Internet Draft M. Lind
<draft-ietf-v6ops-isp-scenarios-analysis-01.txt><draft-ietf-v6ops-isp-scenarios-analysis-02.txt> TeliaSonera V. Ksinant 6WINDThales Communications S. Park Samsung Electronics A. Baudot France Telecom P. Savola CSC/Funet Expires: AugustOctober 2004 FebruaryApril 2004 Scenarios and Analysis 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 first describes different scenarios for the introduction of IPv6 into an ISP's existing IPv4 network without disrupting the IPv4 service. Then, this document analyses these scenarios and evaluates the relevance of the already defined transition mechanisms in this context. Known challenges are also identified. Table of Contents 1. Introduction................................................2 1.1 Goal and Scope of the Document...........................2 2. Brief Description of a Generic ISP Network..................3 3. Transition Scenarios........................................4 3.1 Identification of Stages and Scenarios...................4 3.2 Stages...................................................5 3.2.1 Stage 1 Scenarios: Launch..............................5 3.2.2 Stage 2a Scenarios: Backbone...........................6 3.2.3 Stage 2b Scenarios: Customer Connection................6 3.2.4 Stage 3 Scenarios: Complete............................6 3.2.5 Stages 2a and 3: Combination Scenarios.................7 3.3 Transition Scenarios.....................................7 3.4 Actions Needed When Deploying IPv6 in an ISP's network...7 4. Backbone Transition Actions.................................8 4.1 Steps in Transitioningthe Transition of Backbone Networks.................8Networks.............8 4.1.1 MPLS Backbone..........................................9 4.2 Configuration of Backbone Equipment.....................10 4.3 Routing.................................................10 4.3.1 IGP...................................................10 4.3.2 EGP...................................................11EGP...................................................12 4.3.3 Transport of Routing Protocols........................12 4.4 Multicast...............................................12 5. Customer Connection Transition Actions.....................12 5.1 Steps in Transitioningthe Transition of Customer Connection Networks.....12Networks.12 5.1.1 Small end sites.......................................14 5.1.2 Large end sites.......................................14 5.2 AccessUser Authentication/Access Control Requirements.............................14Requirements.........15 5.3 Configuration of Customer Equipment.....................15 5.4 Requirements for Traceability...........................16 5.5 Ingress Filtering in the Customer Connection Network....16 5.6 Multi-Homing............................................16Multihoming.............................................16 5.7 Quality of Service......................................16Service......................................17 6. Network and Service Operation Actions......................17 7. Future Stages..............................................17Stages..............................................18 8. Example Networks...........................................18 8.1 Example 1...............................................19 8.2 Example 2...............................................21 8.3 Example 3...............................................21 9. Security Considerations....................................22 10. Acknowledgements...........................................22 11. Informative References.....................................22 1. Introduction 1.1 Goal and Scope of the Document When an ISP deploys IPv6, its goal is to provide IPv6 connectivity and global address space to its customers. The new IPv6 service must be added to an already existing IPv4 service, and the introduction of IPv6 must not interrupt this IPv4 service. An ISP offering IPv4 service will find different ways to add IPv6 to this service. This document discusses a small set of scenarios for the introduction of IPv6 into an ISP's IPv4 network. It evaluates the relevance of the existing transition mechanisms in the context of these deployment scenarios, and points out the lack of functionalityessential functionality in these methods to the ISP's operation of an IPv6 service. The present document is focused on services that include both IPv6 and IPv4 and does not cover issues surrounding IPv6-only service. It is also outside the scope of this document to describe different types of access or network technologies. 2. Brief Description of a Generic ISP Network A generic network topology for an ISP can be divided into two main parts: the backbone network and thecustomer connection networks connecting the customers.networks. It includes, in addition to these, some other building blocks such as network and service operations. The additional building blocks used in this document are defined as follows: "CPE" : Customer Premises Equipment "PE" : Provider Edge equipment "Network and service operation" : This is the part of the ISP's network that hosts the services required for the correct operation of the ISP's network. These services usually include management, supervision, accounting, billing, and customer management applications. "Customer connection" : This is the part of the network used by a customer when connecting to an ISP's network. It includes the CPE, the last hop link and the parts of the PE interfacing to the last hop link. "Backbone" : This is the rest of the ISP's network infrastructure. It includes the parts of the PE interfacing to the core, the core routers of the ISP, and the border routers used to exchange routing information with other ISPs (or other administrative entities). "Dual-stack network": A network that supports natively both IPv4 and IPv6. It is noted that, in some cases (e.g., incumbent national or regional operators), a given customer connection network may have to be shared between or among different ISPs. According to the type of customer connection network used (e.g., one involving only layer 2 devices or one involving non-IP technology), this constraint may result in architectural considerations relevant to this document. The basic components in the ISP's network are depicted in Figure 1. ------------ ---------- | Network and| | | | Service |--| Backbone | | Operation | | |\ ------------ ---------- \ . / | \ \ . / | \ \_Peering( Direct and IX ) . / | \ . / | \ . / | \ ---------- / ---------- \ ---------- | Customer | / | Customer | \ | Customer | |Connection|--/ |Connection| \--|Connection| | 1 | | 2 | | 3 | ---------- ---------- ---------- | | | ISP's Network ------------------------------------------------------- | | | Customers' Networks +--------+ +--------+ +--------+ | | | | | | |Customer| |Customer| |Customer| | | | | | | +--------+ +--------+ +--------+ Figure 1: ISP Network Topology. 3. Transition Scenarios 3.1 Identification of Stages and Scenarios This section describes different stages an ISP might consider when introducing IPv6 connectivity into its existing IPv4 network and the different scenarios that might occur in the respective stages. The stages here are snapshots of the ISP's network with respect to IPv6 maturity. Because the ISP's network is continually evolving, a stage is a measure of how far along the ISP has come in terms of implementing the functionality necessary to offer IPv6 to theits customers. It is possible tofor a transition to occur freely between different stages. Although a network segment can only be in one stage at a time, the ISP's network as a whole can be in different stages. Different transition paths can be followed from the first to the final stage. The transition between two stages does not have to be instantaneous; it can occur gradually. Each stage has different IPv6 properties. An ISP can, therefore, based on its requirements, decide which set of stages it will follow and in what order to transform its network. This document is not aimed to coverat covering small ISPs, hosting providers, or data centers; only the scenarios applicable to ISPs eligible for at least a /32 IPv6 prefix allocation from a RIR are covered. 3.2 Stages The stages are derived from the generic description of an ISP's network in Section 2. Combinations of different building blocks that constitute an ISP's environment lead to a number of scenarios from which the ISP can choose. The scenarios most relevant forto this document are the onesthose that maximize ISP's ability to offer IPv6 to its customers in the most efficient and feasible way. The assumption in all stages is that the ISP's goal is to offer both IPv4 and IPv6 to the customer. The four most probable stages are: o Stage 1 Launch o Stage 2a Backbone o Stage 2b Customer connection o Stage 3 Complete Generally, an ISP is able to upgrade a current IPv4 network to an IPv4/IPv6 dual-stack network via Stage 2b, but the IPv6 service can also be implemented at a small cost by adding simple tunnel mechanisms to the existing configuration. When designing a new network, Stage 3 might be the first and last step, because there are no legacy concerns. Nevertheless, the absence of IPv6 capability in the network equipment can still be a limiting factor. Note that in every stage except Stage 1, the ISP can offer both IPv4 and IPv6 services to its customers. 3.2.1 Stage 1 Scenarios: Launch The first stage is an IPv4-only ISP with an IPv4 customer. This is the most common case today and the natural starting point for the introduction of IPv6. From this stage, the ISP can move (transition)(undergo a transition) from Stage 1 to any other stage with the goal of offering IPv6 to its customer. The immediate first step consists of gettingobtaining a prefix allocation (typically a /32) from the appropriate RIR (e.g. AfriNIC, APNIC, ARIN, LACNIC, RIPE, ...) according to allocation procedures. 3.2.2 Stage 2a Scenarios: Backbone Stage 2a consists ofdeal with an ISP with IPv4-only customer connection networks and a backbone that supports both IPv4 and IPv6. In particular, the ISP has the possibility of making the backbone IPv6- capableIPv6-capable through either software upgrades, hardware upgrades, or a combination of both. Since the customer connections arehave not yet been upgraded, a tunneling mechanism has to be used to provide IPv6 connectivity through the IPv4 customer connection networks. The customer can terminate the tunnel at the CPE (if it has IPv6 support) or at each individual device. In the former case,some set of devices internal to its network. That is, either the CPE will thenor a device inside the network could provide global IPv6 connectivity to allthe rest of the devices in the customer's network. 3.2.3 Stage 2b Scenarios: Customer Connection Stage 2b consists of an ISP with an IPv4 backbone network and a customer connection network that supports both IPv4 and IPv6. Because the service to the customer is native IPv6, the customer is not required to support both IPv4 and IPv6. This is the biggest difference in comparison withto the previous stage. The need to exchange IPv6 traffic still exists but might be more complicated than in the previous case, because the backbone is not IPv6-enabled. After completing Stage 2b, the original IPv4 backbone is unchanged. This means that the IPv6 traffic is transported byeither tunnellingby tunneling over the existing IPv4 backbone, or in an IPv6 overlay network more or less separated from the IPv4 backbone. Normally the ISP will continue to provide IPv4 connectivity; in many casesconnectivity using private (NATted by the ISP) or public IPv4 addressesaddress; in many cases, the customer also has a NAT of his/her own, and NATs will continueif so, this likely continues to be used.used for IPv4 connectivity. 3.2.4 Stage 3 Scenarios: Complete Stage 3 can be said to be the final step in introducing IPv6, at least within the scope of this document. This stage consists of ubiquitous IPv6 service with native support for IPv6 and IPv4 in both backbone and customer connection networks. This stageIt is identical to the previous stage from the customer's perspective, because the customer connection network has not changed. The requirement for exchanging IPv6 traffic is identical to Stage 2. 3.2.5 Stages 2a and 3: Combination Scenarios Some ISPs may use different access technologies of varying IPv6 maturity. This may result in a combination of the Stages 2a and 3: some customer connections do not support IPv6, but others do; in both cases the backbone is dual-stack. This scenario is equivalent to Stage 2a, but it requires support for native IPv6 customer connections on some access technologies. 3.3 Transition Scenarios Given the different stages, it is clear that an ISP has to be able to make a transition from one stage to another. The initial stage,stage in this document,document is IPv4-only service and network. The end stage is dual IPv4/IPv6 service and network. The transition starts with an IPv4 ISP and then moves in one of three directions. This choice corresponds to the different transition scenarios. Stage 2a consists of upgrading the backbone first. Stage 2b consists of upgrading the customer connection network. Finally, Stage 3 consists of introducing IPv6 in both the backbone and customer connections as needed. Because most of ISPs continually evolve theirISP backbone IPv4 networks continually evolve (firmware replacements in routers, new routers, etc.), they willcan be able to get themmade ready for IPv6 without additional investment (except staff training). This may be a slower but still useful transition path, because it allows for IPv6the introduction of IPv6 without any actual customer demand. This process may be superior to doing everything at the last minute, which may entail a higher investment. However, it is important to start consideringconsider (and requestingto request from thevendors) IPv6 features in all new equipment from the start.outset. Otherwise, the time and effort required to remove non-IPv6-capablenon- IPv6-capable hardware from the network willmay be significant. 3.4 Actions Needed When Deploying IPv6 in an ISP's network Examination of the transitions described above reveals that it is possible to split the work required for each transition into a small set of actions. Each action is largely independent fromof the others, and some actions may be common to multiple transitions. Analysis of the possible transitions leads to a small list of actions: * Actions required for backbone transition: - Connect dual-stack customer connection networks to other IPv6 networks through an IPv4 backbone. - Transform an IPv4 backbone into a dual-stack one. This action can be performed directly or through intermediate steps. * Actions required for customer connection transition: - Connect IPv6 customers to an IPv6 backbone through an IPv4 network. - Transform an IPv4 customer connection network into a dual- stack one. * Actions required for network and service operation transition: - Configure IPv6 functions into network components. - Upgrade regular network management and monitoring applications to take IPv6 into account. - Extend customer management (e.g., RADIUS) mechanisms to be able to supply IPv6 prefixes and other information to customers. - Enhance accounting, billing, etc. to work with IPv6 as needed. (Note: if dual-stack service is offered, this may not be necessary.) - Implement security for network and service operation. Sections 4, 5, and 6 contain detailed descriptions of each action. 4. Backbone Transition Actions 4.1 Steps in Transitioningthe Transition of Backbone Networks In terms of physical equipment, backbone networks consist mainly of high-speed core and edge routers. Border routers provide peering with other providers. Filtering, routing policy, and policing functions are generally managed on border routers. The initial step isIn the beginning, an ISP has an IPv4-only backbone, andbackbone. In the final stepend, the backbone is acompletely dual-stack backbone.dual-stack. In between, intermediate steps may be identified: Tunnels Tunnels IPv4-only ----> or ---> or + DS -----> Full DS dedicated IPv6 dedicated IPv6 routers links links Figure 2: MigrationTransition Path. The first step involves tunnels or dedicated links but leaves existing routers unchanged. Only a small set of routers then have IPv6 capabilities. UsingThe use of configured tunnels is adequate during this step. In the second step, some dual stackdual-stack routers are added, progressively, to this network. The final step is reached when all or almost all routers are dual- stack. For many reasons (technical, financial, etc.), the ISP may progress step by step or jump directly to the final one. One of theimportant criteriacriterion in planning this evolution is the number of IPv6 customers the ISP expects during its initial deployments. If few customers connect to the original IPv6 infrastructure, then the ISP is likely to remain in the initial steps for a long time. In short, each intermediate step is possible, but none is mandatory. 4.1.1 MPLS Backbone If MPLS is already deployed in the backbone, it may be desirable to provide IPv6-over-MPLS connectivity. However, setting up an IPv6 Label Switched Path (LSP) requires signaling through the MPLS network; both LDP and RSVP-TE can set up IPv6 LSPs, but this wouldmight require a software upgradeupgrade/change in the MPLS core network. An alternative approach is to use BGP for signaling or to perform, for example, IPv6-over-IPv4/MPLS or IPv6-over-IPv4-over-IPv4/MPLS encapsulation,example IPv6-over-IPv4/MPLS, as described in [BGPTUNNEL]. Some of the multiple possibilities are preferable to others depending on the specific environment under consideration. More analysis is needed, case by case, to determineconsideration; the best approach or approaches:approaches seem to be: 1) Require that MPLS networks deploy native IPv6 support or use configured tunneling for IPv6.routing and forwarding support. 2) Require that MPLS networks support native routing and setting up of IPv6 LSPs, and set upused for IPv6 connectivity by using either these or configured tunneling.connectivity. 3) Use only configured tunneling over IPv4 LSPs; this seems practical with small-scale deployments having few tunnels.LSPs. 4) Use [BGPTUNNEL] or something comparableto perform IPv6-over- IPv4/MPLSIPv6-over-IPv4/MPLS encapsulation for IPv6 connectivity. Approaches 11) and 22) are clearly the most attractive if the ISP is willing to perform an upgrade to the MPLS network. Approach 3 does not require any upgrades but may lack scalability. Approach 4best target approaches. However, 1) may be economically attractive for an operator who doesnot wish to upgradebe possible if the MPLS network and has a large-scale deployment. MPLS networks have typically been deployedISP is not willing to facilitate services such as Provider-Provisioned VPNs. Software upgrades are commonplaceadd IPv6 support in MPLS networks. No particular reason exists to avoid addingthe network, or if the installed equipment is not capable of high performance native IPv6 functionality, exceptforwarding. 2) may not be possible if the vendorISP is unablenot willing or able to provide sufficientadd IPv6 forwarding capability (e.g., line-speed)LSP set-up support in the existing hardware (independent of the capabilities for handlingMPLS frames). Therefore, recommending mechanisms like [BGPTUNNEL]control plane. Approach 4) can be used as an interim mechanism where other options are unfeasible or undesirable for the final solution mightreasons discussed above. Approach 3) is roughly equivalent to 4) except that it does not be such a good idea.require additional mechanisms but may lack scalability in the larger networks especially if IPv6 is widely deployed. 4.2 Configuration of Backbone Equipment In the backbone, the number of devices is small and IPv6 configuration mainly deals with routing protocol parameters, interface addresses, loop-back addresses, ACLs, etc. These IPv6 parameters are not supposedneed to be configured automatically.manually. 4.3 Routing ISPs need routing protocols to advertise reachability and to find the shortest working paths, both internally and externally. Either OSPFv2 andor IS-IS areis typically used as anthe IPv4 IGP. RIPv2 is not typicallyusually used in operatorservice provider networks. BGP is the only IPv4 EGP. Static routes also are used in both cases. Note that it is possible to configure a given network so that it results in having an IPv6 topology different from its IPv4 topology. For example, some links or interfaces may be dedicated to IPv4-only or IPv6-only traffic, or some routers may be dual-stack whereas others may be IPv4 or IPv6 only. In this case, routing protocols must be able to understand and cope with multiple topologies. 4.3.1 IGP Once the IPv6 topology has been determined, the choice of IPv6 IGP must be made: either OSPFv3 or IS-IS for IPv6. RIPng is lessnot appropriate in manymost contexts and is therefore not discussed here. The IGP typically includes the routers' point-to-point and loop-back addresses. The most important decision is whether one wishes to have separate routing protocol processes for IPv4 and IPv6. Separating them requires more memory and CPU for route calculations, e.g., when the links flap. On the other hand, separation provides a certain measure of assurance that if problems arise with IPv6 routing, they will not affect IPv4the IPv4 routing protocol at all. In the initial phases, if it is uncertain whether joint IPv4-IPv6 networking is working as intended, running separate processes may be desirable and easier to manage. Thus the possible combinations are: - with separate processes: o OSPFv2 for IPv4, IS-IS for IPv6 (only) o OSPFv2 for IPv4, OSPFv3 for IPv6, or o IS-IS for IPv4, OSPFv3 for IPv6 - with the same process: o IS-IS for both IPv4 and IPv6 Note that if IS-IS is used for both IPv4 and IPv6, the IPv4/IPv6 topologies must be "convex," unless the Multiple-topologymultiple-topology IS-IS extensions [MTISIS] have been implemented.implemented (note that using IS-IS for only IPv4 or only IPv6 requires no convexity). In simpler networks or with careful planning of IS-IS link costs, it is possible to keep even incongruent IPv4/IPv6 topologies "convex." Therefore, the use of same processThe convexity problem is recommended especially for large ISPs intending to deploy,explained in more detail with an example in Appendix A. When deploying full dual-stack in the short-term, a fully dual- stack backbone infrastructure. If the topologies will notusing single- topology IS-IS is recommended. This may be similar in the short term,applicable particularly for some larger ISPs. In other scenarios, determining between one or two separate processes (or Multi-topology IS-IS extensions) are recommended. The IGP is not typically usedoften depends on the perceived risk to carry customer prefixesthe IPv4 routing infrastructure, i.e., whether one wishes to keep them separate for the time being. If that is not a factor, using a single process is usually preferable due to operational reasons: not having to manage two protocols and topologies. The IGP is typically only used to carry loopback and point-to-point addresses and doesn't include customer prefixes or external routes. Internal BGP (iBGP), as described in the next section, is most often deployed in all routers (PE and core) to distribute such otherrouting information. Because someinformation about customer prefixes and external routes. Some of the simplest devices, e.g., CPE routers, may not implement routing protocols other than RIPng, inRIPng. In some casescases, therefore, it may alsobe necessary to run RIPng in addition to one of the above IGPs, at least in a limited fashion, and somehowthen, by some mechanism, to redistribute routing information between the routing protocols. 4.3.2 EGP BGP is used for both internal and external BGP sessions. BGP with Multi-protocolmultiprotocol extensions [RFC 2858] can be used for IPv6 [RFC 2545]. These extensions enable exchanging boththe exchange of IPv6 routing information and establishingas well as the establishment of BGP sessions using TCP over IPv6. It is possible to use a single BGP session to advertise both IPv4 and IPv6 prefixes between two peers. However, typically,the most common practice today is to use separate BGP sessions are used.sessions. 4.3.3 Transport of Routing Protocols IPv4 routing information should be carried by IPv4 transport and similarly IPv6 routing information by IPv6 for several reasons: * IPv6 connectivity may work when IPv4 connectivity is down (or vice-versa). * The best route for IPv4 is not always the best one for IPv6. * The IPv4 logical topologyand theIPv6 onelogical topologies may be different, because the administrator may want to assign different metrics to a physical link for load balancing or because tunnels may be used.in use. 4.4 Multicast Currently, IPv6 multicast is not a major concern for most ISPs. However, some of them are considering deploying it. Multicast is achieved using the PIM-SM and PIM-SSM protocols. These also work with IPv6. Information about multicast sources is exchanged using MSDP in IPv4, but MSDP is intentionally not defined for IPv6. Instead, one should use only PIM-SSM or an alternative mechanism for conveying the information [EMBEDRP]. 5. Customer Connection Transition Actions 5.1 Steps in Transitioningthe Transition of Customer Connection Networks Customer connection networks are generally composed of a small set of PEs connected to a large set of CPEs.CPEs, and may be based on different technologies depending on the customer type or size, as well as the required bandwidth or even quality of service. Basically, public customers or small/unmanaged networks connection networks usually rely on a different technologies (e.g. dial-up or DSL) than the ones used for large customers typically running managed networks. Transitioning this infrastructurethese infrastructures to IPv6 can be accomplished in several steps, but some ISPs, depending on their perception of the risks, may avoid some of the steps. Connecting IPv6 customers to an IPv6 backbone through an IPv4 network can be considered as a first careful step taken by an ISP to provide IPv6 services to its IPv4 customers. In addition, some ISPs may also choose to provide IPv6 services to customers who get their IPv4 servicesservice independently from another ISP. Thisthe regular IPv4 service. In any case, IPv6 service can be provided by using tunneling techniques. The tunnel may terminate at the CPE corresponding to the IPv4 service or in some other part of the customer's infrastructure (for instance, on IPv6-specific CPE or even on a host). Several tunneling techniques have already been defined: configured tunnels with tunnel broker, 6to4, Teredo, etc. The selectionSome of one candidate depends largelythem are based on a specific addressing plan independent of the ISP's allocated prefix(es), while some others use a part of the ISP's prefix. In most cases using ISP's address space is preferable. A key factor is the presence or absence of NATs between the two tunnel end-points and whether the user's IPv4 tunnel end-point address is static or dynamic.end-points. In most cases, 6to4 and ISATAP are incompatible with NATs, and UDP encapsulation for configured tunnels has not been specified. However, NAT traversal canDynamic and non-permanent IPv4 address allocation is another factor a tunneling technique may have to deal with. In this case the tunneling techniques may be avoided ifmore difficult to deploy at the NAT supports forwarding protocol-41 [PROTO41].ISP's end, especially if a protocol including authentication (like PPP for IPv6) is not used. This may need to be considered in more detail. However, NAT traversal can be avoided if the NAT supports forwarding protocol-41 [PROTO41] and is configured to do so. Firewalls in the path can also break these typestunnels of tunnels.these types. The administrator of the firewall needs to create a hole for the tunnel. This is usually manageable, as long as the firewall is controlled by either the customer or the ISP, which is almost always the case. When the CPE is performing NAT or firewall functions, terminating the tunnels directly at the CPE typically simplifies the scenario considerably, avoiding the NAT and firewall traversal. If such an approach is adopted, the CPE has to support the tunneling mechanism used, or be upgraded to do so. In practice, an ISP has two kinds of customers in its customer connection networks: small5.1.1 Small end users (mostly unmanaged networks-- home and SOHO users) and others. The former category typically uses a dynamic IPv4 address, which is often non-routable; a reasonably static address is also possible. The latter category typically has static IPv4 addresses, and at least some of them are public; however, NAT traversal or configuration may be required to reach an internal IPv6 access router.sites Tunneling considerationconsiderations for small end sites are discussed in [UNMANCON] and[UNMANEVA]. These identify solutions relevant to the first category of unmanaged networks. The tunneling requirements applicable in these scenarios are described in [TUNREQS] The connectivity mechanisms can be categorized as "managed" or "opportunistic." The former consist of native service or a configured tunnel (with or without a tunnel broker); the latter include 6to4 and, e.g., Teredo;Teredo -- they provide "short-cuts" between nodes using the same mechanisms and are available without contracts with the ISP. The ISP may offer opportunistic services, mainly a 6to4 relay, especially as a test when no "real"actual service is offered yet. At the later phases, ISPs might also deploy 6to4 relays orand Teredo servers (or similar) to optimize their customers' connectivity to 6to4 orand Teredo nodes. It is to be noticed that opportunistic services are typically based on techniques that don't use IPv6 addresses out of the ISP's allocated prefix(es), and that the services have very limited functions to control the origin and the number of customers connected to a given relay. Most interesting are the managed services. When dual-stack is not an option, a form of tunneling must be used. When configured tunneling is not an option (e.g., due to dynamic IPv4 addressing), some form of automation has to be used. TheBasically, the options are basicallyeither to deploy an L2TP architecture (whereby the customers would run L2TP clients and PPP over it to initiate IPv6 sessions) or to deploy a tunnel configuration service. The prime candidates for tunnel configuration are STEP [STEP] and TSP [TSP], which are notboth also work in the presence of NATs. Neither is analyzed further in this document. For connecting larger customers: *5.1.2 Large end sites Large end sites are usually running managed network. Dual-stack access service is often a realistic possibility since the customer network is managed. *managed (although CPE upgrades may be necessary). Configured tunnels, as-is, are a good solution when a NAT is not in the way and the IPv4 end-point addresses are static. In this scenario, NAT traversal is not typically required. If fine-grained access control is needed, an authentication protocol needs to be used. * A tunnelimplemented. Tunnel brokering solution,solutions, to help facilitate the set-up of a bi-directionalbi- directional tunnel, hashave been proposed: the Tunnel Set-up Protocol. Whether this is the right approach needs to be determined. * Automatic tunnelingproposed. Such mechanisms suchare typically unnecessary for large end-sites, as 6to4simple configured tunneling or native access can be used instead. However, if such mechanisms would already be deployed, large sites starting to deploy IPv6 might be able to benefit from them in any case. Teredo areis not suggestedapplicable in this scenario. Other ISPs may take a more direct approach and avoid the use of tunnels as muchscenario as possible. Note that when customers use dynamic IPv4 addresses, the tunneling techniques may be more difficultit can only provide IPv6 connectivity to deploy at the ISP's end, especially ifa protocol including authentication (like PPP for IPv6)single host, not the whole site. 6to4 is not used. This may needrecommended due to be considered in more detail with tunneling mechanisms.its reliance on the relays and provider- independent address space, which make it impossible to guarantee the required service quality and manageability large sites typically want. 5.2 AccessUser Authentication/Access Control Requirements Access control is usually required in ISP networks, because the ISPs needUser authentication can be used to control to whom they are granting access. For instance, it is important to check whetherwho can use the userIPv6 connectivity service in the first place or who tries to connect is really a valid customer. In some cases, itcan access specific IPv6 services (e.g., NNTP servers meant for customers only, etc.). The former is also importantdescribed at more length below. The latter can be achieved by ensuring that for billing. However, IPv6-specificall the service-specific IPv4 access controllists, there are also equivalent IPv6 access lists. IPv6-specific user authentication is not always required. ThisAn example is the case, for instance, whena customer of the IPv4 service hasautomatically having access to the IPv6 service. Then,In this case the IPv4 access control also provides access to the IPv6 services. When a provider does not wish to give its IPv4 customers automatic access to IPv6 services, specific IPv6 access control must be performed in parallel with the IPv4 access control. This does not imply that different user authentication must be performed for IPv6, but merely that the authentication process may lead to different results for IPv4 and IPv6 access. Access control traffic may use IPv4 or IPv6 transport. For instance, Radius traffic related to IPv6 service can be transported over IPv4. 5.3 Configuration of Customer Equipment The customer connection networks are composed of PE and CPE(s). Usually, each PE connects multiple CPE components to the backbone network infrastructure. This number may reach tens of thousands or more. The configuration of CPE is, in general,is a difficult task for the ISP, and it is even more so in this case, because configurationdifficult when it must be done remotely. In this context, the use of auto-configuration mechanisms is beneficial, even if manual configuration is still an option. The parameters that usually need to be provided to customers automatically are: - The network prefix delegated by the ISP, - The address of the Domain Name System server (DNS), - Possibly other parameters, e.g., the address of aan NTP server. When user identification is required on the ISP's network, DHCPv6 may be used to provide configurations otherwiseconfigurations; otherwise, either DHCPv6 or a stateless mechanism can be used. This is discussed in more detail in [DUAL ACCESS]. Note that when the customer connection network is shared between the users or the ISPs, and not just a point-to-point link, authenticating the configuration of the parameters (esp.(especially prefix delegation) requires further study. As long as IPv4 service is available alongside of IPv6, no critical need exists to be ableIPv6 it is not required to autoconfigureauto configure IPv6 parameters (except for the prefix)in the CPE--CPE, except the prefix, because the IPv4 settings work as well.may be used. 5.4 Requirements for Traceability Most ISPs have some kind of mechanism to trace the origin of traffic in their networks. This also has to be available for IPv6 traffic, which meansmeaning that a specific IPv6 address or prefix has to be tied to a certain customer, or that records of which customer had which address or prefix must be maintained. This also applies to the customers with tunneled connectivity. This can be done, for example, by mapping a DHCP response to a physical connection and storing thisthe result in a database. It can also be done by assigning a static address or prefix to the customer. A tunnel server could also provide this mapping. 5.5 Ingress Filtering in the Customer Connection Network Ingress filtering must be deployed towards the customers, everywhere, to ensure traceability, to prevent DoS attacks using spoofed addresses, to prevent illegitimate access to the management infrastructure, etc. Ingress filtering can be done, for example, by using access lists or Unicast Reverse Path Forwarding (uRPF). Mechanisms for these are described in [BCP38UPD]. 5.6 Multi-HomingMultihoming Customers may desire multi-homingmultihoming or multi-connecting for a number of reasons [RFC3582]. Multi-homingMechanisms for multihoming to more than one ISP is a subjectare still under debate. Deploying multiple addresses from each ISPdiscussion. One working model could be to deploy at least one prefix per ISP, and usingto choose the addresses ofprefix from the ISP when sending trafficto that ISPwhich traffic is at least one working model; insent. In addition, tunnels may be used for robustness [RFC3178]. Currently, there are no provider-independent addresses for end- sites.end-sites. Such addresses would enable IPv4-style multihoming, with associated disadvantages. Multi-connecting more than once to just one ISP is a simple practice, and this can be done, e.g., by using BGP with public or private AS numbers and a prefix assigned to the customer. 5.7 Quality of Service In most networks, quality of service in one form or another is important. Naturally, the introduction of IPv6 should not impair existing Service Level Agreements (SLAs) or similar quality reassurances. Depending onassurances. During the deployment of the IPv6 service, the service could be best-effort, at least initially,best- effort or similar even if the IPv4 service hadhas a SLA. BothIn the end both IP version should be treated equally. IntServ and DiffServ are equally applicable into IPv6 as well as into IPv4 and work in a similar fashion.fashion independent of IP version. Of these, typically only DiffServ has been implemented. 6. Network and Service Operation Actions The network and service operation actions fall into different categories as listed below: - IPv6 network device configuration: for initial configuration and updates - IPv6 network management - IPv6 monitoring - IPv6 customer management - IPv6 network and service operation security Some of these items will require an IPv6 native transport layer to be available, whereas others will not. As a first step, network device configuration and regular network management operations can be performed over an IPv4 transport, because IPv6 MIBs are also available over IPv4 transport. Nevertheless, some monitoring functions require the availability of IPv6 transport. This is the case, for instance, when ICMPv6 messages are used by the monitoring applications. The current inability on many platforms to getretrieve separate IPv4 and IPv6 traffic statistics from dual-stack interfaces for management purposes by using SNMP separately from dual-stack interfacesis an issue. As a second step, IPv6 transport can be provided for any of these network and service operation facilities. 7. Future Stages At some point, an ISP might want to transition to a service that is IPv6 only, at least in certain parts of its network. ThisSuch a transition creates a lot ofmany new cases into which it must factor how to maintaincontinued maintenance of the IPv4 service.service must be factored. Providing an IPv6-only service is not much different from the dual IPv4/IPv6 service described in stage 3 except for the need to phase out the IPv4 service. The delivery of IPv4 services over an IPv6 network and the phase out of IPv4 are left for a subsequent document. 8. Example Networks In this section, a number of different network examplesexample networks are presented. These are only example networks andwill not necessarily match any existing networks. Nevertheless, the examplesmatch any existing networks but are intended to be useful even in cases in which they do not matchcorrespond to specific target networks. The purpose of the example networksthese examples is to exemplify the applicability of the transition mechanisms described in this document to a number of different situations with different prerequisites. The sample network layout will be the same in all network examples. The network examplesThese should be viewed as specific representations of a generic network with a limited number of network devices. A small number of routers have been used in the networkexamples. However, because the network examples follow the implementation strategies recommended for the generic network scenario, it should be possible to scale the examples to fit a network with an arbitrary number, e.g. several hundreds or thousands, of routers. The routers in the sample network layout are interconnected with each other as well as with another ISP. The connection to another ISP can be either direct or through an exchange point. In addition to these connections, a number of customer connection networks are also connected to the routers. Customer connection networks can be, for example, xDSL or cable network equipment. ISP1 | ISP2 +------+ | +------+ | | | | | |Router|--|--|Router| | | | | | +------+ | +------+ / \ +----------------------- / \ / \ +------+ +------+ | | | | |Router|----|Router| | | | | +------+ +------+\ | | \ | Exchange point +------+ +------+ \ +------+ | +------+ | | | | \_| | | | |-- |Router|----|Router|----\|Router|--|--|Switch|-- | | | | | | | | |-- +------+ /+------+ +------+ | +------+ | / | | +-------+/ +-------+ | | | | | |Access1| |Access2| | | | | +-------+ +-------+ ||||| ||||| ISP Network ----|-----------|---------------------- | | Customer Networks +--------+ +--------+ | | | | |Customer| |Customer| | | | | +--------+ +--------+ Figure 3: ISP Sample Network Layout. 8.1 Example 1 Example 1 presents a network built according to the sample network layout with a native IPv4 backbone. The backbone is running IS-IS and IBGP as routing protocols for internal and external routes, respectively. MBGPMultiprotocol BGP is used to exchange routes over the connections to ISP2 and the exchange point. Multicast using PIM-SM routing is present. QoS using DiffServ is deployed. Access 1 is xDSL connected to the backbone through an access router. The xDSL equipment, except for the access router, is considered to be layer 2 only, e.g., Ethernet or ATM. IPv4 addresses are dynamically assigned to the customer using DHCP. No routing information is exchanged with the customer. Access control and traceability are preformedperformed in the access router. Customers are separated into VLANs or separate ATM PVCs up to the access router. Access 2 is Fiber"fiber to the building or homehome" (FTTB/H) connected directly to the backbone router. This connection is considered to be layer-3-aware, because it is using layer 3 switches and it performs access control and traceability through its layer 3 awareness by using DHCP snooping. IPv4 addresses are dynamically assigned to the customers using DHCP. No routing information is exchanged with the customer. The actual IPv6 deployment might start by enabling IPv6 on a couple of backbone routers, configuring tunnels between them (if not adjacent), and connecting to a few peers or upstream providers (either through tunnels or at an internet exchange). After a trial period, the rest of the backbone is upgraded to dual- stack, and IS-IS without multi-topology extensions (the upgrade order is considered with care) is used as an IPv6 and IPv4 IGP. When upgrading, it's important to note that until IPv6 customers are connected behind a backbone router, the convexity requirement is not critical: the routers justwill just not be able to be reachedreachable using IPv6. That is, asoftware supporting IPv6 could be installed even though the routers would not be used for (customer) IPv6 traffic yet. That way, IPv6 could be enabled in the backbone on a need-to-enable basis when needed. Separate IPv6 BGP sessions are built, similar to IPv4. Multicast (through SSM and Embedded-RP) and DiffServ are offered at a later phase of the network, e.g., after a year of stable IPv6 unicast operations. Customers (with some exceptions) are not connected using a tunnel broker, because offeringOffering native service fasteras quickly as possible is considered more important -- and then there will not be unnecessary parallel infrastructures to tear down later on.most important. However, a 6to4 relay ismay be provided in the meantime for optimized 6to4 connectivity.connectivity and it may also be combined with a tunnel broker for extended functionality. xDSL equipment, operating as bridges at Layer 2 only, dodoes not require changes in CPE: IPv6 connectivity can be offered to the customers by upgrading the PE router to IPv6. In the initial phase, only Router Advertisements are used; DHCPv6 Prefix Delegation can be added as the next step if no other mechanisms are available. The FTTB/H access has to be upgraded to support access control and traceability in the switches, probably by using DHCP snooping or a similar IPv6 capability, but it also has to be compatible with prefix delegation and not just address assignment. This could, however, lead to the need to use DHCPv6 for address assignment. 8.2 Example 2 In example 2 the backbone is running IPv4 with MPLS and is using OSPF and IBGP are for internal and external routes respectively. The connectionconnections to ISP2 and the exchange point run BGP to exchange routes. Multicast and QoS are not deployed. Access 1 is a fixed line, e.g., fiber, connected directly to the backbone. Routing information is in some cases exchanged with CPE at the customer's site; otherwise static routing is used. Access 1 can also be connected to a BGP/MPLS-VPN running in the backbone. Access 2 is xDSL connected directly to the backbone router. The xDSL is layer 2 only, and access control and traceability are achieved through PPPoE/PPPoA. PPP also provides address assignment. No routing information is exchanged with the customer. IPv6 deployment might start with an upgrade of a couple of PE routers to support [BGPTUNNEL], because this will allow large-scale IPv6 support without hardware or software upgrades in the core. In a later phase, perhaps years later,phase native IPv6 traffic or IPv6 LSPs would run nativelybe used in the whole network. In that case IS-IS or OSPF could be used for the internal routing, and a separate IPv6 BGP session would be run. For the fixed-line customerscustomers, the CPE has to be upgraded and prefix delegation using DHCPv6 or static assignment would be used. An IPv6 MBGP session would be used when routing information has to be exchanged. In the xDSL case the same conditions for IP-tunneling as in Example 1 apply. In addition to IP-tunneling an additional PPP session can be used to offer IPv6 access to a limited number of customers. Later, when clients and servers have been updated, the IPv6 PPP session can be replaced with a combined PPP session for both IPv4 and IPv6. PPP has to be used for address and prefix assignment. 8.3 Example 3 A transit provider offers IP connectivity to other providers, but not to end users or enterprises. IS-IS and IBGP are used internally and BGP externally. Its accesses connect Tier-2 provider cores. No multicast or QoS is used. Even though the RIR policies on getting IPv6 prefixes require the assignment of at least 200 /48 prefixes to the customers, this type of transit provider obtains an allocation nonetheless, as the number of customers their customers serve is significant. The whole backbone can be upgraded to dual-stack in a reasonably rapid pace after trialing ita trial with a couple of routers. IPv6 routing is performed using the same IS-IS process and separate IPv6 BGP sessions. The ISP provides IPv6 transit to its customers for free, as a competitive advantage. It also provides, at the first phase only, a configured tunnel service with BGP peering to the significant sites and customers (those with an AS number) which are the customers of its customers whenever its own customer networks are not offering IPv6. This is done both to introduce them to IPv6 and to create a beneficial side-effect: a bit of extra revenue is generated from its direct customers as the total amount of transited traffic grows. 9. Security Considerations This document analyses scenarios and identifies some transition mechanisms that could be used for the scenarios. It does not introduce any new security issues. Security considerations of each mechanism are described in the respective documents. However, a few generic observations are in order. o introducing IPv6 adds new classes of security threats or requires adopting new protocols or operational models than with IPv6;IPv4; typically these are generic issues, and to be further discussed in other documents, for example, [V6SEC]. o the more complex the transition mechanisms employed become, the more difficult it will be to manage or analyze their impact on security; consequently,security. Consequently, simple mechanisms are to be preferred. o this document has identified a number of requirements for analysis or further work which should be explicitly considered when adopting IPv6: how to perform access control over shared media or shared ISP customer connection media, how to manage the configuration management security on such environments (e.g., DHCPv6 authentication keying), and how to manage customer traceability if stateless address autoconfiguration is used. 10. Acknowledgements This draft has greatly benefited from inputs by Marc Blanchet, Jordi Palet, Francois Le FaucheurFaucheur, Ronald van der Pol and Cleve Mickles. Special thanks to Richard Graveman and Michael Lambert for proofreading the document. 11. Informative References [EMBEDRP] Savola, P., Haberman, B., "Embedding the Address of RP in IPv6 Multicast Address" - Work in progress [MTISIS] Przygienda, T., Naiming Shen, Nischal Sheth, "M- ISIS: Multi Topology (MT) Routing in IS-IS" Work in progress [RFC 2858] T. Bates, Y. Rekhter, R. Chandra, D. Katz, "Multiprotocol Extensions for BGP-4" RFC 2858 [RFC 2545] P. Marques, F. Dupont, "Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing" RFC 2545 [BCP38UPD] F. Baker, P. Savola "Ingress Filtering for Multihomed Networks" Work in progress [RFC3582] J. Abley, B. Black, V. Gill, "Goals for IPv6 Site- Multihoming Architectures" RFC 3582 [RFC3178] J. Hagino, H. Snyder, "IPv6 Multihoming Support at Site Exit Routers" RFC 3178 [BGPTUNNEL] J. De Clercq, G. Gastaud, D. Ooms, S. Prevost, F. Le Faucheur "Connecting IPv6 Islands across IPv4 Clouds with BGP" draft-ooms-v6ops-bgp-tunnel-00.txtWork in progress [DUAL ACCESS] Y. Shirasaki, S. Miyakawa, T. Yamasaki, A. Takenouchi "A Model of IPv6/IPv4 Dual Stack Internet Access Service" Work in progress [UNMANCON] T.Chown, R. van der Pol,[STEP] P. Savola, "Considerations for IPv6 Tunneling Solutions"Simple IPv6-in-IPv4 Tunnel Establishment Procedure (STEP)" Work in Small End Sites"progress [TSP] M. Blanchet, "IPv6 Tunnel broker with Tunnel Setup Protocol (TSP)" Work in progress [TUNREQS] A. Durand, F. Parent "Requirements for assisted tunneling" Work in progress [UNMANEVA] C. Huitema, R. Austein, S. Satapati, R. van der Pol, "Evaluation of Transition Mechanisms for Unmanaged Networks" Work in progress [PROTO41] J. Palet, C. Olvera, D. Fernandez, "Forwarding Protocol 41 in NAT Boxes" Work in progress [V6SEC] P. Savola, "IPv6 Transition/Co-existence Security Considerations" Work in progress Authors' Addresses Mikael Lind TeliaSonera Vitsandsgatan 9B SE-12386 Farsta, Sweden Email: email@example.com Vladimir Ksinant 6WIND S.A. Immeuble Central Gare - Bat.C 1, place CharlesThales Communications 160, boulevard de Gaulle 78180, Montigny-Le-Bretonneux -Valmy 92704 Colombes, France Phone: +33 1 39 30 92 36Email: firstname.lastname@example.org@fr.thalesgroup.com Soohong Daniel Park Mobile Platform Laboratory, SAMSUNG Electronics. 416, Maetan-3dong, Paldal-Gu, Suwon, Gyeonggi-do, Korea Email: email@example.com Alain Baudot France Telecom R&D 42, rue des coutures 14066 Caen - FRANCE Email: firstname.lastname@example.org Pekka Savola CSC/FUNET Espoo, Finland EMail: email@example.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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 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. Appendix A: Convexity Requirements in Single Topology IS-IS The single-topology IS-IS convexity requirements could be summarized, from IPv4/6 perspective, as follows: 1) "any IP-independent path from an IPv4 router to any other IPv4 router must only go through routers which are IPv4-capable", and 2) "any IP-independent path from an IPv6 router to any other IPv6 router must only go through routers which are IPv6-capable". As IS-IS is based upon CLNS, these are not trivially accomplished. The single-topology IS-IS builds paths which are agnostic of IP versions. Consider an example scenario of three IPv4/IPv6-capable routers and an IPv4-only router: cost 5 R4 cost 5 ,------- [v4/v6] -----. / \ [v4/v6] ------ [ v4 ] -----[v4/v6] R1 cost 3 R3 cost 3 R2 Here the second requirement would not hold. IPv6 packets from R1 to R2 (or vice versa) would go through R3, which does not support IPv6, and the packets would get discarded. By reversing the costs between R1-R3, R3-R2 and R1-R4,R4-R2 the traffic would work in the normal case, but if a link fails and the routing changes to go through R3, the packets would start being discarded again.