





Independent Submission                                          D. Binet
Request for Comments: 7849                                  M. Boucadair
Category: Informational                                           Orange
ISSN: 2070-1721                                                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
                                                             W. Haeffner
                                                                Vodafone
                                                                May 2016


                An IPv6 Profile for 3GPP Mobile Devices

Abstract

   This document defines a profile that is a superset of the connection
   to IPv6 cellular networks defined in the IPv6 for Third Generation
   Partnership Project (3GPP) Cellular Hosts document.  This document
   defines a profile that is a superset of the connections to IPv6
   cellular networks defined in "IPv6 for Third Generation Partnership
   Project (3GPP) Cellular Hosts" (RFC 7066).

   Both mobile hosts and mobile devices with the capability to share
   their 3GPP mobile connectivity are in scope.

IESG Note

   The consensus-based IETF description of IPv6 functionality for
   cellular hosts is described in RFC 7066.













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Status of This Memo

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

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7849.

Copyright Notice

   Copyright (c) 2016 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Connectivity Recommendations  . . . . . . . . . . . . . . . .   6
   3.  Recommendations for Cellular Devices with LAN Capabilities  .  11
   4.  Advanced Recommendations  . . . . . . . . . . . . . . . . . .  13
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21









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1.  Introduction

   IPv6 deployment in 3GPP mobile networks is the only viable 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 lack of availability of working 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 should be considered.

   This document fills this void.  Concretely, this document lists means
   to ensure IPv4 service over an IPv6-only connectivity 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 the Global System for Mobile
   Communications Association (GSMA)).  The objectives of this effort
   are as follows:

   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 packet
       core architectures such as General Packet Radio Service (GPRS) or
       Evolved Packet Core (EPC).

   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.  Inform vendors 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 release details, the reader may refer to
   Section 6.2 of [RFC6459].  More details can be found at [R3GPP].






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   Some of the features listed in this profile document could require
   that dedicated functions be activated 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 over an IPv6-only connectivity.

   o  Section 3 enumerates a set of recommendations for cellular devices
      with Local Area Network (LAN) capabilities (e.g., Customer Edge
      (CE) routers with cellular access link, 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).

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 that can be connected to 3GPP mobile networks.

   o  3GPP cellular device (or "cellular device" for short): refers to a
      cellular host that supports the capability to share its 3GPP
      mobile 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 Network Address and Protocol Translation
      from IPv6 Clients to IPv4 Servers (NAT64) [RFC6146].

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










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1.2.  Scope

   A 3GPP mobile network can be used to connect various User Equipment
   (UE) such as a mobile telephone or a CE router.  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.

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

   This document is structured to provide the generic IPv6
   recommendations that 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 Evolved Packet System (EPS).  For EPS, the term "PDN-Connection"
   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, that require features to ensure IPv4 service delivery over
   an IPv6-only transport in addition to the base IPv6 service.
   Moreover, this profile also covers cellular CE routers that are used
   in various mobile broadband deployments.  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 an IPv6
   prefix towards the 3GPP cellular device.  In particular, Maximum
   Transmission Unit (MTU) communication via Router Advertisement (RA)
   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



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   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 Application Programming
   Interfaces (APIs) 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; and (3) applications relying upon Uniform Resource
   Identifiers (URIs) must follow [RFC3986] and its updates.  Note, some
   IETF specifications (e.g., SIP [RFC3261]) contains broken IPv6
   Augmented Backus-Naur Form (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
   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.  These
   recommendations apply also for cellular devices (see Section 3).

   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.




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   C_REC#2:  The cellular host must comply with the behavior defined in
             [TS.23060], [TS.23401], and [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., a 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 of the other
                address family in addition to the one already activated
                for a given Access Point Name (APN).  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.

             The network informs the cellular host about allowed Packet
             Data Protocol (PDP) types by means of Session Management
             (SM) cause codes.  In particular, the following cause codes
             can be returned:

             *  cause #50 "PDP type IPv4 only allowed" - This cause code
                is used by the network to indicate that only PDP type
                IPv4 is allowed for the requested Public Data Network
                (PDN) connectivity.

             *  cause #51 "PDP type IPv6 only allowed" - This cause code
                is used by the network to indicate that only PDP type
                IPv6 is allowed for the requested PDN connectivity.

             *  cause #52 "single address bearers only allowed" - This
                cause code is used by the network to indicate that the
                requested PDN connectivity is accepted with the
                restriction that only single IP version bearers are
                allowed.





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

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

                The 3GPP network communicates parameters by means of the
                protocol configuration options information element when
                activating, modifying, or deactivating a PDP-Context.
                PCO is a convenient method to inform the cellular host
                about various services, including DNS server
                information.  It does not require additional protocol to
                be supported by the cellular host 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 (TFTs) [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:  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.



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

                The configuration can be either local to the device or
                be managed dynamically using, for example, Open Mobile
                Alliance (OMA) management.  The support of dynamic means
                is encouraged.

   C_REC#7:  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 will not be able to make use of an IPv4
                address received in a referral.  This feature allows for
                solving the referral problem (because an IPv6-enabled
                application can construct IPv4-embedded IPv6 addresses
                [RFC6052]) and, also, for distinguishing between
                IPv4-converted IPv6 addresses and native IPv6 addresses.

                In other words, this feature contributes to offload both
                the CLAT module and NAT64 devices.  Refer to Section 3
                of [RFC7051] for an inventory of the issues related to
                the discovery of PREFIX64(s).

                In environments based on the Port Control Protocol
                (PCP), 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#8:  In order to ensure IPv4 service continuity in an IPv6-only
             deployment context, the cellular host should implement the
             CLAT [RFC6877] function in compliance with [RFC6052],
             [RFC6145], and [RFC6146].

                The CLAT function in the cellular host allows for
                IPv4-only application and IPv4 referrals to work on an
                IPv6-only connectivity.  The more applications are
                address family independent, the less the CLAT function
                is solicited.  The CLAT function requires a NAT64
                capability [RFC6146] in the network.

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



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                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.

                CLAT may not be required in some contexts, e.g., if
                other solutions such as Bump-in-the-Host (BIH) [RFC6535]
                are supported.

                The cellular device can act as a CE router connecting
                various IP hosts on a LAN segment; this is also the case
                with using WLAN (Wireless LAN) tethering or a WLAN
                hotspot from the cellular device.  Some of these IP
                hosts can be dual-stack, others are IPv6-only or
                IPv4-only.  IPv6-only connectivity on the cellular
                device does not allow IPv4-only sessions to be
                established for hosts connected on the LAN segment of
                the cellular device.  IPv4 session establishment
                initiated from hosts located on the LAN segment side and
                destined for IPv4 nodes must be maintained.  A solution
                is to integrate the CLAT function to the LAN segment in
                the cellular device.

   C_REC#9:  The cellular host may 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, (2) network
                conditions with regard to the support of specific PDP
                types (e.g., IPv4v6 PDP-Context is not supported), (3)
                IPv4 sunset objectives, (4) subscription data, etc.

                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.

                The configuration can be either local to the device or
                be managed dynamically using, for example, OMA
                management.  The support of dynamic means is encouraged.



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3.  Recommendations for Cellular Devices with LAN Capabilities

   This section focuses on cellular devices (e.g., CE routers,
   smartphones, or dongles with tethering features) that provide IP
   connectivity to other devices connected to them.  In this 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:  For deployments that require that the same /64 prefix be
             shared, the cellular device should support [RFC7278] to
             enable sharing a /64 prefix between the LAN and the WAN
             interfaces.  The WAN interface is the one towards the
             Gateway GPRS Support Node (GGSN) / Packet Data Network
             Gateway (PGW).

                Prefix Delegation (refer to L_REC#2) is the target
                solution for distributing prefixes in the LAN side but,
                because the device may attach to earlier 3GPP release
                networks, a means to share a /64 prefix is also
                recommended [RFC7278].

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

   L_REC#2:  The cellular device must support Prefix Delegation
             capabilities [RFC3633] and must support the 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 broadband 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 the 3GPP link allocated using the Stateless
                     Address Autoconfiguration (SLAAC) mechanism and





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

                Note that the 3GPP network architecture requires both
                the WAN 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 compliance with [RFC3633]
                (e.g., halving the delegated prefix and assigning the
                WAN prefix out of the first half and the prefix to be
                delegated to the terminal from the second half).

                Because Prefix Delegation capabilities may not be
                available in some attached networks, L_REC#1 is strongly
                recommended to accommodate early deployments.

   L_REC#3:  The cellular CE router must be compliant with the
             requirements specified in [RFC7084].

                There are several deployments, particularly in emerging
                countries, that rely 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 Section 4.4 of [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., Digital Subscriber
                Line (DSL), LTE, WLAN, etc.) or offloading the traffic
                via a subset of interfaces.  Ensuring IPv6 feature
                parity among these interface types is important for the
                sake of specification efficiency, service design
                simplification, and validation effort optimization.







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   L_REC#4:  If an RA MTU is advertised from the 3GPP network, the
             cellular device should send RAs to the downstream attached
             LAN devices with the same MTU as seen on the mobile
             interface.

                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 tunnels that use the GPRS
                Tunneling Protocol (GTP).

                [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.  More details
                about link MTU considerations can be found in Annex C of
                [TS.23060].

4.  Advanced Recommendations

   This section identifies a set of advanced recommendations to fulfill
   requirements of critical services such as VoLTE.  These
   recommendations apply for mobile hosts, including mobile devices.

   A_REC#1:  The cellular host must support the RObust Header
             Compression (ROHC) RTP Profile (0x0001) and the 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.

                The "RTP/UDP/IP" ROHC profile (0x0001) to compress RTP
                packets and the "UDP/IP" ROHC profile (0x0002) to
                compress Real-time Transport Control Protocol (RTCP)
                packets are required for VoLTE by Section 4.1 of
                IR.92.7.0 [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 keep-alive messages.  PCP
                also gives the possibility of enabling incoming
                connections to the cellular device.  Indeed, because



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                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 that 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
                (which 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 (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.).

                Deploying PCP allows cellular hosts to manage protocols
                that convey IP addresses and/or port numbers (see
                Section 2.2 of [RFC6889]) without requiring Application
                Level Gateways (ALGs) to be enabled at the network side
                (e.g., NAT64).  Avoiding soliciting ALGs makes it easier
                to develop a service without any adherence with 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#7.






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                [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 a native IPv6 connection over a
             connection established through translation devices (e.g.,
             NAT44 and NAT64).

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

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

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#3 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 the IETF makes 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 that
   preserve privacy.  The activation of the 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).





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6.  References

6.1.  Normative References

   [IR92]     GSMA, "IMS Profile for Voice and SMS", Official Document
              IR.92 - IMS Profile for Voice and SMS, V7.0, March 2013,
              <http://www.gsma.com/newsroom/wp-content/uploads/2013/04/
              IR.92-v7.0.pdf>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
              "DNS Extensions to Support IP Version 6", RFC 3596,
              DOI 10.17487/RFC3596, October 2003,
              <http://www.rfc-editor.org/info/rfc3596>.

   [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,
              <http://www.rfc-editor.org/info/rfc3633>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC5795]  Sandlund, K., Pelletier, G., and L-E. Jonsson, "The RObust
              Header Compression (ROHC) Framework", RFC 5795,
              DOI 10.17487/RFC5795, March 2010,
              <http://www.rfc-editor.org/info/rfc5795>.

   [RFC5954]  Gurbani, V., Ed., Carpenter, B., Ed., and B. Tate, Ed.,
              "Essential Correction for IPv6 ABNF and URI Comparison in
              RFC 3261", RFC 5954, DOI 10.17487/RFC5954, August 2010,
              <http://www.rfc-editor.org/info/rfc5954>.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              DOI 10.17487/RFC6052, October 2010,
              <http://www.rfc-editor.org/info/rfc6052>.

   [RFC6603]  Korhonen, J., Ed., Savolainen, T., Krishnan, S., and O.
              Troan, "Prefix Exclude Option for DHCPv6-based Prefix
              Delegation", RFC 6603, DOI 10.17487/RFC6603, May 2012,
              <http://www.rfc-editor.org/info/rfc6603>.




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   [RFC7066]  Korhonen, J., Ed., Arkko, J., Ed., Savolainen, T., and S.
              Krishnan, "IPv6 for Third Generation Partnership Project
              (3GPP) Cellular Hosts", RFC 7066, DOI 10.17487/RFC7066,
              November 2013, <http://www.rfc-editor.org/info/rfc7066>.

   [TS.23060]
              3GPP, "General Packet Radio Service (GPRS); Service
              description; Stage 2", 3GPP TS 23.060 13.6.0, March 2016,
              <http://www.3gpp.org/DynaReport/23060.htm>.

   [TS.23401]
              3GPP, "General Packet Radio Service (GPRS) enhancements
              for Evolved Universal Terrestrial Radio Access Network
              (E-UTRAN) access", 3GPP TS 23.401 13.6.1, March 2016,
              <http://www.3gpp.org/DynaReport/23401.htm>.

   [TS.24008]
              3GPP, "Mobile radio interface Layer 3 specification; Core
              network protocols; Stage 3", 3GPP TS 24.008 13.5.0, March
              2016, <http://www.3gpp.org/DynaReport/24008.htm>.

6.2.  Informative References

   [OECD]     Organisation for Economic Co-operation and Development
              (OECD), "The Economics of the Transition to Internet
              Protocol version 6 (IPv6)", DOI 10.1787/5jxt46d07bhc-en,
              November 2014, <http://www.oecd.org/officialdocuments/publ
              icdisplaydocumentpdf/?cote=DSTI/ICCP/CISP%282014%293/
              FINAL&docLanguage=En>.

   [Power]    Haverinen, H., Siren, J., and P. Eronen, "Energy
              Consumption of Always-On Applications in WCDMA Networks",
              Proceedings of IEEE 65: Vehicular Technology
              Conference, VTC2007-Spring, pp 964-968,
              DOI 10.1109/VETECS.2007.207, April 2007,
              <http://ieeexplore.ieee.org/xpl/
              articleDetails.jsp?arnumber=4212635>.

   [R3GPP]    3GPP, "The Mobile Broadband Standard: Releases", 2016,
              <http://www.3gpp.org/specifications/67-releases>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.





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   [RFC3948]  Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets",
              RFC 3948, DOI 10.17487/RFC3948, January 2005,
              <http://www.rfc-editor.org/info/rfc3948>.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <http://www.rfc-editor.org/info/rfc4033>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <http://www.rfc-editor.org/info/rfc4034>.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
              <http://www.rfc-editor.org/info/rfc4035>.

   [RFC6092]  Woodyatt, J., Ed., "Recommended Simple Security
              Capabilities in Customer Premises Equipment (CPE) for
              Providing Residential IPv6 Internet Service", RFC 6092,
              DOI 10.17487/RFC6092, January 2011,
              <http://www.rfc-editor.org/info/rfc6092>.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
              <http://www.rfc-editor.org/info/rfc6145>.

   [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, <http://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,
              <http://www.rfc-editor.org/info/rfc6147>.

   [RFC6342]  Koodli, R., "Mobile Networks Considerations for IPv6
              Deployment", RFC 6342, DOI 10.17487/RFC6342, August 2011,
              <http://www.rfc-editor.org/info/rfc6342>.

   [RFC6434]  Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
              Requirements", RFC 6434, DOI 10.17487/RFC6434, December
              2011, <http://www.rfc-editor.org/info/rfc6434>.



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   [RFC6459]  Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
              T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
              Partnership Project (3GPP) Evolved Packet System (EPS)",
              RFC 6459, DOI 10.17487/RFC6459, January 2012,
              <http://www.rfc-editor.org/info/rfc6459>.

   [RFC6535]  Huang, B., Deng, H., and T. Savolainen, "Dual-Stack Hosts
              Using "Bump-in-the-Host" (BIH)", RFC 6535,
              DOI 10.17487/RFC6535, February 2012,
              <http://www.rfc-editor.org/info/rfc6535>.

   [RFC6724]  Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
              <http://www.rfc-editor.org/info/rfc6724>.

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,
              <http://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,
              <http://www.rfc-editor.org/info/rfc6887>.

   [RFC6889]  Penno, R., Saxena, T., Boucadair, M., and S. Sivakumar,
              "Analysis of Stateful 64 Translation", RFC 6889,
              DOI 10.17487/RFC6889, April 2013,
              <http://www.rfc-editor.org/info/rfc6889>.

   [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,
              <http://www.rfc-editor.org/info/rfc7050>.

   [RFC7051]  Korhonen, J., Ed. and T. Savolainen, Ed., "Analysis of
              Solution Proposals for Hosts to Learn NAT64 Prefix",
              RFC 7051, DOI 10.17487/RFC7051, November 2013,
              <http://www.rfc-editor.org/info/rfc7051>.

   [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,
              <http://www.rfc-editor.org/info/rfc7084>.






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   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,
              <http://www.rfc-editor.org/info/rfc7217>.

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

   [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,
              DOI 10.17487/RFC7278, June 2014,
              <http://www.rfc-editor.org/info/rfc7278>.

   [RFC7335]  Byrne, C., "IPv4 Service Continuity Prefix", RFC 7335,
              DOI 10.17487/RFC7335, August 2014,
              <http://www.rfc-editor.org/info/rfc7335>.

   [RFC7445]  Chen, G., Deng, H., Michaud, D., Korhonen, J., and M.
              Boucadair, "Analysis of Failure Cases in IPv6 Roaming
              Scenarios", RFC 7445, DOI 10.17487/RFC7445, March 2015,
              <http://www.rfc-editor.org/info/rfc7445>.

   [TS.23402]
              3GPP, "Architecture enhancements for non-3GPP accesses",
              3GPP TS 23.401 13.5.0, March 2016,
              <http://www.3gpp.org/DynaReport/23402.htm>.

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, F. Baker,
   L.M. Contreras Murillo, and M. Abrahamsson for their detailed reviews
   and comments.






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Authors' Addresses

   David Binet
   Orange
   Rennes
   France

   Email: david.binet@orange.com


   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Ales Vizdal
   Deutsche Telekom AG
   Tomickova 2144/1
   Prague, 148 00
   Czech Republic

   Email: Ales.Vizdal@T-Mobile.cz


   Gang Chen
   China Mobile
   29, Jinrong Avenue
   Xicheng District, Beijing  100033
   China

   Email: phdgang@gmail.com, chengang@chinamobile.com


   Nick Heatley
   EE
   The Point, 37 North Wharf Road,
   London  W2 1AG
   United Kingdom

   Email: nick.heatley@ee.co.uk








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   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


   Walter Haeffner
   Vodafone D2 GmbH
   Ferdinand-Braun-Platz 1
   Duesseldorf  40549
   Germany

   Email: walter.haeffner@vodafone.com















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