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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 CCAMP WG 2 Internet Draft Jean-Philippe Vasseur (Ed) 3 Proposed status: Standard Cisco Systems 4 Yuichi Ikejiri 5 NTT Communications 6 Corporation 7 Raymond Zhang 8 Infonet Service Corporation 9 Document: draft-vasseur-ccamp-loose-path- 10 reopt-02.txt 11 Expires: January 2005 July 2004 13 Reoptimization of MPLS Traffic Engineering loosely routed LSP 15 draft-vasseur-ccamp-loose-path-reopt-02.txt 17 Status of this Memo 19 By submitting this Internet-Draft, I certify that any applicable 20 patent or IPR claims of which I am aware have been disclosed, and any 21 of which I become aware will be disclosed, in accordance with RFC 22 3668. 24 This document is an Internet-Draft and is in full conformance with 25 all provisions of Section 10 of RFC2026 [i]. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF), its areas, and its working groups. Note that 29 other groups may also distribute working documents as Internet- 30 Drafts. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 The list of current Internet-Drafts can be accessed at 38 http://www.ietf.org/ietf/1id-abstracts.txt 39 The list of Internet-Draft Shadow Directories can be accessed at 40 http://www.ietf.org/shadow.html. 42 Abstract 44 This document defines a mechanism for the reoptimization of loosely 45 routed MPLS Traffic Engineering LSPs. A loosely routed LSP follows a 46 path specified as a combination of strict and loose hop(s) that 47 contains at least one loose hop and zero or more strict hop(s). The 48 path calculation (which implies an ERO expansion) to reach a loose 49 hop is performed by the previous hop defined in the TE LSP path. This 50 document proposes a mechanism that allows: 52 - The TE LSP head-end LSR to trigger a new path re-evaluation on 53 every hop having a next hop defined as a loose hop, 55 - A mid-point LSR to signal to the head-end LSR that either a better 56 path exists to reach a loose hop (compared to the current path in 57 use) or that the TE LSP must be reoptimized because of some 58 maintenance required on the TE LSP path. A better path is defined as 59 a lower cost path, where the cost is determined by the metric used to 60 compute the path. 62 The proposed mechanism applies to intra-domain and inter-domain (IGP 63 area or Autonomous System) packet and non-packet TE LSPs when the 64 path is defined as a list of loose hops or when a strict hop is a 65 non-specific abstract node (e.g. IGP area, Autonomous Systems). 67 Conventions used in this document 69 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 70 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 71 document are to be interpreted as described in RFC-2119 [ii]. 73 Table of contents 75 1. Introduction...................................................3 76 2. Establishment of a loosely routed TE LSP.......................3 77 3. Reoptimization of a loosely routed TE LSP path.................4 78 4. Signalling extensions..........................................5 79 4.1 Path re-evaluation request.................................5 80 4.2 New error value sub-code...................................5 81 5. Mode of operation..............................................6 82 5.1 Head-end reoptimization control............................6 83 5.2 Reoptimization triggers....................................6 84 5.3 Head-end request versus mid-point explicit notification modes 85 ...............................................................6 86 5.3.1 Head-end request mode.......................................7 87 5.3.2 Mid-point explicit notification mode........................8 88 5.3.3 ERO caching.................................................9 89 6. Interoperability...............................................9 90 7. Security considerations........................................9 91 8. Acknowledgments................................................9 92 9. Intellectual property considerations...........................9 93 9.1 IPR Disclosure Acknowledgement............................10 94 10. References...................................................10 95 Normative references.............................................10 96 Informative references...........................................10 97 11. Author's Addresses...........................................11 98 Full Copyright Statement.........................................11 100 1. Introduction 102 The Traffic Engineering Work Group has specified a set of 103 requirements for inter-area [INTER-AREA-TE-REQ] and inter-AS [INTER- 104 AS-TE-REQ] MPLS Traffic Engineering. Both requirements documents 105 specify the need for some mechanism providing an option for the head- 106 end to control the reoptimization process, should a more optimal path 107 exist in a downstream domain (IGP area or Autonomous System). 109 This document defines a solution to meet this requirement, in 110 addition to a mechanism to notify a Head-end LSR of the existence of 111 such a more optimal path or the need to reoptimize due to some 112 maintenance required in a downstream domain. 114 2. Establishment of a loosely routed TE LSP 116 A loosely routed explicit path is a path specified as a combination 117 of strict and loose hop(s) that contains at least one loose hop and a 118 set of zero or more strict hop(s). Loose hops are listed in the ERO 119 object of the RSVP Path message with the L flag of the Ipv4 or the 120 IPv6 prefix sub-object set, as defined in [RSVP-TE]. In this case, 121 each LSR along the path whose next hop is specified as a loose hop or 122 a non-specific abstract node triggers a path computation (also 123 referred to as an ERO expansion), before forwarding the RSVP Path 124 message downstream. The path computation may either be performed by 125 means of CSPF or any Path Computation Element (PCE) and can be 126 partial (up to the next loose hop) or complete (up to the TE LSP 127 destination). 129 Note that the examples in the rest of this document are provided in 130 the context of MPLS inter-area TE but the proposed mechanism equally 131 applies to loosely routed paths within a single routing domain and 132 across multiple Autonomous Systems. 134 The examples below are provided with OSPF as the IGP but the 135 described set of mechanisms similarly apply to IS-IS. 137 An example of an explicit loosely routed TE LSP signaling. 139 <---area 1--><-area 0--><-area 2-> 141 R1---R2----R3---R6 R8---R10 142 | | | / | \ | 143 | | | / | \ | 144 | | | / | \| 145 R4---------R5---R7----R9---R11 147 Assumptions 148 - R3, R5, R8 and R9 are ABRs 149 - The path an inter-area TE LSP T1 from R1 (head-End LSR) to R11 150 (tail-end LSR) is defined on R1 as the following loosely routed path: 151 R1-R3(loose)-R8(loose)-R11(loose). R3, R8 and R11 are defined as 152 loose hops. 154 Step 1: R1 determines that the next hop (R3) is a loose hop (not 155 directly connected to R1) and then performs an ERO expansion 156 operation to reach the next loose hops R3 either by means of CSPF or 157 any other PCE-based path computation method. The new ERO becomes: 158 R2(S)-R3(S)-R8(L)-R11(L) where: 159 S: Strict hop (L=0) 160 L: Loose hop (L=1) 162 The R1-R2-R3 path obeys T1�s set of constraints. 164 Step 2: the RSVP Path message is then forwarded by R1 following the 165 ERO path and reaches R3 with the following content: R8(L)-R11(L) 167 Step 3: R3 determines that the next hop (R8) is a loose hop (not 168 directly connected to R3) and then performs an ERO expansion 169 operation to reach the next loose hops R8 either by means of CSPF or 170 any other PCE-based path computation method. The new ERO becomes: 171 R6(S)-R7(S)-R8(S)-R11(L) 173 Note: in this example, the assumption is made that the path is 174 computed on a per loose hop basis, also referred to a partial route 175 computation. Note that PCE-based mechanisms may also allow for full 176 route computation (up to the final destination). 178 Step 4: the same procedure applies at R8 to reach T1�s destination 179 (R11). 181 3. Reoptimization of a loosely routed TE LSP path 183 Once a loosely routed explicit TE LSP is set up, it is maintained 184 through normal RSVP procedures. During TE LSP life time, a more 185 optimal path might appear between an LSR and its next loose hop (for 186 the sake of illustration, suppose in the example above that a link 187 between R6 and R8 is added or restored that provides a preferable 188 path between R3 and R8 (R3-R6-R8) than the existing R3-R6-R7-R8 189 path). Since a preferable (e.g. shorter) path might not be visible 190 from the head-end LSR by means of the IGP if it does not belong to 191 the head-end IGP area, the head-end cannot make use of this shorter 192 path (and reroute the LSP using a make before break) when 193 appropriate. Hence, some mechanism is required to detect the 194 existence of such a preferable path and to notify the head-end 195 accordingly. 197 This document defines a mechanism that allows: 199 - A head-end LSR to trigger on every LSR whose next hop is a 200 loose hop or an abstract node the re-evaluation of the current 201 path in order to detect a potential more optimal path, 203 - A mid-point LSR whose next hop is a loose-hop or an abstract 204 node to signal (using a new Error value sub-code carried in a 205 Path Error message) to the head-end that a more preferable path 206 exists (a path with a lower cost, where the cost definition is 207 determined by some metric). 209 Then once the existence of such a preferable path is notified to the 210 head-end LSR, the head-end LSR can decide (depending on the TE LSP 211 characteristics) whether to perform a TE LSP graceful reoptimization. 213 There is another scenario whereby notifying the head-end of the 214 existence of a better path is desirable: if the current path is about 215 the fail due to some (link or node) required maintenance (see also 216 [GR-SHUT]). 218 This allows the head-end to reoptimize a TE LSP making use of the non 219 disruptive make before break procedure if and only if a preferable 220 path exists and if such a reoptimization is desired. 222 4. Signalling extensions 224 New ERO flags and Error value sub-codes are proposed in this document 225 (to be assigned by IANA). 227 4.1 Path re-evaluation request 229 The following new flag of the SESSION_ATTRIBUTE object (C-Type 1 and 230 7) is defined (suggested value to be confirmed by IANA): 232 Path re-evaluation request: 0x20 234 This flag indicates that a path re-evaluation (of the current path in 235 use) is requested. Note that this does not trigger any LSP Reroute 236 but instead just signal the request to evaluate whether a preferable 237 path exists. 239 Note: in case of link bundling for instance, although the resulting 240 ERO might be identical, this might give the opportunity for a mid- 241 point LSR to locally select another link within a bundle, although 242 strictly speaking, the ERO has not changed. 244 4.2 New error value sub-code 246 As defined in [RSVP-TE], the ERROR-CODE 25 in ERROR SPEC object 247 corresponds to a Notify Error. 249 This document adds three new error value sub-codes (suggested values 250 to be confirmed by IANA): 252 6 Preferable path exists 253 7 Local link maintenance required 254 8 Local node maintenance required 256 The details about the local maintenance required modes are detailed 257 in section 5.3.2 259 5. Mode of operation 261 5.1 Head-end reoptimization control 263 The notification process of a preferable path (shorter path or new 264 path due to some maintenance required on the current path) is by 265 nature de-correlated from the reoptimization operation. In other 266 words, the location where a potentially preferable path is discovered 267 does not have to be where the TE LSP is actually reoptimized. This 268 document applies to the context of a head-end reoptimization. 270 5.2 Reoptimization triggers 272 There are three possible reoptimization triggers: 274 - Timer-based: a reoptimization is triggered (process evaluating 275 whether a more optimal path can be found) when a configurable timer 276 expires, 277 - Event-driven: a reoptimization is triggered when a particular 278 network event occurs (such as a ��Link-UP�� event), 279 - Operator-driven: a reoptimization is manually triggered by the 280 Operator. 282 It is RECOMMENDED for an implementation supporting the extensions 283 proposed in this document to support the aforementioned modes as path 284 re-evaluation triggers. 286 5.3 Head-end request versus mid-point explicit notification modes 288 This document defines two modes: 290 1) ��Head-end requesting mode��: the request for a new path 291 evaluation of a loosely routed TE LSP is requested by the head- 292 end LSR. 294 2) ��Mid-point explicit notification��: a mid-point LSR having 295 determined that a preferable path (than the current path is use) 296 exists or having the need to perform a link/node local 297 maintenance explicitly notifies the head-end LSR which will in 298 turn decide whether to perform a reoptimization. 300 5.3.1 Head-end request mode 302 In this mode, when a timer-based reoptimization is triggered on the 303 head-end LSR or the operator manually requests a reoptimization, the 304 head-end LSR immediately sends an RSVP Path message with the ��Path 305 re-evaluation request�� bit of the SESSION-ATTRIBUTE object set. This 306 bit is then cleared in subsequent RSVP path messages sent downstream. 308 Upon receiving a Path message with the ��Path re-evaluation request�� 309 bit set, every LSR for which the next abstract node contained in the 310 ERO is defined as a loose hop/abstract node, performs the following 311 set of actions: 313 A path re-evaluation is triggered and the newly computed path is 314 compared to the existing path: 316 - If a preferable path can be found, the LSR MUST immediately 317 send a Path Error to the head-end LSR (Error code 25 (Notify), 318 Error sub-code=6 (better path exists)). At this point, the LSR 319 MAY decide to clear the ��Path re-evaluation request�� bit of the 320 SESSION-ATTRIBUTE object in subsequent RSVP Path messages sent 321 downstream: this mode is the RECOMMENDED mode for the reasons 322 described below. 324 The sending of a Path Error Notify message ��Preferable path 325 exists�� to the head-end LSR will notify the head-end LSR of the 326 existence of a preferable path (e.g in a downstream area/AS or 327 in another location within a single domain). Hence, triggering 328 additional path re-evaluations on downstream nodes is 329 unnecessary. The only motivation to forward subsequent RSVP Path 330 messages with the ��Path re-evaluation request�� bit of the 331 SESSION-ATTRIBUTE object set would be to trigger path re- 332 evaluation on downstream nodes that could in turn cache some 333 potentially better paths downstream with the objective to reduce 334 the signaling setup delay, should a reoptimization be performed 335 by the head-end LSR. 337 - If no preferable path can be found, the recommended mode is 338 for an LSR to relay the request (by setting the ��Path re- 339 evaluation�� bit of the SESSION-ATTRIBUTE object in RSVP path 340 message sent downstream). 342 By preferable path, we mean a path having a lower cost. By default, 343 an LSR uses the TE metric to compute the shortest path that obeys a 344 set of constraints. Note that the head-end LSR might use the METRIC- 345 TYPE object (defined in [PATH-COMP]) in its path message to request 346 the LSR having a next hop defined as a loose hop or an abstract node 347 in the ERO to use another metric to determine a preferable path. 349 If the RSVP Path message with the ��Path re-evaluation request�� bit 350 set is lost, then the next request will be sent when the next 351 reoptimization trigger will occur on the head-end LSR. The solution 352 to handle RSVP reliable messaging has been defined in [REFRESH- 353 REDUCTION]. 355 The network administrator may decide to establish some local policy 356 specifying to ignore such request or to consider those requests not 357 more frequently than a certain rate. 359 The proposed mechanism does not make any assumption of the path 360 computation method performed by the ERO expansion process: it can 361 either be local to each LSR in charge of computing the path to the 362 next loose hop/abstract node or PCE based. 364 5.3.2 Mid-point explicit notification mode 366 In this mode, a mid-point LSR whose next hop is a loose hop or an 367 abstract node can locally trigger a path re-evaluation when a 368 configurable timer expires, some specific events occur (e.g. link-up 369 event for example) or the user explicitly requests it. If a 370 preferable path is found compared to the existing one, the LSR sends 371 a Path Error to the head-end LSR (Error code 25 (Notify), Error sub- 372 code=6 (��preferable path exists��). 374 There are other circumstances whereby a mid-point LSR MAY send an 375 RSVP PathError message with the objective for the TE LSP to be 376 rerouted by its head-end LSR: when a link or a node will go down for 377 local maintenance reasons. In this case, the mid-point LSR where the 378 local maintenance must be performed is responsible for sending an 379 RSVP PathError message with Error code 25 and Error sub-code=7 or 8 380 depending on the affected network element (link or node). Then the 381 first upstream node having performed the ERO expansion MUST perform 382 the following set of actions: 384 - The link (sub-code=7) or the node (sub-code=8) MUST be 385 locally registered for further reference (the TE database must 386 be updated) 388 - The RSVP Path Error message MUST be immediately forwarded 389 upstream to the head-end LSR. Note that in the case of TE LSP 390 spanning multiple administrative domains, it may be desirable 391 for the boundary LSR to modify the RSVP PathError message and 392 insert its own address for confidentiality reason. 394 Upon receiving a PathError message with Error code 25 and Error sub- 395 code 7 or 8, the Head-end LSR MUST perform a TE LSP reoptimization. 397 Note that those modes are not exclusive: both the timer and event- 398 driven reoptimization triggers can be implemented on the head-end 399 and/or any mid-point LSR with potentially different timer values for 400 the timer driven reoptimization case. 402 A head-end LSR MAY decide upon receiving an explicit mid-point 403 notification to delay its next path re-evaluation request. 405 5.3.3 ERO caching 407 Once a mid-point LSR has determined that a preferable path exists 408 (after a reoptimization request has been received by the head-end LSR 409 or the reoptimization timer on the mid-point has fired), the more 410 optimal path MAY be cached on the mid-point LSR for a limited amount 411 of time to avoid having to recompute a path once the head-LSR 412 performs a make before break. This mode is optional. 414 6. Interoperability 416 An LSR not supporting the ��Path re-evaluation request�� bit of the 417 SESSION-ATTRIBUTE object SHALL forward it unmodified. 419 Any head-end LSR not supporting a PathError Error code 25 message 420 with Error sub-code = 6, 7 or 8 MUST just silently ignore such Path 421 Error messages. 423 7. Security considerations 425 This document defines a mechanism for a mid-point LSR to notify the 426 head-end LSR of this existence of a preferable path or the need to 427 reroute the TE LSP for maintenance purposes. Hence, in case of a TE 428 LSP spanning multiple administrative domains, it may be desirable for 429 a boundary LSR to modify the PathError message (Code 25, Error sub- 430 code=6 or 7) so as to preserve confidentiality across domains. 432 8. Acknowledgments 434 The authors would like to thank Carol Iturralde, Miya Kohno, Francois 435 Le Faucheur, Philip Matthews, Jim Gibson, Raymond Zhang, Jean-Louis 436 Le Roux, Kenji Kumaki, Anca Zafir for their useful comments. A 437 special thank to Adrian Farrel for his very valuable inputs. 439 9. Intellectual property considerations 441 The IETF takes no position regarding the validity or scope of any 442 Intellectual Property Rights or other rights that might be claimed to 443 pertain to the implementation or use of the technology described in 444 this document or the extent to which any license under such rights 445 might or might not be available; nor does it represent that it has 446 made any independent effort to identify any such rights. Information 447 on the procedures with respect to rights in RFC documents can be 448 found in BCP 78 and BCP 79. 450 Copies of IPR disclosures made to the IETF Secretariat and any 451 assurances of licenses to be made available, or the result of an 452 attempt made to obtain a general license or permission for the use of 453 such proprietary rights by implementers or users of this 454 specification can be obtained from the IETF on-line IPR repository at 455 http://www.ietf.org/ipr. 457 The IETF invites any interested party to bring to its attention any 458 copyrights, patents or patent applications, or other proprietary 459 rights that may cover technology that may be required to implement 460 this standard. Please address the information to the IETF at ietf- 461 ipr@ietf.org. 463 9.1 IPR Disclosure Acknowledgement 465 By submitting this Internet-Draft, I certify that any applicable 466 patent or other IPR claims of which I am aware have been disclosed, 467 and any of which I become aware will be disclosed, in accordance with 468 RFC 3668. 470 10. References 472 Normative references 474 [RFC] Bradner, S., "Key words for use in RFCs to Indicate Requirement 475 Levels," RFC 2119. 477 [RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP 478 Tunnels", RFC3209, December 2001. 480 [REFRESH-REDUCTION] Berger et al, ��RSVP Refresh Overhead Reduction 481 Extensions��, April 2001 483 Informative references 485 [TE-REQ] Awduche et al, Requirements for Traffic Engineering over 486 MPLS, RFC2702, September 1999. 488 [INTER-AREA-TE-REQ], Le Roux, Vasseur, Boyle et al. � Requirements 489 for Inter-area MPLS Traffic Engineering �, draft-ietf-tewg-interarea- 490 mpls-te-req-01, April 2004 (Work in progress). 492 [INTER-AS-TE-REQ] Zhang et al, ��MPLS Inter-AS Traffic Engineering 493 requirements��, draft-ietf-tewg-interas-mpls-te-req-06.txt, February 494 2004, Work in progress. 496 [INTER-AREA-AS] Vasseur and Ayyangar, ��Inter-area and Inter-AS 497 Traffic Engineering��, draft-vasseur-inter-area-AS-TE-00.txt, February 498 2004, work in progress. 500 [GR-SHUT], Z. Ali et al, ��Graceful Shutdown in MPLS Traffic 501 Engineering Networks��, draft-ali-ccamp-mpls-graceful-shutdown-00.txt, 502 June 2004. 504 11. Author's Addresses 506 Jean-Philippe Vasseur 507 CISCO Systems, Inc. 508 300 Beaver Brook 509 Boxborough, MA 01719 510 USA 511 Email: jpv@cisco.com 513 Yuichi Ikejiri 514 NTT Communications Corporation 515 1-1-6, Uchisaiwai-cho, Chiyoda-ku 516 Tokyo 100-8019 517 JAPAN 518 Email: y.ikejiri@ntt.com 520 Raymond Zhang 521 Infonet Services Corporation 522 2160 E. Grand Ave. 523 El Segundo, CA 90025 524 USA 525 Email: raymond_zhang@infonet.com 527 Full Copyright Statement 529 "Copyright (C) The Internet Society (year). This document is subject 530 to the rights, licenses and restrictions contained in BCP 78, and 531 except as set forth therein, the authors retain all their rights." 533 "This document and the information contained herein are provided on 534 an 535 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 536 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 537 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 538 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 539 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 540 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."