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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-18) exists of draft-ietf-bess-nsh-bgp-control-plane-04 == Outdated reference: A later version (-22) exists of draft-ietf-spring-segment-routing-mpls-14 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MPLS Working Group A. Farrel 3 Internet-Draft Juniper Networks 4 Intended status: Standards Track S. Bryant 5 Expires: April 16, 2019 Huawei 6 J. Drake 7 Juniper Networks 8 October 13, 2018 10 An MPLS-Based Forwarding Plane for Service Function Chaining 11 draft-ietf-mpls-sfc-03 13 Abstract 15 Service Function Chaining (SFC) is the process of directing packets 16 through a network so that they can be acted on by an ordered set of 17 abstract service functions before being delivered to the intended 18 destination. An architecture for SFC is defined in RFC7665. 20 The Network Service Header (NSH) can be inserted into packets to 21 steer them along a specific path to realize a Service Function Chain. 23 Multiprotocol Label Switching (MPLS) is a widely deployed forwarding 24 technology that uses labels placed in a packet in a label stack to 25 identify the forwarding actions to be taken at each hop through a 26 network. Actions may include swapping or popping the labels as well, 27 as using the labels to determine the next hop for forwarding the 28 packet. Labels may also be used to establish the context under which 29 the packet is forwarded. 31 This document describes how Service Function Chaining can be achieved 32 in an MPLS network by means of a logical representation of the NSH in 33 an MPLS label stack. It does not deprecate or replace the NSH, but 34 acknowledges that there may be a need for an interim deployment of 35 SFC functionality in brownfield networks. 37 Status of This Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at https://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on April 16, 2019. 54 Copyright Notice 56 Copyright (c) 2018 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (https://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 72 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 73 3. Choice of Data Plane SPI/SI Representation . . . . . . . . . 4 74 4. Use Case Scenarios . . . . . . . . . . . . . . . . . . . . . 5 75 4.1. Label Swapping for Logical NSH . . . . . . . . . . . . . 5 76 4.2. Hierarchical Encapsulation . . . . . . . . . . . . . . . 5 77 4.3. Fine Control of Service Function Instances . . . . . . . 5 78 4.4. Micro Chains and Label Stacking . . . . . . . . . . . . . 6 79 4.5. SFC and Segment Routing . . . . . . . . . . . . . . . . . 6 80 5. Basic Unit of Representation . . . . . . . . . . . . . . . . 6 81 6. MPLS Label Swapping . . . . . . . . . . . . . . . . . . . . . 7 82 7. MPLS Label Stacking . . . . . . . . . . . . . . . . . . . . . 10 83 8. Mixed Mode Forwarding . . . . . . . . . . . . . . . . . . . . 12 84 9. A Note on Service Function Capabilities and SFC Proxies . . . 13 85 10. Control Plane Considerations . . . . . . . . . . . . . . . . 13 86 11. Use of the Entropy Label . . . . . . . . . . . . . . . . . . 14 87 12. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . 15 88 12.1. Indicating Metadata in User Data Packets . . . . . . . . 15 89 12.2. Inband Programming of Metadata . . . . . . . . . . . . . 17 90 13. Worked Examples . . . . . . . . . . . . . . . . . . . . . . . 20 91 14. Implementation Notes . . . . . . . . . . . . . . . . . . . . 24 92 15. Security Considerations . . . . . . . . . . . . . . . . . . . 25 93 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 94 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26 95 18. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26 96 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 97 19.1. Normative References . . . . . . . . . . . . . . . . . . 26 98 19.2. Informative References . . . . . . . . . . . . . . . . . 27 99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28 101 1. Introduction 103 Service Function Chaining (SFC) is the process of directing packets 104 through a network so that they can be acted on by an ordered set of 105 abstract service functions before being delivered to the intended 106 destination. An architecture for SFC is defined in [RFC7665]. 108 When applying a particular Service Function Chain to the traffic 109 selected by a service classifier, the traffic needs to be steered 110 through an ordered set of Service Functions (SFs) in the network. 111 This ordered set of SFs is termed a Service Function Path (SFP), and 112 the traffic is passed between Service Function Forwarders (SFFs) that 113 are responsible for delivering the packets to the SFs and for 114 forwarding them onward to the next SFF. 116 In order to steer the selected traffic between SFFs and to the 117 correct SFs the service classifier needs to attach information to 118 each packet. This information indicates the SFP on which the packet 119 is being forwarded and hence the SFs to which it must be delivered. 120 The information also indicates the progress the packet has already 121 made along the SFP. 123 The Network Service Header (NSH) [RFC8300] has been defined to carry 124 the necessary information for Service Function Chaining in packets. 125 The NSH can be inserted into packets and contains various information 126 including a Service Path Indicator (SPI), a Service Index (SI), and a 127 Time To Live (TTL) counter. 129 Multiprotocol Label Switching (MPLS) [RFC3031] is a widely deployed 130 forwarding technology that uses labels placed in a packet in a label 131 stack to identify the forwarding actions to be taken at each hop 132 through a network. Actions may include swapping or popping the 133 labels as well, as using the labels to determine the next hop for 134 forwarding the packet. Labels may also be used to establish the 135 context under which the packet is forwarded. In many cases, MPLS 136 will be used as a tunneling technology to carry packets through 137 networks between SFFs. 139 This document describes how Service Function Chaining can be achieved 140 in an MPLS network by means of a logical representation of the NSH in 141 an MPLS label stack. This approach is applicable to all forms of 142 MPLS forwarding (where labels are looked up at each hop, and swapped 143 or popped [RFC3031]). It does not deprecate or replace the NSH, but 144 acknowledges that there may be a need for an interim deployment of 145 SFC functionality in brownfield networks. The mechanisms described 146 in this document are a compromise between the full function that can 147 be achieved using the NSH, and the benefits of reusing the existing 148 MPLS forwarding paradigms. 150 Section 4 provides a short overview of several use case scenarios 151 that help to explain the relationship between the MPLS label 152 operations (swapping, popping, stacking) and the MPLS encoding of the 153 logical NSH described in this document). 155 It is assumed that the reader is fully familiar with the terms and 156 concepts introduced in [RFC7665] and [RFC8300]. 158 Note that one of the features of the SFC architecture described in 159 [RFC7665] is the "SFC proxy" that exists to include legacy SFs that 160 are not able to process NSH-encapsulated packets. This issue is 161 equally applicable to the use of MPLS-encapsulated packets that 162 encode a logical representation of an NSH. It is discussed further 163 in Section 9. 165 2. Requirements Language 167 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 168 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 169 "OPTIONAL" in this document are to be interpreted as described in BCP 170 14 [RFC2119] [RFC8174] when, and only when, they appear in all 171 capitals, as shown here. 173 3. Choice of Data Plane SPI/SI Representation 175 While [RFC8300] defines the NSH that can be used in a number of 176 environments, this document provides a mechanism to handle situations 177 in which the NSH is not ubiquitously deployed. In this case it is 178 possible to use an alternative data plane representation of the SPI/ 179 SI by carrying the identical semantics in MPLS labels. 181 In order to correctly select the mechanism by which SFC information 182 is encoded and carried between SFFs, it may be necessary to configure 183 the capabilities and choices either within the whole Service Function 184 Overlay Network, or on a hop by hop basis. It is a requirement that 185 both ends of a tunnel over the underlay network (i.e., a pair of SFFs 186 adjacent in the SFC) know that the tunnel is used for SFC and know 187 what form of NSH representation is used. A control plane signalling 188 approach to achieve these objectives is provided using BGP in 189 [I-D.ietf-bess-nsh-bgp-control-plane]. 191 Note that the encoding of the SFC information is independent of the 192 choice of tunneling technology used between SFFs. Thus, an MPLS 193 representation of the logical NSH (as defined in this document) may 194 be used even if the tunnel between a pair of SFFs is not an MPLS 195 tunnel. Conversely, MPLS tunnels may be used to carry other 196 encodings of the logical NSH (specifically, the NSH itself). 198 4. Use Case Scenarios 200 There are five scenarios that can be considered for the use of an 201 MPLS encoding in support of SFC. These are set out in the following 202 sub-sections. 204 4.1. Label Swapping for Logical NSH 206 The primary use case for SFC is described in [RFC7665] and delivered 207 using the NSH which, as described in [RFC8300], uses an encapsulation 208 with a position indicator that is modified at each SFC hop along the 209 chain to indicate the next hop. 211 The label swapping use case scenario effectively replaces the NSH 212 with an MPLS encapsulation as described in Section 6. The MPLS 213 labels encode the same information as the NSH to form a logical NSH. 214 The labels are modified (swapped per [RFC3031]) at each SFC hop along 215 the chain to indicate the next hop. The processing and forwarding 216 state for a chain (i.e., the actions to take on a received label) are 217 programmed in to the network using a control plane or management 218 plane. 220 4.2. Hierarchical Encapsulation 222 [RFC8459] describes an architecture for hierarchical encapsulation 223 using the NSH. It facilitates partitioning of SFC domains for 224 administrative reasons, and allows concatenation of service function 225 chains under the control of a service classifier. 227 The same function can be achieved in an MPLS network using an MPLS 228 encoding of the logical NSH, and label stacking as defined in 229 [RFC3031] and described in Section 7. In this model, swapping is 230 used per Section 4.1 to navigate one chain, and when the end of the 231 chain is reached, the final label is popped revealing the label for 232 another chain. Thus, the primary mode is swapping, but stacking is 233 used to enable the ingress classifier to control concatenation of 234 service function chains. 236 4.3. Fine Control of Service Function Instances 238 It may be that a service function chain (as described in Section 4.1 239 allows some leeway in the choice of service function instances along 240 the chain. However, it may be that a service classifier wishes to 241 constrain the choice and this can be achieved using chain 242 concatenation so that the first chain ends at the point of choice, 243 the next label in the stack indicates the specific service function 244 instance to be executed, and the next label in the stack starts a new 245 chain. Thus, a mixture of label swapping and stacking is used. 247 4.4. Micro Chains and Label Stacking 249 The scenario in Section 4.2 may be extended to its logical extreme by 250 making each concatenated chain as short as it can be: one service 251 function. Each label in the stack indicates the next service 252 function to be executed, and the network is programmed through the 253 control plane or management plane to know how to route to the next 254 (i.e., first) hop in each chain just as it would be to support the 255 scenarios in Section 4.1 and Section 4.2. 257 This scenario is functionally identical to the use of MPLS-SR for SFC 258 as described Section 4.5, and the discussion in that section applies 259 to this section as well. 261 4.5. SFC and Segment Routing 263 Segment Routing (SR) in an MPLS network (known as MPLS-SR) uses a 264 stack of MPLS labels to encode information about the path and network 265 functions that a packet should traverse. MPLS-SR is achieved by 266 applying control plane and management plane techniques to program the 267 MPLS forwarding plane, and by imposing labels on packets at the 268 entrance to the MPLS-SR network. 270 The application of SR to SFC was considered in early versions of the 271 SR architecture [RFC8402] and the MPLS-SR specification 272 [I-D.ietf-spring-segment-routing-mpls], but has since been moved out 273 of those documents. An implementation proposal for achieving SFC 274 using MPLS-SR can be found in [I-D.xuclad-spring-sr-service-chaining] 275 and is not discussed further in this document. 277 5. Basic Unit of Representation 279 When an MPLS label stack is used to carry a logical NSH, a basic unit 280 of representation is used. This unit comprises two MPLS labels as 281 shown below. The unit may be present one or more times in the label 282 stack as explained in subsequent sections. 284 In order to convey the same information as is present in the NSH, two 285 MPLS label stack entries are used. One carries a label to provide 286 context within the SFC scope (the SFC Context Label), and the other 287 carries a label to show which service function is to be actioned (the 288 SF Label). This two-label unit is shown in Figure 1. 290 0 1 2 3 291 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 1 292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 293 | SFC Context Label | TC |S| TTL | 294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 295 | SF Label | TC |S| TTL | 296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 298 Figure 1: The Basic Unit of MPLS Label Stack for SFC 300 The fields of these two label stack entries are encoded as follows: 302 Label: The Label fields contain the values of the SFC Context Label 303 and the SF Label encoded as 20 bit integers. The precise 304 semantics of these label fields are dependent on whether the label 305 stack entries are used for MPLS label swapping (see Section 6) or 306 MPLS label stacking (see Section 7). 308 TC: The TC bits have no meaning. They SHOULD be set to zero in both 309 label stack entries when a packet is sent and MUST be ignored on 310 receipt. 312 S: The bottom of stack bit has its usual meaning in MPLS. It MUST be 313 clear in the SFC Context label stack entry and MAY be set in the 314 SF label stack entry depending on whether the label is the bottom 315 of stack. 317 TTL: The TTL field in the SFC Context label stack entry SHOULD be 318 set to 1. The TTL in SF label stack entry (called the SF TTL) is 319 set according to its use for MPLS label swapping (see Section 6) 320 or MPLS label stacking (see Section 7 and is used to mitigate 321 packet loops. 323 The sections that follow show how this basic unit of MPLS label stack 324 may be used for SFC in the MPLS label swapping case and in the MPLS 325 label stacking. For simplicity, these sections do not describe the 326 use of metadata: that is covered separately in Section 12. 328 6. MPLS Label Swapping 330 This section describes how the basic unit of MPLS label stack for SFC 331 introduced in Section 5 is used when MPLS label swapping is in use. 332 The use case scenario for this approach is introduced in Section 4.1. 334 As can be seen from Figure 2, the top of the label stack comprises 335 the labels necessary to deliver the packet over the MPLS tunnel 336 between SFFs. Any MPLS encapsulation may be used (i.e., MPLS, MPLS 337 in UDP, MPLS in GRE, and MPLS in VXLAN or GPE), thus the tunnel 338 technology does not need to be MPLS, but that is shown here for 339 simplicity. 341 An entropy label ([RFC6790]) may also be present as described in 342 Section 11 344 Under these labels (or other encapsulation) comes a single instance 345 of the basic unit of MPLS label stack for SFC. In addition to the 346 interpretation of the fields of these label stack entries provided in 347 Section 5 the following meanings are applied: 349 SPI Label: The Label field of the SFC Context label stack entry 350 contains the value of the SPI encoded as a 20 bit integer. The 351 semantics of the SPI is exactly as defined in [RFC8300]. Note 352 that an SPI as defined by [RFC8300] can be encoded in 3 octets 353 (i.e., 24 bits), but that the Label field allows for only 20 bits 354 and reserves the values 0 though 15 as 'special purpose' labels 355 [RFC7274]. Thus, a system using MPLS representation of the 356 logical NSH MUST NOT assign SPI values greater than 2^20 - 1 or 357 less than 16. 359 SI Label: The Label field of the SF label stack entry contains the 360 value of the SI exactly as defined in [RFC8300]. Since the SI 361 requires only 8 bits, and to avoid overlap with the 'special 362 purpose' label range of 0 through 15 [RFC7274], the SI is carried 363 in the top (most significant) 8 bits of the Label field with the 364 low order 12 bits set to zero. 366 TC: The TC fields are as described in Section 5. 368 S: The S bits are as described in Section 5. 370 TTL: The TTL field in the SPI label stack entry SHOULD be set to 1 371 as stated in Section 5. The TTL in SF label stack entry is 372 decremented once for each forwarding hop in the SFP, i.e., for 373 each SFF transited, and so mirrors the TTL field in the NSH. 375 --------------- 376 ~ Tunnel Labels ~ 377 +---------------+ 378 ~ Optional ~ 379 ~ Entropy Label ~ 380 +---------------+ - - - 381 | SPI Label | 382 +---------------+ Basic unit of MPLS label stack for SFC 383 | SI Label | 384 +---------------+ - - - 385 | | 386 ~ Payload ~ 387 | | 388 --------------- 390 Figure 2: The MPLS SFC Label Stack 392 The following processing rules apply to the Label fields: 394 o When a classifier inserts a packet onto an SFP it sets the SPI 395 Label to indicate the identity of the SFP, and sets the SI Label 396 to indicate the first SF in the path. 398 o When a component of the SFC system processes a packet it uses the 399 SPI Label to identify the SFP and the SI Label to determine to 400 which SFF or instance of an SF (an SFI) to deliver the packet. 401 Under normal circumstances (with the exception of branching and 402 reclassification - see [I-D.ietf-bess-nsh-bgp-control-plane]) the 403 SPI Label value is preserved on all packets. The SI Label value 404 is modified by SFFs and through reclassification to indicate the 405 next hop along the SFP. 407 The following processing rules apply to the TTL field of the SF label 408 stack entry, and are derived from section 2.2 of [RFC8300]: 410 o When a classifier places a packet onto an SFP it MUST set the TTL 411 to a value between 1 and 255. It SHOULD set this according to the 412 expected length of the SFP (i.e., the number of SFs on the SFP), 413 but it MAY set it to a larger value according to local 414 configuration. The maximum TTL value supported in an NSH is 63, 415 and so the practical limit here may also be 63. 417 o When an SFF receives a packet from any component of the SFC system 418 (classifier, SFI, or another SFF) it MUST discard any packets with 419 TTL set to zero. It SHOULD log such occurrences, but MUST apply 420 rate limiting to any such logs. 422 o An SFF MUST decrement the TTL by one each time it performs a 423 forwarding lookup. 425 o If an SFF decrements the TTL to zero it MUST NOT send the packet, 426 and MUST discard the packet. It SHOULD log such occurrences, but 427 MUST apply rate limiting to any such logs. 429 o SFIs MUST ignore the TTL, but MUST mirror it back to the SFF 430 unmodified along with the SI (which may have been changed by local 431 reclassification). 433 o If a classifier along the SFP makes any change to the intended 434 path of the packet including for looping, jumping, or branching 435 (see [I-D.ietf-bess-nsh-bgp-control-plane] it MUST NOT change the 436 SI TTL of the packet. In particular, each component of the SFC 437 system MUST NOT increase the SI TTL value otherwise loops may go 438 undetected. 440 7. MPLS Label Stacking 442 This section describes how the basic unit of MPLS label stack for SFC 443 introduced in Section 5 is used when MPLS label stacking is used to 444 carry information about the SFP and SFs to be executed. The use case 445 scenarios for this approach is introduced in Section 4. 447 As can be seen in Figure 3, the top of the label stack comprises the 448 labels necessary to deliver the packet over the MPLS tunnel between 449 SFFs. Any MPLS encapsulation may be used. 451 An entropy label ([RFC6790]) may also be present as described in 452 Section 11 454 Under these labels comes one of more instances of the basic unit of 455 MPLS label stack for SFC. In addition to the interpretation of the 456 fields of these label stack entries provided in Section 5 the 457 following meanings are applied: 459 SFC Context Label: The Label field of the SFC Context label stack 460 entry contains a label that delivers SFC context. This label may 461 be used to indicate the SPI encoded as a 20 bit integer using the 462 semantics of the SPI is exactly as defined in [RFC8300] and noting 463 that in this case a system using MPLS representation of the 464 logical NSH MUST NOT assign SPI values greater than 2^20 - 1 or 465 less than 16. This label may also be used to convey other SFC 466 context-speific semantics such as indicating how to interpret the 467 SF Label or how to forward the packet to the node that offers the 468 SF. 470 SF Label: The Label field of the SF label stack entry contains a 471 value that identifies the next SFI to be actioned for the packet. 472 This label may be scoped globally or within the context of the 473 preceding SFC Context Label and comes from the range 16 ... 2^20 - 474 1. 476 TC: The TC fields are as described in Section 5. 478 S: The S bits are as described in Section 5. 480 TTL: The TTL fields in the SFC Context label stack entry SF label 481 stack entry SHOULD be set to 1 as stated in Section 5, but MAY be 482 set to larger values if the label indicated a forwarding operation 483 towards the node that hosts the SF. 485 ------------------- 486 ~ Tunnel Labels ~ 487 +-------------------+ 488 ~ Optional ~ 489 ~ Entropy Label ~ 490 +-------------------+ - - - 491 | SFC Context Label | 492 +-------------------+ Basic unit of MPLS label stack for SFC 493 | SF Label | 494 +-------------------+ - - - 495 | SFC Context Label | 496 +-------------------+ Basic unit of MPLS label stack for SFC 497 | SF Label | 498 +-------------------+ - - - 499 ~ ~ 500 +-------------------+ - - - 501 | SFC Context Label | 502 +-------------------+ Basic unit of MPLS label stack for SFC 503 | SF Label | 504 +-------------------+ - - - 505 | | 506 ~ Payload ~ 507 | | 508 ------------------- 510 Figure 3: The MPLS SFC Label Stack for Label Stacking 512 The following processing rules apply to the Label fields: 514 o When a classifier inserts a packet onto an SFP it adds a stack 515 comprising one or more instances of the basic unit of MPLS label 516 stack for SFC. Taken together, this stack defines the SFs to be 517 actioned and so defines the SFP that the packet will traverse. 519 o When a component of the SFC system processes a packet it uses the 520 top basic unit of label stack for SFC to determine to which SFI to 521 next deliver the packet. When an SFF receives a packet it 522 examines the top basic unit of MPLS label stack for SFC to 523 determine where to send the packet next. If the next recipient is 524 a local SFI, the SFC strips the basic unit of MPLS label stack for 525 SFC before forwarding the packet. 527 8. Mixed Mode Forwarding 529 The previous sections describe homogeneous networks where SFC 530 forwarding is either all label swapping or all label popping 531 (stacking). This simplification helps to clarify the explanation of 532 the mechanisms. 534 However, as described in Section 4.2, some uses cases may use label 535 swapping and stacking at the same time. Furthermore, it is also 536 possible that different parts of the network utilize swapping or 537 popping such that an end-to-end service chain has to utilize a 538 combination of both techniques. It is also worth noting that a 539 classifier may be content to use an SFP as installed in the network 540 by a control plane or management plane and so would use label 541 swapping, but that there may be a point in the SFP where a choice of 542 SFIs can be made (perhaps for load balancing) and where, in this 543 instance, the classifier wishes to exert control over that choice by 544 use of a specific entry on the label stack as described in 545 Section 4.3. 547 When an SFF receives a packet containing an MPLS label stack, it 548 checks whether it is processing an {SFP, SI} label pair for label 549 swapping or a {context label, SFI index} label pair for label 550 stacking. It then selects the appropriate SFI to which to send the 551 packet. When it receives the packet back from the SFI, it has four 552 cases to consider. 554 o If the current hop requires an {SFP, SI} and the next hop requires 555 an {SFP, SI}, it sets the SI label to the SI value of the current 556 hop, selects an instance of the SF to be executed at the next hop, 557 and tunnels the packet to the SFF for that SFI. 559 o If the current hop requires an {SFP, SI} and the next hop requires 560 a {context label, SFI label}, it pops the {SFP, SI} from the top 561 of the MPLS label stack and tunnels the packet to the SFF 562 indicated by the context label. 564 o If the current hop requires a {context label, SFI label}, it pops 565 the {context label, SFI label} from the top of the MPLS label 566 stack. 568 * If the new top of the MPLS label stack contains an {SFP, SI} 569 label pair, it selects an SFI to use at the next hop, and 570 tunnels the packet to SFF for that SFI. 572 * If the top of the MPLS label stack contains a {context label, 573 SFI label}, it tunnels the packet to the SFF indicated by the 574 context label. 576 9. A Note on Service Function Capabilities and SFC Proxies 578 The concept of an "SFC proxy" is introduced in [RFC7665]. An SFC 579 proxy is logically located between an SFF and an SFI that is not 580 "SFC-aware". Such SFIs are not capable of handling the SFC 581 encapsulation (whether that be NSH or MPLS) and need the 582 encapsulation stripped from the packets they are to process. In many 583 cases, legacy SFIs that were once deployed as "bumps in the wire" fit 584 into this category until they have been upgraded to be SFC-aware. 586 The job of an SFC proxy is to remove and then reimpose SFC 587 encapsulation so that the SFF is able to process as though it was 588 communication with an SFC-aware SFI, and so that the SFI is unaware 589 of the SFC encapsulation. In this regard, the job of an SFC proxy is 590 no different when NSH encapsulation is used and when MPLS 591 encapsulation is used as described in this document, although (of 592 course) it is different encapsulation bytes that must be removed and 593 reimposed. 595 It should be noted that the SFC proxy is a logical function. It 596 could be implemented as a separate physical component on the path 597 from the SFF to SFI, but it could be coresident with the SFF or it 598 could be a component of the SFI. This is purely an implementation 599 choice. 601 Note also that the delivery of metadata (see Section 12) requires 602 specific processing if an SFC proxy is in use. This is also no 603 different when NSH or the MPLS encoding defined in this document is 604 in use, and how it is handled will depend on how (or if) each non- 605 SFC-aware SFI can receive metadata. 607 10. Control Plane Considerations 609 In order that a packet may be forwarded along an SFP several 610 functional elements must be executed. 612 o Discovery/advertisement of SFIs. 614 o Computation of SFP. 616 o Programming of classifiers. 618 o Advertisement of forwarding instructions. 620 Various approaches may be taken. These include a fully centralized 621 model where SFFs report to a central controller the SFIs that they 622 support, the central controller computes the SFP and programs the 623 classifiers, and (if the label swapping approach is taken) the 624 central controller installs forwarding state in the SFFs that lie on 625 the SFP. 627 Alternatively, a dynamic control plane may be used such as that 628 described in [I-D.ietf-bess-nsh-bgp-control-plane]. In this case the 629 SFFs use the control plane to advertise the SFIs that they support, a 630 central controller computes the SFP and programs the classifiers, and 631 (if the label swapping approach is taken) the central controller uses 632 the control plane to advertise the SFPs so that SFFs that lie on the 633 SFP can install the necessary forwarding state. 635 11. Use of the Entropy Label 637 Entropy is used in ECMP situations to ensure that packets from the 638 same flow travel down the same path, thus avoiding jitter or re- 639 ordering issues within a flow. 641 Entropy is often determined by hashing on specific fields in a packet 642 header such as the "five-tuple" in the IP and transport headers. 643 However, when an MPLS label stack is present, the depth of the stack 644 could be too large for some processors to correctly determine the 645 entropy hash. This problem is addressed by the inclusion of an 646 Entropy Label as described in [RFC6790]. 648 When entropy is desired for packets as they are carried in MPLS 649 tunnels over the underlay network, it is RECOMMENDED that an Entropy 650 Label is included in the label stack immediately after the tunnel 651 labels and before the SFC labels as shown in Figure 2 and Figure 3. 653 If an Entropy Label is present in an MPLS payload, it is RECOMMENDED 654 that the initial classifier use that value in an Entropy Label 655 inserted in the label stack when the packet is forwarded (on the 656 first tunnel) to the first SFF. In this case it is not necessary to 657 remove the Entropy Label from the payload. 659 12. Metadata 661 Metadata is defined in [RFC7665] as providing "the ability to 662 exchange context information between classifiers and SFs, and among 663 SFs." [RFC8300] defines how this context information can be directly 664 encoded in fields that form part of the NSH encapsulation. 666 The next two sections describe how metadata is associated with user 667 data packets, and how metadata may be exchanged between SFC nodes in 668 the network, when using an MPLS encoding of the logical 669 representation of the NSH. 671 It should be noted that the MPLS encoding is less functional than the 672 direct use of the NSH. Both methods support metadata that is "per- 673 SFP" or "per-packet-flow" (see [RFC8393] for definitions of these 674 terms), but "per-packet" metadata (where the metadata must be carried 675 on each packet because it differs from one packet to the next even on 676 the same flow or SFP) is only supported using the NSH and not using 677 the mechanisms defined in this document. 679 12.1. Indicating Metadata in User Data Packets 681 Metadata is achieved in the MPLS realization of the logical NSH by 682 the use of an SFC Metadata Label which uses the Extended Special 683 Purpose Label construct [RFC7274]. Thus, three label stack entries 684 are present as shown in Figure 4: 686 o The Extension Label (value 15) 688 o An extended special purpose label called the Metadata Label 689 Indicator (MLI) (value TBD1 by IANA) 691 o The Metadata Label (ML). 693 ---------------- 694 | Extension = 15 | 695 +----------------+ 696 | MLI | 697 +----------------+ 698 | Metadata Label | 699 --------------- 701 Figure 4: The MPLS SFC Metadata Label 703 The Metadata Label value is an index into a table of metadata that is 704 programmed into the network using in-band or out-of-band mechanisms. 706 Out-of-band mechanisms potentially include management plane and 707 control plane solutions (such as 708 [I-D.ietf-bess-nsh-bgp-control-plane]), but are out of scope for this 709 document. The in-band mechanism is described in Section 12.2 711 The SFC Metadata Label (as a set of three labels as indicated in 712 Figure 4) may be present zero, one, or more times in an MPLS SFC 713 packet. For MPLS label swapping, the SFC Metadata Labels are placed 714 immediately after the basic unit of MPLS label stack for SFC as shown 715 in Figure 5. For MPLS label stacking, the SFC Metadata Labels can be 716 present zero, one, or more times and are placed at the bottom of the 717 label stack as shown in Figure 6. 719 ---------------- 720 ~ Tunnel Labels ~ 721 +----------------+ 722 ~ Optional ~ 723 ~ Entropy Label ~ 724 +----------------+ 725 | SPI Label | 726 +----------------+ 727 | SI Label | 728 +----------------+ 729 | Extension = 15 | 730 +----------------+ 731 | MLI | 732 +----------------+ 733 | Metadata Label | 734 +----------------+ 735 ~ Other ~ 736 | Metadata | 737 ~ Label Triples ~ 738 +----------------+ 739 | | 740 ~ Payload ~ 741 | | 742 ---------------- 744 Figure 5: The MPLS SFC Label Stack for Label Swapping with Metadata 745 Label 747 ------------------- 748 ~ Tunnel Labels ~ 749 +-------------------+ 750 ~ Optional ~ 751 ~ Entropy Label ~ 752 +-------------------+ 753 | SFC Context Label | 754 +-------------------+ 755 | SF Label | 756 +-------------------+ 757 ~ ~ 758 +-------------------+ 759 | SFC Context Label | 760 +-------------------+ 761 | SF Label | 762 +-------------------+ 763 | Extension = 15 | 764 +-------------------+ 765 | MLI | 766 +-------------------+ 767 | Metadata Label | 768 +-------------------+ 769 ~ Other ~ 770 | Metadata | 771 ~ Label Triples ~ 772 +-------------------+ 773 | | 774 ~ Payload ~ 775 | | 776 ------------------- 778 Figure 6: The MPLS SFC Label Stack for Label Stacking with Metadata 779 Label 781 12.2. Inband Programming of Metadata 783 A mechanism for sending metadata associated with an SFP without a 784 payload packet is described in [RFC8393]. The same approach can be 785 used in an MPLS network where the NSH is logically represented by an 786 MPLS label stack. 788 The packet header is formed exactly as previously described in this 789 document so that the packet will follow the SFP through the SFC 790 network. However, instead of payload data, metadata is included 791 after the bottom of the MPLS label stack. An Extended Special 792 Purpose Label is used to indicate that the metadata is present. 793 Thus, three label stack entries are present: 795 o The Extension Label (value 15) 797 o An extended special purpose label called the Metadata Present 798 Indicator (MPI) (value TBD2 by IANA) 800 o The Metadata Label (ML) that is associated with this metadata on 801 this SFP and can be used to indicate the use of the metadata as 802 described in Section 12. 804 The SFC Metadata Present Label, if present, is placed immediately 805 after the last basic unit of MPLS label stack for SFC. The resultant 806 label stacks are shown in Figure 7 for the MPLS label swapping case 807 and Figure 8 for the MPLS label stacking case. 809 --------------- 810 ~ Tunnel Labels ~ 811 +---------------+ 812 ~ Optional ~ 813 ~ Entropy Label ~ 814 +---------------+ 815 | SPI Label | 816 +---------------+ 817 | SI Label | 818 +---------------+ 819 | Extension = 15| 820 +---------------+ 821 | MPI | 822 +---------------+ 823 | Metadata Label| 824 +---------------+ 825 | | 826 ~ Metadata ~ 827 | | 828 --------------- 830 Figure 7: The MPLS SFC Label Stack for Label Swapping Carrying 831 Metadata 833 ------------------- 834 ~ Tunnel Labels ~ 835 +-------------------+ 836 ~ Optional ~ 837 ~ Entropy Label ~ 838 +-------------------+ 839 | SFC Context Label | 840 +-------------------+ 841 | SF Label | 842 +-------------------+ 843 | SFC Context Label | 844 +-------------------+ 845 | SF Label | 846 +-------------------+ 847 ~ ~ 848 +-------------------+ 849 | SFC Context Label | 850 +-------------------+ 851 | SF Label | 852 +-------------------+ 853 | Extension = 15 | 854 +-------------------+ 855 | MPI | 856 +-------------------+ 857 | Metadata Label | 858 +-------------------+ 859 | | 860 ~ Metadata ~ 861 | | 862 ------------------- 864 Figure 8: The MPLS SFC Label Stack for Label Stacking Carrying 865 Metadata 867 In both cases the metadata is formatted as a TLV as shown in 868 Figure 9. 870 0 1 2 3 871 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 1 872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 873 | Length | Metadata Type | 874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 875 ~ Metadata ~ 876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 878 Figure 9: The Metadata TLV 880 The fields of this TLV are interpreted as follows: 882 Length: The length of the metadata carried in the Metadata field in 883 octets not including any padding. 885 Metadata Type: The type of the metadata present. Values for this 886 field are taken from the "MD Types" registry maintained by IANA 887 and defined in [RFC8300]. 889 Metadata: The actual metadata formatted as described in whatever 890 document defines the metadata. This field is end-padded with zero 891 to three octets of zeroes to take it up to a four octet boundary. 893 13. Worked Examples 895 This section reverts to the simplified descriptions of networks that 896 rely wholly on label swapping or label stacking. As described in 897 Section 4, actual deployment scenarios may depend on the use of both 898 mechanisms and utilize a mixed mode as described in Section 8. 900 Consider the simplistic MPLS SFC overlay network shown in Figure 10. 901 A packet is classified for an SFP that will see it pass through two 902 Service Functions, SFa and SFb, that are accessed through Service 903 Function Forwarders SFFa and SFFb respectively. The packet is 904 ultimately delivered to destination, D. 906 Let us assume that the SFP is computed and assigned the SPI of 239. 907 The forwarding details of the SFP are distributed (perhaps using the 908 mechanisms of [I-D.ietf-bess-nsh-bgp-control-plane]) so that the SFFs 909 are programmed with the necessary forwarding instructions. 911 The packet progresses as follows: 913 a. The classifier assigns the packet to the SFP and imposes two 914 label stack entries comprising a single basic unit of MPLS SFC 915 representation: 917 * The higher label stack entry contains a label carrying the SPI 918 value of 239. 920 * The lower label stack entry contains a label carrying the SI 921 value of 255. 923 Further labels may be imposed to tunnel the packet from the 924 classifier to SFFa. 926 b. When the packet arrives at SFFa it strips any labels associated 927 with the tunnel that runs from the classifier to SFFa. SFFa 928 examines the top labels and matches the SPI/SI to identify that 929 the packet should be forwarded to SFa. The packet is forwarded 930 to SFa unmodified. 932 c. SFa performs its designated function and returns the packet to 933 SFFa. 935 d. SFFa modifies the SI in the lower label stack entry (to 254) and 936 uses the SPI/SI to look up the forwarding instructions. It sends 937 the packet with two label stack entries: 939 * The higher label stack entry contains a label carrying the SPI 940 value of 239. 942 * The lower label stack entry contains a label carrying the SI 943 value of 254. 945 Further labels may be imposed to tunnel the packet from the SFFa 946 to SFFb. 948 e. When the packet arrives at SFFb it strips any labels associated 949 with the tunnel from SFFa. SFFb examines the top labels and 950 matches the SPI/SI to identify that the packet should be 951 forwarded to SFb. The packet is forwarded to SFb unmodified. 953 f. SFb performs its designated function and returns the packet to 954 SFFb. 956 g. SFFb modifies the SI in the lower label stack entry (to 253) and 957 uses the SPI/SI to lookup up the forwarding instructions. It 958 determines that it is the last SFF in the SFP so it strips the 959 two SFC label stack entries and forwards the payload toward D 960 using the payload protocol. 962 +---------------------------------------------------+ 963 | MPLS SFC Network | 964 | | 965 | +---------+ +---------+ | 966 | | SFa | | SFb | | 967 | +----+----+ +----+----+ | 968 | ^ | | ^ | | | 969 | (b)| | |(c) (e)| | |(f) | 970 | (a) | | V (d) | | V (g) | 971 +----------+ ---> +----+----+ ----> +----+----+ ---> +-------+ 972 |Classifier+------+ SFFa +-------+ SFFb +------+ D | 973 +----------+ +---------+ +---------+ +-------+ 974 | | 975 +---------------------------------------------------+ 977 Figure 10: Service Function Chaining in an MPLS Network 979 Alternatively, consider the MPLS SFC overlay network shown in 980 Figure 11. A packet is classified for an SFP that will see it pass 981 through two Service Functions, SFx and SFy, that are accessed through 982 Service Function Forwarders SFFx and SFFy respectively. The packet 983 is ultimately delivered to destination, D. 985 Let us assume that the SFP is computed and assigned the SPI of 239. 986 However, the forwarding state for the SFP is not distributed and 987 installed in the network. Instead it will be attached to the 988 individual packets using the MPLS label stack. 990 The packet progresses as follows: 992 1. The classifier assigns the packet to the SFP and imposes two 993 basic units of MPLS SFC representation to describe the full SFP: 995 * The top basic unit comprises two label stack entries as 996 follows: 998 + The higher label stack entry contains a label carrying the 999 SFC context. 1001 + The lower label stack entry contains a label carrying the 1002 SF indicator for SFx. 1004 * The lower basic unit comprises two label stack entries as 1005 follows: 1007 + The higher label stack entry contains a label carrying the 1008 SFC context. 1010 + The lower label stack entry contains a label carrying the 1011 SF indicator for SFy. 1013 Further labels may be imposed to tunnel the packet from the 1014 classifier to SFFx. 1016 2. When the packet arrives at SFFx it strips any labels associated 1017 with the tunnel from the classifier. SFFx examines the top 1018 labels and matches the context/SF values to identify that the 1019 packet should be forwarded to SFx. The packet is forwarded to 1020 SFx unmodified. 1022 3. SFx performs its designated function and returns the packet to 1023 SFFx. 1025 4. SFFx strips the top basic unit of MPLS SFC representation 1026 revealing the next basic unit. It then uses the revealed 1027 context/SF values to determine how to route the packet to the 1028 next SFF, SFFy. It sends the packet with just one basic unit of 1029 MPLS SFC representation comprising two label stack entries: 1031 * The higher label stack entry contains a label carrying the SFC 1032 context. 1034 * The lower label stack entry contains a label carrying the SF 1035 indicator for SFy. 1037 Further labels may be imposed to tunnel the packet from the SFFx 1038 to SFFy. 1040 5. When the packet arrives at SFFy it strips any labels associated 1041 with the tunnel from SFFx. SFFy examines the top labels and 1042 matches the context/SF values to identify that the packet should 1043 be forwarded to SFy. The packet is forwarded to SFy unmodified. 1045 6. SFy performs its designated function and returns the packet to 1046 SFFy. 1048 7. SFFy strips the top basic unit of MPLS SFC representation 1049 revealing the payload packet. It forwards the payload toward D 1050 using the payload protocol. 1052 +---------------------------------------------------+ 1053 | MPLS SFC Network | 1054 | | 1055 | +---------+ +---------+ | 1056 | | SFx | | SFy | | 1057 | +----+----+ +----+----+ | 1058 | ^ | | ^ | | | 1059 | (2)| | |(3) (5)| | |(6) | 1060 | (1) | | V (4) | | V (7) | 1061 +----------+ ---> +----+----+ ----> +----+----+ ---> +-------+ 1062 |Classifier+------+ SFFx +-------+ SFFy +------+ D | 1063 +----------+ +---------+ +---------+ +-------+ 1064 | | 1065 +---------------------------------------------------+ 1067 Figure 11: Service Function Chaining Using MPLS Label Stacking 1069 14. Implementation Notes 1071 It is not the job of an IETF specification to describe the internals 1072 of an implementation except where that directly impacts upon the bits 1073 on the wire that change the likelihood of interoperability, or where 1074 the availability of configuration or security options directly affect 1075 the utility of an implementation. 1077 However, in view of the objective of this document to acknowledge 1078 that there may be a need for an interim deployment of SFC 1079 functionality in brownfield MPLS networks, this section provides some 1080 observations about how an SFF might utilize MPLS features that are 1081 available in existing routers. This section is not intended to be 1082 definitive or technically complete, but is indicative. 1084 Consider the mechanism used to indicate to which Virtual Routing and 1085 Forwarding (VRF) an incoming MPLS packet should be routed in a Layer 1086 3 Virtual Private Network (L3VPN) [RFC4364]. In this case, the top 1087 MPLS label is an indicator of the VRF that is to be used to route the 1088 payload. 1090 A similar approach can be taken with the label swapping SFC technique 1091 described in Section 6 such that the SFC Context Label identifies a 1092 routing table specific to the SFP. The SF Label can be looked up in 1093 the context of this routing table to determine to which SF to direct 1094 the packet, and how to forward it to the next SFF. 1096 Advanced features (such as metadata) are not inspected by SFFs. The 1097 packets are passed to SFIs that are MPLS-SFC-aware or to SFC proxies, 1098 and those components are responsible for handling all metadata 1099 issues. 1101 Of course, an actual implementation might make considerable 1102 optimizations on this approach, but this section should provide hints 1103 about how MPLS-based SFC might be achieved with relatively small 1104 modifications to deployed MPLS devices. 1106 15. Security Considerations 1108 Discussion of the security properties of SFC networks can be found in 1109 [RFC7665]. Further security discussion for the NSH and its use is 1110 present in [RFC8300]. 1112 It is fundamental to the SFC design that the classifier is a trusted 1113 resource which determines the processing that the packet will be 1114 subject to, including for example the firewall. It is also 1115 fundamental to the MPLS design that packets are routed through the 1116 network using the path specified by the node imposing the labels, and 1117 that labels are swapped or popped correctly. Where an SF is not 1118 encapsulation aware the encapsulation may be stripped by an SFC proxy 1119 such that packet may exist as a native packet (perhaps IP) on the 1120 path between SFC proxy and SF, however this is an intrinsic part of 1121 the SFC design which needs to define how a packet is protected in 1122 that environment. 1124 Additionally, where a tunnel is used to link two non-MPLS domains, 1125 the tunnel design needs to specify how the tunnel is secured. 1127 Thus the security vulnerabilities are addressed (or should be 1128 addressed) in all the underlying technologies used by this design, 1129 which itself does not introduce any new security vulnerabilities. 1131 16. IANA Considerations 1133 This document requests IANA to make allocations from the "Extended 1134 Special-Purpose MPLS Label Values" subregistry of the "Special- 1135 Purpose Multiprotocol Label Switching (MPLS) Label Values" registry 1136 as follows: 1138 Value | Description | 1139 -------+-----------------------------------+-------------- 1140 TBD1 | Metadata Label Indicator (MLI) | [This.I-D] 1141 TBD2 | Metadata Present Indicator (MPI) | [This.I-D] 1143 17. Acknowledgements 1145 This document derives ideas and text from 1146 [I-D.ietf-bess-nsh-bgp-control-plane]. 1148 The authors are grateful to all those who contributed to the 1149 discussions that led to this work: Loa Andersson, Andrew G. Malis, 1150 Alexander Vainshtein, Joel M. Halpern, Tony Przygienda, Stuart 1151 Mackie, Keyur Patel, and Jim Guichard. Loa Andersson provided 1152 helpful review comments. 1154 Thanks to Loa Andersson, Lizhong Jin, Matthew Bocci, Joel Halpern, 1155 and Mach Chen for reviews of this text. 1157 The authors would like to be able to thank the authors of 1158 [I-D.xuclad-spring-sr-service-chaining] and [RFC8402] whose original 1159 work on service chaining and the identification of services using 1160 SIDs, and conversation with whom helped clarify the application of 1161 MPLS-SR to SFC. 1163 Particular thanks to Loa Andersson for conversations and advice about 1164 working group process. 1166 18. Contributors 1168 The following people contributed text to this document: 1170 Andrew Malis 1171 Email: agmalis@gmail.com 1173 19. References 1175 19.1. Normative References 1177 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1178 Requirement Levels", BCP 14, RFC 2119, 1179 DOI 10.17487/RFC2119, March 1997, 1180 . 1182 [RFC7274] Kompella, K., Andersson, L., and A. Farrel, "Allocating 1183 and Retiring Special-Purpose MPLS Labels", RFC 7274, 1184 DOI 10.17487/RFC7274, June 2014, 1185 . 1187 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1188 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1189 May 2017, . 1191 [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., 1192 "Network Service Header (NSH)", RFC 8300, 1193 DOI 10.17487/RFC8300, January 2018, 1194 . 1196 [RFC8393] Farrel, A. and J. Drake, "Operating the Network Service 1197 Header (NSH) with Next Protocol "None"", RFC 8393, 1198 DOI 10.17487/RFC8393, May 2018, 1199 . 1201 19.2. Informative References 1203 [I-D.ietf-bess-nsh-bgp-control-plane] 1204 Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L. 1205 Jalil, "BGP Control Plane for NSH SFC", draft-ietf-bess- 1206 nsh-bgp-control-plane-04 (work in progress), July 2018. 1208 [I-D.ietf-spring-segment-routing-mpls] 1209 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 1210 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 1211 data plane", draft-ietf-spring-segment-routing-mpls-14 1212 (work in progress), June 2018. 1214 [I-D.xuclad-spring-sr-service-chaining] 1215 Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca, 1216 d., Li, C., Decraene, B., Ma, S., Yadlapalli, C., 1217 Henderickx, W., and S. Salsano, "Segment Routing for 1218 Service Chaining", draft-xuclad-spring-sr-service- 1219 chaining-01 (work in progress), March 2018. 1221 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol 1222 Label Switching Architecture", RFC 3031, 1223 DOI 10.17487/RFC3031, January 2001, 1224 . 1226 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 1227 Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 1228 2006, . 1230 [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and 1231 L. Yong, "The Use of Entropy Labels in MPLS Forwarding", 1232 RFC 6790, DOI 10.17487/RFC6790, November 2012, 1233 . 1235 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 1236 Chaining (SFC) Architecture", RFC 7665, 1237 DOI 10.17487/RFC7665, October 2015, 1238 . 1240 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 1241 Decraene, B., Litkowski, S., and R. Shakir, "Segment 1242 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 1243 July 2018, . 1245 [RFC8459] Dolson, D., Homma, S., Lopez, D., and M. Boucadair, 1246 "Hierarchical Service Function Chaining (hSFC)", RFC 8459, 1247 DOI 10.17487/RFC8459, September 2018, 1248 . 1250 Authors' Addresses 1252 Adrian Farrel 1253 Juniper Networks 1255 Email: adrian@olddog.co.uk 1257 Stewart Bryant 1258 Huawei 1260 Email: stewart.bryant@gmail.com 1262 John Drake 1263 Juniper Networks 1265 Email: jdrake@juniper.net