Internet DRAFT - draft-augustyn-ppvpn-l2vpn-requirements

draft-augustyn-ppvpn-l2vpn-requirements





   INTERNET DRAFT                                           W. Augustyn
   Internet Engineering Task Force
   Document:                                                 Y. Serbest
   draft-augustyn-ppvpn-l2vpn-requirements-                         SBC
   02.txt
   February 2003                                           (Co-Editors)
   Category: Informational
   Expires: August 2003



 Service Requirements for Layer 2 Provider Provisioned Virtual Private
                                Networks

   Status of this memo

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

   This document is a product of the IETF's Provider Provisioned
   Virtual Private Network (ppvpn) working group. Comments SHOULD be
   addressed to WG's mailing list at ppvpn@ppvpn.francetelecom.com. The
   charter for ppvpn may be found at
   http://www.ietf.org/html.charters/ppvpn-charter.html

   Copyright (C) The Internet Society (2000). All Rights Reserved.
   Distribution of this memo is unlimited.

   Abstract

   This document provides requirements for Layer 2 Provider Provisioned
   Virtual Private Networks (PPVPNs). It first provides taxonomy and
   terminology and states generic and general service requirements. It
   covers point to point VPNs referred to as Virtual Private Wire
   Service (VPWS), as well as multipoint to multipoint VPNs also known
   as Virtual Private LAN Service (VPLS). Detailed requirements are
   expressed from a customer as well as a service provider perspective.

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   Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119 ([RFC-
   2119]).

   Table of Contents
1  Contributing Authors..............................................4
2  Introduction......................................................4
 2.1Scope of this document...........................................4
 2.2Outline..........................................................5
3  Definitions and Taxonomy..........................................5
 3.1Definitions......................................................5
 3.2Taxonomy of Layer 2 PPVPN Types..................................5
 3.3VPWS.............................................................6
 3.4VPLS.............................................................6
4  Service Requirements Common to Customers and Service Providers....7
 4.1Scope of emulation...............................................7
 4.2Traffic Types....................................................8
 4.3Topology.........................................................8
 4.4Isolated Exchange of Data and Forwarding Information.............8
 4.5Security.........................................................8
   4.5.1   User data security........................................9
   4.5.2   Access control............................................9
 4.6Addressing.......................................................9
 4.7Quality of Service..............................................10
   4.7.1   QoS Standards............................................10
   4.7.2   Service Models...........................................10
 4.8Service Level Specifications....................................10
 4.9Protection and Restoration......................................10
 4.10 CE-to-CE and CE-to-PE link requirements.......................11
 4.11 Management....................................................11
 4.12 Interoperability..............................................11
 4.13 Inter-working.................................................12
5  Customer Requirements............................................12
 5.1Service Provider Independence...................................12
 5.2Layer 3 Support.................................................12
 5.3Quality of Service and Traffic Parameters.......................12
 5.4Service Level Specification.....................................13
 5.5Security........................................................13
   5.5.1   Isolation................................................13
   5.5.2   Access control...........................................13
   5.5.3   Value added security services............................13
 5.6Network Access..................................................13
   5.6.1   Physical/Link Layer Technology...........................13
   5.6.2   Access Connectivity......................................13
 5.7Customer traffic................................................15
   5.7.1   Unicast, Unknown Unicast, Multicast, and Broadcast
   forwarding.......................................................15
   5.7.2   Packet Re-ordering.......................................15
   5.7.3   Minimum MTU..............................................15

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   5.7.4   End-point VLAN tag translation...........................15
   5.7.5   Transparency.............................................15
 5.8Support for Layer 2 Control Protocols...........................16
 5.9CE Provisioning.................................................16
6  Service Provider Network Requirements............................16
 6.1Scalability.....................................................16
   6.1.1   Service Provider Capacity Sizing Projections.............16
   6.1.2   Solution-Specific Metrics................................17
 6.2Identifiers.....................................................17
 6.3Discovering L2VPN Related Information...........................18
 6.4SLS Support.....................................................18
 6.5Quality of Service (QoS)........................................18
 6.6Isolation of Traffic and Forwarding Information.................19
 6.7Security........................................................19
 6.8Inter-AS (SP) L2VPNs............................................19
   6.8.1   Management...............................................19
   6.8.2   Bandwidth and QoS Brokering..............................20
 6.9L2VPN Wholesale.................................................20
 6.10 Tunneling Requirements........................................20
 6.11 Support for Access Technologies...............................20
 6.12 Backbone Networks.............................................21
 6.13 Network Resource Partitioning and Sharing Between L2VPNs......21
 6.14 Interoperability..............................................21
 6.15 Testing.......................................................22
 6.16 Support on Existing PEs.......................................22
7  Service Provider Management Requirements.........................22
8  Engineering Requirements.........................................22
 8.1Control Plane Requirements......................................22
 8.2Data Plane Requirements.........................................23
   8.2.1   Encapsulation............................................23
   8.2.2   Responsiveness to Congestion.............................23
   8.2.3   Broadcast Domain.........................................23
   8.2.4   Virtual Switching Instance...............................23
   8.2.5   MAC address learning.....................................24
9  Security Considerations..........................................24
10 Acknowledgments..................................................24
11 References.......................................................24
 11.1 Normative References..........................................24
 11.2 Non-normative References......................................25
12 Editors' Addresses...............................................25













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1 Contributing Authors
   This document was the combined effort of several individuals.  The
   following are the authors that contributed to this document:

          Waldemar Augustyn
          Marco Carugi
          Giles Heron
          Vach Kompella
          Marc Lasserre
          Pascal Menezes
          Hamid Ould-Brahim
          Tissa Senevirathne
          Yetik Serbest

2 Introduction
   This section describes the scope and outline of the document.

2.1 Scope of this document
   This document provides requirements for Layer 2 Provider Provisioned
   Virtual Private Networks (L2-PPVPN). It identifies requirements that
   MAY apply to one or more individual approaches that a Service
   Provider MAY use for the provisioning of a Layer 2 VPN service. The
   content of this document makes use of the terminology defined in
   [TERMINOLOGY] and common components for deploying Layer 2 PPVPNs
   (will be referred to as L2VPNs) described in [PPVPN-L2-FR].
   The technical specifications to provide L2VPN services are outside
   the scope of this document. The framework document [PPVPN-L2-FR] and
   several documents, which explain technical approaches providing
   Layer 2 PPVPN services, are available to cover this aspect.

   This document describes requirements for two types of L2VPNs: 1.
   Virtual Private Wire Service (VPWS), and 2. Virtual Private LAN
   Service (VPLS). The approach followed in this document distinguishes
   L2VPN types as to how the connectivity is provided (point-point or
   multipoint-multipoint) as detailed in [PPVPN-L2-FR].

   This document is intended as a "checklist" of requirements that will
   provide a consistent way to evaluate and document how well each
   individual approach satisfies specific requirements. The
   applicability statement documents for each individual approach
   SHOULD document the results of this evaluation.

   In the context of provider provisioned VPNs, there are two entities
   involved in operation of such services, the Provider and the
   Customer.  The Provider engages in a binding agreement with the
   Customer as to the behavior of the service in normal situation as
   well as exceptional situations.  Such agreement is known as Service
   Level Specification (SLS) which is part of the Service Level
   Agreement (SLA) established between the Provider and the Customer.



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   A proper design of L2VPNs aids formulation of SLSs in that it
   provides means for proper separation between CE/PE, allows proper
   execution of the SLS offer, and supports flexible and rich set of
   capabilities.

   This document provides requirements from both the ProviderĂs and the
   CustomerĂs point of view. It begins with common customerĂs and
   service providerĂs point of view, followed by a customerĂs
   perspective, and concludes with specific needs of a Service Provider
   (SP). These requirements provide high-level L2VPN features expected
   by a SP in provisioning L2VPNs, which include SP requirements for
   security, privacy, manageability, interoperability and scalability,
   in addition to service provider projections for number, complexity,
   and rate of change of customer VPNs over the next several years.

2.2 Outline
   The outline of the rest of this document is as follows. Section 3
   defines terminology. Section 4 provides common requirements that
   apply to both customer and service providers respectively. Section 5
   states requirements from a customer perspective. Section 6 states
   network requirements from a service provider perspective. Section 7
   states service provider management requirements. Section 8 describes
   the engineering requirements, particularly control and data plane
   requirements. Section 9 provides security considerations. Section 10
   lists acknowledgements. Section 11 provides a list of references
   cited herein. Section 12 lists the editorsĂ addresses.

3 Definitions and Taxonomy
3.1 Definitions
   The terminology used in this document is defined in [TERMINOLOGY].
   The Layer 2 PPVPN framework document [PPVPN-L2-FR] further describes
   these concepts in the context of a reference model that defines
   layered service relationships between devices and one or more levels
   of tunnels.

3.2 Taxonomy of Layer 2 PPVPN Types
   The requirements distinguish two major L2VPNs models, a Virtual
   Private Wire Service (VPWS), and a Virtual Private LAN Service
   (VPLS).

   The following diagram shows a L2VPN reference model.

    +-----+                                       +-----+
    + CE1 +--+                                +---| CE2 |
    +-----+  |    ........................    |   +-----+
    L2VPN A  |  +----+                +----+  |   L2VPN A
             +--| PE |--- Service  ---| PE |--+
                +----+    Provider    +----+
               /  .       Backbone       .  \     -   /\-_
    +-----+   /   .          |           .   \   / \ /   \     +-----+
    + CE4 +--+    .          |           .    +--\ Access \----| CE5 |
    +-----+       .        +----+        .       | Network |   +-----+

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    L2VPN B       .........| PE |.........        \       /    L2VPN B
                           +----+     ^            -------
                             |        |
                             |        |
                          +-----+     |
                          | CE3 |     +-- Logical switching instance
                          +-----+
                          L2VPN A

                     Figure 1 L2VPN Reference Model
3.3 VPWS
   The PE devices provide a logical interconnect such that a pair of CE
   devices appear to be connected by a single logical Layer 2 circuit.
   PE devices act as Layer 2 circuit switches. Layer 2 circuits are
   then mapped onto tunnels in the service provider network. These
   tunnels can either be specific to a particular VPWS, or shared among
   several VPWSs. VPWS applies for all services including Ethernet,
   ATM, Frame Relay etc. In Figure 1, L2VPN B represents a VPWS case.

   Each PE device is responsible for allocating customer Layer 2 frames
   to the appropriate VPWS and for proper forwarding to the intended
   destinations.

3.4 VPLS
   In case of VPLS, the PE devices provide a logical interconnect such
   that CE devices belonging to a specific VPLS appear to be connected
   by a single LAN. End-to-end VPLS consists of a bridge module and a
   LAN emulation module ([PPVPN-L2-FR]). A VPLS can contain a single
   VLAN or multiple VLANs. A variation of this service is IPLS, which
   is limited to supporting only customer IP traffic.

   In a VPLS, a customer site receives layer 2 service from the SP. The
   PE is attached via an access connection to one or more CEs. The PE
   performs forwarding of user data packets based on information in the
   Layer 2 header, such as a MAC destination address. The CE sees a
   bridge.

   In VPLS, the PE can be viewed as containing a Virtual Switching
   Instance (VSI) for each Layer 2 VPN that it serves. A CE device
   attaches, possibly through an access network, to a "Bridge" module
   of a PE. Within the PE, the Bridge module attaches, through an
   "Emulated LAN Interface" to an Emulated LAN. For each VPLS, there is
   an Emulated LAN instance. In Figure 1, the top PE routers maintain
   separate Emulated LAN instances for VPLS A and VPLS B. The Emulated
   LAN consists of "VPLS Forwarder" module (one per PE per VPLS
   instance) connected by pseudowires, where the pseudowires may be
   traveling through Packet Switched Network (PSN) tunnels over a
   routed backbone. VSI is a logical entity that contains a VPLS
   forwarder module and part of the bridge module relevant to the VPLS
   instance [PPVPN-L2-FR]. Hence, the VSI terminates pseudo-wires for
   interconnection with other VSIs and also terminates attachment
   circuits for accommodating CEs. A VSI includes the forwarding

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   information base for a L2VPN [PPVPN-L2-FR] which is the set of
   information regarding how to forward Layer 2 frames received over
   the attachment circuit from the CE to VSIs in other PEs supporting
   the same L2VPN (and/or to other attachment circuits), and contains
   information regarding how to forward Layer 2 frames received from
   pseudowires to attachment circuits.  Forwarding information bases
   can be populated dynamically (such as by source MAC address
   learning) or statically (e.g., by configuration). Each PE device is
   responsible for proper forwarding of the customer traffic to the
   appropriate destination(s) based on the forwarding information base
   of the corresponding VSI.

4 Service Requirements Common to Customers and Service Providers
   This section contains requirements that apply to both the customer
   and the provider, or are of an otherwise general nature.

4.1 Scope of emulation
   L2VPN protocols SHOULD NOT interfere with existing Layer 2 protocols
   and standards of the Layer 2 network the customer is managing.  If
   they may impact customer Layer 2 protocols that are sent over the
   VPLS, then these impacts MUST be documented.

   Some possibly salient differences between VPLS and a real LAN are:
     - The reliability MAY likely be less, i.e., the probability that a
     message broadcast over the VPLS is not seen by one of the bridge
     modules in PEs  is higher than in a true Ethernet.
     - If sequencing is not turned on, BPDUs on a pseudowire may get
     out of order with respect to data packets and with respect to each
     other.
     - VPLS frames can get duplicated if the sequencing option isn't
     turned on. The data frames on the pseudowires are sent in IP
     datagrams, and under certain failure scenarios, IP networks can
     duplicate packets. If the pseudowire data transmission protocol
     does not ensure sequence of data packets, frames can be duplicated
     or received out of sequence. If the customerĂs BPDU frames are
     sent as data packets, then BPDU frames can be duplicated or mis-
     sequenced.
     - Delayed delivery of packets (e.g., more than half a second)
     rather than dropping them could have adverse effect on the
     performance of the service.
     - 802.3x Pause frames will not be transported over a VPLS, as the
     bridge module ([PPVPN-L2-FR]) in the PE terminates them.
     - Since the IPLS solution aims at transporting encapsulated
     traffic (rather than Layer 2 frames themselves), the IPLS solution
     is NOT REQUIRED to preserve the Layer 2 Header transparently from
     CE to CE. For example, Source MAC address may not be preserved by
     the IPLS solution.

   The interaction between L2VPN and the customer equipment SHOULD
   comply with existing native protocols and specifications. In case, a
   L2VPN solution supports only a subset of these specifications, the
   exceptions MUST be documented.

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4.2 Traffic Types
   A VPLS MUST support unicast, multicast, and broadcast traffic.  It
   is desirable to support efficient replication of broadcast and
   multicast traffic.

4.3 Topology
   A SP network MAY be realized using one or more network tunnel
   topologies to interconnect PEs, ranging from simple point-to-point
   to distributed hierarchical arrangements. The typical topologies
   include:

     o Point-to-point
     o Point-to-multipoint, a.k.a. hub and spoke
     o Any-to-any, a.k.a. full mesh
     o Mixed, a.k.a. partial mesh
     o Hierarchical

   Regardless of the SP topology employed, the service to the customers
   MUST retain the connectivity type implied by the type of L2VPN. For
   example, a VPLS SHOULD allow multipoint to multipoint connectivity
   even if implemented with point to point circuits.  This requirement
   does not imply that all traffic characteristics (such as bandwidth,
   QoS, delay, etc.) be necessarily the same between any two end points
   of a L2VPN. It is important to note that SLS requirements of a
   service have a bearing on the type of topology that can be used.

   To the extent possible, a L2VPN service SHOULD be capable of
   crossing multiple administrative boundaries.

   To the extent possible, the L2VPN services SHOULD be independent of
   access network technology.

4.4 Isolated Exchange of Data and Forwarding Information
   L2VPN solutions SHALL define means that prevent CEs in a L2VPN from
   interaction with unauthorized entities.

   L2VPN solutions SHALL avoid introducing undesired forwarding
   information that could corrupt the L2VPN forwarding information
   base.

   A means to constrain, or isolate, the distribution of addressed data
   to only those VPLS sites determined either by MAC learning and/or
   configuration MUST be provided.

   The internal structure of a L2VPN SHOULD not be advertised nor
   discoverable from outside that L2VPN.

4.5 Security
   A range of security features SHOULD be supported by the suite of
   L2VPN solutions. Each L2VPN solution SHOULD state which security


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   features it supports and how such features can be configured on a
   per customer basis.

   A number of security concerns arise in the setup and operation of a
   L2VPN, ranging from mis-configurations to attacks that may be
   launched on a L2VPN.  This section lists some potential security
   hazards. There MUST be methods available to protect against the
   following situations.

     - Protocol attacks
       o Excessive protocol adjacency setup/teardown
       o Excessive protocol signaling/withdrawal
     - Resource Utilization
       o Forwarding plane replication (VPLS)
       o Looping (VPLS primarily)
       o MAC learning table size limit (VPLS)
     - Unauthorized access
       o Unauthorized member of VPN
       o Incorrect customer interface
       o Incorrect service delimiting VLAN tag
       o Unauthorized access to PE
     - Tampering with signaling
       o Incorrect FEC signaling
       o Incorrect label assignment
       o Incorrect signaled VPN parameters (e.g., QoS, MTU, etc.)
     - Tampering with data forwarding
       o Incorrect MAC learning entry
       o Incorrect label
       o Incorrect customer facing encapsulation
       o Incorrect pseudo-wire encapsulation
       o Hijacking pseudowires using the wrong tunnel
       o Incorrect tunnel encapsulation

4.5.1  User data security
   L2VPN solution MUST provide traffic separation between different
   L2VPNs.

   In case of VPLS, VLAN Ids MAY be used as service delimiters.  When
   used in this manner, they MUST be honored and traffic separation
   MUST be provided.

4.5.2  Access control
   A L2VPN solution MAY also have the ability to activate the
   appropriate filtering capabilities upon request of a customer.

4.6 Addressing
   A L2VPN solution MUST support overlapping addresses of different
   L2VPNs. For instance, customers SHOULD not be prevented from using


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   the same MAC addresses and/or the same VLAN Ids when used with
   different L2VPNs. Actually, for VLANs, there are two cases. First, a
   L2VPN is oblivious to customer VLANs. In this case, customers can
   have overlapping VLAN Ids. Second, VLAN Ids MAY be used as service
   delimiters, in which case it depends on whether the SP assigns the
   VLANs or not. If it does, then there is no overlapping. If it
   doesn't, then overlapping VLAN Ids can occur and the SP has to put
   safeguards in place to avoid this situation.

4.7 Quality of Service
   To the extent possible, L2VPN QoS SHOULD be independent of the
   access network technology.

4.7.1  QoS Standards
   As provided in [PPVPN-REQTS] a L2PVN SHALL be able to support QoS in
   one or more of the following already standardized modes:
     - Best Effort  (support mandatory for all PPVPN types)
     - Aggregate CE Interface Level QoS (i.e., ˘hose÷ level)
     - Site-to-site, or ˘pipe÷ level QoS

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

   Mappings or translations of Layer 2 QoS parameters into Packet
   Switched Network QoS (e.g., DSCPs or MPLS EXP field) as well as QoS
   mapping based on VC (e.g., FR/ATM or VLAN) MAY be performed in order
   to provide QoS transparency. The actual mechanisms for these
   mappings or translations are outside the scope of this document. In
   addition, the Diffserv support of underlying tunneling technologies
   (e.g., [RFC3270] or [RFC3308]) and the Intserv model ([RFC2205]) MAY
   be used.  As such, the L2VPN SLS requirements should be supported by
   appropriate core mechanisms.

4.7.2  Service Models
   A service provider MUST be able to offer QoS service to a customer
   for at least the following generic service types: managed access VPN
   service or an edge-to-edge QoS service. The details of the service
   models can be found in [PPVPN-REQTS] and in [L3REQTS]. In L2VPN
   service, both DSCP and 802.1p fields MAY be used for this purpose.

4.8 Service Level Specifications
   For a L2VPN service, the capabilities for Service Level
   Specification (SLS) monitoring and reporting stated in [PPVPN-REQTS]
   SHOULD be provided as appropriate.

4.9 Protection and Restoration
   The L2VPN service infrastructure SHOULD provide redundant paths to
   assure high availability.  The reaction to failures SHOULD result in
   an attempt to restore the service using alternative paths.

   The intention is to keep the restoration time small. The restoration
   time MUST be less than the time it takes the CE devices, or customer

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   Layer 2 control protocols as well as Layer 3 routing protocols, to
   detect a failure in the L2VPN.

4.10 CE-to-CE and CE-to-PE link requirements
   The CE-to-PE links MAY either be direct physical links, e.g.
   100BaseTX, T1/E1 TDM or logical links, e.g. ATM PVC, or RFC2427-
   encapsulated link, or transport networks carrying Ethernet, or a
   Layer 2 tunnel that go through a layer 3 network (e.g., L2TP
   sessions), over which Layer 2 traffic is carried.

   Layer 2 frames MAY be tunneled through a layer 3 backbone from PE to
   PE, using one of a variety of tunneling technologies (e.g., IP-in-
   IP, GRE, MPLS, L2TP, etc.).

4.11 Management
   Standard interfaces to manage L2VPN services MUST be provided
   (e.g., standard SNMP MIBs).  These interfaces SHOULD provide access
   to configuration, verification and runtime monitoring protocols.

   Service management MAY include the TMN 'FCAPS' functionalities, as
   follows: Fault, Configuration, Accounting, Provisioning, and
   Security, as detailed in [L3REQTS].

   The ITU-T Telecommunications Management Network (TMN) model has the
   following generic requirements structure:
     o Engineer, deploy and manage the switching, routing and
     transmission resources supporting the service, from a network
     perspective (network element management);
     o Manage the L2VPNs deployed over these resources (network
     management);
     o Manage the L2VPN service (service management);
     o Manage the L2VPN business, mainly provisioning, administrative
     and accounting information related to the L2VPN service customers
     (business management).

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

   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 L2VPN service.

   A L2VPN solution SHOULD NOT preclude different access technologies.
   For instance, customer access connections to a L2VPN service MAY be
   different at different CE devices (e.g., Frame Relay, ATM, 802.1d,
   MPLS).



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4.13 Inter-working
   Inter-working scenarios among different solutions, providing L2VPN
   services, are highly desirable. Inter-working SHOULD be supported in
   a scalable manner.

   Inter-working scenarios MUST consider at least traffic isolation,
   security, QoS, access, and management aspects. This requirement is
   essential in the case of network migration, to ensure service
   continuity among sites belonging to different portions of the
   network.

5 Customer Requirements
   This section captures requirements from a customer perspective.

5.1 Service Provider Independence
   Customers MAY require L2VPN service that spans multiple
   administrative domains or service provider networks. Therefore, a
   L2VPN service MUST be able to span multiple AS and SP networks, but
   still to act and to appear as a single, homogenous L2VPN from a
   customer point of view.

   A customer might also start with a L2VPN provided in a single AS
   with a certain SLS but then ask for an expansion of the service
   spanning multiple ASs/SPs. In this case, as well as for all kinds of
   multi-AS/SP L2VPNs, L2VPN service SHOULD be able to deliver the same
   SLS to all sites in a VPN regardless of the AS/SP to which it homes.

5.2 Layer 3 Support
   With the exception of IPLS, a L2VPN service SHOULD be agnostic to
   customerĂs layer 3 traffic (e.g., IP, IPX, Appletalk) encapsulated
   within Layer 2 frames.

   IPLS MUST allow transport of IPv4 and IPv6 customerĂs traffic
   encapsulated within Layer 2 frames. IPLS SHOULD also allow CEs to
   run ISIS and MPLS protocols transparently among them when those are
   used in conjunction with IP.

5.3 Quality of Service and Traffic Parameters
   QoS is expected to be an important aspect of a L2VPN service for
   some customers.

   A customer requires that the L2VPN service provide the QoS
   applicable to his or her application, which can range from pseudo-
   wires (e.g., SONET emulation) to voice and interactive video, and
   multimedia applications. Hence, best-effort as well as delay and
   loss sensitive traffic MUST be supported over a L2VPN service.
   A customer application SHOULD experience consistent QoS independent
   of the access network technology used at different sites connected
   to the same L2VPN.




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5.4 Service Level Specification
   Most customers simply want their applications to perform well. A SLS
   is a vehicle for a customer to measure the quality of the service
   that SP(s) provide. Therefore, when purchasing a service, a customer
   requires access to the measures from the SP(s) that support the SLS.

   Standard interfaces to monitor usage of L2VPN services SHOULD be
   provided (e.g., standard SNMP MIBs).

5.5 Security
5.5.1  Isolation
   A L2VPN solution MUST provide traffic as well as forwarding
   information base isolation for customers similar to that obtained in
   private lines, FR, or ATM services.

   A L2VPN service MAY use customer VLAN identifications as service
   delimiters. In that case, they MUST be honored and traffic
   separation MUST be provided.

5.5.2  Access control
   A L2VPN solution MAY have the mechanisms to activate the appropriate
   filtering capabilities upon request of a customer. For instance, MAC
   and/or VLAN filtering MAY be considered between CE and PE for a
   VPLS.

5.5.3  Value added security services
   A L2VPN solution MAY provide value added security services such as
   encryption and/or authentication of customer packets, certificate
   management, and similar.

   Security measures employed by a L2VPN service SHOULD NOT restrict
   implementation of customer based security add-ons.

5.6 Network Access
   Every packet exchanged between the customer and the SP over the
   access connection MUST appear as it would on a private network
   providing an equivalent service to that offered by the L2VPN.

5.6.1  Physical/Link Layer Technology
   L2VPNs SHOULD support a broad range of physical and link layer
   access technologies, such as PSTN, ISDN, xDSL, cable modem, leased
   line, Ethernet, Ethernet VLAN, ATM, Frame Relay, Wireless local
   loop, mobile radio access, etc. The capacity and QoS achievable MAY
   be dependent on the specific access technology in use.

5.6.2  Access Connectivity
   Various types of physical connectivity scenarios MUST be supported,
   such as multi-homed sites, backdoor links between customer sites,
   devices homed to two or more SP networks. In case of VPLS, multi-
   link access for CE devices SHOULD be supported. L2VPN solutions
   SHOULD support at least the types of physical or link-layer
   connectivity arrangements shown in Figure 2 (in addition to the case

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   shown in Figure 1). For example, in case (b) a CE MAY connect to two
   different SPs via diverse access networks. Resiliency MAY be further
   enhanced as shown in case (d), where CE's, connected via a "back
   door" connection, connect to different SPs. Furthermore, arbitrary
   combinations of the above methods, with a few examples shown in
   cases (e) and (f) SHOULD be supportable by any L2VPN solution.

                  +----------------                    +---------------
                  |                                    |
               +------+                            +------+
     +---------|  PE  |                  +---------|  PE  |
     |         |device|                  |         |device| SP network
     |         +------+                  |         +------+
  +------+         |                  +------+         |
  |  CE  |         |                  |  CE  |         +---------------
  |device|         |   SP network     |device|         +---------------
  +------+         |                  +------+         |
     |         +------+                  |         +------+
     |         |  PE  |                  |         |  PE  |
     +---------|device|                  +---------|device| SP network
               +------+                            +------+
                   |                                   |
                   +----------------                   +---------------
                  (a)                                 (b)
                   +----------------                  +---------------
                   |                                  |
  +------+     +------+               +------+     +------+
  |  CE  |-----|  PE  |               |  CE  |-----|  PE  |
  |device|     |device|               |device|     |device| SP network
  +------+     +------+               +------+     +------+
     |             |                     |             |
     | Backdoor    |                     | Backdoor    +---------------
     | link        |   SP network        | link        +---------------
     |             |                     |             |
  +------+     +------+               +------+     +------+
  |  CE  |     |  PE  |               |  CE  |     |  PE  |
  |device|-----|device|               |device|-----|device| SP network
  +------+     +------+               +------+     +------+
                   |                                   |
                   +----------------                   +---------------
                  (c)                                  (d)
                   +----------------                   +---------------
                   |                                   |
  +------+     +------+               +------+     +------+
  |  CE  |-----|  PE  |               |  CE  |-----|  PE  |
  |device|     |device|               |device|     |device| SP network
  +------+\    +------+               +------+\    +------+
     |     \       |                     |     \       |
     |Back  \      |                     |Back  \      +---------------
     |door   \     |   SP network        |door   \     +---------------
     |link    \    |                     |link    \    |
  +------+     +------+               +------+     +------+

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  |  CE  |     |  PE  |               |  CE  |     |  PE  |
  |device|-----|device|               |device|-----|device| SP network
  +------+     +------+               +------+     +------+
                   |                                   |
                   +----------------                   +---------------
                  (e)                                 (f)
         Figure 2 Representative types of access arrangements.

5.7 Customer traffic
5.7.1  Unicast, Unknown Unicast, Multicast, and Broadcast forwarding
   A VPLS MUST deliver every packet at least to its intended
   destination(s) within the scope of the VPLS subject to the ingress
   policing and security policies.

5.7.2  Packet Re-ordering
   The queuing and forwarding policies SHOULD preserve packet order for
   packets with the same QoS parameters.

5.7.3  Minimum MTU
   A VPLS MUST support the theoretical MTU of the offered service.

   The committed minimum MTU size MUST be the same for a given VPLS
   instance. Different L2VPN services MAY have different committed MTU
   sizes. If the customer VLANs are used as service delimiters, all
   VLANs within a given VPLS MUST inherit the same MTU size.

   A VPLS MAY fragment packets as long as it is transparent to the
   customer.

5.7.4  End-point VLAN tag translation
   The L2VPN service MAY support translation of customers' attachment
   circuit identifiers (e.g., VLAN tags, if the customer VLANs are used
   as service delimiters). Such service simplifies connectivity of
   sites that want to keep their attachment circuit assignments or
   sites that belong to different administrative domains. In the latter
   case, the connectivity is sometimes referred to as Layer 2 extranet.
   On the other hand, it SHOULD be noted that VLAN tag translation
   affects the support for multiple spanning trees (i.e., 802.1s) and
   can break the proper operation.

5.7.5  Transparency
   The L2VPN service is intended to be transparent to Layer 2 customer
   networks.  A L2VPN solution SHOULD NOT require any special packet
   processing by the end users before sending packets to the provider's
   network.

   If VLAN-ids are assigned by the SP, then VLANs are not transparent.
   Transparency does not apply in this case, as it is the same as
   FR/ATM service model.

   Since the IPLS solution aims at transporting encapsulated traffic
   (rather than L2 frames themselves) the IPLS solution MUST not alter

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   the packets encapsulated inside Layer 2 frames which are transported
   by the IPLS. However, the IPLS solution is NOT REQUIRED to preserve
   the L2 Header transparently from CE to CE. For example, Source MAC
   address may not be preserved by the IPLS solution. The IPLS solution
   MAY remove Layer 2 headers for transport over the backbone when
   those can be reconstructed on egress without compromising transport
   of encapsulated traffic.

5.8 Support for Layer 2 Control Protocols
   The L2VPN solution SHOULD allow transparent operation of Layer 2
   control protocols employed by customers.

   In case of VPLS, the L2VPN service MUST ensure that loops be
   prevented. This can be accomplished through a loop free topologies
   or appropriate forwarding rules.  Control protocols such as Spanning
   Tree (STP) or similar could be employed.  The L2VPN solution MAY use
   indications from customer Layer 2 control protocols, e.g. STP BPDU
   snooping, to improve the operation of a VPLS.

5.9 CE Provisioning
   The L2VPN solution MUST require only minimal or no configuration on
   the CE devices, depending on the CE device that connects into the
   infrastructure.

6 Service Provider Network Requirements
   This section describes requirements from a service provider
   perspective.

6.1 Scalability
   This section contains projections regarding L2VPN sizing projections
   and scalability requirements and metrics specific to particular
   solutions.

6.1.1  Service Provider Capacity Sizing Projections
   This section captures projections for scaling requirements over the
   next several years in terms of number of L2VPNs, number of
   interfaces per L2VPN, the size of forwarding information base per
   L2VPN, and the rate of L2VPN configuration changes. The examples are
   provided in [PPVPN-REQTS].

   The numbers provided in this section are examples and MUST be
   treated as such. A L2VPN solution MAY scale much more than the
   examples provided here. Each requirement in this section MUST be
   considered independently.

   A L2VPN solution SHOULD be scalable to support a very large number
   of L2VPNs per Service Provider network. The estimate is that a large
   service provider will require support O(10^5) VPWSs and O(10^4)
   VPLSs within the next four years.

   A L2VPN solution SHOULD be scalable to support of a wide range of
   number of site interfaces per VPLS, depending on the size and/or

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   structure of the customer organization. The number of site
   interfaces SHOULD range from a few site interfaces to O(10^2) site
   interfaces per VPLS.

   A L2VPN solution SHOULD be scalable to support a wide range of
   number of customer addresses (e.g., MAC) per VPLS. The number of
   customer addresses per VPLS MAY range from just a few (i.e., the
   number of sites when the CE devices are routers or when the service
   is IPLS) to a very large number such as 1,000 (i.e., when CE devices
   are switches). The number of customer addresses would be on the
   order of addresses supported in a typical native Layer 2 backbone.

   A L2VPN solution SHOULD support high values of the frequency of
   configuration setup and change, e.g., for real-time provisioning of
   an on-demand videoconferencing or addition/deletion of sites.

   Approaches SHOULD articulate scaling and performance limits for more
   complex deployment scenarios, such as inter-AS(S) L2VPNs and
   carriers' carrier.  Approaches SHOULD also describe other dimensions
   of interest, such as capacity requirements or limits, number of
   inter-working instances supported as well as any scalability
   implications on management systems.

   The number of users per VPLS is the combination of servers and hosts
   connected to the VPLS. It needs to scale from a handful to high
   numbers. A VPLS MUST scale from 2 users to a few hundred.

   The number of users per VPLS interface follows the same logic as for
   users per VPLS. Further, it MUST be possible to have single user
   sites connected to the same VPLS as very large sites are connected
   to. VPLSs MUST scale from 1 user to a few hundred per site.

   The number of sites per VPLS is clearly limited by the number of
   users for a VPLS. The largest number of sites in a VPLS would be
   equal to the largest number of users, distributed one per site.

   The number of L2VPNs SHOULD scale linearly with the size of the
   access network and with the number of PEs.

6.1.2  Solution-Specific Metrics
   Each L2VPN solution SHALL document its scalability characteristics
   in quantitative terms.

6.2 Identifiers
   A SP domain MUST be uniquely identified at least within the set of
   all interconnected SP networks when supporting a L2VPN that spans
   multiple SPs. Ideally, this identifier SHOULD be globally unique
   (e.g., an AS number).

   An identifier for each L2VPN SHOULD be unique, at least within each
   SP's network, as it MAY be used in auto-discovery, management (e.g,
   alarm and service correlation, troubleshooting, performance

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   statistics collection), and signaling. Ideally, the L2VPN identifier
   SHOULD be globally unique to support the case, where a L2VPN spans
   multiple SPs (e.g., [RFC2685]). Globally unique identifiers
   facilitate the support of inter-AS/SP L2VPNs.

6.3 Discovering L2VPN Related Information
   Configuration of PE devices (i.e., U-PE and N-PE) is a significant
   task for a service provider. Solutions SHOULD provide methods that
   dynamically allow L2VPN information to be discovered by the PEs to
   minimize the configuration steps.

   Each device in a L2VPN SHOULD be able to determine which other
   devices belong to the same L2VPN.  Such a membership discovery
   scheme MUST prevent unauthorized access and allows authentication of
   the source.

   Distribution of L2VPN information SHOULD be limited to those devices
   involved in that L2VPN. A L2VPN solution SHOULD employ discovery
   mechanisms to minimize the amount of operational information
   maintained by the SPs.  For example, if a SP adds or removes a
   customer port on a given PE, the remaining PEs SHOULD determine the
   necessary actions to take without the SP having to explicitly
   reconfigure those PEs.

   A L2VPN solution SHOULD support the means for attached CEs to
   authenticate each other and verify that the service provider L2VPN
   is correctly configured.

   The mechanism SHOULD respond to L2VPN membership changes in a timely
   manner. A "timely manner" is no longer than the provisioning
   timeframe, typically on the order of minutes, and MAY be as short as
   the timeframe required for "rerouting," typically on the order of
   seconds.

   Dynamically creating, changing, and managing multiple L2VPN
   assignments to sites and/or customers is another aspect of
   membership that MUST be addressed in a L2VPN solution.

6.4 SLS Support
   Typically, a SP offering a L2VPN service commits to specific Service
   Level Specifications (SLS) as part of a contract with the customer.
   Such a Service Level Agreement (SLA) drives the specific SP
   requirements for measuring Specific Service Level Specifications
   (SLS) for quality, availability, response time, and configuration
   intervals.

6.5 Quality of Service (QoS)
   A significant aspect of a PPVPN is support for QoS. A SP has control
   over the provisioning of resources and configuration of parameters
   in at least the PE and P devices, and in some cases, the CE devices
   as well. Therefore, the SP is to provide either managed QoS access
   service, or edge-to-edge QoS service, as defined in [L3REQTS].

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6.6 Isolation of Traffic and Forwarding Information
   From a high level SP perspective, a L2VPN MUST isolate the exchange
   of traffic and forwarding information to only those sites that are
   authenticated and authorized members of a L2VPN.

   A L2VPN solution SHOULD provide a means for meeting PPVPN QoS SLS
   requirements that isolates L2VPN traffic from the affects of traffic
   offered by non-VPN customers. Also, L2VPN solutions SHOULD provide a
   means so that traffic congestion produced by sites as part of one
   L2VPN does not affect another L2VPN.

6.7 Security
   The security requirements are stated in Section 4.5. The
   requirements provided in [PPVPN-REQTS] and in [L3REQTS] SHOULD be
   met as appropriate.

   In addition, a SP network MUST be immune to malformed or maliciously
   constructed customer traffic. This includes but not limited to
   duplicate or invalid Layer 2 addresses, customer side loops,
   short/long packets, spoofed management packets, spoofed VLAN tags,
   high volume traffic.

   The SP network devices MUST NOT be accessible from any L2VPN, unless
   specifically authorized. The devices in the PPVPN network SHOULD
   provide some means of reporting intrusion attempts to the SP, if the
   intrusion is detected.

6.8 Inter-AS (SP) L2VPNs
   All applicable SP requirements, such as traffic and forwarding
   information isolation, SLS's, management, security, provisioning,
   etc. MUST be preserved across adjacent ASĂs. The solution MUST
   describe the inter-SP network interface, encapsulation method(s),
   routing protocol(s), and all applicable parameters [VPN-IW].

   A L2VPN solution MUST provide the specifics of offering L2VPN
   services spanning multiple ASs and/or SPs.

   A L2VPN solution MUST support proper dissemination of operational
   parameters to all elements of a L2VPN service in the presence of
   multiple ASs and/or SPs. A L2VPN solution MUST employ mechanisms for
   sharing operational parameters between different ASs

   A L2VPN solution SHOULD support policies for proper selection of
   operational parameters coming from different ASs. Similarly, a L2VPN
   solution SHOULD support policies for selecting information to be
   disseminated to different ASs.

6.8.1  Management
   The general requirements for managing a single AS apply to a
   concatenation of AS's. A minimum subset of such capabilities is the
   following:

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     - Diagnostic tools
     - Secured access to one AS management system by another
     - Configuration request and status query tools
     - Fault notification and trouble tracking tools

6.8.2  Bandwidth and QoS Brokering
   When a L2VPN spans multiple AS's, there is a need for a brokering
   mechanism that requests certain SLS parameters, such as bandwidth
   and QoS, from the other domains and/or networks involved in
   transferring traffic to various sites. The essential requirement is
   that a solution MUST be able to determine whether a set of AS's can
   establish and guarantee uniform QoS in support of a PPVPN.

6.9 L2VPN Wholesale
   The architecture MUST support the possibility of one SP offering
   L2VPN service to another SP.  One example is when one SP sells L2VPN
   service at wholesale to another SP, who then resells that L2VPN
   service to his or her customers.

6.10 Tunneling Requirements
   Connectivity between CE sites or PE devices in the backbone SHOULD
   be able to use a range of tunneling technologies, such as L2TP, GRE,
   IP-in-IP, MPLS, etc.

   Every PE MUST support a tunnel setup protocol, if tunneling is used.
   A PE MAY support static configuration. If employed, a tunnel
   establishment protocol SHOULD be capable of conveying information,
   such as the following:
     - Relevant identifiers
     - QoS/SLS parameters
     - Restoration parameters
     - Multiplexing identifiers
     - Security parameters

   There MUST be a means to monitor the following aspects of tunnels:
     - Statistics, such as amount of time spent in the up and down
      state
     - Count of transitions between the up and down state
     - Events, such as transitions between the up and down states

   The tunneling technology used by the VPN Service Provider and its
   associated mechanisms for tunnel establishment, multiplexing, and
   maintenance MUST meet the requirements on scaling, isolation,
   security, QoS, manageability, etc.

   Regardless of the tunneling choice, the existence of the tunnels and
   their operations MUST be transparent to the customers.

6.11 Support for Access Technologies
   The connectivity between PE and CE devices is referred to as an
   Attachment Circuit (AC). ACs MAY span networks of other providers or
   public networks.

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   There are several choices for implementing ACs. Some popular choices
   include Ethernet, ATM (DSL), Frame Relay, MPLS-based virtual
   circuits etc.

   In case of VPLS, the AC MUST use Ethernet frames as the Service
   Protocol Data Unit (SPDU).

   A CE access connection over an AC MUST be bi-directional in nature.

   PE devices MAY support multiple ACs on a single physical interface.
   In such cases, PE devices MUST NOT rely on customer controlled
   parameters for distinguishing between different access connections.
   For example, if VLAN tags were used for that purpose, the provider
   would be controlling the assignment of the VLAN tag values and would
   strictly enforce compliance by the CEs.

   An AC, whether direct or virtual, MUST maintain all committed
   characteristics of the customer traffic, such as QoS, priorities
   etc. The characteristics of an AC are only applicable to that
   connection.

6.12 Backbone Networks
   Ideally, the backbone interconnecting SP PE and P devices SHOULD be
   independent of physical and link layer technology. Nevertheless, the
   characteristics of backbone technology MUST be taken into account
   when specifying the QoS aspects of SLSs for VPN service offerings.

6.13 Network Resource Partitioning and Sharing Between L2VPNs
   In case network resources such as memory space, FIB table, bandwidth
   and CPU processing are shared between L2VPNs, the solution SHOULD
   guarantee availability of resources necessary to prevent any
   specific L2VPN instance from taking up available network resources
   and causing others to fail. The solution SHOULD be able to limit the
   resources consumed by a L2VPN instance. The solution SHOULD
   guarantee availability of resources necessary to fulfill the
   obligation of committed SLSs.

6.14 Interoperability
   Service providers are interested in interoperability in at least the
   following scenarios:
     - To facilitate use of PE and managed CE devices within a single
     SP network
     - To implement L2VPN services across two or more interconnected SP
     networks
     - To achieve inter-working or interconnection between customer
     sites using different L2VPN solutions or different implementations
     of the same approach

   Each approach MUST describe whether any of the above objectives can
   be met. If an objective can be met, the approach MUST describe how
   such interoperability could be achieved.

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6.15 Testing
   The L2VPN solution SHOULD provide the ability to test and verify
   operational and maintenance activities on a per L2VPN service basis,
   and in case of VPLS, on a per VLAN basis if customer VLANs are used
   as service delimiters.

   The L2VPN solution SHOULD provide mechanisms for connectivity
   verification, and for detecting/locating faults.

   Examples of testing mechanisms are as follows:
     o Checking connectivity between "service-aware" network nodes
     o Verifying data plane and control plane integrity
     o Verifying service membership

   The provided mechanisms MUST satisfy the following: the
   connectivity checking for a given customer MUST enable the end-to-
   end testing of the data path used by that customer's data packets
   and the test packets MUST not propagate beyond the boundary of the
   SP network.

6.16 Support on Existing PEs
   To the extent possible, the IPLS solution SHOULD facilitate support
   of IPLS on existing PE devices that may be already deployed by the
   Service Provider and may have been designed primarily for ˘Layer 3÷
   services.

7 Service Provider Management Requirements
   A service provider desires to have a means to view the topology,
   operational state, and other parameters associated with each
   customer's L2VPN. Furthermore, the service provider requires a means
   to view the underlying logical and physical topology, operational
   state, provisioning status, and other parameters associated with the
   equipment providing the L2VPN service(s) to its customers.
   Therefore, the devices SHOULD provide standards-based interfaces
   (e.g., L2VPN MIBs) wherever feasible.

   The details of service provider management requirements for a
   Network Management System (NMS) in the traditional fault,
   configuration, accounting, performance, and security (FCAPS)
   management categories can be found in [Y.1311.1].

8 Engineering Requirements
   These requirements are driven by implementation characteristics that
   make service and SP requirements achievable.

8.1 Control Plane Requirements
   A L2VPN service SHOULD be provisioned with minimum number of steps.
   Therefore, the control protocols SHOULD provide methods for
   signaling between PEs. The signaling SHOULD inform of membership,
   tunneling information, and other relevant parameters.


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   The infrastructure MAY employ manual configuration methods to
   provide this type of information.

   The infrastructure SHOULD use policies to scope the membership and
   reachability advertisements for a particular L2VPN service. A
   mechanism for isolating the distribution of reachability information
   to only those sites associated with a L2VPN MUST be provided.

   The control plane traffic increases with the growth of L2VPN
   membership. Similarly, the control plane traffic increases with the
   number of supported L2VPN services. The use of control plane
   resources MAY increase as the number of hosts connected to a L2VPN
   service grows.

   A L2VPN solution SHOULD minimize control plane traffic and the
   consumption of control plane resources. The control plane MAY offer
   means for enforcing a limit on the number of customer hosts attached
   to a L2VPN service.

8.2 Data Plane Requirements
8.2.1  Encapsulation
   A L2VPN solution SHOULD utilize the encapsulation techniques defined
   by PWE3 ([PWE3-FR]), and SHOULD not impose any new requirements on
   these techniques.

8.2.2  Responsiveness to Congestion
   A L2VPN solution SHOULD utilize the congestion avoidance techniques
   defined by PWE3 ([PWE3-FR]).

8.2.3  Broadcast Domain
   A separate Broadcast Domain MUST be maintained for each VPLS.

   In addition to VPLS Broadcast Domains, a L2VPN service MAY honor
   customer VLAN Broadcast Domains, if customer VLANs are used as
   service delimiters. In that case, the L2VPN solution SHOULD maintain
   a separate VLAN Broadcast Domain for each customer VLAN.

8.2.4  Virtual Switching Instance
   L2VPN Provider Edge devices MUST maintain a separate Virtual
   Switching Instance (VSI) per each VPLS. Each VSI MUST have
   capabilities to forward traffic based on customer's traffic
   parameters such as MAC addresses, VLAN tags (if supported), etc. as
   well as local policies.

   L2VPN Provider Edge devices MUST have capabilities to classify
   incoming customer traffic into the appropriate VSI.

   Each VSI MUST have flooding capabilities for its Broadcast Domain to
   facilitate proper forwarding of Broadcast, Multicast and Unknown
   Unicast customer traffic.



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8.2.5  MAC address learning
   A VPLS SHOULD derive all topology and forwarding information from
   packets originating at customer sites.  Typically, MAC address
   learning mechanisms are used for this purpose. With IPLS, snooping
   of particular packets originating at customer sites and signaling
   might also be used.

   Dynamic population of the Forwarding Information Base (e.g. via MAC
   address learning) MUST take place on a per Virtual Switching
   Instance (VSI) basis, i.e. in the context of a VPLS and, if
   supported, in the context of VLANs therein.

9 Security Considerations
   Security considerations occur at several levels and dimensions
   within Layer 2 Provider Provisioned VPNs, as detailed within this
   document.

   The requirements in this document separate the notion of traditional
   security requirements, such as integrity, confidentiality, and
   authentication as detailed in section 4.5 from that of isolating (or
   separating) the exchange of forwarded packets and exchange of
   forwarding information between specific sets of sites. Further
   details on security requirements are given from the customer and
   service provider perspectives in sections 5.5 and 6.7, respectively.
   In an analogous manner, further detail on traffic and routing
   isolation requirements are given from the customer and service
   provider perspectives in sections 4.4 and 6.6, respectively.
   Safeguards to protect network resources such as CPU, memory, and
   bandwidth are required in section 6.13.

   IPSec can be also be applied after tunneling Layer-2 traffic to
   provide additional security.

10 Acknowledgments
   The authors would like to acknowledge extensive comments and
   contributions provided by Loa Andersson, Joel Halpern, Eric Rosen,
   Ali Sajassi, Muneyoshi Suzuki, Ananth Nagarajan, Dinesh Mohan, Yakov
   Rekhter, Matt Squire, Norm Finn, Scott Bradner, and Francois Le
   Faucheur. The authors, also, wish to extend their appreciationĂs to
   their respective employers and various other people who volunteered
   to review this work and provided feedback. This work was done in
   consultation with the entire Layer 2 PPVPN design team. A lot of the
   text was adapted from the Layer 3 requirements document produced by
   Layer 3 requirements design team.

11 References
11.1 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


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               Service requirements for Layer 2 PPVPNs February, 2003


   [TERMINOLOGY]    Andersson, L, Madsen, T. "PPVPN Terminology", work
               in progress

11.2 Non-normative References
   [GENERIC-REQTS]  Nagarajan, A., et al. "Generic Requirements for
               Provider Provisioned VPN", work in progress
   [PPVPN-L2-FR]    Andersson, L, et al. "PPVPN L2 Framework", work in
               progress
   [RFC3270]   Le Faucheur, F., et al. "Multi-Protocol Label Switching
               (MPLS) Support of Differentiated Services", RFC 3270,
               May 2002.
   [RFC3308]   Calhoun, P., et al, "Layer 2 Tunneling Protocol (L2TP)
               Differentiated Services Extension", RFC 3308, November
               2002.
   [RFC2205]   Braden, R., et al, "Resource ReSerVation Protocol
               (RSVP)", RFC 2205, September 1997.
   [L3REQTS]   Carugi, M., McDysan, D. et. al., "Service Requirements
               for Layer 3 Provider Provisioned Virtual Private
               Networks", work in progress
   [Y.1311.1]  Carugi, M. (editor), "Network Based IP VPN over MPLS
               architecture",Y.1311.1 ITU-T Recommendation, May 2001
               (http://standards.nortelnetworks.com/ppvpn/relateditu.ht
               m)
   [RFC2685]   Fox B., et al, "Virtual Private Networks Identifier",
               RFC 2685, September 1999.
   [VPN-IW]    H. Kurakami et al, "Provider-Provisioned VPNs
               Interworking," work in progress.
   [PWE3-FR]   Pate, P, et al. "Framework for Pseudo Wire Emulation
               Edge-to-Edge (PWE3)", work in progress


12 Editors' Addresses

   Waldemar Augustyn
   Email: waldemar@nxp.com

   Yetik Serbest
   SBC Technology Resources
   9505 Arboretum Blvd.
   Austin, TX 78759
   Email: serbest@tri.sbc.com


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   provided that the above copyright notice and this paragraph are

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               Service requirements for Layer 2 PPVPNs February, 2003


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