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Softwires                                                        C. Zhou
Internet-Draft                                                   T. Tsou
Intended status: Standards Track                     Huawei Technologies
Expires: January 12, 2011                                    Y. Lee, Ed.
                                                                 Comcast
                                                                 G. Yang
                                                           China Telecom
                                                           July 11, 2010


          Deployment DS-lite in Point-to-Point Access Network
                   draft-zhou-softwire-ds-lite-p2p-02

Abstract

   Gateway-Initiated Dual-Stack lite (GI-DS-lite) is a proposal to
   logically extend existing access tunnels beyond the access gateway to
   DS-Lite Address Family Transition Router element (AFTR) using
   softwires with an embedded context identifier.  This memo describes a
   deployment model using GI-DS-lite in Point-to-Point access network.

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
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   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 January 12, 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



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   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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Scope and Requirements  . . . . . . . . . . . . . . . . . . . . 3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Current Deployment  . . . . . . . . . . . . . . . . . . . . 4
     3.2.  DS-lite in Point-to-Point Access Network  . . . . . . . . . 5
   4.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 6
   5.  Proposed Alternative Context Identifier . . . . . . . . . . . . 6
   6.  Management of Devices behind CPE  . . . . . . . . . . . . . . . 7
   7.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   10. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     11.1. Normative References  . . . . . . . . . . . . . . . . . . . 8
     11.2. Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9



























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1.  Introduction

   GI-DS-lite [I-D.ietf-softwire-gateway-init-ds-lite] describes the use
   of Gateway-Initiated softwire tunnels operating between the Gateway
   and the Address Family Transition Router (AFTR) to conserve IPv4
   addresses.  Flows from multiple access devices (CPEs) can be
   distinguished through use of Context Identifiers (CID).  GI-DS-lite
   describes an architecture where each CPE is a single device.  It does
   not cover the case where each CPE manages multiple hosts.  This is
   common in fixed network deployment and home network deployment over
   air.

   GI-DS-lite proposes few tunnel modes used for CID.  One option is to
   use Plain IP-in-IP.  In this mode, a unique IPv4 address must be
   assigned for each CPE from the gateway.  As such, it does not support
   CPEs using overlapped address.  To support overlapped address space,
   stateful tunnel (eg.  GRE) is required between gateway and AFTR.  It
   is expensive to create one stateful tunnel per CPE especially in
   fixed network non-mobility deployment.

   DS-Extra-lite [I-D.arkko-dual-stack-extra-lite] describes that when
   the CPE is connected to the gateway by point-to-point link rather
   than shared media connection, it is unnecessary for the CID to be an
   IP address.  If another identifier with the required uniqueness
   properties can be found (eg.  VLAN and ATM PVC), the gateway can use
   the per-interface identity to uniquely identify the CPE.  This
   relaxes the contraint of using CPE's IPv4 address for uniqueness.

   This memo describes a framework to use the point-to-point identifier
   and the IPv6 Flow Label [RFC3697] to create a unique binding in the
   AFTR for CPEs using overlapped address space in the point-to-point
   access network.


2.  Scope and Requirements

   This specification focuses on the point-to-point access network
   deployment using GI-DS-lite.  Other deployment scenarios are out of
   scope.  These are the assumptions of the network:

   1.  The access network is point-to-point.

   2.  The access network is not yet IPv6 enabled.

   3.  Avoid double-NAT.

   4.  Edge router does not perform NAT.




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   5.  Edge router uses plain IP-in-IPv6 to connect to AFTR.

   6.  Extend the point-to-point mapping to AFTR.


3.  Overview

3.1.  Current Deployment

   Many operators use point-to-point (eg.  PPP) to connect to their
   customers.  The operators give each customer a public IPv4 address.
   Many customers also have a gateway (managed or unmanaged) which is a
   NAT device managing the customer's internal network.  Figure 1 shows
   a common deployment architecture.



                                      |
                                      | IPv4 Internet
                                      |
                               +------+------+
                               |   Gateway   |
                               +-------------+
                                   /     \
                          Layer-3 /       \ Layer-3
                            +----+         +----+
                            | ER |         | ER |
                            +----+         +----+
                              /\             /\
                             /  \           /  \ Pt-to-Pt
                         NAT/    \NAT   NAT/    \NAT
                         +===+  +===+   +===+  +===+
                         | A |  | B |   | C |  | D |
                         +===+  +===+   +===+  +===+
                           |      |       |      |
                         --+--  --+--   --+--  --+--
                          | |    | |     | |    | |
                         H1 H2  H3 H4   H5 H6  H7 H8

                   Access CPEs A,B,C,D all use 192.168.1.0/24
                   for their internal network.


                                 Figure 1

   Each CPE has been assigned a unique global IPv4 address and performs
   NAT for the hosts, so Edge Router (ER) can uniquely identify the CPEs
   by their IP addresses.



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3.2.  DS-lite in Point-to-Point Access Network

   When IPv4 addresses are scarce, operators may want to increase the
   IPv4 address utilization by sharing a single IPv4 address to multiple
   users.  DS-Lite [I-D.ietf-softwire-dual-stack-lite] describes a
   framework to implement B4 element in the CPE and encapsulate the IPv4
   datagram inside an IPv6 datagram (IP-in-IPv6) to AFTR in the operator
   network for NAT-ing.  The AFTR uses the unique IPv6 address of the B4
   to identify the CPE.  This framework works well for both shared media
   network and point-to-point access network, but it requires the
   operator to upgrade the access network to IPv6.

   In point-to-point access network, each CPE has a unique point-to-
   point link.  The operator can use the link information to identify
   the CPE.  In this specification, the operator does not give any IPv4
   or IPv6 address to the CPE.  Instead, each point-to-point interface
   is an unnumbered interface.  The CPE is still an IPv4 DHCP server for
   its internal network, it continues to offer [RFC1918] addresses to
   its managed hosts.  In this memo, the CPE does not NAT the packets
   coming from its hosts.  Instead, the CPE simply puts the packets to
   the point-to-point link and forward to the ER.  When ER receives the
   packet, it maps the point-to-point identifier to the IPv6 Flow Label
   [RFC3697] and send to the AFTR for NAT.  Figure 2 shows the
   architecture.



























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                               |
                               |  IPv4 Internet
                          +--------+
                          | DS-lite| NAT Mappings:
                          |  AFTR  | (Flow Label, TCP port1 <->
                          +---++---+              a.b.c.d, TCP port2)
                              ||
                         IPv6 ||  Softwire Tunnel (IP-in-IPv6)
                              ||    (CID is the Flow Label)
                              ||
                        +-----++------+
                        | Edge Router | Map IPv6 Flow Label to CID
                        +-------------+
                           /       \  Pt-to-Pt
                          /         \ unnumbered I/F
                      +===+         +===+
                      | A |         | B | Access CPE A and B
                      +===+         +===+ use 192.168.1.0/24
                        |             |
                      --+--         --+--
                       | |           | |
                      H1 H2         H3 H4
                      .5 .6         .5 .6



                                 Figure 2

   In Figure 2, H1 and H3, and H2 and H4 use duplicate IP addresses.
   Since CPE A and B do not have IP address, the ER cannot use the IP
   address to returned packets to the hosts behind CPE A and B. Instead,
   ER creates a binding table to map the point-to-point identifier to
   the CPEs.  Then, ER uses the IPv6 Flow Label [RFC3697] as the Context
   Identifier for the GI-DS-lite tunnel.  No stateful tunnel is required
   between AFTR and ER.


4.  Requirements Language

   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 RFC 2119 [RFC2119].


5.  Proposed Alternative Context Identifier

   This memo proposes that an additional type of context identifier be
   added to the set identified in GI-DS-lite.  Where the tunnel between



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   the Gateway and the AFTR is IP-in-IPv6, it is proposed to use the
   IPv6 Flow Label as the context identifier.

   The Flow Label is 20 bits, where the Context ID in GI-DS-lite is 32
   bits.  So, each softwire can support up to 2^20 or 1,048,576 CPEs.
   To support more CPEs in a single ER, multiple softwires can be
   provisioned between the ER and the AFTR.


6.  Management of Devices behind CPE

   Some operators manage the home devices (eg.  IP STB and VoIP adaptor)
   behind the CPE.  This is done by port-forwarding the pre-configured
   ports in the CPE.  If the CPE implemented this specification, the
   home device management traffic would be tunneled to the AFTR.  The
   AFTR would also need to support special port-forwarding rules to
   allow in-bound connections to the home devices.  This adds extra
   complexity to the AFTR and consumes many ports in the AFTR for port-
   forwarding.

   Since this management traffic is internally used by the operator
   only, the operator could address the CPE with [RFC1918].  This
   address space is managed by the operator and each CPE is assigned a
   unique RFC1918 address.  The CPE contains the same port-forwarding
   rules for the managed home devices.  When the CPE receives packets
   from the home devices, it will NAT the packet to the address assigned
   to the point-to-point link and forward to the ER.  For the packets
   generated by the hosts, the CPE will use the specification to send
   the traffic unmodified to the ER.

   When the ER receives packets sourced from this [RFC1918] address
   space, it should not forward these packets to the AFTR via the
   softwire.  Instead, the ER should forward the packets to the internal
   management network.  To make the ER forwarding rule simple, the CPE
   management address space must not overlap with the address space used
   by the CPE for its internal hosts.


7.  Conclusion

   We present a framework to deploy GI-DS-lite in point-to-point access
   network.  This framework promotes IPv6 deployment from the core to
   the edge.  When IPv6 is ready in the access network, the operators
   can either upgrade the CPE to B4 element and migrate to classic DS-
   lite deployment or provision dual-stack to the CPE and continue to
   use GI-DS-lite.





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8.  Acknowledgements

   TBD


9.  IANA Considerations

   This memo includes no request to IANA.


10.  Security Considerations

   See the security considerations for [RFC3697] and
   [I-D.ietf-softwire-dual-stack-lite].  This proposal adds no further
   security considerations.


11.  References

11.1.  Normative References

   [I-D.ietf-softwire-dual-stack-lite]
              Durand, A., Droms, R., Haberman, B., Woodyatt, J., Lee,
              Y., and R. Bush, "Dual-Stack Lite Broadband Deployments
              Following IPv4 Exhaustion",
              draft-ietf-softwire-dual-stack-lite-05 (work in progress),
              July 2010.

   [I-D.ietf-softwire-gateway-init-ds-lite]
              Brockners, F., Gundavelli, S., Speicher, S., and D. Ward,
              "Gateway Initiated Dual-Stack Lite Deployment",
              draft-ietf-softwire-gateway-init-ds-lite-00 (work in
              progress), May 2010.

   [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.

   [RFC3697]  Rajahalme, J., Conta, A., Carpenter, B., and S. Deering,
              "IPv6 Flow Label Specification", RFC 3697, March 2004.

11.2.  Informative References

   [I-D.arkko-dual-stack-extra-lite]
              Arkko, J. and L. Eggert, "Scalable Operation of Address



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              Translators with Per-Interface Bindings",
              draft-arkko-dual-stack-extra-lite-00 (work in progress),
              February 2010.


Authors' Addresses

   Cathy Zhou
   Huawei Technologies
   Section B, Huawei Industrial Base
   Bantian Longgang
   Shenzhen  518129
   P.R. China

   Email: cathyzhou@huawei.com
   URI:   http://www.huawei.com


   Tina Tsou
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Email: tena@huawei.com
   URI:   http://www.huawei.com


   Yiu L. Lee (editor)
   Comcast
   One Comcast Center
   Philadelphia  19103
   U.S.A.

   Email: yiu_lee@cable.comcast.com
   URI:   http://www.comcast.com


   GL Yang
   China Telecom
   109 East Zhongshan Road, Tiahne District
   Guangzhou
   P.R. China

   Email: yanggl@gsta.com
   URI:   http://www.chinatelecom.com.cn





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