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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Seisho Yasukawa 2 Internet Draft NTT 3 Category: Informational Adrian Farrel 4 Expires: August 2007 Old Dog Consulting 5 February 2007 7 PCC-PCE Communication Requirements for Point to Multipoint 8 Multiprotocol Label Switching Traffic Engineering (MPLS-TE) 10 draft-yasukawa-pce-p2mp-req-02.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 [P2MP-RSVP]. P2MP MPLS TE 74 networks are considered in support of various features including 75 layer 3 multicast VPNs. 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, requires the addition of the 102 parameters described in the following sections to the PCC-PCE 103 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. Non-Support of P2MP Path Computation 116 Not all PCEs are required to support P2MP path computation. Therefore 117 it MUST be possible for a PCE to reject a P2MP Path Computation 118 Request message with a reason code that indicates no support for P2MP 119 path computation. 121 2.1.3. Non-Support by Back-Level PCE Implementations 123 It is possible that initial PCE implementations will be developed 124 without support for P2MP path computation and without the ability to 125 recognize the explicit parameter described in section 2.1.1. 126 Therefore, at least one parameter required for a P2MP path 127 computation request MUST be defined in such a way as to cause 128 automatic rejection as unprocessable or unrecognized by a back-level 129 PCE implementation without requiring any changes to that PCE. It is 130 RECOMMENDED that the parameter that causes this result is the 131 parameter described in section 2.1.1. 133 2.1.4. Specification of Destinations 135 Since P2MP LSPs have more than one destination, it MUST be possible 136 for a single Path Computation Request to list multiple destinations. 138 2.1.5. Indication of P2MP Paths 140 The Path Computation Response MUST be able to carry the path of a 141 P2MP LSP. This SHOULD be expressed as a compacted series of routes as 142 described in [P2MP-RSVP] although not necessarily using an identical 143 encoding. This path MAY be expressed as a non-compacted series of 144 source-to-destination routes. 146 2.1.6. Multi-Message Requests and Responses 148 A single P2MP LSP may have very many destinations, and the computed 149 path (tree) may be very extensive. In these cases it is possible that 150 the entire Path Computation Request or Response cannot fit within one 151 PCE message. Therefore it MUST be possible for a single request or 152 response to be conveyed by a sequence of messages. 154 Note that there is a requirement in [RFC4657] for reliable and 155 in-order message delivery, so it is assumed that components of the 156 sequence will be delivered in order and without missing components. 158 2.1.7. Non-Specification of Per-Destination Constraints and Parameters 160 It MUST NOT be possible to set different constraints, traffic 161 parameters, or quality of service requirements for different 162 destinations of a P2MP LSP within a single computation request. 164 2.1.8. Path Modification and Path Diversity 166 No changes are made to the requirement to support path modification 167 and path diversity as described in [RFC4657]. Note, however, that a 168 consequence of this requirement is that it MUST be possible to supply 169 an existing path on a Path Computation Request. This requirement is 170 unchanged from [RFC4657], but it is a new requirement that such paths 171 MUST be able to be P2MP paths. 173 2.1.9. Reoptimization of P2MP TE LSPs 175 Reoptimization MUST be supported for P2MP TE LSPs as described for 176 P2P LSPs in [RFC4657]. To support this, the existing path MUST be 177 supplied as described in Section 2.1.8. 179 Because P2MP LSPs are more complex it is often the case that small 180 optimization improvements can be made after changes in network 181 resource availability. But re-signaling any LSP introduces risks to 182 the stability of the service provided to the customer and the 183 stability of the network even when techniques like make-before-break 184 [RFC3209] are used. Therefore, a path computation request SHOULD 185 contain a parameter that allows the PCC to express a cost-benefit 186 reoptimization threshold for the whole LSP as well as per 187 destination. The setting of this parameter is subject to local policy 188 at the PCC and SHOULD be subject to policy at the PCE [PCE-POLICY]. 190 Path reoptimization responses SHOULD indicate which of the routes (as 191 supplied according to Section 2.1.5) have been modified from the 192 paths supplied on the request. 194 2.1.10. Addition and Removal of Destinations from Existing Paths 196 A variation of path modification described in Section 2.1.8 is that 197 destinations may be added to or removed from existing P2MP TE LSPs. 199 In the case of the addition of one or more destinations it is 200 necessary to compute a path for a new branch of the P2MP LSP. It may 201 be desirable to recompute the whole P2MP tree, to add the new branch 202 as a simple spur from the existing tree, or to recompute part of the 203 P2MP tree. 205 To support this function for leaf additions it MUST be possible to 206 make the following indications on a path computation request: 208 - The path of an existing P2MP LSP (as described in Section 2.1.8). 210 - Which destinations are new additions to the tree. 212 - Which destinations of the existing tree must not have their paths 213 modified. 215 It MAY also be possible to indicate on a path computation request a 216 cost-benefit reoptimization threshold such that the tree and/or a new 217 path to any individual destination is not supplied unless a certain 218 improvement is made. Compare with Section 2.1.9. 220 In the case of the deletion of one or more destinations it is not 221 necessary to compute a new path for the P2MP TE LSP, but such a 222 computation may yield optimizations over a simple pruning of the 223 tree. The recomputation function in this case is essentially the same 224 as that described in Section 2.1.9, but note that it MAY be possible 225 to supply the full previous path of the entire P2MP TE LSP (that is, 226 before the deletion of the destinations) on the path computation 227 request. 229 For both addition and deletion of destinations, the path computation 230 response SHOULD indicate which of the routes (as supplied according 231 to Section 2.1.5) have been modified from the paths supplied on the 232 request as described in Section 2.1.9. 234 Note that the selection of all of these options is subject to local 235 policy at the PCC, and SHOULD be subject to policy at the PCE 236 [PCE-POLICY]. 238 2.1.11. Capabilities Exchange 240 PCE capabilities exchange forms part of PCE discovery [RFC4674], but 241 MAY also be included in the PCECP message exchanges. 243 The ability to perform P2MP path computation SHOULD be advertised as 244 part of PCE discovery. In the event that the PCE ability to perform 245 P2MP computation is not advertised as part of PCE discovery, the 246 PCECP MUST allow a PCC to discover which PCEs with which it 247 communicates support P2MP path computation and which objective 248 functions specific to P2MP path computation are supported by each 249 PCE. 251 3. Manageability Considerations 253 3.1. Control of Function and Policy 255 PCE implementations MAY provide a configuration switch to allow 256 support of P2MP MPLS TE computations to be enabled or disabled. When 257 the level of support is changed, this SHOULD be re-advertised as 258 described in Section 2.1.11. 260 Support for, and advertisement of support for, P2MP MPLS TE path 261 computation MAY be subject to policy and a PCE MAY hide its P2MP 262 capabilities from certain PCCs by not advertising them through the 263 discovery protocol, and not reporting them to the specific PCCs in 264 any PCECP capabilities exchange. Further, a PCE MAY be directed by 265 policy to refuse a P2MP path computation for any reason including, 266 but not limited to, the identity of the PCC that makes the request. 268 3.2. Information and Data Models 270 PCECP protocol extensions to support P2MP MPLS TE MUST be accompanied 271 by MIB objects for the control and monitoring of the protocol and the 272 PCE that performs the computations. The MIB objects MAY be provided 273 in the same MIB module as used for general PCECP control and 274 monitoring or MAY be provided in a new MIB module. 276 The MIB objects MUST provide the ability to control and monitor all 277 aspects of PCECP relevant to P2MP MPLS TE path computation. 279 3.3. Liveness Detection and Monitoring 281 No changes are necessary to the liveness detection and monitoring 282 requirements as already embodied in [RFC4657]. It should be noted, 283 however, that in general P2MP computations are likely to take longer 284 than P2P computations. The liveness detection and molnitoring 285 features of the PCECP SHOULD take this into account. 287 3.4. Verifying Correct Operation 289 There are no additional requirements beyond those expressed in 290 [RFC4657] for verifying the correct operation of the PCECP. Note that 291 verification of the correct operation of the PCE and its algorithms 292 is out of scope for the protocol requirements, but a PCC MAY send the 293 same request to more than one PCE and compare the results. 295 3.5. Requirements on Other Protocols and Functional Components 297 A PCE operates on a topology graph that may be built using 298 information distributed by TE extensions to the routing protocol 299 operating within the network. In order that the PCE can select a 300 suitable path for the signaling protocol to use to install the P2MP 301 LSP, the topology graph must include information about the P2MP 302 signaling and branching capabilities of each LSR in the network. 304 Whatever means is used to collect the information to build the 305 topology graph MUST include the requisite information. If the TE 306 extensions to the routing protocol are used, these SHOULD be as 307 described in [TE-NODE-CAP]. 309 3.6. Impact on Network Operation 311 The use of a PCE to compute P2MP paths is not expected to have 312 significant impact on network operations. But it should be noted that 313 the introduction of P2MP support to a PCE that already provides P2P 314 path computation might change the loading of the PCE significantly 315 and that might have an impact on the network behavior especially 316 during recovery periods immediately after a network failure. 318 4. Security Considerations 320 P2MP computation requests do not raise any additional security issues 321 for the PCECP. 323 Note, however, that P2MP computation requests are more CPU-intensive 324 and also use more link bandwidth. Therefore if the PCECP was 325 susceptible to denial of service attacks based on the injection of 326 spurious Path Computation Requests, the support of P2MP path 327 computation would exacerbate the effect. 329 It would be possible to consider applying different authorization 330 policies for P2MP path computation requests compared to other 331 requests. 333 5. IANA Considerations 335 This document makes no requests for IANA action. 337 6. Acknowledgments 339 Thanks to Dean Cheng for his comments on this document. 341 7. References 343 7.1. Normative Reference 345 [RFC2119] Bradner, S., "Key words for use in RFCs to indicate 346 requirements levels", RFC 2119, March 1997. 348 [RFC4657] Ash, J., and Le Roux, J.L., "Path Computation Element 349 (PCE) Communication Protocol Generic Requirements", 350 RFC 4657, September 2006. 352 [PCE-POLICY] Bryskin, I., Papadimitriou, D., and Berger, L., 353 "Policy-Enabled Path Computation Framework", 354 draft-ietf-pce-policy-enabled-path-comp, work in 355 progress. 357 7.2. Informative Reference 359 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, 360 V., and G. Swallow, "RSVP-TE: Extensions to RSVP for 361 LSP Tunnels", RFC 3209, December 2001. 363 [RFC4461] S. Yasukawa, Editor "Signaling Requirements for 364 Point-to-Multipoint Traffic Engineered MPLS LSPs", 365 RFC4461, April 2006. 367 [RFC4655] Farrel, A., Vasseur, J.P., and Ash, G., "A Path 368 Computation Element (PCE)-Based Architecture", 369 RFC 4655, August 2006. 371 [RFC4674] J.L. Le Roux, Editor, "Requirements for Path 372 Computation Element (PCE) Discovery", RFC 4674, 373 October 2006. 375 [PCE-P2MP-APP] S. Yasukawa et al., "Applicability of the Path 376 Computation Element to Point-to-Multipoint Traffic 377 Engineering", draft-yasukawa-pce-p2mp-app, work in 378 progress. 380 [P2MP-RSVP] Aggarwal, R., Papadimitriou, D., and Yasukawa, S., 381 "Extensions to RSVP-TE for Point to Multipoint TE 382 LSPs", draft-ietf-mpls-rsvp-te-p2mp, work in progress. 384 [TE-NODE-CAP] Vasseur, J.P, and Le Roux, J.L., Editors, "IGP Routing 385 Protocol Extensions for Discovery of Traffic 386 Engineering Node Capabilities", draft-ietf-ccamp-te- 387 node-cap, work in progress. 389 8. Authors' Addresses 391 Seisho Yasukawa 392 NTT Corporation 393 (R&D Strategy Department) 394 3-1, Otemachi 2-Chome Chiyodaku, Tokyo 100-8116 Japan 395 Phone: +81 3 5205 5341 396 Email: s.yasukawa@hco.ntt.co.jp 398 Adrian Farrel 399 Old Dog Consulting 400 Email: adrian@olddog.co.uk 402 9. 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