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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SPRING W. Cheng 3 Internet-Draft China Mobile 4 Intended status: Informational S. Steffann 5 Expires: May 17, 2021 SJM Steffann Consultancy 6 November 13, 2020 8 Compressed SRv6 SID List Requirements 9 draft-srcompdt-spring-compression-requirement-01 11 Abstract 13 This document specifies requirements for solutions to compress SRv6 14 SID lists. 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at https://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on May 17, 2021. 33 Copyright Notice 35 Copyright (c) 2020 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (https://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 51 2. Conventions used in this document . . . . . . . . . . . . . . 3 52 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 53 2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 54 3. SRv6 SID List Compression Requirements . . . . . . . . . . . 4 55 3.1. Dataplane Efficiency and Performance Requirements . . . . 4 56 3.1.1. Encapsulation Header Size . . . . . . . . . . . . . . 4 57 3.1.2. Forwarding Efficiency . . . . . . . . . . . . . . . . 5 58 3.1.3. State Efficiency . . . . . . . . . . . . . . . . . . 5 59 4. SRv6 Specific Requirements . . . . . . . . . . . . . . . . . 5 60 4.1. Functional Requirements . . . . . . . . . . . . . . . . . 5 61 4.1.1. SID list length . . . . . . . . . . . . . . . . . . . 5 62 4.1.2. SID summarization . . . . . . . . . . . . . . . . . . 6 63 4.2. Operational Requirements . . . . . . . . . . . . . . . . 6 64 4.2.1. Lossless Compression . . . . . . . . . . . . . . . . 6 65 4.3. Scalability Requirements . . . . . . . . . . . . . . . . 6 66 4.3.1. Adjacency segment scale . . . . . . . . . . . . . . . 6 67 4.3.2. Prefix segment scale . . . . . . . . . . . . . . . . 7 68 4.3.3. Service Scale . . . . . . . . . . . . . . . . . . . . 7 69 5. Protocol Design Requirements . . . . . . . . . . . . . . . . 7 70 5.1. SRv6 Base Coexistence . . . . . . . . . . . . . . . . . . 7 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 72 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 73 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 74 9. Normative References . . . . . . . . . . . . . . . . . . . . 8 75 Appendix A. Proposed Requirements . . . . . . . . . . . . . . . 10 76 A.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 10 77 A.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 10 78 A.2.1. SRv6 Based . . . . . . . . . . . . . . . . . . . . . 10 79 A.2.2. SRv6 Functionality . . . . . . . . . . . . . . . . . 11 80 A.2.3. Heterogeneous SID lists . . . . . . . . . . . . . . . 13 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 83 1. Introduction 85 The SPRING working group defined SRv6, with [RFC8402] describing how 86 the Segment Routing (SR) architecture is instantiated on two data- 87 planes: SR over MPLS (SR-MPLS) and SR over IPv6 (SRv6). SRv6 uses a 88 routing header called the SR Header (SRH) [RFC8754] and defines SRv6 89 SID behaviors and a registry for identifying them in 90 [I-D.ietf-spring-srv6-network-programming]. SRv6 is a proposed 91 standard and is deployed today. 93 The SPRING working group has observed that some use cases, such as 94 strict path TE, may require long SRv6 SID lists. There are several 95 proposed methods to reduce the resulting SRv6 encapsulation size by 96 compressing the SID list. 98 The SPRING working group formed a design team to define requirements 99 for, and analyze proposals to, compress SRv6 SID lists. 101 It is a goal of the design team to identify the requirements for 102 proposals to SR over IPv6 SID list compression. 104 For each requirement, a description, rationale and metrics are 105 described. 107 The design team will produce a separate document to analyze the 108 proposals. 110 This document is a draft; additional requirements are under review, 111 additional requirements will be added, and current requirements may 112 change. Appendix A contains a subset of requirements without 113 unanimous consensus. Additional requirements without unanimous 114 consensus are not in the appendix. 116 2. Conventions used in this document 118 2.1. Requirements Language 120 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 121 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 122 "OPTIONAL" in this document are to be interpreted as described in BCP 123 14 [RFC2119] [RFC8174] when, and only when, they appear in all 124 capitals, as shown here. 126 2.2. Terminology 128 SR: Segment Routing 130 SRH: Segment Routing Header 132 MPLS: Multiprotocol Label Switching 134 SR-MPLS: Segment Routing over MPLS data plane 136 SID: Segment Identifier 138 SRv6: Segment Routing over IPv6 140 SRv6 SID List: A list of SRv6 SIDs 142 Compression proposal: A proposal to compress SRv6 SID lists 143 SRv6 base: SRv6 as defined in [RFC8402], [RFC8754], 144 [I-D.ietf-spring-srv6-network-programming] 146 SID numbering space: may be implemented as 148 o a single IGP instance 150 o a single IGP level or area 152 o two or more autonomous systems that coordinate SID numbering space 154 o two or more IGP instances that coordinate SID numbering space 156 SRv6 Encapsulation Header: The IPv6 header, and any extension headers 157 preceding a payload, used to implement a SRv6 base or compression 158 proposal. 160 3. SRv6 SID List Compression Requirements 162 3.1. Dataplane Efficiency and Performance Requirements 164 3.1.1. Encapsulation Header Size 166 Description: The compression proposal MUST reduce the size of the 167 SRv6 encapsulation header. 169 Rationale: A smaller SRv6 encapsulation results in better MTU 170 efficiency. 172 Metric: Compression is the ratio of the IPv6 encapsulation size of 173 SRv6 as defined in [RFC8402], [RFC8754], 174 [I-D.ietf-spring-srv6-network-programming] vs the IPv6 encapsulation 175 size of a given proposal. The encapsulation savings of a compression 176 proposal vs the SRv6 base is a useful measurement to compare 177 proposals. 179 The encapsulation metric (E) records the number of bytes required for 180 a proposal to encapsulate a packet given a specific segment list. 182 o E(proposal, segment list). 184 The encapsulation savings(ES)records the encapsulation savings for a 185 proposal to encapsulate a packet given a specific segment list. 187 o ES(proposal, segment list) = 1 - E(proposal, segment list)/E(SRv6 188 base, segment list). 190 3.1.2. Forwarding Efficiency 192 Description: The compression proposal SHOULD minimize the number of 193 required hardware resources accessed to process a segment. 195 Rationale: Efficiency in bits on the wire and processing efficiency 196 are both important. Optimizing one at the expense of the other may 197 lead to significant performance impact. 199 Metric: The data plane efficiency metric (D) records the data plane 200 forwarding efficiency of the proposed solution. Two metrics are used 201 and recorded at each segment endpoint: 203 o D.PRS(segment list): number of headers parsed during processing of 204 the segment list, starting from and including the IPv6 header. 206 o D.LKU(segment list): number of FIB lookups during processing of 207 the segment list. The type of lookup is also recorded as longest 208 prefix match (LPM) or exact match (EM) 210 3.1.3. State Efficiency 212 Description: The compression proposal SHOULD minimize the amount of 213 additional forwarding state stored at a node. 215 Rationale: Additional state increases the complexity of the control 216 plane and data plane. It can also result in an increase in memory 217 usage. 219 Metric: The state efficiency metric (S) records the amount of 220 additional forwarding state required by the proposed solution. 222 o S(node parameters): the number of additional forwarding states 223 that need to be stored at a node, given a set of node parameters 224 consisting of the number of nodes in the network, number of local 225 interfaces, number of adjacencies. The forwarding state is 226 counted as entries required in a Forwarding Information Base (FIB) 227 at a node. 229 4. SRv6 Specific Requirements 231 4.1. Functional Requirements 233 4.1.1. SID list length 235 Description: The compression proposal MUST be able to represent SR 236 paths that contain up to 16 segments. 238 Rationale: Strict TE paths require SID list lengths proportional to 239 the diameter of the SR domain. 241 Metric: The compression proposal must be able to steer a packet 242 through an SR path that contains up to sixteen segments. 244 4.1.2. SID summarization 246 Description: The solution MUST be compatible with segment 247 summarization. 249 Rationale: Summarization of segments is a key benefit of SRv6 vs SR 250 MPLS. In interdomain deployments, any node can reach any other node 251 via a single prefix segment. Without summarization, border router 252 SIDs must be leaked, and an additional global prefix segment is 253 required for each domain border to be traversed. 255 Metric: A solution supports summarization when segments can be 256 summarized for advertisement into other IGP domains or levels. 258 4.2. Operational Requirements 260 4.2.1. Lossless Compression 262 Description: The segments of the compressed SID list MUST be 263 equivalent to the original SID List. For example, a strict path TE 264 SID List is not compressed to a loose path TE SID list. 266 Rationale: In SRv6, we can represent a path to meet certain 267 objectives. A compression proposal needs to support the objectives 268 with the same path. 270 Metric: Information present in the pre-compression segment list MUST 271 also be present in the post-compression SID list. 273 4.3. Scalability Requirements 275 4.3.1. Adjacency segment scale 277 Description: The compression proposal MUST be capable of representing 278 65000 adjacency segments per node 280 Rationale: Typically, network operators deploy networks with tens or 281 hundreds of adjacency segments per node, but some network operators 282 may deploy networks that use more adjacency segments per node. 284 Metric: A proposal that allows 65000 adjacency segments per node 285 satisfies this requirement. 287 4.3.2. Prefix segment scale 289 Description: The compression proposal MUST be capable of representing 290 1 million prefix segments per SID numbering space. 292 Rationale: Typically, network operators deploy networks with 293 thousands of prefix segments per SID numbering space, but some 294 network operators may deploy networks that use more prefix segments 295 per SID numbering space. 297 Metric: A proposal that allows 1 million prefix segments per SID 298 numbering space satisfies this requirement. 300 4.3.3. Service Scale 302 Description: The compression proposal MUST be capable of representing 303 1 million services per node. 305 Rationale: Typically, network operators deploy networks with tens to 306 hundreds of thousands of services per node, but some network 307 operators may deploy networks that use more services per node. 309 Metric: A proposal that allows 1 million services per node satisfies 310 this requirement. 312 5. Protocol Design Requirements 314 5.1. SRv6 Base Coexistence 316 Description: The compression proposal MUST support deployment in 317 existing SRv6 networks. 319 Rationale: SRv6 is deployed today. A compression proposal that 320 interoperates well with SRv6, as deployed, will reduce the overhead 321 and simplify operations. For Network operators who would migrate to 322 compressed SRv6 SID lists, the migration is expected to gradually 323 occur over a period of time as they upgrade networks, domains, device 324 families and software instances. 326 Metric: A compliant compression proposal provides the following 328 o Supports simultaneous deployment at a node with current SRv6 SIDs. 330 o Supports simultaneous deployment at a node with current SRv6 331 control plane. 333 o Supports simultaneous operation of current SRv6 paths with 334 compressed paths. 336 o Supports the behaviors in 337 [I-D.ietf-spring-srv6-network-programming]. 339 o Does not require removal of existing IPv6 address planning. 341 6. IANA Considerations 343 This document has no requests to IANA. 345 7. Security Considerations 347 TBD 349 8. Contributors 351 The following individuals contributed to this draft 353 Chongfeng Xie, China Telecom, xiechf@chinatelecom.cn 355 Ron Bonica, Juniper Networks, rbonica@juniper.net 357 Darren Dukes, Cisco Systems, ddukes@cisco.com 359 Cheng Li, Huawei, c.l@huawei.com 361 Peng Shaofu, ZTE, peng.shaofu@zte.com.cn 363 Wim Henderickx, Nokia, wim.henderickx@nokia.com 365 9. Normative References 367 [I-D.ietf-6man-spring-srv6-oam] 368 Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M. 369 Chen, "Operations, Administration, and Maintenance (OAM) 370 in Segment Routing Networks with IPv6 Data plane (SRv6)", 371 draft-ietf-6man-spring-srv6-oam-08 (work in progress), 372 October 2020. 374 [I-D.ietf-bess-srv6-services] 375 Dawra, G., Filsfils, C., Talaulikar, K., Raszuk, R., 376 Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based 377 Overlay services", draft-ietf-bess-srv6-services-05 (work 378 in progress), November 2020. 380 [I-D.ietf-idr-bgpls-srv6-ext] 381 Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., 382 daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link 383 State Extensions for SRv6", draft-ietf-idr-bgpls- 384 srv6-ext-04 (work in progress), November 2020. 386 [I-D.ietf-lsr-flex-algo] 387 Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and 388 A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex- 389 algo-13 (work in progress), October 2020. 391 [I-D.ietf-lsr-isis-srv6-extensions] 392 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 393 Z. Hu, "IS-IS Extension to Support Segment Routing over 394 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11 395 (work in progress), October 2020. 397 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 398 Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B., 399 Francois, P., Voyer, D., Clad, F., and P. Camarillo, 400 "Topology Independent Fast Reroute using Segment Routing", 401 draft-ietf-rtgwg-segment-routing-ti-lfa-04 (work in 402 progress), August 2020. 404 [I-D.ietf-spring-segment-routing-policy] 405 Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and 406 P. Mattes, "Segment Routing Policy Architecture", draft- 407 ietf-spring-segment-routing-policy-09 (work in progress), 408 November 2020. 410 [I-D.ietf-spring-sr-service-programming] 411 Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca, 412 d., Li, C., Decraene, B., Ma, S., Yadlapalli, C., 413 Henderickx, W., and S. Salsano, "Service Programming with 414 Segment Routing", draft-ietf-spring-sr-service- 415 programming-03 (work in progress), September 2020. 417 [I-D.ietf-spring-srv6-network-programming] 418 Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., 419 Matsushima, S., and Z. Li, "SRv6 Network Programming", 420 draft-ietf-spring-srv6-network-programming-24 (work in 421 progress), October 2020. 423 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 424 Requirement Levels", BCP 14, RFC 2119, 425 DOI 10.17487/RFC2119, March 1997, 426 . 428 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 429 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 430 May 2017, . 432 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 433 Decraene, B., Litkowski, S., and R. Shakir, "Segment 434 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 435 July 2018, . 437 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 438 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 439 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 440 . 442 Appendix A. Proposed Requirements 444 This appendix contains requirements that the design team discussed 445 but could not be agreed upon. 447 A.1. Introduction 449 It is a goal of the design team to identify solutions to SRv6 SID 450 list compression that are based on the SRv6 standards. As such, this 451 document provides requirements for SRv6 SID list compression 452 solutions that utilize the existing SRv6 data plane and control 453 plane. 455 It is also a goal of the design team to consider proposals that are 456 not based on the SRv6 data plane and control plane. As such, this 457 document includes requirements to evaluate whether a compression 458 proposal provides all the functionality of SRv6 (section "SRv6 459 Functionality") in addition to satisfying compression specific 460 requirements. 462 A.2. Requirements 464 A.2.1. SRv6 Based 466 Description: A solution to compress SRv6 SID Lists SHOULD be based on 467 the SRv6 architecture, control plane and data plane. 469 Rationale: A compression proposal built on existing IETF standards is 470 preferable to creating new standards with equivalent functionality 471 and performance. 473 Metric: The utilization metric (U) records whether a proposal 474 utilizes the SRv6 specifications. 476 Utilization is recorded in a table, with a column per proposal and 477 rows consisting of the following metrics: 479 o U.RFC8402: utilizes [RFC8402]. 481 o U.RFC8754: utilizes [RFC8754]. 483 o U.PGM: utilizes [I-D.ietf-spring-srv6-network-programming]. 485 o U.IGP: utilizes [I-D.ietf-lsr-isis-srv6-extensions]. 487 o U.BGP: utilizes [I-D.ietf-bess-srv6-services]. 489 o U.POL: utilizes [I-D.ietf-spring-segment-routing-policy]. 491 o U.BLS: utilizes [I-D.ietf-idr-bgpls-srv6-ext]. 493 o U.SVC: utilizes [I-D.ietf-spring-sr-service-programming]. 495 o U.OAM: utilizes [I-D.ietf-6man-spring-srv6-oam]. 497 o U.ALG: utilizes [I-D.ietf-lsr-flex-algo]. 499 o U.TOT: the total number of specifications utilized. 501 Each cell contains "yes" for utilizes, or "no" for does not utilize. 502 U.TOT counts the number of "yes" in each column. 504 A.2.2. SRv6 Functionality 506 Description: A solution to compress an SRv6 SID list MUST support the 507 functionality of SRv6. This requirement and set of metrics is meant 508 to assess whether a proposal that is not fully SRv6 based, as 509 evaluated in section "SRv6 Based", provides equivalent functionality 510 to SRv6. Such a proposal may utilize different control planes and or 511 data planes. 513 Rationale: Operators require SRv6 functionality. Evaluating the 514 extent to which a proposal supports SRv6 functionality is important 515 for operators and implementors to understand the impact on network 516 operations. 518 Metric: The Functionality metric (F) records whether a proposal 519 supports SRv6 functionality and how the functionality is provided. 521 Functionality is recorded in a table with columns for each proposal 522 and rows consisting of the following metrics: 524 o F.SID: Supports SRv6 SIDs described in [RFC8402] 526 o F.SCOPE: Supports globally and locally scoped SIDs described in 527 [RFC8402] 529 o F.PFX: Supports prefix SIDs described in [RFC8402] and 530 [I-D.ietf-spring-srv6-network-programming] 532 o F.ADJ: Supports adjacency SIDs described in [RFC8402] and 533 [I-D.ietf-spring-srv6-network-programming] 535 o F.BIND: Supports binding SIDs described in [RFC8402] and 536 [I-D.ietf-spring-srv6-network-programming] 538 o F.PEER: Supports BGP peering SIDs described in [RFC8402] and 539 [I-D.ietf-spring-srv6-network-programming] 541 o F.SVC: Supports L3 and L2 VPN service SIDs described in 542 [I-D.ietf-spring-srv6-network-programming] 544 o F.ALG: Supports flexible algorithms described in 545 [I-D.ietf-lsr-flex-algo] 547 o F.TILFA: Supports TI-LFA as described in 548 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 550 o F.SEC: Supports securing an SR domain with ingress filtering as 551 defined in [RFC8754] 553 o F.IGP: Supports distributing topological SIDs and behaviors via 554 ISIS as described in [I-D.ietf-lsr-isis-srv6-extensions] 556 o F.BGP: Supports BGP VPNs as described in 557 [I-D.ietf-bess-srv6-services] 559 o F.POL: Supports SR policies and steering traffic over those 560 policies as described in [I-D.ietf-spring-segment-routing-policy] 562 o F.BLS: Supports Link State distribution via BGP as described in 563 [I-D.ietf-idr-bgpls-srv6-ext] 565 o F.SFC: Supports stateless service programming as described in 566 [I-D.ietf-spring-sr-service-programming] 568 o F.PING: Supports pinging a SID to verify the SID is implemented as 569 described in [I-D.ietf-6man-spring-srv6-oam] 571 o F.TOT: The total number of SRv6 functionality metrics supported by 572 a proposal 574 Each cell contains the specification name documenting the 575 functionality. F.TOT counts the number of specifications in each 576 column. 578 A.2.3. Heterogeneous SID lists 580 Description: The compression proposal SHOULD support a combination of 581 compressed and non-compressed segments in a single path. 583 Rationale: Support of SID lists with compressed and non-compressed 584 SIDs reduces encapsulation size when not all SRv6 nodes deploy the 585 compression proposal or 128-bit SIDs are required. 587 Metric: A compliant compression proposal supports both: 589 o classic 128-bit SRv6 SIDs in the IPv6 Destination Address field 591 o segment lists (i.e., paths) with both compressed and 128-bit SRv6 592 SIDs. 594 Authors' Addresses 596 Weiqiang Cheng 597 China Mobile 599 Email: chengweiqiang@chinamobile.com 601 Sanders Steffann 602 SJM Steffann Consultancy 604 Email: sander@steffann.nl