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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PCE Working Group C. Li 3 Internet-Draft M. Chen 4 Intended status: Standards Track Huawei Technologies 5 Expires: September 9, 2019 W. Cheng 6 China Mobile 7 Z. Li 8 J. Dong 9 Huawei Technologies 10 R. Gandhi 11 Cisco Systems, Inc. 12 March 08, 2019 14 PCEP Extension for Segment Routing (SR) Bidirectional Associated Paths 15 draft-li-pce-sr-bidir-path-03 17 Abstract 19 The Path Computation Element Communication Protocol (PCEP) provides 20 mechanisms for Path Computation Elements (PCEs) to perform path 21 computations in response to Path Computation Clients (PCCs) requests. 22 The Stateful PCE extensions allow stateful control of Multiprotocol 23 Label Switching (MPLS) Traffic Engineering (TE) Label Switched Paths 24 (LSPs) using PCEP. Furthermore, PCEP can be used for computing paths 25 in SR networks. 27 This document defines PCEP extensions for grouping two reverse 28 unidirectional SR Paths into an Associated Bidirectional SR path when 29 using a Stateful PCE for both PCE-Initiated and PCC-Initiated LSPs as 30 well as when using a Stateless PCE. 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at https://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on September 9, 2019. 49 Copyright Notice 51 Copyright (c) 2019 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (https://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 69 3. PCEP Extension for Bidirectional SR Path . . . . . . . . . . 4 70 3.1. Double-sided Bidirectional SR Path Association Group 71 Object . . . . . . . . . . . . . . . . . . . . . . . . . 5 72 4. Bidirectional Flag . . . . . . . . . . . . . . . . . . . . . 5 73 5. Procedures of Bidirectional Path Computation . . . . . . . . 6 74 5.1. PCE Initiated SR Paths . . . . . . . . . . . . . . . . . 6 75 5.2. PCC Initiated SR Paths . . . . . . . . . . . . . . . . . 7 76 5.3. Error Handling . . . . . . . . . . . . . . . . . . . . . 9 77 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 78 6.1. Association Type . . . . . . . . . . . . . . . . . . . . 10 79 6.2. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 10 80 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 81 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11 82 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 83 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 84 10.1. Normative References . . . . . . . . . . . . . . . . . . 11 85 10.2. Informative References . . . . . . . . . . . . . . . . . 13 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 88 1. Introduction 90 Segment routing (SR) [RFC8402] leverages the source routing and 91 tunneling paradigms. SR supports to steer packets into an explicit 92 forwarding path at the ingress node. 94 [RFC5440] describes the Path Computation Element (PCE) Communication 95 Protocol (PCEP). PCEP enables the communication between a Path 96 Computation Client (PCC) and a PCE, or between PCE and PCE, for the 97 purpose of computation of Multiprotocol Label Switching (MPLS) as 98 well as Generalized MPLS (GMPLS) Traffic Engineering Label Switched 99 Path (TE LSP) characteristics. 101 [RFC8231] specifies a set of extensions to PCEP to enable stateful 102 control of TE LSPs within and across PCEP sessions in compliance with 103 [RFC4657]. It includes mechanisms to effect LSP State 104 Synchronization between PCCs and PCEs, delegation of control over 105 LSPs to PCEs, and PCE control of timing and sequence of path 106 computations within and across PCEP sessions. The model of operation 107 where LSPs are initiated from the PCE is described in [RFC8281]. 109 [I-D.ietf-pce-segment-routing] specifies extensions to the Path 110 Computation Element Protocol (PCEP) [RFC5440] for SR networks, that 111 allow a stateful PCE to compute and initiate SR-TE paths, as well as 112 a PCC to request, report or delegate SR paths. 113 [I-D.negi-pce-segment-routing-ipv6] extend PCEP to support SR for 114 IPv6 data plane. 116 [I-D.ietf-pce-association-group] introduces a generic mechanism to 117 create a grouping of LSPs which can then be used to define 118 associations between a set of LSPs and/or a set of attributes, for 119 example primary and secondary LSP associations, and is equally 120 applicable to the active and passive modes of a Stateful PCE 121 [RFC8231] or a stateless PCE [RFC5440]. 123 Currently, SR network only supports unidirectional path, but the 124 bidirectional SR path is required in some scenarios, for example, 125 mobile backhaul transport network. The requirement of SR 126 bidirectional path is specified in 127 [I-D.cheng-spring-mpls-path-segment]. 129 [I-D.ietf-pce-association-bidir] defines PCEP extensions for grouping 130 two reverse unidirectional MPLS TE LSPs into an Associated 131 Bidirectional LSP when using a Stateful PCE for both PCE-Initiated 132 and PCC-Initiated LSPs as well as when using a Stateless PCE. 134 This document extends the bidirectional association to segment 135 routing by specifying PCEP extensions for grouping two reverse 136 unidirectional SR paths into a bidirectional SR path. 138 [I-D.ietf-pce-association-bidir] specify the Double-sided 139 Bidirectional procedure, where the PCE creates the association and 140 provisions at the both ends, the RSVP-TE does the signaling to the 141 egress the status of the forward LSP and the ingress about the 142 reverse LSP. Thus, the both ends learn both the LSPs forming the 143 bidirectional association. In case of SR, to support the 144 bidirectional use-case, this is done via the PCEP protocol itself as 145 described in Section 3.1. This is done so that both ends are aware 146 of the Path Segment used by each of the unidirectional LSP, as well 147 as the status, the ERO etc. 149 [I-D.li-pce-sr-path-segment] defines a procedure for Path Segment in 150 PCEP for SR by defining the PATH-SEGMENT TLV. The Path Segment can 151 be a Path Segment in SR-MPLS [I-D.cheng-spring-mpls-path-segment], or 152 a Path Segment in SRv6 [I-D.li-spring-srv6-path-segment], or other 153 IDs that can identify an SR path. The PATH-SEGMENT TLV SHOULD be 154 included for associated bidirectional SR paths. 156 2. Terminology 158 This document makes use of the terms defined in 159 [I-D.ietf-pce-segment-routing]. The reader is assumed to be familiar 160 with the terminology defined in [RFC5440], [RFC8231], [RFC8281], 161 [I-D.ietf-pce-association-group] and 162 [I-D.ietf-pce-association-bidir]. 164 2.1. Requirements Language 166 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 167 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 168 "OPTIONAL" in this document are to be interpreted as described in BCP 169 14 [RFC2119] [RFC8174] when, and only when, they appear in all 170 capitals, as shown here. 172 3. PCEP Extension for Bidirectional SR Path 174 As per [I-D.ietf-pce-association-group], LSPs are associated by 175 adding them to a common association group. 176 [I-D.ietf-pce-association-bidir] specifies PCEP extensions for 177 grouping two reverse unidirectional MPLS-TE LSPs into an Associated 178 Bidirectional LSP for both single-sided and double-sided initiation 179 cases by defining two new Bidirectional LSP Association Groups. 181 This document extends the procedure for SR bidirectional associated 182 paths by defining a new bidirectional association type (i.e. Double- 183 sided Bidirectional SR Path Association Group). The document further 184 describes the mechanism of associating two unidirectional SR path 185 into a bidirectional SR path. [I-D.li-pce-sr-path-segment] defines a 186 procedure for Path Segment in PCEP for SR by defining the PATH- 187 SEGMENT TLV. The bidirectional SR path can also use the PATH-SEGMENT 188 TLV. 190 Note that a new association type is created by this document to 191 create new procedures applicable to SR-path (and are quite different 192 than the RSVP-TE bidirectional association groups). 194 3.1. Double-sided Bidirectional SR Path Association Group Object 196 As defined in [I-D.ietf-pce-association-bidir], two LSPs are 197 associated as a bidirectional MPLS-TE LSP by a common bidirectional 198 LSP association group. For associating two SR paths, this document 199 defines a new association group called 'Double-sided Bidirectional SR 200 Path Association Group' as follows: 202 o Association Type (TBD1 to be assigned by IANA) = Double-sided 203 Bidirectional SR Path Association Group 205 Similar to other bidirectional associations, this Association Type is 206 operator-configured in nature and statically created by the operator 207 on the PCEP peers. The paths belonging to this association is 208 conveyed via PCEP messages to the PCEP peer. Operator-configured 209 Association Range TLV [I-D.ietf-pce-association-group] MUST NOT be 210 sent for these Association Types, and MUST be ignored, so that the 211 entire range of association ID can be used for them. The handling of 212 the Association ID, Association Source, optional Global Association 213 Source and optional Extended Association ID in this association are 214 set in the same way as [I-D.ietf-pce-association-bidir]. 216 A member of the Double-sided Bidirectional SR Path Association Group 217 can take the role of a forward or reverse SR path and follows the 218 rules similar to the rules defined in 219 [I-D.ietf-pce-association-bidir] for LSPs. 221 o An SR path (forward or reverse) can not be part of more than one 222 Double-sided Bidirectional SR Path Association Group. 224 o The endpoints of the SR paths in this associations cannot be 225 different. 227 For describing the SR paths in this association group, such as 228 direction and co-routed information, this association group reuses 229 the Bidirectional LSP Association Group TLV defined in 230 [I-D.ietf-pce-association-bidir]. All fields and processing rules 231 are as per [I-D.ietf-pce-association-bidir]. 233 4. Bidirectional Flag 235 As defined in [RFC5440], the B-flag in RP object MUST be set when the 236 PCC specifies that the path computation request relates to a 237 bidirectional TE LSP. In this document, the B-flag also MUST be set 238 when the PCC specifies that the path computation request relates to a 239 bidirectional SR path. When a stateful PCE initiates or updates a 240 bidirectional SR paths including LSPs and SR paths, the B-flag in SRP 241 object [I-D.ietf-pce-pcep-stateful-pce-gmpls] may be set as well. 243 5. Procedures of Bidirectional Path Computation 245 Two unidirectional SR paths can be associated by the association 246 group object as specified in [I-D.ietf-pce-association-group]. A 247 bidirectional LSP association group object is defined in 248 [I-D.ietf-pce-association-bidir] (for MPLS-TE). This documents 249 extends the mechanism for bidirectional SR paths. Two SR paths can 250 be associated together by including the Bidirectional SR Path 251 Association Group in the PCEP messages. The PATH-SEGMENT TLV 252 [I-D.li-pce-sr-path-segment] SHOULD also be included in the LSP 253 object for these SR paths to support required use-cases. 255 There is also a need to include the reverse direction path in the 256 PCEP messages, so the PCE SHOULD inform the reverse SR path to the 257 ingress PCC and vice versa. To achieve this, a PCInitiate message 258 for the reverse SR path is sent to the ingress PCC and a PCInitiate 259 message for the forward SR path is sent to the egress PCC (with the 260 same association group). These PCInitiate message MUST NOT trigger 261 initiation of SR paths. The information of reverse direction path 262 can be used for several scenarios, such as directed BFD 263 [I-D.ietf-mpls-bfd-directed]. 265 In a bidirectional LSP computaion, a same LSP would be identified via 266 2 different PLSP-IDs based on the PCEP session to the ingress or the 267 egress. In other words, a LSP will have a PLSP-ID A at the ingress 268 node while have the PLSP-ID B at the egress node. The PCE could 269 maintain the two PLSP-ID for the same LSP. 271 For instance, an ingress PCC requests a bidirectional SR path 272 computation, and the PCE compute a forward LSP1 with PLSP-ID 100, and 273 reverse LSP from the egress to the ingress with PLSP-ID 200 allocated 274 by the egress PCC. Since the PLSP-ID space is isolated at each PCC, 275 so the PLSP-ID allocated by egress PCC can not be used at the ingress 276 PCC(PSLD-ID confliction may occur), so the PCE needs to allocate a 277 PLSP-ID for LSP2 from the ingress PCC's PSLP-ID space , such as 101. 278 It is the same situtaion for LSP1, it has PLSP-ID 100 at the ingress, 279 and may has PLSP-ID 201 at the egress. 281 5.1. PCE Initiated SR Paths 283 As specified in [I-D.ietf-pce-association-group] Bidirectional SR 284 Association Group can be created by a Stateful PCE. 286 o Stateful PCE can create and update the forward and reverse SR path 287 independently for Double-sided Bidirectional SR Path Association 288 Groups. 290 o Stateful PCE can establish and remove the association relationship 291 on a per SR path basis. 293 o Stateful PCE can create and update the SR path and the association 294 on a PCC via PCInitiate and PCUpd messages, respectively, using 295 the procedures described in [I-D.ietf-pce-association-group]. 297 o The PATH-SEGMENT TLV SHOULD be included for each SR path in the 298 LSP object. 300 o The opposite direction SR path (LSP2(R) at S, LSP1(R) at D ) 301 SHOULD be informed via PCInitiate message with the matching 302 association group. 304 +-----+ 305 | PCE | 306 +-----+ 307 PCUpd/PCInitiate / \ PCUpd/PCInitiate 308 Tunnel 1 (F) / \ Tunnel 2 (R) 309 (LSP1 (F), LSP2 (R)) / \ (LSP2 (F), LSP1 (R)) 310 Assoc#1 / \ Assoc#1 311 / \ 312 v v 313 +-----+ LSP1 +-----+ 314 | S |------------>| D | 315 | |<------------| | 316 +-----+ LSP2 +-----+ 317 319 Figure 1: PCE-Initiated Double-sided Bidirectional SR Path 321 5.2. PCC Initiated SR Paths 323 As specified in [I-D.ietf-pce-association-group] Bidirectional SR 324 Association Group can also be created by a PCC. 326 o PCC can create and update the forward and reverse SR paths 327 independently for Double-sided Bidirectional SR Path Association 328 Groups. 330 o PCC can establish and remove the association relationship on a per 331 SR path basis. 333 o PCC MUST report the change in the association group of an SR path 334 to PCE(s) via PCRpt message. 336 o PCC can report the forward and reverse SR paths independently to 337 PCE(s) via PCRpt message. 339 o PCC can delegate the forward and reverse SR paths independently to 340 a Stateful PCE, where PCE would control the SR paths. 342 o Stateful PCE can update the SR paths in the Double-sided 343 Bidirectional SR Path Association Group via PCUpd message, using 344 the procedures described in [I-D.ietf-pce-association-group]. 346 o The PATH-SEGMENT TLV MUST be handled as defined in 347 [I-D.li-pce-sr-path-segment]. 349 o The opposite direction SR path (LSP2(R) at S, LSP1(R) at D ) 350 SHOULD be informed via PCInitiate message with the matching 351 association group. 353 +-----+ 354 | PCE | 355 +-----+ 356 Reports/Delegates: ^ ^ Reports/Delegates 357 Tunnel 1 (F) / \ Tunnel 2 (R) 358 (LSP1 (F)) / \ (LSP2 (R)) 359 / \ 360 / \ 361 / \ 362 +-----+ LSP1 +-----+ 363 | S |------------>| D | 364 | |<------------| | 365 +-----+ LSP2 +-----+ 367 Figure 2a: PCC-Initiated Double-sided Bidirectional SR Path 369 +-----+ 370 | PCE | 371 +-----+ 372 PCUpd/PCInitiate / \ PCUpd/PCInitiate 373 Tunnel 1 (F) / \ Tunnel 2 (R) 374 (LSP1 (F), LSP2 (R)) / \ (LSP2 (F), LSP1 (R)) 375 Assoc#1 / \ Assoc#1 376 / \ 377 v v 378 +-----+ LSP1 +-----+ 379 | S |------------>| D | 380 | |<------------| | 381 +-----+ LSP2 +-----+ 383 Figure 2b: PCC-Initiated Double-sided Bidirectional SR Path 384 along with opposite direction SR path 386 5.3. Error Handling 388 The error handling as described in section 5.5 of 389 [I-D.ietf-pce-association-bidir] continue to apply. 391 The Path Setup Type (PST) MUST be set to SR for the LSP belonging to 392 the 'Double-sided Bidirectional SR Path Association Group', in case a 393 PCEP speaker receives a different PST value, it MUST send an PCErr 394 message with Error-Type = 29 (Early allocation by IANA) (Association 395 Error) and Error-Value = TBD2 (Bidirectional LSP Association - PST 396 Mismatch). 398 6. IANA Considerations 400 6.1. Association Type 402 This document defines a new Association Type for the Association 403 Object defined [I-D.ietf-pce-association-group]. IANA is requested 404 to make the assignment of a value for the sub-registry "ASSOCIATION 405 Type Field" (to be created in [I-D.ietf-pce-association-group]), as 406 follows: 408 Value Name Reference 409 ------------------------------------------------------------------- 410 TBD1 Double-sided Bidirectional This document 411 SR Path Association Group 413 6.2. PCEP Errors 415 This document defines new Error value for Error Type 29 (Association 416 Error). IANA is requested to allocate new Error value within the 417 "PCEP-ERROR Object Error Types and Values" sub-registry of the PCEP 418 Numbers registry, as follows: 420 Error Type Description Reference 421 ------------------------------------------------------------------- 422 29 Association Error 424 Error value: TBD2 This document 425 Bidirectional LSP Association - PST Mismatch 427 7. Security Considerations 429 The security considerations described in [RFC5440], [RFC8231], 430 [RFC8281], and [I-D.ietf-pce-segment-routing] apply to the extensions 431 defined in this document as well. 433 A new Association Type for the Association Object, Double-sided 434 Associated Bidirectional SR Path Association Group is introduced in 435 this document. Additional security considerations related to LSP 436 associations due to a malicious PCEP speaker is described in 437 [I-D.ietf-pce-association-group] and apply to this Association Type. 438 Hence, securing the PCEP session using Transport Layer Security (TLS) 439 [RFC8253] is recommended. 441 8. Contributors 443 The following people have substantially contributed to this document: 445 Dhruv Dhody 446 Huawei Technologies 447 Divyashree Techno Park, Whitefield 448 Bangalore, Karnataka 560066 449 India 451 Email: dhruv.ietf@gmail.com 453 Quan Xiong 454 ZTE Corporation 455 No.6 Huashi Park Rd 456 Wuhan, Hubei 430223 457 China 459 Email: xiong.quan@zte.com.cn 461 9. Acknowledgments 463 Many thanks to Marina's review and professional comments. 465 10. References 467 10.1. Normative References 469 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 470 Requirement Levels", BCP 14, RFC 2119, 471 DOI 10.17487/RFC2119, March 1997, 472 . 474 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 475 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 476 DOI 10.17487/RFC5440, March 2009, 477 . 479 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 480 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 481 May 2017, . 483 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 484 Computation Element Communication Protocol (PCEP) 485 Extensions for Stateful PCE", RFC 8231, 486 DOI 10.17487/RFC8231, September 2017, 487 . 489 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 490 Computation Element Communication Protocol (PCEP) 491 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 492 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 493 . 495 [I-D.ietf-pce-association-group] 496 Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H., 497 Dhody, D., and Y. Tanaka, "PCEP Extensions for 498 Establishing Relationships Between Sets of LSPs", draft- 499 ietf-pce-association-group-08 (work in progress), March 500 2019. 502 [I-D.ietf-pce-association-bidir] 503 Barth, C., Gandhi, R., and B. Wen, "PCEP Extensions for 504 Associated Bidirectional Label Switched Paths (LSPs)", 505 draft-ietf-pce-association-bidir-02 (work in progress), 506 November 2018. 508 [I-D.ietf-pce-pcep-stateful-pce-gmpls] 509 Lee, Y., Zhang, F., Casellas, R., Dios, O., and Z. Ali, 510 "Path Computation Element (PCE) Protocol Extensions for 511 Stateful PCE Usage in GMPLS-controlled Networks", draft- 512 ietf-pce-pcep-stateful-pce-gmpls-10 (work in progress), 513 March 2019. 515 [I-D.negi-pce-segment-routing-ipv6] 516 Negi, M., Li, C., Sivabalan, S., and P. Kaladharan, "PCEP 517 Extensions for Segment Routing leveraging the IPv6 data 518 plane", draft-negi-pce-segment-routing-ipv6-04 (work in 519 progress), February 2019. 521 [I-D.li-pce-sr-path-segment] 522 Li, C., Chen, M., Dhody, D., Cheng, W., Dong, J., Li, Z., 523 and R. Gandhi, "Path Computation Element Communication 524 Protocol (PCEP) Extension for Path Segment in Segment 525 Routing (SR)", draft-li-pce-sr-path-segment-03 (work in 526 progress), October 2018. 528 [I-D.li-spring-srv6-path-segment] 529 Li, C., Chen, M., Dhody, D., Li, Z., Dong, J., and R. 530 Gandhi, "Path Segment for SRv6 (Segment Routing in IPv6)", 531 draft-li-spring-srv6-path-segment-00 (work in progress), 532 October 2018. 534 10.2. Informative References 536 [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation 537 Element (PCE) Communication Protocol Generic 538 Requirements", RFC 4657, DOI 10.17487/RFC4657, September 539 2006, . 541 [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, 542 "PCEPS: Usage of TLS to Provide a Secure Transport for the 543 Path Computation Element Communication Protocol (PCEP)", 544 RFC 8253, DOI 10.17487/RFC8253, October 2017, 545 . 547 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 548 Decraene, B., Litkowski, S., and R. Shakir, "Segment 549 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 550 July 2018, . 552 [I-D.ietf-pce-segment-routing] 553 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 554 and J. Hardwick, "PCEP Extensions for Segment Routing", 555 draft-ietf-pce-segment-routing-16 (work in progress), 556 March 2019. 558 [I-D.ietf-mpls-bfd-directed] 559 Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen, 560 "Bidirectional Forwarding Detection (BFD) Directed Return 561 Path", draft-ietf-mpls-bfd-directed-10 (work in progress), 562 September 2018. 564 [I-D.cheng-spring-mpls-path-segment] 565 Cheng, W., Wang, L., Li, H., Chen, M., Gandhi, R., Zigler, 566 R., and S. Zhan, "Path Segment in MPLS Based Segment 567 Routing Network", draft-cheng-spring-mpls-path-segment-03 568 (work in progress), October 2018. 570 Authors' Addresses 572 Cheng Li 573 Huawei Technologies 574 Huawei Campus, No. 156 Beiqing Rd. 575 Beijing 100095 576 China 578 Email: chengli13@huawei.com 579 Mach(Guoyi) Chen 580 Huawei Technologies 581 Huawei Campus, No. 156 Beiqing Rd. 582 Beijing 100095 583 China 585 Email: Mach.chen@huawei.com 587 Weiqiang Cheng 588 China Mobile 589 China 591 Email: chengweiqiang@chinamobile.com 593 Zhenbin Li 594 Huawei Technologies 595 Huawei Campus, No. 156 Beiqing Rd. 596 Beijing 100095 597 China 599 Email: lizhenbin@huawei.com 601 Jie Dong 602 Huawei Technologies 603 Huawei Campus, No. 156 Beiqing Rd. 604 Beijing 100095 605 China 607 Email: jie.dong@huawei.com 609 Rakesh Gandhi 610 Cisco Systems, Inc. 611 Canada 613 Email: rgandhi@cisco.com