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Busschbach 4 Intended status: Standards Track Alcatel-Lucent 5 Expires: September 8, 2010 M. Morrow 6 L. Martini 7 Cisco Systems, Inc. 8 Y(J). Stein 9 RAD Data Communications 10 D. Allan 11 Ericsson 12 T. Nadeau 13 BT 14 March 7, 2010 16 Pseudowire (PW) OAM Message Mapping 17 draft-ietf-pwe3-oam-msg-map-12.txt 19 Abstract 21 This document specifies the mapping and notification of defect states 22 between a pseudowire (PW) and the Attachment Circuits (ACs) of the 23 end-to-end emulated service. It standardizes the behavior of 24 Provider Edges (PEs) with respect to PW and AC defects. It addresses 25 ATM, frame relay, TDM, and SONET/SDH PW services, carried over MPLS, 26 MPLS/IP and L2TPV3/IP Packet Switched Networks (PSNs). 28 Status of this Memo 30 This Internet-Draft is submitted to IETF in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF), its areas, and its working groups. Note that 35 other groups may also distribute working documents as Internet- 36 Drafts. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 The list of current Internet-Drafts can be accessed at 44 http://www.ietf.org/ietf/1id-abstracts.txt. 46 The list of Internet-Draft Shadow Directories can be accessed at 47 http://www.ietf.org/shadow.html. 49 This Internet-Draft will expire on September 8, 2010. 51 Copyright Notice 53 Copyright (c) 2010 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the BSD License. 66 Table of Contents 68 1. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4 69 2. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 71 4. Abbreviations and Conventions . . . . . . . . . . . . . . . . 5 72 4.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5 73 4.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 5 74 5. Reference Model and Defect Locations . . . . . . . . . . . . . 7 75 6. Abstract Defect States . . . . . . . . . . . . . . . . . . . . 8 76 7. OAM Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 9 77 8. PW Defect States and Defect Notifications . . . . . . . . . . 11 78 8.1. PW Defect Notification Mechanisms . . . . . . . . . . . . 11 79 8.1.1. LDP Status TLV . . . . . . . . . . . . . . . . . . . . 12 80 8.1.2. L2TP Circuit Status AVP . . . . . . . . . . . . . . . 14 81 8.1.3. BFD Diagnostic Codes . . . . . . . . . . . . . . . . . 15 82 8.2. PW Defect State Entry/Exit . . . . . . . . . . . . . . . . 17 83 8.2.1. PW receive defect state entry/exit criteria . . . . . 17 84 8.2.2. PW transmit defect state entry/exit criteria . . . . . 18 85 9. Procedures for ATM PW Service . . . . . . . . . . . . . . . . 18 86 9.1. AC receive defect state entry/exit criteria . . . . . . . 18 87 9.2. AC transmit defect state entry/exit criteria . . . . . . . 19 88 9.3. Consequent Actions . . . . . . . . . . . . . . . . . . . . 20 89 9.3.1. PW receive defect state entry/exit . . . . . . . . . . 20 90 9.3.2. PW transmit defect state entry/exit . . . . . . . . . 20 91 9.3.3. PW defect state in ATM Port Mode PW Service . . . . . 20 92 9.3.4. AC receive defect state entry/exit . . . . . . . . . . 21 93 9.3.5. AC transmit defect state entry/exit . . . . . . . . . 22 94 10. Procedures for Frame Relay PW Service . . . . . . . . . . . . 22 95 10.1. AC receive defect state entry/exit criteria . . . . . . . 22 96 10.2. AC transmit defect state entry/exit criteria . . . . . . . 22 97 10.3. Consequent Actions . . . . . . . . . . . . . . . . . . . . 23 98 10.3.1. PW receive defect state entry/exit . . . . . . . . . . 23 99 10.3.2. PW transmit defect state entry/exit . . . . . . . . . 23 100 10.3.3. PW defect state in the FR Port Mode PW Service . . . . 24 101 10.3.4. AC receive defect state entry/exit . . . . . . . . . . 24 102 10.3.5. AC transmit defect state entry/exit . . . . . . . . . 24 103 11. Procedures for TDM PW Service . . . . . . . . . . . . . . . . 24 104 11.1. AC receive defect state entry/exit criteria . . . . . . . 25 105 11.2. AC transmit defect state entry/exit criteria . . . . . . . 25 106 11.3. Consequent Actions . . . . . . . . . . . . . . . . . . . . 25 107 11.3.1. PW receive defect state entry/exit . . . . . . . . . . 25 108 11.3.2. PW transmit defect state entry/exit . . . . . . . . . 26 109 11.3.3. AC receive defect state entry/exit . . . . . . . . . . 26 110 12. Procedures for CEP PW Service . . . . . . . . . . . . . . . . 26 111 12.1. Defect states . . . . . . . . . . . . . . . . . . . . . . 27 112 12.1.1. PW receive defect state entry/exit . . . . . . . . . . 27 113 12.1.2. PW transmit defect state entry/exit . . . . . . . . . 27 114 12.1.3. AC receive defect state entry/exit . . . . . . . . . . 27 115 12.1.4. AC receive defect state entry/exit . . . . . . . . . . 28 116 12.2. Consequent Actions . . . . . . . . . . . . . . . . . . . . 28 117 12.2.1. PW receive defect state entry/exit . . . . . . . . . . 28 118 12.2.2. PW transmit defect state entry/exit . . . . . . . . . 28 119 12.2.3. AC receive defect state entry/exit . . . . . . . . . . 28 120 13. Security Considerations . . . . . . . . . . . . . . . . . . . 29 121 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 122 Appendix A. Native Service Management (informative) . . . . . . . 30 123 A.1. Frame Relay Management . . . . . . . . . . . . . . . . . . 30 124 A.2. ATM Management . . . . . . . . . . . . . . . . . . . . . . 30 125 Appendix B. PW Defects and Detection tools . . . . . . . . . . . 32 126 B.1. PW Defects . . . . . . . . . . . . . . . . . . . . . . . . 32 127 B.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 32 128 B.3. PW Defect Detection Tools . . . . . . . . . . . . . . . . 32 129 B.4. PW specific defect detection mechanisms . . . . . . . . . 33 130 Appendix C. References . . . . . . . . . . . . . . . . . . . . . 34 131 C.1. Normative References . . . . . . . . . . . . . . . . . . . 34 132 C.2. Informative References . . . . . . . . . . . . . . . . . . 35 133 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 135 1. Acknowledgments 137 The editors would like to acknowledge the important contributions of 138 Hari Rakotoranto, Eric Rosen, Mark Townsley, Michel Khouderchah, 139 Bertrand Duvivier, Vanson Lim, Chris Metz, Ben Washam, Tiberiu 140 Grigoriu, Neil McGill, and Amir Maleki. 142 2. Contributors 144 Matthew Bocci, matthew.bocci@alcatel-lucent.co.uk 145 David Watkinson, david.watkinson@alcatel-lucent.com 146 Yuichi Ikejiri, y.ikejiri@ntt.com 147 Kenji Kumaki, kekumaki@kddi.com 148 Satoru Matsushima, satoru.matsushima@tm.softbank.co.jp 149 Himanshu Shah, hshah@ciena.com 150 Simon Delord, Simon.A.DeLord@team.telstra.com 151 Vasile Radoaca, vasile.radoaca@alcatel-lucent.com 152 Carlos Pignataro, cpignata@cisco.com 153 Teruyuki Oya, teruyuki.oya@tm.softbank.co.jp 155 3. Introduction 157 This document specifies the mapping and notification of defect states 158 between a Pseudowire and the Attachment Circuits (AC) of the end-to- 159 end emulated service. It covers the case whereby the ACs and the PWs 160 are of the same type in accordance to the PWE3 architecture [RFC3985] 161 such that a homogeneous PW service can be constructed. 163 This document is motivated by the requirements put forth in [RFC4377] 164 and [RFC3916]. Its objective is to standardize the behavior of PEs 165 with respect to defects on PWs and ACs, so that there is no ambiguity 166 about the alarms generated and consequent actions undertaken by PEs 167 in response to specific failure conditions. 169 This document addresses PWs over MPLS, MPLS/IP and L2TPV3/IP PSNs, 170 and ATM, frame relay, TDM, and SONET/SDH PW services. Due to its 171 unique characteristics, the Ethernet PW service is covered in a 172 separate document [ETH-OAM-IWK]. 174 4. Abbreviations and Conventions 176 4.1. Abbreviations 178 AAL5 ATM Adaptation Layer 5 179 AIS Alarm Indication Signal 180 AC Attachment Circuit 181 ATM Asynchronous Transfer Mode 182 AVP Attribute Value Pair 183 BDI Backward Defect Indication 184 BFD Bidirectional Forwarding Detection 185 CC Continuity Check 186 CDN Call Disconnect Notify 187 CE Customer Edge 188 CV Connectivity Verification 189 CPCS Common Part Convergence Sub-layer 190 DBA Dynamic Bandwidth Allocation 191 DLC Data Link Connection 192 FDI Forward Defect Indication 193 FR Frame Relay 194 FRBS Frame Relay Bearer Service 195 ICMP Internet Control Message Protocol 196 IWF Interworking Function 197 LB Loopback 198 LCCE L2TP Control Connection Endpoint 199 LDP Label Distribution Protocol 200 LSP label Switched Path 201 L2TP Layer 2 Tunneling Protocol 202 MPLS Multiprotocol Label Switching 203 NE Network Element 204 NS Native Service 205 OAM Operations, Administration and Maintenance 206 PE Provider Edge 207 PSN Packet Switched Network 208 PW Pseudowire 209 RDI Remote Defect Indication 210 PDU Protocol Data Unit 211 SDU Service Data Unit 212 TLV Type Length Value 213 VCC Virtual Channel Connection 214 VCCV Virtual Connection Connectivity Verification 215 VPC Virtual Path Connection 217 4.2. Conventions 219 The words "defect" and "fault" are used interchangeably to mean any 220 condition that obstructs forwarding of user traffic between the CE 221 endpoints of the PW service. 223 The words "defect notification" and "defect indication" are used 224 interchangeably to mean any OAM message generated by a PE and sent to 225 other nodes in the network to convey the defect state local to this 226 PE. 228 The PW can be carried over three types of Packet Switched Networks 229 (PSNs). An "MPLS PSN" makes use of MPLS Label Switched Paths [LSPs] 230 as the tunneling technology to forward the PW packets. An "MPLS/IP 231 PSN" makes use of MPLS-in-IP tunneling [RFC4023], with an MPLS shim 232 header used as PW demultiplexer. An "L2TPv3/IP PSN" makes use of 233 L2TPv3/IP [RFC3931] as the tunneling technology with the L2TPv3/IP 234 Session ID as the PW demultiplexer. 236 If LSP-Ping [RFC4379] is run over a PW as described in [RFC4377], it 237 will be referred to as "VCCV-Ping". If BFD is run over a PW as 238 described in [RFC4377], it will be referred to as "VCCV-BFD" [VCCV- 239 BFD]. 241 While PWs are inherently bidirectional entities, defects and OAM 242 messaging are related to a specific traffic direction. We use the 243 terms "upstream" and "downstream" to identify PEs in relation to the 244 traffic direction. A PE is upstream for the traffic it is forwarding 245 and is downstream for the traffic it is receiving. 247 We use the terms "local" and "remote" to identify native service 248 networks and ACs in relation to a specific PE. The local AC is 249 attached to the PE in question, while the remote AC is attached to 250 the PE at the other end of the PW. 252 A "transmit defect" is any defect that impacts traffic that is meant 253 to be sent or relayed by the observing PE. A "receive defect" is any 254 defect that impacts traffic that is meant to be received by the 255 observing PE. Note that a receive defect also impacts traffic meant 256 to be relayed, and thus can be considered to incorporate two defect 257 states. Thus when a PE enters both receive and transmit defect 258 states of a PW service, the receive defect takes precedence over the 259 transmit defect in terms of the consequent actions. 261 A "forward defect indication" (FDI) is sent in the same direction as 262 the user traffic impacted by the defect. A "reverse defect 263 indication" (RDI) is sent in the direction opposite to that of the 264 impacted traffic. 266 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 267 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 268 document are to be interpreted as described in [RFC2119]. 270 5. Reference Model and Defect Locations 272 Figure 1 illustrates the PWE3 network reference model with an 273 indication of the possible defect locations. This model will be 274 referenced in the remainder of this document for describing the OAM 275 procedures. 277 ACs PSN tunnel ACs 278 +----+ +----+ 279 +----+ | PE1|==================| PE2| +----+ 280 | |---(a)---(b)..(c)......PW1..(d)..(c)..(f)---(e)---| | 281 | CE1| (N1) | | | | (N2) |CE2 | 282 | |----------|............PW2.............|----------| | 283 +----+ | |==================| | +----+ 284 ^ +----+ +----+ ^ 285 | Provider Edge 1 Provider Edge 2 | 286 | | 287 |<-------------- Emulated Service ---------------->| 288 Customer Customer 289 Edge 1 Edge 2 291 Figure 1: PWE3 Network Defect Locations 293 The procedures will be described in this document from the viewpoint 294 of PE1, so that N1 is the local native service network and N2 is the 295 remote native service network. PE2 will typically implement the same 296 functionality. Note that PE1 is the upstream PE for traffic 297 originating in the local NS network N1, while it is the downstream PE 298 for traffic originating in the remote NS network N2. 300 The following is a brief description of the defect locations: 302 a. Defect in NS network N1. This covers any defect in network N1 303 that impacts all or some ACs attached to PE1, and is thus a local 304 AC defect. The defect is conveyed to PE1 and to NS network N2 305 using NS specific OAM defect indications. 306 b. Defect on a PE1 AC interface (another local AC defect). 307 c. Defect on a PE1 PSN interface. 308 d. Defect in the PSN network. This covers any defect in the PSN that 309 impacts all or some PWs between PE1 and PE2. The defect is 310 conveyed to the PE using a PSN and/or a PW specific OAM defect 311 indication. Note that both data plane defects and control plane 312 defects must be taken into consideration. Although control 313 messages may follow a different path than PW data plane traffic, a 314 control plane defect may affect the PW status. 316 e. Defect on a PE2 AC interface (a remote AC defect). 317 f. Defect in NS network N2 (another remote AC defect). This covers 318 any defect in N2 which impacts all or a subset of ACs attached to 319 PE2. The defect is conveyed to PE2 and to NS network N1 using the 320 NS OAM defect indication. 322 6. Abstract Defect States 324 PE1 must track four defect states that reflect the observed states of 325 both directions of the PW service on both the AC and the PW sides. 326 Defects may impact one or both directions of the PW service. 328 The observed state is a combination of defects directly detected by 329 PE1 and defects of which it has been made aware via notifications. 331 +-----+ 332 ----AC receive---->| |-----PW transmit----> 333 CE1 | PE1 | PE2/CE2 334 <---AC transmit----| |<----PW receive----- 335 +-----+ 336 (arrows indicate direction of user traffic impacted by a defect) 338 Figure 2: Receive and Transmit Defect States 340 PE1 will directly detect or be notified of AC receive or PW receive 341 defects as they occur upstream of PE1 and impact traffic being sent 342 to PE1. As a result, PE1 enters the AC or PW receive defect state. 344 In Figure 2, PE1 may be notified of a receive defect in the AC by 345 receiving a Forward Defect indication, e.g., ATM AIS, from CE1 or an 346 intervening network. This defect notification indicates that user 347 traffic sent by CE1 may not be received by PE1 due to a defect. PE1 348 can also directly detect an AC receive defect if it resulted from a 349 failure of the receive side in the local port or link over which the 350 AC is configured. 352 Similarly, PE1 may detect or be notified of a receive defect in the 353 PW by receiving a Forward Defect indication from PE2. If PW status 354 is used for fault notification, this message will indicate a Local 355 PSN-facing PW (egress) Transmit Fault or a Local AC (ingress) Receive 356 Fault at PE2, as described in Section 8.1.1. This defect 357 notification indicates that user traffic sent by CE2 may not be 358 received by PE1 due to a defect. As a result, PE1 enters the PW 359 receive defect state. 361 Note that a Forward Defect Indication is sent in the same direction 362 as the user traffic impacted by the defect. 364 Generally, a PE cannot detect transmit defects directly and will 365 therefore need to be notified of AC transmit or PW transmit defects 366 by other devices. 368 In Figure 2, PE1 may be notified of a transmit defect in the AC by 369 receiving a Reverse Defect indication, e.g., ATM RDI, from CE1. This 370 defect relates to the traffic sent by PE1 to CE1 on the AC. 372 Similarly, PE1 may be notified of a transmit defect in the PW by 373 receiving a Reverse Defect indication from PE2. If PW status is used 374 for fault notification, this message will indicate a Local PSN- 375 facing PW (ingress) Receive Fault or a Local Attachment Circuit 376 (egress) Transmit Fault at PE2, as described in Section 8.1.1. This 377 defect impacts the traffic sent by PE1 to CE2. As a result, PE1 378 enters the PW transmit defect state. 380 Note that a Reverse Defect indication is sent in the reverse 381 direction to the user traffic impacted by the defect. 383 The procedures outlined in this document define the entry and exit 384 criteria for each of the four states with respect to the set of PW 385 services within the document scope and the consequent actions that 386 PE1 must perform. 388 When a PE enters both receive and transmit defect states related to 389 the same PW service, then the receive defect takes precedence over 390 transmit defect in terms of the consequent actions. 392 7. OAM Modes 394 A homogeneous PW service forwards packets between an AC and a PW of 395 the same type. It thus implements both NS OAM and PW OAM mechanisms. 396 PW OAM defect notification messages are described in Section 8.1 NS 397 OAM messages are described in Appendix A. 399 This document defines two different OAM modes, the distinction being 400 the method of mapping between the NS and PW OAM defect notification 401 messages. 403 The first mode, illustrated in Figure 3, is called the "single 404 emulated OAM loop" mode. Here a single end-to-end NS OAM loop is 405 emulated by transparently passing NS OAM messages over the PW. Note 406 that the PW OAM is shown outside the PW in Figure 3, as it is 407 transported in LDP messages or in the associated channel, not inside 408 the PW itself. 410 +-----+ +-----+ 411 +-----+ | |=================| | +-----+ 412 | CE1 |-=NS-OAM=>| PE1 |----=NS-OAM=>----| PE2 |-=NS-OAM=>| CE2 | 413 +-----+ | |=================| | +-----+ 414 +-----+ +-----+ 415 \ / 416 -------=PW-OAM=>------- 418 Figure 3: Single Emulated OAM Loop mode 420 The single emulated OAM loop mode implements the following behavior: 422 a. The upstream PE (PE1) MUST transparently relay NS OAM messages 423 over the PW. 424 b. The upstream PE MUST signal local defects affecting the AC using a 425 NS defect notification message sent over the PW. In the case that 426 it is not possible to generate NS OAM messages (e.g., because the 427 defect interferes with NS OAM message generation) the PE MUST 428 signal local defects affecting the AC using a PW defect 429 notification message. 430 c. The upstream PE MUST signal local defects affecting the PW using a 431 PW defect notification message. 432 d. The downstream PE (PE2) MUST insert NS defect notification 433 messages into its local AC when it detects or is notified of a 434 defect in the PW or remote AC. This includes translating received 435 PW defect notification messages into NS defect notification 436 messages for defects signaled by the upstream PE. 438 The single emulated OAM loop mode is suitable for PW services that 439 have a widely deployed NS OAM mechanism. This document specifies the 440 use of this mode for ATM PW, TDM PW, and CEP PW services. It is the 441 default mode of operation for all ATM cell-mode PW services and the 442 only mode specified for CEP and SAToP/CESoPSN TDM PW services. It is 443 optional for AAL5 PDU transport and AAL5 SDU transport modes. 445 The second OAM mode operates three OAM loops joined at the AC/PW 446 boundaries of the PEs. This is referred to as the "coupled OAM 447 loops" mode and is illustrated in Figure 4. Note that in contrast to 448 Figure 3, NS OAM messages are never carried over the PW. 450 +-----+ +-----+ 451 +-----+ | |=================| | +-----+ 452 | CE1 |-=NS-OAM=>| PE1 | | PE2 |-=NS-OAM=>| CE2 | 453 +-----+ | |=================| | +-----+ 454 +-----+ +-----+ 455 \ / 456 -------=PW-OAM=>------- 458 Figure 4: Coupled OAM Loops mode 460 The coupled OAM loops mode implements the following behavior: 462 a. The upstream PE (PE1) MUST terminate and translate a received NS 463 defect notification message into a PW defect notification message. 464 b. The upstream PE MUST signal local failures affecting its local AC 465 using PW defect notification messages to the downstream PE. 466 c. The upstream PE MUST signal local failures affecting the PW using 467 PW defect notification messages. 468 d. The downstream PE (PE2) MUST insert NS defect notification 469 messages into the AC when it detects or is notified of defects in 470 the PW or remote AC. This includes translating received PW defect 471 notification messages into NS defect notification messages. 473 This document specifies the coupled OAM loops mode as the default 474 mode for the frame relay, ATM AAL5 PDU transport, and AAL5 SDU 475 transport services. It is an optional mode for ATM VCC cell mode 476 services. This mode is not specified for TDM, CEP, or ATM VPC cell 477 mode PW services. RFC5087 defines a similar but distinct mode, as 478 will be explained in Section 11 below. For the ATM VPC cell mode 479 case a pure coupled OAM loops mode is not possible as a PE MUST 480 transparently pass VC-level (F5) ATM OAM cells over the PW while 481 terminating and translating VP-level (F4) OAM cells. 483 8. PW Defect States and Defect Notifications 485 8.1. PW Defect Notification Mechanisms 487 For MPLS and MPLS/IP PSNs, a PE that establishes a PW using Label 488 Distribution Protocol [LDP] MUST use the LDP status TLV as the 489 mechanism for AC and PW status and defect notification, as explained 490 in [RFC4447]. Additionally, a PE MAY use VCCV-BFD Connectivity 491 Verification (CV) for fault detection only (CV types 0x04 and 0x10 492 [VCCV-BFD]) but SHOULD notify the remote PE using the LDP Status TLV. 494 A PE that establishes a PW using means other than LDP, e.g., by 495 static configuration or by use of BGP, MAY use VCCV-BFD CV (CV types 496 0x08 and 0x20 [VCCV-BFD]) for AC and PW status and defect 497 notification. Note that these CV types SHOULD NOT be used when the 498 PW is established with the LDP control plane. 500 For a L2TPV3/IP PSN, a PE SHOULD use the Circuit Status Attribute 501 Value Pair [AVP] as the mechanism for AC and PW status and defect 502 notification. In its most basic form, the Circuit Status AVP 503 [RFC3931] in a Set-Link-Info (SLI) message can signal active/inactive 504 AC status. The Circuit Status AVP as described in [RFC 5641] is 505 proposed to be extended to convey status and defects in the AC and 506 the PSN-facing PW in both ingress and egress directions, i.e., four 507 independent status bits, without the need to tear down the sessions 508 or control connection [L2TP-Status]. 510 When a PE does not support the Circuit Status AVP, it MAY use the 511 Stop-Control-Connection-Notification [StopCCN] and the Call- 512 Disconnect-Notify [CDN] messages to tear down L2TP sessions in a 513 fashion similar to LDP's use of Label Withdrawal to tear down a PW. 514 A PE may use the StopCCN to shutdown the L2TP control connection, and 515 implicitly all L2TP sessions associated with that control connection, 516 without any explicit session control messages. This is useful for 517 the case of a failure which impacts all L2TP sessions (i.e., all PWs) 518 managed by the control connection. It MAY use the CDN message to 519 disconnect a specific L2TP session when a failure affects a specific 520 PW. 522 Additionally, a PE MAY use VCCV-BFD CV types 0x04 and 0x10 for fault 523 detection only, but SHOULD notify the remote PE using the Circuit 524 Status AVP. A PE that establishes a PW using means other than the 525 L2TP control plane, e.g., by static configuration or by use of BGP, 526 MAY use VCCV-BFD CV types 0x08 and 0x20 for AC and PW status and 527 defect notification. These CV types SHOULD NOT be used when the PW 528 is established via the L2TP control plane. 530 The CV types are defined in Section 8.1.3 of this document. 532 8.1.1. LDP Status TLV 534 [RFC4446] defines the following PW status code points: 536 0x00000000 - Pseudowire forwarding (clear all failures) 537 0x00000001 - Pseudowire Not Forwarding 538 0x00000002 - Local Attachment Circuit (ingress) Receive Fault 539 0x00000004 - Local Attachment Circuit (egress) Transmit Fault 540 0x00000008 - Local PSN-facing PW (ingress) Receive Fault 541 0x00000010 - Local PSN-facing PW (egress) Transmit Fault 543 [RFC4447] specifies that "Pseudowire forwarding" code point is used 544 to clear all faults. It also specifies that "Pseudowire Not 545 Forwarding" code is used to convey any defect that cannot be 546 represented by the other code points. 548 The code points used in the LDP status TLV in a PW status 549 notification message conveys defects from the viewpoint of the 550 originating PE. The originating PE conveys this state in the form of 551 a forward defect or a reverse defect indication. 553 The forward and reverse defect indication definitions used in this 554 document map to the LDP Status TLV codes as follows: 556 Forward defect indication corresponds to the logical OR of: 557 * Local Attachment Circuit (ingress) Receive Fault, 558 * Local PSN-facing PW (egress) Transmit Fault, and 559 * PW Not Forwarding. 560 Reverse defect indication corresponds to the logical OR of: 561 * Local Attachment Circuit (egress) Transmit Fault and 562 * Local PSN-facing PW (ingress) Receive Fault. 564 A PE MUST use PW status notification messages to report all defects 565 affecting the PW service including, but not restricted, to the 566 following: 568 o defects detected through fault detection mechanisms in the MPLS 569 and MPLS/IP PSN, 570 o defects detected through VCCV-Ping or VCCV-BFD CV types 0x04 and 571 0x10 for fault detection only, 572 o defects within the PE that result in an inability to forward 573 traffic between the AC and the PW, 574 o defects of the AC or in the Layer 2 network affecting the AC as 575 per the rules detailed in Section 7 for the "single emulated OAM 576 loop" mode and "coupled OAM loops" modes. 578 Note that there are two situations that require PW label withdrawal 579 as opposed to a PW status notification by the PE. The first one is 580 when the PW is taken down administratively in accordance with 581 [RFC4447]. The second one is when the Target LDP session established 582 between the two PEs is lost. In the latter case, the PW labels will 583 need to be re-signaled when the Targeted LDP session is re- 584 established. 586 8.1.2. L2TP Circuit Status AVP 588 [RFC3931] defines the Circuit Status AVP in the Set-Link-Info (SLI) 589 message to exchange initial status and status changes in the circuit 590 to which the pseudowire is bound. [L2TP-Status] defines extensions 591 to the Circuit Status AVP that are analogous to the PW Status TLV 592 defined for LDP. Consequently, for L2TPv3/IP the Circuit Status AVP 593 is used in the same fashion as the PW Status described in the 594 previous section. Extended circuit status for L2TPv3/IP is described 595 in [RFC 5641]. 597 If the extended Circuit Status bits are not supported, and instead 598 only the "A-bit" (Active) is used as described in [RFC3931], a PE MAY 599 use CDN messages to clear L2TPv3/IP sessions in the presence of 600 session-level failures detected in the L2TPv3/IP PSN. 602 A PE MUST set the Active bit in the Circuit Status to clear all 603 faults, and it MUST clear the Active bit in the Circuit Status to 604 convey any defect that cannot be represented explicitly with specific 605 Circuit Status flags from [RFC3931] or [L2TP-Status]. 607 The forward and reverse defect indication definitions used in this 608 document map to the L2TP Circuit Status AVP as follows: 610 Forward defect indication corresponds to the logical OR of: 611 * Local Attachment Circuit (ingress) Receive Fault, 612 * Local PSN-facing PW (egress) Transmit Fault, and 613 * PW Not Forwarding. 614 Reverse defect indication corresponds to the logical OR of: 615 * Local Attachment Circuit (egress) Transmit Fault and 616 * Local PSN-facing PW (ingress) Receive Fault. 618 The status notification conveys defects from the viewpoint of the 619 originating LCCE (PE). 621 When the extended Circuit Status definition of [L2TP-Status] is 622 supported, a PE SHALL use the Circuit Status to report all failures 623 affecting the PW service including, but not restricted, to the 624 following: 626 o defects detected through defect detection mechanisms in the 627 L2TPV3/IP PSN, 628 o defects detected through VCCV-Ping or VCCV-BFD CV types 0x04 (BFD 629 IP/UDP-encapsulated, for PW Fault Detection only) and 0x10 (BFD 630 PW-ACH-encapsulated (without IP/UDP headers), for PW. Fault 631 Detection and AC/PW Fault Status Signaling) for fault detection 632 only which are described in Section 8.1.3 of this document, 634 o defects within the PE that result in an inability to forward 635 traffic between the AC and the PW, 636 o defects of the AC or in the L2 network affecting the AC as per the 637 rules detailed in Section 7 for the "single emulated OAM loop" 638 mode and the "coupled OAM loops" modes. 640 When the extended Circuit Status definition of [L2TP-Status] is not 641 supported, a PE SHALL use the A-bit in the Circuit Status AVP in SLI 642 to report: 644 o defects of the AC or in the L2 network affecting the AC as per the 645 rules detailed in Section 7 for the "single emulated OAM loop" 646 mode and the "coupled OAM loops" modes. 648 When the extended Circuit Status definition of [L2TP-Status] is not 649 supported, a PE MAY use the CDN and StopCCN messages in a similar way 650 to an MPLS PW label withdrawal to report: 652 o defects detected through defect detection mechanisms in the 653 L2TPV3/IP PSN (using StopCCN), 654 o defects detected through VCCV (pseudowire level) (using CDN), 655 o defects within the PE that result in an inability to forward 656 traffic between ACs and PW (using CDN). 658 For ATM L2TPv3/IP pseudowires, in addition to the Circuit Status AVP, 659 a PE MAY use the ATM Alarm Status AVP [RFC4454] to indicate the 660 reason for the ATM circuit status and the specific alarm type, if 661 any. This AVP is sent in the SLI message to indicate additional 662 information about the ATM circuit status. 664 L2TP control connections use Hello messages as a keep-alive facility. 665 It is important to note that if PSN failure is detected by keep-alive 666 timeout, the control connection is cleared. L2TP Hello messages are 667 sent in-band so as to follow the data plane with respect to the 668 source and destination addresses, IP protocol number and UDP port 669 (when UDP is used). 671 8.1.3. BFD Diagnostic Codes 673 [BFD] defines a set of diagnostic codes that partially overlap the 674 set of defects that can be communicated through LDP Status TLV or 675 L2TP Circuit Status AVP. This section describes the behavior of the 676 PEs with respect to using one or both of these methods for detecting 677 and propagating defect state. 679 In the case of an PW using LDP signaling, the PEs negotiate the use 680 of the VCCV capabilities during the label mapping messages exchange 681 used to establish the two directions of the PW. This is achieved by 682 including a capability TLV in the PW FEC interface parameters TLV. 683 In the L2TPV3/IP case, the PEs negotiate the use of VCCV during the 684 pseudowire session initialization using the VCCV AVP [RFC5085]. 686 The CV Type Indicators field in the OAM capability TLV or VCCV AVP 687 defines a bitmask used to indicate the specific OAM capabilities that 688 the PE can use over the PW being established. 690 A CV type of 0x04 or 0x10 [VCCV-BFD] indicates that BFD is used for 691 PW fault detection only. These CV types MAY be used any time the PW 692 is established using LDP or L2TP control planes. In this mode, only 693 the following diagnostic (Diag) codes specified in [BFD] will be 694 used: 696 0 - No diagnostic 697 1 - Control detection time expired 698 3 - Neighbor signaled session down 699 7 - Administratively Down 701 A PE MUST use diagnostic code 0 to indicate to its peer PE that is 702 correctly receiving BFD control messages. It MUST use diagnostic 703 code 1 to indicate that to its peer it has stopped receiving BFD 704 control messages and will thus declare the PW to be down in the 705 receive direction. It MUST use diagnostic code 3 to confirm to its 706 peer that the BFD session is going down after receiving diagnostic 707 code 1 from this peer. In this case, it will declare the PW to be 708 down in the transmit direction. A PE MUST use diagnostic code 7 to 709 bring down the BFD session when the PW is brought down 710 administratively. All other defects, such as AC/PW defects and PE 711 internal failures that prevent it from forwarding traffic, MUST be 712 communicated through the LDP Status TLV in the case of MPLS PSN or 713 MPLS/IP PSN, or through the appropriate L2TP codes in the Circuit 714 Status AVP in the case of L2TPV3/IP PSN. 716 A CV type of 0x08 or 0x20 in the OAM capabilities TLV indicates that 717 BFD is used for both PW fault detection and Fault Notification. In 718 addition to the above diagnostic codes, a PE uses the following codes 719 to signal AC defects and other defects impacting forwarding over the 720 PW service: 722 6 - Concatenated Path Down 723 8 - Reverse Concatenated Path Down 725 As specified in [RFC 5085], a PE negotiates the use of VCCV during PW 726 set-up. When a PW transported over an MPLS-PSN is established using 727 LDP, the PEs negotiate the use of the VCCV capabilities using the 728 optional VCCV Capability Advertisement Sub- TLV parameter in the 729 Interface Parameter Sub-TLV field of the LDP PW ID FEC or using an 730 Interface Parameters TLV of the LDP Generalized PW ID FEC. In the 731 case of L2TPv3/IP PSNs, the PEs negotiate the use of VCCV during the 732 pseudowire session initialization using VCCV AVP. 734 Note that a defect that causes the generation of the "PW not 735 forwarding code" (diagnostic code 6 or 8) does not necessarily result 736 in the BFD session going down. However, if the BFD session times 737 out, then diagnostic code 1 must be used since it signals a state 738 change of the BFD session itself. In general, when a BFD session 739 changes state, the PEs must use the state change diagnostic codes 0, 740 1, 3, and 7 in accordance to [BFD] and they MUST override any of the 741 AC/PW status diagnostic codes (codes 6 or 8) that may have been 742 signaled prior to the BFD session changing state. 744 The forward and reverse defect indications used in this document map 745 to the following BFD codes: 747 Forward defect indication corresponds to the logical OR of: 748 * Concatenated Path Down (BFD diagnostic code 06) 749 * Pseudowire Not Forwarding (PW status code 0x00000001). 750 Reverse defect indication- corresponds to: 751 * Reverse Concatenated Path Down (BFD diagnostic code 08). 753 These diagnostic codes are used to signal forward and reverse defect 754 states, respectively, when the PEs negotiated the use of BFD as the 755 mechanism for AC and PW fault detection and status signaling 756 notification. As stated in Section 8.1, these CV types SHOULD NOT be 757 used when the PW is established with the LDP or L2TP control plane. 759 8.2. PW Defect State Entry/Exit 761 8.2.1. PW receive defect state entry/exit criteria 763 PE1, as downstream PE, will enter the PW receive defect state if one 764 or more of the following occurs: 766 o It receives a Forward Defect Indication (FDI) from PE2 indicating 767 either a receive defect on the remote AC, or that PE2 detected or 768 was notified of downstream PW fault. 769 o It detects loss of connectivity on the PSN tunnel upstream of PE1 770 which affects the traffic it receives from PE2. 771 o It detects a loss of PW connectivity through VCCV-BFD or VCCV-PING 772 which affects the traffic it receives from PE2. 774 Note that if the PW control session (LDP session, the L2TP session, 775 or the L2TP control connection) between the PEs fails, the PW is torn 776 down and needs to be re-established. However, the consequent actions 777 towards the ACs are the same as if the PW entered the receive defect 778 state. 780 PE1 will exit the PW receive defect state when the following 781 conditions are met. Note that this may result in a transition to the 782 PW operational state or the PW transmit defect state. 784 o All previously detected defects have disappeared, and 785 o PE2 cleared the FDI, if applicable. 787 8.2.2. PW transmit defect state entry/exit criteria 789 PE1, as upstream PE, will enter the PW transmit defect state if the 790 following conditions occur: 792 o It receives a Reverse Defect Indication (RDI) from PE2 indicating 793 either a transmit fault on the remote AC, or that PE2 detected or 794 was notified of a upstream PW fault, and 795 o it is not already in the PW receive defect state. 797 PE1 will exit the transmit defect state if it receives an OAM message 798 from PE2 clearing the RDI, or it has entered the PW receive defect 799 state. 801 For a PWE3 over a L2TPV3/IP PSN using the basic Circuit Status AVP 802 [RFC3931], the PW transmit defect state is not valid and a PE can 803 only enter the PW receive defect state. 805 9. Procedures for ATM PW Service 807 Asynchronous Transfer Mode (ATM) Terminology is explained in Appendix 808 A.2 of this document. 810 9.1. AC receive defect state entry/exit criteria 812 When operating in the coupled OAM loops mode, PE1 enters the AC 813 receive defect state when any of the following conditions are met: 815 a. It detects or is notified of a physical layer fault on the ATM 816 interface. 817 b. It receives an end-to-end Flow 4 OAM [F4] Alarm Indication Signal 818 [AIS] AIS OAM flow on a Virtual Path [VP] AC, or an end-to-end 819 Flow 5 [F5] AIS OAM flow on a Virtual Circuit [VC] as per ITU-T 820 Recommendation I.610 [I.610 AC, indicating that the ATM VPC or VCC 821 is down in the adjacent Layer 2 ATM network. 823 c. It receives a segment F4 AIS OAM flow on a Virtual Path[VP] AC, or 824 a segment F5 AIS OAM flow on a VC AC, provided that the operator 825 has provisioned segment OAM and the PE is not a segment end-point. 826 d. It detects loss of connectivity on the ATM VPC/VCC while 827 terminating segment or end-to-end ATM continuity check (ATM CC) 828 cells with the local ATM network and CE. 830 When operating in the coupled OAM loops mode, PE1 exits the AC 831 Receive defect state when all previously detected defects have 832 disappeared. 834 When operating in the single emulated OAM loop mode, PE1 enters the 835 AC receive defect state if any of the following conditions are met: 837 a. It detects or is notified of a physical layer fault on the ATM 838 interface. 839 b. It detects loss of connectivity on the ATM VPC/VCC while 840 terminating segment ATM continuity check (ATM CC) cells with the 841 local ATM network and CE. 843 When operating in the single emulated OAM loop mode, PE1 exits the AC 844 receive defect state when all previously detected defects have 845 disappeared. 847 The exact conditions under which a PE enters and exits the AIS state, 848 or declares that connectivity is restored via ATM CC, are defined in 849 Section 9.2 of ITU-T Recommendation I.610 [I.610]. 851 9.2. AC transmit defect state entry/exit criteria 853 When operating in the coupled OAM loops mode, PE1 enters the AC 854 transmit defect state if any of the following conditions are met: 856 a. It terminates an end-to-end F4 RDI OAM flow, in the case of a VPC, 857 or an end-to-end F5 RDI OAM flow, in the case of a VCC, indicating 858 that the ATM VPC or VCC is down in the adjacent L2 ATM. 859 b. It receives a segment F4 RDI OAM flow on a VP AC, or a segment F5 860 RDI OAM flow on a VC AC, provided that the operator has 861 provisioned segment OAM and the PE is not a segment end-point. 863 PE1 exits the AC transmit defect state if the AC state transitions to 864 working or to the AC receive defect state. The exact conditions for 865 exiting the RDI state are described in Section 9.2 of ITU-T 866 Recommendation I.610 [I.610]. 868 Note that the AC transmit defect state is not valid when operating in 869 the single emulated OAM loop mode, as PE1 transparently forwards the 870 received RDI cells as user cells over the ATM PW to the remote CE. 872 9.3. Consequent Actions 874 In the remainder of this section, the text refers to AIS, RDI and CC 875 without specifying whether there is an F4 (VP-level) flow or an F5 876 (VC- level) flow, or whether it is an end-to-end or a segment flow. 877 Precise ATM OAM procedures for each type of flow are specified in 878 Section 9.2 of ITU-T Recommendation I.610 [I.610]. 880 9.3.1. PW receive defect state entry/exit 882 On entry to the PW receive defect state: 884 a. PE1 MUST commence AIS insertion into the corresponding AC. 885 b. PE1 MUST cease generation of CC cells on the corresponding AC, if 886 applicable. 887 c. If the PW defect was detected by PE1 without receiving FDI from 888 PE2, PE1 MUST assume PE2 has no knowledge of the defect and MUST 889 notify PE2 by sending RDI. 891 On exit from the PW receive defect state: 893 a. PE1 MUST cease AIS insertion into the corresponding AC. 894 b. PE1 MUST resume any CC cell generation on the corresponding AC, if 895 applicable. 896 c. PE1 MUST clear the RDI to PE2, if applicable. 898 9.3.2. PW transmit defect state entry/exit 900 On entry to the PW Transmit Defect State: 902 a. PE1 MUST commence RDI insertion into the corresponding AC. 903 b. If the PW failure was detected by PE1 without receiving an RDI 904 from PE2, PE1 MUST assume PE2 has no knowledge of the defect and 905 MUST notify PE2 by sending FDI. 907 On exit from the PW Transmit Defect State: 909 a. PE1 MUST cease RDI insertion into the corresponding AC. 910 b. PE1 MUST clear the FDI to PE2, if applicable. 912 9.3.3. PW defect state in ATM Port Mode PW Service 914 In case of transparent cell transport PW service, i.e., "port mode", 915 where the PE does not keep track of the status of individual ATM VPCs 916 or VCCs, a PE cannot relay PW defect state over these VCCs and VPCs. 917 If ATM CC is run on the VCCs and VPCs end-to-end (CE1 to CE2), or on 918 a segment originating and terminating in the ATM network and spanning 919 the PSN network, it will timeout and cause the CE or ATM switch to 920 enter the ATM AIS state. 922 9.3.4. AC receive defect state entry/exit 924 On entry to the AC receive defect state and when operating in the 925 coupled OAM loops mode: 927 a. PE1 MUST send FDI to PE2. 928 b. PE1 MUST commence insertion of ATM RDI cells into the AC towards 929 CE1. 931 When operating in the single emulated OAM loop mode, PE1 must be able 932 to support two options, subject to the operator's preference. The 933 default option is the following: 935 On entry to the AC receive defect state: 937 a. PE1 MUST transparently relay ATM AIS cells, or, in the case of a 938 local AC defect, commence insertion of ATM AIS cells into the 939 corresponding PW towards CE2. 940 b. If the defect interferes with NS OAM message generation, PE1 MUST 941 send an FDI indication to PE2. 942 c. PE1 MUST cease the generation of CC cells on the corresponding PW, 943 if applicable. 945 In certain operational models, for example in the case that the ATM 946 access network is owned by a different provider than the PW, an 947 operator may want to distinguish between defects detected in the ATM 948 access network and defects detected on the AC directly adjacent to 949 the PE. Therefore, the following option MUST also be supported: 951 a. PE1 MUST transparently relay ATM AIS cells over the corresponding 952 PW towards CE2. 953 b. Upon detection of a defect on the ATM interface on the PE or in 954 the PE itself, PE1 MUST send FDI to PE2. 955 c. PE1 MUST cease generation of CC cells on the corresponding PW, if 956 applicable. 958 On exit from the AC receive defect state and when operating in the 959 coupled OAM loops mode: 961 a. PE1 MUST clear the FDI to PE2. 962 b. PE1 MUST cease insertion of ATM RDI cells into the AC. 964 On exit from the AC receive defect state and when operating in the 965 single emulated OAM loop mode: 967 a. PE1 MUST cease insertion of ATM AIS cells into the corresponding 968 PW. 969 b. PE1 MUST clear the FDI to PE2, if applicable. 970 c. PE1 MUST resume any CC cell generation on the corresponding PW, if 971 applicable. 973 9.3.5. AC transmit defect state entry/exit 975 On entry to the AC transmit defect state and when operating in the 976 coupled OAM loops mode: 978 * PE1 MUST send RDI to PE2. 980 On exit from the AC transmit defect state and when operating in the 981 coupled OAM loops mode: 983 * PE1 MUST clear the RDI to PE2. 985 10. Procedures for Frame Relay PW Service 987 Frame Relay (FR) terminology is explained in Appendix A.1 of this 988 document. 990 10.1. AC receive defect state entry/exit criteria 992 PE1 enters the AC receive defect state if one or more of the 993 following conditions are met: 995 a. A Permanent Virtual Circuit (PVC) is not deleted from the FR 996 network and the FR network explicitly indicates in a full status 997 report (and optionally by the asynchronous status message) that 998 this PVC is inactive [Q.933]. In this case, this status maps 999 across the PE to the corresponding PW only. 1000 b. The Link Integrity Verification (LIV) indicates that the link from 1001 the PE to the Frame Relay network is down [Q.933]. In this case, 1002 the link down indication maps across the PE to all corresponding 1003 PWs. 1004 c. A physical layer alarm is detected on the FR interface. In this 1005 case, this status maps across the PE to all corresponding PWs. 1007 PE1 exits the AC receive defect state when all previously detected 1008 defects have disappeared. 1010 10.2. AC transmit defect state entry/exit criteria 1012 The AC transmit defect state is not valid for a FR AC. 1014 10.3. Consequent Actions 1016 10.3.1. PW receive defect state entry/exit 1018 The A (Active) bit indicates whether the FR PVC is ACTIVE (1) or 1019 INACTIVE (0) as explained in [RFC 4591]. 1021 On entry to the PW receive defect state: 1023 a. PE1 MUST clear the Active bit for the corresponding FR AC in a 1024 full status report, and optionally in an asynchronous status 1025 message, as per Q.933 Annex A [Q.933]. 1026 b. If the PW failure was detected by PE1 without receiving FDI from 1027 PE2, PE1 MUST assume PE2 has no knowledge of the defect and MUST 1028 notify PE2 by sending RDI. 1030 On exit from the PW receive defect state: 1032 a. PE1 MUST set the Active bit for the corresponding FR AC in a full 1033 status report, and optionally in an asynchronous status message, 1034 as per Q.933 annex A. PE1 does not apply this procedure on a 1035 transition from the PW receive defect state to the PW transmit 1036 defect state. 1037 b. PE1 MUST clear the RDI to PE2, if applicable. 1039 10.3.2. PW transmit defect state entry/exit 1041 On entry to the PW transmit defect state: 1043 a. PE1 MUST clear the Active bit for the corresponding FR AC in a 1044 full status report, and optionally in an asynchronous status 1045 message, as per Q.933 Annex A. 1046 b. If the PW failure was detected by PE1 without RDI from PE2, PE1 1047 MUST assume PE2 has no knowledge of the defect and MUST notify PE2 1048 by sending FDI. 1050 On exit from the PW transmit defect state: 1052 a. PE1 MUST set the Active bit for the corresponding FR AC in a full 1053 status report, and optionally in an asynchronous status message, 1054 as per Q.933 annex A. PE1 does not apply this procedure on a 1055 transition from the PW transmit defect state to the PW receive 1056 defect state. 1057 b. PE1 MUST clear the FDI to PE2, if applicable. 1059 10.3.3. PW defect state in the FR Port Mode PW Service 1061 In case of port mode PW service, STATUS ENQUIRY and STATUS messages 1062 are transported transparently over the PW. A PW Failure will 1063 therefore result in timeouts of the Q.933 link and PVC management 1064 protocol at the Frame Relay devices at one or both sites of the 1065 emulated interface. 1067 10.3.4. AC receive defect state entry/exit 1069 On entry to the AC receive defect state: 1071 * PE1 MUST send FDI to PE2. 1073 On exit from the AC receive defect state: 1075 * PE1 MUST clear FDI to PE2. 1077 10.3.5. AC transmit defect state entry/exit 1079 The AC transmit defect state is not valid for a FR AC. 1081 11. Procedures for TDM PW Service 1083 The following procedures apply to SAToP ([RFC4553]), CESoPSN 1084 ([RFC5086]) and TDMoIP ([RFC5087]). These technologies utilize the 1085 single emulated OAM loop mode. RFC 5087 distinguishes between trail- 1086 extended and trail-terminated scenarios; the former is essentially 1087 the single emulated loop model. The latter applies to cases where 1088 the NS networks are run by different operators and defect 1089 notifications are not propagated across the PW. 1091 Since TDM is inherently real-time in nature, many OAM indications 1092 must be generated or forwarded with minimal delay. This requirement 1093 rules out the use of messaging protocols, such as PW status messages. 1094 Thus, for TDM PWs, alternate mechanisms are employed. 1096 The fact that TDM PW packets are sent at a known constant rate can be 1097 exploited as an OAM mechanism. Thus, a PE enters the PW receive 1098 defect state whenever a preconfigured number of TDM PW packets do not 1099 arrive in a timely fashion. It exits this state when packets once 1100 again arrive at their proper rate. 1102 Native TDM carries OAM indications in overhead fields that travel 1103 along with the data. TDM PWs emulate this behavior by sending urgent 1104 OAM messages in the PWE control word. 1106 The TDM PWE3 control word contains a set of flags used to indicate PW 1107 and AC defect conditions. The L bit is an AC forward defect 1108 indication used by the upstream PE to signal NS network defects to 1109 the downstream PE. The M field may be used to modify the meaning of 1110 receive defects. The R bit is a PW reverse defect indication used by 1111 the PE to signal PSN failures to the remote PE. Upon reception of 1112 packets with the R bit set, a PE enters the PW transmit defect state. 1113 L bits and R bits are further described in [RFC5087]. 1115 11.1. AC receive defect state entry/exit criteria 1117 PE1 enters the AC receive defect state if any of the following 1118 conditions are met: 1120 a. It detects a physical layer fault on the TDM interface (Loss of 1121 Signal, Loss of Alignment, etc., as described in [G.775]). 1122 b. It is notified of a previous physical layer fault by detecting 1123 AIS. 1125 The exact conditions under which a PE enters and exits the AIS state 1126 are defined in [G.775]. Note that Loss of Signal and AIS detection 1127 can be performed by PEs for both structure-agnostic and structure- 1128 aware TDM PW types. Note that PEs implementing structure- agnostic 1129 PWs can not detect Loss of Alignment. 1131 11.2. AC transmit defect state entry/exit criteria 1133 PE1 enters the AC transmit defect state when it detects RDI according 1134 to the criteria in [G.775]. Note that PEs implementing structure- 1135 agnostic PWs can not detect RDI. 1137 11.3. Consequent Actions 1139 11.3.1. PW receive defect state entry/exit 1141 On entry to the PW receive defect state: 1143 a. PE1 MUST commence AIS insertion into the corresponding TDM AC. 1144 b. PE1 MUST set the R bit in all PW packets sent back to PE2. 1146 On exit from the PW receive defect state: 1148 a. PE1 MUST cease AIS insertion into the corresponding TDM AC. 1149 b. PE1 MUST clear the R bit in all PW packets sent back to PE2. 1151 Note that AIS generation can in general be performed by both 1152 structure-aware and structure-agnostic PEs. 1154 11.3.2. PW transmit defect state entry/exit 1156 On entry to the PW Transmit Defect State: 1158 * A structure-aware PE1 MUST commence RDI insertion into the 1159 corresponding AC. 1161 On exit from the PW Transmit Defect State: 1163 * A structure-aware PE1 MUST cease RDI insertion into the 1164 corresponding AC. 1166 Note that structure-agnostic PEs are not capable of injecting RDI 1167 into an AC. 1169 11.3.3. AC receive defect state entry/exit 1171 On entry to the AC receive defect state and when operating in the 1172 single emulated OAM loop mode: 1174 a. PE1 SHOULD overwrite the TDM data with AIS in the PW packets sent 1175 towards PE2. 1176 b. PE1 MUST set the L bit in these packets. 1177 c. PE1 MAY omit the payload in order to conserve bandwidth. 1178 d. A structure-aware PE1 SHOULD send RDI back towards CE1. 1179 e. A structure-aware PE1 that detects a potentially correctable AC 1180 defect MAY use the M field to indicate this. 1182 On exit from the AC receive defect state and when operating in the 1183 single emulated OAM loop mode: 1185 a. PE1 MUST cease overwriting PW content with AIS and return to 1186 forwarding valid TDM data in PW packets sent towards PE2. 1187 b. PE1 MUST clear the L bit in PW packets sent towards PE2. 1188 c. A structure-aware PE1 MUST cease sending RDI towards CE1. 1190 12. Procedures for CEP PW Service 1192 The following procedures apply to SONET/SDH Circuit Emulation 1193 ([RFC4842]). They are based on the single emulated OAM loop mode. 1195 Since SONET and SDH are inherently real-time in nature, many OAM 1196 indications must be generated or forwarded with minimal delay. This 1197 requirement rules out the use of messaging protocols, such as PW 1198 status messages. Thus, for CEP PWs alternate mechanisms are 1199 employed. 1201 The CEP PWE3 control word contains a set of flags used to indicate PW 1202 and AC defect conditions. The L bit is a forward defect indication 1203 used by the upstream PE to signal to the downstream PE a defect in 1204 its local attachment circuit. The R bit is a PW reverse defect 1205 indication used by the PE to signal PSN failures to the remote PE. 1206 The combination of N and P bits is used by the local PE to signal 1207 loss of pointer to the remote PE. 1209 The fact that CEP PW packets are sent at a known constant rate can be 1210 exploited as an OAM mechanism. Thus, a PE enters the PW receive 1211 defect state when it loses packet synchronization. It exits this 1212 state when it regains packet synchronization. See [RFC4842] for 1213 further details. 1215 12.1. Defect states 1217 12.1.1. PW receive defect state entry/exit 1219 In addition to the conditions specified in Section 8.2.1, PE1 will 1220 enter the PW receive defect state when one of the following becomes 1221 true: 1223 o It receives packets with the L bit set. 1224 o It receives packets with both the N and P bits set. 1225 o It loses packet synchronization. 1227 12.1.2. PW transmit defect state entry/exit 1229 In addition to the conditions specified in Section 8.2.2 PE1 will 1230 enter the PW transmit defect state if it receives packets with the R 1231 bit set. 1233 12.1.3. AC receive defect state entry/exit 1235 PE1 enters the AC receive defect state when any of the following 1236 conditions are met: 1238 a. It detects a physical layer fault on the TDM interface (Loss of 1239 Signal, Loss of Alignment, etc.). 1240 b. It is notified of a previous physical layer fault by detecting of 1241 AIS. 1243 The exact conditions under which a PE enters and exits the AIS state 1244 are defined in [G.707] and [G.783]. 1246 12.1.4. AC receive defect state entry/exit 1248 The AC transmit defect state is not valid for CEP PWs. RDI signals 1249 are forwarded transparently. 1251 12.2. Consequent Actions 1253 12.2.1. PW receive defect state entry/exit 1255 On entry to the PW receive defect state: 1257 a. PE1 MUST commence AIS-P/V insertion into the corresponding AC. 1258 See [RFC4842]. 1259 b. PE1 MUST set the R bit in all PW packets sent back to PE2. 1261 On exit from the PW receive defect state: 1263 a. PE1 MUST cease AIS-P/V insertion into the corresponding AC. 1264 b. PE1 MUST clear the R bit in all PW packets sent back to PE2. 1266 See [RFC4842] for further details. 1268 12.2.2. PW transmit defect state entry/exit 1270 On entry to the PW Transmit Defect State: 1272 a. A structure-aware PE1 MUST commence RDI insertion into the 1273 corresponding AC. 1275 On exit from the PW Transmit Defect State: 1277 a. A structure-aware PE1 MUST cease RDI insertion into the 1278 corresponding AC. 1280 12.2.3. AC receive defect state entry/exit 1282 On entry to the AC receive defect state: 1284 a. PE1 MUST set the L bit in these packets. 1285 b. If Dynamic Bandwidth Allocation (DBA) has been enabled, PE1 MAY 1286 omit the payload in order to conserve bandwidth. 1287 c. If Dynamic Bandwidth Allocation (DBA) is not enabled PE1 SHOULD 1288 insert AIS-V/P in the SDH/SONET client layer in the PW packets 1289 sent towards PE2. 1291 On exit from the AC receive defect state: 1293 a. PE1 MUST cease overwriting PW content with AIS-P/V and return to 1294 forwarding valid data in PW packets sent towards PE2. 1295 b. PE1 MUST clear the L bit in PW packets sent towards PE2. 1297 See [RFC4842] for further details. 1299 13. Security Considerations 1301 The mapping messages described in this document do not change the 1302 security functions inherent in the actual messages. All generic 1303 security considerations applicable to PW traffic specified in Section 1304 10 of RFC 3985 are applicable to NS OAM messages transferred inside 1305 the PW. 1307 Security considerations in Section 10 of RFC 5085 for VCCV apply to 1308 the OAM messages thus transferred. Security considerations 1309 applicable to the PWE3 control protocol of RFC 4447 Section 8.2 apply 1310 to OAM indications transferred using the LDP status message. 1312 14. IANA Considerations 1314 This document requires no IANA actions. 1316 Appendix A. Native Service Management (informative) 1318 A.1. Frame Relay Management 1320 The management of Frame Relay Bearer Service (FRBS) connections can 1321 be accomplished through two distinct methodologies: 1323 a. Based on ITU-T Q.933 Annex A, Link Integrity Verification 1324 procedure, where STATUS and STATUS ENQUIRY signaling messages are 1325 sent using DLCI=0 over a given UNI and NNI physical link [Q.933]. 1326 b. Based on FRBS LMI, and similar to ATM ILMI where LMI is common in 1327 private Frame Relay networks. 1329 In addition, ITU-T I.620 addresses Frame Relay loopback, but the 1330 deployment of this standard is relatively limited [I.620]. 1332 It is possible to use either, or both, of the above options to manage 1333 Frame Relay interfaces. This document will refer exclusively to 1334 Q.933 messages. 1336 The status of any provisioned Frame Relay PVC may be updated through: 1338 a. Frame Relay STATUS messages in response to Frame Relay STATUS 1339 ENQUIRY messages; these are mandatory. 1340 b. Optional unsolicited STATUS updates independent of STATUS ENQUIRY 1341 (typically under the control of management system, these updates 1342 can be sent periodically (continuous monitoring) or only upon 1343 detection of specific defects based on configuration. 1345 In Frame Relay, a Data Link Connection [DLC] is either up or down. 1346 There is no distinction between different directions. To achieve 1347 commonality with other technologies, down is represented as a receive 1348 defect. 1350 Frame relay connection management is not implemented over the PW 1351 using either of the techniques native to FR, therefore PW mechanisms 1352 are used to synchronize the view each PE has of the remote Native 1353 Service/Attachment Circuit [NS/AC]. A PE will treat a remote NS/AC 1354 failure in the same way it would treat a PW or PSN failure; that is 1355 using AC facing FR connection management to notify the CE that FR is 1356 down. 1358 A.2. ATM Management 1360 ATM management and OAM mechanisms are much more evolved than those of 1361 Frame Relay. There are five broad management-related categories, 1362 including fault management (FT), Performance management (PM), 1363 configuration management (CM), Accounting management (AC), and 1364 Security management (SM). [I.610] describes the functions for the 1365 operation and maintenance of the physical layer and the ATM layer, 1366 that is, management at the bit and cell levels [I.610]. Because of 1367 its scope, this document will concentrate on ATM fault management 1368 functions. Fault management functions include the following: 1370 a. Alarm indication signal (AIS). 1371 b. Remote Defect indication (RDI). 1372 c. Continuity Check (CC). 1373 d. Loopback (LB). 1375 Some of the basic ATM fault management functions are described as 1376 follows: Alarm indication signal (AIS) sends a message in the same 1377 direction as that of the signal, to the effect that an error has been 1378 detected. 1380 Remote defect indication (RDI) sends a message to the transmitting 1381 terminal that an error has been detected. Alarms related to the 1382 physical layer are indicated using path AIS/RDI. Virtual path AIS/ 1383 RDI and virtual channel AIS/RDI are also generated for the ATM layer. 1385 OAM cells (F4 and F5 cells) are used to instrument virtual paths and 1386 virtual channels respectively with regard to their performance and 1387 availability. OAM cells in the F4 and F5 flows are used for 1388 monitoring a segment of the network and end-to-end monitoring. OAM 1389 cells in F4 flows have the same VPI as that of the connection being 1390 monitored. OAM cells in F5 flows have the same VPI and VCI as that 1391 of the connection being monitored. The AIS and RDI messages of the 1392 F4 and F5 flows are sent to the other network nodes via the VPC or 1393 the VCC to which the message refers. The type of error and its 1394 location can be indicated in the OAM cells. Continuity check is 1395 another fault management function. To check whether a VCC that has 1396 been idle for a period of time is still functioning, the network 1397 elements can send continuity-check cells along that VCC. 1399 Appendix B. PW Defects and Detection tools 1401 B.1. PW Defects 1403 Possible defects that impact PWs are the following: 1405 a. Physical layer defect in the PSN interface. 1406 b. PSN tunnel failure which results in a loss of connectivity between 1407 ingress and egress PE. 1408 c. Control session failures between ingress and egress PE. 1410 In case of an MPLS PSN and an MPLS/IP PSN there are additional 1411 defects: 1413 a. PW labeling error, which is due to a defect in the ingress PE, or 1414 to an over-writing of the PW label value somewhere along the LSP 1415 path. 1416 b. LSP tunnel Label swapping errors or LSP tunnel label merging 1417 errors in the MPLS network. This could result in the termination 1418 of a PW at the wrong egress PE. 1419 c. Unintended self-replication; e.g., due to loops or denial- of- 1420 service attacks. 1422 B.2. Packet Loss 1424 Persistent congestion in the PSN or in a PE could impact the proper 1425 operation of the emulated service. 1427 A PE can detect packet loss resulting from congestion through several 1428 methods. If a PE uses the sequence number field in the PWE3 Control 1429 Word for a specific Pseudowire [RFC3985] and [RFC4385], it has the 1430 ability to detect packet loss. Translation of congestion detection 1431 to PW defect states is outside the scope of this specification. 1433 There are congestion alarms that are raised in the node and to the 1434 management system when congestion occurs. The decision to declare 1435 the PW Down and to select another path is usually at the discretion 1436 of the network operator. 1438 B.3. PW Defect Detection Tools 1440 To detect the defects listed above, Service Providers have a variety 1441 of options available. 1443 Physical Layer defect detection and notification mechanisms include 1444 SONET/SDH Los of Signal (LOS), Loss of Alignment (LOA), and AIS/RDI. 1446 PSN defect detection mechanisms vary according to the PSN type. 1448 For PWE3 over an L2TPV3/IP PSN, with L2TP as encapsulation protocol, 1449 the defect detection mechanisms described in [RFC3931] apply. This 1450 includes, for example, the keep-alive mechanism performed with Hello 1451 messages for detection of loss of connectivity between a pair of 1452 LCCEs (i.e., dead PE peer and path detection). Furthermore, the 1453 tools Ping and Traceroute, based on ICMP Echo Messages [RFC792] apply 1454 and can be used to detect defects on the IP PSN. Additionally, VCCV- 1455 Ping [RFC5085] and VCCV-BFD [VCCV-BFD] can also be used to detect 1456 defects at the individual pseudowire level. 1458 For PWE3 over an MPLS PSN and an MPLS/IP PSN, several tools can be 1459 used. 1461 a. LSP-Ping and LSP-Traceroute [RFC4379] for LSP tunnel connectivity 1462 verification. 1463 b. LSP-Ping with Bi-directional Forwarding Detection [VCCV-BFD] for 1464 LSP tunnel continuity checking. 1465 c. Furthermore, if RSVP-TE is used to setup the PSN Tunnels between 1466 ingress and egress PE, the hello protocol can be used to detect 1467 loss of connectivity [RFC3209], but only at the control plane. 1469 B.4. PW specific defect detection mechanisms 1471 [RFC4377] describes how LSP-Ping and BFD can be used over individual 1472 PWs for connectivity verification and continuity checking 1473 respectively. 1475 Furthermore, the detection of a fault could occur at different points 1476 in the network and there are several ways the observing PE determines 1477 a fault exists: 1479 a. Egress PE detection of failure (e.g., BFD). 1480 b. Ingress PE detection of failure (e.g., LSP-PING). 1481 c. Ingress PE notification of failure (e.g. RSVP Path-err). 1483 Appendix C. References 1485 C.1. Normative References 1487 [BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection", 1488 draft-ietf-bfd-base-11.txt, work in progress, January 2010. 1489 [FRF.19] Frame Relay Forum, "Frame Relay Operations, Administration, 1490 and Maintenance Implementation Agreement", March 2001. 1491 [ICMP] Postel, J. "Internet Control Message Protocol" RFC 792. 1492 [G.707] ITU-T Recommendation G.707 "Network Node Interface For The 1493 Synchronous Digital Hierarchy", December 2003. 1494 [G.775] ITU-T Recommendation G.775 "Loss of Signal (LOS), Alarm 1495 Indication Signal(AIS) and Remote Defect Indication (RDI) defect 1496 detection and clearance criteria for PDH signals", October 1998. 1497 [G.783] ITU-T Recommendation G.783 "Characteristics of synchronous 1498 digital hierarchy (SDH) equipment functional blocks ", March 2006. 1499 [I.610] ITU-T Recommendation I.610 "B-ISDN operation and maintenance 1500 principles and functions", February 1999. 1501 [I.620] ITU-T Recommendation I.620 "Frame relay operation and 1502 maintenance principles and functions", October 1996. 1503 [Q.933] ITU-T Recommendation Q.933 "ISDN Digital Subscriber 1504 Signalling System No. 1 (DSS1) Signalling specifications for frame 1505 mode switched and permanent virtual connection control and status 1506 monitoring", February 2003. 1507 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1508 Requirement Levels", BCP 14, RFC 2119, March 1997. 1509 [RFC3931] Lau, J., et. al. "Layer Two Tunneling Protocol (Version 1510 3", RFC 3931, March 2005. 1511 [RFC4023] Worster. T., et al., "Encapsulating MPLS in IP or Generic 1512 Routing Encapsulation (GRE)", RFC 4023, March 2005. 1513 [RFC4379] Kompella, K., et. al., "Detecting MPLS Data Plane 1514 Failures", RFC4379, February 2006. 1515 [RFC4446] Martini, L., et al., "IANA Allocations for pseudo Wire 1516 Edge to Edge Emulation (PWE3)", RFC4446, April 2006. 1517 [RFC4447] Martini, L., Rosen, E., Smith, T., "Pseudowire Setup and 1518 Maintenance using LDP", RFC4447, April 2006. 1519 [RFC4842] Malis, A., et. al., "SONET/SDH Circuit Emulation over 1520 Packet (CEP)", RFC 4842, April 2007. 1521 [RFC5085] Nadeau, T., et al., "Pseudowire Virtual Circuit Connection 1522 Verification (VCCV)", RFC 5085, December 2007. 1523 [VCCV-BFD] Nadeau, T., Pignataro, C., "Bidirectional Forwarding 1524 Detection (BFD) for the Pseudowire Virtual Circuit Connectivity 1525 Verification (VCCV)", draft-ietf-pwe3-vccv-bfd-07, July 2009. 1527 C.2. Informative References 1529 [CONGESTION] Rosen, E., Bryant, S., Davie, B., "PWE3 Congestion 1530 Control Framework", draft-ietf-pwe3-congestion-frmwk-02.txt, work 1531 in progress, June 2009. 1532 [ETH-OAM-IWK] Mohan, D., et al., "MPLS and Ethernet OAM 1533 Interworking", draft-ietf-pwe3-mpls-eth-oam-iwk-01, work in 1534 progress, October 2009. 1535 [L2TP-Status] McGill, N. Pignataro, C., "L2TPv3/IP Extended Circuit 1536 Status Values", draft-ietf-l2tpext-circuit-status-extensions-04, 1537 work in progress, April 2009. 1538 [RFC3916] Xiao, X., McPherson, D., Pate, P., "Requirements for 1539 Pseudowire Emulation Edge to-Edge (PWE3)", RFC 3916, September 1540 2004. 1541 [RFC3985] Bryant, S., Pate, P., "PWE3 Architecture", RFC 3985, March 1542 2005. 1543 [RFC4377] Nadeau, T. et.al., "OAM Requirements for MPLS Networks", 1544 RFC4377, February 2006. 1545 [RFC4385] Bryant, S. et al., "Pseudowire Emulation Edge-to-Edge 1546 (PWE3) Control Word for Use over an MPLS PSN," RFC 4385, February 1547 2006. 1548 [RFC4454] Singh, S., Townsley, M., and C. Pignataro, "Asynchronous 1549 Transfer Mode (ATM) over Layer 2 Tunneling Protocol Version 3 1550 (L2TPv3/IP)", RFC 4454, May 2006. 1551 [RFC4553] Vainshtein, A. et al., "Structure-Agnostic Time Division 1552 Multiplexing (TDM) over Packet (SAToP)", RFC 4553, June 2006. 1553 [RFC4591] Townsley, Market al.,"Frame Relay over Layer 2 Tunnelling 1554 Protocol Version 3 (L2TPv3/IP)", RFC 4591, July 2006. 1555 [RFC4717] Martini, L., et al., "Encapsulation Methods for Transport 1556 of ATM Cells/Frame Over IP and MPLS Networks", RFC4717, December 1557 2006. 1558 [RFC5085] Nadeau,T et al., "Pseudowire Virtual Circuit Connectivity 1559 Verification: A Control Channel for Pseudowires",(VCCV), RFC 1560 5085,December 2007. 1561 [RFC5086] Vainshtein ,A..,et al., "Structure-Aware Time Division 1562 Multiplexed (TDM) Circuit Emulation Service over Packet Switched 1563 Network (CESoPSN)", RFC 5086, December 2007. 1564 [RFC5087] Y.(J) Stein et al., "Time Division Multiplexing over IP 1565 (TDMoIP)", RFC 5087, December 2007. 1566 [RFC5641] McGill,N., et al., "Layer 2 Tunnelling Protocol Version 3 1567 (L2TPv3) Extended Circuit Status Values," RFC 5641, August 2009. 1569 Authors' Addresses 1571 Mustapha Aissaoui 1572 Alcatel-Lucent 1573 600 March Rd 1574 Kanata, ON K2K 2E6 1575 Canada 1577 Email: mustapha.aissaoui@alcatel-lucent.com 1579 Peter Busschbach 1580 Alcatel-Lucent 1581 67 Whippany Rd 1582 Whippany, NJ 07981 1583 USA 1585 Email: busschbach@alcatel-lucent.com 1587 Monique Morrow 1588 Cisco Systems, Inc. 1589 Richtistrase 7 1590 CH-8304 Wallisellen 1591 Switzerland 1593 Email: mmorrow@cisco.com 1595 Luca Martini 1596 Cisco Systems, Inc. 1597 9155 East Nichols Avenue, Suite 400 1598 Englewood, CO 80112 1599 USA 1601 Email: lmartini@cisco.com 1603 Yaakov (Jonathan) Stein 1604 RAD Data Communications 1605 24 Raoul Wallenberg St., Bldg C 1606 Tel Aviv 69719 1607 ISRAEL 1609 Email: yaakov_s@rad.com 1610 Dave Allan 1611 Ericsson 1613 Email: david.i.allan@ericsson.com 1615 Thomas Nadeau 1616 BT 1617 BT Centre, 81 Newgate Street 1618 London EC1A 7AJ 1619 UK 1621 Email: tom.nadeau@bt.com