Network Working Group Thomas D. Nadeau Internet Draft Monique Morrow Expires: November 2003 George Swallow Cisco Systems, Inc. David Allan Nortel Networks Satoru Matsushima Japan Telecom June 2003 OAM Requirements for MPLS Networks
draft-ietf-mpls-oam-requirements-01.txtdraft-ietf-mpls-oam-requirements-02.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026 [RFC2026]. 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 As transport of diverse traffic types such as voice, frame relay, and ATM over MPLS become more common, the ability to detect, handle and diagnose control and data plane defects becomes critical. Detection and specification of how to handle those defects is not only important because such defects may not only affect the fundamental operation of an MPLS network, but also because they may impact SLA commitments for customers of that network. This Internet draft 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, similarly some of these requirements have appeared in other documents [Y1710]. This draft specifies OAM requirements for MPLS, as well as for applications of MPLS such as pseudowire voice and VPN services. Those interested in specific issues relating to instrumenting MPLS for OAM purposes are directed to [FRAMEWORK] Table of Contents Introduction.....................................................2 Terminology......................................................2 Motivations......................................................3 Requirements.....................................................4 Security Considerations..........................................8 Acknowledgments..................................................9 References.......................................................9 Authors' Addresses..............................................10 Intellectual Property Rights Notices............................11 Full Copyright Statement........................................11 1. Introduction This Internet draft 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 such as pseudowire [PWE3FRAME] voice, and VPN services. 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. Specifically, a set of requirements that apply to the most common set of MPLS networks deployed by service provider organizations today. 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 email@example.com. This memo does not, in its draft form, specify a standard for the Internet community. 2. Terminology CE: Customer Edge Defect: Any error condition that prevents an LSP functioning correctly. For example, loss of an IGP path will most likely also result in an LSP 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 SLA impacts can be specified. ECMP: Equal Cost Multipath LSP: Label Switch Path LSR: Label Switch Router OAM: Operations and Management PE: Provider Edge PW: Pseudowire SLA: Service Level Agreement VCC: Virtual Channel Connection VPC: Virtual Path Connection 3 Motivations MPLS OAM has been tackled in numerous Internet drafts. However all existing drafts focus on single provider solutions or focus on a single aspect of the MPLS architecture or application of MPLS. For example, the use of RSVP or LDP signaling and defects may be covered in some deployments, and a corresponding SNMP MIB module exists to manage this application; however, the handling of defects and specification of which types of defects are interesting to operational networks may not have been created in concert with those for other applications of MPLS such as L3 VPN. This leads to inconsistent and inefficient applicability across the MPLS architecture, and/or requires significant modifications to operational procedure and systems in order to provide consistent and useful OAM functionality. As MPLS matures relationships between providers has become more complex. Furthermore, the deployment of multiple concurrent applications of MPLS is common place. This has led to a need to consider deployments that span arbitrary networking arrangements and boundaries; so that broader and more uniform applicability to the MPLS architecture for OAM is possible. 3. Requirements The following sections enumerate the OAM requirements gathered from service providers. Each requirement is further specified in detail to further clarify its applicability. 3.1 Detection of Broken Label Switch Paths The ability to detect a broken Label Switch Path (LSP) should 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 should be automated and performed from the origination of that LSP. Furthermore, the automation of path liveliness is desired in cases where large amounts of LSPs might be tested. For example, automated PE-to-PE LSP testing functionality is desired. The goal is to detect LSP problems before customers do, and this requires detection of problems in a "reasonable" amount of time. One useful definition of reasonable is both predictable and consistent. If the time to detect defects is specified and tools designed accordingly then a harmonized operational framework can be established both within MPLS levels, and with MPLS applications. If the time to detect is known, then automated responses can be specified both w.r.t.with regard to resiliency and SLA reporting. One consequence is that ambiguity in maintenance procedures MUST be minimized as ambiguity in test results impacts detection time. Although ICMP-based ping can be sent through an LSP, the use of this tool to verify the LSP path liveliness has the potential for returning erroneous results (both positive and negative) given the nature of MPLS LSPs. For example, failures can be may occur where inconsistencies exist between the IP and MPLS forwarding tables, inconsistencies in the MPLS control and data plane or problems with the reply path (i.e.: a reverse MPLS path does not exist). Detection tools should have minimal dependencies on network components that do not implement the LSP. 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 multipath (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, it is required 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. [GUIDELINES] discusses some of the issues and offers suggestions for ensuring mutual compatibility of ECMP and maintenance functions (both detection and diagnostic). 3.2 Diagnosis of a Broken Label Switch Path The ability to diagnose a broken LSP and to isolate the failed resource in the path is required. This is particularly true for misbranching defects which are particularly difficult to specify recovery actions in an LDP network. Experience suggests that this 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) is required. The tracing capability should include the ability to trace recursive paths, such as when nested LSPs are used, or when LSPs enter and exit traffic-engineered tunnels [TUNTRACE]. 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 Switch Router (LSR) and any mid-point LSR. Additionally, the path trace function MUST have the ability to support equal cost multipath scenarios as described above in section 3.1. 3.3 Path characterization The ability of a path trace function to reveal details of LSR forwarding operations relevant to OAM functionality. This would include but not be limited to: - use of pipe or uniform TTL models by an LSR - externally visible aspects of load spreading (such as ECMP), including type of algorithm used examples of how algorithm will spread traffic - data/control plane OAM capabilities of the LSR - stack operations performed by the LSR (pushes and pops) 3.4 Service Level Agreement Measurement Mechanisms are required to measure diverse aspects of Service Level Agreements: - availability - in which the service is considered to be available and the other aspects of performance measurement listed below have meaning, or 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 quantity (i.e.: number of packets) of OAM packets. In addition, the ability to measure the qualitative aspects of OAM probing must be available to specifically compute the latency of OAM packets generated and received at each end of a tested LSP. Latency is considered in this context as a measurable parameter for SLA reporting. There is no assumption that bursts of OAM packets are required to characterize the performance of an LSP, but it is suggested that any method considered be capable of measuring the latency of an LSP with minimal impact on network resources. 3.5 Frequency of OAM Execution The operator MUST be have the flexibility to configure OAM parameters and the frequency of the execution of any OAM functions provided that there is some synchronization possible of tool usage for availability metrics. The motivation for this is to permit the network to function as a system of harmonious OAM functions consistent across the entire network. To elaborate, there are defect conditions (specifically misbranching or misdirection of traffic) for probe based detection mechanisms combined with automated network response requires harmonization of probe insertion rates and probe handling across the network in order to avoid flapping. One observation would be that commoditization of MPLS, common optimized implementation of monitoring tools and the need for inter- carrier harmonization of defect and SLA 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 misconfiguration can result in churn, alarm flapping etc. 3.5 Alarm Suppression and layer coordination Devices must provide alarm suppression functionality that prevents the generation of superfluous generation of alarms. When viewed in conjuction with requirement 3.6 below, this typically requires fault notification to the LSP egress, that may have specific time constraints if the client PW independently implements path continuity testing (for example ATM I.610 Continuity check (CC)[I610]). This would also be true for LSPs that have client LSPs that are monitored. MPLS arbitrary hierarchy introduces the opportunity to have multiple MPLS levels attempt to respond to defects simultaneously. Mechanisms are required to coordinate network response to defects. 3.6 Support for OAM Interworking for Fault Notification An LSR supporting OAM functions for pseudo-wire functions that join 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 the MPLS transport LSP that supports an emulated ATM VC must translate errors into native ATM OAM AIS cells at the edges of the pseudo- wire. The mechanism SHOULD consider possible bounded detection time parameters, e.g., a "hold off" function before reacting as to harmonize with the client OAM. One goal would be alarm suppression in the psuedo-wire's client layer. As observed in section 3.5, this requires that the MPLS layer perform detection in a bounded timeframe in order to initiate alarm suppression prior to the psuedo-wire client layer independently detecting the defect. 3.7 Error Detection and Recovery. Mechanisms are needed to detect an error, react to it (ideally in some form of automated response by the network), recover from it and alert the network operator prior to the customer informing the network operator of the error condition. The ideal situation would be where the network is resilient and can restore service prior any significant impact on the customer perception of the service. There are also defects that by virtue of available network resources or topology that cannot be recovered automatically. It is however, sometimes a requirement that the customer be notified of the defect condition at the same time that the network operator is made aware of the defect (as in the example of alarm suppression for PW clients discussed above). In these situations, the customer network may be capable of processing automated responses based on notification of a defect condition. It is preferred that the format of these notifications be made consistent (i.e.: standardized) as to increase the applicability of such messages. Depending on the device's capabilities, the device may be programmed to take automatic corrective actions as a result of detection of defect conditions. These actions may be user or operator-specified, or may simply be inherent to the underlying transport technology (i.e.: MPLS Fast-Reroute, graceful restart or high-availability functionality). 3.8 The commoditization of MPLS will require common information modeling of management and control of OAM functionality. This will be reflected in the the integration of standard MPLS-related MIBs (e.g. [LSRMIB][TEMIB][LBMIB][FTNMIB]) for fault, statistics and configuration management. These standard interfaces provide operators with common programmatic interface access to operations and management functions and their status. 3.9 Detection of Denial of Service attacks as part of security management. 3.10 Per-LSP Accounting Requirements In an MPLS network, SPs can measure traffic from an LSR to the egress of the MPLS network using some MPLS related MIBs, for example. This means that it is reasonable wish 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 For the purpose of optimized network design, SP offers that the traffic information regarding among POP and/or router. Optimizing network design needs this information. (2) Providing high-level SLA Due to the progress of the recent [MPLS-TE] technology, SPs and their customers may need to verify high-level SLAs. The resource optimization and high-speed restoration by [FRR] is being offered; therefore, continuous improvement of the service is expected. Moreover, bandwidth guaranteed service can be achieved by resource management based on [DS-TE]. To provide services based on these applications, the SP needs to perform traffic accounting to monitor their services. (3) Inter-AS environment SPs which offer inter-as services [Inter-AS TE][Inter-AS VPN] require accounting of the service. 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. 3.10.1 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. (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 measuremented need to have a common key to distinguish each LSP. The key must be unique to each LSP, and its mapping to LSP should be provided from whether manual or automatic configuration. 3.10.2 Scalability It is not realistic to perform the just described operations by LSRs in a network and on all LSPs which 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. 4. Security Considerations 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. Mechanisms are required to prevent unauthorized use of either those tools or protocol features. 5. Acknowledgments 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 Khono, Cisco Systems; Luyuan Fang, AT&T; Danny McPherson, TCB.TCB; Dr.Ken Nagami, Ikuo Nakagawa, Intec Netcore. 6. References [TUNTRACE] Bonica, R., Kompella, K., Meyer, D., "Tracing Requirements for Generic Tunnels", Internet Draft <draft-bonica-tunneltrace- 02.txt>, November 2001. [LSRMIB] Srinivasan, C., Viswanathan, A. and T. Nadeau, "MPLS Label Switch Router Management Information Base Using SMIv2", Internet Draft <draft-ietf-mpls-lsr-mib-07.txt>, January 2001. [TEMIB] Srinivasan, C., Viswanathan, A. and T. Nadeau, "MPLS Traffic Engineering Management Information Base Using SMIv2", Internet Draft <draft-ietf-mpls-te-mib-07.txt>, August 2001. [FTNMIB] Nadeau, T., Srinivasan, C., and A. Viswanathan, "Multiprotocol Label Switching (MPLS) FEC-To-NHLFE (FTN) Management Information Base", Internet Draft <draft- ietf-mpls-ftn-mib-03.txt>, August 2001. [LBMIB] Dubuc, M., Dharanikota, S., Nadeau, T., J. Lang, "Link Bundling Management Information Base Using SMIv2", Internet Draft <draft- ietf-mpls-bundle-mib-00.txt>, September 2001. [MPLS-TE] Awduche et. al., "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001 [FRR] Pan et.al., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", Internet draft, <draft-ietf-mpls-rsvp-lsp-fastreroute-03.txt>, December 2003 [DS-TE] Le Faucheur & Lai., "Requirements for Diff-Serv-aware TE", RFC3564, July 2003 [Inter-AS TE] Zhang, Vasseur, et. al., "MPLS Inter-AS Traffic Engineering requirements", Internet draft <draft-ietf-tewg-interas-mpls-te-req-00.txt>, May 2003 [Inter-AS VPN] Rosen, et al., "BGP/MPLS IP VPNs", Internet draft, <draft-ietf-l3vpn-rfc2547bis-01.txt>, September 2003 [PWE3FRAME] Pate, P., Xiao, X., White., C., Kompella., K., Malis, A., Johnson, T., and T. Nadeau, "Framework for Pseudo Wire Emulation Edge-to- Edge (PWE3)", Internet Draft <draft-ietf- pwe3-framework-00.txt>, September, 2001. [RFC2026] S. Bradner, "The Internet Standards Process -- Revision 3", RFC 2026, October 1996. [Y1710] ITU-T Recommendation Y.1710, "Requirements for OAM Functionality In MPLS Networks" [GUIDELINES] Allan, D., "Guidelines for MPLS load balancing", Internet draft, <draft-allan-mpls-loadbal-01.txt>, February 2003 [I610] ITU-T Recommendation I.610, "B-ISDN operations and maintenance principles and functions", February 1999 [FRAMEWORK] Allan et.al. "A Framework for MPLS OAM", Internet draft <draft-allan-mpls-oam-frmwk-04.txt>, February 2003 7. Authors' Addresses Thomas D. Nadeau Cisco Systems, Inc. 300 Beaver Brook Road Boxboro, MA 01719 Phone: +1-978-936-1470 Email: firstname.lastname@example.org Monique Jeanne Morrow Cisco Systems, Inc. Glatt-Com, 2nd Floor CH-8301 Switzerland Voice: (0)1 878-9412 Email: email@example.com George Swallow Cisco Systems, Inc. 300 Beaver Brook Road Boxboro, MA 01719 Voice: +1-978-936-1398 Email: firstname.lastname@example.org David Allan Nortel Networks 3500 Carling Ave. Ottawa, Ontario, CANADA Voice: 1-613-763-6362 Email: email@example.com Satoru Matsushima Japan Telecom 4-7-1, Hatchobori, Chuo-ku Tokyo, 104-8508 Japan Phone: +81-3-5540-8214 Email: firstname.lastname@example.org 8. Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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