Internet Draft                                      V. Ksinant (ed.)
   <draft-ksinant-v6ops-isp-analysis-00.txt>                      6WIND
   Expires: April 2004                                        P. Savola
                                                              CSC/FUNET
                                                              A. Baudot
                                                         France Telecom
                                                            M. Blanchet
                                                                 Hexago
                                                                M. Lind
                                                           Telia Sonera
                                                    Soohong Daniel Park
                                                    SAMSUNG Electronics
                                                           October 2003


                    Analysis of Transition Mechanisms
                 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

   In a companion document, different scenarios for the introduction of
   IPv6 in an IPv4 ISP network are described.

   This document analyses these ISP scenarios and evaluates the
   suitability 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
      1.2 Terminology used......................................    3
   2. Analysis of the ISP transition scenarios..................    4
      2.1 Stages and transitions between stages.................    4
      2.2 Identification of the actions required................    5
   3. Core Transition actions...................................    5
      3.1 Steps in transitioning core networks..................    5
      3.2 Configuration of core equipment.......................    6
      3.3 Routing...............................................    6
      3.4 Multicast.............................................    8
   4. Access transition actions.................................    8
      4.1 Steps in transitioning access networks................    8
      4.2 Access control requirements...........................   10
      4.3 Configuration of customer equipment...................   10
      4.4 Traceability..........................................   11
      4.5 Multi-homing..........................................   11
      4.6 Filtering in the access network.......................   11
   5. Exchange points actions...................................
   6. Back-Office actions.......................................   12
   7. Security Considerations...................................   12





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
   existing IPv4 service and the introduction of the IPv6 must not
   interrupt this IPv4 service. The case of an IPv6-only service
   provider is not addressed in this document.

   The ngtrans working group of the IETF has designed some transition
   mechanisms which aim at introducing IPv6 in generic IPv4 networks.

   Taking an ISP specific point of view, [ISP_SCENARIOS] discusses a
   small set of scenarios for the introduction of IPv6 in an ISP IPv4
   network. The goal of the present document is to evaluate the
   suitability of the existing transition mechanisms in the context of
   these deployment scenarios.






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   Like [ISP_SCENARIOS], the present document is focused on services
   that include both IPv6 and IPv4 and does not cover issues surrounding
   an IPv6-only service. It is also outside the scope of this document
   to describe different types of access or network technologies.

   Last, this document does not cover deeply issues which are important
   when deploying IPv6, but which do not have a strong impact on the
   evaluation of existing transition mechanisms. This is for instance
   the case of:

     - issues arising when applying for IPv6 addresses from RIR,
     - the definition of addressing plans,
     - the set up of support and technical processes.

1.2 Terminology used

   The terminology used in this document corresponds to the one defined
   in the [ISP_SCENARIOS] document. For clarity, a few terms are defined
   below:

   "CPE"         : Customer Premise Equipment

   "PE"          : Provider Edge equipment

   "Access"      : This is the part of the network which is used by a
                   customer when connecting to an ISP network. It
                   includes the CPEs, the last hop links and the parts
                   of the PE interfacing to the last hop links.

   "Core"        : This is the rest of the ISP network infrastructure.
                   It includes the parts of the PE interfacing to the
                   core backbone, the core routers of the ISP and the
                   border routers used in order to exchange routing
                   information with other ISPs (or other administrative
                   entities).

   "Back Office" : This is the part of the ISP network which hosts the
                   services required for the correct operation of the
                   ISP network. It usually includes DNS servers, Radius
                   servers, monitoring and configuration applications...

   "Dual network": A network which supports natively both IPv4 and IPv6.











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2. Analysis of the ISP transition scenarios

2.1 Stages and transitions between stages

   [ISP_SCENARIOS] defines four transition stages:

   - Launch:      This stage corresponds to an IPv4 only ISP with IPv4
                  customers. This is the most common case today and has
                  to be the starting point for the introduction of IPv6.

   - IPv6 Core:   This stage corresponds to an ISP with an IPv4 and IPv6
                  core, but the access network is only IPv4 capable. The
                  customers using IPv6 services have IPv4 and IPv6
                  capabilities.

   - IPv6 Access: This stage corresponds to an ISP with an IPv4 only
                  core, but with access networks which support IPv4 and
                  IPv6. The customers using IPv6 services have IPv4 and
                  IPv6 capabilities.

   - Complete:    This is the final step in introducing IPv6, at least
                  in the scope of this document. The ISP has then native
                  support for IPv6 and IPv4 in both core and access
                  networks.

   [ISP_SCENARIOS] also describes the possible transitions between
   stages. The next figure sums up these transitions:

     +-------------> IPv6 Core ----------->+
     |                                     |
   Launch ----------------------------> Complete
     |                                     |
     +-------------> IPv6 Access --------->+

   When looking at these transitions, it appears that it is possible to
   split the work required by each transition in a small set of actions.
   Each action is mostly independent from the others and some actions
   may be common to several transitions.

   Below, these actions are first identified and in a second step, they
   are described more in details.












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2.2 Identification of the actions required

   The analysis of the possible transitions leads to a small list
   of actions:

     * Core transition actions:

        - Connect dual access networks to other IPv6 networks through
          an IPv4 core,

        - Transform an IPv4 core in a dual one. This action can be
          performed directly or through intermediate steps,


     * Access transition actions:

        - Connect IPv6 customers to an IPv6 core through an IPv4
          network,

        - Transform an IPv4 access network in a dual one,

     * Exchange points actions,


     * Bring support of IPv6 in the back-office.

   More detailed descriptions of each action follow.


3. Core Transition actions

3.1 Steps in transitioning core networks

   In terms of physical equipment, backbone networks consist mainly in
   core and edge high-speed routers. Border routers provide peering
   with other providers. Filtering, routing policy and policing type
   functions are generally managed on border routers.

   The initial step is an IPv4-only core, and the final step is a whole
   dual-stack core. In between, intermediate steps may be identified:



                        Tunnels         Tunnels
      IPv4-only ---->      or      --->   or         + DS -----> Full DS
                     IPv6 dedicated   IPv6 dedicated  routers
                          links          links

   The first step involves tunnels or dedicated links but existing
   routers are left unchanged. Only a small set of routers then have
   IPv6 capabilities. Configured tunnels are adequate for use during
   this step. They can be can be setup through the use of tunnel broker
   or through another mean of router configuration.

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   When MPLS is already deployed in the backbone, it may be desirable
   to provide IPv6-over-MPLS connectivity. However, the problem is that
   setting up an IPv6 Label Switched Path (LSP) requires some signaling
   through the MPLS network. Currently, there is no direct mechanism to
   do this for IPv6. A workaround is to use BGP for signaling and/or
   perform IPv6-over-IPv4-over-MPLS encapsulation, as described in
   [BGPTUNNEL].  More analysis is needed on what is the right approach
   in this case.

   In the second step, some dual stack routers are added in this
   network in a progressive manner.

   The final stage is reached when all or most routers are dual-stack.

   According to many reasons (technical, financial, etc), an ISP may
   move forward from step to step or reach directly the final one. One
   of the important criteria in this evolution is the number of IPv6
   customers the ISP gets on its initial deployments. If few customers
   connect to the first IPv6 infrastructure, then the ISP is likely to
   remain on the initial steps for a long time.

   In short, each step remains possible, but no one is mandatory.

3.2 Configuration of core equipment

   In the core, the number of devices is small and IPv6 configuration
   mainly deals with routing protocols parameters, interface addresses,
   loop-back addresses, ACLs...

   These IPv6 parameters are not supposed to be automatically
   configured.

3.3 Routing

   ISPs need routing protocols to advertise the 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 typically not in use in operator networks.
   BGP is the only IPv4 EGP.  Static routes are used in both.

   Note that it is possible to configure a given network so that it
   results in having an IPv6 topology different from the 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 while some
   others maybe single stacked (IPv4 or IPv6). In this case, the routing
   must be able to manage multiple topologies.






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3.3.1 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
   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 to make is whether one wishes to have
   separate routing protocol processes for IPv4 and IPv6. Having them
   separate requires more memory and CPU for route calculations e.g.
   when the links flap. On the other hand, the separation provides a
   better reassurance that if problems come up with IPv6 routing, they
   will not affect IPv4 routing protocol at all.  In the first phases
   if it is uncertain whether joint IPv4/IPv6 networks work as intended,
   having separate processes may be desirable and easier to manage.

   Thus the combinations are:

     - 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

     - 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 non-congruent IPv4/IPv6 topologies "convex".

   Therefore, the use of same process is recommended especially for
   large ISPs which intend to deploy, in the short-term, a fully
   dual-stack backbone  infrastructure.  If the topologies are not
   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 spread the other routing
   information.

   As some of the simplest devices, e.g. CPE routers, may not implement
   other routing protocols than RIPng, in some cases it may be
   necessary to also run RIPng in a limited fashion in addition to
   another IGP, and somehow redistribute the routing information to the
   other routing protocol(s).




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3.3.2 EGP

   BGP is used for both internal BGP and external BGP sessions.

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

3.3.3 Routing protocols transport

   IPv4 routing information should be carried by IPv4 transport and
   IPv6 one by IPv6 for several reasons:

    * The IPv6 connectivity may work when the IPv4 one 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 use different metric
       values for one physical link for load balancing or tunnels may be
       used.

3.4 Multicast

   Currently, IPv6 multicast is not a strong concern for most ISPs.
   However, some of them consider deploying it.

   Multicast is achieved using PIM-SM and PIM-SSM protocols. These also
   work with IPv6.

   Information about multicast sources is exchanged using MSDP in IPv4,
   but it is not defined, on purpose, for IPv6. An alternative
   mechanism is to use only PIM-SSM or an alternative mechanism for
   conveying the information [EMBEDRP].

   To be completed.


4. Access transition actions

4.1 Steps in transitioning access networks

   Access networks are generally composed of a large number of CPEs
   connected to a small set of PEs. Transitioning this infrastructure
   to IPv6 can be made in several steps, but some ISPs may avoid some
   of the steps depending on their perception of risks.





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   Connecting IPv6 customers to an IPv6 core through an IPv4 network
   can be considered as a first careful step taken by an ISP in order
   to provide IPv6 services to its IPv4 customers. More, some ISPs
   also provide IPv6 services to customers who get their IPv4 services
   from another ISP.

   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 a IPv6 specific CPE or even on a host).

   Several tunneling techniques have already been defined: configured
   tunnels with tunnel broker, 6to4, Teredo...

   The selection of one candidate depends largely on the presence or
   not 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
   an UDP encapsulation for configured tunnels has not been specified.

   Firewalls in the way can also break these types of tunnels. The
   administrator of the firewall will have to create a hole for the
   tunnel. It is not a big deal as long as the IPv6 ISP controls the
   firewall. This is more painful, although not impossible in other
   cases.

   An ISP has practically two kinds of customers in the access networks:
   small end users (mostly "unmanaged networks"; home and SOHO users),
   and others. The former category typically has a dynamic IPv4 address
   which is often NATted; 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 configuring the
   NAT may be required to reach an internal IPv6 access router, though.

   The first category, the unmanaged tunneling scenarios will be
   discussed in a companion document [UNMANCON]; the discussion is not
   duplicated here until some form of consensus is found.

   For the second category, usually:

      * Configured tunnels as-is are a good solution when an NAT is not
        in the way and the IPv4 end-point addresses are static. A
        mechanism to punch through NATs or to forward packets through
        it may be desirable in some scenarios. 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 way needs to be determined.

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


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

   Note that when the customers use dynamic IPv4 addresses, the
   tunneling techniques may be more difficult at the ISP's end,
   especially if a protocol not including authentication (like PPP for
   IPv6) is not used. This may need to be considered in more detail
   with tunneling mechanisms.

4.2 Access control requirements

   Access control is usually required in ISP networks because the ISPs
   need to control to who they are giving access. For instance, it is
   important to check if the user who tries to connect is really a
   valid customer. In some cases, it is also important for billing
   purposes.

   However, an IPv6 specific access control is not always required. This
   is for instance the case when a customer of the IPv4 service has
   automatically access to the IPv6 service. Then, the IPv4 access
   control also gives access to the IPv6 services.

   When the provider does not wish to give to its IPv4 customers
   automatically access to IPv6 services, a specific access control for
   IPv6 must be performed in parallel to the IPv4 one. It does not mean
   that a different user authentication must be performed for IPv6, but
   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 an IPv6 service can be transported over
   IPv4.

4.3 Configuration of customer equipment

   The access networks are composed of CPEs and PEs. Usually, each PE
   connects a large number of CPEs to the core network infrastructure.
   This number may reach tens of thousands or more. The configuration
   of CPEs is an heavy task for the ISP and this is even made harder as
   the configuration must be done remotely. In this context, the use of
   auto-configuration mechanisms is very beneficial, even if manual
   configuration is still an option.

   The parameters that usually need to be automatically provided to the
   customers are:

      - The network prefix delegated by the ISP,
      - The address of the Domain Name System server (DNS),
      - Some other parameters such as the address of an NTP server may
        also be needed sometimes.




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   When access control is required on the ISP network, DHCPv6 can
   provide the configuration parameters. This is discussed more in
   details in [DUAL ACCESS].

   When access control is not required (unusual case), a stateless
   mechanism could be used, but no standard definition exists at the
   moment.


4.4 Requirements for Traceability

   Most ISPs have some kind of mechanism to trace the origin of traffic
   in their networks. This has also to be available for IPv6 traffic.
   This means that specific IPv6 address or prefix has to be tied to a
   certain customer, or that records of which customer had which
   address/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.

   For any traceability to be useful, ingress filtering must be
   deployed towards all the customers.

4.5 Multi-homing

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

   Multihoming 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. with BGP with public or private
   AS numbers and a prefix assigned to the customer.

   To be further defined as the multihoming situation gets clearer.

4.6 Filtering in the access network

   Ingress filtering must be deployed everywhere towards the customers,
   to ensure traceability, prevent DoS attacks using spoofed addresses,
   prevent illegitimate access to the management infrastructure, etc.

   The ingress filtering can be done for example using access lists or
   Unicast Reverse Path Forwarding (uRPF).  Mechanisms for these are
   described in [BCP38UPD].



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5. Exchange points actions

   To reach an exchange point, an ISP uses IPv6 native or configured
   tunnels. Private peering can be achieved the same way.

   A layer-2 exchange point is agnostic to IP versions. The peering
   can be done IPv6 native. A layer-3 exchange point is IP version
   specific, where configured tunnels can be used over non-dual stack
   routers.

   To be completed.

6. Back-Office actions

   ISPs maintain hosts for supporting and managing the network. The
   standard set of hosts include DNS servers, authentication servers
   (RADIUS, AAA or TACACS) and network management servers.

   One of the most important tasks is to provide monitoring of IPv6
   connectivity.  It is imperative to ensure that the IPv6 core and
   access networks are working without problems.  Typically one runs a
   routing protocol everywhere in the core network: one possibility is
   monitoring whether the routing protocol adjacencies remain up or
   not; another way may be using "ping" to test the reachability in
   the networks.  There are many other ways to achieve the effect.

   Servers are usually distributed to strategic locations for diversity
   purposes. These servers must be protected from unwanted external
   access.

   In a first step, the services can be provided over an IPv4 transport.
   For instance, the DNS traffic corresponding to IPv6 entries can be
   transported over IPv4 without any problems.

   In a second step, IPv6 transport can be provided.


7.  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 is described in the respective documents.


References

 [ISP_SCENARIOS] Lind, M., "Scenarios for Introducing IPv6 into ISP
                 Networks" - draft-lind-v6ops-isp-scenarios-01.txt

 [EMBEDRP]       Savola, P., Haberman, B., "Embedding the Address of
                 RP in IPv6 Multicast Address" -
                 draft-ietf-mboned-embeddedrp-00.txt

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INTERNET DRAFT    Analysis of IPv6 Transition for ISP       October 2004


 [MTISIS]        Przygienda, T., Naiming Shen, Nischal Sheth, "M-ISIS:
                 Multi Topology (MT) Routing in IS-IS"
                 draft-ietf-isis-wg-multi-topology-06.txt

 [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"
                 draft-savola-bcp38-multihoming-update-01.txt

 [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"
                draft-shirasaki-dualstack-service-02.txt

 [UNMANCON]     T.Chown, R. van der Pol, P. Savola, "Considerations for
                IPv6 Tunneling Solutions in Small End Sites"
                draft-chown-v6ops-unmanaged-connectivity-00
















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Acknowledgements

   This draft has benefited from inputs by Jordi Palet.

Authors' Addresses

   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

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

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

   Marc Blanchet
   Hexago
   2875 boul. Laurier, suite 300
   Ste-Foy, Quebec, G1V 2M2
   Canada
   Phone: +1-418-266-5533
   Email: Marc.Blanchet@hexago.com

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

   Soohong Daniel Park
   Mobile Platform Laboratory, SAMSUNG Electronics.
   416, Maetan3-Dong, Paldal-Gu, Suwon, Gyeonggi-Do, Korea
   EMail: soohong.park@samsung.com











Ksinant et al.                                                [Page 15]