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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (August 2007) is 6098 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group S. Yasukawa 2 Internet Draft NTT 3 Category: Informational A. Farrel 4 Expires: February 2008 Old Dog Consulting 5 August 2007 7 PCC-PCE Communication Requirements for Point to Multipoint 8 Multiprotocol Label Switching Traffic Engineering (MPLS-TE) 10 draft-yasukawa-pce-p2mp-req-03.txt 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as 22 Internet-Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 Abstract 37 The Path Computation Element (PCE) provides path computation 38 functions in support of traffic engineering in Multi-Protocol Label 39 Switching (MPLS) and Generalized MPLS (GMPLS) networks. 41 Extensions to the MPLS and GMPLS signaling and routing protocols have 42 been made in support of point-to-multipoint (P2MP) Traffic Engineered 43 (TE) Label Switched Paths (LSPs). Since P2MP TE LSP routes are 44 sometimes complex to compute, and given the use of PCE in MPLS 45 networks it is likely that PCE will be used in P2MP MPLS-TE networks. 47 Generic requirements for a communication protocol between Path 48 Computation Clients (PCCs) and PCEs are presented in "Path 49 Computation Element (PCE) Communication Protocol Generic 50 Requirements". This document complements the generic requirements and 51 presents a detailed set of PCC-PCE communication protocol 52 requirements for point-to-multipoint MPLS traffic engineering. 54 Conventions used in this document 56 Although this document is not a protocol specification, the key words 57 "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", 58 "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be 59 interpreted as described in RFC 2119 [RFC2119] for clarity of 60 description of requirements. 62 1. Introduction 64 The Path Computation Element (PCE) defined in [RFC4655] is an entity 65 that is capable of computing a network path or route based on a 66 network graph, and applying computational constraints. The intention 67 is that the PCE is used to compute the path of Traffic Engineered 68 Label Switched Paths (TE LSPs) within Multiprotocol Label Switching 69 (MPLS) and Generalized MPLS (GMPLS) networks. 71 Requirements for point-to-multipoint (P2MP) MPLS TE LSPs are 72 documented in [RFC4461] and signaling protocol extensions for 73 setting up P2MP MPLS TE LSPs are defined in [RFC4875]. P2MP MPLS TE 74 networks are considered in support of various features including 75 layer 3 multicast VPNs [RFC4834]. 77 Path computation for P2MP TE LSPs presents a significant challenge, 78 and network optimization of multiple P2MP TE LSPs requires 79 considerable computational resources. PCE offers a way to offload 80 such path computations from Label Swiching Routers (LSRs). 82 The applicability of the PCE-based path computation architecture to 83 P2MP MPLS TE is described in a companion document [PCE-P2MP-APP]. No 84 further attempt is made to justify the use of PCE for P2MP MPLS TE 85 within this document. 87 This document presents a set of PCC-PCE communication protocol 88 (PCECP) requirements for P2MP MPLS traffic engineering. It 89 supplements the generic requirements documented in [RFC4657]. 91 2. PCC-PCE Communication Requirements for P2MP MPLS Traffic Engineering 93 This section sets out additional requirements not covered in 94 [RFC4657] specific to P2MP MPLS TE. 96 2.1. PCC-PCE Communication 98 The PCC-PCE communication protocol MUST allow requests and replies 99 for the computation of paths for P2MP LSPs. 101 This requires no additional messages, but requires the addition of 102 the parameters described in the following sections to the existing 103 PCC-PCE communication protocol messages. 105 2.1.1. Indication of P2MP Path Computation Request 107 Although the presence of certain parameters (such as a list of more 108 than one destination) MAY be used to infer that a path computation 109 request is for a P2MP LSP, an explicit parameter SHOULD be placed in 110 a conspicuous place within a Path Computation Request message to 111 allow a receiving PCE to easily identify that the request is for a 112 P2MP path. 114 2.1.2. Indication of P2MP Objective Functions 116 [RFC4657] includes the requirement to be able to specify the 117 objective functions to be applied by a PCE during path computation 118 and for the PCE to indicate which objective functions were applied. 120 This document makes no change to that requirement, but it should be 121 noted that new and different objective functions will be used for 122 P2MP computation, and that these obvjective functions will need to be 123 defined and allocated codepoints in a separate document. 125 2.1.3. Non-Support of P2MP Path Computation 127 PCEs are not required to support P2MP path computation. Therefore, it 128 MUST be possible for a PCE to reject a P2MP Path Computation Request 129 message with a reason code that indicates no support for P2MP path 130 computation. 132 2.1.4. Non-Support by Back-Level PCE Implementations 134 It is possible that initial PCE implementations will be developed 135 without support for P2MP path computation and without the ability to 136 recognize the explicit parameter described in section 2.1.1. Such 137 legacy implementations will not be able to make use of the new 138 reason code described in Section 2.1.3. 140 Therefore, at least one parameter required for inclusion in a P2MP 141 Path Computation Request message MUST be defined in such a way as to 142 cause automatic rejection as unprocessable or unrecognized by a back- 143 level PCE implementation without requiring any changes to that PCE. 144 It is RECOMMENDED that the parameter that causes this result is the 145 parameter described in Section 2.1.1. 147 2.1.5. Specification of Destinations 149 Since P2MP LSPs have more than one destination, it MUST be possible 150 for a single Path Computation Request to list multiple destinations. 152 2.1.6. Indication of P2MP Paths 154 The Path Computation Response MUST be able to carry the path of a 155 P2MP LSP. This SHOULD be expressed as a compacted series of routes as 156 described in [RFC4875] although not necessarily using an identical 157 encoding. This path MAY be expressed as a non-compacted series of 158 source-to-destination routes. 160 2.1.7. Multi-Message Requests and Responses 162 A single P2MP LSP may have very many destinations, and the computed 163 path (tree) may be very extensive. In these cases it is possible that 164 the entire Path Computation Request or Response cannot fit within one 165 PCE message. Therefore, it MUST be possible for a single request or 166 response to be conveyed by a sequence of PCE messages. 168 Note that there is a requirement in [RFC4657] for reliable and 169 in-order message delivery, so it is assumed that components of the 170 sequence will be delivered in order and without missing components. 172 2.1.8. Non-Specification of Per-Destination Constraints and Parameters 174 [RFC4875] requires that all branches of a single P2MP LSP have the 175 same characteristics, and achieves this by not allowing the signaling 176 parameters to be varied for different branches of the same P2MP LSP. 178 It MUST NOT be possible to set different constraints, traffic 179 parameters, or quality of service requirements for different 180 destinations of a P2MP LSP within a single computation request. 182 2.1.9. Path Modification and Path Diversity 184 No changes are made to the requirement to support path modification 185 and path diversity as described in [RFC4657]. Note, however, that a 186 consequence of this requirement is that it MUST be possible to supply 187 an existing path on a Path Computation Request. This requirement is 188 unchanged from [RFC4657], but it is a new requirement that such paths 189 MUST be able to be P2MP paths. 191 2.1.10. Reoptimization of P2MP TE LSPs 193 Reoptimization MUST be supported for P2MP TE LSPs as described for 194 P2P LSPs in [RFC4657]. To support this, the existing path MUST be 195 supplied as described in Section 2.1.9. 197 Because P2MP LSPs are more complex it is often the case that small 198 optimization improvements can be made after changes in network 199 resource availability. But re-signaling any LSP introduces risks to 200 the stability of the service provided to the customer and the 201 stability of the network even when techniques like make-before-break 203 [RFC3209] are used. Therefore, a P2MP Path Computation Request SHOULD 204 contain a parameter that allows the PCC to express a cost-benefit 205 reoptimization threshold for the whole LSP as well as per 206 destination. The setting of this parameter is subject to local policy 207 at the PCC and SHOULD be subject to policy at the PCE [PCE-POLICY]. 209 Path reoptimization responses SHOULD indicate which of the routes (as 210 supplied according to Section 2.1.6) have been modified from the 211 paths supplied on the request. 213 2.1.11. Addition and Removal of Destinations from Existing Paths 215 A variation of path modification described in Section 2.1.9 is that 216 destinations may be added to, or removed from, existing P2MP TE LSPs. 218 In the case of the addition of one or more destinations, it is 219 necessary to compute a path for a new branch of the P2MP LSP. It may 220 be desirable to recompute the whole P2MP tree, to add the new branch 221 as a simple spur from the existing tree, or to recompute part of the 222 P2MP tree. 224 To support this function for leaf additions it MUST be possible to 225 make the following indications on a path computation request: 227 - The path of an existing P2MP LSP (as described in Section 2.1.9). 229 - Which destinations are new additions to the tree. 231 - Which destinations of the existing tree must not have their paths 232 modified. 234 It MAY also be possible to indicate on a path computation request a 235 cost-benefit reoptimization threshold such that the tree and/or a new 236 path to any individual destination is not supplied unless a certain 237 improvement is made. Compare with Section 2.1.10. 239 In the case of the deletion of one or more destinations, it is not 240 necessary to compute a new path for the P2MP TE LSP, but such a 241 computation may yield optimizations over a simple pruning of the 242 tree. The recomputation function in this case is essentially the same 243 as that described in Section 2.1.10, but note that it MAY be possible 244 to supply the full previous path of the entire P2MP TE LSP (that is, 245 before the deletion of the destinations) on the Path Computation 246 Request. 248 For both addition and deletion of destinations, the Path Computation 249 Response SHOULD indicate which of the routes (as supplied according 250 to Section 2.1.6) have been modified from the paths supplied on the 251 request as described in Section 2.1.10. 253 Note that the selection of all of these options is subject to local 254 policy at the PCC, and SHOULD be subject to policy at the PCE 255 [PCE-POLICY]. 257 2.1.12. Specification of Applicable Branch Nodes 259 For administrative or security reasons, or for other policy reasons, 260 it may be desirable to limit the set of nodes within the network that 261 may be used as branch points for a given LSP. That is, to provide to 262 the path computation a limiting set of nodes that can be used as 263 branches for a P2MP path computation, or to provide a list of nodes 264 that must not be used as branch points. 266 The PCC MUST be able to specify on a Path Computation Request a list 267 of nodes that constitues a limiting superset of the branch nodes for 268 a P2MP path computation. 270 A PCC MUST be able to specify on a Path Computation Request a list of 271 nodes that must not be used as branch nodes for a P2MP path 272 computation. 274 2.1.13. Capabilities Exchange 276 PCE capabilities exchange forms part of PCE discovery [RFC4674], but 277 MAY also be included in the PCECP message exchanges [RFC4657]. 279 The ability to perform P2MP path computation and the objective 280 functions supported by a PCE SHOULD be advertised as part of PCE 281 discovery. In the event that the PCE ability to perform P2MP 282 computation is not advertised as part of PCE discovery, the PCECP 283 MUST allow a PCC to discover which PCEs with which it communicates 284 support P2MP path computation and which objective functions specific 285 to P2MP path computation are supported by each PCE. 287 The list of objective functions is assumed to be coordinated with 288 those that can be requested as described in Section 2.1.2. 290 These requirements do not represent a change to [RFC4657] except to 291 add more capabilities and objective functions. 293 3. Manageability Considerations 295 3.1. Control of Function and Policy 297 PCE implementations MAY provide a configuration switch to allow 298 support of P2MP MPLS TE computations to be enabled or disabled. When 299 the level of support is changed, this SHOULD be re-advertised as 300 described in Section 2.1.13. 302 Support for, and advertisement of support for, P2MP MPLS TE path 303 computation MAY be subject to policy and a PCE MAY hide its P2MP 304 capabilities from certain PCCs by not advertising them through the 305 discovery protocol, and not reporting them to the specific PCCs in 306 any PCECP capabilities exchange. Further, a PCE MAY be directed by 307 policy to refuse a P2MP path computation for any reason including, 308 but not limited to, the identity of the PCC that makes the request. 310 3.2. Information and Data Models 312 PCECP protocol extensions to support P2MP MPLS TE MUST be accompanied 313 by MIB objects for the control and monitoring of the protocol and the 314 PCE that performs the computations. The MIB objects MAY be provided 315 in the same MIB module as used for general PCECP control and 316 monitoring or MAY be provided in a new MIB module. 318 The MIB objects MUST provide the ability to control and monitor all 319 aspects of PCECP relevant to P2MP MPLS TE path computation. 321 3.3. Liveness Detection and Monitoring 323 No changes are necessary to the liveness detection and monitoring 324 requirements as already embodied in [RFC4657]. It should be noted, 325 however, that in general P2MP computations are likely to take longer 326 than P2P computations. The liveness detection and molnitoring 327 features of the PCECP SHOULD take this into account. 329 3.4. Verifying Correct Operation 331 There are no additional requirements beyond those expressed in 332 [RFC4657] for verifying the correct operation of the PCECP. Note that 333 verification of the correct operation of the PCE and its algorithms 334 is out of scope for the protocol requirements, but a PCC MAY send the 335 same request to more than one PCE and compare the results. 337 3.5. Requirements on Other Protocols and Functional Components 339 A PCE operates on a topology graph that may be built using 340 information distributed by TE extensions to the routing protocol 341 operating within the network. In order that the PCE can select a 342 suitable path for the signaling protocol to use to install the P2MP 343 LSP, the topology graph must include information about the P2MP 344 signaling and branching capabilities of each LSR in the network. 346 Whatever means is used to collect the information to build the 347 topology graph MUST include the requisite information. If the TE 348 extensions to the routing protocol are used, these SHOULD be as 349 described in [TE-NODE-CAP]. 351 3.6. Impact on Network Operation 353 The use of a PCE to compute P2MP paths is not expected to have 354 significant impact on network operations. But it should be noted that 355 the introduction of P2MP support to a PCE that already provides P2P 356 path computation might change the loading of the PCE significantly 357 and that might have an impact on the network behavior especially 358 during recovery periods immediately after a network failure. 360 4. Security Considerations 362 P2MP computation requests do not raise any additional security issues 363 for the PCECP as there are no new messages and no new PCC-PCE 364 relationships or transactions introduced. 366 Note, however, that P2MP computation requests are more CPU-intensive 367 and also use more link bandwidth. Therefore, if the PCECP was 368 susceptible to denial of service attacks based on the injection of 369 spurious Path Computation Requests, the support of P2MP path 370 computation would exacerbate the effect. 372 It would be possible to consider applying different authorization 373 policies for P2MP Path Computation Requests compared to other 374 requests. 376 5. IANA Considerations 378 This document makes no requests for IANA action. 380 6. Acknowledgments 382 Thanks to Dean Cheng and Young Lee for their comments and suggestions 383 on this document. 385 7. References 387 7.1. Normative Reference 389 [RFC2119] Bradner, S., "Key words for use in RFCs to indicate 390 requirements levels", RFC 2119, March 1997. 392 [RFC4657] Ash, J., and Le Roux, J.L., "Path Computation Element 393 (PCE) Communication Protocol Generic Requirements", 394 RFC 4657, September 2006. 396 [PCE-POLICY] Bryskin, I., Papadimitriou, D., and Berger, L., 397 "Policy-Enabled Path Computation Framework", 398 draft-ietf-pce-policy-enabled-path-comp, work in 399 progress. 401 7.2. Informative Reference 403 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, 404 V., and G. Swallow, "RSVP-TE: Extensions to RSVP for 405 LSP Tunnels", RFC 3209, December 2001. 407 [RFC4461] S. Yasukawa, Editor "Signaling Requirements for 408 Point-to-Multipoint Traffic Engineered MPLS LSPs", 409 RFC4461, April 2006. 411 [RFC4655] Farrel, A., Vasseur, J.P., and Ash, G., "A Path 412 Computation Element (PCE)-Based Architecture", 413 RFC 4655, August 2006. 415 [RFC4674] J.L. Le Roux, Editor, "Requirements for Path 416 Computation Element (PCE) Discovery", RFC 4674, 417 October 2006. 419 [PCE-P2MP-APP] S. Yasukawa et al., "Applicability of the Path 420 Computation Element to Point-to-Multipoint Traffic 421 Engineering", draft-yasukawa-pce-p2mp-app, work in 422 progress. 424 [RFC4834] Morin, T., "Requirements for Multicast in Layer 3 425 Provider-Provisioned Virtual Private Networks 426 (PPVPNs)", RFC 4834, April 2007. 428 [RFC4875] Aggarwal, R., Papadimitriou, D., and Yasukawa, S., 429 "Extensions to Resource Reservation Protocol - Traffic 430 Engineering (RSVP-TE) for Point-to-Multipoint TE Label 431 Switched Paths (LSPs)", RFC 4875, May 2007. 433 [TE-NODE-CAP] Vasseur, J.P, and Le Roux, J.L., Editors, "IGP Routing 434 Protocol Extensions for Discovery of Traffic 435 Engineering Node Capabilities", draft-ietf-ccamp-te- 436 node-cap, work in progress. 438 8. Authors' Addresses 440 Seisho Yasukawa 441 NTT Corporation 442 (R&D Strategy Department) 443 3-1, Otemachi 2-Chome Chiyodaku, Tokyo 100-8116 Japan 444 Phone: +81 3 5205 5341 445 Email: s.yasukawa@hco.ntt.co.jp 447 Adrian Farrel 448 Old Dog Consulting 449 Email: adrian@olddog.co.uk 451 9. Intellectual Property Statement 453 The IETF takes no position regarding the validity or scope of any 454 Intellectual Property Rights or other rights that might be claimed to 455 pertain to the implementation or use of the technology described in 456 this document or the extent to which any license under such rights 457 might or might not be available; nor does it represent that it has 458 made any independent effort to identify any such rights. Information 459 on the procedures with respect to rights in RFC documents can be 460 found in BCP 78 and BCP 79. 462 Copies of IPR disclosures made to the IETF Secretariat and any 463 assurances of licenses to be made available, or the result of an 464 attempt made to obtain a general license or permission for the use of 465 such proprietary rights by implementers or users of this 466 specification can be obtained from the IETF on-line IPR repository at 467 http://www.ietf.org/ipr. 469 The IETF invites any interested party to bring to its attention any 470 copyrights, patents or patent applications, or other proprietary 471 rights that may cover technology that may be required to implement 472 this standard. Please address the information to the IETF at ietf- 473 ipr@ietf.org. 475 10. Full Copyright Statement 477 Copyright (C) The IETF Trust (2007). 479 This document is subject to the rights, licenses and restrictions 480 contained in BCP 78, and except as set forth therein, the authors 481 retain all their rights. 483 This document and the information contained herein are provided on an 484 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 485 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 486 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 487 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 488 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 489 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.