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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 Z. Li 4 Intended status: Informational Huawei Technologies 5 Expires: December 28, 2019 June 26, 2019 7 A Framework for Constructing Service Function Chaining Systems Based on 8 Segment Routing 9 draft-li-spring-sr-sfc-control-plane-framework-00 11 Abstract 13 Segment Routing (SR) allows for a flexible definition of end-to-end 14 paths by encoding paths as sequences of topological sub-paths, called 15 "segments". Segment routing architecture can be implemented over an 16 MPLS data plane as well as an IPv6 data plane. 18 Service Function Chaining (SFC) provides support for the creation of 19 composite services that consist of an ordered set of Service 20 Functions (SF) that are to be applied to packets and/or frames 21 selected as a result of classification. 23 SFC can be implemented based on several technologies, such as Network 24 Service Header (NSH) and SR. This document describes a framework for 25 constructing SFC based on Segment Routing. The document reviews the 26 control plane solutions for route distribution of service function 27 instance and service function path,and steering packets into a 28 service function chain. 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 December 28, 2019. 47 Copyright Notice 49 Copyright (c) 2019 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 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 66 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 67 2. Overview of SR Based SFC Control Plane . . . . . . . . . . . 4 68 3. Stateless SR Based SFC . . . . . . . . . . . . . . . . . . . 6 69 3.1. Service Function Instance Route Distribution . . . . . . 7 70 3.2. Service Function Path Route Distribution . . . . . . . . 7 71 3.3. Steer Packets into SFC . . . . . . . . . . . . . . . . . 8 72 4. Stateful SR Based SFC . . . . . . . . . . . . . . . . . . . . 8 73 4.1. Service Function Route Distribution . . . . . . . . . . . 8 74 4.2. Service Function Path Route Distribution . . . . . . . . 8 75 4.3. Steer Packets into SFC . . . . . . . . . . . . . . . . . 9 76 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 77 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 78 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 79 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 80 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 81 8.2. Informative References . . . . . . . . . . . . . . . . . 9 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 84 1. Introduction 86 Segment routing (SR) [RFC8402]is a source routing paradigm that 87 explicitly indicates the forwarding path for packets at the ingress 88 node by inserting an ordered list of instructions, called segments. 89 When segment routing is deployed on MPLS dataplane, it is called SR- 90 MPLS [I-D.ietf-spring-segment-routing-mpls]. When segment routing is 91 deployed on IPv6 dataplane, it is called SRv6 92 [I-D.ietf-6man-segment-routing-header]. 94 Service Function Chaining (SFC) [RFC7665] provides an architecture 95 that supports the creation of composite service instances that 96 consist of an ordered set of Service Functions (SF) that are to be 97 applied to packets and/or frames selected as a result of 98 classification. 100 SFC can be implemented based on Network Service Header [RFC8300]. In 101 NSH-based SFC, per-SFC state, such as a mapping between Service Path 102 ID (SPI) and Service Index (SI) to next-hop forwarding, needs to be 103 maintained on nodes along the service function path, and it can 104 therefore be termed as "stateful SFC". 105 [I-D.ietf-bess-nsh-bgp-control-plane] defines the use of BGP as a 106 control plane for networks that support Service Function Chaining 107 (SFC) based on NSH and MPLS. The document introduces a new BGP 108 address family called the SFC AFI/SAFI with two route types: Service 109 Function Instance Route (SFIR) and Service Function Path Route 110 (SFPR). A NSH or MPLS based SFC can be constructed based on the 111 information of SFIR and SFPR. 113 SFC can also be instantiated based on SR. In SR, the forwarding path 114 is explicitly encoded into the packets on the SR source node. In SR- 115 based SFC, an SFC can be represented by a SID list explicitly 116 indicated by the source SR node. The SID in SID list may need to be 117 associated with service information in order to indicate network 118 service, such as Deep Packet Inspection (DPI). Therefore, no per-SFC 119 state needs to be maintained along with the service function path, 120 and it can therefore be termed "stateless SFC". 122 In order to construct SR-based SFC, several mechanisms are proposed, 123 including the mechanisms of Service Function Instance Route(SFIR) and 124 Service Function Path Route(SFPR) distribution, as well as the 125 mechanism of steering packets into an SFP. This document reviews 126 these solutions to describe a framework for the construction of a 127 service function chaining system based on Segment Routing. 129 1.1. Requirements Language 131 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 132 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 133 "OPTIONAL" in this document are to be interpreted as described in BCP 134 14 [RFC2119] [RFC8174] when, and only when, they appear in all 135 capitals, as shown here. 137 1.2. Terminology 139 MPLS: Multiprotocol Label Switching. 141 SID: Segment Identifier. 143 SR: Segment Routing. 145 SR-MPLS: Segment Routing with MPLS data plane. 147 SRH: Segment Routing Header. 149 SFIR: Service Function Instance Route 151 SFPR: Service Function Path Route 153 Further, this document makes use of the terms defined in [RFC7665] 154 and [I-D.xuclad-spring-sr-service-programming]. 156 2. Overview of SR Based SFC Control Plane 158 As per [RFC7665], the architecture of SFC consists of classifiers, 159 Service Function Forwarders (SFFs), Service Functions (SFs) and SFC 160 proxies, see Figure 1. 162 +-----+ +-----+ +-----+ 163 | | | SFC | | | 164 | SF1 | |Proxy|---| SF2 | 165 +-----+ +-----+ +-----+ 166 | | 167 +--------------+ | | 168 | Service | SFC +------+ +------+ 169 |Classification| Encapsulation | SFF1 | | SFF2 | 170 ---->| Function |+---------------->| |--------| |--------> 171 | | | | | | 172 +--------------+ +------+ +------+ 174 SFC-enabled Domain 176 Figure 1. SFC Architecture 178 In order to construct a service function chain, SFIR and SFPR should 179 be distributed to classifiers and SFFs. Also, the rules of steering 180 packets into specific service function paths should be configured at 181 the classifier. [I-D.ietf-bess-nsh-bgp-control-plane]. 183 In SR, a source node can explicitly indicate the forwarding path for 184 packets by inserting an ordered list of instructions. These packets 185 steering policies, known as SR policy, can be installed by a central 186 controller via BGP [I-D.ietf-idr-segment-routing-te-policy] or other 187 mechanisms. 189 When SFC is constructed based on SR, SFPR and pakcet steering rules 190 can be installed by SR policy at the ingress node, which plays the 191 role of classifier in the SFC architecture. In other words, SFPR 192 does not need to be distributed to all the nodes along the service 193 function path. The architecture of SR based SFC is illustrated in 194 Figure 2. 196 +-----+ +-----+ +-----+ +-----+ 197 | | | | | SR | | | 198 |SR-C | | SF1 | |Proxy|---| SF2 | 199 +-----+ +-----+ +-----+ +-----+ 200 | | | 201 | | | 202 +--------------+ +------+ +------+ 203 | | SFC Encap/SR | SFF1/| | SFF2/| 204 ---->|CF/SR ingress |+---------------->| SR |--------| SR |--------> 205 | | | | | | 206 +--------------+ +------+ +------+ 208 SFC-enabled Domain 210 Figure 2. SR based SFC architecture. 212 o CF/SR ingress: an SR ingress node plays the role of Classifier in 213 the SFC architecture, and it connects to an SR controller, where 214 the SR policies originate. 216 o SR-C: SR Controller (SR-C) is connected to the SR ingress node, 217 and may be attached to any node in the network. SR-C is capable 218 of discovering topology, and calculating constrained paths for 219 service function chains. 221 o SFF/SR nodes: the SFF component in SFC architecture, which enables 222 SR to steer packets to SFs. 224 o SFn: Service Functions, can be SR-aware or SR-unaware. If an SF 225 is SR-unaware then SR proxy is needed. 227 o SR proxy: A proxy between SR nodes/SFF and SR-unaware SF. 229 There are two solutions to encode SFC in the SR data plane. 230 [I-D.xuclad-spring-sr-service-programming] defines data plane 231 functionality required to implement service segments and achieve 232 service programming in SR-enabled MPLS and IP networks. It can be 233 termed "Stateless SFC" since no per-SFC state is maintained on the SR 234 nodes along the service function path. 236 The second solution can be termed "Stateful 237 SFC"[I-D.guichard-spring-nsh-sr], since it still maintains per-SFC 238 state on nodes. [I-D.guichard-spring-nsh-sr]describes two modes: 240 o NSH-based SFC with SR-based transport tunnel: SR is used as 241 transport tunnel to route packets between classifier and SFF or 242 SFFs. Service plane routing relies on NSH. 244 o SR-based SFC with Integrated NSH Service Plane: The Service 245 Function Path is encoded within the SR segment-list, while the NSH 246 only maintains the service plane context information, which will 247 be used at NSH-aware SFs, and at SFFs for caching of SR segment- 248 lists. 250 In order to support these data plane encodings, control plane 251 mechanisms are required. The existing control plane mechanisms are 252 shown in table 1. 254 +------------------------------------------------------------+ 255 | SR based SFC | SFIR | SFPR | Steering policy| 256 +-------------------+-----------+-----------+----------------+ 257 | | BGP | BGP | BGP | 258 |Stateless | BGP-LS | PCEP | PCEP | 259 | | IGP | | | 260 +-------------------+-----------+-----------+----------------+ 261 |NSH-based SFC | BGP | BGP | BGP | 262 |with SR-based | | PCEP | | 263 |transport tunnel | | | | 264 | | | | | 265 | | | | | 266 +-------------------+-----------+-----------+----------------+ 267 |SR-based SFC | BGP | BGP | BGP | 268 |with Integrated | BGP-LS | PCEP | PCEP | 269 |NSH Service Plane | IGP | | | 270 | | | | | 271 +-------------------+-----------+-----------+----------------+ 272 Table 1. SR based SFC Control Plane Solutions 274 3. Stateless SR Based SFC 276 As describe in [I-D.xuclad-spring-sr-service-programming], service 277 instances are associated with a segment, called a service SID. These 278 service SIDs are leveraged as part of a SID-list to steer packets 279 through the corresponding services. 281 3.1. Service Function Instance Route Distribution 283 To associate a segment with a service, service information, such as 284 Service Function Type(SFT), should be included in segment 285 distribution. 287 To associate a segment with a service, service information, such as 288 Service Function Type (SFT), should be included in segment 289 distribution. [I-D.dawra-idr-bgp-ls-sr-service-segments] specifies 290 the extensions to BGP-LS for discovery and advertisement of service 291 segments so as to enable setup of service programming paths using 292 Segment Routing. [I-D.dawra-idr-bgp-ls-sr-service-segments]extends 293 SRv6 Node SID TLV [I-D.dawra-idr-bgpls-srv6-ext] and SR-MPLS SID/ 294 Label TLV [I-D.ietf-idr-bgp-ls-segment-routing-ext] to associate the 295 Service SID Value with Service-related Information using Service 296 Chaining Sub-TLV. The Service Chaining Sub-TLV contains information 297 of Service SID value, Function Identifier (Static Proxy, Dynamic 298 Proxy, Shared Memory Proxy, Masquerading Proxy, SR Aware Service 299 Etc.), Service Type (DPI, Firewall, Classifier, LB etc.), Traffic 300 Type (IPv4 OR IPv6 OR Ethernet) and Opaque Data (such as brand and 301 version, other extra information). This extension works for both SR- 302 MPLS and SRv6. 304 [I-D.ietf-bess-nsh-bgp-control-plane] proposes a BGP-based SFC 305 control plane solution, and it works for SR-MPLS as well. Service 306 function instance route distribution can use SFIR in SFC AFI/SAFI. 307 SFPR and steering rules for the classifier can be distributed by SR 308 policy, which is defined in [I-D.ietf-idr-segment-routing-te-policy]. 309 BGP control plane of SRv6-based SFC still needs to be defined. 311 IGP extensions are proposed by [I-D.xu-isis-service-function-adv] and 312 [I-D.xu-ospf-service-function-adv]. . In IS-IS solution, SFFs within 313 the SFC domain need to advertise each SF they are offering by using a 314 new sub-TLV of the IS-IS Router CAPABILITY TLV [RFC4971]. This new 315 sub-TLV is called Service Function sub-TLV, and it can appear 316 multiple times within a given IS-IS Router CAPABILITY TLV or when 317 more than one SF needs to be advertised. OSPF extensions are 318 similar, and use the OSPF Router Information (RI) Opaque LSA 319 [RFC4970] to carry Service Function sub-TLV. 321 However, due to IGP flooding issues, IGP extensions are not very 322 appropriate, and the drafts have expired for a long time. 324 3.2. Service Function Path Route Distribution 326 With SR, the SFPR does not need to be distributed to nodes along the 327 SFP but only to the ingress node. SFPR and steering rules for the 328 classifier can be distributed by SR policy. The BGP extension is 329 defined in [I-D.ietf-idr-segment-routing-te-policy]. The PCEP 330 extension is defined in [I-D.barth-pce-segment-routing-policy-cp]. 332 3.3. Steer Packets into SFC 334 In SR, packet steering rules are learned through SR policy. Thus, 335 there is no need to install other rules in the classifier, which is 336 the SR source node. 338 4. Stateful SR Based SFC 340 "Stateful SFC" [I-D.guichard-spring-nsh-sr]proposes two modes of SR 341 based SFC: 343 o NSH-based SFC with SR-based transport tunnel 345 o SR-based SFC with Integrated NSH Service Plane 347 4.1. Service Function Route Distribution 349 For NSH-based SFC with SR-based transport tunnel, service information 350 is maintained by NSH while SR is only used for transport between 351 SFFs, so [I-D.ietf-bess-nsh-bgp-control-plane] can be used for this 352 mode. 354 To indicate NSH, an SFF label [I-D.ietf-mpls-sfc-encapsulation] 355 should be inserted as the last label in the label stack in SR-MPLS. 356 The control plane of SFF is also described in 357 [I-D.ietf-bess-nsh-bgp-control-plane]. For choosing/configuring SR 358 as the transport tunnel, BGP route of SFF's BGP Tunnel Encapsulation 359 Attribute Type should be "SR TE Policy Type" 360 [I-D.ietf-idr-segment-routing-te-policy]. For SR-based SFC with 361 Integrated NSH Service Plane, there is no control plane solution as 362 yet defined. 364 4.2. Service Function Path Route Distribution 366 Same as SFIR distribution, SFPR BGP distribution in NSH-based SFC 367 with SR-based transport tunnel is identical to the mechanism defined 368 in [I-D.ietf-bess-nsh-bgp-control-plane]. PCEP extension for SFPR 369 distribution can reuse the NSH based SFC extension defined in 370 [I-D.wu-pce-traffic-steering-sfc]. For SR-based SFC with Integrated 371 NSH Service Plane, control plane solution is to be added in other 372 documents. 374 4.3. Steer Packets into SFC 376 For NSH-based SFC with SR-based transport tunnel, it is the same with 377 the NSH based SFC. The Classifier is responsible for determining to 378 which packet flow a packet belongs (usually by inspecting the packet 379 header), imposing an NSH, and initializing the NSH with the SPI of 380 the selected SFP and the SI of its first hop 381 [I-D.ietf-bess-nsh-bgp-control-plane]. For SR-based SFC with 382 Integrated NSH Service Plane, control plane solution is to be added 383 in other document. 385 5. IANA Considerations 387 This document does not require any IANA actions. 389 6. Security Considerations 391 This document does not introduce additional security requirements and 392 mechanisms. 394 7. Acknowledgements 396 TBA 398 8. References 400 8.1. Normative References 402 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 403 Requirement Levels", BCP 14, RFC 2119, 404 DOI 10.17487/RFC2119, March 1997, 405 . 407 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 408 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 409 May 2017, . 411 8.2. Informative References 413 [I-D.barth-pce-segment-routing-policy-cp] 414 Barth, C., Koldychev, M., Sivabalan, S., and C. Li, "PCEP 415 extension to support Segment Routing Policy Candidate 416 Paths", draft-barth-pce-segment-routing-policy-cp-02 (work 417 in progress), March 2019. 419 [I-D.dawra-idr-bgp-ls-sr-service-segments] 420 Dawra, G., Filsfils, C., daniel.bernier@bell.ca, d., 421 Uttaro, J., Decraene, B., Elmalky, H., Xu, X., Clad, F., 422 and K. Talaulikar, "BGP-LS Advertisement of Segment 423 Routing Service Segments", draft-dawra-idr-bgp-ls-sr- 424 service-segments-01 (work in progress), January 2019. 426 [I-D.dawra-idr-bgpls-srv6-ext] 427 Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., 428 daniel.bernier@bell.ca, d., Uttaro, J., Decraene, B., and 429 H. Elmalky, "BGP Link State Extensions for SRv6", draft- 430 dawra-idr-bgpls-srv6-ext-06 (work in progress), March 431 2019. 433 [I-D.filsfils-spring-srv6-network-programming] 434 Filsfils, C., Camarillo, P., Leddy, J., 435 daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6 436 Network Programming", draft-filsfils-spring-srv6-network- 437 programming-07 (work in progress), February 2019. 439 [I-D.gandhi-spring-udp-pm] 440 Gandhi, R., Filsfils, C., daniel.voyer@bell.ca, d., 441 Salsano, S., Ventre, P., and M. Chen, "UDP Path for In- 442 band Performance Measurement for Segment Routing 443 Networks", draft-gandhi-spring-udp-pm-02 (work in 444 progress), September 2018. 446 [I-D.guichard-spring-nsh-sr] 447 Guichard, J., Song, H., Tantsura, J., Halpern, J., 448 Henderickx, W., Boucadair, M., and S. Hassan, "NSH and 449 Segment Routing Integration for Service Function Chaining 450 (SFC)", draft-guichard-spring-nsh-sr-01 (work in 451 progress), March 2019. 453 [I-D.ietf-6man-segment-routing-header] 454 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 455 Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment 456 Routing Header (SRH)", draft-ietf-6man-segment-routing- 457 header-21 (work in progress), June 2019. 459 [I-D.ietf-bess-nsh-bgp-control-plane] 460 Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L. 461 Jalil, "BGP Control Plane for NSH SFC", draft-ietf-bess- 462 nsh-bgp-control-plane-11 (work in progress), May 2019. 464 [I-D.ietf-idr-bgp-ls-segment-routing-ext] 465 Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., 466 and M. Chen, "BGP Link-State extensions for Segment 467 Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-15 468 (work in progress), May 2019. 470 [I-D.ietf-idr-segment-routing-te-policy] 471 Previdi, S., Filsfils, C., Jain, D., Mattes, P., Rosen, 472 E., and S. Lin, "Advertising Segment Routing Policies in 473 BGP", draft-ietf-idr-segment-routing-te-policy-06 (work in 474 progress), May 2019. 476 [I-D.ietf-mpls-sfc-encapsulation] 477 Malis, A., Bryant, S., Halpern, J., and W. Henderickx, 478 "MPLS Transport Encapsulation For The SFC NSH", draft- 479 ietf-mpls-sfc-encapsulation-04 (work in progress), March 480 2019. 482 [I-D.ietf-spring-segment-routing-mpls] 483 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 484 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 485 data plane", draft-ietf-spring-segment-routing-mpls-22 486 (work in progress), May 2019. 488 [I-D.ietf-spring-segment-routing-policy] 489 Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d., 490 bogdanov@google.com, b., and P. Mattes, "Segment Routing 491 Policy Architecture", draft-ietf-spring-segment-routing- 492 policy-03 (work in progress), May 2019. 494 [I-D.li-idr-sr-policy-path-segment-distribution] 495 Li, C., Chen, M., Dong, J., and Z. Li, "Segment Routing 496 Policies for Path Segment and Bidirectional Path", draft- 497 li-idr-sr-policy-path-segment-distribution-01 (work in 498 progress), October 2018. 500 [I-D.li-pce-sr-bidir-path] 501 Li, C., Chen, M., Cheng, W., Li, Z., Dong, J., Gandhi, R., 502 and Q. Xiong, "PCEP Extensions for Associated 503 Bidirectional Segment Routing (SR) Paths", draft-li-pce- 504 sr-bidir-path-05 (work in progress), March 2019. 506 [I-D.li-pce-sr-path-segment] 507 Li, C., Chen, M., Cheng, W., Dong, J., Li, Z., Gandhi, R., 508 and Q. Xiong, "Path Computation Element Communication 509 Protocol (PCEP) Extension for Path Segment in Segment 510 Routing (SR)", draft-li-pce-sr-path-segment-05 (work in 511 progress), March 2019. 513 [I-D.wu-pce-traffic-steering-sfc] 514 Wu, Q., Dhody, D., Boucadair, M., Jacquenet, C., and J. 515 Tantsura, "PCEP Extensions for Service Function Chaining 516 (SFC)", draft-wu-pce-traffic-steering-sfc-12 (work in 517 progress), June 2017. 519 [I-D.xu-isis-service-function-adv] 520 Xu, X., Wu, N., Shah, H., and L. Contreras, "Advertising 521 Service Functions Using IS-IS", draft-xu-isis-service- 522 function-adv-05 (work in progress), May 2017. 524 [I-D.xu-ospf-service-function-adv] 525 Xu, X., Wu, N., Shah, H., and L. Contreras, "Advertising 526 Service Functions Using OSPF", draft-xu-ospf-service- 527 function-adv-02 (work in progress), June 2014. 529 [I-D.xuclad-spring-sr-service-programming] 530 Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca, 531 d., Li, C., Decraene, B., Ma, S., Yadlapalli, C., 532 Henderickx, W., and S. Salsano, "Service Programming with 533 Segment Routing", draft-xuclad-spring-sr-service- 534 programming-02 (work in progress), April 2019. 536 [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 537 S. Shaffer, "Extensions to OSPF for Advertising Optional 538 Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 539 2007, . 541 [RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed., 542 "Intermediate System to Intermediate System (IS-IS) 543 Extensions for Advertising Router Information", RFC 4971, 544 DOI 10.17487/RFC4971, July 2007, 545 . 547 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 548 Chaining (SFC) Architecture", RFC 7665, 549 DOI 10.17487/RFC7665, October 2015, 550 . 552 [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., 553 "Network Service Header (NSH)", RFC 8300, 554 DOI 10.17487/RFC8300, January 2018, 555 . 557 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 558 Decraene, B., Litkowski, S., and R. Shakir, "Segment 559 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 560 July 2018, . 562 Authors' Addresses 564 Cheng Li 565 Huawei Technologies 567 Email: chengli13@huawei.com 569 Zhenbin Li 570 Huawei Technologies 571 Huawei Campus, No. 156 Beiqing Rd. 572 Beijing 100095 573 China 575 Email: lizhenbin@huawei.com