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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PCE S. Sivabalan 3 Internet-Draft C. Filsfils 4 Intended status: Standards Track Cisco Systems, Inc. 5 Expires: December 31, 2018 J. Tantsura 6 Individual 7 W. Henderickx 8 Nokia 9 J. Hardwick 10 Metaswitch Networks 11 June 29, 2018 13 PCEP Extensions for Segment Routing 14 draft-ietf-pce-segment-routing-12 16 Abstract 18 Segment Routing (SR) enables any head-end node to select any path 19 without relying on a hop-by-hop signaling technique (e.g., LDP or 20 RSVP-TE). It depends only on "segments" that are advertised by Link- 21 State Interior Gateway Protocols (IGPs). A Segment Routed Path can 22 be derived from a variety of mechanisms, including an IGP Shortest 23 Path Tree (SPT), explicit configuration, or a Path Computation 24 Element (PCE). This document specifies extensions to the Path 25 Computation Element Protocol (PCEP) that allow a stateful PCE to 26 compute and initiate Traffic Engineering (TE) paths, as well as a PCC 27 to request a path subject to certain constraints and optimization 28 criteria in SR networks. 30 Requirements Language 32 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 33 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 34 "OPTIONAL" in this document are to be interpreted as described in BCP 35 14 [RFC2119] [RFC8174] when, and only when, they appear in all 36 capitals, as shown here. 38 Status of This Memo 40 This Internet-Draft is submitted in full conformance with the 41 provisions of BCP 78 and BCP 79. 43 Internet-Drafts are working documents of the Internet Engineering 44 Task Force (IETF). Note that other groups may also distribute 45 working documents as Internet-Drafts. The list of current Internet- 46 Drafts is at https://datatracker.ietf.org/drafts/current/. 48 Internet-Drafts are draft documents valid for a maximum of six months 49 and may be updated, replaced, or obsoleted by other documents at any 50 time. It is inappropriate to use Internet-Drafts as reference 51 material or to cite them other than as "work in progress." 53 This Internet-Draft will expire on December 31, 2018. 55 Copyright Notice 57 Copyright (c) 2018 IETF Trust and the persons identified as the 58 document authors. All rights reserved. 60 This document is subject to BCP 78 and the IETF Trust's Legal 61 Provisions Relating to IETF Documents 62 (https://trustee.ietf.org/license-info) in effect on the date of 63 publication of this document. Please review these documents 64 carefully, as they describe your rights and restrictions with respect 65 to this document. Code Components extracted from this document must 66 include Simplified BSD License text as described in Section 4.e of 67 the Trust Legal Provisions and are provided without warranty as 68 described in the Simplified BSD License. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 73 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 74 3. Overview of PCEP Operation in SR Networks . . . . . . . . . . 5 75 4. SR-Specific PCEP Message Extensions . . . . . . . . . . . . . 7 76 5. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 7 77 5.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 7 78 5.1.1. The SR PCE Capability sub-TLV . . . . . . . . . . . . 7 79 5.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . . . 8 80 5.3. ERO . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 81 5.3.1. SR-ERO Subobject . . . . . . . . . . . . . . . . . . 9 82 5.3.2. NAI Associated with SID . . . . . . . . . . . . . . . 11 83 5.4. RRO . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 84 5.5. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 13 85 6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 13 86 6.1. Exchanging the SR PCE Capability . . . . . . . . . . . . 13 87 6.2. ERO Processing . . . . . . . . . . . . . . . . . . . . . 15 88 6.2.1. SR-ERO Validation . . . . . . . . . . . . . . . . . . 15 89 6.2.2. Interpreting the SR-ERO . . . . . . . . . . . . . . . 17 90 6.3. RRO Processing . . . . . . . . . . . . . . . . . . . . . 20 91 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 20 92 8. Management Considerations . . . . . . . . . . . . . . . . . . 21 93 8.1. Controlling the Path Setup Type . . . . . . . . . . . . . 21 94 8.2. Migrating a Network to Use PCEP Segment Routed Paths . . 22 95 8.3. Verification of Network Operation . . . . . . . . . . . . 23 96 8.4. Relationship to Existing Management Models . . . . . . . 24 97 9. Security Considerations . . . . . . . . . . . . . . . . . . . 24 98 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 99 10.1. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . 24 100 10.2. New NAI Type Registry . . . . . . . . . . . . . . . . . 24 101 10.3. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 25 102 10.4. PCEP-Error Object . . . . . . . . . . . . . . . . . . . 25 103 10.5. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 27 104 10.6. New Path Setup Type . . . . . . . . . . . . . . . . . . 27 105 10.7. New Metric Type . . . . . . . . . . . . . . . . . . . . 27 106 10.8. SR PCE Capability Flags . . . . . . . . . . . . . . . . 27 107 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28 108 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 109 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 110 13.1. Normative References . . . . . . . . . . . . . . . . . . 28 111 13.2. Informative References . . . . . . . . . . . . . . . . . 30 112 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 114 1. Introduction 116 Segment Routing (SR) technology leverages the source routing and 117 tunneling paradigms. A source node can choose a path without relying 118 on hop-by-hop signaling protocols such as LDP or RSVP-TE. Each path 119 is specified as a set of "segments" advertised by link-state routing 120 protocols (IS-IS or OSPF). [I-D.ietf-spring-segment-routing] 121 provides an introduction to the SR architecture. The corresponding 122 IS-IS and OSPF extensions are specified in 123 [I-D.ietf-isis-segment-routing-extensions] and 124 [I-D.ietf-ospf-segment-routing-extensions], respectively. The SR 125 architecture defines a "segment" as a piece of information advertised 126 by a link-state routing protocols, e.g., an IGP prefix or an IGP 127 adjacency. Several types of segments are defined. A Node segment 128 represents an ECMP-aware shortest-path computed by IGP to a specific 129 node, and is always identified uniquely within the SR/IGP domain. An 130 Adjacency Segment represents a unidirectional adjacency. An 131 Adjacency Segment is local to the node which advertises it. Both 132 Node segments and Adjacency segments can be used for SR Traffic 133 Engineering (SR-TE). 135 The SR architecture can be implemented using either an MPLS 136 forwarding plane [I-D.ietf-spring-segment-routing-mpls] or an IPv6 137 forwarding plane [I-D.ietf-6man-segment-routing-header]. The MPLS 138 forwarding plane can be applied to SR without any change, in which 139 case an SR path corresponds to an MPLS Label Switching Path (LSP). 140 This document is relevant to the MPLS forwarding plane only. In this 141 document, "Node-SID" and "Adjacency-SID" denote Node Segment 142 Identifier and Adjacency Segment Identifier respectively. 144 A Segment Routed path (SR path) can be derived from an IGP Shortest 145 Path Tree (SPT). SR-TE paths may not follow an IGP SPT. Such paths 146 may be chosen by a suitable network planning tool and provisioned on 147 the ingress node of the SR-TE path. 149 [RFC5440] describes the Path Computation Element Protocol (PCEP) for 150 communication between a Path Computation Client (PCC) and a Path 151 Computation Element (PCE) or between a pair of PCEs. A PCE computes 152 paths for MPLS Traffic Engineering LSPs (MPLS-TE LSPs) based on 153 various constraints and optimization criteria. [RFC8231] specifies 154 extensions to PCEP that allow a stateful PCE to compute and recommend 155 network paths in compliance with [RFC4657] and defines objects and 156 TLVs for MPLS-TE LSPs. Stateful PCEP extensions provide 157 synchronization of LSP state between a PCC and a PCE or between a 158 pair of PCEs, delegation of LSP control, reporting of LSP state from 159 a PCC to a PCE, controlling the setup and path routing of an LSP from 160 a PCE to a PCC. Stateful PCEP extensions are intended for an 161 operational model in which LSPs are configured on the PCC, and 162 control over them is delegated to the PCE. 164 A mechanism to dynamically initiate LSPs on a PCC based on the 165 requests from a stateful PCE or a controller using stateful PCE is 166 specified in [RFC8281]. This mechanism is useful in Software Defined 167 Networking (SDN) applications, such as on-demand engineering, or 168 bandwidth calendaring. 170 It is possible to use a stateful PCE for computing one or more SR-TE 171 paths taking into account various constraints and objective 172 functions. Once a path is chosen, the stateful PCE can initiate an 173 SR-TE path on a PCC using PCEP extensions specified in [RFC8281] 174 using the SR specific PCEP extensions specified in this document. 175 Additionally, using procedures described in this document, a PCC can 176 request an SR path from either a stateful or a stateless PCE. 178 This specification relies on the procedures specified in 179 [I-D.ietf-pce-lsp-setup-type] to exchange the segment routing 180 capability and to specify that the path setup type of an LSP is 181 segment routing. 183 2. Terminology 185 The following terminologies are used in this document: 187 ERO: Explicit Route Object 189 IGP: Interior Gateway Protocol 191 IS-IS: Intermediate System to Intermediate System 192 LSR: Label Switching Router 194 MSD: Maximum SID Depth 196 NAI: Node or Adjacency Identifier 198 OSPF: Open Shortest Path First 200 PCC: Path Computation Client 202 PCE: Path Computation Element 204 PCEP: Path Computation Element Protocol 206 RRO: Record Route Object 208 SID: Segment Identifier 210 SR: Segment Routing 212 SR-TE: Segment Routed Traffic Engineering 214 3. Overview of PCEP Operation in SR Networks 216 In an SR network, the ingress node of an SR path prepends an SR 217 header to all outgoing packets. The SR header consists of a list of 218 SIDs (or MPLS labels in the context of this document). The header 219 has all necessary information so that, in combination with the 220 information distributed by the IGP, the packets can be guided from 221 the ingress node to the egress node of the path; hence, there is no 222 need for any signaling protocol. 224 In PCEP messages, LSP route information is carried in the Explicit 225 Route Object (ERO), which consists of a sequence of subobjects. In 226 SR networks, an ingress node of an SR path prepends an SR header to 227 all outgoing packets. The SR header consists of a list of SIDs (or 228 MPLS labels in the context of this document). SR-TE paths computed 229 by a PCE can be represented in an ERO in one of the following forms: 231 o An ordered set of IP addresses representing network nodes/links: 232 In this case, the PCC needs to convert the IP addresses into the 233 corresponding MPLS labels by consulting its Link State Database 234 (LSDB). 236 o An ordered set of SIDs, with or without the corresponding IP 237 addresses. 239 o An ordered set of MPLS labels and IP addresses: In this case, the 240 PCC needs to convert the IP addresses into the corresponding SIDs 241 by consulting its LSDB. 243 This document defines a new ERO subobject denoted by "SR-ERO 244 subobject" capable of carrying a SID as well as the identity of the 245 node/adjacency represented by the SID. SR-capable PCEP speakers 246 should be able to generate and/or process such ERO subobject. An ERO 247 containing SR-ERO subobjects can be included in the PCEP Path 248 Computation Reply (PCRep) message defined in [RFC5440], the PCEP LSP 249 Initiate Request message (PCInitiate) defined in [RFC8281], as well 250 as in the PCEP LSP Update Request (PCUpd) and PCEP LSP State Report 251 (PCRpt) messages defined in [RFC8231]. 253 When a PCEP session between a PCC and a PCE is established, both PCEP 254 speakers exchange their capabilites to indicate their ability to 255 support SR-specific functionality. 257 An PCE can update an LSP that is initially established via RSVP-TE 258 signaling to use an SR-TE path, by sending a PCUpd to the PCC that 259 delegated the LSP to it ([RFC8231]). Similarly, an LSP initially 260 created with an SR-TE path can be updated to use RSVP-TE signaling, 261 if necessary. This capability is useful when a network is migrated 262 from RSVP-TE to SR-TE technology. 264 A PCC MAY include an RRO containing the recorded LSP in PCReq and 265 PCRpt messages as specified in [RFC5440] and [RFC8231], respectively. 266 This document defines a new RRO subobject for SR networks. The 267 methods used by a PCC to record the SR-TE LSP are outside the scope 268 of this document. 270 In summary, this document: 272 o Defines a new ERO subobject, a new RRO subobject and new PCEP 273 error codes. 275 o Specifies how two PCEP speakers can establish a PCEP session that 276 can carry information about SR-TE paths. 278 o Specifies processing rules for the ERO subobject. 280 o Defines a new path setup type to be used in the PATH_SETUP_TYPE 281 and PATH_SETUP_TYPE_CAPABILITY TLVs 282 ([I-D.ietf-pce-lsp-setup-type]). 284 o Defines a new sub-TLV for the PATH_SETUP_TYPE_CAPABILITY TLV. 286 The extensions specified in this document complement the existing 287 PCEP specifications to support SR-TE paths. As such, the PCEP 288 messages (e.g., Path Computation Request, Path Computation Reply, 289 Path Computation Report, Path Computation Update, Path Computation 290 Initiate, etc.,) MUST be formatted according to [RFC5440], [RFC8231], 291 [RFC8281], and any other applicable PCEP specifications. 293 4. SR-Specific PCEP Message Extensions 295 As defined in [RFC5440], a PCEP message consists of a common header 296 followed by a variable length body made up of mandatory and/or 297 optional objects. This document does not require any changes in the 298 format of the PCReq and PCRep messages specified in [RFC5440], 299 PCInitiate message specified in [RFC8281], and PCRpt and PCUpd 300 messages specified in [RFC8231]. 302 5. Object Formats 304 5.1. The OPEN Object 306 5.1.1. The SR PCE Capability sub-TLV 308 This document defines a new Path Setup Type (PST) for SR, as follows: 310 o PST = 1: Path is setup using Segment Routing Traffic Engineering. 312 A PCEP speaker SHOULD indicate its support of the function described 313 in this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV in the 314 OPEN object with this new PST included in the PST list. 316 This document also defines the SR-PCE-CAPABILITY sub-TLV. PCEP 317 speakers use this sub-TLV to exchange information about their SR 318 capability. If a PCEP speaker includes PST=1 in the PST List of the 319 PATH-SETUP-TYPE-CAPABILITY TLV then it MUST also include the SR-PCE- 320 CAPABILITY sub-TLV inside the PATH-SETUP-TYPE-CAPABILITY TLV. 322 The format of the SR-PCE-CAPABILITY sub-TLV is shown in the following 323 figure: 325 0 1 2 3 326 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 1 327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 328 | Type=26 | Length=4 | 329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 330 | Reserved | Flags |N|L| MSD | 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 Figure 1: SR-PCE-CAPABILITY sub-TLV format 335 The code point for the TLV type is 26. The TLV length is 4 octets. 337 The 32-bit value is formatted as follows. The "Maximum SID Depth" (1 338 octet) field (MSD) specifies the maximum number of SIDs (MPLS label 339 stack depth in the context of this document) that a PCC is capable of 340 imposing on a packet. The "Reserved" (2 octets) field is unused, and 341 MUST be set to zero on transmission and ignored on reception. The 342 "Flags" field is 1 octet long, and this document defines the 343 following flags: 345 o L flag: A PCC sets this flag to 1 to indicate that it does not 346 impose any limit on the MSD. 348 o N flag: A PCC sets this flag to 1 to indicate that it is capable 349 of resolving a Node or Adjacency Identifier (NAI) to a SID. 351 5.2. The RP/SRP Object 353 To set up an SR-TE LSP using SR, the RP or SRP object MUST include 354 the PATH-SETUP-TYPE TLV, specified in [I-D.ietf-pce-lsp-setup-type], 355 with the PST set to 1 (path setup using SR-TE). 357 The LSP-IDENTIFIERS TLV MAY be present for the above PST type. 359 5.3. ERO 361 An SR-TE path consists of one or more SIDs where each SID MAY be 362 associated with the identifier that represents the node or adjacency 363 corresponding to the SID. This identifier is referred to as the 364 'Node or Adjacency Identifier' (NAI). As described later, a NAI can 365 be represented in various formats (e.g., IPv4 address, IPv6 address, 366 etc). Furthermore, a NAI is used for troubleshooting purposes and, 367 if necessary, to derive SID value as described below. 369 The ERO specified in [RFC5440] is used to carry SR-TE path 370 information. In order to carry SID and/or NAI, this document defines 371 a new ERO subobject referred to as "SR-ERO subobject" whose format is 372 specified in the following section. An ERO carrying an SR-TE path 373 consists of one or more ERO subobjects, and MUST carry only SR-ERO 374 subobjects. Note that an SR-ERO subobject does not need to have both 375 SID and NAI. However, at least one of them MUST be present. 377 When building the MPLS label stack from ERO, a PCC MUST assume that 378 SR-ERO subobjects are organized as a last-in-first-out stack. The 379 first subobject relative to the beginning of ERO contains the 380 information about the topmost label. The last subobject contains 381 information about the bottommost label. 383 5.3.1. SR-ERO Subobject 385 An SR-ERO subobject consists of a 32-bit header followed by the SID 386 and/or the NAI associated with the SID. The SID is a 32-bit number. 387 The size of the NAI depends on its respective type, as described in 388 the following sections. At least one of the SID and the NAI MUST be 389 included in the SR-ERO subobject, and both MAY be included. 391 0 1 2 3 392 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 1 393 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 394 |L| Type=36 | Length | NT | Flags |F|S|C|M| 395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 396 | SID (optional) | 397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 398 // NAI (variable, optional) // 399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 401 Figure 2: SR-ERO Subobject format 403 The fields in the SR-ERO Subobject are as follows: 405 The 'L' Flag indicates whether the subobject represents a loose-hop 406 in the LSP [RFC3209]. If this flag is set to zero, a PCC MUST NOT 407 overwrite the SID value present in the SR-ERO subobject. 408 Otherwise, a PCC MAY expand or replace one or more SID values in 409 the received SR-ERO based on its local policy. 411 Type is set to 36. 413 Length contains the total length of the subobject in octets, 414 including the L, Type and Length fields. The Length MUST be at 415 least 8, and MUST be a multiple of 4. As mentioned earlier, an 416 SR-ERO subobject MUST contain at least one of a SID or an NAI. 418 The length should include the SID and NAI fields if and only if 419 they are not absent. The flags described below indicate whether 420 the SID or NAI fields are absent. 422 NAI Type (NT) indicates the type and format of the NAI associated 423 with the SID contained in the object body. This document 424 describes the following NT values: 426 NT=0 The NAI is absent. 428 NT=1 The NAI is an IPv4 node ID. 430 NT=2 The NAI is an IPv6 node ID. 432 NT=3 The NAI is an IPv4 adjacency. 434 NT=4 The NAI is an IPv6 adjacency. 436 NT=5 The NAI is an unnumbered adjacency with IPv4 node IDs. 438 Flags is used to carry additional information pertaining to the SID. 439 This document defines the following flag bits. The other bits 440 MUST be set to zero by the sender and MUST be ignored by the 441 receiver. 443 * M: If this bit is set to 1, the SID value represents an MPLS 444 label stack entry as specified in [RFC3032]. Otherwise, the 445 SID value is an administratively configured value which acts as 446 an index into an MPLS label space. 448 * C: If the M bit and the C bit are both set to 1, then the TC, 449 S, and TTL fields in the MPLS label stack entry are specified 450 by the PCE. However, a PCC MAY choose to override these values 451 according its local policy and MPLS forwarding rules. If the M 452 bit is set to 1 but the C bit is set to zero, then the TC, S, 453 and TTL fields MUST be ignored by the PCC. The PCC MUST set 454 these fields according to its local policy and MPLS forwarding 455 rules. If the M bit is set to zero then the C bit MUST be set 456 to zero. 458 * S: When this bit is set to 1, the SID value in the subobject 459 body is absent. In this case, the PCC is responsible for 460 choosing the SID value, e.g., by looking up in its LSDB using 461 the NAI which, in this case, MUST be present in the subobject. 462 If the S bit is set to 1 then the M and C bits MUST be set to 463 zero. 465 * F: When this bit is set to 1, the NAI value in the subobject 466 body is absent. The F bit MUST be set to 1 if NT=0, and 467 otherwise MUST be set to zero. The S and F bits MUST NOT both 468 be set to 1. 470 SID is the Segment Identifier. 472 NAI contains the NAI associated with the SID. The NAI's format 473 depends on the value in the NT field, and is described in the 474 following section. 476 5.3.2. NAI Associated with SID 478 This document defines the following NAIs: 480 'IPv4 Node ID' is specified as an IPv4 address. In this case, the 481 NT value is 1. 483 'IPv6 Node ID' is specified as an IPv6 address. In this case, the 484 NT value is 2. 486 'IPv4 Adjacency' is specified as a pair of IPv4 addresses. In this 487 case, the NT value is 3. The format of the NAI is shown in the 488 following figure: 490 0 1 2 3 491 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 1 492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 493 | Local IPv4 address | 494 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 495 | Remote IPv4 address | 496 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 498 Figure 3: NAI for IPv4 adjacency 500 'IPv6 Adjacency' is specified as a pair of IPv6 addresses. In this 501 case, the NT value is 4. The format of the NAI is shown in the 502 following figure: 504 0 1 2 3 505 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 1 506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 507 // Local IPv6 address (16 bytes) // 508 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 509 // Remote IPv6 address (16 bytes) // 510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 512 Figure 4: NAI for IPv6 adjacency 514 'Unnumbered Adjacency with IPv4 NodeIDs' is specified as a pair of 515 Node ID / Interface ID tuples. In this case, the NT value is 5. 516 The format of the NAI is shown in the following figure: 518 0 1 2 3 519 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 1 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 | Local Node-ID | 522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 523 | Local Interface ID | 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 | Remote Node-ID | 526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 527 | Remote Interface ID | 528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 Figure 5: NAI for Unnumbered adjacency with IPv4 Node IDs 532 5.4. RRO 534 A PCC can record an SR-TE LSP and report the LSP to a PCE via the 535 RRO. An RRO contains one or more subobjects called "SR-RRO 536 subobjects" whose format is shown below: 538 0 1 2 3 539 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 1 540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 541 | Type=36 | Length | NT | Flags |F|S|C|M| 542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 543 | SID | 544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 545 // NAI (variable) // 546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 548 Figure 6: SR-RRO Subobject format 550 The format of the SR-RRO subobject is the same as that of the SR-ERO 551 subobject, but without the L flag. 553 A PCC MUST assume that the SR-RRO subobjects are organized such that 554 the first subobject relative to the beginning of the RRO contains the 555 information about the topmost label, and the last subobject contains 556 information about the bottommost label of the SR-TE LSP. 558 5.5. METRIC Object 560 If a PCEP session is established with an MSD value of zero, then the 561 PCC MAY specify the MSD for an individual path computation request 562 using the METRIC object defined in [RFC5440]. This document defines 563 a new type for the METRIC object to be used for this purpose as 564 follows: 566 o T = 11: Maximum SID Depth of the requested path. 568 The PCC sets the metric-value to the MSD for this path. The PCC MUST 569 set the B (bound) bit to 1 in the METRIC object, which specifies that 570 the SID depth for the computed path MUST NOT exceed the metric-value. 572 If a PCEP session is established with a non-zero MSD value, then the 573 PCC MUST NOT send an MSD METRIC object. If the PCE receives a path 574 computation request with an MSD METRIC object on a session with a 575 non-zero MSD value then it MUST consider the request invalid and send 576 a PCErr with Error-Type = 10 ("Reception of an invalid object") and 577 Error-Value 9 ("Default MSD is specified for the PCEP session"). 579 6. Procedures 581 6.1. Exchanging the SR PCE Capability 583 A PCC indicates that it is capable of supporting the head-end 584 functions for SR-TE LSP by including the SR-PCE-CAPABILITY sub-TLV in 585 the Open message that it sends to a PCE. A PCE indicates that it is 586 capable of computing SR-TE paths by including the SR-PCE-CAPABILITY 587 sub-TLV in the Open message that it sends to a PCC. 589 If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV with a 590 PST list containing PST=1, and supports that path setup type, then it 591 checks for the presence of the SR-PCE-CAPABILITY sub-TLV. If that 592 sub-TLV is absent, then the PCEP speaker MUST send a PCErr message 593 with Error-Type 10 (Reception of an invalid object) and Error-Value 594 TBD1 (to be assigned by IANA) (Missing PCE-SR-CAPABILITY sub-TLV) and 595 MUST then close the PCEP session. If a PCEP speaker receives a PATH- 596 SETUP-TYPE-CAPABILITY TLV with a SR-PCE-CAPABILITY sub-TLV, but the 597 PST list does not contain PST=1, then the PCEP speaker MUST ignore 598 the SR-PCE-CAPABILITY sub-TLV. 600 If a PCC sets the N flag to 1, then the PCE MAY send NAI to the PCC 601 within the SR-ERO subobject (see Section 6.2). Otherwise, the PCE 602 MUST NOT send NAI to the PCC. 604 The number of SIDs that can be imposed on a packet depends on the 605 PCC's data plane's capability. If a PCC sets the L flag to 1 then 606 the MSD is not used and MUST be set to zero. If a PCE receives an 607 SR-PCE-CAPABILITY sub-TLV with the L flag set to 1 then it MUST 608 ignore the MSD field and MUST assume that the sender can impose a SID 609 stack of any depth. If a PCC sets the L flag to zero, then it sets 610 the MSD field to the maximum number of SIDs that it can impose on a 611 packet. If a PCE receives an SR-PCE-CAPABILITY sub-TLV with the L 612 flag and MSD both set to zero then it MUST assume that the PCC is not 613 capable of imposing a SID stack of any depth and hence is not SR-TE 614 capable, unless it learns a non-zero MSD for the PCC through some 615 other means. 617 Note that the MSD value exchanged via the SR-PCE-CAPABILITY sub-TLV 618 indicates the SID/label imposition limit for the PCC node. However, 619 if a PCE learns the MSD value of a PCC node via different means, e.g 620 routing protocols, as specified in: 621 [I-D.ietf-isis-segment-routing-msd]; 622 [I-D.ietf-ospf-segment-routing-msd]; 623 [I-D.ietf-idr-bgp-ls-segment-routing-msd], then it ignores the MSD 624 value in the SR-PCE-CAPABILITY sub-TLV. Furthermore, whenever a PCE 625 learns the MSD for a link via different means, it MUST use that value 626 for that link regardless of the MSD value exchanged in the SR-PCE- 627 CAPABILITY sub-TLV. 629 Once an SR-capable PCEP session is established with a non-zero MSD 630 value, the corresponding PCE MUST NOT send SR-TE paths with a number 631 of SIDs exceeding that MSD value. If a PCC needs to modify the MSD 632 value, it MUST close the PCEP session and re-establish it with the 633 new MSD value. If a PCEP session is established with a non-zero MSD 634 value, and the PCC receives an SR-TE path containing more SIDs than 635 specified in the MSD value, the PCC MUST send a PCErr message with 636 Error-Type 10 (Reception of an invalid object) and Error-Value 3 637 (Unsupported number of Segment ERO subobjects). If a PCEP session is 638 established with an MSD value of zero, then the PCC MAY specify an 639 MSD for each path computation request that it sends to the PCE, by 640 including a "maximum SID depth" metric object on the request, as 641 defined in Section 5.5. 643 The N flag, L flag and MSD value inside the SR-PCE-CAPABILITY sub-TLV 644 are meaningful only in the Open message sent from a PCC to a PCE. As 645 such, a PCE MUST set the N flag to zero, the L flag to 1 and MSD 646 value to zero in an outbound message to a PCC. Similarly, a PCC MUST 647 ignore any MSD value received from a PCE. If a PCE receives multiple 648 SR-PCE-CAPABILITY sub-TLVs in an Open message, it processes only the 649 first sub-TLV received. 651 6.2. ERO Processing 653 6.2.1. SR-ERO Validation 655 If a PCC does not support the SR PCE Capability and thus cannot 656 recognize the SR-ERO or SR-RRO subobjects, it will respond according 657 to the rules for a malformed object per [RFC5440]. 659 On receiving an SR-ERO, a PCC MUST validate that the Length field, 660 the S bit, the F bit and the NT field are consistent, as follows. 662 o If NT=0, the F bit MUST be 1, the S bit MUST be zero and the 663 Length MUST be 8. 665 o If NT=1, the F bit MUST be zero. If the S bit is 1, the Length 666 MUST be 8, otherwise the Length MUST be 12. 668 o If NT=2, the F bit MUST be zero. If the S bit is 1, the Length 669 MUST be 20, otherwise the Length MUST be 24. 671 o If NT=3, the F bit MUST be zero. If the S bit is 1, the Length 672 MUST be 12, otherwise the Length MUST be 16. 674 o If NT=4, the F bit MUST be zero. If the S bit is 1, the Length 675 MUST be 36, otherwise the Length MUST be 40. 677 o If NT=5, the F bit MUST be zero. If the S bit is 1, the Length 678 MUST be 20, otherwise the Length MUST be 24. 680 If a PCC finds that the NT field, Length field, S bit and F bit are 681 not consistent, it MUST consider the entire ERO invalid and MUST send 682 a PCErr message with Error-Type = 10 ("Reception of an invalid 683 object") and Error-Value = 11 ("Malformed object"). 685 If a PCC does not recognise or support the value in the NT field, it 686 MUST consider the entire ERO invalid and MUST send a PCErr message 687 with Error-Type = 10 ("Reception of an invalid object") and Error- 688 Value = TBD2 ("Unsupported NAI Type in Segment ERO subobject"). 690 If a PCC receives an SR-ERO subobject in which the S and F bits are 691 both set to 1 (that is, both the SID and NAI are absent), it MUST 692 consider the entire ERO invalid and send a PCErr message with Error- 693 Type = 10 ("Reception of an invalid object") and Error-Value = 6 694 ("Both SID and NAI are absent in SR-ERO subobject"). 696 If a PCC receives an SR-ERO subobject in which the S bit is set to 1 697 and the F bit is set to zero (that is, the SID is absent and the NAI 698 is present), but the PCC does not support NAI resolution, it MUST 699 consider the entire ERO invalid and send a PCErr message with Error- 700 Type = 4 ("Not supported object") and Error-Value = 4 ("Unsupported 701 parameter"). 703 If a PCC receives an SR-ERO subobject in which the S bit is set to 1 704 and either or both of the M or C bits is set to 1, it MUST consider 705 the entire ERO invalid and send a PCErr message with Error-Type = 10 706 ("Reception of an invalid object") and Error-Value = 11 ("Malformed 707 object"). 709 If a PCC receives an SR-ERO subobject in which the S bit is set to 710 zero and the M bit is set to 1 (that is, it represents an MPLS label 711 value), its value (20 most significant bits) MUST be larger than 15, 712 unless it is a special purpose label, such as an Entropy Label 713 Indicator (ELI). If a PCC receives an invalid MPLS label value, it 714 MUST send a PCErr message with Error-Type = 10 ("Reception of an 715 invalid object") and Error Value = 2 ("Bad label value"). 717 If both M and C bits of an SR-ERO subobject are set to 1, and if a 718 PCC finds erroneous setting in one or more of TC, S, and TTL fields, 719 it MAY overwrite those fields with values chosen according to its own 720 policy. If the PCC does not overwite them, it MUST send a PCErr 721 message with Error-Type = 10 ("Reception of an invalid object") and 722 Error-Value = 4 ("Bad label format"). 724 If the M bit of an SR-ERO subobject is set to zero but the C bit is 725 set to 1, then the PCC MUST consider the entire ERO invalid and MUST 726 send a PCErr message with Error-Type = 10 ("Reception of an invalid 727 object") and Error-Value = 11 ("Malformed object"). 729 If the first SR-ERO represents an MPLS label value then the NAI field 730 MUST NOT be absent (that is, the F bit MUST be zero). The PCC needs 731 the NAI field to determine the first hop router in the segment routed 732 path. If the NAI is not present then the PCC MUST send a PCErr 733 message with Error-Type = 10 ("Reception of an invalid object") and 734 Error Value = TBD9 ("Cannot derive a next hop from SR-ERO"). 736 If a PCC receives an SR-ERO subobject in which the S bit is set to 737 zero and the M bit is set to zero (that is, it represents an index 738 value), then the SID MUST be a node-SID, an adjacency-SID or a 739 binding-SID. If the SID is not one of these types, the PCC MUST send 740 a PCErr message with Error-Type = 10 ("Reception of an invalid 741 object") and Error Value = TBD10 ("Bad SID type in SR-ERO"). If the 742 SID is an Adjacency-SID then the L flag MUST NOT be set. If the L 743 flag is set for an Adjacency-SID then the PCC MUST send a PCErr 744 message with Error-Type = 10 ("Reception of an invalid object") and 745 Error-Value = 11 ("Malformed object"). 747 If a PCC detects that the subobjects of an ERO are a mixture of SR- 748 ERO subobjects and subobjects of other types, then it MUST send a 749 PCErr message with Error-Type = 10 ("Reception of an invalid object") 750 and Error-Value = 5 ("ERO mixes SR-ERO subobjects with other 751 subobject types"). 753 The SR-ERO subobjects can be classified according to whether they 754 contain a SID representing an MPLS label value, a SID representing an 755 index value, or no SID. If a PCC detects that the SR-ERO subobjects 756 are a mixture of more than one of these types, then it MUST send a 757 PCErr message with Error-Type = 10 ("Reception of an invalid object") 758 and Error-Value = TBD11 ("Inconsistent SIDs in SR-ERO subobjects"). 760 6.2.2. Interpreting the SR-ERO 762 The PCC creates a segment routed path by converting the sequence of 763 SR-ERO subobjects into an MPLS label stack plus a next hop. The PCC 764 sends packets along the segment routed path by prepending the MPLS 765 label stack onto the packets and sending the resulting, modified 766 packet to the next hop. The following subsections explain how the 767 PCC converts the SR-ERO subobject sequence to an MPLS label stack and 768 a next hop. 770 6.2.2.1. SR-ERO subobjects contain MPLS Labels 772 If the SR-ERO subobjects contain SIDs with MPLS label values, then 773 proceed as follows: 775 (a) Initialize next_hop to null. Initialize label_stack to an empty 776 label stack. 778 (b) Get the first SR-ERO subobject from the ERO. Append its label 779 value to label_stack, setting the TC, S and TTL fields according 780 to the C bit and/or local policy. Set current_router and 781 next_hop to the router identified by the NAI. If the NAI is 782 absent from the first SR-ERO, then this is an error, and the ERO 783 should have failed the validation checks of Section 6.2.1. 785 (c) Loop through the remaining SR-ERO subobjects. For each SR-ERO 786 subobject, append it to label_stack, setting the TC, S and TTL 787 fields according to the C bit and/or local policy. 789 6.2.2.2. SR-ERO subobjects contain Index SIDs 791 If the SR-ERO subobjects contain SIDs with index values, then proceed 792 as follows: 794 (a) Initialize current_router to the local router. Initialize 795 next_hop to null. Initialize label_stack to an empty label 796 stack. 798 (b) Get the first SR-ERO subobject from the ERO and look the SID 799 index up in the LSDB. 801 * If the SID is a node-SID, set current_router to the node 802 identified by the node-SID, compute the shortest path to that 803 node and set next_hop to the next hop from the shortest path. 804 If next_hop is the router identified by the node-SID, and 805 that router advertised its node-SID with the P flag clear 806 (indicating that PHP is allowed), then do not add a label to 807 label_stack. Otherwise, look up the next_hop router's SRGB 808 in the LSDB. Get the label that is at offset node-SID 809 relative to the SRGB base label and append it to label_stack. 811 * If the SID is an adjacency-SID, set next_hop to the 812 corresponding routing adjacency. Do not add a label the 813 label_stack. Set current_router to the adjacent router. 815 * If the SID is a binding-SID, then append the binding SID's 816 associated label stack to label_stack. Set next_hop to the 817 first hop router in the binding SID tunnel. Set 818 current_router to the router that is the endpoint of the 819 binding-SID tunnel. 821 * Any other type of SID is an error, and the SR-ERO should have 822 failed the validation checks of Section 6.2.1. 824 (c) Loop through the remaining SR-ERO subobjects. For each SR-ERO 825 subobject, look the SID index up in the LSDB. 827 * If the SID is a node-SID, then look up the current_router's 828 SRGB in the LSDB. Get the label that is at offset node-SID 829 relative to the SRGB base label and append it to label_stack. 831 * If the SID is an adjacency-SID, then look up the 832 current_router's SRLB in the LSDB. Get the label that is at 833 offset adjacency-SID relative to the SRLB base label and 834 append it to label_stack. 836 * If the SID is a binding-SID, then look up the 837 current_router's SRGB in the LSDB. Get the label that is at 838 offset binding-SID relative to the SRGB base label and append 839 it to label_stack. 841 * Any other type of SID is an error, and the SR-ERO should have 842 failed the validation checks of Section 6.2.1. 844 6.2.2.3. SR-ERO subobjects contain NAI only 846 If the SR-ERO subobjects do not contain SIDs (that is, contain only 847 NAI), then look each NAI up in the LSDB to find the corresponding SID 848 index. Then proceed as described above for SID index values. 850 6.2.2.4. Handling Errors During SR-ERO Conversion 852 There are several errors that can occur during the process of 853 converting an SR-ERO sequence to an MPLS label stack and a next hop. 854 The PCC deals with them as follows. 856 o If the PCC cannot find a SID index in the LSDB, it MUST send a 857 PCErr message with Error-Type = 10 ("Reception of an invalid 858 object") and Error-Value = TBD3 ("Unknown SID"). 860 o If the PCC cannot find an NAI in the LSDB, it MUST send a PCErr 861 message with Error-Type = 10 ("Reception of an invalid object") 862 and Error-Value = TBD4 ("NAI cannot be resolved to a SID"). 864 o If the PCC cannot find an SRGB in the LSDB, it MUST send a PCErr 865 message with Error-Type = 10 ("Reception of an invalid object") 866 and Error-Value = TBD5 ("Could not find SRGB"). 868 o If the PCC finds that a router's SRGB is not large enough for a 869 SID index value, it MUST send a PCErr message with Error-Type = 10 870 ("Reception of an invalid object") and Error-Value = TBD6 ("SID 871 index exceeds SRGB size"). 873 o If the PCC cannot find an SRLB in the LSDB, it MUST send a PCErr 874 message with Error-Type = 10 ("Reception of an invalid object") 875 and Error-Value = TBD7 ("Could not find SRLB"). 877 o If the PCC finds that a router's SRLB is not large enough for a 878 SID index value, it MUST send a PCErr message with Error-Type = 10 879 ("Reception of an invalid object") and Error-Value = TBD8 ("SID 880 index exceeds SRLB size"). 882 o If the number of labels in label_stack exceeds the maximum number 883 of SIDs that the PCC can impose on the packet, it MUST send a 884 PCErr message with Error-Type = 10 ("Reception of an invalid 885 object") and Error-Value = 3 ("Unsupported number of Segment ERO 886 subobjects"). 888 6.3. RRO Processing 890 The syntax checking rules that apply to the SR-RRO subobject are 891 identical to those of the SR-ERO subobject, except as noted below. 893 If a PCEP speaker receives an SR-RRO subobject in which both SID and 894 NAI are absent, it MUST consider the entire RRO invalid and send a 895 PCErr message with Error-Type = 10 ("Reception of an invalid object") 896 and Error-Value = 7 ("Both SID and NAI are absent in SR-RRO 897 subobject"). 899 If a PCE detects that all subobjects of the RRO are not identical, 900 and if it does not support such an RRO, it MUST send a PCErr message 901 with Error-Type = 10 ("Reception of an invalid object") and Error- 902 Value = 10 ("Non-identical RRO subobjects"). 904 7. Backward Compatibility 906 A PCEP speaker that does not support the SR PCEP capability cannot 907 recognize the SR-ERO or SR-RRO subobjects. As such, it responds 908 according to the rules for a malformed object, per [RFC5440]. 910 Some implementations, which are compliant with an earlier version of 911 this specification, do not send the PATH-SETUP-TYPE-CAPABILITY TLV in 912 their OPEN objects. Instead, to indicate that they support SR, these 913 implementations include the SR-CAPABILITY-TLV as a top-level TLV in 914 the OPEN object. Unfortunately, some of these implementations made 915 it into the field before this document was published in its final 916 form. Therefore, if a PCEP speaker receives an OPEN object in which 917 the SR-CAPABILITY-TLV appears as a top-level TLV, then it MUST 918 interpret this as though the sender had sent a PATH-SETUP-TYPE- 919 CAPABILITY TLV with a PST list of (0, 1) (that is, both RSVP-TE and 920 SR-TE PSTs are supported) and with the SR-CAPABILITY-TLV as a sub- 921 TLV. If a PCEP speaker receives an OPEN object in which both the SR- 922 CAPABILITY-TLV and PATH-SETUP-TYPE-CAPABILITY TLV appear as top-level 923 TLVs, then it MUST ignore the top-level SR-CAPABILITY-TLV and process 924 only the PATH-SETUP-TYPE-CAPABILITY TLV. 926 8. Management Considerations 928 This document adds a new path setup type to PCEP to allow LSPs to be 929 set up using segment routing techniques. This path setup type may be 930 used with PCEP alongside other path setup types, such as RSVP-TE, or 931 it may be used exclusively. 933 8.1. Controlling the Path Setup Type 935 The following factors control which path setup type is used for a 936 given LSP. 938 o The available path setup types are constrained to those that are 939 supported by, or enabled on, the PCEP speakers. The PATH-SETUP- 940 TYPE-CAPABILITY TLV indicates which path setup types a PCEP 941 speaker supports. To use segment routing as a path setup type, it 942 is a prerequisite that the PCC and PCE both include PST=1 in the 943 list of supported path setup types in this TLV, and also include 944 the SR-PCE-CAPABILITY sub-TLV. 946 o When a PCE initiates an LSP, it proposes which path setup type to 947 use by including it in the PATH-SETUP-TYPE TLV in the SRP object 948 of the PCInitiate message. The PCE chooses the path setup type 949 based on the capabilities of the network nodes on the path and on 950 its local policy. The PCC MAY choose to accept the proposed path 951 setup type, or to reject the PCInitiate request, based on its 952 local policy. 954 o When a PCC requests a path for an LSP, it can nominate a preferred 955 path setup type by including it in the PATH-SETUP-TYPE TLV in the 956 RP object of the PCInitiate message. The PCE MAY choose to reply 957 with a path of the requested type, or to reply with a path of a 958 different type, or to reject the request, based on the 959 capabilities of the network nodes on the path and on its local 960 policy. 962 The operator can influence the path setup type as follows. 964 o Implementations MUST allow the operator to enable and disable the 965 segment routing path setup type on a PCEP-speaking device. 966 Implementations MAY also allow the operator to enable and disable 967 the RSVP-TE path setup type. 969 o PCE implementations MUST allow the operator to specify that an LSP 970 should be instantiated using segment routing or RSVP-TE as the 971 proposed path setup type. 973 o PCE implementations MAY allow the operator to configure a 974 preference for the PCE to propose paths using segment routing or 975 RSVP-TE in the absence of a specified path setup type. 977 o PCC implementations MUST allow the operator to specify that a path 978 requested for an LSP nominates segment routing or RSVP-TE as the 979 path setup type. 981 o PCC implementations MAY allow the operator to configure a 982 preference for the PCC to nominate segment routing or RSVP-TE as 983 the path setup type if none is specified for an LSP. 985 o PCC implementations SHOULD allow the operator to configure a PCC 986 to refuse to set up an LSP using an undesired path setup type. 988 8.2. Migrating a Network to Use PCEP Segment Routed Paths 990 This section discusses the steps that the operator takes when 991 migrating a network to enable PCEP to set up paths using segment 992 routing as the path setup type. 994 o The operator enables the segment routing PST on the PCE servers. 996 o The operator enables the segment routing PST on the PCCs. 998 o The operator resets each PCEP session. The PCEP sessions come 999 back up with segment routing enabled. 1001 o If the operator detects a problem, they can roll the network back 1002 to its initial state by disabling the segment routing PST on the 1003 PCEP speakers and resetting the PCEP sessions. 1005 Note that the data plane is unaffected if a PCEP session is reset. 1006 Any LSPs that were set up before the session reset will remain in 1007 place and will still be present after the session comes back up. 1009 An implementation SHOULD allow the operator to manually trigger a 1010 PCEP session to be reset. 1012 An implementation MAY automatically reset a PCEP session when an 1013 operator reconfigures the PCEP speaker's capabilities. However, note 1014 that if the capabilities at both ends of the PCEP session are not 1015 reconfigured simultaneously, then the session could be reset twice, 1016 which could lead to unnecessary network traffic. Therefore, such 1017 implementations SHOULD allow the operator to override this behaviour 1018 and wait instead for a manual reset. 1020 Once segment routing is enabled on a PCEP session, it can be used as 1021 the path setup type for future LSPs. 1023 User traffic is not automatically be migrated from existing LSPs onto 1024 segment routed LSPs just by enabling the segment routing PST in PCEP. 1025 The migration of user traffic from existing LSPs onto segment routing 1026 LSPs is beyond the scope of this document. 1028 8.3. Verification of Network Operation 1030 The operator needs the following information to verify that PCEP is 1031 operating correctly with respect to the segment routing path setup 1032 type. 1034 o An implementation SHOULD allow the operator to view whether the 1035 PCEP speaker sent the segment routing PST capability to its peer. 1036 If the PCEP speaker is a PCC, then the implementation SHOULD also 1037 allow the operator to view the value of the L flag that was sent, 1038 and the value of the MSD field that was sent. 1040 o An implementation SHOULD allow the operator to view whether the 1041 peer sent a the segment routing PST capability. If the peer is a 1042 PCC, then the implementation SHOULD also allow the operator to 1043 view the values of the L flag and MSD fields that the peer sent 1044 sent. 1046 o An implementation SHOULD allow the operator to view whether the 1047 segment routing PST is enabled on the PCEP session. 1049 o If one PCEP speaker advertises the segment routing PST capability, 1050 but the other does not, then the implementation SHOULD create a 1051 log to inform the operator of the capability mismatch. 1053 o An implementation SHOULD allow the operator to view the PST that 1054 was proposed, or requested, for an LSP, and the PST that was 1055 actually used. 1057 o If a PCEP speaker decides to use a different PST to the one that 1058 was proposed, or requested, for an LSP, then the implementation 1059 SHOULD create a log to inform the operator that the expected PST 1060 has not been used. The log SHOULD give the reason for this choice 1061 (local policy, equipment capability etc.) 1063 o If a PCEP speaker rejects a segment routed path, then it SHOULD 1064 create a log to inform the operator, giving the reson for the 1065 decision (local policy, MSD exceeded etc.) 1067 8.4. Relationship to Existing Management Models 1069 The PCEP YANG module [I-D.ietf-pce-pcep-yang] should include: 1071 o advertised PST capabilities and MSD per PCEP session. 1073 o the PST configured for, and used by, each LSP. 1075 The PCEP MIB [RFC7420] could also be updated to include this 1076 information. 1078 9. Security Considerations 1080 The security considerations described in [RFC5440], [RFC8281] and 1081 [I-D.ietf-pce-lsp-setup-type] are applicable to this specification. 1082 No additional security measure is required. 1084 10. IANA Considerations 1086 10.1. PCEP Objects 1088 This document defines a new subobject type for the PCEP explicit 1089 route object (ERO), and a new subobject type for the PCEP record 1090 route object (RRO). The code points for subobject types of these 1091 objects is maintained in the RSVP parameters registry, under the 1092 EXPLICIT_ROUTE and ROUTE_RECORD objects. IANA is requested to 1093 confirm the early allocation of the following code points in the RSVP 1094 Parameters registry for each of the new subobject types defined in 1095 this document. 1097 Object Subobject Subobject Type 1098 --------------------- -------------------------- ------------------ 1099 EXPLICIT_ROUTE SR-ERO (PCEP-specific) 36 1100 ROUTE_RECORD SR-RRO (PCEP-specific) 36 1102 10.2. New NAI Type Registry 1104 IANA is requested to create a new sub-registry within the "Path 1105 Computation Element Protocol (PCEP) Numbers" registry called "PCEP 1106 SR-ERO NAI Types". The allocation policy for this new registry 1107 should be by IETF Review. The new registry should contain the 1108 following values: 1110 Value Description Reference 1112 0 NAI is absent. This document 1113 1 NAI is an IPv4 node ID. This document 1114 2 NAI is an IPv6 node ID. This document 1115 3 NAI is an IPv4 adjacency. This document 1116 4 NAI is an IPv6 adjacency. This document 1117 5 NAI is an unnumbered This document 1118 adjacency with IPv4 node IDs. 1120 10.3. New SR-ERO Flag Registry 1122 IANA is requested to create a new sub-registry, named "SR-ERO Flag 1123 Field", within the "Path Computation Element Protocol (PCEP) Numbers" 1124 registry to manage the Flag field of the SR-ERO subobject. New 1125 values are to be assigned by Standards Action [RFC8126]. Each bit 1126 should be tracked with the following qualities: 1128 o Bit number (counting from bit 0 as the most significant bit) 1130 o Capability description 1132 o Defining RFC 1134 The following values are defined in this document: 1136 Bit Description Reference 1138 0-7 Unassigned 1139 8 NAI is absent (F) This document 1140 9 SID is absent (S) This document 1141 10 SID specifies TC, S This document 1142 and TTL in addition 1143 to an MPLS label (C) 1144 11 SID specifies an MPLS This document 1145 label (M) 1147 10.4. PCEP-Error Object 1149 IANA is requested to confirm the early allocation of the code-points 1150 in the PCEP-ERROR Object Error Types and Values registry for the 1151 following new error-values: 1153 Error-Type Meaning 1154 ---------- ------- 1155 10 Reception of an invalid object. 1157 Error-value = 2: Bad label value 1158 Error-value = 3: Unsupported number 1159 of SR-ERO 1160 subobjects 1161 Error-value = 4: Bad label format 1162 Error-value = 5: ERO mixes SR-ERO 1163 subobjects with 1164 other subobject 1165 types 1166 Error-value = 6: Both SID and NAI 1167 are absent in SR- 1168 ERO subobject 1169 Error-value = 7: Both SID and NAI 1170 are absent in SR- 1171 RRO subobject 1172 Error-value = 9: Default MSD is 1173 specified for the 1174 PCEP session 1175 Error-value = 10: RRO mixes SR-RRO 1176 subobjects with 1177 other subobject 1178 types 1179 Error-value = TBD1: Missing PCE-SR- 1180 CAPABILITY sub-TLV 1181 Error-value = TBD2: Unsupported NAI 1182 Type in SR-ERO 1183 subobject 1184 Error-value = TBD3: Unknown SID 1185 Error-value = TBD4: NAI cannot be 1186 resolved to a SID 1187 Error-value = TBD5: Could not find SRGB 1188 Error-value = TBD6: SID index exceeds 1189 SRGB size 1190 Error-value = TBD7: Could not find SRLB 1191 Error-value = TBD8: SID index exceeds 1192 SRLB size 1193 Error-value = TBD9: Cannot derive a 1194 next hop from SR- 1195 ERO 1196 Error-value = TBD10: Bad SID type in SR- 1197 ERO 1198 Error-value = TBD11: Inconsistent SIDs 1199 in SR-ERO 1200 subobjects 1202 Note to IANA: this draft originally had an early allocation for 1203 Error-value=11 (Malformed object) in the above list. However, we 1204 have since moved the definition of that code point to draft-ietf-pce- 1205 lsp-setup-type and we included an instruction in that draft for you 1206 to update the reference in the indicated registry. Please ensure 1207 that this has happened when you process the present draft. 1209 Note to IANA: some Error-values in the above list were defined after 1210 the early allocation took place, and so do not currently have a code 1211 point assigned. Please assign code points from the indicated 1212 registry and replace each instance of "TBD1", "TBD2" etc. in this 1213 document with the respective code points. 1215 Note to IANA: some of the Error-value descriptive strings above have 1216 changed since the early allocation. Please refresh the registry. 1218 10.5. PCEP TLV Type Indicators 1220 IANA is requested to confirm the early allocation of the following 1221 code point in the PCEP TLV Type Indicators registry. 1223 Value Meaning Reference 1224 ------------------------- ---------------------------- -------------- 1225 26 SR-PCE-CAPABILITY This document 1227 10.6. New Path Setup Type 1229 [I-D.ietf-pce-lsp-setup-type] requests that IANA creates a sub- 1230 registry within the "Path Computation Element Protocol (PCEP) 1231 Numbers" registry called "PCEP Path Setup Types". IANA is requested 1232 to allocate a new code point within this registry, as follows: 1234 Value Description Reference 1235 ------------------------- ---------------------------- -------------- 1236 1 Traffic engineering path is This document 1237 setup using Segment Routing. 1239 10.7. New Metric Type 1241 IANA is requested to confirm the early allocation of the following 1242 code point in the PCEP METRIC object T field registry: 1244 Value Description Reference 1245 ------------------------- ---------------------------- -------------- 1246 11 Segment-ID (SID) Depth. This document 1248 10.8. SR PCE Capability Flags 1250 IANA is requested to create a new sub-registry, named "SR Capability 1251 Flag Field", within the "Path Computation Element Protocol (PCEP) 1252 Numbers" registry to manage the Flag field of the SR-PCE-CAPABILITY 1253 TLV. New values are to be assigned by Standards Action [RFC8126]. 1254 Each bit should be tracked with the following qualities: 1256 o Bit number (counting from bit 0 as the most significant bit) 1257 o Capability description 1258 o Defining RFC 1260 The following values are defined in this document: 1262 Bit Description Reference 1264 0-5 Unassigned 1265 6 Node or Adjacency This document 1266 Identifier (NAI) is 1267 supported (N) 1268 7 Unlimited Maximum SID This document 1269 Depth (L) 1271 11. Contributors 1273 The following people contributed to this document: 1275 - Lakshmi Sharma 1276 - Jan Medved 1277 - Edward Crabbe 1278 - Robert Raszuk 1279 - Victor Lopez 1281 12. Acknowledgements 1283 We thank Ina Minei, George Swallow, Marek Zavodsky, Dhruv Dhody, Ing- 1284 Wher Chen and Tomas Janciga for the valuable comments. 1286 13. References 1288 13.1. Normative References 1290 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 1291 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 1292 "Signaling Maximum SID Depth using Border Gateway Protocol 1293 Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 1294 (work in progress), October 2017. 1296 [I-D.ietf-isis-segment-routing-extensions] 1297 Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., 1298 Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura, 1299 "IS-IS Extensions for Segment Routing", draft-ietf-isis- 1300 segment-routing-extensions-18 (work in progress), June 1301 2018. 1303 [I-D.ietf-isis-segment-routing-msd] 1304 Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 1305 "Signaling MSD (Maximum SID Depth) using IS-IS", draft- 1306 ietf-isis-segment-routing-msd-12 (work in progress), May 1307 2018. 1309 [I-D.ietf-ospf-segment-routing-extensions] 1310 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 1311 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1312 Extensions for Segment Routing", draft-ietf-ospf-segment- 1313 routing-extensions-25 (work in progress), April 2018. 1315 [I-D.ietf-ospf-segment-routing-msd] 1316 Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, 1317 "Signaling MSD (Maximum SID Depth) using OSPF", draft- 1318 ietf-ospf-segment-routing-msd-14 (work in progress), May 1319 2018. 1321 [I-D.ietf-pce-lsp-setup-type] 1322 Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J. 1323 Hardwick, "Conveying path setup type in PCEP messages", 1324 draft-ietf-pce-lsp-setup-type-10 (work in progress), May 1325 2018. 1327 [I-D.ietf-pce-pcep-yang] 1328 Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A 1329 YANG Data Model for Path Computation Element 1330 Communications Protocol (PCEP)", draft-ietf-pce-pcep- 1331 yang-08 (work in progress), June 2018. 1333 [I-D.ietf-spring-segment-routing] 1334 Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., 1335 Litkowski, S., and R. Shakir, "Segment Routing 1336 Architecture", draft-ietf-spring-segment-routing-15 (work 1337 in progress), January 2018. 1339 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1340 Requirement Levels", BCP 14, RFC 2119, 1341 DOI 10.17487/RFC2119, March 1997, 1342 . 1344 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 1345 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 1346 Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, 1347 . 1349 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 1350 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 1351 DOI 10.17487/RFC5440, March 2009, 1352 . 1354 [RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J. 1355 Hardwick, "Path Computation Element Communication Protocol 1356 (PCEP) Management Information Base (MIB) Module", 1357 RFC 7420, DOI 10.17487/RFC7420, December 2014, 1358 . 1360 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1361 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1362 May 2017, . 1364 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 1365 Computation Element Communication Protocol (PCEP) 1366 Extensions for Stateful PCE", RFC 8231, 1367 DOI 10.17487/RFC8231, September 2017, 1368 . 1370 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 1371 Computation Element Communication Protocol (PCEP) 1372 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 1373 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 1374 . 1376 13.2. Informative References 1378 [I-D.ietf-6man-segment-routing-header] 1379 Previdi, S., Filsfils, C., Leddy, J., Matsushima, S., and 1380 d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header 1381 (SRH)", draft-ietf-6man-segment-routing-header-13 (work in 1382 progress), May 2018. 1384 [I-D.ietf-spring-segment-routing-mpls] 1385 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 1386 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 1387 data plane", draft-ietf-spring-segment-routing-mpls-14 1388 (work in progress), June 2018. 1390 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 1391 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 1392 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 1393 . 1395 [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation 1396 Element (PCE) Communication Protocol Generic 1397 Requirements", RFC 4657, DOI 10.17487/RFC4657, September 1398 2006, . 1400 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1401 Writing an IANA Considerations Section in RFCs", BCP 26, 1402 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1403 . 1405 Authors' Addresses 1407 Siva Sivabalan 1408 Cisco Systems, Inc. 1409 2000 Innovation Drive 1410 Kanata, Ontario K2K 3E8 1411 Canada 1413 Email: msiva@cisco.com 1415 Clarence Filsfils 1416 Cisco Systems, Inc. 1417 Pegasus Parc 1418 De kleetlaan 6a, DIEGEM BRABANT 1831 1419 BELGIUM 1421 Email: cfilsfil@cisco.com 1423 Jeff Tantsura 1424 Individual 1425 444 San Antonio Rd, 10A 1426 Palo Alto, CA 94306 1427 USA 1429 Email: jefftant.ietf@gmail.com 1430 Wim Henderickx 1431 Nokia 1432 Copernicuslaan 50 1433 Antwerp 2018, CA 95134 1434 BELGIUM 1436 Email: wim.henderickx@alcatel-lucent.com 1438 Jon Hardwick 1439 Metaswitch Networks 1440 100 Church Street 1441 Enfield, Middlesex 1442 UK 1444 Email: jonathan.hardwick@metaswitch.com