Operations and Management (OAM) Requirements for Multi-Protocol Label Switched (MPLS) Networks
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This is an older version of an Internet-Draft that was ultimately published as RFC 4377.
|David Allan , George Swallow , Monique Morrow, Thomas Nadeau , Satoru Matsushima
|2020-01-21 (Latest revision 2005-12-15)
|Internet Engineering Task Force (IETF)
|Intended RFC status
|Mailing list discussion
|Became RFC 4377 (Informational)
|Alex D. Zinin
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|email@example.com, firstname.lastname@example.org, email@example.com
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 draft-ietf-mpls-oam-requirements-07.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 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 Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document specifies Operations and Management requirements for Multi-Protocol Label Switching, as well as for applications MPLS Working Group Expires May 2006 [Page 1] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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 at firstname.lastname@example.org. MPLS Working Group Expires May 2006 [Page 2] draft-ietf-mpls-oam-requirements-07 December 7, 2005 2. Document Conventions 2.1 Terminology 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]. 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 MPLS Working Group Expires May 2006 [Page 3] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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 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. 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 MPLS Working Group Expires May 2006 [Page 4] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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 MPLS Working Group Expires May 2006 [Page 5] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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 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 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 applications. 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 MPLS Working Group Expires May 2006 [Page 6] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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: MPLS Working Group Expires May 2006 [Page 7] draft-ietf-mpls-oam-requirements-07 December 7, 2005 - 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 requirements. 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 MPLS Working Group Expires May 2006 [Page 8] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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 MPLS Working Group Expires May 2006 [Page 9] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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 them. 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 MPLS Working Group Expires May 2006 [Page 10] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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 functions: (1) At an ingress LSR accounting of traffic through LSPs beginning at each egress in question. MPLS Working Group Expires May 2006 [Page 11] draft-ietf-mpls-oam-requirements-07 December 7, 2005 (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 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 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 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 which the network operator MAY consider private. 6. IANA Considerations MPLS Working Group Expires May 2006 [Page 12] draft-ietf-mpls-oam-requirements-07 December 7, 2005 This document creates no new requirements on IANA namespaces [RFC2434]. 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. MPLS Working Group Expires May 2006 [Page 13] draft-ietf-mpls-oam-requirements-07 December 7, 2005 [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 Email: email@example.com Monique Jeanne Morrow Cisco Systems, Inc. Glatt-Com, 2nd Floor CH-8301 Switzerland Voice: (0)1 878-9412 Email: firstname.lastname@example.org George Swallow Cisco Systems, Inc. 300 Beaver Brook Road Boxboro, MA 01719 Voice: +1-978-936-1398 Email: email@example.com David Allan Nortel Networks 3500 Carling Ave. Ottawa, Ontario, CANADA Voice: 1-613-763-6362 Email: firstname.lastname@example.org Satoru Matsushima Japan Telecom 1-9-1, <, Minato-ku Tokyo, 105-7316 Japan Phone: +81-3-6889-1092 Email: email@example.com MPLS Working Group Expires May 2006 [Page 14] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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 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- firstname.lastname@example.org. 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 "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. 11. Acknowledgment MPLS Working Group Expires May 2006 [Page 15] draft-ietf-mpls-oam-requirements-07 December 7, 2005 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. MPLS Working Group Expires May 2006 [Page 16]