Operations and Management Area Working Group T. Mizrahi Internet Draft Marvell Intended status: Informational October 7, 2009 Expires: April 2010 An Overview of Operations, Administration, and Maintenance (OAM) Mechanisms draft-mizrahi-opsawg-oam-overview-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 7, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Mizrahi Expires April 7, 2010 [Page 1] Internet-Draft Overview of OAM Mechanisms October 2009 Abstract Operations, Administration, and Maintenance (OAM) is a general term that refers to detecting and reporting link failures. OAM mechanisms have been defined for various layers in the protocol stack, and are used with a variety of protocols. This document presents an overview of the OAM mechanisms that have been defined and are currently being defined by the IETF, as well as a comparison to other OAM mechanisms that have been defined by the IEEE and ITU-T. Table of Contents 1. Introduction................................................3 2. Conventions used in this document............................5 3. Basic Terminology...........................................5 3.1. Abbreviations..........................................5 3.2. Terminology used in OAM Standards.......................6 3.2.1. General Terms......................................6 3.2.2. OAM Maintenance Entities...........................7 3.2.3. OAM Maintenance Points.............................7 3.2.4. OAM Link Failures..................................7 3.2.5. Summary of OAM Terms used in the Standards..........7 4. OAM Functions...............................................9 4.1. ICMP Ping..............................................9 4.2. Bidirectional Forwarding Detection (BFD)................9 4.2.1. Overview..........................................9 4.2.2. BFD Control........................................9 4.2.3. BFD Echo.........................................10 4.3. LSP Ping..............................................10 4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV)...10 4.5. ITU-T Y.1711..........................................10 4.5.1. Overview.........................................10 4.5.2. Connectivity Verification (CV)....................11 4.5.3. Fast Failure Detection (FFD)......................11 4.5.4. Forward Defect Indication (FDI)...................11 4.5.5. Backward Defect Indication (BDI)..................12 4.6. ITU-T Y.1731..........................................12 4.6.1. Overview.........................................12 4.6.2. ETH-CC...........................................12 4.6.3. ETH-LB...........................................13 4.6.4. ETH-TST..........................................13 4.6.5. ETH-LT...........................................13 4.6.6. ETH-AIS..........................................13 4.6.7. ETH-LCK..........................................14 Mizrahi Expires April 7, 2010 [Page 2] Internet-Draft Overview of OAM Mechanisms October 2009 4.6.8. ETH-RDI..........................................14 4.6.9. ETH-APS..........................................14 4.6.10. ETH-LM..........................................14 4.6.11. ETH-DM..........................................15 4.7. IEEE 802.1ag..........................................15 4.7.1. Overview.........................................15 4.7.2. Continuity Check..................................16 4.7.3. Loopback.........................................16 4.7.4. Linktrace........................................16 4.8. IEEE 802.3ah..........................................16 4.8.1. Overview.........................................16 4.8.2. Remote Failure Indication.........................16 4.8.3. Remote Loopback...................................16 4.8.4. Link Monitoring...................................16 4.9. MPLS-TP OAM...........................................16 4.9.1. Overview.........................................16 4.9.2. Continuity Checks.................................17 4.9.3. Connectivity Verification.........................17 4.9.4. Diagnostic Tests..................................17 4.9.5. Route Tracing.....................................17 4.9.6. Lock Instruct.....................................17 4.9.7. Lock Reporting....................................17 4.9.8. Alarm Reporting...................................17 4.9.9. Remote Defect Indication..........................18 4.9.10. Client Failure Indication........................18 4.9.11. Packet Loss Measurement..........................18 4.9.12. Packet Delay Measurement.........................18 4.10. Summary of OAM Functions..............................18 4.11. Summary of Unidirectional Connectivity Check Mechanisms19 5. Security Considerations.....................................20 6. IANA Considerations........................................20 7. Acknowledgments............................................20 8. References.................................................21 8.1. Normative References...................................21 8.2. Informative References.................................21 1. Introduction OAM is a general term that refers to detecting and reporting link failures and defects. The term OAM has been used over the years in several different contexts, as discussed in [OAM Soup]. In the context of this document OAM refers to Operations, Administration, and Maintenance. OAM was originally used in the world of telephony, and has been adopted in packet based networks. OAM mechanisms are used in various layers in the protocol stack, and are applied to a variety of different protocols. Mizrahi Expires April 7, 2010 [Page 3] Internet-Draft Overview of OAM Mechanisms October 2009 The IETF has defined OAM for several protocols, and is currently working on defining several new OAM protocols. These protocols are listed below. o MPLS LSP Ping, as defined in [LSP Ping] is an OAM mechanism for point to point MPLS LSPs. The IETF is currently working on an extension to the LSP Ping for point to multipoint MPLS - [P2MP Ping]. o Virtual Circuit Connectivity Check (VCCV) for Pseudowires, as defined in [VCCV]. o ICMP Echo request, also known as Ping, as defined in [ICMPv4], and [ICMPv6]. ICMP Ping is a very simple and basic mechanism in failure diagnosis, and is not typically associated with OAM, but it is presented in this document for the sake of completeness, since both LSP Ping and VCCV are to some extent based on ICMP Ping. o Bidirectional Forwarding Detection (BFD) is a family of standards that are currently being defined by the IETF. BFD is intended to be a generic OAM mechanism that can be used with various encapsulation types, and in various medium types. o OAM for MPLS-TP is currently being defined in the MPLS workgroup. In addition to the OAM mechanisms defined by the IETF, the IEEE and ITU-T have also defined various OAM mechanisms. These various mechanisms defined by the three standard organizations are often tightly coupled, and have had a mutual effect on each other. For example, the emerging MPLS-TP OAM is in many ways based on [ITU-T Y.1731]. The ITU-T and IETF have both defined OAM mechanisms for MPLS LSPs, [ITU-T Y.1711] and [LSP Ping]. The following OAM standards by the IEEE and ITU-T are to some extent linked to IETF OAM mechanisms listed above, and are also discussed in this document: o OAM mechanisms for Ethernet based networks have been defined by both the ITU-T in [ITU-T Y.1731], and by the IEEE in [IEEE 802.1ag]. The IEEE 802.3 standard defines OAM for one-hop Ethernet links [IEEE 802.3ah]. o The ITU-T has defined OAM for MPLS LSPs in [ITU-T Y.1711]. This document summarizes the OAM mechanisms defined in the standards above. The focus is on OAM mechanisms defined by the IETF, compared with the relevant OAM mechanisms defined by the ITU-T and IEEE. We first present a comparison of the terminology used in various OAM Mizrahi Expires April 7, 2010 [Page 4] Internet-Draft Overview of OAM Mechanisms October 2009 standards, and then summarize the OAM functions that each OAM standard provides. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [KEYWORDS]. 3. Basic Terminology 3.1. Abbreviations AIS Alarm Indication Signal APS Automatic Protection Switching BDI Backward Defect Indication BFD Bidirectional Forwarding Detection CC Continuity Check CCM Continuity Check Message CV Connectivity Verification DM Delay Measurement DTE Data Terminal Equipment FDI Forward Defect Indication FFD Fast Failure Detection ICMP Internet Control Message Protocol L2TP Layer Two Tunneling Protocol LCCE L2TP Control Connection Endpoint LM Loss Measurement LSP Label Switching Path LSR Label Switching Router Mizrahi Expires April 7, 2010 [Page 5] Internet-Draft Overview of OAM Mechanisms October 2009 MA Maintenance Association ME Maintenance Entity MEG Maintenance Entity Group MEP Maintenance End Point MIP Maintenance Intermediate Point MP Maintenance Point MPLS Multiprotocol Label Switching MPLS-TP MPLS Transport Profile OAM Operations, Administration, and Maintenance PE Provider Edge PW Pseudowire PWE3 Pseudowire Emulation Edge-to-Edge RDI Remote Defect Indication TTSI Trail Termination Source Identifier VCCV Virtual Circuit Connectivity Verification 3.2. Terminology used in OAM Standards 3.2.1. General Terms A wide variety of terms is used in various OAM standards. Each of the OAM standards listed in the reference section includes a section that defines the relevant terms. A thesaurus of terminology for MPLS-TP terms is presented in [MPLS-TP Term], and provides a good summary of some of the OAM related terminology. This section presents a comparison of the terms used in various OAM standards, without fully quoting the definition of each term. For a formal definition of each term, refer to the references at the end of this document. The comparison focuses on three basic terms, and is summarized in section 3 ..2.5. Mizrahi Expires April 7, 2010 [Page 6] Internet-Draft Overview of OAM Mechanisms October 2009 3.2.2. OAM Maintenance Entities A Maintenance Entity (ME) can be either a point-to-point or a point- to-multipoint relationship between two or more Maintenance Points. The connectivity between these Maintenance Points is mangaged and monitored by the OAM protocol. The term Maintenance Entity (ME) is defined in ITU-T standards (e.g. [ITU-T Y.1731]). Various terms are used to refer to an ME. For example, in MPLS terminology, an ME is simply referred to as an LSP. BFD does not explicitly use a term that is equivalent to ME, but rather uses the term "session", referring to the relationship between two nodes using a BFD protocol. 3.2.3. OAM Maintenance Points A Maintenance Point (MP) is a node that uses an OAM protocol. A Maintenance End Point (MEP) is one of the end points of an ME. A Maintenance Intermediate Point (MIP) is a point between two MEPs, that is able to respond to OAM frames, but does not initiate them. The terms MEP and MIP are defined in ITU-T standards (e.g. [ITU-T Y.1731]). The term Maintenance Point is a general term for MEPs and MIPs, and is used in [IEEE 802.1ag]. 3.2.4. OAM Link Failures The terms Failure, Fault, and Defect are intermittently used in the standards. In some standards, such as [IEEE 802.1ag], there is no distinction between these terms, while in other standards each of these terms refers to a different type of malfunction. The ITU-T distinguishes between these terms in [ITU-T G.806]. The term Fault refers to an inability to perform a required action, e.g., an unsuccessful attempt to deliver a packet. The term Defect refers to an interruption in the normal operation, such as a consecutive period of time where no packets are delivered successfully. The term Failure refers to the termination of the required function. While a Defect typically refers to a limited period of time, a failure refers to a long period of time. 3.2.5. Summary of OAM Terms used in the Standards Table 1 provides a comparison of the terminology used in different OAM standards. Mizrahi Expires April 7, 2010 [Page 7] Internet-Draft Overview of OAM Mechanisms October 2009 +-----------+-------------+-----------+----------------------------+ | |Maintenance |Maintenance|Link Failure Terminology | | |Point |Entity | | | |Terminology |Terminology| | +-----------+-------------+-----------+----------------------------+ |ICMPv4 Ping|-Host | | | | |-Gateway | | | + --------- + ----------- + --------- + -------------------------- + |ICMPv6 Ping| Node | | | + --------- + ----------- + --------- + -------------------------- + |BFD | System | Session |-Failure | | | | |-Session is declared down | + --------- + ----------- + --------- + -------------------------- + |LSP Ping | LSR | LSP |-Failure | | | | |-Fault = typically a local | | | | | isolated failure | + --------- + ----------- + --------- + -------------------------- + |PW VCCV |-PE | PW |-Failure | | |-LCCE | |-Fault | + --------- + ----------- + --------- + -------------------------- + |ITU-T | LSR | LSP |-Fault, Defect, Failure: as | |Y.1711 | | | defined in [ITU-T G.806] | + --------- + ----------- + --------- + -------------------------- + |ITU-T |-MEP | ME |-Fault, Defect, Failure: as | |Y.1731 |-MIP | | defined in [ITU-T G.806] | | | | | | + --------- + ----------- + --------- + -------------------------- + |MPLS-TP |-End Point |-LSP |-Fault, Defect, Failure: as | |OAM |-Intermediate|-PW | defined in [ITU-T G.806] | | |Point |-Section | | + --------- + ----------- + --------- + -------------------------- + |IEEE |-MEP | ME |-Failure | |802.1ag |-MIP | |-Fault | | |-MP | |-Defect | + --------- + ----------- + --------- + -------------------------- + |IEEE | DTE | Link |-Failure | |802.3ah | | |-Fault | +-----------+-------------+-----------+----------------------------+ Table 1 Summary of OAM Terms Mizrahi Expires April 7, 2010 [Page 8] Internet-Draft Overview of OAM Mechanisms October 2009 4. OAM Functions 4.1. ICMP Ping ICMP provides a bidirectional connectivity check for the Internet Protocol. The originator transmits an echo request packet, and the receiver replies with an echo reply. ICMP ping is defined in two variants, [ICMPv4] is used for IPv4, and [ICMPv6] is used for IPv6. 4.2. Bidirectional Forwarding Detection (BFD) 4.2.1. Overview While multiple OAM mechanisms have been defined for various protocols in the protocol stack, Bidirectional Forwarding Detection (BFD), currently being defined by the IETF [BFD], defines a generic OAM mechanism that can be run over various encapsulating protocols, and in various medium types. The IETF is working on defining variants of the protocol for IP, for MPLS LSPs, and for PWE3. BFD includes two main OAM functions, using two types of BFD packets: BFD Control packets, and BFD Echo packets. 4.2.2. BFD Control BFD supports a unidirectional connectivity check, using BFD control packets. BFD control packets are be sent in one of two modes: o Asynchronous mode: in this mode BFD control packets are sent periodically. When the receiver detects that no BFD control packet have been received during a predetermined period of time, a failure is detected. o Demand mode: in this mode, BFD control packets are sent on-demand. Upon need, a system initiates a series of BFD control packets to verify the link. BFD control packets are sent independently in each direction of the link. The transmission interval of BFD packets that are sent periodically, is a result of negotiation between the two systems. Each BFD Control packet includes the desired transmission interval, and the desired reception interval, allowing the two systems to agree on common intervals. If no BFD Control packets are received during a fixed period of time called the Detection Time, the session is declared to be down. The detection time is a function of the negotiated transmission time, and Mizrahi Expires April 7, 2010 [Page 9] Internet-Draft Overview of OAM Mechanisms October 2009 a parameter called Detect Mult. Detect Mult determines the number of missing BFD Control packets that cause the session to be declared as down. This parameter is included in the BFD Control packet. The BFD Control packet also includes two fields that specify the transmitting and receiving systems, called My Discriminator and Your Discriminator, respectively. 4.2.3. BFD Echo The echo function is a bidirectional connectivity check. A BFD echo packet is sent to a peer system, and is looped back to the originator. The echo function can be used proactively, or on-demand. 4.3. LSP Ping The IETF defined an OAM mechanisms for MPLS LSPs in [LSP Ping]. LSP ping is used to detect data plain failures in MPLS LSPs. The transmitting LSR sends an echo request to a remote LSR, and in turn receives an echo reply. LSP ping is used in one of two modes: o "Ping" mode: In this mode LSP ping is used for end-to-end connectivity verification between two LSRs. o "Traceroute" mode: This mode is used for hop-by-hop fault localization. 4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV) VCCV, as defined in [VCCV], maintains the connectivity status of a pseudowire. VCCV is supported for both MPLS PWs and L2TPv3 PWs. VCCV supports two possible Connectivity Verification (CV) types, i.e., two modes of operation: o ICMP Ping: In this mode the CV is performed using an ICMP ping packet format, as defined in [ICMPv4] or [ICMPv6]. o LSP Ping: In this mode the LSP Ping packet format, as defined in [LSP Ping] is used for CV. 4.5. ITU-T Y.1711 4.5.1. Overview As mentioned above (4.3.), the IETF defined LSP Ping as an OAM mechanism for MPLS. The ITU-T has also defined an OAM protocol for Mizrahi Expires April 7, 2010 [Page 10] Internet-Draft Overview of OAM Mechanisms October 2009 MPLS, defined in [ITU-T Y.1711]. The standard defines mechanisms for connectivity verification and fast failure detection, as well as mechanism for reporting defects that have been identified in an LSP. 4.5.2. Connectivity Verification (CV) The CV function is used to detect connectivity defects in an LSP. CV frames are sent proactively at a rate of 1 per second. Each frame contains the Trail-Termination Source Identifier (TTSI), indicating the identity of the transmitting LSR. The CV function can detect any of the following defect conditions. o Loss of Connectivity Verification (LOCV): A loss of connectivity is detected when no CV OAM packets are received in a period of 3 consecutive transmission periods. o TTSI Mismatch: A TTSI mismatch is detected when a CV frame with an unexpected TTSI is received. o TTSI Mismerge: A TTSI mismerge is detected when the CV frames received in a given LSP contain some frame with an expected TTSI, and some frames with an unexpected TTSI. o Excess: An excess is detected when at least 5 CV frames are received during a period of 3 consecutive transmission periods. 4.5.3. Fast Failure Detection (FFD) The FFD function is a proactive function, used for fast detection of connectivity defects. While CV is typically sufficient for path failure detection and reporting, protection switching mechanisms typically require faster detection. FFD is very similar to CV in terms of the packet format, and the possible defect conditions, but FFD allows a configurable transmission frequency. The default transmission rate of FFD frames is 20 per second, i.e., every 50 ms, allowing fast detection for protection switching applications. 4.5.4. Forward Defect Indication (FDI) The FDI function is used by an LSR to report a defect to affected client layers, allowing them to suppress alarms about this defect. An FDI packets are sent at a rate of 1 per second. Mizrahi Expires April 7, 2010 [Page 11] Internet-Draft Overview of OAM Mechanisms October 2009 4.5.5. Backward Defect Indication (BDI) The BDI function is used to inform the LSR at an LSP trail termination source point about a defect condition in the forward direction of an LSP. The LSR at the LSP trail termination sink point transmits the BDI to the upstream LSR through the return path. BDI packets are sent at the same transmission rate as FDI. 4.6. ITU-T Y.1731 4.6.1. Overview The [ITU-T Y.1731] is a protocol for Ethernet OAM. It is presented in this document as a reference point, since the OAM mechanisms that are currently being defined by the IETF for MPLS-TP are in many ways based on this standard. The standard defines various OAM functions, including unidirectional and bidirectional continuity check, and functions for performance monitoring. 4.6.2. ETH-CC The Ethernet Continuity Check function is a proactive function that allows a MEP to detect loss of continuity with any of the other MEPs in the MEG. This function also allows detection of other defect conditions, such as unintended connectivity between two MEGs. The ETH-CC function is used for one of three possible applications: fault management, performance monitoring (see 4.6.10.), and protection switching. Continuity Check Messages (CCM) are transmitted periodically at a constant rate. There are 7 possible transmission periods, from 3.33 ms to 10 min. When the ETH-CC function detects a defect, it reports one of the following defect conditions: o Loss of continuity (LOC): Occurs when at least when no CCM messages have been received from a peer MEP during a period of 3.5 times the configured transmission period. o Unexpected MEG level: The MEG level is a 3-bit number that defines the level of hierarchy of the MEG. This defect condition occurs when a CCM is received from a peer MEP with a MEG level that is lower than the expected MEG level. o Mismerge: Occurs when a CCM is received from a peer MEP with an unexpected MEG ID. Mizrahi Expires April 7, 2010 [Page 12] Internet-Draft Overview of OAM Mechanisms October 2009 o Unexpected MEP: Occurs when a CCM is received from a peer MEP with an unexpected transmitting MEP ID. o Unexpected period: Occurs when the transmission period field in the CCM does not match the expected transmission period value. 4.6.3. ETH-LB The Ethernet loopback function verifies connectivity with a peer MEP or MIP. The loopback function is performed on-demand, by sending a loopback message (LBM) to the peer MEP or MIP. The peer node then responds with a loopback reply (LBR). More precisely, it is used for one of two purposes: o Bidirectional connectivity test. o Bidirectional in-service / out-of-service test. The in-service mode refers to a test that is run under traffic, while the out-of- service test requires other traffic to be halted. 4.6.4. ETH-TST The test function is very similar to the loopback function, but is unidirectional, i.e., the ETH-TST PDUs are terminated by the receiver rather than being looped back to the sender. 4.6.5. ETH-LT The Ethernet linktrace is an on-demand function that is used for path discovery to a given target, or for locating a failure in a broken path. 4.6.6. ETH-AIS The Alarm Indication Signal indicates that a MEG should suppress alarms about a defect condition at a lower MEG level, i.e., since a defect has occurred in a lower hierarchy in the network, it should not be reported by the current node. A MEP that detects a failure periodically sends AIS messages to higher hierarchies. AIS messages are sent periodically at a recommended rate of 1 packet per second, until the defect condition is resolved. Mizrahi Expires April 7, 2010 [Page 13] Internet-Draft Overview of OAM Mechanisms October 2009 4.6.7. ETH-LCK The lock function is used for administrative locking. A MEP can initiate administrative locking, resulting in interruption of data, e.g., for out-of-service ETH-LB or ETH-TST. A MEP that initiates an administrative locking notifies its peer MEPs to halt all relevant traffic until administrative/diagnostic condition is removed. ETH-LCK frames are used to report to higher MEG levels about the lock. The LCK frame, much like an AIS frame, indicates to the receiving MEP that it should suppress alarms about the locked link. 4.6.8. ETH-RDI The Remote Defect Indication allows the sender to indicate that it encountered a defect conditions. The receiving MEPs are then aware that there is a defect condition in the MEG. 4.6.9. ETH-APS The Y.1731 standard defines the frame format for Automatic Protection Switching frames. The protection switching operations are defined in other ITU-T standards. 4.6.10. ETH-LM The loss measurement function allows a MEP to measure the packet loss rate from/to a given MEP in the MEG. Each MEP maintains counters of transmitted and received in-profile packets to/from each of its peer MEPs. These counters are incorporated in the ETH-LM frames, allowing the MEPs to compute the packet loss rate. The ETH-LM function measures the far-end loss, referring to traffic FROM the MEP to its peer, as well as the near-end loss, referring to traffic from the peer MEP TO the local MEP. ETH-LM is performed in one of two possible modes: o Single-ended LM: in this mode loss measurement is performed on- demand. The initiator sends an LM message (LMM) to its peer MEP, and the peer responds with an LM reply (LMR). o Dual-ended LM: in this mode loss measurement is performed proactively. The continuity check message (CCM) is used for proactive LM. The LM counters are piggy-backed into the CCM, and allow proactive loss measurement. Mizrahi Expires April 7, 2010 [Page 14] Internet-Draft Overview of OAM Mechanisms October 2009 4.6.11. ETH-DM The delay measurement function is an on-demand function that allows a MEP to measure the frame delay and frame delay variation to a peer MEP. ETH-DM can be performed in one of two modes of operation: o One-way DM: in this mode, a MEP transmits a 1DM frame containing the time of its transmission, TxTimeStampf. The receiving MEP receives the 1DM frame and records the time of reception, RxTimef. The receiving MEP can then compute the one-way delay by: RxTimef - TxTimeStampf. o Two-way DM: in this mode, a MEP transmits a delay measurement message (DMM) containing its transmission time, TxTimeStampf. The peer MEP receives the DMM and responds with a delay measurement reply (DMR). Upon receiving the DMR, the initiating MEP records the time of its reception, RxTimef, and computes the round trip delay by: RxTimef - TxTimeStampf. Each MEP maintains a time-of-day clock that is used for timestamping delay measurement frames. It should be noted that in one-way DM it is implicitly assumed that the clocks of the two peer MEPs are synchronized by a time synchronization protocol. 4.7. IEEE 802.1ag 4.7.1. Overview While the [ITU-T Y.1731] was defined in the ITU-T, the IEEE defined the [IEEE 802.1ag] as a standard for connectivity fault management in Ethernet based networks. While the two standards are to some extent overlapping, they can also be viewed as two complementary parts of a single Ethernet OAM picture. The two standards use a common packet format. There are a few differences between the two standards in terms of terminology: the term MEG level, used in Y.1731, as referred to as Maintenance Domain level in 802.1ag; the Y.1731 standard uses the term MEG, while the 802.1ag equivalent is Maintenance Association (MA). While Y.1731 defines multiple OAM functions (see section 4.6), the 802.1ag standard focuses on three main OAM functions: continuity check, loopback, and linktrace, and defines them with great detail. Mizrahi Expires April 7, 2010 [Page 15] Internet-Draft Overview of OAM Mechanisms October 2009 4.7.2. Continuity Check See 4.6.2. 4.7.3. Loopback See 4.6.3. 4.7.4. Linktrace See 4.6.5. 4.8. IEEE 802.3ah 4.8.1. Overview The [IEEE 802.3ah] defines an Ethernet link-layer OAM, for single-hop Ethernet links. The OAM functions in this standard are described below. 4.8.2. Remote Failure Indication This function allows a node to notify a peer about a defect in the receive path. Some physical interfaces allow unidirectional traffic, where even if one direction of the link fails, the reverse direction can still be used to convey the remote failure indication. 4.8.3. Remote Loopback The remote loopback function provides a diagnostic mode that is used to verify the link connectivity, and to measure the packet loss rate. When a bridge interface is configured to loopback mode, all incoming traffic through the interface is looped and sent back to the originator. 4.8.4. Link Monitoring Link monitoring provides an event notification function, allowing peer devices to communicate defect conditions and diagnostic information. 4.9. MPLS-TP OAM 4.9.1. Overview The MPLS-TP is currently working on defining the OAM requirements and mechanisms for MPLS-TP. The requirements of MPLS-TP OAM are defined Mizrahi Expires April 7, 2010 [Page 16] Internet-Draft Overview of OAM Mechanisms October 2009 in [MPLS-TP OAM], and are described below. It is noted that these requirements are in many ways similar to the requirement of Ethernet OAM, as defined in [ITU-T Y.1731]. 4.9.2. Continuity Checks The continuity check is a proactive function that allows an End Point to determine whether or not it receives traffic from its peer End Points. 4.9.3. Connectivity Verification The connectivity verification is a function that allows an End Point to verify its connectivity to a peer node. The connectivity check is performed by sending a connectivity verification PDU to the peer node, and receiving a reply within an expected time frame. This function can be performed proactively or on-demand. 4.9.4. Diagnostic Tests This function allows an End Point to perform an on-demand test, e.g., for bandwidth measurement. 4.9.5. Route Tracing This on-demand function is used for path discovery and for locating link failures. 4.9.6. Lock Instruct The lock instruct function allows an End Point to instruct its peers to enter an administrative status where all traffic is halted except the test traffic and OAM PDUs. 4.9.7. Lock Reporting This function allows an Intermediate Point to report to an End Point about a lock condition. 4.9.8. Alarm Reporting This function allows an Intermediate Point to report to an End Point about a defect condition. Mizrahi Expires April 7, 2010 [Page 17] Internet-Draft Overview of OAM Mechanisms October 2009 4.9.9. Remote Defect Indication This is a proactive function that allows the sender to indicate that it encountered a defect conditions. 4.9.10. Client Failure Indication This function allows the MPLS-TP network to relay information about a fault condition in a client network, allowing the failure indication to propagate from end to end over the MPLS-TP network. 4.9.11. Packet Loss Measurement This function measures the packet loss ratio between two peer End Points. It can be performed proactively or on-demand. 4.9.12. Packet Delay Measurement This function measures the frame delay between two peer End Points. Two modes of operation are supported, one-way DM, and two-way DM. 4.10. Summary of OAM Functions Table 2 summarizes the OAM functions that are supported in each of the standards that were analyzed in this section. +-----------+-------+--------+--------+-----------+-------+--------+ | Standard |Unidire|Bidirect|Path |Defect |Perform|Other | | |ctional|ional |Discover|Indications|ance |Function| | |Connect|Connecti|y | |Monitor|s | | |ivity |vity | | |ing | | | |Check |Check | | | | | +-----------+-------+--------+--------+-----------+-------+--------+ |ICMP Ping | | Echo | | | | | + --------- + ----- + ------ + ------ + --------- + ----- + ------ + |BFD |BFD |BFD | | | | | | |Control|Echo | | | | | + --------- + ----- + ------ + ------ + --------- + ----- + ------ + |LSP Ping | |"Ping" |"Tracero| | | | | | |mode |ute" | | | | | | | |mode | | | | + --------- + ----- + ------ + ------ + --------- + ----- + ------ + |PW VCCV | |VCCV | | | | | + --------- + ----- + ------ + ------ + --------- + ----- + ------ + Mizrahi Expires April 7, 2010 [Page 18] Internet-Draft Overview of OAM Mechanisms October 2009 |ITU-T |-CV | | | | | | |Y.1711 |-FFD | | | | | | + --------- + ----- + ------ + ------ + --------- + ----- + ------ + |ITU-T |ETH-CC |ETH-LB |ETH-LT |-ETH-RDI |-ETH-LM|-ETH-LCK| |Y.1731 | | | |-ETH-AIS |-ETH-DM|-ETH-APS| | | | | | | |-ETH-TST| + --------- + ----- + ------ + ------ + --------- + ----- + ------ + |IEEE |CC |Loopback|Linktrac| | | | |802.1ag | | |e | | | | + --------- + ----- + ------ + ------ + --------- + ----- + ------ + |IEEE | |Remote | |-Remote | | | |802.3ah | |Loopback| | Failure | | | | | | | | Indication| | | | | | | |-Link | | | | | | | | Monitoring| | | + --------- + ----- + ------ + ------ + --------- + ----- + ------ + |MPLS-TP |CC |CV |Route |-Alarm |-LM |-Diagnos| |OAM | | |Tracing | Reporting |-DM | tic Tes| | | | | |-Client | | s | | | | | | Failure | |-Lock | | | | | | Indication| | | | | | | |-Remote | | | | | | | | Defect | | | | | | | | Indication| | | +-----------+-------+--------+--------+-----------+-------+--------+ Table 2 Summary of OAM Functions 4.11. Summary of Unidirectional Connectivity Check Mechanisms A key element in some of the OAM standards that are analyzed in this document is the unidirectional connectivity check. It is thus interesting to present a more detailed comparison of the connectivity check mechanisms defined in OAM standards. Table 3 can be viewed as an extension of Table 2, but is presented separately for convenience. The table compares the OAM standards that support a unidirectional connectivity check. MPLS-TP is not included in the comparison, as the continuity check mechanism in MPLS-TP has not yet been defined. The "Tx Interval" column in the table specifies the period between two consequent message transmissions, while the "Source Identifier" column specifies the name of the field in the OAM packet that is used as the identifier of the transmitter. The "Error Codes" column Mizrahi Expires April 7, 2010 [Page 19] Internet-Draft Overview of OAM Mechanisms October 2009 specifies the possible error codes when the unidirectional connectivity check detects a failure. +-----------+-------+--------+---+--------+------------------------+ | |Mechani|Tx |UC/|Source | Error | | |sm |Interval|MC |Identifi| Codes | | | | | |er | | +-----------+-------+--------+---+--------+------------------------+ |BFD |BFD |Negotiat|UC |My Discr| Control Detection Time | | |Control|ed durin| |iminator| Expired | | | |g sessio| | | | | | |n | | | | + --------- + ----- + ------ + - + ------ + ---------------------- + |ITU-T |CV |CV: 1s |UC |TTSI |-Loss of CV (LOCV) | |Y.1711 |FFD |FFD: par| | |-TTSI Mismatch | | | |ameter, | | |-TTSI Mismerge | | | |default:| | |-Excess | | | |50 ms | | | | + --------- + ----- + ------ + - + ------ + ---------------------- + |ITU-T |CC |7 possib|UC/|MEP ID |-Loss of Continuity(LOC)| |Y.1731 / | |le perio|MC | |-Unexpected MEG level | |IEEE | |ds: | | |-Mismerge | |802.1ag | |3 1/3 ms| | |-Unexpected MEP | | | |10 ms | | |-Unexpected period | | | |100 ms | | | | | | |1 s | | | | | | |10 s | | | | | | |1 min | | | | | | |10 min | | | | +-----------+-------+--------+---+--------+------------------------+ Table 3 Summary of OAM Terms 5. Security Considerations There are no security implications imposed by this document. 6. IANA Considerations There are no new IANA considerations implied by this document. 7. Acknowledgments This document was prepared using 2-Word-v2.0.template.dot. Mizrahi Expires April 7, 2010 [Page 20] Internet-Draft Overview of OAM Mechanisms October 2009 8. References 8.1. Normative References [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [LSP Ping] Kompella, K., Swallow, G., "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, February 2006. [VCCV] Nadeau, T., Pignataro, C., "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", RFC 5085, December 2007. [ICMPv4] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981. [ICMPv6] Conta, A., Deering, S., and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 2006. [IEEE 802.1ag]"Connectivity Fault Management", December 2007. [ITU-T Y.1731]"OAM Functions and Mechanisms for Ethernet-based Networks", February 2008. [ITU-T Y.1711]"Operation & Maintenance mechanism for MPLS networks", February 2004. [IEEE 802.3ah]"Media Access Control Parameters, Physical Layers, and Management Parameters for Subscriber Access Networks", clause 57, September 2004. 8.2. Informative References [MPLS-TP OAM] Vigoureux, M., Ward, D., Betts, M., "Requirements for OAM in MPLS Transport Networks", draft-ietf-mpls-tp- oam-requirements, August 2009. [BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection", draft-ietf-bfd-base, February 2009. [P2MP Ping] Farrel, A. , Yasukawa, S., "Detecting Data Plane Failures in Point-to-Multipoint Multiprotocol Label Switching (MPLS) - Extensions to LSP Ping", draft- ietf-mpls-p2mp-lsp-ping, August 2009. Mizrahi Expires April 7, 2010 [Page 21] Internet-Draft Overview of OAM Mechanisms October 2009 [OAM Soup] Betts, M., Van Helvoort, H., Bonica, R., Romascanu, D., "The OAM Acronym Soup", draft-ietf-opsawg-mpls-tp-oam- def, September 2009. [ITU-T G.806] "Characteristics of transport equipment - Description methodology and generic functionality", January 2009. [MPLS-TP Term]Van Helvoort, H., Andersson, L., Sprecher, N., "A Thesaurus for the Terminology used in Multiprotocol Label Switching Transport Profile (MPLS-TP) drafts/RFCs and ITU-T's Transport Network Recommendations", draft-ietf-mpls-tp-rosetta-stone, June 2009. Authors' Addresses Tal Mizrahi Marvell Email: talmi@marvell.com Mizrahi Expires April 7, 2010 [Page 22]