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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document doesn't use any RFC 2119 keywords, yet seems to have RFC 2119 boilerplate text. -- The document date (October 7, 2009) is 5314 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'ITU-T Y.1711' is mentioned on line 456, but not defined == Missing Reference: 'ITU-T Y.1731' is mentioned on line 733, but not defined Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Operations and Management Area Working Group T. Mizrahi 2 Internet Draft Marvell 3 Intended status: Informational October 7, 2009 4 Expires: April 2010 6 An Overview of 7 Operations, Administration, and Maintenance (OAM) Mechanisms 8 draft-mizrahi-opsawg-oam-overview-00.txt 10 Status of this Memo 12 This Internet-Draft is submitted to IETF in full conformance with the 13 provisions of BCP 78 and BCP 79. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as Internet- 18 Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six months 21 and may be updated, replaced, or obsoleted by other documents at any 22 time. It is inappropriate to use Internet-Drafts as reference 23 material or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt. 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 This Internet-Draft will expire on April 7, 2010. 33 Copyright Notice 35 Copyright (c) 2009 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents in effect on the date of 40 publication of this document (http://trustee.ietf.org/license-info). 41 Please review these documents carefully, as they describe your rights 42 and restrictions with respect to this document. 44 Abstract 46 Operations, Administration, and Maintenance (OAM) is a general term 47 that refers to detecting and reporting link failures. OAM mechanisms 48 have been defined for various layers in the protocol stack, and are 49 used with a variety of protocols. 51 This document presents an overview of the OAM mechanisms that have 52 been defined and are currently being defined by the IETF, as well as 53 a comparison to other OAM mechanisms that have been defined by the 54 IEEE and ITU-T. 56 Table of Contents 58 1. Introduction................................................3 59 2. Conventions used in this document............................5 60 3. Basic Terminology...........................................5 61 3.1. Abbreviations..........................................5 62 3.2. Terminology used in OAM Standards.......................6 63 3.2.1. General Terms......................................6 64 3.2.2. OAM Maintenance Entities...........................7 65 3.2.3. OAM Maintenance Points.............................7 66 3.2.4. OAM Link Failures..................................7 67 3.2.5. Summary of OAM Terms used in the Standards..........7 68 4. OAM Functions...............................................9 69 4.1. ICMP Ping..............................................9 70 4.2. Bidirectional Forwarding Detection (BFD)................9 71 4.2.1. Overview..........................................9 72 4.2.2. BFD Control........................................9 73 4.2.3. BFD Echo.........................................10 74 4.3. LSP Ping..............................................10 75 4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV)...10 76 4.5. ITU-T Y.1711..........................................10 77 4.5.1. Overview.........................................10 78 4.5.2. Connectivity Verification (CV)....................11 79 4.5.3. Fast Failure Detection (FFD)......................11 80 4.5.4. Forward Defect Indication (FDI)...................11 81 4.5.5. Backward Defect Indication (BDI)..................12 82 4.6. ITU-T Y.1731..........................................12 83 4.6.1. Overview.........................................12 84 4.6.2. ETH-CC...........................................12 85 4.6.3. ETH-LB...........................................13 86 4.6.4. ETH-TST..........................................13 87 4.6.5. ETH-LT...........................................13 88 4.6.6. ETH-AIS..........................................13 89 4.6.7. ETH-LCK..........................................14 90 4.6.8. ETH-RDI..........................................14 91 4.6.9. ETH-APS..........................................14 92 4.6.10. ETH-LM..........................................14 93 4.6.11. ETH-DM..........................................15 94 4.7. IEEE 802.1ag..........................................15 95 4.7.1. Overview.........................................15 96 4.7.2. Continuity Check..................................16 97 4.7.3. Loopback.........................................16 98 4.7.4. Linktrace........................................16 99 4.8. IEEE 802.3ah..........................................16 100 4.8.1. Overview.........................................16 101 4.8.2. Remote Failure Indication.........................16 102 4.8.3. Remote Loopback...................................16 103 4.8.4. Link Monitoring...................................16 104 4.9. MPLS-TP OAM...........................................16 105 4.9.1. Overview.........................................16 106 4.9.2. Continuity Checks.................................17 107 4.9.3. Connectivity Verification.........................17 108 4.9.4. Diagnostic Tests..................................17 109 4.9.5. Route Tracing.....................................17 110 4.9.6. Lock Instruct.....................................17 111 4.9.7. Lock Reporting....................................17 112 4.9.8. Alarm Reporting...................................17 113 4.9.9. Remote Defect Indication..........................18 114 4.9.10. Client Failure Indication........................18 115 4.9.11. Packet Loss Measurement..........................18 116 4.9.12. Packet Delay Measurement.........................18 117 4.10. Summary of OAM Functions..............................18 118 4.11. Summary of Unidirectional Connectivity Check Mechanisms19 119 5. Security Considerations.....................................20 120 6. IANA Considerations........................................20 121 7. Acknowledgments............................................20 122 8. References.................................................21 123 8.1. Normative References...................................21 124 8.2. Informative References.................................21 126 1. Introduction 128 OAM is a general term that refers to detecting and reporting link 129 failures and defects. The term OAM has been used over the years in 130 several different contexts, as discussed in [OAM Soup]. In the 131 context of this document OAM refers to Operations, Administration, 132 and Maintenance. OAM was originally used in the world of telephony, 133 and has been adopted in packet based networks. OAM mechanisms are 134 used in various layers in the protocol stack, and are applied to a 135 variety of different protocols. 137 The IETF has defined OAM for several protocols, and is currently 138 working on defining several new OAM protocols. These protocols are 139 listed below. 141 o MPLS LSP Ping, as defined in [LSP Ping] is an OAM mechanism for 142 point to point MPLS LSPs. The IETF is currently working on an 143 extension to the LSP Ping for point to multipoint MPLS - [P2MP 144 Ping]. 146 o Virtual Circuit Connectivity Check (VCCV) for Pseudowires, as 147 defined in [VCCV]. 149 o ICMP Echo request, also known as Ping, as defined in [ICMPv4], and 150 [ICMPv6]. ICMP Ping is a very simple and basic mechanism in 151 failure diagnosis, and is not typically associated with OAM, but 152 it is presented in this document for the sake of completeness, 153 since both LSP Ping and VCCV are to some extent based on ICMP 154 Ping. 156 o Bidirectional Forwarding Detection (BFD) is a family of standards 157 that are currently being defined by the IETF. BFD is intended to 158 be a generic OAM mechanism that can be used with various 159 encapsulation types, and in various medium types. 161 o OAM for MPLS-TP is currently being defined in the MPLS workgroup. 163 In addition to the OAM mechanisms defined by the IETF, the IEEE and 164 ITU-T have also defined various OAM mechanisms. These various 165 mechanisms defined by the three standard organizations are often 166 tightly coupled, and have had a mutual effect on each other. For 167 example, the emerging MPLS-TP OAM is in many ways based on [ITU-T 168 Y.1731]. The ITU-T and IETF have both defined OAM mechanisms for MPLS 169 LSPs, [ITU-T Y.1711] and [LSP Ping]. The following OAM standards by 170 the IEEE and ITU-T are to some extent linked to IETF OAM mechanisms 171 listed above, and are also discussed in this document: 173 o OAM mechanisms for Ethernet based networks have been defined by 174 both the ITU-T in [ITU-T Y.1731], and by the IEEE in [IEEE 175 802.1ag]. The IEEE 802.3 standard defines OAM for one-hop Ethernet 176 links [IEEE 802.3ah]. 178 o The ITU-T has defined OAM for MPLS LSPs in [ITU-T Y.1711]. 180 This document summarizes the OAM mechanisms defined in the standards 181 above. The focus is on OAM mechanisms defined by the IETF, compared 182 with the relevant OAM mechanisms defined by the ITU-T and IEEE. We 183 first present a comparison of the terminology used in various OAM 184 standards, and then summarize the OAM functions that each OAM 185 standard provides. 187 2. Conventions used in this document 189 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 190 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 191 document are to be interpreted as described in [KEYWORDS]. 193 3. Basic Terminology 195 3.1. Abbreviations 197 AIS Alarm Indication Signal 199 APS Automatic Protection Switching 201 BDI Backward Defect Indication 203 BFD Bidirectional Forwarding Detection 205 CC Continuity Check 207 CCM Continuity Check Message 209 CV Connectivity Verification 211 DM Delay Measurement 213 DTE Data Terminal Equipment 215 FDI Forward Defect Indication 217 FFD Fast Failure Detection 219 ICMP Internet Control Message Protocol 221 L2TP Layer Two Tunneling Protocol 223 LCCE L2TP Control Connection Endpoint 225 LM Loss Measurement 227 LSP Label Switching Path 229 LSR Label Switching Router 230 MA Maintenance Association 232 ME Maintenance Entity 234 MEG Maintenance Entity Group 236 MEP Maintenance End Point 238 MIP Maintenance Intermediate Point 240 MP Maintenance Point 242 MPLS Multiprotocol Label Switching 244 MPLS-TP MPLS Transport Profile 246 OAM Operations, Administration, and Maintenance 248 PE Provider Edge 250 PW Pseudowire 252 PWE3 Pseudowire Emulation Edge-to-Edge 254 RDI Remote Defect Indication 256 TTSI Trail Termination Source Identifier 258 VCCV Virtual Circuit Connectivity Verification 260 3.2. Terminology used in OAM Standards 262 3.2.1. General Terms 264 A wide variety of terms is used in various OAM standards. Each of the 265 OAM standards listed in the reference section includes a section that 266 defines the relevant terms. A thesaurus of terminology for MPLS-TP 267 terms is presented in [MPLS-TP Term], and provides a good summary of 268 some of the OAM related terminology. 270 This section presents a comparison of the terms used in various OAM 271 standards, without fully quoting the definition of each term. For a 272 formal definition of each term, refer to the references at the end of 273 this document. The comparison focuses on three basic terms, and is 274 summarized in section 3 ..2.5. 276 3.2.2. OAM Maintenance Entities 278 A Maintenance Entity (ME) can be either a point-to-point or a point- 279 to-multipoint relationship between two or more Maintenance Points. 280 The connectivity between these Maintenance Points is mangaged and 281 monitored by the OAM protocol. 283 The term Maintenance Entity (ME) is defined in ITU-T standards (e.g. 284 [ITU-T Y.1731]). Various terms are used to refer to an ME. For 285 example, in MPLS terminology, an ME is simply referred to as an LSP. 286 BFD does not explicitly use a term that is equivalent to ME, but 287 rather uses the term "session", referring to the relationship between 288 two nodes using a BFD protocol. 290 3.2.3. OAM Maintenance Points 292 A Maintenance Point (MP) is a node that uses an OAM protocol. A 293 Maintenance End Point (MEP) is one of the end points of an ME. A 294 Maintenance Intermediate Point (MIP) is a point between two MEPs, 295 that is able to respond to OAM frames, but does not initiate them. 297 The terms MEP and MIP are defined in ITU-T standards (e.g. [ITU-T 298 Y.1731]). The term Maintenance Point is a general term for MEPs and 299 MIPs, and is used in [IEEE 802.1ag]. 301 3.2.4. OAM Link Failures 303 The terms Failure, Fault, and Defect are intermittently used in the 304 standards. In some standards, such as [IEEE 802.1ag], there is no 305 distinction between these terms, while in other standards each of 306 these terms refers to a different type of malfunction. 308 The ITU-T distinguishes between these terms in [ITU-T G.806]. The 309 term Fault refers to an inability to perform a required action, e.g., 310 an unsuccessful attempt to deliver a packet. The term Defect refers 311 to an interruption in the normal operation, such as a consecutive 312 period of time where no packets are delivered successfully. The term 313 Failure refers to the termination of the required function. While a 314 Defect typically refers to a limited period of time, a failure refers 315 to a long period of time. 317 3.2.5. Summary of OAM Terms used in the Standards 319 Table 1 provides a comparison of the terminology used in different 320 OAM standards. 322 +-----------+-------------+-----------+----------------------------+ 323 | |Maintenance |Maintenance|Link Failure Terminology | 324 | |Point |Entity | | 325 | |Terminology |Terminology| | 326 +-----------+-------------+-----------+----------------------------+ 327 |ICMPv4 Ping|-Host | | | 328 | |-Gateway | | | 329 + --------- + ----------- + --------- + -------------------------- + 330 |ICMPv6 Ping| Node | | | 331 + --------- + ----------- + --------- + -------------------------- + 332 |BFD | System | Session |-Failure | 333 | | | |-Session is declared down | 334 + --------- + ----------- + --------- + -------------------------- + 335 |LSP Ping | LSR | LSP |-Failure | 336 | | | |-Fault = typically a local | 337 | | | | isolated failure | 338 + --------- + ----------- + --------- + -------------------------- + 339 |PW VCCV |-PE | PW |-Failure | 340 | |-LCCE | |-Fault | 341 + --------- + ----------- + --------- + -------------------------- + 342 |ITU-T | LSR | LSP |-Fault, Defect, Failure: as | 343 |Y.1711 | | | defined in [ITU-T G.806] | 344 + --------- + ----------- + --------- + -------------------------- + 345 |ITU-T |-MEP | ME |-Fault, Defect, Failure: as | 346 |Y.1731 |-MIP | | defined in [ITU-T G.806] | 347 | | | | | 348 + --------- + ----------- + --------- + -------------------------- + 349 |MPLS-TP |-End Point |-LSP |-Fault, Defect, Failure: as | 350 |OAM |-Intermediate|-PW | defined in [ITU-T G.806] | 351 | |Point |-Section | | 352 + --------- + ----------- + --------- + -------------------------- + 353 |IEEE |-MEP | ME |-Failure | 354 |802.1ag |-MIP | |-Fault | 355 | |-MP | |-Defect | 356 + --------- + ----------- + --------- + -------------------------- + 357 |IEEE | DTE | Link |-Failure | 358 |802.3ah | | |-Fault | 359 +-----------+-------------+-----------+----------------------------+ 360 Table 1 Summary of OAM Terms 362 4. OAM Functions 364 4.1. ICMP Ping 366 ICMP provides a bidirectional connectivity check for the Internet 367 Protocol. The originator transmits an echo request packet, and the 368 receiver replies with an echo reply. ICMP ping is defined in two 369 variants, [ICMPv4] is used for IPv4, and [ICMPv6] is used for IPv6. 371 4.2. Bidirectional Forwarding Detection (BFD) 373 4.2.1. Overview 375 While multiple OAM mechanisms have been defined for various protocols 376 in the protocol stack, Bidirectional Forwarding Detection (BFD), 377 currently being defined by the IETF [BFD], defines a generic OAM 378 mechanism that can be run over various encapsulating protocols, and 379 in various medium types. The IETF is working on defining variants of 380 the protocol for IP, for MPLS LSPs, and for PWE3. 382 BFD includes two main OAM functions, using two types of BFD packets: 383 BFD Control packets, and BFD Echo packets. 385 4.2.2. BFD Control 387 BFD supports a unidirectional connectivity check, using BFD control 388 packets. BFD control packets are be sent in one of two modes: 390 o Asynchronous mode: in this mode BFD control packets are sent 391 periodically. When the receiver detects that no BFD control packet 392 have been received during a predetermined period of time, a 393 failure is detected. 395 o Demand mode: in this mode, BFD control packets are sent on-demand. 396 Upon need, a system initiates a series of BFD control packets to 397 verify the link. BFD control packets are sent independently in 398 each direction of the link. 400 The transmission interval of BFD packets that are sent periodically, 401 is a result of negotiation between the two systems. Each BFD Control 402 packet includes the desired transmission interval, and the desired 403 reception interval, allowing the two systems to agree on common 404 intervals. 406 If no BFD Control packets are received during a fixed period of time 407 called the Detection Time, the session is declared to be down. The 408 detection time is a function of the negotiated transmission time, and 409 a parameter called Detect Mult. Detect Mult determines the number of 410 missing BFD Control packets that cause the session to be declared as 411 down. This parameter is included in the BFD Control packet. 413 The BFD Control packet also includes two fields that specify the 414 transmitting and receiving systems, called My Discriminator and Your 415 Discriminator, respectively. 417 4.2.3. BFD Echo 419 The echo function is a bidirectional connectivity check. A BFD echo 420 packet is sent to a peer system, and is looped back to the 421 originator. The echo function can be used proactively, or on-demand. 423 4.3. LSP Ping 425 The IETF defined an OAM mechanisms for MPLS LSPs in [LSP Ping]. LSP 426 ping is used to detect data plain failures in MPLS LSPs. The 427 transmitting LSR sends an echo request to a remote LSR, and in turn 428 receives an echo reply. LSP ping is used in one of two modes: 430 o "Ping" mode: In this mode LSP ping is used for end-to-end 431 connectivity verification between two LSRs. 433 o "Traceroute" mode: This mode is used for hop-by-hop fault 434 localization. 436 4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV) 438 VCCV, as defined in [VCCV], maintains the connectivity status of a 439 pseudowire. VCCV is supported for both MPLS PWs and L2TPv3 PWs. 441 VCCV supports two possible Connectivity Verification (CV) types, 442 i.e., two modes of operation: 444 o ICMP Ping: In this mode the CV is performed using an ICMP ping 445 packet format, as defined in [ICMPv4] or [ICMPv6]. 447 o LSP Ping: In this mode the LSP Ping packet format, as defined in 448 [LSP Ping] is used for CV. 450 4.5. ITU-T Y.1711 452 4.5.1. Overview 454 As mentioned above (4.3.), the IETF defined LSP Ping as an OAM 455 mechanism for MPLS. The ITU-T has also defined an OAM protocol for 456 MPLS, defined in [ITU-T Y.1711]. The standard defines mechanisms for 457 connectivity verification and fast failure detection, as well as 458 mechanism for reporting defects that have been identified in an LSP. 460 4.5.2. Connectivity Verification (CV) 462 The CV function is used to detect connectivity defects in an LSP. CV 463 frames are sent proactively at a rate of 1 per second. Each frame 464 contains the Trail-Termination Source Identifier (TTSI), indicating 465 the identity of the transmitting LSR. 467 The CV function can detect any of the following defect conditions. 469 o Loss of Connectivity Verification (LOCV): A loss of connectivity 470 is detected when no CV OAM packets are received in a period of 3 471 consecutive transmission periods. 473 o TTSI Mismatch: A TTSI mismatch is detected when a CV frame with an 474 unexpected TTSI is received. 476 o TTSI Mismerge: A TTSI mismerge is detected when the CV frames 477 received in a given LSP contain some frame with an expected TTSI, 478 and some frames with an unexpected TTSI. 480 o Excess: An excess is detected when at least 5 CV frames are 481 received during a period of 3 consecutive transmission periods. 483 4.5.3. Fast Failure Detection (FFD) 485 The FFD function is a proactive function, used for fast detection of 486 connectivity defects. While CV is typically sufficient for path 487 failure detection and reporting, protection switching mechanisms 488 typically require faster detection. FFD is very similar to CV in 489 terms of the packet format, and the possible defect conditions, but 490 FFD allows a configurable transmission frequency. The default 491 transmission rate of FFD frames is 20 per second, i.e., every 50 ms, 492 allowing fast detection for protection switching applications. 494 4.5.4. Forward Defect Indication (FDI) 496 The FDI function is used by an LSR to report a defect to affected 497 client layers, allowing them to suppress alarms about this defect. An 498 FDI packets are sent at a rate of 1 per second. 500 4.5.5. Backward Defect Indication (BDI) 502 The BDI function is used to inform the LSR at an LSP trail 503 termination source point about a defect condition in the forward 504 direction of an LSP. The LSR at the LSP trail termination sink point 505 transmits the BDI to the upstream LSR through the return path. BDI 506 packets are sent at the same transmission rate as FDI. 508 4.6. ITU-T Y.1731 510 4.6.1. Overview 512 The [ITU-T Y.1731] is a protocol for Ethernet OAM. It is presented in 513 this document as a reference point, since the OAM mechanisms that are 514 currently being defined by the IETF for MPLS-TP are in many ways 515 based on this standard. The standard defines various OAM functions, 516 including unidirectional and bidirectional continuity check, and 517 functions for performance monitoring. 519 4.6.2. ETH-CC 521 The Ethernet Continuity Check function is a proactive function that 522 allows a MEP to detect loss of continuity with any of the other MEPs 523 in the MEG. This function also allows detection of other defect 524 conditions, such as unintended connectivity between two MEGs. The 525 ETH-CC function is used for one of three possible applications: fault 526 management, performance monitoring (see 4.6.10.), and protection 527 switching. 529 Continuity Check Messages (CCM) are transmitted periodically at a 530 constant rate. There are 7 possible transmission periods, from 3.33 531 ms to 10 min. When the ETH-CC function detects a defect, it reports 532 one of the following defect conditions: 534 o Loss of continuity (LOC): Occurs when at least when no CCM 535 messages have been received from a peer MEP during a period of 3.5 536 times the configured transmission period. 538 o Unexpected MEG level: The MEG level is a 3-bit number that defines 539 the level of hierarchy of the MEG. This defect condition occurs 540 when a CCM is received from a peer MEP with a MEG level that is 541 lower than the expected MEG level. 543 o Mismerge: Occurs when a CCM is received from a peer MEP with an 544 unexpected MEG ID. 546 o Unexpected MEP: Occurs when a CCM is received from a peer MEP with 547 an unexpected transmitting MEP ID. 549 o Unexpected period: Occurs when the transmission period field in 550 the CCM does not match the expected transmission period value. 552 4.6.3. ETH-LB 554 The Ethernet loopback function verifies connectivity with a peer MEP 555 or MIP. The loopback function is performed on-demand, by sending a 556 loopback message (LBM) to the peer MEP or MIP. The peer node then 557 responds with a loopback reply (LBR). 559 More precisely, it is used for one of two purposes: 561 o Bidirectional connectivity test. 563 o Bidirectional in-service / out-of-service test. The in-service 564 mode refers to a test that is run under traffic, while the out-of- 565 service test requires other traffic to be halted. 567 4.6.4. ETH-TST 569 The test function is very similar to the loopback function, but is 570 unidirectional, i.e., the ETH-TST PDUs are terminated by the receiver 571 rather than being looped back to the sender. 573 4.6.5. ETH-LT 575 The Ethernet linktrace is an on-demand function that is used for path 576 discovery to a given target, or for locating a failure in a broken 577 path. 579 4.6.6. ETH-AIS 581 The Alarm Indication Signal indicates that a MEG should suppress 582 alarms about a defect condition at a lower MEG level, i.e., since a 583 defect has occurred in a lower hierarchy in the network, it should 584 not be reported by the current node. 586 A MEP that detects a failure periodically sends AIS messages to 587 higher hierarchies. AIS messages are sent periodically at a 588 recommended rate of 1 packet per second, until the defect condition 589 is resolved. 591 4.6.7. ETH-LCK 593 The lock function is used for administrative locking. A MEP can 594 initiate administrative locking, resulting in interruption of data, 595 e.g., for out-of-service ETH-LB or ETH-TST. 597 A MEP that initiates an administrative locking notifies its peer MEPs 598 to halt all relevant traffic until administrative/diagnostic 599 condition is removed. ETH-LCK frames are used to report to higher MEG 600 levels about the lock. The LCK frame, much like an AIS frame, 601 indicates to the receiving MEP that it should suppress alarms about 602 the locked link. 604 4.6.8. ETH-RDI 606 The Remote Defect Indication allows the sender to indicate that it 607 encountered a defect conditions. The receiving MEPs are then aware 608 that there is a defect condition in the MEG. 610 4.6.9. ETH-APS 612 The Y.1731 standard defines the frame format for Automatic Protection 613 Switching frames. The protection switching operations are defined in 614 other ITU-T standards. 616 4.6.10. ETH-LM 618 The loss measurement function allows a MEP to measure the packet loss 619 rate from/to a given MEP in the MEG. Each MEP maintains counters of 620 transmitted and received in-profile packets to/from each of its peer 621 MEPs. These counters are incorporated in the ETH-LM frames, allowing 622 the MEPs to compute the packet loss rate. 624 The ETH-LM function measures the far-end loss, referring to traffic 625 FROM the MEP to its peer, as well as the near-end loss, referring to 626 traffic from the peer MEP TO the local MEP. 628 ETH-LM is performed in one of two possible modes: 630 o Single-ended LM: in this mode loss measurement is performed on- 631 demand. The initiator sends an LM message (LMM) to its peer MEP, 632 and the peer responds with an LM reply (LMR). 634 o Dual-ended LM: in this mode loss measurement is performed 635 proactively. The continuity check message (CCM) is used for 636 proactive LM. The LM counters are piggy-backed into the CCM, and 637 allow proactive loss measurement. 639 4.6.11. ETH-DM 641 The delay measurement function is an on-demand function that allows a 642 MEP to measure the frame delay and frame delay variation to a peer 643 MEP. 645 ETH-DM can be performed in one of two modes of operation: 647 o One-way DM: in this mode, a MEP transmits a 1DM frame containing 648 the time of its transmission, TxTimeStampf. The receiving MEP 649 receives the 1DM frame and records the time of reception, RxTimef. 650 The receiving MEP can then compute the one-way delay by: RxTimef - 651 TxTimeStampf. 653 o Two-way DM: in this mode, a MEP transmits a delay measurement 654 message (DMM) containing its transmission time, TxTimeStampf. The 655 peer MEP receives the DMM and responds with a delay measurement 656 reply (DMR). Upon receiving the DMR, the initiating MEP records 657 the time of its reception, RxTimef, and computes the round trip 658 delay by: RxTimef - TxTimeStampf. 660 Each MEP maintains a time-of-day clock that is used for timestamping 661 delay measurement frames. It should be noted that in one-way DM it is 662 implicitly assumed that the clocks of the two peer MEPs are 663 synchronized by a time synchronization protocol. 665 4.7. IEEE 802.1ag 667 4.7.1. Overview 669 While the [ITU-T Y.1731] was defined in the ITU-T, the IEEE defined 670 the [IEEE 802.1ag] as a standard for connectivity fault management in 671 Ethernet based networks. While the two standards are to some extent 672 overlapping, they can also be viewed as two complementary parts of a 673 single Ethernet OAM picture. The two standards use a common packet 674 format. There are a few differences between the two standards in 675 terms of terminology: the term MEG level, used in Y.1731, as referred 676 to as Maintenance Domain level in 802.1ag; the Y.1731 standard uses 677 the term MEG, while the 802.1ag equivalent is Maintenance Association 678 (MA). 680 While Y.1731 defines multiple OAM functions (see section 4.6), the 681 802.1ag standard focuses on three main OAM functions: continuity 682 check, loopback, and linktrace, and defines them with great detail. 684 4.7.2. Continuity Check 686 See 4.6.2. 688 4.7.3. Loopback 690 See 4.6.3. 692 4.7.4. Linktrace 694 See 4.6.5. 696 4.8. IEEE 802.3ah 698 4.8.1. Overview 700 The [IEEE 802.3ah] defines an Ethernet link-layer OAM, for single-hop 701 Ethernet links. The OAM functions in this standard are described 702 below. 704 4.8.2. Remote Failure Indication 706 This function allows a node to notify a peer about a defect in the 707 receive path. Some physical interfaces allow unidirectional traffic, 708 where even if one direction of the link fails, the reverse direction 709 can still be used to convey the remote failure indication. 711 4.8.3. Remote Loopback 713 The remote loopback function provides a diagnostic mode that is used 714 to verify the link connectivity, and to measure the packet loss rate. 715 When a bridge interface is configured to loopback mode, all incoming 716 traffic through the interface is looped and sent back to the 717 originator. 719 4.8.4. Link Monitoring 721 Link monitoring provides an event notification function, allowing 722 peer devices to communicate defect conditions and diagnostic 723 information. 725 4.9. MPLS-TP OAM 727 4.9.1. Overview 729 The MPLS-TP is currently working on defining the OAM requirements and 730 mechanisms for MPLS-TP. The requirements of MPLS-TP OAM are defined 731 in [MPLS-TP OAM], and are described below. It is noted that these 732 requirements are in many ways similar to the requirement of Ethernet 733 OAM, as defined in [ITU-T Y.1731]. 735 4.9.2. Continuity Checks 737 The continuity check is a proactive function that allows an End Point 738 to determine whether or not it receives traffic from its peer End 739 Points. 741 4.9.3. Connectivity Verification 743 The connectivity verification is a function that allows an End Point 744 to verify its connectivity to a peer node. The connectivity check is 745 performed by sending a connectivity verification PDU to the peer 746 node, and receiving a reply within an expected time frame. This 747 function can be performed proactively or on-demand. 749 4.9.4. Diagnostic Tests 751 This function allows an End Point to perform an on-demand test, e.g., 752 for bandwidth measurement. 754 4.9.5. Route Tracing 756 This on-demand function is used for path discovery and for locating 757 link failures. 759 4.9.6. Lock Instruct 761 The lock instruct function allows an End Point to instruct its peers 762 to enter an administrative status where all traffic is halted except 763 the test traffic and OAM PDUs. 765 4.9.7. Lock Reporting 767 This function allows an Intermediate Point to report to an End Point 768 about a lock condition. 770 4.9.8. Alarm Reporting 772 This function allows an Intermediate Point to report to an End Point 773 about a defect condition. 775 4.9.9. Remote Defect Indication 777 This is a proactive function that allows the sender to indicate that 778 it encountered a defect conditions. 780 4.9.10. Client Failure Indication 782 This function allows the MPLS-TP network to relay information about a 783 fault condition in a client network, allowing the failure indication 784 to propagate from end to end over the MPLS-TP network. 786 4.9.11. Packet Loss Measurement 788 This function measures the packet loss ratio between two peer End 789 Points. It can be performed proactively or on-demand. 791 4.9.12. Packet Delay Measurement 793 This function measures the frame delay between two peer End Points. 794 Two modes of operation are supported, one-way DM, and two-way DM. 796 4.10. Summary of OAM Functions 798 Table 2 summarizes the OAM functions that are supported in each of 799 the standards that were analyzed in this section. 801 +-----------+-------+--------+--------+-----------+-------+--------+ 802 | Standard |Unidire|Bidirect|Path |Defect |Perform|Other | 803 | |ctional|ional |Discover|Indications|ance |Function| 804 | |Connect|Connecti|y | |Monitor|s | 805 | |ivity |vity | | |ing | | 806 | |Check |Check | | | | | 807 +-----------+-------+--------+--------+-----------+-------+--------+ 808 |ICMP Ping | | Echo | | | | | 809 + --------- + ----- + ------ + ------ + --------- + ----- + ------ + 810 |BFD |BFD |BFD | | | | | 811 | |Control|Echo | | | | | 812 + --------- + ----- + ------ + ------ + --------- + ----- + ------ + 813 |LSP Ping | |"Ping" |"Tracero| | | | 814 | | |mode |ute" | | | | 815 | | | |mode | | | | 816 + --------- + ----- + ------ + ------ + --------- + ----- + ------ + 817 |PW VCCV | |VCCV | | | | | 818 + --------- + ----- + ------ + ------ + --------- + ----- + ------ + 819 |ITU-T |-CV | | | | | | 820 |Y.1711 |-FFD | | | | | | 821 + --------- + ----- + ------ + ------ + --------- + ----- + ------ + 822 |ITU-T |ETH-CC |ETH-LB |ETH-LT |-ETH-RDI |-ETH-LM|-ETH-LCK| 823 |Y.1731 | | | |-ETH-AIS |-ETH-DM|-ETH-APS| 824 | | | | | | |-ETH-TST| 825 + --------- + ----- + ------ + ------ + --------- + ----- + ------ + 826 |IEEE |CC |Loopback|Linktrac| | | | 827 |802.1ag | | |e | | | | 828 + --------- + ----- + ------ + ------ + --------- + ----- + ------ + 829 |IEEE | |Remote | |-Remote | | | 830 |802.3ah | |Loopback| | Failure | | | 831 | | | | | Indication| | | 832 | | | | |-Link | | | 833 | | | | | Monitoring| | | 834 + --------- + ----- + ------ + ------ + --------- + ----- + ------ + 835 |MPLS-TP |CC |CV |Route |-Alarm |-LM |-Diagnos| 836 |OAM | | |Tracing | Reporting |-DM | tic Tes| 837 | | | | |-Client | | s | 838 | | | | | Failure | |-Lock | 839 | | | | | Indication| | | 840 | | | | |-Remote | | | 841 | | | | | Defect | | | 842 | | | | | Indication| | | 843 +-----------+-------+--------+--------+-----------+-------+--------+ 844 Table 2 Summary of OAM Functions 846 4.11. Summary of Unidirectional Connectivity Check Mechanisms 848 A key element in some of the OAM standards that are analyzed in this 849 document is the unidirectional connectivity check. It is thus 850 interesting to present a more detailed comparison of the connectivity 851 check mechanisms defined in OAM standards. Table 3 can be viewed as 852 an extension of Table 2, but is presented separately for convenience. 853 The table compares the OAM standards that support a unidirectional 854 connectivity check. MPLS-TP is not included in the comparison, as the 855 continuity check mechanism in MPLS-TP has not yet been defined. 857 The "Tx Interval" column in the table specifies the period between 858 two consequent message transmissions, while the "Source Identifier" 859 column specifies the name of the field in the OAM packet that is used 860 as the identifier of the transmitter. The "Error Codes" column 861 specifies the possible error codes when the unidirectional 862 connectivity check detects a failure. 864 +-----------+-------+--------+---+--------+------------------------+ 865 | |Mechani|Tx |UC/|Source | Error | 866 | |sm |Interval|MC |Identifi| Codes | 867 | | | | |er | | 868 +-----------+-------+--------+---+--------+------------------------+ 869 |BFD |BFD |Negotiat|UC |My Discr| Control Detection Time | 870 | |Control|ed durin| |iminator| Expired | 871 | | |g sessio| | | | 872 | | |n | | | | 873 + --------- + ----- + ------ + - + ------ + ---------------------- + 874 |ITU-T |CV |CV: 1s |UC |TTSI |-Loss of CV (LOCV) | 875 |Y.1711 |FFD |FFD: par| | |-TTSI Mismatch | 876 | | |ameter, | | |-TTSI Mismerge | 877 | | |default:| | |-Excess | 878 | | |50 ms | | | | 879 + --------- + ----- + ------ + - + ------ + ---------------------- + 880 |ITU-T |CC |7 possib|UC/|MEP ID |-Loss of Continuity(LOC)| 881 |Y.1731 / | |le perio|MC | |-Unexpected MEG level | 882 |IEEE | |ds: | | |-Mismerge | 883 |802.1ag | |3 1/3 ms| | |-Unexpected MEP | 884 | | |10 ms | | |-Unexpected period | 885 | | |100 ms | | | | 886 | | |1 s | | | | 887 | | |10 s | | | | 888 | | |1 min | | | | 889 | | |10 min | | | | 890 +-----------+-------+--------+---+--------+------------------------+ 891 Table 3 Summary of OAM Terms 893 5. Security Considerations 895 There are no security implications imposed by this document. 897 6. IANA Considerations 899 There are no new IANA considerations implied by this document. 901 7. Acknowledgments 903 This document was prepared using 2-Word-v2.0.template.dot. 905 8. References 907 8.1. Normative References 909 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 910 Requirement Levels", BCP 14, RFC 2119, March 1997. 912 [LSP Ping] Kompella, K., Swallow, G., "Detecting Multi-Protocol 913 Label Switched (MPLS) Data Plane Failures", RFC 4379, 914 February 2006. 916 [VCCV] Nadeau, T., Pignataro, C., "Pseudowire Virtual Circuit 917 Connectivity Verification (VCCV): A Control Channel 918 for Pseudowires", RFC 5085, December 2007. 920 [ICMPv4] Postel, J., "Internet Control Message Protocol", STD 5, 921 RFC 792, September 1981. 923 [ICMPv6] Conta, A., Deering, S., and M. Gupta, "Internet Control 924 Message Protocol (ICMPv6) for the Internet Protocol 925 Version 6 (IPv6) Specification", RFC 4443, March 2006. 927 [IEEE 802.1ag]"Connectivity Fault Management", December 2007. 929 [ITU-T Y.1731]"OAM Functions and Mechanisms for Ethernet-based 930 Networks", February 2008. 932 [ITU-T Y.1711]"Operation & Maintenance mechanism for MPLS networks", 933 February 2004. 935 [IEEE 802.3ah]"Media Access Control Parameters, Physical Layers, and 936 Management Parameters for Subscriber Access Networks", 937 clause 57, September 2004. 939 8.2. Informative References 941 [MPLS-TP OAM] Vigoureux, M., Ward, D., Betts, M., "Requirements for 942 OAM in MPLS Transport Networks", draft-ietf-mpls-tp- 943 oam-requirements, August 2009. 945 [BFD] Katz, D., Ward, D., "Bidirectional Forwarding 946 Detection", draft-ietf-bfd-base, February 2009. 948 [P2MP Ping] Farrel, A. , Yasukawa, S., "Detecting Data Plane 949 Failures in Point-to-Multipoint Multiprotocol Label 950 Switching (MPLS) - Extensions to LSP Ping", draft- 951 ietf-mpls-p2mp-lsp-ping, August 2009. 953 [OAM Soup] Betts, M., Van Helvoort, H., Bonica, R., Romascanu, D., 954 "The OAM Acronym Soup", draft-ietf-opsawg-mpls-tp-oam- 955 def, September 2009. 957 [ITU-T G.806] "Characteristics of transport equipment - Description 958 methodology and generic functionality", January 2009. 960 [MPLS-TP Term]Van Helvoort, H., Andersson, L., Sprecher, N., "A 961 Thesaurus for the Terminology used in Multiprotocol 962 Label Switching Transport Profile (MPLS-TP) 963 drafts/RFCs and ITU-T's Transport Network 964 Recommendations", draft-ietf-mpls-tp-rosetta-stone, 965 June 2009. 967 Authors' Addresses 969 Tal Mizrahi 970 Marvell 972 Email: talmi@marvell.com