Softwires Working Group                                M. Boucadair, Ed.
Internet-Draft                                            France Telecom
Intended status: Informational                             S. Matsushima
Expires: May 17, 2013                                   Softbank Telecom
                                                                  Y. Lee
                                                              O. Bonness
                                                        Deutsche Telekom
                                                               I. Borges
                                                        Portugal Telecom
                                                                 G. Chen
                                                            China Mobile
                                                       November 13, 2012

    Motivations for Carrier-side Stateless IPv4 over IPv6 Migration


   IPv4 service continuity is one of the most pressing problems that
   must be resolved by Service Providers during the IPv6 transition
   period - especially after the exhaustion of the public IPv4 address
   space.  Current standardization effort that addresses IPv4 service
   continuity focuses on stateful mechanisms.  This document elaborates
   on the motivations for the need to undertake a companion effort to
   specify stateless IPv4 over IPv6 approaches.

Status of this Memo

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Copyright Notice

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Why Stateless IPv4 over IPv6 Solutions are Needed? . . . . . .  4
     3.1.  Network Architecture Simplification  . . . . . . . . . . .  4
       3.1.1.  Network Dimensioning . . . . . . . . . . . . . . . . .  4
       3.1.2.  No Intra-domain Constraint . . . . . . . . . . . . . .  5
       3.1.3.  Logging - No Need for Dynamic Binding Notifications  .  5
       3.1.4.  No Additional Protocol for Port Control is Required  .  5
     3.2.  Operational Tasks and Network Maintenance Efficiency . . .  6
       3.2.1.  Preserve Current Practices . . . . . . . . . . . . . .  6
       3.2.2.  Planned Maintenance Operations . . . . . . . . . . . .  6
       3.2.3.  Reliability and Robustness . . . . . . . . . . . . . .  6
       3.2.4.  Support of Multi-Vendor Redundancy . . . . . . . . . .  6
       3.2.5.  Simplification of Qualification Procedures . . . . . .  7
     3.3.  Facilitating Service Evolution . . . . . . . . . . . . . .  7
       3.3.1.  Implicit Host Identification . . . . . . . . . . . . .  7
       3.3.2.  No Organizational Impact . . . . . . . . . . . . . . .  8
     3.4.  Cost Minimization Opportunities  . . . . . . . . . . . . .  8
   4.  Discussion . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Dependency Between IPv4 and IPv6 Address Assignments . . . 10
     4.2.  IPv4 Port Utilisation Efficiency . . . . . . . . . . . . . 10
     4.3.  IPv4 Port Randomization  . . . . . . . . . . . . . . . . . 11
   5.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
   10. Informative References . . . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14

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1.  Introduction

   When the global IPv4 address space is exhausted, Service Providers
   will be left with an address pool that cannot be increased anymore.
   Many services and network scenarios will be impacted by the lack of
   IPv4 public addresses.  Providing access to the (still limited) IPv6
   Internet only won't be sufficient to address the needs of customers,
   as most of them will continue to access legacy IPv4-only services.
   Service Providers must guarantee their customers that they can still
   access IPv4 contents although they will not be provisioned with a
   global IPv4 address anymore.  Means to share IPv4 public addresses
   are unavoidable [RFC6269].

   Identifying the most appropriate solution(s) to the IPv4 address
   exhaustion as well as IPv4 service continuity problems and deploying
   them in a real network with real customers is a very challenging and
   complex process for all Service Providers.  There is no one size fits
   all solution.  Each Service Provider has to take into account its own
   context (e.g., service infrastructures), policies and marketing
   strategy (a document that informs Service Providers about the impact
   of the IPv4 address shortage, and provides some recommendations and
   guidelines, is available at [EURESCOM]).

   Current standardization efforts to address the IPv4 service
   continuity issue focuses on stateful mechanisms that share global
   IPv4 addresses between customers with NAT (Network Address
   Translation) capabilities in the network.  Because of some caveats of
   such stateful approaches, the Service Provider community feels that a
   companion effort is required to specify stateless IPv4 over IPv6
   approaches.  In the context of address sharing, states should be
   maintained in other equipments, e.g. customer premises equipment or

   This document focuses on carrier-side stateless IPv4 over IPv6.

   More discussions about stateless vs. stateful can be found at

2.  Terminology

   This document makes use of the following terms:

   State:  as used in [RFC1958].

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   Session state:  refers to an information state as defined in Section
        2.3 of [RFC2663].  In particular, it refers to the state
        maintained by the NAT so that datagrams pertaining to a session
        are routed to the right node.  Note, TCP/UDP sessions are
        uniquely identified by the tuple of (source IP address, source
        TCP/UDP port, target IP address, target TCP/UDP port) while ICMP
        query sessions are identified by the tuple of (source IP
        address, ICMP query ID, target IP address).

   User-session state:  refers to session state belonging to a given

   Stateful 4/6 solution  (or stateful solution in short): denotes a
        solution where a NAT in the Service Provider's network maintains
        user-session states [I-D.ietf-behave-lsn-requirements].  The NAT
        function is responsible for sharing the same IPv4 address among
        several subscribers and for maintaining user-session state.

   Stateless 4/6 solution  (or stateless solution in short): denotes a
        solution which does not require any per-user state (see Section
        2.3 of [RFC1958]) to be maintained by any IP address sharing
        function in the Service Provider's network.  A dependency
        between an IPv6 prefix and IPv4 address is assumed.  In an IPv4
        address sharing context, dedicated functions are enabled in the
        CPE router to restrict the source IPv4 port numbers.  Within
        this document, "port set" and "port range" terms are used

3.  Why Stateless IPv4 over IPv6 Solutions are Needed?

   The following sub-sections discuss different aspects that motivate
   this effort.

3.1.  Network Architecture Simplification

   The activation of the stateless function in the Service Provider's
   network does not introduce any major constraint on the network
   architecture and its engineering.  The following sub-sections
   elaborate on these aspects.

3.1.1.  Network Dimensioning

   Because no per-user state [RFC1958] is required, a stateless solution
   does not need to take into account the maximum number of simultaneous
   user-sessions and the maximum number of new user-sessions per second
   to dimension its networking equipment.  Like current network
   dimensioning practices, only considerations related to the customers

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   number, traffic trends and the bandwidth usage need be taken into

3.1.2.  No Intra-domain Constraint

   Stateless IPv4/IPv6 interconnection functions can be ideally located
   at the boundaries of an Autonomous System (e.g., Autonomous System
   Border Routers (ASBRs) that peer with external IPv4 domains); in such
   case intra-domain paths are not altered: there is no need to force IP
   packets to cross a given node for instance; intra-domain routing
   processes are not tweaked to direct the traffic to dedicated nodes.
   Stateless solutions optimize CPE-to-CPE communication in that packets
   don't go through the interconnection function.

3.1.3.  Logging - No Need for Dynamic Binding Notifications

   Network abuse reporting requires traceability [RFC6269].  To provide
   such traceability, prior to IPv4 address sharing, logging the IPv4
   address assigned to a user was sufficient and generates relatively
   small logs.  The advent of stateful IPv4 address allows dynamic port
   assignment, which then requires port assignment logging.  This
   logging of port assignments can be considerable.

   In contrast, static port assignments do not require such considerable
   logging.  The volume of the logging file may not be seen as an
   important criterion for privileging a stateless approach because
   stateful approaches can also be configured (or designed) to assign
   port ranges and therefore lead to acceptable log volumes.

   If a dynamic port assignment mode is used, dedicated interfaces and
   protocols must be supported to forward binding data records towards
   dedicated platforms.  The activation of these dynamic notifications
   may impact the performance of the dedicated device.  For stateless
   solutions, there is no need for dynamic procedures (e.g., using
   SYSLOG) to notify a mediation platform about assigned bindings.

   Some Service Providers have a requirement to use only existing
   logging systems and to avoid introducing new ones (mainly because of
   Capital Expenditure (CAPEX) considerations).  This requirement is
   easily met with stateless solutions.

3.1.4.  No Additional Protocol for Port Control is Required

   Stateless solutions do not require activating a new dynamic signaling
   protocol in the end-user CPE in addition to those already used.  In
   particular, existing protocols (e.g., UPnP IGD:2 [UPnP-IGD]) can be
   used to control the NAT mappings in the CPE.

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      Note: To overcome some security concerns, IGD:2 authorization
      framework [UPnP-IGD] should be used and security considerations
      elaborated in [Sec_DCP] should be taken into account.

3.2.  Operational Tasks and Network Maintenance Efficiency

3.2.1.  Preserve Current Practices

   If stateless solutions are deployed, common practices are preserved.
   In particular, the maintenance and operation of the network do not
   require any additional constraints such as: path optimization
   practices, enforcing traffic engineering policies, issues related to
   traffic oscillation between stateful devices, load-balancing the
   traffic or load sharing the traffic among egress/ingress points can
   be used, etc.  Particularly,

   o  anycast-based schemes can be used for load-balancing and
      redundancy purposes between nodes embedding the Stateless IPv4/
      IPv6 interconnection function.

   o  asymmetric routing to/from the IPv4 Internet is natively supported
      and no path-pinning mechanisms have to be additionally

3.2.2.  Planned Maintenance Operations

   Since no state is maintained by stateless IPv4/IPv6 interconnection
   nodes, no additional constraint needs to be taken into account when
   upgrading these nodes (e.g., adding a new service card, upgrading
   hardware, periodic reboot of the devices, etc.).  In particular,
   current practices that are enforced to (gracefully) reboot or to
   shutdown routers can be maintained.

3.2.3.  Reliability and Robustness

   Compared to current practices (i.e., without a Carrier Grade NAT
   (CGN) in place), no additional capabilities are required to ensure
   reliability and robustness in the context of stateless solutions.
   Since no state is maintained in the Service Provider's network, state
   synchronization procedures are not required.

   High availability (including failure recovery) is ensured owing to
   best current practices in the field.

3.2.4.  Support of Multi-Vendor Redundancy

   Deploying stateful techniques, especially when used in the Service
   Providers networks, constrains severely deploying multi-vendor

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   redundancy since very often proprietary vendor-specific protocols are
   used to synchronize state.  This is not an issue for the stateless
   case.  Concretely, the activation of the stateless IPv4/IPv6
   interconnection function does not prevent nor complicate deploying
   devices from different vendors.

   This criterion is very important for Service Providers because they
   want to avoid being locked into one vendor for their entire network
   and they want to operate multi-vendor-supplied networks.

3.2.5.  Simplification of Qualification Procedures

   The introduction of new functions and nodes into operational networks
   follows strict procedures elaborated by Service Providers.  These
   procedures include in-lab testing and field trials.  Because of their
   nature, stateless implementations optimize testing time and

   o  The specification of test suites to be conducted should be

   o  The required testing resources (in terms of manpower) are likely
      to be less solicited that they are for stateful approaches.

   One of the privileged approaches to integrate stateless IPv4/IPv6
   interconnection function consists in embedding stateless capabilities
   in existing operational nodes (e.g., IP router).  In this case, any
   software or hardware update would require to execute non-regression
   testing activities.  In the context of the stateless solutions, the
   non-regression testing load due to an update of the stateless code is
   expected to be minimal.

   For the stateless case, testing effort and non-regression testing are
   to be taken into account for the CPE side.  This effort is likely to
   be lightweight compared to the testing effort, including the non-
   regression testing, of a stateful function which is co-located with
   other routing functions for instance.

3.3.  Facilitating Service Evolution

3.3.1.  Implicit Host Identification

   Service Providers do not offer only IP connectivity services but also
   added value services (a.k.a., internal services).  Upgrading these
   services to be IPv6-enabled is not sufficient because of legacy
   devices.  In some deployments, the delivery of these added-value
   services relies on implicit identification mechanism based on the
   source IPv4 address.  Due to address sharing, implicit identification

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   will fail [RFC6269]; replacing implicit identification with explicit
   authentication will be seen as a non acceptable service regression by
   the end users (less Quality of Experience (QoE); refer to Section 4.2

   When a stateless solution is deployed, implicit identification for
   internal services is likely to be easier to implement: the implicit
   identification should be updated to take into account the port range
   and the IPv4 address.  Techniques as those analyzed in
   [I-D.ietf-intarea-nat-reveal-analysis] are not required for the
   delivery of these internal services if a stateless solution is

   Note stateful approaches configured to assign port ranges allow also
   to support implicit host identification.

3.3.2.  No Organizational Impact

   Stateless solutions adopt a clear separation between the IP/transport
   layers and the service layers; no service interference is to be
   observed when a stateless solution is deployed.  This clear

   Facilitates service evolution:  Stateless solutions admit
      applications which can be deployed without enabling any
      application-specific function (e.g., Application Level Gateway
      (ALG)) in the Service Provider's network.  Avoiding ALGs is highly

   Limits vendor dependency:  The upgrade of value-added services does
      not involve any particular action from vendors that provide
      devices embedding the stateless IPv4/IPv6 interconnection

   No service-related skills are required for network operators who
   manage devices that embed the IPv4/IPv6 interconnection function:  IP
      teams can be in charge of these devices; there is a priori no need
      to create a dedicated team to manage and to operate devices
      embedding the stateless IPv4/IPv6 interconnection function.  The
      introduction of stateless capabilities in the network are unlikely
      to degrade management costs.

3.4.  Cost Minimization Opportunities

   To make decision for which solution is to be adopted, Service
   Providers usually undertake comparative studies about viable
   technical solutions.  It is not only about technical aspects but also
   economical optimization (both CAPEX and Operational Expenditure

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   (OPEX) considerations).  From a Service Provider perspective,
   stateless solutions may be more attractive because it impacts the
   current network operations and maintenance model less than stateful
   solutions.  Table 1 shows the general correspondence between
   technical benefits and potential economic reduction opportunities.

   While not all Service Providers environments are the same, a detailed
   case study from one Service Provider
   [I-D.matsushima-v6ops-transition-experience] reports that stateless
   transition solutions can be considerably less expensive than stateful
   transition solutions.

   |    Section    |    Technical and Operation Benefit   |  Cost Area |
   | Section 3.1.1 |         Network dimensioning         |   Network  |
   | Section 3.1.2 |      No Intra-domain constraint      |   Network  |
   | Section 3.1.3 |                Logging               |  Network & |
   |               |                                      |     Ops    |
   | Section 3.1.4 |    No additional control protocol    |   Network  |
   | Section 3.2.1 |      Preserve current practices      |     Ops    |
   | Section 3.2.2 |          Planned maintenance         |     Ops    |
   | Section 3.2.3 |      Reliability and robustness      |  Network & |
   |               |                                      |     Ops    |
   | Section 3.2.4 |        Multi-Vendor Redundancy       |   Network  |
   | Section 3.2.5 |         Simple qualification         |     Ops    |
   | Section 3.3.1 |   Implicit Host Identification for   |     Ops    |
   |               |           internal services          |            |
   | Section 3.3.2 |         Organizational Impact        |     Ops    |

                 Table 1: Cost minimization considerations

4.  Discussion

   Issues common to all address sharing solutions are documented in
   [RFC6269].  The following sub-sections enumerate some open questions

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   for a CPE-based stateless solution.  There are no universal answers
   to these open questions since each Service Provider has its own
   constraints (e.g., available address pool, address sharing ratio,

4.1.  Dependency Between IPv4 and IPv6 Address Assignments

   Complete stateless mapping implies that the IPv4 address and the
   significant bits that are used to encode the set of assigned ports
   can be retrieved from the IPv6 prefix assigned to the CPE.  This
   requirement can be addressed by either using the IPv6 prefix also
   used to forward IPv6 traffic natively, or allocating two prefixes to
   the CPE (one that will be used to forward IPv6 traffic natively, and
   the other one to forward IPv4 traffic).

   o  Providing two IPv6 prefixes avoids the complexity that may be
      related to the adaptation of the IPv6 addressing scheme to the
      IPv4 addressing scheme.  The drawback is the need to allocate two
      prefixes instead of one to each CPE and to announce them
      accordingly, possibly at the cost of jeopardizing the routing and
      forwarding efficiencies.

   o  The use of a single prefix to cover both the forwarding of IPv6
      and IPv4-in-IPv6 traffic avoids the need to maintain a double
      information (e.g., for customer identification and management
      purposes and for forwarding table maintenance purposes).  This
      scheme somewhat links strongly the IPv4 addressing scheme to the
      allocated IPv6 prefixes.  For Service Providers requiring to apply
      specific policies on per Address-Family (e.g., IPv4, IPv6), some
      provisioning tools (e.g., DHCPv6 option) may be required to derive
      in a deterministic way the IPv6 address to be used for the IPv4
      traffic based on the IPv6 prefix delegated to the home network.

4.2.  IPv4 Port Utilisation Efficiency

   CGN-based solutions, because they can dynamically assign ports,
   provide better IPv4 address sharing ratio than stateless solutions
   (i.e., can share the same IP address among a larger number of
   customers).  For Service Providers who desire an aggressive IPv4
   address sharing, a CGN-based solution is more suitable than the
   stateless.  However

   1:  When port overloading is used, some applications are likely to be

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   2:  in case a CGN pre-allocates port ranges, e.g.- to alleviate
       traceability complexity (see Section 3.1.3), it also reduces its
       port utilization efficiency.

4.3.  IPv4 Port Randomization

   Preserving port randomization [RFC6056] may be more or less difficult
   depending on the address sharing ratio (i.e., the size of the port
   space assigned to a CPE).  The CPE can only randomize the ports
   inside a fixed port range.

   More discussion to improve the robustness of TCP against Blind In-
   Window Attacks can be found at [RFC5961].  Other means than the
   (IPv4) source port randomization to provide protection against
   attacks should be used (e.g., use [I-D.vixie-dnsext-dns0x20] to
   protect against DNS attacks, [RFC5961] to improve the robustness of
   TCP against Blind In-Window Attacks, use IPv6).

5.  Conclusion

   As discussed in Section 3, stateless solutions provide several
   interesting features.  Trade-off between the positive vs. negative
   aspects of stateless solutions is left to Service Providers.  Each
   Service Provider will have to select the appropriate solution
   (stateless, stateful or even both) meeting its requirements.

   This document recommends to undertake as soon as possible the
   appropriate standardization effort to specify a stateless IPv4 over
   IPv6 solution.

6.  IANA Considerations

   No action is required from IANA.

7.  Security Considerations

   Except for the less efficient port randomization of and routing loops
   [RFC6324], stateless 4/6 solutions are expected to introduce no more
   security vulnerabilities than stateful ones.  Because of their
   stateless nature, they may in addition reduce denial of service

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8.  Contributors

   The following individuals have contributed to this document:

         Christian Jacquenet
         France Telecom

         Pierre Levis
         France Telecom

         Masato Yamanishi
         SoftBank BB

         Yuji Yamazaki
         Softbank Mobile

         Hui Deng
         China Mobile

9.  Acknowledgments

   Many thanks to the following individuals who provided valuable
     | X. Deng       | W. Dec        | D. Wing       | A. Baudot     |
     | E. Burgey     | L. Cittadini  | R. Despres    | J. Zorz       |
     | M. Townsley   | L. Meillarec  | R. Maglione   | J. Queiroz    |
     | C. Xie        | X. Li         | O. Troan      | J. Qin        |
     | B. Sarikaya   | N. Skoberne   | J. Arkko      | D. Lui        |

10.  Informative References

              Levis, P., Borges, I., Bonness, O. and L. Dillon L., "IPv4
              address exhaustion: Issues and Solutions for Service
              Providers", March 2010, <

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              Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common requirements for Carrier Grade NATs
              (CGNs)", draft-ietf-behave-lsn-requirements-09 (work in
              progress), August 2012.

              Boucadair, M., Touch, J., Levis, P., and R. Penno,
              "Analysis of Solution Candidates to Reveal a Host
              Identifier (HOST_ID) in Shared Address Deployments",
              draft-ietf-intarea-nat-reveal-analysis-04 (work in
              progress), August 2012.

              Matsushima, S., Yamazaki, Y., Sun, C., Yamanishi, M., and
              J. Jiao, "Use case and consideration experiences of IPv4
              to IPv6 transition",
              draft-matsushima-v6ops-transition-experience-02 (work in
              progress), March 2011.

              Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to
              Improve Transaction Identity",
              draft-vixie-dnsext-dns0x20-00 (work in progress),
              March 2008.

   [RFC1958]  Carpenter, B., "Architectural Principles of the Internet",
              RFC 1958, June 1996.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [RFC5961]  Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
              Robustness to Blind In-Window Attacks", RFC 5961,
              August 2010.

   [RFC6056]  Larsen, M. and F. Gont, "Recommendations for Transport-
              Protocol Port Randomization", BCP 156, RFC 6056,
              January 2011.

   [RFC6144]  Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation", RFC 6144, April 2011.

   [RFC6269]  Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
              Roberts, "Issues with IP Address Sharing", RFC 6269,
              June 2011.

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   [RFC6324]  Nakibly, G. and F. Templin, "Routing Loop Attack Using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", RFC 6324, August 2011.

   [RFC6462]  Cooper, A., "Report from the Internet Privacy Workshop",
              RFC 6462, January 2012.

   [Sec_DCP]  UPnP Forum, "Device Protection:1", November 2009.

              UPnP Forum, "Universal Plug and Play (UPnP) Internet
              Gateway Device (IGD) V 2.0", December 2010,

Authors' Addresses

   Mohamed Boucadair (editor)
   France Telecom
   Rennes,   35000


   Satoru Matsushima
   Softbank Telecom


   Yiu Lee


   Olaf Bonness
   Deutsche Telekom


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   Isabel Borges
   Portugal Telecom


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


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