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Network Working Group                                        S. Jiang
Internet Draft                                                 D. Guo
Intended status: Informational            Huawei Technologies Co., Ltd
Expires: August 29, 2009                                  B. Carpenter
                                                University of Auckland
                                                         March 1, 2009

       An Incremental Carrier-Grade NAT (CGN) for IPv6 Transition
                   draft-jiang-incremental-cgn-00.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on August 29, 2009.



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Abstract

   Global IPv6 deployment was slower than originally expected in the
   last ten years. As IPv4 address exhaustion gets closer, the IPv4/IPv6
   transition issues become more critical and complicated. Host-based
   transition mechanisms are not able to meet the requirements while
   most end users are not sufficiently expert to configure or maintain
   these transition mechanisms. Carrier Grade NAT with integrated
   transition mechanisms can simplify the operation of end users during
   the IPv4/IPv6 migration or coexistence period. This document proposes
   an incremental Carrier-Grade NAT (CGN) solution for IPv6 transition.
   It can provide IPv6 access services for IPv6-enabled end hosts and
   IPv4 access services for IPv4 end hosts while remaining most of
   legacy IPv4 ISP networks unchanged. It is suitable for the initial
   stage of IPv4/IPv6 migration. Unlike CGN alone, it also supports and
   encourages transition towards dual-stack or IPv6-only ISP networks.

Table of Contents


   1. Introduction................................................3
   2. Terminology.................................................4
   3. An Incremental CGN Solution..................................4
      3.1. Incremental CGN Solution Overview.......................4
      3.2. Behaviour of Dual-stack Home Gateway....................5
      3.3. Behaviour of Dual-stack Carrier-Grade NAT...............5
      3.4. Impact for end hosts and remaining networks.............6
   4. Migration towards IPv6 Core Network..........................6
   5. Security Considerations......................................6
   6. IANA Considerations.........................................7
   7. References..................................................7
      7.1. Normative References....................................7
      7.2. Informative References..................................7
   Author's Addresses.............................................9












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1. Introduction

   Up to now, global IPv6 deployment does not happen as was expected 10
   years ago. The progress was much slower than originally expected.
   Network providers were hesitant to take the first move while IPv4 was
   and is still working well. However, IPv4 address exhaustion is now
   confirmed to happen soon. The dynamically-updated IPv4 Address Report
   [IPUSAGE] has analyzed this issue. It predicts early 2011 for IANA
   unallocated address pool exhaustion and middle 2012 for RIR
   unallocated address pool exhaustion. Based on this fact, the Internet
   industry appears to have reached consensus that global IPv6
   deployment is inevitable and has to be done quite quickly.

   IPv4/IPv6 transition issues therefore become more critical and
   complicated for the soon-coming global IPv6 deployment. Host-based
   transition mechanisms alone are not able to meet the requirements.
   They are too complicated for most end users who do not have enough
   technical knowledge to configure or maintain these transition
   mechanisms. New transition mechanisms with simple user-side operation
   are needed.

   Carried Grade NAT (CGN) alone creates operational problems, but does
   nothing to help IPv4/IPv6 transition. In fact it allows ISPs to delay
   the transition, and therefore causes double transition costs (once to
   add CGN, and again to support IPv6).

   Carrier-Grade NAT that integrates multiple transition mechanisms can
   simplify the operation of end user services during the IPv4/IPv6
   migration or coexistence period. CGNs are deployed on the network
   side and managed/maintained by professionals. On the user side, new
   CPE devices may be needed too. They may be provided by network
   providers, depending on the specific business model. Dual-stack lite
   [DSLite] is a CGN-based solution that supports transition, but it
   requires the ISP to upgrade its network to IPv6 immediately. Many
   ISPs hesitate to do this as the first step.

   This document proposes an incremental CGN solution for IPv6
   transition. The solution is similar to DSLite, but the other way
   around. Technically, it mainly combines v4-v4 NAT with v6-over-v4
   tunnelling functions along with some minor adjustment. It can provide
   IPv6 access services for IPv6-enabled end hosts and IPv4 access
   services for IPv4 end hosts, while leaving most of legacy IPv4 ISP
   networks unchanged. The deployment of this solution does not affect
   legacy IPv4 hosts with global IPv4 addresses at all. It is suitable
   for the initial stage of IPv4/IPv6 migration. It also supports
   transition towards dual-stack or IPv6-only ISP networks.


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2. Terminology

   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].

3. An Incremental CGN Solution

   Most ISP networks are still IPv4. Network providers are starting to
   provide IPv6 access services for end users. However, at the initial
   stage of IPv4/IPv6 migration, IPv4 connectivity and traffic would be
   the majority for ISP networks. ISPs would like to minimize the
   changes on their IPv4 networks. Switching the whole ISP network into
   IPv6-only would be considered as a radical strategy. Switching the
   whole ISP network to dual stack is less radical, but introduces
   operational costs and complications.

        3.1. Incremental CGN Solution Overview

   The incremental CGN solution we propose is illustrated as the
   following figure.

                                 +-------------+
                                 |IPv6 Internet|
                                 +-------------+
                                        |
     +-----+    +--+    +-------+    +-----+         +--------+
     |v4/v6|----|DS|----| IPv4  |----| CGN |---------|  IPv4  |
     |Host |    |HG|    |Network|    |     |    |    |Internet|
     +-----+    +--+    +-------+    +-----+    |    +--------+
                  _ _ _ _ _ _ _ _ _ _ _     +---------------------+
                ()_6_o_4_ _t_u_n_n_e_l_()   | Existing IPv4 hosts |
                                            +---------------------+

    Figure 1: Phase 1 of incremental CGN solution with IPv4 ISP network

   DS HG = Dual-Stack Home Gateway.

   The above figure shows only Phase 1, in which the ISP has not
   significantly changed its IPv4 network. This solution enables IPv4
   hosts to access the IPv4 Internet and IPv6 hosts to access the IPv6
   Internet. A dual stack host can be treated as an IPv4 host when it
   uses IPv4 access service and as an IPv6 host when it uses IPv6 access
   service. In order to enable IPv4 hosts to access IPv6 Internet and
   IPv6 hosts to access IPv4 Internet, NAT-PT [RFC2766, RFC4966] (or its
   replacement) can be integrated with CGN. The integration of NAT-PT is
   out of scope for this document


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   Two new types of devices need to be deployed in this solution: a
   dual-stack home gateway, which may follow the requirements of [6CPE],
   and dual-stack Carrier-Grade NAT. The dual-stack home gateway
   integrates IPv4 forwarding and v6-over-v4 tunnelling functions. It
   may integrate v4-v4 NAT function, too. The dual-stack CGN integrates
   v6-over-v4 tunnelling and carrier-grade v4-v4 NAT functions. Modified
   6RD [6RD] technology may be used to support v6-over-v4 tunnelling.
   Other tunnelling mechanisms such as ISATAP [RFC5214] could also be
   considered, but 6RD appears to fit well and allows re-use of existing
   support for 6to4 [RFC3056].

        3.2. Behaviour of Dual-stack Home Gateway

   When a dual-stack home gateway receives a data packet from an end
   host, it firstly checks whether the packet is IPv4 or IPv6. For IPv4
   data, the HG can directly forward it if there is no v4-v4 NAT running
   on the HG. Or the HG translates packet source address from a HG-scope
   private IPv4 address into a CGN-scope private IPv4 address. The HG
   should record the v4-v4 address mapping information for inbound
   packets, just like normal NAT does.

   For IPv6 data, the HG needs to encapsulate the data into an IPv4
   tunnel, which sets the dual-stack CGN as another end. Then the HG
   sends the new IPv4 packet towards CGN.

   The HG should record the mapping information between the tunnel and
   the source IPv6 address for inbound packets if HG uplinks to more
   than one CGN. Detailed considerations for the use of multiple CGNs by
   one HG are for further study.

        3.3. Behaviour of Dual-stack Carrier-Grade NAT

   When a dual-stack CGN receives a data packet from a dual-stack home
   gateway, it firstly checks whether the packet is a normal IPv4 packet
   or a v6-over-v4 tunnel packet. For a normal IPv4 packet, the CGN
   translates packet source address from a CGN-scope private IPv4
   address into a public IPv4 address, and then send it to IPv4 Internet.
   The CGN should record the v4-v4 address mapping information for
   inbound packets, just like normal NAT does. For a v6-over-v4 tunnel
   packet, the CGN needs to decapsulate it into the original IPv6 packet
   and then send it to IPv6 Internet. The CGN should record the mapping
   information between the tunnel and the source IPv6 address for
   inbound packets.

   Depending on the deployed location of the CGN, it may use v6-over-v4
   tunnels to connect to the IPv6 Internet.



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3.4. Impact for end hosts and remaining networks

   This solution does not affect the remaining networks at all. Legacy
   IPv4 ISP networks and their IPv4 devices remain in use. The existing
   IPv4 hosts, shown as the right box in Figure 1, either having global
   IPv4 addresses or behind v4-v4 NAT can connect to IPv4 Internet as it
   is now.

3.5. Discussion

   It should be noted that for IPv4 traffic, this solution inherits all
   the problems of CGN (e.g., scaling, and the difficulty of supporting
   well-known ports for inbound traffic). Application layer problems
   created by double NAT are for further study.

   However, for IPv6 traffic, a user behind the DS HG will see normal
   IPv6 service. It is strongly recommended that all IPv6 tunnels
   support a large MTU, at least 1500 bytes, to avoid fragmentation
   problems. This, and the absence of NAT problems for IPv6, will create
   an incentive for users and application service providers to prefer
   IPv6.

4. Migration towards IPv6 Core Network

   When the core network starts transition to IPv6, this solution can
   easily be transited into Phase 2, in which the ISP network is either
   dual-stack or IPv6-only. For dual-stack ISP networks, dual-stack home
   gateways can simply switch off the v6-over-v4 function and forward
   both IPv6 and IPv4 traffic directly; dual-stack CGN should only keep
   v4-v4 NAT function. For IPv6-only ISP networks, the dual-stack lite
   solution, which also has dual-stack home gateway and CGN devices, can
   be adopted for Phase 2. The best business model for this solution is
   that CPE has integrated the functions for both Phase 1 and 2, and can
   automatically detect the change. Then when ISPs decide to switch from
   Phase 1 to Phase 2, it may be that only a configuration change or a
   minor software update is needed on the CGNs. The DS HG will then
   switch automatically to basic dual stack or DSLite mode. The only
   impact on the home user will be to receive a different IPv6 prefix.
   Note that if the 6RD mechanism is used in Phase 1, the user will most
   likely have a /64 prefix during Phase 1, but could get a shorter
   prefix such as /56 in Phase 2. This would be an improved service
   offering available as a result of the Phase 1 to Phase 2 transition.

5. Security Considerations

   Security issues associated with NAT have been documented in [RFC2663]
   and [RFC2993].


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   Further security analysis will be needed to understand double NAT
   security issues and tunnel security issues. However, since the tunnel
   exists entirely in a single ISP network, between the CPE and the CGN,
   the threat model is relatively simple. [RFC4891] describes how to
   protect tunnels using IPSec, but it is not clear whether this would
   be an important requirement.

   The dual-stack home gateway will need to provide basic security for
   IPv6 [6CPESec]. Other aspects are described in [RFC4864].

6. IANA Considerations

   This draft does not request any IANA action.

7. References

        7.1. Normative References

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

        7.2. Informative References

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

   [RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address Translation
             - Protocol Translation (NAT-PT)", RFC 2766, February 2000.

   [RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993,
             November 2000.

   [RFC3056] B. Carpenter, K. Moore, "Connection of IPv6 Domains via
             IPv4 Clouds", RFC3056, February 2001.

   [RFC4864] G. Van de Velde, T. Hain, R. Droms, B. Carpenter, E. Klein,
             "Local Network Protection for IPv6", RFC4864, May 2007.

   [RFC4891] R. Graveman, "Using IPsec to Secure IPv6-in-IPv4 Tunnels",
             RFC4891, May 2007.

   [RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
             Address Translator - Protocol Translator (NAT-PT) to
             Historic Status", RFC 4966, July 2007.




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   [RFC5214] F. Templin, T. Gleeson, and D. Thaler, "Intra-Site
             Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
             March 2008.

   [DSLite] A. Durand, R. Droms, B. Haberman, J. Woodyatt, "Dual-stack
             lite broadband deployments post IPv4 exhaustion", draft-
             durand-softwire-dual-stack-lite-01, work in progress.

   [IPUSAGE] Huston, G., IPv4 Address Report, March 2009,
             http://www.potaroo.net/tools/ipv4/index.html.

   [6RD]    R. Despres, "IPv6 Rapid Deployment on IPv4 infrastructures
             (6rd)", draft-despres-6rd-02, work in progress.

   [6CPE]   H. Singh, "IPv6 CPE Router Recommendations", draft-wbeebee-
             ipv6-cpe-router-03, work in progress.

   [6CPESec] J. Woodyatt, "Recommended Simple Security Capabilities in
             Customer Premises Equipment for Providing Residential IPv6
             Internet Service", draft-ietf-v6ops-cpe-simple-security-03,
             work in progress.



























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Author's Addresses

   Sheng Jiang
   Huawei Technologies Co., Ltd
   KuiKe Building, No.9 Xinxi Rd.,
   Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085
   P.R. China
   Phone: 86-10-82836774
   Email: shengjiang@huawei.com

   Dayong Guo
   Huawei Technologies Co., Ltd
   KuiKe Building, No.9 Xinxi Rd.,
   Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085
   P.R. China
   Phone: 86-10-82836284
   Email: guoseu@huawei.com

   Brian Carpenter
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland, 1142
   New Zealand
   Email: brian.e.carpenter@gmail.com























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