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Versions: 00 01 02 03 RFC 4029

   Internet Draft                                               M. Lind
   <draft-ietf-v6ops-isp-scenarios-analysis-01.txt>         TeliaSonera
                                                             V. Ksinant
                                                                  6WIND
                                                                S. Park
                                                    Samsung Electronics
                                                              A. Baudot
                                                         France Telecom
                                                              P. Savola
                                                              CSC/Funet
   Expires: August 2004                                   February 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.







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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 Transitioning Backbone Networks.................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...................................................11
      4.3.3  Transport of Routing Protocols........................12
      4.4  Multicast...............................................12
   5.   Customer Connection Transition Actions.....................12
      5.1  Steps in Transitioning Customer Connection Networks.....12
      5.2  Access Control Requirements.............................14
      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............................................16
      5.7  Quality of Service......................................16
   6.   Network and Service Operation Actions......................17
   7.   Future Stages..............................................17
   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
   to its customers. The new IPv6 service must be added to an already




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   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 functionality
   essential 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 the customer connection networks
   connecting the customers. 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



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                   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 the
   customers.



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   It is possible to transition 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
   to transform its network.

   This document is not aimed to cover small ISPs, hosting providers, or
   data centers; only the scenarios applicable to ISPs eligible for 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 for this
   document are the ones 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



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   introduction of IPv6.  From this stage, the ISP can move (transition)
   from Stage 1 to any other stage with the goal of offering IPv6 to its
   customer.

   The immediate first step consists of getting a prefix allocation
   (typically a /32) from the appropriate RIR according to allocation
   procedures.

3.2.2 Stage 2a Scenarios: Backbone

   Stage 2a consists of 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-
   capable through either software upgrades, hardware upgrades, or a
   combination of both.

   Since the customer connections are not yet 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, the CPE will then provide global IPv6
   connectivity to all 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 with 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 by either tunnelling 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 cases private IPv4 addresses and NATs will continue to be used.

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 consists of ubiquitous
   IPv6 service with native support for IPv6 and IPv4 in both backbone
   and customer connection networks. This stage 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.



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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 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 transition from one stage to another. The initial stage, in this
   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 their backbone IPv4 networks
   (firmware replacements in routers, new routers, etc.), they will be
   able to get them ready for IPv6 without additional investment
   (except staff training). This may be a slower but still useful
   transition path, because it allows for IPv6 introduction without any
   actual customer demand. This may be superior to doing everything
   at the last minute, which may entail a higher investment. However, it
   is important to start considering (and requesting from the vendors)
   IPv6 features in all new equipment from the start. Otherwise, the
   time and effort to remove non-IPv6-capable hardware from the network
   will 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 from 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:




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        - 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 Transitioning 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 is an IPv4-only backbone, and the final step is a
   completely dual-stack backbone. In between, intermediate steps may be
   identified:






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                     Tunnels         Tunnels
   IPv4-only ---->      or      --->   or         +  DS -----> Full DS
                  dedicated IPv6   dedicated IPv6  routers
                      links           links
          Figure 2: Migration Path.

   The first step involves tunnels or dedicated links but leaves
   existing routers unchanged. Only a small set of routers then have
   IPv6 capabilities. Using configured tunnels is adequate during
   this step.

   In the second step, some dual 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 the final one. One of the important
   criteria 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 would
   require a software upgrade 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,
   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 determine
   the best approach or approaches:

        1) Require that MPLS networks deploy native IPv6 support or
           use configured tunneling for IPv6.

        2) Require that MPLS networks support setting up IPv6 LSPs,
           and set up IPv6 connectivity by using either these or
           configured tunneling.

        3) Use only configured tunneling over IPv4 LSPs; this seems



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           practical with small-scale deployments having few tunnels.

        4) Use [BGPTUNNEL] or something comparable to perform IPv6-over-
           IPv4/MPLS encapsulation for IPv6 connectivity.

   Approaches 1 and 2 are 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 4 may be economically
   attractive for an operator who does not wish to upgrade the MPLS
   network and has a large-scale deployment.

   MPLS networks have typically been deployed to facilitate services
   such as Provider-Provisioned VPNs. Software upgrades are commonplace
   in MPLS networks. No particular reason exists to avoid adding IPv6
   functionality, except if the vendor is unable to provide sufficient
   IPv6 forwarding capability (e.g., line-speed) in the existing
   hardware (independent of the capabilities for handling MPLS frames).
   Therefore, recommending mechanisms like [BGPTUNNEL] as the final
   solution might not be such a good idea.

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 supposed to be configured
   automatically.

4.3 Routing

   ISPs need routing protocols to advertise reachability and to
   find the shortest working paths, both internally and externally.

   OSPFv2 and IS-IS are typically used as an IPv4 IGP. RIPv2 is not
   typically used in operator 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 less



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   appropriate in many contexts and is 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 IPv4 the 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-topology IS-IS
   extensions [MTISIS] have been implemented. 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 process is recommended especially for
   large ISPs intending to deploy, in the short-term, a fully dual-
   stack backbone infrastructure.  If the topologies will not be similar
   in the short term, two processes (or Multi-topology IS-IS
   extensions) are recommended.

   The IGP is not typically used to carry customer prefixes or external
   routes. Internal BGP (iBGP), as described in the next section, is
   most often deployed in all routers to distribute such other routing
   information.

   Because some of the simplest devices, e.g., CPE routers, may not
   implement routing protocols other than RIPng, in some cases it may
   also be necessary to run RIPng in addition to one of the above IGPs,
   at least in a limited fashion, and somehow to redistribute routing
   information between the routing protocols.

4.3.2 EGP




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   BGP is used for both internal and external BGP sessions.

   BGP with Multi-protocol extensions [RFC 2858] can be used for IPv6
   [RFC 2545].  These extensions enable exchanging both IPv6 routing
   information and establishing 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, separate
   BGP sessions are used.

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 topology and the IPv6 one may be different,
         because the administrator may want to assign different metrics
         to a physical link for load balancing or tunnels may be used.

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 Transitioning Customer Connection Networks

   Customer connection networks are generally composed of a small set of
   PEs connected to a large set of CPEs. Transitioning this
   infrastructure 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 provide IPv6 services to customers who get their IPv4
   services from another ISP.




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   This 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 selection of one candidate depends largely on 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. In most
   cases, 6to4 and ISATAP are incompatible with NATs, and UDP
   encapsulation for configured tunnels has not been specified.

   However, NAT traversal can be avoided if the NAT supports
   forwarding protocol-41 [PROTO41].

   Firewalls in the path can also break these types of tunnels. 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: 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.

   Tunneling consideration for small end sites are discussed in
   [UNMANCON] and [UNMANEVA].  These identify solutions relevant to the
   first category of unmanaged networks.

   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; they provide "short-cuts" between
   nodes using the same mechanisms and are available without contracts
   with the ISP.




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   The ISP may offer opportunistic services, mainly a 6to4 relay,
   especially as a test when no "real" service is offered yet. At the
   later phases, ISPs might also deploy 6to4 relays or Teredo servers
   (or similar) to optimize their customers' connectivity to 6to4 or
   Teredo nodes.

   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. The options are basically either 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 not analyzed further in this
   document.

   For connecting larger customers:

   * Dual-stack access service is often a realistic possibility since
     the customer network is managed.

   * 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 tunnel brokering solution, to help facilitate the set-up of a
     bi-directional tunnel, has been proposed: the Tunnel Set-up
     Protocol. Whether this is the right approach needs to be
     determined.

   * Automatic tunneling mechanisms such as 6to4 or Teredo are not
     suggested in this scenario.

   Other ISPs may take a more direct approach and avoid the use of
   tunnels as much as possible.

   Note that when customers use dynamic IPv4 addresses, the
   tunneling techniques may be more difficult to deploy at the 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
   with tunneling mechanisms.

5.2 Access Control Requirements

   Access control is usually required in ISP networks, because the ISPs
   need to control to whom they are granting access. For instance, it is




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   important to check whether the user who tries to connect is really a
   valid customer. In some cases, it is also important for billing.

   However, IPv6-specific access control is not always required.
   This is the case, for instance, when a customer of the IPv4 service
   has automatically access to IPv6 service. Then, 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, a difficult task for
   the ISP, and even more so in this case, because configuration 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 a NTP server.

   When user identification is required on the ISP's network, DHCPv6 may
   be used to provide configurations 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. prefix delegation) requires
   further study.






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   As long as IPv4 service is available alongside of IPv6, no critical
   need exists to be able to autoconfigure IPv6 parameters (except for
   the prefix) in the CPE-- IPv4 settings work as well.

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 means 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 this in a database. It can also be
   done by assigning a static address or prefix to the customer.

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-Homing

   Customers may desire multi-homing or multi-connecting for a number of
   reasons [RFC3582].

   Multi-homing to more than one ISP is a subject still under debate.
   Deploying multiple addresses from each ISP and using the addresses
   of the ISP when sending traffic to that ISP is at least one working
   model; in addition, tunnels may be used for robustness [RFC3178].
   Currently, there are no provider-independent addresses for end-
   sites.

   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.




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   Naturally, the introduction of IPv6 should not impair existing
   Service Level Agreements (SLAs) or similar quality reassurances.

   Depending on the deployment of the IPv6 service, the service could
   be best-effort, at least initially, even if the IPv4 service had a
   SLA.

   Both IntServ and DiffServ are equally applicable in IPv6 as well as
   in IPv4 and work in a similar fashion.  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 to get IPv4 and IPv6 traffic statistics for
   management purposes by using SNMP separately from dual-stack
   interfaces is 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.  This
   transition creates a lot of new cases into which it must factor how
   to maintain the IPv4 service.  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




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   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 examples are
   presented. These are only example networks and will not necessarily
   match any existing networks. Nevertheless, the examples are intended
   be useful even in cases in which they do not match specific target
   networks. The purpose of the example networks 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 examples 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 network examples. 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.























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                       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. MBGP 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



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   are dynamically assigned to the customer using DHCP. No routing
   information is exchanged with the customer. Access control and
   traceability are preformed in the access router. Customers are
   separated into VLANs or separate ATM PVCs up to the access router.

   Access 2 is Fiber to the building or home (FTTB/H) connected directly
   to the backbone router. This 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 just will not be able to be reached using IPv6.
   That is, a software 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 offering native service faster is considered more
   important -- and then there will not be unnecessary parallel
   infrastructures to tear down later on.  However, a 6to4 relay is
   provided in the meantime for optimized 6to4 connectivity. xDSL
   equipment, operating as bridges at Layer 2 only, do 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.



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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
   connection 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 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, IPv6 traffic would run natively 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 customers 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 it with a couple of routers.  IPv6 routing is performed
   using the same IS-IS and separate IPv6 BGP sessions.



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   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; 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, 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 Faucheur and Cleve Mickles. Special thanks to
   Richard Graveman for proofreading the document.

11. Informative References

   [EMBEDRP]       Savola, P., Haberman, B., "Embedding the Address of
                   RP in IPv6 Multicast Address" -



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                   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.txt

   [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, P. Savola, "Considerations
                  for IPv6 Tunneling Solutions in Small End Sites"
                  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




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   [V6SEC]        P. Savola, "IPv6 Transition/Co-existence Security
                  Considerations"
                  Work in progress

Authors' Addresses

   Mikael Lind
   TeliaSonera
   Vitsandsgatan 9B
   SE-12386 Farsta, Sweden
   Email: mikael.lind@teliasonera.com

   Vladimir Ksinant
   6WIND S.A.
   Immeuble Central Gare - Bat.C
   1, place Charles de Gaulle
   78180, Montigny-Le-Bretonneux - France
   Phone: +33 1 39 30 92 36
   Email: vladimir.ksinant@6wind.com

   Soohong Daniel Park
   Mobile Platform Laboratory, SAMSUNG Electronics.
   416, Maetan-3dong, Paldal-Gu,
   Suwon, Gyeonggi-do, Korea
   Email: soohong.park@samsung.com

   Alain Baudot
   France Telecom R&D
   42, rue des coutures
   14066 Caen - FRANCE
   Email: alain.baudot@rd.francetelecom.com

   Pekka Savola
   CSC/FUNET
   Espoo, Finland
   EMail: psavola@funet.fi


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   of licenses to be made available, or the result of an attempt made
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