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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SPRING Working Group C. Li 3 Internet-Draft Huawei Technologies 4 Intended status: Standards Track W. Cheng 5 Expires: November 27, 2021 China Mobile 6 M. Chen 7 D. Dhody 8 Huawei Technologies 9 R. Gandhi 10 Cisco Systems, Inc. 11 Y. Zhu 12 China Telecom 13 May 26, 2021 15 Path Segment for SRv6 (Segment Routing in IPv6) 16 draft-ietf-spring-srv6-path-segment-02 18 Abstract 20 Segment Routing (SR) allows for a flexible definition of end-to-end 21 paths by encoding an ordered list of instructions, called "segments". 22 The SR architecture can be implemented over an MPLS data plane as 23 well as an IPv6 data plane. 25 Currently, Path Segment has been defined to identify an SR path in 26 SR-MPLS networks, and is used for various use-cases such as end-to- 27 end SR Path Protection and Performance Measurement (PM) of an SR 28 path. This document defines the Path Segment to identify an SRv6 29 path in an IPv6 network. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on November 27, 2021. 48 Copyright Notice 50 Copyright (c) 2021 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (https://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 66 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 67 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 68 2. Use Cases for SRv6 Path Segment . . . . . . . . . . . . . . . 4 69 3. SRv6 Path Segment . . . . . . . . . . . . . . . . . . . . . . 5 70 3.1. Format of an SRv6 Path Segment . . . . . . . . . . . . . 5 71 3.1.1. SRv6 Path Segment: Locator and Local ID . . . . . . . 5 72 3.1.2. SRv6 Path Segment: Global ID . . . . . . . . . . . . 6 73 4. Encoding of an SRv6 Path Segment . . . . . . . . . . . . . . 6 74 4.1. SRH.P-flag . . . . . . . . . . . . . . . . . . . . . . . 6 75 5. SRv6 Path Segment Allocation . . . . . . . . . . . . . . . . 8 76 6. Processing of SRv6 Path Segment . . . . . . . . . . . . . . . 8 77 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 78 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 79 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 80 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 81 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 82 11.1. Normative References . . . . . . . . . . . . . . . . . . 10 83 11.2. Informative References . . . . . . . . . . . . . . . . . 11 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 86 1. Introduction 88 Segment routing (SR) [RFC8402] is a source routing paradigm that 89 explicitly indicates the forwarding path for packets at the ingress 90 node by inserting an ordered list of instructions, called segments. 92 When segment routing is deployed on an MPLS data plane, called SR- 93 MPLS [RFC8660], a segment identifier (SID) is present as an MPLS 94 label. When segment routing is deployed on an IPv6 data plane, a SID 95 is presented as a 128-bit value, and it can be an IPv6 address of a 96 local interface but it does not have to be. To support SR in an IPv6 97 network, a Segment Routing Header (SRH) [RFC8754] is used. 99 In an SR-MPLS network, when a packet is transmitted along an SR path, 100 the labels in the MPLS label stack will be swapped or popped, so no 101 label or only the last label may be left in the MPLS label stack when 102 the packet reaches the egress node. Thus, the egress node can not 103 determine from which ingress node or SR path the packet came from. 104 Therefore, to identify an SR-MPLS path, a Path Segment is defined in 105 [I-D.ietf-spring-mpls-path-segment]. 107 Likewise, a path needs to be identified in an SRv6 network for 108 several use cases such as binding bidirectional paths 109 [I-D.ietf-pce-sr-bidir-path] and end-to-end performance measurement 110 [I-D.gandhi-spring-udp-pm]. 112 An SRv6 path MAY be identified by the content of a segment list. 113 However, the segment list may not be a good key, since the length of 114 a segment list is flexible according to the number of required SIDs. 115 Also, the length of a segment list may be too long to be a key when 116 it contains many SIDs. For instance, if packet A uses an SRH with 3 117 SIDs while Packet B uses an SRH with 10 SIDs, the key to identify 118 these two paths will be a 384-bits value and a 1280-bits value, 119 respectively. Further, an SRv6 path cannot be identified by the 120 information carried by the SRH in reduced mode [RFC8754] as the first 121 SID is not present. 123 Furthermore, different SRv6 policies may use the same segment list 124 for different candidate paths, so the traffic of different SRv6 125 policies are merged, resulting in the inability to measure the 126 performance of the specific path. 128 To solve the above issues, this document defines a new SRv6 segment 129 called "SRv6 Path Segment", which is a 128-bits value, to identify an 130 SRv6 path. 132 When the SRv6 Path Segment is used in reduced mode SRH [RFC8754], the 133 entire path information is indicated by the Path Segment, and the 134 performance will be better than using the entire segment list as the 135 path identifier, while the overhead is equivalent to the SRH in 136 normal mode. Furthermore, with SRv6 Path Segment, each SRv6 137 candidate path can be identified and measured, even when they use the 138 same segment list. 140 An SRv6 Path Segment MUST NOT be copied to the IPv6 destination 141 address, so it is not routable. 143 1.1. Requirements Language 145 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 146 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 147 "OPTIONAL" in this document are to be interpreted as described in BCP 148 14 [RFC2119] [RFC8174] when, and only when, they appear in all 149 capitals, as shown here. 151 1.2. Terminology 153 MPLS: Multiprotocol Label Switching. 155 PM: Performance Measurement. 157 SID: Segment ID. 159 SR: Segment Routing. 161 SR-MPLS: Segment Routing with MPLS data plane. 163 SRH: Segment Routing Header. 165 PSID: Path Segment Identifier. 167 PSP: Penultimate Segment Popping. 169 Further, this document makes use of the terms defined in [RFC8402] 170 and [RFC8986]. 172 2. Use Cases for SRv6 Path Segment 174 Similar to SR-MPLS Path Segment [I-D.ietf-spring-mpls-path-segment], 175 SRv6 Path Segment may also be used to identify an SRv6 Path in some 176 use cases: 178 o Performance Measurement: For Passive measurement [RFC7799], path 179 identification at the measuring points is the pre-requisite 180 [I-D.ietf-spring-mpls-path-segment]. SRv6 Path segment can be 181 used by the measuring points (e.g., the ingress/egress nodes of an 182 SRv6 path) or a centralized controller to correlate the packets 183 counts/timestamps, then packet loss/delay can be calculated. 185 o Bi-directional SRv6 Path Association: In some scenarios, such as 186 mobile backhaul transport networks, there are requirements to 187 support bidirectional paths. Like SR-MPLS 188 [I-D.ietf-spring-mpls-path-segment], to support bidirectional SRv6 189 paths, a straightforward way is to bind two unidirectional SRv6 190 paths to a single bidirectional path. SRv6 Path segments can be 191 used to correlate the two unidirectional SRv6 paths at both ends 192 of the path. [I-D.ietf-pce-sr-bidir-path] defines how to use PCEP 193 and Path Segment to initiate a bidirectional SR path. 195 o End-to-end Path Protection: For end-to-end 1+1 path protection 196 (i.e., Live-Live case), the egress node of an SRv6 path needs to 197 know the set of paths that constitute the primary and the 198 secondary(s), to select the primary packet for onward 199 transmission, and to discard the packets from the secondary(s), so 200 each SRv6 path needs a unique path identifier at the egress node, 201 which can be an SRv6 Path Segment. 203 3. SRv6 Path Segment 205 As defined in [RFC8986], an SRv6 segment is a 128-bit value. 207 To identify an SRv6 path, this document defines a new segment called 208 SRv6 Path Segment. 210 Depending on the use case, an SRv6 Path Segment identifies: 212 o an SRv6 path within an SRv6 domain 214 o an SRv6 Policy 216 o a Candidate-path or a SID-List in a SRv6 Policy 217 [I-D.ietf-spring-segment-routing-policy] 219 Note that, based on the use-case, a SRv6 Path Segment can be used for 220 different SID-Lists within an SR Policy. 222 3.1. Format of an SRv6 Path Segment 224 This document proposes two types of SRv6 Path Segment format. 226 3.1.1. SRv6 Path Segment: Locator and Local ID 228 As per [RFC8986], an SRv6 segment is a 128-bit value, which can be 229 represented as LOC:FUNCT, where LOC is the L most significant bits 230 and FUNCT is the 128-L least significant bits. L is called the 231 locator length and is flexible. Each network operator is free to use 232 the locator length it chooses. Most often the LOC part of the SID is 233 routable and leads to the node which instantiates that SID. The 234 FUNCT part of the SID is an opaque identification of a local function 235 bound to the SID. The FUNCT value zero is invalid. 237 SRv6 Path Segment can follow the format, where the LOC part 238 identifies the egress node that allocates the Path Segment, and the 239 FUNCT part is a unique local ID to identify an SRv6 Path and its 240 endpoint behavior. 242 The Function Type of an SRv6 Path Segment is END.PSID (End Function 243 with Path Segment Identifier). 245 +--------------------------------------------------------------+ 246 | Locator | Function ID | 247 +--------------------------------------------------------------+ 249 |<-------------------------128 bits--------------------------->| 251 Figure 2. PSID in Format LOC:FUNCT 253 3.1.2. SRv6 Path Segment: Global ID 255 An SRv6 Path Segment ID can be a Global ID, and its format depends on 256 the use case. 258 The SRv6 Path Segment will not be copied to the IPv6 Destination 259 Address, so the SRv6 Path Segment ID can be allocated from an 260 independent 128-bits ID Space. In this case, a new table should be 261 maintained at the node for SRv6 Path Segment. 263 +--------------------------------------------------------------+ 264 | Global ID/PSID | 265 +--------------------------------------------------------------+ 267 |<-------------------------128 bits--------------------------->| 269 Figure 3. A Global ID as an PSID 271 4. Encoding of an SRv6 Path Segment 273 This section describes the SRv6 Path Segment encoding in SRH. 275 The SRv6 Path Segment MUST appear only once in a segment list, and it 276 MUST appear as the last entry in the segment list. 278 4.1. SRH.P-flag 280 To indicate the existence of a Path Segment in the SRH, this document 281 defines a P-flag in the SRH flag field. The encapsulation of SRv6 282 Path Segment is shown below. 284 0 1 2 3 285 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 1 286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 287 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 289 | Last Entry | Flags |P| Tag | 290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 291 | | 292 | Segment List[0] (128 bits IPv6 address) | 293 | | 294 | | 295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 | | 297 | | 298 ... 299 | | 300 | | 301 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 302 | | 303 | Segment List[n-1] (128 bits IPv6 address) | 304 | | 305 | | 306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 | | 308 | SRv6 Path Segment (Segment List[n],128 bits IPv6 value) | 309 | | 310 | | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 // // 313 // Optional Type Length Value objects (variable) // 314 // // 315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 317 Figure 1. SRv6 Path Segment in SID List 319 o P-bit: set when SRv6 Path Segment is inserted. It MUST be ignored 320 when a node does not support SRv6 Path Segment processing. 322 SRH.P-bit processing can be enabled or disabled by configuration on 323 devices, it can be done by CLI, NETCONF YANG or other ways, and this 324 is out of the scope of this document. 326 The pseudo code of SRH.P-bit processing is described as below. 328 S01. if SRH.P-flag processing is enabled: 329 S02. if SRH.P-flag is set: 330 S03. SRv6 Path Segment processing ;;ref1 332 Ref1: The SRv6 Path Segment processing is accosiated with the 333 specific application, such as SRv6 Path Segment based Performance 334 measurement, so this is out of the scope of this document. 336 In some use cases, only the egress need to process the SRv6 Path 337 Segment, therefore, the P-bit processing can be done at the egress 338 node only while the intermediate nodes do not need to process it. 339 This feature can be enabled by configuration like CLI , NETCONF YANG 340 or other ways. In this case, the pseudo code is described as below. 342 S01. if SRH.P-flag processing is enabled: 343 S02. if intermediate node processing is disabled: 344 S03. if SRH.P-flag is set and SRH.SL == 0: 345 S03. SRv6 Path Segment processing 346 S04 else: 347 S05. if SRH.P-flag is set: 348 S06. SRv6 Path Segment processing 350 5. SRv6 Path Segment Allocation 352 A Path Segment is a local segment allocated by an egress node. A 353 Path Segment can be allocated through several ways, such as CLI, BGP 354 [I-D.ietf-idr-sr-policy-path-segment], PCEP 355 [I-D.ietf-pce-sr-path-segment] or other ways. The mechanisms through 356 which a Path Segment is allocated are out of scope of this document. 358 When a Path Segment is allocated by the egress, it MUST be 359 distributed to the ingress node of the path that identified by the 360 path segment. In this case, only the egress will process the Path 361 Segment, and other nodes specified by SIDs in the segment list do not 362 know how to process the Path Segment. 364 Depending on the use case, a Path Segment may be distributed to the 365 SRv6 nodes along the SRv6 path. In this case, the SRv6 nodes that 366 learned the Path Segment may process the Path Segment depending on 367 the use case. 369 6. Processing of SRv6 Path Segment 371 When the SRv6 Path Segment is used, the following rules apply: 373 o The SRv6 Path Segment MUST appear only once in a segment list, and 374 it MUST appear as the last entry. Only the one that appears as 375 the last entry in the SID list will be processed. An SRv6 Path 376 Segment that appears at any other location in the SID list will be 377 treated as an error. 379 o When an SRv6 Path Segment is inserted, the SL MUST be initiated to 380 be less than the value of Last Entry, and will not point to SRv6 381 Path Segment. For instance, when the Last entry is 4, the SID 382 List[4] is the SRv6 Path Segment, so the SL MUST be set to 3 or 383 other numbers less than Last entry. 385 o The SRv6 Path Segment MUST NOT be copied to the IPv6 destination 386 address. 388 o Penultimate Segment Popping (PSP, as defined in [RFC8986]) MUST be 389 disabled. 391 o The ingress needs to set the P-bit when an SRv6 Path Segment is 392 inserted in the SID List. Nodes that support SRv6 Path Segment 393 processing will inspect the last entry to process SRv6 Path 394 Segment when the P-bit is set. When the P-bit is unset, the nodes 395 will not inspect the last entry. 397 o The specific SRv6 Path Segment processing depends on use cases, 398 and it is out of scope of this document. 400 7. IANA Considerations 402 This I-D requests the IANA to allocate, within the "SRv6 Endpoint 403 Behaviors" sub-registry belonging to the top-level "Segment-routing 404 with IPv6 data plane (SRv6) Parameters" registry, the following 405 allocations: 407 Value Description Reference 408 -------------------------------------------------------------- 409 TBA1 End.PSID - SRv6 Path Segment [This.ID] 411 This document also requests IANA to allocate bit position TBA within 412 the "Segment Routing Header Flags" registry defined in [RFC8402]. 414 8. Security Considerations 416 This document does not introduce additional security requirements and 417 mechanisms other than the ones described in [RFC8402]. 419 9. Contributors 420 Zhenbin Li 421 Huawei Technologies 422 Huawei Campus, No. 156 Beiqing Rd. 423 Beijing 100095 424 China 426 Email: lizhenbin@huawei.com 428 Jie Dong 429 Huawei Technologies 430 Huawei Campus, No. 156 Beiqing Rd. 431 Beijing 100095 432 China 434 Email: jie.dong@huawei.com 436 10. Acknowledgements 438 The authors would like to thank Stefano Previdi and Zafar Ali for 439 their valuable comments and suggestions. 441 11. References 443 11.1. Normative References 445 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 446 Requirement Levels", BCP 14, RFC 2119, 447 DOI 10.17487/RFC2119, March 1997, 448 . 450 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 451 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 452 May 2017, . 454 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 455 Decraene, B., Litkowski, S., and R. Shakir, "Segment 456 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 457 July 2018, . 459 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 460 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 461 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 462 . 464 [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, 465 D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 466 (SRv6) Network Programming", RFC 8986, 467 DOI 10.17487/RFC8986, February 2021, 468 . 470 11.2. Informative References 472 [I-D.gandhi-spring-udp-pm] 473 Gandhi, R., Filsfils, C., Voyer, D., Salsano, S., Ventre, 474 P. L., and M. Chen, "UDP Path for In-band Performance 475 Measurement for Segment Routing Networks", draft-gandhi- 476 spring-udp-pm-02 (work in progress), September 2018. 478 [I-D.ietf-idr-sr-policy-path-segment] 479 Li, C., Li, Z., Chen, H., Cheng, W., and K. Talaulikar, 480 "SR Policy Extensions for Path Segment and Bidirectional 481 Path", draft-ietf-idr-sr-policy-path-segment-03 (work in 482 progress), March 2021. 484 [I-D.ietf-pce-sr-bidir-path] 485 Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong, 486 "Path Computation Element Communication Protocol (PCEP) 487 Extensions for Associated Bidirectional Segment Routing 488 (SR) Paths", draft-ietf-pce-sr-bidir-path-05 (work in 489 progress), January 2021. 491 [I-D.ietf-pce-sr-path-segment] 492 Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong, 493 "Path Computation Element Communication Protocol (PCEP) 494 Extension for Path Segment in Segment Routing (SR)", 495 draft-ietf-pce-sr-path-segment-03 (work in progress), 496 February 2021. 498 [I-D.ietf-spring-mpls-path-segment] 499 Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler, 500 "Path Segment in MPLS Based Segment Routing Network", 501 draft-ietf-spring-mpls-path-segment-04 (work in progress), 502 April 2021. 504 [I-D.ietf-spring-segment-routing-policy] 505 Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and 506 P. Mattes, "Segment Routing Policy Architecture", draft- 507 ietf-spring-segment-routing-policy-11 (work in progress), 508 April 2021. 510 [RFC7799] Morton, A., "Active and Passive Metrics and Methods (with 511 Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, 512 May 2016, . 514 [RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S., 515 Decraene, B., Litkowski, S., and R. Shakir, "Segment 516 Routing with the MPLS Data Plane", RFC 8660, 517 DOI 10.17487/RFC8660, December 2019, 518 . 520 Authors' Addresses 522 Cheng Li 523 Huawei Technologies 525 Email: c.l@huawei.com 527 Weiqiang Cheng 528 China Mobile 530 Email: chengweiqiang@chinamobile.com 532 Mach(Guoyi) Chen 533 Huawei Technologies 535 Email: mach.chen@huawei.com 537 Dhruv Dhody 538 Huawei Technologies 539 Divyashree Techno Park, Whitefield 540 Bangalore, Karnataka 560066 541 India 543 Email: dhruv.ietf@gmail.com 545 Rakesh Gandhi 546 Cisco Systems, Inc. 547 Canada 549 Email: rgandhi@cisco.com 550 Yongqing Zhu 551 China Telecom 552 Guangzhou 554 Email: zhuyq8@chinatelecom.cn