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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PCE WG Quan Xiong 3 Internet-Draft Fangwei Hu 4 Intended status: Standards Track Greg Mirsky 5 Expires: January 8, 2020 ZTE Corporation 6 Weiqiang Cheng 7 China Mobile 8 July 7, 2019 10 Stateful PCE for SR-MPLS Inter-domain 11 draft-xiong-pce-stateful-pce-sr-inter-domain-01 13 Abstract 15 This document proposes two solutions to perform the Segment Routing 16 with MPLS data plane (SR-MPLS) inter-domain path computation and 17 initiation with stateful PCEs and the use of Path Segment. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on January 8, 2020. 36 Copyright Notice 38 Copyright (c) 2019 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (https://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 55 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. The SR-MPLS Inter-domain with PCE . . . . . . . . . . . . . . 3 57 2.1. The Stitching LSP Association Solution . . . . . . . . . 5 58 2.2. The Stitching Label Solution . . . . . . . . . . . . . . 6 59 3. Inter-domain Path Segment Allocation . . . . . . . . . . . . 6 60 3.1. PCC Allocated . . . . . . . . . . . . . . . . . . . . . . 6 61 3.2. PCE Allocated . . . . . . . . . . . . . . . . . . . . . . 7 62 4. PCEP Procedure . . . . . . . . . . . . . . . . . . . . . . . 7 63 4.1. HPCE-initiated LSP . . . . . . . . . . . . . . . . . . . 7 64 4.2. PCC-initiated LSP . . . . . . . . . . . . . . . . . . . . 8 65 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 66 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 67 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 68 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 69 8.1. Informative References . . . . . . . . . . . . . . . . . 9 70 8.2. Normative References . . . . . . . . . . . . . . . . . . 9 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 73 1. Introduction 75 The Path Computation Element (PCE) architecture is defined in 76 [RFC4655] for MPLS Traffic Engineering (MPLS-TE) and Generalized MPLS 77 (GMPLS) networks. The Path Computation Element Communication 78 Protocol (PCEP) defined in [RFC5440] provides mechanisms for PCEs to 79 perform path computations in response to Path Computation Clients 80 (PCCs) requests. 82 [I-D.ietf-pce-segment-routing] proposes extensions to PCEP that allow 83 a stateful PCE to compute TE paths in segment routing (SR) networks. 84 As defined in [I-D.ietf-spring-mpls-path-segment], a path segment is 85 used to identify a SR path and support bidirectional SR paths 86 correlation. [I-D.li-pce-sr-path-segment] proposed the extension for 87 PCEP to operate with Path Segment. [I-D.li-pce-sr-bidir-path] 88 proposed the extension for PCEP to group two unidirectional SR Paths 89 into an Associated Bidirectional SR Path. 90 [I-D.xiong-spring-path-segment-sr-inter-domain] proposes the use of 91 Path Segment in inter-domain scenarios for SR-MPLS network. It is 92 required to perform the SR inter-domain path computation and 93 initiation with PCE deployment. 95 The path computation requirments for Label Switched Paths (LSPs) 96 across multiple domains are discussed in [RFC4105] and [RFC4216]. 97 Inter-domain path computation can be performed by a single stateful 98 PCE and multiple stateful PCEs. The PCE may has no ability to 99 collect the topologies all over the domains. So the single PCE model 100 is not applied in deployment. Three multiple PCEs models can be uesd 101 to perform PCE-based inter-domain path computation including Per- 102 Domain Path Computation [RFC5152], Backward-Recursive PCE-Based 103 Computation (BRPC) [RFC5441] and Hierarchical PCE (H-PCE) [RFC6805]. 104 Computing the optimum inter-domain path requires co-operation between 105 multiple PCEs. But the sequence of domains need to be known before 106 the path computation in BRPC mechanism. Stateful H-PCE architecture 107 is appropriate to compute an optimal end-to-end path across multiple 108 domains. 110 As defined in [I-D.xiong-spring-path-segment-sr-inter-domain], the 111 SR-MPLS inter-domain models includes stitching and nesting inter- 112 domain models between inter-Area or inter-AS domains. This document 113 proposes two solutions to perform the SR-MPLS inter-domain path 114 computation and initiation with stateful PCEs and the use of Path 115 Segment. 117 1.1. Requirements Language 119 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 120 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 121 document are to be interpreted as described in [RFC2119]. 123 1.2. Terminology 125 The terminology is defined as [RFC5440], 126 [I-D.ietf-pce-segment-routing] , [I-D.ietf-spring-mpls-path-segment]. 128 2. The SR-MPLS Inter-domain with PCE 130 The SR-MPLS inter-domain scenario is described in 131 [I-D.xiong-spring-path-segment-sr-inter-domain]. The domains of the 132 networks may be IGP Areas or ASes and the inter- domain scenario may 133 be inter-Area or inter-AS. The multiple SR-MPLS domains may be 134 interconnect with a ABR within areas or inter-link between ASes. As 135 the Figure 1 shown, SR-AS1, SR-AS2 and SR-AS3 interconnect with 136 logical links and SR-Area1, SR-Area2 and SR-Area3 interconnect within 137 border nodes. The SR end-to-end bidirectional LSP needs to be 138 provided along the multi-domain paths. The Path 1~5 are forwarding 139 path segments and Path 1'~5' are the related reverse path segments 140 and these are all inter-domain path segments. 142 +-------+ 143 +------------------+ H-PCE +-------------------+ 144 | +---+---+ | 145 | | | 146 v v v 147 +--+--+ +--+--+ +--+--+ 148 |PCE-1| |PCE-2| |PCE-3| 149 +--+--+ +--+--+ +--+--+ 150 | | | 151 v v v 152 SR Inter-Area: 153 .................. ................. .................... 154 . . . . . . 155 +-----+ +-----+ +-----+ +-----+ 156 | A | | X | | Y | | Z | 157 +-----+ +-----+ +-----+ +-----+ 158 . SR-Area1 . . SR-Area2 . . SR-Area3 . 159 .................. ................. .................... 161 Forwarding Path Segments: 162 |------Path1------->|-----Path2------->|--------Path3------>| 163 Reverse Path Segments: 164 |<-----Path1'-------|<----Path2'-------|<--------Path3'-----| 166 SR Inter-AS: 167 .................... .................... ..................... 168 . . . . . . 169 . +---+ +---+ . . +---+ +---+ . . +---+ +----+ . 170 . | A |------| B |-------| C |-----| X |---------| Y |-----| Z | . 171 . +---+ +---+ . . +---+ +---+ . . +---+ +----+ . 172 . SR-AS1 . . SR-AS2 . . SR-AS3 . 173 .................... .................... ..................... 175 Forwarding Path Segments: 176 |----Path1---->|-Path2-->|----Path3--->|-Path4-->|-----Path5------>| 177 Reverse Path Segments: 178 |<---Path1'----|<-Path2'-|<---Path3'---|<-Path4'-|<----Path5'------| 180 Figure 1 The SR Inter-Domain with H-PCE 182 The hierarchical PCE architecture is described in [RFC6805], a parent 183 PCE maintains a domain topology map that contains the child domains 184 (seen as vertices in the topology) and their interconnections (links 185 in the topology) but no information about the content of the child 186 domains. Each child domain has one PCE taking in charge of computing 187 paths across its own domain. These PCEs are known as child PCEs and 188 have a relationship with the parent PCE. As the Figure 1 shown, 189 H-PCE is parent PCE and PCE-1, PCE-2 and PCE-3 are child PCEs which 190 is responsible for each own SR-AS. 192 When an optimal inter-domain path is required, the ingress PCE sends 193 a request to the parent PCE or the stateful parent PCE itself to 194 initiate the path computation. The parent PCE selects a set of 195 candidate domain paths based on the domain topology and the state of 196 the inter-domain links. It then sends computation requests to the 197 child PCEs responsible for each of the domains on the candidate 198 domain paths. The stateful child PCE in each domain performs active 199 stateful procedure as defined [RFC8231]. 201 2.1. The Stitching LSP Association Solution 203 The LSPs of multiple domains can be stitched together by adding them 204 to a stitching LSP association group as defined in 205 [I-D.hu-pce-stitching-lsp-association]. As the Figure 2 shown, the 206 stateful H-PCE sends the PCInit message defined in [RFC8281] to 207 initiate the inter-domain path computation adding the forwarding LSP 208 1~3 to Assoc#1 and reverse LSP 1'~3' to Assoc#2. The child PCEs may 209 initiate the intra-domain LSPs when receiving the message from parent 210 PCE. 212 +-------+ 213 +------------------+ H-PCE +-----------------+ 214 PCInit | +---+---+ | 215 (LSP1,Assoc#1) | PCInit(LSP2,Assoc#1)| PCInit(LSP3,Assoc#1)| 216 PCInit | PCInit(LSP2',Assoc#2 |PCInit(LSP3',Assoc#2 | 217 (LSP1',Assoc#2)| | | 218 v v v 219 +-----+ +-----+ +-----+ 220 |PCE-1| |PCE-2| |PCE-3| 221 +-----+ +-----+ +-----+ 222 PCInit/ \PCInit PCInit/ \PCInit PCInit/ \PCInit 223 LSP1/ \LSP1' LSP2/ \LSP2' LSP3/ \LSP3' 224 Assoc#1/ \Assoc#2 Assoc#1/ \Assoc#2 Assoc#1/ \Assoc#2 225 v v v v v v 226 +-----+ LSP1 +-----------+ LSP2 +-----------+ LSP3 +-----+ 227 | A |-------->| X |--------->| Y |-------->| Z | 228 | |<--------| |<---------| |<--------| | 229 +-----+ LSP1' +-----------| LSP2' +-----------+ LSP3' +-----+ 231 Figure 2 The SR inter-domain Stitching LSP Association 233 2.2. The Stitching Label Solution 235 The Path Segment can be used for path stithing. The SR sub-paths can 236 be correlated with the use of Path Segment. This section defined the 237 path segments as stitching Labels which used to stitch per-domain LSP 238 tunnels in order to create end-to-end path that cross multiple 239 domains. 241 SR intra-domain path is setup as part of inter-domain SR path. When 242 PCC requests the PCE or the PCE itself to initiate The SR path, the 243 inter-domain path segments should be carried as a stitching Label 244 with the associated link. 246 +-------+ 247 +------------------+ H-PCE +-----------------+ 248 PCInit | +---+---+ | 249 (LSP1,LSP1')| PCInit(LSP2,LSP2')| PCInit(LSP3,LSP3')| 250 SL1,SL1' | SL1,SL1',SL2,SL2' | SL2,SL2' | 251 v v v 252 .................... .................... ..................... 253 . . . . . . 254 . +---+ LSP1 +---+ . . +---+ LSP2+---+ . . +---+ LSP3+----+ . 255 . | A |----->| B |--SL1->| C |---->| X |---SL2-->| Y |---->| Z | . 256 . | |<-----| |<-SL1'-| |<----| |<--SL2'--| |<----| | . 257 . +---+ LSP1'+---+ . . +---+LSP2'+---+ . . +---+LSP3'+----+ . 258 . SR-AS1 . . SR-AS2 . . SR-AS3 . 259 .................... .................... ..................... 261 SL:Stiching Label 263 Figure 3 The SR Inter-Domain Stitching Label 265 3. Inter-domain Path Segment Allocation 267 The inter-domain path segment may be allocated by PCC or PCE. The 268 PCE may be the single domain PCE which taking in charge of the 269 respective domain. The inter-domain path segments is a unique value 270 in the domain which PCC or PCE belongs to. The operation of path 271 segment request and reply may be the same with that in single domain 272 as defined in [I-D.li-pce-sr-path-segment]. 274 3.1. PCC Allocated 276 As defined in [I-D.xiong-spring-path-segment-sr-inter-domain], an 277 inter-domain path segment can be allocated by egress PCC and may be 278 maintained on the PCC itself. The inter-domain path segment connects 279 two domains and the ingress and egress PCC are belong to different 280 domains. The ingress and egress PCC need to exchange messages which 281 carrying path segment information between the two PCEs. 283 The Ingress PCC may request to allocate a path segment from egress 284 PCC. Once egress PCC allocated the inter-domain path segment, it 285 need to inform the PCE in respective domain with the PCRpt message. 286 The PCE need to communicate with the PCE which the ingress PCC 287 belongs to inform the value allocated. 289 3.2. PCE Allocated 291 The ingress PCC may request the inter-domain path segment to be 292 allocated by the PCE in PCC-Initiated LSP. The PCE may allocate the 293 inter-domain path segment on its own domain in PCEs-Initiated LSP. 294 The allocated path segment needs to be informed to the ingress and 295 egress PCC. 297 The inter-domain path segments may be allocated separately by the 298 PCEs which control the ingress and egress PCC along with the LSP 299 initiation. 301 4. PCEP Procedure 303 [RFC8281] describes setup, maintenance and teardown of PCE-initiated 304 LSPs under the stateful PCE model, without the need for local 305 configuration on the PCC. Similar to LSP updation, the inter-domain 306 LSP can be initiated by the ingress PCE using the PCInitiate message 307 to the ingress LSR. The inter-domain path segment is viewed as 308 stitching label. Per-domain LSP may also be initiated by respective 309 domain's PCE and stitched together. 311 4.1. HPCE-initiated LSP 313 In H-PCE [RFC6805] architecture, the parent PCE is used to compute a 314 multi-domain path based on the domain connectivity information. The 315 stateful H-PCE in active model can be used to initiate the inter- 316 domain bidirectional path for SR networks. PCE sends PCInitiate 317 message to its domain SR nodes with ERO={SID LIST} and carrying 318 stitching association group TLV and path segments. If the SR nodes 319 is the border nodes of the SR domain, it correlates the two path 320 segments and the related SID list if the related association ID is 321 the same value. 323 The PECP procedure for the HPCE-initiated LSP is following: 325 The stateful H-PCE initiates the end-to-end path computation across 326 multiple domains and selects a set of candidate domain paths based on 327 the topology. 329 The stateful H-PCE sends PCInitiate message to every PCEs which the 330 end-to-end path traversed, carrying inter-domain path segments 331 allocated by H-PCE, stitching LSP association group and the SID list 332 in the ERO object. 334 The stateful child PCE in each domain perform active stateful 335 procedure as defined in [I-D.li-pce-sr-path-segment]. 337 4.2. PCC-initiated LSP 339 In case of passive path computation request to the ingress PCE from 340 the ingress LSR, the H-PCE path computation procedure is applied to 341 compute sequence of domains or end-to-end path by using PCReq and 342 PCRep messages among stateful PCEs in passive mode. 344 In case of delegation to the ingress PCE (active stateful PCE), the 345 ingress child PCE may further delegate to parent PCE as per 346 [I-D.ietf-pce-stateful-hpce]. The parent PCE could update the path 347 of the inter-domain LSP. 349 The ingress nodes of the source AS sends the PCReq message to its 350 PCE, then the PCE sends PCReq message to the H-PCE or stateful PCEs 351 in other domains. The PECP procedure for the PCC-initiated LSP in 352 H-PCE model is as follow. 354 The ingress PCC from the ingress domain sends a PCReq request to the 355 PCE which is responsible for the domain containing the destination 356 information. 358 The ingress PCE sends the path computation request direct to the 359 parent PCE. 361 The parent PCE computes the optimal end-to-end path and initiates the 362 inter-domain paths to the child PCEs which the path traversed. 364 Each PCE sends PCInitiate message to ingress or egress nodes of its 365 domain to initiate the LSPs. 367 5. Security Considerations 369 TBD. 371 6. IANA Considerations 373 TBD. 375 7. Acknowledgements 377 TBD. 379 8. References 381 8.1. Informative References 383 [RFC6805] King, D., Ed. and A. Farrel, Ed., "The Application of the 384 Path Computation Element Architecture to the Determination 385 of a Sequence of Domains in MPLS and GMPLS", RFC 6805, 386 DOI 10.17487/RFC6805, November 2012, 387 . 389 8.2. Normative References 391 [I-D.hu-pce-stitching-lsp-association] 392 hu, f., Xiong, Q., Mirsky, G., and W. Cheng, "Stitching 393 LSP Association", draft-hu-pce-stitching-lsp- 394 association-00 (work in progress), December 2018. 396 [I-D.ietf-pce-segment-routing] 397 Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 398 and J. Hardwick, "PCEP Extensions for Segment Routing", 399 draft-ietf-pce-segment-routing-16 (work in progress), 400 March 2019. 402 [I-D.ietf-pce-stateful-hpce] 403 Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., and D. King, 404 "Hierarchical Stateful Path Computation Element (PCE).", 405 draft-ietf-pce-stateful-hpce-11 (work in progress), July 406 2019. 408 [I-D.ietf-spring-mpls-path-segment] 409 Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler, 410 "Path Segment in MPLS Based Segment Routing Network", 411 draft-ietf-spring-mpls-path-segment-00 (work in progress), 412 March 2019. 414 [I-D.li-pce-sr-bidir-path] 415 Li, C., Chen, M., Cheng, W., Li, Z., Dong, J., Gandhi, R., 416 and Q. Xiong, "PCEP Extensions for Associated 417 Bidirectional Segment Routing (SR) Paths", draft-li-pce- 418 sr-bidir-path-05 (work in progress), March 2019. 420 [I-D.li-pce-sr-path-segment] 421 Li, C., Chen, M., Cheng, W., Dong, J., Li, Z., Gandhi, R., 422 and Q. Xiong, "Path Computation Element Communication 423 Protocol (PCEP) Extension for Path Segment in Segment 424 Routing (SR)", draft-li-pce-sr-path-segment-05 (work in 425 progress), March 2019. 427 [I-D.xiong-spring-path-segment-sr-inter-domain] 428 Xiong, Q., Mirsky, G., and W. Cheng, "The Use of Path 429 Segment in SR Inter-domain Scenarios", draft-xiong-spring- 430 path-segment-sr-inter-domain-00 (work in progress), July 431 2019. 433 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 434 Requirement Levels", BCP 14, RFC 2119, 435 DOI 10.17487/RFC2119, March 1997, 436 . 438 [RFC4105] Le Roux, J., Ed., Vasseur, J., Ed., and J. Boyle, Ed., 439 "Requirements for Inter-Area MPLS Traffic Engineering", 440 RFC 4105, DOI 10.17487/RFC4105, June 2005, 441 . 443 [RFC4216] Zhang, R., Ed. and J. Vasseur, Ed., "MPLS Inter-Autonomous 444 System (AS) Traffic Engineering (TE) Requirements", 445 RFC 4216, DOI 10.17487/RFC4216, November 2005, 446 . 448 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 449 Element (PCE)-Based Architecture", RFC 4655, 450 DOI 10.17487/RFC4655, August 2006, 451 . 453 [RFC5152] Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A 454 Per-Domain Path Computation Method for Establishing Inter- 455 Domain Traffic Engineering (TE) Label Switched Paths 456 (LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008, 457 . 459 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 460 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 461 DOI 10.17487/RFC5440, March 2009, 462 . 464 [RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux, 465 "A Backward-Recursive PCE-Based Computation (BRPC) 466 Procedure to Compute Shortest Constrained Inter-Domain 467 Traffic Engineering Label Switched Paths", RFC 5441, 468 DOI 10.17487/RFC5441, April 2009, 469 . 471 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 472 Computation Element Communication Protocol (PCEP) 473 Extensions for Stateful PCE", RFC 8231, 474 DOI 10.17487/RFC8231, September 2017, 475 . 477 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 478 Computation Element Communication Protocol (PCEP) 479 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 480 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 481 . 483 Authors' Addresses 485 Quan Xiong 486 ZTE Corporation 487 No.6 Huashi Park Rd 488 Wuhan, Hubei 430223 489 China 491 Phone: +86 27 83531060 492 Email: xiong.quan@zte.com.cn 494 Fangwei Hu 495 ZTE Corporation 496 No.889 Bibo Rd 497 Shanghai 201203 498 China 500 Phone: +86 21 68896273 501 Email: hu.fangwei@zte.com.cn 503 Greg Mirsky 504 ZTE Corporation 505 USA 507 Email: gregimirsky@gmail.com 508 Weiqiang Cheng 509 China Mobile 510 Beijing 511 China 513 Email: chengweiqiang@chinamobile.com