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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: draft-ietf-spring-segment-routing-mpls has been published as RFC 8660 == Outdated reference: draft-ietf-6man-segment-routing-header has been published as RFC 8754 == Outdated reference: draft-ietf-idr-bgp-ls-segment-routing-msd has been published as RFC 8814 == Outdated reference: draft-ietf-isis-segment-routing-extensions has been published as RFC 8667 == Outdated reference: draft-ietf-ospf-segment-routing-extensions has been published as RFC 8665 == Outdated reference: A later version (-18) exists of draft-ietf-pce-pcep-yang-09 == Outdated reference: A later version (-22) exists of draft-ietf-spring-segment-routing-policy-02 Summary: 0 errors (**), 0 flaws (~~), 8 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PCE S. Sivabalan 3 Internet-Draft C. Filsfils 4 Updates: 8408 (if approved) Cisco Systems, Inc. 5 Intended status: Standards Track J. Tantsura 6 Expires: August 16, 2019 Apstra, Inc. 7 W. Henderickx 8 Nokia 9 J. Hardwick 10 Metaswitch Networks 11 February 12, 2019 13 PCEP Extensions for Segment Routing 14 draft-ietf-pce-segment-routing-15 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 Routing 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 Communication Protocol (PCEP) that allow a 26 stateful PCE to compute and initiate Traffic Engineering (TE) paths, 27 as well as a PCC to request a path subject to certain constraints and 28 optimization 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 August 16, 2019. 55 Copyright Notice 57 Copyright (c) 2019 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5 74 3. Overview of PCEP Operation in SR Networks . . . . . . . . . . 5 75 4. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 7 76 4.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 7 77 4.1.1. The Path Setup Type Capability TLV . . . . . . . . . 7 78 4.1.2. The SR PCE Capability sub-TLV . . . . . . . . . . . . 8 79 4.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . . . 9 80 4.3. ERO . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 81 4.3.1. SR-ERO Subobject . . . . . . . . . . . . . . . . . . 9 82 4.3.2. NAI Associated with SID . . . . . . . . . . . . . . . 12 83 4.4. RRO . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 84 4.5. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 14 85 5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 14 86 5.1. Exchanging the SR PCE Capability . . . . . . . . . . . . 14 87 5.2. ERO Processing . . . . . . . . . . . . . . . . . . . . . 16 88 5.2.1. SR-ERO Validation . . . . . . . . . . . . . . . . . . 16 89 5.2.2. Interpreting the SR-ERO . . . . . . . . . . . . . . . 18 90 5.3. RRO Processing . . . . . . . . . . . . . . . . . . . . . 20 91 6. Backward Compatibility . . . . . . . . . . . . . . . . . . . 20 92 7. Management Considerations . . . . . . . . . . . . . . . . . . 21 93 7.1. Controlling the Path Setup Type . . . . . . . . . . . . . 21 94 7.2. Migrating a Network to Use PCEP Segment Routed Paths . . 22 95 7.3. Verification of Network Operation . . . . . . . . . . . . 23 96 7.4. Relationship to Existing Management Models . . . . . . . 24 97 8. Security Considerations . . . . . . . . . . . . . . . . . . . 24 98 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 99 9.1. PCEP ERO and RRO subobjects . . . . . . . . . . . . . . . 25 100 9.2. New NAI Type Registry . . . . . . . . . . . . . . . . . . 25 101 9.3. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 25 102 9.4. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 26 103 9.5. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 27 104 9.6. PATH-SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators . . . 27 105 9.7. New Path Setup Type . . . . . . . . . . . . . . . . . . . 28 106 9.8. New Metric Type . . . . . . . . . . . . . . . . . . . . . 28 107 9.9. SR PCE Capability Flags . . . . . . . . . . . . . . . . . 28 108 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 29 109 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 110 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 111 12.1. Normative References . . . . . . . . . . . . . . . . . . 29 112 12.2. Informative References . . . . . . . . . . . . . . . . . 30 113 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 115 1. Introduction 117 Segment Routing (SR) leverages the source routing paradigm. Using 118 SR, a source node steers a packet through a path without relying on 119 hop-by-hop signaling protocols such as LDP or RSVP-TE. Each path is 120 specified as an ordered list of instructions called "segments". Each 121 segment is an instruction to route the packet to a specific place in 122 the network, or to perform a function on the packet. A database of 123 segments can be distributed through the network using a routing 124 protocol (such as IS-IS or OSPF) or by any other means. Several 125 types of segment are defined. A node segment uniquely identifies a 126 specific node in the SR domain. Each router in the SR domain 127 associates a node segment with an ECMP-aware shortest path to the 128 node that it identifies. An adjacency segment represents a 129 unidirectional adjacency. An adjacency segment is local to the node 130 which advertises it. Both node segments and adjacency segments can 131 be used for SR. 133 [RFC8402] describes the SR architecture. The corresponding IS-IS and 134 OSPF extensions are specified in 135 [I-D.ietf-isis-segment-routing-extensions] and 136 [I-D.ietf-ospf-segment-routing-extensions], respectively. 138 The SR architecture can be implemented using either an MPLS 139 forwarding plane [I-D.ietf-spring-segment-routing-mpls] or an IPv6 140 forwarding plane [I-D.ietf-6man-segment-routing-header]. The MPLS 141 forwarding plane can be applied to SR without any change, in which 142 case an SR path corresponds to an MPLS Label Switching Path (LSP). 143 This document is relevant to the MPLS forwarding plane only. In this 144 document, "Node-SID" and "Adjacency-SID" denote Node Segment 145 Identifier and Adjacency Segment Identifier respectively. 147 A Segment Routing path (SR path) can be derived from an IGP Shortest 148 Path Tree (SPT). SR-TE paths may not follow an IGP SPT. Such paths 149 may be chosen by a suitable network planning tool and provisioned on 150 the ingress node of the SR-TE path. 152 [RFC5440] describes the Path Computation Element Communication 153 Protocol (PCEP) for communication between a Path Computation Client 154 (PCC) and a Path Computation Element (PCE) or between a pair of PCEs. 155 A PCE computes paths for MPLS Traffic Engineering LSPs (MPLS-TE LSPs) 156 based on various constraints and optimization criteria. [RFC8231] 157 specifies extensions to PCEP that allow a stateful PCE to compute and 158 recommend network paths in compliance with [RFC4657] and defines 159 objects and TLVs for MPLS-TE LSPs. Stateful PCEP extensions provide 160 synchronization of LSP state between a PCC and a PCE or between a 161 pair of PCEs, delegation of LSP control, reporting of LSP state from 162 a PCC to a PCE, controlling the setup and path routing of an LSP from 163 a PCE to a PCC. Stateful PCEP extensions are intended for an 164 operational model in which LSPs are configured on the PCC, and 165 control over them is delegated to the PCE. 167 A mechanism to dynamically initiate LSPs on a PCC based on the 168 requests from a stateful PCE or a controller using stateful PCE is 169 specified in [RFC8281]. This mechanism is useful in Software Defined 170 Networking (SDN) applications, such as on-demand engineering, or 171 bandwidth calendaring [RFC8413]. 173 It is possible to use a stateful PCE for computing one or more SR-TE 174 paths taking into account various constraints and objective 175 functions. Once a path is chosen, the stateful PCE can initiate an 176 SR-TE path on a PCC using PCEP extensions specified in [RFC8281] 177 using the SR specific PCEP extensions specified in this document. 178 Additionally, using procedures described in this document, a PCC can 179 request an SR path from either a stateful or a stateless PCE. 181 This specification relies on the procedures specified in [RFC8408] to 182 exchange the segment routing capability and to specify that the path 183 setup type of an LSP is segment routing. This specification also 184 updates [RFC8408] to clarify the use of sub-TLVs in the PATH-SETUP- 185 TYPE-CAPABILITY TLV. See Section 4.1.1 for details. 187 This specification provides a mechanism for a network controller 188 (acting as a PCE) to instantiate candidate paths for an SR Policy 189 onto a head-end node (acting as a PCC) using PCEP. For more 190 information on the SR Policy Architecture, see 191 [I-D.ietf-spring-segment-routing-policy]. 193 2. Terminology 195 The following terminologies are used in this document: 197 ERO: Explicit Route Object 199 IGP: Interior Gateway Protocol 201 IS-IS: Intermediate System to Intermediate System 203 LSR: Label Switching Router 205 MSD: Base MPLS Imposition Maximum SID Depth, as defined in [RFC8491] 207 NAI: Node or Adjacency Identifier 209 OSPF: Open Shortest Path First 211 PCC: Path Computation Client 213 PCE: Path Computation Element 215 PCEP: Path Computation Element Communication Protocol 217 RRO: Record Route Object 219 SID: Segment Identifier 221 SR: Segment Routing 223 SR-DB: Segment Routing Database: the collection of SRGBs, SRLBs and 224 SIDs and the objects they map to, advertised by a link state IGP 226 SRGB: Segment Routing Global Block 228 SRLB: Segment Routing Local Block 230 SR-TE: Segment Routing Traffic Engineering 232 3. Overview of PCEP Operation in SR Networks 234 In an SR network, the ingress node of an SR path prepends an SR 235 header to all outgoing packets. The SR header consists of a list of 236 SIDs (or MPLS labels in the context of this document). The header 237 has all necessary information so that, in combination with the 238 information distributed by the IGP, the packets can be guided from 239 the ingress node to the egress node of the path; hence, there is no 240 need for any signaling protocol. 242 In PCEP messages, LSP route information is carried in the Explicit 243 Route Object (ERO), which consists of a sequence of subobjects. SR- 244 TE paths computed by a PCE can be represented in an ERO in one of the 245 following forms: 247 o An ordered set of IP addresses representing network nodes/links. 249 o An ordered set of SIDs, with or without the corresponding IP 250 addresses. 252 o An ordered set of MPLS labels, with or without corresponding IP 253 address. 255 The PCC converts these into an MPLS label stack and next hop, as 256 described in Section 5.2.2. 258 This document defines a new ERO subobject denoted by "SR-ERO 259 subobject" capable of carrying a SID as well as the identity of the 260 node/adjacency represented by the SID. SR-capable PCEP speakers 261 should be able to generate and/or process such ERO subobject. An ERO 262 containing SR-ERO subobjects can be included in the PCEP Path 263 Computation Reply (PCRep) message defined in [RFC5440], the PCEP LSP 264 Initiate Request message (PCInitiate) defined in [RFC8281], as well 265 as in the PCEP LSP Update Request (PCUpd) and PCEP LSP State Report 266 (PCRpt) messages defined in [RFC8231]. 268 When a PCEP session between a PCC and a PCE is established, both PCEP 269 speakers exchange their capabilities to indicate their ability to 270 support SR-specific functionality. 272 A PCE can update an LSP that is initially established via RSVP-TE 273 signaling to use an SR-TE path, by sending a PCUpd to the PCC that 274 delegated the LSP to it ([RFC8231]). A PCC can update an undelegated 275 LSP that is initially established via RSVP-TE signaling to use an SR- 276 TE path as follows. First, it requests an SR-TE Path from a PCE by 277 sending a PCReq message. If it receives a suitable path, it 278 establishes the path in the data plane, and then tears down the 279 original RSVP-TE path. If the PCE is stateful, then the PCC sends 280 PCRpt messages indicating that the new path is set up and the old 281 path is torn down, per [RFC8231]. 283 Similarly, a PCE or PCC can update an LSP initially created with an 284 SR-TE path to use RSVP-TE signaling, if necessary. This capability 285 is useful for rolling back a change when a network is migrated from 286 RSVP-TE to SR-TE technology. 288 A PCC MAY include an RRO containing the recorded LSP in PCReq and 289 PCRpt messages as specified in [RFC5440] and [RFC8231], respectively. 291 This document defines a new RRO subobject for SR networks. The 292 methods used by a PCC to record the SR-TE LSP are outside the scope 293 of this document. 295 In summary, this document: 297 o Defines a new ERO subobject, a new RRO subobject and new PCEP 298 error codes. 300 o Specifies how two PCEP speakers can establish a PCEP session that 301 can carry information about SR-TE paths. 303 o Specifies processing rules for the ERO subobject. 305 o Defines a new path setup type to be used in the PATH-SETUP-TYPE 306 and PATH-SETUP-TYPE-CAPABILITY TLVs ([RFC8408]). 308 o Defines a new sub-TLV for the PATH-SETUP-TYPE-CAPABILITY TLV. 310 The extensions specified in this document complement the existing 311 PCEP specifications to support SR-TE paths. As such, the PCEP 312 messages (e.g., Path Computation Request, Path Computation Reply, 313 Path Computation Report, Path Computation Update, Path Computation 314 Initiate, etc.,) are formatted according to [RFC5440], [RFC8231], 315 [RFC8281], and any other applicable PCEP specifications. 317 4. Object Formats 319 4.1. The OPEN Object 321 4.1.1. The Path Setup Type Capability TLV 323 [RFC8408] defines the PATH-SETUP-TYPE-CAPABILITY TLV for use in the 324 OPEN object. The PATH-SETUP-TYPE-CAPABILITY TLV contains an optional 325 list of sub-TLVs which are intended to convey parameters that are 326 associated with the path setup types supported by a PCEP speaker. 328 This specification updates [RFC8408], as follows. It creates a new 329 registry which defines the valid type indicators of the sub-TLVs of 330 the PATH-SETUP-TYPE-CAPABILITY TLV (see Section 9.6). A PCEP speaker 331 MUST NOT include a sub-TLV in the PATH-SETUP-TYPE-CAPABILITY TLV 332 unless it appears in this registry. If a PCEP speaker receives a 333 sub-TLV whose type indicator does not match one of those from the 334 registry, or else is not recognised by the speaker, then the speaker 335 MUST ignore the sub-TLV. 337 4.1.2. The SR PCE Capability sub-TLV 339 This document defines a new Path Setup Type (PST) for SR, as follows: 341 o PST = 1: Path is setup using Segment Routing Traffic Engineering. 343 A PCEP speaker SHOULD indicate its support of the function described 344 in this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV in the 345 OPEN object with this new PST included in the PST list. 347 This document also defines the SR-PCE-CAPABILITY sub-TLV. PCEP 348 speakers use this sub-TLV to exchange information about their SR 349 capability. If a PCEP speaker includes PST=1 in the PST List of the 350 PATH-SETUP-TYPE-CAPABILITY TLV then it MUST also include the SR-PCE- 351 CAPABILITY sub-TLV inside the PATH-SETUP-TYPE-CAPABILITY TLV. 353 The format of the SR-PCE-CAPABILITY sub-TLV is shown in the following 354 figure: 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 | Type=TBD11 | Length=4 | 360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 361 | Reserved | Flags |N|X| MSD | 362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 364 Figure 1: SR-PCE-CAPABILITY sub-TLV format 366 The code point for the TLV type is TBD11. The TLV length is 4 367 octets. 369 The 32-bit value is formatted as follows. 371 Reserved: MUST be set to zero by the sender and MUST be ignored by 372 the receiver. 374 Flags: This document defines the following flag bits. The other 375 bits MUST be set to zero by the sender and MUST be ignored by the 376 receiver. 378 * N: A PCC sets this flag bit to 1 to indicate that it is capable 379 of resolving a Node or Adjacency Identifier (NAI) to a SID. 381 * X: A PCC sets this flag bit to 1 to indicate that it does not 382 impose any limit on the MSD. 384 Maximum SID Depth (MSD): specifies the maximum number of SIDs (MPLS 385 label stack depth in the context of this document) that a PCC is 386 capable of imposing on a packet. Section 5.1 explains the 387 relationship between this field and the X flag. 389 4.2. The RP/SRP Object 391 To set up an SR-TE LSP using SR, the RP (Request Parameters) or SRP 392 (Stateful PCE Request Parameters) object MUST include the PATH-SETUP- 393 TYPE TLV, specified in [RFC8408], with the PST set to 1 (path setup 394 using SR-TE). 396 The LSP-IDENTIFIERS TLV MAY be present for the above PST type. 398 4.3. ERO 400 An SR-TE path consists of one or more SIDs where each SID MAY be 401 associated with the identifier that represents the node or adjacency 402 corresponding to the SID. This identifier is referred to as the 403 'Node or Adjacency Identifier' (NAI). As described later, a NAI can 404 be represented in various formats (e.g., IPv4 address, IPv6 address, 405 etc). Furthermore, a NAI is used for troubleshooting purposes and, 406 if necessary, to derive SID value as described below. 408 The ERO specified in [RFC5440] is used to carry SR-TE path 409 information. In order to carry SID and/or NAI, this document defines 410 a new ERO subobject referred to as "SR-ERO subobject" whose format is 411 specified in the following section. An ERO carrying an SR-TE path 412 consists of one or more ERO subobjects, and MUST carry only SR-ERO 413 subobjects. Note that an SR-ERO subobject does not need to have both 414 SID and NAI. However, at least one of them MUST be present. 416 When building the MPLS label stack from ERO, a PCC MUST assume that 417 SR-ERO subobjects are organized as a last-in-first-out stack. The 418 first subobject relative to the beginning of ERO contains the 419 information about the topmost label. The last subobject contains 420 information about the bottommost label. 422 4.3.1. SR-ERO Subobject 424 An SR-ERO subobject is formatted as shown in the following diagram. 426 0 1 2 3 427 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 1 428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 |L| Type=36 | Length | NT | Flags |F|S|C|M| 430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 431 | SID (optional) | 432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 433 // NAI (variable, optional) // 434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 436 Figure 2: SR-ERO subobject format 438 The fields in the SR-ERO Subobject are as follows: 440 The 'L' Flag: Indicates whether the subobject represents a loose-hop 441 in the LSP [RFC3209]. If this flag is set to zero, a PCC MUST NOT 442 overwrite the SID value present in the SR-ERO subobject. 443 Otherwise, a PCC MAY expand or replace one or more SID values in 444 the received SR-ERO based on its local policy. 446 Type: Set to 36. 448 Length: Contains the total length of the subobject in octets. The 449 Length MUST be at least 8, and MUST be a multiple of 4. An SR-ERO 450 subobject MUST contain at least one of a SID or an NAI. The flags 451 described below indicate whether the SID or NAI fields are absent. 453 NAI Type (NT): Indicates the type and format of the NAI contained in 454 the object body, if any is present. If the F bit is set to zero 455 (see below) then the NT field has no meaning and MUST be ignored 456 by the receiver. This document describes the following NT values: 458 NT=0 The NAI is absent. 460 NT=1 The NAI is an IPv4 node ID. 462 NT=2 The NAI is an IPv6 node ID. 464 NT=3 The NAI is an IPv4 adjacency. 466 NT=4 The NAI is an IPv6 adjacency. 468 NT=5 The NAI is an unnumbered adjacency with IPv4 node IDs. 470 Flags: Used to carry additional information pertaining to the SID. 471 This document defines the following flag bits. The other bits 472 MUST be set to zero by the sender and MUST be ignored by the 473 receiver. 475 * M: If this bit is set to 1, the SID value represents an MPLS 476 label stack entry as specified in [RFC3032]. Otherwise, the 477 SID value is an administratively configured value which 478 represents an index into an MPLS label space (either SRGB or 479 SRLB) per [RFC8402]. 481 * C: If the M bit and the C bit are both set to 1, then the TC, 482 S, and TTL fields in the MPLS label stack entry are specified 483 by the PCE. However, a PCC MAY choose to override these values 484 according its local policy and MPLS forwarding rules. If the M 485 bit is set to 1 but the C bit is set to zero, then the TC, S, 486 and TTL fields MUST be ignored by the PCC. The PCC MUST set 487 these fields according to its local policy and MPLS forwarding 488 rules. If the M bit is set to zero then the C bit MUST be set 489 to zero. 491 * S: When this bit is set to 1, the SID value in the subobject 492 body is absent. In this case, the PCC is responsible for 493 choosing the SID value, e.g., by looking up in the SR-DB using 494 the NAI which, in this case, MUST be present in the subobject. 495 If the S bit is set to 1 then the M and C bits MUST be set to 496 zero. 498 * F: When this bit is set to 1, the NAI value in the subobject 499 body is absent. The F bit MUST be set to 1 if NT=0, and 500 otherwise MUST be set to zero. The S and F bits MUST NOT both 501 be set to 1. 503 SID: The Segment Identifier. Depending on the M bit, it contains 504 either: 506 * A 4 octet index defining the offset into an MPLS label space 507 per [RFC8402]. 509 * A 4 octet MPLS Label Stack Entry, where the 20 most significant 510 bits encode the label value per [RFC3032]. 512 NAI: The NAI associated with the SID. The NAI's format depends on 513 the value in the NT field, and is described in the following 514 section. 516 At least one of the SID and the NAI MUST be included in the SR-ERO 517 subobject, and both MAY be included. 519 4.3.2. NAI Associated with SID 521 This document defines the following NAIs: 523 'IPv4 Node ID' is specified as an IPv4 address. In this case, the 524 NT value is 1 and the NAI field length is 4 octets. 526 'IPv6 Node ID' is specified as an IPv6 address. In this case, the 527 NT value is 2 and the NAI field length is 16 octets. 529 'IPv4 Adjacency' is specified as a pair of IPv4 addresses. In this 530 case, the NT value is 3 and the NAI field length is 8 octets. The 531 format of the NAI is shown in the following figure: 533 0 1 2 3 534 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 1 535 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 536 | Local IPv4 address | 537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 538 | Remote IPv4 address | 539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 541 Figure 3: NAI for IPv4 adjacency 543 'IPv6 Adjacency' is specified as a pair of IPv6 addresses. In this 544 case, the NT value is 4 and the NAI field length is 32 octets. 545 The format of the NAI is shown in the following figure: 547 0 1 2 3 548 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 1 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 550 // Local IPv6 address (16 octets) // 551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 552 // Remote IPv6 address (16 octets) // 553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 555 Figure 4: NAI for IPv6 adjacency 557 'Unnumbered Adjacency with IPv4 NodeIDs' is specified as a pair of 558 Node ID / Interface ID tuples. In this case, the NT value is 5 559 and the NAI field length is 16 octets. The format of the NAI is 560 shown in the following figure: 562 0 1 2 3 563 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 1 564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 565 | Local Node-ID | 566 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 567 | Local Interface ID | 568 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 569 | Remote Node-ID | 570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 571 | Remote Interface ID | 572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 Figure 5: NAI for Unnumbered adjacency with IPv4 Node IDs 576 4.4. RRO 578 A PCC reports an SR-TE LSP to a PCE by sending a PCRpt message, per 579 [RFC8231]. The RRO on this message represents the SID list that was 580 applied by the PCC, that is, the actual path taken by the LSP. The 581 procedures of [RFC8231] with respect to the RRO apply equally to this 582 specification without change. 584 An RRO contains one or more subobjects called "SR-RRO subobjects" 585 whose format is shown below: 587 0 1 2 3 588 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 1 589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 590 | Type=36 | Length | NT | Flags |F|S|C|M| 591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 592 | SID | 593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 594 // NAI (variable) // 595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 597 Figure 6: SR-RRO Subobject format 599 The format of the SR-RRO subobject is the same as that of the SR-ERO 600 subobject, but without the L flag. 602 A PCC MUST order the SR-RRO subobjects such that the first subobject 603 relative to the beginning of the RRO identifies the first segment 604 visited by the SR-TE LSP, and the last subobject identifies the final 605 segment of the SR-TE LSP, that is, its endpoint. 607 4.5. METRIC Object 609 A PCC MAY request that PCE optimizes an individual path computation 610 request to minimize the SID depth of the computed path by using the 611 METRIC object defined in [RFC5440]. This document defines a new type 612 for the METRIC object to be used for this purpose, as follows: 614 o T = 11: Maximum SID Depth of the requested path. 616 If the PCC includes a METRIC object of this type on a path 617 computation request, then the PCE minimizes the SID depth of the 618 computed path. If the B (bound) bit is set to to 1 in the METRIC 619 object, then the PCE MUST NOT return a path whose SID depth exceeds 620 the given metric-value. If the PCC did not set the X flag in its SR- 621 PCE-CAPABILITY TLV, then it MUST set the B bit to 1. If the PCC set 622 the X flag in its SR-PCE-CAPABILITY TLV, then it MAY set the B bit to 623 1 or zero. 625 If a PCEP session is established with a non-zero default MSD value, 626 then the PCC MUST NOT send an MSD METRIC object with an MSD greater 627 than the session's default MSD. If the PCE receives a path 628 computation request with an MSD METRIC object on such a session that 629 is greater than the session's default MSD, then it MUST consider the 630 request invalid and send a PCErr with Error-Type = 10 ("Reception of 631 an invalid object") and Error-Value 9 ("MSD exceeds the default for 632 the PCEP session"). 634 5. Procedures 636 5.1. Exchanging the SR PCE Capability 638 A PCC indicates that it is capable of supporting the head-end 639 functions for SR-TE LSP by including the SR-PCE-CAPABILITY sub-TLV in 640 the Open message that it sends to a PCE. A PCE indicates that it is 641 capable of computing SR-TE paths by including the SR-PCE-CAPABILITY 642 sub-TLV in the Open message that it sends to a PCC. 644 If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV with a 645 PST list containing PST=1, and supports that path setup type, then it 646 checks for the presence of the SR-PCE-CAPABILITY sub-TLV. If that 647 sub-TLV is absent, then the PCEP speaker MUST send a PCErr message 648 with Error-Type 10 (Reception of an invalid object) and Error-Value 649 TBD1 (Missing PCE-SR-CAPABILITY sub-TLV) and MUST then close the PCEP 650 session. If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV 651 with a SR-PCE-CAPABILITY sub-TLV, but the PST list does not contain 652 PST=1, then the PCEP speaker MUST ignore the SR-PCE-CAPABILITY sub- 653 TLV. 655 If a PCC sets the N flag to 1, then the PCE MAY send an SR-ERO 656 subobject containing NAI and no SID (see Section 5.2). Otherwise, 657 the PCE MUST NOT send an SR-ERO subobject containing NAI and no SID. 659 The number of SIDs that can be imposed on a packet depends on the 660 PCC's data plane's capability. If a PCC sets the X flag to 1 then 661 the MSD is not used and MUST be set to zero. If a PCE receives an 662 SR-PCE-CAPABILITY sub-TLV with the X flag set to 1 then it MUST 663 ignore the MSD field and assumes that the sender can impose a SID 664 stack of any depth. If a PCC sets the X flag to zero, then it sets 665 the MSD field to the maximum number of SIDs that it can impose on a 666 packet. In this case, the PCC MUST set the MSD to a number greater 667 than zero. If a PCE receives an SR-PCE-CAPABILITY sub-TLV with the X 668 flag and MSD both set to zero then it MUST send a PCErr message with 669 Error-Type 10 (Reception of an invalid object) and Error-Value TBD10 670 (Maximum SID depth must be nonzero) and MUST then close the PCEP 671 session. 673 Note that the MSD value exchanged via the SR-PCE-CAPABILITY sub-TLV 674 indicates the SID/label imposition limit for the PCC node. It is 675 anticipated that, in many deployments, the PCCs will have network 676 interfaces that are homogeneous with respect to MSD (that is, each 677 interface has the same MSD). In such cases, having a per-node MSD on 678 the PCEP session is sufficient; the PCE SHOULD interpret this to mean 679 that all network interfaces on the PCC have the given MSD. However, 680 the PCE MAY also learn a per-node MSD and a per-interface MSD from 681 the routing protocols, as specified in: [RFC8491]; [RFC8476]; 682 [I-D.ietf-idr-bgp-ls-segment-routing-msd]. If the PCE learns the 683 per-node MSD of a PCC from a routing protocol, then it MUST ignore 684 the per-node MSD value in the SR-PCE-CAPABILITY sub-TLV and use the 685 per-node MSD learned from the routing protocol instead. If the PCE 686 learns the MSD of a network interface on a PCC from a routing 687 protocol, then it MUST use the per-interface MSD instead of the MSD 688 value in the SR-PCE-CAPABILITY sub-TLV when it computes a path that 689 uses that interface. 691 Once an SR-capable PCEP session is established with a non-zero MSD 692 value, the corresponding PCE MUST NOT send SR-TE paths with a number 693 of SIDs exceeding that MSD value. If a PCC needs to modify the MSD 694 value, it MUST close the PCEP session and re-establish it with the 695 new MSD value. If a PCEP session is established with a non-zero MSD 696 value, and the PCC receives an SR-TE path containing more SIDs than 697 specified in the MSD value, the PCC MUST send a PCErr message with 698 Error-Type 10 (Reception of an invalid object) and Error-Value 3 699 (Unsupported number of Segment ERO subobjects). If a PCEP session is 700 established with an MSD value of zero, then the PCC MAY specify an 701 MSD for each path computation request that it sends to the PCE, by 702 including a "maximum SID depth" metric object on the request, as 703 defined in Section 4.5. 705 The N flag, X flag and MSD value inside the SR-PCE-CAPABILITY sub-TLV 706 are meaningful only in the Open message sent from a PCC to a PCE. As 707 such, a PCE MUST set the N flag to zero, the X flag to 1 and MSD 708 value to zero in an outbound message to a PCC. Similarly, a PCC MUST 709 ignore any MSD value received from a PCE. If a PCE receives multiple 710 SR-PCE-CAPABILITY sub-TLVs in an Open message, it processes only the 711 first sub-TLV received. 713 5.2. ERO Processing 715 5.2.1. SR-ERO Validation 717 If a PCC does not support the SR PCE Capability and thus cannot 718 recognize the SR-ERO or SR-RRO subobjects, it will respond according 719 to the rules for a malformed object per [RFC5440]. 721 On receiving an SR-ERO, a PCC MUST validate that the Length field, 722 the S bit, the F bit and the NT field are consistent, as follows. 724 o If NT=0, the F bit MUST be 1, the S bit MUST be zero and the 725 Length MUST be 8. 727 o If NT=1, the F bit MUST be zero. If the S bit is 1, the Length 728 MUST be 8, otherwise the Length MUST be 12. 730 o If NT=2, the F bit MUST be zero. If the S bit is 1, the Length 731 MUST be 20, otherwise the Length MUST be 24. 733 o If NT=3, the F bit MUST be zero. If the S bit is 1, the Length 734 MUST be 12, otherwise the Length MUST be 16. 736 o If NT=4, the F bit MUST be zero. If the S bit is 1, the Length 737 MUST be 36, otherwise the Length MUST be 40. 739 o If NT=5, the F bit MUST be zero. If the S bit is 1, the Length 740 MUST be 20, otherwise the Length MUST be 24. 742 If a PCC finds that the NT field, Length field, S bit and F bit are 743 not consistent, it MUST consider the entire ERO invalid and MUST send 744 a PCErr message with Error-Type = 10 ("Reception of an invalid 745 object") and Error-Value = 11 ("Malformed object"). 747 If a PCC does not recognise or support the value in the NT field, it 748 MUST consider the entire ERO invalid and MUST send a PCErr message 749 with Error-Type = 10 ("Reception of an invalid object") and Error- 750 Value = TBD2 ("Unsupported NAI Type in Segment ERO subobject"). 752 If a PCC receives an SR-ERO subobject in which the S and F bits are 753 both set to 1 (that is, both the SID and NAI are absent), it MUST 754 consider the entire ERO invalid and send a PCErr message with Error- 755 Type = 10 ("Reception of an invalid object") and Error-Value = 6 756 ("Both SID and NAI are absent in SR-ERO subobject"). 758 If a PCC receives an SR-ERO subobject in which the S bit is set to 1 759 and the F bit is set to zero (that is, the SID is absent and the NAI 760 is present), but the PCC does not support NAI resolution, it MUST 761 consider the entire ERO invalid and send a PCErr message with Error- 762 Type = 4 ("Not supported object") and Error-Value = 4 ("Unsupported 763 parameter"). 765 If a PCC receives an SR-ERO subobject in which the S bit is set to 1 766 and either or both of the M or C bits is set to 1, it MUST consider 767 the entire ERO invalid and send a PCErr message with Error-Type = 10 768 ("Reception of an invalid object") and Error-Value = 11 ("Malformed 769 object"). 771 If a PCC receives an SR-ERO subobject in which the S bit is set to 772 zero and the M bit is set to 1, then the subobject contains an MPLS 773 label. The PCC MAY choose not to accept a label provided by the PCE, 774 based on it local policy. The PCC MUST NOT accept MPLS label value 3 775 (Implicit NULL), but it MAY accept other special purpose MPLS label 776 values. If the PCC decides not to accept an MPLS label value, it 777 MUST send a PCErr message with Error-Type = 10 ("Reception of an 778 invalid object") and Error Value = 2 ("Bad label value"). 780 If both M and C bits of an SR-ERO subobject are set to 1, and if a 781 PCC finds erroneous setting in one or more of TC, S, and TTL fields, 782 it MAY overwrite those fields with values chosen according to its own 783 policy. If the PCC does not overwrite them, it MUST send a PCErr 784 message with Error-Type = 10 ("Reception of an invalid object") and 785 Error-Value = 4 ("Bad label format"). 787 If the M bit of an SR-ERO subobject is set to zero but the C bit is 788 set to 1, then the PCC MUST consider the entire ERO invalid and MUST 789 send a PCErr message with Error-Type = 10 ("Reception of an invalid 790 object") and Error-Value = 11 ("Malformed object"). 792 If a PCC receives an SR-ERO subobject in which the S bit is set to 793 zero and the M bit is set to zero, then the subobject contains a SID 794 index value. If the SID is an Adjacency-SID then the L flag MUST NOT 795 be set. If the L flag is set for an Adjacency-SID then the PCC MUST 796 send a PCErr message with Error-Type = 10 ("Reception of an invalid 797 object") and Error-Value = 11 ("Malformed object"). 799 If a PCC detects that the subobjects of an ERO are a mixture of SR- 800 ERO subobjects and subobjects of other types, then it MUST send a 801 PCErr message with Error-Type = 10 ("Reception of an invalid object") 802 and Error-Value = 5 ("ERO mixes SR-ERO subobjects with other 803 subobject types"). 805 The SR-ERO subobjects can be classified according to whether they 806 contain a SID representing an MPLS label value, a SID representing an 807 index value, or no SID. If a PCC detects that the SR-ERO subobjects 808 are a mixture of more than one of these types, then it MUST send a 809 PCErr message with Error-Type = 10 ("Reception of an invalid object") 810 and Error-Value = TBD9 ("Inconsistent SIDs in SR-ERO / SR-RRO 811 subobjects"). 813 If an ERO specifies a new SR-TE path for an existing LSP and the PCC 814 determines that the ERO contains SR-ERO subobjects that are not 815 valid, then the PCC MUST NOT update the LSP. 817 5.2.2. Interpreting the SR-ERO 819 The SR-ERO contains a sequence of subobjects. Each SR-ERO subobject 820 in the sequence identifies a segment that the traffic will be 821 directed to, in the order given. That is, the first subobject 822 identifies the first segment the traffic will be directed to, the 823 second subobject represents the second segment, and so on. 825 The PCC interprets the SR-ERO by converting it to an MPLS label stack 826 plus a next hop. The PCC sends packets along the segment routed path 827 by prepending the MPLS label stack onto the packets and sending the 828 resulting, modified packet to the next hop. 830 The PCC uses a different procedure to do this conversion, depending 831 on the information that the PCE has provided in the subobjects. 833 o If the subobjects contain SID index values, then the PCC converts 834 them into the corresponding MPLS labels by following the procedure 835 defined in [I-D.ietf-spring-segment-routing-mpls]. 837 o If the subobjects contain NAI only, the PCC first converts each 838 NAI into a SID index value and then proceeds as above. To convert 839 an NAI to a SID index, the PCC looks for a fully-specified prefix 840 or adjacency matching the fields in the NAI. If the PCC finds a 841 matching prefix/adjacency, and the matching prefix/adjacency has a 842 SID associated with it, then the PCC uses that SID. If the PCC 843 cannot find a matching prefix/adjacency, or if the matching 844 prefix/adjacency has no SID associated with it, the PCC behaves as 845 specified in Section 5.2.2.1. 847 o If the subobjects contain MPLS labels, then the PCC looks up the 848 offset of the first subobject's label in its SRGB or SRLB. This 849 gives the first SID. The PCC pushes the labels in any remaining 850 subobjects onto the packet (with the final subobject specifying 851 the bottom-of-stack label). 853 For all cases above, after the PCC has imposed the label stack on the 854 packet, it sends the packet to the segment identified by the first 855 SID. 857 5.2.2.1. Handling Errors During SR-ERO Conversion 859 There are several errors that can occur during the process of 860 converting an SR-ERO sequence to an MPLS label stack and a next hop. 861 The PCC deals with them as follows. 863 o If the PCC cannot find a SID index in the SR-DB, it MUST send a 864 PCErr message with Error-Type = 10 ("Reception of an invalid 865 object") and Error-Value = TBD3 ("Unknown SID"). 867 o If the PCC cannot find an NAI in the SR-DB, it MUST send a PCErr 868 message with Error-Type = 10 ("Reception of an invalid object") 869 and Error-Value = TBD4 ("NAI cannot be resolved to a SID"). 871 o If the PCC needs to convert a SID into an MPLS label value but 872 cannot find the corresponding router's SRGB in the SR-DB, it MUST 873 send a PCErr message with Error-Type = 10 ("Reception of an 874 invalid object") and Error-Value = TBD5 ("Could not find SRGB"). 876 o If the PCC finds that a router's SRGB is not large enough for a 877 SID index value, it MUST send a PCErr message with Error-Type = 10 878 ("Reception of an invalid object") and Error-Value = TBD6 ("SID 879 index exceeds SRGB size"). 881 o If the PCC needs to convert a SID into an MPLS label value but 882 cannot find the corresponding router's SRLB in the SR-DB, it MUST 883 send a PCErr message with Error-Type = 10 ("Reception of an 884 invalid object") and Error-Value = TBD7 ("Could not find SRLB"). 886 o If the PCC finds that a router's SRLB is not large enough for a 887 SID index value, it MUST send a PCErr message with Error-Type = 10 888 ("Reception of an invalid object") and Error-Value = TBD8 ("SID 889 index exceeds SRLB size"). 891 o If the number of labels in the computed label stack exceeds the 892 maximum number of SIDs that the PCC can impose on the packet, it 893 MUST send a PCErr message with Error-Type = 10 ("Reception of an 894 invalid object") and Error-Value = 3 ("Unsupported number of 895 Segment ERO subobjects"). 897 If an ERO specifies a new SR-TE path for an existing LSP and the PCC 898 encounters an error while processing the ERO, then the PCC MUST NOT 899 update the LSP. 901 5.3. RRO Processing 903 The syntax checking rules that apply to the SR-RRO subobject are 904 identical to those of the SR-ERO subobject, except as noted below. 906 If a PCEP speaker receives an SR-RRO subobject in which both SID and 907 NAI are absent, it MUST consider the entire RRO invalid and send a 908 PCErr message with Error-Type = 10 ("Reception of an invalid object") 909 and Error-Value = 7 ("Both SID and NAI are absent in SR-RRO 910 subobject"). 912 If a PCE detects that the subobjects of an RRO are a mixture of SR- 913 RRO subobjects and subobjects of other types, then it MUST send a 914 PCErr message with Error-Type = 10 ("Reception of an invalid object") 915 and Error-Value = 10 ("RRO mixes SR-RRO subobjects with other 916 subobject types"). 918 The SR-RRO subobjects can be classified according to whether they 919 contain a SID representing an MPLS label value or a SID representing 920 an index value, or no SID. If a PCE detects that the SR-RRO 921 subobjects are a mixture of more than one of these types, then it 922 MUST send a PCErr message with Error-Type = 10 ("Reception of an 923 invalid object") and Error-Value = TBD9 ("Inconsistent SIDs in SR-ERO 924 / SR-RRO subobjects"). 926 6. Backward Compatibility 928 A PCEP speaker that does not support the SR PCEP capability cannot 929 recognize the SR-ERO or SR-RRO subobjects. As such, it responds 930 according to the rules for a malformed object, per [RFC5440]. 932 Some implementations, which are compliant with an earlier version of 933 this specification, do not send the PATH-SETUP-TYPE-CAPABILITY TLV in 934 their OPEN objects. Instead, to indicate that they support SR, these 935 implementations include the SR-CAPABILITY-TLV as a top-level TLV in 936 the OPEN object. Unfortunately, some of these implementations made 937 it into the field before this document was published in its final 938 form. Therefore, if a PCEP speaker receives an OPEN object in which 939 the SR-CAPABILITY-TLV appears as a top-level TLV, then it MUST 940 interpret this as though the sender had sent a PATH-SETUP-TYPE- 941 CAPABILITY TLV with a PST list of (0, 1) (that is, both RSVP-TE and 942 SR-TE PSTs are supported) and with the SR-CAPABILITY-TLV as a sub- 943 TLV. If a PCEP speaker receives an OPEN object in which both the SR- 944 CAPABILITY-TLV and PATH-SETUP-TYPE-CAPABILITY TLV appear as top-level 945 TLVs, then it MUST ignore the top-level SR-CAPABILITY-TLV and process 946 only the PATH-SETUP-TYPE-CAPABILITY TLV. 948 7. Management Considerations 950 This document adds a new path setup type to PCEP to allow LSPs to be 951 set up using segment routing techniques. This path setup type may be 952 used with PCEP alongside other path setup types, such as RSVP-TE, or 953 it may be used exclusively. 955 7.1. Controlling the Path Setup Type 957 The following factors control which path setup type is used for a 958 given LSP. 960 o The available path setup types are constrained to those that are 961 supported by, or enabled on, the PCEP speakers. The PATH-SETUP- 962 TYPE-CAPABILITY TLV indicates which path setup types a PCEP 963 speaker supports. To use segment routing as a path setup type, it 964 is a prerequisite that the PCC and PCE both include PST=1 in the 965 list of supported path setup types in this TLV, and also include 966 the SR-PCE-CAPABILITY sub-TLV. 968 o When a PCE initiates an LSP, it proposes which path setup type to 969 use by including it in the PATH-SETUP-TYPE TLV in the SRP object 970 of the PCInitiate message. The PCE chooses the path setup type 971 based on the capabilities of the network nodes on the path and on 972 its local policy. The PCC MAY choose to accept the proposed path 973 setup type, or to reject the PCInitiate request, based on its 974 local policy. 976 o When a PCC requests a path for an LSP, it can nominate a preferred 977 path setup type by including it in the PATH-SETUP-TYPE TLV in the 978 RP object of the PCReq message. The PCE MAY choose to reply with 979 a path of the requested type, or to reply with a path of a 980 different type, or to reject the request, based on the 981 capabilities of the network nodes on the path and on its local 982 policy. 984 The operator can influence the path setup type as follows. 986 o Implementations MUST allow the operator to enable and disable the 987 segment routing path setup type on a PCEP-speaking device. 988 Implementations MAY also allow the operator to enable and disable 989 the RSVP-TE path setup type. 991 o PCE implementations MUST allow the operator to specify that an LSP 992 should be instantiated using segment routing or RSVP-TE as the 993 proposed path setup type. 995 o PCE implementations MAY allow the operator to configure a 996 preference for the PCE to propose paths using segment routing or 997 RSVP-TE in the absence of a specified path setup type. 999 o PCC implementations MUST allow the operator to specify that a path 1000 requested for an LSP nominates segment routing or RSVP-TE as the 1001 path setup type. 1003 o PCC implementations MAY allow the operator to configure a 1004 preference for the PCC to nominate segment routing or RSVP-TE as 1005 the path setup type if none is specified for an LSP. 1007 o PCC implementations SHOULD allow the operator to configure a PCC 1008 to refuse to set up an LSP using an undesired path setup type. 1010 7.2. Migrating a Network to Use PCEP Segment Routed Paths 1012 This section discusses the steps that the operator takes when 1013 migrating a network to enable PCEP to set up paths using segment 1014 routing as the path setup type. 1016 o The operator enables the segment routing PST on the PCE servers. 1018 o The operator enables the segment routing PST on the PCCs. 1020 o The operator resets each PCEP session. The PCEP sessions come 1021 back up with segment routing enabled. 1023 o If the operator detects a problem, they can roll the network back 1024 to its initial state by disabling the segment routing PST on the 1025 PCEP speakers and resetting the PCEP sessions. 1027 Note that the data plane is unaffected if a PCEP session is reset. 1028 Any LSPs that were set up before the session reset will remain in 1029 place and will still be present after the session comes back up. 1031 An implementation SHOULD allow the operator to manually trigger a 1032 PCEP session to be reset. 1034 An implementation MAY automatically reset a PCEP session when an 1035 operator reconfigures the PCEP speaker's capabilities. However, note 1036 that if the capabilities at both ends of the PCEP session are not 1037 reconfigured simultaneously, then the session could be reset twice, 1038 which could lead to unnecessary network traffic. Therefore, such 1039 implementations SHOULD allow the operator to override this behaviour 1040 and wait instead for a manual reset. 1042 Once segment routing is enabled on a PCEP session, it can be used as 1043 the path setup type for future LSPs. 1045 User traffic is not automatically migrated from existing LSPs onto 1046 segment routed LSPs just by enabling the segment routing PST in PCEP. 1047 The migration of user traffic from existing LSPs onto segment routing 1048 LSPs is beyond the scope of this document. 1050 7.3. Verification of Network Operation 1052 The operator needs the following information to verify that PCEP is 1053 operating correctly with respect to the segment routing path setup 1054 type. 1056 o An implementation SHOULD allow the operator to view whether the 1057 PCEP speaker sent the segment routing PST capability to its peer. 1058 If the PCEP speaker is a PCC, then the implementation SHOULD also 1059 allow the operator to view the values of the L and N flags that 1060 were sent, and the value of the MSD field that was sent. 1062 o An implementation SHOULD allow the operator to view whether the 1063 peer sent the segment routing PST capability. If the peer is a 1064 PCC, then the implementation SHOULD also allow the operator to 1065 view the values of the L and N flags and MSD fields that the peer 1066 sent. 1068 o An implementation SHOULD allow the operator to view whether the 1069 segment routing PST is enabled on the PCEP session. 1071 o If one PCEP speaker advertises the segment routing PST capability, 1072 but the other does not, then the implementation SHOULD create a 1073 log to inform the operator of the capability mismatch. 1075 o An implementation SHOULD allow the operator to view the PST that 1076 was proposed, or requested, for an LSP, and the PST that was 1077 actually used. 1079 o If a PCEP speaker decides to use a different PST to the one that 1080 was proposed, or requested, for an LSP, then the implementation 1081 SHOULD create a log to inform the operator that the expected PST 1082 has not been used. The log SHOULD give the reason for this choice 1083 (local policy, equipment capability etc.) 1085 o If a PCEP speaker rejects a segment routing path, then it SHOULD 1086 create a log to inform the operator, giving the reason for the 1087 decision (local policy, MSD exceeded etc.) 1089 7.4. Relationship to Existing Management Models 1091 The PCEP YANG module is defined in [I-D.ietf-pce-pcep-yang]. In 1092 future, this YANG module should be extended or augmented to provide 1093 the following additional information relating to segment routing: 1095 o The advertised PST capabilities and MSD per PCEP session. 1097 o The PST configured for, and used by, each LSP. 1099 The PCEP MIB [RFC7420] could also be updated to include this 1100 information. 1102 8. Security Considerations 1104 The security considerations described in [RFC5440], [RFC8231], 1105 [RFC8281] and [RFC8408] are applicable to this specification. No 1106 additional security measure is required. 1108 Note that this specification enables a network controller to 1109 instantiate a path in the network without the use of a hop-by-hop 1110 signaling protocol (such as RSVP-TE). This creates an additional 1111 vulnerability if the security mechanisms of [RFC5440], [RFC8231] and 1112 [RFC8281] are not used. If there is no integrity protection on the 1113 session, then an attacker could create a path which is not subjected 1114 to the further verification checks that would be performed by the 1115 signaling protocol. 1117 Note that this specification adds the MSD field to the OPEN message 1118 (see Section 4.1.2) which discloses how many MPLS labels the sender 1119 can push onto packets that it forwards into the network. If the 1120 security mechanisms of [RFC8231] and [RFC8281] are not used with 1121 strong encryption, then an attacker could use this new field to gain 1122 intelligence about the capabilities of the edge devices in the 1123 network. 1125 9. IANA Considerations 1126 9.1. PCEP ERO and RRO subobjects 1128 This document defines a new subobject type for the PCEP explicit 1129 route object (ERO), and a new subobject type for the PCEP record 1130 route object (RRO). The code points for subobject types of these 1131 objects is maintained in the RSVP parameters registry, under the 1132 EXPLICIT_ROUTE and ROUTE_RECORD objects. IANA is requested to 1133 confirm the early allocation of the following code points in the RSVP 1134 Parameters registry for each of the new subobject types defined in 1135 this document. 1137 Object Subobject Subobject Type 1138 --------------------- -------------------------- ------------------ 1139 EXPLICIT_ROUTE SR-ERO (PCEP-specific) 36 1140 ROUTE_RECORD SR-RRO (PCEP-specific) 36 1142 9.2. New NAI Type Registry 1144 IANA is requested to create a new sub-registry within the "Path 1145 Computation Element Protocol (PCEP) Numbers" registry called "PCEP 1146 SR-ERO NAI Types". The allocation policy for this new registry 1147 should be by IETF Review. The new registry should contain the 1148 following values: 1150 Value Description Reference 1152 0 NAI is absent. This document 1153 1 NAI is an IPv4 node ID. This document 1154 2 NAI is an IPv6 node ID. This document 1155 3 NAI is an IPv4 adjacency. This document 1156 4 NAI is an IPv6 adjacency. This document 1157 5 NAI is an unnumbered This document 1158 adjacency with IPv4 node IDs. 1160 9.3. New SR-ERO Flag Registry 1162 IANA is requested to create a new sub-registry, named "SR-ERO Flag 1163 Field", within the "Path Computation Element Protocol (PCEP) Numbers" 1164 registry to manage the Flag field of the SR-ERO subobject. New 1165 values are to be assigned by Standards Action [RFC8126]. Each bit 1166 should be tracked with the following qualities: 1168 o Bit number (counting from bit 0 as the most significant bit) 1170 o Capability description 1172 o Defining RFC 1173 The following values are defined in this document: 1175 Bit Description Reference 1177 0-7 Unassigned 1178 8 NAI is absent (F) This document 1179 9 SID is absent (S) This document 1180 10 SID specifies TC, S This document 1181 and TTL in addition 1182 to an MPLS label (C) 1183 11 SID specifies an MPLS This document 1184 label (M) 1186 9.4. PCEP-Error Object 1188 IANA is requested to confirm the early allocation of the code-points 1189 in the PCEP-ERROR Object Error Types and Values registry for the 1190 following new error-values: 1192 Error-Type Meaning 1193 ---------- ------- 1194 10 Reception of an invalid object. 1196 Error-value = 2: Bad label value 1197 Error-value = 3: Unsupported number 1198 of SR-ERO 1199 subobjects 1200 Error-value = 4: Bad label format 1201 Error-value = 5: ERO mixes SR-ERO 1202 subobjects with 1203 other subobject 1204 types 1205 Error-value = 6: Both SID and NAI 1206 are absent in SR- 1207 ERO subobject 1208 Error-value = 7: Both SID and NAI 1209 are absent in SR- 1210 RRO subobject 1211 Error-value = 9: MSD exceeds the 1212 default for the 1213 PCEP session 1214 Error-value = 10: RRO mixes SR-RRO 1215 subobjects with 1216 other subobject 1217 types 1218 Error-value = TBD1: Missing PCE-SR- 1219 CAPABILITY sub-TLV 1221 Error-value = TBD2: Unsupported NAI 1222 Type in SR-ERO 1223 subobject 1224 Error-value = TBD3: Unknown SID 1225 Error-value = TBD4: NAI cannot be 1226 resolved to a SID 1227 Error-value = TBD5: Could not find SRGB 1228 Error-value = TBD6: SID index exceeds 1229 SRGB size 1230 Error-value = TBD7: Could not find SRLB 1231 Error-value = TBD8: SID index exceeds 1232 SRLB size 1233 Error-value = TBD9: Inconsistent SIDs 1234 in SR-ERO / SR-RRO 1235 subobjects 1236 Error-value = TBD10: MSD must be nonzero 1238 Note to IANA: this draft originally had an early allocation for 1239 Error-value=11 (Malformed object) in the above list. However, we 1240 have since moved the definition of that code point to RFC8408. 1242 Note to IANA: some Error-values in the above list were defined after 1243 the early allocation took place, and so do not currently have a code 1244 point assigned. Please assign code points from the indicated 1245 registry and replace each instance of "TBD1", "TBD2" etc. in this 1246 document with the respective code points. 1248 Note to IANA: some of the Error-value descriptive strings above have 1249 changed since the early allocation. Please refresh the registry. 1251 9.5. PCEP TLV Type Indicators 1253 IANA is requested to confirm the early allocation of the following 1254 code point in the PCEP TLV Type Indicators registry. Note that this 1255 TLV type indicator is deprecated but retained to ensure backwards 1256 compatibility with early implementations of this specification. See 1257 Section 6 for details. 1259 Value Meaning Reference 1260 ------------------------- ---------------------------- -------------- 1261 26 SR-PCE-CAPABILITY This document 1262 (deprecated) 1264 9.6. PATH-SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators 1266 IANA is requested to create a new sub-registry, named "PATH-SETUP- 1267 TYPE-CAPABILITY Sub-TLV Type Indicators", within the "Path 1268 Computation Element Protocol (PCEP) Numbers" registry to manage the 1269 type indicator space for sub-TLVs of the PATH-SETUP-TYPE-CAPABILITY 1270 TLV. New values are to be assigned by Standards Action [RFC8126]. 1271 The valid range of values in the registry is 0-65535. IANA is 1272 requested to initialize the registry with the following values. All 1273 other values in the registry should be marked as "Unassigned". 1275 Value Meaning Reference 1276 ------------------------- ---------------------------- -------------- 1277 0 Reserved This document 1278 TBD11 (recommended 26) SR-PCE-CAPABILITY This document 1280 Note to IANA: Please replace each instance of "TBD11" in this 1281 document with the allocated code point. We have recommended that 1282 value 26 be used for consistency with the deprecated value in the 1283 PCEP TLV Type Indicators registry. 1285 9.7. New Path Setup Type 1287 [RFC8408] created a sub-registry within the "Path Computation Element 1288 Protocol (PCEP) Numbers" registry called "PCEP Path Setup Types". 1289 IANA is requested to allocate a new code point within this registry, 1290 as follows: 1292 Value Description Reference 1293 ------------------------- ---------------------------- -------------- 1294 1 Traffic engineering path is This document 1295 setup using Segment Routing. 1297 9.8. New Metric Type 1299 IANA is requested to confirm the early allocation of the following 1300 code point in the PCEP METRIC object T field registry: 1302 Value Description Reference 1303 ------------------------- ---------------------------- -------------- 1304 11 Segment-ID (SID) Depth. This document 1306 9.9. SR PCE Capability Flags 1308 IANA is requested to create a new sub-registry, named "SR Capability 1309 Flag Field", within the "Path Computation Element Protocol (PCEP) 1310 Numbers" registry to manage the Flag field of the SR-PCE-CAPABILITY 1311 TLV. New values are to be assigned by Standards Action [RFC8126]. 1312 Each bit should be tracked with the following qualities: 1314 o Bit number (counting from bit 0 as the most significant bit) 1315 o Capability description 1316 o Defining RFC 1317 The following values are defined in this document: 1319 Bit Description Reference 1321 0-5 Unassigned 1322 6 Node or Adjacency This document 1323 Identifier (NAI) is 1324 supported (N) 1325 7 Unlimited Maximum SID This document 1326 Depth (X) 1328 Note to IANA: The name of bit 7 has changed from "Unlimited Maximum 1329 SID Depth (L)" to "Unlimited Maximum SID Depth (X)". 1331 10. Contributors 1333 The following people contributed to this document: 1335 - Lakshmi Sharma 1336 - Jan Medved 1337 - Edward Crabbe 1338 - Robert Raszuk 1339 - Victor Lopez 1341 11. Acknowledgements 1343 We thank Ina Minei, George Swallow, Marek Zavodsky, Dhruv Dhody, Ing- 1344 Wher Chen and Tomas Janciga for the valuable comments. 1346 12. References 1348 12.1. Normative References 1350 [I-D.ietf-spring-segment-routing-mpls] 1351 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 1352 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 1353 data plane", draft-ietf-spring-segment-routing-mpls-18 1354 (work in progress), December 2018. 1356 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1357 Requirement Levels", BCP 14, RFC 2119, 1358 DOI 10.17487/RFC2119, March 1997, 1359 . 1361 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 1362 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 1363 Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, 1364 . 1366 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 1367 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 1368 DOI 10.17487/RFC5440, March 2009, 1369 . 1371 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1372 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1373 May 2017, . 1375 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 1376 Computation Element Communication Protocol (PCEP) 1377 Extensions for Stateful PCE", RFC 8231, 1378 DOI 10.17487/RFC8231, September 2017, 1379 . 1381 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 1382 Computation Element Communication Protocol (PCEP) 1383 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 1384 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 1385 . 1387 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 1388 Decraene, B., Litkowski, S., and R. Shakir, "Segment 1389 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 1390 July 2018, . 1392 [RFC8408] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J. 1393 Hardwick, "Conveying Path Setup Type in PCE Communication 1394 Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408, 1395 July 2018, . 1397 [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 1398 "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, 1399 DOI 10.17487/RFC8491, November 2018, 1400 . 1402 12.2. Informative References 1404 [I-D.ietf-6man-segment-routing-header] 1405 Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and 1406 d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header 1407 (SRH)", draft-ietf-6man-segment-routing-header-16 (work in 1408 progress), February 2019. 1410 [I-D.ietf-idr-bgp-ls-segment-routing-msd] 1411 Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, 1412 "Signaling MSD (Maximum SID Depth) using Border Gateway 1413 Protocol Link-State", draft-ietf-idr-bgp-ls-segment- 1414 routing-msd-02 (work in progress), August 2018. 1416 [I-D.ietf-isis-segment-routing-extensions] 1417 Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., 1418 Gredler, H., and B. Decraene, "IS-IS Extensions for 1419 Segment Routing", draft-ietf-isis-segment-routing- 1420 extensions-22 (work in progress), December 2018. 1422 [I-D.ietf-ospf-segment-routing-extensions] 1423 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 1424 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 1425 Extensions for Segment Routing", draft-ietf-ospf-segment- 1426 routing-extensions-27 (work in progress), December 2018. 1428 [I-D.ietf-pce-pcep-yang] 1429 Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A 1430 YANG Data Model for Path Computation Element 1431 Communications Protocol (PCEP)", draft-ietf-pce-pcep- 1432 yang-09 (work in progress), October 2018. 1434 [I-D.ietf-spring-segment-routing-policy] 1435 Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d., 1436 bogdanov@google.com, b., and P. Mattes, "Segment Routing 1437 Policy Architecture", draft-ietf-spring-segment-routing- 1438 policy-02 (work in progress), October 2018. 1440 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 1441 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 1442 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 1443 . 1445 [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation 1446 Element (PCE) Communication Protocol Generic 1447 Requirements", RFC 4657, DOI 10.17487/RFC4657, September 1448 2006, . 1450 [RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J. 1451 Hardwick, "Path Computation Element Communication Protocol 1452 (PCEP) Management Information Base (MIB) Module", 1453 RFC 7420, DOI 10.17487/RFC7420, December 2014, 1454 . 1456 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1457 Writing an IANA Considerations Section in RFCs", BCP 26, 1458 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1459 . 1461 [RFC8413] Zhuang, Y., Wu, Q., Chen, H., and A. Farrel, "Framework 1462 for Scheduled Use of Resources", RFC 8413, 1463 DOI 10.17487/RFC8413, July 2018, 1464 . 1466 [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, 1467 "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, 1468 DOI 10.17487/RFC8476, December 2018, 1469 . 1471 Authors' Addresses 1473 Siva Sivabalan 1474 Cisco Systems, Inc. 1475 2000 Innovation Drive 1476 Kanata, Ontario K2K 3E8 1477 Canada 1479 Email: msiva@cisco.com 1481 Clarence Filsfils 1482 Cisco Systems, Inc. 1483 Pegasus Parc 1484 De kleetlaan 6a, DIEGEM BRABANT 1831 1485 BELGIUM 1487 Email: cfilsfil@cisco.com 1489 Jeff Tantsura 1490 Apstra, Inc. 1491 333 Middlefield Rd #200 1492 Menlo Park, CA 94025 1493 USA 1495 Email: jefftant.ietf@gmail.com 1496 Wim Henderickx 1497 Nokia 1498 Copernicuslaan 50 1499 Antwerp 2018, CA 95134 1500 BELGIUM 1502 Email: wim.henderickx@alcatel-lucent.com 1504 Jon Hardwick 1505 Metaswitch Networks 1506 100 Church Street 1507 Enfield, Middlesex 1508 UK 1510 Email: jonathan.hardwick@metaswitch.com