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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Networking Working Group Rich Bradford (Ed) 2 Internet-Draft JP Vasseur 3 Intended Status: Standards Track Cisco Systems, Inc. 4 Created: November 17, 2008 Adrian Farrel 5 Expires: May 17, 2009 Old Dog Consulting 7 Preserving Topology Confidentiality in Inter-Domain Path 8 Computation Using a Key-Based Mechanism 10 draft-ietf-pce-path-key-04.txt 12 Status of this Memo 14 This Internet-Draft is submitted to IETF in full conformance with 15 the provisions of BCP 78 and BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 Abstract 35 Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) 36 Traffic Engineering (TE) Label Switched Paths (LSPs) may be 37 computed by Path Computation Elements (PCEs). Where the TE LSP 38 crosses multiple domains, such as Autonomous Systems (ASes), the 39 path may be computed by multiple PCEs that cooperate, with each 40 responsible for computing a segment of the path. However, in some 41 cases (e.g., when ASes are administered by separate Service 42 Providers), it would break confidentiality rules for a PCE to 43 supply a path segment to a PCE in another domain, thus disclosing 44 AS-internal topology information. This issue may be circumvented 45 by returning a loose hop and by invoking a new path computation 46 from the domain boundary Label Switching Router (LSR) during TE 47 LSP setup as the signaling message enters the second domain, but 48 this technique has several issues including the problem of 49 maintaining path diversity. 51 This document defines a mechanism to hide the contents of a 52 segment of a path, called the Confidential Path Segment (CPS). The 53 CPS may be replaced by a path-key that can be conveyed in the PCE 54 Communication Protocol (PCEP) and signaled within in a Resource 55 Reservation Protocol TE (RSVP-TE) explicit route object. 57 Conventions used in this document 59 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 60 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and 61 "OPTIONAL" in this document are to be interpreted as described in 62 RFC-2119 [RFC2119]. 64 Table of contents 66 1. Introduction.................................................3 67 1.1. Terminology.................................................4 68 2. Path-Key Solution............................................5 69 2.1. Mode of Operation...........................................5 70 2.2. Example.....................................................6 71 3. PCEP Protocol Extensions.....................................7 72 3.1. Path Keys in PCRep Messages.................................7 73 3.1.1. PKS with 32-bit PCE ID....................................8 74 3.1.2. PKS with 128-bit PCE ID...................................9 75 3.2. Unlocking Path Keys.........................................9 76 3.2.1. Path Key Bit.............................................10 77 3.2.2. PATH-KEY Object..........................................10 78 3.2.3. Path Computation Request (PCReq) message with Path Key...10 79 4. PCEP Mode of Operation for Path Key Expansion...............11 80 5. Security Considerations.....................................12 81 6. Manageability Considerations................................13 82 6.1. Control of Function Through Configuration and Policy.......13 83 6.2. Information and Data Models................................14 84 6.3. Liveness Detection and Monitoring..........................14 85 6.4. Verifying Correct Operation................................14 86 6.5. Requirements on Other Protocols and Functional Components..15 87 6.6. Impact on Network Operation................................15 88 7. IANA Considerations.........................................15 89 7.1. New Subobjects for the ERO Object..........................15 90 7.2. New PCEP Object............................................16 91 7.3. New RP Object Bit Flag.....................................16 92 7.4. New NO-PATH-VECTOR TLV Bit Flag............................16 93 8. Normative References........................................17 94 9. Informational References....................................17 95 10. Acknowledgements...........................................18 96 11. Authors' Addresses.........................................18 98 1. Introduction 100 Path computation techniques using the Path Computation Element 101 (PCE) are described in [RFC4655] and allow for path computation of 102 inter-domain Multiprotocol Label Switching (MPLS) Traffic 103 Engineering (TE) and Generalized MPLS (GMPLS) Label Switched Paths 104 (LSPs). 106 An important element of inter-domain TE is that TE information is 107 not shared between domains for scalability and confidentiality 108 reasons ([RFC4105] and [RFC4216]). Therefore, a single PCE is 109 unlikely to be able to compute a full inter-domain path. 111 Two path computation scenarios can be used for inter-domain TE 112 LSPs: one using per-domain path computation (defined in [RFC5152]), 113 and the other using a PCE-based path computation technique with 114 cooperation between PCEs (as described in [RFC4655]). In this second 115 case, paths for inter-domain LSPs can be computed by cooperation 116 between PCEs each of which computes a segment of the path across one 117 domain. Such a path computation procedure is described in [BRPC]. 119 If confidentiality is required between domains (such as would very 120 likely be the case between Autonomous Systems (ASes) belonging to 121 different Service Providers) then cooperating PCEs cannot exchange 122 path segments or else the receiving PCE and the Path Computation 123 Client (PCC) will be able to see the individual hops through 124 another domain thus breaking the confidentiality requirement 125 stated in [RFC4105] and [RFC4216]. We define the part of the path 126 which we wish to keep confidential as the Confidential Path 127 Segment (CPS). 129 One mechanism for preserving the confidentiality of the CPS is for 130 the PCE to return a path containing a loose hop in place of the 131 segment that must be kept confidential. The concept of loose and 132 strict hops for the route of a TE LSP is described in [RFC3209]. 133 The Path Computation Element Communication Protocol (PCEP) defined 134 in [PCEP] supports the use of paths with loose hops, and it is a 135 local policy decision at a PCE whether it returns a full explicit 136 path with strict hops or uses loose hops. Note that a Path 137 computation Request may request an explicit path with strict hops 138 or may allow loose hops as detailed in [PCEP]. 140 The option of returning a loose hop in place of the CPS can be 141 achieved without further extensions to PCEP or the signaling 142 protocol. If loose hops are used, the TE LSPs are signaled as 143 normal ([RFC3209]), and when a loose hop is encountered in the 144 explicit route it is resolved by performing a secondary path 145 computation to reach the resource or set of resources identified 146 by the loose hop. Given the nature of the cooperation between PCEs 147 in computing the original path, this secondary computation occurs 148 at or on behalf of a Label Switching Router (LSR) at a domain 149 boundary (i.e., an Area Border Router (ABR) or an AS Border Router 150 (ASBR)) and the path is expanded as described in [RFC5152]. 152 The PCE-based computation model is particularly useful for 153 determining mutually disjoint inter-domain paths such as might be 154 required for service protection [RFC5298]. A single path computation 155 request is used. However, if loose hops are returned, the path of 156 each TE LSP must be recomputed at the domain boundaries as the TE 157 LSPs are signaled, and since the TE LSP signaling proceeds 158 independently for each TE LSP, disjoint paths cannot be guaranteed 159 since the LSRs in charge of expanding the EROs are not synchronized. 160 Therefore, if the loose hop technique is used without further 161 extensions, path segment confidentiality and path diversity are 162 mutually incompatible requirements. 164 This document defines the notion of a Path Key that is a token 165 that replaces a path segment in an explicit route. The Path Key is 166 encoded as a Path Key Subobject (PKS) returned in the PCEP Path 167 Computation Reply message (PCRep) ([PCEP]). Upon receiving the 168 computed path, the PKS will be carried in an RSVP-TE Path message 169 (RSVP-TE [RFC3209] and [RSVP-PKS]) during signaling. 171 1.1. Terminology 173 This document makes use of the following terminology and acronyms. 175 AS: Autonomous System. 177 ASBR: Autonomous System Border Routers used to connect to another 178 AS of a different or the same Service Provider via one or more 179 links inter-connecting between ASes. 181 CPS: Confidential Path Segment. A segment of a path that contains 182 nodes and links that the AS policy requires to not be disclosed 183 outside the AS. 185 Inter-AS TE LSP: A TE LSP that crosses an AS boundary. 187 LSR: Label Switching Router. 189 LSP: Label Switched Path. 191 PCC: Path Computation Client: Any client application requesting a 192 path computation to be performed by a Path Computation Element. 194 PCE: Path Computation Element: An entity (component, application 195 or network node) that is capable of computing a network path or 196 route based on a network graph and applying computational 197 constraints. 199 TE LSP: Traffic Engineering Label Switched Path 201 2. Path-Key Solution 203 The Path-Key solution may be applied in the PCE-based path 204 computation context as follows. A PCE computes a path segment 205 related to a particular domain and replaces any CPS in the path 206 reported to the requesting PCC (or another PCE) by one or more 207 subobjects referred to as PKSes. The entry boundary LSR of each 208 CPS SHOULD be specified using its TE Router Id as a hop in the 209 returned path immediately preceding the CPS, and other sub-objects 210 MAY be included in the path immediately before the hop identifying 211 the boundary LSR to indicate link and label choices. Where two 212 PKSes are supplied in sequence with no intervening nodes, the 213 entry node to the second CPS MAY be part of the first CPS and does 214 not need to be explicitly present in the returned path. The exit 215 node of a CPS MAY be present as a strict hop immediately following 216 the PKS. 218 2.1. Mode of Operation 220 During path computation, when local policy dictates that 221 confidentiality must be preserved for all or part of the path 222 segment being computed or if explicitly requested by the Path 223 Computation Request, the PCE associates a path-key with the 224 computed path for the CPS, places its own identifier (its PCE ID 225 as defined in Section 3.1) along with the path-key in a PKS, and 226 inserts the PKS object in the path returned to the requesting PCC 227 or PCE immediately after the subobject that identifies (using the 228 TE Router Id) the LSR that will expand the PKS into explicit path 229 hops.This will usually be the LSR that is the start point of the 230 CPS. The PCE that generates a PKS SHOULD store the computed path 231 segment and the path-key for later retrieval. A local policy 232 SHOULD be used to determine for how long to retain such stored 233 information, and whether to discard the information after it has 234 been queried using the procedures described below. It is 235 RECOMMENDED for a PCE to store the PKS for a period of 10 minutes. 237 A path-key value is scoped to the PCE that computed it as 238 identified by the PCE-ID carried in the PKS. A PCE MUST NOT re-use 239 a path-key value to represent a new CPS for at least 30 minutes 240 after discarding the previous use of the same path-key. A PCE that 241 is unable to retain information about previously used path-key 242 values over a restart SHOULD use some other mechanism to guarantee 243 uniqueness of path-key values such as embedding a timestamp or 244 version number in the path-key. 246 A head-end LSR that is a PCC converts the path returned by a PCE 247 into an explicit route object (ERO) that it includes in the 248 Resource Reservation Protocol (RSVP) Path message. If the path 249 returned by the PCE contains a PKS, this is included in the ERO. 250 Like any other subobjects, the PKS is passed transparently from 251 hop to hop, until it becomes the first subobject in the ERO. This 252 will occur at the start of the CPS which will usually be the 253 domain boundary. The PKS MUST be preceded by an ERO subobject that 254 identifies the LSR that must expand the PKS. This means that 255 (following the rules for ERO processing set out in [RFC3209]) 256 the PKS will not be encountered in ERO processing until the ERO is 257 being processed by the LSR that is capable of correctly handling the 258 PKS. 260 An LSR that encounters a PKS when trying to identify the next-hop 261 retrieves the PCE-ID from the PKS and sends a Path Computation 262 Request (PCReq) message as defined in [PCEP] to the PCE identified 263 by the PCE-ID that contains the path-key object . 265 Upon receiving the PCReq message, the PCE identifies the computed 266 path segment using the supplied path-key, and returns the 267 previously computed path segment in the form of explicit hops 268 using an ERO object contained in the Path Computation Reply 269 (PCReqp) to the requesting node as defined in [PCEP]. The 270 requesting node inserts the explicit hops into the ERO and 271 continues to process the TE LSP setup as per [RFC3209]. 273 2.2. Example 275 Figure 1 shows a simple two-AS topology with a PCE responsible 276 for the path computations in each AS. An LSP is requested from 277 the ingress LSR in one AS to the egress LSR in the other AS. The 278 ingress, acting as PCC, sends a path computation request to PCE- 279 1. PCE-1 is unable to compute an end-to-end path and invokes PCE- 280 2 (possibly using the techniques described in [BRPC]). PCE-2 281 computes a path segment from ASBR-2 to the egress as {ASBR-2, C, 282 D, Egress}. It could pass this path segment back to PCE-1 in 283 full, or it could send back the path {ASBR-2, Egress} where the 284 second hop is a loose hop. 286 However, in order to protect the confidentiality of the topology 287 in the second AS while still specifying the path in full, PCE-2 288 may send PCE-1 a path segment expressed as {ASBR-2, PKS, Egress} 289 where the PKS is a Path Key Subobject as defined in this 290 document. In this case, PCE-2 has identified the segment {ASBR-2, 291 C, D, Egress} as a Confidential Path Segment (CPS). PCE-1 will 292 compute the path segment that it is responsible for, and will 293 supply the full path to the PCC as {Ingress, A, B, ASBR-1, ASBR- 294 2, PKS, Egress}. 296 Signaling proceeds in the first AS as normal, but when the Path 297 message reaches ASBR-2 the next hop is the PKS, and this must be 298 expanded before signaling can progress further. ASBR-2 uses the 299 information in the PKS to request PCE-2 for a path segment, and 300 PCE-2 will return the segment {ASBR-2, C, D, Egress} allowing 301 signaling to continue to set up the LSP. 303 ----------------------------- ---------------------------- 304 | ------- | | ------- | 305 | | PCE-1 |<---------------+--+-->| PCE-2 | | 306 | ------- | | ------- | 307 | ^ | | ^ | 308 | | | | | | 309 | v | | v | 310 | ------- ---- | | ---- | 311 | | PCC | - - |ASBR| | | |ASBR| - - ------ | 312 | |Ingress|--|A|--|B|--| 1 |-+--+-| 2 |--|C|--|D|--|Egress| | 313 | ------- - - ----- | | ---- - - ------ | 314 | | | | 315 ----------------------------- ---------------------------- 317 Figure 1 : A Simple network to demonstrate the use of the PKS 319 3. PCEP Protocol Extensions 321 3.1. Path Keys in PCRep Messages 323 Path Keys are carried in PCReq and PCRep messages as part of the 324 various objects that carry path definitions. In particular, a Path 325 Key is carried in the Explicit Route Object (ERO) on PCRep 326 messages. 328 In all cases, the Path Key is carried in a Path Key Subobject 329 (PKS). 331 The PKS is a fixed-length subobject containing a Path-Key and a 332 PCE-ID. The Path Key is an identifier, or token used to represent 333 the CPS within the context of the PCE identified by the PCE-ID. 334 The PCE-ID identifies the PCE that can decode the Path Key using 335 an identifier that is unique within the domain that the PCE 336 serves. The PCE-ID has to be mapped to a reachable IPv4 or IPv6 337 address of the PCE by the first node of the CPS (usually a domain 338 border router) and a PCE MAY use one of its reachable IP addresses 339 as its PCE-ID. Alternatively and to provide greater security (see 340 Section 5) or increased confidentiality, according to domain-local 341 policy, the PCE MAY use some other identifier that is scoped only 342 within the domain. 344 To allow IPv4 and IPv6 addresses to be carried, two subobjects are 345 defined as follows. 347 The Path Key Subobject may be present in the PCEP ERO or the PCEP 348 PATH-KEY object (see Section 3.2). 350 3.1.1. PKS with 32-bit PCE ID 352 The Subobject Type for the PKS with 32-bit PCE ID is to be 353 assigned by IANA (recommended value 64). The format of this 354 subobject is as follows: 356 0 1 2 3 357 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 1 358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 359 |L| Type | Length | Path Key | 360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 361 | PCE ID (4 bytes) | 362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 364 L 366 The L bit SHOULD NOT be set, so that the subobject represents a 367 strict hop in the explicit route. 369 Type 371 Subobject Type for a Path Key with 32-bit PCE ID as assigned by 372 IANA. 374 Length 376 The Length contains the total length of the subobject in bytes, 377 including the Type and Length fields. The Length is always 8. 379 PCE ID 381 A 32-bit identifier of the PCE that can decode this key. The 382 identifier MUST be unique within the scope of the domain that 383 the CPS crosses, and MUST be understood by the LSR that will 384 act as PCC for the expansion of the PKS. The interpretation of 385 the PCE-ID is subject to domain-local policy. It MAY be an IPv4 386 address of the PCE that is always reachable, and MAY be an 387 address that is restricted to the domain in which the LSR that 388 is called upon to expand the CPS lies. Other values that have 389 no meaning outside the domain (for example, the Router ID of 390 the PCE) MAY be used to increase security or confidentiality 391 (see Section 5). 393 3.1.2. PKS with 128-bit PCE ID 395 The Subobject Type for the PKS with 128-bit PCE ID is to be 396 assigned by IANA (recommended value 65). The format of the 397 subobject is as follows. 399 0 1 2 3 400 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 1 401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 402 |L| Type | Length | Path Key | 403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 404 | PCE ID (16 bytes) | 405 | | 406 | | 407 | | 408 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 410 L 412 As above. 414 Type 416 Subobject Type for a Path Key with 128-bit PCE ID as assigned 417 by IANA. 419 Length 421 The Length contains the total length of the subobject in bytes, 422 including the Type and Length fields. The Length is always 20. 424 PCE ID 426 A 128-bit identifier of the PCE that can decode this key. The 427 identifier MUST be unique within the scope of the domain that 428 the CPS crosses, and MUST be understood by the LSR that will 429 act as PCC for the expansion of the PKS. The interpretation of 430 the PCE-ID is subject to domain-local policy. It MAY be an IPv6 431 address of the PCE that is always reachable, but MAY be an 432 address that is restricted to the domain in which the LSR that 433 is called upon to expand the CPS lies. Other values that have 434 no meaning outside the domain (for example, the IPv6 TE Router 435 ID) MAY be used to increase security (see Section 5). 437 3.2. Unlocking Path Keys 439 When a network node needs to decode a Path Key so that it can 440 continue signaling for an LSP, it must send a PCReq to the 441 designated PCE. The PCReq defined in [PCEP] needs to be modified 442 to support this usage which differs from the normal path 443 computation request. To that end, a new flag is defined to show 444 that the PCReq relates to the expansion of a PKS, and a new object 445 is defined to carry the PKS in the PCReq. These result in an 446 update to the BNF for the message. 448 3.2.1. Path Key Bit 450 [PCEP] defines the Request Parameters (RP) object that is used to 451 specify various characteristics of the path computation request 452 (PCReq). 454 In this document we define a new bit named the Path Key bit as 455 follows. See Section 7.3 for the IANA assignment of the 456 appropriate bit number. 458 Path Key bit: When set, the requesting PCC requires the retrieval 459 of a Confidential Path Segment that corresponds to the PKS carried 460 in a PATH_KEY object in the path computation request. The Path Key 461 bit MUST be cleared when the path computation request is not 462 related to a CPS retrieval. 464 3.2.2. PATH-KEY Object 466 When a PCC needs to expand a path-key in order to expand a CPS it 467 issues a path computation request (PCReq) to the PCE identified in 468 the PKS in the RSVP-TE ERO that it is processing. The PCC supplies 469 the PKS to be expanded in a PATH-KEY Object in the PCReq message. 471 The PATH-KEY Object is defined as follows. 473 PATH-KEY Object-Class is to be assigned by IANA (recommended 474 value=16) 476 Path Key Object-Type is to be assigned by IANA (recommended 477 value=1) 479 The PATH-KEY Object MUST contain at least one Path Key Subobject 480 (see Section 3.1). The first PKS MUST be processed by the PCE. 481 Subsequent subobjects SHOULD be ignored. 483 3.2.3. Path Computation Request (PCReq) message with Path Key 485 The format of a PCReq message including a PATH-KEY object is 486 unchanged as follows: 488 ::= 489 [] 490 492 where: 493 ::=[] 494 ::=[] 496 To support the use of the message to expand a PKS, the definition 497 of is modified as follows : 499 ::= 500 | 502 where: 503 ::= 504 [] 505 [] 506 [] 507 [] 508 [] 509 [] 510 [] 511 ::= 513 Thus, the format of the message for use in normal path computation 514 is unmodified. 516 4. PCEP Mode of Operation for Path Key Expansion 518 The retrieval of the explicit path (the CPS) associated with a PKS 519 by a PCC is no different than any other path computation request 520 with the exception that the PCReq message MUST contain a PATH_KEY 521 object and the Path Key bit of the RP object MUST the set. On 522 receipt of a PCRep containing a CPS, the requesting PCC SHOULD 523 use insert the CPS into the ERO that it will signal, in accordance 524 with local policy. 526 If the receiving PCE does not recognize itself as identified by the 527 PCE ID carried in the PKS it MAY forward the PCReq message to 528 another PCE according to local policy. If the PCE does not forward 529 such a PCReq, it MUST respond with a PCRep message containing a NO- 530 PATH object. 532 If the receiving PCE recognizes itself, but cannot find the 533 related CPS, or if the retrieval of the CPS is not allowed by 534 policy, the PCE MUST send a PCRep message that contains a NO-PATH 535 object. The NO-PATH-VECTOR TLV SHOULD be used as described in 536 [PCEP] and a new bit-number (see Section 7.4) is assigned to 537 indicate "Cannot expand PKS". 539 Upon receipt of a negative reply, the requesting LSR MUST fail the 540 LSP setup and SHOULD use the procedures associated with loose hop 541 expansion failure [RFC3209]. 543 5. Security Considerations 545 This document describes tunneling confidential path information 546 across an untrusted domain (such as an AS). There are many 547 security considerations that apply to PCEP and RSVP-TE. 549 Issues include: 551 - Confidentiality of the CPS (can other network elements probe for 552 expansion of path-keys, possibly at random?). 554 - Authenticity of the path-key (resilience to alteration by 555 intermediaries, resilience to fake expansion of path-keys). 557 - Resilience from DoS attacks (insertion of spurious path-keys; 558 flooding of bogus path-key expansion requests). 560 Most of the interactions required by this extension are point to 561 point, can be authenticated and made secure as described in [PCEP] 562 and [RFC3209]. These interactions include the: 564 - PCC->PCE request 565 - PCE->PCE request(s) 566 - PCE->PCE response(s) 567 - PCE->PCC response 568 - LSR->LSR request and response (Note that a rogue LSR could 569 modify the ERO and insert or modify Path Keys. This would 570 result in an LSR (which is downstream in the ERO) sending 571 decode requests to a PCE. This is actually a larger problem 572 with RSVP. The rogue LSR is an existing issue with RSVP and 573 will not be addressed here. 574 - LSR->PCE request. Note that the PCE can check that the LSR 575 requesting the decode is the LSR at the head of the Path Key. 576 This largely contains the previous problem to DoS rather than 577 a security issue. A rogue LSR can issue random decode 578 requests, but these will amount only to DoS. 579 - PCE->LSR response. 581 Thus, the major security issues can be dealt with using standard 582 techniques for securing and authenticating point-to-point 583 communications. In addition, it is recommended that the PCE 584 providing a decode response should check that the LSR that issued 585 the decode request is the head end of the decoded ERO segment. 587 Further protection can be provided by using a PCE ID to identify 588 the decoding PCE that is only meaningful within the domain that 589 contains the LSR at the head of the CPS. This may be an IP address 590 that is only reachable from within the domain, or some not-address 591 value. The former requires configuration of policy on the PCEs, 592 the latter requires domain-wide policy. 594 6. Manageability Considerations 596 6.1. Control of Function Through Configuration and Policy 598 The treatment of a path segment as a CPS, and its substitution in 599 a PCReq ERO with a PKS, is a function that MUST be under operator 600 and policy control where a PCE supports the function. The operator 601 MUST be given the ability to specify which path segments are to be 602 replaced and under what circumstances. For example, an operator 603 might set a policy that states that every path segment for the 604 operator's domain will be replaced by a PKS when the PCReq has 605 been issued from outside the domain. 607 The operation of the PKS extensions require that path-keys are 608 retained by the issuing PCE to be available for retrieval by an 609 LSR (acting as a PCC) at a later date. But it is possible that the 610 retrieval request will never be made, so good housekeeping 611 requires that a timer is run to discard unwanted path-keys. A 612 default value for this timer is suggested in Section 2.1. 613 Implementations SHOULD provide the ability for this value to be over- 614 ridden through operator configuration or policy. 616 After a PKS has been expanded in response to a retrieval request, 617 it may be valuable to retain the path-key and CPS for debug 618 purposes. Such retention SHOULD NOT be the default behavior of an 619 implementation, but MAY be available in response to operator request. 621 Once a path-key has been discarded, the path-key value SHOULD NOT 622 be immediately available for re-use for a new CPS since this might 623 lead to accidental misuse. A default timer value is suggested in 624 Section 2.1. Implementations SHOULD provide the ability for this 625 value to be over-ridden through operator configuration or policy. 627 A PCE must set a PCE-ID value in each PKS it creates so that PCCs 628 can correctly identify it and send PCReq messages to expand the 629 PKS to a path segment. A PCE implementation SHOULD allow operator 630 or policy control of the value to use as the PCE-ID. If the PCE 631 allows PCE-ID values that are not routable addresses to be used, 632 the PCCs MUST be configurable (by the operator or through policy) 633 to allow them to map from the PCE-ID to a routable address of the 634 PCE. Such mapping may be algorithmic, procedural (for example, 635 mapping a PCE-ID equal to the IGP Router ID into a routable 636 address), or configured through a local or remote mapping table. 638 6.2. Information and Data Models 640 A MIB module for PCEP is already defined in [PCEP-MIB]. The 641 configurable items listed in Section 6.1 MUST be added as readable 642 objects in the module and SHOULD be added as writable objects. 644 A new MIB module MUST be created to allow inspection of path-keys. 645 For a given PCE, this MIB module MUST provide a mapping from path- 646 key to path segment (that is, a list of hops), and MUST supply 647 other information including: 649 - The identity of the PCC that issued the original request that 650 led to the creation of the path-key. 651 - The request ID of the original PCReq. 652 - Whether the path-key has been retrieved yet, and if so, by which 653 PCC. 654 - How long until the path segment associated with the path-key 655 will be discarded. 656 - How long until the path-key will be available for re-use. 658 6.3. Liveness Detection and Monitoring 660 The procedures in this document extend PCEP, but do not introduce 661 new interactions between network entities. Thus, no new liveness 662 detection or monitoring is required. 664 It is possible that a head-end LSR that has be given a path 665 including PKSs replacing specific CPSs will want to know whether 666 the path-keys are still valid (or have timed out). However, rather 667 than introduce a mechanism to poll the PCE that is responsible for 668 the PKS, it is considered pragmatic to simply signal the 669 associated LSP. 671 6.4. Verifying Correct Operation 673 The procedures in this document extend PCEP, but do not introduce 674 new interactions between network entities. Thus, no new tools for 675 verifying correct operation are required. 677 A PCE SHOULD maintain counters and logs of the following events 678 that might indicate incorrect operation (or might indicate 679 security issues). 681 - Attempts to expand an unknown path-key. 682 - Attempts to expand an expired path-key. 683 - Duplicate attempts to expand the same path-key. 684 - Expiry of path-key without attempt to expand it. 686 6.5. Requirements on Other Protocols and Functional Components 688 The procedures described in this document require that the LSRs 689 signal PKSs as defined in [RSVP-PKS]. Note that the only changes 690 to LSRs are at the PCCs. Specifically, changes are only needed at 691 the head-end LSRs that build RSVP-TE Path messages containing 692 Path-Key Subobjects in their EROs, and the LSRs that discover such 693 subobjects as next hops and must expand them. Other LSRs in the 694 network, even if they are on the path of the LSP, will not be 695 called upon to process the PKS. 697 6.6. Impact on Network Operation 699 As well as the security and confidentiality aspects addressed by 700 the use of the PKS, there may be some scaling benefits associated 701 with the procedures described in this document. For example, a 702 single PKS in an explicit route may substitute for many subobjects 703 and can reduce the overall message size correspondingly. In some 704 circumstances, such as when the explicit route contains multiple 705 subobjects for each hop (including node IDs, TE link IDs, 706 component link IDs for each direction of a bidirectional LSP, and 707 label IDs for each direction of a bidirectional LSP) or when the 708 LSP is a point-to-multipoint LSP, this scaling improvement may be 709 very significant. 711 Note that a PCE will not supply a PKS unless it is knows that the 712 LSR that will receive the PKS through signaling will be able to 713 handle it. Furthermore, as noted in Section 6.5, only those LSRs 714 specifically called upon to expand the PKS will be required to 715 process the subobjects during signaling. Thus, the only backward 716 compatibility issues associated with the procedures introduced in 717 this document arise when a head-end LSR receives a PCRep with an 718 ERO containing a PKS and does not know how to encode this into 719 signaling. 721 Since the PCE that inserted the PKS requires to keep the CPS 722 confidential, the legacy head-end LSR cannot be protected. It must 723 either fail the LSP setup, or request a new path computation 724 avoiding the domain that has supplied it with unknown subobjects. 726 7. IANA Considerations 728 IANA assigns values to PCEP parameters in registries defined in 729 [PCEP]. IANA is requested to make the following additional 730 assignments. 732 7.1. New Subobjects for the ERO Object 734 IANA has previously assigned an Object-Class and Object-Type to 735 the ERO carried in PCEP messages [PCEP]. IANA also maintains a 736 list of subobject types valid for inclusion in the ERO. 738 IANA is requested to assign two new subobject types for inclusion 739 in the ERO as follows: 741 Subobject Type 742 64 Path Key with 32-bit PCE ID [This.I-D] 743 65 Path Key with 128-bit PCE ID [This.I-D] 745 7.2. New PCEP Object 747 IANA is requested to assign a new object class in the registry of 748 PCEP Objects as follows. 750 Object Name Object Name Reference 751 Class Type 753 16 PATH-KEY 1 Path Key [This.I-D] 755 Subobjects 756 This object may carry the following subobjects as defined 757 for the ERO object. 759 64 Path Key with 32-bit PCE ID [This.I-D] 760 65 Path Key with 128-bit PCE ID [This.I-D] 762 7.3. New RP Object Bit Flag 764 IANA maintains a registry of bit flags carried in the PCEP RP 765 object as defined in [PCEP]. IANA is requested to assign a new bit 766 flag as follows: 768 Bit Hex Name Reference 769 Number 770 15 0x000100 Path Key (P-bit) [This.I-D] 772 7.4. New NO-PATH-VECTOR TLV Bit Flag 774 IANA maintains a registry of bit flags carried in the PCEP NO- 775 PATH-VECTOR TLV in the PCEP NO-PATH object as defined in [PCEP]. 776 IANA is requested to assign a new bit flag as follows: 778 Bits Number Name Flag Reference 779 1 PKS expansion failure [This.I-D] 781 8. Normative References 783 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 784 Requirement Levels", BCP 14, RFC 2119, March 1997. 786 [PCEP] Vasseur, J.P., Le Roux, J.L., Ayyangar, A., Oki, E., 787 Ikejiri, A., Atlas, A., Dolganow, A., "Path Computation 788 Element (PCE) communication Protocol (PCEP)", draft-ietf- 789 pce-pcep, work in progress. 791 9. Informative References 793 [RFC3209] Awduche, Berger, Gan, Li, Srinivasan and Swallow, "RSVP-TE: 794 Extensions to RSVP for LSP Tunnels", RFC 3209, December 795 2001. 797 [RFC4655] Farrel, Vasseur & Ash, "A Path Computation Element (PCE)- 798 Based Architecture", RFC 4655, August 2006. 800 [RSVP-PKS] Bradford, R., Vasseur, J.P., Farrel, A., "RSVP Extensions 801 for Path Key Support", draft-bradford-ccamp-path-key-ero, 802 work in progress. 804 [RFC5152] Vasseur, J., et al "A Per-Domain Path Computation Method 805 for Establishing Inter-Domain Traffic Engineering (TE) 806 Label Switched Paths (LSPs)", RFC 5152, Fenruary 2008. 808 [BRPC] Vasseur, J., et al "A Backward Recursive PCE-based 809 Computation (BRPC) procedure to compute shortest inter- 810 domain Traffic Engineering Label Switched Path", draft- 811 ietf-pce-brpc, work in progress. 813 [RFC4105] Le Roux, J., Vasseur, JP, Boyle, J., "Requirements for 814 Support of Inter-Area and Inter-AS MPLS Traffic 815 Engineering", RFC 4105, June 2005. 817 [RFC4216] Zhang, R., Vasseur, JP., et. al., "MPLS Inter-AS Traffic 818 Engineering requirements", RFC 4216, November 2005. 820 [RFC5298] Takeda, T., et al, "Analysis of Inter-domain Label 821 Switched Path (LSP) Recovery", RFC 5298, August 2008. 823 [PCEP-MIB] Kiran Koushik, A., and Stephan, E., "PCE communication 824 protocol (PCEP) Management Information Base", draft- 825 kkoushik-pce-pcep-mib, work in progress. 827 10. Acknowledgements 829 The authors would like to thank Eiji Oki for his comments on this 830 document. 832 11. Authors' Addresses 834 Rich Bradford (Editor) 835 Cisco Systems, Inc. 836 1414 Massachusetts Avenue 837 Boxborough, MA - 01719 838 USA 839 EMail: rbradfor@cisco.com 841 J.-P Vasseur 842 Cisco Systems, Inc. 843 1414 Massachusetts Avenue 844 Boxborough, MA - 01719 845 USA 846 EMail: jpv@cisco.com 848 Adrian Farrel 849 Old Dog Consulting 850 EMail: adrian@olddog.co.uk 852 Full Copyright Statement 854 Copyright (c) 2008 IETF Trust and the persons identified as the 855 document authors. All rights reserved. 857 This document is subject to BCP 78 and the IETF Trust's Legal 858 Provisions Relating to IETF Documents 859 (http://trustee.ietf.org/license-info) in effect on the date of 860 publication of this document. 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