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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force H. Chen 3 Internet-Draft Huawei Technologies 4 Intended status: Standards Track March 7, 2011 5 Expires: September 8, 2011 7 A Fordward-Search P2P TE LSP Inter-Domain Path Computation 8 draft-chen-pce-forward-search-p2p-path-computation-00.txt 10 Abstract 12 This document presents a forward search procedure for computing 13 Point-to-Point (P2P) Traffic Engineering (TE) Label Switched Paths 14 (LSPs) crossing a number of domains through using multiple Path 15 Computation Elements (PCEs). In addition, extensions to the Path 16 Computation Element Communication Protocol (PCEP) for supporting the 17 forward search procedure are described. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on September 8, 2011. 36 Copyright Notice 38 Copyright (c) 2011 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3. Conventions Used in This Document . . . . . . . . . . . . . . 4 56 4. Forward Search Path Computation . . . . . . . . . . . . . . . 4 57 4.1. Overview of Procedure . . . . . . . . . . . . . . . . . . 4 58 4.2. Description of Procedure . . . . . . . . . . . . . . . . . 6 59 5. Extensions to PCEP . . . . . . . . . . . . . . . . . . . . . . 8 60 5.1. RP Object Extension . . . . . . . . . . . . . . . . . . . 8 61 5.2. PCE Object . . . . . . . . . . . . . . . . . . . . . . . . 8 62 5.3. Node Flags Object . . . . . . . . . . . . . . . . . . . . 9 63 5.4. Candidate Node List Object . . . . . . . . . . . . . . . . 10 64 5.5. Request Message Extension . . . . . . . . . . . . . . . . 10 65 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 66 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 67 7.1. Request Parameter Bit Flags . . . . . . . . . . . . . . . 11 68 8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 12 69 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 70 9.1. Normative References . . . . . . . . . . . . . . . . . . . 12 71 9.2. Informative References . . . . . . . . . . . . . . . . . . 12 72 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12 74 1. Introduction 76 Methods or procedures exist for computing MPLS TE P2P LSP inter- 77 domain paths. They include RFC 5152 "A Per-Domain Path Computation 78 Method for Establishing Inter-Domain Traffic Engineering (TE) Label 79 Switched Paths (LSPs)" and RFC 5441 "A Backward-Recursive PCE-Based 80 Computation (BRPC) Procedure to Compute Shortest Constrained Inter- 81 Domain Traffic Engineering Label Switched Paths". These methods or 82 procedures have some issues. 84 There are a few of issues with the Backward Recursive Path 85 Computation (BRPC) algorithm or procedure for computing an MPLS TE 86 P2P LSP path from a source node to a destination node crossing 87 multiple domains. These issues include: 89 The sequence of domains from the source node to the destination node 90 must be known in advance. 92 Navigating a mesh of domains may be complex. 94 More importantly, the BRPC procedure can not find the optimal path if 95 the optimal path is not in the sequence of domains from the source 96 node to the destination node. Thus the BRPC procedure can not 97 guarantee that the path crossing multiple domains computed by the 98 BRPC procedure is optimal. 100 This document presents a forward search procedure for computing 101 Point-to-Point (P2P) Traffic Engineering (TE) Label Switched Paths 102 (LSPs) crossing a number of domains through using multiple Path 103 Computation Elements (PCEs). This procedure resolves the issues 104 mentioned above. It guarantees that the path found from the source 105 to the destination is optimal. It does not depend on any sequence of 106 domains from the source node to the destination node. Navigating a 107 mesh of domains is simple and efficient. 109 2. Terminology 111 ABR: Area Border Router. Routers used to connect two IGP areas 112 (areas in OSPF or levels in IS-IS). 114 ASBR: Autonomous System Border Router. Routers used to connect 115 together ASes of the same or different service providers via one or 116 more inter-AS links. 118 Boundary Node (BN): a boundary node is either an ABR in the context 119 of inter-area Traffic Engineering or an ASBR in the context of 120 inter-AS Traffic Engineering. 122 Entry BN of domain(n): a BN connecting domain(n-1) to domain(n) along 123 a determined sequence of domains. 125 Exit BN of domain(n): a BN connecting domain(n) to domain(n+1) along 126 a determined sequence of domains. 128 Inter-area TE LSP: A TE LSP that crosses an IGP area boundary. 130 Inter-AS TE LSP: A TE LSP that crosses an AS boundary. 132 LSP: Label Switched Path. 134 LSR: Label Switching Router. 136 PCC: Path Computation Client. Any client application requesting a 137 path computation to be performed by a Path Computation Element. 139 PCE: Path Computation Element. An entity (component, application, or 140 network node) that is capable of computing a network path or route 141 based on a network graph and applying computational constraints. 143 PCE(i) is a PCE with the scope of domain(i). 145 TED: Traffic Engineering Database. 147 This document uses terminologies defined in RFC5440. 149 3. Conventions Used in This Document 151 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 152 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 153 document are to be interpreted as described in RFC2119. 155 4. Forward Search Path Computation 157 This section gives an overview of the forward search path computation 158 procedure and describes the procedure in details. 160 4.1. Overview of Procedure 162 Simply speaking, the idea of the forward search path computation 163 procedure for computing a path for an MPLS TE P2P LSP crossing 164 multiple domains from a source node to a destination node includes: 166 Start from the source node and the source domain. 168 Consider the optimal path segment from the source node to every exit 169 boundary node of the source domain as a special link; 171 Consider the optimal path segment from an entry boundary node to 172 every exit boundary node of a domain as a special link; and the 173 optimal path segment is computed as needed. 175 The whole topology consisting of many domains can be considered as a 176 special topology, which contains those special links, the normal 177 links in the destination domain and the inter-domain links. 179 Compute an optimal path in this special topology from the source node 180 to the destination node using CSPF. 182 The forward search path computation procedure for computing a path 183 for an MPLS TE P2P LSP starts at the source domain, in which the 184 source (or ingress) node of the MPLS TE LSP locates. When a PCE in 185 the source domain receives a PCReq for the path for the MPLS TE LSP, 186 it computes the optimal path from the source node to every exit 187 boundary node of the domain towards the destination node. 189 There are two lists involved in the path computation. One list is 190 called candidate node list, which contains the nodes with brief 191 information about the temporary optimal paths from the source node to 192 each of these nodes currently found. The nodes in the candidate list 193 are ordered by the cost of the path. Initially, the candidate node 194 list contains only source node with cost 0. 196 The other is called result path list or tree, which contains the 197 final optimal paths from the source node to the boundary nodes or the 198 nodes in the destination domain. Initially, the result path list is 199 empty. 201 When a PCE responsible for a domain (called current domain) receives 202 a PCReq for computing the path for the MPLS TE LSP, it removes the 203 node with the minimum cost from the candidate node list and put or 204 graft the node to the result path list or tree. 206 If the destination node is in the current domain, the PCE computes 207 the optimal path from the source node to the destination node and 208 sends a PCRep with the optimal path to the PCE or PCC from which the 209 PCReq is received. 211 Otherwise (i.e., if the destination is not in the domain), the PCE 212 computes the optimal path from the source node to every exit boundary 213 node of the current domain towards the destination node and further 214 to the entry boundary nodes of the domain connected to the current 215 domain, puts the new node into the candidate list in order by path 216 cost, updates the existing node in the candidate node list with the 217 new node with lower cost, and then sends a PCReq with the new 218 candidate node list to the PCE that is responsible for the domain 219 with the first node in the candidate node list. 221 4.2. Description of Procedure 223 Suppose that we have the following variables: 225 A current PCE named as CurrentPCE which is currently computing the 226 path. 228 A candidate node list named as CandidateNodeList, which contains the 229 nodes to each of which the temporary optimal path from the source 230 node is currently found. The information about each node C in 231 CandidateNodeList consists of 233 the cost of the path from the source node to node C, 235 the previous hop node P and the link between P and C, 237 the PCE responsible for C, and 239 the flags for C. The flags include 241 one bit D indicating that node C is a Destination node if it is set; 243 one bit S indicating that C is the Source node if it is set; 245 one bit E indicating that C is an Exit boundary node if it is set; 247 one bit I indicating that C is an entry boundary node if it is set; 248 and 250 one bit N indicating that C is a Node in the destination domain if it 251 is set. 253 The nodes in CandidateNodeList are ordered by path cost. Initially, 254 CandidateNodeList contains only a Source Node, with path cost 0, PCE 255 responsible for the source domain, and flags with S bit set. 257 A result path list or tree named as ResultPathTree, which contains 258 the final optimal paths from the source node to the boundary nodes or 259 the nodes in the destination domain. Initially, ResultPathTree is 260 empty. 262 The Forward Search Path Computation procedure for computing the path 263 for the MPLS TE P2P LSP is described as follows: 265 Initially, a PCC sets ResultPathTree to empty and CandidateNodeList 266 to contain the source node and sends PCE responsible for the source 267 domain a PCReq with the source node, the destination node, 268 CandidateNodeList and ResultPathTree. 270 When the PCE responsible for a domain (called current domain) 271 receives a request for computing the path for the MPLS TE P2MP LSP, 272 it checks whether the current PCE is the PCE responsible for the node 273 C with the minimum cost in the CandidateNodeList. If it is, then 274 remove C from CandidateNodeList and graft it into ResultPathTree; 275 otherwise, a PCReq message is sent to the PCE for node C. 277 Suppose that node C has Flags. The ResultPathTree is built from C in 278 the following steps. 280 If the D (Destination Node) bit in the Flags is set, then the optimal 281 path from the source node to the destination node is found, and a 282 PCRep message with the path is sent to the PCE/PCC which sends the 283 request to the current PCE. 285 If the N (Node in Destination domain) bit in the Flags is set, then 286 for every node N connected to node C and not on ResultPathTree, it is 287 merged into CandidateNodeList. The cost to node N is the sum of the 288 cost to node C and the cost of the link between C and N. The PCE for 289 node N is the current PCE. 291 If the Entry/Incoming Boundary Node (I) bit or the Source Node (S) 292 bit is set), then path segments from node C to every exit boundary 293 node of the current domain that is not on the result path tree are 294 computed through using CSPF and as special links. For every node N 295 connected to node C through a special link (i.e., a path segment), it 296 is merged into CandidateNodeList. The cost to node N is the sum of 297 the cost to node C and the cost of the special link (i.e., path 298 segment ) between C and N. The PCE for node N is the current PCE. 300 If the Exit Boundary Node (E) bit is set and there exist inter-domain 301 links connected to it, then for every node N connected to C and not 302 on the result path tree, it is merged into the candidate node list. 303 The cost to node N is the sum of the cost to node C and the cost of 304 the link between C and N. The PCE for node N is the PCE responsible 305 for node N. 307 If the CurrentPCE is the same as the PCE of the node with the minimum 308 cost in CandidateNodeList, then the node is removed from 309 CandidateNodeList, grafted to ResultPathTree, and the above steps are 310 repeated; otherwise, the CurrentPCE sends the PCE a request with the 311 source node, CandidateNodeList and ResultPathTree. 313 5. Extensions to PCEP 315 This section describes the extensions to PCEP for Forward Search Path 316 Computation. The extensions include the definition of a new flag in 317 the RP object, a result path list and a candidate node list in the 318 PCReq message. 320 5.1. RP Object Extension 322 The following flag is added into the RP Object: 324 The F bit is added in the flag bits field of the RP object to tell 325 the receiver of the message that the request/reply is for Forward 326 Search Path Computation. 328 o F (Forward search Path Computation bit - 1 bit): 330 0: This indicates that this is not PCReq/PCRep 331 for Forward Search Path Computation. 333 1: This indicates that this is PCReq or PCRep message 334 for Forward Search Path Computation. 336 The IANA request is referenced in Section below (Request Parameter 337 Bit Flags) of this document. 339 This F bit with the N bit defined in RFC6006 can indicate whether the 340 request/reply is for Forward Search Path Computation of an MPLS TE 341 P2P LSP or an MPLS TE P2MP LSP. 343 o F = 1 and N = 0: This indicates that this is a PCReq/PCRep 344 message for Forward Search Path Computation 345 of an MPLS TE P2P LSP. 347 o F = 1 and N = 1: This indicates that this is a PCReq/PCRep 348 message for Forward Search Path Computation 349 of an MPLS TE P2MP LSP. 351 5.2. PCE Object 353 The figure below illustrates a PCE IPv4 object body (Object-Type=2), 354 which comprises a PCE IPv4 address. The PCE IPv4 address object 355 indicates the IPv4 address of a PCE , with which a PCE session may be 356 established and to which a request message may be sent. 358 0 1 2 3 359 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 1 360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 361 | PCE IPv4 address | 362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 364 The format of the PCE object body for IPv6 (Object-Type=2) is as 365 follows: 367 0 1 2 3 368 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 1 369 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 370 | | 371 | PCE IPv6 address (16 bytes) | 372 | | 373 | | 374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 376 5.3. Node Flags Object 378 The Node Flags object is used to indicate the characteristics of the 379 node in a candidate node list in a request or reply message for 380 Forward Search Inter-domain Path Computation. The Node Flags object 381 comprises a Reserved field, and a number of Flags. 383 The format of the Node Flags object body is as follows: 385 0 1 2 3 386 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 1 387 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 388 |D|S|I|E|N| Flags | Reserved | 389 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 391 where 393 o D = 1: The node is a destination node. 394 o S = 1: The node is a source node. 395 o I = 1: The node is an entry boundary node. 396 o E = 1: The node is an exit boundary node. 397 o N = 1: The node is a node in a destination domain. 399 5.4. Candidate Node List Object 401 The candidate-node-list-obj object contains the nodes in the 402 candidate node list. A new PCEP object class and type are requested 403 for it. The format of the candidate-node-list-obj object body is as 404 follows: 406 0 1 2 3 407 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 1 408 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 409 | | 410 // (a list of s) // 411 | | 412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 414 The following is the definition of candidate node list, which may 415 contain Node Flags. 417 ::= 418 [] 419 ::= 420 422 ::= [] 423 [] 424 [] 426 The ERO in a candidate node contain just the path segment of the last 427 link of the path, which is from the previous hop node of the tail end 428 node of the path to the tail end node. With this information, we can 429 graft the candidate node into the existing result path list or tree. 431 Simply speaking, a candidate node has the same or similar format of a 432 path defined in RFC 5440, but the ERO in the candidate node just 433 contain the tail end node of the path and its previous hop, and the 434 candidate path may contain two new objects PCE and node flags. 436 5.5. Request Message Extension 438 Below is the message format for a request message with the extension 439 of a result path list and a candidate node list: 441 ::= 442 [] 443 444 ::=[] 445 ::= 446 447 [] 448 [] 449 [] 450 [] 451 [[]] 452 [] 453 [] 454 [] 455 [] 457 where: 458 ::=[] 459 ::= 460 ::=[] 461 [] 462 [] 463 [] 465 contains a 467 Figure 1: The Format for a Request Message 469 The definition for the result path list that may be added into a 470 request message is the same as that for the path list in a reply 471 message that is described in RFC5440. 473 6. Security Considerations 475 The mechanism described in this document does not raise any new 476 security issues for the PCEP protocols. 478 7. IANA Considerations 480 This section specifies requests for IANA allocation. 482 7.1. Request Parameter Bit Flags 484 A new RP Object Flag has been defined in this document. IANA is 485 requested to make the following allocation from the "PCEP RP Object 486 Flag Field" Sub-Registry: 488 Bit Description Reference 490 18 Forward Path Computation (F-bit) This I-D 492 8. Acknowledgement 494 The author would like to thank people for their valuable comments on 495 this draft. 497 9. References 499 9.1. Normative References 501 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 502 Requirement Levels", BCP 14, RFC 2119, March 1997. 504 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 505 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 506 Tunnels", RFC 3209, December 2001. 508 [RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element 509 (PCE) Communication Protocol (PCEP)", RFC 5440, 510 March 2009. 512 [RFC6006] Zhao, Q., King, D., Verhaeghe, F., Takeda, T., Ali, Z., 513 and J. Meuric, "Extensions to the Path Computation Element 514 Communication Protocol (PCEP) for Point-to-Multipoint 515 Traffic Engineering Label Switched Paths", RFC 6006, 516 September 2010. 518 9.2. Informative References 520 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 521 Element (PCE)-Based Architecture", RFC 4655, August 2006. 523 [RFC5862] Yasukawa, S. and A. Farrel, "Path Computation Clients 524 (PCC) - Path Computation Element (PCE) Requirements for 525 Point-to-Multipoint MPLS-TE", RFC 5862, June 2010. 527 Author's Address 529 Huaimo Chen 530 Huawei Technologies 531 Boston, MA 532 US 534 Email: Huaimochen@huawei.com