Internet Engineering Task Force (IETF) S. Jiang
Request for Comments: 6264 D. Guo
Category: Informational Huawei
ISSN: 2070-1721 B. Carpenter
University of Auckland
June 2011
An Incremental Carrier-Grade NAT (CGN) for IPv6 Transition
Abstract
Global IPv6 deployment was slower than originally expected. As IPv4
address exhaustion approaches, IPv4 to IPv6 transition issues become
more critical and less tractable. Host-based transition mechanisms
used in dual-stack environments cannot meet all transition
requirements. Most end users are not sufficiently expert to
configure or maintain host-based transition mechanisms. Carrier-
Grade NAT (CGN) devices with integrated transition mechanisms can
reduce the operational changes required during the IPv4 to IPv6
migration or coexistence period.
This document proposes an incremental CGN approach for IPv6
transition. It can provide IPv6 access services for IPv6 hosts and
IPv4 access services for IPv4 hosts while leaving much of a legacy
ISP network unchanged during the initial stage of IPv4 to IPv6
migration. Unlike CGN alone, incremental CGN also supports and
encourages smooth transition towards dual-stack or IPv6-only ISP
networks. An integrated configurable CGN device and an adaptive home
gateway (HG) device are described. Both are reusable during
different transition phases, avoiding multiple upgrades. This
enables IPv6 migration to be incrementally achieved according to real
user requirements.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Jiang, et al. Informational [Page 1]RFC 6264 Incremental CGN for IPv6 Transition June 2011
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/rfc6264.
Copyright Notice
Copyright (c) 2011 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. Introduction ....................................................2
2. An Incremental CGN Approach .....................................4
2.1. Incremental CGN Approach Overview ..........................4
2.2. Choice of Tunneling Technology .............................5
2.3. Behavior of Dual-Stack Home Gateway ........................6
2.4. Behavior of Dual-Stack CGN .................................6
2.5. Impact for Existing Hosts and Unchanged Networks ...........7
2.6. IPv4/IPv6 Intercommunication ...............................7
2.7. Discussion .................................................8
3. Smooth Transition towards IPv6 Infrastructure ...................8
4. Security Considerations ........................................10
5. Acknowledgements ...............................................10
6. References .....................................................10
6.1. Normative References ......................................10
6.2. Informative References ....................................11
1. Introduction
Global IPv6 deployment did not happen as was forecast 10 years ago.
Network providers were hesitant to make the first move while IPv4 was
and is still working well. However, IPv4 address exhaustion is
imminent. The dynamically updated IPv4 Address Report [IPUSAGE] has
analyzed this issue. IANA unallocated address pool exhaustion
occurred in February 2011, and at the time of publication, the site
predicts imminent exhaustion for Regional Internet Registry (RIR)
Jiang, et al. Informational [Page 2]RFC 6264 Incremental CGN for IPv6 Transition June 2011
unallocated address pools. Based on this fact, the Internet industry
appears to have reached consensus that global IPv6 deployment is
inevitable and has to be done expeditiously.
IPv4 to IPv6 transition issues therefore become more critical and
complicated for the approaching global IPv6 deployment. Host-based
transition mechanisms alone are not able to meet the requirements in
all cases. Therefore, network-based supporting functions and/or new
transition mechanisms with simple user-side operation are needed.
Carrier-Grade NAT (CGN) [CGN-REQS], also called NAT444 CGN or Large
Scale NAT, compounds IPv4 operational problems when used alone but
does nothing to encourage IPv4 to IPv6 transition. Deployment of
NAT444 CGN allows ISPs to delay the transition and therefore causes
double transition costs (once to add CGN and again to support IPv6).
CGN deployments that integrate multiple transition mechanisms can
simplify the operation of end-user services during the IPv4 to IPv6
migration and coexistence periods. 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 [DS-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 in this document.
This document proposes an incremental CGN approach for IPv6
transition. It does not define any new protocols or mechanisms but
describes how to combine existing proposals in an incremental
deployment. The approach is similar to DS-Lite but the other way
around. It mainly combines v4-v4 NAT with v6-over-v4 tunneling
functions. It can provide IPv6 access services for IPv6-enabled
hosts and IPv4 access services for IPv4 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 for the initial stage of IPv4 to
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 reusable devices during different
transition periods, so they do not need to be replaced as the
transition proceeds. This enables IPv6 migration to be incrementally
achieved according to the real user requirements.
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2. An Incremental CGN Approach
Today, most consumers primarily use IPv4. Network providers are
starting to provide IPv6 access services for end users. At the
initial stage of IPv4 to IPv6 migration, IPv4 connectivity and
traffic would continue to represent the majority of traffic for most
ISP networks. ISPs would like to minimize the changes to their IPv4
networks. Switching the whole ISP network into IPv6-only would be
considered 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 networks, 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 use of
deployment of IPv6 address space and services. ISPs facing only one
pressure out of two could adopt either CGN (for shortage of IPv4
addresses) or 6rd (to provide IPv6 connectivity services). The
approach described in this document is intended to address both of
these pressures at the same time by combining v4-v4 CGN with v6-over-
v4 tunneling technologies.
2.1. Incremental CGN Approach Overview
The incremental CGN approach we propose is illustrated in the
following figure.
+-------------+
|IPv6 Internet|
+-------------+
|
+---------------+----------+
+-----+ +--+ | IPv4 ISP +--+--+ | +--------+
|v4/v6|---|DS|=======+============| CGN |-------+---| IPv4 |
|Host | |HG| | Network +-----+ | | |Internet|
+-----+ +--+ +----------------------+---+ +--------+
_ _ _ _ _ _ _ _ _ _ _ |
()_6_over_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 - Customer Premises Equipment).
As shown in the figure above, 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-
Jiang, et al. Informational [Page 4]RFC 6264 Incremental CGN for IPv6 Transition June 2011
stack host is treated as an IPv4 host when it uses IPv4 access
service and as an IPv6 host when it uses an IPv6 access service. In
order to enable IPv4 hosts to access the IPv6 Internet and IPv6 hosts
to access IPv4 Internet, NAT64 can be integrated with the CGN; see
Section 2.6 for details regarding IPv4/IPv6 intercommunication. The
integration of such mechanisms is out of scope for this document.
Two types of devices need to be deployed in this approach: a dual-
stack home gateway (HG) and a dual-stack CGN. The dual-stack home
gateway integrates both IPv6 and IPv4 forwarding and v6-over-v4
tunneling functions. It should follow the requirements of [RFC6204],
including IPv6 prefix delegation. It may also integrate v4-v4 NAT
functionality. The dual-stack CGN integrates v6-over-v4 tunneling
and v4-v4 CGN functions as well as standard IPv6 and IPv4 routing.
The approach does not require any new mechanisms for IP packet
forwarding or encapsulation or decapsulation at tunnel endpoints.
The following sections describe how the HG and the incremental CGN
interact.
2.2. Choice of Tunneling Technology
In principle, this model will work with any form of tunnel between
the dual-stack 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 and be unsuitable
for home users.
6rd [RFC5569, RFC5969] technology appears suitable to support
v6-over-v4 tunneling with low operational cost. Generic Routing
Encapsulation (GRE) [RFC2784] with an additional auto-configuration
mechanism is also able to support v6-over-v4 tunneling. Other
tunneling mechanisms such as 6over4 [RFC2529], 6to4 [RFC3056], the
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214],
or Virtual Enterprise Traversal (VET) [RFC5558] could be considered.
If the ISP has an entirely MPLS infrastructure between the HG and the
dual-stack CGN, it would also be possible to use a IPv6 Provider Edge
(6PE) [RFC4798] tunnel directly over MPLS. This would, however, only
be suitable for an advanced HG that is unlikely to be found as a
consumer device and is not further discussed here. To simplify the
discussion, we assume the use of 6rd.
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2.3. Behavior of Dual-Stack Home Gateway
When a dual-stack home gateway receives a data packet from a host, it
will determine whether the packet is an IPv4 or IPv6 packet. The
packet will be handled by an IPv4 or IPv6 stack as appropriate. For
IPv4, and in the absence of v4-v4 NAT on the HG, the stack will
simply forward the packet to the CGN, which will normally be the IPv4
default router. If v4-v4 NAT is enabled, the HG translates the
packet source address from an HG-scope private IPv4 address into a
CGN-scope IPv4 address, performs port mapping if needed, and then
forwards the packet towards the CGN. The HG records the v4-v4
address and port mapping information for inbound packets, like any
other NAT.
For IPv6, the HG needs to encapsulate the data into an IPv4 tunnel
packet, which has the dual-stack CGN as the IPv4 destination. The HG
sends the new IPv4 packet towards the CGN, for example, using 6rd.
If the HG is linked to more than one CGN, it will record the mapping
information between the tunnel and the source IPv6 address for
inbound packets. Detailed considerations for the use of multiple
CGNs by one HG are for further study.
IPv4 packets from the CGN and encapsulated IPv6 packets from the CGN
will be translated or decapsulated according to the stored mapping
information and forwarded to the customer side of the HG.
2.4. Behavior of Dual-Stack CGN
When a dual-stack CGN receives an IPv4 data packet from a dual-stack
home gateway, it will determine whether the packet is a normal IPv4
packet, which is non-encapsulated, or a v6-over-v4 tunnel packet
addressed to a tunnel endpoint within the CGN. For a normal IPv4
packet, the CGN translates the packet source address from a CGN-scope
IPv4 address into a public IPv4 address, performs port mapping if
necessary, and then forwards it normally to the IPv4 Internet. The
CGN records the v4-v4 address and port mapping information for
inbound packets, just like a normal NAT does. For a v6-over-v4
tunnel packet, the tunnel endpoint within the CGN will decapsulate it
into the original IPv6 packet and then forward it to the 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 a further
v6-over-v4 tunnel to connect to the IPv6 Internet.
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Packets from the IPv4 Internet will be appropriately translated by
the CGN and forwarded to the HG, and packets from the IPv6 Internet
will be tunneled to the appropriate HG, using the stored mapping
information as necessary.
2.5. Impact for Existing Hosts and Unchanged Networks
This approach does not affect the unchanged parts of ISP networks at
all. Legacy IPv4 ISP networks and their IPv4 devices remain in use.
The existing IPv4 hosts, shown as the lower right box in Figure 1,
having either global IPv4 addresses or behind v4-v4 NAT, can connect
to the IPv4 Internet as it is now. These hosts, if they are upgraded
to become dual-stack hosts, can access the IPv6 Internet through the
IPv4 ISP network by using IPv6-over-IPv4 tunnel technologies. (See
Section 2.7 for a comment on MTU size.)
2.6. IPv4/IPv6 Intercommunication
For obvious commercial reasons, IPv6-only public services are not
expected as long as there is a significant IPv4-only customer base in
the world. However, IPv4/IPv6 intercommunication may become an issue
in many scenarios.
The IETF is expected to standardize a recommended IPv4/IPv6
translation algorithm, sometimes referred to as NAT64. It is
specified in the following:
o "Framework for IPv4/IPv6 Translation" [RFC6144]
o "IPv6 Addressing of IPv4/IPv6 Translators" [RFC6052]
o "DNS64: DNS Extensions for Network Address Translation from IPv6
Clients to IPv4 Servers" [RFC6147]
o "IP/ICMP Translation Algorithm" [RFC6145]
o "Stateful NAT64: Network Address and Protocol Translation from
IPv6 Clients to IPv4 Servers" [RFC6146]
o "An FTP ALG for IPv6-to-IPv4 Translation" [FTP-ALG]
The service, as described in the IETF's "Guidelines for Using IPv6
Transition Mechanisms during IPv6 Deployment" [RFC6180], provides for
stateless translation between hosts in an IPv4-only domain or hosts
that offer an IPv4-only service and hosts with an IPv4-embedded IPv6
address in an IPv6-only domain. It additionally provides access from
IPv6 hosts with general format addresses to hosts in an IPv4-only
domain or hosts that offer an IPv4-only service. It does not provide
any-to-any translation. One result is that client-only hosts in the
IPv6 domain gain access to IPv4 services through stateful
translation. Another result is that the IPv6 network operator has
Jiang, et al. Informational [Page 7]RFC 6264 Incremental CGN for IPv6 Transition June 2011
the option of moving servers into the IPv6-only domain while
retaining accessibility for IPv4-only clients through stateless
translation of an IPv4-embedded IPv6 address.
Also, "Architectural Implications of NAT" [RFC2993] applies across
the service just as in IPv4/IPv4 translation: apart from the fact
that a system with an IPv4-embedded IPv6 address is reachable across
the NAT, which is unlike IPv4, any assumption on the application's
part that a local address is meaningful to a remote peer and any use
of an IP address literal in the application payload is a source of
service issues. In general, the recommended mitigation for this is
as follows:
o Ideally, applications should use DNS names rather than IP address
literals in URLs, URIs, and referrals, and in general be network
layer agnostic.
o If they do not, the network may provide a relay or proxy that
straddles the domains. For example, an SMTP Mail Transfer Agent
(MTA) with both IPv4 and IPv6 connectivity handles IPv4/IPv6
translation cleanly at the application layer.
2.7. Discussion
For IPv4 traffic, the incremental CGN approach inherits all the
problems of CGN address-sharing techniques [ADDR-ISSUES] (e.g.,
scaling and the difficulty of supporting well-known ports for inbound
traffic). Application-layer problems created by double NAT are
beyond the scope of this document.
For IPv6 traffic, a user behind the DS HG will see normal IPv6
service. We observe that an IPv6 tunnel MTU of at least 1500 bytes
would ensure that the mechanism does not cause excessive
fragmentation of IPv6 traffic or excessive IPv6 path MTU discovery
interactions. 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] may be included as part of CGN functions.
3. Smooth Transition towards IPv6 Infrastructure
Transition from pure NAT444 CGN or 6rd to the incremental CGN
approach is straightforward. The HG and CGN devices and their
locations do not have to be changed; only software upgrading may be
needed. In the ideal model, described below, even software upgrading
is not necessary; reconfiguration of the devices is enough. NAT444
CGN solves the public address shortage issues in the current IPv4
Jiang, et al. Informational [Page 8]RFC 6264 Incremental CGN for IPv6 Transition June 2011
infrastructure. However, it does not contribute towards IPv6
deployment at all. The incremental CGN approach can inherit NAT444
CGN functions while providing overlay IPv6 services. 6rd mechanisms
can also transform smoothly into this incremental CGN model.
However, the home gateways need to be upgraded correspondingly to
perform the steps described below
The incremental CGN can also easily be transitioned to an IPv6-
enabled infrastructure, in which the ISP network is either dual-stack
or IPv6-only.
If the ISP prefers to move to dual-stack routing, the HG should
simply switch off its v6-over-v4 function when it observes native
IPv6 Router Advertisement (RA) or DHCPv6 traffic and then forward
both IPv6 and IPv4 traffic directly while the dual-stack CGN keeps
only its v4-v4 NAT function.
However, we expect ISPs to choose the approach described as
incremental CGN here because they intend to avoid dual-stack routing
and to move incrementally from IPv4-only routing to IPv6-only
routing. In this case, the ideal model for the incremental CGN
approach is that of an integrated configurable CGN device and an
adaptive HG device. The integrated CGN device will be able to
support multiple functions, including NAT444 CGN, 6rd router (or an
alternative tunneling mechanism), DS-Lite, and dual-stack forwarding.
The HG has to integrate the corresponding functions and be able to
detect relevant incremental changes on the CGN side. Typically, the
HG will occasionally poll the CGN to discover which features are
operational. For example, starting from a pure IPv4-only scenario
(in which the HG treats the CGN only as an IPv4 default router), the
HG would discover (by infrequent polling) when 6rd became available.
The home user would then acquire an IPv6 prefix. At a later stage,
the HG would observe the appearance of native IPv6 Route
Advertisement messages or DHCPv6 messages to discover the
availability of an IPv6 service including DS-Lite. Thus, when an ISP
decides to switch from incremental CGN to DS-Lite CGN, only a
configuration change or a minor software update is needed on the
CGNs. The home gateway would 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 the smooth transition model, both CGN and HG are reusable devices
during different transition periods. This avoids potential multiple
upgrades. Different regions of the same ISP network may be at
different stages of the incremental process, using identical
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equipment but with different configurations of the incremental CGN
devices in each region. Thus, IPv6 migration may be incrementally
achieved according to the real ISP and customer requirements.
4. Security Considerations
Security issues associated with NAT have been documented in [RFC2663]
and [RFC2993]. Security issues for large-scale address sharing,
including CGN, are discussed in [ADDR-ISSUES]. The present
specification does not introduce any new features to CGN itself and
hence no new security considerations. Security issues for 6rd are
documented in [RFC5569] and [RFC5969], and those for DS-Lite are
discussed in [DS-LITE].
Since the tunnels proposed here exist 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 an ISP could reasonably deem its infrastructure to provide
adequate security without the additional protection and overhead of
IPsec. The intrinsic risks of tunnels are described in [RFC6169],
which recommends that tunneled traffic should not cross border
routers. The incremental CGN approach respects this recommendation.
To avoid other risks caused by tunnels, it is important that any
security mechanisms based on packet inspection and any implementation
of ingress filtering are applied to IPv6 packets after they have been
decapsulated by the CGN. The dual-stack home gateway will need to
provide basic security functionality for IPv6 [RFC6092]. Other
aspects are described in [RFC4864].
5. Acknowledgements
Useful comments were made by Fred Baker, Dan Wing, Fred Templin,
Seiichi Kawamura, Remi Despres, Janos Mohacsi, Mohamed Boucadair,
Shin Miyakawa, Joel Jaeggli, Jari Arkko, Tim Polk, Sean Turner, and
other members of the IETF V6OPS working group.
6. References
6.1. Normative References
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
Jiang, et al. Informational [Page 10]RFC 6264 Incremental CGN for IPv6 Transition June 2011
[RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd)", RFC 5569, January 2010.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification", RFC
5969, August 2010.
6.2. Informative References
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC
2663, August 1999.
[RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993,
November 2000.
[RFC3053] Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
Tunnel Broker", RFC 3053, January 2001.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4798] De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
"Connecting IPv6 Islands over IPv4 MPLS Using IPv6
Provider Edge Routers (6PE)", RFC 4798, February 2007.
[RFC4864] Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
E. Klein, "Local Network Protection for IPv6", RFC 4864,
May 2007.
[RFC4890] Davies, E. and J. Mohacsi, "Recommendations for Filtering
ICMPv6 Messages in Firewalls", RFC 4890, May 2007.
[RFC4891] Graveman, R., Parthasarathy, M., Savola, P., and H.
Tschofenig, "Using IPsec to Secure IPv6-in-IPv4 Tunnels",
RFC 4891, May 2007.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, February 2010.
Jiang, et al. Informational [Page 11]RFC 6264 Incremental CGN for IPv6 Transition June 2011
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6092] Woodyatt, J., Ed., "Recommended Simple Security
Capabilities in Customer Premises Equipment (CPE) for
Providing Residential IPv6 Internet Service", RFC 6092,
January 2011.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, April 2011.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
April 2011.
[RFC6169] Krishnan, S., Thaler, D., and J. Hoagland, "Security
Concerns with IP Tunneling", RFC 6169, April 2011.
[RFC6180] Arkko, J. and F. Baker, "Guidelines for Using IPv6
Transition Mechanisms during IPv6 Deployment", RFC 6180,
May 2011.
[RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O.
Troan, Ed., "Basic Requirements for IPv6 Customer Edge
Routers", RFC 6204, April 2011.
[IPUSAGE] G. Huston, IPv4 Address Report, June 2011,
http://www.potaroo.net/tools/ipv4/index.html.
[DS-LITE] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", Work in Progress, May 2011.
[ADDR-ISSUES]
Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", Work in
Progress, March 2011.
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[CGN-REQS] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
A., and H. Ashida, "Common requirements for IP address
sharing schemes", Work in Progress, March 2011.
[FTP-ALG] van Beijnum, I., "An FTP ALG for IPv6-to-IPv4
Translation", Work in Progress, May 2011.
Authors' 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: jiangsheng@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
Jiang, et al. Informational [Page 13]
