behave F. Baker Internet-Draft Cisco Systems Intended status: Informational X. Li Expires: June 20, 2010 C. Bao CERNET Center/Tsinghua University K. Yin Cisco Systems December 17, 2009 Framework for IPv4/IPv6 Translation draft-ietf-behave-v6v4-framework-04 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. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 20, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. Baker, et al. Expires June 20, 2010 [Page 1] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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 BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Why Translation? . . . . . . . . . . . . . . . . . . . . . 4 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Translation Objectives . . . . . . . . . . . . . . . . . . 7 1.4. Transition Plan . . . . . . . . . . . . . . . . . . . . . 8 2. Scenarios for 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 State . . . . . . . . . . . . 19 3.1.4. DNS64 and DNS46 . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Baker, et al. Expires June 20, 2010 [Page 2] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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 businesses, 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. Baker, et al. Expires June 20, 2010 [Page 3] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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 an IPv4-only deployment. This could be an enterprise's IPv4-only network, an ISP's IPv4-only network or even an IPv4-only host. The IPv4 Internet is the set of all interconnected IPv4 networks. Baker, et al. Expires June 20, 2010 [Page 4] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 An IPv6 network: A specific network that has an IPv6-only deployment. This could be an enterprise's IPv6-only network, an ISP's IPv6-only network or even an IPv6-only host. The IPv6 Internet is the set of all interconnected IPv6 networks. Dual-Stack implementation: A Dual-Stack implementation, in this context, comprises an IPv4/IPv6 enabled end system stack, applications 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-converted addresses: They are the IPv6 addresses used to represent IPv4 hosts. They have an explicit mapping relationship to IPv4 addresses. This relationship is self described by mapping IPv4 address in the IPv6 address. Both stateless and stateful translators are using IPv4-converted IPv6 addresses to represent IPv4 hosts. IPv4-only: An IPv4-only implementation, in this context, comprises an IPv4-enabled end system stack, applications 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. IPv4-translatable addresses: They are the IPv6 addresses to be assigned to IPv6 hosts for the stateless translator. They have an explicit mapping relationship to IPv4 addresses. This relationship is self described by mapping IPv4 address in the IPv6 address. The stateless translator is using the corresponding IPv4 addresses to represent the IPv6 hosts. The stateful translator does not use this kind of addresses, since the IPv6 hosts are represnted by the IPv4 address pool in the translator via dynamic states. IPv6-only: An IPv6-only implementation, in this context, comprises an IPv6 enabled end system stack, applications directly or indirectly using that IPv6 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. Baker, et al. Expires June 20, 2010 [Page 5] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 Network-Specific Prefix (NSP): IPv6 prefixes are assigned to a network operator by its regional internet registrar (RIR). From an IPv6 prefix assigned to the operator, the operator chooses a longer prefix for use by the operator's translator(s). Hence a given IPv4 address would have different IPv6 representations in different networks that use different prefixes. A network- specific prefix is also known as a Local Internet Registry (LIR) prefix. 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 protocol, 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. Stateful Translator: A translator that uses stateful translation for either the source or destination address. A stateful translator also uses a stateless translation algorithm for the other type of address. Stateless Translation: A translation algorithm that is not "stateful" is "stateless". It derives its needed information algorithmically from the messages it is translating. Stateless Translator: A translator that uses only stateless translation for both destination address and source address. Well-Known Prefix (WKP): A prefix assigned by IANA. In this case, there would be a single representation of a public IPv4 address in the IPv6 address space. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this Baker, et al. Expires June 20, 2010 [Page 6] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 document are to be interpreted as described in RFC 2119 [RFC2119]. 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 [RFC4966] . 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 resolution. Peer-to-Peer (P2P) 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 sessions are important, are able to learn about the reliability of peers from history or by reputation. They use the long-term Baker, et al. Expires June 20, 2010 [Page 7] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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. 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 Baker, et al. Expires June 20, 2010 [Page 8] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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 the above three transition phases, also known as an "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 as the early stage of the "S" curve. Baker, et al. Expires June 20, 2010 [Page 9] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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. Baker, et al. Expires June 20, 2010 [Page 10] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 2. Scenarios for 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 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 (applications) that only communicate using IPv4 and a set of systems that only communicate using IPv6", but the differences at a detailed level make them interesting. Based on the transition plan described in Section 1.4, there are four types of IPv4/IPv6 translation scenarios: 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, depending on whether the IPv6 side or the IPv4 side initiates communication, so there are a total of 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 the next section. Baker, et al. Expires June 20, 2010 [Page 11] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 2.1. Scenario 1: an IPv6 network to the IPv4 Internet Due to the lack of the publicly routable IPv4 addresses or under other technical or economical constraints, the 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 "green_field" 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 green_field enterprise scenario is different from ISP's network 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: DNS64 \ / \\ // \\ // ----------- -------- <==== 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 communicating with the IPv4 Internet, while IVI can support a subset of the IPv6 addresses in an IPv6 network communicating with Baker, et al. Expires June 20, 2010 [Page 12] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 the IPv4 Internet. 2.2. Scenario 2: the IPv4 Internet to an IPv6 network This scenario is predicted to become increasingly important as the network administrators are under pressure to put 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 a translation 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: DNS46 \ / \\ // \\ // ---------- -------- ====> Figure 2: Scenario 2 In general, this scenario presents a hard case for translation. Stateful translation such as NAT-PT [RFC2766] can be used in this scenario, but it requires tightly coupled DNS ALG in the translator and this technique was deprecated by the 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 a 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 a legacy IPv4 network to provide services to IPv6 hosts. Baker, et al. Expires June 20, 2010 [Page 13] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 ----------- ---------- // \\ // \\ / \ / +----+ \ | |XLAT| | | An IPv4 +----+ The IPv6 | | Network +----+ Internet | XLAT: v4/v6 | |DNS | | Translator \ +----+ / DNS: DNS64 \\ // \ / --------- \\ // ----------- <==== Figure 3: Scenario 3 The stateless translation will not work for this scenario, because an IPv4 network needs to communicate with all of the IPv6 Internet, not just a small subset, and stateless can only support a small subset. However, IPv6-initiated communication can be achieved through stateful translation. 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 technical or economical constraints, the network is IPv4-only, and IPv4-only hosts (applications) may require communicating with the global IPv6 Internet. ----------- ---------- // \\ // \\ / \ / +----+ \ | |XLAT| | | An IPv4 +----+ The IPv6 | XLAT: v4/v6 | Network +----+ Internet | Translator | |DNS | | DNS: DNS46 \ +----+ / \\ // \ / --------- \\ // ---------- =====> Figure 4: Scenario 4 In general, this scenario presents a hard case for translation. Stateful translation such as NAT-PT [RFC2766] can be used in this Baker, et al. Expires June 20, 2010 [Page 14] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 scenario, but it requires a tightly coupled DNS ALG in the translator and this technique was deprecated by the IETF [RFC4966]. From the transition phase discussion in Section 1.4, this scenario will probably only occur when we are well past the early stage of the "S" curve and the v4/v6 transition has already moved to the right direction. Therefore, 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 the scenarios where both an IPv4 network and an IPv6 network are within the same organization. The IPv4 addresses used are either public IPv4 addresses or [RFC1918] addresses. The IPv6 addresses used are either public IPv6 addresses or ULAs (Unique Local Addresses) [RFC4193]. --------- --------- // \\ // \\ / +----+ \ | |XLAT| | | An IPv4 +----+ An IPv6 | | Network +----+ Network | XLAT: v4/v6 | |DNS | | Translator \ +----+ / DNS: DNS64 \\ // \\ // -------- --------- <==== Figure 5: Scenario 5 The translation requirement from this scenario has no significant difference from scenario 1, so both the stateful and stateless translation 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. The IPv4 addresses used are either public IPv4 addresses or [RFC1918] addresses. The IPv6 addresses used are either public IPv6 addresses or ULAs (Unique Local Addresses) [RFC4193]. Baker, et al. Expires June 20, 2010 [Page 15] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 -------- --------- // \\ // \\ / +----+ \ | |XLAT| | | An IPv4 +----+ An IPv6 | | Network +----+ Network | XLAT: v4/v6 | |DNS | | Translator \ +----+ / DNS: DNS46 \\ // \\ // -------- --------- ====> Figure 6: Scenario 6 The translation requirement from this scenario has no significant difference from scenario 2, so the translation 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 or application on the global Internet can initiate communication with any IPv4-only host or application on the global Internet. -------- --------- // \\ // \\ / \ / \ / +----+ \ | |XLAT| | | The IPv4 +----+ The IPv6 | | Internet +----+ Internet | XLAT: v4/v6 | |DNS | | Translator \ +----+ / DNS: DNS64 \ / \ / \\ // \\ // -------- --------- <==== Figure 7: Scenario 7 Due to the huge difference in size between the address spaces of the IPv4 Internet and the IPv6 Internet, there is no viable translation technique to handle unlimited IPv6 address translation. Baker, et al. Expires June 20, 2010 [Page 16] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 If we ever run into this scenario, fortunately, the IPv4-IPv6 transition has already past the early stage of the "S" curve, therefore, there is no obvious business reason to demand a translation solution as the 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 host or application on the global Internet can open connection to any IPv6-only host or application on the global Internet. -------- --------- // \\ // \\ / \ / \ / +----+ \ | |XLAT| | | The IPv4 +----+ The IPv6 | | Internet +----+ Internet | XLAT: v4/v6 | |DNS | | Translator \ +----+ / DNS: DNS46 \ / \ / \\ // \\ // -------- --------- ====> Figure 8: Scenario 8 Due to the huge difference in size between the address spaces of the IPv4 Internet and the IPv6 Internet, there is no viable translation technique to handle unlimited IPv6 address translation. If we ever run into this scenario, fortunately, the IPv4-IPv6 transition has already past the early stage of the "S" curve, therefore, there is no obvious business reason to demand a translation solution as the 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 Baker, et al. Expires June 20, 2010 [Page 17] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 components: o Address translation o IP and ICMP translation o Maintaining translation state o DNS64 and DNS46 o ALGs for other application-layer protocols (e.g., FTP) 3.1. Translation Components 3.1.1. Address Translation When 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 [I-D.ietf-behave-address-format]. Note that translating IPv4 address to IPv6 address and translating IPv6 address to IPv4 address are different for stateless translation and stateful translation. [I-D.ietf-behave-address-format]. o For stateless translation, the algorithmic mapping algorithm is used both to translate IPv4 addresses to IPv6 addresses and to translate IPv6 addresses to IPv4 addresses. 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 stateful translation, the algorithmic mapping algorithm is used to translate IPv4 addresses to IPv6 addresses, while a session initiated state table is used to translate IPv6 addresses to IPv4 addresses. 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 dynamic binding, stateful translation in general only supports IPv6-initiated communication. Baker, et al. Expires June 20, 2010 [Page 18] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 3.1.2. IP and ICMP Translation The IPv4/IPv6 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 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 State 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 state. 3.1.4. DNS64 and DNS46 [I-D.ietf-behave-dns64] and possible future documents 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 two possible implementations of a DNS64 and DNS46: 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 DNS64 if and only if no reachable AAAA record exists, or for an AAAA record to be (retrieved and) translated by the DNS46 if and only if no reachable A record exists. Baker, et al. Expires June 20, 2010 [Page 19] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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 [RFC1928] [RFC3089]. 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 work 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 IPv6/IPv4 translation are classified into stateless translation and stateful translation. 3.2.1. Stateless Translation For 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 Scenario 1 ("an IPv6 network to the IPv4 Internet"), it is not a serious drawback, since the address 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"), which 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. Stateless translation can be used for Scenarios 1, 2, 5 and 6, i.e. Baker, et al. Expires June 20, 2010 [Page 20] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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: DNS64/DNS46 \ / \\ // \\ // ---------- -------- <====> Figure 9: Stateless translation for Scenarios 1 and 2 -------- --------- // \\ // \\ / +----+ \ | |XLAT| | | An IPv4 +----+ An IPv6 | | Network +----+ Network | XLAT: v4/v6 | |DNS | | Translator \ +----+ / DNS: DNS64/DNS46 \\ // \\ // -------- --------- <====> 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], [I-D.ietf-behave-address-format], and [I-D.ietf-behave-dns64]. Baker, et al. Expires June 20, 2010 [Page 21] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 3.2.2. Stateful Translation For 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]. Stateful translator can be used for Scenarios 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 stateful translation, however it typically only supports initiation from the IPv6 side (NAT64 doesn't support IPv4-initiation), and does not result in stable addresses that can be used in DNS, 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: DNS64 \ / \\ // \\ // ----------- -------- <==== 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. Baker, et al. Expires June 20, 2010 [Page 22] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 ----------- ---------- // \\ // \\ / \ / +----+ \ | |XLAT| | | An IPv4 +----+ The IPv6 | | Network +----+ Internet | XLAT: v4/v6 | |DNS | | Translator \ +----+ / DNS: DNS64 \\ // \ / --------- \\ // ----------- <==== Figure 12: Stateful translator for Scenario 3 Similarly, the stateful translator can also be used for Scenario 5. -------- --------- // \\ // \\ / +----+ \ | |XLAT| | | An IPv4 +----+ An IPv6 | | Network +----+ Network | XLAT: v4/v6 | |DNS | | Translator \ +----+ / DNS: DNS64 \\ // \\ // -------- --------- <==== Figure 13: Stateful translator for Scenario 5 The implementation of the stateful translator needs to refer to [I-D.ietf-behave-v6v4-xlate], [I-D.ietf-behave-v6v4-xlate-stateful], [I-D.ietf-behave-address-format], 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). o Address translation (The choice of IPv6 prefix and the choice of method by which the remainder of the IPv6 address is derived from Baker, et al. Expires June 20, 2010 [Page 23] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 an IPv4 address, part of the SIIT update) [I-D.ietf-behave-address-format], o IP and ICMP Translation (Header translation and ICMP handling, part of the SIIT update.) [I-D.ietf-behave-v6v4-xlate]. o Xlate-stateful (Stateful translation including session database and mapping table handing) [I-D.ietf-behave-v6v4-xlate-stateful]. o DNS64/DNS46 (DNS64: A to AAAA mapping and DNSSec discussion) [I-D.ietf-behave-dns64]. 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/DNS46 | | | Table Maintenance | | | ----------------- | --------------------- | ------------------------------------------------------------------- /\ /\ || || ----------------- -------------------- | FTP ALG | | Others | ----------------- -------------------- Figure 14: Document Layout In the document layout, the IP/ICMP Translation and DNS64/DNS46 refer Baker, et al. Expires June 20, 2010 [Page 24] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 to Address Translation. The Table Maintenance and IP/ICMP Translation refer to each other. The FTP ALG and other documents refer to the Address Format, IP/ICMP Translation and Table Maintenance 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. 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| | |-|64 |-|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 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 Baker, et al. Expires June 20, 2010 [Page 25] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 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, 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 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, Bo Zhou, Brian Carpenter, Dan Wing, Dave Thaler, Ed Jankiewicz, Gang Chen, Hui Deng, Hiroshi Miyata, Iljitsch van Beijnum, John Schnizlein, Magnus Westerlund, Marcelo Bagnulo Braun, Margaret Wasserman, Masahito Endo, Phil Roberts, Philip Matthews, Remi Denis-Courmont and Remi Despres. Ed Jankiewicz described the transition plan. 9. References Baker, et al. Expires June 20, 2010 [Page 26] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 9.1. Normative References [I-D.ietf-behave-address-format] Huitema, C., Bao, C., Bagnulo, M., Boucadair, M., and X. Li, "IPv6 Addressing of IPv4/IPv6 Translators", draft-ietf-behave-address-format-02 (work in progress), December 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-dns64-03 (work in progress), December 2009. [I-D.ietf-behave-v6v4-xlate] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation Algorithm", draft-ietf-behave-v6v4-xlate-04 (work in progress), November 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-05 (work in progress), December 2009. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 9.2. Informative References [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.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.venaas-behave-mcast46] Venaas, S., Asaeda, H., SUZUKI, S., and T. Fujisaki, "An IPv4 - IPv6 multicast translator", draft-venaas-behave-mcast46-01 (work in progress), July 2009. Baker, et al. Expires June 20, 2010 [Page 27] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 [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-05 (work in progress), December 2009. [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. [RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and L. Jones, "SOCKS Protocol Version 5", RFC 1928, March 1996. [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. [RFC3089] Kitamura, H., "A SOCKS-based IPv6/IPv4 Gateway Mechanism", RFC 3089, April 2001. [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. [RFC4864] Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and E. Klein, "Local Network Protection for IPv6", RFC 4864, May 2007. Baker, et al. Expires June 20, 2010 [Page 28] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 [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 Cisco Systems Santa Barbara, California 93117 USA Phone: +1-408-526-4257 Fax: +1-413-473-2403 Email: fred@cisco.com Xing Li CERNET Center/Tsinghua University Room 225, Main Building, Tsinghua University Beijing, 100084 China Phone: +86 10-62785983 Email: xing@cernet.edu.cn Congxiao Bao CERNET Center/Tsinghua University Room 225, Main Building, Tsinghua University Beijing, 100084 China Phone: +86 10-62785983 Email: congxiao@cernet.edu.cn Baker, et al. Expires June 20, 2010 [Page 29] Internet-Draft Framework for IPv4/IPv6 Translation December 2009 Kevin Yin Cisco Systems No. 2 Jianguomenwai Ave, Chaoyang District Beijing, 100022 China Phone: +86-10-8515-5094 Email: kyin@cisco.com Baker, et al. Expires June 20, 2010 [Page 30]