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Versions: (draft-softwire-gateway-init-ds-lite) 00 01 02 03 04 05 06 07 08 RFC 6674

SOFTWIRE WG                                                 F. Brockners
Internet-Draft                                             S. Gundavelli
Intended status: Standards Track                                   Cisco
Expires: October 30, 2012                                    S. Speicher
                                                     Deutsche Telekom AG
                                                                 D. Ward
                                                                   Cisco
                                                          April 28, 2012


              Gateway Initiated Dual-Stack Lite Deployment
              draft-ietf-softwire-gateway-init-ds-lite-08

Abstract

   Gateway-Initiated Dual-Stack lite (GI-DS-lite) is a variant of Dual-
   Stack lite (DS-lite) applicable to certain tunnel-based access
   architectures.  GI-DS-lite extends existing access tunnels beyond the
   access gateway to an IPv4-IPv4 NAT using softwires with an embedded
   context identifier that uniquely identifies the end-system the
   tunneled packets belong to.  The access gateway determines which
   portion of the traffic requires NAT using local policies and sends/
   receives this portion to/from this softwire.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 30, 2012.

Copyright Notice

   Copyright (c) 2012 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



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Gateway Initiated DS-Lite  . . . . . . . . . . . . . . . . . .  4
   4.  Protocol and related Considerations  . . . . . . . . . . . . .  6
   5.  Softwire Management and related Considerations . . . . . . . .  7
   6.  Softwire Embodiments . . . . . . . . . . . . . . . . . . . . .  7
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 10
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 11
   Appendix A.  GI-DS-lite deployment . . . . . . . . . . . . . . . . 12
     A.1.   Connectivity establishment: Example call flow . . . . . . 12
     A.2.   GI-DS-lite applicability: Examples  . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
























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1.  Overview

   Gateway-Initiated Dual-Stack lite (GI-DS-lite) is a variant of the
   Dual-Stack lite (DS-lite) [RFC6333], applicable to network
   architectures which use point to point tunnels between the access
   device and the access gateway.  The access gateway in these models is
   designed to serve large numbers of access devices.  Mobile
   architectures based on Mobile IPv6 [RFC6275], Proxy Mobile IPv6
   [RFC5213], or GTP [TS29060], as well as broadband architectures based
   on PPP or point-to-point VLANs as defined by the Broadband Forum
   [TR59] and [TR101] are examples for this type of architecture.

   The DS-lite approach leverages IPv4-in-IPv6 tunnels (or other
   tunneling modes) for carrying the IPv4 traffic from the customer
   network to the Address Family Transition Router (AFTR).  An
   established softwire between the AFTR and the access device is used
   for traffic forwarding purposes.  This turns the inner IPv4 address
   irrelevant for traffic routing and allows sharing private IPv4
   addresses [RFC1918] between customer sites within the service
   provider network.

   Similar to DS-lite, GI-DS-lite enables the service provider to share
   public IPv4 addresses among different customers by combining
   tunneling and NAT.  It allows multiple access devices behind the
   access gateway to share the same private IPv4 address [RFC1918].
   Rather than initiating the tunnel right on the access device, GI-DS-
   lite logically extends the already existing access tunnels beyond the
   access gateway towards the Address Family Transition Router (AFTR)
   using a tunneling mechanism with semantics for carrying context state
   related to the encapsulated traffic.  This approach results in
   supporting overlapping IPv4 addresses in the access network,
   requiring no changes to either the access device, or to the access
   architecture.  Additional tunneling overhead in the access network is
   also omitted.  If e.g., GRE based encapsulation mechanisms is chosen,
   it allows the network between the access gateway and the AFTR to be
   either IPv4 or IPv6 and provides the operator to migrate to IPv6 in
   incremental steps.


2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The following abbreviations are used within this document:





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      AFTR: Address Family Transition Router.  An AFTR combines IP-in-IP
      tunnel termination and IPv4-IPv4 NAT.

      AD: Access Device.  It is the end host, also known as the mobile
      node in mobile architectures.

      CID: Context Identifier

      DS-lite: Dual-stack lite

      GI-DS-lite: Gateway-initiated DS-lite

      NAT: Network Address Translator

      SW: Softwire [RFC4925]

      SWID: Softwire Identifier


3.  Gateway Initiated DS-Lite

   The section provides an overview of Gateway Initiated DS-Lite (GI-DS-
   lite).  Figure 1 outlines the generic deployment scenario for GI-DS-
   lite.  This generic scenario can be mapped to multiple different
   access architectures, some of which are described in Appendix A.

   In Figure 1, access devices (AD-1 and AD-2) are connected to the
   Gateway using some form of tunnel technology and the same is used for
   carrying IPv4 (and optionally IPv6) traffic of the access device.
   These access devices may also be connected to the Gateway over point-
   to-point links.  The details on how the network delivers the IPv4
   address configuration to the access devices are specific to the
   access architecture and are outside the scope of this document.  With
   GI-DS-lite, Gateway and AFTR are connected by a softwire [RFC4925].
   The softwire is identified by a softwire identifier (SWID).  The SWID
   does not need to be globally unique, i.e. different SWIDs could be
   used to identify a softwire at the different ends of a softwire.  The
   form of the SWID depends on the tunneling technology used for the
   softwire.  The SWID could e.g. be the endpoints of a GRE-tunnel or a
   VPN-ID, Section 6 for details.  A Context-Identifier (CID) is used to
   multiplex flows associated with the individual access devices onto
   the softwire.  Deployment dependent, the flows from a particular AD
   can be identified using either the source IP-address or an access
   tunnel identifier.  Local policies at the Gateway determine which
   part of the traffic received from an access device is tunneled over
   the softwire to the AFTR.  The combination of CID and SWID must be
   unique between gateway and AFTR to identify the flows associated with
   an AD.  The CID is typically a 32-bit wide identifier and is assigned



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   by the Gateway.  It is retrieved either from a local or remote (e.g.
   AAA) repository.  Like the SWID, the embodiment of the CID depends on
   the tunnel mode used and the type of the network connecting Gateway
   and AFTR.  If, for example GRE [RFC2784] with "GRE Key and Sequence
   Number Extensions" [RFC2890] is used as softwire technology, the
   network connecting Gateway and AFTR could be either IPv4-only, IPv6-
   only, or a dual-stack IP network.  The CID would be carried within
   the GRE-key field.  Section 6 for details on different softwire types
   supported with GI-DS-lite.

                        Access Device: AD-1
                        Context Id: CID-1
                                             NAT Mappings:
      IPv4: a.b.c.d            +---+         (CID-1, TCP port1 <->
      +------+  access tunnel  |   |                 e.f.g.h, TCP port2)
      | AD-1 |=================| G |                          +---+
      +------+                 | A |                          | A |
                               | T |    Softwire SWID-1       | F |
                               | E |==========================| T |
      IPv4: a.b.c.d            | W |  (e.g. IPv4-over-GRE     | R |
      +------+                 | A |   over IPv4 or IPv6)     +---+
      | AD-2 |=================| Y |
      +------+  access tunnel  |   |         (CID-2, TCP port3 <->
                               |   |                 e.f.g.h, TCP port4)
                               +---+

                        Access Device: AD-2
                        Context Id: CID-2


    Figure 1: Gateway-initiated dual-stack lite reference architecture

   The AFTR combines softwire termination and IPv4-IPv4 NAT.  The NAT
   binding of the AD's address could be assigned autonomously by the
   AFTR from a local address pool, configured on a per-binding basis
   (either by a remote control entity through a NAT control protocol or
   through manual configuration), or derived from the CID (e.g., the
   CID, in case 32-bit wide, could be mapped 1:1 to an external IPv4-
   address).  A simple example of a translation table at the AFTR is
   shown in Figure 2.  The choice of the appropriate translation scheme
   for a traffic flow can take parameters such as destination IP-
   address, incoming interface, etc. into account.  The IP-address of
   the AFTR, which, depending on the transport network between the
   Gateway and the AFTR, will either be an IPv6 or an IPv4 address, is
   configured on the Gateway.  A variety of methods, such as out-of-band
   mechanisms, or manual configuration apply.





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       +=====================================+======================+
       |  Softwire-Id/Context-Id/IPv4/Port   |  Public IPv4/Port    |
       +=====================================+======================+
       |  SWID-1/CID-1/a.b.c.d/TCP-port1     |  e.f.g.h/TCP-port2   |
       |                                     |                      |
       |  SWID-1/CID-2/a.b.c.d/TCP-port3     |  e.f.g.h/TCP-port4   |
       +-------------------------------------+----------------------+


              Figure 2: Example translation table on the AFTR

   GI-DS-lite does not require a 1:1 relationship between Gateway and
   AFTR, but more generally applies to (M:N) scenarios, where M Gateways
   are connected to N AFTRs.  Multiple Gateways could be served by a
   single AFTR.  AFTRs could be dedicated to specific groups of access-
   devices, groups of Gateways, or geographic regions.  An AFTR could,
   but does not have to be co-located with a Gateway.


4.  Protocol and related Considerations

   o  Depending on the embodiment of the CID (e.g. for GRE-encapsulation
      with GRE-key), the NAT binding entry maintained at the AFTR, which
      reflects an active flow between an access device inside the
      network and a node in the Internet, SHOULD be extended to include
      the CID and the identifier of the softwire (SWID).

   o  When creating an IPv4 to IPv4 NAT binding for an IPv4 packet flow
      received from the Gateway over the softwire, the AFTR SHOULD
      associate the CID with that NAT binding.  It SHOULD use the
      combination of CID and SWID as the unique identifier and use those
      parameters in the NAT binding entry.

   o  When forwarding a packet to the access device, the AFTR SHOULD
      obtain the CID from the NAT binding associated with that flow.
      E.g., in case of GRE-encapsulation, it SHOULD add the CID to the
      GRE Key and Sequence number extension of the GRE header and tunnel
      it to the Gateway.

   o  On receiving any packet from the softwire, the AFTR SHOULD obtain
      the CID from the incoming packet and use it for performing the NAT
      binding look up and for performing the packet translation before
      forwarding the packet.

   o  The Gateway, on receiving any IPv4 packet from the access device
      SHOULD lookup the CID for that access device.  In case of GRE
      encapsulation it can for example add the CID to the GRE Key and
      Sequence number extension of the GRE header and tunnel it to the



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      AFTR.

   o  On receiving any packet from the softwire, the Gateway SHOULD
      obtain the CID from the packet and use it for making the
      forwarding decision.

   o  When encapsulating an IPv4 packet, Gateway and AFTR SHOULD use its
      Diffserv Codepoint (DSCP) to derive the DSCP (or MPLS Traffic-
      Class Field in case of MPLS) of the softwire.


5.  Softwire Management and related Considerations

   The following are the considerations related to the operational
   management of the softwire between AFTR and Gateway.

   o  The softwire between the Gateway and the AFTR MAY be created at
      system startup time, OR dynamically established on-demand.
      Deployment dependent, Gateway and AFTR can employ OAM mechanisms
      such as ICMP, BFD [RFC5880], or LSP ping [RFC4379] for softwire
      health management and corresponding protection strategies.

   o  The softwire peers MAY be provisioned to perform policy
      enforcement, such as for determining the protocol-type or overall
      portion of traffic that gets tunneled, or for any other quality of
      service related settings.  The specific details on how this is
      achieved or the types of policies that can be applied are outside
      the scope for this document.

   o  The softwire peers SHOULD use the correct path MTU value for the
      tunnel path between the access gateway and the AFTR.  This value
      MAY be statically configured at softwire creation time, or
      dynamically discovered using the standard path MTU discovery
      techniques.

   o  A Gateway and an AFTR can have multiple softwires established
      between them (e.g. to separate address domains, provide for load-
      sharing etc.).


6.  Softwire Embodiments

   Deployment and requirements dependent, different tunnel technologies
   apply for the softwire connecting Gateway and AFTR.  GRE
   encapsulation with GRE-key extensions, MPLS VPNs [RFC4364], or plain
   IP-in-IP encapsulation can be used.  Softwire identification and
   Context-ID depend on the tunneling technology employed:




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   o  GRE with GRE-key: SWID is the tunnel identifier of the GRE tunnel
      between the GW and the AFTR.  The CID is the GRE-key associated
      with the AD.

   o  MPLS VPN: The SWID is a generic identifier which uniquely
      identifies the VPN at either the Gateway or AFTR.  Depending on
      whether the Gateway or AFTR are acting as customer edge (CE) or,
      provider edge (PE), the SWID could e.g. be an attachment circuit
      identifier, an identifier representing the set of VPN route labels
      pointing to the routes within the VPN, etc.  The AD's IPv4-address
      is the CID.  For a given VPN, the AD's IPv4 address must be
      unique.

   o  IPv4/IPv6-in-MPLS: The SWID is the top MPLS label.  CID might be
      the next MPLS label in the stack, if present, or the IP address of
      the AD.

   o  IPv4-in-IPv4: SWID is the outer IPv4 source address.  The AD's
      IPv4 address is the CID.  For a given outer IPv4 source address,
      the AD's IPv4 address must be unique.

   o  IPv4-in-IPv6: SWID is the outer IPv6 source address.  If the AD's
      IPv4 address is used as CID, the AD's IPv4 address must be unique.
      If the IPv6-Flow-Label [RFC6437] is used as CID, the IPv4
      addresses of the ADs may overlap.  Given that the IPv6-Flow-Label
      is 20-bit wide, which is shorter than the recommended 32-bit CID,
      large scale deployments may require additional scaling
      considerations.  In addition, one should ensure sufficient
      randomization of the IP-Flow-Label to avoid possible interference
      with other uses of the IP-Flow-Label, such as Equal Cost Multipath
      (ECMP) support.

   Figure 3 gives an overview of the different tunnel modes as they
   apply to different deployment scenarios. "x" indicates that a certain
   deployment scenario is supported.  The following abbreviations are
   used:

   o  IPv4 address

      *  "up": Deployments with "unique private IPv4 addresses" assigned
         to the access devices are supported.

      *  "op": Deployments with "overlapping private IPv4 addresses"
         assigned to the access devices are supported.

      *  "s": Deployments where all access devices are assigned the same
         IPv4 address are supported.




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   o  Network-type

      *  "v4": Gateway and AFTR are connected by an IPv4-only network

      *  "v6": Gateway and AFTR are connected by an IPv6-only network

      *  "v4v6": Gateway and AFTR are connected by a dual stack network,
         supporting IPv4 and IPv4.

      *  "MPLS": Gateway and AFTR are connected by a MPLS network


        +===================+==============+=======================+
        |                    | IPv4 address|      Network-type     |
        |    Softwire        +----+----+---+----+----+------+------+
        |                    | up | op | s | v4 | v6 | v4v6 | MPLS |
        +====================+====+====+===+====+====+======+======+
        | GRE with GRE-key   |  x |  x | x |  x |  x |   x  |      |
        | MPLS VPN           |  x |  x |   |    |    |      |   x  |
        | IPv4/IPv6-in-MPLS  |  x |  x | x |    |    |      |   x  |
        | IPv4-in-IPv4       |  x |    |   |  x |    |      |      |
        | IPv4-in-IPv6       |  x |    |   |    |  x |      |      |
        | IPv4-in-IPv6 w/ FL |  x |  x | x |    |  x |      |      |
        +====================+====+====+===+====+====+======+======+

              Figure 3: Tunnel modes and their applicability


7.  IANA Considerations

   This specification does not require any IANA actions.


8.  Security Considerations

   The approach specified in this document allows the use of Dual-stack
   lite for tunnel-based access architectures.  Rather than initiating
   the tunnel from the access device, GI-DS-lite logically extends the
   already existing access tunnel beyond the access gateway towards the
   Address Family Transition Router, and builds a virtual softwire
   between the AFTR and the access device.  This approach requires the
   use of an additional context identifier in the AFTR and at the access
   gateway, which is required for making IP packet forwarding decisions.

   A packet when received with an Incorrect context identifier at the
   access gateway/AFTR will result in associating the packet to an
   incorrect access device.  Therefore, care must be taken to ensure an
   IP packet tunneled between the access gateway and the AFTR is carried



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   with the context identifier of the access device associated with that
   IP packet.  The context identifier is not carried from the access
   device and it is not possible for one access device to claim the
   context identifier of some other access device.  However, It is
   possible an on-path attacker between the access gateway and the AFTR
   can potentially modify the context identifier in the packet,
   resulting in association of the packet to an incorrect access device.
   This threat is no different from an on-path attacker modifying the
   source/destination address of an IP packet.  However, this threat can
   be prevented by enabling IPsec security with integrity protection
   turned on, between the access gateway and the AFTR, that will ensure
   the correct binding of the context identifier and the inner packet.
   This specification does not require any other new security
   considerations other than those specified in dual-stack lite
   specification [RFC6333], and in the security considerations specified
   for the given access architecture, such as Proxy Mobile IPv6,
   leveraging this transitioning scheme.


9.  Acknowledgements

   The authors would like to acknowledge the discussions on this topic
   with Mark Grayson, Jay Iyer, Kent Leung, Vojislav Vucetic, Flemming
   Andreasen, Dan Wing, Jouni Korhonen, Teemu Savolainen, Parviz Yegani,
   Farooq Bari, Mohamed Boucadair, Vinod Pandey, Jari Arkko, Eric Voit,
   Yiu L. Lee, Tina Tsou, Guo-Liang Yang, Cathy Zhou, Olaf Bonness, Paco
   Cortes, Jim Guichard, Stephen Farrell, Pete Resnik, Ralph Droms.


10.  References

10.1.  Normative References

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

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

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              March 2000.

   [RFC2890]  Dommety, G., "Key and Sequence Number Extensions to GRE",
              RFC 2890, September 2000.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private



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              Networks (VPNs)", RFC 4364, February 2006.

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

   [RFC5555]  Soliman, H., "Mobile IPv6 Support for Dual Stack Hosts and
              Routers", RFC 5555, June 2009.

   [RFC5844]  Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
              Mobile IPv6", RFC 5844, May 2010.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, June 2010.

   [RFC6275]  Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
              in IPv6", RFC 6275, July 2011.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437, November 2011.

10.2.  Informative References

   [I-D.draft-ietf-dime-nat-control]
              Brockners, F., Bhandari, S., Singh, V., and V. Fajardo,
              "Diameter NAT Control Application", August 2009.

   [RFC4925]  Li, X., Dawkins, S., Ward, D., and A. Durand, "Softwire
              Problem Statement", RFC 4925, July 2007.

   [TR101]    Broadband Forum, "TR-101: Migration to Ethernet-Based DSL
              Aggregation", April 2006.

   [TR59]     Broadband Forum, "TR-059: DSL Evolution - Architecture
              Requirements for the Support of QoS-Enabled IP Services",
              September 2003.

   [TS23060]  "3rd Generation Partnership Project; Technical
              Specification Group Services and System Aspects; General
              Packet Radio Service (GPRS); Service description; Stage
              2.", 2009.



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   [TS23401]  "3rd Generation Partnership Project; Technical
              Specification Group Services and System Aspects; General
              Packet Radio Service (GPRS) enhancements for Evolved
              Universal Terrestrial Radio Access Network (E-UTRAN)
              access.", 2009.

   [TS29060]  "3rd Generation Partnership Project; Technical
              Specification Group Core Network and Terminals; General
              Packet Radio Service (GPRS); GPRS Tunnelling Protocol
              (GTP), V9.1.0", 2009.


Appendix A.  GI-DS-lite deployment

A.1.  Connectivity establishment: Example call flow

   Figure 4 shows an example call flow - linking access tunnel
   establishment on the Gateway with the softwire to the AFTR.  This
   simple example assumes that traffic from the AD uses a single access
   tunnel and that the Gateway will use local polices to decide which
   portion of the traffic received over this access tunnel needs to be
   forwarded to the AFTR.

             AD            Gateway         AAA/Policy       AFTR
             |                |                 |            |
             |----(1)-------->|                 |            |
             |               (2)<-------------->|            |
             |               (3)                |            |
             |                |<------(4)------------------->|
             |               (5)                |            |
             |<---(6)-------->|                 |            |
             |                |                 |            |


           Figure 4: Example call flow for session establishment

   1.  Gateway receives a request to create an access tunnel endpoint.

   2.  The Gateway authenticates and authorizes the access tunnel.
       Based on local policy or through interaction with the AAA/Policy
       system the Gateway recognizes that IPv4 service should be
       provided using GI-DS-lite.

   3.  The Gateway creates an access tunnel endpoint.  The access tunnel
       links AD and Gateway.

   4.  (Optional): The Gateway and the AFTR establish a control session
       between each other.  This session can for example be used to



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       exchange accounting or NAT-configuration information.  Accounting
       information could be supplied to the Gateway, AAA/Policy, or
       other network entities which require information about the
       externally visible address/port pairs of a particular access
       device.  The Diameter NAT Control Application
       [I-D.draft-ietf-dime-nat-control] could for example be used for
       this purpose.

   5.  The Gateway allocates a unique CID and associates those flows
       received from the access tunnel that need to be tunneled towards
       the AFTR with the softwire linking Gateway and AFTR.  Local
       forwarding policy on the Gateway determines which traffic will
       need to be tunneled towards the AFTR.

   6.  Gateway and AD complete the access tunnel establishment
       (depending on the procedures and mechanisms of the corresponding
       access network architecture this step can include the assignment
       of an IPv4 address to the AD).

A.2.  GI-DS-lite applicability: Examples

   The section outlines deployment examples of the generic GI-DS-lite
   architecture described in Section 3.

   o  Mobile IP based access architectures: In a DSMIPv6 [RFC5555] based
      network scenario, the Mobile IPv6 home agent will implement the
      GI-DS-lite Gateway function along with the dual-stack Mobile IPv6
      functionality.

   o  Proxy Mobile IPv6 based access architectures: In a PMIPv6
      [RFC5213] scenario the local mobility anchor (LMA) will implement
      the GI-DS-lite Gateway function along with the PMIPv6 IPv4 support
      [RFC5844] functionality.

   o  GTP based access architectures: 3GPP TS 23.401 [TS23401] and 3GPP
      TS 23.060 [TS23060] define mobile access architectures using GTP.
      For GI-DS-lite, the PDN-Gateway/GGSN will also assume the Gateway
      function.

   o  Fixed WiMAX architecture: If GI-DS-lite is applied to fixed WiMAX,
      the ASN-Gateway will implement the GI-DS-lite Gateway function.

   o  Mobile WiMAX: If GI-DS-lite is applied to mobile WiMAX, the home
      agent will implement the Gateway function.

   o  PPP-based broadband access architectures: If GI-DS-lite is applied
      to PPP-based access architectures the Broadband Remote Access
      Server (BRAS) or Broadband Network Gateway (BNG) will implement



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      the GI-DS-lite Gateway function.

   o  In broadband access architectures using per-subscriber VLANs the
      BNG will implement the GI-DS-lite Gateway function.


Authors' Addresses

   Frank Brockners
   Cisco
   Hansaallee 249, 3rd Floor
   DUESSELDORF, NORDRHEIN-WESTFALEN  40549
   Germany

   Email: fbrockne@cisco.com


   Sri Gundavelli
   Cisco
   170 West Tasman Drive
   SAN JOSE, CA  95134
   USA

   Email: sgundave@cisco.com


   Sebastian Speicher
   Deutsche Telekom AG
   Landgrabenweg 151
   BONN, NORDRHEIN-WESTFALEN  53277
   Germany

   Email: sebastian.speicher@telekom.de


   David Ward
   Cisco
   170 West Tasman Drive
   SAN JOSE, CA  95134
   USA

   Email: wardd@cisco.com









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