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Versions: 00 01 02 03 04 05 06 07 RFC 5254

Network Working Group                              Luca Martini (Editor)
Internet Draft                                        Cisco Systems Inc.
Expiration Date: December 2005

Matthew Bocci (Editor)                              Nabil Bitar (Editor)
Alcatel                                                          Verizon




                                                               June 2005


               Requirements for inter domain Pseudo-Wires


               draft-ietf-pwe3-ms-pw-requirements-00.txt

Status of this Memo

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Abstract

   This document describes the necessary requirements to allow a service
   provider to extend the reach of pseudo-wires across multiple domains.
   These domains can be autonomous systems under one provider
   administrative control, IGP areas in one autonomous system, different
   autonomous systems under the administrative control of two or more



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   service providers, or administratively established pseudo-wire
   domains.



Table of Contents

    1        Specification of Requirements  ........................   2
    2        Acknowledgments  ......................................   3
    3        Introduction  .........................................   3
    3.1      Scope  ................................................   3
    3.2      Architecture  .........................................   3
    4        Terminology  ..........................................   6
    5        Use Cases  ............................................   6
    6        Multi-Segment Pseudo-Wire Requirements  ...............   9
    6.1      Architecture  .........................................   9
    6.2      Resiliency  ...........................................  10
    6.3      Quality of Service and Class of Service  ..............  11
    6.3.1    Traffic Engineering  ..................................  12
    6.4      MS-PW Setup Mechanisms.  ..............................  12
    6.4.1    Routing  ..............................................  14
    7        Operations and Maintenance (OAM)  .....................  14
    8        Security Considerations  ..............................  16
    8.1      Data-plane Security Requirements  .....................  16
    8.2      Control-plane Security Requirements  ..................  17
    9        Full Copyright Statement  .............................  18
   10        Intellectual Property Statement  ......................  18
   11        IANA Considerations  ..................................  19
   12        Normative References  .................................  19
   13        Informative References  ...............................  19
   14        Author Information  ...................................  19





1. Specification of Requirements

   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










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2. Acknowledgments

   The editors gratefully acknowledge the following contributors:
   Dimitri Papadimitriou (Alcatel), Peter Busschbach (Lucent), Sasha
   Vainshtein (Axerra), Richard Spencer (British Telecom), Simon Delord
   (France Telecom), Deborah Brungard (AT&T), Rahul Aggawal (Juniper),
   Du Ke (ZTE), Cagatay Buyukkoc (ZTE).


3. Introduction

3.1. Scope

   This document specifies requirements for extending pseudo-wires
   across more than one packet switched network (PSN) domain and more
   than one PSN tunnel.  These pseudo-wires are called multi-segment
   pseudo-wires (MS-PW).  Requirements for single-segment pseudo wires
   (SS-PW) that extend edge to edge across only one PSN domain are
   specified in [PWE3-REQ].

   This document specifies additional requirements that apply to MS-PWs.
   These requirements do not apply to PSNs that only support SS-PWs.


3.2. Architecture

   The following three figures describe the reference models which are
   derived from [PWE3-ARCH] to support PW emulated services.























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         |<-------------- Emulated Service ---------------->|
         |                                                  |
         |          |<------- Pseudo Wire ------>|          |
         |          |                            |          |
         |          |    |<-- PSN Tunnel -->|    |          |
         | PW End   V    V                  V    V  PW End  |
         V Service  +----+                  +----+  Service V
   +-----+    |     | PE1|==================| PE2|     |    +-----+
   |     |----------|............PW1.............|----------|     |
   | CE1 |    |     |    |                  |    |     |    | CE2 |
   |     |----------|............PW2.............|----------|     |
   +-----+  ^ |     |    |==================|    |     | ^  +-----+
         ^  |       +----+                  +----+     | |  ^
         |  |   Provider Edge 1         Provider Edge 2  |  |
         |  |                                            |  |
   Customer |                                            | Customer
   Edge 1   |                                            | Edge 2
            |                                            |
            |                                            |
    Attachment Circuit (AC)                    Attachment Circuit (AC)
      Native service                              Native service

                Figure 1: PWE3 Reference Configuration



   Figure 1 shows the PWE3 reference architecture [PWE3-ARCH]. This
   architecture applies to the case where a PSN tunnel extends between
   two edges of a single PSN domain to transport a PW with endpoints at
   these edges.





















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           Native  |<-----------Pseudo Wire----------->|  Native
           Service |                                   |  Service
            (AC)   |    |<-PSN1-->|     |<--PSN2->|    |   (AC)
             |     V    V         V     V         V    V     |
             |     +----+         +-----+         +----+     |
   +----+    |     | PE1|=========| PE2 |=========| PE3|     |    +----+
   |    |----------|........PW1.........|...PW3........|----------|    |
   | CE1|    |     |    |         |     |         |    |     |    |CE2 |
   |    |----------|........PW2.........|...PW4........|----------|    |
   +----+    |     |    |=========|     |=========|    |     |    +----+
        ^          +----+         +-----+         +----+     |    ^
        |      Provider Edge 1       ^        Provider Edge 3     |
        |                            |                            |
        |                            |                            |
        |                    PW switching point                   |
        |                                                         |
        |                                                         |
        |<------------------- Emulated Service ------------------>|

                 Figure 2: PW switching Reference Model


   Figure 2 extends this architecture to show a multi-segment case. PE1
   and PE3 provide PWE3 to CE1 and CE2. These PEs reside in different
   PSNs. A PSN tunnel extends from PE1 to PE2 across PSN1, and a second
   PSN tunnel extends from PE2 to PE3 across PSN2. PWs are used to
   connect the Attachment circuits (ACs) attached to PE1 to the
   corresponding ACs attached to PE3. Each PW on the tunnel across PSN1
   is stitched to a PW in the tunnel across PSN2 at PE2 to complete the
   multi-segment PW (MS-PW) between PE1 and PE3. PE2 is therefore the PW
   switching point and will be referred to as the PW switching provider
   edge (S-PE). PW1 and PW3 are segments of the same MS-PW while PW2 and
   PW4 are segments of another pseudo-wire. PW segments of the same MS-
   PW (e.g., PW1 and PW3) MAY be of the same PW type or different type,
   and PSN tunnels (e.g., PSN1 and PSN2) can be the same or different
   technology. This document requires support for MS-PWs with segments
   of the same type. An S-PE switches an MS-PW from one segment to
   another based on the PW identifiers (e.g., PW label in case of MPLS
   PWs).

   Note that although Figure 2 only shows a single S-PE, a PW may
   transit more one S-PE along its path. For instance, in the multi-
   provider case shown in Figure 3, there can be an S-PE at the border
   of one provider domain and another S-PE at the border of the other
   provider domain. A MS-PW that extends from the edge of one provider
   (PE1) to the edge of the other provider (PE4) is composed of three
   segments: (1) PW1, a segment in provider1 network, (2) PW2, a segment
   between the two borderrouters that are S-PEs, and (3) PWE3, a segment



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   in the provider2 network.


4. Terminology

   [PWE3-REQ] provides terminology for PWE3. This document defines the
   following additional terms:

     - Ultimate PE (U-PE).  A PE where the customer-facing ACs
       (attachment circuits) are bound to a PW forwarder. An ultimate PE
       is present in the first and last segments of a MS-PW.

     - Single-Segment PW (SS-PW). A PW setup directly between two U-PE
       devices. Each LSP in one direction of a SS-PW traverses one PSN
       tunnel that connects the two U-PEs.

     - Multi-Segment PW (MS-PW).  A static or dynamically configured set
       of two or more contiguous PW segments
        that behave and function as a single point-to-point PW. Each end
       of a MS-PW by definition MUST terminate on a U-PE.

     - PW Switching Provider Edge (S-PE).  A PE capable of switching the
       control and data planes of the preceding and succeeding PW
       segments in a MS-PW. It is therefore a PW switching point for a
       MS-PW. A PW Switching Point is never the S-PE and the U-PE for
       the same MS-PW. A PW switching point runs necessary protocols to
       setup and manage PW segments with other PW switching points and
       ultimate PEs.

     - PW Segment. A part of a single-segment or multi-segment PW, which
       is set up between two PE devices, U-PEs and/or S-PEs.



5. Use Cases

   PWE3 defines the signaling and encapsulation techniques for
   establishing SS-PWs between a pair of ultimate PEs and in the vast
   majority of cases this will be sufficient. MS-PWs may be useful in
   the following situations:

        -i. Inter-Provider PWs:  An Inter-Provider PW is a PW that
            extends from a U-PE in one provider domain to a U-PE in
            another provider domain.







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       -ii. It may not be possible, desirable or feasible to establish a
            direct PW control channel between the ultimate source and
            destination PEs to setup and maintain PWs. At minimum, a
            direct PW control channel establishment (e.g., targeted LDP
            session) requires knowledge of and reachability to the
            remote U-PE IP address. The local U-PE may not have access
            to this information due to operational or security
            constraints. Moreover, a SS-PW would require the existence
            of a PSN tunnel between the local U-PE and the remote U-PE.
            It may not be feasible or desirable to extend single,
            contiguous PSN tunnels between U-PEs in one domain and U-PEs
            in another domain for security and/or scalability reasons or
            for the fact that the two domains may be using different PSN
            technologies.

      -iii. MS-PW setup, maintenance and forwarding procedures must
            satisfy requirements placed by the constraints of a multi-
            provider environment.  An example is the inter-AS L2VPN
            scenario where the ultimate PEs reside in different provider
            networks (ASs) and it is the practice to MD5-key all control
            traffic exchanged between two networks. An MS-PW allows the
            providers to confine MD5 key administration to just the PW
            switching points connecting the two domains.

       -iv. PSN Internetworking: PWE3 signaling protocols and PSN types
            may differ in different provider networks. The ultimate PEs
            may be connected to networks employing different PW
            signaling and /or PSN protocols. In this case it is not
            possible to use a SS-PW. A MS-PW with the appropriate
            interworking performed at the PW switching points can enable
            PW connectivity between the ultimate PEs in this scenario.

        -v. Traffic Engineered PSN Tunnels and bandwidth-managed PWs:
            There is a requirement to deploy PWs edge to edge in large
            service provider networks. Such networks typically encompass
            hundreds or thousands of aggregation devices at the edge,
            each of which would be a PE. Furthermore, there is a
            requirement That these PWs have explicit bandwidth
            guarantees. To satisfy these requirements, the PWs will be
            tunneled over PSN TE-tunnels with bandwidth constraints. A
            single segment pseudo-wire architecture would require that a
            full mesh of PSN TE-tunnels be provisioned to allow PWs to
            be established between all PEs. Inter provider PWs riding
            traffic engineered tunnels further add to the number of
            tunnels that would have to be supported by the PEs and the
            core network as the total number of PEs increases.

            In this environment, there is a requirement either to



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            support a sparse mesh of PSN TE-tunnels and PW signaling
            adjacencies, or to partition the network into a number of
            smaller PWE3 domains. In either case, a PW would have to
            pass through more than one PSN tunnel hop along its path. An
            objective is to reduce the number of tunnels that must be
            supported, and thus the complexity and scalability problem
            that may arise. The following use case would benefit from
            this solution.

       -vi. Pseudo-Wires in Access and Metro Networks: Service providers
            are looking to extend PWs to access and metro networks. The
            prime motive is cost reduction in capital and operation
            expenses. For instance, in metro networks, providers are
            looking into extending PWs to next generation SONET ADMs
            using MPLS mechanisms. The objective is to achieve
            statistical multiplexing of packets closer to the edge of
            the network, reducing the recurring costs of SONET circuits
            or maximizing the utilization of existing SONET
            infrastructure. In access and metro Ethernet networks,
            providers are looking to take advantage of MPLS mechanisms
            to setup point to point Ethernet virtual circuits with
            endpoints in the same or different access/metro networks.

            Using the MS-PW solution, access and metro network elements
            need only maintain PW signaling adjacencies with the PEs to
            which they directly connect. They do not need PW signaling
            adjacencies with every other access and metro network
            device. PEs in the PSN backbone in turn maintain PW
            signaling adjacencies among each other. In addition, a PSN
            tunnel is setup between an access element and the PE to
            which it connects. Another PSN tunnel needs to be
            established between every PE pair in the PSN backbone. A
            MS-PW may be setup from one access network element to
            another another access element with three segments: (1)
            access-element - PSN PE, (2) PSN-PE to PSN-PE, and (3) PSN-
            PE to access element. In this MS-PW setup, access elements
            are U-PEs while PSN-PEs are S-PEs. It should be noted that
            the PSN backbone can be also segmented into PWE3 domains
            resulting in more segments per PW.












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6. Multi-Segment Pseudo-Wire Requirements

                |<--------------Pseudo Wire----------->|
                |       Provider         Provider      |
            AC  |    |<----1---->|     |<----2--->|    |  AC
            |   V    V           V     V          V    V  |
            |   +----+     +-----+     +----+     +----+  |
   +----+   |   |    |=====|     |=====|    |=====|    |  |    +----+
   |    |-------|.....PW1..........PW2.........PW3.....|-------|    |
   | CE1|   |   |    |     |     |     |    |     |    |  |    |CE2 |
   +----+   |   |    |=====|     |=====|    |=====|    |  |    +----+
        ^       +----+     +-----+     +----+     +----+       ^
        |         PE1        PE2        PE3         PE4        |
        |                     ^          ^                     |
        |                     |          |                     |
        |                  PW switching points                 |
        |                                                      |
        |                                                      |
        |<------------------- Emulated Service --------------->|

         Figure 3: PW switching inter provider Reference Model


6.1. Architecture

   The following requirements apply to the architecture for MS-PWs:

        -i. S-PEs MAY only support switching PWs of the same PW type. In
            this case, the PW type is transparent to the S-PE in the
            forwarding plane, except for functions needed to provide for
            interworking between different PSN technologies.

       -ii. If MS-PWs are tunneled, using a PSN tunnel overlay, across a
            PSN that only supports SS-PWs, then only the requirements of
            [PWE3-REQ] apply to that PSN.  The fact that the overlay is
            carrying MS-PWs MUST be transparent to the routers in the
            PSN.

      -iii. The PWs MUST remain transparent to the P-routers. A P-router
            is not an S-PE or an U-PE from the MS-PW architecture
            viewpoint. P-routers provide transparent PSN transport for
            PWs and MUST not have any knowledge of PW traversing them.

       -iv. The MS-PWs MUST use the same encapsulation modes specified
            for SS-PWs.






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        -v. S-PEs MAY change the type or encapsulation mode of a PW in
            the NSP function.  This enables the establishment of a MS-PW
            between two PEs with different attachment circuit
            encapsulation but with the same PW type.

       -vi. A MS-PW SHOULD be able to pass across PSNs of all
            technologies specified by PWE3 for SS-PWs. When crossing
            from one PSN technology to another, an S-PE must provide the
            necessary PSN interworking functions in that case.

      -vii. MS-PWs are composed of SS-PW, and SS-PW are bi-directional,
            therefore both directions of a PW segment MUST terminate on
            the same S-PE/U-PE.


6.2. Resiliency

   Mechanisms to protect an MS-PW when the existing path of a MS-PW
   fails (including S-PE failure or any segment failure) MUST be
   provided. These mechanisms will depend on the methods of a MS-PW
   setup. The following are the resiliency requirements:

        -i. The ability to configure an end-end backup PW path for a
            primary PW path MUST be supported. The backup and primary
            paths should have the ability to traverse separate S-PEs.
            The backup path MAY be signaled at configuration time or
            after failure detection.

       -ii. The ability to configure a backup PW for a primary PW. The
            backup and primary PWs should have the ability to traverse
            separate S-PEs.

      -iii. When a MS-PW segment is tunneled over PSN tunnels with fast
            reroute capability fast re-route events SHOULD be
            transparent to the MS-PW.

       -iv. Automatic Mechanisms to perform a fast switchover from a
            primary PW to a backup PW upon failure detection SHOULD be
            provided to minimize packet loss.

        -v. Configuration Mechanisms to perform a switchover from a
            primary PW to a backup PW upon failure detection SHOULD be
            provided.

       -vi. A mechanism to automatically revert to a primary PW from a
            backup PW MAY be provided. When provided, it SHOULD be
            enabled/disabled by configuration.




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      -vii. Mechanisms for PW segment failure detection and notification
            to other segments of a MS-PW MUST be provided.


6.3. Quality of Service and Class of Service

   Pseudo-wires are intended to support emulated services (e.g., TDM and
   ATM) which may have strict per-connection quality of service
   requirements. This may include either absolute or relative guarantees
   on packet loss, delay, and jitter. These guarantees are in part
   delivered by reserving sufficient network resources (e.g. BW), and by
   providing appropriate per-packet treatment (e.g. scheduling priority
   and drop precedence) throughout the network.

   In SS-PWs, a traffic engineered PSN tunnel (i.e., MPLS-TE) may be
   used to ensure that sufficient resources are reserved in the P-
   routers to provide QoS to PWs on the tunnel. In this case, the
   ability to automatically manage the PSN tunnel resources (e.g.
   admission control of PWs onto the PSN tunnel) is a requirement at
   each PW segment. The ability to associate the appropriate QoS class
   with each PW PDU is a strict requirement at each router transited in
   the network.

   For MS-PWs, each S-PE maps a PW to a PSN tunnel. That is, an S-PE
   decides what PW to bind to which PSN tunnel. Control over binding a
   PW to a specific PSN tunnel SHOULD be provided as a matter of policy
   configuration.

   When the U-PE attempts to signal a PW the following capability is
   required:

        -i. Admission control to the PSN tunnel needs to be performed
            against available resources. PW admission control into a PSN
            tunnel MUST be configurable.

       -ii. A method to select per PW/QoS class setup/holding priority
            should be provided.

      -iii. In case the PSN tunnel lacks the resources necessary to
            accommodate the new PW, a PW setup failure message MUST be
            returned and the PW MUST fail to setup.  Alternatively:  In
            case the PSN tunnel lacks the resources necessary to
            accommodate the new PW, an attempt to signal an new PSN
            tunnel, or increase the capacity of the existing PSN tunnel
            MUST be made. If the expanded PSN tunnels fails to setup the
            PW MUST fail to setup.





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       -iv. PW traffic parameter representations MUST be the same for
            all types of PW.

        -v. The PW signaling MUST enable separate traffic parameter
            values to be specified for the forward and reverse
            directions of the PW.


6.3.1. Traffic Engineering

   The following requirements apply to the traffic engineering of MS-
   PWs:

        -i. When setting up a MS-PW, S-PEs and U-PEs MUST be able to
            select a tunnel across the PSN in such a way as to satisfy
            the MS-PW QoS and bandwidth requirements. Restrictions may
            apply depending on the method used for setting up a PW
            segment and on PSN tunnel types.

       -ii. Upon setting up a MS-PW for which QoS/bandwidth commitments
            are made over the PSN, S-PEs and U-PEs SHOULD be able to
            perform admission control for each PW segment over a PSN
            tunnel to ensure that PW bandwidth and QoS requirements can
            be satisfied.


6.4. MS-PW Setup Mechanisms.

   The MS-PW setup mechanisms MUST accommodate Service Provider's
   practices, especially in relation to security and confidentiality and
   traffic engineering. Security and confidentiality are especially
   important when the MS-PW's are setup across ASs in different
   administrative domains.

   There are four different SS-PW signaling protocols that are defined
   to signal PWs:

        -i. Static configuration of the SS-PW (MPLS or L2TPv3).

       -ii. LDP using PWid FEC 128

      -iii. LDP using the generalized PW FEC 129

       -iv. L2TPv3

   Any combination of these signaling protocols MUST be supported.

   Following are further requirements on MS-PW setup mechanisms:



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        -i. Static S-PE selection and PSN tunnel selection MUST be
            provided.

       -ii. The MS-PW path MUST have the ability to be dynamically setup
            between the U-PEs by provisioning only the U-PEs.

      -iii. Dynamic MS-PW pseudowire setup requires that a unique
            identifier be associated with a PW and be carried in the
            signaling message. That identifier must contain sufficient
            information to determine the path to the remote U-PE through
            intermediate S-PEs.

       -iv. It may be required for the PW to traverse a specific S-PE to
            enforce security, or administrative policies.

        -v. In a single-provider domain it is natural to have the U-PE
            identified by one of its IP addresses. This may also apply
            when a MS-PW is setup across multiple domains operated by
            the same provider. However, some service providers have
            security and confidentiality policies that prevent them from
            advertising reachability to routers in their networks to
            other providers (reachability to an ASBR is an exception).
            Thus, procedures MUST be provided to allow dynamic setup of
            MS-PWs under these conditions.

       -vi. Addressing of MS-PW end point at the U-PE MUST be
            independent of the IP address of the U-PEs themselves.




      -vii. Solutions MUST strive to minimize the amount of
            configuration needed to setup an MS-PW.

     -viii. MS-PW signaling procedures MUST define clear rules for
            triggering the setup of segments of a MS-PW.

       -ix. The signaling procedures MUST be defined such that the setup
            of a MS-PW is considered successful if and only if all
            segments of the MS-PW are successfully setup.

        -x. Mechanisms MUST be developed to propagate setup explicit
            failure indications to the S-PEs and U-PEs associated with
            the failed MS-PW.







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6.4.1. Routing

   An objective of MS-PWs is to provide support for the following
   connectivity:

        -i. MS-PW MUST be able to traverse multiple IGP domains.
       -ii. MS-PW MUST be able to traverse multiple autonomous systems
            within the same administrative domain.
      -iii. MS-PW MUST be able to traverse multiple autonomous systems
            belonging to different administrative domains.
       -iv. MS-PW MUST be able to terminate, as well,  in any of above
            mentioned domains.
        -v. MS-PWs MUST be able to support any hybrid combination of the
            aforementioned connectivity scenarios.

   The routing function MUST support the various MS-PW setup methods and
   the various connectivity scenarios. Following are the consequent
   requirements:

        -i. MUST support the setup of a statically configured segment of
            a MS-PW. ( static S-PE selection )
       -ii. The MS-PW MUST have the ability to automatically select the
            S-PEs along the MS-PW path. Some of the S-PEs MAY be
            statically selected.
      -iii. The PW Routing function MUST support dynamic re-routing
            around failure points when segments are setup using the
            dynamic setup method.
       -iv. The PW Routing function MUST support re-routing around
            failures that occur between the statically configured
            segment endpoints. This may be done by choosing another PSN
            tunnel between the two segment endpoints or setting up an
            alternative tunnel.
        -v. Routing MUST support the operation of backup protection of
            primary paths.
       -vi. Manual routing SHOULD be supported to allow diversity for
            1:1 protected PWs.


7. Operations and Maintenance (OAM)

   OAM mechanisms for the attachment circuits are defined in the
   specifications for PW emulated specific technologies (e.g., ITU-T
   I.610 for ATM). These mechanisms enable, among other things, defects
   in the network to be detected, localized and diagnosed. They also
   enable communication of PW defect states on the PW attachment
   circuit.

   The interworking of OAM mechanisms for SS-PWs between ACs and PWs is



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   defined in [PWE3-OAM]. These enable defect states to be propagated
   across a PWE3 network following the failure and recovery from faults.

   OAM mechanisms for MS-PWs MUST provide at least the same capabilities
   as those for SS-PWs.

   In addition, it should be possible to support both segment and end-
   to-end OAM mechanisms for both defect notifications and connectivity
   verification in order to allow defects to be localized in a multi-
   segment network. That is, PW OAM segments can be U-PE to U-PE, U-PE
   to S-PE, or S-PE to S-PE.

   It is desirable to use existing PW OAM mechanisms for MS-PWs or
   extensions to them if needed.

   The following requirements apply to OAM for MS-PWs:

        -i. MS-PW OAM SHOULD be supported end-to-end across the network.

       -ii. OAM activation/deactivation SHOULD be tied to MS-PW
            setup/tear down.

      -iii. The MS-PW SHOULD support a Forward Defect Indicator (FDI).

       -iv. Single ended monitoring SHOULD be supported for both
            directions of the MS-PW.

        -v. MS-PW OAM SHOULD support switch over between 1:1 protected
            LSPs end-to-end.

       -vi. In-band monitoring SHOULD be provided both end-to-end across
            the MS-PW, and on a segment (i.e. SS-PW) basis.

      -vii. At the S-PE, defect notifications on the upstream segment of
            PWs must be propagated to the downstream PW segment.

     -viii. All PE routers along the MS-PW MUST agree on a common PW OAM
            mechanism to use to the MS-PW.

       -ix. At the S-PE, defects on an PSN tunnel must be propagated to
            all PWs that utilize that particular PSN tunnel.

        -x. The directionality of defect notifications must be
            maintained across the S-PE.







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       -xi. The S-PE should be able to behave as a segment endpoint for
            PW OAM mechanisms.

      -xii. The S-PE MUST be able to pass U-PE to U-PE PW OAM messages
            transparently.


8. Security Considerations

   This document specifies the requirements for MS-PWs that can be setup
   across domain boundaries administered by one ore more service
   providers. The security requirements for MS-PWs setup across domains
   administered by one service provider are the same as those described
   under security considerations in [PWE3_control]. These requirements
   also apply to interprovider MS-PWs. In this section, the focus is on
   the additional security requirements for interprovider operation of
   MS-PWs in both the control plane and data plane.


8.1. Data-plane Security Requirements

   MS-PWs that cross SP domain boundaries may connect one U-PE in one SP
   domain to a U-PE in another SP-domain. They may also transit other SP
   domains even if the two U-PEs are under the control of one SP. Under
   these scenarios, theere is a chance that one or more PDUs be falsely
   inserted into a MS-PW at any of the orginating, terminating or
   transit domains. Such false injection can be the result of a
   malicious attack or fault in the MS-PW crossconnects.  Solutions MAY
   provide mechanisms for ensuring the end-end authenticity of MS-PW
   PDUs.

   One of the crossed domains may decide to selectively mirror the PDUs
   of a MS-PW for eavesdropping purposes. It may also decide to
   selectively hijack the PDUs of a MS-PW by directing the PDUs away
   from their destination. In either case, the privacy of a MS-PDU can
   be violated. This document does not place any requirements on
   protecting the privacy of a MS-PW PDU via encryption for instance.
   Encryption may be performed at a higher layer in the protocol stack,
   based on the application or network requirements.

   The data plane of an S-PE at a domain boundary MUST be able to police
   an incoming MS-PW traffic to the MS-PW traffic parameters or to an
   administratively configured profile. The option to enable/diable
   policing MUST be provided to the network administor. This is to
   ensure that a MS-PW or a group of MS-PWs do not grab more resources
   then they are allocated. In addition, the data plane of an S-PE MUST
   be able to police OAM messages to a preconfigured traffic profile or
   to filter out these messages upon adminsitrative configuration.



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   An ingress S-PE MUST ensure that an MS-PW receive the CoS treatment
   configured or signaled for that MS-PW at the S-PE. Specifically, an
   S-PE MUST guard against packets marked in the exp bits or IP-header
   DS field (depending on the PSN) for a better CoS than they should
   receive.

   An ingresss S-PE MUST be able to define per-interface or interface-
   group (a group may correspond to interfaces to a peer-provider) label
   space for MPLS-PWs. An S-PE MUST be configurable not to accept labled
   packets from another provider unless the bottom label is a PW-label
   assigned by the S-PE on the interface on which the packet arrived.


8.2. Control-plane Security Requirements

   A MS-PW connects two attachment circuits. It is important to make
   sure that PW connections are not arbitrarily accepted from anywhere,
   or else a local attachment circuit might get connected to an
   arbitrary remote attachment circuit. The fault in the connection can
   start at a remote U-PE or an S-PE.

   An incoming MS-PW request/reply MUST NOT be accepted unless its IP
   source address is known to be the source of an "eligible" peer. If a
   peering adjacency has to be established prior to exchaging setup
   requests/responses, peering MUST only be done with eligible peers.
   The set of eligible peers could be pre-configured (either as a list
   of IP addresses, or as a list of address/mask combinations).
   Furthermore, the restriction of peering sessions to specific
   interfaces SHOULD also be provided. The S-PE and U-PE SHOULD drop the
   unaccepted signaling messages in the data path to avoid a DoS attack
   on the control plane.

   Even if a connection request appears to come from an eligible peer,
   its source address may have been spoofed. So some means of preventing
   source address spoofing must be in place. For example, if eligible
   peers are in the same network, source address filtering at the border
   routers of that network could eliminate the possibility of source
   address spoofing.

   For a greater degree of security, an authentication mechanism that is
   suitable to the associated protocol MUST be available. Furthermore
   authentication using a signature for each indifidual MS-PW setup
   messages MUST be available, in addition to an overall control
   protocol session authentication , and message validation.

   Peer authentication protects against IP address spoofing but does not
   prevent one peer (S-PE or U-PE) from connecting to the wrong
   attachment circuit. Under a single administrative authority, this may



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   be the result of a misconfiguration. When the MS-PW crosses multiple
   provider domains, this may be the result of a malicious act by a
   service provider or a security hole in that provider network. Static
   manual configuration of MS-PWs at S-PEs and U-PEs provide a greater
   degree of security. If an identfication of both ends of a MS-PW is
   configured and carried in the signaling message, an S-PE can verify
   the signaling message against the configuration. To support dynamic
   signaling of MS-PWs, whereby only endpoints are provisioned and S-PEs
   are dynamically discovered, mechanisms SHOULD be provided to
   configure such information on a server and to use that information
   during a connection attempt for validation.

   S-PEs that connect one provider domain to another provider domain
   MUST have the capability to rate-limit signaling traffic in order to
   prevent DoS attacks on the control plane. Furthermore, detection and
   disposition of malformed packets and defense against various forms of
   attacks that can be protocol-specific MUST be provided.


9. Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


10. Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any



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   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   or will be disclosed, and any of which I become aware will be
   disclosed, in accordance with RFC 3668.


11. IANA Considerations

   This document has no IANA Actions.


12. Normative References

   [PWE3-ARCH] "PWE3 Architecture" Bryant, et al., RFC3985.

   [PWE3-OAM] "Pseudo Wire (PW) OAM Message Mapping" Nadeau et al.,
        draft-ietf-pwe3-oam-msg-map-02.txt (work in progress),
        February 2005


13. Informative References

   [ITUQ] ITU-T Recommendation Q.933, and Q.922 Specification for
        Frame Mode Basic call control, ITU Geneva 1995


14. Author Information


   Luca Martini
   Cisco Systems, Inc.
   9155 East Nichols Avenue, Suite 400
   Englewood, CO, 80112
   e-mail: lmartini@cisco.com





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   Matthew Bocci
   Alcatel Telecom Ltd,
   Voyager Place
   Shoppenhangers Road
   Maidenhead
   Berks, UK
   e-mail: matthew.bocci@alcatel.co.uk


   Nabil Bitar
   Verizon
   40 Sylvan Road
   Waltham, MA 02145
   e-mail: nabil.bitar@verizon.com




































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