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Network Working Group T. Nadeau Request for Comments: 4377 M. Morrow Category: Informational G. Swallow

                                                   Cisco Systems, Inc.
                                                              D. Allan
                                                       Nortel Networks
                                                         S. Matsushima
                                                         Japan Telecom
                                                         February 2006
           Operations and Management (OAM) Requirements
         for Multi-Protocol Label Switched (MPLS) Networks

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).


 This document specifies Operations and Management (OAM) requirements
 for Multi-Protocol Label Switching (MPLS), as well as for
 applications of MPLS, such as pseudo-wire voice and virtual private
 network services.  These requirements have been gathered from network
 operators who have extensive experience deploying MPLS networks.

Table of Contents

 1. Introduction ....................................................2
 2. Document Conventions ............................................2
 3. Motivations .....................................................4
 4. Requirements ....................................................4
 5. Security Considerations ........................................11
 6. References .....................................................12
 7. Acknowledgements ...............................................13

Nadeau, et al. Informational [Page 1] RFC 4377 OAM Requirements for MPLS Networks February 2006

1. Introduction

 This document describes requirements for user and data plane
 Operations and Management (OAM) for Multi-Protocol Label Switching
 (MPLS).  These requirements have been gathered from network operators
 who have extensive experience deploying MPLS networks.  This document
 specifies OAM requirements for MPLS, as well as for applications of
 Currently, there are no specific mechanisms proposed to address these
 requirements.  The goal of this document is to identify a commonly
 applicable set of requirements for MPLS OAM at this time.
 Specifically, a set of requirements that apply to the most common set
 of MPLS networks deployed by service provider organizations at the
 time this document was written.  These requirements can then be used
 as a base for network management tool development and to guide the
 evolution of currently specified tools, as well as the specification
 of OAM functions that are intrinsic to protocols used in MPLS

2. Document Conventions

2.1. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 document are to be interpreted as described in RFC 2119 [RFC2119].
 Queuing/buffering Latency: The delay caused by packet queuing (value
                            is variable since it is dependent on the
                            packet arrival rate, the packet length,
                            and the link throughput).
 Probe-based-detection:     Active measurement tool that can measure
                            the consistency of an LSP [RFC4379].
 Defect:                    Any error condition that prevents a Label
                            Switched Path (LSP) from functioning
                            correctly.  For example, loss of an
                            Interior Gateway Protocol (IGP) path will
                            most likely result in an LSP not being
                            able to deliver traffic to its
                            destination.  Another example is the
                            interruption of the path for a TE tunnel.
                            These may be due to physical circuit
                            failures or failure of switching nodes to
                            operate as expected.

Nadeau, et al. Informational [Page 2] RFC 4377 OAM Requirements for MPLS Networks February 2006

                            Multi-vendor/multi-provider network
                            operation typically requires agreed upon
                            definitions of defects (when it is broken
                            and when it is not) such that both
                            recovery procedures and service level
                            specification impact can be specified.
 Head-end Label Switching
 Router (LSR):              The beginning of an LSP.  A head-end LSR
                            is also referred to as an ingress LSR.
 Tail-end Label Switching
 Router (LSR):              The end of an LSP.  A tail-end LSR is also
                            referred to as an egress LSR.
 Propagation Latency:       The delay added by the propagation of the
                            packet through the link (fixed value that
                            depends on the distance of the link and
                            the propagation speed).
 Transmission Latency:      The delay added by the transmission of the
                            packet over the link, i.e., the time it
                            takes to put the packet over the media
                            (value that depends on the link throughput
                            and packet length).
 Processing Latency:        The delay added by all the operations
                            related to the switching of labeled
                            packets (value is node implementation
                            specific and may be considered fixed and
                            constant for a given type of equipment).
 Node Latency:              The delay added by the network element
                            resulting from of the sum of the
                            transmission, processing, and
                            queuing/buffering latency.
 One-hop Delay:             The fixed delay experienced by a packet to
                            reach the next hop resulting from the of
                            the propagation latency, the transmission
                            latency, and the processing latency.
 Minimum Path Latency:      The sum of the one-hop delays experienced
                            by the packet when traveling from the
                            ingress to the egress LSR.

Nadeau, et al. Informational [Page 3] RFC 4377 OAM Requirements for MPLS Networks February 2006

 Variable Path Latency:     The variation in the sum of the delays
                            experienced by packets transiting the
                            path, otherwise know as jitter.

2.2. Acronyms

 ASBR: Autonomous System Border Router
 CE: Customer Edge
 PE: Provider Edge
 SP: Service Provider
 ECMP: Equal-Cost Multi-path
 LSP: Label Switched Path
 LSP Ping: Label Switched Path Ping
 LSR: Label Switching Router
 OAM: Operations and Management
 RSVP: Resource reSerVation Protocol
 LDP: Label Distribution Protocol
 DoS: Denial of Service

3. Motivations

 This document was created to provide requirements that could be used
 to create consistent and useful OAM functionality that meets
 operational requirements of those service providers (SPs) who have
 deployed or are deploying MPLS.

4. Requirements

 The following sections enumerate the OAM requirements gathered from
 service providers who have deployed MPLS and services based on MPLS
 networks.  Each requirement is specified in detail to clarify its
 applicability.  Although the requirements specified herein are
 defined by the IETF, they have been made consistent with requirements
 gathered by other standards bodies such as the ITU [Y1710].

Nadeau, et al. Informational [Page 4] RFC 4377 OAM Requirements for MPLS Networks February 2006

4.1. Detection of Label Switched Path Defects

 The ability to detect defects in a broken LSP MUST not require manual
 hop-by-hop troubleshooting of each LSR used to switch traffic for
 that LSP.  For example, it is not desirable to manually visit each
 LSR along the data plane path transited by an LSP; instead, this
 function MUST be automated and able to be performed at some operator
 specified frequency from the origination point of that LSP.  This
 implies solutions that are interoperable to allow for such automatic
 Furthermore, the automation of path liveliness is desired in cases
 where large numbers of LSPs might be tested.  For example, automated
 ingress LSR to egress LSR testing functionality is desired for some
 LSPs.  The goal is to detect LSP path defects before customers do,
 which requires detection and correction of LSP defects in a manner
 that is both predictable and within the constraints of the service
 level agreement under which the service is being offered.  Simply
 put, the sum of the time it takes an OAM tool to detect a defect and
 the time needed for an operational support system to react to this
 defect, by possibly correcting it or notifying the customer, must
 fall within the bounds of the service level agreement in question.
 Synchronization of detection time bounds by tools used to detect
 broken LSPs is required.  Failure to specify defect detection time
 bounds may result in an ambiguity in test results.  If the time to
 detect broken LSPs is known, then automated responses can be
 specified with respect and regard to resiliency and service level
 specification reporting.  Further, if synchronization of detection
 time bounds is possible, an operational framework can be established
 to guide the design and specification of MPLS applications.
 Although an ICMP-based ping [RFC792] can be sent through an LSP as an
 IP payload, the use of this tool to verify the defect-free operation
 of an LSP has the potential of returning erroneous results (both
 positive and negative) for a number of reasons.  For example, in some
 cases, because the ICMP traffic is based on legally addressable IP
 addressing, it is possible for ICMP messages that are originally
 transmitted inside of an LSP to "fall out of the LSP" at some point
 along the path.  In these cases, since ICMP packets are routable, a
 falsely positive response may be returned.  In other cases, where the
 data plane of a specific LSP needs to be tested, it is difficult to
 guarantee that traffic based on an ICMP ping header is parsed and
 hashed to the same equal-cost multi-paths (ECMP) as the data traffic.
 Any detection mechanisms that depend on receiving the status via a
 return path SHOULD provide multiple return options with the
 expectation that one of them will not be impacted by the original

Nadeau, et al. Informational [Page 5] RFC 4377 OAM Requirements for MPLS Networks February 2006

 defect.  An example of a case where a false negative might occur
 would be a mechanism that requires a functional MPLS return path.
 Since MPLS LSPs are unidirectional, it is possible that although the
 forward LSP, which is the LSP under test, might be functioning, the
 response from the destination LSR might be lost, thus giving the
 source LSR the false impression that the forward LSP is defective.
 However, if an alternate return path could be specified -- say IP for
 example -- then the source could specify this as the return path to
 the destination, and in this case, would receive a response
 indicating that the return LSP is defective.
 The OAM packet MUST follow the customer data path exactly in order to
 reflect path liveliness used by customer data.  Particular cases of
 interest are forwarding mechanisms, such as ECMP scenarios within the
 operator's network, whereby flows are load-shared across parallel
 paths (i.e., equal IGP cost).  Where the customer traffic may be
 spread over multiple paths, the ability to detect failures on any of
 the path permutations is required.  Where the spreading mechanism is
 payload specific, payloads need to have forwarding that is common
 with the traffic under test.  Satisfying these requirements
 introduces complexity into ensuring that ECMP connectivity
 permutations are exercised and that defect detection occurs in a
 reasonable amount of time.

4.2. Diagnosis of a Broken Label Switched Path

 The ability to diagnose a broken LSP and to isolate the failed
 component (i.e., link or node) in the path is required.  For example,
 note that specifying recovery actions for mis-branching defects in an
 LDP network is a particularly difficult case.  Diagnosis of defects
 and isolation of the failed component is best accomplished via a path
 trace function that can return the entire list of LSRs and links used
 by a certain LSP (or at least the set of LSRs/links up to the
 location of the defect).  The tracing capability SHOULD include the
 ability to trace recursive paths, such as when nested LSPs are used.
 This path trace function MUST also be capable of diagnosing LSP mis-
 merging by permitting comparison of expected vs. actual forwarding
 behavior at any LSR in the path.  The path trace capability SHOULD be
 capable of being executed from the head-end Label Switching Router
 (LSR) and may permit downstream path components to be traced from an
 intermediate mid-point LSR.  Additionally, the path trace function
 MUST have the ability to support ECMP scenarios described in Section

Nadeau, et al. Informational [Page 6] RFC 4377 OAM Requirements for MPLS Networks February 2006

4.3. Path Characterization

 The path characterization function is the ability to reveal details
 of LSR forwarding operations.  These details can then be compared
 during subsequent testing relevant to OAM functionality.  This
 includes but is not limited to:
  1. consistent use of pipe or uniform time to live (TTL) models by

an LSR [RFC3443].

  1. sufficient details that allow the test origin to exercise all

path permutations related to load spreading (e.g., ECMP).

  1. stack operations performed by the LSR, such as pushes, pops,

and TTL propagation at penultimate hop LSRs.

4.4. Service Level Agreement Measurement

 Mechanisms are required to measure the diverse aspects of Service
 Level Agreements, which include:
  1. latency - amount of time required for traffic to transit the


  1. packet loss
  1. jitter - measurement of latency variation
  1. defect free forwarding - the service is considered to be

available, or the service is unavailable and other aspects of

       performance measurement do not have meaning.
 Such measurements can be made independently of the user traffic or
 via a hybrid of user traffic measurement and OAM probing.
 At least one mechanism is required to measure the number of OAM
 packets.  In addition, the ability to measure the quantitative
 aspects of LSPs, such as jitter, delay, latency, and loss, MUST be
 available in order to determine whether the traffic for a specific
 LSP is traveling within the operator-specified tolerances.
 Any method considered SHOULD be capable of measuring the latency of
 an LSP with minimal impact on network resources.  See Section 2.1 for
 definitions of the various quantitative aspects of LSPs.

Nadeau, et al. Informational [Page 7] RFC 4377 OAM Requirements for MPLS Networks February 2006

4.5. Frequency of OAM Execution

 The operator MUST have the flexibility to configure OAM parameters to
 meet their specific operational requirements.
 This includes the frequency of the execution of any OAM functions.
 The ability to synchronize OAM operations is required to permit a
 consistent measurement of service level agreements.  To elaborate,
 there are defect conditions, such as mis-branching or misdirection of
 traffic, for which probe-based detection mechanisms that incur
 significant mismatches in their detection frequency may result in
 flapping.  This can be addressed either by synchronizing the rate or
 having the probes self-identify their probe rate.  For example, when
 the probing mechanisms are bootstrapping, they might negotiate and
 ultimately agree on a probing rate, therefore providing a consistent
 probing frequency and avoiding the aforementioned problems.
 One observation would be that wide-spread deployment of MPLS, common
 implementation of monitoring tools, and the need for inter-carrier
 synchronization of defect and service level specification handling
 will drive specification of OAM parameters to commonly agreed on
 values.  Such values will have to be harmonized with the surrounding
 technologies (e.g., SONET/SDH, ATM) to be useful.  This will become
 particularly important as networks scale and mis-configuration can
 result in churn, alarm flapping, etc.

4.6. Alarm Suppression, Aggregation, and Layer Coordination

 Network elements MUST provide alarm suppression functionality that
 prevents the generation of a superfluous generation of alarms by
 simply discarding them (or not generating them in the first place),
 or by aggregating them together, thereby greatly reducing the number
 of notifications emitted.  When viewed in conjunction with the
 requirement in Section 4.7 below, this typically requires fault
 notification to the LSP egress that may have specific time
 constraints if the application using the LSP independently implements
 path continuity testing (for example, ATM I.610 Continuity check
 (CC)[I610]).  These constraints apply to LSPs that are monitored.
 The nature of MPLS applications allows for the possibility of having
 multiple MPLS applications attempt to respond to defects
 simultaneously, e.g., layer-3 MPLS VPNs that utilize Traffic
 Engineered tunnels where a failure occurs on the LSP carrying the
 Traffic Engineered tunnel.  This failure would affect the VPN traffic
 that uses the tunnel's LSP.  Mechanisms are required to coordinate
 network responses to defects.

Nadeau, et al. Informational [Page 8] RFC 4377 OAM Requirements for MPLS Networks February 2006

4.7. Support for OAM Inter-working for Fault Notification

 An LSR supporting the inter-working of one or more networking
 technologies over MPLS MUST be able to translate an MPLS defect into
 the native technology's error condition.  For example, errors
 occurring over an MPLS transport LSP that supports an emulated ATM VC
 MUST translate errors into native ATM OAM Alarm Indication Signal
 (AIS) cells at the termination points of the LSP.  The mechanism
 SHOULD consider possible bounded detection time parameters, e.g., a
 "hold off" function before reacting to synchronize with the OAM
 One goal would be alarm suppression by the upper layer using the LSP.
 As observed in Section 4.5, this requires that MPLS perform detection
 in a bounded timeframe in order to initiate alarm suppression prior
 to the upper layer independently detecting the defect.

4.8. Error Detection and Recovery

 Recovery from a fault by a network element can be facilitated by MPLS
 OAM procedures.  These procedures will detect a broader range of
 defects than that of simple link and node failures.  Since MPLS LSPs
 may span multiple routing areas and service provider domains, fault
 recovery and error detection should be possible in these
 configurations as well as in the more simplified single-area/domain
 Recovery from faults SHOULD be automatic.  It is a requirement that
 faults SHOULD be detected (and possibly corrected) by the network
 operator prior to customers of the service in question detecting

4.9. Standard Management Interfaces

 The wide-spread deployment of MPLS requires common information
 modeling of management and control of OAM functionality.  Evidence of
 this is reflected in the standard IETF MPLS-related MIB modules
 (e.g., [RFC3813][RFC3812][RFC3814]) for fault, statistics, and
 configuration management.  These standard interfaces provide
 operators with common programmatic interface access to Operations and
 Management functions and their statuses.  However, gaps in coverage
 of MIB modules to OAM and other features exist; therefore, MIB
 modules corresponding to new protocol functions or network tools are

Nadeau, et al. Informational [Page 9] RFC 4377 OAM Requirements for MPLS Networks February 2006

4.10. Detection of Denial of Service Attacks

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

4.11. Per-LSP Accounting Requirements

 In an MPLS network, service providers can measure traffic from an LSR
 to the egress of the network using some MPLS related MIBs, for
 example.  This means that it is reasonable to know how much traffic
 is traveling from location to location (i.e., a traffic matrix) by
 analyzing the flow of traffic.  Therefore, traffic accounting in an
 MPLS network can be summarized as the following three items:
    (1) Collecting information to design network
        For the purpose of optimized network design, a service
        provider may offer the traffic information.  Optimizing
        network design needs this information.
    (2) Providing a Service Level Specification
        Providers and their customers MAY need to verify high-level
        service level specifications, either to continuously optimize
        their networks, or to offer guaranteed bandwidth services.
        Therefore, traffic accounting to monitor MPLS applications is
    (3) Inter-AS environment
        Service providers that offer inter-AS services require
        accounting of those services.
    These three motivations need to satisfy the following:
  1. In (1) and (2), collection of information on a per-LSP

basis is a minimum level of granularity for collecting

           accounting information at both of ingress and egress of an
  1. In (3), SP's ASBR carry out interconnection functions as an

intermediate LSR. Therefore, identifying a pair of ingress

           and egress LSRs using each LSP is needed to determine the
           cost of the service that a customer is using.

Nadeau, et al. Informational [Page 10] RFC 4377 OAM Requirements for MPLS Networks February 2006

4.11.1. Requirements

 Accounting on a per-LSP basis encompasses the following set of
    (1) At an ingress LSR, accounting of traffic through LSPs that
        begin at each egress in question.
    (2) At an intermediate LSR, accounting of traffic through LSPs for
        each pair of ingress to egress.
    (3) At egress LSR, accounting of traffic through LSPs for each
    (4) All LSRs containing LSPs that are being measured need to have
        a common identifier to distinguish each LSP.  The identifier
        MUST be unique to each LSP, and its mapping to LSP SHOULD be
        provided whether from manual or automatic configuration.
    In the case of non-merged LSPs, this can be achieved by simply
    reading traffic counters for the label stack associated with the
    LSP at any LSR along its path.  However, in order to measure
    merged LSPs, an LSR MUST have a means to distinguish the source of
    each flow so as to disambiguate the statistics.

4.11.2. Location of Accounting

 It is not realistic for LSRs to perform the described operations on
 all LSPs that exist in a network.  At a minimum, per-LSP based
 accounting SHOULD be performed on the edges of the network -- at the
 edges of both LSPs and the MPLS domain.

5. Security Considerations

 Provisions to any of the network mechanisms designed to satisfy the
 requirements described herein are required to prevent their
 unauthorized use.  Likewise, these network mechanisms MUST provide a
 means by which an operator can prevent denial of service attacks if
 those network mechanisms are used in such an attack.
 LSP mis-merging has security implications beyond that of simply being
 a network defect.  LSP mis-merging can happen due to a number of
 potential sources of failure, some of which (due to MPLS label
 stacking) are new to MPLS.
 The performance of diagnostic functions and path characterization
 involve extracting a significant amount of information about network
 construction that the network operator MAY consider private.

Nadeau, et al. Informational [Page 11] RFC 4377 OAM Requirements for MPLS Networks February 2006

6. References

6.1. Normative References

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

6.2. Informative References

 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
           Label Switched (MPLS) Data Plane Failures", RFC 4379,
           February 2006.
 [RFC3812] Srinivasan, C., Viswanathan, A., and T. Nadeau,
           "Multiprotocol Label Switching (MPLS) Traffic Engineering
           (TE) Management Information Base (MIB)", RFC 3812, June
 [RFC3813] Srinivasan, C., Viswanathan, A., and T. Nadeau,
           "Multiprotocol Label Switching (MPLS) Label Switching
           Router (LSR) Management Information Base (MIB)", RFC 3813,
           June 2004.
 [RFC3814] Nadeau, T., Srinivasan, C., and A. Viswanathan,
           "Multiprotocol Label Switching (MPLS) Forwarding
           Equivalence Class To Next Hop Label Forwarding Entry
           (FEC-To-NHLFE) Management Information Base (MIB)", RFC
           3814, June 2004.
 [Y1710]   ITU-T Recommendation Y.1710, "Requirements for OAM
           Functionality In MPLS Networks"
 [I610]    ITU-T Recommendation I.610, "B-ISDN operations and
           maintenance principles and functions", February 1999
 [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
           IANA Considerations Section in RFCs", BCP 26, RFC 2434,
           October 1998.
 [RFC792]  Postel, J., "Internet Control Message Protocol", STD 5, RFC
           792, September 1981.

Nadeau, et al. Informational [Page 12] RFC 4377 OAM Requirements for MPLS Networks February 2006

 [RFC3443] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in
           Multi-Protocol Label Switching (MPLS) Networks", RFC 3443,
           January 2003.

7. Acknowledgements

 The authors wish to acknowledge and thank the following individuals
 for their valuable comments to this document:  Adrian Smith, British
 Telecom; Chou Lan Pok, SBC; Mr. Ikejiri, NTT Communications; and Mr.
 Kumaki, KDDI.  Hari Rakotoranto, Miya Kohno, Cisco Systems; Luyuan
 Fang, AT&T; Danny McPherson, TCB; Dr. Ken Nagami, Ikuo Nakagawa,
 Intec Netcore, and David Meyer.

Authors' Addresses

 Comments should be made directly to the MPLS mailing list
 Thomas D. Nadeau
 Cisco Systems, Inc.
 300 Beaver Brook Road
 Boxboro, MA 01719
 Phone: +1-978-936-1470
 Monique Jeanne Morrow
 Cisco Systems, Inc.
 Glatt-Com, 2nd Floor
 Phone:  (0)1 878-9412
 George Swallow
 Cisco Systems, Inc.
 300 Beaver Brook Road
 Boxboro, MA 01719
 Phone: +1-978-936-1398

Nadeau, et al. Informational [Page 13] RFC 4377 OAM Requirements for MPLS Networks February 2006

 David Allan
 Nortel Networks
 3500 Carling Ave.
 Ottawa, Ontario, CANADA
 Phone: 1-613-763-6362
 Satoru Matsushima
 Japan Telecom
 1-9-1, Higashi-Shinbashi, Minato-ku
 Tokyo, 105-7316 Japan
 Phone: +81-3-6889-1092

Nadeau, et al. Informational [Page 14] RFC 4377 OAM Requirements for MPLS Networks February 2006

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Nadeau, et al. Informational [Page 15]

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