/info/rfc8026>.

   [RFC8114]  Boucadair, M., Qin, C., Jacquenet, C., Lee, Y., and Q.
              Wang, "Delivery of IPv4 Multicast Services to IPv4 Clients
              over an IPv6 Multicast Network", RFC 8114,
              DOI 10.17487/RFC8114, March 2017,
              <https://www.rfc-editor.org/info/rfc8114>.

   [RFC8115]  Boucadair, M., Qin, J., Tsou, T., and X. Deng, "DHCPv6
              Option for IPv4-Embedded Multicast and Unicast IPv6
              Prefixes", RFC 8115, DOI 10.17487/RFC8115, March 2017,
              <https://www.rfc-editor.org/info/rfc8115>.

22.2.  Informative References

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   [IPv6Survey]
              Palet Martinez, J., "IPv6 Deployment Survey", January
              2018,
              <https://indico.uknof.org.uk/event/41/contribution/5/
              material/slides/0.pdf>.

   [OpenWRT]  OpenWRT, "OpenWRT Packages", January 2018,
              <https://openwrt.org/packages/start>.

   [RFC7788]  Stenberg, M., Barth, S., and P. Pfister, "Home Networking
              Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
              2016, <https://www.rfc-editor.org/info/rfc7788>.

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

   [UPnP-WANIPC]
              UPnP Forum, "WANIPConnection:2 Service", December 2010,
              <http://upnp.org/specs/gw/
              UPnP-gw-WANIPConnection-v2-Service.pdf>.

Authors' Addresses

   Jordi Palet Martinez
   The IPv6 Company
   Molino de la Navata, 75
   La Navata - Galapagar, Madrid  28420
   Spain

   Email: jordi.palet@theipv6company.com
   URI:   http://www.theipv6company.com/

   Hans M.-H. Liu
   D-Link Systems, Inc.
   17595 Mount Herrmann St.
   Fountain Valley, California  92708
   US

   Email: hans.liu@dlinkcorp.com
   URI:   http://www.dlink.com/

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   Masanobu Kawashima
   NEC Platforms, Ltd.
   800, Shimomata
   Kakegawa-shi, Shizuoka  436-8501
   Japan

   Email: kawashimam@vx.jp.nec.com
   URI:   https://www.necplatforms.co.jp/en/

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