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rfc:rfc6674

Internet Engineering Task Force (IETF) F. Brockners Request for Comments: 6674 S. Gundavelli Category: Standards Track Cisco ISSN: 2070-1721 S. Speicher

                                                   Deutsche Telekom AG
                                                               D. Ward
                                                                 Cisco
                                                             July 2012
            Gateway-Initiated Dual-Stack Lite Deployment

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 to which
 the tunneled packets belong.  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 is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6674.

Brockners, et al. Standards Track [Page 1] RFC 6674 Gateway-Initiated DS-Lite July 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
 (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 . . . . . . . . . . . . . . . . . . . . .  8
 7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
 8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
 9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   9.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
   9.2.  Informative References . . . . . . . . . . . . . . . . . . 12
 Appendix A.  GI-DS-Lite Deployment . . . . . . . . . . . . . . . . 13
   A.1.  Connectivity Establishment: Example Call Flow  . . . . . . 13
   A.2.  GI-DS-Lite Applicability: Examples . . . . . . . . . . . . 14

Brockners, et al. Standards Track [Page 2] RFC 6674 Gateway-Initiated DS-Lite July 2012

1. Overview

 Gateway-Initiated Dual-Stack Lite (GI-DS-Lite) is a variant of Dual-
 Stack Lite (DS-Lite) [RFC6333], applicable to network architectures
 that 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 GPRS
 Tunnelling Protocol (GTP) [TS29060], as well as broadband
 architectures based on PPP or point-to-point VLANs as defined by the
 Broadband Forum [TR59][TR101], are examples of 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 makes the inner IPv4 address
 irrelevant for traffic routing and allows sharing private IPv4
 addresses [RFC1918] between customer sites within the service
 provider network.
 Similarly 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 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 the access architecture.
 Additional tunneling overhead in the access network is also omitted.
 If, for example, an encapsulation mechanism based on Generic Routing
 Encapsulation (GRE) is chosen, it allows the network between the
 access gateway and the AFTR to be either IPv4 or IPv6 and allows 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].

Brockners, et al. Standards Track [Page 3] RFC 6674 Gateway-Initiated DS-Lite July 2012

 The following abbreviations are used within this document:
    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.
    AG: Access Gateway.  A gateway in the access network, such as LMA,
    Home Agent (HA), GGSN, or PDN-GW in mobile architectures.
    CID: Context Identifier
    DS-Lite: Dual-Stack Lite
    GGSN: Gateway GPRS Support Node
    GI-DS-Lite: Gateway-Initiated DS-Lite
    NAT: Network Address Translator
    PDN-GW: Packet Data Network Gateway
    SW: Softwire [RFC4925]
    SWID: Softwire Identifier

3. Gateway-Initiated DS-Lite

 This 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
 access 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 access
 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, the access 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, for

Brockners, et al. Standards Track [Page 4] RFC 6674 Gateway-Initiated DS-Lite July 2012

 example, be the endpoints of a GRE tunnel or a VPN-ID.  See Section 6
 for details.  A Context Identifier (CID) is used to multiplex flows
 associated with the individual access devices onto the softwire.  It
 is deployment dependent whether the flows from a particular AD are
 identified using the source IP address or an access tunnel
 identifier.  Local policies at the access 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 the access gateway and AFTR to identify the flows
 associated with an AD.  The CID is typically a 32-bit-wide identifier
 and is assigned by the access gateway.  It is retrieved either from a
 local or remote (e.g., Authentication, Authorization, and Accounting
 (AAA)) repository.  Like the SWID, the embodiment of the CID depends
 on the tunnel mode used and the type of the network connecting the
 access gateway and AFTR.  If, for example, GRE [RFC2784] with GRE Key
 and Sequence Number extensions [RFC2890] is used as the softwire
 technology, the network connecting the access gateway and AFTR could
 be a IPv4-only, IPv6-only, or dual-stack IP network.  The CID would
 be carried within the GRE Key field.  Section 6 details the 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 |=================|   |                          +---+
    +------+                 |   |                          | A |
                             |   |    Softwire SWID-1       | F |
                             | A |==========================| T |
    IPv4: a.b.c.d            | G |  (e.g., IPv4-over-GRE    | R |
    +------+                 |   |   over IPv4 or IPv6)     +---+
    | AD-2 |=================|   |
    +------+  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, if 32 bits wide, could be mapped 1:1 to an external IPv4

Brockners, et al. Standards Track [Page 5] RFC 6674 Gateway-Initiated DS-Lite July 2012

 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 into account parameters such as
 destination IP address, incoming interface, etc.  The IP address of
 the AFTR, which will either be an IPv6 or an IPv4 address depending
 on the transport network between the access gateway and the AFTR, is
 configured on the access gateway.  A variety of methods, such as out-
 of-band mechanisms or manual configuration, apply.
     +=====================================+======================+
     |  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 at the AFTR
 GI-DS-Lite does not require a 1:1 relationship between an access
 gateway and AFTR, but more generally applies to (M:N) scenarios,
 where M access gateways are connected to N AFTRs.  Multiple access
 gateways could be served by a single AFTR.  AFTRs could be dedicated
 to specific groups of access-devices, groups of access gateways, or
 geographic regions.  An AFTR could be, but does not have to be, co-
 located with an access 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 access 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.
    For example, 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 access gateway.

Brockners, et al. Standards Track [Page 6] RFC 6674 Gateway-Initiated DS-Lite July 2012

 o  On receiving any packet from the softwire, the AFTR SHOULD obtain
    the CID from the incoming packet and use it for performing NAT
    binding lookup and packet translation before forwarding the
    packet.
 o  The access 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 AFTR.
 o  On receiving any packet from the softwire, the access gateway
    SHOULD obtain the CID from the packet and use it for making the
    forwarding decision.
 o  When encapsulating an IPv4 packet, the access gateway and AFTR
    SHOULD use its Diffserv Codepoint (DSCP) to derive the DSCP (or
    MPLS Traffic-Class Field in the 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 the AFTR and access gateway.
 o  The softwire between the access gateway and the AFTR MAY be
    created at system startup time OR dynamically established on-
    demand.  It is deployment dependent which Operations,
    Administration, and Maintenance (OAM) mechanisms (such as ICMP,
    Bidirectional Forwarding Detection (BFD) [RFC5880], or Label
    Switched Path (LSP) ping [RFC4379]) are employed by the access
    gateway and AFTR 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 settings
    related to quality of service.  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.

Brockners, et al. Standards Track [Page 7] RFC 6674 Gateway-Initiated DS-Lite July 2012

 o  An access 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

 Which tunnel technologies can be applied for the softwire connecting
 an access gateway and AFTR are dependent on the deployment and the
 requirements.  GRE encapsulation with GRE Key extension, MPLS VPNs
 [RFC4364], or plain IP-in-IP encapsulation can be used.  Softwire
 identification and CID depend on the tunneling technology employed:
 o  GRE with GRE Key: SWID is the tunnel identifier of the GRE tunnel
    between the access gateway and the AFTR.  The CID is the GRE Key
    associated with the AD.
 o  MPLS VPN: The SWID is a generic identifier that uniquely
    identifies the VPN at either the access gateway or AFTR.
    Depending on whether the access gateway or AFTR is acting as
    customer edge (CE) or provider edge (PE), the SWID could, for
    example, 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 bits 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.

Brockners, et al. Standards Track [Page 8] RFC 6674 Gateway-Initiated DS-Lite July 2012

 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.

 o  Network-type
  • "v4": The access gateway and AFTR are connected by an IPv4-only

network.

  • "v6": The access gateway and AFTR are connected by an IPv6-only

network.

  • "v4v6": The access gateway and AFTR are connected by a dual-

stack network, supporting IPv4 and IPv6.

  • "MPLS": The access gateway and AFTR are connected by an 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

Brockners, et al. Standards Track [Page 9] RFC 6674 Gateway-Initiated DS-Lite July 2012

7. 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
 AFTR 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.
 If a packet is received with an incorrect Context Identifier at the
 access gateway/AFTR, it will be associated with an incorrect access
 device.  Therefore, care must be taken to ensure an IP packet
 tunneled between the access gateway and the AFTR is carried 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 that 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 new security considerations
 other than those specified in the 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.

8. 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, and Ralph Droms.

Brockners, et al. Standards Track [Page 10] RFC 6674 Gateway-Initiated DS-Lite July 2012

9. References

9.1. 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
            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.

Brockners, et al. Standards Track [Page 11] RFC 6674 Gateway-Initiated DS-Lite July 2012

9.2. Informative References

 [NAT-CONTROL]
            Brockners, F., Bhandari, S., Singh, V., and V. Fajardo,
            "Diameter Network Address and Port Translation Control
            Application", Work in Progress, April 2012.
 [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]  3GPP, "Technical Specification Group Services and System
            Aspects; General Packet Radio Service (GPRS); Service
            description; Stage 2, V11.2.0", TS 23.060, 2012.
 [TS23401]  3GPP, "Technical Specification Group Services and System
            Aspects; General Packet Radio Service (GPRS) enhancements
            for Evolved Universal Terrestrial Radio Access Network
            (E-UTRAN) access, V11.1.0", TS 23.401, 2012.
 [TS29060]  3GPP, "Technical Specification Group Core Network and
            Terminals; General Packet Radio Service (GPRS); GPRS
            Tunnelling Protocol (GTP), V11.3.0", TS 29.060, 2012.

Brockners, et al. Standards Track [Page 12] RFC 6674 Gateway-Initiated DS-Lite July 2012

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 access gateway with the softwire to the AFTR.
 This simple example assumes that traffic from the AD uses a single
 access tunnel and that the access gateway will use local policies to
 decide which portion of the traffic received over this access tunnel
 needs to be forwarded to the AFTR.
           AD         Access Gateway       AAA/Policy     AFTR
           |                |                 |            |
           |----(1)-------->|                 |            |
           |               (2)<-------------->|            |
           |               (3)                |            |
           |                |<------(4)------------------->|
           |               (5)                |            |
           |<---(6)-------->|                 |            |
           |                |                 |            |
         Figure 4: Example Call Flow for Session Establishment
 1.  The access gateway receives a request to create an access tunnel
     endpoint.
 2.  The access gateway authenticates and authorizes the access
     tunnel.  Based on local policy or through interaction with the
     AAA/Policy system, the access gateway recognizes that IPv4
     service should be provided using GI-DS-Lite.
 3.  The access gateway creates an access tunnel endpoint.  The access
     tunnel links AD and access gateway.
 4.  (Optional): The access gateway and the AFTR establish a control
     session between themselves.  This session can, for example, be
     used to exchange accounting or NAT-configuration information.
     Accounting information could be supplied to the access gateway,
     AAA/Policy, or other network entities that require information
     about the externally visible address/port pairs of a particular
     access device.  The Diameter NAT Control Application
     [NAT-CONTROL] could, for example, be used for this purpose.
 5.  The access 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 the access gateway and
     AFTR.  Local forwarding policy on the access gateway determines
     which traffic will need to be tunneled towards the AFTR.

Brockners, et al. Standards Track [Page 13] RFC 6674 Gateway-Initiated DS-Lite July 2012

 6.  The access 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  Access architectures based on Mobile-IP: In a network scenario
    based on Dual-Stack Mobile IPv6 (DSMIPv6) [RFC5555], the Mobile
    IPv6 home agent will implement the GI-DS-Lite access gateway
    function along with the dual-stack Mobile IPv6 functionality.
 o  Access architectures based on Proxy Mobile IPv6 (PMIPv6): In a
    PMIPv6 [RFC5213] scenario, the local mobility anchor (LMA) will
    implement the GI-DS-Lite access gateway function along with the
    PMIPv6 IPv4 support [RFC5844] functionality.
 o  GTP-based access architectures: Third Generation Partnership
    Project (3GPP) TS 23.401 [TS23401] and 3GPP TS 23.060 [TS23060]
    define mobile access architectures using GTP.  For GI-DS-Lite, the
    PDN-GW or GGSN will also assume the access gateway function.
 o  Fixed Worldwide Interoperability for Microwave Access (WiMAX)
    architecture: If GI-DS-Lite is applied to fixed WiMAX, the Access
    Service Network Gateway (ASN-GW) will implement the GI-DS-Lite
    access gateway function.
 o  Mobile WiMAX: If GI-DS-Lite is applied to mobile WiMAX, the home
    agent will implement the access 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
    the GI-DS-Lite access gateway function.
 o  In broadband access architectures using per-subscriber VLANs, the
    BNG will implement the GI-DS-Lite access gateway function.

Brockners, et al. Standards Track [Page 14] RFC 6674 Gateway-Initiated DS-Lite July 2012

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

Brockners, et al. Standards Track [Page 15]

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