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Versions: (draft-binet-v6ops-cellular-host-requirements) 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 RFC 7849

V6OPS Working Group                                             D. Binet
Internet-Draft                                              M. Boucadair
Intended status: Informational                            France Telecom
Expires: September 3, 2015                                     A. Vizdal
                                                     Deutsche Telekom AG
                                                                 G. Chen
                                                            China Mobile
                                                              N. Heatley
                                                                      EE
                                                             R. Chandler
                                                         eircom | meteor
                                                              D. Michaud
                                                   Rogers Communications
                                                                D. Lopez
                                                          Telefonica I+D
                                                           March 2, 2015


 An Internet Protocol Version 6 (IPv6) Profile for 3GPP Mobile Devices
               draft-ietf-v6ops-mobile-device-profile-20

Abstract

   This document defines a profile that is a superset of that of the
   connection to IPv6 cellular networks defined in the IPv6 for Third
   Generation Partnership Project (3GPP) Cellular Hosts document.  This
   document defines an IPv6 profile that a number of operators recommend
   in order to connect 3GPP mobile devices to an IPv6-only or dual-stack
   wireless network (including 3GPP cellular network) with a special
   focus on IPv4 service continuity features.

   Both hosts and devices with capability to share their WAN (Wide Area
   Network) connectivity are in scope.

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."



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   This Internet-Draft will expire on September 3, 2015.

Copyright Notice

   Copyright (c) 2015 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Connectivity Recommendations  . . . . . . . . . . . . . . . .   6
   3.  Recommendations for Cellular Devices with LAN Capabilities  .   9
   4.  Advanced Recommendations  . . . . . . . . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   IPv6 deployment in 3GPP mobile networks is the only perennial
   solution to the exhaustion of IPv4 addresses in those networks.
   Several mobile operators have already deployed IPv6 [RFC2460] or are
   in the pre-deployment phase.  One of the major hurdles as perceived
   by some mobile operators is the availability of non-broken IPv6
   implementation in mobile devices (e.g., Section 3.3 of [OECD]).

   [RFC7066] lists a set of features to be supported by cellular hosts
   to connect to 3GPP mobile networks.  In the light of recent IPv6
   production deployments, additional features to facilitate IPv6-only
   deployments while accessing IPv4-only services are to be considered.
   This document fills this void.  Concretely, this document lists means
   to ensure IPv4 service continuity over an IPv6-only connectivity



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   given the adoption rate of this model by mobile operators.  Those
   operators require that no service degradation is experienced by
   customers serviced with an IPv6-only model compared to the level of
   service of customers with legacy IPv4-only devices.

   This document defines an IPv6 profile for mobile devices listing
   specifications produced by various Standards Developing Organizations
   (including 3GPP, IETF, and GSMA).  The objectives of this effort are:

   1.  List in one single document a comprehensive list of IPv6 features
       for a mobile device, including both IPv6-only and dual-stack
       mobile deployment contexts.  These features cover various network
       types such as GPRS (General Packet Radio Service) or EPC (Evolved
       Packet Core).

   2.  Help Operators with the detailed device requirement list
       preparation (to be exchanged with device suppliers).  This is
       also a contribution to harmonize Operators' requirements towards
       device vendors.

   3.  Vendors to be aware of a set of features to allow for IPv6
       connectivity and IPv4 service continuity (over an IPv6-only
       transport).

   The recommendations do not include 3GPP release details.  For more
   information on the 3GPP releases detail, the reader may refer to
   Section 6.2 of [RFC6459].

   Some of the features listed in this profile document require to
   activate dedicated functions at the network side.  It is out of scope
   of this document to list these network-side functions.

   A detailed overview of IPv6 support in 3GPP architectures is provided
   in [RFC6459].  IPv6-only considerations in mobile networks are
   further discussed in [RFC6342].

   This document is organized as follows:

   o  Section 2 lists generic recommendations including functionalities
      to provide IPv4 service continuity over an IPv6-only connectivity.

   o  Section 3 enumerates a set of recommendations for cellular devices
      with LAN capabilities (e.g., CE Routers, dongles with tethering
      features).

   o  Section 4 identifies a set of advanced recommendations to fulfill
      requirements of critical services such as VoLTE (Voice over LTE).




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1.1.  Terminology

   This document makes use of the terms defined in [RFC6459].  In
   addition, the following terms are used:

   o  "3GPP cellular host" (or cellular host for short) denotes a 3GPP
      device which can be connected to 3GPP mobile networks.

   o  "3GPP cellular device" (or cellular device for short) refers to a
      cellular host which supports the capability to share its WAN (Wide
      Area Network) connectivity.

   o  "IPv4 service continuity" denotes the features used to provide
      access to IPv4-only services to customers serviced with an
      IPv6-only connectivity.  A typical example of IPv4 service
      continuity technique is NAT64 [RFC6146].

   PREFIX64 denotes an IPv6 prefix used to build IPv4-converted IPv6
   addresses [RFC6052].

1.2.  Scope

   A 3GPP mobile network can be used to connect various user equipments
   such as a mobile telephone or a Customer Edge Routers.  Because of
   this diversity of terminals, it is necessary to define a set of IPv6
   functionalities valid for any node directly connecting to a 3GPP
   mobile network.  This document describes these functionalities.

   Machine-to-machine (M2M) devices profile is out of scope.

   This document is structured to provide the generic IPv6
   recommendations which are valid for all nodes, whatever their
   function (e.g., host or CE router) or service (e.g., Session
   Initiation Protocol (SIP, [RFC3261])) capability.  The document also
   contains sections covering specific functionalities for devices
   providing some LAN functions (e.g., mobile CE router or broadband
   dongles).

   The recommendations listed below are valid for both 3GPP GPRS and
   3GPP EPS (Evolved Packet System) access.  For EPS, PDN-Connection
   term is used instead of PDP-Context.  Other non-3GPP accesses
   [TS.23402] are out of scope of this document.

   This profile is a superset of that of the IPv6 profile for 3GPP
   Cellular Hosts [RFC7066], which is in turn a superset of IPv6 Node
   Requirements [RFC6434].  It targets cellular nodes, including GPRS
   and EPC (Evolved Packet Core), that require features to ensure IPv4
   service delivery over an IPv6-only transport in addition to the base



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   IPv6 service.  Moreover, this profile also covers cellular CE routers
   that are used in various deployments to offer fixed-like services.
   Recommendations inspired from real deployment experiences (e.g.,
   roaming) are included in this profile.  Also, this profile sketches
   recommendations for the sake of deterministic behaviors of cellular
   devices when the same configuration information is received over
   several channels.

   For conflicting recommendations in [RFC7066] and [RFC6434] (e.g.,
   Neighbor Discovery Protocol), this profile adheres to [RFC7066].
   Indeed, the support of Neighbor Discovery Protocol is mandatory in
   3GPP cellular environment as it is the only way to convey IPv6 prefix
   towards the 3GPP cellular device.  In particular, MTU (Maximum
   Transmission Unit) communication via Router Advertisement must be
   supported since many 3GPP networks do not have a standard MTU
   setting.

   This profile uses a stronger language for the support of Prefix
   Delegation compared to [RFC7066].  The main motivation is that
   cellular networks are more and more perceived as an alternative to
   fixed networks for home IP-based services delivery; especially with
   the advent of smartphones and 3GPP data dongles.  There is a need for
   an efficient mechanism to assign larger prefixes to cellular hosts so
   that each LAN segment can get its own /64 prefix and multi-link
   subnet issues to be avoided.  The support of this functionality in
   both cellular and fixed networks is key for fixed-mobile convergence.

   The use of address family dependent APIs (Application Programming
   Interfaces) or hard-coded IPv4 address literals may lead to broken
   applications when IPv6 connectivity is in use.  As such, means to
   minimize broken applications when the cellular host is attached to an
   IPv6-only network should be encouraged.  Particularly, (1) name
   resolution libraries (e.g., [RFC3596]) must support both IPv4 and
   IPv6; (2) applications must be independent of the underlying IP
   address family; (3) and applications relying upon Uniform Resource
   Identifiers (URIs) must follow [RFC3986] and its updates.  Note, some
   IETF specifications (e.g., SIP [RFC3261]) contains broken IPv6 ABNF
   and rules to compare URIs with embedded IPv6 addresses; fixes (e.g.,
   [RFC5954]) must be used instead.

   The recommendations included in each section are listed in a priority
   order.

   This document is not a standard, and conformance with it is not
   required in order to claim conformance with IETF standards for IPv6.
   Compliance with this profile does not require the support of all
   enclosed items.  Obviously, the support of the full set of features
   may not be required in some deployment contexts.  However, the



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   authors believe that not supporting relevant features included in
   this profile (e.g., Customer Side Translator (CLAT, [RFC6877])) may
   lead to a degraded level of service.

2.  Connectivity Recommendations

   This section identifies the main connectivity recommendations to be
   followed by a cellular host to attach to a network using IPv6 in
   addition to what is defined in [RFC6434] and [RFC7066].  Both dual-
   stack and IPv6-only deployment models are considered.  IPv4 service
   continuity features are listed in this section because these are
   critical for Operators with an IPv6-only deployment model.

   C_REC#1:  In order to allow each operator to select their own
             strategy regarding IPv6 introduction, the cellular host
             must support both IPv6 and IPv4v6 PDP-Contexts [TS.23060].

             IPv4, IPv6 or IPv4v6 PDP-Context request acceptance depends
             on the cellular network configuration.

   C_REC#2:  The cellular host must comply with the behavior defined in
             [TS.23060] [TS.23401] [TS.24008] for requesting a PDP-
             Context type.

             In particular, the cellular host must request by default an
             IPv6 PDP-Context if the cellular host is IPv6-only and
             request an IPv4v6 PDP-Context if the cellular host is dual-
             stack or when the cellular host is not aware of
             connectivity types requested by devices connected to it
             (e.g., cellular host with LAN capabilities as discussed in
             Section 3):

             *  If the requested IPv4v6 PDP-Context is not supported by
                the network, but IPv4 and IPv6 PDP types are allowed,
                then the cellular host will be configured with an IPv4
                address or an IPv6 prefix by the network.  It must
                initiate another PDP-Context activation in addition to
                the one already activated for a given APN (Access Point
                Name).  The purpose of initiating a second PDP-Context
                is to achieve dual-stack connectivity by means of two
                PDP-Contexts.

             *  If the subscription data or network configuration allows
                only one IP address family (IPv4 or IPv6), the cellular
                host must not request a second PDP-Context to the same
                APN for the other IP address family.





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             The text above focuses on the specification (excerpt from
             [TS.23060] [TS.23401] [TS.24008]) which explains the
             behavior for requesting IPv6-related PDP-Context(s).

   C_REC#3:  The cellular host must support the PCO (Protocol
             Configuration Options) [TS.24008] to retrieve the IPv6
             address(es) of the Recursive DNS server(s).

                In-band signaling is a convenient method to inform the
                cellular host about various services, including DNS
                server information.  It does not require any specific
                protocol to be supported and it is already deployed in
                IPv4 cellular networks to convey such DNS information.

   C_REC#4:  The cellular host must support IPv6 aware Traffic Flow
             Templates (TFT) [TS.24008].

                Traffic Flow Templates are employing a packet filter to
                couple an IP traffic with a PDP-Context.  Thus a
                dedicated PDP-Context and radio resources can be
                provided by the cellular network for certain IP traffic.

   C_REC#5:  If the cellular host receives the DNS information in
             several channels for the same interface, the following
             preference order must be followed:

                1.  PCO

                2.  RA

                3.  DHCPv6

             The purpose of this recommendation is to guarantee for a
             deterministic behavior to be followed by all cellular hosts
             when the DNS information is received in various channels.

   C_REC#6:  The cellular host must be able to be configured to limit
             PDP type(s) for a given APN.  The default mode is to allow
             all supported PDP types.  Note, C_REC#2 discusses the
             default behavior for requesting PDP-Context type(s).

                This feature is useful to drive the behavior of the UE
                to be aligned with: (1) service-specific constraints
                such as the use of IPv6-only for VoLTE (Voice over LTE),
                (2) network conditions with regards to the support of
                specific PDP types (e.g., IPv4v6 PDP-Context is not
                supported), (3) IPv4 sunset objectives, (4) subscription
                data, etc.



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                Note, a cellular host changing its connection between an
                IPv6-specific APN and an IPv4-specific APN will
                interrupt related network connections.  This may be
                considered as a brokenness situation by some
                applications.

   C_REC#7:  Because of potential operational deficiencies to be
             experienced in some roaming situations, the cellular host
             must be able to be configured with a home PDP-Context
             type(s) and a roaming PDP-Context type(s).  The purpose of
             the roaming profile is to limit the PDP type(s) requested
             by the cellular host when out of the home network.  Note
             that distinct PDP type(s) and APN(s) can be configured for
             home and roaming cases.

                A detailed analysis of roaming failure cases is included
                in [RFC7445].

   C_REC#8:  In order to ensure IPv4 service continuity in an IPv6-only
             deployment context, the cellular host should support a
             method to learn PREFIX64(s).

                In the context of NAT64, IPv6-enabled applications
                relying on address referrals will fail because an
                IPv6-only client won't be able to make use of an IPv4
                address received in a referral.  This feature allows to
                solve the referral problem (because an IPv6-enabled
                application can construct IPv4-embedded IPv6 addresses
                [RFC6052]) and, also, to distinguish between
                IPv4-converted IPv6 addresses and native IPv6 addresses.
                In other words, this feature contributes to offload both
                CLAT module (C_REC#9) and NAT64 devices.  Refer to
                Section 3 of [RFC7051] for an inventory of the issues
                related to the discovery of PREFIX64(s).

                In PCP-based environments, cellular hosts should follow
                [RFC7225] to learn the IPv6 Prefix used by an upstream
                PCP-controlled NAT64 device.  If PCP is not enabled, the
                cellular host should implement the method specified in
                [RFC7050] to retrieve the PREFIX64.

   C_REC#9:  In order to ensure IPv4 service continuity in an IPv6-only
             deployment context, the cellular host should implement the
             Customer Side Translator (CLAT, [RFC6877]) function in
             compliance with [RFC6052][RFC6145][RFC6146].

                CLAT function in the cellular host allows for IPv4-only
                application and IPv4-referals to work on an IPv6-only



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                connectivity.  The more applications are address family
                independent, the less CLAT function is solicited.  CLAT
                function requires a NAT64 capability [RFC6146] in the
                network.

                The cellular host should only invoke the CLAT in the
                absence of the IPv4 connectivity on the cellular side,
                i.e., when the network does not assign an IPv4 address
                on the cellular interface.  Note, NAT64 assumes an
                IPv6-only mode [RFC6146].

                The IPv4 Service Continuity Prefix used by CLAT is
                defined in [RFC7335].

                CLAT and/or NAT64 do not interfere with native IPv6
                communications.

3.  Recommendations for Cellular Devices with LAN Capabilities

   This section focuses on cellular devices (e.g., CE router,
   smartphones, or dongles with tethering features) which provide IP
   connectivity to other devices connected to them.  In such case, all
   connected devices are sharing the same 2G, 3G or LTE connection.  In
   addition to the generic recommendations listed in Section 2, these
   cellular devices have to meet the recommendations listed below.

   L_REC#1:  The cellular device must support Prefix Delegation
             capabilities [RFC3633] and must support Prefix Exclude
             Option for DHCPv6-based Prefix Delegation as defined in
             [RFC6603].  Particularly, it must behave as a Requesting
             Router.

                Cellular networks are more and more perceived as an
                alternative to fixed networks for home IP-based services
                delivery; especially with the advent of smartphones and
                3GPP data dongles.  There is a need for an efficient
                mechanism to assign larger prefixes (other than /64s) to
                cellular hosts so that each LAN segment can get its own
                /64 prefix and multi-link subnet issues to be avoided.

                In case a prefix is delegated to a cellular host using
                DHCPv6, the cellular device will be configured with two
                prefixes:

                   (1) one for 3GPP link allocated using SLAAC mechanism
                   and





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                   (2) another one delegated for LANs acquired during
                   Prefix Delegation operation.

                Note that the 3GPP network architecture requires both
                the WAN (Wide Area Network) and the delegated prefix to
                be aggregatable, so the subscriber can be identified
                using a single prefix.

                Without the Prefix Exclude Option, the delegating router
                (GGSN/PGW) will have to ensure [RFC3633] compliancy
                (e.g., halving the delegated prefix and assigning the
                WAN prefix out of the 1st half and the prefix to be
                delegated to the terminal from the 2nd half).

                Because Prefix Delegation capabilities may not be
                available in some attached networks, L_REC#3 is strongly
                recommended to accommodate early deployments.

   L_REC#2:  The cellular CE router must be compliant with the
             requirements specified in [RFC7084].

                There are several deployments, particularly in emerging
                countries, that relies on mobile networks to provide
                broadband services (e.g., customers are provided with
                mobile CE routers).

                Note, this profile does not require IPv4 service
                continuity techniques listed in [RFC7084] because those
                are specific to fixed networks.  IPv4 service continuity
                techniques specific to the mobile networks are included
                in this profile.

                This recommendation does not apply to handsets with
                tethering capabilities; it is specific to cellular CE
                routers in order to ensure the same IPv6 functional
                parity for both fixed and cellular CE routers.  Note,
                modern CE routers are designed with advanced functions
                such as link aggregation that consists in optimizing the
                network usage by aggregating the connectivity resources
                offered via various interfaces (e.g., DSL, LTE, WLAN,
                etc.) or offloading the traffic via a subset of
                interfaces.  Mutualizing IPv6 features among these
                interface types is important for the sake of
                specification efficiency, service design simplification
                and validation effort optimization.

   L_REC#3:  For deployments requiring to share the same /64 prefix, the
             cellular device should support [RFC7278] to enable sharing



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             a /64 prefix between the 3GPP interface towards the GGSN/
             PGW (WAN interface) and the LAN interfaces.

                Prefix Delegation (refer to L_REC#1) is the target
                solution for distributing prefixes in the LAN side but,
                because the device may attach to earlier 3GPP release
                networks, a mean to share a /64 prefix is also
                recommended [RFC7278].

                [RFC7278] must be invoked only if Prefix Delegation is
                not in use.

   L_REC#4:  In order to allow IPv4 service continuity in an IPv6-only
             deployment context, the cellular device should support the
             Customer Side Translator (CLAT) [RFC6877].

                Various IP devices are likely to be connected to
                cellular device, acting as a CE router.  Some of these
                devices can be dual-stack, others are IPv6-only or
                IPv4-only.  IPv6-only connectivity for cellular device
                does not allow IPv4-only sessions to be established for
                hosts connected on the LAN segment of cellular devices.

                In order to allow IPv4 sessions establishment initiated
                from devices located on LAN segment side and target IPv4
                nodes, a solution consists in integrating the CLAT
                function in the cellular device.  As elaborated in
                Section 2, the CLAT function allows also IPv4
                applications to continue running over an IPv6-only
                device.

                The cellular host should only invoke the CLAT in the
                absence of the IPv4 connectivity on the cellular side,
                i.e., when the network does not assign an IPv4 address
                on the cellular interface.

                The IPv4 Service Continuity Prefix used by CLAT is
                defined in [RFC7335].

   L_REC#5:  If a RA MTU is advertised from the 3GPP network, the
             cellular device should relay that upstream MTU information
             to the downstream attached LAN devices in RA.

                Receiving and relaying RA MTU values facilitates a more
                harmonious functioning of the mobile core network where
                end nodes transmit packets that do not exceed the MTU
                size of the mobile network's GTP tunnels.




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                [TS.23060] indicates providing a link MTU value of 1358
                octets to the 3GPP cellular device will prevent the IP
                layer fragmentation within the transport network between
                the cellular device and the GGSN/PGW.

4.  Advanced Recommendations

   This section identifies a set of advanced recommendations to fulfill
   requirements of critical services such as VoLTE.

   A_REC#1:  The cellular host must support ROHC RTP Profile (0x0001)
             and ROHC UDP Profile (0x0002) for IPv6 ([RFC5795]).  Other
             ROHC profiles may be supported.

                Bandwidth in cellular networks must be optimized as much
                as possible.  ROHC provides a solution to reduce
                bandwidth consumption and to reduce the impact of having
                bigger packet headers in IPv6 compared to IPv4.

                "RTP/UDP/IP" ROHC profile (0x0001) to compress RTP
                packets and "UDP/IP" ROHC profile (0x0002) to compress
                RTCP packets are required for Voice over LTE (VoLTE) by
                IR.92.4.0 section 4.1 [IR92].  Note, [IR92] indicates
                that the host must be able to apply the compression to
                packets that are carried over the voice media dedicated
                radio bearer.

   A_REC#2:  The cellular host should support PCP [RFC6887].

                The support of PCP is seen as a driver to save battery
                consumption exacerbated by keepalive messages.  PCP also
                gives the possibility of enabling incoming connections
                to the cellular device.  Indeed, because several
                stateful devices may be deployed in wireless networks
                (e.g., NAT64 and/or IPv6 Firewalls), PCP can be used by
                the cellular host to control network-based NAT64 and
                IPv6 Firewall functions which will reduce per-
                application signaling and save battery consumption.

                According to [Power], the consumption of a cellular
                device with a keep-alive interval equal to 20 seconds
                (that is the default value in [RFC3948] for example) is
                29 mA (2G)/34 mA (3G).  This consumption is reduced to
                16 mA (2G)/24 mA (3G) when the interval is increased to
                40 seconds, to 9.1 mA (2G)/16 mA (3G) if the interval is
                equal to 150 seconds, and to 7.3 mA (2G)/14 mA (3G) if
                the interval is equal to 180 seconds.  When no keep-
                alive is issued, the consumption would be 5.2 mA



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                (2G)/6.1 mA (3G).  The impact of keepalive messages
                would be more severe if multiple applications are
                issuing those messages (e.g., SIP, IPsec, etc.).

                PCP allows to avoid embedding ALGs (Application Level
                Gateways) at the network side (e.g., NAT64) to manage
                protocols which convey IP addresses and/or port numbers
                (see Section 2.2 of [RFC6889]).  Avoiding soliciting
                ALGs allows for more easiness to make evolve a service
                independently of the underlying transport network.

   A_REC#3:  In order for host-based validation of DNS Security
             Extensions (DNSSEC) to continue to function in an IPv6-only
             connectivity with NAT64 deployment context, the cellular
             host should embed a DNS64 function ([RFC6147]).

                This is called "DNS64 in stub-resolver mode" in
                [RFC6147].

                As discussed in Section 5.5 of [RFC6147], a security-
                aware and validating host has to perform the DNS64
                function locally.

                Because synthetic AAAA records cannot be successfully
                validated in a host, learning the PREFIX64 used to
                construct IPv4-converted IPv6 addresses allows the use
                of DNSSEC [RFC4033] [RFC4034], [RFC4035].  Means to
                configure or discover a PREFIX64 are required on the
                cellular device as discussed in C_REC#8.

                [RFC7051] discusses why a security-aware and validating
                host has to perform the DNS64 function locally and why
                it has to be able to learn the proper PREFIX64(s).

   A_REC#4:  When the cellular host is dual-stack connected (i.e.,
             configured with an IPv4 address and IPv6 prefix), it should
             support means to prefer native IPv6 connection over
             connection established through translation devices (e.g.,
             NAT44 and NAT64).

                When both IPv4 and IPv6 DNS servers are configured, a
                dual-stack host must contact first its IPv6 DNS server.
                This preference allows to offload IPv4-only DNS servers.

                Cellular hosts should follow the procedure specified in
                [RFC6724] for source address selection.





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5.  Security Considerations

   The security considerations identified in [RFC7066] and [RFC6459] are
   to be taken into account.

   In the case of cellular CE routers, compliance with L_REC#2 entails
   compliance with [RFC7084], which in turn recommends compliance with
   Recommended Simple Security Capabilities in Customer Premises
   Equipment (CPE) for Providing Residential IPv6 Internet Service
   [RFC6092].  Therefore, the security considerations in Section 6 of
   [RFC6092] are relevant.  In particular, it bears repeating here that
   the true impact of stateful filtering may be a reduction in security,
   and that IETF make no statement, expressed or implied, as to whether
   using the capabilities described in any of these documents ultimately
   improves security for any individual users or for the Internet
   community as a whole.

   The cellular host must be able to generate IPv6 addresses which
   preserve privacy.  The activation of privacy extension (e.g., using
   [RFC7217]) makes it more difficult to track a host over time when
   compared to using a permanent Interface Identifier.  Tracking a host
   is still possible based on the first 64 bits of the IPv6 address.
   Means to prevent against such tracking issues may be enabled in the
   network side.  Note, privacy extensions are required by regulatory
   bodies in some countries.

   Host-based validation of DNSSEC is discussed in A_REC#3 (see
   Section 4).

6.  IANA Considerations

   This document does not require any action from IANA.

7.  Acknowledgements

   Many thanks to C.  Byrne, H.  Soliman, H.  Singh, L.  Colliti, T.
   Lemon, B.  Sarikaya, M.  Mawatari, M.  Abrahamsson, P.  Vickers, V.
   Kuarsingh, E.  Kline, S.  Josefsson, A.  Baryun, J.  Woodyatt, T.
   Kossut, B.  Stark, and A.  Petrescu for the discussion in the v6ops
   mailing list and for the comments.

   Thanks to A.  Farrel, B.  Haberman and K.  Moriarty for the comments
   during the IESG review.

   Special thanks to T.  Savolainen, J.  Korhonen, J.  Jaeggli, and F.
   Baker for their detailed reviews and comments.





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8.  References

8.1.  Normative References

   [IR92]     GSMA, "IR.92.V4.0 - IMS Profile for Voice and SMS", March
              2011, <http://www.gsma.com/newsroom/
              ir-92-v4-0-ims-profile-for-voice-and-sms>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
              "DNS Extensions to Support IP Version 6", RFC 3596,
              October 2003.

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

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC5795]  Sandlund, K., Pelletier, G., and L-E. Jonsson, "The RObust
              Header Compression (ROHC) Framework", RFC 5795, March
              2010.

   [RFC5954]  Gurbani, V., Carpenter, B., and B. Tate, "Essential
              Correction for IPv6 ABNF and URI Comparison in RFC 3261",
              RFC 5954, August 2010.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

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

   [RFC7066]  Korhonen, J., Arkko, J., Savolainen, T., and S. Krishnan,
              "IPv6 for Third Generation Partnership Project (3GPP)
              Cellular Hosts", RFC 7066, November 2013.

   [TS.23060]
              3GPP, "General Packet Radio Service (GPRS); Service
              description; Stage 2", September 2011,
              <http://www.3gpp.org/DynaReport/23060.htm>.




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   [TS.23401]
              3GPP, "General Packet Radio Service (GPRS) enhancements
              for Evolved Universal Terrestrial Radio Access Network
              (E-UTRAN) access", September 2011,
              <http://www.3gpp.org/DynaReport/23401.htm>.

   [TS.24008]
              3GPP, "Mobile radio interface Layer 3 specification; Core
              network protocols; Stage 3", June 2011,
              <http://www.3gpp.org/DynaReport/24008.htm>.

8.2.  Informative References

   [OECD]     Organisation for Economic Cooperation and Development
              (OECD), "The Economics of the Transition to Internet
              Protocol version 6 (IPv6)", November 2014, <http://www.oec
              d.org/officialdocuments/publicdisplaydocumentpdf/?cote=DST
              I/ICCP/CISP%282014%293/FINAL&docLanguage=En>.

   [Power]    Haverinen, H., Siren, J., and P. Eronen, "Energy
              Consumption of Always-On Applications in WCDMA Networks",
              April 2007, <http://ieeexplore.ieee.org/xpl/
              articleDetails.jsp?arnumber=4212635>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3948]  Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets", RFC
              3948, January 2005.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.







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

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [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,
              April 2011.

   [RFC6342]  Koodli, R., "Mobile Networks Considerations for IPv6
              Deployment", RFC 6342, August 2011.

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

   [RFC6459]  Korhonen, J., Soininen, J., Patil, B., Savolainen, T.,
              Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
              Partnership Project (3GPP) Evolved Packet System (EPS)",
              RFC 6459, January 2012.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation", RFC
              6877, April 2013.

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

   [RFC6889]  Penno, R., Saxena, T., Boucadair, M., and S. Sivakumar,
              "Analysis of Stateful 64 Translation", RFC 6889, April
              2013.

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis", RFC
              7050, November 2013.




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   [RFC7051]  Korhonen, J. and T. Savolainen, "Analysis of Solution
              Proposals for Hosts to Learn NAT64 Prefix", RFC 7051,
              November 2013.

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              November 2013.

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217, April 2014.

   [RFC7225]  Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the
              Port Control Protocol (PCP)", RFC 7225, May 2014.

   [RFC7278]  Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6
              /64 Prefix from a Third Generation Partnership Project
              (3GPP) Mobile Interface to a LAN Link", RFC 7278, June
              2014.

   [RFC7335]  Byrne, C., "IPv4 Service Continuity Prefix", RFC 7335,
              August 2014.

   [RFC7445]  Chen, G., Deng, H., Michaud, D., Korhonen, J., Boucadair,
              M., and V. Ales, "Analysis of Failure Cases in IPv6
              Roaming Scenarios", February 2015.

   [TS.23402]
              3GPP, "Architecture enhancements for non-3GPP accesses",
              September 2011,
              <http://www.3gpp.org/DynaReport/23402.htm>.

Authors' Addresses

   David Binet
   France Telecom
   Rennes
   France

   EMail: david.binet@orange.com


   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   EMail: mohamed.boucadair@orange.com



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   Ales Vizdal
   Deutsche Telekom AG

   EMail: ales.vizdal@t-mobile.cz


   Gang Chen
   China Mobile

   EMail: phdgang@gmail.com


   Nick Heatley
   EE
   The Point, 37 North Wharf Road,
   London  W2 1AG
   U.K

   EMail: nick.heatley@ee.co.uk


   Ross Chandler
   eircom | meteor
   1HSQ
   St. John's Road
   Dublin 8
   Ireland

   EMail: ross@eircom.net


   Dave Michaud
   Rogers Communications
   8200 Dixie Rd.
   Brampton, ON L6T 0C1
   Canada

   EMail: dave.michaud@rci.rogers.com


   Diego R. Lopez
   Telefonica I+D
   Don Ramon de la Cruz, 82
   Madrid  28006
   Spain

   Phone: +34 913 129 041
   EMail: diego.r.lopez@telefonica.com



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