Internet Draft                                       Ananth Nagarajan
Expiration Date: December 2003
Category: Informational                                      (Editor)
                                                            June 2003

           Generic Requirements for Provider Provisioned VPN

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of [RFC-2026].

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

The list of Internet-Draft Shadow Directories can be accessed at


This document describes generic requirements for Provider Provisioned
Virtual Private Networks (PPVPN). The requirements are categorized into
service requirements, provider requirements and engineering
requirements.   These requirements are not specific to any particular
type of PPVPN  technology, but rather apply to all PPVPN technologies.
All PPVPN technologies are expected to meet the umbrella set of
requirements described in this document.

Conventions used in this document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL

                                                                [Page 1]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

this document are to  be interpreted as described in [RFC-2119].

Table of Contents

    1.         Introduction  ....................................   3
    1.1.       Problem Statement  ...............................   3
    1.2.       Outline of this document  ........................   4
    2.         Contributing Authors  ............................   5
    3.         Definitions and Taxonomy  ........................   6
    4.         Service Requirements  ............................   7
    4.1.       Availability  ....................................   7
    4.2.       Stability  .......................................   7
    4.3.       Traffic types  ...................................   7
    4.4.       Data Isolation  ..................................   8
    4.5.       Security  ........................................   8
    4.5.1.     User data security  ..............................   9
    4.5.2.     Access Control  ..................................   9
    4.5.3.     Site authentication and authorization  ...........   9
    4.5.4.     Inter domain security  ...........................   9
    4.6.       Topology  ........................................  10
    4.7.       Addressing  ......................................  10
    4.8.       Quality of Service  ..............................  10
    4.9.       Service Level Agreement and Service Level
               Specification Monitoring and Reporting  ..........  11
    4.10.      Network Resource Partitioning and Sharing
               between VPNs  ....................................  12
    5.         Provider requirements  ...........................  13
    5.1.       Scalability  .....................................  13
    5.1.1.     Service Provider Capacity Sizing Projections  ....  13
    5.1.2.     VPN Scalability aspects  .........................  14
    5.1.3.     Solution-Specific Metrics  .......................  16
    5.2.       Management  ......................................  17
    5.2.1.     Customer Management of a VPN  ....................  17
    6.         Engineering requirements  ........................  18
    6.1.       Forwarding plane requirements  ...................  18
    6.2.       Control plane requirements  ......................  18
    6.3.       Control Plane Containment  .......................  19
    6.4.       Requirements related to commonality of PPVPN
               mechanisms with each other and with generic
               Internet mechanisms  .............................  19
    6.5.       Interoperability  ................................  20
    7.         Security Considerations  .........................  20
    8.         References  ......................................  21
    8.1.       Normative References  ............................  21
    8.2.       Informative References  ..........................  22
    9.         Acknowledgements  ................................  22
    10.        Editor's Address  ................................  23
    11.        Full Copyright Statement  ........................  23

                                                                [Page 2]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

1. Introduction

   This document is an output of the design team formed to develop
   requirements  for PPVPNs in the PPVPN working group.  As such this
   work fits within the  scope of the PPVPN working group.  This
   document discusses generic PPVPN  requirements categorized as
   service, provider and engineering requirements.   These are
   independent of any particular type of PPVPN technology. In other
   words, all PPVPN technologies are expected to meet the umbrella set
   of requirements described in this document.  Specific requirements
   related to Layer 3 PPVPNs are described in [L3REQTS].  Similarly,
   requirements that are specific to layer 2 PPVPNs are described in

1.1. Problem Statement

   Corporations and other organizations have become increasingly
   dependent on their networks for tele and data communication. The data
   communication  networks were originally built as Local Area Networks
   (LAN). Over time the possibility to interconnect the networks on
   different sites has become more  and more  important. The
   connectivity for corporate networks has been  supplied by service
   providers, mainly as Frame Relay (FR) or Asynchronous Transfer Mode
   (ATM) connections, and more recently as Ethernet and IP-based
   tunnels. This type of network,  interconnecting a number of sites
   over a shared network infrastructure is called Virtual Private
   Network (VPN).  If the sites belong to the same organization, the VPN
   is called an Intranet.  If the sites belong to different
   organizations that share a common interest, the VPN is called an

   Customers are looking for service providers to deliver data and
   telecom connectivity over one or more shared networks, with service
   level assurances  in the form of security, QoS and other parameters.

   In order to provide isolation between the traffic belonging to
   different customers, mechanisms such as Layer 2 connections or Layer
   2/3 tunnels are  necessary. When the shared infrastructure is an IP
   network, the tunneling  technologies that are typically used are
   IPsec, MPLS, L2TP, GRE, IP-in-IP  etc.

   Traditional Internet VPNs have been based on IPsec to provide
   security over the Internet. Service providers are now beginning to
   deploy enhanced VPN  services that provide features such as service
   differentiation, traffic  management, Layer 2 and Layer 3
   connectivity, etc. in addition to security.  Newer tunneling
   mechanisms have certain features that allow the service  providers to

                                                                [Page 3]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

   provide these enhanced VPN services.

   The VPN solutions we define now must be able to accommodate the
   traditional types of VPNs as well as the enhanced services now being
   deployed. They need  to be able to run in a single service provider's
   network, as well as between a set of service providers and across the
   Internet. In doing so the VPNs should not be allowed to violate basic
   Internet design principles or overload the Internet core routers or
   accelarate the growths of the Internet  routing tables. Specifically,
   Internet core routers shall not be required to maintain VPN-related
   information, regardless of whether the Internet routing protocols are
   used to distribute this information or not. In order to achieve this,
   the mechanisms used to develop  various PPVPN solutions shall be as
   common as possible with generic Internet infrastructure mechanisms
   like discovery, signaling, routing and management.  At the same time,
   existing Internet infrastructure mechanisms shall not be overloaded.

   Another generic requirement from a standardization perspective is to
   limit the number of different solution approaches to provide a
   specific type of VPN to as small a number as possible.

1.2. Outline of this document

   This document describes generic requirements for Provider Provisioned
   Virtual Private Networks (PPVPN). The document contains several
   sections,  with each set representing a significant aspect of PPVPN
   requirements.  Section 2 lists authors who contributed to this
   document. Section 3 defines terminology and presents a taxonomy of
   PPVPN technologies. The taxonomy contains two broad classes,
   representing Layer 2 and Layer 3 VPNs. Each top level VPN class
   contains subordinate classes. For example, the Layer 3 VPN class
   contains a subordinate class of PE-based Layer 3 VPNs.  Sections 4,
   5, 6 describe generic PPVPN requirements.

   The requirements are broadly classified under the following

   1) Service requirements - Service attributes that the customer can
   observe or measure. For example, does the service forward frames or
   route datagrams? What security guarantees does the service provide?
   Availability and stability are key requirements in this category.

   2) Provider requirements - Characteristics that Service Providers use
   to determine the cost-effectiveness of a PPVPN service.  Scaling and
   management are examples of Provider requirements.

                                                                [Page 4]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

   3) Engineering requirements - Implementation characteristics that
   make service and provider requirements achievable.  These can be
   further classified as:

   3a) Forwarding plane requirements - e.g., requirements related to
   router forwarding behavior.

   3b) Control plane requirements - e.g., requirements related to
   reachability and distribution of reachability information.

   3c) Requirements related to the commonality of PPVPN mechanisms with
   each other and with generic Internet mechanisms.

2. Contributing Authors

   This document was the combined effort of several individuals that
   were part  of the Service Provider focus group whose intentions were
   to present Service Provider view on the general requirements for
   PPVPN. A significant set of requirements were directly taken from
   previous work by the PPVPN WG to develop requirements for Layer 3
   PPVPN [L3REQTS]. The existing work in the L2 requirements area has
   also influenced the contents of this document [L2REQTS].

   Besides the editor, the following are the authors that contributed to
   this document:

       Loa Andersson
       Ron Bonica
       Dave McDysan
       Junichi Sumimoto
       Muneyoshi Suzuki
       David Meyer
       Marco Carugi
       Yetik Serbest
       Luyuan Fang
       Javier Achirica

                                                                [Page 5]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

3.  Definitions and Taxonomy

   The terminology used in this document is defined in [TERMINOLOGY]. In
   addition the following terminology is used:

   Site: a geographical location with one or more users or one or more
   servers or a combination of servers and users.

   User: the end user equipment (hosts), e.g., a workstation.

            |                                 |
         Layer 2 (L2)                     Layer 3 (L3)
      ______|_____                      ______|________
      |          |                      |             |
     PE-based   CE-based             PE-based       CE-based
      |          |
     P2P        P2MP

   The figure above presents a taxonomy of PPVPN technologies.  Although
   the above figure shows the classification for PE-based Layer 2  VPNs,
   it should be noted that CE-based Layer 2 PPVPNs may also be further
   classified as point-to-point (P2P) or point-to-multipoint (P2MP). It
   is also the intention of the working group to have a limited number
   of solutions, and this goal must be kept in mind when proposing
   solutions that meet the requirements specified in this document.
   Definitions for CE-based and PE-based PPVPNs can be obtained from
   [L3FRAMEWORK].  Layer 2 specific definitions can be obtained from

                                                                [Page 6]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

4. Service requirements

   These are the requirements that a customer can observe or measure, in
   order to verify if the PPVPN service that the Service Provider (SP)
   provides is satisfactory.

4.1. Availability

   VPN services must have high availability.  VPNs that are distributed
   over several sites require connectivity to be maintained even in the
   event of network failures or degraded service.

   This can be achieved via various redundancy techniques such as:

   1. Physical Diversity

   A single site connected to multiple CEs (for CE-based PPVPN) or PEs
   (for PE-based PPVPNs), or different POPs, or even different service


   2. via tunnel redundancy.

4.2. Stability

   In addition to availability, VPN services must also be stable.
   Stability is a function of several components such as VPN routing,
   signaling and discovery mechanisms, in addition to tunnel stability.
   For example, in the case of routing, route flapping or routing loops
   must be avoided in order to ensure stability. Stability of the VPN
   service is directly related to the stability of the mechanisms and
   protocols used to establish the service.  It should also be possible
   to allow network upgrades and maintenance procedures without
   impacting the VPN service.

4.3. Traffic types

   VPN services must support unicast (or point to point) traffic and
   should  support any-to-any or point-to-multipoint traffic including
   multicast and broadcast traffic. In the broadcast model, the network
   delivers a stream to all members of a subnetwork, regardless of their

                                                                [Page 7]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

   interest in that stream. In the multicast model, the network delivers
   a stream to a set of destinations that have registered interest in
   the stream. All destinations need not belong to the same subnetwork.
   Multicast is more applicable to L3 VPNs while broadcast is more
   applicable to L2VPNs.  It is desirable  to support multicast limited
   in scope to an intranet or extranet. The solution should be able to
   support a large number of such intranet or extranet specific
   multicast groups in a scalable manner.

   All PPVPN approaches shall support both IPv4 and IPv6 traffic.
   Specific L2 traffic types (e.g., ATM, Frame Relay and Ethernet) shall
   be supported via encapsulation in IP or MPLS tunnels in the case of

4.4. Data isolation

   The PPVPN must support forwarding plane isolation. The network must
   never deliver user data accross VPN boundaries unless the two VPNs
   participate in an intranet or extranet.

   Furthermore, if the provider network receives signaling or routing
   information from one VPN, it must not reveal that information to
   another VPN unless the two VPNs participate in an intranet or
   extranet.  It should be noted that the disclosure of any
   signaling/routing information across an extranet must be filtered per
   the extranet agreement between the organizations participating in the

4.5. Security

   A range of security features should be supported by the suite of
   PPVPN solutions in the form of securing customer flows, providing
   authentication services for temporary, remote or mobile users, and
   the need to protect service provider resources involved in supporting
   a PPVPN [VPN SEC]. Each PPVPN solution should state which security
   features it supports and how such features can be configured on a per
   customer basis. Protection against Denial of Service (DoS) attacks is
   a key component of security mechanisms. Examples of DoS attacks
   include mail spamming, attacks to the PE or CE CPUs, access
   connection congestion, TCP SYN attacks, ping attacks and intrusion
   attempts such as Trojan horse attack.

                                                                [Page 8]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

4.5.1. User data security

   PPVPN solutions that support user data security should use standard
   methods  (e.g., IPsec) to achieve confidentiality, integrity,
   authentication and  replay attack prevention. Such security methods
   must be configurable between different end points, such as CE-CE, PE-
   PE, and CE-PE. It is also desirable to configure security on a per-
   route or per-VPN basis.

4.5.2. Access control

   A PPVPN solution may also have the ability to activate the
   appropriate filtering capabilities upon request of a customer. A
   filter provides a mechanism so that access control can be invoked at
   the point(s) of communication between different organizations
   involved in an extranet. Access control can be implemented by a
   firewall, access control lists on routers, cryptographic mechanisms
   or similar mechanisms to apply policy-based access control. Access
   control must also be applicable between CE-CE, PE-PE and CE-PE.

4.5.3. Site authentication and authorization

   A PPVPN solution requires authentication and authorization of the

       - temporary and permanent access for users connecting to sites
         (authentication and authorization BY the site)

       - the site itself (authentication and authorization FOR the site)

4.5.4. Inter domain security

   The VPN solution must have appropriate security mechanisms to prevent
   the different kinds of Distributed Denial of Service (DDoS) attacks
   mentioned earlier, misconfiguration or unauthorized accesses in inter
   domain PPVPN connections.

                                                                [Page 9]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

4.6. Topology

   A VPN should support arbitrary, customer-defined inter-site
   connectivity, ranging, for example, from hub-and-spoke, partial mesh
   to full  mesh topology.  These can actually be different from the
   topology used by the service provider. To the extent possible, a
   PPVPN service should be independent  of the geographic extent of the

   Multiple VPNs per customer site should be supported without requiring
   additional hardware resources per VPN. This should also include a
   free mix of L2 and L3 VPNs.

   To the extent possible, the PPVPN services should be independent of
   access network technology.

4.7. Addressing

   Each customer resource must be identified by an address that is
   unique within its VPN. It need not be identified by a globally unique

   Support for private addresses as described in RFC 1918, as well as
   overlapping customer addresses shall be supported.  One or more VPNs
   for each customer can be built over the same infrastructure without
   requiring any of them to renumber. The solution MUST NOT use NAT to
   the customer traffic to achieve that goal. Interconnection of two
   networks with overlapping IP addresses is outside the scope of this

   A VPN service shall be capable of supporting non-IP customer
   addresses via encapsulation techniques, if it  is a Layer 2 VPN
   (e.g., Frame Relay, ATM, Ethernet).  Support for non-IP Layer 3
   addresses may be desirable in some cases, but is beyond the scope of
   VPN solutions developed in the IETF, and therefore, this document.

4.8. Quality of Service

   A PPVPN shall be able to support QoS via IETF standardized mechanisms
   such as Diffserv.  Support for best-effort traffic shall be mandatory
   for all PPVPN types.

   Note that all cases involving QoS may require that the CE and/or PE
   perform shaping and/or policing.

                                                               [Page 10]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

   The need to provide QoS will occur primarily in the access network,
   since that will often be the bottleneck. This is likely to occur
   since the backbone effectively statistically multiplexes many users,
   and is traffic engineered or includes capacity for restoration and
   growth. Hence PE-PE QoS is not a major issue. As far as access QoS is
   concerned, there are two directions of QoS management that should be
   considered in any PPVPN service regarding QoS:

        - From the CE across the access network to the PE
        - From the PE across the access network to CE

   PPVPN CE and PE devices should be capable of supporting QoS across at
   least the following subset of access networks, as applicable to the
   specific type of PPVPN (L2 or L3). However, to the extent possible,
   the QoS capability of a PPVPN should be independent  of the access
   network technology:

        - ATM Virtual Connections (VCs)
        - Frame Relay Data Link Connection Identifiers (DLCIs)
        - 802.1d Prioritized Ethernet
        - MPLS-based access
        - Multilink Multiclass PPP
        - QoS-enabled wireless (e.g., LMDS, MMDS)
        - Cable modem
        - QoS-enabled Digital Subscriber Line (DSL)

   Different service models for QoS may be supported.  Examples of PPVPN
   QoS service models are:

      - Managed access service : Provides QoS on the access connection
   between CE and the customer facing ports of the PE.  No QoS support
   is required in the provider core network in this case.

      - Edge-to-edge QoS : Provides QoS across the provider core, either
   between CE pairs or PE pairs, depending on the tunnel demarcation
   points.  This scenario requires QoS support in the provider core

4.9. Service Level Agreement and Service Level Specification Monitoring
   and Reporting

   A Service Level Specification (SLS) may be defined per access network
   connection, per VPN, per VPN site, and/or per VPN route. The service
   provider may define objectives and the measurement interval for at
   least the SLS using the following Service Level Objective (SLO)

                                                               [Page 11]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

        - QoS and traffic parameters for the Intserv flow or Diffserv
   class [Y.1541]

        - Availability for the site, VPN, or access connection

        - Duration of outage intervals per site, route or VPN

        - Service activation interval (e.g., time to turn up a new site)

        - Trouble report response time interval

        - Time to repair interval

        - Total traffic offered to the site, route or VPN

        - Measure of non-conforming traffic for the site, route or VPN

        - Delay and delay variation (jitter) bounds

        - Packet ordering, at least when transporting L2 services
   sensitive to reordering (e.g., ATM).

   The above list contains items from [Y.1241], as well as other items
   typically part of SLAs for currently deployed VPN services [FRF.13].
   See [RFC3198] for generic definitions of SLS, SLA, and SLO.

   The provider network management system shall measure, and report as
   necessary, whether measured performance meets or fails to meet the
   above SLS objectives.

   The service provider and the customer may negotiate a contractual
   arrangement that includes a Service Level Agreement (SLA) regarding
   compensation if the provider does not meet an SLS performance
   objective. Details of such compensation are outside the scope of this

4.10. Network Resource Partitioning and Sharing between VPNs

   Network resources such as memory space, FIB table, bandwidth and CPU
   processing shall be shared between VPNs and with non-VPN Internet
   traffic. Mechanisms should be provided to prevent any specific VPN
   from taking up available network resources and causing others to
   fail. SLAs to this effect should be provided to the customer.

   Similarly, resources used for control plane mechanisms are also
   shared.  When the service provider's control plane is used to
   distribute VPN specific information and provide other control

                                                               [Page 12]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

   mechanisms for VPNs, there shall be mechanisms to ensure that control
   plane performance is not degraded below acceptable limits when
   scaling the VPN service, or during network events such as failure,
   routing instabilities etc.  Since a service provider's network would
   also be used to provide Internet service, in addition to VPNs,
   mechanisms to ensure the stable operation of Internet services and
   other VPNs shall be made in order to avoid adverse effects of
   resource hogging by large VPN customers.

5. Provider requirements

   This section describes operational requirements for a cost-effective,
   profitable VPN service offering.

5.1. Scalability

   The scalability for VPN solutions has many aspects. The list below is
   intended to comprise of the aspects that PPVPN solutions should
   address. Clearly these aspects in absolute figures are very different
   for different types of VPNs - i.e., a point to point service has only
   two sites, while a VPLS or L3VPN may have a larger number of sites.
   It is also important to verify that PPVPN solutions not only scales
   on the high end, but also on the low end - i.e., a VPN with three
   sites and three users should be as viable as a VPN with hundreds of
   sites and thousands of users.

5.1.1. Service Provider Capacity Sizing Projections

   A PPVPN solution should be scalable to support a very large number of
   VPNs per Service Provider network. The estimate is that a large
   service provider  will require support for O(10^4) VPNs within four

   A PPVPN solution should be scalable to support a wide range of number
   of  site interfaces per VPN, depending on the size and/or structure
   of the  customer organization. The number of site interfaces should
   range from a few  site interfaces to over 50,000 site interfaces per

   A PPVPN solution should be scalable to support of a wide range of
   number of  routes per VPN. The number of routes per VPN may range
   from just a few to  the number of routes exchanged between ISPs

                                                               [Page 13]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

   (O(10^5)), with typical values being in the O(10^3) range. The high
   end number is especially true considering the fact that many large
   ISPs may provide VPN services to smaller ISPs or large corporations.
   Typically, the number of routes per VPN is at least twice the number
   of site interfaces.

   A PPVPN solution should support high values of the frequency of
   configuration setup and change, e.g., for real-time provisioning of
   an on-demand videoconferencing VPN or addition/deletion of sites.

   Approaches should articulate scaling and performance limits for more
   complex deployment scenarios, such as inter-AS(S) VPNs and carriers'
   carrier.  Approaches should also describe other dimensions of
   interest, such as  capacity requirements or limits, number of
   interworking instances supported  as well as any scalability
   implications on management systems.

   A PPVPN solution should support a large number of customer interfaces
   on a single PE (for PE-based PPVPN) or CE (for CE-based PPVPN) with
   current Internet protocols.

5.1.2. VPN Scalability aspects

   This section describes the metrics for scaling PPVPN solutions,
   points out some of the scaling differences between L2 and L3 VPNs. It
   should be noted that the scaling numbers used in this document must
   be treated as typical examples as seen by the authors of this
   document. These numbers are only representative and different service
   providers may have different requirements for scaling. Further
   discussion on service provider sizing projections are in Section
   5.1.1. Number of users per site

   The number of users per site follows the same logic as for users per
   VPN. Further, it must be possible to have single user sites connected
   to the same VPN as very large sites are connected to.

   L3 VPNs must scale from 1 user per site to O(10^3) per site. L2 VPNs
   must scale from 1 user to O(10^2) per site.

                                                               [Page 14]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003 Number of sites per VPN

   The number of sites per VPN clearly depends on the number of users
   per site. VPNs must scale from 2 to O(10^2) sites per VPN. These
   numbers are usually limited by device memory. Number of PEs and CEs

   The number of PEs that supports the same set of VPNs, i.e., the
   number of PEs that needs to directly exchange information on VPN de-
   multiplexing information is clearly a scaling factor in a PE-based
   VPN.  Similarly, in a CE-based VPN, the number of cEs is a scaling
   factor. This number is driven by the type of VPN service, and also by
   whether the service is within a single AS/domain or involves a multi-
   SP or multi-AS network.  Typically, this number should be as low as
   possible in order to make the VPN cost effective and manageable. Number of sites per PE

   The number of sites per PE needs to be discussed based on several
   different scenarios. On the one hand there is a limitation to the
   number of customer facing interfaces that the PE can support. On the
   other hand the access network may aggregate several sites connected
   on comparatively low bandwidth on to one single high bandwidth
   interface on the PE. The scaling point here is that the PE must be
   able to support a few or even a single site on the low end and
   O(10^4) sites on the high end. This number is also limited by device
   memory. Implementations of PPVPN solutions may be evaluated based on
   this requirement, because it directly impacts cost and manageability
   of a VPN. Number of VPNs in the network

   The number of VPNs should scale linearly with the size of the access
   network and with the number of PEs. As mentioned in Section 5.1.1,
   the number of VPNs in the network should be O(10^4). This requirement
   also effectively places a requirement on the number of tunnels that
   must be supported in the network. For a PE-based VPN, the number of
   tunnels is of the same order as the number of VPNs. For a CE-based
   VPN, the number of tunnels in the core network may be fewer, because
   of the possibility of tunnel aggregation or multiplexing across the

                                                               [Page 15]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003 Number of VPNs per customer

   For a large service provider it is fully conceivable that the number
   of VPNs could be fairly large as both service diversification and
   separation of different work groups contributes to this. It is
   possible that one customer will run up to O(100) VPNs. Number of addresses per VPN

   Since any VPN solution shall support private customer addresses, the
   number of addresses supported for a L3 VPN needs to scale from very
   few (for smaller customers) to very large numbers seen in typical
   Service Provider backbones. The high end is especially true
   considering that many Tier 1 SPs may provide VPN services to Tier 2
   SPs or to large corporations. For a L2 VPN this number would be on
   the order of addresses supported in typical native Layer 2 backbones.

5.1.3. Solution-Specific Metrics

   Each PPVPN solution shall document its scalability characteristics in
   quantitative terms.  A VPN solution should quantify the amount of
   state that a PE and P device must support. This should be stated in
   terms of the order of magnitude of the number of VPNs and site
   interfaces supported by the service provider. Ideally, all VPN-
   specific state should be contained in the PE device for a PE-based
   VPN. Similarly, all VPN-specific state should be contained in the CE
   device for a CE-based VPN.  In all cases, the backbone routers (P
   devices) shall not maintain VPN-specific state as far as possible.

   Another metric is that of complexity. In a PE-based solution the PE
   is more complex in that it must maintain tunnel-specific information
   for each VPN, but the CE is simpler since it does not need to support
   tunnels. On the other hand, in a CE-based solution, the CE is more
   complex since it must implement routing across a number of tunnels to
   other CEs in the VPN, but the PE is simpler since it has only one
   routing and forwarding instance. Thus, the complexity of the PE or CE
   must be noted in terms of their processing and management functions.

                                                               [Page 16]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

5.2. Management

   A service provider must have a means to view the topology,
   operational state, service order status, and other parameters
   associated with each customer's VPN. Furthermore, the service
   provider must have a means to view the underlying logical and
   physical topology, operational state, provisioning status, and other
   parameters associated with the equipment providing the VPN service(s)
   to its customers.

   VPN devices should provide standards-based management interfaces
   wherever feasible.

5.2.1. Customer Management of a VPN

   A customer must have a means to view the topology, operational state,
   service order status, and other parameters associated with his or her

   All aspects of management information about CE devices and customer
   attributes of a PPVPN manageable by an SP should be capable of being
   configured and maintained by the customer after being authenticated
   and authorized.

   A customer should be able to make dynamic requests for changes to
   traffic parameters. A customer should be able to receive real-time
   response from the SP network in response to these requests.  One
   example of such as service is a "Dynamic Bandwidth management"
   capability, that enables real-time response to customer requests for
   changes of allocated bandwidth allocated to their VPN(s). A possible
   outcome of giving customers such capabilities is Denial of Service
   attacks on other VPN customers or Internet users. This possibility is
   documented in the Security Considerations section.

                                                               [Page 17]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

6. Engineering requirements

   These requirements are driven by implementation characteristics that
   make service and provider requirements achievable.

6.1. Forwarding plane requirements

   VPN solutions should not pre-suppose or preclude the use of IETF
   developed tunneling techniques such as IP-in-IP, L2TP, GRE, MPLS or
   IPsec. The separation of VPN solution and tunnels will facilitate
   adaptability with extensions to current tunneling techniques or
   development of new tunneling techniques. It should be noted that the
   choice of the tunneling techniques may impact the service
   capabilities of the VPN solution.

   For Layer 2 VPNs, solutions should utilize the encapsulation
   techniques defined by PWE3, and should not impose any new
   requirements on these techniques.

   PPVPN solutions must not impose any restrictions on the backbone
   traffic engineering and management techniques.  Conversely, backbone
   engineering and management techniques must not affect the basic
   operation of a PPVPN, apart from influencing the SLA/SLS guarantees
   associated with the service.  The SP should, however, be required to
   provide per-VPN management, tunnel maintenance and other maintenance
   required in order to meet the SLA/SLS.

   By definition, VPN traffic should be segregated from each other, and
   from non-VPN traffic in the network. After all, VPNs are a means of
   dividing a physical network into several logical (virtual) networks.
   VPN traffic separation should be done in a scalable fashion. However,
   safeguards should be made available against misbehaving VPNs to not
   affect the network and other VPNs.

   A VPN solution should not impose any hard limit on the number of VPNs
   provided in the network.

6.2.  Control plane requirements

   The plug and play feature of a VPN solution with minimum
   configuration requirements is an important consideration. The VPN
   solutions should have mechanisms for protection against customer
   interface and/or routing instabilities so that they do not impact
   other customers' services or impact general Internet traffic handling
   in any way.

                                                               [Page 18]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

   A VPN should be provisioned with minimum number of steps. For
   instance,a VPN need not be configured in every PE. For this to be
   accomplished, an auto-configuration and an auto-discovery protocol,
   which should be as common as possible to all VPN solutions, should be
   defined. However, these mechanisms should not adversely affect the
   cost, scalability or stability of a service by being overly complex,
   or by increasing layers in the protocol stack.

   Mechanisms to protect the SP network from effects of misconfiguration
   of VPNs should be provided.

6.3. Control Plane Containment

   The PPVPN control plane must include a mechanism through which the
   service provider can filter PPVPN related control plane information
   as it passes between Autonomous Systems. For example, if a service
   provider supports a PPVPN offering, but the service provider's
   neighbors do not participate in that offering, the service provider
   should not leak PPVPN control information into neighboring networks.
   Neighboring networks must be equipped with mechanisms that filter
   this information should the service provider leak it.

6.4. Requirements related to commonality of PPVPN mechanisms with each
   other and with generic Internet mechanisms

   As far as possible, the mechanisms used to establish a VPN service
   should re-use well-known IETF protocols, limiting the need to define
   new protocols from scratch. It should, however, be noted that the use
   of Internet mechanisms for the establishment and running of an
   Internet-based VPN service, shall not affect the stability,
   robustness, and scalability of the Internet or Internet services. In
   other words, these mechanisms should not conflict with the
   architectural principles of the Internet, nor should it put at risk
   the existing Internet systems. For example, IETF-developed routing
   protocols should be used for routing of L3 PPVPN traffic, without
   adding VPN-specific state to the Internet core routers. Similarly,
   well-known L2 technologies should be used in VPNs offering L2
   services, without imposing risks to the Internet routers.    A
   solution must be implementable without requiring to add additional
   funcionality to the P devices in a network, and minimal functionality
   to the PE in a PE-based VPN and CE in a CE-based VPN.

   In addition to commonality with generic Internet mechanisms,
   infrastructure mechanisms used in different PPVPN solutions (both L2
   and  L3), e.g., discovery, signaling, routing and management, should
   be as common as possible.

                                                               [Page 19]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

6.5. Interoperability

   Each technical solution is expected to be based on interoperable
   Internet standards.

   Multi-vendor interoperability at network element, network and service
   levels among different implementations of the same technical solution
   should be ensured (that will likely rely on the completeness of the
   corresponding standard). This is a central requirement for SPs and

   The technical solution must be multi-vendor interoperable not only
   within the SP network infrastructure, but also with the customer's
   network equipment and services making usage of the PPVPN service.

   Customer access connections to a PPVPN solution may be different at
   different sites (e.g., Frame Relay on one site and Ethernet on

   Interconnection of a L2VPN over an L3VPN as if it were a customer
   site shall be supported.  However, interworking of Layer 2
   technologies is not required, and is outside the scope of the working
   group, and therefore, of this document.

   Inter-domain interoperability - It should be possible to deploy a
   PPVPN solution across domains, Autonomous Systems, or the Internet.

7. Security Considerations

   Security requirements for Provider Provisioned VPNs have been
   described in Section 4.5. In addition, the following considerations
   need to be kept in mind when a provider provisioned VPN service is
   provided across a public network infrastructure that is also used to
   provide Internet connectivity.

   The PE device has a lot of functionality required for the successful
   operation of the VPN service.  The PE device is also part of the
   backbone providing Internet services, and is therefore susceptible to
   security and denial of service attacks.  The PE control plane CPU is
   vulnerable from this point of view, and it may impact not only VPN
   services but also general Internet services if not adequately
   protected.  In addition to VPN configuration, if mechanisms such as
   QoS are provisioned on the PE, it is possible for attackers to
   recognize the highest priority traffic or customers and launch
   directed attacks.  Care should be taken to prevent such attacks

                                                               [Page 20]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

   whenever any value added services such as QoS are offered.

   When a service such as "Dynamic Bandwidth Management" as described in
   Section 5.2.1 is provided, it allows customers to dynamically request
   for changes to their bandwidth allocation.  The provider must take
   care to authenticate such requests and detect and prevent possible
   Denial-of-Service attacks.  These DoS attacks are possible when a
   customer maliciously or accidentally may cause a change in bandwidth
   allocation that may impact the bandwidth allocated to other VPN
   customers or Internet users.

   Different choices of VPN technology have different assurance levels
   of the privacy of a customer's network.  For example, CE-based
   solutions may enjoy more privacy than PE-based VPNs by virtue of
   tunnels extending from CE to CE, even if the tunnels are not
   encrypted.  In a PE-based VPN, a PE has many more sites than those
   attached to a CE in a CE-based VPN. A large number of these sites may
   use RFC 1918 addresses.  Provisioning mistakes and PE software bugs
   may make traffic more prone to being misdirected as opposed to a CE-
   based VPN.  Care must be taken to prevent misconfiguration in all
   kinds of PPVPNs, but more care must be taken in the case of PE-based
   VPNs, as this could impact other customers and Internet services.
   Similarly, there should be mechanisms to prevent the flooding of
   Internet routing tables whenever there is a misconfiguration or
   failure of PPVPN control mechanisms that use Internet routing
   protocols for relay of VPN-specific information.

8. References

8.1. Normative References

      [RFC2026]   Bradner, S., "The Internet Standards Process - Revision
                  3", BCP 9, RFC 2026, October 1996.
      [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

                                                               [Page 21]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

8.2. Informative References

     [TERMINOLOGY] Andersson, L., Madsen, T., "Terminology for Provider
                   Provisioned Virtual Private Networks", work in progress.
     [L3FRAMEWORK] Callon, R., Suzuki, M., et al. "A Framework for
                   Layer 3 Provider Provisioned Virtual Private Networks",
                   work in progress.
     [L2FRAMEWORK] Andersson, L., et al. "A Framework for Layer 2 Provider
                   Provisioned Virtual Private Networks", work in progress.
     [L3REQTS]     Carugi, M., McDysan, D. et al., "Service Requirements
                   for Layer 3 Provider Provisioned Virtual Private
                   Networks", work in progress.
     [L2REQTS]     Augustyn, W., Serbest, Y., et al., "Service Requirements
                   for Layer 2 Provider Provisioned Virtual Private
                   Networks", work in progress.
     [Y.1241]      "IP Transfer Capability for the support of IP based
                   Services", Y.1241 ITU-T Draft Recommendation, March 2000.
     [Y.1311]      Knightson, K. (editor), "Network based IP VPN Service
                   - Generic Framework and Service Requirements ", Y.1311
                   ITU-T Recommendation, January, 2002.
     [RFC 3198]    A. Westerinen et al, "Terminology for Policy-Based
                   Management," November, 2001.
     [VPN SEC]     J. De Clercq et al, "Considerations about possible
                   security extensions to BGP/MPLS VPN," work in progress.
     [FRF.13]      Frame Relay Forum, "Service Level Definitions
                   Implementation Agreement," August, 1998.
     [Y.1541]      "Network Performance Objectives for IP-based
                   Services," Y.1541, ITU-T Recommendation.

9. Acknowledgements

   This work was done in consultation with the entire design team for
   PPVPN requirements. A lot of the text was adapted from the Layer 3
   requirements document produced by the Layer 3 requirements design
   team. The authors would also like to acknowledge the constructive
   feedback from Scott Bradner, Alex Zinin, Steve Bellovin and other
   IESG members.

                                                               [Page 22]

Internet Draft    draft-ietf-ppvpn-generic-reqts-03.txt        June 2003

10. Editor's Address

        Ananth Nagarajan

11. 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

      The limited permissions granted above are perpetual and will not be
      revoked by the Internet Society or its successors or assigns.

      This document and the information contained herein is provided on an

                                                               [Page 23]