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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-18) exists of draft-ietf-bess-nsh-bgp-control-plane-03 == Outdated reference: A later version (-11) exists of draft-ietf-sfc-hierarchical-08 == Outdated reference: A later version (-22) exists of draft-ietf-spring-segment-routing-mpls-13 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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: November 16, 2018 Huawei 6 J. Drake 7 Juniper Networks 8 May 15, 2018 10 An MPLS-Based Forwarding Plane for Service Function Chaining 11 draft-ietf-mpls-sfc-01 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 November 16, 2018. 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. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 96 18.1. Normative References . . . . . . . . . . . . . . . . . . 26 97 18.2. Informative References . . . . . . . . . . . . . . . . . 27 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28 100 1. Introduction 102 Service Function Chaining (SFC) is the process of directing packets 103 through a network so that they can be acted on by an ordered set of 104 abstract service functions before being delivered to the intended 105 destination. An architecture for SFC is defined in [RFC7665]. 107 When applying a particular Service Function Chain to the traffic 108 selected by a service classifier, the traffic needs to be steered 109 through an ordered set of Service Functions (SFs) in the network. 110 This ordered set of SFs is termed a Service Function Path (SFP), and 111 the traffic is passed between Service Function Forwarders (SFFs) that 112 are responsible for delivering the packets to the SFs and for 113 forwarding them onward to the next SFF. 115 In order to steer the selected traffic between SFFs and to the 116 correct SFs the service classifier needs to attach information to 117 each packet. This information indicates the SFP on which the packet 118 is being forwarded and hence the SFs to which it must be delivered. 119 The information also indicates the progress the packet has already 120 made along the SFP. 122 The Network Service Header (NSH) [RFC8300] has been defined to carry 123 the necessary information for Service Function Chaining in packets. 124 The NSH can be inserted into packets and contains various information 125 including a Service Path Indicator (SPI), a Service Index (SI), and a 126 Time To Live (TTL) counter. 128 Multiprotocol Label Switching (MPLS) [RFC3031] is a widely deployed 129 forwarding technology that uses labels placed in a packet in a label 130 stack to identify the forwarding actions to be taken at each hop 131 through a network. Actions may include swapping or popping the 132 labels as well, as using the labels to determine the next hop for 133 forwarding the packet. Labels may also be used to establish the 134 context under which the packet is forwarded. In many cases, MPLS 135 will be used as a tunneling technology to carry packets through 136 networks between SFFs. 138 This document describes how Service Function Chaining can be achieved 139 in an MPLS network by means of a logical representation of the NSH in 140 an MPLS label stack. This approach is applicable to all forms of 141 MPLS forwarding (where labels are looked up at each hop, and swapped 142 or popped [RFC3031]). It does not deprecate or replace the NSH, but 143 acknowledges that there may be a need for an interim deployment of 144 SFC functionality in brownfield networks. The mechanisms described 145 in this document are a compromise between the full function that can 146 be achieved using the NSH, and the benefits of reusing the existing 147 MPLS forwarding paradigms. 149 Section 4 provides a short overview of several use case scenarios 150 that help to explain the relationship between the MPLS label 151 operations (swapping, popping, stacking) and the MPLS encoding of the 152 logical NSH described in this document). 154 It is assumed that the reader is fully familiar with the terms and 155 concepts introduced in [RFC7665] and [RFC8300]. 157 Note that one of the features of the SFC architecture described in 158 [RFC7665] is the "SFC proxy" that exists to include legacy SFs that 159 are not able to process NSH-encapsulated packets. This issue is 160 equally applicable to the use of MPLS-encapsulated packets that 161 encode a logical representation of an NSH. It is discussed further 162 in Section 9. 164 2. Requirements Language 166 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 167 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 168 "OPTIONAL" in this document are to be interpreted as described in BCP 169 14 [RFC2119] [RFC8174] when, and only when, they appear in all 170 capitals, as shown here. 172 3. Choice of Data Plane SPI/SI Representation 174 While [RFC8300] defines the NSH that can be used in a number of 175 environments, this document provides a mechanism to handle situations 176 in which the NSH is not ubiquitously deployed. In this case it is 177 possible to use an alternative data plane representation of the SPI/ 178 SI by carrying the identical semantics in MPLS labels. 180 In order to correctly select the mechanism by which SFC information 181 is encoded and carried between SFFs, it may be necessary to configure 182 the capabilities and choices either within the whole Service Function 183 Overlay Network, or on a hop by hop basis. It is a requirement that 184 both ends of a tunnel over the underlay network (i.e., a pair of SFFs 185 adjacent in the SFC) know that the tunnel is used for SFC and know 186 what form of NSH representation is used. A control plane signalling 187 approach to achieve these objectives is provided using BGP in 188 [I-D.ietf-bess-nsh-bgp-control-plane]. 190 Note that the encoding of the SFC information is independent of the 191 choice of tunneling technology used between SFFs. Thus, an MPLS 192 representation of the logical NSH (as defined in this document) may 193 be used even if the tunnel between a pair of SFFs is not an MPLS 194 tunnel. Conversely, MPLS tunnels may be used to carry other 195 encodings of the logical NSH (specifically, the NSH itself). 197 4. Use Case Scenarios 199 There are five scenarios that can be considered for the use of an 200 MPLS encoding in support of SFC. These are set out in the following 201 sub-sections. 203 4.1. Label Swapping for Logical NSH 205 The primary use case for SFC is described in [RFC7665] and delivered 206 using the NSH which, as described in [RFC8300], uses an encapsulation 207 with a position indicator that is modified at each SFC hop along the 208 chain to indicate the next hop. 210 The label swapping use case scenario effectively replaces the NSH 211 with an MPLS encapsulation as described in Section 6. The MPLS 212 labels encode the same information as the NSH to form a logical NSH. 213 The labels are modified (swapped per [RFC3031]) at each SFC hop along 214 the chain to indicate the next hop. The processing and forwarding 215 state for a chain (i.e., the actions to take on a received label) are 216 programmed in to the network using a control plane or management 217 plane. 219 4.2. Hierarchical Encapsulation 221 [I-D.ietf-sfc-hierarchical] describes an architecture for 222 hierarchical encapsulation using the NSH. It facilitates 223 partitioning of SFC domains for administrative reasons, and allows 224 concatenation of service function chains under the control of a 225 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 4.5. SFC and Segment Routing 259 Segment Routing (SR) in an MPLS network (known as MPLS-SR) uses a 260 stack of MPLS labels to encode information about the path and network 261 functions that a packet should traverse. MPLS-SR is achieved by 262 applying control plane and management plane techniques to program the 263 MPLS forwarding plane, and by imposing labels on packets at the 264 entrance to the MPLS-SR network. 266 The application of SR to SFC was considered in early versions of the 267 SR architecture [I-D.ietf-spring-segment-routing] and the MPLS-SR 268 specification [I-D.ietf-spring-segment-routing-mpls], but has since 269 been moved out of those documents. An implementation proposal for 270 achieving SFC using MPLS-SR can be found in 271 [I-D.xuclad-spring-sr-service-chaining] and is not discussed further 272 in this document. 274 5. Basic Unit of Representation 276 When an MPLS label stack is used to carry a logical NSH, a basic unit 277 of representation is used. This unit comprises two MPLS labels as 278 shown below. The unit may be present one or more times in the label 279 stack as explained in subsequent sections. 281 In order to convey the same information as is present in the NSH, two 282 MPLS label stack entries are used. One carries a label to provide 283 context within the SFC scope (the SFC Context Label), and the other 284 carries a label to show which service function is to be actioned (the 285 SF Label). This two-label unit is shown in Figure 1. 287 0 1 2 3 288 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 1 289 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 290 | SFC Context Label | TC |S| TTL | 291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 | SF Label | TC |S| TTL | 293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 295 Figure 1: The Basic Unit of MPLS Label Stack for SFC 297 The fields of these two label stack entries are encoded as follows: 299 Label: The Label fields contain the values of the SFC Context Label 300 and the SF Label encoded as 20 bit integers. The precise 301 semantics of these label fields are dependent on whether the label 302 stack entries are used for MPLS label swapping (see Section 6) or 303 MPLS label stacking (see Section 7). 305 TC: The TC bits have no meaning. They SHOULD be set to zero in both 306 label stack entries when a packet is sent and MUST be ignored on 307 receipt. 309 S: The bottom of stack bit has its usual meaning in MPLS. It MUST be 310 clear in the SFC Context label stack entry and MAY be set in the 311 SF label stack entry depending on whether the label is the bottom 312 of stack. 314 TTL: The TTL field in the SFC Context label stack entry SHOULD be 315 set to 1. The TTL in SF label stack entry (called the SF TTL) is 316 set according to its use for MPLS label swapping (see Section 6) 317 or MPLS label stacking (see Section 7 and is used to mitigate 318 packet loops. 320 The sections that follow show how this basic unit of MPLS label stack 321 may be used for SFC in the MPLS label swapping case and in the MPLS 322 label stacking. For simplicity, these sections do not describe the 323 use of metadata: that is covered separately in Section 12. 325 6. MPLS Label Swapping 327 This section describes how the basic unit of MPLS label stack for SFC 328 introduced in Section 5 is used when MPLS label swapping is in use. 329 The use case scenario for this approach is introduced in Section 4.1. 331 As can be seen from Figure 2, the top of the label stack comprises 332 the labels necessary to deliver the packet over the MPLS tunnel 333 between SFFs. Any MPLS encapsulation may be used (i.e., MPLS, MPLS 334 in UDP, MPLS in GRE, and MPLS in VXLAN or GPE), thus the tunnel 335 technology does not need to be MPLS, but that is shown here for 336 simplicity. 338 An entropy label ([RFC6790]) may also be present as described in 339 Section 11 341 Under these labels (or other encapsulation) comes a single instance 342 of the basic unit of MPLS label stack for SFC. In addition to the 343 interpretation of the fields of these label stack entries provided in 344 Section 5 the following meanings are applied: 346 SPI Label: The Label field of the SFC Context label stack entry 347 contains the value of the SPI encoded as a 20 bit integer. The 348 semantics of the SPI is exactly as defined in [RFC8300]. Note 349 that an SPI as defined by [RFC8300] can be encoded in 3 octets 350 (i.e., 24 bits), but that the Label field allows for only 20 bits 351 and reserves the values 0 though 15 as 'special purpose' labels 352 [RFC7274]. Thus, a system using MPLS representation of the 353 logical NSH MUST NOT assign SPI values greater than 2^20 - 1 or 354 less than 16. 356 SI Label: The Label field of the SF label stack entry contains the 357 value of the SI exactly as defined in [RFC8300]. Since the SI 358 requires only 8 bits, and to avoid overlap with the 'special 359 purpose' label range of 0 through 15 [RFC7274], the SI is carried 360 in the top (most significant) 8 bits of the Label field with the 361 low order 12 bits set to zero. 363 TC: The TC fields are as described in Section 5. 365 S: The S bits are as described in Section 5. 367 TTL: The TTL field in the SPI label stack entry SHOULD be set to 1 368 as stated in Section 5. The TTL in SF label stack entry is 369 decremented once for each forwarding hop in the SFP, i.e., for 370 each SFF transited, and so mirrors the TTL field in the NSH. 372 --------------- 373 ~ Tunnel Labels ~ 374 +---------------+ 375 ~ Optional ~ 376 ~ Entropy Label ~ 377 +---------------+ - - - 378 | SPI Label | 379 +---------------+ Basic unit of MPLS label stack for SFC 380 | SI Label | 381 +---------------+ - - - 382 | | 383 ~ Payload ~ 384 | | 385 --------------- 387 Figure 2: The MPLS SFC Label Stack 389 The following processing rules apply to the Label fields: 391 o When a classifier inserts a packet onto an SFP it sets the SPI 392 Label to indicate the identity of the SFP, and sets the SI Label 393 to indicate the first SF in the path. 395 o When a component of the SFC system processes a packet it uses the 396 SPI Label to identify the SFP and the SI Label to determine to 397 which SFF or instance of an SF (an SFI) to deliver the packet. 398 Under normal circumstances (with the exception of branching and 399 reclassification - see [I-D.ietf-bess-nsh-bgp-control-plane]) the 400 SPI Label value is preserved on all packets. The SI Label value 401 is modified by SFFs and through reclassification to indicate the 402 next hop along the SFP. 404 The following processing rules apply to the TTL field of the SF label 405 stack entry, and are derived from section 2.2 of [RFC8300]: 407 o When a classifier places a packet onto an SFP it MUST set the TTL 408 to a value between 1 and 255. It SHOULD set this according to the 409 expected length of the SFP (i.e., the number of SFs on the SFP), 410 but it MAY set it to a larger value according to local 411 configuration. The maximum TTL value supported in an NSH is 63, 412 and so the practical limit here may also be 63. 414 o When an SFF receives a packet from any component of the SFC system 415 (classifier, SFI, or another SFF) it MUST discard any packets with 416 TTL set to zero. It SHOULD log such occurrences, but MUST apply 417 rate limiting to any such logs. 419 o An SFF MUST decrement the TTL by one each time it performs a 420 forwarding lookup. 422 o If an SFF decrements the TTL to zero it MUST NOT send the packet, 423 and MUST discard the packet. It SHOULD log such occurrences, but 424 MUST apply rate limiting to any such logs. 426 o SFIs MUST ignore the TTL, but MUST mirror it back to the SFF 427 unmodified along with the SI (which may have been changed by local 428 reclassification). 430 o If a classifier along the SFP makes any change to the intended 431 path of the packet including for looping, jumping, or branching 432 (see [I-D.ietf-bess-nsh-bgp-control-plane] it MUST NOT change the 433 SI TTL of the packet. In particular, each component of the SFC 434 system MUST NOT increase the SI TTL value otherwise loops may go 435 undetected. 437 7. MPLS Label Stacking 439 This section describes how the basic unit of MPLS label stack for SFC 440 introduced in Section 5 is used when MPLS label stacking is used to 441 carry information about the SFP and SFs to be executed. The use case 442 scenarios for this approach is introduced in Section 4. 444 As can be seen in Figure 3, the top of the label stack comprises the 445 labels necessary to deliver the packet over the MPLS tunnel between 446 SFFs. Any MPLS encapsulation may be used. 448 An entropy label ([RFC6790]) may also be present as described in 449 Section 11 451 Under these labels comes one of more instances of the basic unit of 452 MPLS label stack for SFC. In addition to the interpretation of the 453 fields of these label stack entries provided in Section 5 the 454 following meanings are applied: 456 SFC Context Label: The Label field of the SFC Context label stack 457 entry contains a label that delivers SFC context. This label may 458 be used to indicate the SPI encoded as a 20 bit integer using the 459 semantics of the SPI is exactly as defined in [RFC8300] and noting 460 that in this case a system using MPLS representation of the 461 logical NSH MUST NOT assign SPI values greater than 2^20 - 1 or 462 less than 16. This label may also be used to convey other SFC 463 context-speific semantics such as indicating how to interpret the 464 SF Label or how to forward the packet to the node that offers the 465 SF. 467 SF Label: The Label field of the SF label stack entry contains a 468 value that identifies the next SFI to be actioned for the packet. 469 This label may be scoped globally or within the context of the 470 preceding SFC Context Label and comes from the range 16 ... 2^20 - 471 1. 473 TC: The TC fields are as described in Section 5. 475 S: The S bits are as described in Section 5. 477 TTL: The TTL fields in the SFC Context label stack entry SF label 478 stack entry SHOULD be set to 1 as stated in Section 5, but MAY be 479 set to larger values if the label indicated a forwarding operation 480 towards the node that hosts the SF. 482 ------------------- 483 ~ Tunnel Labels ~ 484 +-------------------+ 485 ~ Optional ~ 486 ~ Entropy Label ~ 487 +-------------------+ - - - 488 | SFC Context Label | 489 +-------------------+ Basic unit of MPLS label stack for SFC 490 | SF Label | 491 +-------------------+ - - - 492 | SFC Context Label | 493 +-------------------+ Basic unit of MPLS label stack for SFC 494 | SF Label | 495 +-------------------+ - - - 496 ~ ~ 497 +-------------------+ - - - 498 | SFC Context Label | 499 +-------------------+ Basic unit of MPLS label stack for SFC 500 | SF Label | 501 +-------------------+ - - - 502 | | 503 ~ Payload ~ 504 | | 505 ------------------- 507 Figure 3: The MPLS SFC Label Stack for Label Stacking 509 The following processing rules apply to the Label fields: 511 o When a classifier inserts a packet onto an SFP it adds a stack 512 comprising one or more instances of the basic unit of MPLS label 513 stack for SFC. Taken together, this stack defines the SFs to be 514 actioned and so defines the SFP that the packet will traverse. 516 o When a component of the SFC system processes a packet it uses the 517 top basic unit of label stack for SFC to determine to which SFI to 518 next deliver the packet. When an SFF receives a packet it 519 examines the top basic unit of MPLS label stack for SFC to 520 determine where to send the packet next. If the next recipient is 521 a local SFI, the SFC strips the basic unit of MPLS label stack for 522 SFC before forwarding the packet. 524 8. Mixed Mode Forwarding 526 The previous sections describe homogeneous networks where SFC 527 forwarding is either all label swapping or all label popping 528 (stacking). This simplification helps to clarify the explanation of 529 the mechanisms. 531 However, as described in Section 4.2, some uses cases may use label 532 swapping and stacking at the same time. Furthermore, it is also 533 possible that different parts of the network utilize swapping or 534 popping such that an end-to-end service chain has to utilize a 535 combination of both techniques. It is also worth noting that a 536 classifier may be content to use an SFP as installed in the network 537 by a control plane or management plane and so would use label 538 swapping, but that there may be a point in the SFP where a choice of 539 SFIs can be made (perhaps for load balancing) and where, in this 540 instance, the classifier wishes to exert control over that choice by 541 use of a specific entry on the label stack as described in 542 Section 4.3. 544 When an SFF receives a packet containing an MPLS label stack, it 545 checks whether it is processing an {SFP, SI} label pair for label 546 swapping or a {context label, SFI index} label pair for label 547 stacking. It then selects the appropriate SFI to which to send the 548 packet. When it receives the packet back from the SFI, it has four 549 cases to consider. 551 o If the current hop requires an {SFP, SI} and the next hop requires 552 an {SFP, SI}, it sets the SI label to the SI value of the current 553 hop, selects an instance of the SF to be executed at the next hop, 554 and tunnels the packet to the SFF for that SFI. 556 o If the current hop requires an {SFP, SI} and the next hop requires 557 a {context label, SFI label}, it pops the {SFP, SI} from the top 558 of the MPLS label stack and tunnels the packet to the SFF 559 indicated by the context label. 561 o If the current hop requires a {context label, SFI label}, it pops 562 the {context label, SFI label} from the top of the MPLS label 563 stack. 565 * If the new top of the MPLS label stack contains an {SFP, SI} 566 label pair, it selects an SFI to use at the next hop, and 567 tunnels the packet to SFF for that SFI. 569 * If the top of the MPLS label stack contains a {context label, 570 SFI label}, it tunnels the packet to the SFF indicated by the 571 context label. 573 9. A Note on Service Function Capabilities and SFC Proxies 575 The concept of an "SFC proxy" is introduced in [RFC7665]. An SFC 576 proxy is logically located between an SFF and an SFI that is not 577 "SFC-aware". Such SFIs are not capable of handling the SFC 578 encapsulation (whether that be NSH or MPLS) and need the 579 encapsulation stripped from the packets they are to process. In many 580 cases, legacy SFIs that were once deployed as "bumps in the wire" fit 581 into this category until they have been upgraded to be SFC-aware. 583 The job of an SFC proxy is to remove and then reimpose SFC 584 encapsulation so that the SFF is able to process as though it was 585 communication with an SFC-aware SFI, and so that the SFI is unaware 586 of the SFC encapsulation. In this regard, the job of an SFC proxy is 587 no different when NSH encapsulation is used and when MPLS 588 encapsulation is used as described in this document, although (of 589 course) it is different encapsulation bytes that must be removed and 590 reimposed. 592 It should be noted that the SFC proxy is a logical function. It 593 could be implemented as a separate physical component on the path 594 from the SFF to SFI, but it could be coresident with the SFF or it 595 could be a component of the SFI. This is purely an implementation 596 choice. 598 Note also that the delivery of metadata (see Section 12) requires 599 specific processing if an SFC proxy is in use. This is also no 600 different when NSH or the MPLS encoding defined in this document is 601 in use, and how it is handled will depend on how (or if) each non- 602 SFC-aware SFI can receive metadata. 604 10. Control Plane Considerations 606 In order that a packet may be forwarded along an SFP several 607 functional elements must be executed. 609 o Discovery/advertisement of SFIs. 611 o Computation of SFP. 613 o Programming of classifiers. 615 o Advertisement of forwarding instructions. 617 Various approaches may be taken. These include a fully centralized 618 model where SFFs report to a central controller the SFIs that they 619 support, the central controller computes the SFP and programs the 620 classifiers, and (if the label swapping approach is taken) the 621 central controller installs forwarding state in the SFFs that lie on 622 the SFP. 624 Alternatively, a dynamic control plane may be used such as that 625 described in [I-D.ietf-bess-nsh-bgp-control-plane]. In this case the 626 SFFs use the control plane to advertise the SFIs that they support, a 627 central controller computes the SFP and programs the classifiers, and 628 (if the label swapping approach is taken) the central controller uses 629 the control plane to advertise the SFPs so that SFFs that lie on the 630 SFP can install the necessary forwarding state. 632 11. Use of the Entropy Label 634 Entropy is used in ECMP situations to ensure that packets from the 635 same flow travel down the same path, thus avoiding jitter or re- 636 ordering issues within a flow. 638 Entropy is often determined by hashing on specific fields in a packet 639 header such as the "five-tuple" in the IP and transport headers. 640 However, when an MPLS label stack is present, the depth of the stack 641 could be too large for some processors to correctly determine the 642 entropy hash. This problem is addressed by the inclusion of an 643 Entropy Label as described in [RFC6790]. 645 When entropy is desired for packets as they are carried in MPLS 646 tunnels over the underlay network, it is RECOMMENDED that an Entropy 647 Label is included in the label stack immediately after the tunnel 648 labels and before the SFC labels as shown in Figure 2 and Figure 3. 650 If an Entropy Label is present in an MPLS payload, it is RECOMMENDED 651 that the initial classifier use that value in an Entropy Label 652 inserted in the label stack when the packet is forwarded (on the 653 first tunnel) to the first SFF. In this case it is not necessary to 654 remove the Entropy Label from the payload. 656 12. Metadata 658 Metadata is defined in [RFC7665] as providing "the ability to 659 exchange context information between classifiers and SFs, and among 660 SFs." [RFC8300] defines how this context information can be directly 661 encoded in fields that form part of the NSH encapsulation. 663 The next two sections describe how metadata is associated with user 664 data packets, and how metadata may be exchanged between SFC nodes in 665 the network, when using an MPLS encoding of the logical 666 representation of the NSH. 668 It should be noted that the MPLS encoding is slightly less functional 669 than the direct use of the NSH. Both methods support metadata that 670 is "per-SFP" or "per-packet-flow" (see [RFC8393] for definitions of 671 these terms), but "per-packet" metadata (where the metadata must be 672 carried on each packet because it differs from one packet to the next 673 even on the same flow or SFP) is only supported using the NSH and not 674 using the mechanisms defined in this document. 676 12.1. Indicating Metadata in User Data Packets 678 Metadata is achieved in the MPLS realization of the logical NSH by 679 the use of an SFC Metadata Label which uses the Extended Special 680 Purpose Label construct [RFC7274]. Thus, three label stack entries 681 are present as shown in Figure 4: 683 o The Extension Label (value 15) 685 o An extended special purpose label called the Metadata Label 686 Indicator (MLI) (value TBD1 by IANA) 688 o The Metadata Label (ML). 690 ---------------- 691 | Extension = 15 | 692 +----------------+ 693 | MLI | 694 +----------------+ 695 | Metadata Label | 696 --------------- 698 Figure 4: The MPLS SFC Metadata Label 700 The Metadata Label value is an index into a table of metadata that is 701 programmed into the network using in-band or out-of-band mechanisms. 703 Out-of-band mechanisms potentially include management plane and 704 control plane solutions (such as 705 [I-D.ietf-bess-nsh-bgp-control-plane]), but are out of scope for this 706 document. The in-band mechanism is described in Section 12.2 708 The SFC Metadata Label (as a set of three labels as indicated in 709 Figure 4) may be present zero, one, or more times in an MPLS SFC 710 packet. For MPLS label swapping, the SFC Metadata Labels are placed 711 immediately after the basic unit of MPLS label stack for SFC as shown 712 in Figure 5. For MPLS label stacking, the SFC Metadata Labels can be 713 present zero, one, or more times and are placed at the bottom of the 714 label stack as shown in Figure 6. 716 ---------------- 717 ~ Tunnel Labels ~ 718 +----------------+ 719 ~ Optional ~ 720 ~ Entropy Label ~ 721 +----------------+ 722 | SPI Label | 723 +----------------+ 724 | SI Label | 725 +----------------+ 726 | Extension = 15 | 727 +----------------+ 728 | MLI | 729 +----------------+ 730 | Metadata Label | 731 +----------------+ 732 ~ Other ~ 733 | Metadata | 734 ~ Label Triples ~ 735 +----------------+ 736 | | 737 ~ Payload ~ 738 | | 739 ---------------- 741 Figure 5: The MPLS SFC Label Stack for Label Swapping with Metadata 742 Label 744 ------------------- 745 ~ Tunnel Labels ~ 746 +-------------------+ 747 ~ Optional ~ 748 ~ Entropy Label ~ 749 +-------------------+ 750 | SFC Context Label | 751 +-------------------+ 752 | SF Label | 753 +-------------------+ 754 ~ ~ 755 +-------------------+ 756 | SFC Context Label | 757 +-------------------+ 758 | SF Label | 759 +-------------------+ 760 | Extension = 15 | 761 +-------------------+ 762 | MLI | 763 +-------------------+ 764 | Metadata Label | 765 +-------------------+ 766 ~ Other ~ 767 | Metadata | 768 ~ Label Triples ~ 769 +-------------------+ 770 | | 771 ~ Payload ~ 772 | | 773 ------------------- 775 Figure 6: The MPLS SFC Label Stack for Label Stacking with Metadata 776 Label 778 12.2. Inband Programming of Metadata 780 A mechanism for sending metadata associated with an SFP without a 781 payload packet is described in [RFC8393]. The same approach can be 782 used in an MPLS network where the NSH is logically represented by an 783 MPLS label stack. 785 The packet header is formed exactly as previously described in this 786 document so that the packet will follow the SFP through the SFC 787 network. However, instead of payload data, metadata is included 788 after the bottom of the MPLS label stack. An Extended Special 789 Purpose Label is used to indicate that the metadata is present. 790 Thus, three label stack entries are present: 792 o The Extension Label (value 15) 794 o An extended special purpose label called the Metadata Present 795 Indicator (MPI) (value TBD2 by IANA) 797 o The Metadata Label (ML) that is associated with this metadata on 798 this SFP and can be used to indicate the use of the metadata as 799 described in Section 12. 801 The SFC Metadata Present Label, if present, is placed immediately 802 after the last basic unit of MPLS label stack for SFC. The resultant 803 label stacks are shown in Figure 7 for the MPLS label swapping case 804 and Figure 8 for the MPLS label stacking case. 806 --------------- 807 ~ Tunnel Labels ~ 808 +---------------+ 809 ~ Optional ~ 810 ~ Entropy Label ~ 811 +---------------+ 812 | SPI Label | 813 +---------------+ 814 | SI Label | 815 +---------------+ 816 | Extension = 15| 817 +---------------+ 818 | MPI | 819 +---------------+ 820 | Metadata Label| 821 +---------------+ 822 | | 823 ~ Metadata ~ 824 | | 825 --------------- 827 Figure 7: The MPLS SFC Label Stack for Label Swapping Carrying 828 Metadata 830 ------------------- 831 ~ Tunnel Labels ~ 832 +-------------------+ 833 ~ Optional ~ 834 ~ Entropy Label ~ 835 +-------------------+ 836 | SFC Context Label | 837 +-------------------+ 838 | SF Label | 839 +-------------------+ 840 | SFC Context Label | 841 +-------------------+ 842 | SF Label | 843 +-------------------+ 844 ~ ~ 845 +-------------------+ 846 | SFC Context Label | 847 +-------------------+ 848 | SF Label | 849 +-------------------+ 850 | Extension = 15 | 851 +-------------------+ 852 | MPI | 853 +-------------------+ 854 | Metadata Label | 855 +-------------------+ 856 | | 857 ~ Metadata ~ 858 | | 859 ------------------- 861 Figure 8: The MPLS SFC Label Stack for Label Stacking Carrying 862 Metadata 864 In both cases the metadata is formatted as a TLV as shown in 865 Figure 9. 867 0 1 2 3 868 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 1 869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 870 | Length | Metadata Type | 871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 872 ~ Metadata ~ 873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 875 Figure 9: The Metadata TLV 877 The fields of this TLV are interpreted as follows: 879 Length: The length of the metadata carried in the Metadata field in 880 octets not including any padding. 882 Metadata Type: The type of the metadata present. Values for this 883 field are taken from the "MD Types" registry maintained by IANA 884 and defined in [RFC8300]. 886 Metadata: The actual metadata formatted as described in whatever 887 document defines the metadata. This field is end-padded with zero 888 to three octets of zeroes to take it up to a four octet boundary. 890 13. Worked Examples 892 This section reverts to the simplified descriptions of networks that 893 rely wholly on label swapping or label stacking. As described in 894 Section 4, actual deployment scenarios may depend on the use of both 895 mechanisms and utilize a mixed mode as described in Section 8. 897 Consider the simplistic MPLS SFC overlay network shown in Figure 10. 898 A packet is classified for an SFP that will see it pass through two 899 Service Functions, SFa and SFb, that are accessed through Service 900 Function Forwarders SFFa and SFFb respectively. The packet is 901 ultimately delivered to destination, D. 903 Let us assume that the SFP is computed and assigned the SPI of 239. 904 The forwarding details of the SFP are distributed (perhaps using the 905 mechanisms of [I-D.ietf-bess-nsh-bgp-control-plane]) so that the SFFs 906 are programmed with the necessary forwarding instructions. 908 The packet progresses as follows: 910 a. The classifier assigns the packet to the SFP and imposes two 911 label stack entries comprising a single basic unit of MPLS SFC 912 representation: 914 * The higher label stack entry contains a label carrying the SPI 915 value of 239. 917 * The lower label stack entry contains a label carrying the SI 918 value of 255. 920 Further labels may be imposed to tunnel the packet from the 921 classifier to SFFa. 923 b. When the packet arrives at SFFa it strips any labels associated 924 with the tunnel that runs from the classifier to SFFa. SFFa 925 examines the top labels and matches the SPI/SI to identify that 926 the packet should be forwarded to SFa. The packet is forwarded 927 to SFa unmodified. 929 c. SFa performs its designated function and returns the packet to 930 SFFa. 932 d. SFFa modifies the SI in the lower label stack entry (to 254) and 933 uses the SPI/SI to look up the forwarding instructions. It sends 934 the packet with two label stack entries: 936 * The higher label stack entry contains a label carrying the SPI 937 value of 239. 939 * The lower label stack entry contains a label carrying the SI 940 value of 254. 942 Further labels may be imposed to tunnel the packet from the SFFa 943 to SFFb. 945 e. When the packet arrives at SFFb it strips any labels associated 946 with the tunnel from SFFa. SFFb examines the top labels and 947 matches the SPI/SI to identify that the packet should be 948 forwarded to SFb. The packet is forwarded to SFb unmodified. 950 f. SFb performs its designated function and returns the packet to 951 SFFb. 953 g. SFFb modifies the SI in the lower label stack entry (to 253) and 954 uses the SPI/SI to lookup up the forwarding instructions. It 955 determines that it is the last SFF in the SFP so it strips the 956 two SFC label stack entries and forwards the payload toward D 957 using the payload protocol. 959 +---------------------------------------------------+ 960 | MPLS SFC Network | 961 | | 962 | +---------+ +---------+ | 963 | | SFa | | SFb | | 964 | +----+----+ +----+----+ | 965 | ^ | | ^ | | | 966 | (b)| | |(c) (e)| | |(f) | 967 | (a) | | V (d) | | V (g) | 968 +----------+ ---> +----+----+ ----> +----+----+ ---> +-------+ 969 |Classifier+------+ SFFa +-------+ SFFb +------+ D | 970 +----------+ +---------+ +---------+ +-------+ 971 | | 972 +---------------------------------------------------+ 974 Figure 10: Service Function Chaining in an MPLS Network 976 Alternatively, consider the MPLS SFC overlay network shown in 977 Figure 11. A packet is classified for an SFP that will see it pass 978 through two Service Functions, SFx and SFy, that are accessed through 979 Service Function Forwarders SFFx and SFFy respectively. The packet 980 is ultimately delivered to destination, D. 982 Let us assume that the SFP is computed and assigned the SPI of 239. 983 However, the forwarding state for the SFP is not distributed and 984 installed in the network. Instead it will be attached to the 985 individual packets using the MPLS label stack. 987 The packet progresses as follows: 989 1. The classifier assigns the packet to the SFP and imposes two 990 basic units of MPLS SFC representation to describe the full SFP: 992 * The top basic unit comprises two label stack entries as 993 follows: 995 + The higher label stack entry contains a label carrying the 996 SFC context. 998 + The lower label stack entry contains a label carrying the 999 SF indicator for SFx. 1001 * The lower basic unit comprises two label stack entries as 1002 follows: 1004 + The higher label stack entry contains a label carrying the 1005 SFC context. 1007 + The lower label stack entry contains a label carrying the 1008 SF indicator for SFy. 1010 Further labels may be imposed to tunnel the packet from the 1011 classifier to SFFx. 1013 2. When the packet arrives at SFFx it strips any labels associated 1014 with the tunnel from the classifier. SFFx examines the top 1015 labels and matches the context/SF values to identify that the 1016 packet should be forwarded to SFx. The packet is forwarded to 1017 SFx unmodified. 1019 3. SFx performs its designated function and returns the packet to 1020 SFFx. 1022 4. SFFx strips the top basic unit of MPLS SFC representation 1023 revealing the next basic unit. It then uses the revealed 1024 context/SF values to determine how to route the packet to the 1025 next SFF, SFFy. It sends the packet with just one basic unit of 1026 MPLS SFC representation comprising two label stack entries: 1028 * The higher label stack entry contains a label carrying the SFC 1029 context. 1031 * The lower label stack entry contains a label carrying the SF 1032 indicator for SFy. 1034 Further labels may be imposed to tunnel the packet from the SFFx 1035 to SFFy. 1037 5. When the packet arrives at SFFy it strips any labels associated 1038 with the tunnel from SFFx. SFFy examines the top labels and 1039 matches the context/SF values to identify that the packet should 1040 be forwarded to SFy. The packet is forwarded to SFy unmodified. 1042 6. SFy performs its designated function and returns the packet to 1043 SFFy. 1045 7. SFFy strips the top basic unit of MPLS SFC representation 1046 revealing the payload packet. It forwards the payload toward D 1047 using the payload protocol. 1049 +---------------------------------------------------+ 1050 | MPLS SFC Network | 1051 | | 1052 | +---------+ +---------+ | 1053 | | SFx | | SFy | | 1054 | +----+----+ +----+----+ | 1055 | ^ | | ^ | | | 1056 | (2)| | |(3) (5)| | |(6) | 1057 | (1) | | V (4) | | V (7) | 1058 +----------+ ---> +----+----+ ----> +----+----+ ---> +-------+ 1059 |Classifier+------+ SFFx +-------+ SFFy +------+ D | 1060 +----------+ +---------+ +---------+ +-------+ 1061 | | 1062 +---------------------------------------------------+ 1064 Figure 11: Service Function Chaining Using MPLS Label Stacking 1066 14. Implementation Notes 1068 It is not the job of an IETF specification to describe the internals 1069 of an implementation except where that directly impacts upon the bits 1070 on the wire that change the likelihood of interoperability, or where 1071 the availability of configuration or security options directly affect 1072 the utility of an implementation. 1074 However, in view of the objective of this document to acknowledge 1075 that there may be a need for an interim deployment of SFC 1076 functionality in brownfield MPLS networks, this section provides some 1077 observations about how an SFF might utilize MPLS features that are 1078 available in existing routers. This section is not intended to be 1079 definitive or technically complete, but is indicative. 1081 Consider the mechanism used to indicate to which Virtual Routing and 1082 Forwarding (VRF) an incoming MPLS packet should be routed in a Layer 1083 3 Virtual Private Network (L3VPN) [RFC4364]. In this case, the top 1084 MPLS label is an indicator of the VRF that is to be used to route the 1085 payload. 1087 A similar approach can be taken with the label swapping SFC technique 1088 described in Section 6 such that the SFC Context Label identifies a 1089 routing table specific to the SFP. The SF Label can be looked up in 1090 the context of this routing table to determine to which SF to direct 1091 the packet, and how to forward it to the next SFF. 1093 Advanced features (such as metadata) are not inspected by SFFs. The 1094 packets are passed to SFIs that are MPLS-SFC-aware or to SFC proxies, 1095 and those components are responsible for handling all metadata 1096 issues. 1098 Of course, an actual implementation might make considerable 1099 optimizations on this approach, but this section should provide hints 1100 about how MPLS-based SFC might be achieved with relatively small 1101 modifications to deployed MPLS devices. 1103 15. Security Considerations 1105 Discussion of the security properties of SFC networks can be found in 1106 [RFC7665]. Further security discussion for the NSH and its use is 1107 present in [RFC8300]. 1109 It is fundamental to the SFC design that the classifier is a trusted 1110 resource which determines the processing that the packet will be 1111 subject to, including for example the firewall. It is also 1112 fundamental to the MPLS design that packets are routed through the 1113 network using the path specified by the node imposing the labels, and 1114 that labels are swapped or popped correctly. Where an SF is not 1115 encapsulation aware the encapsulation may be stripped by an SFC proxy 1116 such that packet may exist as a native packet (perhaps IP) on the 1117 path between SFC proxy and SF, however this is an intrinsic part of 1118 the SFC design which needs to define how a packet is protected in 1119 that environment. 1121 Additionally, where a tunnel is used to link two non-MPLS domains, 1122 the tunnel design needs to specify how the tunnel is secured. 1124 Thus the security vulnerabilities are addressed (or should be 1125 addressed) in all the underlying technologies used by this design, 1126 which itself does not introduce any new security vulnerabilities. 1128 16. IANA Considerations 1130 This document requests IANA to make allocations from the "Extended 1131 Special-Purpose MPLS Label Values" subregistry of the "Special- 1132 Purpose Multiprotocol Label Switching (MPLS) Label Values" registry 1133 as follows: 1135 Value | Description | 1136 -------+-----------------------------------+-------------- 1137 TBD1 | Metadata Label Indicator (MLI) | [This.I-D] 1138 TBD2 | Metadata Present Indicator (MPI) | [This.I-D] 1140 17. Acknowledgements 1142 This document derives ideas and text from 1143 [I-D.ietf-bess-nsh-bgp-control-plane]. 1145 The authors are grateful to all those who contributed to the 1146 discussions that led to this work: Loa Andersson, Andrew G. Malis, 1147 Alexander Vainshtein, Joel M. Halpern, Tony Przygienda, Stuart 1148 Mackie, Keyur Patel, and Jim Guichard. Loa Andersson provided 1149 helpful review comments. 1151 Thanks to Loa Andersson, Lizhong Jin, Matthew Bocci, Joel Halpern, 1152 and Mach Chen for reviews of this text. 1154 The authors would like to be able to thank the authors of 1155 [I-D.xuclad-spring-sr-service-chaining] and 1156 [I-D.ietf-spring-segment-routing] whose original work on service 1157 chaining and the identification of services using SIDs, and 1158 conversation with whom helped clarify the application of MPLS-SR to 1159 SFC. 1161 Particular thanks to Loa Andersson for conversations and advice about 1162 working group process. 1164 18. References 1166 18.1. Normative References 1168 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1169 Requirement Levels", BCP 14, RFC 2119, 1170 DOI 10.17487/RFC2119, March 1997, 1171 . 1173 [RFC7274] Kompella, K., Andersson, L., and A. Farrel, "Allocating 1174 and Retiring Special-Purpose MPLS Labels", RFC 7274, 1175 DOI 10.17487/RFC7274, June 2014, 1176 . 1178 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1179 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1180 May 2017, . 1182 [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., 1183 "Network Service Header (NSH)", RFC 8300, 1184 DOI 10.17487/RFC8300, January 2018, 1185 . 1187 [RFC8393] Farrel, A. and J. Drake, "Operating the Network Service 1188 Header (NSH) with Next Protocol "None"", RFC 8393, 1189 DOI 10.17487/RFC8393, May 2018, 1190 . 1192 18.2. Informative References 1194 [I-D.ietf-bess-nsh-bgp-control-plane] 1195 Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L. 1196 Jalil, "BGP Control Plane for NSH SFC", draft-ietf-bess- 1197 nsh-bgp-control-plane-03 (work in progress), March 2018. 1199 [I-D.ietf-sfc-hierarchical] 1200 Dolson, D., Homma, S., Lopez, D., and M. Boucadair, 1201 "Hierarchical Service Function Chaining (hSFC)", draft- 1202 ietf-sfc-hierarchical-08 (work in progress), April 2018. 1204 [I-D.ietf-spring-segment-routing] 1205 Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., 1206 Litkowski, S., and R. Shakir, "Segment Routing 1207 Architecture", draft-ietf-spring-segment-routing-15 (work 1208 in progress), January 2018. 1210 [I-D.ietf-spring-segment-routing-mpls] 1211 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 1212 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 1213 data plane", draft-ietf-spring-segment-routing-mpls-13 1214 (work in progress), April 2018. 1216 [I-D.xuclad-spring-sr-service-chaining] 1217 Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca, 1218 d., Li, C., Decraene, B., Ma, S., Yadlapalli, C., 1219 Henderickx, W., and S. Salsano, "Segment Routing for 1220 Service Chaining", draft-xuclad-spring-sr-service- 1221 chaining-01 (work in progress), March 2018. 1223 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol 1224 Label Switching Architecture", RFC 3031, 1225 DOI 10.17487/RFC3031, January 2001, 1226 . 1228 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 1229 Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 1230 2006, . 1232 [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and 1233 L. Yong, "The Use of Entropy Labels in MPLS Forwarding", 1234 RFC 6790, DOI 10.17487/RFC6790, November 2012, 1235 . 1237 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 1238 Chaining (SFC) Architecture", RFC 7665, 1239 DOI 10.17487/RFC7665, October 2015, 1240 . 1242 Authors' Addresses 1244 Adrian Farrel 1245 Juniper Networks 1247 Email: afarrel@juniper.net 1249 Stewart Bryant 1250 Huawei 1252 Email: stewart.bryant@gmail.com 1254 John Drake 1255 Juniper Networks 1257 Email: jdrake@juniper.net