Network Working Group                                            G. Chen
Internet-Draft                                                   H. Deng
Intended status: Informational                              China Mobile
Expires: April 24, 2014                                       D. Michaud
                                                   Rogers Communications
                                                             J. Korhonen
                                                          Renesas Mobile
                                                            M. Boucadair
                                                          France Telecom
                                                               A. Vizdal
                                                     Deutsche Telekom AG
                                                                C. Byrne
                                                            T-Mobile USA
                                                        October 21, 2013

                     IPv6 Roaming Behavior Analysis


   This document intends to enumerate failure cases when a IPv6
   subscriber roams into visited network areas.  The investigations on
   those failed cases reveal the causes in order to notice improper
   configurations, equipment's incomplete functions or inconsistent IPv6

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
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   This Internet-Draft will expire on April 24, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Roaming Architecture Descriptions . . . . . . . . . . . . . .   3
   3.  Roaming Scenario Overview . . . . . . . . . . . . . . . . . .   4
   4.  Failure Cases with Dual-stack Requests  . . . . . . . . . . .   5
     4.1.  Failure Case 1: Roaming to IPv4-only networks . . . . . .   5
     4.2.  Failure Case 2: Roaming to early dual-stack networks  . .   6
     4.3.  Failure Case 3: Roaming to IPv6-only networks . . . . . .   6
   5.  Failure Cases with IPv6-only Requests . . . . . . . . . . . .   6
     5.1.  Failure Case 4: Roaming to IPv4-only networks . . . . . .   6
     5.2.  Failure Case 5: Roaming to IPv6-only or dual-stack
           networks with 464xlat . . . . . . . . . . . . . . . . . .   7
   6.  Discussions . . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   IPv6 has been deployed globally to overcome the IPv4 depletion.
   Operators likely start or plan to upgrade the networks that allow
   IPv6 subscribers to access.  As the dramatical uses of Internet
   services with a mobile access, IPv6 is an essential part to be
   considered in the mobile network evolution. 3rd Generation
   Partnership Project (3GPP) published the IPv6 migration guidance
   [TR23.975], which describes different technical evolution paths.  In
   general, operators may deploy dual-stack or IPv6 single-stack
   depending on network's conditions.  It has been observed that those
   deployments are rolled out in multiple provisioning domains.  In the
   early IPv6 stage, a mobile subscriber roaming around the different
   areas may experience service degradations or interruptions due to the
   inconsistent configurations and incomplete functions in the networks
   nodes.  This memo intends to document the observed failed cases and

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   analyze the causes.  It's expected that operators could notice the
   issues and prevent potential risks.

2.  Roaming Architecture Descriptions

   When a mobile device 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).  There are two
   cases related to the roaming behavior.

   o  International roaming: a mobile subscriber may entry a visited
      network, where different PLMN identity is used.  The subscribers
      could either in an automatic mode or a manual mode to attach a
      PLMN cell.

   o  Intra-PLMN mobility: a subscriber moves to a visited network as
      that of the Home Public Land Mobile Network (HPLMN).  However, the
      subscriber profiles may not be stored in the area.  Once the
      subscriber attaches to the network, the subscriber profile should
      be traced from the home network for the network registration.

   When the visited network receives the registration requests from a
   subscriber, it should contact the home network and request the
   subscriber profile from Home Location Register(HLR) or Home
   Subscriber Server (HSS).  Once the registration process is completed,
   the traffic flows may transmitted differently according to the
   subscriber data configuration.  Two modes have been shown in the
   figure to illustrate the traffic flow paths, that are "Home routed
   traffic" and "Local breakout".

   +---------------------------------+             +------------------------+
   |Visited Network                  |             |Home Network            |
   |  +----+           +--------+    |             |    +--------+ Traffic Flow
   |  | UE |==========>|SGSN/SGW|======================>|GGSN/PGW|============>
   |  +----+           +--------+    | Signa ling  |    +--------+          |
   |                        |-------------------------->+--------+          |
   |                                 |             |    |HLR/HSS |          |
   |                                 |             |    +--------+          |
   +---------------------------------+             +------------------------+

                       Figure 1: Home Routed Traffic

   In the home routed mode, subscribers will get addresses from the home
   network.  All traffic would be routed back to the home networks.
   That is the default case for an international roaming except for IMS

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

                          Figure2: Local Breakout

   In the local breakout mode, the subscriber address will be assigned
   in the visited network.  The traffic flow would directly offloaded
   locally at a network node close to that device's point of attachment
   in the visited networks.  Therefore, more efficient route would be
   achieved.  There are several usages for the local breakout mode.

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

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

   o  3GPP specified Selected IP Traffic Offload (SIPTO)
      function[TS23401] 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 IMS international roaming
      architecture.  Local breakout mode has been adopted for the
      roaming architecture.

3.  Roaming Scenario Overview

   3GPP specified three types of Packet Data Protocol (PDP)/Packet Data
   Networks (PDN) to describe each connection, i.e. IPv4 PDP/PDN, IPv6
   PDP/PDN and IPv4v6 PDP/PDN.  Those PDP/PDN types should also be
   restored in Home Subscriber Server (HSS) as a part of subscriber

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   profile.  When a subscriber roams to a visited network, the new
   visited network notices that it is not registered with its own
   system, and attempts to identify its home network.  Afterwards, the
   visited network will contact the home network and request the
   subscriber profile from HSS.  In this process, service may be
   provided in a home routed or local breakout mode.  The IP address can
   be allocated from home network or visited network accordingly.  There
   may be a mismatch between the subscriber request and network
   capability.  The following table lists the potential failure cases.

   | UE Request  |  Visited Network  | Home routed  |Local Breakout|
   |             |     Capability    |              |              |
   | Dual stack  |    IPv4-only      |Failure case 1|Failure case 1|
   | Dual stack  |IPv4-only/IPv6-only|    OK        |Failure case 2|
   | Dual stack  |    IPv6-only      |    OK        |Failure case 3|
   | IPv6-only   |    IPv4-only      |    OK        |Failure case 4|
   | IPv6-only   |   Dual stack      |    OK        |Failure case 5|
   | with 464xlat|                   |              |              |
   | IPv6-only   |   IPv6-only       |    OK        |Failure case 5|
   | with 464xlat|                   |              |              |
   | IPv4-only   |    Dual stack     |    OK        |     OK       |

                  Table 1: Roaming Scenario Descriptions

4.  Failure Cases with Dual-stack Requests

4.1.  Failure Case 1: Roaming to IPv4-only networks

   A mobile host in a dual-stack network likely requests PDP/PDN type
   IPv4v6 to allocate address.  Such PDP/PDN type should be
   understandable in the network nodes, including Serving GPRS Support
   Node(SGSN), Gateway GPRS Support Node(GGSN), Serving Gateway(SGW),
   PDN Gateway(PGW), Home Location Registrar(HLR) and Home Subscriber
   Server(HSS).  When the subscriber roams to the IPv4 network, the
   visited SGSN or SGW has to communicate with HLR/HSS in the home land
   to retrieve the subscriber profile.  The visited pre-R9 SGSN don't
   understand the IPv4v6 PDP attribute for dual-stack, thus it refuse
   the subscriber registration.  Resolving the issue may request the
   deletion of a IPv4v6 PDP attribute in home HLR/HSS.  That may

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   restrict UEs only initiates IPv4 PDP or IPv6 PDP activation.  As
   alternative, operators have to upgrade the visited SGSN and SGW to
   support the IPv4v6 feature.  However, operator may didn't control the
   visited nodes which belong to different operators.

4.2.  Failure Case 2: Roaming to early dual-stack networks

   Dual-stack capability can be provided in a early mobile network(i.e.
   Pre-Release 8 network) using separate PDP/PDN activations.  That
   means a single IPv4 and IPv6 PDP/PDN to be initiated to allocate IPv4
   and IPv6 address separately.  A roaming subscriber with IPv4v6 PDP/
   PDN type should change the request to two separated PDP/PDN messages
   of single IP version in order to achieve equivalent results.  Some
   operators may turn off the function only allow one PDP/PDN is alive
   for each subscriber.  For example, IPv6 PDP/PDN would be rejected if
   the subscriber has an active IPv4 PDP/PDN.  Therefore, the subscriber
   may lost IPv6 connection in the visited network.  Even the two
   parallel PDP/PDN activations are allowed, it will double the
   investment of core networks.  It requires additional correlation of
   those two sessions of single IP version on the charging system.  If
   there are Policy and Charging Rules Function(PCRF)/Policy and
   Charging Enforcement Function (PCEF) deployed, the system would treat
   IPv4 and IPv6 session as independent and perform different Quality of
   Service(QoS) policies.  The subscriber may have unstable experiences
   due to different behaviors on each IP version connection.

4.3.  Failure Case 3: Roaming to IPv6-only networks

   If the visited network is only IPv6 capable, a dual-stack subscriber
   can be assigned with IPv6 address.  There is no IPv4 address
   returned.  Several IPv4 applications can't work in this case as
   reported in [RFC6586].  A translation-based method, for example Bump-
   in-the-host (BIH)[RFC6535] and 464xlat[RFC6877] , may help to address
   the issue.  Those techniques are superior in a IPv6 single-stack
   environment.  Operators may automatically enable the function in a
   IPv6-only network and disable in a dual-stack or IPv4 network.

5.  Failure Cases with IPv6-only Requests

5.1.  Failure Case 4: Roaming to IPv4-only networks

   3GPP specified the PDP/PDN type IPv6 as early as IPv4 type.
   Therefore, the IPv6 single PDP/PDN type has been well supported and
   interpretable in the 3GPP network nodes.  When a subscriber requests
   IPv6 PDP/PDN type, the network should only return the expected IPv6
   address.  Otherwise, the request should be dropped and the error code
   should be sent to the user.  Roaming to IPv4-only networks with IPv6
   PDP/PDN request would fail to get addresses.  A proper fallback is

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   desirable however the behavior is implementation specific.  Android
   system solves the issue by setting the roaming Access Point
   Name(APN).  The mobile terminal is allowed to ignore the original
   requested protocol and always adhere to IPv4 when roaming.  Those
   fallback mechanisms are deserved to be implemented timely.

5.2.  Failure Case 5: Roaming to IPv6-only or dual-stack networks with

   464xlat[RFC6877] is proposed to address IPv4 compability issue in a
   IPv6 single-stack environment.  The function on a mobile terminal
   likely gets along with PDP/PDN IPv6 type request to cooperate with a
   remote NAT64[RFC6146] gateway. 464xlat may use the mechanism defined
   in [I-D.ietf-behave-nat64-discovery-heuristic] to automatically
   discover NAT64 prefixes.  Those behaviors depend on the network
   deployment, which may has three possibilities, i.e. DNS64/NAT64,
   NAT64 and non-NAT64.  In those cases, the mobile terminal could only
   use DNS64[RFC6147] to detect the existence of NAT64.  The alternative
   way is to manually configure the NAT64 prefix or Well-Known Prefix
   (i.e. 64:ff9b::/96)[RFC6052].  However, those configurations may
   mismatch the status of visited networks.  Considering the various
   network's situations, operators may adopt 464xlat in the home
   networks and use IPv4-only in the roaming networks.

6.  Discussions

   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 type IPv4v6 in the early release.  Such PDP/PDN type is supported
   in new-built Long Term Evolution(LTE)/System Architecture
   Evolution(SAE) network, but didn't support well in the third
   generation network.  The situations may cause the roaming issues
   dropping the attachment from dual-stack subscribers in the case of
   LTE to 3G and IPv6-enabled 3G to IPv4 3G. It may be unsolvable unless
   all the interworking nodes(i.e. SSGN and SGW) have been upgraded to
   support IPv4v6 PDP/PDN type.

   Conversely, a user profile with IPv4-only PDP or IPv6 only PDP may
   temporarily get easy through roaming areas.  Some operators may
   choose IPv6 PDP/PDN along with 464xlat in the home network to advance
   IPv6 deployment.  Since IPv6 PDP/PDN has been introduced in 3GPP
   early release, it didn't require upgrading on the interworking nodes
   to parse such IPv6 PDP/PDN type.  But it requires IPv4 fallback
   should be supported either on the mobile terminal or network
   equipments.  Therefore, there is no working solution other than IPv4
   to guarantee roaming if roaming has to be enabled.

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   In general, home routed is the default mode for international roaming
   cases.  Local breakout or SIPTO may be only considered for some
   specific services, for example IMS roaming or intra-PLMN mobility
   optimization.  Therefore, the most roaming scenairos may take less
   risks if the host only initiate IPv4 or IPv6 PDP/PDN other than
   extended IPv4v6 PDP/PDN for the time being.

7.  IANA Considerations

   This document makes no request of IANA.

8.  Security Considerations

   The draft didn't introduce additional security concerns to the

9.  Acknowledgements

   The authors would like to thank V6ops chairs(Fred Baker and John
   Brzozowski) to encourage us to continue the work.  This document is
   the result of the IETF V6ops IPv6-Roaming design team effort.

10.  References

10.1.  Normative References

              Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis", draft-
              ietf-behave-nat64-discovery-heuristic-17 (work in
              progress), April 2013.

   [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.

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   [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.

10.2.  Informative References

   [IR.65]    , "IMS Roaming & Interworking Guidelines", May 2012.

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

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

              3GPP, "IPv6 migration guidelines", June 2011.

   [TS23401]  , "General Packet Radio Service (GPRS) enhancements for
              Evolved Universal Terrestrial Radio Access Network
              (E-UTRAN) access", .

              , "Mobility Management Entity (MME) and Serving GPRS
              Support Node (SGSN) related interfaces based on Diameter
              protocol", .

Authors' Addresses

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


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


   Dave Michaud
   Rogers Communications


   Jouni Korhonen
   Renesas Mobile
   Porkkalankatu 24
   FIN-00180 Helsinki


   Mohamed Boucadair
   France Telecom
   No.32 Xuanwumen West Street


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


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   Cameron Byrne
   T-Mobile USA
   Washington  98105


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