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Operations and Management (OAM) Requirements for Multi-Protocol Label Switched (MPLS) Networks

The information below is for an old version of the document that is already published as an RFC.
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This is an older version of an Internet-Draft that was ultimately published as RFC 4377.
Authors David Allan , George Swallow , Monique Morrow, Thomas Nadeau , Satoru Matsushima
Last updated 2020-01-21 (Latest revision 2005-12-15)
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IESG IESG state Became RFC 4377 (Informational)
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Network Working Group                         Thomas D. Nadeau
Internet Draft                                Monique Morrow
Expires: June 2006                            George Swallow
                                              Cisco Systems, Inc.

                                              David Allan
                                              Nortel Networks

                                              Satoru Matsushima
                                              Japan Telecom

                                              December 2005

           Operations and Management Requirements 
         for Multi-Protocol Label Switched Networks


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 have been or will be disclosed, and any of which he or she
   becomes aware will be disclosed, in accordance with Section 6 of
   BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts as reference material or to cite them other than
   as "work in progress."

   The list of current Internet-Drafts can be accessed at

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   This document specifies Operations and Management requirements 
   for Multi-Protocol Label Switching, as well as for applications 

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   of Multi-Protocol Label Switching such as pseudo-wire voice and 
   virtual private network services. These requirements 
   have been gathered from network operators who have extensive 
   experience deploying Multi-Protocol Label Switching networks. 

Table of Contents
     Abstract ....................................................1 
 1.  Introduction ................................................2 
 2.  Document Conventions ........................................2 
 2.1 Terminology .................................................2 
 2.2 Acronyms ....................................................2  
 3.  Motivations .................................................2  
 4.  Requirements ................................................2  
 5.  Security Considerations ....................................26 
 6.  IANA considerations ........................................27 
 7.  References .................................................27 
 7.1 Normative references .......................................27 
 7.2 Informative references .....................................29 
 8.  Author's Addresses .........................................29 
 9.  Intellectual Property Notice ...............................30 
 10. Full Copyright Statement ...................................29 

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 draft specifies OAM requirements
   for MPLS, as well as for applications of MPLS.

   No specific mechanisms are proposed to address these
   requirements at this time.  The goal of this draft 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 today 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 networks.

   Comments should be made directly to the MPLS mailing list

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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: delay caused by packet queuing (value is
                              variable since depending on the packet 
                              arrival rate in addition to the
                              dependence on the packet length and the 
                              link throughput).

   Probe-based-detection:     Active measurement tool which can measure
                              the consistency of an LSP [LSPPING].

   Defect:                    Any error condition that prevents an Label 
                              Switched Path functioning correctly. For 
                              example, loss of an IGP path will most 
                              likely also result in a Label Switched 
                              Path not being able to deliver traffic to 
                              its destination. Another example is the 
                              breakage of a TE tunnel. These may be due 
                              to physical circuit failures or failure 
                              of switching nodes to operate as expected.

                              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 impacts can be specified.

   Head-end Label Switching 
   Router (LSR):              The beginning of a label switched path. A 
                              head-end LSR is also referred to as an 
                              ingress LSR.

   Tail-end Label Switching 
   Router (LSR):              The end of a label switched path. A 
                              tail-end LSR is also referred to as an 
                              egress LSR.

   Propagation Latency:       The delay added by the propagation of the 

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                              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 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 
                              packet (value is node implementation 
                              specific and may be considered as fixed 
                              and constant for a given type of 

   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 

   Minimum Path Latency:      The sum of the one-hop delays experienced 
                              by the packet when traveling from the 
                              ingress to the egress LSR.

   Variable Path Latency:     The sum of the delays caused by the 
                              queuing latency experienced by the 
                              packet at each node over the path. 
                              Otherwise known as jitter.

2.2 Acronyms 

 ASBR:   Autonomous System Border Router

   CE:   Customer Edge

   PE:   Provider Edge

   SP:   Service Provider

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   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 in order to provide requirements
   which could be used to create consistent and useful OAM 
   functionality that meets operational requirements of those
   service providers who have 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].

   4.1 Detection of Label Switched Path Defects

   The ability to detect defects in a broken Label Switched Path 
   (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 used to transport 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 as to allow for
   such automatic operation. 

   Furthermore, the automation of path liveliness is desired in 

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   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, and this requires detection and correction  
   of LSP defects in a manner that is both predictable and 
   sufficiently 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

   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 is known, then automated responses can be specified 
   both with respect to and with regard to resiliency and service 
   level specification reporting. Further, if synchronization of 
   detection time bounds is possible, an operational framework can be 
   established that can guide the design and specification of MPLS 
   Although 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 for returning erroneous 
   results (both positive and negative) for a number of reasons. First, 
   since 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
   as the data traffic.  

   Any detection mechanisms that depend on receiving status via a 
   return path SHOULD provide multiple return options with the 
   expectation that one of them will not be impacted by the original 
   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

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   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 to it that
   the return LSP is defective.

   The OAM packet MUST follow exactly the customer data path in order 
   to reflect path liveliness used by customer data. Particular cases 
   of interest are forwarding mechanisms such as equal cost multi-path 
   (ECMP) scenarios within the operator's network whereby flows are 
   load-shared across parallel (i.e., equal IGP cost) paths. Where 
   the customer traffic may be spread over multiple paths, what is 
   required is to be able to detect failures on any of the path 
   permutations.  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 which can return the 
   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) is 
   required. 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 both 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 equal cost multi-path scenarios described above in 
   section 4.1.

  4.3 Path characterization

   The path characterization function is the ability to reveal details 
   of LSR forwarding operations. These details can then be compared 
   later during subsequent testing relevant to OAM functionality.
   This would include but is not limited to:

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     - consistent use of pipe or uniform time to live (TTL) models by 
       an LSR [RFC3443].
     - sufficient details that allow the test origin to 
       excursive all path permutations related to load spreading
       (e.g. ECMP).
     - 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:
     - defect free forwarding. The service is considered to be
       available and the other aspects of performance measurement 
       listed below have meaning, or the service is unavailable and 
       other aspects of performance measurement do not.
     - latency - amount of time required for traffic to transit
       the network
     - packet loss
     - jitter - measurement of latency variation

   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 or not the 
   traffic for a specific LSP are 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.

   4.5 Frequency of OAM Execution

   The operator MUST have the flexibility to configure OAM
   parameters insofar-as to meet their specific operational 

   This includes the frequency of the execution of any OAM
   functions. The capability to synchronize OAM operations is required
   as to to permit consistent measurement of service level agreements.
   To elaborate, there are defect conditions such as mis-branching or 

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   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 and such values will have to be 
   harmonized with the surrounding technologies (e.g. SONET/SDH, 
   ATM etc.) in order 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 superfluous generation of alarms by 
   simply discarding them (or not generating them in the first place), 
   or by aggregating them together, and thereby greatly reducing the 
   number of notifications emitted.  When viewed in conjunction with 
   requirement 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 to have multiple MPLS 
   applications attempt to respond to defects simultaneously. For 
   example, 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 he VPN traffic that uses the 
   tunnel's LSP. Mechanisms are required to coordinate network response 
   to defects.

   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 a MPLS transport LSP that supports an emulated 

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   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 as to 
   synchronize with the OAM functions. 
   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 configuration as well as in the more simplified 
   single-area/domain configurations.

   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 status.  However,
   gaps in coverage of MIB modules to OAM and other features
   exists; therefore, MIB modules corresponding to new protocol 
   functions or network tools are required.

   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

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   In an MPLS network, service providers (SPs) can measure traffic 
   from an LSR to the egress of the network using some MPLS related 
   MIBs, for example. This means that it is a reasonable to know how 
   much traffic is traveling from where to where (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

         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 required. 

     (2) Providing a Service Level Specification

         For the purpose of optimized network design, a service 
         provider may offer the traffic information. Optimizing 
         network design needs this information.

     (3) Inter-AS environment

         Service providers that offer inter-AS services require 
         accounting of those services.

     These three motivations need to satisfy the following.

        - In (1) and (2), collection of information on a per-LSP 
          basis is a minimum level of granularity of collecting 
          accounting information at both of ingress and egress 
          of an LSP.

        - 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.

    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
          beginning at each egress in question.

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      (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 ingress.

      (4) All LSRs that contain 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 from whether manual or automatic

       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 to perform the just described operations by
     LSRs in a network 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 

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 which the network operator MAY consider 

6. IANA Considerations

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   This document creates no new requirements on IANA namespaces

7. References

7.1 Normative References

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

7.2 Informative References

   [LSPPING]  Kompella, K., G. Swallow, " Detecting MPLS Data Plane
              Failures", Internet Draft draft-ietf-mpls-lsp-ping-11.txt,
              November 2005.
   [RFC3812]     Srinivasan, C., Viswanathan, A. and T.
                 Nadeau, "Multiprotocol Label Switching 
                 (MPLS) Traffic Engineering (TE)
                 Management Information Base (MIB)",
                 RFC3812, June 2004.

   [RFC3813]     Srinivasan, C., Viswanathan, A. and T.
                 Nadeau, "Multiprotocol Label Switching 
                 (MPLS) Label Switching Router (LSR) 
                 Management Information Base (MIB)", RFC3813, 
                 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)", RFC3814, 
                 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.

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   [RFC792]  Postel, J., "Internet Control Message Protocol", RFC792,
             September 1981.

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

8. Authors' Addresses

   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
   Voice:  (0)1 878-9412

   George Swallow
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxboro, MA 01719  
   Voice: +1-978-936-1398

   David Allan
   Nortel Networks
   3500 Carling Ave.
   Ottawa, Ontario, CANADA
   Voice: 1-613-763-6362

   Satoru Matsushima
   Japan Telecom
   1-9-1, <, Minato-ku
   Tokyo, 105-7316 Japan
   Phone: +81-3-6889-1092

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9. 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
   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

   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-

10.  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

11. Acknowledgment

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   Funding for the RFC Editor function is currently provided by the
   Internet Society.

   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 of KDDI.
   Hari Rakotoranto, Miya Kohno, Cisco Systems; Luyuan Fang, AT&T;
   Danny McPherson, TCB; Dr.Ken Nagami, Ikuo Nakagawa, Intec Netcore,
   and David Meyer.

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