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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.