Network Working Group                                            G. Chen
Internet-Draft                                                   H. Deng
Intended status: Informational                              China Mobile
Expires: February 4, 10, 2015                                    D. Michaud
                                                   Rogers Communications
                                                             J. Korhonen
                                                          Renesas Mobile
                                                            M. Boucadair
                                                          France Telecom
                                                               A. Vizdal
                                                     Deutsche Telekom AG
                                                          August 3, 9, 2014

                     IPv6 Roaming Behavior Analysis
               draft-ietf-v6ops-ipv6-roaming-analysis-02
               draft-ietf-v6ops-ipv6-roaming-analysis-03

Abstract

   This document identifies a set of failure cases that may be
   encountered by an IPv6-enabled mobile customers in roaming scenarios.
   The investigations on those failed cases reveal the causes in order
   to notice improper configurations, equipment's incomplete functions
   or inconsistent IPv6 introduction strategy.

Status of This Memo

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   This Internet-Draft will expire on February 4, 10, 2015.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Roaming Architecture Description  . . . . . . . . . . . . . .   3
     2.1.  Home Routed Mode  . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Local Breakout Mode . . . . . . . . . . . . . . . . . . .   4
   3.  Roaming Scenario  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Failure Case in Attachment Stage  . . . . . . . . . . . . . .   6
   5.  Failure Cases in PDP/PDN Creation . . . . . . . . . . . . . .   7
     5.1.  Case 1: Splitting Dual-stack Bearer . . . . . . . . . . .   7
     5.2.  Case 2: Lack of IPv6 support in applications  . . . . . .   8
     5.3.  Case 3: Fallback Incapability . . . . . . . . . . . . . .   8   9
     5.4.  Case 4: 464xlat Support . . . . . . . . . . . . . . . . .   9
   6.  HLR/HSS User Profile Setting  . . . . . . . . . . . . . . . .   9
   7.  Discussions  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12  13
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12  13
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12  13
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Many Mobile Operators have deployed IPv6, or are about to, in their
   operational networks.  A customer in such a network can be provided
   IPv6 connectivity if their User Equipment (UE) is IPv6-compliant.  A
   detailed overview of IPv6 support in 3GPP architectures is provided
   in [RFC6459].  Operators may adopt various approaches to deploy IPv6
   in mobile networks, for example the solutions described in
   [TR23.975]).  Depending on network conditions either dual-stack or
   single-stack IPv6 is selected.

   In production networks, it has been observed that a mobile subscriber
   roaming around a different operator's areas may experience service
   degradations
   degradation or interruptions due to inconsistent configurations and
   incomplete functionality of equipment in the network.

   A mobile subscriber roaming to different operator's network may
   experience service degradations or interruptions due to inconsistent
   configurations and incomplete functions in the visited network.

2.  Roaming Architecture Description

   Roaming occurs in several two scenarios:

   o  International roaming: a mobile UE may enter a visited network,
      where a different Public Land Mobile Network (PLMN) identity is
      used.  The UEs could, either in an automatic mode or a manual
      mode, attach to the visited PLMN.

   o  Intra-PLMN mobility: a mobile UE moves to a different area of the
      Home Public Land Mobile Network (HPLMN).  However, the subscriber
      profile may not be stored in the area.  To allow network
      attachment the subscribers profile needs to be downloaded from the
      home network area.

   When a UE is turned on or is transferred via a handover to a visited
   network, the mobile device will scan all radio channels and find
   available Public Land Mobile Networks (PLMNs) to attach to.  The
   Serving GPRS Support Node (SGSN) or the Mobility Management Entity
   (MME) in the visited networks must contact the Home Location
   Register(HLR) or Home Subscriber Server(HSS) and obtain the
   subscriber profile.  After the authentication and registration
   process is completed, the Packet Data Protocol (PDP) or Packet Data
   Networks (PDN) activation and traffic flows may be operated
   differently according to the subscriber profile stored in HLR or HSS.
   Two modes are shown in the figure to illustrate, these

   There are two roaming modes illustrated below, i.e.  "Home routed
   traffic" (Figure 1) and "Local breakout" (Figure 2).

+---------------------------------+             +------------------------+
|Visited Network                  |             |Home Network            |
|  +----+           +--------+    |             |    +--------+ Traffic Flow
|  | UE |==========>|SGSN/MME|======================>|GGSN/PGW|============>
|  +----+           +--------+    | Signaling   |    +--------+          |
|                        |-------------------------->+--------+          |
|                                 |             |    |HLR/HSS |          |
|                                 |             |    +--------+          |
+---------------------------------+             +------------------------+

                       Figure 1:

2.1.  Home Routed Traffic

+---------------------------------+             +------------------------+
|Visited Network                  |             |Home Network            |
|  +----+           +--------+    | Signaling   |    +--------+          |
|  | UE |==========>|SGSN/MME|---------------------->|HLR/HSS |          |
|  +----+           +--------+    |             |    +--------+          |
|                       ||        |             |                        |
|                   +--------+    |             |                        |
|                   |GGSN/PGW|    |             |                        |
|                   +--------+    |             |                        |
|         Traffic Flow  ||        |             |                        |
+-----------------------||--------+             +------------------------+
                        \/

                         Figure 2: Local Breakout Mode

   In the home routed mode, the subscriber's UE activates the PDP/PDN
   context and get an address from the home network.  All traffic is
   routed back to the home network.  This is likely to be the case
   international roaming of Internet data services to facilitate the
   charging process between the two operators concerned.

 +-----------------------------+            +------------------------+
 |Visited Network              |            |Home Network            |
 |  +----+        +--------+   | (GRX/IPX)  |    +--------+ Traffic Flow
 |  | UE |=======>|SGSN/MME|====================>|GGSN/PGW|============>
 |  +----+        +--------+   | Signaling  |    +--------+          |
 |                     |------------------------>+--------+          |
 |                             |            |    |HLR/HSS |          |
 |                             |            |    +--------+          |
 +-----------------------------+            +------------------------+

                       Figure 1: Home Routed Traffic

2.2.  Local Breakout Mode

   In the local breakout mode, the subscriber address is assigned by the
   visited network.  The traffic flow is directly offloaded locally at a
   network node close to that device's point of attachment in the
   visited network.  Therefore,a more efficient route to the data
   service is achieved.  The international roaming of IP Multimedia
   Subsystem (IMS) based services, e.g.  Voice over LTE (VoLTE)[IR.92] ,
   is claimed to select the local breakout mode in [IR.65].  Data
   service roaming across different areas within an operator network
   might use local breakout mode in order to get more efficient traffic
   routing.  The local breakout mode could be also applied to an
   operator's alliance for international roaming of data service.  EU
   Roaming Regulation III[EU-Roaming-III] involves local breakout mode
   allowing European subscribers roaming in European 2G/3G networks can
   choose to have their Internet data routed directly to the Internet
   from their current VPLMN.

   +----------------------------+            +----------------+
   |Visited Network             |            |Home Network    |
   |  +----+        +--------+  | Signaling  |    +--------+  |
   |  | UE |=======>|SGSN/MME|------------------->|HLR/HSS |  |
   |  +----+        +--------+  | (GRX/IPX)  |    +--------+  |
   |                    ||      |            |                |
   |                +--------+  |            |                |
   |                |GGSN/PGW|  |            |                |
   |                +--------+  |            |                |
   |      Traffic Flow  ||      |            |                |
   +--------------------||------+            +----------------+
                        \/

                         Figure 2: Local Breakout

   The following enumerates the more specific configuration
   considerations.

   o  Operators may add the APN-OI-Replacement flag defined in 3GPP
      [TS29.272] into user's subscription-data.  The visited network
      indicates a local domain name to replace the user requested Access
      Point Name (APN).  Consequently, the traffic would be steered to
      the visited network.  Those functions are normally deployed for
      the Intra-PLMN mobility cases.

   o  Operators may also configure the VPLMN-Dynamic-Address-Allowed
      flag[TS29.272] in the user profile to enable local breakout mode
      in a Visited Public Land Mobile Networks (VPLMNs).

   o  3GPP specified Selected IP Traffic Offload (SIPTO)
      function[TS23.401] since Release 10 in order to get efficient
      route paths.  It enables an operator to offload certain types of
      traffic at a network node close to that device's point of
      attachment to the access network.

   o  GSMA has defined RAVEL[IR.65] as the IMS international roaming
      architecture.  Local breakout mode has been adopted for the IMS
      roaming architecture.

3.  Roaming Scenario

   Two stages occur when a subscriber roams to a visited network and
   intends to start data services.

   o  Network attachment: this occurs when the subscriber enters a
      visited network.  During an attachment, the visited network should
      authenticate the subscriber and make a location update to the HSS/
      HLR in the home network of the subscriber.  Accordingly, the
      subscriber profile is offered from the HSS/HLR.  The subscriber
      profile contains the allowed Access Point Names (APN), the allowed
      PDP/PDN Types and rules regarding the routing of data sessions
      (i.e.  home routed or local breakout mode) [TS29.272].  The SGSN/
      MME in the visited network can use this information to facilitate
      the subsequent PDP/PDN session creation.

   o  PDP/PDN context creation: this occurs after the subscriber makes a
      successful attachment.  This stage is integrated with the
      attachment stage in the case of 4G, but is a seperate process in
      2/3G. 3GPP specifies three types of Packet Data Protocol
      (PDP)/Packet Data Networks (PDN) to describe connections, i.e.
      PDP/PDN Type IPv4, PDP/PDN Type IPv6 and PDP/ PDN Type IPv4v6.
      When a subscriber creates a data session, their device requests a
      particular PDP/PDN Type.  The allowed PDP/PDN types for that
      subscriber are learned in the attachment stage.  Hence, SGSN/MME
      could initiate PDP/PDN request to GGSN/PGW if the subscription
      profile is allowed.

   The failures

   In both stages, the failure cases described are likely to occur in both stages due
   to an incompliant implementation in the visited network or a mismatch
   between the subscriber requested and the capability of the visited
   network.  The failures described in the attachment stage are
   independent of home routed or the local breakout mode, while most mode.  Most failure
   cases in the PDP/PDN context creation stage occur in the local
   breakout cases. mode.  Section 4 and 5 describe each case.  The below table lists several cases
   concerning the PDP/PDN creation stage.

   +-------------+-------------------+--------------+
   | UE request  |  PDN/PDP IP Type  |Local breakout|
   |             |     permitted     |              |
   +-------------+-------------------+--------------+
   | IPv4v6      |  IPv4 or IPv6     |Failure case 1|
   +-------------+-------------------+--------------+
   | IPv4v6      |      IPv6         |Failure case 2|
   +-------------+-------------------+--------------+
   | IPv6        |      IPv4         |Failure case 3|
   +-------------+-------------------+--------------+
   | IPv6        |       IPv6        |Failure case 4|
   | with 464xlat|   without NAT64   |              |
   +-------------+-------------------+--------------+

                  Table 1: Roaming Scenario Descriptions

4.  Failure Case in Attachment Stage

   3GPP specified PDP/PDN type IPv4v6 in order to allow a UE request get both
   IPv4 and IPv6 address within a single PDP/PDN request. bearer.  This option is
   stored as a part of subscription data for a subscriber in the HLR/
   HSS.  PDP/PDN type IPv4v6 has been introduced at the inception of
   Evolved Packet System (EPS) in 4G networks.  The nodes in 4G networks
   should present no issues with the handling of this PDN type.
   However, support varies in 2/3G networks depending on Serving GPRS
   Support Node (SGSN) software version.  In theory, S4-SGSN (i.e. an
   SGSN with S4 interface) supports the PDP/PDN type IPv4v6 since
   Release8 and a Gn-SGSN (i.e. the SGSN with Gn interface) supports it
   since Release 9.  In most cases, operators normally use Gn-SGSN to
   connect either GGSN in 3G or Packet Data Network Gateway (PGW) in 4G.
   The MAP (Mobile Application Part) protocol, as defined in 3GPP
   [TS29.002], is used over the Gr interface between SGSN and HLR.  The
   MAP Information Element (IE) "ext-pdp-Type" contains the IPv4v6 PDP
   Type that is conveyed to SGSN from the HLR within the Insert
   Subscriber Data (ISD) MAP operation.  If the SGSN does not support
   the IPv4v6 PDP Type, it will not support the "ext-pdp-Type" IE and
   consequently it must silently discard that IE and continue processing
   of the rest of the ISD MAP message.  The issue we observe is that
   multiple SGSNs will be unable to correctly process a subscriber's
   data received in the Insert Subscriber Data Procedure[TS23.060].  As
   a consequence, it will likely refuse the subscriber attach request.
   This is erroneous behavior due to the equipment not being 3GPP
   Release 9 compliant.

   Operators may have to remove the PDP/PDN type IPv4v6 from the HLR/HSS
   in the home network, that will restrict UEs to only initiate IPv4 PDP
   or IPv6 PDP activation.  In order to avoid this situation, operators
   should make a comprehensive roaming agreement to support IPv6 and
   ensure that it aligns with the GSMA documents, e.g.  [IR.33], [IR.88]
   and [IR.21].  Such an agreement requires the visited operator to get
   the necessary patch on all their SGSN nodes to support PDP/PDN type
   IPv4v6.

   As an alternative solution there are some specific implementations
   (not standardised standardized by 3GPP) in the HLS/HSS of the home network.  When
   the HLR/HSS receives an Update Location message from a visited SGSN
   known to not support the PDP type IPv4v6, subscription data with only
   PDP/PDN type IPv4 will be sent to that SGSN in the Insert Subscriber
   Data procedure.  It guarantees the user profile is compatible with
   visited SGSN/MME capability.

5.  Failure Cases in PDP/PDN Creation

   When a subscriber succeeds in the attach stage, the IP allocation
   process takes place to allocate IP addresses to the subscriber.  In
   general, a PDP/PDN type IPv4v6 request implicitly allows a network
   side to make several IP assignment options, including IPv4-only,
   IPv6-only, IPv4 and IPv6 in single PDP/PDN bearer, IPv4 and IPv6 in
   separated PDP/PDN bearers.  A PDP/PDN type IPv4 or IPv6 restricts the
   network side only allocates requested IP family.  This section
   summarizes several failures in the break-out cases. Local Breakout mode.

   +-------------+-------------------+--------------+
   | UE request  |  PDN/PDP IP Type  |Local breakout|
   |             |     permitted     |              |
   +-------------+-------------------+--------------+
   | IPv4v6      |  IPv4 or IPv6     |Failure case 1|
   +-------------+-------------------+--------------+
   | IPv4v6      |      IPv6         |Failure case 2|
   +-------------+-------------------+--------------+
   | IPv6        |      IPv4         |Failure case 3|
   +-------------+-------------------+--------------+
   | IPv6        |       IPv6        |Failure case 4|
   | with 464xlat|   without NAT64   |              |
   +-------------+-------------------+--------------+

                   Table 1: Local Breakout Failure Cases

5.1.  Case 1: Splitting Dual-stack Bearer

   Dual-stack capability can be provided using separate PDP/PDN
   activations.
   activation.  That means only separate parallel single-stack IPv4 and
   IPv6 PDP/PDN connections are allowed to be initiated to separately
   allocate IPv4 and IPv6 addresses.

   The cases are listed below:

   o  The SGSN/MME returns Session Management (SM) Cause #52, "Single
      address bearers only allowed", or SM Cause #28 "Unknown PDP
      address or PDP type" as per[TS24.008] and [TS24.301].

   o  The SGSN/MME does not set the Dual Address Bearer Flag (DAF)
      because the operator uses single addressing per bearer to support
      interworking with nodes of earlier releases

   A roaming subscriber's UE with IPv4v6 PDP/PDN type has to change the
   request into two separated PDP/PDN requests with a single IP version
   in order to achieve equivalent results.  Some drawbacks of this case
   are listed as below:

   o  The parallel PDP/PDN activations activation would likely double PDP/PDN
      resources consumptions. consumption.  It also impacts the capacity of GGSN/PGW,
      since a certain amount of PDP/PDN activations are activation is only allowed on
      those nodes.

   o  Some networks may only allow one PDP/PDN is alive for each
      subscriber.  For example, an IPv6 PDP/PDN will be rejected if the
      subscriber has an active IPv4 PDP/PDN.  Therefore, the subscriber
      will lose the IPv6 connection in the visited network.  It is even
      worse as they may have a risk of losing all data connectivity if
      the IPv6 PDP gets rejected with a permanent error at the APN-level
      and not specific to the PDP-Type IPv6 requested.

   o  Additional correlations between those two PDP/PDN contexts are
      required on the charging system.

   o  Policy and Charging Rules Function(PCRF)/Policy and Charging
      Enforcement Function (PCEF) treats the IPv4 and IPv6 session as
      independent and performs different Quality of Service (QoS)
      policies.  The subscriber may have unstable experiences due to
      different behaviors on each IP version connection.

   o  Mobile devices may have a limitation on allowed simultaneous PDP/
      PDN activations. activation.  Excessive PDP/PDN activation may result in other
      unrelated services broken.

   Operators may have to disable the local-break mode to avoid the
   risks.  Another approach is to set a dedicated Access Point Name
   (APN) profile to only request PDP/PDN type IPv4 in the roaming
   network.

5.2.  Case 2: Lack of IPv6 support in applications

   Some operators may adopt an IPv6-only configuration for the IMS
   service, e.g.  Voice over LTE (VoLTE)[IR.92] or Rich Communication
   Suite (RCS)[RCC.07].  Since the IMS roaming architecture will offload
   all traffic in the visited network, a dual-stack subscriber can only
   be assigned with an IPv6 prefix and no IPv4 address returned.  This
   requires that all the IMS based applications should be IPv6 capable.
   A translation-based method, for example Bump-in-the-host
   (BIH)[RFC6535] or 464xlat [RFC6877] may help to address the issue if
   there are IPv6 compatibility problems.  Those functions could be
   automatically enabled in an IPv6-only network and disabled in a dual-
   stack or IPv4 network.

5.3.  Case 3: Fallback Incapability

   3GPP specified the PDP/PDN type IPv6 as early as PDP/PDN type IPv4.
   Therefore, the IPv6 single PDP/PDN type has been well supported and
   interpretable in the 3GPP network nodes.  Roaming to IPv4-only
   networks and making an IPv6 PDP/PDN request should could guarantee that the
   subscription data is compatible with the visited pre-Release 9 SGSN.
   When a subscriber requests PDP/PDN type IPv6, the network should only
   return the expected IPv6 prefix.  The mobile device may fail to get
   an IPv6 prefix if the visited network only allocates an IPv4 address
   to the subscriber.  In that case, the request will be dropped and the
   cause code should be sent to the user.

   A proper fallback is desirable, however the behavior is
   implementation specific.  There are some mobile devices have the
   ability to provide a different configuration for home network and
   visited network respectively.  For instance, the Android system
   solves the issue by setting the roaming protocol to IPv4 for the
   Access Point Name(APN).  It guarantees that UE will always initiate
   an PDP/PDN type IPv4 in the roaming area.

5.4.  Case 4: 464xlat Support

   464xlat[RFC6877] is proposed to address the IPv4 compatibility issue
   in an IPv6 single-stack environment.  The function on a mobile device
   is likely in conjunction with a PDP/PDN IPv6 type request and
   cooperates with a remote NAT64[RFC6146] gateway. 464xlat may use the
   mechanism defined in [RFC7050] to automatically detect the presence
   of DNS64 and to learn the IPv6 prefix used for protocol translation.
   In the local breakout approach when a mobile device with 464xlat
   function roams to an IPv6 visited network without the presence of
   NAT64 or DNS64, 464xlat will fail to function.

   The issue has been found mostly in intra-PLMN mobility cases for the
   time being.  Considering the various network's situations, operators
   may turn off the local breakout and use the home routed mode to
   perform 464xlat.  Some devices may support the configuration to adopt
   464xlat in the home networks and use IPv4-only in the visited
   networks with different roaming profile configurations.  This could
   also be a solution to address this issue.

6.  HLR/HSS User Profile Setting

   A proper user profile configuration could would provide a deterministic
   network control of
   outcome to the connectivity requests from PDP/PDN Creation stage where dual-stack, IPv4-only and
   IPv6-only devices.  It's desirable that the network
   could set-up proper connectivity for any type of the devices.The HLR/
   HSS requests may come from devices.  The HLR/HSS
   may have to apply extra logic to achieve this.  It's also desirable
   that the network could set-up connectivity of any requested PDP/PDN
   context type.

   The following are examples to demonstrate the settings for the
   scenarios and decision criteria to apply when returning user profile
   information to visited SGSN.

   Scenario 1: Support IPv6-only, IPv4-only and dual-stack devices

   user profile #1:

   PDP-Context ::= SEQUENCE {
   pdp-ContextId ContextId,
   pdp-Type  PDP-Type-IPv4
     ....
   ext-pdp-Type PDP-Type-IPv4v6
     ...
   }

   user profile #2:

   PDP-Context ::= SEQUENCE {
   pdp-ContextId ContextId,
   pdp-Type  PDP-Type-IPv6
     ....
   }

   The full PDP-context parameters is refered referred to Section 17.7.1 "Mobile
   Sevice date types" of [TS29.002].  User profile 1 and 2 share the
   same contextId.  The setting of user profile #1 enables IPv4-only and
   dual-stack devices to work.  And, the user profile #2 fulfills the
   request if the device asks for IPv6 only PDP context.

   Scenario 2: Support dual-stack devices with pre-R9 vSGSN access

   user profile #1:

   PDP-Context ::= SEQUENCE {
   pdp-ContextId ContextId,
   pdp-Type  PDP-Type-IPv4
     ....
   ext-pdp-Type PDP-Type-IPv4v6
     ...
   }

   user profile #2:

   PDP-Context ::= SEQUENCE {
   pdp-ContextId ContextId,
   pdp-Type  PDP-Type-IPv4
     ....
   }

   User profile 1 and 2 share the same contextId.  If a visited SGSN is
   identified as early as pre-Release 9, the HLR/HSS should only send
   user profile#2 to visited SGSN.

7.  Discussions  Discussion

   Several failure cases have been discussed in this document.  It has
   been testified that the major issues happened at two stages, i.e.,
   the initial network attach attachment and the IP allocation process.

   During the initial network attach, PDP/PDN type IPv4v6 is the major
   concern to the visited pre-Release 9 SGSN.  The dual-stack deployment
   is recommended in most cases.  However, it may take some times in a
   mobile environment. 3GPP didn't specify PDP/PDN PDP/
   PDN type IPv4v6 in the early release.  Such PDP/PDN type is supported
   in new-built EPS network, but didn't support well in the third
   generation network.  The situations may cause the roaming issues
   dropping with the attach request from dual-stack subscribers.
   Operators may have to adopt temporary solution unless all the
   interworking nodes(i.e. the SSGN) in the visited network have been
   upgraded to support the ext-PDP-Type feature.

   The issues

   PDP/PDN type IPv6 has good compatibility to visited networks during
   the network attachment.  It has been observed that IPv6 single stack
   with the home routed mode is a viable approach to deploy IPv6.  In
   order to support the IPv6-only visitors, SGSN/MME in the IP address allocation process are caused visited
   network is required to accept IPv6-only PDP/PDN activation requests
   and enable IPv6 on user plane towards the home network.  In some
   cases, IPv6-only visitors may still be subject to the SGSN capability
   in visited networks.  This becomes especially apparent if the home
   operator performs roaming steering targeted to an operator that
   doesn't allow IPv6.  Therefore, it's expected that visited network is
   IPv6 roaming friendly to enable the functions on SGSN/MME by a default.

   In the local breakout policy.  Since mode, the IP address is allocated by the
   visited GGSN or PGW, the PGW.  The mismatch is found in the following aspects.

   o  The mismatch between the requested PDP/PDN type and the permitted
      PDP/PDN type

   o  The mismatch between the application capability and allowed
      network connections

   o  The mismatch between mobile device function (e.g., 464xlat) and
      the support for that function in the vistited visited network

   There are some solutions to overcome the issue.  Those solutions can
   be made either in the network side or mobile device side.  There
   exist several potential workarounds.

   o  Change local breakout to the home routed mode

   o  A dedicated roaming APN profile is implemented for the roamer.
      When a subscriber roams to a visited network, PDP/PDN type IPv4 is
      to be always selected for session activation.

   o  Networks could deploy an AAA server to coordinate the mobile
      device capability.  Once the GGSN/PGW receives the session
      creation request, it will initiate an Access-Request to an AAA
      server in the home network via the Radius protocol.  The Access-
      Request contains subscriber and visited network information, e.g.
      PDP/PDN Type, International Mobile Equipment Id (IMEI), Software
      Version(SV) and visited SGSN/MME location code, etc.  The AAA
      server could take mobile device capability and combine it with the
      visited network information to ultimately determine the type of
      session to be created, i.e.  IPv4, IPv6 or IPv4v6.

8.  IANA Considerations

   This document makes no request of IANA.

9.  Security Considerations

   Although this document defines neither a new architecture nor a new
   protocol, it is encouraged to refer to [RFC6459] for a generic
   discussion on IPv6-related security considerations.

10.  Acknowledgements

   Many thanks to F.  Baker and J.  Brzozowski for their support.

   This document is the result of the IETF v6ops IPv6-Roaming design
   team effort.

   The authors would like to thank Mikael Abrahamsson, Victor Kuarsingh,
   Heatley Nick, Alexandru Petrescu, Tore Anderson and Anderson, Cameron Byrne and
   Holger Metschulat for their helpful comments.

   The authors especially thank Fred Baker and Ross Chandler for his
   efforts and contributions on editing which substantially improves the
   legibility of the document.

11.  References

11.1.  Normative References

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

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

   [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.

   [RFC6535]  Huang, B., Deng, H., and T. Savolainen, "Dual-Stack Hosts
              Using "Bump-in-the-Host" (BIH)", RFC 6535, February 2012.

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

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

11.2.  Informative References

   [EU-Roaming-III]
              "http://www.amdocs.com/Products/Revenue-
              Management/Documents/
              amdocs-eu-roaming-regulation-III-solution.pdf", July 2013.

   [IR.21]    Global System for Mobile Communications Association,
              GSMA., "Roaming Database, Structure and Updating
              Procedures", July 2012.

   [IR.33]    Global System for Mobile Communications Association,
              GSMA., "GPRS Roaming Guidelines", July 2012.

   [IR.65]    Global System for Mobile Communications Association,
              GSMA., "IMS Roaming & Interworking Guidelines", May 2012.

   [IR.88]    Global System for Mobile Communications Association,
              GSMA., "LTE Roaming Guidelines", January 2012.

   [IR.92]    Global System for Mobile Communications Association
              (GSMA), , "IMS Profile for Voice and SMS Version 7.0",
              March 2013.

   [RCC.07]   Global System for Mobile Communications Association
              (GSMA), , "Rich Communication Suite 5.1 Advanced
              Communications Services and Client Specification Version
              4.0", November 2013.

   [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.

   [RFC6586]  Arkko, J. and A. Keranen, "Experiences from an IPv6-Only
              Network", RFC 6586, April 2012.

   [TR23.975]
              3rd Generation Partnership Project, 3GPP., "IPv6 migration
              guidelines", June 2011.

   [TS23.060]
              3rd Generation Partnership Project, 3GPP., "General Packet
              Radio Service (GPRS); Service description; Stage 2 v9.00",
              March 2009.

   [TS23.401]
              3rd Generation Partnership Project, 3GPP., "General Packet
              Radio Service (GPRS) enhancements for Evolved Universal
              Terrestrial Radio Access Network (E-UTRAN) access v9.00",
              March 2009.

   [TS24.008]
              3rd Generation Partnership Project, 3GPP., "Mobile radio
              interface Layer 3 specification; Core network protocols;
              Stage 3 v9.00", September 2009.

   [TS24.301]
              3rd Generation Partnership Project, 3GPP., "Non-Access-
              Stratum (NAS) protocol for Evolved Packet System (EPS) ;
              Stage 3 v9.00", September 2009.

   [TS29.002]
              3rd Generation Partnership Project, 3GPP., "Mobile
              Application Part (MAP) specification v9.12.0", December
              2009.

   [TS29.272]
              3rd Generation Partnership Project, 3GPP., "Mobility
              Management Entity (MME) and Serving GPRS Support Node
              (SGSN) related interfaces based on Diameter protocol
              v9.00", September 2009.

Authors' Addresses

   Gang Chen
   China Mobile
   53A,Xibianmennei Ave.,
   Xuanwu District,
   Beijing  100053
   China

   Email: phdgang@gmail.com

   Hui Deng
   China Mobile
   53A,Xibianmennei Ave.,
   Xuanwu District,
   Beijing  100053
   China

   Email: denghui@chinamobile.com

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

   Email: dave.michaud@rci.rogers.com

   Jouni Korhonen
   Renesas Mobile
   Porkkalankatu 24
   FIN-00180 Helsinki, Finland

   Email: jouni.nospam@gmail.com
   Mohamed Boucadair
   France Telecom
   Rennes,
   35000
   France

   Email: mohamed.boucadair@orange.com

   Vizdal Ales
   Deutsche Telekom AG
   Tomickova 2144/1
   Prague 4,  149 00
   Czech Republic

   Email: ales.vizdal@t-mobile.cz