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Internet Engineering Task Force (IETF)                      I. Busi, Ed.Request for Comments: 6371                                Alcatel-LucentCategory: Informational                                    D. Allan, Ed.ISSN: 2070-1721                                                 Ericsson                                                          September 2011Operations, Administration, and Maintenance Framework forMPLS-Based Transport NetworksAbstract   The Transport Profile of Multiprotocol Label Switching (MPLS-TP) is a   packet-based transport technology based on the MPLS Traffic   Engineering (MPLS-TE) and pseudowire (PW) data-plane architectures.   This document describes a framework to support a comprehensive set of   Operations, Administration, and Maintenance (OAM) procedures that   fulfill the MPLS-TP OAM requirements for fault, performance, and   protection-switching management and that do not rely on the presence   of a control plane.   This document is a product of a joint Internet Engineering Task Force   (IETF) / International Telecommunications Union Telecommunication   Standardization Sector (ITU-T) effort to include an MPLS Transport   Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge   (PWE3) architectures to support the capabilities and functionalities   of a packet transport network as defined by the ITU-T.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6371.Busi & Allan                  Informational                     [Page 1]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................32. Conventions Used in This Document ...............................52.1. Terminology ................................................52.2. Definitions ................................................73. Functional Components ..........................................103.1. Maintenance Entity and Maintenance Entity Group ...........103.2. MEG Nesting: SPMEs and Tandem Connection Monitoring .......133.3. MEG End Points (MEPs) .....................................143.4. MEG Intermediate Points (MIPs) ............................183.5. Server MEPs ...............................................203.6. Configuration Considerations ..............................213.7. P2MP Considerations .......................................213.8. Further Considerations of Enhanced Segment Monitoring .....224. Reference Model ................................................234.1. MPLS-TP Section Monitoring (SMEG) .........................264.2. MPLS-TP LSP End-to-End Monitoring Group (LMEG) ............274.3. MPLS-TP PW Monitoring (PMEG) ..............................274.4. MPLS-TP LSP SPME Monitoring (LSMEG) .......................284.5. MPLS-TP MS-PW SPME Monitoring (PSMEG) .....................304.6. Fate-Sharing Considerations for Multilink .................315. OAM Functions for Proactive Monitoring .........................325.1. Continuity Check and Connectivity Verification ............335.1.1. Defects Identified by CC-V .........................355.1.2. Consequent Action ..................................375.1.3. Configuration Considerations .......................385.2. Remote Defect Indication ..................................405.2.1. Configuration Considerations .......................405.3. Alarm Reporting ...........................................415.4. Lock Reporting ............................................425.5. Packet Loss Measurement ...................................445.5.1. Configuration Considerations .......................45Busi & Allan                  Informational                     [Page 2]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20115.5.2. Sampling Skew ......................................455.5.3. Multilink Issues ...................................455.6. Packet Delay Measurement ..................................465.6.1. Configuration Considerations .......................465.7. Client Failure Indication .................................475.7.1. Configuration Considerations .......................476. OAM Functions for On-Demand Monitoring .........................486.1. Connectivity Verification .................................486.1.1. Configuration Considerations .......................496.2. Packet Loss Measurement ...................................506.2.1. Configuration Considerations .......................506.2.2. Sampling Skew ......................................506.2.3. Multilink Issues ...................................506.3. Diagnostic Tests ..........................................506.3.1. Throughput Estimation ..............................516.3.2. Data-Plane Loopback ................................526.4. Route Tracing .............................................546.4.1. Configuration Considerations .......................546.5. Packet Delay Measurement ..................................546.5.1. Configuration Considerations .......................557. OAM Functions for Administration Control .......................557.1. Lock Instruct .............................................557.1.1. Locking a Transport Path ...........................567.1.2. Unlocking a Transport Path .........................568. Security Considerations ........................................579. Acknowledgments ................................................5810. References ....................................................5810.1. Normative References .....................................5810.2. Informative References ...................................5911. Contributing Authors ..........................................601.  Introduction   As noted in the MPLS Transport Profile (MPLS-TP) framework RFCs (RFC5921 [8] andRFC 6215 [9]), MPLS-TP is a packet-based transport   technology based on the MPLS Traffic Engineering (MPLS-TE) and   pseudowire (PW) data-plane architectures defined inRFC 3031 [1],RFC3985 [2], andRFC 5659 [4].   MPLS-TP utilizes a comprehensive set of Operations, Administration,   and Maintenance (OAM) procedures for fault, performance, and   protection-switching management that do not rely on the presence of a   control plane.   In line with [15], existing MPLS OAM mechanisms will be used wherever   possible, and extensions or new OAM mechanisms will be defined only   where existing mechanisms are not sufficient to meet the   requirements.  Some extensions discussed in this framework may end upBusi & Allan                  Informational                     [Page 3]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   as aspirational capabilities and may be determined to be not   tractably realizable in some implementations.  Extensions do not   deprecate support for existing MPLS OAM capabilities.   The MPLS-TP OAM framework defined in this document provides a   protocol-neutral description of the required OAM functions and of the   data-plane OAM architecture to support a comprehensive set of OAM   procedures that satisfy the MPLS-TP OAM requirements ofRFC 5860   [11].  In this regard, it defines similar OAM functionality as for   existing Synchronous Optical Network / Synchronous Digital Hierarchy   (SONET/SDH) and Optical Transport Network (OTN) OAM mechanisms (e.g.,   [19]).   The MPLS-TP OAM framework is applicable to Sections, Label Switched   Paths (LSPs), Multi-Segment Pseudowires (MS-PWs), and Sub-Path   Maintenance Elements (SPMEs).  It supports co-routed and associated   bidirectional P2P transport paths as well as unidirectional P2P and   P2MP transport paths.   OAM packets that instrument a particular direction of a transport   path are subject to the same forwarding treatment (i.e., fate-share)   as the user data packets and in some cases, where Explicitly TC-   encoded-PSC LSPs (E-LSPs) are employed, may be required to have   common per-hop behavior (PHB) Scheduling Class (PSC) End-to-End (E2E)   with the class of traffic monitored.  In case of Label-Only-Inferred-   PSC LSP (L-LSP), only one class of traffic needs to be monitored, and   therefore the OAM packets have common PSC with the monitored traffic   class.   OAM packets can be distinguished from the used data packets using the   Generic Associated Channel Label (GAL) and Associated Channel Header   (ACH) constructs ofRFC 5586 [7] for LSP, SPME, and Section, or the   ACH construct ofRFC 5085 [3] andRFC 5586 [7] for (MS-)PW.  OAM   packets are never fragmented and are not combined with user data in   the same packet payload.   This framework makes certain assumptions as to the utility and   frequency of different classes of measurement that naturally suggest   different functions are implemented as distinct OAM flows or packets.   This is dictated by the combination of the class of problem being   detected and the need for timeliness of network response to the   problem.  For example, fault detection is expected to operate on an   entirely different time base than performance monitoring, which is   also expected to operate on an entirely different time base than in-   band management transactions.Busi & Allan                  Informational                     [Page 4]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   The remainder of this memo is structured as follows:Section 2 covers the definitions and terminology used in this memo.Section 3 describes the functional component that generates and   processes OAM packets.Section 4 describes the reference models for applying OAM functions   to Sections, LSP, MS-PW, and their SPMEs.   Sections5,6, and7 provide a protocol-neutral description of the   OAM functions, defined inRFC 5860 [11], aimed at clarifying how the   OAM protocol solutions will behave to achieve their functional   objectives.Section 8 discusses the security implications of OAM protocol design   in the MPLS-TP context.   The OAM protocol solutions designed as a consequence of this document   are expected to comply with the functional behavior described in   Sections5,6, and7.  Alternative solutions to required functional   behaviors may also be defined.   OAM specifications following this OAM framework may be provided in   different documents to cover distinct OAM functions.   This document is a product of a joint Internet Engineering Task Force   (IETF) / International Telecommunication Union Telecommunication   Standardization Sector (ITU-T) effort to include an MPLS Transport   Profile within the IETF MPLS and PWE3 architectures to support the   capabilities and functionalities of a packet transport network as   defined by the ITU-T.2.  Conventions Used in This Document2.1.  Terminology   AC     Attachment Circuit   AIS    Alarm Indication Signal   CC     Continuity Check   CC-V   Continuity Check and Connectivity Verification   CV     Connectivity Verification   DBN    Domain Border NodeBusi & Allan                  Informational                     [Page 5]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   E-LSP  Explicitly TC-encoded-PSC LSP   ICC    ITU Carrier Code   LER    Label Edge Router   LKR    Lock Report   L-LSP  Label-Only-Inferred-PSC LSP   LM     Loss Measurement   LME    LSP Maintenance Entity   LMEG   LSP ME Group   LSP    Label Switched Path   LSR    Label Switching Router   LSME   LSP SPME ME   LSMEG  LSP SPME ME Group   ME     Maintenance Entity   MEG    Maintenance Entity Group   MEP    Maintenance Entity Group End Point   MIP    Maintenance Entity Group Intermediate Point   NMS    Network Management System   PE     Provider Edge   PHB    Per-Hop Behavior   PM     Performance Monitoring   PME    PW Maintenance Entity   PMEG   PW ME Group   PSC    PHB Scheduling Class   PSME   PW SPME MEBusi & Allan                  Informational                     [Page 6]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   PSMEG  PW SPME ME Group   PW     Pseudowire   SLA    Service Level Agreement   SME    Section Maintenance Entity   SMEG   Section ME Group   SPME   Sub-Path Maintenance Element   S-PE   Switching Provider Edge   TC     Traffic Class   T-PE   Terminating Provider Edge2.2.  Definitions   This document uses the terms defined inRFC 5654 [5].   This document uses the term 'per-hop behavior' as defined inRFC 2474   [16].   This document uses the term 'LSP' to indicate either a service LSP or   a transport LSP (as defined inRFC 5921 [8]).   This document uses the term 'Section' exclusively to refer to the n=0   case of the term 'Section' defined inRFC 5960 [10].   This document uses the term 'Sub-Path Maintenance Element (SPME)' as   defined inRFC 5921 [8].   This document uses the term 'traffic profile' as defined inRFC 2475   [13].   Where appropriate, the following definitions are aligned with ITU-T   recommendation Y.1731 [21] in order to have a common, unambiguous   terminology.  They do not however intend to imply a certain   implementation but rather serve as a framework to describe the   necessary OAM functions for MPLS-TP.   Adaptation function: The adaptation function is the interface between   the client (sub-)layer and the server (sub-)layer.   Branch Node: A node along a point-to-multipoint transport path that   is connected to more than one downstream node.Busi & Allan                  Informational                     [Page 7]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   Bud Node: A node along a point-to-multipoint transport path that is   at the same time a branch node and a leaf node for this transport   path.   Data-plane loopback: An out-of-service test where a transport path at   either an intermediate or terminating node is placed into a data-   plane loopback state, such that all traffic (including both payload   and OAM) received on the looped back interface is sent on the reverse   direction of the transport path.      Note: The only way to send an OAM packet to a node that has been      put into data-plane loopback mode is via Time to Live (TTL)      expiry, irrespective of whether the node is hosting MIPs or MEPs.   Domain Border Node (DBN): An intermediate node in an MPLS-TP LSP that   is at the boundary between two MPLS-TP OAM domains.  Such a node may   be present on the edge of two domains or may be connected by a link   to the DBN at the edge of another OAM domain.   Down MEP: A MEP that receives OAM packets from, and transmits them   towards, the direction of a server layer.   Forwarding Engine: An abstract functional component, residing in an   LSR, that forwards the packets from an ingress interface toward the   egress interface(s).   In-Service: The administrative status of a transport path when it is   unlocked.   Interface: An interface is the attachment point to a server   (sub-)layer, e.g., a MPLS-TP Section or MPLS-TP tunnel.   Intermediate Node: An intermediate node transits traffic for an LSP   or a PW.  An intermediate node may originate OAM flows directed to   downstream intermediate nodes or MEPs.   Loopback: See data-plane loopback and OAM loopback definitions.   Maintenance Entity (ME): Some portion of a transport path that   requires management bounded by two points (called MEPs), and the   relationship between those points to which maintenance and monitoring   operations apply (details inSection 3.1).   Maintenance Entity Group (MEG): The set of one or more maintenance   entities that maintain and monitor a section or a transport path in   an OAM domain.Busi & Allan                  Informational                     [Page 8]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   MEP: A MEG End Point (MEP) is capable of initiating (source MEP) and   terminating (sink MEP) OAM packets for fault management and   performance monitoring.  MEPs define the boundaries of an ME (details   inSection 3.3).   MIP: A MEG intermediate point (MIP) terminates and processes OAM   packets that are sent to this particular MIP and may generate OAM   packets in reaction to received OAM packets.  It never generates   unsolicited OAM packets itself.  A MIP resides within a MEG between   MEPs (details inSection 3.3).   OAM domain: A domain, as defined in [5], whose entities are grouped   for the purpose of keeping the OAM confined within that domain.  An   OAM domain contains zero or more MEGs.      Note: Within the rest of this document, the term "domain" is used      to indicate an "OAM domain".   OAM flow: The set of all OAM packets originating with a specific   source MEP that instrument one direction of a MEG (or possibly both   in the special case of data-plane loopback).   OAM loopback: The capability of a node to be directed by a received   OAM packet to generate a reply back to the sender.  OAM loopback can   work in-service and can support different OAM functions (e.g.,   bidirectional on-demand connectivity verification).   OAM Packet: A packet that carries OAM information between MEPs and/or   MIPs in a MEG to perform some OAM functionality (e.g., connectivity   verification).   Originating MEP: A MEP that originates an OAM transaction packet   (toward a target MIP/MEP) and expects a reply, either in-band or out-   of-band, from that target MIP/MEP.  The originating MEP always   generates the OAM request packets in-band and expects and processes   only OAM reply packets returned by the target MIP/MEP.   Out-of-Service: The administrative status of a transport path when it   is locked.  When a path is in a locked condition, it is blocked from   carrying client traffic.   Path Segment: It is either a segment or a concatenated segment, as   defined inRFC 5654 [5].   Signal Degrade: A condition declared by a MEP when the data   forwarding capability associated with a transport path has   deteriorated, as determined by performance monitoring (PM).  See also   ITU-T recommendation G.806 [14].Busi & Allan                  Informational                     [Page 9]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   Signal Fail: A condition declared by a MEP when the data forwarding   capability associated with a transport path has failed, e.g., loss of   continuity.  See also ITU-T recommendation G.806 [14].   Sink MEP: A MEP acts as a sink MEP for an OAM packet when it   terminates and processes the packets received from its associated   MEG.   Source MEP: A MEP acts as source MEP for an OAM packet when it   originates and inserts the packet into the transport path for its   associated MEG.   Tandem Connection: A tandem connection is an arbitrary part of a   transport path that can be monitored (via OAM) independent of the   end-to-end monitoring (OAM).  The tandem connection may also include   the forwarding engine(s) of the node(s) at the boundaries of the   tandem connection.  Tandem connections may be nested but cannot   overlap.  See also ITU-T recommendation G.805 [20].   Target MEP/MIP: A MEP or a MIP that is targeted by OAM transaction   packets and that replies to the originating MEP that initiated the   OAM transactions.  The target MEP or MIP can reply either in-band or   out-of-band.  The target sink MEP function always receives the OAM   request packets in-band, while the target source MEP function only   generates the OAM reply packets that are sent in-band.   Up MEP: A MEP that transmits OAM packets towards, and receives them   from, the direction of the forwarding engine.3.  Functional Components   MPLS-TP is a packet-based transport technology based on the MPLS and   PW data plane architectures ([1], [2], and [4]) and is capable of   transporting service traffic where the characteristics of information   transfer between the transport path end points can be demonstrated to   comply with certain performance and quality guarantees.   In order to describe the required OAM functionality, this document   introduces a set of functional components.3.1.  Maintenance Entity and Maintenance Entity Group   MPLS-TP OAM operates in the context of Maintenance Entities (MEs)   that define a relationship between two points of a transport path to   which maintenance and monitoring operations apply.  The two points   that define a maintenance entity are called Maintenance Entity Group   End Points (MEPs).  The collection of one or more MEs that belongs to   the same transport path and that are maintained and monitored as aBusi & Allan                  Informational                    [Page 10]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   group are known as a Maintenance Entity Group (MEG).  In between   MEPs, there are zero or more intermediate points, called Maintenance   Entity Group Intermediate Points (MIPs).  MEPs and MIPs are   associated with the MEG and can be shared by more than one ME in a   MEG.   An abstract reference model for an ME is illustrated in Figure 1   below.                         +-+    +-+    +-+    +-+                         |A|----|B|----|C|----|D|                         +-+    +-+    +-+    +-+                   Figure 1: ME Abstract Reference Model   The instantiation of this abstract model to different MPLS-TP   entities is described inSection 4.  In Figure 1, nodes A and D can   be Label Edge Routers (LERs) for an LSP or the Terminating Provider   Edges (T-PEs) for an MS-PW, nodes B and C are LSRs for an LSP or   Switching PEs (S-PEs) for an MS-PW.  MEPs reside in nodes A and D,   while MIPs reside in nodes B and C and may reside in A and D.  The   links connecting adjacent nodes can be physical links, (sub-)layer   LSPs/SPMEs, or server-layer paths.   This functional model defines the relationships between all OAM   entities from a maintenance perspective and it allows each   Maintenance Entity to provide monitoring and management for the   (sub-)layer network under its responsibility and efficient   localization of problems.   An MPLS-TP Maintenance Entity Group may be defined to monitor the   transport path for fault and/or performance management.   The MEPs that form a MEG bound the scope of an OAM flow to the MEG   (i.e., within the domain of the transport path that is being   monitored and managed).  There are two exceptions to this:   1) A misbranching fault may cause OAM packets to be delivered to a      MEP that is not in the MEG of origin.   2) An out-of-band return path may be used between a MIP or a MEP and      the originating MEP.   In case of a unidirectional point-to-point transport path, a single   unidirectional Maintenance Entity is defined to monitor it.Busi & Allan                  Informational                    [Page 11]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   In case of associated bidirectional point-to-point transport paths,   two independent unidirectional Maintenance Entities are defined to   independently monitor each direction.  This has implications for   transactions that terminate at or query a MIP, as a return path from   MIP to the originating MEP does not necessarily exist in the MEG.   In case of co-routed bidirectional point-to-point transport paths, a   single bidirectional Maintenance Entity is defined to monitor both   directions congruently.   In case of unidirectional point-to-multipoint transport paths, a   single unidirectional Maintenance Entity for each leaf is defined to   monitor the transport path from the root to that leaf.   In all cases, portions of the transport path may be monitored by the   instantiation of SPMEs (seeSection 3.2).   The reference model for the P2MP MEG is represented in Figure 2.                                             +-+                                          /--|D|                                         /   +-+                                      +-+                                   /--|C|                        +-+    +-+/   +-+\   +-+                        |A|----|B|        \--|E|                        +-+    +-+\   +-+    +-+                                   \--|F|                                      +-+                 Figure 2: Reference Model for P2MP MEG   In the case of P2MP transport paths, the OAM measurements are   independent for each ME (A-D, A-E, and A-F):   o  Fault conditions - some faults may impact more than one ME      depending on where the failure is located;   o  Packet loss - packet dropping may impact more than one ME      depending from where the packets are lost;   o  Packet delay - will be unique per ME.   Each leaf (i.e., D, E, and F) terminates OAM flows to monitor the ME   between itself and the root while the root (i.e., A) generates OAM   packets common to all the MEs of the P2MP MEG.  All nodes may   implement a MIP in the corresponding MEG.Busi & Allan                  Informational                    [Page 12]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20113.2.  MEG Nesting: SPMEs and Tandem Connection Monitoring   In order to verify and maintain performance and quality guarantees,   there is a need to apply OAM functionality not only on a transport   path granularity (e.g., LSP or MS-PW), but also on arbitrary parts of   transport paths, defined as tandem connections, between any two   arbitrary points along a transport path.   Sub-Path Maintenance Elements (SPMEs), as defined in [8], are   hierarchical LSPs instantiated to provide monitoring of a portion of   a set of transport paths (LSPs or MS-PWs) that follow the same path   between the ingress and the egress of the SPME.  The operational   aspects of instantiating SPMEs are out of scope of this memo.   SPMEs can also be employed to meet the requirement to provide tandem   connection monitoring (TCM), as defined by ITU-T Recommendation G.805   [20].   TCM for a given path segment of a transport path is implemented by   creating an SPME that has a 1:1 association with the path segment of   the transport path that is to be monitored.   In the TCM case, this means that the SPME used to provide TCM can   carry one and only one transport path, thus allowing direct   correlation between all fault management and performance monitoring   information gathered for the SPME and the monitored path segment of   the end-to-end transport path.   There are a number of implications to this approach:   1) The SPME would use the uniform model [23] of Traffic Class (TC)      code point copying between sub-layers for Diffserv such that the      E2E markings and PHB treatment for the transport path were      preserved by the SPMEs.   2) The SPME normally would use the short-pipe model for TTL handling      [6] (no TTL copying between sub-layers) such that the TTL distance      to the MIPs for the E2E entity would not be impacted by the      presence of the SPME, but it should be possible for an operator to      specify use of the uniform model.   Note that points 1 and 2 above assume that the TTL copying mode and   TC copying modes are independently configurable for an LSP.   The TTL distance to the MIPs plays a critical role for delivering   packets to these MIPs as described inSection 3.4.Busi & Allan                  Informational                    [Page 13]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   There are specific issues with the use of the uniform model of TTL   copying for an SPME:   1. A MIP in the SPME sub-layer is not part of the transport-path MEG;      hence, only an out-of-band return path for OAM originating in the      transport-path MEG that addressed an SPME MIP might be available.   2. The instantiation of a lower-level MEG or protection-switching      actions within a lower-level MEG may change the TTL distances to      MIPs in the higher-level MEGs.   The end points of the SPME are MEPs and limit the scope of an OAM   flow within the MEG that the MEPs belong to (i.e., within the domain   of the SPME that is being monitored and managed).   When considering SPMEs, it is important to consider that the   following properties apply to all MPLS-TP MEGs (regardless of whether   they instrument LSPs, SPMEs, or MS-PWs):   o  They can be nested but not overlapped, e.g., a MEG may cover a      path segment of another MEG and may also include the forwarding      engine(s) of the node(s) at the edge(s) of the path segment.      However, when MEGs are nested, the MEPs and MIPs in the SPME are      no longer part of the encompassing MEG.   o  It is possible that MEPs of MEGs that are nested reside on a      single node but again are implemented in such a way that they do      not overlap.   o  Each OAM flow is associated with a single MEG.   o  When an SPME is instantiated after the transport path has been      instantiated, the TTL distance to the MIPs may change for the      short-pipe model of TTL copying, and may change for the uniform      model if the SPME is not co-routed with the original path.3.3.  MEG End Points (MEPs)   MEG End Points (MEPs) are the source and sink points of a MEG.  In   the context of an MPLS-TP LSP, only LERs can implement MEPs, while in   the context of an SPME, any LSR of the MPLS-TP LSP can be an LER of   SPMEs that contributes to the overall monitoring infrastructure of   the transport path.  Regarding PWs, only T-PEs can implement MEPs;   while for SPMEs supporting one or more PWs, both T-PEs and S-PEs can   implement SPME MEPs.  Any MPLS-TP LSR can implement a MEP for an   MPLS-TP Section.Busi & Allan                  Informational                    [Page 14]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   MEPs are responsible for originating almost all of the proactive and   on-demand monitoring OAM functionality for the MEG.  There is a   separate class of notifications (such as Lock Report (LKR) and Alarm   Indication Signal (AIS)) that are originated by intermediate nodes   and triggered by server-layer events.  A MEP is capable of   originating and terminating OAM packets for fault management and   performance monitoring.  These OAM packets are carried within the   Generic Associated Channel (G-ACh) with the proper encapsulation and   an appropriate channel type as defined inRFC 5586 [7].  A MEP   terminates all the OAM packets it receives from the MEG it belongs to   and silently discards those that do not.  (Note that in the   particular case of Connectivity Verification (CV) processing, a CV   packet from an incorrect MEG will result in a mis-connectivity defect   and there are further actions taken.)  The MEG the OAM packet belongs   to is associated with the MPLS or PW label, whether the label is used   to infer the MEG or the content of the OAM packet is an   implementation choice.  In the case of an MPLS-TP Section, the MEG is   inferred from the port on which an OAM packet was received with the   GAL at the top of the label stack.   OAM packets may require the use of an available "out-of-band" return   path (as defined in [8]).  In such cases, sufficient information is   required in the originating transaction such that the OAM reply   packet can be constructed and properly forwarded to the originating   MEP (e.g., IP address).   Each OAM solution document will further detail the applicability of   the tools it defines as a proactive or on-demand mechanism as well as   its usage when:   o  The "in-band" return path exists and it is used.   o  An "out-of-band" return path exists and it is used.   o  Any return path does not exist or is not used.   Once a MEG is configured, the operator can configure which proactive   OAM functions to use on the MEG, but the MEPs are always enabled.   MEPs terminate all OAM packets received from the associated MEG.  As   the MEP corresponds to the termination of the forwarding path for a   MEG at the given (sub-)layer, OAM packets never leak outside of a MEG   in a properly configured fault-free implementation.Busi & Allan                  Informational                    [Page 15]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   A MEP of an MPLS-TP transport path coincides with transport path   termination and monitors it for failures or performance degradation   (e.g., based on packet counts) in an end-to-end scope.  Note that   both the source MEP and sink MEP coincide with transport paths'   source and sink terminations.   The MEPs of an SPME are not necessarily coincident with the   termination of the MPLS-TP transport path.  They are used to monitor   a path segment of the transport path for failures or performance   degradation (e.g., based on packet counts) only within the boundary   of the MEG for the SPME.   An MPLS-TP sink MEP passes a fault indication to its client   (sub-)layer network as a consequent action of fault detection.  When   the client layer is not MPLS-TP, the consequent actions in the client   layer (e.g., ignore or generate client-layer-specific OAM   notifications) are outside the scope of this document.   A node hosting a MEP can either support per-node MEP or per-interface   MEP(s).  A per-node MEP resides in an unspecified location within the   node, while a per-interface MEP resides on a specific side of the   forwarding engine.  In particular, a per-interface MEP is called an   "Up MEP" or a "Down MEP" depending on its location relative to the   forwarding engine.  An "Up MEP" transmits OAM packets towards, and   receives them from, the direction of the forwarding engine, while a   "Down MEP" receives OAM packets from, and transmits them towards, the   direction of a server layer.Busi & Allan                  Informational                    [Page 16]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011         Source node Up MEP             Destination node Up MEP       ------------------------         ------------------------      |                        |       |                        |      |-----              -----|       |-----              -----|      | MEP |            |     |       |     |            | MEP |      |     |    ----    |     |       |     |    ----    |     |      | In  |->-| FW |->-| Out |->- ->-| In  |->-| FW |->-| Out |      | i/f |    ----    | i/f |       | i/f |    ----    | i/f |      |-----              -----|       |-----              -----|      |                        |       |                        |       ------------------------         ------------------------                  (1)                               (2)         Source node Down MEP           Destination node Down MEP       ------------------------         ------------------------      |                        |       |                        |      |-----              -----|       |-----              -----|      |     |            | MEP |       | MEP |            |     |      |     |    ----    |     |       |     |    ----    |     |      | In  |->-| FW |->-| Out |->- ->-| In  |->-| FW |->-| Out |      | i/f |    ----    | i/f |       | i/f |    ----    | i/f |      |-----              -----|       |-----              -----|      |                        |       |                        |       ------------------------         ------------------------                  (3)                               (4)                Figure 3: Examples of Per-Interface MEPs   Figure 3 describes four examples of per-interface Up MEPs: an Up   Source MEP in a source node (case 1), an Up Sink MEP in a destination   node (case 2), a Down Source MEP in a source node (case 3), and a   Down Sink MEP in a destination node (case 4).   The usage of per-interface Up MEPs extends the coverage of the ME for   both fault and performance monitoring closer to the edge of the   domain and determines that the location of a failure or performance   degradation is within a node or on a link between two adjacent nodes.   Each OAM solution document will further detail the implications of   the tools it defines when used with per-interface or per-node MEPs,   if necessary.   It may occur that multiple MEPs for the same MEG are on the same   node, and are all Up MEPs, each on one side of the forwarding engine,   such that the MEG is entirely internal to the node.Busi & Allan                  Informational                    [Page 17]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   It should be noted that an ME may span nodes that implement per-node   MEPs and per-interface MEPs.  This guarantees backward compatibility   with most of the existing LSRs that can implement only a per-node   MEP.  In fact, in many current implementations, label operations are   largely performed on the ingress interface; hence, the exposure of   the GAL as top label will occur at the ingress interface.   Note that a MEP can only exist at the beginning and end of a   (sub-)layer in MPLS-TP.  If there is a need to monitor some portion   of that LSP or PW, a new sub-layer (in the form of an SPME) must be   created that permits MEPs and associated MEGs to be created.   In the case where an intermediate node sends an OAM packet to a MEP,   it uses the top label of the stack at that point.3.4.  MEG Intermediate Points (MIPs)   A MEG Intermediate Point (MIP) is a function located at a point   between the MEPs of a MEG for a PW, LSP, or SPME.   A MIP is capable of reacting to some OAM packets and forwarding all   the other OAM packets while ensuring fate-sharing with user data   packets.  However, a MIP does not initiate unsolicited OAM packets,   but may be addressed by OAM packets initiated by one of the MEPs of   the MEG.  A MIP can generate OAM packets only in response to OAM   packets that it receives from the MEG it belongs to.  The OAM packets   generated by the MIP are sent to the originating MEP.   An intermediate node within a MEG can either:   o  support per-node MIPs (i.e., a single MIP per node in an      unspecified location within the node); or   o  support per-interface MIPs (i.e., two or more MIPs per node on      both sides of the forwarding engine).   Support of per-interface or per-node MIPs is an implementation   choice.  It is also possible that a node could support per-interface   MIPs on some MEGs and per-node MIPs on other MEGs for which it is a   transit node.Busi & Allan                  Informational                    [Page 18]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011                            Intermediate node                        ------------------------                       |                        |                       |-----              -----|                       | MIP |            | MIP |                       |     |    ----    |     |                    ->-| In  |->-| FW |->-| Out |->-                       | i/f |    ----    | i/f |                       |-----              -----|                       |                        |                        ------------------------                Figure 4: Example of Per-Interface MIPs   Figure 4 describes an example of two per-interface MIPs at an   intermediate node of a point-to-point MEG.   Using per-interface MIPs allows the network operator to determine   that the location of a failure or performance degradation is within a   node or on a link between two adjacent nodes.   When sending an OAM packet to a MIP, the source MEP should set the   TTL field to indicate the number of hops necessary to reach the node   where the MIP resides.   The source MEP should also include target MIP information in the OAM   packets sent to a MIP to allow proper identification of the MIP   within the node.  The MEG the OAM packet belongs to is associated   with the MPLS label, whether the label is used to infer the MEG or   the content of the OAM packet is an implementation choice.  In the   latter case, the MPLS label is checked to be the expected one.   The use of TTL expiry to deliver OAM packets to a specific MIP is not   a fully reliable delivery mechanism because the TTL distance of a MIP   from a MEP can change.  Any MPLS-TP node silently discards any OAM   packet that is received with an expired TTL and that is not addressed   to any of its MIPs or MEPs.  An MPLS-TP node that does not support   OAM is also expected to silently discard any received OAM packet.   Packets directed to a MIP may not necessarily carry specific MIP   identification information beyond that of TTL distance.  In this   case, a MIP would promiscuously respond to all MEP queries on its   MEG.  This capability could be used for discovery functions (e.g.,   route tracing as defined inSection 6.4) or when it is desirable to   leave to the originating MEP the job of correlating TTL and MIP   identifiers and noting changes or irregularities (via comparison with   information previously extracted from the network).Busi & Allan                  Informational                    [Page 19]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   MIPs are associated to the MEG they belong to, and their identity is   unique within the MEG.  However, their identity is not necessarily   unique to the MEG, e.g., all nodal MIPs in a node can have a common   identity.   A node hosting a MEP can also support per-interface Up MEPs and per-   interface MIPs on either side of the forwarding engine.   Once a MEG is configured, the operator can enable/disable the MIPs on   the nodes within the MEG.  All the intermediate nodes and possibly   the end nodes host MIP(s).  Local policy allows them to be enabled   per function and per MEG.  The local policy is controlled by the   management system, which may delegate it to the control plane.  A   disabled MIP silently discards any received OAM packets.3.5.  Server MEPs   A server MEP is a MEP of a MEG that is either:   o  defined in a layer network that is "below", which is to say      encapsulates and transports the MPLS-TP layer network being      referenced; or   o  defined in a sub-layer of the MPLS-TP layer network that is      "below", which is to say encapsulates and transports the sub-layer      being referenced.   A server MEP can coincide with a MIP or a MEP in the client (MPLS-TP)   (sub-)layer network.   A server MEP also provides server-layer OAM indications to the   client/server adaptation function between the client (MPLS-TP)   (sub-)layer network and the server (sub-)layer network.  The   adaptation function maintains state on the mapping of MPLS-TP   transport paths that are set up over that server (sub-)layer's   transport path.   For example, a server MEP can be:   o  a non-MPLS MEP at a termination point of a physical link (e.g.,      802.3, an SDH Virtual Circuit, or OTN Optical Data Unit (ODU)),      for the MPLS-TP Section layer network, defined inSection 4.1;   o  an MPLS-TP Section MEP for MPLS-TP LSPs, defined inSection 4.2;   o  an MPLS-TP LSP MEP for MPLS-TP PWs, defined inSection 4.3;Busi & Allan                  Informational                    [Page 20]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   o  an MPLS-TP SPME MEP used for LSP path segment monitoring, as      defined inSection 4.4, for MPLS-TP LSPs or higher-level SPMEs      providing LSP path segment monitoring; or   o  an MPLS-TP SPME MEP used for PW path segment monitoring, as      defined inSection 4.5, for MPLS-TP PWs or higher-level SPMEs      providing PW path segment monitoring.   The server MEP can run appropriate OAM functions for fault detection   within the server (sub-)layer network and provides a fault indication   to its client MPLS-TP layer network via the client/server adaptation   function.  When the server layer is not MPLS-TP, server MEP OAM   functions are simply assumed to exist but are outside the scope of   this document.3.6.  Configuration Considerations   When a control plane is not present, the management plane configures   these functional components.  Otherwise, they can be configured by   either the management plane or the control plane.   Local policy allows disabling the usage of any available "out-of-   band" return path, as defined in [8], irrespective of what is   requested by the node originating the OAM packet.   SPMEs are usually instantiated when the transport path is created by   either the management plane or the control plane (if present).   Sometimes an SPME can be instantiated after the transport path is   initially created.3.7.  P2MP Considerations   All the traffic sent over a P2MP transport path, including OAM   packets generated by a MEP, is sent (multicast) from the root to all   the leaves.  As a consequence:   o  To send an OAM packet to all leaves, the source MEP can send a      single OAM packet that will be delivered by the forwarding plane      to all the leaves and processed by all the leaves.  Hence, a      single OAM packet can simultaneously instrument all the MEs in a      P2MP MEG.   o  To send an OAM packet to a single leaf, the source MEP sends a      single OAM packet that will be delivered by the forwarding plane      to all the leaves but contains sufficient information to identify      a target leaf, and therefore is processed only by the target leaf      and can be silently discarded by the other leaves.Busi & Allan                  Informational                    [Page 21]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   o  To send an OAM packet to a single MIP, the source MEP sends a      single OAM packet with the TTL field indicating the number of hops      necessary to reach the node where the MIP resides.  This packet      will be delivered by the forwarding plane to all intermediate      nodes at the same TTL distance of the target MIP and to any leaf      that is located at a shorter distance.  The OAM packet must      contain sufficient information to identify the target MIP and      therefore is processed only by the target MIP and can be silently      discarded by the others.   o  In order to send an OAM packet to M leaves (i.e., a subset of all      the leaves), the source MEP sends M different OAM packets targeted      to each individual leaf in the group of M leaves.  Aggregating or      subsetting mechanisms are outside the scope of this document.   A bud node with a Down MEP or a per-node MEP will both terminate and   relay OAM packets.  Similar to how fault coverage is maximized by the   explicit utilization of Up MEPs, the same is true for MEPs on a bud   node.   P2MP paths are unidirectional; therefore, any return path to an   originating MEP for on-demand transactions will be out-of-band.  A   mechanism to target "on-demand" transactions to a single MEP or MIP   is required as it relieves the originating MEP of an arbitrarily   large processing load and of the requirement to filter and discard   undesired responses.  This is because normally TTL exhaustion will   address all MIPs at a given distance from the source, and failure to   exhaust TTL will address all MEPs.3.8.  Further Considerations of Enhanced Segment Monitoring   Segment monitoring, like any in-service monitoring, in a transport   network should meet the following network objectives:   1. The monitoring and maintenance of existing transport paths has to      be conducted in service without traffic disruption.   2. Segment monitoring must not modify the forwarding of the segment      portion of the transport path.   SPMEs defined inSection 3.2 meet the above two objectives, when they   are pre-configured or pre-instantiated as exemplified inSection 3.6.   However, sometimes pre-design and pre-configuration of all the   considered patterns of SPME are not preferable in real operation due   to the burden of design works, a number of header consumptions,   bandwidth consumption, and so on.Busi & Allan                  Informational                    [Page 22]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   When SPMEs are configured or instantiated after the transport path   has been created, network objective (1) can be met: application and   removal of SPME to a faultless monitored transport entity can be   performed in such a way as not to introduce any loss of traffic,   e.g., by using a non-disruptive "make before break" technique.   However, network objective (2) cannot be met due to new assignment of   MPLS labels.  As a consequence, generally speaking, the results of   SPME monitoring are not necessarily correlated with the behavior of   traffic in the monitored entity when it does not use SPME.  For   example, application of SPME to a problematic/faulty monitoring   entity might "fix" the problem encountered by the latter -- for as   long as SPME is applied.  And vice versa, application of SPME to a   faultless monitored entity may result in making it faulty -- again,   as long as SPME is applied.   Support for a more sophisticated segment-monitoring mechanism   (temporal and hitless segment monitoring) to efficiently meet the two   network objectives may be necessary.   One possible option to instantiate non-intrusive segment monitoring   without the use of SPMEs would require the MIPs selected as   monitoring end points to implement enhanced functionality and state   for the monitored transport path.   For example, the MIPs need to be configured with the TTL distance to   the peer or with the address of the peer, when out-of-band return   paths are used.   A further issue that would need to be considered is events that   result in changing the TTL distance to the peer monitoring entity,   such as protection events that may temporarily invalidate OAM   information gleaned from the use of this technique.   Further considerations on this technique are outside the scope of   this document.4.  Reference Model   The reference model for the MPLS-TP OAM framework builds upon the   concept of a MEG, and its associated MEPs and MIPs, to support the   functional requirements specified inRFC 5860 [11].   The following MPLS-TP MEGs are specified in this document:   o  A Section Maintenance Entity Group (SMEG), allowing monitoring and      management of MPLS-TP Sections (between MPLS LSRs).Busi & Allan                  Informational                    [Page 23]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   o  An LSP Maintenance Entity Group (LMEG), allowing monitoring and      management of an end-to-end LSP (between LERs).   o  A PW Maintenance Entity Group (PMEG), allowing monitoring and      management of an end-to-end Single-Segment Pseudowire (SS-PW) or      MS-PW (between T-PEs).   o  An LSP SPME ME Group (LSMEG), allowing monitoring and management      of an SPME (between a given pair of LERs and/or LSRs along an      LSP).   o  A PW SPME ME Group (PSMEG), allowing monitoring and management of      an SPME (between a given pair of T-PEs and/or S-PEs along an      (MS-)PW).   The MEGs specified in this MPLS-TP OAM framework are compliant with   the architecture framework for MPLS-TP [8] that includes both MS-PWs   [4] and LSPs [1].   Hierarchical LSPs are also supported in the form of SPMEs.  In this   case, each LSP in the hierarchy is a different sub-layer network that   can be monitored, independently from higher- and lower-level LSPs in   the hierarchy, on an end-to-end basis (from LER to LER) by an SPME.   It is possible to monitor a portion of a hierarchical LSP by   instantiating a hierarchical SPME between any LERs/LSRs along the   hierarchical LSP.Busi & Allan                  Informational                    [Page 24]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011    Native |<------------------ MS-PW1Z ---------------->|  Native    Layer  |                                             |   Layer   Service |    |<LSP13>|    |<-LSP3X->|    |<LSPXZ>|    |  Service    (AC1)  V    V       V    V         V    V       V    V   (AC2)           +----+ +---+ +----+         +----+ +---+ +----+   +----+  |T-PE| |LSR| |S-PE|         |S-PE| |LSR| |T-PE|   +----+   |    |  | 1  | | 2 | | 3  |         | X  | | Y | | Z  |   |    |   |    |  |    |=======|    |=========|    |=======|    |   |    |   | CE1|--|.......PW13......|...PW3X..|......PWXZ.......|---|CE2 |   |    |  |    |=======|    |=========|    |=======|    |   |    |   |    |  |    | |   | |    |         |    | |   | |    |   |    |   +----+  |    | |   | |    |         |    | |   | |    |   +----+           +----+ +---+ +----+         +----+ +---+ +----+           .                 .         .                 .           |                 |         |                 |           |<--- Domain 1 -->|         |<--- Domain Z -->|           ^----------------- PW1Z  PMEG ----------------^           ^--- PW13 PSMEG --^         ^--- PWXZ PSMEG --^                ^-------^                   ^-------^                LSP13 LMEG                  LSPXZ LMEG                ^--^ ^--^    ^---------^    ^--^ ^--^               Sec12 Sec23      Sec3X      SecXY SecYZ                SMEG  SMEG       SMEG       SMEG  SMEG   ^---^ ME   ^     MEP   ====  LSP   .... PW   T-PE 1: Terminating Provider Edge 1   LSR 2:  Label Switching Router 2   S-PE 3: Switching Provider Edge 3   S-PE X: Switching Provider Edge X   LSR Y:  Label Switching Router Y   T-PE Z: Terminating Provider Edge Z        Figure 5: Reference Model for the MPLS-TP OAM Framework   Figure 5 depicts a high-level reference model for the MPLS-TP OAM   framework.  The figure depicts portions of two MPLS-TP-enabled   network domains, Domain 1 and Domain Z.  In Domain 1, T-PE 1 is   adjacent to LSR 2 via the MPLS-TP Section Sec12, and LSR 2 is   adjacent to S-PE 3 via the MPLS-TP Section Sec23.  Similarly, in   Domain Z, S-PE X is adjacent to LSR Y via the MPLS-TP Section SecXY,   and LSR Y is adjacent to T-PE Z via the MPLS-TP Section SecYZ.  In   addition, S-PE 3 is adjacent to S-PE X via the MPLS-TP Section Sec3X.Busi & Allan                  Informational                    [Page 25]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   Figure 5 also shows a bidirectional MS-PW (MS-PW1Z) between AC1 on   T-PE1 and AC2 on T-PE Z.  The MS-PW consists of three bidirectional   PW path segments: 1) PW13 path segment between T-PE 1 and S-PE 3 via   the bidirectional LSP13 LSP, 2) PW3X path segment between S-PE 3 and   S-PE X via the bidirectional LSP3X LSP, and 3) PWXZ path segment   between S-PE X and T-PE Z via the bidirectional LSPXZ LSP.   The MPLS-TP OAM procedures that apply to a MEG are expected to   operate independently from procedures on other MEGs.  Yet, this does   not preclude that multiple MEGs may be affected simultaneously by the   same network condition -- for example, a fiber cut event.   Note that there are no constraints imposed by this OAM framework on   the number or type (P2P, P2MP, LSP, or PW), of MEGs that may be   instantiated on a particular node.  In particular, when looking at   Figure 5, it should be possible to configure one or more MEPs on the   same node if that node is the end point of one or more MEGs.   Figure 5 does not describe a PW3X PSMEG because typically SPMEs are   used to monitor an OAM domain (like PW13 and PWXZ PSMEGs) rather than   the segment between two OAM domains.  However, the OAM framework does   not pose any constraints on the way SPMEs are instantiated as long as   they are not overlapping.   The subsections below define the MEGs specified in this MPLS-TP OAM   architecture framework document.  Unless otherwise stated, all   references to domains, LSRs, MPLS-TP Sections, LSPs, pseudowires, and   MEGs in this section are made in relation to those shown in Figure 5.4.1.  MPLS-TP Section Monitoring (SMEG)   An MPLS-TP Section MEG (SMEG) is an MPLS-TP maintenance entity   intended to monitor an MPLS-TP Section.  An SMEG may be configured on   any MPLS-TP section.  SMEG OAM packets must fate-share with the user   data packets sent over the monitored MPLS-TP Section.   An SMEG is intended to be deployed for applications where it is   preferable to monitor the link between topologically adjacent (next   hop in this layer network) MPLS-TP LSRs rather than monitoring the   individual LSP or PW path segments traversing the MPLS-TP Section and   where the server-layer technology does not provide adequate OAM   capabilities.Busi & Allan                  Informational                    [Page 26]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   Figure 5 shows five Section MEGs configured in the network between   AC1 and AC2:   1. Sec12 MEG associated with the MPLS-TP Section between T-PE 1 and      LSR 2,   2. Sec23 MEG associated with the MPLS-TP Section between LSR 2 and      S-PE 3,   3. Sec3X MEG associated with the MPLS-TP Section between S-PE 3 and      S-PE X,   4. SecXY MEG associated with the MPLS-TP Section between S-PE X and      LSR Y, and   5. SecYZ MEG associated with the MPLS-TP Section between LSR Y and      T-PE Z4.2.  MPLS-TP LSP End-to-End Monitoring Group (LMEG)   An MPLS-TP LSP MEG (LMEG) is an MPLS-TP maintenance entity group   intended to monitor an end-to-end LSP between its LERs.  An LMEG may   be configured on any MPLS LSP.  LMEG OAM packets must fate-share with   user data packets sent over the monitored MPLS-TP LSP.   An LMEG is intended to be deployed in scenarios where it is desirable   to monitor an entire LSP between its LERs, rather than, say,   monitoring individual PWs.   Figure 5 depicts two LMEGs configured in the network between AC1 and   AC2: 1) the LSP13 LMEG between T-PE 1 and S-PE 3, and 2) the LSPXZ   LMEG between S-PE X and T-PE Z.  Note that the presence of a LSP3X   LMEG in such a configuration is optional, and hence, not precluded by   this framework.  For instance, the network operator may prefer to   monitor the MPLS-TP Section between the two LSRs rather than the   individual LSPs.4.3.  MPLS-TP PW Monitoring (PMEG)   An MPLS-TP PW MEG (PMEG) is an MPLS-TP maintenance entity intended to   monitor a SS-PW or MS-PW between its T-PEs.  A PMEG can be configured   on any SS-PW or MS-PW.  PMEG OAM packets must fate-share with the   user data packets sent over the monitored PW.   A PMEG is intended to be deployed in scenarios where it is desirable   to monitor an entire PW between a pair of MPLS-TP-enabled T-PEs   rather than monitoring the LSP that aggregates multiple PWs between   PEs.Busi & Allan                  Informational                    [Page 27]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   Figure 5 depicts an MS-PW (MS-PW1Z) consisting of three path segments   (PW13, PW3X, and PWXZ) and its associated end-to-end PMEG (PW1Z   PMEG).4.4.  MPLS-TP LSP SPME Monitoring (LSMEG)   An MPLS-TP LSP SPME MEG (LSMEG) is an MPLS-TP SPME with an associated   maintenance entity group intended to monitor an arbitrary part of an   LSP between the MEPs instantiated for the SPME, independent from the   end-to-end monitoring (LMEG).  An LSMEG can monitor an LSP path   segment, and it may also include the forwarding engine(s) of the   node(s) at the edge(s) of the path segment.   When an SPME is established between non-adjacent LSRs, the edges of   the SPME become adjacent at the LSP sub-layer network and any LSR   that was previously in between becomes an LSR for the SPME.   Multiple hierarchical LSMEGs can be configured on any LSP.  LSMEG OAM   packets must fate-share with the user data packets sent over the   monitored LSP path segment.   A LSME can be defined between the following entities:   o  The LER and LSR of a given LSP.   o  Any two LSRs of a given LSP.   An LSMEG is intended to be deployed in scenarios where it is   preferable to monitor the behavior of a part of an LSP or set of LSPs   rather than the entire LSP itself, for example, when there is a need   to monitor a part of an LSP that extends beyond the administrative   boundaries of an MPLS-TP-enabled administrative domain.Busi & Allan                  Informational                    [Page 28]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011            |<-------------------- PW1Z ------------------->|            |                                               |            |    |<-------------LSP1Z LSP------------->|    |            |    |<-LSP13->|    |<LSP3X>|    |<-LSPXZ->|    |            V    V         V    V       V    V         V    V            +----+  +---+  +----+       +----+  +---+  +----+   +----+   | PE |  |LSR|  |DBN |       |DBN |  |LSR|  | PE |   +----+   |    |   | 1  |  | 2 |  | 3  |       | X  |  | Y |  | Z  |   |    |   |    |AC1|    |=====================================|    |AC2|    |   | CE1|---|.....................PW1Z......................|---|CE2 |   |    |   |    |=====================================|    |   |    |   |    |   |    |  |   |  |    |       |    |  |   |  |    |   |    |   +----+   |    |  |   |  |    |       |    |  |   |  |    |   +----+            +----+  +---+  +----+       +----+  +---+  +----+            .                   .       .                   .            |                   |       |                   |            |<---- Domain 1 --->|       |<---- Domain Z --->|                 ^---------^                 ^---------^                 LSP13 LSMEG                 LSPXZ LSMEG                 ^-------------------------------------^                                LSP1Z LMEG   DBN: Domain Border Node   PE 1:  Provider Edge 1   LSR 2: Label Switching Router 2   DBN 3: Domain Border Node 3   DBN X: Domain Border Node X   LSR Y: Label Switching Router Y   PE Z:  Provider Edge Z                 Figure 6: MPLS-TP LSP SPME MEG (LSMEG)   Figure 6 depicts a variation of the reference model in Figure 5 where   there is an end-to-end LSP (LSP1Z) between PE 1 and PE Z.  LSP1Z   consists of, at least, three LSP Concatenated Segments: LSP13, LSP3X,   and LSPXZ.  In this scenario, there are two separate LSMEGs   configured to monitor the LSP1Z: 1) a LSMEG monitoring the LSP13   Concatenated Segment on Domain 1 (LSP13 LSMEG), and 2) a LSMEG   monitoring the LSPXZ Concatenated Segment on Domain Z (LSPXZ LSMEG).   It is worth noticing that LSMEGs can coexist with the LMEG monitoring   the end-to-end LSP and that LSMEG MEPs and LMEG MEPs can be   coincident in the same node (e.g., PE 1 node supports both the LSP1Z   LMEG MEP and the LSP13 LSMEG MEP).Busi & Allan                  Informational                    [Page 29]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20114.5.  MPLS-TP MS-PW SPME Monitoring (PSMEG)   An MPLS-TP MS-PW SPME Monitoring MEG (PSMEG) is an MPLS-TP SPME with   an associated maintenance entity group intended to monitor an   arbitrary part of an MS-PW between the MEPs instantiated for the   SPME, independently of the end-to-end monitoring (PMEG).  A PSMEG can   monitor a PW path segment, and it may also include the forwarding   engine(s) of the node(s) at the edge(s) of the path segment.  A PSMEG   is no different than an SPME; it is simply named as such to discuss   SPMEs specifically in a PW context.   When SPME is established between non-adjacent S-PEs, the edges of the   SPME become adjacent at the MS-PW sub-layer network, and any S-PE   that was previously in between becomes an LSR for the SPME.   S-PE placement is typically dictated by considerations other than   OAM.  S-PEs will frequently reside at operational boundaries such as   the transition from distributed control plane (CP) to centralized   Network Management System (NMS) control or at a routing area   boundary.  As such, the architecture would appear not to have the   flexibility that arbitrary placement of SPME segments would imply.   Support for an arbitrary placement of PSMEG would require the   definition of additional PW sub-layering.  Multiple hierarchical   PSMEGs can be configured on any MS-PW.  PSMEG OAM packets fate-share   with the user data packets sent over the monitored PW path Segment.   A PSMEG does not add hierarchical components to the MPLS   architecture; it defines the role of existing components for the   purposes of discussing OAM functionality.   A PSME can be defined between the following entities:   o  The T-PE and any S-PE of a given MS-PW.   o  Any two S-PEs of a given MS-PW.   Note that, in line with the SPME description inSection 3.2, when a   PW SPME is instantiated after the MS-PW has been instantiated, the   TTL distance of the MIPs may change and MIPs in the PW SPME are no   longer part of the encompassing MEG.  This means that the S-PE nodes   hosting these MIPs are no longer S-PEs but P nodes at the SPME LSP   level.  The consequences are that the S-PEs hosting the PSMEG MEPs   become adjacent S-PEs.  This is no different than the operation of   SPMEs in general.   A PSMEG is intended to be deployed in scenarios where it is   preferable to monitor the behavior of a part of an MS-PW rather than   the entire end-to-end PW itself, for example, when monitoring an MS-Busi & Allan                  Informational                    [Page 30]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   PW path segment within a given network domain of an inter-domain MS-   PW.   Figure 5 depicts an MS-PW (MS-PW1Z) consisting of three path   segments: PW13, PW3X, and PWXZ with two separate PSMEGs: 1) a PSMEG   monitoring the PW13 MS-PW path segment on Domain 1 (PW13 PSMEG) and   2) a PSMEG monitoring the PWXZ MS-PW path segment on Domain Z with   (PWXZ PSMEG).   It is worth noticing that PSMEGs can coexist with the PMEG monitoring   the end-to-end MS-PW and that PSMEG MEPs and PMEG MEPs can be   coincident in the same node (e.g., T-PE 1 node supports both the PW1Z   PMEG MEP and the PW13 PSMEG MEP).4.6.  Fate-Sharing Considerations for Multilink   Multilink techniques are in use today and are expected to continue to   be used in future deployments.  These techniques include Ethernet   link aggregation [22] and the use of link bundling for MPLS [18]   where the option to spread traffic over component links is supported   and enabled.  While the use of link bundling can be controlled at the   MPLS-TP layer, use of link aggregation (or any server-layer-specific   multilink) is not necessarily under the control of the MPLS-TP layer.   Other techniques may emerge in the future.  These techniques   frequently share the characteristic that an LSP may be spread over a   set of component links and therefore be reordered, but no flow within   the LSP is reordered (except when very infrequent and minimally   disruptive load rebalancing occurs).   The use of multilink techniques may be prohibited or permitted in any   particular deployment.  If multilink techniques are used, the   deployment can be considered to be only partially MPLS-TP compliant;   however, this is unlikely to prevent their use.   The implications for OAM are that not all components of a multilink   will be exercised, independent server-layer OAM being required to   exercise the aggregated link components.  This has further   implications for MIP and MEP placement, as per-interface MIPs or Down   MEPs on a multilink interface are akin to a layer violation, as they   instrument at the granularity of the server layer.  The implications   for reduced OAM loss measurement functionality are documented in   Sections5.5.3 and6.2.3.Busi & Allan                  Informational                    [Page 31]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20115.  OAM Functions for Proactive Monitoring   In this document, proactive monitoring refers to OAM operations that   are either configured to be carried out periodically and continuously   or preconfigured to act on certain events such as alarm signals.   Proactive monitoring is usually performed "in-service".  Such   transactions are universally MEP to MEP in operation, while   notifications can be node to node (e.g., some MS-PW transactions) or   node to MEPs (e.g., AIS).  The control and measurement considerations   are:   1. Proactive monitoring for a MEG is typically configured at the      creation time of the transport path.   2. The operational characteristics of in-band measurement      transactions (e.g., CV, Loss Measurement (LM), etc.) are      configured at the MEPs.   3. Server-layer events are reported by OAM packets originating at      intermediate nodes.   4. The measurements resulting from proactive monitoring are typically      reported outside of the MEG (e.g., to a management system) as      notification events such as faults or indications of performance      degradations (such as signal degrade conditions).   5. The measurements resulting from proactive monitoring may be      periodically harvested by an NMS.   Proactive fault reporting is assumed to be subject to unreliable   delivery and soft-state, and it needs to operate in cases where a   return path is not available or faulty.  Therefore, periodic   repetition is assumed to be used for reliability, instead of   handshaking.   Delay measurement also requires periodic repetition to allow   estimation of the packet delay variation for the MEG.   For statically provisioned transport paths, the above information is   statically configured; for dynamically established transport paths,   the configuration information is signaled via the control plane or   configured via the management plane.   The operator may enable/disable some of the consequent actions   defined inSection 5.1.2.Busi & Allan                  Informational                    [Page 32]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20115.1.  Continuity Check and Connectivity Verification   Proactive Continuity Check functions, as required inSection 2.2.2 of   RFC 5860 [11], are used to detect a loss of continuity (LOC) defect   between two MEPs in a MEG.   Proactive Connectivity Verification functions, as required inSection2.2.3 of RFC 5860 [11], are used to detect an unexpected connectivity   defect between two MEGs (e.g., mismerging or misconnection), as well   as unexpected connectivity within the MEG with an unexpected MEP.   Both functions are based on the (proactive) generation, at the same   rate, of OAM packets by the source MEP that are processed by the peer   sink MEP(s).  As a consequence, in order to save OAM bandwidth   consumption, CV, when used, is linked with CC into Continuity Check   and Connectivity Verification (CC-V) OAM packets.   In order to perform proactive Connectivity Verification, each CC-V   OAM packet also includes a globally unique Source MEP identifier,   whose value needs to be configured on the source MEP and on the peer   sink MEP(s).  In some cases, to avoid the need to configure the   globally unique Source MEP identifier, it is preferable to perform   only proactive Continuity Check.  In this case, the CC-V OAM packet   does not need to include any globally unique Source MEP identifier.   Therefore, a MEG can be monitored only for CC or for both CC and CV.   CC-V OAM packets used for CC-only monitoring are called CC OAM   packets, while CC-V OAM packets used for both CC and CV are called CV   OAM packets.   As a consequence, it is not possible to detect misconnections between   two MEGs monitored only for continuity as neither the OAM packet type   nor the OAM packet content provides sufficient information to   disambiguate an invalid source.  To expand:   o  For a CC OAM packet leaking into a CC monitored MEG -      undetectable.   o  For a CV OAM packet leaking into a CC monitored MEG - reception of      CV OAM packets instead of a CC OAM packets (e.g., with the      additional Source MEP identifier) allows detecting the fault.   o  For a CC OAM packet leaking into a CV monitored MEG - reception of      CC OAM packets instead of CV OAM packets (e.g., lack of additional      Source MEP identifier) allows detecting the fault.   o  For a CV OAM packet leaking into a CV monitored MEG - reception of      CV OAM packets with different Source MEP identifier permits fault      to be identified.Busi & Allan                  Informational                    [Page 33]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   Having a common packet format for CC-V OAM packets would simplify   parsing in a sink MEP to properly detect all the misconfiguration   cases described above.   MPLS-TP OAM supports different formats of MEP identifiers to address   different environments.  When an alternative to IP addressing is   desired (e.g., MPLS-TP is deployed in transport network environments   where consistent operations with other transport technologies defined   by the ITU-T are required), the ITU Carrier Code (ICC)-based format   for MEP identification is used: this format is under definition in   [25].  When MPLS-TP is deployed in an environment where IP   capabilities are available and desired for OAM, the IP-based MEP   identification is used: this format is described in [24].   CC-V OAM packets are transmitted at a regular, operator-configurable   rate.  The default CC-V transmission periods are application   dependent (seeSection 5.1.3).   Proactive CC-V OAM packets are transmitted with the "minimum loss   probability PHB" within the transport path (LSP, PW) they are   monitoring.  For E-LSPs, this PHB is configurable on the network   operator's basis, while for L-LSPs this is determined as perRFC 3270   [23].  PHBs can be translated at the network borders by the same   function that translates them for user data traffic.  The implication   is that CC-V fate-shares with much of the forwarding implementation,   but not all aspects of PHB processing are exercised.  Either on-   demand tools are used for finer-grained fault finding or an   implementation may utilize a CC-V flow per PHB to ensure a CC-V flow   fate-shares with each individual PHB.   In a co-routed or associated, bidirectional point-to-point transport   path, when a MEP is enabled to generate proactive CC-V OAM packets   with a configured transmission rate, it also expects to receive   proactive CC-V OAM packets from its peer MEP at the same transmission   rate.  This is because a common SLA applies to all components of the   transport path.  In a unidirectional transport path (either point-to-   point or point-to-multipoint), the source MEP is enabled only to   generate CC-V OAM packets, while each sink MEP is configured to   expect these packets at the configured rate.   MIPs, as well as intermediate nodes not supporting MPLS-TP OAM, are   transparent to the proactive CC-V information and forward these   proactive CC-V OAM packets as regular data packets.   During path setup and tear down, situations arise where CC-V checks   would give rise to alarms, as the path is not fully instantiated.  In   order to avoid these spurious alarms, the following procedures are   recommended.  At initialization, the source MEP function (generatingBusi & Allan                  Informational                    [Page 34]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   proactive CC-V packets) should be enabled prior to the corresponding   sink MEP function (detecting continuity and connectivity defects).   When disabling the CC-V proactive functionality, the sink MEP   function should be disabled prior to the corresponding source MEP   function.   It should be noted that different encapsulations are possible for   CC-V packets, and therefore it is possible that in case of   misconfigurations or mis-connectivity, CC-V packets are received with   an unexpected encapsulation.   There are practical limitations to detecting unexpected   encapsulation.  It is possible that there are misconfiguration or   mis-connectivity scenarios where OAM packets can alias as payload,   e.g., when a transport path can carry an arbitrary payload without a   pseudowire.   When CC-V packets are received with an unexpected encapsulation that   can be parsed by a sink MEP, the CC-V packet is processed as if it   were received with the correct encapsulation.  If it is not a   manifestation of a mis-connectivity defect, a warning is raised (seeSection 5.1.1.4).  Otherwise, the CC-V packet may be silently   discarded as unrecognized and a LOC defect may be detected (seeSection 5.1.1.1).   The defect conditions are described in no specific order.5.1.1.  Defects Identified by CC-V   Proactive CC-V functions allow a sink MEP to detect the defect   conditions described in the following subsections.  For all of the   described defect cases, a sink MEP should notify the equipment fault   management process of the detected defect.   Sequential consecutive loss of CC-V packets is considered indicative   of an actual break and not of congestive loss or physical-layer   degradation.  The loss of 3 packets in a row (implying a detection   interval that is 3.5 times the insertion time) is interpreted as a   true break and a condition that will not clear by itself.   A CC-V OAM packet is considered to carry an unexpected globally   unique Source MEP identifier if it is a CC OAM packet received by a   sink MEP monitoring the MEG for CV; it is a CV OAM packet received by   a sink MEP monitoring the MEG for CC, or it is a CV OAM packet   received by a sink MEP monitoring the MEG for CV but carrying a   unique Source MEP identifier that is different that the expected one.   Conversely, the CC-V packet is considered to have an expected   globally unique Source MEP identifier; it is a CC OAM packet receivedBusi & Allan                  Informational                    [Page 35]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   by a sink MEP monitoring the MEG for CC, or it is a CV OAM packet   received by a sink MEP monitoring the MEG for CV and carrying a   unique Source MEP identifier that is equal to the expected one.5.1.1.1.  Loss of Continuity Defect   When proactive CC-V is enabled, a sink MEP detects a loss of   continuity (LOC) defect when it fails to receive proactive CC-V OAM   packets from the source MEP.   o  Entry criteria:  If no proactive CC-V OAM packets from the source      MEP (and in the case of CV, this includes the requirement to have      the expected globally unique Source MEP identifier) are received      within the interval equal to 3.5 times the receiving MEP's      configured CC-V reception period.   o  Exit criteria: A proactive CC-V OAM packet from the source MEP      (and again in the case of CV, with the expected globally unique      Source MEP identifier) is received.5.1.1.2.  Mis-Connectivity Defect   When a proactive CC-V OAM packet is received, a sink MEP identifies a   mis-connectivity defect (e.g., mismerge, misconnection, or unintended   looping) when the received packet carries an unexpected globally   unique Source MEP identifier.   o  Entry criteria: The sink MEP receives a proactive CC-V OAM packet      with an unexpected globally unique Source MEP identifier or with      an unexpected encapsulation.   o  Exit criteria: The sink MEP does not receive any proactive CC-V      OAM packet with an unexpected globally unique Source MEP      identifier for an interval equal at least to 3.5 times the longest      transmission period of the proactive CC-V OAM packets received      with an unexpected globally unique Source MEP identifier since      this defect has been raised.  This requires the OAM packet to      self-identify the CC-V periodicity, as not all MEPs can be      expected to have knowledge of all MEGs.5.1.1.3.  Period Misconfiguration Defect   If proactive CC-V OAM packets are received with the expected globally   unique Source MEP identifier but with a transmission period different   than the locally configured reception period, then a CC-V period   misconfiguration defect is detected.Busi & Allan                  Informational                    [Page 36]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   o  Entry criteria: A MEP receives a CC-V proactive packet with the      expected globally unique Source MEP identifier but with a      transmission period different than its own CC-V-configured      transmission period.   o  Exit criteria: The sink MEP does not receive any proactive CC-V      OAM packet with the expected globally unique Source MEP identifier      and an incorrect transmission period for an interval equal at      least to 3.5 times the longest transmission period of the      proactive CC-V OAM packets received with the expected globally      unique Source MEP identifier and an incorrect transmission period      since this defect has been raised.5.1.1.4.  Unexpected Encapsulation Defect   If proactive CC-V OAM packets are received with the expected globally   unique Source MEP identifier but with an unexpected encapsulation,   then a CC-V unexpected encapsulation defect is detected.   It should be noted that there are practical limitations to detecting   unexpected encapsulation (seeSection 5.1.1).   o  Entry criteria: A MEP receives a CC-V proactive packet with the      expected globally unique Source MEP identifier but with an      unexpected encapsulation.   o  Exit criteria: The sink MEP does not receive any proactive CC-V      OAM packet with the expected globally unique Source MEP identifier      and an unexpected encapsulation for an interval equal at least to      3.5 times the longest transmission period of the proactive CC-V      OAM packets received with the expected globally unique Source MEP      identifier and an unexpected encapsulation since this defect has      been raised.5.1.2.  Consequent Action   A sink MEP that detects any of the defect conditions defined inSection 5.1.1 declares a defect condition and performs the following   consequent actions.   If a MEP detects a mis-connectivity defect, it blocks all the traffic   (including also the user data packets) that it receives from the   misconnected transport path.   If a MEP detects a LOC defect that is not caused by a period   misconfiguration, it should block all the traffic (including also the   user data packets) that it receives from the transport path, if this   consequent action has been enabled by the operator.Busi & Allan                  Informational                    [Page 37]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   It is worth noticing that the OAM requirements document [11]   recommends that CC-V proactive monitoring be enabled on every MEG in   order to reliably detect connectivity defects.  However, CC-V   proactive monitoring can be disabled by an operator for a MEG.  In   the event of a misconnection between a transport path that is   proactively monitored for CC-V and a transport path that is not, the   MEP of the former transport path will detect a LOC defect   representing a connectivity problem (e.g., a misconnection with a   transport path where CC-V proactive monitoring is not enabled)   instead of a continuity problem, with a consequence of delivery of   traffic to an incorrect destination.  For these reasons, the traffic   block consequent action is applied even when a LOC condition occurs.   This block consequent action can be disabled through configuration.   This deactivation of the block action may be used for activating or   deactivating the monitoring when it is not possible to synchronize   the function activation of the two peer MEPs.   If a MEP detects a LOC defect (Section 5.1.1.1) or a mis-connectivity   defect (Section 5.1.1.2), it declares a signal fail condition of the   ME.   It is a matter of local policy whether or not a MEP that detects a   period misconfiguration defect (Section 5.1.1.3) declares a signal   fail condition of the ME.   The detection of an unexpected encapsulation defect does not have any   consequent action: it is just a warning for the network operator.  An   implementation able to detect an unexpected encapsulation but not   able to verify the source MEP ID may choose to declare a mis-   connectivity defect.5.1.3.  Configuration Considerations   At all MEPs inside a MEG, the following configuration information   needs to be configured when a proactive CC-V function is enabled:   o  MEG-ID: the MEG identifier to which the MEP belongs.   o  MEP-ID: the MEP's own identity inside the MEG.   o  list of the other MEPs in the MEG.  For a point-to-point MEG, the      list would consist of the single MEP ID from which the OAM packets      are expected.  In case of the root MEP of a P2MP MEG, the list is      composed of all the leaf MEP IDs inside the MEG.  In case of the      leaf MEP of a P2MP MEG, the list is composed of the root MEP ID      (i.e., each leaf needs to know the root MEP ID from which it      expects to receive the CC-V OAM packets).Busi & Allan                  Informational                    [Page 38]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   o  PHB for E-LSPs.  It identifies the per-hop behavior of a CC-V      packet.  Proactive CC-V packets are transmitted with the "minimum      loss probability PHB" previously configured within a single      network operator.  This PHB is configurable on network operator's      basis.  PHBs can be translated at the network borders.   o  transmission rate.  The default CC-V transmission periods are      application dependent (depending on whether they are used to      support fault management, performance monitoring, or protection-      switching applications):      *  Fault Management: default transmission period is 1 s (i.e.,         transmission rate of 1 packet/second).      *  Performance Management: default transmission period is 100 ms         (i.e., transmission rate of 10 packets/second).  CC-V         contributes to the accuracy of performance monitoring         statistics by permitting the defect-free periods to be properly         distinguished as described in Sections5.5.1 and5.6.1.      *  Protection Switching: If protection switching with CC-V, defect         entry criteria of 12 ms is required (for example, in         conjunction with the requirement to support 50 ms recovery time         as indicated inRFC 5654 [5]), then an implementation should         use a default transmission period of 3.33 ms (i.e.,         transmission rate of 300 packets/second).  Sometimes, the         requirement of 50 ms recovery time is associated with the         requirement for a CC-V defect entry criteria period of 35 ms;         in these cases a transmission period of 10 ms (i.e.,         transmission rate of 100 packets/second) can be used.         Furthermore, when there is no need for so small CC-V defect         entry criteria periods, a larger transmission period can be         used.   It should be possible for the operator to configure these   transmission rates for all applications, to satisfy specific network   requirements.   Note that the reception period is the same as the configured   transmission rate.   For management-provisioned transport paths, the above parameters are   statically configured; for dynamically signaled transport paths, the   configuration information is distributed via the control plane.   The operator should be able to enable/disable some of the consequent   actions.  Which consequent actions can be enabled/disabled is   described inSection 5.1.2.Busi & Allan                  Informational                    [Page 39]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20115.2.  Remote Defect Indication   The Remote Defect Indication (RDI) function, as required inSection2.2.9 of RFC 5860 [11], is an indicator that is transmitted by a sink   MEP to communicate to its source MEP that a signal fail condition   exists.  In case of co-routed and associated bidirectional transport   paths, RDI is associated with proactive CC-V, and the RDI indicator   can be piggy-backed onto the CC-V packet.  In case of unidirectional   transport paths, the RDI indicator can be sent only using an out-of-   band return path if it exists and its usage is enabled by policy   actions.   When a MEP detects a signal fail condition (e.g., in case of a   continuity or connectivity defect), it should begin transmitting an   RDI indicator to its peer MEP.  When incorporated into CC-V, the RDI   information will be included in all proactive CC-V packets that it   generates for the duration of the signal fail condition's existence.   A MEP that receives packets from a peer MEP with the RDI information   should determine that its peer MEP has encountered a defect condition   associated with a signal fail condition.   MIPs as well as intermediate nodes not supporting MPLS-TP OAM are   transparent to the RDI indicator and forward OAM packets that include   the RDI indicator as regular data packets, i.e., the MIP should not   perform any actions nor examine the indicator.   When the signal fail condition clears, the MEP should stop   transmitting the RDI indicator to its peer MEP.  When incorporated   into CC-V, the RDI indicator will not be set for subsequent   transmission of proactive CC-V packets.  A MEP should clear the RDI   defect upon reception of an RDI indicator cleared.5.2.1.  Configuration Considerations   In order to support RDI, the indication may be carried in a unique   OAM packet or may be embedded in a CC-V packet.  The in-band RDI   transmission rate and PHB of the OAM packets carrying RDIs should be   the same as that configured for CC-V to allow both far-end and near-   end defect conditions being resolved in a timeframe that has the same   order of magnitude.  This timeframe is application specific as   described inSection 5.1.3.  Methods of the out-of-band return paths   will dictate how out-of-band RDIs are transmitted.Busi & Allan                  Informational                    [Page 40]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20115.3.  Alarm Reporting   The Alarm Reporting function, as required in Section 2.2.8 ofRFC5860 [11], relies upon an Alarm Indication Signal (AIS) packet to   suppress alarms following detection of defect conditions at the   server (sub-)layer.   When a server MEP asserts a signal fail condition, it notifies that   to the co-located MPLS-TP client/server adaptation function that then   generates OAM packets with AIS information in the downstream   direction to allow the suppression of secondary alarms at the MPLS-TP   MEP in the client (sub-)layer.   The generation of packets with AIS information starts immediately   when the server MEP asserts a signal fail condition.  These periodic   OAM packets, with AIS information, continue to be transmitted until   the signal fail condition is cleared.   It is assumed that to avoid spurious alarm generation a MEP detecting   a loss of continuity defect (seeSection 5.1.1.1) will wait for a   hold-off interval prior to asserting an alarm to the management   system.  Therefore, upon receiving an OAM packet with AIS   information, an MPLS-TP MEP enters an AIS defect condition and   suppresses reporting of alarms to the NMS on the loss of continuity   with its peer MEP, but it does not block traffic received from the   transport path.  A MEP resumes loss of continuity alarm generation   upon detecting loss of continuity defect conditions in the absence of   AIS condition.   MIPs, as well as intermediate nodes, do not process AIS information   and forward these AIS OAM packets as regular data packets.   For example, let's consider a fiber cut between T-PE 1 and LSR 2 in   the reference network of Figure 5.  Assuming that all of the MEGs   described in Figure 5 have proactive CC-V enabled, a LOC defect is   detected by the MEPs of Sec12 SMEG, LSP13 LMEG, PW1 PSMEG, and PW1Z   PMEG; however, in a transport network, only the alarm associated to   the fiber cut needs to be reported to an NMS, while all secondary   alarms should be suppressed (i.e., not reported to the NMS or   reported as secondary alarms).   If the fiber cut is detected by the MEP in the physical layer (in LSR   2), LSR 2 can generate the proper alarm in the physical layer and   suppress the secondary alarm associated with the LOC defect detected   on Sec12 SMEG.  As both MEPs reside within the same node, this   process does not involve any external protocol exchange.  Otherwise,Busi & Allan                  Informational                    [Page 41]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   if the physical layer does not have enough OAM capabilities to detect   the fiber cut, the MEP of Sec12 SMEG in LSR 2 will report a LOC   alarm.   In both cases, the MEP of Sec12 SMEG in LSR 2 notifies the adaptation   function for LSP13 LMEG that then generates AIS packets on the LSP13   LMEG in order to allow its MEP in S-PE 3 to suppress the LOC alarm.   S-PE 3 can also suppress the secondary alarm on PW13 PSMEG because   the MEP of PW13 PSMEG resides within the same node as the MEP of   LSP13 LMEG.  The MEP of PW13 PSMEG in S-PE 3 also notifies the   adaptation function for PW1Z PMEG that then generates AIS packets on   PW1Z PMEG in order to allow its MEP in T-PE Z to suppress the LOC   alarm.   The generation of AIS packets for each MEG in the MPLS-TP client   (sub-)layer is configurable (i.e., the operator can enable/disable   the AIS generation).   The AIS condition is cleared if no AIS packet has been received in   3.5 times the AIS transmission period.   The AIS transmission period is traditionally one per second, but an   option to configure longer periods would be also desirable.  As a   consequence, OAM packets need to self-identify the transmission   period such that proper exit criteria can be established.   AIS packets are transmitted with the "minimum loss probability PHB"   within a single network operator.  For E-LSPs, this PHB is   configurable on network operator's basis, while for L-LSPs, this is   determined as perRFC 3270 [23].5.4.  Lock Reporting   The Lock Reporting function, as required inSection 2.2.7 of RFC 5860   [11], relies upon a Lock Report (LKR) packet used to suppress alarms   following administrative locking action in the server (sub-)layer.   When a server MEP is locked, the MPLS-TP client (sub-)layer   adaptation function generates packets with LKR information to allow   the suppression of secondary alarms at the MEPs in the client   (sub-)layer.  Again, it is assumed that there is a hold-off for any   loss of continuity alarms in the client-layer MEPs downstream of the   node originating the Lock Report.  In case of client (sub-)layer co-   routed bidirectional transport paths, the LKR information is sent on   both directions.  In case of client (sub-)layer unidirectional   transport paths, the LKR information is sent only in the downstream   direction.  As a consequence, in case of client (sub-)layer point-to-   multipoint transport paths, the LKR information is sent only to theBusi & Allan                  Informational                    [Page 42]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   MEPs that are downstream from the server (sub-)layer that has been   administratively locked.  Client (sub-)layer associated bidirectional   transport paths behave like co-routed bidirectional transport paths   if the server (sub-)layer that has been administratively locked is   used by both directions; otherwise, they behave like unidirectional   transport paths.   The generation of packets with LKR information starts immediately   when the server MEP is locked.  These periodic packets, with LKR   information, continue to be transmitted until the locked condition is   cleared.   Upon receiving a packet with LKR information, an MPLS-TP MEP enters   an LKR defect condition and suppresses the loss of continuity alarm   associated with its peer MEP but does not block traffic received from   the transport path.  A MEP resumes loss of continuity alarm   generation upon detecting loss of continuity defect conditions in the   absence of the LKR condition.   MIPs, as well as intermediate nodes, do not process the LKR   information; they forward these LKR OAM packets as regular data   packets.   For example, let's consider the case where the MPLS-TP Section   between T-PE 1 and LSR 2 in the reference network of Figure 5 is   administratively locked at LSR 2 (in both directions).   Assuming that all the MEGs described in Figure 5 have proactive CC-V   enabled, a LOC defect is detected by the MEPs of LSP13 LMEG, PW1   PSMEG, and PW1Z PMEG; however, in a transport network all these   secondary alarms should be suppressed (i.e., not reported to the NMS   or reported as secondary alarms).   The MEP of Sec12 SMEG in LSR 2 notifies the adaptation function for   LSP13 LMEG that then generates LKR packets on the LSP13 LMEG in order   to allow its MEPs in T-PE 1 and S-PE 3 to suppress the LOC alarm.   S-PE 3 can also suppress the secondary alarm on PW13 PSMEG because   the MEP of PW13 PSMEG resides within the same node as the MEP of   LSP13 LMEG.  The MEP of PW13 PSMEG in S-PE 3 also notifies the   adaptation function for PW1Z PMEG that then generates AIS packets on   PW1Z PMEG in order to allow its MEP in T-PE Z to suppress the LOC   alarm.   The generation of LKR packets for each MEG in the MPLS-TP client   (sub-)layer is configurable (i.e., the operator can enable/disable   the LKR generation).Busi & Allan                  Informational                    [Page 43]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   The locked condition is cleared if no LKR packet has been received   for 3.5 times the transmission period.   The LKR transmission period is traditionally one per second, but an   option to configure longer periods would be also desirable.  As a   consequence, OAM packets need to self-identify the transmission   period such that proper exit criteria can be established.   LKR packets are transmitted with the "minimum loss probability PHB"   within a single network operator.  For E-LSPs, this PHB is   configurable on network operator's basis, while for L-LSPs, this is   determined as perRFC 3270 [23].5.5.  Packet Loss Measurement   Packet Loss Measurement (LM) is one of the capabilities supported by   the MPLS-TP Performance Monitoring (PM) function in order to   facilitate reporting of Quality of Service (QoS) information for a   transport path as required inSection 2.2.11 of RFC 5860 [11].  LM is   used to exchange counter values for the number of ingress and egress   packets transmitted and received by the transport path monitored by a   pair of MEPs.   Proactive LM is performed by periodically sending LM OAM packets from   a MEP to a peer MEP and by receiving LM OAM packets from the peer MEP   (if a co-routed or associated bidirectional transport path) during   the lifetime of the transport path.  Each MEP performs measurements   of its transmitted and received user data packets.  These   measurements are then correlated in real time with the peer MEP in   the ME to derive the impact of packet loss on a number of performance   metrics for the ME in the MEG.  The LM transactions are issued such   that the OAM packets will experience the same PHB scheduling class as   the measured traffic while transiting between the MEPs in the ME.   For a MEP, near-end packet loss refers to packet loss associated with   incoming data packets (from the far-end MEP), while far-end packet   loss refers to packet loss associated with egress data packets   (towards the far-end MEP).   Proactive LM can be operated in two ways:   o  One-way: a MEP sends an LM OAM packet to its peer MEP containing      all the required information to facilitate near-end packet loss      measurements at the peer MEP.   o  Two-way: a MEP sends an LM OAM packet with an LM request to its      peer MEP, which replies with an LM OAM packet as an LM response.      The request/response LM OAM packets contain all the requiredBusi & Allan                  Informational                    [Page 44]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011      information to facilitate both near-end and far-end packet loss      measurements from the viewpoint of the originating MEP.   One-way LM is applicable to both unidirectional and bidirectional   (co-routed or associated) transport paths, while two-way LM is   applicable only to bidirectional (co-routed or associated) transport   paths.   MIPs, as well as intermediate nodes, do not process the LM   information; they forward these proactive LM OAM packets as regular   data packets.5.5.1.  Configuration Considerations   In order to support proactive LM, the transmission rate and, for   E-LSPs, the PHB class (associated with the LM OAM packets originating   from a MEP) need to be configured as part of the LM provisioning.  LM   OAM packets should be transmitted with the PHB that yields the lowest   drop precedence within the measured PHB Scheduling Class (seeRFC3260 [17]), in order to maximize reliability of measurement within   the traffic class.   If that PHB class is not an ordered aggregate where the ordering   constraint is all packets with the PHB class being delivered in   order, LM can produce inconsistent results.   Performance monitoring (e.g., LM) is only relevant when the transport   path is defect free.  CC-V contributes to the accuracy of PM   statistics by permitting the defect-free periods to be properly   distinguished.  Therefore, support of proactive LM has implications   on the CC-V transmission period (seeSection 5.1.3).5.5.2.  Sampling Skew   If an implementation makes use of a hardware forwarding path that   operates in parallel with an OAM processing path, whether hardware or   software based, the packet and byte counts may be skewed if one or   more packets can be processed before the OAM processing samples   counters.  If OAM is implemented in software, this error can be quite   large.5.5.3.  Multilink Issues   If multilink is used at the ingress or egress of a transport path,   there may not be a single packet-processing engine where an LM packet   can be injected or extracted as an atomic operation while having   accurate packet and byte counts associated with the packet.Busi & Allan                  Informational                    [Page 45]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   In the case where multilink is encountered along the route of the   transport path, the reordering of packets within the transport path   can cause inaccurate LM results.5.6.  Packet Delay Measurement   Packet Delay Measurement (DM) is one of the capabilities supported by   the MPLS-TP PM function in order to facilitate reporting of QoS   information for a transport path as required in Section 2.2.12 ofRFC5860 [11].  Specifically, proactive DM is used to measure the long-   term packet delay and packet delay variation in the transport path   monitored by a pair of MEPs.   Proactive DM is performed by sending periodic DM OAM packets from a   MEP to a peer MEP and by receiving DM OAM packets from the peer MEP   (if a co-routed or associated bidirectional transport path) during a   configurable time interval.   Proactive DM can be operated in two ways:   o  One-way: a MEP sends a DM OAM packet to its peer MEP containing      all the required information to facilitate one-way packet delay      and/or one-way packet delay variation measurements at the peer      MEP.  Note that this requires precise time synchronization at      either MEP by means outside the scope of this framework.   o  Two-way: a MEP sends a DM OAM packet with a DM request to its peer      MEP, which replies with a DM OAM packet as a DM response.  The      request/response DM OAM packets contain all the required      information to facilitate two-way packet delay and/or two-way      packet delay variation measurements from the viewpoint of the      originating MEP.   One-way DM is applicable to both unidirectional and bidirectional   (co-routed or associated) transport paths, while two-way DM is   applicable only to bidirectional (co-routed or associated) transport   paths.   MIPs, as well as intermediate nodes, do not process the DM   information; they forward these proactive DM OAM packets as regular   data packets.5.6.1.  Configuration Considerations   In order to support proactive DM, the transmission rate and, for   E-LSPs, the PHB (associated with the DM OAM packets originating from   a MEP) need to be configured as part of the DM provisioning.  DM OAM   packets should be transmitted with the PHB that yields the lowestBusi & Allan                  Informational                    [Page 46]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   drop precedence within the measured PHB Scheduling Class (seeRFC3260 [17]).   Performance monitoring (e.g., DM) is only relevant when the transport   path is defect free.  CC-V contributes to the accuracy of PM   statistics by permitting the defect-free periods to be properly   distinguished.  Therefore, support of proactive DM has implications   on the CC-V transmission period (seeSection 5.1.3).5.7.  Client Failure Indication   The Client Failure Indication (CFI) function, as required inSection2.2.10 of RFC 5860 [11], is used to help process client defects and   propagate a client signal defect condition from the process   associated with the local attachment circuit where the defect was   detected (typically the source adaptation function for the local   client interface).  It is propagated to the process associated with   the far-end attachment circuit (typically the source adaptation   function for the far-end client interface) for the same transmission   path, in case the client of the transport path does not support a   native defect/alarm indication mechanism, e.g., AIS.   A source MEP starts transmitting a CFI to its peer MEP when it   receives a local client signal defect notification via its local   client signal fail indication.  Mechanisms to detect local client   signal fail defects are technology specific.  Similarly, mechanisms   to determine when to cease originating client signal fail indication   are also technology specific.   A sink MEP that has received a CFI reports this condition to its   associated client process via its local CFI function.  Consequent   actions toward the client attachment circuit are technology specific.   There needs to be a 1:1 correspondence between the client and the   MEG; otherwise, when multiple clients are multiplexed over a   transport path, the CFI packet requires additional information to   permit the client instance to be identified.   MIPs, as well as intermediate nodes, do not process the CFI   information; they forward these proactive CFI OAM packets as regular   data packets.5.7.1.  Configuration Considerations   In order to support CFI indication, the CFI transmission rate and,   for E-LSPs, the PHB of the CFI OAM packets should be configured as   part of the CFI configuration.Busi & Allan                  Informational                    [Page 47]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20116.  OAM Functions for On-Demand Monitoring   In contrast to proactive monitoring, on-demand monitoring is   initiated manually and for a limited amount of time, usually for   operations such as diagnostics to investigate a defect condition.   On-demand monitoring covers a combination of "in-service" and "out-   of-service" monitoring functions.  The control and measurement   implications are:   1. A MEG can be directed to perform an "on-demand" functions at      arbitrary times in the lifetime of a transport path.   2. "Out-of-service" monitoring functions may require a priori      configuration of both MEPs and intermediate nodes in the MEG      (e.g., data-plane loopback) and the issuance of notifications into      client layers of the transport path being removed from service      (e.g., lock reporting)   3. The measurements resulting from "on-demand" monitoring are      typically harvested in real time, as they are frequently initiated      manually.  These do not necessarily require different harvesting      mechanisms than for harvesting proactive monitoring telemetry.   The functions that are exclusively out-of-service are those described   inSection 6.3.  The remainder are applicable to both in-service and   out-of-service transport paths.6.1.  Connectivity Verification   The on-demand connectivity verification function, as required inSection 2.2.3 of RFC 5860 [11], is a transaction that flows from the   originating MEP to a target MIP or MEP to verify the connectivity   between these points.   Use of on-demand CV is dependent on the existence of a bidirectional   ME or an associated return ME, or the availability of an out-of-band   return path, because it requires the ability for target MIPs and MEPs   to direct responses to the originating MEPs.   One possible use of on-demand CV would be to perform fault management   without using proactive CC-V, in order to preserve network resources,   e.g., bandwidth, processing time at switches.  In this case, network   management periodically invokes on-demand CV.Busi & Allan                  Informational                    [Page 48]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   An additional use of on-demand CV would be to detect and locate a   problem of connectivity when a problem is suspected or known to be   based on other tools.  In this case, the functionality will be   triggered by the network management in response to a status signal or   alarm indication.   On-demand CV is based upon generation of on-demand CV packets that   should uniquely identify the MEG that is being checked.  The on-   demand functionality may be used to check either an entire MEG (end-   to-end) or between the originating MEP and a specific MIP.  This   functionality may not be available for associated bidirectional   transport paths or unidirectional paths, as the MIP may not have a   return path to the originating MEP for the on-demand CV transaction.   When on-demand CV is invoked, the originating MEP issues a sequence   of on-demand CV packets that uniquely identifies the MEG being   verified.  The number of packets and their transmission rate should   be pre-configured at the originating MEP to take into account normal   packet-loss conditions.  The source MEP should use the mechanisms   defined in Sections3.3 and3.4 when sending an on-demand CV packet   to a target MEP or target MIP, respectively.  The target MEP/MIP   shall return a reply on-demand CV packet for each packet received.   If the expected number of on-demand CV reply packets is not received   at the originating MEP, this is an indication that a connectivity   problem may exist.   On-demand CV should have the ability to carry padding such that a   variety of MTU sizes can be originated to verify the MTU transport   capability of the transport path.   MIPs that are not targeted by on-demand CV packets, as well as   intermediate nodes, do not process the CV information; they forward   these on-demand CV OAM packets as regular data packets.6.1.1.  Configuration Considerations   For on-demand CV, the originating MEP should support the   configuration of the number of packets to be transmitted/received in   each sequence of transmissions and their packet size.   In addition, when the CV packet is used to check connectivity toward   a target MIP, the number of hops to reach the target MIP should be   configured.   For E-LSPs, the PHB of the on-demand CV packets should be configured   as well.  This permits the verification of correct operation of QoS   queuing as well as connectivity.Busi & Allan                  Informational                    [Page 49]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20116.2.  Packet Loss Measurement   On-demand Packet Loss Measurement (LM) is one of the capabilities   supported by the MPLS-TP Performance Monitoring function in order to   facilitate the diagnosis of QoS performance for a transport path, as   required inSection 2.2.11 of RFC 5860 [11].   On-demand LM is very similar to proactive LM described inSection5.5.  This section focuses on the differences between on-demand and   proactive LM.   On-demand LM is performed by periodically sending LM OAM packets from   a MEP to a peer MEP and by receiving LM OAM packets from the peer MEP   (if a co-routed or associated bidirectional transport path) during a   pre-defined monitoring period.  Each MEP performs measurements of its   transmitted and received user data packets.  These measurements are   then correlated to evaluate the packet-loss performance metrics of   the transport path.   Use of packet loss measurement in an out-of-service transport path   requires a traffic source such as a test device that can inject   synthetic traffic.6.2.1.  Configuration Considerations   In order to support on-demand LM, the beginning and duration of the   LM procedures, the transmission rate, and, for E-LSPs, the PHB class   (associated with the LM OAM packets originating from a MEP) must be   configured as part of the on-demand LM provisioning.  LM OAM packets   should be transmitted with the PHB that yields the lowest drop   precedence as described inSection 5.5.1.6.2.2.  Sampling Skew   The same considerations described inSection 5.5.2 for the proactive   LM are also applicable to on-demand LM implementations.6.2.3.  Multilink Issues   Multilink issues are as described inSection 5.5.3.6.3.  Diagnostic Tests   Diagnostic tests are tests performed on a MEG that has been taken out   of service.Busi & Allan                  Informational                    [Page 50]

RFC 6371         OAM Framework for MPLS-Based Transport   September 20116.3.1.  Throughput Estimation   Throughput estimation is an on-demand out-of-service function, as   required inSection 2.2.5 of RFC 5860 [11], that allows verifying the   bandwidth/throughput of an MPLS-TP transport path (LSP or PW) before   it is put in service.   Throughput estimation is performed between MEPs and between a MEP and   a MIP.  It can be performed in one-way or two-way modes.   According toRFC 2544 [12], this test is performed by sending OAM   test packets at increasing rates (up to the theoretical maximum),   computing the percentage of OAM test packets received, and reporting   the rate at which OAM test packets begin to drop.  In general, this   rate is dependent on the OAM test packet size.   When configured to perform such tests, a source MEP inserts OAM test   packets with a specified packet size and transmission pattern at a   rate to exercise the throughput.   The throughput test can create congestion within the network, thus   impacting other transport paths.  However, the test traffic should   comply with the traffic profile of the transport path under test, so   the impact of the test will not be worse than the impact caused by   the customers, whose traffic would be sent over that transport path,   sending the traffic at the maximum rate allowed by their traffic   profiles.  Therefore, throughput tests are not applicable to   transport paths that do not have a defined traffic profile, such as   LSPs in a context where statistical multiplexing is leveraged for   network capacity dimensioning.   For a one-way test, the remote sink MEP receives the OAM test packets   and calculates the packet loss.  For a two-way test, the remote MEP   loops the OAM test packets back to the original MEP, and the local   sink MEP calculates the packet loss.   It is worth noting that two-way throughput estimation is only   applicable to bidirectional (co-routed or associated) transport paths   and can only evaluate the minimum of available throughput of the two   directions.  In order to estimate the throughput of each direction   uniquely, two one-way throughput estimation sessions have to be set   up.  One-way throughput estimation requires coordination between the   transmitting and receiving test devices as described inSection 6 of   RFC 2544 [12].   It is also worth noting that if throughput estimation is performed on   transport paths that transit oversubscribed links, the test may not   produce comprehensive results if viewed in isolation because theBusi & Allan                  Informational                    [Page 51]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   impact of the test on the surrounding traffic needs to also be   considered.  Moreover, the estimation will only reflect the bandwidth   available at the moment when the measure is made.   MIPs that are not targeted by on-demand test OAM packets, as well as   intermediate nodes, do not process the throughput test information;   they forward these on-demand test OAM packets as regular data   packets.6.3.1.1.  Configuration Considerations   Throughput estimation is an out-of-service tool.  The diagnosed MEG   should be put into a locked state before the diagnostic test is   started.   A MEG can be put into a locked state either via an NMS action or   using the Lock Instruct OAM tool as defined inSection 7.   At the transmitting MEP, provisioning is required for a test signal   generator that is associated with the MEP.  At a receiving MEP,   provisioning is required for a test signal detector that is   associated with the MEP.   In order to ensure accurate measurement, care needs to be taken to   enable throughput estimation only if all the MEPs within the MEG can   process OAM test packets at the same rate as the payload data rates   (seeSection 6.3.1.2).6.3.1.2.  Limited OAM Processing Rate   If an implementation is able to process payload at much higher data   rates than OAM test packets, then accurate measurement of throughput   using OAM test packets is not achievable.  Whether OAM packets can be   processed at the same rate as payload is implementation dependent.6.3.1.3.  Multilink Considerations   If multilink is used, then it may not be possible to perform   throughput measurement, as the throughput test may not have a   mechanism for utilizing more than one component link of the   aggregated link.6.3.2.  Data-Plane Loopback   Data-plane loopback is an out-of-service function, as required inSection 2.2.5 of RFC 5860 [11].  This function consists in placing a   transport path, at either an intermediate or terminating node, into a   data-plane loopback state, such that all traffic (including bothBusi & Allan                  Informational                    [Page 52]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   payload and OAM) received on the looped back interface is sent on the   reverse direction of the transport path.  The traffic is looped back   unmodified except for normal per-hop processing such as TTL   decrement.   The data-plane loopback function requires that the MEG is locked such   that user data traffic is prevented from entering/exiting that MEG.   Instead, test traffic is inserted at the ingress of the MEG.  This   test traffic can be generated from an internal process residing   within the ingress node or injected by external test equipment   connected to the ingress node.   It is also normal to disable proactive monitoring of the path as the   MEP located upstream with respect to the node set in the data-plane   loopback mode will see all the OAM packets originated by itself, and   this may interfere with other measurements.   The only way to send an OAM packet (e.g., to remove the data-plane   loopback state) to the MIPs or MEPs hosted by a node set in the data-   plane loopback mode is via TTL expiry.  It should also be noted that   MIPs can be addressed with more than one TTL value on a co-routed   bidirectional path set into data-plane loopback.   If the loopback function is to be performed at an intermediate node,   it is only applicable to co-routed bidirectional paths.  If the   loopback is to be performed end to end, it is applicable to both co-   routed bidirectional and associated bidirectional paths.   It should be noted that data-plane loopback function itself is   applied to data-plane loopback points that can reside on different   interfaces from MIPs/MEPs.  Where a node implements data-plane   loopback capability and whether it implements it in more than one   point is implementation dependent.6.3.2.1.  Configuration Considerations   Data-plane loopback is an out-of-service tool.  The MEG that defines   a diagnosed transport path should be put into a locked state before   the diagnostic test is started.  However, a means is required to   permit the originated test traffic to be inserted at the ingress MEP   when data-plane loopback is performed.   A transport path, at either an intermediate or terminating node, can   be put into data-plane loopback state via an NMS action or using an   OAM tool for data-plane loopback configuration.Busi & Allan                  Informational                    [Page 53]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   If the data-plane loopback point is set somewhere at an intermediate   point of a co-routed bidirectional transport path, the side of the   loopback function (east/west side or both sides) needs to be   configured.6.4.  Route Tracing   It is often necessary to trace a route covered by a MEG from an   originating MEP to the peer MEP(s) including all the MIPs in between.   This may be conducted after provisioning an MPLS-TP transport path   for, e.g., troubleshooting purposes such as fault localization.   The route tracing function, as required inSection 2.2.4 of RFC 5860   [11], is providing this functionality.  Based on the fate-sharing   requirement of OAM flows, i.e., OAM packets receive the same   forwarding treatment as data packets, route tracing is a basic means   to perform connectivity verification and, to a much lesser degree,   continuity check.  For this function to work properly, a return path   must be present.   Route tracing might be implemented in different ways, and this   document does not preclude any of them.   Route tracing should always discover the full list of MIPs and of   peer MEPs.  In case a defect exists, the route tracing function will   only be able to trace up to the defect, and it needs to be able to   return the incomplete list of OAM entities that it was able to trace   so that the fault can be localized.6.4.1.  Configuration Considerations   The configuration of the route tracing function must at least support   the setting of the number of trace attempts before it gives up.6.5.  Packet Delay Measurement   Packet Delay Measurement (DM) is one of the capabilities supported by   the MPLS-TP PM function in order to facilitate reporting of QoS   information for a transport path, as required inSection 2.2.12 of   RFC 5860 [11].  Specifically, on-demand DM is used to measure packet   delay and packet delay variation in the transport path monitored by a   pair of MEPs during a pre-defined monitoring period.   On-demand DM is performed by sending periodic DM OAM packets from a   MEP to a peer MEP and by receiving DM OAM packets from the peer MEP   (if a co-routed or associated bidirectional transport path) during a   configurable time interval.Busi & Allan                  Informational                    [Page 54]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   On-demand DM can be operated in two modes:   o  One-way: a MEP sends a DM OAM packet to its peer MEP containing      all the required information to facilitate one-way packet delay      and/or one-way packet delay variation measurements at the peer      MEP.  Note that this requires precise time synchronization at      either MEP by means outside the scope of this framework.   o  Two-way: a MEP sends a DM OAM packet with a DM request to its peer      MEP, which replies with a DM OAM packet as a DM response.  The      request/response DM OAM packets contain all the required      information to facilitate two-way packet delay and/or two-way      packet delay variation measurements from the viewpoint of the      originating MEP.   MIPs, as well as intermediate nodes, do not process the DM   information; they forward these on-demand DM OAM packets as regular   data packets.6.5.1.  Configuration Considerations   In order to support on-demand DM, the beginning and duration of the   DM procedures, the transmission rate and, for E-LSPs, the PHB   (associated with the DM OAM packets originating from a MEP) need to   be configured as part of the DM provisioning.  DM OAM packets should   be transmitted with the PHB that yields the lowest drop precedence   within the measured PHB Scheduling Class (seeRFC 3260 [17]).   In order to verify different performances between long and short   packets (e.g., due to the processing time), it should be possible for   the operator to configure the packet size of the on-demand OAM DM   packet.7.  OAM Functions for Administration Control7.1.  Lock Instruct   The Lock Instruct (LKI) function, as required in Section 2.2.6 ofRFC5860 [11], is a command allowing a MEP to instruct the peer MEP(s) to   put the MPLS-TP transport path into a locked condition.   This function allows single-side provisioning for administratively   locking (and unlocking) an MPLS-TP transport path.   Note that it is also possible to administratively lock (and unlock)   an MPLS-TP transport path using two-side provisioning, where the NMS   administratively puts both MEPs into an administrative lock   condition.  In this case, the LKI function is not required/used.Busi & Allan                  Informational                    [Page 55]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   MIPs, as well as intermediate nodes, do not process the Lock Instruct   information; they forward these on-demand LKI OAM packets as regular   data packets.7.1.1.  Locking a Transport Path   A MEP, upon receiving a single-side administrative lock command from   an NMS, sends an LKI request OAM packet to its peer MEP(s).  It also   puts the MPLS-TP transport path into a locked state and notifies its   client (sub-)layer adaptation function upon the locked condition.   A MEP, upon receiving an LKI request from its peer MEP, can either   accept or reject the instruction and replies to the peer MEP with an   LKI reply OAM packet indicating whether or not it has accepted the   instruction.  This requires either an in-band or out-of-band return   path.  The LKI reply is needed to allow the MEP to properly report to   the NMS the actual result of the single-side administrative lock   command.   If the lock instruction has been accepted, it also puts the MPLS-TP   transport path into a locked state and notifies its client   (sub-)layer adaptation function upon the locked condition.   Note that if the client (sub-)layer is also MPLS-TP, Lock Report   (LKR) generation at the client MPLS-TP (sub-)layer is started, as   described inSection 5.4.7.1.2.  Unlocking a Transport Path   A MEP, upon receiving a single-side administrative unlock command   from NMS, sends an LKI removal request OAM packet to its peer MEP(s).   The peer MEP, upon receiving an LKI removal request, can either   accept or reject the removal instruction and replies with an LK   removal reply OAM packet indicating whether or not it has accepted   the instruction.  The LKI removal reply is needed to allow the MEP to   properly report to the NMS the actual result of the single-side   administrative unlock command.   If the lock removal instruction has been accepted, it also clears the   locked condition on the MPLS-TP transport path and notifies its   client (sub-)layer adaptation function of this event.   The MEP that has initiated the LKI clear procedure, upon receiving a   positive LKI removal reply, also clears the locked condition on the   MPLS-TP transport path and notifies this event to its client   (sub-)layer adaptation function.Busi & Allan                  Informational                    [Page 56]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   Note that if the client (sub-)layer is also MPLS-TP, Lock Report   (LKR) generation at the client MPLS-TP (sub-)layer is terminated, as   described inSection 5.4.8.  Security Considerations   A number of security considerations are important in the context of   OAM applications.   OAM traffic can reveal sensitive information, such as performance   data and details, about the current state of the network.  Insertion   or modification of OAM transactions can mask the true operational   state of the network, and in the case of transactions for   administration control, such as lock or data-plane loopback   instructions, these can be used for explicit denial-of-service   attacks.  The effect of such attacks is mitigated only by the fact   that, for in-band messaging, the managed entities whose state can be   masked is limited to those that transit the point of malicious access   to the network internals due to the fate-sharing nature of OAM   messaging.  This is not true when an out-of-band return path is   employed.   The sensitivity of OAM data therefore suggests that one solution is   that some form of authentication, authorization, and encryption is in   place.  This will prevent unauthorized access to vital equipment, and   it will prevent third parties from learning about sensitive   information about the transport network.  However, it should be   observed that the combination of the frequency of some OAM   transactions, the need for timeliness of OAM transaction exchange,   and all permutations of unique MEP to MEP, MEP to MIP, and   intermediate-system-originated transactions mitigates against the   practical establishment and maintenance of a large number of security   associations per MEG either in advance or as required.   For this reason, it is assumed that the internal links of the network   are physically secured from malicious access such that OAM   transactions scoped to fault and performance management of individual   MEGs are not encumbered with additional security.  Further, it is   assumed in multi-provider cases where OAM transactions originate   outside of an individual provider's trusted domain that filtering   mechanisms or further encapsulation will need to constrain the   potential impact of malicious transactions.  Mechanisms that the   framework does not specify might be subject to additional security   considerations.   In case of misconfiguration, some nodes can receive OAM packets that   they cannot recognize.  In such a case, these OAM packets should be   silently discarded in order to avoid malfunctions whose effects mayBusi & Allan                  Informational                    [Page 57]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   be similar to malicious attacks (e.g., degraded performance or even   failure).  Further considerations about data-plane attacks via G-ACh   are provided inRFC 5921 [8].9.  Acknowledgments   The authors would like to thank all members of the teams (the Joint   Working Team, the MPLS Interoperability Design Team in IETF, and the   Ad Hoc Group on MPLS-TP in ITU-T) involved in the definition and   specification of the MPLS Transport Profile.   The editors gratefully acknowledge the contributions of Adrian   Farrel, Yoshinori Koike, Luca Martini, Yuji Tochio, and Manuel Paul   for the definition of per-interface MIPs and MEPs.   The editors gratefully acknowledge the contributions of Malcolm   Betts, Yoshinori Koike, Xiao Min, and Maarten Vissers for the Lock   Report and Lock Instruct descriptions.   The authors would also like to thank Alessandro D'Alessandro, Loa   Andersson, Malcolm Betts, Dave Black, Stewart Bryant, Rui Costa,   Xuehui Dai, John Drake, Adrian Farrel, Dan Frost, Xia Liang, Liu   Gouman, Peng He, Russ Housley, Feng Huang, Su Hui, Yoshionori Koike,   Thomas Morin, George Swallow, Yuji Tochio, Curtis Villamizar, Maarten   Vissers, and Xuequin Wei for their comments and enhancements to the   text.10.  References10.1.  Normative References   [1]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label        Switching Architecture",RFC 3031, January 2001.   [2]  Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation Edge-        to-Edge (PWE3) Architecture",RFC 3985, March 2005.   [3]  Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire Virtual        Circuit Connectivity Verification (VCCV): A Control Channel for        Pseudowires",RFC 5085, December 2007.   [4]  Bocci, M. and S. Bryant, "An Architecture for Multi-Segment        Pseudowire Emulation Edge-to-Edge",RFC 5659, October 2009.   [5]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,        Sprecher, N., and S. Ueno, "Requirements of an MPLS Transport        Profile",RFC 5654, September 2009.Busi & Allan                  Informational                    [Page 58]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   [6]  Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in        Multi-Protocol Label Switching (MPLS) Networks",RFC 3443,        January 2003.   [7]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., "MPLS        Generic Associated Channel",RFC 5586, June 2009.   [8]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau, L., and        L. Berger, "A Framework for MPLS in Transport Networks",RFC5921, July 2010.   [9]  Bocci, M., Levrau, L., and D. Frost, "MPLS Transport Profile        User-to-Network and Network-to-Network Interfaces",RFC 6215,        April 2011.   [10] Frost, D., Ed., Bryant, S., Ed., and M. Bocci, Ed., "MPLS        Transport Profile Data Plane Architecture",RFC 5960, August        2010.   [11] Vigoureux, M., Ed., Ward, D., Ed., and M. Betts, Ed.,        "Requirements for Operations, Administration, and Maintenance        (OAM) in MPLS Transport Networks",RFC 5860, May 2010.   [12] Bradner, S. and J. McQuaid, "Benchmarking Methodology for        Network Interconnect Devices",RFC 2544, March 1999.   [13] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., and W.        Weiss, "An Architecture for Differentiated Service",RFC 2475,        December 1998.   [14] ITU-T Recommendation G.806 (01/09), "Characteristics of        transport equipment - Description methodology and generic        functionality", January 2009.10.2.  Informative References   [15] Sprecher, N. and L. Fang, "An Overview of the OAM Tool Set for        MPLS based Transport Networks", Work in Progress, June 2011.   [16] Nichols, K., Blake, S., Baker, F., and D. Black, "Definition of        the Differentiated Services Field (DS Field) in the IPv4 and        IPv6 Headers",RFC 2474, December 1998.   [17] Grossman, D., "New Terminology and Clarifications for Diffserv",RFC 3260, April 2002.   [18] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling in MPLS        Traffic Engineering (TE)",RFC 4201, October 2005.Busi & Allan                  Informational                    [Page 59]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   [19] ITU-T Recommendation G.707/Y.1322 (01/07), "Network node        interface for the synchronous digital hierarchy (SDH)", January        2007.   [20] ITU-T Recommendation G.805 (03/00), "Generic functional        architecture of transport networks", March 2000.   [21] ITU-T Recommendation Y.1731 (02/08), "OAM functions and        mechanisms for Ethernet based networks", February 2008.   [22] IEEE Standard 802.1AX-2008, "IEEE Standard for Local and        Metropolitan Area Networks - Link Aggregation", November 2008.   [23] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, P.,        Krishnan, R., Cheval, P., and J. Heinanen, "Multi-Protocol Label        Switching (MPLS) Support of Differentiated Services",RFC 3270,        May 2002.   [24] Bocci, M., Swallow, G., and E. Gray, "MPLS Transport Profile        (MPLS-TP) Identifiers",RFC 6370, September 2011.   [25] Winter, R., Ed., van Helvoort, H., and M. Betts, "MPLS-TP        Identifiers Following ITU-T Conventions", Work in Progress, July        2011.11.  Contributing Authors   Ben Niven-Jenkins   Velocix   EMail: ben@niven-jenkins.co.uk   Annamaria Fulignoli   Ericsson   EMail: annamaria.fulignoli@ericsson.com   Enrique Hernandez-Valencia   Alcatel-Lucent   EMail: Enrique.Hernandez@alcatel-lucent.comBusi & Allan                  Informational                    [Page 60]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011   Lieven Levrau   Alcatel-Lucent   EMail: Lieven.Levrau@alcatel-lucent.com   Vincenzo Sestito   Alcatel-Lucent   EMail: Vincenzo.Sestito@alcatel-lucent.com   Nurit Sprecher   Nokia Siemens Networks   EMail: nurit.sprecher@nsn.com   Huub van Helvoort   Huawei Technologies   EMail: hhelvoort@huawei.com   Martin Vigoureux   Alcatel-Lucent   EMail: Martin.Vigoureux@alcatel-lucent.com   Yaacov Weingarten   Nokia Siemens Networks   EMail: yaacov.weingarten@nsn.com   Rolf Winter   NEC   EMail: Rolf.Winter@nw.neclab.euBusi & Allan                  Informational                    [Page 61]

RFC 6371         OAM Framework for MPLS-Based Transport   September 2011Authors' Addresses   Dave Allan   Ericsson   EMail: david.i.allan@ericsson.com   Italo Busi   Alcatel-Lucent   EMail: Italo.Busi@alcatel-lucent.comBusi & Allan                  Informational                    [Page 62]