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'TER' -- Possible downref: Normative reference to a draft: ref. 'VPN1' -- Possible downref: Normative reference to a draft: ref. 'VPN2' -- Possible downref: Normative reference to a draft: ref. 'SIN' Summary: 10 errors (**), 0 flaws (~~), 12 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MPLS Working Group L. Andersson, A. Fredette, B. Jamoussi 3 Internet Draft Nortel Networks 4 Expiration Date: July 1999 5 R. Callon 6 IronBridge Networks 8 P. Doolan 9 Ennovate Networks 11 N. Feldman 12 IBM Corp 14 E. Gray 15 Lucent Technologies 17 J. Halpern 18 Newbridge Networks 20 J. Heinanen 21 Telia Finland 23 T. E. Kilty 24 Northchurch Communications 26 A. G. Malis 27 Ascend Communications, Inc. 29 M. Girish 30 SBC Technology Resources, Inc. 32 K. Sundell 33 Ericsson 35 P. Vaananen 36 Nokia Telecommunications 38 T. Worster 39 General DataComm, Inc. 41 L. Wu, R. Dantu 42 Alcatel 44 January 1998 46 Constraint-Based LSP Setup using LDP 48 draft-ietf-mpls-cr-ldp-00.txt 50 Status of this Memo 52 This document is an Internet-Draft. Internet-Drafts are working 54 CR-LDP Specification - 2 - Exp. Apr 1999 56 documents of the Internet Engineering Task Force (IETF), its areas, 57 and its working groups. Note that other groups may also distribute 58 working documents as Internet-Drafts. 60 Internet-Drafts are draft documents valid for a maximum of six months 61 and may be updated, replaced, or obsoleted by other documents at any 62 time. It is inappropriate to use Internet-Drafts as reference 63 material or to cite them other than as "work in progress." 65 To learn the current status of any Internet-Draft, please check the 66 "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow 67 Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), 68 munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or 69 ftp.isi.edu (US West Coast). 71 Abstract 73 Label Distribution Protocol (LDP) is defined in [LDP] for 74 distribution of labels inside one MPLS domain. One of the most 75 important services that may be offered using MPLS in general and LDP 76 in particular is support for constraint-based routing of traffic 77 across the routed network. Constraint-based routing offers the 78 opportunity to extend the information used to setup paths beyond what 79 is available for the routing protocol. For instance, an LSP can be 80 setup based on an explicit route constraint, a Service Class (SC) 81 constraint, or both. Constraint-based routing (CR) and Traffic 82 Engineering requirements have been proposed by [FRAME], [ARCH] and 83 [TER]. These requirements may be met by extending LDP for support of 84 constraint-based routed label switched paths (CRLSPs). Other uses 85 exist for CRLSPs as well ([VPN1] and [VPN2]). 87 This draft specifies mechanisms and TLVs for support of CRLSPs using 88 LDP. The Explicit Route object and procedures are extracted from 89 [ER]. 91 1. Introduction 93 The need for constraint-based routing (CR) in MPLS has been explored 94 elsewhere [ARCH], [FRAME], and [TER]. Explicit routing is a subset 95 of the more general constraint-based routing function. At the MPLS WG 96 meeting held during the Washington IETF there was consensus that LDP 97 should support explicit routing of LSPs with provision for indication 98 of associated (forwarding) priority. In the Chicago meeting, the 99 decision was made that support for explicit path setup in LDP will be 100 moved to a separate document. This document provides that support. We 101 propose an end-to-end setup mechanism of a constraint-based routed 102 LSP (CRLSP) initiated by the ingress LSR. We also specify mechanisms 103 to provide means for reservation of resources for the explicitly 104 routed LSP. 106 We introduce TLVs and procedures that provide support for: 108 CR-LDP Specification - 3 - Exp. Apr 1999 110 - Strict and Loose Explicit Routing 111 - Specification of Service Class 112 - Specification of Traffic Parameters 113 - Route Pinning 114 - CRLSP bumping though setup/holding priority 115 - Handling Failures 117 2. CRLSP Overview 119 CRLSP over LDP Specification is designed with several goals in mind: 121 1. Meet the requirements outlined in [TER] for performing traffic 122 engineering and provide a solid foundation for performing more 123 general constrain-based routing. 125 2. Build on already specified functionality that meets the 126 requirements whenever possible. Hence, this specifications is 127 based on [LDP] and the Explicit Route object and procedures 128 defined in [ER]. 130 3. Keep the solution simple and tractable. 132 In this document, support for unidirectional point-to-point CRLSPs is 133 specified. Support for point-to-multipoint, multipoint-to-point, is 134 for further study (FFS). 136 Support for explicitly routed LSPs in this specification depends on 137 the following minimal LDP behaviors as specified in [LDP]: 139 - Basic and/or Extended Discovery Mechanisms. 141 - Use the Label Request Message defined in [LDP] in downstream on 142 demand label advertisement mode with ordered control. 144 - Use the Label Mapping Message defined in [LDP] in downstream on 145 demand mode with ordered control. 147 - Use the Notification Message defined in [LDP]. 149 - Use the Withdraw and Release Messages defined in [LDP]. 151 - Loop detection (in the case of loosely routed segments of a 152 CRLSP) mechanisms. 154 In addition, the following functionality is added to what's defined 155 in [LDP]: 157 - The Label Request Message used to setup a CRLSP includes a CR- 158 TLV based on the path vector defined in [ER] and specified in 159 Section 4 of this document. 161 CR-LDP Specification - 4 - Exp. Apr 1999 163 - An LSR implicitly infers ordered control from the existence of a 164 CR-TLV in the Label Request Message. This means that the LSR can 165 still be configured for independent control for LSPs established 166 as a result of dynamic routing. However, when a Label Request 167 Message includes a CR TLV, then ordered control is used to setup 168 the CRLSP. Note that this is also true for the loosely routed 169 parts of a CRLSP. 171 - Traffic Parameters TLVs may optionally be carried in the Label 172 Request Message to specify the CRLSP traffic characteristics. 174 - New status codes are defined to handle error notification for 175 failure of established paths specified in the CR-TLV. 177 Examples of CRLSP establishment are given in Appendix A to illustrate 178 how the mechanisms described in this draft work. 180 3. Required Messages and TLVs 182 Any Messages, TLVs, and procedures not defined explicitly in this 183 document are defined in the [LDP] Specification. The following 184 subsections are meant as a cross reference to the [LDP] document and 185 indication of additional functionality beyond what's defined in [LDP] 186 where necessary. 188 3.1 Label Request Message 190 The Label Request Message is as defined in 3.5.8 of [LDP] with the 191 following modifications (required only if the CR-TLV is included in 192 the Label Request Message): 194 - Only a single FEC-TLV may be included in the Label Request 195 Message. 197 - The Optional Parameters TLV includes the definition of the 198 Constraint-based TLV specified in Section 4 and the Traffic 199 Parameters TLV specified in Section 5. 201 - The Procedures to handle the Label Request are augmented by the 202 procedures for processing of the CR-TLV as defined in Section 4. 204 - The Procedures to handle Service Classes are defined in Section 205 5. 207 3.2 Label Mapping Message 209 The Label Mapping Message is as defined in 3.5.7 of [LDP] with the 210 following modifications: 212 - Only a single Label-TLV may be included in the Label Mapping 213 Message. 215 CR-LDP Specification - 5 - Exp. Apr 1999 217 - The FEC-Label Mapping TLV does not include any of the optional 218 TLVs. 220 - The Label Mapping Message Procedures are limited to downstream 221 on demand ordered control mode of mapping. 223 A Mapping message is transmitted by a downstream LSR to an upstream 224 LSR under one of the following conditions: 226 1. The LSR is the egress end of the CRLSP and an upstream mapping 227 has been requested. 229 2. The LSR received a mapping from its downstream next hop LSR for 230 an CRLSP for which an upstream request is still pending. 232 3.3. Notification Message 234 The Notification message is as defined in Section 3.5.1 of [LDP] and 235 the Status TLV encoding is as defined in Section 3.4.7 of [LDP]. 237 Establishment of an Explicitly Routed LSP may fail for a variety of 238 reasons. All such failures are considered advisory conditions and 239 they are signaled by the Notification Message. 241 Notification messages carry Status TLVs to specify events being 242 signaled. New status codes are defined in Section 4.8.3 to signal 243 error notifications associated with the establishment of a CRLSP and 244 the processing of the CR-TLV. 246 4. Constraint-based Routing TLV 248 Label Request Messages defined in [LDP] optionally carry the 249 Constraint-based Routing TLV (CR-TLV) based on the path vector 250 defined in [ER] and described in this section of the specification. 251 The inclusion of the CR TLV in the Label Request Message indicates 252 the path to be taken in the network even if normal routing indicates 253 otherwise. 255 The format of the CR-TLV is described below. 257 4.1 CR-TLV 259 The CR-TLV is an object that specifies the path to be taken by the 260 LSP being established. In addition, the CR-TLV may also include the 261 the Service Class (SC) constraints associated with the LSP, a setup 262 and a holding priority used for path bumping, and an LSP pinning 263 request flag. Reserved bits in the CR-TLV allow for the 264 specification of other LSP attributes in the future. If the reserved 265 bits are exhausted, additional TLVs may be specified to allow for the 266 indication of other LSP attributes during the CRLSP setup. 268 CR-LDP Specification - 6 - Exp. Apr 1999 270 0 1 2 3 271 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 1 272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 273 |U|F| CR-TLV (0x0800) | Length | 274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 275 | Reserved | Reserved | SC |P| Hp | Sp | 276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 | ER-Hop TLV 1 | 278 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 279 | ER-Hop TLV 2 | 280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 281 ~ ............ ~ 282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 283 | ER-Hop TLV n | 284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 286 U bit 288 Unknown TLV bit. Upon receipt of an unknown TLV, if clear (=0), a 289 notification must be returned to the message originator and the 290 entire message must be ignored; if set (=1), the unknown TLV is 291 silently ignored and the rest of the message is processed as if the 292 unknown TLV did not exist. 294 F bit 296 Forward unknown TLV bit. This bit only applies when the U bit is set 297 and the LDP message containing the unknown TLV is to be forwarded. 298 If clear (=0), the unknown TLV is not forwarded with the containing 299 message; if set (=1), the unknown TLV is forwarded with the 300 containing message. 302 Type 304 A two byte field carrying the value of the CR-TLV type which is 305 0x800. 307 Length 309 Specifies the length of the value field in bytes. 311 Reserved 313 This field is reserved. It must be set to zero on transmission and 314 must be ignored on receipt. We expect to use these fields for 315 carrying information that support other constrain-based routing 316 information. 318 P bit 320 CR-LDP Specification - 7 - Exp. Apr 1999 322 When set indicates that the loosely routed segments must remain 323 pinned-down. CRLSP must be rerouted only when adjacency is lost 324 along the segment. When not set, it indicates that the loose segment 325 is not pinned down and must be changed to match the underlying hop- 326 by-hop path. 328 SC 330 The SC Field is used to specify the Service Class of the CRLSP. This 331 field allows for the definition of up to 8 different Service Classes. 332 Currently, Three Service Classes are defined: Best Effort (0), 333 Throughput Sensitive (1), and Delay Sensitive (2) Service Classes. 334 These SCs are further defined in Section 5. 336 Sp 338 A SetupPriority of value zero (0) is the priority assigned to the 339 most important path. It is referred to as the highest priority. Four 340 (4) is the priority for the least important path. The higher the 341 setup priority, the more paths CR-LDP can bump to set up the path. 342 The default value is 2. Values 5, 6, and 7 are reserved. 344 Hp 346 A HoldingPriority of value zero (0) is the priority assigned to the 347 most important path. It is referred to as the highest priority. Four 348 (4) is the priority for the least important path. The higher the 349 holding priority, the less likely it is for CR-LDP to reallocate its 350 bandwidth to a new path. The default value is 2. Values 5, 6, and 7 351 are reserved. 353 4.1.1 Setup and holding priorities 355 CR-LDP signals the resources required by a path on each hop of the 356 route. If a route with sufficient resources can not be found, 357 existing paths may be rerouted to reallocate resources to the new 358 path. This is the process of bumping paths. Setup and holding 359 priorities are used to rank existing paths (holding priority) and the 360 new path (setup priority) to determine if the new path can bump an 361 existing path. 363 The setupPriority of a new CRLSP and the holdingPriority attributes 364 of the existing CRLSP are used to specify these priorities. The 365 higher the holding priority, the less likely it is for CR-LDP to 366 reallocate its bandwidth to a new path. Similarly, the higher the 367 setup priority, the more paths CR-LDP can bump to set up the path. 369 The setup and holding priority values range from zero (0) to four 370 (4). The value zero (0) is the priority assigned to the most 371 important path. It is referred to as the highest priority. Four (4) 372 is the priority for the least important path. The default values for 374 CR-LDP Specification - 8 - Exp. Apr 1999 376 both setup and holding priority should be 2. By setting the default 377 value of both setup and holding priorities at the middle of the 378 range, all connections are initially treated the same. However, when 379 network operators see a need for the use of path bumping, the values 380 of setup and holding priorities can be gracefully adjusted up or down 381 from the middle of the range. 383 An existing path can be bumped if and only if the setupPriority of 384 the new path is numerically less than the holdingPriority of the 385 existing path. 387 To illustrate the use of the setup and holding priority, consider a 388 network which supports two service types (e.g., video and data 389 services). The video traffic is given a low setup priority because 390 new video paths can use an alternate public network if the primary 391 network cannot accommodate the new path. However, the video traffic 392 is given a high holding priority since it is undesirable for the path 393 to be rerouted during an active LSP. For data traffic, high setup and 394 holding priorities are desirable since data paths cannot be 395 established on an alternate network. 397 The setup and holding priorities can be different to allow setup at 398 one priority and holding at an independent priority. This would allow 399 some calls not to invoke bumping and not to be bumped at the same 400 time. 402 The setupPriority of a CRLSP should not be higher (numerically less) 403 than its holdingPriority since it might bump an LSP and be bumped by 404 next "equivalent" request. 406 Bumping by default only happens as a last resort when there are no 407 routes available for a given path. 409 During the instantiation of a path that must bump other paths, lower 410 holding priority paths are bumped before higher priority paths. The 411 decision as to which of the available paths are bumped at each 412 intermediate node by the new path is arbitrary. 414 4.2 ER-Hop TLV 416 The contents of a constraint-based route TLV are a series of variable 417 length ER-Hop TLVs. Each ER-Hop TLV has the form: 419 0 1 420 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------//--------------+ 422 |L| Type | Length | Contents | 423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------//--------------+ 425 L 427 CR-LDP Specification - 9 - Exp. Apr 1999 429 The L bit is an attribute of the ER-Hop. The L bit is set if the 430 ER-Hop represents a loose hop in the explicit route. If the bit is 431 not set, the ER-Hop represents a strict hop in the explicit route. 433 Type 435 A seven-bit field indicating the type of contents of the ER-Hop. 436 Currently defined values are: 438 Value Type 439 ----- ------------------------ 440 0 Reserved 441 1 IPv4 prefix 442 2 IPv6 prefix 443 32 Autonomous system number 445 Length 447 The Length field contains the total length of the ER-Hop in bytes. It 448 includes the L bit, Type and Length fields. The length must always be 449 a multiple of 4, and at least 4. 451 Contents 453 A variable length field containing the node or abstract node that is 454 the consecutive nodes that make up the explicit routed LSP. 456 4.3 Applicability 458 The CR-TLV in this version of the specification is intended for 459 unicast only. CRLSPs for multicast are FFS. 461 4.4 Semantics of the CR-TLV 463 Like any other LSP an CRLSP is a path through a network. The 464 difference is that while other paths are setup solely based on 465 information in routing tables or from a management system, the 466 constraint-based route is calculated at one point at the edge of 467 network based on criteria, including but not limited to routing 468 information. The intention is that this functionality shall give 469 desired special characteristics to the LSP in order to better support 470 the traffic sent over the LSP. The reason for setting up CRLSPs, 471 might be that one wants to assign certain bandwidth or other Service 472 Class characteristics to the LSP, or that one wants to make sure that 473 alternative routes use physically separate paths through the network. 475 A CRLSP is represented in a Label Request Message as a list of nodes 476 or groups of nodes along the constraint-based route. When the CRLSP 477 is established, all or a subset of the nodes in a group may be 479 CR-LDP Specification - 10 - Exp. Apr 1999 481 traversed by the LSP. Certain operations to be performed along the 482 path can also be encoded in the constraint-based route. 484 The capability to specify, in addition to specified nodes, groups of 485 nodes, of which a subset will be traversed by the CRLSP, allows the 486 system a significant amount of local flexibility in fulfilling a 487 request for a constraint-based route. This allows the generator of 488 the constraint-based route to have some degree of imperfect 489 information about the details of the path. 491 The constraint-based route is encoded as a series of ER-Hops 492 contained in a constraint-based route TLV. Each ER-Hop may identify 493 a group of nodes in the constraint-based route. A constraint-based 494 route is then a path including all of the identified groups of nodes. 496 To simplify the discussion, we call each group of nodes an abstract 497 node. Thus, we can also say that a constraint-based route is a path 498 including all of the abstract nodes, with the specified operations 499 occurring along that path. 501 4.5 Strict and Loose ER-Hops 503 The L bit in the ER-Hop is a one-bit attribute. If the L bit is set, 504 then the value of the attribute is "loose." Otherwise, the value of 505 the attribute is "strict." For brevity, we say that if the value of 506 the ER-Hop attribute is loose then it is a "loose ER-Hop." 507 Otherwise, it's a "strict ER-Hop." Further, we say that the abstract 508 node of a strict or loose ER-Hop is a strict or a loose node, 509 respectively. Loose and strict nodes are always interpreted relative 510 to their prior abstract nodes. 512 The path between a strict node and its prior node MUST include only 513 network nodes from the strict node and its prior abstract node. 515 The path between a loose node and its prior node MAY include other 516 network nodes which are not part of the strict node or its prior 517 abstract node. 519 4.6 Loops 521 While the constraint-based route TLV is of finite length, the 522 existence of loose nodes implies that it is possible to construct 523 forwarding loops during transients in the underlying routing 524 protocol. This may be detected by the originator of the constraint- 525 based route through the use a path vector object as defined in [LDP]. 527 4.7 ER-Hop semantics 529 4.7.1. ER-Hop 1: The IPv4 prefix 531 The contents of an IPv4 prefix ER-Hop are a 4 byte IPv4 address, 1 533 CR-LDP Specification - 11 - Exp. Apr 1999 535 byte of prefix length, and 1 byte of padding. The abstract node 536 represented by this ER-Hop is the set of nodes which have an IP 537 address which lies within this prefix. Note that a prefix length of 538 32 indicates a single IPv4 node. 540 The length of the IPv4 prefix ER-Hop is 8 bytes. The contents of the 541 1 byte of padding must be zero on transmission and must not be 542 checked on receipt. 544 0 1 2 3 545 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 1 546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 547 |L| Type | Length | IPv4 Address (4 bytes) | 548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 549 | IPv4 Address (Continued) | Prefix |0 0 0 0 0 0 0 0| 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 552 Type 554 IPv4 Address 0x01 556 Length 558 A one byte field indicating the total length of the TLV in bytes. It 559 includes the L-bit, the Type, Length, the IP Address, and the Prefix 560 fields. The length is always 8 bytes. 562 IP Address 564 A four byte field indicating the IP Address. 566 Prefix Length 568 1-32 570 Padding 572 Zero on transmission. Ignored on receipt. 574 4.7.2. ER-Hop 2: The IPv6 address 576 CR-LDP Specification - 12 - Exp. Apr 1999 578 0 1 2 3 579 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 1 580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 581 |L| Type | Length | IPV6 address (16 bytes) | 582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 583 | IPV6 address (continued) | 584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 585 | IPV6 address (continued) | 586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 587 | IPV6 address (continued) | 588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 589 | IPV6 address (continued) | Prefix |0 0 0 0 0 0 0 0| 590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 592 Type 594 0x02 IPv6 address 596 Length 598 The Length contains the total length of the ER-Hop TLV in bytes, 599 including the Type and Length fields. The Length is always 20. 601 IPv6 address 603 A 128-bit unicast host address. 605 Prefix Length 607 1-128 609 Padding 611 Zero on transmission. Ignored on receipt. 613 4.7.3. ER-Hop 32: The autonomous system number 615 The contents of an autonomous system (AS) number ER-Hop are a 2 byte 616 autonomous system number. The abstract node represented by this ER- 617 Hop is the set of nodes belonging to the autonomous system. 619 The length of the AS number ER-Hop is 4 bytes. 621 0 1 2 3 622 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 1 623 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 624 |L| Type | Length | Autonomous System number | 625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 627 Type 629 CR-LDP Specification - 13 - Exp. Apr 1999 631 AS Number 0x20 633 Length 635 A one byte field indicating the total length of the TLV in bytes. It 636 includes the L-bit, the Type, and Length, and the AS number fields. 637 The length is always 4 bytes. 639 AS number 641 A two byte field indicating the AS number. 643 4.8. Processing of the Constraint-Based Route TLV 645 4.8.1. Selection of the next hop 647 A Label Request message containing a constraint-based route TLV must 648 determine the next hop for this path. Selection of this next hop may 649 involve a selection from a set of possible alternatives. The 650 mechanism for making a selection from this set is implementation 651 dependent and is outside of the scope of this specification. 652 Selection of particular paths is also outside of the scope of this 653 specification, but it is assumed that each node will make a best 654 effort attempt to determine a loop-free path. Note that such best 655 efforts may be overridden by local policy. 657 To determine the next hop for the path, a node performs the following 658 steps: 660 1) The node receiving the Label Request message must first 661 evaluate the first ER-Hop. If the L bit is not set in the first 662 ER-Hop and if the node is not part of the abstract node described 663 by the first ER-Hop, it has received the message in error, and 664 should return a "Bad initial ER-Hop" error. If the L bit is set 665 and the local node is not part of the abstract node described by 666 the first ER-Hop, the node selects a next hop that is along the 667 path to the abstract node described by the first ER-Hop. If there 668 is no first ER-Hop, the message is also in error and the system 669 should return a "Bad Constraint-Based Routing TLV" error. 671 2) If there is no second ER-Hop, this indicates the end of the 672 constraint-based route. The constraint-based route TLV should be 673 removed from the Label Request message. This node may or may not 674 be the end of the LSP. Processing continues with section 4.8.2, 675 where a new constraint-based route TLV may be added to the Label 676 Request message. 678 3) If the node is also a part of the abstract node described by 679 the second ER-Hop, then the node deletes the first ER-Hop and 680 continues processing with step 2, above. Note that this makes the 681 second ER-Hop into the first ER-Hop of the next iteration. 683 CR-LDP Specification - 14 - Exp. Apr 1999 685 4) The node determines if it is topologically adjacent to the 686 abstract node described by the second ER-Hop. If so, the node 687 selects a particular next hop which is a member of the abstract 688 node. The node then deletes the first ER-Hop and continues 689 processing with section 4.8.2. 691 5) Next, the node selects a next hop within the abstract node of 692 the first ER-Hop that is along the path to the abstract node of 693 the second ER-Hop. If no such path exists then there are two 694 cases: 696 5a) If the second ER-Hop is a strict ER-Hop, then there is an 697 error and the node should return a "Bad strict node" error. 699 5b) Otherwise, if the second ER-Hop is a loose ER-Hop, then the 700 node selects any next hop that is along the path to the next 701 abstract node. If no path exists, then there is an error, and the 702 node should return a "Bad loose node" error. 704 6) Finally, the node replaces the first ER-Hop with any ER-Hop 705 that denotes an abstract node containing the next hop. This is 706 necessary so that when the constraint-based route is received by 707 the next hop, it will be accepted. 709 7) Progress the Label Request Message to the next hop. 711 4.8.2. Adding ER-Hops to the constraint-based route TLV 713 After selecting a next hop, the node may alter the constraint-based 714 route in the following ways. 716 If, as part of executing the algorithm in section 4.8.1, the 717 constraint-based route TLV is removed, the node may add a new 718 constraint-based route TLV. 720 Otherwise, if the node is a member of the abstract node for the first 721 ER-Hop, then a series of ER-Hops may be inserted before the first 722 ER-Hop or may replace the first ER-Hop. Each ER-Hop in this series 723 must denote an abstract node that is a subset of the current abstract 724 node. 726 Alternately, if the first ER-Hop is a loose ER-Hop, an arbitrary 727 series of ER-Hops may be inserted prior to the first ER-Hop. 729 4.8.3. Error subcodes 731 In the processing described above, certain errors need to be reported 732 as part of the Notification message. This section defines the status 733 codes for the errors described above. 735 CR-LDP Specification - 15 - Exp. Apr 1999 737 Status Code Type 738 -------------------------------------- ---------- 739 Bad Constraint-Based Routing TLV Error 0x04000001 740 Bad Strict Node Error 0x04000002 741 Bad Loose Node Error 0x04000003 742 Bad Initial ER-Hop Error 0x04000004 743 Resource Unavailable 0x04000005 744 Service Class Unavailable 0x04000006 745 Traffic Parameters Unavailable 0x04000007 747 5.0 CRLSP Service Classes and Traffic Parameters 749 The following sections describe the CRLSP Service Classes (SCs), and 750 their associated traffic parameters. 752 The CRLSP Service Class is signaled in the SC Field of the CR-TLV 753 defined in Section 4.1. 755 Three Service Classes are currently supported by CR-LDP: 757 Service Class Value 758 -------------------------- ----- 759 Best Effort (BE) 0x0 760 Throughput Sensitive (TS) 0x1 761 Delay Sensitive (DS) 0x2 763 These service classes are specified in the following sections. 765 5.1 Best Effort (BE) 767 The request of the BE SC implies that there are no expected service 768 guarantees from the network. The service provided by the network is 769 the familiar best effort service. 771 The Peak Date Rate (PDR) is the only traffic parameter that may be 772 specified with the BE SC. The specification of the PDR allows the 773 network to perform traffic shaping and policing functions. 775 5.2 Throughput Sensitive (TS) 777 In the service model for the Throughput Sensitive SC, the network 778 commits to deliver with high probability user datagrams at a rate of 779 at least CDR (Committed Data Rate). The user may transmit at a rate 780 higher than CDR but datagrams in excess of CDR would have a lower 781 probability of being delivered. If the user sends at a rate of CDR or 782 lower the network commits to deliver with high probability all the 783 user datagrams. 785 The TS SC has an associated tolerance to the burstiness of arriving 787 CR-LDP Specification - 16 - Exp. Apr 1999 789 user datagrams. This tolerance is defined by the traffic parameter 790 Committed Burst Tolerance (CBT). 792 Ideally, a TS CRLSP request carries with it a rich set of three 793 traffic parameters (PDR, CDR, and CBT) that accurately describe its 794 traffic characteristics. This allows the network to perform resource 795 reservation, traffic shaping, and traffic policing. 797 However, for the sake of simplicity of the service definition, the 798 CDR is the only parameter that MUST always be specified for a TS 799 CRLSP. A peak data rate parameter (PDR) and a CBT are optional 800 traffic parameters for the TS SC. 802 The network should make every effort to preserve ordering of the 803 delivered datagrams of a TS CRLSP. 805 Network traffic that requires a low packet loss ratio at a given CDR 806 but is not particularly sensitive to delay and jitter (e.g., network 807 control traffic) is suited to the TS SC. The selection of the TS SC 808 is used to signal to the various nodes along the path that the 809 queuing and scheduling mechanisms used to handle the CRLSP should 810 provide a low packet loss ratio. 812 5.3 Delay Sensitive (DS) 814 In the service model for the Delay Sensitive SC, the network commits 815 to deliver with high probability user datagrams at a rate of CDR 816 (Committed Data Rate) with minimum delay and delay variation. The 817 user MUST transmit data at a rate of CDR or lower in order to be 818 eligible for DS service. Datagrams in excess of CDR may be discarded 819 by the network. If the user sends at a rate of CDR or lower the 820 network commits to deliver with high probability all user datagrams 821 with low delay and delay variation. If the user sends at a rate 822 higher than CDR the network does not provide any guarantees on the 823 excess traffic. 825 The Delay Sensitive SC has an associated tolerance to the burstiness 826 of arriving user datagrams. This tolerance is defined by the traffic 827 parameter Committed Burst Tolerance (CBT). 829 Ideally, a DS CRLSP request carries with it a rich set of three 830 traffic parameters (PDR, CDR, and CBT) that accurately describe its 831 traffic characteristics. This allows the network to perform resource 832 reservation, traffic shaping and policing. 834 However, for the sake of simplicity of the service definition, the 835 CDR is the only parameter that MUST always be specified for a DS 836 CRLSP. A peak data rate parameter (PDR) and a CBT are optional 837 traffic parameters for the DS SC. 839 The network should make every effort to preserve ordering of the 841 CR-LDP Specification - 17 - Exp. Apr 1999 843 delivered datagrams of a DS CRLSP. 845 Network traffic that requires a low delay and delay variation at a 846 given CDR (e.g., voice traffic) is suited to the DS SC. The selection 847 of the DS SC is used to signal to the various nodes along the path 848 that the queuing and scheduling mechanisms used to handle the CRLSP 849 should provide low delay and delay variation. 851 5.4 Traffic Parameters 853 The CRLSP traffic parameters are defined in this section. 855 The traffic parameters CDR, CBT and PDR are defined in terms of a 856 TOKEN_BUCKET_TSPEC as specified in [RFC2215]. The following mapping 857 of parameters in the TOKEN_BUCKET_TSPEC is used: 859 Token rate, r = CDR 860 Bucket depth, b = CBT 861 Peak traffic rate, p = PDR 862 Minimum policed unit, m = 1 863 Maximum packet size, M = MTU 865 The Traffic Parameters TLV is used to signal the traffic 866 characteristics of the CRLSP. These traffic parameters are used to 867 perform functions such as resource reservation, Shaping, and 868 Policing. See [SIN] for more details. The encoding for the Traffic 869 Parameters TLV is: 871 0 1 2 3 872 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 1 873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 874 |U|F| Traffic TLV (0x0810) | Length | 875 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 876 | PDR TLV | 877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 878 | CDR TLV | 879 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 880 | CBT TLV | 881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 883 5.4.1 Peak data rate (PDR) TLV 885 The value of traffic parameter PDR is given as a positive integer in 886 bytes per second. Zero is not a valid value of PDR. 888 The user may specify the value of PDR depending the SC of the CRLSP. 889 Specifying the PDR allows the network to use traffic management 890 functions such as shaping. 892 CR-LDP Specification - 18 - Exp. Apr 1999 894 0 1 2 3 895 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 1 896 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 897 |U|F| PDR TLV (0x0811) | Length | 898 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 899 | PDR in Bytes/sec | 900 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 902 5.4.2. Committed Data Rate (CDR) 904 The value of traffic parameter CDR is given as a positive integer in 905 bytes per second. Zero is not a valid value of CDR. 907 The user may provide a requested value of CDR in the CRLSP request 908 depending on the SC of the CRLSP. 910 0 1 2 3 911 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 1 912 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 913 |U|F| CDR TLV (0x0812) | Length | 914 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 915 | CDR in Bytes/sec | 916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 918 5.4.3. Committed Burst Tolerance (CBT) 920 The value of traffic parameter CBT is given in bytes. Zero is not a 921 valid value of CBT. 923 The requested value of CBT MUST be no smaller than the MTU of the 924 originating interface. 926 The user may provide a requested value of CBT in the CRLSP request. 927 If the user chooses not to specify a requested value of CBT and the 928 network is policing the traffic, then any excess traffic will be 929 dropped by the network. 931 0 1 2 3 932 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 1 933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 934 |U|F| CBT TLV (0x0813) | Length | 935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 936 | CBT in Bytes | 937 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 939 6. Open Issues 941 This section captures the issues that need further study. 943 CR-LDP Specification - 19 - Exp. Apr 1999 945 1) Review the FSM described in Appendix B and extend it by the CR-TLV 946 processing defined in Sections 4.8.1 and 4.8.2. 948 2) Consider if all three traffic parameters have to be signaled at 949 all times and if the network should supply default values for the 950 missing parameters. 952 3) Consider the following extensions to the CR-TLV: 954 3.1) Changing the 'P' bit to "next hop flag" and making it a 2-bit 955 wide field with the following values: 957 - 00 "local repair", which means if it belongs to a loosely 958 routed segment, and the LSR detects a next hop change, the LSR 959 will try to establish a new LSP from this point on and switch 960 it over to the new LSP when it is setup. 962 - 01 "global repair", which means when the LSR detects a next 963 hop change, the LSR will tear down the LSP, the ingress LSR 964 will try to reestablish another LSP through the new path. 966 - 10 "pinned", which means that the loosely routed segments 967 must remain pinned down. 969 - 11 Reserved. 971 3.2) Adding one more field "LSPID" before ER-Hop TLV. LSPID can 972 be used to identify a network wide unique CRLSP. 974 - The first 4 bytes carrying the ingress LSR IP address 976 - The second 4 bytes carrying the unique ID value assigned by 977 the ingress LSR. 979 4) Consider the following extension to the ER-Hop TLV: 981 For Type field, add one more type, LSPID, which means the current 982 CRLSP will go through another CRLSP which is identified with this 983 LSPID value: 985 Value Type 986 ----- ----- 987 4 LSPID 989 Extend processing the LSPID ER-Hop as follows: If the type of ER- 990 Hop is LSPID, and the other end of this CRLSP is not part of the 991 constraint-based route TLV, add it to the constraint-based TLV 992 with L bit turned off. 994 5) Consider traffic parameter negotiation and the ability to change 995 the traffic parameters associated with an already established path 997 CR-LDP Specification - 20 - Exp. Apr 1999 999 without tearing the old path down. 1001 7. Security 1003 No security issues are discussed in this version of the draft. 1005 8. Acknowledgments 1007 The messages used to signal the CRLSP setup are based on the work 1008 done by the [LDP] team. The Explicit Route object and procedures used 1009 in this specification are based on [ER]. 1011 The authors would also like to acknowledge the careful review and 1012 comments of Osama Aboul-Magd, Ken Hayward, Greg Wright, Geetha Brown, 1013 Brian Williams, Peter Ashwood-smith, Paul Beaubien, Matthew Yuen, 1014 Liam Casey, and Ankur Anand. 1016 9. References 1018 [FRAME] Callon et al, "Framework for Multiprotocol Label Switching", 1019 work in progress (draft-ietf-mpls-framework-02), November 1997. 1021 [ARCH] Rosen et al, "Multiprotocol Label Switching Architecture", 1022 work in progress (draft-ietf-mpls-arch-02), July 1998. 1024 [LDP] Andersson et al, "Label Distribution Protocol Specification" 1025 work in progress (draft-ietf-mpls-ldp-02.txt), November 1998. 1027 [ER] Guerin et al, "Setting up Reservations on Explicit Paths using 1028 RSVP", work in progress (draft-guerin-expl-path-rsvp-01.txt, November 1029 1997. 1031 [TER] Awduche et al, "Requirements for Traffic Engineering Over 1032 MPLS", work in progress (draft-awduche-mpls-traffic-eng-00), April 1033 1998. 1035 [VPN1] Heinanen et al, "MPLS Mappings of Generic VPN Mechanisms", 1036 work in progress (draft-heinanen-generic-vpn-mpls-00), August 1998. 1038 [VPN2] Jamieson et al, "MPLS VPN Architecture" work in progress 1039 (draft-jamieson-mpls-vpn-00), August 1998. 1041 [RFC2215] S. Shenker and J. Wroclawski, General Characterization 1042 Parameters for Integrated Service Network Elements, RFC 2215, Sep 1043 1997. 1045 [SIN] B. Jamoussi, N. Feldman, and L. Andersson, "MPLS Ships in the 1046 Night with ATM", (draft-jamoussi-mpls-sin-00.txt), August 1998. 1048 CR-LDP Specification - 21 - Exp. Apr 1999 1050 10. Author Information 1052 Loa Andersson 1053 Director Bay Architecture Lab, EMEA 1054 Kungsgatan 34, PO Box 1788 1055 111 97 Stockholm, Sweden 1056 phone: +46 8 441 78 34 1057 mobile +46 70 522 78 34 1058 e-mail: loa_andersson@baynetworks.com 1060 Ross Callon 1061 IronBridge Networks 1062 55 Hayden Avenue, 1063 Lexington, MA 02173 1064 Phone: +1-781-402-8017 1065 Email: rcallon@ironbridgenetworks.com 1067 Ram Dantu 1068 Alcatel USA Inc. 1069 IP Competence Center 1070 1201 E. Campbell Road.,446-315 1071 Richadson, TX USA., 75081-2206 1072 Phone: 972 996 2938 1073 Fax: 972 996 5902 1074 Email: ram.dantu@aud.alcatel.com 1076 Paul Doolan 1077 Ennovate Networks 1078 330 Codman Hill Rd 1079 Marlborough MA 01719 1080 Phone: 978-263-2002 1081 email: pdoolan@ennovatenetworks.com 1083 Nancy Feldman 1084 IBM Corp. 1085 17 Skyline Drive 1086 Hawthorne NY 10532 1087 Phone: 914-784-3254 1088 email: nkf@us.ibm.com 1090 Andre Fredette 1091 Nortel Networks 1092 3 Federal Street 1093 Billerica, MA 01821 1094 email: fredette@baynetworks.com 1096 Eric Gray 1097 Lucent Technologies, Inc 1098 1600 Osgood St. 1099 North Andover, MA 01847 1100 email: ewgray@lucent.com 1102 CR-LDP Specification - 22 - Exp. Apr 1999 1104 Joel M. Halpern 1105 Newbridge Networks Inc. 1106 593 Herndon Parkway 1107 Herndon, VA 20170 1108 email: jhalpern@newbridge.com 1109 phone: 1-703-736-5954 1110 fax: 1-703-736-5959 1112 Juha Heinanen 1113 Telia Finland, Inc. 1114 Myyrmaentie 2 1115 01600 VANTAA 1116 Finland 1117 Tel: +358 303 944 808 1118 Email: jh@telia.fi 1120 Bilel Jamoussi 1121 Nortel Networks 1122 P O Box 3511 Station C 1123 Ottawa, ON K1Y 4H7 1124 Canada 1125 phone: +1 613 765-4814 1126 email: jamoussi@NortelNetworks.com 1128 Timothy E. Kilty 1129 Northchurch Communications 1130 5 Corporate Drive, 1131 Andover, MA 018110 1132 phone: 978 691-4656 1133 Email: tkilty@northc.com 1135 Andrew G. Malis 1136 Ascend Communications, Inc. 1137 1 Robbins Road 1138 Westford, MA 01886 1139 phone: 978 952-7414 1140 fax: 978 392-2074 1141 Email: malis@ascend.com 1143 Muckai K Girish 1144 SBC Technology Resources, Inc. 1145 4698 Willow Road 1146 Pleasanton, CA 94588 1147 Phone: (925) 598-1263 1148 Fax: (925) 598-1321 1149 Email: mgirish@tri.sbc.com 1151 Kenneth Sundell 1152 Ericsson 1153 SE-126 25 Stockholm 1154 Sweden 1156 CR-LDP Specification - 23 - Exp. Apr 1999 1158 email: kenneth.sundell@etx.ericsson.se 1160 Pasi Vaananen 1161 Nokia Telecommunications 1162 3 Burlington Woods Drive, Suite 250 1163 Burlington, MA 01803 1164 Phone: +1-781-238-4981 1165 Email: pasi.vaananen@ntc.nokia.com 1167 Tom Worster 1168 General DataComm, Inc. 1169 5 Mount Royal Ave. 1170 Marlboro MA 01752 1171 Email: tom.worster@gdc.com 1173 Liwen Wu 1174 Alcatel U.S.A 1175 44983 Knoll Square 1176 Ashburn, Va. 20147 1177 USA 1178 Phone: (703) 724-2619 1179 FAX: (703) 724-2005 1180 Inet: liwen.wu@adn.alcatel.com 1182 Appendix A: CRLSP Establishment Examples 1184 A.1 Strict Constraint-Based Route Example 1186 This appendix provides an example for the setup of a strictly routed 1187 CRLSP. In this example, each abstract node is represented by a 1188 specific node. 1190 The sample network used here is a four node network with two edge 1191 LSRs and two core LSRs as follows: 1193 a b c 1194 LSR1------LSR2------LSR3------LSR4 1196 LSR1 generates a Label Request Message as described in Section 3.1 of 1197 this draft and sends it to LSR2. This message includes the CR-TLV. 1199 The CR-TLV is composed by a vector of three ER-Hop TLVs . 1200 The ER-Hop TLVs used in this example are of type 0x01 (IPv4 prefix) 1201 with a prefix length of 32. Hence, each ER-Hop TLV identifies a 1202 specific node as opposed to a group of nodes. 1204 At LSR2, the following processing of the CR-TLV per Section 4.8.1 of 1205 this draft takes place: 1207 1) The first hop is part of the abstract node LSR2. Therefore, 1208 the first step passes the test. Go to step 2. 1210 CR-LDP Specification - 24 - Exp. Apr 1999 1212 2) There is a second ER-Hop, . Go to step 3. 1214 3) LSR2 is not part of the abstract node described by the second 1215 ER-Hop . Go to Step 4. 1217 4) LSR2 determines that it is topologically adjacent to the 1218 abstract node described by the second ER-Hop . LSR2 selects a 1219 next hop (LSR3) which is the abstract node. LSR2 deletes the first 1220 ER-Hop from the CR-TLV which now becomes . Go to 1221 Section 4.8.2. 1223 At LSR2, the following processing of Section 4.8.2 takes place: 1225 Executing algorithm 4.8.1 did not result in the removal of the 1226 CR-TLV. 1228 Also, LSR2 is not a member of the abstract node described by the 1229 first ER-Hop . 1231 Finally, the first ER-Hop is a strict hop. 1233 Therefore, processing section 4.8.2 does not result in the 1234 insertion of new ER-Hops. The selection of the next hop has been 1235 already done is step 4 of Section 4.8.1 and the processing of the 1236 CR-TLV is completed at LSR2. In this case, the Label Request 1237 Message including the CR-TLV is progressed by LSR2 to LSR3. 1239 At LSR3, a similar processing to the CR-TLV takes place except that 1240 the incoming CR-TLV = and the outgoing CR-TLV is . 1242 At LSR4, the following processing of section 4.8.1 takes place: 1244 1) The first hop is part of the abstract node LSR4. Therefore, 1245 the first step passes the test. Go to step 2. 1247 2) There is no second ER-Hop, this indicates the end of the CRLSP. 1248 The CR-TLV is removed from the Label Request Message. Processing 1249 continues with Section 4.8.2. 1251 At LSR4, the following processing of Section 4.8.2 takes place: 1253 Executing algorithm 4.8.1 resulted in the removal of the CR-TLV. 1254 LSR4 does not add a new CR-TLV. 1256 Therefore, processing section 4.8.2 does not result in the 1257 insertion of new ER-Hops. This indicates the end of the CRLSP and 1258 the processing of the CR-TLV is completed at LSR4. 1260 At LSR4, processing of Section 3.2 is invoked. The first condition is 1261 satisfied (LSR4 is the egress end of the CRLSP and upstream mapping 1262 has been requested). Therefore, a Label Mapping Message is generated 1264 CR-LDP Specification - 25 - Exp. Apr 1999 1266 by LSR4 and sent to LSR3. 1268 At LSR3, the processing of Section 3.2 is invoked. The second 1269 condition is satisfied (LSR3 received a mapping from its downstream 1270 next hop LSR4 for a CRLSP for which an upstream request is still 1271 pending). Therefore, a Label Mapping Message is generated by LSR3 and 1272 sent to LSR2. 1274 At LSR2, a similar processing to LSR 3 takes place and a Label 1275 Mapping Message is sent back to LSR1 which completes the end-to-end 1276 CRLSP setup. 1278 A.2. Node Groups and Specific Nodes Example 1280 A request at an ingress LSR to setup a CRLSP might originate from a 1281 management system or an application, the details are implementation 1282 specific. 1284 The ingress LSR uses information provided by the management system or 1285 the application and possibly also information from the routing 1286 database to calculated the constraint-based route and to create the 1287 Label Request Message. 1289 The Label request message carries together with other necessary 1290 information a CR-TLV defining the constraint-based routed path. In 1291 our example the list of hops in the ER-Hop TLV is supposed to contain 1292 an abstract node representing a group of nodes, an abstract node 1293 representing a specific node, another abstract node representing a 1294 group of nodes, and an abstract node representing a specific egress 1295 point. 1297 In--{Group 1}--{Specific A}--{Group 2}--{Specific Out: B} 1299 The CR-TLV contains four ER-Hop TLVs: 1301 1. An ER-Hop TLV that specifies a group of LSR valid for the first 1302 abstract node representing a group of nodes (Group 1). 1304 2. An ER-Hop TLV that indicates the specific node (Node A). 1306 3. An ER-Hop TLV that specifies a group of LSRs valid for the 1307 second abstract node representing a group of nodes (Group 2). 1309 4. An ER-Hop TLV that indicates the specific egress point for the 1310 CRLSP (Node B). 1312 All the ER-Hop TLVs are strictly routed nodes. 1314 The setup procedure for this CRLSP works as follows: 1316 CR-LDP Specification - 26 - Exp. Apr 1999 1318 1. The ingress node sends the Label Request to a node that is a 1319 member the group of nodes indicated in the first ER-Hop TLV, 1320 following normal routing for the specific node (A). 1322 2. The node that receives the message identifies itself as part of 1323 the group indicated in the first ER-Hop TLV, and that it is not 1324 the specific node (A) in the second. Further it realizes that the 1325 specific node (A) is not one of its next hops. 1327 3. It keeps the ER-Hop TLVs intact and sends a Label Request 1328 Message to a node that is part of the group indicated in the first 1329 ER-Hop TLV (Group 1), following normal routing for the specific 1330 node (A). 1332 4. The node that receives the message identifies itself as part of 1333 the group indicated in the first ER-Hop TLV, and that it is not 1334 the specific node (A) in the second ER-Hop TLV. Further it 1335 realizes that the specific node (A) is one of its next hops. 1337 5. It removes the first ER-Hop TLVs and sends a Label Request 1338 Message to the specific node (A). 1340 6. The specific node (A) recognizes itself in the first ER-Hop 1341 TLV. Removes the specific ER-Hop TLV. 1343 7. It sends a Label Request message to a node that is a member of 1344 the group (Group 2) indicated in the ER-Hop TLV. 1346 8. The node that receives the message identifies itself as part of 1347 the group indicated in the first ER-Hop TLV, further it realizes 1348 that the specific egress node (B) is one of its next hops. 1350 9. It sends a Label Request message to the specific egress node 1351 (B). 1353 10. The specific egress node (B) recognizes itself as the egress 1354 for the CRLSP, it returns a Label Mapping Message, that will 1355 traverse the same path as the Label Request Message in the 1356 opposite direction. 1358 CR-LDP Specification - 27 - Exp. Apr 1999 1360 Appendix B. CR-LDP Finite State Machine 1362 In this description of the CR-LDP FSM, behavior relating to the 1363 state of LDP messages is assumed to be defined (implicitly or 1364 explicitly) in [LDP]. In particular, LDP is assumed to retain 1365 state information relating a Label Request made of a downstream 1366 neighbor to the Label Request message(s) of upstream neighbors 1367 (downstream-on-demand mode) which the (downstream) Label Request 1368 is meant to satisfy. This will be true of many potential 1369 applications of LDP, of which CR-LDP is an example. Minimally, 1370 this state should include message IDs of Label Requests (both sent 1371 and received) and the LSR(s) from which pending Label Request(s) 1372 were received. 1374 The FSM describes CR-LDP behavior in the following operations: 1376 - Start of CRLSP setup (in which a Label Request is sent); 1378 - Processing the CR-TLV portion of Label Requests; 1380 - Completion of CRLSP setup (via Label Mapping messages); 1382 - Notification of originator when: 1384 - a loop is detected in a loose constraint-based route segment, 1386 - an ER-Hop is not reachable from a previous ER-Hop, 1388 - a next ER-Hop is strict and not directly connected to the 1389 current LSR or 1391 - the current LSR is strict and is not (part of the abstract 1392 node in) the first ER-Hop in the CR-TLV; 1394 - Withdrawing a CRLSP. 1396 For the description, the following pictorial representations may be 1397 used as an aid to understanding: 1399 LSR 1 LSR 2 ... LSR n 1401 .-----. .-----. .-----. 1402 | ER | | ER | | ER | 1403 `-----' `-----' `-----' 1404 | CR-TLV CR-TLV ^ | CR-TLV CR-TLV ^ 1405 | Next | | Next | 1406 | Hop | | Hop | 1407 V | V | 1408 .-----. Label .-----. Label Label .-----. 1409 | LDP |----------->| LDP |-------> ... ------->| LDP | 1410 `-----' Request `-----' Request Request `-----' 1412 CR-LDP Specification - 28 - Exp. Apr 1999 1414 CRLSP Setup propagation 1416 LSR 1 LSR 2 ... LSR n 1418 .-----. .-----. .-----. 1419 | ER | | ER | | ER | 1420 `-----' `-----' `-----' 1421 ^ Status Status | 1422 | Previous | 1423 | Hop | 1424 | V 1425 .-----. Label .-----. Label Label .-----. 1426 | LDP |<-----------| LDP |<------- ... <-------| LDP | 1427 `-----' Mapping `-----' Mapping Mapping `-----' 1429 CRLSP Status propagation 1431 .---------------. 1432 | ER | .---------------. 1433 | Link/Call | | LDP | 1434 | Admission | | | 1435 | Control | | Label | 1436 `---------------' | Allocation | 1437 `---------------' 1439 Related Tasks 1441 B.1. CR-LDP Primitives 1443 The following sections describe the logical interactions between 1444 Constrain-based Route and LDP state machines in terms of 1445 primitives that describe the minimal information exchange 1446 required. These assume an asynchronous exchange model involving 1447 locally significant IDs that is used to tie status of a request to 1448 the initial setup and to allow LDP to relate incoming/outgoing 1449 Label Request messages. A synchronous model - possibly based on 1450 multiple threads - is also possible and would eliminate the need 1451 for IDs. 1453 B.1.1. CR to LDP Primitives 1455 LDP_SEND_REQ( TLV_List, To_LSR, Identifier ) 1457 TLV_List 1459 TLVs to be sent to a neighboring LSR; includes at least an 1461 CR-LDP Specification - 29 - Exp. Apr 1999 1463 CR-TLV and may contain additional TLVs (i.e. QoS TLVs). 1465 To_LSR 1467 The neighbor LSR to which a Label Request is to be sent. 1469 Identifier 1471 Locally significant unique identifier. May be used to 1472 associate the Label Request to be sent either with a Label 1473 Request that was previously received (e.g. - LSR 2 above) 1474 or a subsequent CRLSP Status (e.g. - LSR 1 above). 1476 LDP_SEND_RSP( Status, Identifier ) 1478 Status 1480 Status of a specific CRLSP Setup Request. A Status of zero 1481 indicates success; other Status values are given in Error 1482 Subcodes section. This Status is carried in Label Mapping or 1483 Notification messages to the originator of the CRLSP setup. 1485 Identifier 1487 Locally significant unique identifier used to associate the 1488 Label Mapping to be sent with a Label Request received (e.g. 1489 LSR n above). 1491 B.1.2. LDP to CR Primitives 1493 CR_RECEIVED_REQ( TLV_List, Identifier ) 1495 TLV_List 1497 TLVs to be processed by the local constraint-based route 1498 function. 1500 Identifier 1502 Locally significant unique identifier used to associate the 1503 received request either with a subsequent further request 1504 or a response. For example, the identifier provided here 1505 would be used in a subsequent LDP_SEND_REQ or LDP_SEND_RSP. 1507 CR_LSP_STATUS( Status, Identifier ) 1509 Status 1511 Status of a specific CRLSP Setup Request. A Status of zero 1512 indicates success; other Status values are given in section 1513 Error Subcodes. This Status originated at the remote LSR 1515 CR-LDP Specification - 30 - Exp. Apr 1999 1517 which either completed the CRLSP setup or determined that 1518 CRLSP setup could not be done. 1520 Identifier 1522 Locally significant unique identifier used to associate the 1523 received response with the original request. For example, 1524 this identifier would be the same as was used in the initial 1525 LDP_SEND_REQ. 1527 B.2. CR-LDP States 1529 This document defines 3 states relative to any one specific CRLSP. 1530 They are: 1532 CR_Non_Existant - no state information exists relative to this 1533 CRLSP; 1535 CR_In_Progress - LDP_SEND_REQ has been called in result 1536 of external input (e.g. - management); 1538 CR_Established - a successful status has been received from 1539 an earlier setup. 1541 These states are defined such that no additional state is required 1542 to support CRLSPs using LDP at intermediate LSRs than is already 1543 required in LDP. 1545 B.3. CR-LDP Events 1547 This document defines 4 events impacting any one specific CRLSP. 1548 They are: 1550 CR_Start - a CRLSP is required based on an external stimulus 1551 (e.g. - management); 1553 CR_Req_Received - further CRLSP setup processing is required 1554 based on CR_RECEIVED_REQ (i.e. - from an upstream LSR's CRLSP 1555 Label Request); 1557 CR_Setup_Complete - CRLSP setup has been successfully completed 1558 based on CR_LSP_STATUS (with success status); 1560 CR_LSP_Failure - Either a CRLSP could not be established as 1561 requested, or a setup CRLSP has dropped; based on CR_LSP_STATUS 1562 (with error status). 1564 B.4. CR-LDP Transitions 1566 State transitions are defined as follows: 1568 CR-LDP Specification - 31 - Exp. Apr 1999 1570 State Event Action New State 1571 ==================== ================= ====== =============== 1572 CR_Non_Existant CR_Start 1 CR_In_Progress 1573 CR_Non_Existant CR_Req_Rec 2 CR_Non_Existant 1574 CR_In_Progress CR_Setup_Complete CR_Established 1575 CR_In_Progress CR_LSP_Failure 3 CR_Non_Existant 1576 CR_Established CR_LSP_Failure 3 CR_Non_Existant 1578 Actions: 1580 1) Establish CRLSP state, create CR-TLV information, 1581 LDP_SEND_REQ. 1582 2) Process CR-TLV (as described in "Processing of 1583 the Constraint-Based Route TLV" section) and either 1584 LDP_SEND_REQ or LDP_SEND_RSP. 1585 3) Remove state information relative to this CRLSP (may notify 1586 management, other external source initially requiring 1587 setup). 1589 For the purposes of this transition table, illegal transitions 1590 (not included in the table) are ignored.