TOC 
Internet Engineering Task ForceF. Brockners
Internet-DraftS. Gundavelli
Intended status: Standards TrackCisco
Expires: April 18, 2011S. Speicher
 Deutsche Telekom AG
 D. Ward
 Juniper Networks
 October 15, 2010


Gateway Initiated Dual-Stack Lite Deployment
draft-ietf-softwire-gateway-init-ds-lite-01

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/.

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This Internet-Draft will expire on April 18, 2011.

Copyright Notice

Copyright (c) 2010 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
2.  Conventions
3.  Gateway Initiated DS-Lite
4.  Protocol and related Considerations
5.  Softwire Management and related Considerations
6.  Softwire Embodiments
7.  new section
8.  GI-DS-lite deployment
    8.1.  Connectivity establishment: Example call flow
    8.2.  GI-DS-lite applicability: Examples
9.  Acknowledgements
10.  IANA Considerations
11.  Security Considerations
12.  Change History (to be removed prior to publication as an RFC)
13.  References
    13.1.  Normative References
    13.2.  Informative References
§  Authors' Addresses




 TOC 

1.  Overview

Gateway-Initiated Dual-Stack lite (GI-DS-lite) is a variant of the Dual-Stack lite (DS-lite) [I‑D.ietf‑softwire‑dual‑stack‑lite] (Durand, A., Droms, R., Woodyatt, J., and Y. Lee, “Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion,” August 2010.), 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 [RFC3775] (Johnson, D., Perkins, C., and J. Arkko, “Mobility Support in IPv6,” June 2004.), Proxy Mobile IPv6 [RFC5213] (Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., and B. Patil, “Proxy Mobile IPv6,” August 2008.), or GTP [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.), as well as broadband architectures based on PPP or point-to-point VLANs as defined by the Broadband Forum (see [TR59] (Broadband Forum, “TR-059: DSL Evolution - Architecture Requirements for the Support of QoS-Enabled IP Services,” September 2003.) and [TR101] (Broadband Forum, “TR-101: Migration to Ethernet-Based DSL Aggregation,” April 2006.)) 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] (Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, “Address Allocation for Private Internets,” February 1996.) 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] (Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, “Address Allocation for Private Internets,” February 1996.). 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 IPv4-IPv4 NAT 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., a GRE based encapsulation mechanisms is chosen, it allows the network between the access gateway and the NAT to be either IPv4 or IPv6 and provides the operator to migrate to IPv6 in incremental steps.



 TOC 

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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

The following abbreviations are used within this document:

AFTR: Address Family Transition Router (also known as "Large Scale NAT (LSN)" or "Dual-Stack lite Tunnel Concentrator", or "Carrier Grade NAT"). 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 (see [RFC4925] (Li, X., Dawkins, S., Ward, D., and A. Durand, “Softwire Problem Statement,” July 2007.))

SWID: Softwire Identifier

TID: Access Tunnel Identifier. The interface identifier of the point-to-point access tunnel.



 TOC 

3.  Gateway Initiated DS-Lite

The section provides an overview of Gateway Initiated DS-Lite (GI-DS-lite). Figure 1 (Gateway-initiated dual-stack lite reference architecture) 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 Section 8 (GI-DS-lite deployment).

In Figure 1 (Gateway-initiated dual-stack lite reference architecture), 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] (Li, X., Dawkins, S., Ward, D., and A. Durand, “Softwire Problem Statement,” July 2007.). The softwire is identified by a softwire identifier (SWID). 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, see Section 6 (Softwire Embodiments) for details. A Context-Identifier (CID) is used to multiplex flows associated with the individual access devices onto the softwire. 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 (potentially along with other traffic identifiers such as e.g. interface, VLAN, port, etc.) serves as common context between Gateway and AFTR to uniquely identify flows associated with an access device. The CID is a 32-bit wide identifier and is assigned 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] (Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, “Generic Routing Encapsulation (GRE),” March 2000.) with “GRE Key and Sequence Number Extensions” [RFC2890] (Dommety, G., “Key and Sequence Number Extensions to GRE,” September 2000.) 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. See Section 6 (Softwire Embodiments) 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 <->
   +------+ Tunnel (TID-1)  |   |                 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 |
   +------+ Tunnel (TID-2)  |   |         (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 outer/external IPv4 address of a NAT-binding at the AFTR is either 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 32-bit CID 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 (Example translation table on the AFTR). 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.




+=====================================+======================+
|  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 specifc groups of access-devices, groups of Gateways, or geographic regions. An AFTR could, but does not have to be co-located with a Gateway.



 TOC 

4.  Protocol and related Considerations



 TOC 

5.  Softwire Management and related Considerations

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



 TOC 

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, or plain IP-in-IP encapsulation can be used. Softwire identification and Context-ID depend on the tunneling technology employed:

Figure 3 (Tunnel modes and their applicability) 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:



+==================+==================+=======================+
|                  | IPv4 address     |      Network-type     |
|    Softwire      +----+----+----+---+----+----+------+------+
|                  | up | op | nm | s | v4 | v6 | v4v6 | MPLS |
+==================+====+====+====+===+====+====+======+======+
| GRE with GRE-key |  x |  x |  x | x |  x |  x |   x  |      |
| MPLS VPN         |  x |  x |  x |   |    |    |      |   x  |
| Plain IP-in-IP   |  x |  x |  x | x |  x |  x |   x  |      |
+==================+====+====+====+===+====+====+======+======+

 Figure 3: Tunnel modes and their applicability 

Note: For "Plain IP-in-IP", support for 'op' and 's' requires the use of IPv6-transport with the IPv6-Flow-Label serving as CID.



 TOC 

7.  new section



 TOC 

8.  GI-DS-lite deployment



 TOC 

8.1.  Connectivity establishment: Example call flow

Figure 4 (Example call flow for session establishment) 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 and is uniquely identified by Tunnel Identifier (TID) on the Gateway.
  4. (Optional): The Gateway and the AFTR establish a control session between each other. This session can for example be used to 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 (see [I‑D.draft‑ietf‑dime‑nat‑control] (Brockners, F., Bhandari, S., Singh, V., and V. Fajardo, “Diameter NAT Control Application,” August 2009.) could for example be used for this purpose.
  5. The Gateway allocates a unique CID and associates those flows received from the access tunnel (identified by the TID) 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).


 TOC 

8.2.  GI-DS-lite applicability: Examples

The section outlines deployment examples of the generic GI-DS-lite architecture described in Section 3 (Gateway Initiated DS-Lite).



 TOC 

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 and Yiu L. Lee.



 TOC 

10.  IANA Considerations

This document includes no request to IANA.

All drafts are required to have an IANA considerations section (see the update of RFC 2434 (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226] for a guide). If the draft does not require IANA to do anything, the section contains an explicit statement that this is the case (as above). If there are no requirements for IANA, the section will be removed during conversion into an RFC by the RFC Editor.



 TOC 

11.  Security Considerations

All the security considerations from GTP [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.), Mobile IPv6 [RFC3775] (Johnson, D., Perkins, C., and J. Arkko, “Mobility Support in IPv6,” June 2004.), Proxy Mobile IPv6 [RFC5213] (Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., and B. Patil, “Proxy Mobile IPv6,” August 2008.), and Dual-Stack lite [I‑D.ietf‑softwire‑dual‑stack‑lite] (Durand, A., Droms, R., Woodyatt, J., and Y. Lee, “Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion,” August 2010.) apply to this specification as well.



 TOC 

12.  Change History (to be removed prior to publication as an RFC)

Changes from -00 to -01

a.
clarified the applicability of GI-DS-lite to scenarios with M Gateways and N AFTRs.
b.
clarification of the nomenclature and use of the identifier of the softwire connecting Gateway and AFTR: Introduced softwire identifier (SWID), updated figure 2 accordingly.
c.
cleanup of editorial nits.


 TOC 

13.  References



 TOC 

13.1. Normative References

[I-D.ietf-softwire-dual-stack-lite] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, “Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion,” draft-ietf-softwire-dual-stack-lite-06 (work in progress), August 2010 (TXT).
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, “Address Allocation for Private Internets,” BCP 5, RFC 1918, February 1996 (TXT).
[RFC2119] Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, “Generic Routing Encapsulation (GRE),” RFC 2784, March 2000 (TXT).
[RFC2890] Dommety, G., “Key and Sequence Number Extensions to GRE,” RFC 2890, September 2000 (TXT).
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, “Mobility Support in IPv6,” RFC 3775, June 2004 (TXT).
[RFC4379] Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” RFC 4379, February 2006 (TXT).
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., and B. Patil, “Proxy Mobile IPv6,” RFC 5213, August 2008 (TXT).
[RFC5226] Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” BCP 26, RFC 5226, May 2008 (TXT).
[RFC5555] Soliman, H., “Mobile IPv6 Support for Dual Stack Hosts and Routers,” RFC 5555, June 2009 (TXT).
[RFC5565] Wu, J., Cui, Y., Metz, C., and E. Rosen, “Softwire Mesh Framework,” RFC 5565, June 2009 (TXT).
[RFC5880] Katz, D. and D. Ward, “Bidirectional Forwarding Detection (BFD),” RFC 5880, June 2010 (TXT).


 TOC 

13.2. Informative References

[I-D.draft-ietf-dime-nat-control] Brockners, F., Bhandari, S., Singh, V., and V. Fajardo, “Diameter NAT Control Application,” August 2009.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, “Multiprotocol Label Switching Architecture,” RFC 3031, January 2001 (TXT).
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, “MPLS Label Stack Encoding,” RFC 3032, January 2001 (TXT).
[RFC4925] Li, X., Dawkins, S., Ward, D., and A. Durand, “Softwire Problem Statement,” RFC 4925, July 2007 (TXT).
[RFC5036] Andersson, L., Minei, I., and B. Thomas, “LDP Specification,” RFC 5036, October 2007 (TXT).
[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.
[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.


 TOC 

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
  Juniper Networks
  1194 N. Mathilda Ave.
  Sunnyvale, California 94089-1206
  USA
Email:  dward@juniper.net