Internet Draft M. Lind (ed.) TeliaSonera Expires: December 2003 June 2003 Scenarios for Introducing IPv6 into ISP Networks Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Abstract This document describes different scenarios for the introduction of IPv6 in an IPv4 ISP network. The goal is the addition of a native IPv6 service to the already existing IPv4 service without interruption of the IPv4 service. During the IPv6 introduction the network can go through 4 different stages including the initial IPv4 only stage. To move between the stages there will be some form of transition that can be defined in different transition scenarios. Lind Expires - December 2003 [Page 1] INTERNET DRAFT ISP Networks IPv6 Scenarios June 2003 Table of Contents 1. Introduction...................................................2 2. Scope..........................................................3 3. Brief description of a generic ISP network.....................3 4. Stages.........................................................4 4.1 Assumptions................................................4 4.2 Customer requirements and ISP offerings....................5 4.3 Stage 1 û Launch...........................................5 4.4 Stage 2a - Core............................................6 4.5 Stage 2b - Access..........................................6 4.6 Stage 3 û Complete.........................................6 4.7 Future stages..............................................7 5. Transition Scenarios...........................................7 6. Security Considerations........................................8 1. Introduction An ISP offering an IPv4 service will find that there are different ways to add IPv6 to this service. During the introduction of IPv6 the network will go through different stages of IPv6 maturity. In addition to this there has to be a transition between these stages to make them feasible to implement. In some cases it might not be possible to introduce IPv6 as a native part of the network, due to hardware limitations or similar. Instead some coexistence mechanism has to be used. This leaves two choices; a native IPv6 transport in a part of the network or some mechanism to transport IPv6 over the existing IPv4 network. From the customer perspective this can be seen as the ISP offering a native IPv6 service or not depending on what is relevant in the access network. If the ISP is not offering native IPv6 transport, then the service is limited in the sense that the customer has to have a dual stack network, or some kind of coexistence mechanism. In this document different transition scenarios and situations during the introduction of IPv6 are covered in a broader perspective and deals only with a generic view of how an ISP network is build. This should be seen as the starting point for further documentation of how the introduction of IPv6 can be done in an ISP network in companion. What also will be included in these documents are issues specific to different network configurations and special network equipment. This document should therefore be seen as the working frame for the transition steps of the IPv6 introduction that will be documented in companion documents. Lind Expires - December 2003 [Page 2] INTERNET DRAFT ISP Networks IPv6 Scenarios June 2003 2. Scope The scope of the document is to describe different cases for the introduction of an IPv6 service in a generic IPv4 ISP network. This means that the document will be limited to services that include both IPv6 and IPv4 and will not cover issues surrounding an IPv6 only service. The scope also includes transition scenarios between the different stages. The different building blocks that will be considered are a customer network, an access network, a core network and exchange points. It is outside the scope of this document to describe different types of access or network technologies. It is also outside of the scope to propose different solutions. Solutions will be covered in a separate document. 3. Brief description of a generic ISP network A generic ISP network topology can be divided into two main parts; core network and access network. The core network or the backbone is the part of the network that interconnects the different access networks and provides transport to the rest of the Internet via exchange points or other means. The core network can be built on different technologies but in this document the only interest is whether it is capable of carrying IPv6 traffic natively or not. The same applies to the access network. The access network provides connectivity to enterprise and private customers. Other ISPs might as well be customers and connected to the ISP's network. __________ _________ | | | | |Backoffice|----| CORE | |__________| |_________|\ . / | \ \ . / | \ \_Peering( Direct & IX ) . / | \ . / | \ ___.___ / ___|___ \ _______ | |____/ | | \____| | |Access1| |Access2| |Access3| |_______| |_______| |_______| | | | | | | ISP Network ----|---------------|---------------|----------------- | | | Customer Networks ___|____ ___|____ ___|____ | | | | | | |Customer| |Customer| |Customer| |________| |________| |________| Figure 1: ISP network topology Lind Expires - December 2003 [Page 3] INTERNET DRAFT ISP Networks IPv6 Scenarios June 2003 It doesn't matter if these customer networks have a single node or a large routed network. What is of interest is if routing information is exchanged or not since it will affect the ISP's network. The existence of customer placed equipment will also affect how a service can be delivered. In addition to the ISP's actual network components there are a lot of support and backend systems that have to be considered. 4. Stages The stages here are snapshots of an ISP's network with respect to IPv6 maturity. Since an ISP's network is constantly evolving, a stage is a measure of how far an ISP has come in turn of implementing necessary functionality to offer IPv6 to the customers. It is possible to freely transition between different stages. However, a network segment can only be in one stage at a time but an ISP network as a whole can be in different stages. There are different transition paths between the first and final stage. The transition between two stages does not have to be immediate but can occur gradually. Each stage has different IPv6 properties. An ISP can therefore, based on the requirements it has, decide into which stage it will transform its network. 4.1 Assumptions The stages are derived from the generic description of an ISP network in section 3. A combination of different building blocks that constitute an ISP environment will lead to a number of scenarios, which an ISP can choose from. The scenarios of most relevance to this document are considered to be the ones that in the most efficient and feasible way maximizes the ability for an ISP to offer IPv6 to its customers. The most predominant case today is considered to be an operator with a core and access IPv4 network delivering IPv4 service to a customer that is running IPv4 as well. At some point in the future, it is expected that the customer will want to have an IPv6 service, in addition to the already existing IPv4 service. The challenge for the ISP is to deliver the requested IPv6 service over the existing infrastructure and at the same time keep the IPv4 service intact. The next step, which is not covered in this document, will be to remove the IPv4 service when there no longer is a demand for it or deliver the IPv4 service over an IPv6 only network. Lind Expires - December 2003 [Page 4] INTERNET DRAFT ISP Networks IPv6 Scenarios June 2003 4.2 Customer requirements and ISP offerings Looking at the scenarios from the end customer's perspective there might be a demand for three different services; the customer might demand IPv4 service, IPv6 service or both services. This can lead to two scenarios depending on the stage the ISP's network is in. If an ISP only offer IPv4 or IPv6 service and a customer wants to connect a device or network that only supports one service and if that service is not offered, it will lead to a dead-end. If the customer or ISP instead connects a dual stack device it is possible to circumvent the lack of the missing service in the access network by using some kind of coexistence mechanism. This scenario will only be considered in the perspective of the ISP offering a mechanism to bridge the access and reach the IPv6 core. In the case where the customer connects a single stack device to a corresponding single stack access network, there will be no problem from the customer's perspective. The same is valid if a single stack device is connected to a dual stack access network. Therefore, neither of these cases need further be explored in this document but can be seen as a part of a full dual stack case. After eliminating a number of cases explained above, there are four stages that are most probable and where an ISP will find its network in. Which stage a network is in; depend on whether or not some part of the network previously has been upgraded to support IPv6 or if it is easier to enable IPv6 in one part or another. For instance, routers in the core might have IPv6 support or might be easily upgradeable, while the hardware in the access might have to be completely replaced in order to handle IPv6 traffic. Note that in every stage except Stage 1, the ISP can offer both IPv4 and IPv6 services to the customer. The four most probable stages are: Stage 1 û Launch Stage 2a û Core Stage 2b û Access Stage 3 û Complete 4.3 Stage 1 û Launch The first stage is an IPv4 only ISP with an IPv4 customer. This is the most common case today and has to be the starting point for the introduction of IPv6. From this stage, an ISP can move (transition) to any other stage with the goal to offer IPv6 to its customer. Lind Expires - December 2003 [Page 5] INTERNET DRAFT ISP Networks IPv6 Scenarios June 2003 Customer Access Core Exchange ------ ------ ------ ------ | | | | | | | | | IPv4 |---| IPv4 |---| IPv4 |---| IPv4 | | | | | | | | | ------ ------ ------ ------ Figure 2. IPv4 network 4.4 Stage 2a - Core Stage 2a is an ISP with an access network that is IPv4 only and a core that is IPv4 and IPv6. In this stage the customer should have support for both IPv4 and IPv6 and use a coexistence mechanism to be able to run the IPv6 service. To offer the IPv6 service, the ISP also has to connect to an IPv6 exchange point or somehow else exchange IPv6 traffic with other ISPs. Customer Access Core Exchange ------ ------ ------ ------ | | | | | | | IPv4 | | Dual |---| IPv4 |---| Dual |---| + | | | | | | | | IPv6 | ------ ------ ------ ------ Figure 3. Upgraded core 4.5 Stage 2b - Access Stage 2b is an ISP with a core network that is IPv4 and an access that is IPv4 and IPv6. Since the service to the customer is native IPv6 there is no requirement for the customer to support both IPv4 and IPv6. This is the biggest difference in comparison to the previous stage. The need to exchange IPv6 traffic or similar still exists but might be more complicated than in the previous case since the core isn't IPv6 enabled. Customer Access Core Exchange ------ ------ ------ ------ | | | | | | | IPv4 | | Dual |---| Dual |---| IPv4 |---| + | | | | | | | | IPv6 | ------ ------ ------ ------ Figure 4. Upgraded access 4.6 Stage 3 û Complete Stage 3 can be said to be the final step in introducing IPv6, at least in the scope of this document. This is an all over IPv6 service with native support for IPv6 and IPv4 in both core and access networks. This stage is identical to the previous stage in the Lind Expires - December 2003 [Page 6] INTERNET DRAFT ISP Networks IPv6 Scenarios June 2003 customer's perspective since the access network hasn't changed. The connection to the IPv6 exchange point is identical to stage 2. Customer Access Core Exchange ------ ------ ------ ------ | | | | | | | IPv4 | | Dual |---| Dual |---| Dual |---| + | | | | | | | | IPv6 | ------ ------ ------ ------ Figure 5. Completely upgraded network 4.7 Future stages After a while the ISP might want to transition to a service that is IPv6 only, at least in certain parts of the network. This transition creates a lot of new cases in which to factor in how to maintain the IPv4 service. Providing an IPv6 only service is not much different than the dual IPv4/IPv6 service described in stage 3 except from the need to phase out the IPv4 service. The delivery of IPv4 services over an IPv6 network and the phase out will be left for a future document. 5. Transition Scenarios Given the different stages it is clear that the ISP has to be able to transition from one stage to another. The initial stage, in this document, is the IPv4 only service and network. The end stage is the dual IPv4/IPv6 service and network. As mentioned in the scope, this document does not cover the IPv6 only service and network and its implications on IPv4 customers. This has nothing to do with the usability of an IPv6 only service. The transition starts out with the IPv4 ISP and then moves to one of three choices. These choices are the different transition scenarios. One way would be to upgrade the core first which leads to stage 2a. Another way to go could be to upgrade the access network which leads to stage 2b. The final possibility is to introduce IPv6 in the whole network at once which would lead to stage 3. The choice is dependent on many different issues. For example it might not be possible to upgrade the core or the access network without large investments in new equipment which could lead to any of the two first choices. In another case it might be easier to take the direct step to a complete IPv6/IPv4 network due to routing protocol issues or similar. If a partially upgraded network (stage 2a or 2b) was chosen as the first step, a second step remains before the network is all over native IPv6/IPv4. This is the transition to an all over dual stack Lind Expires - December 2003 [Page 7] INTERNET DRAFT ISP Networks IPv6 Scenarios June 2003 network. This step is perhaps not necessary for stage 2b with an already native IPv6 service to the customer but might still occur when the timing is right. For stage 2a it is more obvious that a transition to a dual stack network is necessary since it has to be done to offer a native IPv6 service. 6. Security Considerations This document describes different cases for the introduction of IPv6 in an IPv4 ISP network. Solutions are described in other documents hence this document has no security considerations. 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However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be Lind Expires - December 2003 [Page 8] INTERNET DRAFT ISP Networks IPv6 Scenarios June 2003 followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgements This draft has benefited from input by Jordi Palet, Suresh Satapati, Myung-Ki Shin, Vladmir Ksinant, Alain Baudot, Soohong Daniel Park, Cleve Mickles, Pekka Savola and Margaret Wasserman. Authors' Addresses Mikael Lind TeliaSonera Vitsandsgatan 9B SE-12386 Farsta Email: mikael.lind@teliasonera.com Jasminko Mulahusic TeliaSonera Vitsandsgatan 9B SE-12386 Farsta Email: jasminko.mulahusic@teliasonera.com Lind Expires - December 2003 [Page 9]