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Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust Copyright Line does not match the current year == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: A change in PCED information MUST not trigger any SPF computation at a receiving router. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (May 2007) is 5484 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO' ** Obsolete normative reference: RFC 3784 (Obsoleted by RFC 5305) == Outdated reference: draft-ietf-isis-caps has been published as RFC 4971 ** Downref: Normative reference to an Informational RFC: RFC 4655 ** Downref: Normative reference to an Informational RFC: RFC 4674 ** Obsolete normative reference: RFC 3567 (Obsoleted by RFC 5304) -- No information found for draft-ietf-pce-disco-proto-ospf - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'PCED-OSPF' == Outdated reference: draft-ietf-pce-pcep has been published as RFC 5440 Summary: 5 errors (**), 0 flaws (~~), 4 warnings (==), 10 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J.L. Le Roux (Editor) 3 Internet Draft France Telecom 4 Category: Standard Track 5 Expires: November 2007 J.P. Vasseur (Editor) 6 Cisco System Inc. 8 Yuichi Ikejiri 9 NTT Communications 11 Raymond Zhang 12 BT Infonet 14 May 2007 16 IS-IS protocol extensions for Path Computation Element (PCE) Discovery 18 draft-ietf-pce-disco-proto-isis-04.txt 20 Status of this Memo 22 By submitting this Internet-Draft, each author represents that any 23 applicable patent or other IPR claims of which he or she is aware 24 have been or will be disclosed, and any of which he or she becomes 25 aware will be disclosed, in accordance with Section 6 of BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF), its areas, and its working groups. Note that 29 other groups may also distribute working documents as Internet- 30 Drafts. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 The list of current Internet-Drafts can be accessed at 38 http://www.ietf.org/ietf/1id-abstracts.txt. 40 The list of Internet-Draft Shadow Directories can be accessed at 41 http://www.ietf.org/shadow.html. 43 This Internet-Draft will expire on November 3, 2007. 45 Copyright Notice 47 Copyright (C) The IETF Trust (2007). All rights reserved. 49 Abstract 51 There are various circumstances where it is highly desirable for a 52 Path Computation Client (PCC) to be able to dynamically and 53 automatically discover a set of Path Computation Elements (PCE), 54 along with some information that can be used for PCE selection. When 55 the PCE is a Label Switching Router (LSR) participating in the 56 Interior Gateway Protocol (IGP), or even a server participating 57 passively in the IGP, a simple and efficient way to discover PCEs 58 consists of using IGP flooding. For that purpose this document 59 defines extensions to the Intermediate System to Intermediate System 60 (IS-IS) routing protocol for the advertisement of PCE Discovery 61 information within an IS-IS area or within the entire IS-IS routing 62 domain. 64 Conventions used in this document 66 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 67 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 68 document are to be interpreted as described in [RFC2119]. 70 Table of Contents 72 1. Terminology.................................................3 73 2. Introduction................................................4 74 3. Overview....................................................5 75 3.1. PCE Information.............................................5 76 3.1.1. PCE Discovery Information...................................5 77 3.1.2. PCE Congestion Information..................................6 78 3.2. Flooding Scope..............................................6 79 4. IS-IS Extensions............................................7 80 4.1. The IS-IS PCED Sub-TLV......................................7 81 4.1.1. PCE-ADDRESS Sub-TLV.........................................8 82 4.1.2. The PATH-SCOPE Sub-TLV......................................8 83 4.1.3. PCE-DOMAIN Sub-TLV.........................................10 84 4.1.4. NEIG-PCE-DOMAIN Sub-TLV....................................11 85 4.1.5. PCE-CAP-FLAGS Sub-TLV......................................11 86 4.1.6. The CONGESTION Sub-TLV.....................................12 87 5. Elements of Procedure......................................13 88 5.1.1. CONGESTION Sub-TLV Specific Procedures.....................14 89 6. Backward Compatibility.....................................14 90 7. IANA Considerations........................................15 91 7.1. IS-IS Sub-TLV..............................................15 92 7.2. PCED Sub-TLVs registry.....................................15 93 8. Security Considerations....................................15 94 9. Manageability Considerations...............................16 95 9.1. Control of Policy and Functions............................16 96 9.2. Information and Data Model.................................16 97 9.3. Liveness Detection and Monitoring..........................16 98 9.4. Verify Correct Operations..................................16 99 9.5. Requirements on Other Protocols and Functional 100 Components...............................................16 101 9.6. Impact on Network Operations...............................16 102 10. Acknowledgments............................................17 103 11. References.................................................17 104 11.1. Normative References.......................................17 105 11.2. Informative References.....................................18 106 12. Editors' Addresses:........................................18 107 13. Contributors' Adresses:....................................18 108 14. Intellectual Property Statement............................19 110 1. Terminology 112 Terminology used in this document 114 AS: Autonomous System. 116 IGP: Interior Gateway Protocol. Either of the two routing 117 protocols Open Shortest Path First (OSPF) or Intermediate System 118 to Intermediate system (IS-IS). 120 Intra-area TE LSP: A TE LSP whose path does not cross IGP area 121 boundaries. 123 Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries. 125 Inter-area TE LSP: A TE LSP whose path transits two or 126 more IGP areas. That is a TE-LSP that crosses at least one IGP 127 area boundary. 129 Inter-AS TE LSP: A TE LSP whose path transits two or more 130 ASes or sub-ASes (BGP confederations). That is a TE-LSP that 131 crosses at least one AS boundary. 133 IS-IS LSP: Link State PDU 135 LSR: Label Switching Router. 137 PCC: Path Computation Client: Any client application requesting a 138 path computation to be performed by a Path Computation Element. 140 PCE: Path Computation Element: An entity (component, application, 141 or network node) that is capable of computing a network path or 142 route based on a network graph, and applying computational 143 constraints. 145 PCE-Domain: In a PCE context this refers to any collection of 146 network elements within a common sphere of address management or 147 path computational responsibility (referred to as "domain" in 148 [RFC4655]). Examples of PCE-Domains include IGP areas and 149 Autonomous Systems. This should be distinguished from an IS-IS 150 routing domain as defined by [ISO]. 152 PCEP: Path Computation Element communication Protocol. 154 TE LSP: Traffic Engineered Label Switched Path. 156 2. Introduction 158 [RFC4655] describes the motivations and architecture for a Path 159 Computation Element (PCE)-based path computation model for Multi 160 Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic 161 Engineered Label Switched Paths (TE-LSPs). The model allows for the 162 separation of the PCE from a Path Computation Client (PCC) (also 163 referred to as a non co-located PCE) and allows for cooperation 164 between PCEs. This relies on a communication protocol between PCC and 165 PCE, and between PCEs. The requirements for such a communication 166 protocol can be found in [RFC4657] and the communication protocol is 167 defined in [PCEP]. 169 The PCE architecture requires that a PCC be aware of the location of 170 one or more PCEs in its domain, and also potentially of some PCEs in 171 other domains, e.g. in case of inter-domain TE LSP computation. 173 A network may contain a large number of PCEs with potentially 174 distinct capabilities. In such a context it is highly desirable to 175 have a mechanism for automatic and dynamic PCE discovery, which 176 allows PCCs to automatically discover a set of PCEs, along with 177 additional information about each PCE that may be required for the 178 PCC to perform PCE selection. Additionally, it is valuable for a PCC 179 to dynamically detect new PCEs or any modification of the PCE 180 information. Detailed requirements for such a PCE discovery mechanism 181 are provided in [RFC4674]. 183 Moreover, it may also be useful to discover when a PCE experiences 184 processing congestion and when it exits such a state, in order for 185 the PCCs to take some appropriate actions (e.g. redirect their 186 requests to another PCE). Note that the PCE selection algorithm 187 applied by a PCC is out of the scope of this document. 189 When PCCs are LSRs participating in the IGP (OSPF, IS-IS), and PCEs 190 are either LSRs or servers also participating in the IGP, an 191 effective mechanism for PCE discovery within an IGP routing domain 192 consists of utilizing IGP advertisements. 194 This document defines IS-IS extensions to allow a PCE in an IS-IS 195 routing domain to advertise its location along with some information 196 useful to a PCC for PCE selection, so as to satisfy dynamic PCE 197 discovery requirements set forth in [RFC4674]. This document also 198 defines extensions allowing a PCE in an IS-IS routing domain to 199 advertise its processing congestion state. 201 Generic capability advertisement mechanisms for IS-IS are defined in 202 [IS-IS-CAP]. These allow a router to advertise its capabilities 203 within an IS-IS area or an entire IS-IS routing domain. This document 204 leverages this generic capability advertisement mechanism to fully 205 satisfy the aforementioned dynamic PCE discovery requirements. 207 This document defines a new sub-TLV (named PCE Discovery (PCED) to be 208 carried within the IS-IS Router Capability TLV ([IS-IS-CAP]). 210 The PCE information advertised is detailed in section 3. Protocol 211 extensions and procedures are defined in section 4 and 5. 213 This document does not define any new IS-IS elements of procedure. 214 The procedures defined in [IS-IS-CAP] MUST be used. 216 The IS-IS extensions defined in this document allow for PCE discovery 217 within an IS-IS Routing domain. Solutions for PCE discovery across AS 218 boundaries are beyond the scope of this document, and for further 219 study. 221 This document defines a set of sub-TLVs that are nested within each 222 other. When the degree of nesting TLVs is 2 (a TLV is carried within 223 another TLV) the TLV carried within a TLV is called a sub-TLV. 224 Strictly speaking, when the degree of nesting is 3, a subsub-TLV is 225 carried within a sub-TLV that is itself carried within a TLV. For the 226 sake of terminology simplicity, we refer to sub-TLV, a TLV carried 227 within a TLV regardless of the degree of nesting. 229 3. Overview 231 3.1. PCE Information 233 The PCE information advertised via IS-IS falls into two categories: 234 PCE Discovery information and PCE Congestion information. 236 3.1.1. PCE Discovery Information 238 The PCE Discovery information is comprised of: 240 - The PCE location: an IPv4 and/or IPv6 address that is used to reach 241 the PCE. It is RECOMMENDED to use an address that is always 242 reachable; 244 - The PCE path computation scope (i.e. inter-area, inter-AS, inter- 245 layer); 247 - The set of one or more PCE-Domain(s) into which the PCE has 248 visibility and can compute paths; 250 - The set of one or more neighbor PCE-Domain(s) towards which a PCE 251 can compute paths; 253 - A set of communication capabilities (e.g. support for request 254 prioritization) and path computation specific capabilities 255 (e.g. supported constraints). 257 Optional elements to describe more complex capabilities may also be 258 advertised. 260 PCE Discovery information is by nature fairly static and does not 261 change with PCE activity. Changes in PCE Discovery information may 262 occur as a result of PCE configuration updates, PCE 263 deployment/activation, PCE deactivation/suppression, or PCE failure. 264 Hence, this information is not expected to change frequently. 266 3.1.2. PCE Congestion Information 268 The PCE Congestion information is optional and can be used to report 269 a PCE's processing congestion state along with an estimated 270 congestion duration. This is dynamic information, which may change 271 with PCE activity. 273 Procedures for a PCE to move from a processing congestion state to a 274 non-congestion state are beyond the scope of this document, but the 275 rate at which a PCE Status change is advertised MUST NOT impact by 276 any means the IGP scalability. Particular attention should be given 277 on procedures to avoid state oscillations. 279 3.2. Flooding Scope 281 The flooding scope for PCE information advertised through IS-IS can 282 be a single L1 area, a L1 area and the L2 sub-domain, or the entire 283 IS-IS routing domain. 285 4. IS-IS Extensions 287 4.1. The IS-IS PCED Sub-TLV 289 The IS-IS PCED sub-TLV is made of a set of non ordered sub-TLVs. 291 The format of the IS-IS PCED sub-TLV and its sub-TLVs is identical to 292 the TLV format used by the Traffic Engineering Extensions to IS-IS 293 [RFC3784]. That is, the TLV is composed of 1 octet for the type, 1 294 octet specifying the TLV length, and a value field. The Length field 295 defines the length of the value portion in bytes. 297 The IS-IS PCED sub-TLV has the following format: 299 TYPE: To be assigned by IANA (suggested value = 5) 300 LENGTH: Variable 301 VALUE: set of sub-TLVs 303 Sub-TLVs types are under IANA control. 305 Currently six sub-TLVs are defined (suggested type values to be 306 assigned by IANA): 307 Sub-TLV type Length Name 308 1 variable PCE-ADDRESS sub-TLV 309 2 3 PATH-SCOPE sub-TLV 310 3 variable PCE-DOMAIN sub-TLV 311 4 variable NEIG-PCE-DOMAIN sub-TLV 312 5 variable PCE-CAP-FLAGS sub-TLV 313 6 1 CONGESTION sub-TLV 315 The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within 316 the PCED sub-TLV. 318 The PCE-DOMAIN and NEIG-PCE-DOMAIN sub-TLVs are optional. They 319 MAY be present in the PCED sub-TLV to facilitate selection of inter- 320 domain PCEs. 322 The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED 323 sub-TLV to facilitate the PCE selection process. 325 The CONGESTION sub-TLV is optional and MAY be present in the PCED 326 sub-TLV, to indicate a PCE's processing congestion state. 328 Any non recognized sub-TLV MUST be silently ignored. 330 Additional sub-TLVs could be added in the future to advertise 331 additional PCE information. 333 The PCED sub-TLV is carried within an IS-IS CAPABILITY TLV defined in 334 [IS-IS-CAP]. 336 The following sub-sections describe the sub-TLVs which may be carried 337 within the PCED sub-TLV. 339 4.1.1. PCE-ADDRESS Sub-TLV 341 The PCE-ADDRESS sub-TLV specifies the IP address that can be 342 used to reach the PCE. It is RECOMMENDED to make use of an address 343 that is always reachable, provided the PCE is alive. 345 The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the 346 PCED sub-TLV. It MAY appear twice, when the PCE has both an IPv4 and 347 IPv6 address. It MUST NOT appear more than once for the same address 348 type. 350 The PCE-ADDRESS sub-TLV has the following format: 352 TYPE: To be assigned by IANA (Suggested value =1) 353 LENGTH: 5 for IPv4 address and 17 for IPv6 address 354 VALUE: This comprises one octet indicating the address-type and 4 355 or 16 bytes encoding the IPv4 or IPv6 address to be used 356 to reach the PCE. 358 Address-type: 359 1 IPv4 360 2 IPv6 362 4.1.2. The PATH-SCOPE Sub-TLV 364 The PATH-SCOPE sub-TLV indicates the PCE path computation scope, 365 which refers to the PCE's ability to compute or take part in the 366 computation of intra-area, inter-area, inter-AS, or inter-layer_TE 367 LSP(s). 369 The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the 370 PCED sub-TLV. There MUST be exactly one instance of the PATH-SCOPE 371 sub-TLV within each PCED sub-TLV. 373 The PATH-SCOPE sub-TLV contains a set of bit flags indicating the 374 supported path scopes, and four fields indicating PCE preferences. 376 The PATH-SCOPE sub-TLV has the following format: 378 TYPE: To be assigned by IANA (Suggested value =2) 379 LENGTH: 3 380 VALUE: This comprises a one-byte flags field where flag 381 represents a supported path scope, followed by a 2-bytes 382 preferences field indicating PCE preferences. 384 Here is the structure of the bits flag: 386 +-+-+-+-+-+-+-+-+ 387 |0|1|2|3|4|5|Res| 388 +-+-+-+-+-+-+-+-+ 390 Bit Path Scope 392 0 L bit: Can compute intra-area path 393 1 R bit: Can act as PCE for inter-area TE LSP computation 394 2 Rd bit: Can act as a default PCE for inter-area TE LSP 395 computation 396 3 S bit: Can act as PCE for inter-AS TE LSP computation 397 4 Sd bit: Can act as a default PCE for inter-AS TE LSPs 398 computation 399 5 Y bit: Can compute or take part into the computation of 400 paths across layers 401 6-7 Reserved for future usage. 403 Here is the structure of the preferences field 405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 406 |PrefL|PrefR|PrefS|PrefY| Res | 407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 409 Res: Reserved for future usage. 411 Pref-L field: PCE's preference for intra-area TE LSPs computation. 413 Pref-R field: PCE's preference for inter-area TE LSPs computation. 415 Pref-S field: PCE's preference for inter-AS TE LSPs computation. 417 Pref-Y field: PCE's preference for inter-layer TE LSPs computation. 419 Res: Reserved for future usage. 421 The L, R, S, and Y bits are set when the PCE can act as a PCE for 422 intra-area, inter-area, inter-AS or inter-layer TE LSPs computation 423 respectively. These bits are non-exclusive. 425 When set the Rd bit indicates that the PCE can act as a default PCE 426 for inter-area TE LSP computation (that is the PCE can compute a path 427 towards any neighbor area). Similarly, when set, the Sd bit indicates 428 that the PCE can act as a default PCE for inter-AS TE LSP computation 429 (the PCE can compute a path towards any neighbor AS). 431 When the Rd and Sd bit are set, the PCED sub-TLV MUST NOT contain any 432 NEIG-PCE-DOMAIN sub-TLV (see 4.1.4). 434 When the R/S bit is cleared, the Rd/Sd bit SHOULD be cleared and MUST 435 be ignored. 437 The PrefL, PrefR, PrefS and PrefY fields are each three bits long and 438 allow the PCE to specify a preference for each computation scope, 439 where 7 reflects the highest preference. Such preference can be used 440 for weighted load balancing of requests. An operator may decide to 441 configure a preference for each computation scope to each PCE so as 442 to balance the path computation load among them. The algorithms used 443 by a PCC to balance its path computation requests according to such 444 PCE preference are out of the scope of this document and is a matter 445 for local or network wide policy. The same or distinct preferences 446 may be used for each scopes. For instance an operator that wants a 447 PCE capable of both inter-area and inter-AS computation to be used 448 preferably for inter-AS computation may configure a PrefS higher than 449 the PrefR. 451 When the L bit, R bit, S bit or Y bit are cleared the PrefL, PrefR, 452 PrefS, PrefY fields SHOULD respectively be set to 0 and MUST be 453 ignored. 455 Both reserved fields SHOULD be set to zero on transmission and MUST 456 be ignored on receipt. 458 4.1.3. PCE-DOMAIN Sub-TLV 460 The PCE-DOMAIN sub-TLV specifies a PCE-Domain (areas and/or ASes) 461 where the PCE has topology visibility and through which the PCE can 462 compute paths. 464 The PCE-DOMAIN sub-TLV MAY be present when PCE-Domains cannot be 465 inferred by other IGP information, for instance when the PCE is 466 inter-domain capable (i.e. when the R bit or S bit is set) and the 467 flooding scope is the entire routing domain (see section 5 for a 468 discussion of how the flooding scope is set and interpreted). 470 A PCED sub-TLV MAY include multiple PCE-DOMAIN sub-TLVs when the PCE 471 has visibility in multiple PCE-Domains. 473 The PCE-DOMAIN sub-TLV has the following format: 475 TYPE: To be assigned by IANA (Suggested value =3) 476 LENGTH: Variable 477 VALUE: This comprises one octet indicating the domain-type (area ID 478 or AS Number) and a variable length IS-IS area ID or a 32 bits AS 479 number, identifying a PCE-domain where the PCE has visibility. 481 Two domain types are defined: 482 1 Area ID 483 2 AS Number 485 The Area ID is the area address as defined in [ISO]. 487 When coded in two bytes (which is the current defined format as the 488 time of writing this document), the AS Number field MUST have its 489 left two bytes set to 0. 491 4.1.4. NEIG-PCE-DOMAIN Sub-TLV 493 The NEIG-PCE-DOMAIN sub-TLV specifies a neighbour PCE-domain (area, 494 AS) toward which a PCE can compute paths. It means that the PCE can 495 take part in the computation of inter-domain TE LSPs whose path 496 transits this neighbour PCE-domain. 498 A PCED sub-TLV MAY include several NEIG-PCE-DOMAIN sub-TLVs when the 499 PCE can compute paths towards several neighbour PCE-domains. 501 The NEIG-PCE-DOMAIN sub-TLV has the same format as the PCE-DOMAIN 502 sub-TLV: 504 TYPE: To be assigned by IANA (Suggested value =4) 505 LENGTH: Variable 506 VALUE: This comprises one octet indicating the domain-type (area ID 507 or AS Number) and a variable length IS-IS area ID or a 32 bits AS 508 number, identifying a PCE-domain towards which the PCE can compute 509 paths. 511 Two domain types are defined: 512 1 Area ID 513 2 AS Number 515 The Area ID is the area address as defined in [ISO]. 517 When coded in two bytes (which is the current defined format as the 518 time of writing this document), the AS Number field MUST have its 519 left two bytes set to 0. 521 The NEIG-PCE-DOMAIN sub-TLV MUST be present if the R bit is set and 522 the Rd bit is cleared, and/or, if the S bit is set and the Sd bit is 523 cleared. 525 4.1.5. PCE-CAP-FLAGS Sub-TLV 527 The PCE-CAP-FLAGs sub-TLV is an optional sub-TLV used to indicate 528 PCEP related capabilities. It MAY be present within the PCED sub-TLV. 529 It MUST NOT be present more than once. 531 The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array 532 of units of 32 bit flags numbered from the most significant as bit 533 zero, where each bit represents one PCE capability. 535 The PCE-CAP-FLAGS sub-TLV has the following format: 537 TYPE: To be assigned by IANA (Suggested value =4) 538 LENGTH: Multiple of 4 539 VALUE: This contains an array of units of 32 bit flags numbered 540 from the most significant as bit zero, where each bit 541 represents one PCE capability. 543 The PCE capability registry is managed by IANA, it is common 544 with OSPF and defined in [PCED-OSPF]. 546 Reserved bits SHOULD be set to zero on transmission and MUST be 547 ignored on receipt. 549 4.1.6. The CONGESTION Sub-TLV 551 The CONGESTION sub-TLV is used to indicate that a PCE is experiencing 552 a processing congestion state and may optionally include expected PCE 553 congestion duration. 554 The CONGESTION sub-TLV is optional, it MAY be carried within the PCED 555 sub-TLV. It MUST NOT be present more than once. 557 The format of the CONGESTION sub-TLV is as follows: 559 TYPE: To be assigned by IANA (Suggested value =6) 560 LENGTH: 3 561 VALUE: This comprises a one byte of bit flags indicating the 562 congestion status, followed by a 2-bytes field indicating the 563 congestion duration. 565 Here is the TLV structure 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 |C| Reserved| Congestion Duration | 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 571 Value 572 -C bit: When set this indicates that the PCE is experiencing 573 congestion and cannot accept any new request. When 574 cleared this indicates that the PCE is not 575 experiencing congestion and can accept new requests. 577 -Congestion Duration: 2-bytes, the estimated PCE congestion 578 duration in seconds. 580 When C is set and the Congestion Duration field is equal to 0, this 581 means that the Congestion Duration is unknown. 583 When C is cleared the Congestion Duration SHOULD be set to 0 and MUST 584 be ignored. 586 5. Elements of Procedure 588 The PCED sub-TLV is advertised within an IS-IS Router Capability TLV 589 defined in [IS-IS-CAP]. As such, elements of procedures are inherited 590 from those defined in [IS-IS-CAP]. 592 The flooding scope is controlled by the S flag in the IS-IS Router 593 Capability TLV (see [IS-IS-CAP]). When the scope of the PCED sub-TLV 594 is area local it MUST be carried within an IS-IS Router Capability 595 TLV having the S bit cleared. When the scope of the PCED sub-TLV is 596 the entire IS-IS routing domain, it MUST be carried within an IS-IS 597 Router Capability TLV having the S bit set. Note that when only the L 598 bit of the PATH-SCOPE sub-TLV is set, the flooding scope MUST be area 599 local. 601 Note that a L1L2 node may include both in its L1 and L2 LSPs a PCED 602 TLV in a Router Capability TLV with the S bit cleared. This allows 603 restricting the flooding scope to the L1 area and the L2 sub-domain. 605 An IS-IS router MUST originate a new IS-IS LSP whenever there is a 606 change in a PCED TLV associated with a PCE it advertises. 608 When a PCE is deactivated, the IS-IS Router advertising this PCE MUST 609 originate a new IS-IS LSP that does no longer include the 610 corresponding PCED TLV. 612 The PCE address(s), i.e. the address(s) indicated within the PCE 613 ADDRESS sub-TLV, must be reachable via some prefix(es) advertised by 614 IS-IS; this allows speeding up the detection of a PCE failure. Note 615 that when the PCE address is no longer reachable, this means that the 616 PCE node has failed or has been torn down, or that there is no longer 617 IP connectivity to the PCE node. 619 The PCED sub-TLV is OPTIONAL. When an IS-IS LSP does not contain any 620 PCED TLV, this means that the PCE information of that node is 621 unknown. 623 A change in PCED information MUST not trigger any SPF computation at 624 a receiving router. 626 The way PCEs determine the information they advertise is out of the 627 scope of this document. Some information may be configured (e.g., 628 address, preferences, scope) and other information may be 629 automatically determined by the PCE (e.g. areas of visibility). 631 5.1.1. CONGESTION Sub-TLV Specific Procedures 633 When a PCE enters into a processing congestion state, the conditions 634 of which are implementation dependent, a new IS-IS LSP with a 635 CONGESTION sub-TLV with the C bit set and optionally a non-null 636 expected congestion duration MAY be generated. 638 When a PCE exists from the processing congestion state, the 639 conditions of which are implementation dependent, two cases are 640 considered: 641 - If the congestion duration in the previously originated 642 CONGESTION sub-TLV was null, a CONGESTION sub-TLV with the C bit 643 cleared SHOULD be generated; 644 - If the congestion duration in the previously originated 645 CONGESTION sub-TLV was non null, a CONGESTION sub-TLV with the C bit 646 cleared MAY be generated. Note that in some particular cases it may 647 be desired to originate a CONGESTION sub-TLV with the C bit cleared 648 if the congestion duration was over estimated. 650 The congestion duration allows a reduction in the amount of IS-IS 651 flooding, as only uncongested-to-congested state transitions are 652 advertised. 654 An IS-IS implementation SHOULD support an appropriate dampening 655 algorithm so as to dampen flooding of PCE Congestion information in 656 order to not impact the IS-IS scalability. It is RECOMMENDED to 657 introduce some hysteresis for congestion state transition, so as to 658 avoid state oscillations that may impact IS-IS performance. For 659 instance two thresholds MAY be configured: a resource congestion 660 upper-threshold and a resource congestion lower-threshold. An LSR 661 enters the congested state when the CPU load reaches the upper 662 threshold and leaves the congested state when the CPU load goes under 663 the lower threshold. 665 Upon receipt of an updated CONGESTION sub-TLV a PCC should take 666 appropriate actions. In particular, the PCC SHOULD stop sending 667 requests to a congested PCE, and SHOULD gradually start sending again 668 requests to a PCE that is no longer congested. 670 6. Backward Compatibility 672 The PCED sub-TLV defined in this document does not introduce any 673 interoperability issues. 675 An IS-IS router not supporting the PCED sub-TLV will just silently 676 ignore the TLV as specified in [IS-IS-CAP]. 678 7. IANA Considerations 680 7.1. IS-IS Sub-TLV 682 Once a registry for the IS-IS Router Capability sub-TLVs, defined in 683 [IS-IS-CAP] has been assigned, IANA will assign a new sub-TLV code- 684 point for the PCED sub-TLV carried within the Router Capability TLV. 686 Value Sub-TLV References 687 ----- -------- ---------- 688 5 PCED sub-TLV (this document) 690 7.2. PCED Sub-TLVs Registry 692 The PCED sub-TLV referenced above is constructed from sub-TLVs. Each 693 sub-TLV includes a 8-bit type identifier. 695 The IANA is requested to create a new sub-registry of the IS-IS 696 Router Capability sub-TLVs registry, named the "PCED sub-TLVs" 697 registry, and manage sub-TLV type identifiers as follows: 699 - sub-TLV Type 700 - sub-TLV Name 701 - Reference 703 This document defines five sub-TLVs as follows (suggested values): 705 Value TLV name References 706 ----- -------- ---------- 707 1 PCE-ADDRESS This document 708 2 PATH-SCOPE This document 709 3 PCE-DOMAIN This document 710 4 NEIG-PCE-DOMAIN This document 711 5 PCE-CAP-FLAGS This document 712 6 CONGESTION This document 714 New sub-TLV type values may be allocated only by an IETF Consensus 715 action. 717 8. Security Considerations 719 This document defines IS-IS extensions for PCE discovery within an 720 administrative domain. Hence the security of the PCE discovery relies 721 on the security of IS-IS. 723 Mechanisms defined to ensure authenticity and integrity of IS-IS LSPs 724 [RFC3567], and their TLVs, can be used to secure the PCED sub-TLV as 725 well. 727 IS-IS provides no mechanism for protecting the privacy of LSPs, and 728 in particular the privacy of the PCE discovery information. 730 9. Manageability Considerations 732 Manageability considerations for PCE Discovery are addressed in 733 section 4.10 of [RFC4674]. 735 9.1. Control of Policy and Functions 737 Requirements on the configuration of PCE discovery parameters on PCCs 738 and PCEs are discussed in section 4.10.1 of [RFC4674]. 740 Particularly, a PCE implementation SHOULD allow configuring the 741 following parameters on the PCE: 742 -The PCE IPv4/IPv6 address(es) (see section 4.1.1) 743 -The PCE Scope, including the inter-domain functions (inter- 744 area, inter-AS, inter-layer), the preferences, and whether the 745 PCE can act as default PCE (see section 4.1.2) 746 -The PCE domains (see section 4.1.3) 747 -The neighbour PCE domains (see section 4.1.4) 748 -The PCE capabilities (see section 4.1.5) 750 9.2. Information and Data Model 752 A MIB module for PCE Discovery is defined in [PCED-MIB]. 754 9.3. Liveness Detection and Monitoring 756 PCE Discovery Protocol liveness detection relies upon IS-IS liveness 757 detection. IS-IS already includes a liveness detection mechanism 758 (Hello PDUs), and PCE discovery does not require additional 759 capabilities. 761 Procedures defined in section 5.1 allow a PCC detecting when a PCE 762 has been deactivated, or is no longer reachable. 764 9.4. Verify Correct Operations 766 The correlation of information advertised against information 767 received can be achieved by comparing the PCED information in the PCC 768 and in the PCE, which is stored in the PCED MIB [PCED-MIB]. The 769 number of dropped, corrupt, and rejected information elements are 770 stored in the PCED MIB. 772 9.5. Requirements on Other Protocols and Functional Components 774 The IS-IS extensions defined in this documents do not imply any 775 requirement on other protocols. 777 9.6. Impact on Network Operations 779 Frequent changes in PCE information, and particularly in PCE 780 congestion information, may have a significant impact on IS-IS and 781 might destabilize the operation of the network by causing the PCCs to 782 swap between PCEs. 784 As discussed in section 5.1, a PCE implementation SHOULD support an 785 appropriate dampening algorithm so as to dampen IS-IS flooding in 786 order to not impact the IS-IS scalability. 788 Also, as discussed in section 4.10.4 of [RFC4674], it MUST be 789 possible to apply at least the following controls: 791 - Configurable limit on the rate of announcement of changed 792 parameters at a PCE. 793 - Control of the impact on PCCs such as through discovery messages 794 rate-limiting. 795 - Configurable control of triggers that cause a PCC to swap to 796 another PCE. 798 10. Acknowledgments 800 We would like to thank Lucy Wong, Adrian Farrel, Les Ginsberg, Mike 801 Shand and Lou Berger for their useful comments and suggestions. 803 11. References 805 11.1. Normative References 807 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 808 Requirement Levels", BCP 14, RFC 2119, March 1997. 810 [ISO] "Intermediate System to Intermediate System Intra-Domain 811 Routeing Exchange Protocol for use in Conjunction with the 812 Protocol for Providing the Connectionless-mode Network Service 813 (ISO 8473)", ISO DP 10589, February 1990. 815 [RFC3784] Li, T., Smit, H., "IS-IS extensions for Traffic 816 Engineering", RFC 3784, June 2004. 818 [IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising 819 router information", draft-ietf-isis-caps, work in progress. 821 [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation 822 Element (PCE)-based Architecture", RFC4655, august 2006. 824 [RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery", 825 RFC4674, October 2006. 827 [RFC3567] Li, T. and R. Atkinson, "Intermediate System to 828 Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, 829 July 2003. 831 [PCED-OSPF] Le Roux, Vasseur, et al. "OSPF protocol extensions for 832 Path Computation Element (PCE) Discovery", draft-ietf-pce-disco- 833 proto-ospf, work in progress. 835 11.2. Informative References 837 [RFC4657] Ash, J., Le Roux, J.L., "PCE Communication Protocol Generic 838 Requirements", RFC4657, September 2006. 840 [PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE) 841 communication Protocol (PCEP) - Version 1", draft-ietf-pce-pcep, work 842 in progress. 844 [PCED-MIB] Stephan, E., "Definitions of Managed Objects for Path 845 Computation Element Discovery", draft-ietf-pce-disc-mib, work in 846 progress. 848 12. Editors' Addresses: 850 Jean-Louis Le Roux (Editor) 851 France Telecom 852 2, avenue Pierre-Marzin 853 22307 Lannion Cedex 854 FRANCE 855 Email: jeanlouis.leroux@orange-ftgroup.com 857 Jean-Philippe Vasseur (Editor) 858 Cisco Systems, Inc. 859 1414 Massachusetts avenue 860 Boxborough , MA - 01719 861 USA 862 Email: jpv@cisco.com 864 13. Contributors' Adresses: 866 Yuichi Ikejiri 867 NTT Communications Corporation 868 1-1-6, Uchisaiwai-cho, Chiyoda-ku 869 Tokyo 100-8019 870 JAPAN 871 Email: y.ikejiri@ntt.com 873 Raymond Zhang 874 BT Infonet 875 2160 E. Grand Ave. 876 El Segundo, CA 90025 877 USA 878 Email: raymond_zhang@bt-infonet.com 880 14. 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