idnits 2.17.1 draft-litkowski-pce-state-sync-08.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 13, 2020) is 1377 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-14) exists of draft-knodel-terminology-03 -- Obsolete informational reference (is this intentional?): RFC 7752 (Obsoleted by RFC 9552) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PCE Working Group S. Litkowski 3 Internet-Draft Cisco 4 Intended status: Standards Track S. Sivabalan 5 Expires: January 14, 2021 Ciena Corporation 6 C. Li 7 H. Zheng 8 Huawei Technologies 9 July 13, 2020 11 Inter Stateful Path Computation Element (PCE) Communication Procedures. 12 draft-litkowski-pce-state-sync-08 14 Abstract 16 The Path Computation Element Communication Protocol (PCEP) provides 17 mechanisms for Path Computation Elements (PCEs) to perform path 18 computations in response to Path Computation Clients (PCCs) requests. 19 The stateful PCE extensions allow stateful control of Multi-Protocol 20 Label Switching (MPLS) Traffic Engineering Label Switched Paths (TE 21 LSPs) using PCEP. 23 A Path Computation Client (PCC) can synchronize an LSP state 24 information to a Stateful Path Computation Element (PCE). The 25 stateful PCE extension allows a redundancy scenario where a PCC can 26 have redundant PCEP sessions towards multiple PCEs. In such a case, 27 a PCC gives control on a LSP to only a single PCE, and only one PCE 28 is responsible for path computation for this delegated LSP. 30 There are some use cases, where an inter-PCE stateful communication 31 can bring additional resiliency in the design, for instance when some 32 PCC-PCE sessions fails. The inter-PCE stateful communication may 33 also provide a faster update of the LSP states when such an event 34 occurs. Finally, when, in a redundant PCE scenario, there is a need 35 to compute a set of paths that are part of a group (so there is a 36 dependency between the paths), there may be some cases where the 37 computation of all paths in the group is not handled by the same PCE: 38 this situation is called a split-brain. This split-brain scenario 39 may lead to computation loops between PCEs or suboptimal path 40 computation. 42 This document describes the procedures to allow a stateful 43 communication between PCEs for various use-cases and also the 44 procedures to prevent computations loops. 46 Requirements Language 48 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 49 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 50 "OPTIONAL" in this document are to be interpreted as described in BCP 51 14 [RFC2119] [RFC8174] when, and only when, they appear in all 52 capitals, as shown here. 54 Status of This Memo 56 This Internet-Draft is submitted in full conformance with the 57 provisions of BCP 78 and BCP 79. 59 Internet-Drafts are working documents of the Internet Engineering 60 Task Force (IETF). Note that other groups may also distribute 61 working documents as Internet-Drafts. The list of current Internet- 62 Drafts is at https://datatracker.ietf.org/drafts/current/. 64 Internet-Drafts are draft documents valid for a maximum of six months 65 and may be updated, replaced, or obsoleted by other documents at any 66 time. It is inappropriate to use Internet-Drafts as reference 67 material or to cite them other than as "work in progress." 69 This Internet-Draft will expire on January 14, 2021. 71 Copyright Notice 73 Copyright (c) 2020 IETF Trust and the persons identified as the 74 document authors. All rights reserved. 76 This document is subject to BCP 78 and the IETF Trust's Legal 77 Provisions Relating to IETF Documents 78 (https://trustee.ietf.org/license-info) in effect on the date of 79 publication of this document. Please review these documents 80 carefully, as they describe your rights and restrictions with respect 81 to this document. Code Components extracted from this document must 82 include Simplified BSD License text as described in Section 4.e of 83 the Trust Legal Provisions and are provided without warranty as 84 described in the Simplified BSD License. 86 Table of Contents 88 1. Introduction and Problem Statement . . . . . . . . . . . . . 3 89 1.1. Reporting LSP changes . . . . . . . . . . . . . . . . . . 4 90 1.2. Split-brain . . . . . . . . . . . . . . . . . . . . . . . 5 91 1.3. Applicability to H-PCE . . . . . . . . . . . . . . . . . 12 92 2. Proposed solution . . . . . . . . . . . . . . . . . . . . . . 12 93 2.1. State-sync session . . . . . . . . . . . . . . . . . . . 12 94 2.2. Primary/Secondary relationship between PCE . . . . . . . 14 95 3. Procedures and Protocol Extensions . . . . . . . . . . . . . 14 96 3.1. Opening a state-sync session . . . . . . . . . . . . . . 14 97 3.1.1. Capability Advertisement . . . . . . . . . . . . . . 14 98 3.2. State synchronization . . . . . . . . . . . . . . . . . . 15 99 3.3. Incremental updates and report forwarding rules . . . . . 16 100 3.4. Maintaining LSP states from different sources . . . . . . 17 101 3.5. Computation priority between PCEs and sub-delegation . . 18 102 3.6. Passive stateful procedures . . . . . . . . . . . . . . . 19 103 3.7. PCE initiation procedures . . . . . . . . . . . . . . . . 20 104 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 20 105 4.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 20 106 4.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 22 107 4.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 24 108 5. Using Primary/Secondary computation and state-sync sessions 109 to increase scaling . . . . . . . . . . . . . . . . . . . . . 25 110 6. PCEP-PATH-VECTOR TLV . . . . . . . . . . . . . . . . . . . . 27 111 7. Security Considerations . . . . . . . . . . . . . . . . . . . 28 112 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 113 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 114 9.1. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 28 115 9.2. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 28 116 9.3. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 29 117 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 118 10.1. Normative References . . . . . . . . . . . . . . . . . . 29 119 10.2. Informative References . . . . . . . . . . . . . . . . . 29 120 Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 30 121 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 123 1. Introduction and Problem Statement 125 The Path Computation Element communication Protocol (PCEP) [RFC5440] 126 provides mechanisms for Path Computation Elements (PCEs) to perform 127 path computations in response to Path Computation Clients' (PCCs) 128 requests. 130 A stateful PCE [RFC8231] is capable of considering, for the purposes 131 of path computation, not only the network state in terms of links and 132 nodes (referred to as the Traffic Engineering Database or TED) but 133 also the status of active services (previously computed paths, and 134 currently reserved resources, stored in the Label Switched Paths 135 Database (LSP-DB). 137 [RFC8051] describes general considerations for a stateful PCE 138 deployment and examines its applicability and benefits, as well as 139 its challenges and limitations through a number of use cases. 141 The examples in this section are for illustrative purpose to showcase 142 the need for inter-PCE stateful PCEP sessions. 144 1.1. Reporting LSP changes 146 When using a stateful PCE ([RFC8231]), a PCC can synchronize an LSP 147 state information to the stateful PCE. If the PCC grants the control 148 on the LSP to the PCE (called delegation [RFC8231]), the PCE can 149 update the LSP parameters at any time. 151 In a multi PCE deployment (redundancy, loadbalancing...), with the 152 current specification defined in [RFC8231], when a PCE makes an 153 update, it is the PCC that is in charge of reporting the LSP status 154 to all PCEs with LSP parameter change which brings additional hops 155 and delays in notifying the overall network of the LSP parameter 156 change. 158 This delay may affect the reaction time of the other PCEs, if they 159 need to take action after being notified of the LSP parameter change. 161 Apart from the synchronization from the PCC, it is also useful if 162 there is synchronization mechanism between the stateful PCEs. As 163 stateful PCE make changes to its delegated LSPs, these changes 164 (pending LSPs and the sticky resources [RFC7399]) can be synchronized 165 immediately to the other PCEs. 167 +----------+ 168 | PCC1 | LSP1 169 +----------+ 170 / \ 171 / \ 172 +---------+ +---------+ 173 | PCE1 | | PCE2 | 174 +---------+ +---------+ 175 \ / 176 \ / 177 +----------+ 178 | PCC2 | LSP2 179 +----------+ 181 In the figure above, we consider a load-balanced PCE architecture, so 182 PCE1 is responsible to compute paths for PCC1 and PCE2 is responsible 183 to compute paths for PCC2. When PCE1 triggers an LSP update for 184 LSP1, it sends a PCUpd message to PCC1 containing the new parameters 185 for LSP1. PCC1 will take the parameters into account and will send a 186 PCRpt message to PCE1 and PCE2 reflecting the changes. PCE2 will so 187 be notified of the change only after receiving the PCRpt message from 188 PCC1. 190 Let's consider that the LSP1 parameters changed in such a way that 191 LSP1 will take over resources from LSP2 with a higher priority. 192 After receiving the report from PCC1, PCE2 will therefore try to find 193 a new path for LSP2. If we consider that there is a round trip delay 194 of about 150 milliseconds (ms) between the PCEs and PCC1 and a round 195 trip delay of 10 ms between the two PCEs, if will take more than 150 196 ms for PCE2 to be notified of the change. 198 Adding a PCEP session between PCE1 and PCE2 may allow to reduce the 199 synchronization time, so PCE2 can react more quickly by taking the 200 pending LSPs and attached resources into account during path 201 computation and re-optimization. 203 1.2. Split-brain 205 In a resiliency case, a PCC has redundant PCEP sessions towards 206 multiple PCEs. In such a case, a PCC gives control on an LSP to a 207 single PCE only, and only this PCE is responsible for the path 208 computation for the delegated LSP: the PCC achieves this by setting 209 the D flag only towards the active PCE [RFC8231] selected for 210 delegation. The election of the active PCE to delegate an LSP is 211 controlled by each PCC. The PCC usually elects the active PCE by a 212 local configured policy (by setting a priority). Upon PCEP session 213 failure, or active PCE failure, PCC may decide to elect a new active 214 PCE by sending new PCRpt message with D flag set to this new active 215 PCE. When the failed PCE or PCEP session comes back online, it will 216 be up to the implementation to do preemption. Doing preemption may 217 lead to some disruption on the existing path if path results from 218 both PCEs are not exactly the same. By considering a network with 219 multiple PCCs and implementing multiple stateful PCEs for redundancy 220 purpose, there is no guarantee that at any time all the PCCs delegate 221 their LSPs to the same PCE. 223 +----------+ 224 | PCC1 | LSP1 225 +----------+ 226 / \ 227 / \ 228 +---------+ +---------+ 229 | PCE1 | | PCE2 | 230 +---------+ +---------+ 231 \ / 232 *fail* \ / 233 +----------+ 234 | PCC2 | LSP2 235 +----------+ 237 In the example above, we consider that by configuration, both PCCs 238 will firstly delegate their LSPs to PCE1. So, PCE1 is responsible 239 for computing a path for both LSP1 and LSP2. If the PCEP session 240 between PCC2 and PCE1 fails, PCC2 will delegate LSP2 to PCE2. So 241 PCE1 becomes responsible only for LSP1 path computation while PCE2 is 242 responsible for the path computation of LSP2. When the PCC2-PCE1 243 session is back online, PCC2 will keep using PCE2 as active PCE 244 (consider no preemption in this example). So the result is a 245 permanent situation where each PCE is responsible for a subset of 246 path computation. 248 This situation is called a split-brain scenario, as there are 249 multiple computation brains running at the same time while a central 250 computation unit was required in some deployments/use cases. 252 Further, there are use cases where a particular LSP path computation 253 is linked to another LSP path computation: the most common use case 254 is path disjointness (see [I-D.ietf-pce-association-diversity]). The 255 set of LSPs that are dependent to each other may start from a 256 different head-end. 258 _________________________________________ 259 / \ 260 / +------+ +------+ \ 261 | | PCE1 | | PCE2 | | 262 | +------+ +------+ | 263 | | 264 | +------+ +------+ | 265 | | PCC1 | ----------------------> | PCC2 | | 266 | +------+ +------+ | 267 | | 268 | | 269 | +------+ +------+ | 270 | | PCC3 | ----------------------> | PCC4 | | 271 | +------+ +------+ | 272 | | 273 \ / 274 \_________________________________________/ 276 _________________________________________ 277 / \ 278 / +------+ +------+ \ 279 | | PCE1 | | PCE2 | | 280 | +------+ +------+ | 281 | | 282 | +------+ 10 +------+ | 283 | | PCC1 | ----- R1 ---- R2 ------- | PCC2 | | 284 | +------+ | | +------+ | 285 | | | | 286 | | | | 287 | +------+ | | +------+ | 288 | | PCC3 | ----- R3 ---- R4 ------- | PCC4 | | 289 | +------+ +------+ | 290 | | 291 \ / 292 \_________________________________________/ 294 In the figure above, the requirement is to create two link-disjoint 295 LSPs: PCC1->PCC2 and PCC3->PCC4. In the topology, all links cost 296 metric is set to 1 except for the link 'R1-R2' which has a metric of 297 10. The PCEs are responsible for the path computation and PCE1 is 298 the active primary PCE for all PCCs in the nominal case. 300 Scenario 1: 302 In the normal case (PCE1 as active primary PCE), consider that 303 PCC1->PCC2 LSP is configured first with the link disjointness 304 constraint, PCE1 sends a PCUpd message to PCC1 with the ERO: 305 R1->R3->R4->R2->PCC2 (shortest path). PCC1 signals and installs the 306 path. When PCC3->PCC4 is configured, the PCEs already knows the path 307 of PCC1->PCC2 and can compute a link-disjoint path : the solution 308 requires to move PCC1->PCC2 onto a new path to let room for the new 309 LSP. PCE1 sends a PCUpd message to PCC1 with the new ERO: 310 R1->R2->PCC2 and a PCUpd to PCC3 with the following ERO: 311 R3->R4->PCC4. In the normal case, there is no issue for PCE1 to 312 compute a link-disjoint path. 314 Scenario 2: 316 Consider that PCC1 lost its PCEP session with PCE1 (all other PCEP 317 sessions are UP). PCC1 delegates its LSP to PCE2. 319 +----------+ 320 | PCC1 | LSP: PCC1->PCC2 321 +----------+ 322 \ 323 \ D=1 324 +---------+ +---------+ 325 | PCE1 | | PCE2 | 326 +---------+ +---------+ 327 D=1 \ / D=0 328 \ / 329 +----------+ 330 | PCC3 | LSP: PCC3->PCC4 331 +----------+ 333 Consider that the PCC1->PCC2 LSP is configured first with the link 334 disjointness constraint, PCE2 (which is the new active primary PCE 335 for PCC1) sends a PCUpd message to PCC1 with the ERO: 336 R1->R3->R4->R2->PCC2 (shortest path). When PCC3->PCC4 is configured, 337 PCE1 is not aware of LSPs from PCC1 any more, so it cannot compute a 338 disjoint path for PCC3->PCC4 and will send a PCUpd message to PCC3 339 with a shortest path ERO: R3->R4->PCC4. When PCC3->PCC4 LSP will be 340 reported to PCE2 by PCC3, PCE2 will ensure disjointness computation 341 and will correctly move PCC1->PCC2 (as it owns delegation for this 342 LSP) on the following path: R1->R2->PCC2. With this sequence of 343 event and these PCEP sessions, disjointness is ensured. 345 Scenario 3: 347 +----------+ 348 | PCC1 | LSP: PCC1->PCC2 349 +----------+ 350 / \ 351 D=1 / \ D=0 352 +---------+ +---------+ 353 | PCE1 | | PCE2 | 354 +---------+ +---------+ 355 / D=1 356 / 357 +----------+ 358 | PCC3 | LSP: PCC3->PCC4 359 +----------+ 361 Consider the above PCEP sessions and the PCC1->PCC2 LSP is configured 362 first with the link disjointness constraint, PCE1 computes the 363 shortest path as it is the only LSP in the disjoint association group 364 that it is aware of: R1->R3->R4->R2->PCC2 (shortest path). When 365 PCC3->PCC4 is configured, PCE2 must compute a disjoint path for this 366 LSP. The only solution found is to move PCC1->PCC2 LSP on another 367 path, but PCE2 cannot do it as it does not have delegation for this 368 LSP. In this set-up, PCEs are not able to find a disjoint path. 370 Scenario 4: 372 +----------+ 373 | PCC1 | LSP: PCC1->PCC2 374 +----------+ 375 / \ 376 D=1 / \ D=0 377 +---------+ +---------+ 378 | PCE1 | | PCE2 | 379 +---------+ +---------+ 380 D=0 \ / D=1 381 \ / 382 +----------+ 383 | PCC3 | LSP: PCC3->PCC4 384 +----------+ 386 Consider the above PCEP sessions and that PCEs are configured to 387 fall-back to shortest path if disjointness cannot be found as 388 described in [I-D.ietf-pce-association-diversity]. The PCC1->PCC2 389 LSP is configured first, PCE1 computes shortest path as it is the 390 only LSP in the disjoint association group that it is aware of: 391 R1->R3->R4->R2->PCC2 (shortest path). When PCC3->PCC4 is configured, 392 PCE2 must compute a disjoint path for this LSP. The only solution 393 found is to move PCC1->PCC2 LSP on another path, but PCE2 cannot do 394 it as it does not have delegation for this LSP. PCE2 then provides 395 shortest path for PCC3->PCC4: R3->R4->PCC4. When PCC3 receives the 396 ERO, it reports it back to both PCEs. When PCE1 becomes aware of 397 PCC3->PCC4 path, it recomputes the constrained shortest path first 398 (CSPF) algorithm and provides a new path for PCC1->PCC2: 399 R1->R2->PCC2. The new path is reported back to all PCEs by PCC1. 400 PCE2 recomputes also CSPF to take into account the new reported path. 401 The new computation does not lead to any path update. 403 Scenario 5: 405 _____________________________________ 406 / \ 407 / +------+ +------+ \ 408 | | PCE1 | | PCE2 | | 409 | +------+ +------+ | 410 | | 411 | +------+ 100 +------+ | 412 | | | -------------------- | | | 413 | | PCC1 | ----- R1 ----------- | PCC2 | | 414 | +------+ | +------+ | 415 | | | | | 416 | 6 | | 2 | 2 | 417 | | | | | 418 | +------+ | +------+ | 419 | | PCC3 | ----- R3 ----------- | PCC4 | | 420 | +------+ 10 +------+ | 421 | | 422 \ / 423 \_____________________________________/ 425 Now, consider a new network topology with the same PCEP sessions as 426 the previous example. Suppose that both LSPs are configured almost 427 at the same time. PCE1 will compute a path for PCC1->PCC2 while PCE2 428 will compute a path for PCC3->PCC4. As each PCE is not aware of the 429 path of the second LSP in the association group (not reported yet), 430 each PCE is computing shortest path for the LSP. PCE1 computes ERO: 431 R1->PCC2 for PCC1->PCC2 and PCE2 computes ERO: R3->R1->PCC2->PCC4 for 432 PCC3->PCC4. When these shortest paths will be reported to each PCE. 433 Each PCE will recompute disjointness. PCE1 will provide a new path 434 for PCC1->PCC2 with ERO: PCC1->PCC2. PCE2 will provide also a new 435 path for PCC3->PCC4 with ERO: R3->PCC4. When those new paths will be 436 reported to both PCEs, this will trigger CSPF again. PCE1 will 437 provide a new more optimal path for PCC1->PCC2 with ERO: R1->PCC2 and 438 PCE2 will also provide a more optimal path for PCC3->PCC4 with ERO: 439 R3->R1->PCC2->PCC4. So we come back to the initial state. When 440 those paths will be reported to both PCEs, this will trigger CSPF 441 again. An infinite loop of CSPF computation is then happening with a 442 permanent flap of paths because of the split-brain situation. 444 This permanent computation loop comes from the inconsistency between 445 the state of the LSPs as seen by each PCE due to the split-brain: 446 each PCE is trying to modify at the same time its delegated path 447 based on the last received path information which de facto 448 invalidates this received path information. 450 Scenario 6: multi-domain 452 Domain/Area 1 Domain/Area 2 453 ________________ ________________ 454 / \ / \ 455 / +------+ | | +------+ \ 456 | | PCE1 | | | | PCE3 | | 457 | +------+ | | +------+ | 458 | | | | 459 | +------+ | | +------+ | 460 | | PCE2 | | | | PCE4 | | 461 | +------+ | | +------+ | 462 | | | | 463 | +------+ | | +------+ | 464 | | PCC1 | | | | PCC2 | | 465 | +------+ | | +------+ | 466 | | | | 467 | | | | 468 | +------+ | | +------+ | 469 | | PCC3 | | | | PCC4 | | 470 | +------+ | | +------+ | 471 \ | | | 472 \_______________/ \________________/ 474 In the example above, suppose that the disjoint LSPs from PCC1 to 475 PCC2 and from PCC4 to PCC3 are created. All the PCEs have the 476 knowledge of both domain topologies (e.g. using BGP-LS [RFC7752]). 477 For operation/management reason, each domain uses its own group of 478 redundant PCEs. PCE1/PCE2 in domain 1 have PCEP sessions with PCC1 479 and PCC3 while PCE3/PCE4 in domain 2 have PCEP sessions with PCC2 and 480 PCC4. As PCE1/2 do not know about LSPs from PCC2/4 and PCE3/4 do not 481 know about LSPs from PCC1/3, there is no possibility to compute the 482 disjointness constraint. This scenario can also be seen as a split- 483 brain scenario. This multi-domain architecture (with multiple groups 484 of PCEs) can also be used in a single domain, where an operator wants 485 to limit the failure domain by creating multiple groups of PCEs 486 maintaining a subset of PCCs. As for the multi-domain example, there 487 will be no possibility to compute disjoint path starting from head- 488 ends managed by different PCE groups. 490 In this document, we propose a solution that address the possibility 491 to compute LSP association based constraints (like disjointness) in 492 split-brain scenarios while preventing computation loops. 494 1.3. Applicability to H-PCE 496 [RFC8751] describes general considerations and use cases for the 497 deployment of Stateful PCE(s) using the Hierarchical PCE [RFC6805] 498 architecture. In this architecture there is a clear need to 499 communicate between a child stateful PCE and a parent stateful PCE. 500 The procedures and extensions as described in Section 3 are equally 501 applicable to H-PCE scenario. 503 2. Proposed solution 505 Our solution is based on : 507 o The creation of the inter-PCE stateful PCEP session with specific 508 procedures. 510 o A Primary/Secondary relationship between PCEs. 512 2.1. State-sync session 514 This document proposes to set-up a PCEP session between the stateful 515 PCEs. Creating such a session is already authorized by multiple 516 scenarios like the one described in [RFC4655] (multiple PCEs that are 517 handling part of the path computation) and [RFC6805] (hierarchical 518 PCE) but was only focused on the stateless PCEP sessions. As 519 stateful PCE brings additional features (LSP state synchronization, 520 path update, delegation, ...), thus some new behaviors need to be 521 defined. 523 This inter-PCE PCEP session will allow exchange of LSP states between 524 PCEs that would help some scenario where PCEP sessions are lost 525 between PCC and PCE. This inter-PCE PCEP session is henceforth 526 called a state-sync session. 528 For example, in the scenario below, there is no possibility to 529 compute disjointness as there is no PCE that is aware of both LSPs. 531 +----------+ 532 | PCC1 | LSP: PCC1->PCC2 533 +----------+ 534 / 535 D=1 / 536 +---------+ +---------+ 537 | PCE1 | | PCE2 | 538 +---------+ +---------+ 539 / D=1 540 / 541 +----------+ 542 | PCC3 | LSP: PCC3->PCC4 543 +----------+ 545 If we add a state-sync session, PCE1 will be able to do state 546 synchronization via PCRpt messages for its LSP to PCE2 and PCE2 will 547 do the same. All the PCEs will be aware of all LSPs even if PCC->PCE 548 session are down. PCEs will then be able to compute disjoint paths. 550 +----------+ 551 | PCC1 | LSP : PCC1->PCC2 552 +----------+ 553 / 554 D=1 / 555 +---------+ PCEP +---------+ 556 | PCE1 | ----- | PCE2 | 557 +---------+ +---------+ 558 / D=1 559 / 560 +----------+ 561 | PCC3 | LSP : PCC3->PCC4 562 +----------+ 564 The procedures associated with this state-sync session are defined in 565 Section 3. 567 By just adding this state-sync session, it does not ensure that a 568 path with LSP association based constraints can always be computed 569 and does not prevent computation loop, but it increases resiliency 570 and ensures that PCEs will have the state information for all LSPs. 571 In addition, this session will allow for a PCE to update the other 572 PCEs providing a faster synchronization mechanism than relying on 573 PCCs only. 575 2.2. Primary/Secondary relationship between PCE 577 As seen in Section 1, performing a path computation in a split-brain 578 scenario (multiple PCEs responsible for computation) may provide a 579 non optimal LSP placement, no path or computation loops. To provide 580 the best efficiency, an LSP association constraint based computation 581 requires that a single PCE performs the path computation for all LSPs 582 in the association group. Note that, it could be all LSPs belonging 583 to a particular association group, or all LSPs from a particular PCC, 584 or all LSPs in the network that need to be delegated to a single PCE 585 based on the deployment scenarios. 587 This document propose to add a priority mechanism between PCEs to 588 elect a single computing PCE. Using this priority mechanism, PCEs 589 can agree on the PCE that will be responsible for the computation for 590 a particular association group, or set of LSPs. The priority could 591 be set per association, per PCC, or for all LSPs. How this priority 592 is set or advertised is out of scope of this document. The rest of 593 the text consider association group as an example. 595 When a single PCE is performing the computation for a particular 596 association group, no computation loop can happen and an optimal 597 placement will be provided. The other PCEs will only act as state 598 collectors and forwarders. 600 In the scenario described in Section 2.1, PCE1 and PCE2 will decide 601 that PCE1 will be responsible for the path computation of both LSPs. 602 If we first configure PCC1->PCC2, PCE1 computes shortest path at it 603 is the only LSP in the disjoint-group that it is aware of: 604 R1->R3->R4->R2->PCC2 (shortest path). When PCC3->PCC4 is configured, 605 PCE2 will not perform computation even if it has delegation but 606 forwards the delegation via PCRpt message to PCE1 through the state- 607 sync session. PCE1 will then perform disjointness computation and 608 will move PCC1->PCC2 onto R1->R2->PCC2 and provides an ERO to PCE2 609 for PCC3->PCC4: R3->R4->PCC4. The PCE2 will further update the PCC3 610 with the new path. 612 3. Procedures and Protocol Extensions 614 3.1. Opening a state-sync session 616 3.1.1. Capability Advertisement 618 A PCE indicates its support of state-sync procedures during the PCEP 619 Initialization phase [RFC5440]. The OPEN object in the Open message 620 MUST contains the "Stateful PCE Capability" TLV defined in [RFC8231]. 621 A new P (INTER-PCE-CAPABILITY) flag is introduced to indicate the 622 support of state-sync. 624 This document adds a new bit in the Flags field with : 626 P (INTER-PCE-CAPABILITY - 1 bit): If set to 1 by a PCEP Speaker, 627 the PCEP speaker indicates that the session MUST follow the state- 628 sync procedures as described in this document. The P bit MUST be 629 set by both speakers: if a PCEP Speaker receives a STATEFUL-PCE- 630 CAPABILITY TLV with P=0 while it advertised P=1 or if both set P 631 flag to 0, the session SHOULD be set-up but the state-sync 632 procedures MUST NOT be applied on this session. 634 The U flag [RFC8231] MUST be set when sending the STATEFUL-PCE- 635 CAPABILITY TLV with the P flag set. In case the U flag is not set 636 along with the P flag, the state sync capability is not enabled and 637 it is considered as if P flag is not set. The S flag MAY be set if 638 optimized synchronization is required as per [RFC8232]. 640 3.2. State synchronization 642 When the state sync capability has been negotiated between stateful 643 PCEs, each PCEP speaker will behave as a PCE and as a PCC at the same 644 time regarding the state synchronization as defined in [RFC8231]. 645 This means that each PCEP Speaker: 647 o MUST send a PCRpt message towards its neighbor with S flag set for 648 each LSP in its LSP database learned from a PCC. (PCC role) 650 o MUST send the End Of Synchronization Marker towards its neighbor 651 when all LSPs have been reported. (PCC role) 653 o MUST wait for the LSP synchronization from its neighbor to end 654 (receiving an End Of Synchronization Marker). (PCE role) 656 The process of synchronization runs in parallel on each PCE (with no 657 defined order). 659 The optimized state synchronization procedures MAY be used, as 660 defined in [RFC8232]. 662 When a PCEP Speaker sends a PCRpt on a state-sync session, it MUST 663 add the SPEAKER-IDENTITY-TLV (defined in [RFC8232]) in the LSP 664 Object, the value used will refer to the 'owner' PCC of the LSP. If 665 a PCEP Speaker receives a PCRpt on a state-sync session without this 666 TLV, it MUST discard the PCRpt message and it MUST reply with a PCErr 667 message using error-type=6 (Mandatory Object missing) and error- 668 value=TBD1 (SPEAKER-IDENTITY-TLV missing). 670 3.3. Incremental updates and report forwarding rules 672 During the life of an LSP, its state may change (path, constraints, 673 operational state...) and a PCC will advertise a new PCRpt to the PCE 674 for each such change. 676 When propagating LSP state changes from a PCE to other PCEs, it is 677 mandatory to ensure that a PCE always uses the freshest state coming 678 from the PCC. 680 When a PCE receives a new PCRpt from a PCC with the LSP-DB-VERSION, 681 the PCE MUST forward the PCRpt to all its state-sync sessions and 682 MUST add the appropriate SPEAKER-IDENTITY-TLV in the PCRpt. In 683 addition, it MUST add a new ORIGINAL-LSP-DB-VERSION TLV (described 684 below). The ORIGINAL-LSP-DB-VERSION contains the LSP-DB-VERSION 685 coming from the PCC. 687 When a PCE receives a new PCRpt from a PCC without the LSP-DB- 688 VERSION, it SHOULD NOT forward the PCRpt on any state-sync sessions 689 and log such an event on the first occurrence. 691 When a PCE receives a new PCRpt from a PCC with the R flag (Remove) 692 set and a LSP-DB-VERSION TLV, the PCE MUST forward the PCRpt to all 693 its state-sync sessions keeping the R flag set (Remove) and MUST add 694 the appropriate SPEAKER-IDENTITY-TLV and ORIGINAL-LSP-DB-VERSION TLV 695 in the PCRpt message. 697 When a PCE receives a PCRpt from a state-sync session, it MUST NOT 698 forward the PCRpt to other state-sync sessions. This helps to 699 prevent message loops between PCEs. As a consequence, a full mesh of 700 PCEP sessions between PCEs is REQUIRED. 702 When a PCRpt is forwarded, all the original objects and values are 703 kept. As an example, the PLSP-ID used in the forwarded PCRpt will be 704 the same as the original one used by the PCC. Thus an implementation 705 supporting this document MUST consider SPEAKER-IDENTITY-TLV and PLSP- 706 ID together to uniquely identify an LSP on the state-sync session. 708 The ORIGINAL-LSP-DB-VERSION TLV is encoded as follows and MUST always 709 contain the LSP-DB-VERSION received from the owner PCC of the LSP: 711 0 1 2 3 712 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 714 | Type=TBD2 | Length=8 | 715 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 716 | LSP State DB Version Number | 717 | | 718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 720 Using the ORIGINAL-LSP-DB-VERSION TLV allows a PCE to keep using 721 optimized synchronization ([RFC8232]) with another PCE. In such a 722 case, the PCE will send a PCRpt to another PCE with both ORIGINAL- 723 LSP-DB-VERSION TLV and LSP-DB-VERSION TLV. The ORIGINAL-LSP-DB- 724 VERSION TLV will contain the version number as allocated by the PCC 725 while the LSP-DB-VERSION will contain the version number allocated by 726 the local PCE. 728 3.4. Maintaining LSP states from different sources 730 When a PCE receives a PCRpt on a state-sync session, it stores the 731 LSP information into the original PCC address context (as the LSP 732 belongs to the PCC). A PCE SHOULD maintain a single state for a 733 particular LSP and SHOULD maintain the list of sources it learned a 734 particular state from. 736 A PCEP speaker may receive a state information for a particular LSP 737 from different sources: the PCC that owns the LSP (through a regular 738 PCEP session) and some PCEs (through PCEP state-sync sessions). A 739 PCEP speaker MUST always keep the freshest state in its LSP database, 740 overriding the previously received information. 742 A PCE, receiving a PCRpt from a PCC, updates the state of the LSP in 743 its LSP-DB with the new received information. When receiving a PCRpt 744 from another PCE, a PCE SHOULD update the LSP state only if the 745 ORIGINAL-LSP-DB-VERSION present in the PCRpt is greater than the 746 current ORIGINAL-LSP-DB-VERSION of the stored LSP state. This 747 ensures that a PCE never tries to update its stored LSP state with an 748 old information. Each time a PCE updates an LSP state in its LSP-DB, 749 it SHOULD reset the source list associated with the LSP state and 750 SHOULD add the source speaker address in the source list. When a PCE 751 receives a PCRpt which has an ORIGINAL-LSP-DB-VERSION (if coming from 752 a PCE) or an LSP-DB-VERSION (if coming from the PCC) equals to the 753 current ORIGINAL-LSP-DB-VERSION of the stored LSP state, it SHOULD 754 add the source speaker address in the source list. 756 When a PCE receives a PCRpt requesting an LSP deletion from a 757 particular source, it SHOULD remove this particular source from the 758 list of sources associated with this LSP. 760 When the list of sources becomes empty for a particular LSP, the LSP 761 state MUST be removed. This means that all the sources must send a 762 PCRpt with R=1 for an LSP to make the PCE remove the LSP state. 764 3.5. Computation priority between PCEs and sub-delegation 766 A computation priority is necessary to ensure that a single PCE will 767 perform the computation for all the LSPs in an association group: 768 this will allow for a more optimized LSP placement and will prevent 769 computation loops. 771 All PCEs in the network that are handling LSPs in a common LSP 772 association group SHOULD be aware of each other including the 773 computation priority of each PCE. Note that there is no need for PCC 774 to be aware of this. The computation priority is a number and the 775 PCE having the highest priority SHOULD be responsible for the 776 computation. If several PCEs have the same priority value, their IP 777 address SHOULD be used as a tie-breaker to provide a rank: the 778 highest IP address has more priority. How PCEs are aware of the 779 priority of each other is out of scope of this document, but as 780 example learning priorities could be done through PCE discovery or 781 local configuration. 783 The definition of the priority could be global so the highest 784 priority PCE will handle all path computations or more granular, so a 785 PCE may have highest priority for only a subset of LSPs or 786 association-groups. 788 A PCEP Speaker receiving a PCRpt from a PCC with D flag set that does 789 not have the highest computation priority, SHOULD forward the PCRpt 790 on all state-sync sessions (as per Section 3.3) and SHOULD set D flag 791 on the state-sync session towards the highest priority PCE, D flag 792 will be unset to all other state-sync sessions. This behavior is 793 similar to the delegation behavior handled at PCC side and is called 794 a sub-delegation (the PCE sub-delegates the control of the LSP to 795 another PCE). When a PCEP Speaker sub-delegates a LSP to another 796 PCE, it looses the control on the LSP and cannot update it any more 797 by its own decision. When a PCE receives a PCRpt with D flag set on 798 a state-sync session, as a regular PCE, it is granted control over 799 the LSP. 801 If the highest priority PCE is failing or if the state-sync session 802 between the local PCE and the highest priority PCE failed, the local 803 PCE MAY decide to delegate the LSP to the next highest priority PCE 804 or to take back control on the LSP. It is a local policy decision. 806 When a PCE has the delegation for an LSP and needs to update this 807 LSP, it MUST send a PCUpd message to all state-sync sessions and to 808 the PCC session on which it received the delegation. The D-Flag 809 would be unset in the PCUpd for state-sync sessions where as D-Flag 810 would be set for the PCC. In case of sub-delegation, the computing 811 PCE will send the PCUpd only to all state-sync sessions (as it has no 812 direct delegation from a PCC). The D-Flag would be set for the 813 state-sync session to the PCE that sub-delegated this LSP and the 814 D-Flag would be unset for other state-sync sessions. 816 The PCUpd sent over a state-sync session MUST contain the SPEAKER- 817 IDENTITY-TLV in the LSP Object (the value used must identify the 818 target PCC). The PLSP-ID used is the original PLSP-ID generated by 819 the PCC and learned from the forwarded PCRpt. If a PCE receives a 820 PCUpd on a state-sync session without the SPEAKER-IDENTITY-TLV, it 821 MUST discard the PCUpd and MUST reply with a PCErr message using 822 error-type=6 (Mandatory Object missing) and error-value=TBD1 823 (SPEAKER-IDENTITY-TLV missing). 825 When a PCE receives a valid PCUpd on a state-sync session, it SHOULD 826 forward the PCUpd to the appropriate PCC (identified based on the 827 SPEAKER-IDENTITY-TLV value) that delegated the LSP originally and 828 SHOULD remove the SPEAKER-IDENTITY-TLV from the LSP Object. The 829 acknowledgment of the PCUpd is done through a cascaded mechanism, and 830 the PCC is the only responsible of triggering the acknowledgment: 831 when the PCC receives the PCUpd from the local PCE, it acknowledges 832 it with a PCRpt as per [RFC8231]. When receiving the new PCRpt from 833 the PCC, the local PCE uses the defined forwarding rules on the 834 state-sync session so the acknowledgment is relayed to the computing 835 PCE. 837 A PCE SHOULD NOT compute a path using an association-group constraint 838 if it has delegation for only a subset of LSPs in the group. In this 839 case, an implementation MAY use a local policy on PCE to decide if 840 PCE does not compute path at all for this set of LSP or if it can 841 compute a path by relaxing the association-group constraint. 843 3.6. Passive stateful procedures 845 In the passive stateful PCE architecture, the PCC is responsible for 846 triggering a path computation request using a PCReq message to its 847 PCE. Similarly to PCRpt Message, which remains unchanged for passive 848 mode, if a PCE receives a PCReq for an LSP and if this PCE finds that 849 it does not have the highest computation priority of this LSP, or 850 groups..., it MUST forward the PCReq message to the highest priority 851 PCE over the state-sync session. When the highest priority PCE 852 receives the PCReq, it computes the path and generates a PCRep 853 message towards the PCE that made the request. This PCE will then 854 forward the PCRep to the requesting PCC. The handling of LSP object 855 and the SPEAKER-IDENTITY-TLV in PCReq and PCRep is similar to PCRpt/ 856 PCUpd messages. 858 3.7. PCE initiation procedures 860 TBD 862 4. Examples 864 The examples in this section are for illustrative purpose to show how 865 the behavior of the state sync inter-PCE sessions. 867 4.1. Example 1 868 _________________________________________ 869 / \ 870 / +------+ +------+ \ 871 | | PCE1 | | PCE2 | | 872 | +------+ +------+ | 873 | | 874 | +------+ 10 +------+ | 875 | | PCC1 | ----- R1 ---- R2 ------- | PCC2 | | 876 | +------+ | | +------+ | 877 | | | | 878 | | | | 879 | +------+ | | +------+ | 880 | | PCC3 | ----- R3 ---- R4 ------- | PCC4 | | 881 | +------+ +------+ | 882 | | 883 \ / 884 \_________________________________________/ 886 +----------+ 887 | PCC1 | LSP : PCC1->PCC2 888 +----------+ 889 / 890 D=1 / 891 +---------+ +---------+ 892 | PCE1 |----| PCE2 | 893 +---------+ +---------+ 894 / D=1 895 / 896 +----------+ 897 | PCC3 | LSP : PCC3->PCC4 898 +----------+ 900 PCE1 computation priority 100 901 PCE2 computation priority 200 903 Consider the PCEP sessions as shown above, where computation priority 904 is global for all the LSPs and link disjoint between LSPs PCC1->PCC2 905 and PCC3->PCC4 is required. 907 Consider the PCC1->PCC2 is configured first and PCC1 delegates the 908 LSP to PCE1, but as PCE1 does not have the highest computation 909 priority, it sub-delegates the LSP to PCE2 by sending a PCRpt with 910 D=1 and including the SPEAKER-IDENTITY-TLV over the state-sync 911 session. PCE2 receives the PCRpt and as it has delegation for this 912 LSP, it computes the shortest path: R1->R3->R4->R2->PCC2. It then 913 sends a PCUpd to PCE1 (including the SPEAKER-IDENTITY-TLV) with the 914 computed ERO. PCE1 forwards the PCUpd to PCC1 (removing the SPEAKER- 915 IDENTITY-TLV). PCC1 acknowledges the PCUpd by a PCRpt to PCE1. PCE1 916 forwards the PCRpt to PCE2. 918 When PCC3->PCC4 is configured, PCC3 delegates the LSP to PCE2, PCE2 919 can compute a disjoint path as it has knowledge of both LSPs and has 920 delegation also for both. The only solution found is to move 921 PCC1->PCC2 LSP on another path, PCE2 can move PCC1->PCC2 as it has 922 sub-delegation for it. It creates a new PCUpd with new ERO: 923 R1->R2-PCC2 towards PCE1 which forwards to PCC1. PCE2 sends a PCUpd 924 to PCC3 with the path: R3->R4->PCC4. 926 In this set-up, PCEs are able to find a disjoint path while without 927 state-sync and computation priority they could not. 929 4.2. Example 2 930 _____________________________________ 931 / \ 932 / +------+ +------+ \ 933 | | PCE1 | | PCE2 | | 934 | +------+ +------+ | 935 | | 936 | +------+ 100 +------+ | 937 | | | -------------------- | | | 938 | | PCC1 | ----- R1 ----------- | PCC2 | | 939 | +------+ | +------+ | 940 | | | | | 941 | 6 | | 2 | 2 | 942 | | | | | 943 | +------+ | +------+ | 944 | | PCC3 | ----- R3 ----------- | PCC4 | | 945 | +------+ 10 +------+ | 946 | | 947 \ / 948 \_____________________________________/ 950 +----------+ 951 | PCC1 | LSP : PCC1->PCC2 952 +----------+ 953 / \ 954 D=1 / \ D=0 955 +---------+ +---------+ 956 | PCE1 |----| PCE2 | 957 +---------+ +---------+ 958 D=0 \ / D=1 959 \ / 960 +----------+ 961 | PCC3 | LSP : PCC3->PCC4 962 +----------+ 964 PCE1 computation priority 200 965 PCE2 computation priority 100 967 In this example, suppose both LSPs are configured almost at the same 968 time. PCE1 sub-delegates PCC1->PCC2 to PCE2 while PCE2 keeps 969 delegation for PCC3->PCC4, PCE2 computes a path for PCC1->PCC2 and 970 PCC3->PCC4 and can achieve disjointness computation easily. No 971 computation loop happens in this case. 973 4.3. Example 3 975 _________________________________________ 976 / \ 977 / +------+ +------+ \ 978 | | PCE1 | | PCE2 | | 979 | +------+ +------+ | 980 | | 981 | +------+ 10 +------+ | 982 | | PCC1 | ----- R1 ---- R2 ------- | PCC2 | | 983 | +------+ | | +------+ | 984 | | | | 985 | | | | 986 | +------+ | | +------+ | 987 | | PCC3 | ----- R3 ---- R4 ------- | PCC4 | | 988 | +------+ +------+ | 989 | | 990 \ / 991 \_________________________________________/ 993 +----------+ 994 | PCC1 | LSP : PCC1->PCC2 995 +----------+ 996 / 997 D=1 / 998 +---------+ +---------+ +---------+ 999 | PCE1 |----| PCE2 |----| PCE3 | 1000 +---------+ +---------+ +---------+ 1001 / D=1 1002 / 1003 +----------+ 1004 | PCC3 | LSP : PCC3->PCC4 1005 +----------+ 1007 PCE1 computation priority 100 1008 PCE2 computation priority 200 1009 PCE3 computation priority 300 1011 With the PCEP sessions as shown above, consider the need to have link 1012 disjoint LSPs PCC1->PCC2 and PCC3->PCC4. 1014 Suppose PCC1->PCC2 is configured first, PCC1 delegates the LSP to 1015 PCE1, but as PCE1 does not have the highest computation priority, it 1016 will sub-delegate the LSP to PCE2 (as it not aware of PCE3 and has no 1017 way to reach it). PCE2 cannot compute a path for PCC1->PCC2 as it 1018 does not have the highest priority and is not allowed to sub-delegate 1019 the LSP again towards PCE3 as per Section 3. 1021 When PCC3->PCC4 is configured, PCC3 delegates the LSP to PCE2 that 1022 performs sub-delegation to PCE3. As PCE3 will have knowledge of only 1023 one LSP in the group, it cannot compute disjointness and can decide 1024 to fall-back to a less constrained computation to provide a path for 1025 PCC3->PCC4. In this case, it will send a PCUpd to PCE2 that will be 1026 forwarded to PCC3. 1028 Disjointness cannot be achieved in this scenario because of lack of 1029 state-sync session between PCE1 and PCE3, but no computation loop 1030 happens. Thus it is advised for all PCEs that support state-sync to 1031 have a full mesh sessions between each other. 1033 5. Using Primary/Secondary computation and state-sync sessions to 1034 increase scaling 1036 The Primary/Secondary computation and state-sync sessions 1037 architecture can be used to increase the scaling of the PCE 1038 architecture. If the number of PCCs is really high, it may be too 1039 resource consuming for a single PCE to maintain all the PCEP sessions 1040 while at the same time performing all path computations. Using 1041 primary/secondary computation and state-sync sessions may allow to 1042 create groups of PCEs that manage a subset of the PCCs and perform 1043 some or no path computations. Decoupling PCEP session maintenance 1044 and computation will allow to increase scaling of the PCE 1045 architecture. 1047 +----------+ 1048 | PCC500 | 1049 +----------+-+ 1050 | PCC1 | 1051 +----------+ 1052 / \ 1053 / \ 1054 +---------+ +---------+ 1055 | PCE1 |---| PCE2 | 1056 +---------+ +---------+ 1057 | \ / | 1058 | \/ | 1059 | /\ | 1060 | / \ | 1061 +---------+ +---------+ 1062 | PCE3 |---| PCE4 | 1063 +---------+ +---------+ 1064 \ / 1065 \ / 1066 +----------+ 1067 | PCC501 | 1068 +----------+-+ 1069 | PCC1000 | 1070 +----------+ 1072 In the figure above, two groups of PCEs are created: PCE1/2 maintain 1073 PCEP sessions with PCC1 up to PCC500, while PCE3/4 maintain PCEP 1074 sessions with PCC501 up to PCC1000. A granular primary/secondary 1075 policy is set-up as follows to load-share computation between PCEs: 1077 o PCE1 has priority 200 for association ID 1 up to 300, association 1078 source 0.0.0.0. All other PCEs have a decreasing priority for 1079 those associations. 1081 o PCE3 has priority 200 for association ID 301 up to 500, 1082 association source 0.0.0.0. All other PCEs have a decreasing 1083 priority for those associations. 1085 If some PCCs delegate LSPs with association ID 1 up to 300 and 1086 association source 0.0.0.0, the receiving PCE (if not PCE1) will sub- 1087 delegate the LSPs to PCE1. PCE1 becomes responsible for the 1088 computation of these LSP associations while PCE3 is responsible for 1089 the computation of another set of associations. 1091 The procedures describe in this document could help greatly in load- 1092 sharing between a group of stateful PCEs. 1094 6. PCEP-PATH-VECTOR TLV 1096 This document allows PCEP messages to be propagated among PCEP 1097 speaker. It may be useful to track informations about the 1098 propagation of the messages. One of the use case is a message loop 1099 detection mechanism, but other use cases like hop by hop information 1100 recording may also be implemented. 1102 This document introduces the PCEP-PATH-VECTOR TLV (type TBD3) with 1103 the following format: 1105 0 1 2 3 1106 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1108 | Type=TBD3 | Length | 1109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1110 | PCEP-SPEAKER-INFORMATION#1 | 1111 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1112 | ... | 1113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1114 | ... | 1115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1116 | PCEP-SPEAKER-INFORMATION#n | 1117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1119 The TLV format and padding rules are as per [RFC5440]. 1121 The PCEP-SPEAKER-INFORMATION field has the following format: 1123 0 1 2 3 1124 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1126 | Length | ID Length | 1127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1128 // Speaker Entity identity (variable) // 1129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1130 // SubTLVs (optional) // 1131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1133 Length: defines the total length of the PCEP-SPEAKER-INFORMATION 1134 field. 1136 ID Length: defines the length of the Speaker identity actual field 1137 (non-padded). 1139 Speaker Entity identity: same possible values as the SPEAKER- 1140 IDENTIFIER-TLV. Padded with trailing zeros to a 4-byte boundary. 1142 The PCEP-SPEAKER-INFORMATION may also carry some optional subTLVs 1143 so each PCEP speaker can add local informations that could be 1144 recorded. This document does not define any subTLV. 1146 The PCEP-PATH-VECTOR TLV MAY be carried in the LSP Object. Its usage 1147 is purely optional. 1149 The list of speakers within the PCEP-PATH-VECTOR TLV MUST be ordered. 1150 When sending a PCEP message (PCRpt, PCUpd or PCInitiate), a PCEP 1151 Speaker MAY add the PCEP-PATH-VECTOR TLV with a PCEP-SPEAKER- 1152 INFORMATION containing its own informations. If the PCEP message 1153 sent is the result of a previously received PCEP message, and if the 1154 PCEP-PATH-VECTOR TLV was already present in the initial message, the 1155 PCEP speaker MAY append a new PCEP-SPEAKER-INFORMATION containing its 1156 own informations. 1158 7. Security Considerations 1160 TBD. 1162 8. Acknowledgements 1164 Thanks to [I-D.knodel-terminology] urging for better use of terms. 1166 9. IANA Considerations 1168 This document requests IANA actions to allocate code points for the 1169 protocol elements defined in this document. 1171 9.1. PCEP-Error Object 1173 IANA is requested to allocate a new Error Value for the Error Type 9. 1175 Error-Type Meaning Reference 1176 6 Mandatory Object Missing [RFC5440] 1177 Error-value=TBD1: SPEAKER-IDENTITY-TLV This document 1178 missing 1180 9.2. PCEP TLV Type Indicators 1182 IANA is requested to allocate new TLV Type Indicator values within 1183 the "PCEP TLV Type Indicators" sub-registry of the PCEP Numbers 1184 registry, as follows: 1186 Value Meaning Reference 1187 TBD2 ORIGINAL-LSP-DB-VERSION TLV This document 1188 TBD3 PCEP-PATH-VECTOR TLV This document 1190 9.3. STATEFUL-PCE-CAPABILITY TLV 1192 IANA is requested to allocate a new bit value in the STATEFUL-PCE- 1193 CAPABILITY TLV Flag Field sub-registry. 1195 Bit Description Reference 1196 TBD INTER-PCE-CAPABILITY This document 1198 10. References 1200 10.1. Normative References 1202 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1203 Requirement Levels", BCP 14, RFC 2119, 1204 DOI 10.17487/RFC2119, March 1997, 1205 . 1207 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 1208 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 1209 DOI 10.17487/RFC5440, March 2009, 1210 . 1212 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1213 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1214 May 2017, . 1216 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 1217 Computation Element Communication Protocol (PCEP) 1218 Extensions for Stateful PCE", RFC 8231, 1219 DOI 10.17487/RFC8231, September 2017, 1220 . 1222 [RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X., 1223 and D. Dhody, "Optimizations of Label Switched Path State 1224 Synchronization Procedures for a Stateful PCE", RFC 8232, 1225 DOI 10.17487/RFC8232, September 2017, 1226 . 1228 10.2. Informative References 1230 [I-D.ietf-pce-association-diversity] 1231 Litkowski, S., Sivabalan, S., Barth, C., and M. Negi, 1232 "Path Computation Element Communication Protocol (PCEP) 1233 Extension for LSP Diversity Constraint Signaling", draft- 1234 ietf-pce-association-diversity-15 (work in progress), June 1235 2020. 1237 [I-D.knodel-terminology] 1238 Knodel, M. and N. Oever, "Terminology, Power, and 1239 Inclusive Language in Internet-Drafts and RFCs", draft- 1240 knodel-terminology-03 (work in progress), July 2020. 1242 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 1243 Element (PCE)-Based Architecture", RFC 4655, 1244 DOI 10.17487/RFC4655, August 2006, 1245 . 1247 [RFC6805] King, D., Ed. and A. Farrel, Ed., "The Application of the 1248 Path Computation Element Architecture to the Determination 1249 of a Sequence of Domains in MPLS and GMPLS", RFC 6805, 1250 DOI 10.17487/RFC6805, November 2012, 1251 . 1253 [RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path 1254 Computation Element Architecture", RFC 7399, 1255 DOI 10.17487/RFC7399, October 2014, 1256 . 1258 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 1259 S. Ray, "North-Bound Distribution of Link-State and 1260 Traffic Engineering (TE) Information Using BGP", RFC 7752, 1261 DOI 10.17487/RFC7752, March 2016, 1262 . 1264 [RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a 1265 Stateful Path Computation Element (PCE)", RFC 8051, 1266 DOI 10.17487/RFC8051, January 2017, 1267 . 1269 [RFC8751] Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., and D. King, 1270 "Hierarchical Stateful Path Computation Element (PCE)", 1271 RFC 8751, DOI 10.17487/RFC8751, March 2020, 1272 . 1274 Appendix A. Contributors 1276 Dhruv Dhody 1277 Huawei Technologies 1278 Divyashree Techno Park, Whitefield 1279 Bangalore, Karnataka 560066 1280 India 1282 Email: dhruv.ietf@gmail.com 1284 Authors' Addresses 1286 Stephane Litkowski 1287 Cisco 1289 Email: slitkows.ietf@gmail.com 1291 Siva Sivabalan 1292 Ciena Corporation 1294 Email: msiva282@gmail.com 1296 Cheng Li 1297 Huawei Technologies 1298 Huawei Campus, No. 156 Beiqing Rd. 1299 Beijing 100095 1300 China 1302 Email: c.l@huawei.com 1304 Haomian Zheng 1305 Huawei Technologies 1306 H1, Huawei Xiliu Beipo Village, Songshan Lake 1307 Dongguan, Guangdong 523808 1308 China 1310 Email: zhenghaomian@huawei.com