idnits 2.17.1 draft-ietf-pce-stateful-hpce-11.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (July 8, 2019) is 1753 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-10) exists of draft-litkowski-pce-state-sync-05 == Outdated reference: A later version (-23) exists of draft-ietf-pce-pcep-yang-12 == Outdated reference: A later version (-04) exists of draft-dugeon-pce-stateful-interdomain-02 == Outdated reference: A later version (-11) exists of draft-ietf-pce-lsp-control-request-06 == Outdated reference: A later version (-13) exists of draft-ietf-pce-enhanced-errors-05 Summary: 0 errors (**), 0 flaws (~~), 6 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PCE Working Group D. Dhody 3 Internet-Draft Huawei Technologies 4 Intended status: Informational Y. Lee 5 Expires: January 9, 2020 Futurewei Technologies 6 D. Ceccarelli 7 Ericsson 8 J. Shin 9 SK Telecom 10 D. King 11 Lancaster University 12 July 8, 2019 14 Hierarchical Stateful Path Computation Element (PCE). 15 draft-ietf-pce-stateful-hpce-11 17 Abstract 19 A Stateful Path Computation Element (PCE) maintains information on 20 the current network state, including: computed Label Switched Path 21 (LSPs), reserved resources within the network, and pending path 22 computation requests. This information may then be considered when 23 computing new traffic engineered LSPs, and for associated and 24 dependent LSPs, received from Path Computation Clients (PCCs). The 25 Path computation response from a PCE is helpful for the PCC to 26 gracefully establish the computed LSP. 28 The Hierarchical Path Computation Element (H-PCE) architecture, 29 provides an architecture to allow the optimum sequence of 30 inter-connected domains to be selected, and network policy to be 31 applied if applicable, via the use of a hierarchical relationship 32 between PCEs. 34 Combining the capabilities of Stateful PCE and the Hierarchical PCE 35 would be advantageous. This document describes general considerations 36 and use cases for the deployment of Stateful, and not Stateless, PCEs 37 using the Hierarchical PCE architecture. 39 Status of This Memo 41 This Internet-Draft is submitted in full conformance with the 42 provisions of BCP 78 and BCP 79. 44 Internet-Drafts are working documents of the Internet Engineering 45 Task Force (IETF). Note that other groups may also distribute 46 working documents as Internet-Drafts. The list of current Internet- 47 Drafts is at https://datatracker.ietf.org/drafts/current/. 48 Internet-Drafts are draft documents valid for a maximum of six months 49 and may be updated, replaced, or obsoleted by other documents at any 50 time. It is inappropriate to use Internet-Drafts as reference 51 material or to cite them other than as "work in progress." 53 This Internet-Draft will expire on December 18, 2019. 55 Copyright Notice 57 Copyright (c) 2019 IETF Trust and the persons identified as the 58 document authors. All rights reserved. 60 This document is subject to BCP 78 and the IETF Trust's Legal 61 Provisions Relating to IETF Documents 62 (https://trustee.ietf.org/license-info) in effect on the date of 63 publication of this document. Please review these documents 64 carefully, as they describe your rights and restrictions with respect 65 to this document. Code Components extracted from this document must 66 include Simplified BSD License text as described in Section 4.e of 67 the Trust Legal Provisions and are provided without warranty as 68 described in the Simplified BSD License. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 73 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . . 3 74 1.2. Use-cases and Applicability of Hierarchical Stateful PCE . 4 75 1.2.1. Applicability to ACTN . . . . . . . . . . . . . . . . 5 76 1.2.2. End-to-End Contiguous LSP . . . . . . . . . . . . . . 5 77 1.2.3. Applicability of a Stateful P-PCE . . . . . . . . . . 6 78 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 79 3. Hierarchical Stateful PCE . . . . . . . . . . . . . . . . . . 8 80 3.1. Passive Operations . . . . . . . . . . . . . . . . . . . . 9 81 3.2. Active Operations . . . . . . . . . . . . . . . . . . . . 11 82 3.3. PCE Initiation of LSPs . . . . . . . . . . . . . . . . . . 12 83 3.3.1. Per Domain Stitched LSP . . . . . . . . . . . . . . . 13 84 4. Security Considerations . . . . . . . . . . . . . . . . . . . 15 85 5. Manageability Considerations . . . . . . . . . . . . . . . . . 16 86 5.1. Control of Function and Policy . . . . . . . . . . . . . . 16 87 5.2. Information and Data Models . . . . . . . . . . . . . . . 16 88 5.3. Liveness Detection and Monitoring . . . . . . . . . . . . 16 89 5.4. Verify Correct Operations . . . . . . . . . . . . . . . . 16 90 5.5. Requirements On Other Protocols . . . . . . . . . . . . . 16 91 5.6. Impact On Network Operations . . . . . . . . . . . . . . . 17 92 5.7. Error Handling between PCEs . . . . . . . . . . . . . . . 17 93 6. Other Considerations . . . . . . . . . . . . . . . . . . . . . 17 94 6.1. Applicability to Inter-Layer Traffic Engineering . . . . . 17 95 6.2. Scalability Considerations . . . . . . . . . . . . . . . . 18 96 6.3. Confidentiality . . . . . . . . . . . . . . . . . . . . . 18 97 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 98 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 99 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 100 9.1. Normative References . . . . . . . . . . . . . . . . . . . 18 101 9.2. Informative References . . . . . . . . . . . . . . . . . . 19 102 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 103 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22 105 1. Introduction 107 1.1. Background 109 The Path Computation Element communication Protocol (PCEP) [RFC5440] 110 provides mechanisms for Path Computation Elements (PCEs) to perform 111 path computations in response to Path Computation Clients' (PCCs) 112 requests. 114 A stateful PCE is capable of considering, for the purposes of path 115 computation, not only the network state in terms of links and nodes 116 (referred to as the Traffic Engineering Database or TED) but also the 117 status of active services (previously computed paths, and currently 118 reserved resources, stored in the Label Switched Paths Database 119 (LSP-DB). 121 [RFC8051] describes general considerations for a stateful PCE 122 deployment and examines its applicability and benefits, as well as 123 its challenges and limitations through a number of use cases. 125 [RFC8231] describes a set of extensions to PCEP to provide stateful 126 control. A stateful PCE has access to not only the information 127 carried by the network's Interior Gateway Protocol (IGP), but also 128 the set of active paths and their reserved resources for its 129 computations. The additional state allows the PCE to compute 130 constrained paths while considering individual LSPs and their 131 interactions. [RFC8281] describes the setup, maintenance and 132 teardown of PCE-initiated LSPs under the stateful PCE model. 134 [RFC8231] also describes the active stateful PCE. The active PCE 135 functionality allows a PCE to reroute an existing LSP or make changes 136 to the attributes of an existing LSP, or delegate control of specific 137 LSPs to a new PCE. 139 The ability to compute shortest constrained TE LSPs in Multiprotocol 140 Label Switching (MPLS) and Generalized MPLS (GMPLS) networks across 141 multiple domains has been identified as a key motivation for PCE 142 development. [RFC6805] describes a Hierarchical PCE (H-PCE) 143 architecture which can be used for computing end-to-end paths for 144 inter-domain MPLS Traffic Engineering (TE) and GMPLS Label Switched 145 Paths (LSPs). Within the Hierarchical PCE (H-PCE) architecture 146 [RFC6805], the Parent PCE (P-PCE) is used to compute a multi-domain 147 path based on the domain connectivity information. A Child PCE 148 (C-PCE) may be responsible for a single domain or multiple domains, 149 it is used to compute the intra-domain path based on its domain 150 topology information. 152 This document presents general considerations for stateful PCEs, and 153 not Stateless PCEs, in the hierarchical PCE architecture. In 154 particular, the behavior changes and additions to the existing 155 stateful PCE mechanisms (including PCE-initiated LSP setup and active 156 PCE usage) in the context of networks using the H-PCE architecture. 158 In this document, Sections 3.1 and 3.2 focus on end to end (E2E) 159 inter-domain TE LSP. Section 3.3.1 describes the operations for 160 stitching Per Domain LSPs. 162 1.2. Use-cases and Applicability of Hierarchical Stateful PCE 164 As per [RFC6805], in the hierarchical PCE architecture, a P-PCE 165 maintains a domain topology map that contains the child domains and 166 their interconnections. Usually, the P-PCE has no information about 167 the content of the child domains. But if the PCE is applied to the 168 Abstraction and Control of TE Networks (ACTN) [RFC8453] as described 169 in [I-D.ietf-pce-applicability-actn], the Provisioning Network 170 Controller (PNC) can provide an abstract topology to the Multi-Domain 171 Service Coordinator (MDSC). Thus the P-PCE in MDSC could be aware of 172 topology information in much more detail than just the domain 173 topology. 175 In a PCEP session between a PCC (Ingress) and a C-PCE, the C-PCE acts 176 as per the stateful PCE operations described in [RFC8231] and 177 [RFC8281]. The same C-PCE behaves as a PCC on the PCEP session 178 towards the P-PCE. The P-PCE is stateful in nature and thus maintains 179 the state of the inter-domain LSPs that are reported to it. The 180 inter-domain LSP could also be delegated by the C-PCE to the P-PCE, 181 so that the P-PCE could update the inter-domain path. The trigger for 182 this update could be the LSP state change reported for this LSP or 183 any other LSP. It could also be a change in topology at the P-PCE 184 such as inter-domain link status change. In case of use of stateful 185 H-PCE in ACTN, a change in abstract topology learned by the P-PCE 186 could also trigger the update. Some other external factors (such as a 187 measurement probe) could also be a trigger at the P-PCE. Any such 188 update would require an inter-domain path recomputation as described 189 in [RFC6805]. 191 The inter-domain LSP could be set up using the end-to-end signaling 192 as described in [RFC6805]. Additionally a per-domain stitched LSP 193 model is also applicable in a P-PCE initiation model. Section 3.1, 194 Section 3.2, and Section 3.3 describe the end-to-end Contiguous LSP 195 setup, whereas Section 3.3.1 describe the per-domain stitching. 197 1.2.1. Applicability to ACTN 199 [RFC8453] describes a framework for the Abstraction and Control of TE 200 Networks (ACTN), where each Provisioning Network Controller (PNC) is 201 equivalent to a C-PCE, and the P-PCE is the Multi-Domain Service 202 Coordinator (MDSC). The Per Domain stitched LSP as per the 203 Hierarchical PCE architecture described in Section 3.3.1 and Section 204 4.1 is well suited for ACTN deployments. 206 [I-D.ietf-pce-applicability-actn] examines the applicability of PCE 207 to the ACTN framework. To support the function of multi domain 208 coordination via hierarchy, the hierarchy of stateful PCEs play a 209 crucial role. 211 In the ACTN framework, a Customer Network Controller (CNC) can 212 request the MDSC to check whether there is a possibility to meet 213 Virtual Network (VN) requirements before requesting for the VN to be 214 provisioned. The H-PCE architecture as described in [RFC6805] can 215 support this function using PCReq and PCRep messages between the 216 P-PCE and C-PCEs. When the CNC requests for VN provisioning, the MDSC 217 decompose this request into multiple inter-domain LSP provisioning 218 requests, which might be further decomposed to per-domain path 219 segments. This is described in Section 3.3.1. The MDSC uses the LSP 220 Initiate Request (PCInitiate) message from the P-PCE towards the 221 C-PCE, and the C-PCE reports the state back to the P-PCE via a Path 222 Computation State Report (PCRpt) message. The P-PCE could make 223 changes to the LSP via the use of a Path Computation Update Request 224 (PCUpd) message. 226 In this case, the P-PCE (as MDSC) interacts with multiple C-PCEs (as 227 PNCs) along the inter-domain path of the LSP. 229 1.2.2. End-to-End Contiguous LSP 231 Different signaling methods for inter-domain RSVP-TE signaling are 232 identified in [RFC4726]. Contiguous LSPs are achieved using the 233 procedures of [RFC3209] and [RFC3473] to create a single end-to-end 234 LSP that spans all domains. [RFC6805] describes the technique to 235 establish the optimum path when the sequence of domains is not known 236 in advance. It shows how the PCE architecture can be extended to 237 allow the optimum sequence of domains to be selected, and the optimum 238 end-to-end path to be derived. 240 In case of a stateful P-PCE, the stateful P-PCE has to be aware of 241 the inter-domain LSPs for it to consider them during path 242 computation. For example, a domain diverse path from another LSP. 243 This is the Passive Stateful P-PCE as described in Section 3.1. 244 Additionally, the inter-domain LSP could be delegated to the P-PCE, 245 so that P-PCE could trigger an update via a PCUpd message. The update 246 could be triggered on receipt of the PCRpt message that indicates a 247 status change of this LSP or some other LSP. The other LSP could be 248 an associated LSP (such as protection) or an unrelated LSP whose 249 resource change leads to re-optimization at the P-PCE. This is the 250 Active Stateful Operation as described in Section 3.2. Further, the 251 P-PCE could be instructed to create an inter-domain LSP on its own 252 using the PCInitiate message for an E2E contiguous LSP. The P-PCE 253 would send the PCInitiate message to the Ingress domain C-PCE, which 254 would further instruct the Ingress PCC. 256 In this document, for the Contiguous LSP, the above interactions are 257 only between the ingress domain C-PCE and the P-PCE. The use of 258 stateful operations for an inter-domain LSP between the 259 transit/egress domain C-PCEs towards the P-PCE is out of scope of 260 this document. 262 1.2.3. Applicability of a Stateful P-PCE 264 [RFC8051] describes general considerations for a stateful PCE 265 deployment and examines its applicability and benefits, as well as 266 its challenges and limitations, through a number of use cases. These 267 are also applicable to the stateful P-PCE when used for the inter- 268 domain LSP path computation and setup. It should be noted that though 269 the stateful P-PCE has limited direct visibility inside the child 270 domain, it could still trigger re-optimization with the help of child 271 PCEs based on LSP state changes, abstract topology changes, or some 272 other external factors. 274 The C-PCE would delegate control of the inter-domain LSP to the P-PCE 275 so that the P-PCE can make changes to it. Note that, if the C-PCE 276 becomes aware of a topology change that is hidden from the P-PCE, it 277 could take back the delegation from the P-PCE to act on it itself. 278 Similarly, a P-PCE could also request for delegation if it needs to 279 make a change to the LSP (refer to 280 [I-D.ietf-pce-lsp-control-request]). 282 2. Terminology 284 The terminology is as per [RFC4655], [RFC5440], [RFC6805], [RFC8051], 285 [RFC8231], and [RFC8281]. 287 3. Hierarchical Stateful PCE 289 As described in [RFC6805], in the hierarchical PCE architecture, a 290 P-PCE maintains a domain topology map that contains the child domains 291 (seen as vertices in the topology) and their interconnections (links 292 in the topology). The P-PCE has no information about the content of 293 the child domains. Each child domain has at least one PCE capable of 294 computing paths across the domain. These PCEs are known as C-PCEs 295 and have a direct relationship with the P-PCE. The P-PCE builds the 296 domain topology map either via direct configuration (allowing network 297 policy to also be applied) or from learned information received from 298 each C-PCE. 300 Note that, in the scope of this document, both the C-PCEs and the P- 301 PCE are stateful in nature. 303 [RFC8231] specifies new functions to support a stateful PCE. It also 304 specifies that a function can be initiated either from a PCC towards 305 a PCE (C-E) or from a PCE towards a PCC (E-C). 307 This document extends these functions to support H-PCE Architecture 308 from a C-PCE towards P-PCE (EC-EP) or from a P-PCE towards C-PCE 309 (EP-EC). All PCE types herein (i.e., EC-EP or EP-EC) are assumed to 310 be "stateful PCE". 312 A number of interactions are expected in the Hierarchical Stateful 313 PCE architecture, these include: 315 LSP State Report (EC-EP): a child stateful PCE sends an LSP state 316 report to a Parent Stateful PCE whenever the state of a LSP 317 changes. 319 LSP State Synchronization (EC-EP): after the session between the 320 Child and Parent stateful PCEs is initialized, the P-PCE must 321 learn the state of C-PCE's TE LSPs. 323 LSP Control Delegation (EC-EP,EP-EC): a C-PCE grants to the P-PCE 324 the right to update LSP attributes on one or more LSPs; the C-PCE 325 may withdraw the delegation or the P-PCE may give up the 326 delegation at any time. 328 LSP Update Request (EP-EC): a stateful P-PCE requests modification 329 of attributes on a C-PCE's TE LSP. 331 PCE LSP Initiation Request (EP-EC): a stateful P-PCE requests C-PCE 332 to initiate a TE LSP. 334 Note that this hierarchy is recursive and thus a Label Switching 335 Router (LSR), as a PCC could delegate the control to a PCE, which may 336 delegate to its parent, which may further delegate it to its parent 337 (if it exist or needed). Similarly update operations could also be 338 applied recursively. 340 [I-D.ietf-pce-hierarchy-extensions] defines the H-PCE Capability TLV 341 that is used in the OPEN message to advertise the H-PCE capability. 342 [RFC8231] defines the Stateful PCE Capability TLV used in the OPEN 343 message to indicate stateful support. The presence of both TLVs in 344 an OPEN message indicates the support for stateful H-PCE operations 345 as described in this document. 347 Further consideration may be made for optional procedures for 348 stateful communication coordination between PCEs, including 349 procedures to minimise computational loops. The procedures described 350 in [I-D.litkowski-pce-state-sync] facilitate stateful communication 351 between PCEs for various use-cases. The procedures and extensions as 352 described in Section 3 of [I-D.litkowski-pce-state-sync] are also 353 applicable to Child and Parent PCE communication. The 354 SPEAKER-IDENTITY-TLV (defined in [RFC8232]) is included in the LSP 355 object to identify the Ingress (PCC). The PLSP-ID used in the 356 forwarded PCRpt by the C-PCE to P-PCE is same as the original one 357 used by the PCC. 359 3.1. Passive Operations 361 Procedures as described in [RFC6805] are applied and where the 362 ingress C-PCE (Child PCE), triggers a path computation request for 363 the LER in the domain where the LSP originates, sends a request to 364 the P-PCE. The P-PCE selects a set of candidate domain paths based on 365 the domain topology and the state of the inter-domain links. It then 366 sends computation requests to the C-PCEs responsible for each of the 367 domains on the candidate domain paths. Each C-PCE computes a set of 368 candidate path segments across its domain and sends the results to 369 the P-PCE. The P-PCE uses this information to select path segments 370 and concatenate them to derive the optimal end-to-end inter-domain 371 path. The end-to-end path is then sent to the C-PCE that received 372 the initial path request, and this C-PCE passes the path on to the 373 PCC that issued the original request. 375 As per [RFC8231], PCC sends an LSP State Report carried on a PCRpt 376 message to the C-PCE, indicating the LSP's status. The C-PCE may 377 further propagate the State Report to the P-PCE. A local policy at 378 C-PCE may dictate which LSPs to be reported to the P-PCE. The PCRpt 379 message is sent from C-PCE to P-PCE. 381 State synchronization mechanism as described in [RFC8231] and 383 [RFC8232] are applicable to a PCEP session between C-PCE and P-PCE as 384 well. 386 We use the sample hierarchical domain topology example from [RFC6805] 387 as the reference topology for the entirety of this document. It is 388 shown in Figure 1. 389 ----------------------------------------------------------------- 390 | Domain 5 | 391 | ----- | 392 | |PCE 5| | 393 | ----- | 394 | | 395 | ---------------- ---------------- ---------------- | 396 | | Domain 1 | | Domain 2 | | Domain 3 | | 397 | | | | | | | | 398 | | ----- | | ----- | | ----- | | 399 | | |PCE 1| | | |PCE 2| | | |PCE 3| | | 400 | | ----- | | ----- | | ----- | | 401 | | | | | | | | 402 | | ----| |---- ----| |---- | | 403 | | |BN11+---+BN21| |BN23+---+BN31| | | 404 | | - ----| |---- ----| |---- - | | 405 | | |S| | | | | |D| | | 406 | | - ----| |---- ----| |---- - | | 407 | | |BN12+---+BN22| |BN24+---+BN32| | | 408 | | ----| |---- ----| |---- | | 409 | | | | | | | | 410 | | ---- | | | | ---- | | 411 | | |BN13| | | | | |BN33| | | 412 | -----------+---- ---------------- ----+----------- | 413 | \ / | 414 | \ ---------------- / | 415 | \ | | / | 416 | \ |---- ----| / | 417 | ----+BN41| |BN42+---- | 418 | |---- ----| | 419 | | | | 420 | | ----- | | 421 | | |PCE 4| | | 422 | | ----- | | 423 | | | | 424 | | Domain 4 | | 425 | ---------------- | 426 | | 427 ----------------------------------------------------------------- 429 Figure 1: Sample Hierarchical Domain Topology 431 Steps 1 to 11 are exactly as described in section 4.6.2 (Hierarchical 432 PCE End-to-End Path Computation Procedure) of [RFC6805], the 433 following additional steps are added for stateful PCE: 435 (A) The Ingress LSR initiates the setup of the LSP as per the path 436 and reports to the PCE1 the LSP status ("GOING-UP"). 438 (B) The PCE1 further reports the status of the LSP to the P-PCE 439 (PCE5). 441 (C) The Ingress LSR notifies the LSP state to PCE1 when the state is 442 "UP". 444 (D) The PCE1 further reports the status of the LSP to the P-PCE 445 (PCE5). 447 The Ingress LSR could trigger path re-optimization by sending the 448 path computation request as described in [RFC6805], at this time it 449 can include the LSP object in the PCReq message as described in 450 [RFC8231]. 452 3.2. Active Operations 454 [RFC8231] describes the case of active stateful PCE. The active PCE 455 functionality uses two specific PCEP messages: 457 o Update Request (PCUpd) 459 o State Report (PCRpt) 461 The first is sent by the PCE to a Path Computation Client (PCC) for 462 modifying LSP attributes. The PCC sends back a PCRpt to acknowledge 463 the requested operation or report any change in LSP's state. 465 As per [RFC8051], Delegation is an operation to grant a PCE, 466 temporary rights to modify a subset of LSP parameters on one or more 467 PCC's LSPs. The C-PCE may further choose to delegate to P-PCE based 468 on a local policy. The PCRpt message with "D" (delegate) flag is 469 sent from C-PCE to P-PCE. 471 To update an LSP, a PCE sends an LSP Update Request to the PCC using 472 a PCUpd message. For LSP delegated to the P-PCE via the child PCE, 473 the P-PCE can use the same PCUpd message to request change to the C- 474 PCE (the Ingress domain PCE), the PCE further propagates the update 475 request to the PCC. 477 The P-PCE uses the same mechanism described in Section 3.1 to compute 478 the end to end path using PCReq and PCRep messages. 480 For active operations, the following steps are required when 481 delegating the LSP, again using the reference architecture described 482 in Figure 1 (Sample Hierarchical Domain Topology). 484 (A) The Ingress LSR delegates the LSP to the PCE1 via PCRpt message 485 with D flag set. 487 (B) The PCE1 further delegates the LSP to the P-PCE (PCE5). 489 (C) Steps 4 to 10 of section 4.6.2 of [RFC6805] are executed to 490 determine the end to end path. 492 (D) The P-PCE (PCE5) sends the update request to the C-PCE (PCE1) 493 via PCUpd message. 495 (E) The PCE1 further updates the LSP to the Ingress LSR (PCC). 497 (F) The Ingress LSR initiates the setup of the LSP as per the path 498 and reports to the PCE1 the LSP status ("GOING-UP"). 500 (G) The PCE1 further reports the status of the LSP to the P-PCE 501 (PCE5). 503 (H) The Ingress LSR notifies the LSP state to PCE1 when the state is 504 "UP". 506 (I) The PCE1 further reports the status of the LSP to the P-PCE 507 (PCE5). 509 3.3. PCE Initiation of LSPs 511 [RFC8281] describes the setup, maintenance and teardown of PCE- 512 initiated LSPs under the stateful PCE model, without the need for 513 local configuration on the PCC, thus allowing for a dynamic network 514 that is centrally controlled and deployed. To instantiate or delete 515 an LSP, the PCE sends the Path Computation LSP Initiate Request 516 (PCInitiate) message to the PCC. In case of inter-domain LSP in 517 Hierarchical PCE architecture, the initiation operations can be 518 carried out at the P-PCE. In which case after P-PCE finishes the E2E 519 path computation, it can send the PCInitiate message to the C-PCE 520 (the Ingress domain PCE), the PCE further propagates the initiate 521 request to the PCC. 523 The following steps are performed, for PCE initiated operations, 524 again using the reference architecture described in Figure 1 (Sample 525 Hierarchical Domain Topology): 527 (A) The P-PCE (PCE5) is requested to initiate a LSP. Steps 4 to 10 528 of section 4.6.2 of [RFC6805] are executed to determine the end 529 to end path. 531 (B) The P-PCE (PCE5) sends the initiate request to the child PCE 532 (PCE1) via PCInitiate message. 534 (C) The PCE1 further propagates the initiate message to the Ingress 535 LSR (PCC). 537 (D) The Ingress LSR initiates the setup of the LSP as per the path 538 and reports to the PCE1 the LSP status ("GOING-UP"). 540 (E) The PCE1 further reports the status of the LSP to the P-PCE 541 (PCE5). 543 (F) The Ingress LSR notifies the LSP state to PCE1 when the state is 544 "UP". 546 (G) The PCE1 further reports the status of the LSP to the P-PCE 547 (PCE5). 549 The Ingress LSR (PCC) would generate the PLSP-ID for the LSP and 550 inform the C-PCE, which is propagated to the P-PCE. 552 3.3.1. Per Domain Stitched LSP 554 The Hierarchical PCE architecture as per [RFC6805] is primarily used 555 for E2E LSP. With PCE-Initiated capability, another mode of 556 operation is possible, where multiple intra-domain LSPs are initiated 557 in each domain which are further stitched to form an E2E LSP. The 558 P-PCE sends PCInitiate message to each C-PCE separately to initiate 559 individual LSP segments along the domain path. These individual per 560 domain LSP are stitched together by some mechanism, which is out of 561 scope of this document (Refer [I-D.dugeon-pce-stateful- 562 interdomain]). 564 The following steps are performed, for the Per Domain stitched LSP 565 operation, again using the reference architecture described in Figure 566 1 (Sample Hierarchical Domain Topology): 568 (A) The P-PCE (PCE5) is requested to initiate a LSP. Steps 4 to 10 569 of section 4.6.2 of [RFC6805] are executed to determine the end 570 to end path, which are broken into per-domain LSPs say - 572 o S-BN41 574 o BN41-BN33 575 o BN33-D 577 It should be noted that the P-PCE may use other mechanisms to 578 determine the suitable per-domain LSPs (apart from [RFC6805]). 580 For LSP (BN33-D) 582 (B) The P-PCE (PCE5) sends the initiate request to the child PCE 583 (PCE3) via PCInitiate message for LSP (BN33-D). 585 (C) The PCE3 further propagates the initiate message to BN33. 587 (D) BN33 initiates the setup of the LSP as per the path and reports 588 to the PCE3 the LSP status ("GOING-UP"). 590 (E) The PCE3 further reports the status of the LSP to the P-PCE 591 (PCE5). 593 (F) The node BN33 notifies the LSP state to PCE3 when the state is 594 "UP". 596 (G) The PCE3 further reports the status of the LSP to the P-PCE 597 (PCE5). 599 For LSP (BN41-BN33) 601 (H) The P-PCE (PCE5) sends the initiate request to the child PCE 602 (PCE4) via PCInitiate message for LSP (BN41-BN33). 604 (I) The PCE4 further propagates the initiate message to BN41. 606 (J) BN41 initiates the setup of the LSP as per the path and reports 607 to the PCE4 the LSP status ("GOING-UP"). 609 (K) The PCE4 further reports the status of the LSP to the P-PCE 610 (PCE5). 612 (L) The node BN41 notifies the LSP state to PCE4 when the state is 613 "UP". 615 (M) The PCE4 further reports the status of the LSP to the P-PCE 616 (PCE5). 618 For LSP (S-BN41) 620 (N) The P-PCE (PCE5) sends the initiate request to the child PCE 621 (PCE1) via PCInitiate message for LSP (S-BN41). 623 (O) The PCE1 further propagates the initiate message to node S. 625 (P) S initiates the setup of the LSP as per the path and reports to 626 the PCE1 the LSP status ("GOING-UP"). 628 (Q) The PCE1 further reports the status of the LSP to the P-PCE 629 (PCE5). 631 (R) The node S notifies the LSP state to PCE1 when the state is 632 "UP". 634 (S) The PCE1 further reports the status of the LSP to the P-PCE 635 (PCE5). 637 Additionally: 639 (T) Once P-PCE receives report of each per-domain LSP, it should use 640 suitable stitching mechanism, which is out of scope of this 641 document. In this step, P-PCE (PCE5) could also initiate an E2E 642 LSP (S-D) by sending the PCInitiate message to Ingress C-PCE 643 (PCE1). 645 Note that each per-domain LSP can be setup in parallel. Further, it 646 is also possible to stitch the per-domain LSP at the same time as the 647 per-domain LSPs are initiated. This option is defined in 648 [I-D.dugeon-pce-stateful-interdomain]. 650 4. Security Considerations 652 The security considerations listed in [RFC8231],[RFC6805] and 653 [RFC5440] apply to this document as well. As per [RFC6805], it is 654 expected that the parent PCE will require all child PCEs to use full 655 security when communicating with the parent. 657 Any multi-domain operation necessarily involves the exchange of 658 information across domain boundaries. This is bound to represent a 659 significant security and confidentiality risk especially when the 660 child domains are controlled by different commercial concerns. PCEP 661 allows individual PCEs to maintain confidentiality of their domain 662 path information using path-keys [RFC5520], and the hierarchical PCE 663 architecture is specifically designed to enable as much isolation of 664 domain topology and capabilities information as is possible. The LSP 665 state in the PCRpt message must continue to maintain the internal 666 domain confidentiality when required. 668 The security consideration for PCE-Initiated LSP as per [RFC8281] is 669 also applicable from P-PCE to C-PCE. 671 Further, section 6.3 describes the use of path-key [RFC5520] for 672 confidentiality between C-PCE and P-PCE. 674 Thus securing the PCEP session (between the P-PCE and the C-PCE) 675 using the TCP Authentication Option (TCP-AO) [RFC5925] or Transport 676 Layer Security (TLS) [RFC8253] mechanisms are recommended. 678 5. Manageability Considerations 680 All manageability requirements and considerations listed in 681 [RFC5440], [RFC6805], [RFC8231], and [RFC8281] apply to Stateful H- 682 PCE defined in this document. In addition, requirements and 683 considerations listed in this section apply. 685 5.1. Control of Function and Policy 687 Support of the hierarchical procedure will be controlled by the 688 management organization responsible for each child PCE. The parent 689 PCE must only accept path computation requests from authorized child 690 PCEs. If a parent PCE receives report from an unauthorized child 691 PCE, the report should be dropped. All mechanism as described in 692 [RFC8231] and [RFC8281] continue to apply. 694 5.2. Information and Data Models 696 An implementation should allow the operator to view the stateful and 697 H-PCE capabilities advertised by each peer. The PCEP YANG module 698 [I-D.ietf-pce-pcep-yang] may be extended to include details for 699 stateful H-PCE deployment and operation, exact attributes to be 700 modeled is out of scope for this document. 702 5.3. Liveness Detection and Monitoring 704 Mechanisms defined in this document do not imply any new liveness 705 detection and monitoring requirements in addition to those already 706 listed in [RFC5440]. 708 5.4. Verify Correct Operations 710 Mechanisms defined in this document do not imply any new operation 711 verification requirements in addition to those already listed in 712 [RFC5440] and [RFC8231]. 714 5.5. Requirements On Other Protocols 716 Mechanisms defined in this document do not imply any new requirements 717 on other protocols. 719 5.6. Impact On Network Operations 721 Mechanisms defined in [RFC5440] and [RFC8231] also apply to PCEP 722 extensions defined in this document. 724 The stateful H-PCE technique brings the applicability of stateful PCE 725 as described in [RFC8051], for the LSP traversing multiple domains. 727 5.7. Error Handling between PCEs 729 Error types and notifications useful for correct PCEP operation may 730 be implemented for managing parent and child PCE interaction. PCEP 731 Error behavior propagation, notification and error criticality level, 732 are further defined in [I-D.ietf-pce-enhanced-errors]. 734 6. Other Considerations 736 6.1. Applicability to Inter-Layer Traffic Engineering 738 [RFC5623] describes a framework for applying the PCE-based 739 architecture to inter-layer (G)MPLS traffic engineering. The H-PCE 740 Stateful architecture with stateful P-PCE coordinating with the 741 stateful C-PCEs of higher and lower layer is shown in the figure 742 below. 744 +----------+ 745 | Parent | 746 /| PCE | 747 / +----------+ 748 / / Stateful 749 / / P-PCE 750 / / 751 / / 752 Stateful+-----+ / / 753 C-PCE | PCE |/ / 754 Hi | Hi | / 755 +-----+ / 756 +---+ +---+ / +---+ +---+ 757 + LSR +--+ LSR +........................+ LSR +--+ LSR + 758 + H1 + + H2 + / + H3 + + H4 + 759 +---+ +---+\ +-----+/ /+---+ +---+ 760 \ | PCE | / 761 \ | Lo | / 762 Stateful \ +-----+ / 763 C-PCE \ / 764 Lo \+---+ +---+/ 765 + LSR +--+ LSR + 766 + L1 + + L2 + 767 +---+ +---+ 769 Figure 2: Sample Inter-Layer Topology 771 All procedures described in Section 3 are applicable to inter-layer 772 (and therefore separate domains) path setup as well. 774 6.2. Scalability Considerations 776 It should be noted that if all the C-PCEs would report all the LSPs 777 in their domain, it could lead to scalability issues for the P-PCE. 778 Thus it is recommended to only report the LSPs which are involved in 779 H-PCE, i.e. the LSPs which are either delegated to the P-PCE or 780 initiated by the P-PCE. Scalability considerations for PCEP as per 781 [RFC8231] continue to apply for the PCEP session between child and 782 parent PCE. 784 6.3. Confidentiality 786 As described in section 4.2 of [RFC6805], information about the 787 content of child domains is not shared for both scaling and 788 confidentiality reasons. Along with the confidentiality during path 789 computation, the child PCE could also conceal the path information, a 790 C-PCE may replace a path segment with a path-key [RFC5520], 791 effectively hiding the content of a segment of a path. 793 7. IANA Considerations 795 There are no IANA considerations. 797 8. Acknowledgments 799 Thanks to Manuela Scarella, Haomian Zheng, Sergio Marmo, Stefano 800 Parodi, Giacomo Agostini, Jeff Tantsura, Rajan Rao, Adrian Farrel and 801 Haomian Zheng, for their reviews and suggestions. 803 Thanks to Tal Mazrahi for the RTGDIR reviews. 805 9. References 807 9.1. Normative References 809 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 810 Element (PCE)-Based Architecture", RFC 4655, 811 DOI 10.17487/RFC4655, August 2006, 812 . 814 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 815 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 816 DOI 10.17487/RFC5440, March 2009, 817 . 819 [RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel, 820 "Preserving Topology Confidentiality in Inter-Domain Path 821 Computation Using a Path-Key-Based Mechanism", RFC 5520, 822 DOI 10.17487/RFC5520, April 2009, 823 . 825 [RFC6805] King, D., Ed. and A. Farrel, Ed., "The Application of the 826 Path Computation Element Architecture to the Determination 827 of a Sequence of Domains in MPLS and GMPLS", RFC 6805, DOI 828 10.17487/RFC6805, November 2012, 829 . 831 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 832 Computation Element Communication Protocol (PCEP) 833 Extensions for Stateful PCE", RFC 8231, 834 DOI 10.17487/RFC8231, September 2017, 835 . 837 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 838 Computation Element Communication Protocol (PCEP) 839 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 840 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 841 . 843 9.2. Informative References 845 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 846 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 847 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 848 . 850 [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label 851 Switching (GMPLS) Signaling Resource ReserVation Protocol- 852 Traffic Engineering (RSVP-TE) Extensions", RFC 3473, 853 DOI 10.17487/RFC3473, January 2003, 854 . 856 [RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for 857 Inter-Domain Multiprotocol Label Switching Traffic 858 Engineering", RFC 4726, DOI 10.17487/RFC4726, November 859 2006, . 861 [RFC5623] Oki, E., Takeda, T., Le Roux, JL., and A. Farrel, 862 "Framework for PCE-Based Inter-Layer MPLS and GMPLS 863 Traffic Engineering", RFC 5623, DOI 10.17487/RFC5623, 864 September 2009, 865 . 867 [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP 868 Authentication Option", RFC 5925, DOI 10.17487/RFC5925, 869 June 2010, . 871 [RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a 872 Stateful Path Computation Element (PCE)", RFC 8051, 873 DOI 10.17487/RFC8051, January 2017, 874 . 876 [RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X., 877 and D. Dhody, "Optimizations of Label Switched Path State 878 Synchronization Procedures for a Stateful PCE", RFC 8232, 879 DOI 10.17487/RFC8232, September 2017, 880 . 882 [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, 883 "PCEPS: Usage of TLS to Provide a Secure Transport for the 884 Path Computation Element Communication Protocol (PCEP)", 885 RFC 8253, DOI 10.17487/RFC8253, October 2017, 886 . 888 [RFC8453] Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for 889 Abstraction and Control of TE Networks (ACTN)", RFC 8453, 890 DOI 10.17487/RFC8453, August 2018, 891 . 893 [I-D.ietf-pce-applicability-actn] 894 Dhody, D., Lee, Y., and D. Ceccarelli, "Applicability of 895 Path Computation Element (PCE) for Abstraction and 896 Control of TE Networks (ACTN)", draft-ietf-pce- 897 applicability-actn-12 (work in progress), May 2019. 899 [I-D.litkowski-pce-state-sync] 900 Litkowski, S., Sivabalan, S., and D. Dhody, "Inter 901 Stateful Path Computation Element communication 902 procedures", draft-litkowski-pce-state-sync-05 (work in 903 progress), March 2019. 905 [I-D.ietf-pce-hierarchy-extensions] 906 Zhang, F., Zhao, Q., Dios, O., Casellas, R., and D. King, 907 "Extensions to Path Computation Element Communication 908 Protocol (PCEP) for Hierarchical Path Computation Elements 909 (PCE)", draft-ietf-pce-hierarchy-extensions-11 (work in 910 progress), June 2019. 912 [I-D.ietf-pce-pcep-yang] 913 Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A 914 YANG Data Model for Path Computation Element 915 Communications Protocol (PCEP)", 916 draft-ietf-pce-pcep-yang-12 (work in progress), July 2019. 918 [I-D.dugeon-pce-stateful-interdomain] 919 Dugeon, O., Meuric, J., Lee, Y., Dhody, D., and D. 920 Ceccarelli, "PCEP Extension for Stateful Inter-Domain 921 Tunnels", draft-dugeon-pce-stateful-interdomain-02 (work 922 in progress), March 2019. 924 [I-D.ietf-pce-lsp-control-request] 925 Raghuram, A., Goddard, A., Yadlapalli, C., Karthik, J., 926 Sivabalan, S., Parker, J., and M. Negi, "Ability for a 927 stateful Path Computation Element (PCE) to request and 928 obtain control of a LSP", draft-ietf-pce-lsp-control- 929 request-06 (work in progress), June 2019. 931 [I-D.ietf-pce-enhanced-errors] 932 Pouyllau, et al., "Extensions to PCEP for Enhanced Errors" 933 , draft-ietf-pce-enhanced-errors-05 (work in progress), 934 February 2019. 936 Contributors 938 Avantika 939 ECI Telecom 940 India 942 EMail: avantika.srm@gmail.com 944 Xian Zhang 945 Huawei Technologies 946 Bantian, Longgang District 947 Shenzhen, Guangdong 518129 948 P.R.China 950 EMail: zhang.xian@huawei.com 952 Udayasree Palle 954 EMail: udayasreereddy@gmail.com 956 Oscar Gonzalez de Dios 957 Telefonica I+D 958 Don Ramon de la Cruz 82-84 959 Madrid, 28045 960 Spain 961 Phone: +34913128832 963 EMail: oscar.gonzalezdedios@telefonica.com 965 Authors' Addresses 967 Dhruv Dhody 968 Huawei Technologies 969 Divyashree Techno Park, Whitefield 970 Bangalore, Karnataka 560066 971 India 973 EMail: dhruv.ietf@gmail.com 975 Young Lee 976 Futurewei Technologies 977 5340 Legacy Drive, Building 3 978 Plano, TX 75023 979 USA 981 EMail: younglee.tx@gmail.com 983 Daniele Ceccarelli 984 Ericsson 985 Torshamnsgatan,48 986 Stockholm 987 Sweden 989 EMail: daniele.ceccarelli@ericsson.com 991 Jongyoon Shin 992 SK Telecom 993 6 Hwangsaeul-ro, 258 beon-gil, Bundang-gu, Seongnam-si, 994 Gyeonggi-do 463-784 995 Republic of Korea 997 EMail: jongyoon.shin@sk.com 999 Daniel King 1000 Lancaster University 1001 UK 1002 EMail: d.king@lancaster.ac.uk