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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Interdomain Routing Working Group C. Li 3 Internet-Draft Z. Li 4 Intended status: Standards Track Huawei Technologies 5 Expires: January 9, 2022 Y. Zhu 6 China Telecom 7 W. Cheng 8 China Mobile 9 K. Talaulikar 10 Cisco Systems 11 July 8, 2021 13 SR Policies Extensions for Path Segment and Bidirectional Path in BGP-LS 14 draft-ietf-idr-bgp-ls-sr-policy-path-segment-01 16 Abstract 18 This document specifies the way of collecting configuration and 19 states of SR policies carrying Path Segment and bidirectional path 20 information by using BPG-LS. Such information can be used by 21 external conponents for many use cases such as performance 22 measurement, path re-optimization and end-to-end protection. 24 Requirements Language 26 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 27 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 28 document are to be interpreted as described in RFC 2119 [RFC2119]. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on January 9, 2022. 47 Copyright Notice 49 Copyright (c) 2021 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 66 3. Carrying SR Path Sub-TLVs in BGP-LS . . . . . . . . . . . . . 3 67 3.1. SR Path Segment Sub-TLV . . . . . . . . . . . . . . . . . 5 68 3.2. Sub-TLVs for Bidirectional Path . . . . . . . . . . . . . 6 69 3.2.1. SR Bidirectional Path Sub-TLV . . . . . . . . . . . . 6 70 3.2.2. SR Reverse Path Segment List Sub-TLV . . . . . . . . 7 71 4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 7 72 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 73 5.1. BGP-LS TLVs . . . . . . . . . . . . . . . . . . . . . . . 7 74 5.2. BGP-LS SR Segment Descriptors . . . . . . . . . . . . . . 8 75 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 76 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 77 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 78 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 79 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 80 9.2. Informative References . . . . . . . . . . . . . . . . . 10 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 83 1. Introduction 85 Segment routing (SR) [RFC8402] is a source routing paradigm that 86 allows the ingress node steers packets into a specific path according 87 to the Segment Routing Policy 88 [I-D.ietf-spring-segment-routing-policy]. 90 However, the SR Policies defined in 91 [I-D.ietf-spring-segment-routing-policy] only supports unidirectional 92 SR paths and there is no path ID in a Segment List to identify an SR 93 path. For identifying an SR path and supporting bidirectional path 94 [I-D.ietf-spring-mpls-path-segment], new policies carrying Path 95 Segment and bidirectional path information are defined in 96 [I-D.li-idr-sr-policy-path-segment-distribution], as well as the 97 extensions to BGP to distribute new SR policies. The Path Segment 98 can be a Path Segment in SR-MPLS [I-D.ietf-spring-mpls-path-segment] 99 , or other IDs that can identify a path. 101 In many network scenarios, the configuration and state of each TE 102 Policy is required by a controller which allows the network operator 103 to optimize several functions and operations through the use of a 104 controller aware of both topology and state information 105 [I-D.ietf-idr-te-lsp-distribution]. 107 To collect the TE Policy information that is locally available in a 108 router, [I-D.ietf-idr-te-lsp-distribution] describes a new mechanism 109 by using BGP-LS update messages. 111 Based on the mechanism defined in [I-D.ietf-idr-te-lsp-distribution], 112 this document describes a mechanism to distribute configuration and 113 states of the new SR policies defined in 114 [I-D.li-idr-sr-policy-path-segment-distribution] to external 115 components using BGP-LS. 117 2. Terminology 119 This memo makes use of the terms defined in [RFC8402] and 120 [I-D.ietf-idr-te-lsp-distribution]. 122 3. Carrying SR Path Sub-TLVs in BGP-LS 124 A mechanism to collect states of SR Policies via BGP-LS is proposed 125 by [I-D.ietf-idr-te-lsp-distribution]. The characteristics of an SR 126 policy can be described by a TE Policy State TLV, which is carried in 127 the optional non-transitive BGP Attribute "LINK_STATE Attribute" 128 defined in [RFC7752]. The TE Policy State TLV contains several sub- 129 TLVs such as SR TE Policy sub-TLVs. Rather than replicating SR TE 130 Policy sub-TLVs, [I-D.ietf-idr-te-lsp-distribution] reuses the 131 equivalent sub-TLVs as defined in 132 [I-D.ietf-idr-segment-routing-te-policy]. 134 [I-D.li-idr-sr-policy-path-segment-distribution] defines the BGP 135 extensions for Path Segment. The Path Segment can appear at both 136 segment-list level and candidate path level upon the use case. The 137 encoding is shown below. 139 SR Policy SAFI NLRI: 140 Attributes: 141 Tunnel Encaps Attribute (23) 142 Tunnel Type: SR Policy 143 Binding SID 144 Preference 145 Priority 146 Policy Name 147 Explicit NULL Label Policy (ENLP) 148 Path Segment 149 Segment List 150 Weight 151 Path Segment 152 Segment 153 Segment 154 ... 155 Segment List 156 Weight 157 Path Segment 158 Segment 159 Segment 160 ... 161 ... 163 Figure 1. Path Segment in SR policy 165 Also, [I-D.li-idr-sr-policy-path-segment-distribution] defines SR 166 policy extensions for bidirectional SR path, the encoding is shown 167 below: 169 SR Policy SAFI NLRI: 170 Attributes: Tunnel Encaps Attribute (23) 171 Tunnel Type: SR Policy 172 Binding SID 173 Preference 174 Priority 175 Policy Name 176 Explicit NULL Label Policy (ENLP) 177 Bidirectioanl Path 178 Segment List 179 Weight 180 Path Segment 181 Segment 182 Segment 183 ... 184 Reverse Segment List 185 Weight 186 Path Segment 187 Segment 188 Segment 189 ... 191 Figure 2. SR policy for Bidirectional path 193 In order to collect configuration and states of unidirectional and 194 bidirectional SR policies defined in 195 [I-D.li-idr-sr-policy-path-segment-distribution], new sub-TLVs in SR 196 TE Policy sub-TLVs should be defined. Likewise, rather than 197 replicating SR Policy sub-TLVs, this document can reuse the 198 equivalent sub-TLVs as defined in 199 [I-D.li-idr-sr-policy-path-segment-distribution]. 201 3.1. SR Path Segment Sub-TLV 203 This section reuses the SR Path Segment sub-TLV defined in 204 [I-D.li-idr-sr-policy-path-segment-distribution] to describe a Path 205 Segment , and it can be included in the Segment List sub-TLV as 206 defined in [I-D.ietf-idr-te-lsp-distribution] . An SR Path Segment 207 sub-TLV can be associated with an SR path specified by a Segment List 208 sub-TLV, and it MUST appear only once within a Segment List sub-TLV. 209 Also, it can be used for identifying an SR candidate path or an SR 210 Policy defined in [I-D.ietf-spring-segment-routing-policy]. 212 The format of Path Segment TLV is included below for reference. 214 0 1 2 3 215 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 1 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | Type | Length | Flag | ST | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | Path Segment (Variable) | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 Figure 2. Path Segment sub-TLV 223 All fields, including type and length, are defined in 224 [I-D.li-idr-sr-policy-path-segment-distribution]. 226 3.2. Sub-TLVs for Bidirectional Path 228 In some scenarios like mobile backhaul transport network, there are 229 requirements to support bidirectional path. In SR, a bidirectional 230 path can be represented as a binding of two unidirectional SR paths 231 [I-D.ietf-spring-mpls-path-segment]. 232 [I-D.li-idr-sr-policy-path-segment-distribution] defines new sub-TLVs 233 to describe an SR bidirectional path. An SR policy carrying SR 234 bidirectional path information is expressed in Figure 1. 236 3.2.1. SR Bidirectional Path Sub-TLV 238 This section reuses the SR bidirectional path sub-TLV defined in 239 [I-D.li-idr-sr-policy-path-segment-distribution] to specify a 240 bidirectional path, which contains a Segment List sub-TLV 241 [I-D.ietf-idr-segment-routing-te-policy] and an associated Reverse 242 Path Segment List as defined in 243 [I-D.li-idr-sr-policy-path-segment-distribution]. The SR 244 bidirectional path sub-TLV has the following format: 246 0 1 2 3 247 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 1 248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 249 | Type | Length | RESERVED | 250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 251 | Sub-TLVs (Variable) | 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 253 Figure 3. SR Bidirectional path sub-TLV 255 All fields, including type and length, are defined in 256 [I-D.li-idr-sr-policy-path-segment-distribution]. 258 3.2.2. SR Reverse Path Segment List Sub-TLV 260 This section reuses the SR Reverse Path Segment List sub-TLV defined 261 in [I-D.li-idr-sr-policy-path-segment-distribution] to specify an 262 reverse SR path associated with the path specified by the Segment 263 List in the same SR Bidirectional Path Sub-TLV, and it has the 264 following format: 266 0 1 2 3 267 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 1 268 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 269 | Type | Length | RESERVED | 270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 271 | Sub-TLVs (Variable) | 272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 273 Figure 4. SR Reverse Path Segment List Sub-TLV 275 All fields, including type and length, are defined in 276 [I-D.li-idr-sr-policy-path-segment-distribution]. 278 4. Operations 280 No new operation procedures are defined in this document, the 281 operations procedures of [RFC7752] can apply to this document. 283 Typically but not limited to, the uni/bidirectional SR policies 284 carrying path identification information can be distributed by the 285 ingress node. 287 Generally, BGP-LS is used for collecting link states and 288 synchronizing with the external component. The consumer of the uni/ 289 bidirectional SR policies carrying path identification information is 290 not BGP LS process by itself, and it can be any applications such as 291 performance measurement [I-D.gandhi-spring-udp-pm] and path re- 292 coputation or re-optimization, etc. The operation of sending 293 information to other precesses is out of scope of this document. 295 5. IANA Considerations 297 5.1. BGP-LS TLVs 299 IANA maintains a registry called "Border Gateway Protocol - Link 300 State (BGP-LS) Parameters" with a sub-registry called "Node Anchor, 301 Link Descriptor and Link Attribute TLVs". The following TLV 302 codepoints are suggested (for early allocation by IANA): 304 Codepoint Description Reference 305 ------------------------------------------------------------- 306 1212 Path Segment sub-TLV This document 307 1213 SR Bidirectional Path sub-TLV This document 308 1214 Reverse Segment List sub-TLV This document 310 5.2. BGP-LS SR Segment Descriptors 312 This document defines new sub-TLVs in the registry "SR Segment 313 Descriptor Types" [I-D.ietf-idr-te-lsp-distribution] to be assigned 314 by IANA: 316 Codepoint Description Reference 317 ------------------------------------------------------------- 318 14 Path Segment sub-TLV This document 320 6. Security Considerations 322 TBA 324 7. Contributors 325 Mach(Guoyi) Chen 326 Huawei Technologies 327 Huawei Campus, No. 156 Beiqing Rd. 328 Beijing 100095 329 China 331 Email: Mach.chen@huawei.com 333 Jie Dong 334 Huawei Technologies 335 Huawei Campus, No. 156 Beiqing Rd. 336 Beijing 100095 337 China 339 Email: jie.dong@huawei.com 341 James N Guichard 342 Futurewei Technologies 343 2330 Central Express Way 344 Santa Clara 345 USA 347 Email: james.n.guichard@futurewei.com 349 8. Acknowledgements 351 Many thanks to Shraddha Hedge for her detailed review and 352 professional comments. 354 9. References 356 9.1. Normative References 358 [I-D.ietf-idr-segment-routing-te-policy] 359 Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., 360 Rosen, E., Jain, D., and S. Lin, "Advertising Segment 361 Routing Policies in BGP", draft-ietf-idr-segment-routing- 362 te-policy-11 (work in progress), November 2020. 364 [I-D.ietf-idr-te-lsp-distribution] 365 Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler, 366 H., and J. Tantsura, "Distribution of Traffic Engineering 367 (TE) Policies and State using BGP-LS", draft-ietf-idr-te- 368 lsp-distribution-14 (work in progress), October 2020. 370 [I-D.ietf-spring-mpls-path-segment] 371 Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler, 372 "Path Segment in MPLS Based Segment Routing Network", 373 draft-ietf-spring-mpls-path-segment-04 (work in progress), 374 April 2021. 376 [I-D.ietf-spring-segment-routing-policy] 377 Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and 378 P. Mattes, "Segment Routing Policy Architecture", draft- 379 ietf-spring-segment-routing-policy-11 (work in progress), 380 April 2021. 382 [I-D.li-idr-sr-policy-path-segment-distribution] 383 Li, C., Chen, M., Dong, J., and Z. Li, "Segment Routing 384 Policies for Path Segment and Bidirectional Path", draft- 385 li-idr-sr-policy-path-segment-distribution-01 (work in 386 progress), October 2018. 388 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 389 Requirement Levels", BCP 14, RFC 2119, 390 DOI 10.17487/RFC2119, March 1997, 391 . 393 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 394 S. Ray, "North-Bound Distribution of Link-State and 395 Traffic Engineering (TE) Information Using BGP", RFC 7752, 396 DOI 10.17487/RFC7752, March 2016, 397 . 399 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 400 Decraene, B., Litkowski, S., and R. Shakir, "Segment 401 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 402 July 2018, . 404 9.2. Informative References 406 [I-D.gandhi-spring-udp-pm] 407 Gandhi, R., Filsfils, C., Voyer, D., Salsano, S., Ventre, 408 P. L., and M. Chen, "UDP Path for In-band Performance 409 Measurement for Segment Routing Networks", draft-gandhi- 410 spring-udp-pm-02 (work in progress), September 2018. 412 [I-D.ietf-mpls-bfd-directed] 413 Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen, 414 "Bidirectional Forwarding Detection (BFD) Directed Return 415 Path for MPLS Label Switched Paths (LSPs)", draft-ietf- 416 mpls-bfd-directed-17 (work in progress), February 2021. 418 Authors' Addresses 420 Cheng Li 421 Huawei Technologies 422 Huawei Campus, No. 156 Beiqing Rd. 423 Beijing 100095 424 China 426 Email: c.l@huawei.com 428 Zhenbin Li 429 Huawei Technologies 430 Huawei Campus, No. 156 Beiqing Rd. 431 Beijing 100095 432 China 434 Email: lizhenbin@huawei.com 436 Yongqing Zhu 437 China Telecom 438 109 West Zhongshan Ave 439 Guangzhou 440 China 442 Email: zhuyq8@chinatelecom.cn 444 Weiqiang Cheng 445 China Mobile 446 Beijing 447 China 449 Email: chengweiqiang@chinamobile.com 451 Ketan Talaulikar 452 Cisco Systems 454 Email: ketant@cisco.com