behave F. Baker, Ed.
Internet-Draft Cisco Systems
Intended status: Standards Track X. Li, Ed.
Expires: January 6, 2010 C. Bao, Ed.
CERNET Center/Tsinghua University
K. Yin, Ed.
Cisco Systems
July 5, 2009
Framework for IPv4/IPv6 Translation
draft-ietf-behave-v6v4-framework-00
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Abstract
This note describes a framework for IPv4/IPv6 translation. This is
in the context of replacing NAT-PT, which was deprecated by RFC 4966,
and to enable networks to have IPv4 and IPv6 coexist in a somewhat
rational manner while transitioning to an IPv6 network.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Why Translation? . . . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Translation Objectives . . . . . . . . . . . . . . . . . . 7
1.4. Transition Plan . . . . . . . . . . . . . . . . . . . . . 9
2. Scenarios of the IPv4/IPv6 Translation . . . . . . . . . . . . 11
2.1. Scenario 1: an IPv6 network to the IPv4 Internet . . . . . 12
2.2. Scenario 2: the IPv4 Internet to an IPv6 network . . . . . 13
2.3. Scenario 3: the IPv6 Internet to an IPv4 network . . . . . 13
2.4. Scenario 4: an IPv4 network to the IPv6 Internet . . . . . 14
2.5. Scenario 5: an IPv6 network to an IPv4 network . . . . . . 15
2.6. Scenario 6: an IPv4 network to an IPv6 network . . . . . . 15
2.7. Scenario 7: the IPv6 Internet to the IPv4 Internet . . . . 16
2.8. Scenario 8: the IPv4 Internet to the IPv6 Internet . . . . 17
3. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1. Translation Components . . . . . . . . . . . . . . . . . . 18
3.1.1. Address Translation . . . . . . . . . . . . . . . . . 18
3.1.2. IP and ICMP Translation . . . . . . . . . . . . . . . 19
3.1.3. Maintaining Translation States . . . . . . . . . . . . 19
3.1.4. DNS ALG . . . . . . . . . . . . . . . . . . . . . . . 19
3.1.5. ALGs for Other Applications Layer Protocols . . . . . 20
3.2. Operation Mode for Specific Scenarios . . . . . . . . . . 20
3.2.1. Stateless Translation . . . . . . . . . . . . . . . . 20
3.2.2. Stateful Translation . . . . . . . . . . . . . . . . . 22
3.3. Layout of the Related Documents . . . . . . . . . . . . . 23
4. Translation in Operation . . . . . . . . . . . . . . . . . . . 25
5. Unsolved Problems . . . . . . . . . . . . . . . . . . . . . . 26
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Normative References . . . . . . . . . . . . . . . . . . . 27
9.2. Informative References . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
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1. Introduction
This note describes a framework for IPv4/IPv6 translation. This is
in the context of replacing NAT-PT [RFC2766], which was deprecated by
[RFC4966], and to enable networks to have IPv4 and IPv6 coexist in a
somewhat rational manner while transitioning to an IPv6-only network.
NAT-PT was deprecated to inform the community that NAT-PT had
operational issues and was not considered a viable medium or long
term strategy for either coexistence or transition. It wasn't
intended to say that IPv4<->IPv6 translation was bad. But the way
that NAT-PT did it was bad, and in particular using NAT-PT as a
general purpose solution was bad. As with the deprecation of the RIP
routing protocol [RFC1923] at the time the Internet was converting to
CIDR, the point was to encourage network operators to actually move
away from technology with known issues.
[RFC4213] describes the IETF's view of the most sensible transition
model. The IETF recommends, in short, that network operators
(transit providers, service providers, enterprise networks, small and
medium business, SOHO and residential customers, and any other kind
of network that may currently be using IPv4) obtain an IPv6 prefix,
turn on IPv6 routing within their networks and between themselves and
any peer, upstream, or downstream neighbors, enable it on their
computers, and use it in normal processing. This should be done
while leaving IPv4 stable, until a point is reached that any
communication that can be carried out could use either protocol
equally well. At that point, the economic justification for running
both becomes debatable, and network operators can justifiably turn
IPv4 off. This process is comparable to that of [RFC4192], which
describes how to renumber a network using the same address family
without a flag day. While running stably with the older system,
deploy the new. Use the coexistence period to work out such kinks as
arise. When the new is also running stably, shift production to it.
When network and economic conditions warrant, remove the old, which
is now no longer necessary.
The question arises: what if that is infeasible due to the time
available to deploy or other considerations? What if the process of
moving a network and its components or customers is starting too late
for contract cycles to affect IPv6 turn-up on important parts at a
point where it becomes uneconomical to deploy global IPv4 addresses
in new services? How does one continue to deploy new services
without balkanizing the network?
This document describes translation as one of the tools networks
might use to facilitate coexistence and ultimate transition.
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1.1. Why Translation?
Besides dual stack deployment, there are two fundamental approaches
one could take to interworking between IPv4 and IPv6: tunneling and
translation. One could - and in the 6NET we did - build an overlay
network using the new protocol inside tunnels. Various proposals
take that model, including 6to4 [RFC3056], Teredo [RFC4380], ISATAP
[RFC5214],and DS-Lite [I-D.durand-softwire-dual-stack-lite]. The
advantage of doing so is that the new is enabled to work without
disturbing the old protocol, providing connectivity between users of
the new protocol. There are two disadvantages to tunneling:
o Operators of old protocol networks are unable to offer services to
users of the new architecture, and those users are unable to use
the services of the underlying infrastructure - it is just
bandwidth, and
o It doesn't enable new protocol users to communicate with old
protocol users without dual-stack hosts.
As noted, in this work, we look at Internet Protocol translation as a
transition strategy. [RFC4864] forcefully makes the point that many
of the reasons people use Network Address Translators are met as well
by routing or protocol mechanisms that preserve the end to end
addressability of the Internet. What it did not consider is the case
in which there is an ongoing requirement to communicate with IPv4
systems, but configuring IPv4 routing is not in the network
operator's view the most desirable strategy, or is infeasible due to
a shortage of global address space. Translation enables the client
of a network, whether a transit network, an access network, or an
edge network, to access the services of the network and communicate
with other network users regardless of their protocol usage - within
limits. Like NAT-PT, IPv4/IPv6 translation under this rubric is not
a long term support strategy, but it is a medium term coexistence
strategy that can be used to facilitate a long term program of
transition.
1.2. Terminology
The following terminology is used in this document and other
documents related to it.
An IPv4 network: A specific network that has IPv4-only
implementation. This could be an enterprise's IPv4-only network
or an ISP's IPv4-only network. The term is used to illustrate an
IPv4 network under discussion is the small site comparing to the
global IPv4 Internet.
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An IPv6 network: A specific network that has IPv6-only
implementation. This could be an enterprise's IPv6-only network
or an ISP's IPv6-only network. The term is used to illustrate an
IPv6 network under discussion is the small site comparing to the
global IPv6 Internet.
Dual Stack implementation: A Dual Stack implementation, in this
context, comprises an enabled end system stack plus routing in the
network. It implies that two application instances are capable of
communicating using either IPv4 or IPv6 - they have stacks, they
have addresses, and they have any necessary network support
including routing.
IPv4-binding IPv6 addresses: The IPv6 addresses which have temporal
mapping relationship to specific IPv4 addresses. This
relationship is established and maintained as the states (mapping
table between IPv4 address/transport port and IPv6 address/
transport port) in the translator. The states are session
initiated, and the IPv4 and IPv6 address relationship is binding
from session initiation to the end.
IPv4-embedded IPv6 addresses: The IPv6 addresses which have explicit
mapping relationship to the IPv4 addresses. This relationship is
self described by embedding IPv4 address in the IPv6 address. The
IPv4-embedded IPv6 addresses can be used either in source address
translation or in destination address translation or in both.
IPv4-only: An IPv4-only implementation, in this context, comprises
an IPv4 enabled end system stack plus routing in the network. It
implies that two application instances are capable of
communicating using IPv4, but not IPv6 - they have an IPv4 stack,
addresses, and network support including IPv4 routing and
potentially IPv4/IPv4 translation, but some element is missing
that prevents communication with IPv6 hosts.
IPv6-only: An IPv6-only implementation, in this context, comprises
an IPv6 enabled end system stack plus routing in the network. It
implies that two application instances are capable of
communicating using IPv6, but not IPv4 - they have an IPv6 stack,
addresses, and network support including routing in IPv6, but some
element is missing that prevents communication with IPv4 hosts.
LIR Prefix: An IPv6 prefix assigned by a network operator for
embedding IPv4 addresses into IPv6 addresses. In this case, each
network running a translator will create a representation of the
whole IPv4 address space in the IPv6 address space.
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LIR: See Local Internet Registry.
Local Internet Registry: A Local Internet Registry (LIR) is an
organization which has received an IP address allocation from a
Regional Internet Registry (RIR), and which may assign parts of
this allocation to its own internal network or those of its
customers. An LIR is thus typically an Internet service provider
or an enterprise network.
State: "State" refers to dynamic information that is stored in a
network element. For example, if two systems are connected by a
TCP connection, each stores information about the connection,
which is called "connection state". In this context, the term
refers to dynamic correlations between IP addresses on either side
of a translator, or {IP Address, Transport type, transport port
number} tuples on either side of the translator. Of stateful
algorithms, there are at least two major flavors depending on the
kind of state they maintain:
Hidden state: the existence of this state is unknown outside the
network element that contains it.
Known state: the existence of this state is known by other
network elements.
Stateful Translation: A translation algorithm may be said to
"require state in a network element" or be "stateful" if the
transmission or reception of a packet creates or modifies a data
structure in the relevant network element.
Stateless Translation: A translation algorithm that is not
"stateful" is "stateless". It derives its needed information
algorithmically from the messages it is translating.
Stateful Translator: A translator if it uses stateful translation
algorithm in one side of address (either source or destination
address) during its session initiating. The stateful translator
also uses the stateless translation algorithm for other side of
address. IPv4-binding IPv6 address procedure will be used in
stateful address translation.
Stateless Translator: A translator if it uses only stateless
translation algorithm in both destination address and source
address. The IPv4-embedded IPv6 addresses will be used in both
destination address and source address translation.
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Well-Known Prefix: The prefix assigned by IANA for embedding IPv4
addresses into IPv6 addresses. In this case, there would be a
single representation of a public IPv4 address in the IPv6 address
space.
1.3. Translation Objectives
In any translation model, there is a question of objectives.
Ideally, one would like to make any system and any application
running on it able to "talk with" - exchange datagrams supporting
applications with - any other system running the same application
regardless of whether they have an IPv4 stack and connectivity or
IPv6 stack and connectivity. That was the model for NAT-PT, and the
things it necessitated led to scaling and operational difficulties.
So the question comes back to what different kinds of connectivity
can be easily supported and what kinds are harder, and what
technologies are needed to at least pick the low-hanging fruit. We
observe that applications today fall into three main categories:
Client/Server Application: Per whatis.com, "'Client/server'
describes the relationship between two computer programs in which
one program, the client, makes a service request from another
program, the server, which fulfills the request." In networking,
the behavior of the applications is that connections are initiated
from client software and systems to server software and systems.
Examples include mail handling between an end user and his mail
system (POP3, IMAP, and MUA->MTA SMTP), FTP, the web, and DNS name
translation.
Peer to Peer Application: A P2P application is an application that
uses the same endpoint to initiate outgoing sessions to peering
hosts as well as accept incoming sessions from peering hosts.
These in turn fall broadly into two categories:
Peer to peer infrastructure applications: Examples of
"infrastructure applications" include SMTP between MTAs,
Network News, and SIP. Any MTA might open an SMTP session with
any other at any time; any SIP Proxy might similarly connect
with any other SIP Proxy. An important characteristic of these
applications is that they use ephemeral sessions - they open
sessions when they are needed and close them when they are
done.
Peer to peer file exchange applications: Examples of these
include Limewire, BitTorrent, and UTorrent. These are
applications that open some sessions between systems and leave
them open for long periods of time, and where ephemeral
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sessions are important, are able to learn about the reliability
of peers from history or by reputation. They use the long term
sessions to map content availability. Short term sessions are
used to exchange content. They tend to prefer to ask for
content from servers that they find reliable and available.
If the question is the ability to open connections between systems,
then one must ask who opens connections.
o We need a technology that will enable systems that act as clients
to be able to open sessions with other systems that act as
servers, whether in the IPv6->IPv4 direction or the IPv4->IPv6
direction. Ideally, this is stateless; especially in a carrier
infrastructure, the preponderance of accesses will be to servers,
and this optimizes access to them. However, a stateful algorithm
is acceptable if the complexity is minimized and a stateless
algorithm cannot be constructed.
o We also need a technology that will allow peers to connect with
each other, whether in the IPv6->IPv4 direction or the IPv4->IPv6
direction. Again, it would be ideal if this was stateless, but a
stateful algorithm is acceptable if the complexity is minimized
and a stateless algorithm cannot be constructed.
o In many situations, hosts are purely clients. In those
situations, we do not need an algorithm to enable connections to
those hosts
The complexity arguments bring us in the direction of hidden state:
if state must be shared between the application and the translator or
between translation components, complexity and deployment issues are
greatly magnified. The objective of the translators is to reduce, as
much as possible, the software changes in the hosts necessary to
support translation.
NAT-PT is an example of a facility with known state - at least two
software components (the data plane translator and the DNS
Application Layer Gateway, which may be implemented in the same or
different systems) share and must coordinate translation state. A
typical IPv4/IPv4 NAT implements an algorithm with hidden state.
Obviously, stateless translation requires less computational overhead
than stateful translation, and less memory to maintain the state,
because the translation tables and their associated methods and
processes exist in a stateful algorithm and don't exist in a
stateless one.
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1.4. Transition Plan
While the design of IPv4 made it impossible for IPv6 to be compatible
on the wire, the designers intended that it would coexist with IPv4
during a period of transition. The primary mode of coexistence was
dual-stack operation - routers would be dual-stacked so that the
network could carry both address families, and IPv6-capable hosts
could be dual-stack to maintain access to IPv4-only partners. The
goal was that the preponderance of hosts and routers in the Internet
would be IPv6-capable long before IPv4 address space allocation was
completed. At this time, it appears the exhaustion of IPv4 address
space will occur before significant IPv6 adoption.
Curran's "A Transition Plan for IPv6" [RFC5211] proposes a three-
phase progression:
Preparation Phase (current): characterized by pilot use of IPv6,
primarily through transition mechanisms defined in [RFC4213], and
planning activities.
Transition Phase (2010 through 2011): characterized by general
availability of IPv6 in provider networks which SHOULD be native
IPv6; organizations SHOULD provide IPv6 connectivity for their
Internet-facing servers, but SHOULD still provide IPv4-based
services via a separate service name.
Post-Transition Phase (2012 and beyond): characterized by a
preponderance of IPv6-based services and diminishing support for
IPv4-based services.
Various timelines have been discussed, but most will agree with the
pattern of above three transition phases, also known as "S" curve
transition pattern.
In each of these phases, the coexistence problem and solution space
has a different focus:
Preparation Phase: Coexistence tools are needed to facilitate early
adopters by removing impediments to IPv6 deployment, and to assure
that nothing is lost by adopting IPv6, in particular that the IPv6
adopter has unfettered access to the global IPv4 Internet
regardless of whether they have a global IPv4 address (or any IPv4
address or stack at all.) While it might appear reasonable for
the cost and operational burden to be borne by the early adopter,
the shared goal of promoting IPv6 adoption would argue against
that model. Additionally, current IPv4 users should not be forced
to retire or upgrade their equipment and the burden remains on
service providers to carry and route native IPv4. This is known
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as the early stage of the "S" curve.
Transition Phase: This is the last stage of "S" curve. During the
middle stage of "S" curve, while IPv6 adoption can be expected to
accelerate, there will still be a significant portion of the
Internet operating in IPv4-only or preferring IPv4. During this
phase the norm shifts from IPv4 to IPv6, and coexistence tools
evolve to ensure interoperability between domains that may be
restricted to IPv4 or IPv6.
Post-Transition Phase: In this phase, IPv6 is ubiquitous and the
burden of maintaining interoperability shifts to those who choose
to maintain IPv4-only systems. While these systems should be
allowed to live out their economic life cycles, the IPv4-only
legacy users at the edges should bear the cost of coexistence
tools, and at some point service provider networks should not be
expected to carry and route native IPv4 traffic.
The choice between the terms "transition" versus "coexistence" has
engendered long philosophical debate. "Transition" carries the sense
that we are going somewhere, while "coexistence" seems more like we
are sitting somewhere. Historically with IETF, "transition" has been
the term of choice [RFC4213][RFC5211], and the tools for
interoperability have been called "transition mechanisms". There is
some perception or conventional wisdom that adoption of IPv6 is being
impeded by the deficiency of tools to facilitate interoperability of
nodes or networks that are constrained (in some way, fully or
partially) from full operation in one of the address families. In
addition, it is apparent that transition will involve a period of
coexistence; the only real question is how long that will last.
Thus, coexistence is an integral part of the transition plan, not in
conflict with it, but there will be a balancing act. It starts out
being a way for early adopters to easily exploit the bigger IPv4
Internet, and ends up being a way for late/never adopters to hang on
with IPv4 (at their own expense, with minimal impact or visibility to
the Internet). One way to look at solutions is that cost incentives
(both monetary cost and the operational overhead for the end user)
should encourage IPv6 and discourage IPv4. That way natural market
forces will keep the transition moving - especially as the legacy
IPv4-only stuff ages out of use. There will come a time to set a
date after which no one is obligated to carry native IPv4 but it
would be premature to attempt to do so yet. The end goal should not
be to eliminate IPv4 by fiat, but rather render it redundant through
ubiquitous IPv6 deployment. IPv4 may never go away completely, but
rational plans should move the costs of maintaining IPv4 to those who
insist on using it after wide adoption of IPv6.
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2. Scenarios of the IPv4/IPv6 Translation
It is important to note that the choice of translation solution and
the assumptions about the network where they are used impact the
consequences. A translator for the general case has a number of
issues that a translator for a more specific situation may not have
at all.
The intention of this document is to focus on the network-based
translation solutions under all kinds of situations. All IPv4/IPv6
translation cases can be easily described in terms of "interoperation
between a set of systems that only communicate using IPv4 and a set
of systems that only communicate using IPv6", but the differences at
a detail level make them interesting.
Based on transition plan described in Section 1.4, there are four
types of IPv4/IPv6 translation interoperation cases:
a. Interoperation between an IPv6 network and the IPv4 Internet
b. Interoperation between an IPv4 network and the IPv6 Internet
c. Interoperation between an IPv6 network and an IPv4 network
d. Interoperation between the IPv6 Internet and the IPv4 Internet
Each one in the above can be divided into two scenarios, depends on
whether the IPv6 initiates communication or the IPv4 initiates
communication. So there are totally eight scenarios.
Scenario 1: an IPv6 network to the IPv4 Internet
Scenario 2: the IPv4 Internet to an IPv6 network
Scenario 3: the IPv6 Internet to an IPv4 network
Scenario 4: an IPv4 network to the IPv6 Internet
Scenario 5: an IPv6 network to an IPv4 network
Scenario 6: an IPv4 network to an IPv6 network
Scenario 7: The IPv6 Internet to the IPv4 Internet
Scenario 8: The IPv4 Internet to the IPv6 Internet
We will discuss each scenario in detail in next section.
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2.1. Scenario 1: an IPv6 network to the IPv4 Internet
Due to the lack of the public routable IPv4 addresses or under other
technical or economical constrains, the ISP's or enterprise's network
is IPv6-only, but the hosts in the network require communicating with
the global IPv4 Internet.
This is the typical scenario for what we sometimes call "greenfield"
deployments. One example is an enterprise network that wishes to
operate only IPv6 for operational simplicity, but still wishes to
reach the content in the IPv4 Internet. The greenfield enterprise
scenario is different in the sense that there is only one place that
the enterprise can easily modify: the border between its network and
the IPv4 Internet. Obviously, the IPv4 Internet operates the way it
already does. But in addition, the hosts in the enterprise network
are commercially available devices, personal computers with existing
operating systems. This restriction drives us to a "one box" type of
solution, where IPv6 can be translated into IPv4 to reach the public
Internet.
Other cases that have been mentioned include wireless ISP networks
and sensor networks. This bears a striking resemblance to this
scenario as well, if one considers the ISP network to simply be a
very special kind of enterprise network.
--------
// \\ -----------
/ \ // \\
/ +----+ \
| |XLAT| |
| The IPv4 +----+ An IPv6 |
| Internet +----+ Network | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS-ALG
\ / \\ //
\\ // -----------
--------
<====
Figure 1: Scenario 1
Currently, there are two proposed solutions for this scenario: NAT64
[I-D.bagnulo-behave-nat64] as the stateful translation and IVI
[I-D.xli-behave-ivi] as the stateless translation schemes,
respectively. The NAT64 can support any IPv6 addresses in an IPv6
network communicate with the IPv4 Internet, while IVI can support a
subset of the IPv6 addresses in an IPv6 network communicate with the
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IPv4 Internet. In addition, IVI can also support Scenario 2, while
NAT64 cannot.
2.2. Scenario 2: the IPv4 Internet to an IPv6 network
This scenario is predicted to become increasingly important as the
network administration under pressure to put the IPv6-only servers in
its network, while the majority of the Internet users are still in
the IPv4 Internet. For example, for an IPv6 operator, it may be a
difficult proposition to leave all IPv4-only devices without
reachability. Thus, with translator solution for this scenario, the
benefits would be clear. Not only could servers move directly to
IPv6 without trudging through a difficult transition period, but they
could do so without risk of losing connectivity with the IPv4-only
Internet.
--------
// \\ ----------
/ \ // \\
/ +----+ \
| |XLAT| |
| The IPv4 +----+ An IPv6 |
| Internet +----+ Network | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS-ALG
\ / \\ //
\\ // ----------
--------
====>
Figure 2: Scenario 2
In general, this scenario presents the hard case for translation
scheme. The stateful translation such as NAT-PT [RFC2766] can be
used in this scenario, but it requires tightly couple DNS ALG in the
translator and this technique is deprecated by IETF [RFC4966].
The stateless translation solution IVI [I-D.xli-behave-ivi] in
Scenario 1 can also work in Scenario 2, since it can support IPv4
initiated communications with the subset of the IPv6 addresses in an
IPv6 network.
2.3. Scenario 3: the IPv6 Internet to an IPv4 network
There is a requirement for the legacy IPv4 network to provide
services to the IPv6 hosts.
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-----------
---------- // \\
// \\ / \
/ +----+ \
| |XLAT| |
| An IPv4 +----+ The IPv6 |
| Network +----+ Internet | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS ALG
\\ // \ /
--------- \\ //
-----------
<====
Figure 3: Scenario 3
The IPv6 initiated communication can be achieved through stateful
translator. For example, NAT64 [I-D.bagnulo-behave-nat64] can
support this scenario.
2.4. Scenario 4: an IPv4 network to the IPv6 Internet
Due to the technical or economical constrains, the ISP's or
enterprise's network is IPv4-only, and the IPv4-only hosts may
require the communicate with the global IPv6 Internet.
-----------
---------- // \\
// \\ / \
/ +----+ \
| |XLAT| |
| An IPv4 +----+ The IPv6 | XLAT: v4/v6
| Network +----+ Internet | Translator
| |DNS | | DNS: DNS ALG
\ +----+ /
\\ // \ /
--------- \\ //
----------
=====>
Figure 4: Scenario 4
In general, this scenario presents the hard case for translation
scheme. The stateful translation such as NAT-PT [RFC2766] can be
used in this scenario, but it requires tightly couple DNS ALG in the
translator and this technique is deprecated by IETF [RFC4966].
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From transition phase discussion in Section 1.4, this scenario will
probably only occur when we well pass the early stage of "S" curve.
The v4/v6 transition already move to right direction. Therefore, the
in-network translation is not viable for this scenario and other
techniques should be considered.
2.5. Scenario 5: an IPv6 network to an IPv4 network
This is one of scenarios when both an IPv4 network and an IPv6
network are within the same organization, or this interoperation
especially as a service within a large network such as an enterprise
or ISP network or between peer networks.
The IPv4 addresses used are either public IPv4 addresses or [RFC1918]
addresses. The IPv6 addresses used are either public IPv6 addresses
or ULA (Unique Local Address) [RFC4193].
--------- ---------
// \\ // \\
/ +----+ \
| |XLAT| |
| An IPv4 +----+ An IPv6 |
| Network +----+ Network | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS ALG
\\ // \\ //
-------- ---------
<====
Figure 5: Scenario 5
The translation requirement from this scenario has no significant
difference from scenario 1, so both the stateful and stateless
translator schemes discussed in Section 2.1 apply here.
2.6. Scenario 6: an IPv4 network to an IPv6 network
This is another scenario when both an IPv4 network and an IPv6
network are within the same organization, or this interoperation
especially as a service within a large network such as an enterprise
or ISP network or between peer networks.
The IPv4 addresses used are either public IPv4 addresses or [RFC1918]
addresses. The IPv6 addresses used are either public IPv6 addresses
or ULA (Unique Local Address) [RFC4193].
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-------- ---------
// \\ // \\
/ +----+ \
| |XLAT| |
| An IPv4 +----+ An IPv6 |
| Network +----+ Network | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS ALG
\\ // \\ //
-------- ---------
====>
Figure 6: Scenario 6
The translation requirement from this scenario has no significant
difference from scenario 2, so the translator scheme discussed in
Section 2.2 applies here.
2.7. Scenario 7: the IPv6 Internet to the IPv4 Internet
This seems the ideal case for in-network translation technology,
where any IPv6-only host on the global Internet can open connection
to any IPv4-only host on the global Internet.
-------- ---------
// \\ // \\
/ \ / \
/ +----+ \
| |XLAT| |
| The IPv4 +----+ The IPv6 |
| Internet +----+ Internet | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS ALG
\ / \ /
\\ // \\ //
-------- ---------
<====
Figure 7: Scenario 7
Due to the huge difference between the address spaces of the IPv4
Internet and the IPv6 Internet, there is no viable translation
techniques to handle the unlimited IPv6 address translation.
If we ever run into this scenario, fortunately, the IPv4-IPv6
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transition already proceeds after early stage of "S" curve,
therefore, there is no obvious business reason to demand translation
solution as only transition strategy.
2.8. Scenario 8: the IPv4 Internet to the IPv6 Internet
This seems the ideal case for in-network translation technology,
where any IPv4-only on the global Internet host can open connection
to any IPv6-only host on the global Internet.
-------- ---------
// \\ // \\
/ \ / \
/ +----+ \
| |XLAT| |
| The IPv4 +----+ The IPv6 |
| Internet +----+ Internet | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS ALG
\ / \ /
\\ // \\ //
-------- ---------
====>
Figure 8: Scenario 8
Due to the huge difference between the address spaces of the IPv4
Internet and the IPv6 Internet, there is no viable translation
techniques to handle the unlimited IPv6 address translation.
If we ever run into this scenario, fortunately, the IPv4-IPv6
transition already proceeds after early stage of "S" curve,
therefore, there is no obvious business reason to demand translation
solution as only transition strategy.
3. Framework
Having laid out the preferred transition model and the options for
implementing it (Section 1.1), defined terms (Section 1.2),
considered the requirements (Section 1.3), considered the transition
model (Section 1.4), and considered the kinds of scenarios the
facility would support (Section 2), we now turn to a framework for
IPv4/IPv6 translation. The framework contains the following
components.
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o Address translation
o IP and ICMP translation
o Maintaining translation states
o DNS ALG
o ALGs for other applications layer protocols (e.g., FTP)
3.1. Translation Components
3.1.1. Address Translation
When the IPv6/IPv4 translation is performed, we should specify how an
individual IPv6 address is translated to a corresponding IPv4
address, and vice versa, in cases where an algorithmic mapping is
used. This includes the choice of IPv6 prefix and the choice of
method by which the remainder of the IPv6 address is derived from an
IPv4 address. [translator-addressing-00] {Editor's Note: Waiting for
the draft}
Note that translating IPv4 address to IPv6 address and translating
IPv6 address to IPv4 address are different for the stateless
translation and the stateful translation.
[I-D.xli-behave-v4v6-prefix].
o For the stateless translation, the algorithmic mapping algorithm
is used both to translate IPv4 address to IPv6 address and to
translate IPv6 address to IPv4 address. In this case, blocks of
service provider's IPv4 addresses are mapped into IPv6 and used by
physical IPv6 hosts. The original IPv4 form of these blocks of
service provider's IPv4 addresses are used to represent the
physical IPv6 hosts in IPv4. Note that the stateless translation
supports both IPv6 initiated as well as IPv4 initiated
communications.
o For the stateful translation, the algorithmic mapping algorithm is
used to translate IPv4 address to IPv6 address, while a session
initiated state table is used to translate IPv6 address to IPv4
address. In this case, blocks of service provider's IPv4
addresses are maintained in the translator as the IPv4 address
pools and dynamically bind to the specific IPv6 addresses. The
original IPv4 form of these blocks of service provider's IPv4
addresses are used to represent the physical IPv6 host in IPv4.
However, due to the dynamical binging, the stateful translation
only supports the IPv6 initiated communication.
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3.1.2. IP and ICMP Translation
The IPv6/IPv4 translator is based on the update to the Stateless IP/
ICMP Translation Algorithm (SIIT) described in [RFC2765]. The
algorithm translates between IPv4 and IPv6 packet headers (including
ICMP headers) [I-D.ietf-behave-v6v4-xlate].
The IP and ICMP translation document [I-D.ietf-behave-v6v4-xlate]
addresses in both stateless and stateful modes. In the stateless
mode, translation information is carried in the address itself,
permitting both IPv4->IPv6 and IPv6->IPv4 session establishment with
neither state nor configuration in the IP/ICMP translator. In the
stateful mode, translation state is maintained between IPv4 address/
transport port tuples and IPv6 address/transport port tuples,
enabling IPv6 systems to open sessions with IPv4 systems. The choice
of operational mode is made by the operator deploying the network and
is critical to the operation of the applications using it.
3.1.3. Maintaining Translation States
For the stateful translator, besides IP and ICMP translation, special
action must be taken to maintain the translation states. NAT64
[I-D.ietf-behave-v6v4-xlate-stateful] describes a mechanism for
maintaining states.
3.1.4. DNS ALG
[I-D.ietf-behave-dns64] describes the mechanisms by which a DNS
Translator is intended to operate. It is designed to operate on the
basis of known but fixed state: the resource records, and therefore
the names and addresses, are known to network elements outside of the
data plane translator, but the process of serving them to
applications does not interact with the data plane translator in any
way.
There are at least three possible implementations of a DNS ALG:
Static records: One could literally populate DNS with corresponding
A and AAAA records. This is most appropriate for stub services
such as access to a legacy printer pool.
Dynamic Translation of static records: In more general operation,
the expected behavior is for the application to request both A and
AAAA records, and for an A record to be (retrieved and) translated
by the DNS ALG if and only if no reachable AAAA record exists.
This has ephemeral issues with cached translations, which can be
dealt with by caching only the source record and forcing it to be
translated whenever accessed.
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Static or Dynamic Translation of Dynamic DNS records: In Dynamic DNS
usage, a system could potentially report the translation of a name
using an IPv4 binding IPv6 Address, or using both an IPv4 binding
IPv6 Address and some other address. The DNS ALG has several
options; it could store a AAAA record for an IPv4 binding IPv6
address and depend on translation of that for A records inline, it
could store both an A and a AAAA record, or (when there is another
IPv6 address as well which is stored as the AAAA record) it could
store only the A record.
3.1.5. ALGs for Other Applications Layer Protocols
In addition, some applications require special support. An example
is FTP. FTP's active mode doesn't work well across NATs without
extra support such as SOCKS. Across NATs, it generally uses passive
mode. However, the designers of FTP inexplicably wrote different and
incompatible passive mode implementations for IPv4 and IPv6 networks.
Hence, either they need to fix FTP, or a translator must be written
for the application. Other applications may be similarly broken.
As a general rule, a simple operational recommendation will work
around many application issues, which is that there should be a
server in each domain or an instance of the server should have an
interface in each domain. For example, an SMTP MTA may be confused
by finding an IPv6 address in its HELO when it is connected to using
IPv4 (or vice versa), but would perfectly well if it had an interface
in both the IPv4 and IPv6 domains and was used as an application
layer bridge between them.
3.2. Operation Mode for Specific Scenarios
Currently, the proposed solutions for the IPv6/IPv4 translation are
classified into stateless translation and stateful translation.
3.2.1. Stateless Translation
For the stateless translation, the translation information is carried
in the address itself, permitting both IPv4->IPv6 and IPv6->IPv4
sessions establishment. The stateless translation supports end-to-
end address transparency and has better scalability compared with the
stateful translation. [I-D.ietf-behave-v6v4-xlate]
[I-D.xli-behave-ivi].
Although the stateless translation mechanisms typically put
constraints on what IPv6 addresses can be assigned to IPv6 hosts that
want to communicate with IPv4 destinations using an algorithmic
mapping. For the Scenarios 1 ("an IPv6 network to the IPv4
Internet"), it is not a serious drawback, since the address
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assignment policy can be applied to satisfy this requirement for the
IPv6 hosts which need the communication ability to the IPv4 Internet.
In addition, the stateless translator supports Scenario 2 ("the IPv4
Internet to an IPv6 network"), it means that not only could servers
move directly to IPv6 without trudging through a difficult transition
period, but they could do so without risk of losing connectivity with
the IPv4-only Internet.
The stateless translator can be used for Scenario 1, 2, 5 and 6, i.e.
it supports "an IPv6 network to the IPv4 Internet", "the IPv4
Internet to an IPv6 network", "an IPv6 network to an IPv4 network"
and "an IPv4 network to an IPv6 network".
--------
// \\ -----------
/ \ // \\
/ +----+ \
| |XLAT| |
| The IPv4 +----+ An IPv6 |
| Internet +----+ Network | XLAT: Stateless v4/v6
| |DNS | (address | Translator
\ +----+ subset) / DNS: DNS-ALG
\ / \\ //
\\ // ----------
--------
<====>
Figure 9: Stateless translator for Scenarios 1 and 2
-------- ---------
// \\ // \\
/ +----+ \
| |XLAT| |
| An IPv4 +----+ An IPv6 |
| Network +----+ Network | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS ALG
\\ // \\ //
-------- ---------
<====>
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Figure 10: Stateless translator for Scenarios 5 and 6
The implementation of the stateless translator needs to refer to
[I-D.ietf-behave-v6v4-xlate], [translator-addressing-00] {Editor's
Note: Waiting for the draft}, and [I-D.ietf-behave-dns64].
3.2.2. Stateful Translation
For the stateful translation, the translation state is maintained
between IPv4 address/port pairs and IPv6 address/port pairs, enabling
IPv6 systems to open sessions with IPv4 systems
[I-D.ietf-behave-v6v4-xlate] [I-D.ietf-behave-v6v4-xlate-stateful].
The stateful translator can be used for Scenario 1, 3 and 5, i.e. it
supports "an IPv6 network to the IPv4 Internet", "the IPv6 Internet
to an IPv4 network" and "an IPv6 network to an IPv4 network".
For Scenario 1, any IPv6 addresses in an IPv6 network can use the
stateful translator, however it typically only supports initiation
from the IPv6 side, and does not result in stable addresses that can
be used in DNS and other protocols and applications that do not deal
well with highly dynamic addresses.
--------
// \\ -----------
/ \ // \\
/ +----+ \
| |XLAT| |
| The IPv4 +----+ An IPv6 |
| Internet +----+ Network | XLAT: Stateful v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS-ALG
\ / \\ //
\\ // -----------
--------
<====
Figure 11: Stateful translator for Scenario 1
For scenario 3, the servers using IPv4 private addresses [RFC1918]
and being reached from the IPv6 Internet basically includes the cases
that for whatever reason the servers cannot be upgraded to IPv6 and
they don't have public IPv4 addresses and it would be useful to allow
IPv6 nodes in the IPv6 Internet to reach those servers.
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-----------
---------- // \\
// \\ / \
/ +----+ \
| |XLAT| |
| An IPv4 +----+ The IPv6 |
| Network +----+ Internet | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS ALG
\\ // \ /
--------- \\ //
-----------
<====
Figure 12: Stateful translator for Scenario 3
Similarly, the stateless translator can also be used for Scenario 5.
-------- ---------
// \\ // \\
/ +----+ \
| |XLAT| |
| An IPv4 +----+ An IPv6 |
| Network +----+ Network | XLAT: v4/v6
| |DNS | | Translator
\ +----+ / DNS: DNS ALG
\\ // \\ //
-------- ---------
<====
Figure 13: Stateful translator for Scenarios 5 and 6
The implementation of the stateful translator needs to refer to
[I-D.ietf-behave-v6v4-xlate], [I-D.ietf-behave-v6v4-xlate-stateful],
[translator-addressing-00] {Editor's Note: Waiting for the draft},
and [I-D.ietf-behave-dns64].
3.3. Layout of the Related Documents
Based on the above analysis, the IPv4/IPv6 translation series
consists of the following documents.
o Framework for IPv4/IPv6 Translation (This document).
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o Address translation (The choice of IPv6 prefix and the choice of
method by which the remainder of the IPv6 address is derived from
an IPv4 address) [translator-addressing-00] {Editor's Note:
Waiting for the draft}.
o IP and ICMP Translation (SIIT update, Header translation and ICMP
handling) [I-D.ietf-behave-v6v4-xlate].
o DNS64 (A to AAAA mapping and DNSSec discussion)
[I-D.ietf-behave-dns64].
o Xlate-stateful (Stateful translation including session database
and mapping table handing) [I-D.ietf-behave-v6v4-xlate-stateful].
o FTP ALG.
o Others (Multicast, etc).
The relationship among these documents is shown in the following
figure.
-----------------------------------------
| Framework for IPv4/IPv6 Translation |
-----------------------------------------
|| ||
-------------------------------------------------------------------
| || stateless and stateful || |
| -------------------- --------------------- |
| |Address Translation | <======== | IP/ICMP Translation | |
| -------------------- --------------------- |
| /\ /\ |
| || ------------------||------------ |
| || | stateful \/ |
| ----------------- | --------------------- |
| | DNS64 | | | Xlate-stateful | |
| ----------------- | --------------------- |
-------------------------------------------------------------------
/\ /\
|| ||
----------------- --------------------
| FTP ALG | | Others |
----------------- --------------------
Figure 14: Document Layout
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In the document layout, the IP/ICMP Translation and DNS64 refer to
Address Translation. The Xlate-stateful and IP/ICMP Translation
refer to each other.
The FTP ALG and other documents refer to the stateless and/or
stateful translation documents.
4. Translation in Operation
Operationally, there are two ways that translation could be used - as
a permanent solution making transition "the other guy's problem", and
as a temporary solution for a new part of one's network while
bringing up IPv6 services in the remaining parts of one's network.
The delay could, for example, be caused by contract cycles that
prevent IPv6 deployment during the life of the contract. We
obviously recommend the latter. For the IPv4 parts of the network,
[RFC4213]'s recommendation holds: bringing IPv6 up in those domains,
moving production to it, and then taking down the now-unnecessary
IPv4 service when economics warrant remains the least risk approach
to transition.
----------------------
////// \\\\\\
/// IPv4 or Dual Stack \\\
|| +----+ Routing +-----+ ||
| |IPv4| |IPv4+| |
| |Host| |IPv6 | |
|| +----+ |Host | ||
\\\ +-----+ ///
\\\\\+----+ +---+ +----+ +----+/////
|XLAT|-|DNS|-|SMTP|-|XLAT|
| |-|ALG|-|MTA |-| |
/////+----+ +---+ +----+ +----+\\\\\
/// \\\
|| +-----+ +----+ ||
| |IPv4+| |IPv6| |
| |IPv6 | |Host| |
|| |Host | +----+ ||
\\\ +-----+ IPv6-only Routing ///
\\\\\\ //////
----------------------
Figure 15: Translation Operational Model
During the coexistence phase, as shown in Figure 15, one expects a
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combination of hosts - IPv6-only gaming devices and handsets, older
computer operating systems that are IPv4-only, and modern mainline
operating systems that support both. One also expects a combination
of networks - dual stack devices operating in single stack networks
are effectively single stack, whether that stack is IPv4 or IPv6, as
the other isn't providing communications services.
5. Unsolved Problems
This framework could support multicast, some discussions are in
[I-D.venaas-behave-mcast46] and [I-D.xli-behave-ivi].
This framework could support stateless translation with IPv4 address
and transport port number multiplexing technique, some discussions
are in [I-D.xli-behave-ivi].
6. IANA Considerations
This memo requires no parameter assignment by the IANA.
Note to RFC Editor: This section will have served its purpose if it
correctly tells IANA that no new assignments or registries are
required, or if those assignments or registries are created during
the RFC publication process. From the author's perspective, it may
therefore be removed upon publication as an RFC at the RFC Editor's
discretion.
7. Security Considerations
One "security" issue has been raised, with an address format that was
considered and rejected for that reason. At this point, the editor
knows of no other security issues raised by the address format that
are not already applicable to the addressing architecture in general.
8. Acknowledgements
This is under development by a large group of people. Those who have
posted to the list during the discussion include Andrew Sullivan,
Andrew Yourtchenko, Brian Carpenter, Congxiao Bao, Dan Wing, Dave
Thaler, Ed Jankiewicz, Fred Baker, Hiroshi Miyata, Iljitsch van
Beijnum, John Schnizlein, Kevin Yin, Magnus Westerlund, Marcelo
Bagnulo Braun, Margaret Wasserman, Masahito Endo, Phil Roberts,
Philip Matthews, Remi Denis-Courmont, Remi Despres, and Xing Li.
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Ed Jankiewicz described the transition plan.
The definition of a "Local Internet Registry" came from the
Wikipedia, and was slightly expanded to cover the present case.
(EDITOR'S QUESTION: Would it be better to describe this as an
"operator-defined prefix"?)
9. References
9.1. Normative References
[I-D.bagnulo-behave-dns64]
Bagnulo, M., Sullivan, A., Matthews, P., Beijnum, I., and
M. Endo, "DNS64: DNS extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers",
draft-bagnulo-behave-dns64-02 (work in progress),
March 2009.
[I-D.bagnulo-behave-nat64]
Bagnulo, M., Matthews, P., and I. Beijnum, "NAT64: Network
Address and Protocol Translation from IPv6 Clients to IPv4
Servers", draft-bagnulo-behave-nat64-03 (work in
progress), March 2009.
[I-D.baker-behave-v4v6-translation]
Baker, F., "IP/ICMP Translation Algorithm",
draft-baker-behave-v4v6-translation-02 (work in progress),
February 2009.
[I-D.ietf-behave-dns64]
Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,
"DNS64: DNS extensions for Network Address Translation
from IPv6 Clients to IPv4 Servers",
draft-ietf-behave-dns64-00 (work in progress), July 2009.
[I-D.ietf-behave-v6v4-xlate]
Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", draft-ietf-behave-v6v4-xlate-00 (work in
progress), June 2009.
[I-D.ietf-behave-v6v4-xlate-stateful]
Bagnulo, M., Matthews, P., and I. Beijnum, "NAT64: Network
Address and Protocol Translation from IPv6 Clients to IPv4
Servers", draft-ietf-behave-v6v4-xlate-stateful-00 (work
in progress), July 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
9.2. Informative References
[I-D.baker-behave-ivi]
Li, X., Bao, C., Baker, F., and K. Yin, "IVI Update to
SIIT and NAT-PT", draft-baker-behave-ivi-01 (work in
progress), September 2008.
[I-D.durand-softwire-dual-stack-lite]
Durand, A., Droms, R., Haberman, B., and J. Woodyatt,
"Dual-stack lite broadband deployments post IPv4
exhaustion", draft-durand-softwire-dual-stack-lite-01
(work in progress), November 2008.
[I-D.ietf-v6ops-addcon]
Velde, G., Popoviciu, C., Chown, T., Bonness, O., and C.
Hahn, "IPv6 Unicast Address Assignment Considerations",
draft-ietf-v6ops-addcon-10 (work in progress),
September 2008.
[I-D.miyata-v6ops-snatpt]
Miyata, H. and M. Endo, "sNAT-PT: Simplified Network
Address Translation - Protocol Translation",
draft-miyata-v6ops-snatpt-02 (work in progress),
September 2008.
[I-D.venaas-behave-mcast46]
Venaas, S., "An IPv4 - IPv6 multicast translator",
draft-venaas-behave-mcast46-00 (work in progress),
December 2008.
[I-D.xli-behave-ivi]
Li, X., Bao, C., Chen, M., Zhang, H., and J. Wu, "The
CERNET IVI Translation Design and Deployment for the IPv4/
IPv6 Coexistence and Transition", draft-xli-behave-ivi-02
(work in progress), June 2009.
[I-D.xli-behave-v4v6-prefix]
Bao, C., Baker, F., and X. Li, "IPv4/IPv6 Translation
Prefix Recommendation", draft-xli-behave-v4v6-prefix-00
(work in progress), April 2009.
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[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC1923] Halpern, J. and S. Bradner, "RIPv1 Applicability Statement
for Historic Status", RFC 1923, March 1996.
[RFC2428] Allman, M., Ostermann, S., and C. Metz, "FTP Extensions
for IPv6 and NATs", RFC 2428, September 1998.
[RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm
(SIIT)", RFC 2765, February 2000.
[RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address
Translation - Protocol Translation (NAT-PT)", RFC 2766,
February 2000.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3142] Hagino, J. and K. Yamamoto, "An IPv6-to-IPv4 Transport
Relay Translator", RFC 3142, June 2001.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, February 2003.
[RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879, September 2004.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
February 2006.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
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Internet-Draft Framework for IPv4/IPv6 Translation July 2009
Address Autoconfiguration", RFC 4862, September 2007.
[RFC4864] Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
E. Klein, "Local Network Protection for IPv6", RFC 4864,
May 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 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.
[RFC5211] Curran, J., "An Internet Transition Plan", RFC 5211,
July 2008.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
Authors' Addresses
Fred Baker (editor)
Cisco Systems
Santa Barbara, California 93117
USA
Phone: +1-408-526-4257
Fax: +1-413-473-2403
Email: fred@cisco.com
Xing Li (editor)
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing, 100084
China
Phone: +86 62785983
Email: xing@cernet.edu.cn
Baker, et al. Expires January 6, 2010 [Page 30]
Internet-Draft Framework for IPv4/IPv6 Translation July 2009
Congxiao Bao (editor)
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing, 100084
China
Phone: +86 62785983
Email: congxiao@cernet.edu.cn
Kevin Yin (editor)
Cisco Systems
No. 2 Jianguomenwai Ave, Chaoyang District
Beijing, 100022
China
Phone: +86-10-8515-5094
Email: kyin@cisco.com
Baker, et al. Expires January 6, 2010 [Page 31]
