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Versions: (draft-yasukawa-mpls-p2mp-oam-reqs) 00 01 RFC 4687

Network Working Group                                Seisho Yasukawa
Internet Draft                                       NTT Corp
Expires: August 2006
                                                     Adrian Farrel
                                                     Old Dog Consulting

                                                     Daniel King
                                                     Aria Networks Ltd.

                                                     Thomas D. Nadeau
                                                     Cisco Systems, Inc.

                                                           February 2006

        OAM Requirements for Point-to-Multipoint MPLS Networks

               draft-ietf-mpls-p2mp-oam-reqs-01.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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Abstract

   Multi-Protocol Label Switching (MPLS) has been extended to encompass
   point-to-multipoint (P2MP) Label Switched Paths (LSPs). As with
   point-to-point MPLS LSPs the requirement to detect, handle and
   diagnose control and data plane defects is critical.

   For operators deploying services based on P2MP MPLS LSPs the
   detection and specification of how to handle those defects is
   important because such defects may not only affect the fundamentals
   of an MPLS network, but also because they may impact service level
   specification commitments for customers of their network.

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   This document describes requirements for data plane operations and
   management for P2MP MPLS LSPs. These requirements apply to all forms
   of P2MP MPLS LSPs, and include P2MP Traffic Engineered (TE) LSPs and
   multicast LSPs.

Table of Contents

   1. Introduction .................................................. 2
   2. Terminology ................................................... 3
     2.1 Conventions ................................................ 3
     2.2 Terminology ................................................ 3
     2.3 Acronyms ................................................... 3
   3. Motivations ................................................... 3
   4. General Requirements .......................................... 4
     4.1 Detection of Label Switch Path Defects ..................... 4
     4.2 Diagnosis of a Broken Label Switch Path .................... 5
     4.3 Path characterization ...................................... 6
     4.4 Service Level Agreement Measurement ........................ 6
     4.5 Frequency of OAM Execution ................................. 7
     4.6 Alarm Suppression, Aggregation and Layer Coordination ...... 7
     4.7 Support for OAM Interworking for Fault Notification ........ 7
     4.8 Error Detection and Recovery ............................... 8
     4.9 Standard Management Interfaces ............................. 8
     4.10 Detection of Denial of Service Attacks .................... 9
     4.11 Per-LSP Accounting Requirements ........................... 9
   5. Security Considerations ....................................... 9
   6. IANA Considerations .......................................... 10
   7. References ................................................... 10
     7.1 Normative References ...................................... 10
     7.2 Informative References .................................... 10
   8. Acknowledgements ............................................. 11
   9. Authors' Addresses ........................................... 11
   10. Intellectual Property Statement ............................. 12
   11. Full Copyright Statement .................................... 12

1. Introduction

   This document describes requirements for data plane operations and
   management (OAM) for point-to-multipoint (P2MP) Multi-Protocol Label
   Switching (MPLS). This draft specifies OAM requirements for P2MP
   MPLS, as well as for applications of P2MP MPLS.

   These requirements apply to all forms of P2MP MPLS LSPs, and include
   P2MP Traffic Engineered (TE) LSPs [P2MP-SIG-REQ] and [P2MP-RSVP], as
   well as multicast LDP LSPs [MCAST-LDP].

   Note that the requirements for OAM for P2MP MPLS build heavily on the
   requirements for OAM for point-to-point MPLS. These latter
   requirements are described in [RFC4377] and are not repeated in this
   document.

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   For a generic framework for OAM in MPLS networks, refer to [RFC4378].

2. Terminology

2.1 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 [RFC2119].

2.2 Terminology

   Definitions of key terms for MPLS OAM are found in [RFC4377] and the
   reader is assumed to be familiar with those definitions which are not
   repeated here.

   [P2MP-SIG-REQ] includes some important definitions and terms for use
   within the context of P2MP MPLS. The reader should be familiar with
   at least the terminology section of that document.

2.3 Acronyms

   The following acronyms are used in this document.

   CE:   Customer Edge
   DoS:  Denial of service
   ECMP: Equal Cost Multipath
   LDP:  Label Distribution Protocol
   LSP:  Label Switch Path
   LSR:  Label Switch Router
   OAM:  Operations and Management
   OA&M: Operations, Administration and Maintenance.
   RSVP: Resource reSerVation Protocol
   P2MP: Point-to-Multipoint
   SP:   Service Provider
   TE:   Traffic Engineering

3. Motivations

   OAM for MPLS networks has been established as a fundamental
   requirement both through operational experience and through its
   documentation in numerous Internet drafts. Many such documents (for
   example, [RFC4379], [RFC3812], [RFC3813], [RFC3814], and [RFC3815])
   developed specific solutions to individual issues or problems.
   Coordination of the full OAM requirements for MPLS was achieved by
   [RFC4377] in recognition of the fact that the previous piecemeal
   approach could lead to inconsistent and inefficient applicability of
   OAM techniques across the MPLS architecture, and might require
   significant modifications to operational procedures and systems in
   order to provide consistent and useful OAM functionality.

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   This document builds on these realizations and extends the statements
   of MPLS OAM requirements to cover the new area of P2MP MPLS. That is,
   this document captures the requirements for P2MP MPLS OAM in advance
   of the development of specific solutions.

   Nevertheless, at the time of writing, some effort had already been
   expended to extend existing MPLS OAM solutions to cover P2MP MPLS
   (for example, [P2MP-LSP-PING]). While this approach of extending
   existing solutions may be reasonable, in order to ensure a consistent
   OAM framework it is necessary to articulate the full set of
   requirements in a single document. This will facilitate a uniform set
   of MPLS OAM solutions spanning multiple MPLS deployments and
   concurrent applications.

4. General Requirements

   The general requirements described in this section are similar to
   those described for point-to-point MPLS in [RFC4377]. The subsections
   below do not repeat material from [RFC4377], but simply give
   references to that document.

   However, where the requirements for P2MP MPLS OAM differ from or are
   more extensive than those expressed in [RFC4377], additional text is
   supplied.

   In general, it should be noted that P2MP LSPs introduce a scalability
   issue with respect to OAM that is not present in point-to-point MPLS.
   That is, an individual P2MP LSP will have more than one egress and
   the path to those egresses will very probably not be linear (for
   example, it may have a tree structure). Since the number of egresses
   for a single P2MP LSP is unknown and not bounded by any small number,
   it follows that all mechanisms defined for OAM support MUST scale
   well with the number of egresses and the complexity of the path of
   the LSP. Mechanisms that are able to deal with individual egresses
   will scale no worse than similar mechanisms for point-to-point LSPs,
   but it is desirable to develop mechanisms that are able to leverage
   the fact that multiple egresses are associated with a single LSP, and
   so achieve better scaling.

4.1 Detection of Label Switch Path Defects

   The ability to detect defects in a P2MP LSP SHOULD not require
   manual, hop-by-hop troubleshooting of each LSR used to switch traffic
   for that LSP, and SHOULD rely on proactive OAM procedures (such as
   continuous path connectivity and SLA measurement mechanisms).  Any
   solutions SHOULD either extend or work in close conjunction with
   existing solutions developed for point-to-point MPLS, such as those
   specified in [RFC4379] where this requirement is not contradicted by
   the other requirements in this section. This will leverage existing
   software and hardware deployments.

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   Note that P2MP LSPs may introduce additional scaling concerns for LSP
   probing by tools such as [RFC4379]. As the number of leaves of a P2MP
   LSP increases it potentially becomes more expensive to inspect the
   LSP to detect defects. Any tool developed for this purpose MUST be
   cognitive of this issue and MUST include techniques to reduce the
   scaling impact of an increase in the number of leaves. Nevertheless,
   it should also be noted that the introduction of additional leaves
   may mean that the use of techniques such as [RFC4379] are less
   appropriate for defect detection with P2MP LSPs, while the technique
   may still remain useful for defect diagnosis as described in the next
   section.

   Due to the above scaling concerns, LSRs or other network resources
   MUST NOT be overwhelmed by the operation of normal proactive OAM
   procedures, and measures taken to protect LSRs and network resources
   against being overwhelmed MUST NOT degrade the operational value or
   responsiveness of proactive OAM procedures.

   By "overwhelmed" we mean that it MUST NOT be possible for an LSR to
   be so busy handling proactive OAM that it is unable to continue to
   process control or data plane traffic at its advertised rate.
   Similarly, a network resource (such as a data link) MUST NOT be
   carrying so much proactive OAM traffic that it is unable to carry the
   advertised data rate. At the same time, it is important to configure
   proactive OAM, if it is in use, to not raise alarms caused by the
   failure to receive an OAM message if the component responsible for
   processing the messages is unable to process because other components
   are consuming too many system resources - such alarms might turn out
   to be false.

   In practice, of course, the requirements in the previous paragraph
   may be overcome by careful specification of the anticipated data
   throughput of LSRs or data links, but it should be recalled that
   proactive OAM procedures may be scaled linearly with the number of
   LSPs, and the number of LSPs is not necessarily a function of the
   available bandwidth in an LSR or on a data link.

4.2 Diagnosis of a Broken Label Switch Path

   The ability to diagnose a broken P2MP LSP and to isolate the failed
   component (i.e., link or node) in the path is REQUIRED. These
   functions include a path connectivity test that can test all branches
   and leaves of a P2MP LSP for reachability, as well as a path tracing
   function. Note that this requirement is distinct from the requirement
   to detect errors or failures described in the previous section. In
   practice Detection and Diagnosis/Isolation MAY be performed by
   separate or the same mechanisms according to the way in which the
   other requirements are met.

   It MUST be possible for the operator (or an automated process) to

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   stipulate a timeout after which the failure to see a response shall
   be flagged as an error.

   Any mechanism developed to perform these functions is subject to the
   scalability concerns expressed in section 4.

4.3 Path Characterization

   The path characterization function [RFC4377] is the ability to reveal
   details of LSR forwarding operations for P2MP LSPs. These details can
   then be compared later during subsequent testing relevant to OAM
   functionality. Therefore, LSRs supporting P2MP LSPs MUST provide
   mechanisms that allow operators to interrogate and characterize P2MP
   paths.

   Since P2MP paths are more complex than the paths of point-to-point
   LSPs, the scaling concerns expressed in section 4 apply.

   Note that path characterization SHOULD lead to the operator being
   able to determine the full tree for a P2MP LSP. That is, it is not
   sufficient to know the list of LSRs in the tree, but it is important
   to know their relative order and where the LSP branches.

   Since, in some cases, the control plane state and data paths may
   branch at different points from the control plane and data plane
   topologies (for example, figure 1), it is not sufficient to present
   the order of LSRs, but it is important that the branching points on
   that tree are clearly identified.

                    E
                   /
      A---B---C===D
                   \
                    F

   Figure 1. An example P2MP tree where the data path and control plane
   state branch at C, but the topology branches at D.

   A diagnostic tool that meets the path characterization requirements
   SHOULD collect information that is easy to process to determine the
   P2MP tree for a P2MP LSP, rather than provide information that must
   be post-processed with some complexity.

4.4 Service Level Agreement Measurement

   Mechanisms are required to measure the diverse aspects of Service
   Level Agreements for services that utilize P2MP LSPs. The aspects
   are listed in [RFC4377].

   Service Level Agreements are often measured in terms of the quality

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   and rate of data delivery. In the context of P2MP MPLS, data is
   delivered to multiple egress nodes. The mechanisms MUST, therefore,
   be capable of measuring the aspects of Service Level Agreements as
   they apply to each of the egress points to a P2MP LSP. At the same
   time, in order to diagnose issues with meeting Service Level
   Agreements, mechanisms SHOULD be provided to measure the aspects of
   the agreements at key points within the network such as at branch
   nodes on the P2MP tree.

4.5 Frequency of OAM Execution

   As stipulated in [RFC4377], the operator MUST have the flexibility
   to configure OAM parameters to meet their specific operational
   requirements. This requirement is potentially more important in P2MP
   deployments where the effects of the execution of OAM functions can
   be potentially much greater than in a non-P2MP configuration. For
   example, a mechanism that causes each egress of a P2MP LSP to respond
   could result in a large burst of responses for a single OAM request.

   Therefore, solutions produced SHOULD NOT impose any fixed limitations
   on the frequency of the execution of any OAM functions.

4.6 Alarm Suppression, Aggregation and Layer Coordination

   As described in [RFC4377], network elements MUST provide alarm
   suppression and aggregation mechanisms to prevent the generation of
   superfluous alarms within or across network layers. The same time
   constraint issues identified in [RFC4377] also apply to P2MP LSPs.

   A P2MP LSP also brings the possibility of a single fault causing a
   larger number of alarms than for a point-to-point LSP. This can
   happen because there are a larger number of downstream LSRs (for
   example, a larger number of egresses). The resultant multiplier in
   the number of alarms could cause swamping of the alarm management
   systems to which the alarms are reported, and serves as a multiplier
   to the number of potentially duplicate alarms raised by the network.

   Alarm aggregation or limitation techniques MUST be applied within any
   solution, or be available within an implementation, so that this
   scaling issue can be reduced. Note that this requirement introduces a
   second dimension to the concept of alarm aggregation. Where
   previously it applied to the correlation and suppression of alarms
   generated by different network layers, it now also applies to similar
   techniques applied to alarms generated by multiple downstream LSRs.

4.7 Support for OAM Interworking for Fault Notification

   [RFC4377] specifies that an LSR supporting the interworking of
   one or more networking technologies over MPLS MUST be able to
   translate an MPLS defect into the native technology's error

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   condition.  This also applies to any LSR supporting P2MP LSPs.
   However, careful attention to the requirements for alarm suppression
   stipulated therein and in section 4.6 SHOULD be observed.

   Note that the time constraints for fault notification and alarm
   propagation impact upon the solutions that might be applied to the
   scalability problem inherent in certain OAM techniques applied to
   P2MP LSPs. For example, a solution to the issue of a large number
   of egresses all responding to some form of probe request at the
   same time, might be to make the probes less frequent - but this
   might impact on the ability to detect and/or report faults.

   Where fault notification to the egress is required, there is the
   possibility that a single fault will give rise to multiple
   notifications, one to each egress node of the P2MP that is downstream
   of the fault. Any mechanisms MUST manage this scaling issue while
   still continuing to deliver fault notifications in a timely manner.

   Where fault notification to the ingress is required, the mechanisms
   MUST ensure that the notification identifies the egress nodes of the
   P2MP LSP that are impacted (that is, those downstream of the fault)
   and does not falsely imply that all egress nodes are impacted.

4.8 Error Detection and Recovery

   Recovery from a fault by a network element can be facilitated by
   MPLS OAM procedures. As described in [RFC4377], these procedures
   will detect a broad range of defects, and SHOULD be operable where
   MPLS P2MP LSPs span multiple routing areas, or multiple Service
   Provider domains.

   The same requirements as those expressed in [RFC4377] with respect
   to automatic repair and operator intervention ahead of customer
   detection of faults apply to P2MP LSPs.

   It should be observed that faults in P2MP LSPs MAY be recovered
   through techniques described in [P2MP-RSVP].

4.9 Standard Management Interfaces

   The wide-spread deployment of MPLS requires common information
   modeling of management and control of OAM functionality. This is
   reflected in the integration of standard MPLS-related MIBs
   [RFC3813], [RFC3812], [RFC3814], [RFC3815] for fault, statistics
   and configuration management. These standard interfaces provide
   operators with common programmatic interface access to
   operations and management functions and their status.

   The standard MPLS-related MIB modules [RFC3812], [RFC3813],
   [RFC3814], and [RFC3815] SHOULD be extended wherever possible, to

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   support P2MP LSPs, the associated OAM functions on these LSPs, and
   the applications that utilize P2MP LSPs. Extending them will
   facilitate the reuse of existing management software both in LSRs
   and in management systems. In cases where the existing MIB modules
   cannot be extended, then new MIB modules MUST be created.

4.10  Detection of Denial of Service Attacks

   The ability to detect denial of service (DoS) attacks against the
   data or control planes which signal P2MP LSPs MUST be part of
   any security management related to MPLS OAM tools or techniques.

4.11 Per-LSP Accounting Requirements

   In an MPLS network where P2MP LSPs are in use, Service Providers can
   measure traffic from an LSR to the egress of the network using some
   MPLS-related MIB modules (see section 4.9), for example. Other
   interfaces MAY exist as well and enable the creation of traffic
   matrices so that it is possible to know how much traffic is
   traveling from where to where within the network.

   Analysis of traffic flows to produce a traffic matrix is more
   complicated where P2MP LSPs are deployed because there is no simple
   pairing relationship between an ingress and a single egress.
   Fundamental to understanding traffic flows within a network that
   supports P2MP LSPs will be the knowledge of where the traffic is
   branched for each LSP within the network. That is, where within the
   network the branch nodes for the LSPs are located and what their
   relationship is to links and other LSRs. Traffic flow and
   accounting tools MUST take this fact into account.

5. Security Considerations

   This document introduces no new security issues compared with
   [RFC4377]. It is worth highlighting, however, that any tool designed
   to satisfy the requirements described in this document MUST include
   provisions to prevent its unauthorized use. Likewise, these tools
   MUST provide a means by which an operator can prevent denial of
   service attacks if those tools are used in such an attack.
   LSP mis-merging is described in [RFC4377] where it is pointed out
   that it has security implications beyond simply being a network
   defect. It needs to be stressed that it is in the nature of P2MP
   traffic flows that any erroneous delivery (such as caused by LSP
   mis-merging) is likely to have more far reaching consequences since
   the traffic will be mis-delivered to multiple receivers.

   As with the OAM functions described in [RFC4377], the
   performance of diagnostic functions and path characterization may
   involve the extraction of a significant amount of information about
   network construction. The network operator MAY consider this

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   information private and wish to take steps to secure it, but further,
   the volume of this information may be considered as a threat to the
   integrity of the network if it is extracted in bulk. This issue may
   be greater in P2MP MPLS because of the potential for a large number
   of receivers on a single LSP and the consequent extensive path of the
   LSP.

6. IANA Considerations

   This document creates no new requirements on IANA namespaces.

7. References

7.1 Normative References

   [RFC4377]        T. Nadeau, M. Morrow, G. Swallow, D. Allan, and
                    S. Matsushima, "Operations and Management (OAM)
                    Requirements for Multi-Protocol Label Switched
                   (MPLS) Networks", RFC 4377, February 2006.

   [RFC2119]        Bradner, S., "Key words for use in RFCs to Indicate
                    Requirement Levels", BCP 14, RFC 2119, March 1997.

7.2 Informative References

   [RFC4378]        Alan, D., Nadeau T., "A Framework for
                    Multi-Protocol Label Switching (MPLS) Operations
                    and Management (OAM)", RFC4378, February 2006.

   [RFC4379]        Kompella, K., and Swallow, G., (Editors), "Detecting
                    MPLS Data Plane Failures", RFC 4379, February 2006.

   [MCAST-LDP]      IJ., Wijnands, I. Minei, et al., "Label Distribution
                    Protocol Extensions for Point-to-Multipoint and
                    Multipoint-to-Multipoint Label Switched Paths",
                    draft-minei-wijnands-mpls-ldp-p2mp, work in
                    progress.

   [P2MP-LSP-PING]  Yasukawa, S., Farrel, A., Ali, Z., and Fenner, B.,
                    "Detecting Data Plane Failures in
                    Point-to-Multipoint MPLS Traffic Engineering -
                    Extensions to LSP Ping",
                    draft-yasukawa-mpls-p2mp-lsp-ping, work in progress.

   [P2MP-RSVP]      Aggarwal, R., Papadimitriou, D., and Yasukawa, S.,
                    "Extensions to RSVP-TE for Point to Multipoint TE
                    LSPs", draft-ietf-mpls-rsvp-te-p2mp, work in
                    progress.



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   [P2MP-SIG-REQ]   Yasukawa, S. (Editor), "Signaling Requirements for
                    Point to Multipoint Traffic Engineered MPLS LSPs",
                    draft-ietf-mpls-p2mp-sig-requirement, work in
                    progress.

   [RFC3812]        Srinivasan, C., Viswanathan, A. and T.
                    Nadeau, "MPLS Traffic Engineering Management
                    Information Base Using SMIv2", RFC3812, June 2004.

   [RFC3813]        Srinivasan, C., Viswanathan, A. and T.
                    Nadeau, "MPLS Label Switch Router Management
                    Information Base Using SMIv2", RFC3813, June 2004.

   [RFC3814]        Nadeau, T., Srinivasan, C., and A.
                    Viswanathan, "Multiprotocol Label Switching
                    (MPLS) FEC-To-NHLFE (FTN) Management
                    Information Base", RFC3814, June 2004.

   [RFC3815]        Cucchiara, J., Sjostrand, H., and Luciani, J.,
                    "Definitions of Managed Objects for the
                    Multiprotocol Label Switching (MPLS), Label
                    Distribution Protocol (LDP)", RFC 3815, June 2004.

8. Acknowledgment

   The authors wish to acknowledge and thank the following
   individuals for their valuable comments to this document:
   Rahul Aggarwal, Neil Harrison, Ben Niven-Jenkins and Dimitri
   Papadimitriou.

9. Authors' Addresses

   Adrian Farrel
   Old Dog Consulting
   Phone: +44 (0) 1978 860944
   Email: adrian@olddog.co.uk

   Daniel King
   Aria Networks Ltd.
   Phone: +44 (0)1249 665923
   Email: daniel.king@aria-networks.com

   Thomas D. Nadeau
   Cisco Systems, Inc.
   1414 Massachusetts Ave.
   Boxborough, MA 01719
   Email: tnadeau@cisco.com




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   Seisho Yasukawa
   NTT Corporation
   9-11, Midori-Cho 3-Chome
   Musashino-Shi, Tokyo 180-8585,
   Japan
   Phone: +81 422 59 4769
   Email: yasukawa.seisho@lab.ntt.co.jp

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
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   Copies of IPR disclosures made to the IETF Secretariat and any
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   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
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   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

11. Full Copyright Statement

   Copyright (C) The Internet Society (2006). 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.






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