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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 : ---------------------------------------------------------------------------- ** There are 2 instances of too long lines in the document, the longest one being 1 character in excess of 72. 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 (June 2007) is 5453 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 'ISO' ** Obsolete normative reference: RFC 3784 (Obsoleted by RFC 5305) == Outdated reference: draft-ietf-isis-caps has been published as RFC 4971 ** Obsolete normative reference: RFC 3567 (Obsoleted by RFC 5304) -- No information found for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 'PCED-OSPF' == Outdated reference: draft-ietf-pce-pcep has been published as RFC 5440 Summary: 4 errors (**), 0 flaws (~~), 4 warnings (==), 10 comments (--).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 Intended Status: Standard Track 5 Expires: December 2007 J.P. Vasseur (Editor) 6 Cisco System Inc. 8 Yuichi Ikejiri 9 NTT Communications 11 Raymond Zhang 12 BT Infonet 14 June 2007 16 IS-IS protocol extensions for Path Computation Element (PCE) Discovery 18 draft-ietf-pce-disco-proto-isis-06.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 Copyright Notice 45 Copyright (C) The IETF Trust (2007). All rights reserved. 47 Abstract 49 There are various circumstances where it is highly desirable for a 50 Path Computation Client (PCC) to be able to dynamically and 51 automatically discover a set of Path Computation Elements (PCE), 52 along with some information that can be used for PCE selection. When 53 the PCE is a Label Switching Router (LSR) participating in the 54 Interior Gateway Protocol (IGP), or even a server participating 55 passively in the IGP, a simple and efficient way to discover PCEs 56 consists of using IGP flooding. For that purpose this document 57 defines extensions to the Intermediate System to Intermediate System 58 (IS-IS) routing protocol for the advertisement of PCE Discovery 59 information within an IS-IS area or within the entire IS-IS routing 60 domain. 62 Conventions used in this document 64 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 65 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 66 document are to be interpreted as described in [RFC2119]. 68 Table of Contents 70 1. Terminology.................................................3 71 2. Introduction................................................4 72 3. Overview....................................................5 73 3.1. PCE Information.............................................5 74 3.1.1. PCE Discovery Information...................................5 75 3.1.2. PCE Overload Information....................................6 76 3.2. Flooding Scope..............................................6 77 4. IS-IS Extensions............................................7 78 4.1. The IS-IS PCED Sub-TLV......................................7 79 4.1.1. PCE-ADDRESS Sub-TLV.........................................8 80 4.1.2. The PATH-SCOPE Sub-TLV......................................8 81 4.1.3. PCE-DOMAIN Sub-TLV.........................................10 82 4.1.4. NEIG-PCE-DOMAIN Sub-TLV....................................11 83 4.1.5. PCE-CAP-FLAGS Sub-TLV......................................11 84 4.1.6. The OVERLOAD Sub-TLV.......................................12 85 5. Elements of Procedure......................................13 86 5.1.1. OVERLOAD Sub-TLV Specific Procedures.......................14 87 6. Backward Compatibility.....................................14 88 7. IANA Considerations........................................14 89 7.1. IS-IS Sub-TLV..............................................14 90 7.2. PCED Sub-TLVs registry.....................................15 91 8. Security Considerations....................................15 92 9. Manageability Considerations...............................16 93 9.1. Control of Policy and Functions............................16 94 9.2. Information and Data Model.................................16 95 9.3. Liveness Detection and Monitoring..........................16 96 9.4. Verify Correct Operations..................................16 97 9.5. Requirements on Other Protocols and Functional 98 Components...............................................16 99 9.6. Impact on Network Operations...............................16 100 10. Acknowledgments............................................17 101 11. References.................................................17 102 11.1. Normative References.......................................17 103 11.2. Informative References.....................................18 104 12. Editors' Addresses:........................................18 105 13. Contributors' Adresses:....................................18 106 14. Intellectual Property Statement............................19 108 1. Terminology 110 Terminology used in this document 112 AS: Autonomous System. 114 IGP: Interior Gateway Protocol. Either of the two routing 115 protocols Open Shortest Path First (OSPF) or Intermediate System 116 to Intermediate system (IS-IS). 118 Intra-area TE LSP: A TE LSP whose path does not cross IGP area 119 boundaries. 121 Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries. 123 Inter-area TE LSP: A TE LSP whose path transits two or 124 more IGP areas. That is a TE-LSP that crosses at least one IGP 125 area boundary. 127 Inter-AS TE LSP: A TE LSP whose path transits two or more 128 ASes or sub-ASes (BGP confederations). That is a TE-LSP that 129 crosses at least one AS boundary. 131 IS-IS LSP: Link State PDU 133 LSR: Label Switching Router. 135 PCC: Path Computation Client: Any client application requesting a 136 path computation to be performed by a Path Computation Element. 138 PCE: Path Computation Element: An entity (component, application, 139 or network node) that is capable of computing a network path or 140 route based on a network graph, and applying computational 141 constraints. 143 PCE-Domain: In a PCE context this refers to any collection of 144 network elements within a common sphere of address management or 145 path computational responsibility (referred to as "domain" in 146 [RFC4655]). Examples of PCE-Domains include IGP areas and ASes. 148 This should be distinguished from an IS-IS routing domain as 149 defined by [ISO]. 151 PCEP: Path Computation Element communication Protocol. 153 TE LSP: Traffic Engineered Label Switched Path. 155 2. Introduction 157 [RFC4655] describes the motivations and architecture for a Path 158 Computation Element (PCE)-based path computation model for Multi 159 Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic 160 Engineered Label Switched Paths (TE-LSPs). The model allows for the 161 separation of the PCE from a Path Computation Client (PCC) (also 162 referred to as a non co-located PCE) and allows for cooperation 163 between PCEs. This relies on a communication protocol between PCC and 164 PCE, and between PCEs. The requirements for such a communication 165 protocol can be found in [RFC4657] and the communication protocol is 166 defined in [PCEP]. 168 The PCE architecture requires that a PCC be aware of the location of 169 one or more PCEs in its domain, and also potentially of some PCEs in 170 other domains, e.g. in case of inter-domain TE LSP computation. 172 A network may contain a large number of PCEs with potentially 173 distinct capabilities. In such a context it is highly desirable to 174 have a mechanism for automatic and dynamic PCE discovery, which 175 allows PCCs to automatically discover a set of PCEs, along with 176 additional information about each PCE that may be required for the 177 PCC to perform PCE selection. Additionally, it is valuable for a PCC 178 to dynamically detect new PCEs or any modification of the PCE 179 information. Detailed requirements for such a PCE discovery mechanism 180 are provided in [RFC4674]. 182 Moreover, it may also be useful to discover when a PCE experiences 183 processing overload and when it exits such a state, in order for the 184 PCCs to take some appropriate actions (e.g. redirect their requests 185 to another PCE). Note that the PCE selection algorithm applied by a 186 PCC is out of the scope of this document. 188 When PCCs are LSRs participating in the IGP (OSPF, IS-IS), and PCEs 189 are either LSRs or servers also participating in the IGP, an 190 effective mechanism for PCE discovery within an IGP routing domain 191 consists of utilizing IGP advertisements. 193 This document defines IS-IS extensions to allow a PCE in an IS-IS 194 routing domain to advertise its location along with some information 195 useful to a PCC for PCE selection, so as to satisfy dynamic PCE 196 discovery requirements set forth in [RFC4674]. This document also 197 defines extensions allowing a PCE in an IS-IS routing domain to 198 advertise its processing congestion state. 200 Generic capability advertisement mechanisms for IS-IS are defined in 201 [IS-IS-CAP]. These allow a router to advertise its capabilities 202 within an IS-IS area or an entire IS-IS routing domain. This document 203 leverages this generic capability advertisement mechanism to fully 204 satisfy the aforementioned dynamic PCE discovery requirements. 206 This document defines a new sub-TLV (named PCE Discovery (PCED)) to 207 be carried within the IS-IS Router Capability TLV ([IS-IS-CAP]). 209 The PCE information advertised is detailed in section 3. Protocol 210 extensions and procedures are defined in section 4 and 5. 212 The IS-IS extensions defined in this document allow for PCE discovery 213 within an IS-IS Routing domain. Solutions for PCE discovery across AS 214 boundaries are beyond the scope of this document, and for further 215 study. 217 This document defines a set of sub-TLVs that are nested within each 218 other. When the degree of nesting TLVs is 2 (a TLV is carried within 219 another TLV) the TLV carried within a TLV is called a sub-TLV. 220 Strictly speaking, when the degree of nesting is 3, a subsub-TLV is 221 carried within a sub-TLV that is itself carried within a TLV. For the 222 sake of terminology simplicity, we refer to sub-TLV, a TLV carried 223 within a TLV regardless of the degree of nesting. 225 3. Overview 227 3.1. PCE Information 229 The PCE information advertised via IS-IS falls into two categories: 230 PCE Discovery information and PCE Overload information. 232 3.1.1. PCE Discovery Information 234 The PCE Discovery information is comprised of: 236 - The PCE location: an IPv4 and/or IPv6 address that is used to reach 237 the PCE. It is RECOMMENDED to use an address that is always 238 reachable; 240 - The PCE path computation scope (i.e. inter-area, inter-AS, inter- 241 layer); 243 - The set of one or more PCE-Domain(s) into which the PCE has 244 visibility and can compute paths; 246 - The set of one or more neighbor PCE-Domain(s) towards which a PCE 247 can compute paths; 249 - A set of communication capabilities (e.g. support for request 250 prioritization) and path computation specific capabilities 251 (e.g. supported constraints). 253 Optional elements to describe more complex capabilities may also be 254 advertised. 256 PCE Discovery information is by nature fairly static and does not 257 change with PCE activity. Changes in PCE Discovery information may 258 occur as a result of PCE configuration updates, PCE 259 deployment/activation, PCE deactivation/suppression, or PCE failure. 260 Hence, this information is not expected to change frequently. 262 3.1.2. PCE Overload Information 264 The PCE Overload Information is optional and can be used to report 265 a PCE's overload state in order to discourage the PCCs to send new 266 path computation requests. 268 A PCE may decide to clear the overload state according to local 269 implementation triggers (e.g. CPU utilization, average queue length 270 below some pre-defined thresholds). The rate at which a PCE status 271 change is advertised MUST NOT impact by any means the IGP 272 scalability. Particular attention should be given on procedures to 273 avoid state oscillations. 275 3.2. Flooding Scope 277 The flooding scope for PCE information advertised through IS-IS can 278 be a single L1 area, a L1 area and the L2 sub-domain, or the entire 279 IS-IS routing domain. 281 4. IS-IS Extensions 283 4.1. The IS-IS PCED Sub-TLV 285 The IS-IS PCED sub-TLV is made of a set of non ordered sub-TLVs. 287 The format of the IS-IS PCED sub-TLV and its sub-TLVs is identical to 288 the TLV format used by the Traffic Engineering Extensions to IS-IS 289 [RFC3784]. That is, the TLV is comprised of 1 octet for the type, 1 290 octet specifying the TLV length, and a value field. The Length field 291 defines the length of the value portion in octets. 293 The IS-IS PCED sub-TLV has the following format: 295 TYPE: To be assigned by IANA (suggested value = 5) 296 LENGTH: Variable 297 VALUE: set of sub-TLVs 299 Sub-TLVs types are under IANA control. 301 Currently six sub-TLVs are defined (suggested type values to be 302 assigned by IANA): 303 Sub-TLV type Length Name 304 1 variable PCE-ADDRESS sub-TLV 305 2 3 PATH-SCOPE sub-TLV 306 3 variable PCE-DOMAIN sub-TLV 307 4 variable NEIG-PCE-DOMAIN sub-TLV 308 5 variable PCE-CAP-FLAGS sub-TLV 309 6 1 OVERLOAD sub-TLV 311 The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within 312 the PCED sub-TLV. 314 The PCE-DOMAIN and NEIG-PCE-DOMAIN sub-TLVs are optional. They 315 MAY be present in the PCED sub-TLV to facilitate selection of inter- 316 domain PCEs. 318 The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED 319 sub-TLV to facilitate the PCE selection process. 321 The OVERLOAD sub-TLV is optional and MAY be present in the PCED sub- 322 TLV, to indicate a PCE's processing congestion state. 324 Any non recognized sub-TLV MUST be silently ignored. 326 Additional sub-TLVs could be added in the future to advertise 327 additional PCE information. 329 The PCED sub-TLV is carried within an IS-IS CAPABILITY TLV defined in 330 [IS-IS-CAP]. 332 The following sub-sections describe the sub-TLVs which may be carried 333 within the PCED sub-TLV. 335 4.1.1. PCE-ADDRESS Sub-TLV 337 The PCE-ADDRESS sub-TLV specifies the IP address that can be 338 used to reach the PCE. It is RECOMMENDED to make use of an address 339 that is always reachable, provided the PCE is alive. 341 The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the 342 PCED sub-TLV. It MAY appear twice, when the PCE has both an IPv4 and 343 IPv6 address. It MUST NOT appear more than once for the same address 344 type. If it appears more than once only the first occurrence MUST be 345 processed and other MUST be ignored. 347 The PCE-ADDRESS sub-TLV has the following format: 349 TYPE: To be assigned by IANA (Suggested value =1) 350 LENGTH: 5 for IPv4 address and 17 for IPv6 address 351 VALUE: This comprises one octet indicating the address-type and 4 352 or 16 octets encoding the IPv4 or IPv6 address to be used 353 to reach the PCE. 355 Address-type: 356 1 IPv4 357 2 IPv6 359 4.1.2. The PATH-SCOPE Sub-TLV 361 The PATH-SCOPE sub-TLV indicates the PCE path computation scope, 362 which refers to the PCE's ability to compute or take part in the 363 computation of intra-area, inter-area, inter-AS, or inter-layer_TE 364 LSP(s). 366 The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the 367 PCED sub-TLV. There MUST be exactly one instance of the PATH-SCOPE 368 sub-TLV within each PCED sub-TLV. If it appears more than once only 369 the first occurrence MUST be processed and other MUST be ignored. 371 The PATH-SCOPE sub-TLV contains a set of bit flags indicating the 372 supported path scopes, and four fields indicating PCE preferences. 374 The PATH-SCOPE sub-TLV has the following format: 376 TYPE: To be assigned by IANA (Suggested value =2) 377 LENGTH: 3 378 VALUE: This comprises a one-octet flags field where flag 379 represents a supported path scope, followed by a 2-octets 380 preferences field indicating PCE preferences. 382 Here is the structure of the bits flag: 384 +-+-+-+-+-+-+-+-+ 385 |0|1|2|3|4|5|Res| 386 +-+-+-+-+-+-+-+-+ 388 Bit Path Scope 390 0 L bit: Can compute intra-area path 391 1 R bit: Can act as PCE for inter-area TE LSP computation 392 2 Rd bit: Can act as a default PCE for inter-area TE LSP 393 computation 394 3 S bit: Can act as PCE for inter-AS TE LSP computation 395 4 Sd bit: Can act as a default PCE for inter-AS TE LSPs 396 computation 397 5 Y bit: Can compute or take part into the computation of 398 paths across layers 399 6-7 Reserved for future usage. 401 Here is the structure of the preferences field 403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 404 |PrefL|PrefR|PrefS|PrefY| Res | 405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 407 Res: Reserved for future usage. 409 Pref-L field: PCE's preference for intra-area TE LSPs computation. 411 Pref-R field: PCE's preference for inter-area TE LSPs computation. 413 Pref-S field: PCE's preference for inter-AS TE LSPs computation. 415 Pref-Y field: PCE's preference for inter-layer TE LSPs computation. 417 Res: Reserved for future usage. 419 The L, R, S, and Y bits are set when the PCE can act as a PCE for 420 intra-area, inter-area, inter-AS or inter-layer TE LSPs computation 421 respectively. These bits are non-exclusive. 423 When set the Rd bit indicates that the PCE can act as a default PCE 424 for inter-area TE LSP computation (that is the PCE can compute a path 425 towards any neighbor area). Similarly, when set, the Sd bit indicates 426 that the PCE can act as a default PCE for inter-AS TE LSP computation 427 (the PCE can compute a path towards any neighbor AS). 429 When the Rd and Sd bit are set, the PCED sub-TLV MUST NOT contain any 430 NEIG-PCE-DOMAIN sub-TLV (see 4.1.4). 432 When the R/S bit is cleared, the Rd/Sd bit SHOULD be cleared and MUST 433 be ignored. 435 The PrefL, PrefR, PrefS and PrefY fields are each three bits long and 436 allow the PCE to specify a preference for each computation scope, 437 where 7 reflects the highest preference. Such preference can be used 438 for weighted load balancing of requests. An operator may decide to 439 configure a preference for each computation scope to each PCE so as 440 to balance the path computation load among them. The algorithms used 441 by a PCC to balance its path computation requests according to such 442 PCE preference are out of the scope of this document and is a matter 443 for local or network wide policy. The same or distinct preferences 444 may be used for each scopes. For instance an operator that wants a 445 PCE capable of both inter-area and inter-AS computation to be used 446 preferably for inter-AS computation may configure a PrefS higher than 447 the PrefR. 449 When the L bit, R bit, S bit or Y bit are cleared the PrefL, PrefR, 450 PrefS, PrefY fields SHOULD respectively be set to 0 and MUST be 451 ignored. 453 Both reserved fields SHOULD be set to zero on transmission and MUST 454 be ignored on receipt. 456 4.1.3. PCE-DOMAIN Sub-TLV 458 The PCE-DOMAIN sub-TLV specifies a PCE-Domain (areas and/or ASes) 459 where the PCE has topology visibility and through which the PCE can 460 compute paths. 462 The PCE-DOMAIN sub-TLV MAY be present when PCE-Domains cannot be 463 inferred by other IGP information, for instance when the PCE is 464 inter-domain capable (i.e. when the R bit or S bit is set) and the 465 flooding scope is the entire routing domain (see section 5 for a 466 discussion of how the flooding scope is set and interpreted). 468 A PCED sub-TLV MAY include multiple PCE-DOMAIN sub-TLVs when the PCE 469 has visibility in multiple PCE-Domains. 471 The PCE-DOMAIN sub-TLV has the following format: 473 TYPE: To be assigned by IANA (Suggested value =3) 474 LENGTH: Variable 475 VALUE: This is comprised of one octet indicating the domain-type 476 (area ID or AS Number) and a variable length IS-IS area ID or a 32 477 bits AS number, identifying a PCE-domain where the PCE has visibility. 479 Two domain types are defined: 480 1 Area ID 481 2 AS Number 482 The Area ID is the area address as defined in [ISO]. 484 When coded in two octets (which is the current defined format as the 485 time of writing this document), the AS Number field MUST have its 486 left two octets set to 0. 488 4.1.4. NEIG-PCE-DOMAIN Sub-TLV 490 The NEIG-PCE-DOMAIN sub-TLV specifies a neighbour PCE-domain (area, 491 AS) toward which a PCE can compute paths. It means that the PCE can 492 take part in the computation of inter-domain TE LSPs whose path 493 transits this neighbour PCE-domain. 495 A PCED sub-TLV MAY include several NEIG-PCE-DOMAIN sub-TLVs when the 496 PCE can compute paths towards several neighbour PCE-domains. 498 The NEIG-PCE-DOMAIN sub-TLV has the same format as the PCE-DOMAIN 499 sub-TLV: 501 TYPE: To be assigned by IANA (Suggested value =4) 502 LENGTH: Variable 503 VALUE: This comprises one octet indicating the domain-type (area ID 504 or AS Number) and a variable length IS-IS area ID or a 32 bits AS 505 number, identifying a PCE-domain towards which the PCE can compute 506 paths. 508 Two domain types are defined: 509 1 Area ID 510 2 AS Number 512 The Area ID is the area address as defined in [ISO]. 514 When coded in two octets (which is the current defined format as the 515 time of writing this document), the AS Number field MUST have its 516 first two octets set to 0. 518 The NEIG-PCE-DOMAIN sub-TLV MUST be present if the R bit is set and 519 the Rd bit is cleared, and/or, if the S bit is set and the Sd bit is 520 cleared. 522 4.1.5. PCE-CAP-FLAGS Sub-TLV 524 The PCE-CAP-FLAGs sub-TLV is an optional sub-TLV used to indicate 525 PCEP related capabilities. It MAY be present within the PCED sub-TLV. 527 It MUST NOT be present more than once. If it appears more than once 528 only the first occurrence MUST be processed and other MUST be ignored. 530 The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array 531 of units of 32 bit flags numbered from the most significant as bit 532 zero, where each bit represents one PCE capability. 534 The PCE-CAP-FLAGS sub-TLV has the following format: 536 TYPE: To be assigned by IANA (Suggested value =4) 537 LENGTH: Multiple of 4 538 VALUE: This contains an array of units of 32 bit flags numbered 539 from the most significant as bit zero, where each bit 540 represents one PCE capability. 542 The PCE capability registry is managed by IANA, it is common 543 with OSPF and defined in [PCED-OSPF]. 545 Reserved bits SHOULD be set to zero on transmission and MUST be 546 ignored on receipt. 548 4.1.6. The OVERLOAD Sub-TLV 550 The CONGESTION sub-TLV is used to indicate that a PCE is experiencing 551 a processing congestion state and may optionally include expected PCE 552 congestion duration. 553 The CONGESTION sub-TLV is optional, it MAY be carried within the PCED 554 sub-TLV. It MUST NOT be present more than once. If it appears more 555 than once only the first occurrence MUST be processed and other MUST 556 be ignored. 558 The format of the CONGESTION sub-TLV is as follows: 560 TYPE: To be assigned by IANA (Suggested value =6) 561 LENGTH: 1 562 VALUE: This comprises a one octet of bit flags indicating the 563 overload status. Currently only the first flag is defined. 565 Here is the TLV structure 567 +-+-+-+-+-+-+-+-+ 568 |C| Reserved| 569 +-+-+-+-+-+-+-+-+ 571 Value 572 -C bit: When set this indicates that the PCE is overloaded 573 and cannot accept any new request. When cleared this 574 indicates that the PCE is not overloaded and can 575 accept new requests. 577 5. Elements of Procedure 579 The PCED sub-TLV is advertised within an IS-IS Router Capability TLV 580 defined in [IS-IS-CAP]. As such, elements of procedures are inherited 581 from those defined in [IS-IS-CAP]. 583 The flooding scope is controlled by the S flag in the IS-IS Router 584 Capability TLV (see [IS-IS-CAP]). When the scope of the PCED sub-TLV 585 is area local it MUST be carried within an IS-IS Router Capability 586 TLV having the S bit cleared. When the scope of the PCED sub-TLV is 587 the entire IS-IS routing domain, it MUST be carried within an IS-IS 588 Router Capability TLV having the S bit set. Note that when only the L 589 bit of the PATH-SCOPE sub-TLV is set, the flooding scope MUST be area 590 local. 592 Note that a L1L2 node may include both in its L1 and L2 LSPs a PCED 593 TLV in a Router Capability TLV with the S bit cleared. This allows 594 restricting the flooding scope to the L1 area and the L2 sub-domain. 596 An IS-IS router MUST originate a new IS-IS LSP whenever there is a 597 change in a PCED TLV associated with a PCE it advertises. 599 When a PCE is deactivated, the IS-IS Router advertising this PCE MUST 600 originate a new IS-IS LSP that no longer includes the corresponding 601 PCED TLV. 603 The PCE address(s), i.e. the address(s) indicated within the PCE 604 ADDRESS sub-TLV, SHOULD be reachable via some prefix(es) advertised 605 by IS-IS; this allows speeding up the detection of a PCE failure. 606 Note that when the PCE address is no longer reachable, this means 607 that the PCE node has failed or has been torn down, or that there is 608 no longer IP connectivity to the PCE node. 610 A change in PCED information MUST not trigger any SPF computation at 611 a receiving router. 613 The way PCEs determine the information they advertise is out of the 614 scope of this document. Some information may be configured (e.g., 615 address, preferences, scope) and other information may be 616 automatically determined by the PCE (e.g. areas of visibility). 618 5.1.1. OVERLOAD Sub-TLV Specific Procedures 620 When a PCE enters into an overload state, the conditions of which are 621 implementation dependent, a new IS-IS LSP with an OVERLOAD sub-TLV 622 with the C bit set MAY be generated. 624 When a PCE exists from an overload state, the conditions of which are 625 implementation dependent (e.g. CPU utilization, average queue length 626 below some pre-defined thresholds), a new IS-IS LSP with an OVERLOAD 627 sub-TLV with the C bit cleared SHOULD be generated, if an OVERLOAD 628 sub-TLV with the C bit set had previously been generated. 630 A PCE implementation supporting the IS-IS extensions defined in this 631 document SHOULD support an appropriate dampening algorithm so as to 632 dampen flooding of PCE Overload information in order to not impact 633 the IS-IS scalability. It is RECOMMENDED to introduce some hysteresis 634 for overload state transition, so as to avoid state oscillations that 635 may impact IS-IS performance. For instance two thresholds MAY be 636 configured: an upper-threshold and a lower-threshold. An LSR enters 637 the overload state when the CPU load reaches the upper threshold and 638 leaves the overload state when the CPU load goes under the lower 639 threshold. 641 Upon receipt of an updated OVERLOAD sub-TLV a PCC should take 642 appropriate actions. In particular, the PCC SHOULD stop sending 643 requests to an overloaded PCE, and SHOULD gradually start sending 644 again requests to a PCE that is no longer overloaded. 646 6. Backward Compatibility 648 The PCED sub-TLV defined in this document does not introduce any 649 interoperability issues. 651 An IS-IS router not supporting the PCED sub-TLV will just silently 652 ignore the TLV as specified in [IS-IS-CAP]. 654 7. IANA Considerations 656 7.1. IS-IS Sub-TLV 658 Once a registry for the IS-IS Router Capability sub-TLVs, defined in 659 [IS-IS-CAP] has been assigned, IANA will assign a new sub-TLV code- 660 point for the PCED sub-TLV carried within the Router Capability TLV. 662 Value Sub-TLV References 663 ----- -------- ---------- 664 5 PCED sub-TLV (this document) 666 7.2. PCED Sub-TLVs registry 668 The PCED sub-TLV referenced above is constructed from sub-TLVs. Each 669 sub-TLV includes a 8-bit type identifier. 671 The IANA is requested to create a new sub-registry of the IS-IS 672 Router Capability sub-TLVs registry, named the "PCED sub-TLVs" 673 registry, and manage sub-TLV type identifiers as follows: 675 - sub-TLV Type 676 - sub-TLV Name 677 - Reference 679 This document defines five sub-TLVs as follows (suggested values): 681 Sub-TLV Sub-TLV 682 Type name References 683 ----- -------- ---------- 684 1 PCE-ADDRESS This document 685 2 PATH-SCOPE This document 686 3 PCE-DOMAIN This document 687 4 NEIG-PCE-DOMAIN This document 688 5 PCE-CAP-FLAGS This document 689 6 OVERLOAD This document 691 New sub-TLV type values may be allocated only by an IETF Consensus 692 action. 694 8. Security Considerations 696 This document defines IS-IS extensions for PCE discovery within an 697 administrative domain. Hence the security of the PCE discovery relies 698 on the security of IS-IS. 700 Mechanisms defined to ensure authenticity and integrity of IS-IS LSPs 701 [RFC3567], and their TLVs, can be used to secure the PCED sub-TLV as 702 well. 704 IS-IS provides no encryption mechanism for protecting the privacy of 705 LSPs, and in particular the privacy of the PCE discovery information. 707 9. Manageability Considerations 709 Manageability considerations for PCE Discovery are addressed in 710 section 4.10 of [RFC4674]. 712 9.1. Control of Policy and Functions 714 Requirements on the configuration of PCE discovery parameters on PCCs 715 and PCEs are discussed in section 4.10.1 of [RFC4674]. 717 Particularly, a PCE implementation SHOULD allow configuring the 718 following parameters on the PCE: 719 -The PCE IPv4/IPv6 address(es) (see section 4.1.1) 720 -The PCE Scope, including the inter-domain functions (inter- 721 area, inter-AS, inter-layer), the preferences, and whether the 722 PCE can act as default PCE (see section 4.1.2) 723 -The PCE domains (see section 4.1.3) 724 -The neighbour PCE domains (see section 4.1.4) 725 -The PCE capabilities (see section 4.1.5) 727 9.2. Information and Data Model 729 A MIB module for PCE Discovery is defined in [PCED-MIB]. 731 9.3. Liveness Detection and Monitoring 733 PCE Discovery Protocol liveness detection relies upon IS-IS liveness 734 detection. IS-IS already includes a liveness detection mechanism 735 (Hello PDUs), and PCE discovery does not require additional 736 capabilities. 738 Procedures defined in section 5.1 allow a PCC detecting when a PCE 739 has been deactivated, or is no longer reachable. 741 9.4. Verify Correct Operations 743 The correlation of information advertised against information 744 received can be achieved by comparing the PCED information in the PCC 745 and in the PCE, which is stored in the PCED MIB [PCED-MIB]. The 746 number of dropped, corrupt, and rejected information elements are 747 stored in the PCED MIB. 749 9.5. Requirements on Other Protocols and Functional Components 751 The IS-IS extensions defined in this document do not imply any 752 requirement on other protocols. 754 9.6. Impact on Network Operations 756 Frequent changes in PCE information, and particularly in PCE 757 overload information, may have a significant impact on IS-IS and 758 might destabilize the operation of the network by causing the PCCs to 759 swap between PCEs. 761 As discussed in section 5.1, a PCE implementation SHOULD support an 762 appropriate dampening algorithm so as to dampen IS-IS flooding in 763 order to not impact the IS-IS scalability. 765 Also, as discussed in section 4.10.4 of [RFC4674], it MUST be 766 possible to apply at least the following controls: 768 - Configurable limit on the rate of announcement of changed 769 parameters at a PCE. 770 - Control of the impact on PCCs such as through discovery messages 771 rate-limiting. 772 - Configurable control of triggers that cause a PCC to swap to 773 another PCE. 775 10. Acknowledgments 777 We would like to thank Lucy Wong, Adrian Farrel, Les Ginsberg, Mike 778 Shand, Lou Berger, and David Ward, for their useful comments and 779 suggestions. 781 11. References 783 11.1. Normative References 785 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 786 Requirement Levels", BCP 14, RFC 2119, March 1997. 788 [ISO] "Intermediate System to Intermediate System Intra-Domain 789 Routeing Exchange Protocol for use in Conjunction with the 790 Protocol for Providing the Connectionless-mode Network Service 791 (ISO 8473)", ISO DP 10589, February 1990. 793 [RFC3784] Li, T., Smit, H., "IS-IS extensions for Traffic 794 Engineering", RFC 3784, June 2004. 796 [IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising 797 router information", draft-ietf-isis-caps, work in progress. 799 [RFC3567] Li, T. and R. Atkinson, "Intermediate System to 800 Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, 801 July 2003. 803 [PCED-OSPF] Le Roux, Vasseur, et al. "OSPF protocol extensions for 804 Path Computation Element (PCE) Discovery", draft-ietf-pce-disco- 805 proto-ospf, work in progress. 807 11.2. Informative References 809 [RFC4657] Ash, J., Le Roux, J.L., "PCE Communication Protocol Generic 810 Requirements", RFC4657, September 2006. 812 [PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE) 813 communication Protocol (PCEP) - Version 1", draft-ietf-pce-pcep, work 814 in progress. 816 [PCED-MIB] Stephan, E., "Definitions of Managed Objects for Path 817 Computation Element Discovery", draft-ietf-pce-disc-mib, work in 818 progress. 820 [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation 821 Element (PCE)-based Architecture", RFC4655, august 2006. 823 [RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery", 824 RFC4674, October 2006. 826 12. Editors' Addresses: 828 Jean-Louis Le Roux (Editor) 829 France Telecom 830 2, avenue Pierre-Marzin 831 22307 Lannion Cedex 832 FRANCE 833 Email: jeanlouis.leroux@orange-ftgroup.com 835 Jean-Philippe Vasseur (Editor) 836 Cisco Systems, Inc. 837 1414 Massachusetts avenue 838 Boxborough , MA - 01719 839 USA 840 Email: jpv@cisco.com 842 13. Contributors' Adresses: 844 Yuichi Ikejiri 845 NTT Communications Corporation 846 1-1-6, Uchisaiwai-cho, Chiyoda-ku 847 Tokyo 100-8019 848 JAPAN 849 Email: y.ikejiri@ntt.com 851 Raymond Zhang 852 BT Infonet 853 2160 E. Grand Ave. 854 El Segundo, CA 90025 855 USA 856 Email: raymond_zhang@bt-infonet.com 858 14. 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