One document matched: draft-ietf-v6ops-incremental-cgn-01.txt
Differences from draft-ietf-v6ops-incremental-cgn-00.txt
Network Working Group S. Jiang
Internet Draft D. Guo
Intended status: Informational Huawei Technologies Co., Ltd
Expires: December 22, 2010 B. Carpenter
University of Auckland
June 18, 2010
An Incremental Carrier-Grade NAT (CGN) for IPv6 Transition
draft-ietf-v6ops-incremental-cgn-01.txt
Status of this Memo
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This Internet-Draft will expire on December 22, 2010.
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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 (CGN) with integrated
transition mechanisms can simplify the operation of end users during
the IPv4/IPv6 migration or coexistence period. This document proposes
an incremental CGN approach 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 NAT444 CGN alone, it also supports and encourages
transition towards dual-stack or IPv6-only ISP networks. A smooth
transition mechanism is also described in this document. It
introduces an integrated configurable CGN device and an adaptive Home
Gateway (HG) device. Both HG and CGN are re-usable devices during
different transition periods. It avoid potential multiple upgrade.
ISPs have NOT to make a big transition decision. It enables IPv6
migration to be incrementally achieved according to the real user
requirements. So ISPs have NOT to make a big transition decision.
Table of Contents
1. Introduction.................................................3
2. An Incremental CGN Approach..................................4
2.1. Incremental CGN Approach Overview.......................4
2.2. Choice of tunnelling technology.........................5
2.3. Behaviour of Dual-stack Home Gateway....................6
2.4. Behaviour of Dual-stack CGN.............................6
2.5. Impact for existing end hosts and remaining networks....7
2.6. IPv4/IPv6 intercommunication............................7
2.7. Discussion..............................................7
3. Smooth transition towards IPv6 infrastructure................8
4. Security Considerations......................................9
5. IANA Considerations..........................................9
6. Acknowledgements.............................................9
7. Change Log [RFC Editor please remove].......................10
8. References..................................................11
8.1. Normative References...................................11
8.2. Informative References.................................11
Author's Addresses.............................................14
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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 in
all cases. Therefore, network supporting functions and/or new
transition mechanisms with simple user-side operation are needed.
Carrier-Grade NAT (CGN) [I-D.nishitani-cgn], also called NAT444 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).
CGN 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 Home
Gateway (HG) devices may be needed too. They may be provided by
network providers, depending on the specific business model. Dual-
stack lite [I-D.ietf-softwire-dual-stack-lite], also called DS-Lite,
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. Theoretically, DS-Lite can be used with
double encapsulation (IPv4-in-IPv6-in-IPv4) but this seems even less
likely to be accepted by an ISP and is not discussed further.
This document proposes an incremental CGN approach for IPv6
transition. The approach is similar to DS-Lite, 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 technology does not affect
legacy IPv4 hosts with global IPv4 addresses at all. It is suitable
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for the initial stage of IPv4/IPv6 migration. It also supports
transition towards dual-stack or IPv6-only ISP networks.
A smooth transition mechanism is also described in this document. It
introduces an integrated configurable CGN device and an adaptive HG
device. Both CGN and HG are re-usable devices during different
transition periods. It avoid potential multiple upgrade. It enables
IPv6 migration to be incrementally achieved according to the real
user requirements. So ISPs have NOT to make a big transition
decision.
2. An Incremental CGN Approach
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 most 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. Although some ISPs have
successfully deployed dual stack routers, others prefer not to do
this as their first step in IPv6. However, they currently face two
urgent pressures - to compensate for an immediate shortage of IPv4
addresses by deploying some method of address sharing, and to prepare
actively for the deployment of IPv6 address space and services. ISPs
facing only one pressure out of two could adopt either CGN (for
shortage of IPv6 addresses) or 6rd (to provide IPv6 connectivity
services). The approach described in this draft is targeting to
addresses both of these pressures at the same time by combining v4-v4
CGN with v6-over-v4 tunnelling technologies.
2.1. Incremental CGN Approach Overview
The incremental CGN approach we propose is illustrated as the
following figure.
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+-------------+
|IPv6 Internet|
+-------------+
|
+-------------+----------+
+-----+ +--+ | IPv4 ISP +--+--+ | +--------+
|v4/v6|----|DS|=====+==========| CGN |-------+---| IPv4 |
|Host | |HG| | Network +-----+ | | |Internet|
+-----+ +--+ +--------------------+---+ +--------+
_ _ _ _ _ _ _ _ _ _ _ |
()_6_o_4_ _t_u_n_n_e_l_() +---------------------+
| Existing IPv4 hosts |
+---------------------+
Figure 1: incremental CGN approach with IPv4 ISP network
DS HG = Dual-Stack Home Gateway (CPE).
As showed in the above figure, the ISP has not significantly changed
its IPv4 network. This approach 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 such mechanisms is out of
scope for this document
Two new types of devices need to be deployed in this approach: a
dual-stack home gateway, which may follow the requirements of
[I-D.ietf-v6ops-ipv6-cpe-router], and dual-stack CGN. 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 v4-v4 CGN functions.
2.2. Choice of tunnelling technology
In principle, this model will work with any form of tunnel between
the DS HG and the dual-stack CGN. However, tunnels that require
individual configuration are clearly undesirable because of their
operational cost. Configured tunnels based directly on [RFC4213] are
therefore not suitable. A tunnel broker according to [RFC3053] would
also have high operational costs.
Modified 6RD [RFC5569, I-D.ietf-softwire-ipv6-6rd] technology appears
suitable to support v6-over-v4 tunnelling with low operational cost.
Modified GRE [RFC2784] with additional auto-configuration mechanism
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is also suitable to support v6-over-v4 tunnelling. Other tunnelling
mechanisms such as 6over4 [RFC2529], 6to4 [RFC3056], the Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214] or Virtual
Enterprise Traversal (VET) [RFC5558] are also considered. If the ISP
has an entirely MPLS infrastructure between the HG and the dual-stack
CGN, it would also be possible to consider a 6PE [RFC4798] tunnel
directly over MPLS. This would, however, only be suitable for an
advanced HG that is unlikely to be found as a home gateway, and is
not further discussed here.
2.3. 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 to CGN 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,
then forwards it to CGN. The HG records 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 has the dual-stack CGN as the other end. Then the HG
sends the new IPv4 packet towards CGN.
The HG records 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.
2.4. Behaviour of Dual-stack CGN
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 records 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 records 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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2.5. Impact for existing end hosts and remaining networks
This approach 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. Of course, these hosts, if they are upgraded to become dual-
stack hosts, can access IPv6 Internet through IPv4 ISP network by
using IPv6-over-IPv4 tunnel technologies.
2.6. IPv4/IPv6 intercommunication
Although IPv6-only public services are not expected as long as there
is an IPv4-only customer base in the world, for obvious commercial
reasons. However, IPv4/IPv6 intercommunication may become issues in
many scenarios.
Each ISP can provide its IPv6-only customers with a network-layer
translation service to satisfy this need. Such a service is not fully
defined at this time, so we refer to it non-specifically as "NAT64".
Current work in the IETF is focussed on one particular proposal
[I-D.ietf-behave-v6v4-xlate-stateful]. The NAT64 service can be
provided as a common service located at the border between the ISP
and the IPv4 Internet, beyond the dual stack CGN from the customer's
viewpoint. It may be integrated into CGN devices too.
[I-D.boucadair-dslite-interco-v4v6] describes a proposal to enhance
DS-lite solution with an additional feature to ease interconnection
between IPv4 and IPv6 realms. Furthermore, home users may encounter
the problem of reaching legacy IPv4-only public services from IPv6-
only clients. This problem could already exist in Phase 1, but will
become more serious as time goes on.
2.7. Discussion
For IPv4 traffic, this approach 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.
If a different technology than v4-v4 NAT is chosen for IPv4 address
sharing, for example [I-D.ymbk-aplusp], the present approach could be
suitably modified, for example replacing the v4-v4 NAT function by
the A+P gateway function.
However, for IPv6 traffic, a user behind the DS HG will see normal
IPv6 service. We therefore observe that an IPv6 tunnel MTU of at
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least 1500 bytes would ensure that the mechanism does not cause
excessive fragmentation of IPv6 traffic nor excessive IPv6 path MTU
discovery interactions.
However, for IPv6 traffic, a user behind the DS HG will see normal
IPv6 service. This, and the absence of NAT problems for IPv6, will
create an incentive for users and application service providers to
prefer IPv6.
ICMP filtering [RFC4890] function may be included as part of CGN
functions.
3. Smooth transition towards IPv6 infrastructure
This incremental CGN approach can easily be transited from NAT444 CGN
or 6rd. NAT444 CGN solves the public address shortage issues in the
current IPv4 infrastructure. However, it does not contribute towards
IPv6 at all. This incremental CGN approach can inherit NAT444 CGN
function while providing overlay IPv6 services. 6rd mechanism can
also transform into this incremental CGN with small modifications.
One consideration is that home gateways also have to be changed
correspondently.
This incremental CGN can also easily be transited into IPv6-enabled
infrastructure, 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 while the dual-stack CGN only keeps its v4-v4
NAT function. However, this is considered an unlikely choice, since
we expect ISPs to choose the approach described here because they
want to avoid dual-stack deployment completely. For IPv6-only ISP
networks, the DS-Lite solution also needs dual-stack home gateway and
CGN devices.
The best business model for this approach is that an integrated
configurable CGN device and an adaptive HG device. The integrated CGN
hardware may be integrated multiple functions, include NAT444 CGN,
6rd router, incremental CGN, DS-Lite CGN and dual-stack forwarding.
It could act as different device with only software configuration
change while the hardware and its physical position/connectivity
remains no change at all. HG has also integrated these correspondent
functions, and be able to automatically detect the change on the CGN
side.
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For example, the appearance of IPv6 Route Advertisement messages or
DHCPv6 messages can be used as a signal of DS-Lite CGN. Then when an
ISP decides to switch from incremental CGN to DS-Lite CGN, it may be
that only a configuration change or a minor software update is needed
on the CGNs. The home gateway will then detect this change and switch
automatically to DS-Lite mode. The only impact on the home user will
be to receive a different IPv6 prefix.
In this smooth transition model, both CGN and HG are re-usable
devices during different transition periods. It avoid potential
multiple upgrade. It enables IPv6 migration to be incrementally
achieved according to the real user requirements. ISPs have NOT to
make a big transition decision.
4. Security Considerations
Security issues associated with NAT have been documented in [RFC2663]
and [RFC2993].
Further security analysis will be needed to understand double NAT
security issues and tunnel security issues. However, since the tunnel
proposed here exists entirely within a single ISP network, between
the HG/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. An ISP could
deem its infrastructure to have sufficient security without
additional protection of the tunnels.
The dual-stack home gateway will need to provide basic security for
IPv6 [I-D.ietf-v6ops-cpe-simple-security]. Other aspects are
described in [RFC4864].
5. IANA Considerations
This draft does not request any IANA action.
6. Acknowledgements
Useful comments were made by Fred Baker, Dan Wing, Fred Templin,
Seiichi Kawamura, Remi Despres, Janos Mohacsi, Mohamed Boucadair,
Shin Miyakawa and other members of the IETF V6OPS working group.
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7. Change Log [RFC Editor please remove]
draft-jiang-incremental-cgn-00, original version, 2009-02-27
draft-jiang-v6ops-incremental-cgn-00, revised after comments at
IETF74, 2009-04-23
draft-jiang-v6ops-incremental-cgn-01, revised after comments at v6ops
mailing list, 2009-06-30
draft-jiang-v6ops-incremental-cgn-02, remove normative parts (to be
documented in other WGs), 2009-07-06
draft-jiang-v6ops-incremental-cgn-03, revised after comments at v6ops
mailing list, 2009-09-24
draft-ietf-v6ops-incremental-cgn-00, accepted as v6ops wg docuemtn,
2009-11-17
draft-ietf-v6ops-incremental-cgn-01, revised after comments at v6ops
mailing list, 2010-06-21
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8. References
8.1. Normative References
[RFC2529] B. Carpenter, and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC2529, March 1999.
[RFC2784] D. Farinacci, T. Li, S. Hanks, D. Meyer and P. Traina,
"Generic Routing Encapsulation (GRE)", RFC 2784, March
2000.
8.2. Informative References
[RFC2663] P. Srisuresh and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC 2663,
August 1999.
[RFC2766] G. Tsirtsis and P. Srisuresh, "Network Address Translation
- Protocol Translation (NAT-PT)", RFC 2766, February 2000.
[RFC2993] T. Hain, "Architectural Implications of NAT", RFC 2993,
November 2000.
[RFC3053] A. Durand, P. Fasano, I. Guardini and D. Lento, "IPv6
Tunnel Broker", RFC 3053, January 2001.
[RFC3056] B. Carpenter and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001.
[RFC4213] E. Nordmark and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4798] J. De Clercq, D. Ooms, S. Prevost and F. Le Faucheur,
"Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider
Edge Routers (6PE)", RFC 4798, February 2007.
[RFC4864] G. Van de Velde, T. Hain, R. Droms, B. Carpenter and E.
Klein, "Local Network Protection for IPv6", RFC 4864, May
2007.
[RFC4890] E. Davies and J. Mohacsi, "Recommendations for Filtering
ICMPv6 Messages in Firewalls", RFC 4890, May 2007.
[RFC4891] R. Graveman, "Using IPsec to Secure IPv6-in-IPv4 Tunnels",
RFC4891, May 2007.
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[RFC4966] C. Aoun and E. Davies, "Reasons to Move the Network Address
Translator - Protocol Translator (NAT-PT) to Historic
Status", RFC 4966, July 2007.
[RFC5214] F. Templin, T. Gleeson and D. Thaler, "Intra-Site Automatic
Tunnel Addressing Protocol (ISATAP)", RFC 5214, March 2008.
[RFC5558] F. Templin, "Virtual Enterprise Traversal (VET)", RFC 5558,
February 2010.
[RFC5569] R. Despres, "IPv6 Rapid Deployment on IPv4 infrastructures
(6rd)", RFC 5569, January 2010.
[IPUSAGE] G. Huston, IPv4 Address Report, March 2009,
http://www.potaroo.net/tools/ipv4/index.html.
[I-D.ietf-softwire-dual-stack-lite]
A. Durand, "Dual-stack lite broadband deployments post IPv4
exhaustion", draft-ietf-softwire-dual-stack-lite, work in
progress.
[I-D.ietf-softwire-ipv6-6rd]
W. Townsley and O. Troan, "IPv6 via IPv4 Service Provider
Networks '6rd'", draft-ietf-softwire-ipv6-6rd, work in
progress.
[I-D.ietf-v6ops-ipv6-cpe-router]
H. Singh, W. Beebee, C. Donley, B. Stark and O. Troan,
"IPv6 CPE Router Recommendations", draft-ietf-v6ops-ipv6-
cpe-router, work in progress.
[I-D.ietf-v6ops-cpe-simple-security]
J. Woodyatt, "Recommended Simple Security Capabilities in
Customer Premises Equipment for Providing Residential IPv6
Internet Service", draft-ietf-v6ops-cpe-simple-security,
work in progress.
[I-D.ietf-behave-v6v4-xlate-stateful]
M. Bagnulo, P. Matthews and I. van Beijnum, "NAT64: Network
Address and Protocol Translation from IPv6 Clients to IPv4
Servers", draft-ietf-behave-v6v4-xlate-stateful, work in
progress.
[I-D.nishitani-cgn]
I. Yamagata, T. Nishitani, S. Miyahawa, A. nakagawa and H.
Ashida, "Common requirements for IP address sharing
schemes", draft-nishitani-cgn, work in progress.
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[I-D.ymbk-aplusp]
R. Bush, "The A+P Approach to the IPv4 Address Shortage",
draft-ymbk-aplusp, work in progress.
[I-D.boucadair-dslite-interco-v4v6]
M. Boucadair, et al, "Stateless IPv4-IPv6 Interconnection
in the Context of DS-lite Deployment", draft-boucadair-
dslite-interco-v4v6, work in progress.
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Author's Addresses
Sheng Jiang
Huawei Technologies Co., Ltd
Huawei Building, No.3 Xinxi Rd.,
Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085
P.R. China
Email: shengjiang@huawei.com
Dayong Guo
Huawei Technologies Co., Ltd
Huawei Building, No.3 Xinxi Rd.,
Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085
P.R. China
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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