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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BESS Working Group A. Farrel 3 Internet-Draft J. Drake 4 Intended status: Standards Track E. Rosen 5 Expires: May 3, 2018 Juniper Networks 6 J. Uttaro 7 AT&T 8 L. Jalil 9 Verizon 10 October 30, 2017 12 BGP Control Plane for NSH SFC 13 draft-ietf-bess-nsh-bgp-control-plane-02 15 Abstract 17 This document describes the use of BGP as a control plane for 18 networks that support Service Function Chaining (SFC). The document 19 introduces a new BGP address family called the SFC AFI/SAFI with two 20 route types. One route type is originated by a node to advertise 21 that it hosts a particular instance of a specified service function. 22 This route type also provides "instructions" on how to send a packet 23 to the hosting node in a way that indicates that the service function 24 has to be applied to the packet. The other route type is used by a 25 Controller to advertise the paths of "chains" of service functions, 26 and to give a unique designator to each such path so that they can be 27 used in conjunction with the Network Service Header. 29 This document adopts the SFC architecture described in RFC 7665. 31 Requirements Language 33 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 34 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 35 document are to be interpreted as described in [RFC2119]. 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 May 3, 2018. 54 Copyright Notice 56 Copyright (c) 2017 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 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 73 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 74 2.1. Functional Overview . . . . . . . . . . . . . . . . . . . 5 75 2.2. Control Plane Overview . . . . . . . . . . . . . . . . . 7 76 3. BGP SFC Routes . . . . . . . . . . . . . . . . . . . . . . . 9 77 3.1. Service Function Instance Route (SFIR) . . . . . . . . . 10 78 3.1.1. SFI Pool Identifier Extended Community . . . . . . . 11 79 3.1.2. MPLS Mixed Swapping/Stacking Extended Community . . . 12 80 3.2. Service Function Path Route (SFPR) . . . . . . . . . . . 13 81 3.2.1. The SFP Attribute . . . . . . . . . . . . . . . . . . 13 82 3.2.2. General Rules For The SFP Attribute . . . . . . . . . 18 83 4. Mode of Operation . . . . . . . . . . . . . . . . . . . . . . 19 84 4.1. Route Targets . . . . . . . . . . . . . . . . . . . . . . 19 85 4.2. Service Function Instance Routes . . . . . . . . . . . . 19 86 4.3. Service Function Path Routes . . . . . . . . . . . . . . 19 87 4.4. Classifier Operation . . . . . . . . . . . . . . . . . . 21 88 4.5. Service Function Forwarder Operation . . . . . . . . . . 22 89 4.5.1. Processing With 'Gaps' in the SI Sequence . . . . . . 23 90 5. Selection in Service Function Paths . . . . . . . . . . . . . 24 91 6. Looping, Jumping, and Branching . . . . . . . . . . . . . . . 26 92 6.1. Protocol Control of Looping, Jumping, and Branching . . . 26 93 6.2. Implications for Forwarding State . . . . . . . . . . . . 27 94 7. Advanced Topics . . . . . . . . . . . . . . . . . . . . . . . 27 95 7.1. Preserving Entropy . . . . . . . . . . . . . . . . . . . 27 96 7.2. Correlating Service Function Path Instances . . . . . . . 28 97 7.3. Considerations for Stateful Service Functions . . . . . . 29 98 7.4. VPN Considerations and Private Service Functions . . . . 30 99 7.5. Flow Spec for SFC Classifiers . . . . . . . . . . . . . . 30 100 7.6. Choice of Data Plane SPI/SI Representation . . . . . . . 32 101 7.6.1. MPLS Representation of the SPI/SI . . . . . . . . . . 33 102 7.7. MPLS Label Swapping/Stacking Operation . . . . . . . . . 33 103 8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 33 104 8.1. Example Explicit SFP With No Choices . . . . . . . . . . 35 105 8.2. Example SFP With Choice of SFIs . . . . . . . . . . . . . 35 106 8.3. Example SFP With Open Choice of SFIs . . . . . . . . . . 36 107 8.4. Example SFP With Choice of SFTs . . . . . . . . . . . . . 36 108 8.5. Example Correlated Bidirectional SFPs . . . . . . . . . . 37 109 8.6. Example Correlated Asymmetrical Bidirectional SFPs . . . 38 110 8.7. Example Looping in an SFP . . . . . . . . . . . . . . . . 38 111 8.8. Example Branching in an SFP . . . . . . . . . . . . . . . 39 112 8.9. Examples of SFPs with Stateful Service Functions . . . . 40 113 8.9.1. Forward and Reverse Choice Made at the SFF . . . . . 40 114 8.9.2. Parallel End-to-End SFPs with Shared SFF . . . . . . 41 115 8.9.3. Parallel End-to-End SFPs with Separate SFFs . . . . . 42 116 8.9.4. Parallel SFPs Downstream of the Choice . . . . . . . 44 117 9. Security Considerations . . . . . . . . . . . . . . . . . . . 47 118 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48 119 10.1. New BGP AF/SAFI . . . . . . . . . . . . . . . . . . . . 48 120 10.2. New BGP Path Attribute . . . . . . . . . . . . . . . . . 48 121 10.3. New SFP Attribute TLVs Type Registry . . . . . . . . . . 48 122 10.4. New SFP Association Type Registry . . . . . . . . . . . 49 123 10.5. New Service Function Type Registry . . . . . . . . . . . 49 124 10.6. New Generic Transitive Experimental Use Extended 125 Community Sub-Types . . . . . . . . . . . . . . . . . . 50 126 10.7. SPI/SI Representation . . . . . . . . . . . . . . . . . 51 127 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 51 128 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 51 129 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 51 130 13.1. Normative References . . . . . . . . . . . . . . . . . . 51 131 13.2. Informative References . . . . . . . . . . . . . . . . . 52 132 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53 134 1. Introduction 136 As described in [RFC7498], the delivery of end-to-end services can 137 require a packet to pass through a series of Service Functions (SFs) 138 (e.g., classifiers, firewalls, TCP accelerators, and server load 139 balancers) in a specified order: this is termed "Service Function 140 Chaining" (SFC). There are a number of issues associated with 141 deploying and maintaining service function chaining in production 142 networks, which are described below. 144 Conventionally, if a packet needs to travel through a particular 145 service chain, the nodes hosting the service functions of that chain 146 are placed in the network topology in such a way that the packet 147 cannot reach its ultimate destination without first passing through 148 all the service functions in the proper order. This need to place 149 the service functions at particular topological locations limits the 150 ability to adapt a service function chain to changes in network 151 topology (e.g., link or node failures), network utilization, or 152 offered service load. These topological restrictions on where the 153 service functions can be placed raise the following issues: 155 1. The process of configuring or modifying a service function chain 156 is operationally complex and may require changes to the network 157 topology. 159 2. Alternate or redundant service functions may need to be co- 160 located with the primary service functions. 162 3. When there is more than one path between source and destination, 163 forwarding may be asymmetric and it may be difficult to support 164 bidirectional service function chains using simple routing 165 methodologies and protocols without adding mechanisms for traffic 166 steering or traffic engineering. 168 In order to address these issues, the SFC architecture describes 169 Service Function Chains that are built in their own overlay network 170 (the service function overlay network), coexisting with other overlay 171 networks, over a common underlay network [RFC7665]. A Service 172 Function Chain is a sequence of Service Functions through which 173 packet flows that satisfy specified criteria will pass. 175 This document describes the use of BGP as a control plane for 176 networks that support Service Function Chaining (SFC). The document 177 introduces a new BGP address family called the SFC AFI/SAFI with two 178 route types. One route type is originated by a node to advertise 179 that it hosts a particular instance of a specified service function. 180 This route type also provides "instructions" on how to send a packet 181 to the hosting node in a way that indicates that the service function 182 has to be applied to the packet. The other route type is used by a 183 Controller to advertise the paths of "chains" of service functions, 184 and to give a unique designator to each such path so that they can be 185 used in conjunction with the Network Service Header. 187 This document adopts the SFC architecture described in [RFC7665]. 189 1.1. Terminology 191 This document uses the following terms from [RFC7665]: 193 o Bidirectional Service Function Chain 195 o Classifier 197 o Service Function (SF) 199 o Service Function Chain (SFC) 201 o Service Function Forwarder (SFF) 203 o Service Function Instance (SFI) 205 o Service Function Path (SFP) 207 o SFC branching 209 Additionally, this document uses the following terms from 210 [I-D.ietf-sfc-nsh]: 212 o Network Service Header (NSH) 214 o Service Index (SI) 216 o Service Path Identifier (SPI) 218 This document introduces the following terms: 220 o Service Function Instance Route (SFIR) 222 o Service Function Overlay Network 224 o Service Function Path Route (SFPR) 226 o Service Function Type (SFT) 228 2. Overview 230 2.1. Functional Overview 232 In [I-D.ietf-sfc-nsh] a Service Function Chain (SFC) is an ordered 233 list of Service Functions (SFs). A Service Function Path (SFP) is an 234 indication of which instances of SFs are acceptable to be traversed 235 in an instantiation of an SFC in a service function overlay network. 236 The Service Path Identifier (SPI) is a 24-bit number that identifies 237 a specific SFP, and a Service Index (SI) is an 8-bit number that 238 identifies a specific point in that path. In the context of a 239 particular SFP (identified by an SPI), an SI represents a particular 240 Service Function, and indicates the order of that SF in the SFP. 242 In fact, each SI is mapped to one or more SFs that are implemented by 243 one or more Service Function Instances (SFIs) that support those 244 specified SFs. Thus an SI may represent a choice of SFIs of one or 245 more Service Function Types. By deploying multiple SFIs for a single 246 SF, one can provide load balancing and redundancy. 248 A special Service Function, called a Classifier, is located at each 249 ingress point to a service function overlay network. It assigns the 250 packets of a given packet flow to a specific Service Function Path. 251 This may be done by comparing specific fields in a packet's header 252 with local policy, which may be customer/network/service specific. 253 The classifier picks an SFP and sets the SPI accordingly, it then 254 sets the SI to the value of the SI for the first hop in the SFP, and 255 then prepends a Network Services Header (NSH) [I-D.ietf-sfc-nsh] 256 containing the assigned SPI/SI to that packet. Note that the 257 Classifier and the node that hosts the first Service Function in a 258 Service Function Path need not be located at the same point in the 259 service function overlay network. 261 Note that the presence of the NSH can make it difficult for nodes in 262 the underlay network to locate the fields in the original packet that 263 would normally be used to constrain equal cost multipath (ECMP) 264 forwarding. Therefore, it is recommended, as described in 265 Section 7.1, that the node prepending the NSH also provide some form 266 of entropy indicator that can be used in the underlay network. 268 The Service Function Forwarder (SFF) receives a packet from the 269 previous node in a Service Function Path, removes the packet's link 270 layer or tunnel encapsulation and hands the packet and the NSH to the 271 Service Function Instance for processing. The SFI has no knowledge 272 of the SFP. 274 When the SFF receives the packet and the NSH back from the SFI it 275 must select the next SFI along the path using the SPI and SI in the 276 NSH and potentially choosing between multiple SFIs (possibly of 277 different Service Function Types) as described in Section 5. In the 278 normal case the SPI remains unchanged and the SI will have been 279 decremented to indicate the next SF along the path. But other 280 possibilities exist if the SF makes other changes to the NSH through 281 a process of re-classification: 283 o The SI in the NSH may indicate: 285 * A previous SF in the path: known as "looping" (see Section 6). 287 * An SF further down the path: known as "jumping" (see also 288 Section 6). 290 o The SPI and the SI may point to an SF on a different SFP: known as 291 "branching" (see also Section 6). 293 Such modifications are limited to within the same service function 294 overlay network. That is, an SPI is known within the scope of 295 service function overlay network. Furthermore, the new SI value is 296 interpreted in the context of the SFP identified by the SPI. 298 An unknown or invalid SPI SHALL be treated as an error and the SFF 299 MUST drop the packet. Such errors SHOULD be logged, and such logs 300 MUST be subject to rate limits. 302 An SFF receiving an SI that is unknown in the context of the SPI MAY 303 reduce the value to the next meaningful SI value in the SFP indicated 304 by the SPI. If no such value exists or if the SFF does not support 305 this function it MUST drop the packet and SHOULD log the event: such 306 logs MUST be subject to rate limits. 308 The SFF then selects an SFI that provides the SF denoted by the SPI/ 309 SI, and forwards the packet to the SFF that supports that SFI. 311 2.2. Control Plane Overview 313 To accomplish the function described in Section 2.1, this document 314 introduces a new BGP AFI/SAFI [values to be assigned by IANA] for 315 "SFC Routes". Two SFC Route Types are defined by this document: the 316 Service Function Instance Route (SFIR), and the Service Function Path 317 Route (SFPR). As detailed in Section 3, the route type is indicated 318 by a sub-field in the NLRI. 320 o The SFIR is advertised by the node hosting the service function 321 instance. The SFIR describes a particular instance of a 322 particular Service Function and the way to forward a packet to it 323 through the underlay network, i.e., IP address and encapsulation 324 information. 326 o The SFPRs are originated by Controllers. One SFPR is originated 327 for each Service Function Path. The SFPR specifies: 329 A. the SPI of the path 331 B. the sequence of SFTs and/or SFIs of which the path consists 332 C. for each such SFT or SFI, the SI that represents it in the 333 identified path. 335 This approach assumes that there is an underlay network that provides 336 connectivity between SFFs and Controllers, and that the SFFs are 337 grouped to form one or more service function overlay networks through 338 which SFPs are built. We assume BGP connectivity between the 339 Controllers and all SFFs within each service function overlay 340 network. 342 In addition, we also introduce the Service Function Type (SFT) that 343 is the category of SF that is supported by an SFF (such as 344 "firewall"). An IANA registry of Service Function Types is 345 introduced in Section 10. An SFF may support SFs of multiple 346 different SFTs, and may support multiple SFIs of each SF. 348 When choosing the next SFI in a path, the SFF uses the SPI and SI as 349 well as the SFT to choose among the SFIs, applying, for example, a 350 load balancing algorithm or direct knowledge of the underlay network 351 topology as described in Section 4. 353 The SFF then encapsulates the packet using the encapsulation 354 specified by the SFIR of the selected SFI and forwards the packet. 355 See Figure 1. 357 Thus the SFF can be seen as a portal in the underlay network through 358 which a particular SFI is reached. 360 Packets 361 | | | 362 | | | 363 | | | 364 ------------ 365 | | 366 | Classifier | 367 | | 368 ------------ 369 | 370 | 371 ------- ------- 372 | | Tunnel | | 373 | SFF |=============| SFF |=========== ......... 374 | | | | # : SFT : 375 | | -+---+- # : ----- : 376 | | / \ # : | SFI | : 377 | | ....../.......\...... # : --+-- : 378 | | : / \ : # ....|.... 379 | | : -+--- ---+- : # | 380 | | : | SFI | | SFI | : # ---+--- 381 | | : ----- ----- : ====| |--- 382 | | : : | SFF |--- Dests 383 | | : ----- : ====| |--- 384 | | : | SFI | : # ------- 385 | | : --+-- : # 386 | | : SFT | : # 387 | | ..........|.......... # 388 | | | # 389 | | | # 390 | | ---+--- # 391 | | | | # 392 | |=============| SFF |=========== 393 ------- | | 394 ------- 396 Figure 1: The SFC Architecture Reference Model 398 3. BGP SFC Routes 400 This document defines a new AFI/SAFI for BGP, known as "SFC", with an 401 NLRI that is described in this section. 403 The format of the SFC NLRI is shown in Figure 2. 405 +---------------------------------------+ 406 | Route Type (2 octets) | 407 +---------------------------------------+ 408 | Length (2 octets) | 409 +---------------------------------------+ 410 | Route Type specific (variable) | 411 +---------------------------------------+ 413 Figure 2: The Format of the SFC NLRI 415 The Route Type field determines the encoding of the rest of the route 416 type specific SFC NLRI. 418 The Length field indicates the length in octets of the route type 419 specific field of the SFC NLRI. 421 This document defines the following Route Types: 423 1. Service Function Instance Route (SFIR) 425 2. Service Function Path Route (SFPR) 427 A Service Function Instance Route (SFIR) is used to identify an SFI. 428 A Service Function Path Route (SFPR) defines a sequence of Service 429 Functions (each of which has at least one instance advertised in an 430 SFIR) that form an SFP. 432 The detailed encoding and procedures for these Route Types are 433 described in subsequent sections. 435 The SFC NLRI is carried in BGP [RFC4271] using BGP Multiprotocol 436 Extensions [RFC4760] with an Address Family Identifier (AFI) of TBD1 437 and a Subsequent Address Family Identifier (SAFI) of TBD2. The NLRI 438 field in the MP_REACH_NLRI/MP_UNREACH_NLRI attribute contains the SFC 439 NLRI, encoded as specified above. 441 In order for two BGP speakers to exchange SFC NLRIs, they must use 442 BGP Capabilities Advertisements to ensure that they both are capable 443 of properly processing such NLRIs. This is done as specified in 444 [RFC4760], by using capability code 1 (Multiprotocol BGP) with an AFI 445 of TBD1 and a SAFI of TBD2. 447 3.1. Service Function Instance Route (SFIR) 449 Figure 3 shows the Route Type specific NLRI of the SFIR. 451 +--------------------------------------------+ 452 | Route Distinguisher (RD) (8 octets) | 453 +--------------------------------------------+ 454 | Service Function Type (2 octets) | 455 +--------------------------------------------+ 457 Figure 3: SFIR Route Type specific NLRI 459 Per [RFC4364] the RD field comprises a two byte Type field and a six 460 byte Value field. Two SFIs of the same SFT must be associated with 461 different RDs, where the association of an SFI with an RD is 462 determined by provisioning. If two SFIRs are originated from 463 different administrative domains, they must have different RDs. In 464 particular, SFIRs from different VPNs (for different service function 465 overlay networks) must have different RDs, and those RDs must be 466 different from any non-VPN SFIRs. 468 The Service Function Type identifies a service function, e.g., 469 classifier, firewall, load balancer, etc. There may be several SFIs 470 that can perform a given Service Function. Each node hosting an SFI 471 must originate an SFIR for each SFI that it hosts. The SFIR 472 representing a given SFI will contain an NLRI with RD field set to an 473 RD as specified above, and with SFT field set to identify that SFI's 474 Service Function Type. The values for the SFT field are taken from a 475 registry administered by IANA (see Section 10). A BGP Update 476 containing one or more SFIRs will also include a Tunnel Encapsulation 477 attribute [I-D.ietf-idr-tunnel-encaps]. If a data packet needs to be 478 sent to an SFI identified in one of the SFIRs, it will be 479 encapsulated as specified by the Tunnel Encapsulation attribute, and 480 then transmitted through the underlay network. 482 3.1.1. SFI Pool Identifier Extended Community 484 This document defines a new transitive extended community with Sub- 485 Type TBD6 called the SFI Pool Identifier. It can be included in SFIR 486 advertisements, and is used to indicate the identity of a pool of 487 SFIRs to which an SFIR belongs. Since an SFIR may be a member of 488 multiple pools, multiple of these extended communities may be present 489 on a single SFIR advertisement. 491 SFIR pools allow SFIRs to be grouped for any purpose. Possible uses 492 include control plane scalability and stability. 494 The SFI Pool Identifier is encoded as an 8 octet value as shown in 495 Figure 4. 497 +--------------------------------------------+ 498 | Type = 0x80 (1 octet) | 499 +--------------------------------------------| 500 | Sub-Type = TBD6 (1 octet) | 501 +--------------------------------------------| 502 | SPI Pool Identifier (6 octets) | 503 +--------------------------------------------| 505 Figure 4: The SFI Pool Identifier 507 The SFI Pool Identifier is a six octet, globally unique value encoded 508 in network byte order. 510 3.1.2. MPLS Mixed Swapping/Stacking Extended Community 512 This document defines a new transitive extended community with Sub- 513 Type TBD7 called the MPLS Mixed Swapping/Stacking Labels. The 514 community is encoded as shown in Figure 5. It contains a pair of 515 MPLS labels: an SFC Context Label and an SF Label as described in 516 [I-D.farrel-mpls-sfc]. Each label is 20 bits encoded in a 3-octet 517 (24 bit) field with 4 trailing bits that MUST be set to zero. 519 +--------------------------------------------+ 520 | Type = 0x80 (1 octet) | 521 +--------------------------------------------| 522 | Sub-Type = TBD7 (1 octet) | 523 +--------------------------------------------| 524 | SFC Context Label (3 octets) | 525 +--------------------------------------------| 526 | SF Label (3 octets) | 527 +--------------------------------------------+ 529 Figure 5: The MPLS Mixed Swapping/Stacking Labels 531 Note that it is assumed that each SFF has one or more globally unique 532 SFC Context Labels and that the context label space and the SPI 533 address space are disjoint. 535 See Section 7.7 for a description of how this extended community is 536 used. 538 3.2. Service Function Path Route (SFPR) 540 Figure 6 shows the Route Type specific NLRI of the SFPR. 542 +-----------------------------------------------+ 543 | Route Distinguisher (RD) (8 octets) | 544 +-----------------------------------------------+ 545 | Service Path Identifier (SPI) (3 octets) | 546 +-----------------------------------------------+ 548 Figure 6: SFPR Route Type Specific NLRI 550 Per [RFC4364] the RD field comprises a two byte Type field and a six 551 byte Value field. All SFPs must be associated with different RDs. 552 The association of an SFP with an RD is determined by provisioning. 553 If two SFPRs are originated from different Controllers they must have 554 different RDs. Additionally, SFPRs from different VPNs (i.e., in 555 different service function overlay networks) must have different RDs, 556 and those RDs must be different from any non-VPN SFPRs. 558 The Service Path Identifier is defined in [I-D.ietf-sfc-nsh] and is 559 the value to be placed in the Service Path Identifier field of the 560 NSH header of any packet sent on this Service Function Path. It is 561 expected that one or more Controllers will originate these routes in 562 order to configure a service function overlay network. 564 The SFP is described in a new BGP Path attribute, the SFP attribute. 565 Section 3.2.1 shows the format of that attribute. 567 3.2.1. The SFP Attribute 569 [RFC4271] defines the BGP Path attribute. This document introduces a 570 new Path attribute called the SFP attribute with value TBD3 to be 571 assigned by IANA. The first SFP attribute MUST be processed and 572 subsequent instances MUST be ignored. 574 The common fields of the SFP attribute are set as follows: 576 o Optional bit is set to 1 to indicate that this is an optional 577 attribute. 579 o The Transitive bit is set to 1 to indicate that this is a 580 transitive attribute. 582 o The Extended Length bit is set according to the length of the SFP 583 attribute as defined in [RFC4271]. 585 o The Attribute Type Code is set to TBD3. 587 The content of the SFP attribute is a series of Type-Length-Variable 588 (TLV) constructs. Each TLV may include sub-TLVs. All TLVs and sub- 589 TLVs have a common format that is: 591 o Type: A single octet indicating the type of the SFP attribute TLV. 592 Values are taken from the registry described in Section 10.3. 594 o Length: A two octet field indicating the length of the data 595 following the Length field counted in octets. 597 o Value: The contents of the TLV. 599 The formats of the TLVs defined in this document are shown in the 600 following sections. The presence rules and meanings are as follows. 602 o The SFP attribute contains a sequence of zero or more Association 603 TLVs. That is, the Association TLV is optional. Each Association 604 TLV provides an association between this SFPR and another SFPR. 605 Each associated SFPR is indicated using the RD with which it is 606 advertised (we say the SFPR-RD to avoid ambiguity). 608 o The SFP attribute contains a sequence of one or more Hop TLVs. 609 Each Hop TLV contains all of the information about a single hop in 610 the SFP. 612 o Each Hop TLV contains an SI value and a sequence of one or more 613 SFT TLVs. Each SFT TLV contains an SFI reference for each 614 instance of an SF that is allowed at this hop of the SFP for the 615 specific SFT. Each SFI is indicated using the RD with which it is 616 advertised (we say the SFIR-RD to avoid ambiguity). 618 3.2.1.1. The Association TLV 620 The Association TLV is an optional TLV in the SFP attribute. It may 621 be present multiple times. Each occurrence provides an association 622 with another SFP as advertised in another SFPR. The format of the 623 Association TLV is shown in Figure 7 624 +--------------------------------------------+ 625 | Type = 1 (1 octet) | 626 +--------------------------------------------| 627 | Length (2 octets) | 628 +--------------------------------------------| 629 | Association Type (1 octet) | 630 +--------------------------------------------| 631 | Associated SFPR-RD (8 octets) | 632 +--------------------------------------------| 633 | Associated SPI (3 octets) | 634 +--------------------------------------------+ 636 Figure 7: The Format of the Association TLV 638 The fields are as follows: 640 Type is set to 1 to indicate an Association TLV. 642 Length indicates the length in octets of the Association Type and 643 Associated SFPR-RD fields. The value of the Length field is 12. 645 The Association Type field indicate the type of association. The 646 values are tracked in an IANA registry (see Section 10.4). Only 647 one value is defined in this document: type 1 indicates 648 association of two unidirectional SFPs to form a bidirectional 649 SFP. An SFP attribute SHOULD NOT contain more than one 650 Association TLV with Association Type 1: if more than one is 651 present, the first one MUST be processed and subsequent instances 652 MUST be ignored. Note that documents that define new Association 653 Types must also define the presence rules for Association TLVs of 654 the new type. 656 The Associated SFPR-RD contains the RD of some other SFPR 657 advertisement that contains the SFP with which this SFP is 658 associated. 660 The Associated SPI contains the SPI of the associated SFP as 661 advertised in the SFPR indicated by the Associated SFPR-RD field. 663 Association TLVs with unknown Association Type values SHOULD be 664 ignored. Association TLVs that contain an Associated SFPR-RD value 665 equal to the RD of the SFPR in which they are contained SHOULD be 666 ignored. If the Associated SPI is not equal to the SPI advertised in 667 the SFPR indicated by the Associated SFPR-RD then the Association TLV 668 SHOULD be ignored. 670 Note that when two SFPRs reference each other using the Association 671 TLV, one SFPR advertisement will be received before the other. 672 Therefore, processing of an association MUST NOT be rejected simply 673 because the Associated SFPR-RD is unknown. 675 Further discussion of correlation of SFPRs is provided in 676 Section 7.2. 678 3.2.1.2. The Hop TLV 680 There is one Hop TLV in the SFP attribute for each hop in the SFP. 681 The format of the Hop TLV is shown in Figure 8. At least one Hop TLV 682 must be present in an SFP attribute. 684 +--------------------------------------------+ 685 | Type = 2 (1 octet) | 686 +--------------------------------------------| 687 | Length (2 octets) | 688 +--------------------------------------------| 689 | Service Index (1 octet) | 690 +--------------------------------------------| 691 | Hop Details (variable) | 692 +--------------------------------------------+ 694 Figure 8: The Format of the Hop TLV 696 The fields are as follows: 698 Type is set to 2 to indicate a Hop TLV. 700 Length indicates the length in octets of the Service Index and Hop 701 Details fields. 703 The Service Index is defined in [I-D.ietf-sfc-nsh] and is the 704 value found in the Service Index field of the NSH header that an 705 SFF will use to lookup to which next SFI a packet should be sent. 707 The Hop Details consist of a sequence of one or more SFT TLVs. 709 3.2.1.3. The SFT TLV 711 There is one or more SFT TLV in each Hop TLV. There is one SFT TLV 712 for each SFT supported in the specific hop of the SFP. The format of 713 the SFT TLV is shown in Figure 9. 715 +--------------------------------------------+ 716 | Type = 3 (1 octet) | 717 +--------------------------------------------| 718 | Length (2 octets) | 719 +--------------------------------------------| 720 | Service Function Type (2 octets) | 721 +--------------------------------------------| 722 | SFIR-RD List (variable) | 723 +--------------------------------------------+ 725 Figure 9: The Format of the SFT TLV 727 The fields are as follows: 729 Type is set to 3 to indicate an SFT TLV. 731 Length indicates the length in octets of the Service Function Type 732 and SFIR-RD List fields. 734 The Service Function Type is used to identify a Service Function 735 Instance Route in the service function overlay network which, in 736 turn, will allow lookup of routes to SFIs implementing the SF. 737 SFT values in the range 1-31 are Special Purpose SFT values and 738 have meanings defined by the documents that describe them - the 739 value 'Change Sequence' is defined in Section 6.1 of this 740 document. 742 The SFIR-RD List is made up of one or more SFIR-RD or SPI Pool 743 Identifiers obtained from the advertisements of SFIs in SFIRs. An 744 SFIR-RD of value zero has special meaning as described in 745 Section 5. Note that If the list contains one or more SPI Pool 746 Identifiers, then for each the SFIR-RD list is effectively 747 expanded to include the SFIR-RD of each SFIR advertised with that 748 SPI Pool Identifier. Each entry in the list is 8 octets long, and 749 the number of entries in the list can be deduced from the value of 750 the Length field. 752 3.2.1.4. MPLS Swapping/Stacking TLV 754 The MPLS Swapping/Stacking TLV (Type value 4) is a zero length sub- 755 TLV that can be carried in the Hop TLV and is used when the data 756 representation is MPLS (see Section 7.6). It indicates to the 757 Classifier that imposes an MPLS label stack whether the current hop 758 is to use an {SPI, SI} label pair for label swapping or a {Context 759 label, SF label}. See Section 7.7 for more details. 761 3.2.1.5. SFP Traversal With MPLS Label Stack 763 The MPLS Swapping/Stacking TLV (Type value 5) is a zero length sub- 764 TLV that can be carried in the SFP Attribute and indicates to the 765 Classifier and the SFFs on the SFP that an MPLS labels stack with 766 label swapping/stacking is to be used for packets traversing the SFP. 767 All of the SFF specified at each the SFP's hops must have advertised 768 an SPI/SI Representation sub-TLV (see Section 7.6) with bit 0 set to 769 0 and bit 1 set to 1 for the SFP to be considered usable. 771 3.2.2. General Rules For The SFP Attribute 773 It is possible for the same SFI, as described by an SFIR, to be used 774 in multiple SFPRs. 776 When two SFPRs have the same SPI but different SFPR-RDs there can be 777 three cases: 779 o Two or more Controllers are originating SFPRs for the same SFP. 780 In this case the content of the SFPRs is identical and the 781 duplication is to ensure receipt and to provide Controller 782 redundancy. 784 o There is a transition in content of the advertised SFP and the 785 advertisements may originate from one or more Controllers. In 786 this case the content of the SFPRs will be different. 788 o The reuse of an SPI may result from a configuration error. 790 In all cases, there is no way for the receiving SFF to know which 791 SFPR to process, and the SFPRs could be received in any order. At 792 any point in time, when multiple SFPRs have the same SPI but 793 different SFPR-RDs, the SFF MUST use the SFPR with the numerically 794 lowest SFPR-RD. The SFF SHOULD log this occurrence to assist with 795 debugging. 797 Furthermore, a Controller that wants to change the content of an SFP 798 is RECOMMENDED to use a new SPI and so create a new SFP onto which 799 the Classifiers can transition packet flows before the SFPR for the 800 old SFP is withdrawn. This avoids any race conditions with SFPR 801 advertisements. 803 Additionally, a Controller SHOULD NOT re-use an SPI after it has 804 withdrawn the SFPR that used it until at least a configurable amount 805 of time has passed. This timer SHOULD have a default of one hour. 807 4. Mode of Operation 809 This document describes the use of BGP as a control plane to create 810 and manage a service function overlay network. 812 4.1. Route Targets 814 The main feature introduced by this document is the ability to create 815 multiple service function overlay networks through the use of Route 816 Targets (RTs) [RFC4364]. 818 Every BGP UPDATE containing an SFIR or SFPR carries one or more RTs. 819 The RT carried by a particular SFIR or SFPR is determined by the 820 provisioning of the route's originator. 822 Every node in a service function overlay network is configured with 823 one or more import RTs. Thus, each SFF will import only the SFPRs 824 with matching RTs allowing the construction of multiple service 825 function overlay networks or the instantiation of Service Function 826 Chains within an L3VPN or EVPN instance (see Section 7.4). An SFF 827 that has a presence in multiple service function overlay networks 828 (i.e., imports more than one RT) may find it helpful to maintain 829 separate forwarding state for each overlay network. 831 4.2. Service Function Instance Routes 833 The SFIR (see Section 3.1) is used to advertise the existence and 834 location of a specific Service Function Instance and consists of: 836 o The RT as just described. 838 o A Service Function Type (SFT) that is the category of Service 839 Function that is provided (such as "firewall"). 841 o A Route Distinguisher (RD) that is unique to a specific instance 842 of a service function. 844 4.3. Service Function Path Routes 846 The SFPR (see Section 3.2) describes a specific path of a Service 847 Function Chain. The SFPR contains the Service Path Identifier (SPI) 848 used to identify the SFP in the NSH in the data plane. It also 849 contains a sequence of Service Indexes (SIs). Each SI identifies a 850 hop in the SFP, and each hop is a choice between one of more SFIs. 852 As described in this document, each Service Function Path Route is 853 identified in the service function overlay network by an RD and an 854 SPI. The SPI is unique within a single VPN instance supported by the 855 underlay network. 857 The SFPR advertisement comprises: 859 o An RT as described in Section 4.1. 861 o A tuple that identifies the SFPR 863 * An RD that identifies an advertisement of an SFPR. 865 * The SPI that uniquely identifies this path within the VPN 866 instance distinguished by the RD. This SPI also appears in the 867 NSH. 869 o A series of Service Indexes. Each SI is used in the context of a 870 particular SPI and identifies one or more SFs (distinguished by 871 their SFTs) and for each SF a set of SFIs that instantiate the SF. 872 The values of the SI indicate the order in which the SFs are to be 873 executed in the SFP that is represented by the SPI. 875 o The SI is used in the NSH to identify the entries in the SFP. 876 Note that the SI values have meaning only relative to a specific 877 path. They have no semantic other than to indicate the order of 878 Service Functions within the path and are assumed to be 879 monotonically decreasing from the start to the end of the path 880 [I-D.ietf-sfc-nsh]. 882 o Each Service Index is associated with a set of one or more Service 883 Function Instances that can be used to provide the indexed Service 884 Function within the path. Each member of the set comprises: 886 * The RD used in an SFIR advertisement of the SFI. 888 * The SFT that indicates the type of function as used in the same 889 SFIR advertisement of the SFI. 891 This may be summarized as follows where the notations "SFPR-RD" and 892 "SFIR-RD" are used to distinguish the two different RDs: 894 RT, {SFPR-RD, SPI}, m * {SI, {n * {SFT, p * SFIR-RD} } } 896 Where: 898 RT: Route Target 900 SFPR-RD: The Route Descriptor of the Service Function Path Route 901 advertisement 902 SPI: Service Path Identifier used in the NSH 904 m: The number of hops in the Service Function Path 906 n: The number of choices of Service Function Type for a specific 907 hop 909 p: The number of choices of Service Function Instance for given 910 Service Function Type in a specific hop 912 SI: Service Index used in the NSH to indicate a specific hop 914 SFT: The Service Function Type used in the same advertisement of 915 the Service Function Instance Route 917 SFIR-RD: The Route Descriptor used in an advertisement of the 918 Service Function Instance Route 920 Note that the values of SI are from the set {255, ..., 1} and are 921 monotonically decreasing within the SFP. SIs MUST appear in order 922 within the SFPR (i.e., monotonically decreasing) and MUST NOT appear 923 more than once. Gaps MAY appear in the sequence as described in 924 Section 4.5.1. Malformed SFPRs MUST be discarded and MUST cause any 925 previous instance of the SFPR (same SFPR-RD and SPI) to be discarded. 927 Note that if the SFIR-RD list in an SFT TLV contains one or more SPI 928 Pool identifiers, then in the above expression, 'p' is the sum of the 929 number of individual SFIR-RD values and the sum for each SPI Pool 930 Identifier of the number of SFIRs advertised with that SPI Pool 931 Identifier. I.e., the list of SFIR-RD values is effectively expanded 932 to include the SFIR-RD of each SFIR advertised with each SPI Pool 933 Identifier in the SFRIR-RD list. 935 The choice of SFI is explained further in Section 5. Note that an 936 SFIR-RD value of zero has special meaning as described in that 937 Section. 939 4.4. Classifier Operation 941 As shown in Figure 1, the Classifier is a special Service Function 942 that is used to assign packets to an SFP. 944 The Classifier is responsible for determining to which packet flow a 945 packet belongs (usually by inspecting the packet header), imposing an 946 NSH, and initializing the NSH to include the SPI of the selected SFPR 947 and to include the SI from first hop of the selected SFP. 949 The Classifier may also provide an entropy indicator as described in 950 Section 7.1. 952 4.5. Service Function Forwarder Operation 954 Each packet sent to an SFF is transmitted encapsulated in an NSH. 955 The NSH includes an SPI and SI: the SPI indicates the SFPR 956 advertisement that announced the Service Function Path; the tuple 957 SPI/SI indicates a specific hop in a specific path and maps to the 958 RD/SFT of a particular SFIR advertisement. 960 When an SFF gets an SFPR advertisement it will first determine 961 whether to import the route by examining the RT. If the SFPR is 962 imported the SFF then determines whether it is on the SFP by looking 963 for its own SFIR-RDs in the SFPR. For each occurrence in the SFP, 964 the SFF creates forwarding state for incoming packets and forwarding 965 state for outgoing packets that have been processed by the specified 966 SFI. 968 The SFF creates local forwarding state for packets that it receives 969 from other SFFs. This state makes the association between the SPI/SI 970 in the NSH of the received packet and one or more specific local SFIs 971 as identified by the SFIR-RD/SFT. If there are multiple local SFIs 972 that match this is because a single advertisement was made for a set 973 of equivalent SFIs and the SFF may use local policy (such as load 974 balancing) to determine to which SFI to forward a received packet. 976 The SFF also creates next hop forwarding state for packets received 977 back from the local SFI that need to be forwarded to the next hop in 978 the SFP. There may be a choice of next hops as described in 979 Section 4.3. The SFF could install forwarding state for all 980 potential next hops, or it could choose to only install forwarding 981 state to a subset of the potential next hops. If a choice is made 982 then it will be as described in Section 5. 984 The installed forwarding state may change over time reacting to 985 changes in the underlay network and the availability of particular 986 SFIs. 988 Note that SFFs only create and store forwarding state for the SFPs on 989 which they are included. They do not retain state for all SFPs 990 advertised. 992 An SFF may also install forwarding state to support looping, jumping, 993 and branching. The protocol mechanism for explicit control of 994 looping, jumping, and branching is described in Section 6.1 using a 995 special value of the SFT within an entry in an SFPR. 997 4.5.1. Processing With 'Gaps' in the SI Sequence 999 The behavior of an SF as described in [I-D.ietf-sfc-nsh] is to 1000 decrement the value of the SI field in the NSH by one before 1001 returning a packet to the local SFF for further processing. This 1002 means that there is a good reason to assume that the SFP is composed 1003 of a series of SFs each indicated by an SI value one less than the 1004 previous. 1006 However, there is an advantage to having non-successive SIs in an 1007 SPI. Consider the case where an SPI needs to be modified by the 1008 insertion or removal of an SF. In the latter case this would lead to 1009 a "gap" in the sequence of SIs, and in the former case, this could 1010 only be achieved if a gap already existed into which the new SF with 1011 its new SI value could be inserted. Otherwise, all "downstream" SFs 1012 would need to be renumbered. 1014 Now, of course, such renumbering could be performed, but would lead 1015 to a significant disruption to the SFC as all the SFFs along the SFP 1016 were "reprogrammed". Thus, to achieve dynamic modification of an SFP 1017 (and even, in-service modification) it is desirable to be able to 1018 make these modifications without changing the SIs of the elements 1019 that were present before the modification. This will produce much 1020 more consistent/predictable behavior during the convergence period 1021 where otherwise the change would need to be fully propagated. 1023 Another approach says that any change to an SFP simply creates a new 1024 SFP that can be assigned a new SPI. All that would be needed would 1025 be to give a new instruction to the Classifier and traffic would be 1026 switched to the new SFP that contains the new set of SFs. This 1027 approach is practical, but neglects to consider that the SFP may be 1028 referenced by other SFPs (through "branch" instructions) and used by 1029 many Classifiers. In those cases the corresponding configuration 1030 resulting from a change in SPI may have wide ripples and give scope 1031 for errors that are hard to trace. 1033 Therefore, while this document requires that the SI values in an SFP 1034 are monotonic decreasing, it makes no assumption that the SI values 1035 are sequential. Configuration tools may apply that rule, but they 1036 are not required to. To support this, an SFF SHOULD process as 1037 follows when it receives a packet: 1039 o If the SI indicates a known entry in the SFP, the SFF MUST process 1040 the packet as normal, looking up the SI and determining whether to 1041 deliver the packet to a local SFI or to forward it to another SFF. 1043 o If the SI does not match an entry in the SFP, the SFF MUST reduce 1044 the SI value to the next (smaller) value present in the SFP and 1045 process the packet using that SI. 1047 o If there is no smaller SI (i.e., if the end of the SFP has been 1048 reached) the SFF MUST treat the SI value as invalid as described 1049 in [I-D.ietf-sfc-nsh]. 1051 SFF implementations MAY choose to only support contiguous SI values 1052 in an SFP. Such an implementation will not support receiving an SI 1053 value that is not present in the SFP and will discard the packets as 1054 described in [I-D.ietf-sfc-nsh]. 1056 5. Selection in Service Function Paths 1058 As described in Section 2 the SPI/SI in the NSH passed back from an 1059 SFI to the SFF may leave the SFF with a choice of next hop SFTs, and 1060 a choice of SFIs for each SFT. That is, the SPI indicates an SFPR, 1061 and the SI indicates an entry in that SFPR. Each entry in an SFPR is 1062 a set of one or more SFT/SFIR-RD pairs. The SFF must choose one of 1063 these, identify the SFF that supports the chosen SFI, and send the 1064 packet to that next hop SFF. 1066 The choice may offered for load balancing across multiple SFIs, or 1067 for discrimination between different actions necessary at a specific 1068 hop in the SFP. Different SFT values may exist at a given hop in an 1069 SFP to support several cases: 1071 o There may be multiple instances of similar service functions that 1072 are distinguished by different SFT values. For example, firewalls 1073 made by vendor A and vendor B may need to be identified by 1074 different SFT values because, while they have similar 1075 functionality, their behavior is not identical. Then, some SFPs 1076 may limit the choice of SF at a given hop by specifying the SFT 1077 for vendor A, but other SFPs might not need to control which 1078 vendor's SF is used and so can indicate that either SFT can be 1079 used. 1081 o There may be an obvious branch needed in an SFP such as the 1082 processing after a firewall where admitted packets continue along 1083 the SFP, but suspect packets are diverted to a "penalty box". In 1084 this case, the next hop in the SFP will be indicated with two 1085 different SFT values. 1087 In the typical case, the SFF chooses a next hop SFF by looking at the 1088 set of all SFFs that support the SFs identified by the SI (that set 1089 having been advertised in individual SFIR advertisements), finding 1090 the one or more that are "nearest" in the underlay network, and 1091 choosing between next hop SFFs using its own load-balancing 1092 algorithm. 1094 An SFI may influence this choice process by passing additional 1095 information back along with the packet and NSH. This information may 1096 influence local policy at the SFF to cause it to favor a next hop SFF 1097 (perhaps selecting one that is not nearest in the underlay), or to 1098 influence the load-balancing algorithm. 1100 This selection applies to the normal case, but also applies in the 1101 case of looping, jumping, and branching (see Section 6). 1103 Suppose an SFF in a particular service overlay network (identified by 1104 a particular import RT, RT-z) needs to forward an NSH-encapsulated 1105 packet whose SPI is SPI-x and whose SI is SI-y. It does the 1106 following: 1108 1. It looks for an installed SFPR that carries RT-z and that has 1109 SPI-x in its NLRI. If there is none, then such packets cannot be 1110 forwarded. 1112 2. From the SFP attribute of that SFPR, it finds the Hop TLV with SI 1113 value set to SI-y. If there is no such Hop TLV, then such 1114 packets cannot be forwarded. 1116 3. It then finds the "relevant" set of SFIRs by going through the 1117 list of SFT TLVs contained in the Hop TLV as follows: 1119 A. An SFIR is relevant if it carries RT-z, the SFT in its NLRI 1120 matches the SFT value in one of the SFT TLVs, and the RD 1121 value in its NLRI matches an entry in the list of SFIR-RDs in 1122 that SFT TLV. 1124 B. If an entry in the SFIR-RD list of an SFT TLV contains the 1125 value zero, then an SFIR is relevant if it carries RT-z and 1126 the SFT in its NLRI matches the SFT value in that SFT TLV. 1127 I.e., any SFIR in the service function overlay network 1128 defined by RT-z and with the correct SFT is relevant. 1130 Each of the relevant SFIRs identifies a single SFI, and contains a 1131 Tunnel Encapsulation attribute that specifies how to send a packet to 1132 that SFI. For a particular packet, the SFF chooses a particular SFI 1133 from the set of relevant SFIRs. This choice is made according to 1134 local policy. 1136 A typical policy might be to figure out the set of SFIs that are 1137 closest, and to load balance among them. But this is not the only 1138 possible policy. 1140 6. Looping, Jumping, and Branching 1142 As described in Section 2 an SFI or an SFF may cause a packets to 1143 "loop back" to a previous SF on a path in order that a sequence of 1144 functions may be re-executed. This is simply achieved by replacing 1145 the SI in the NSH with a higher value instead of decreasing it as 1146 would normally be the case to determine the next hop in the path. 1148 Section 2 also describes how an SFI or an SFF may cause a packets to 1149 "jump forward" to an SF on a path that is not the immediate next SF 1150 in the SFP. This is simply achieved by replacing the SI in the NSH 1151 with a lower value than would be achieved by decreasing it by the 1152 normal amount. 1154 A more complex option to move packets from one SFP to another is 1155 described in [I-D.ietf-sfc-nsh] and Section 2 where it is termed 1156 "branching". This mechanism allows an SFI or SFF to make a choice of 1157 downstream treatments for packets based on local policy and output of 1158 the local SF. Branching is achieved by changing the SPI in the NSH 1159 to indicate the new path and setting the SI to indicate the point in 1160 the path at which the packets should enter. 1162 Note that the NSH does not include a marker to indicate whether a 1163 specific packet has been around a loop before. Therefore, the use of 1164 NSH metadata may be required in order to prevent infinite loops. 1166 6.1. Protocol Control of Looping, Jumping, and Branching 1168 If the SFT value in an SFT TLV in an SFPR has the Special Purpose SFT 1169 value "Change Sequence" (see Section 10) then this is an indication 1170 that the SFF may make a loop, jump, or branch according to local 1171 policy and information returned by the local SFI. 1173 In this case, the SPI and SI of the next hop is encoded in the eight 1174 bytes of an entry in the SFIR-RD list as follows: 1176 3 bytes SPI 1178 2 bytes SI 1180 3 bytes Reserved (SHOULD be set to zero and ignored) 1182 If the SI in this encoding is not part of the SFPR indicated by the 1183 SPI in this encoding, then this is an explicit error that SHOULD be 1184 detected by the SFF when it parses the SFPR. The SFPR SHOULD NOT 1185 cause any forwarding state to be installed in the SFF and packets 1186 received with the SPI that indicates this SFPR SHOULD be silently 1187 discarded. 1189 If the SPI in this encoding is unknown, the SFF SHOULD NOT install 1190 any forwarding state for this SFPR, but MAY hold the SFPR pending 1191 receipt of another SFPR that does use the encoded SPI. 1193 If the SPI matches the current SPI for the path, this is a loop or 1194 jump. In this case, if the SI is greater than to the current SI it 1195 is a loop. If the SPI matches and the SI is less than the next SI, 1196 it is a jump. 1198 If the SPI indicates anther path, this is a branch and the SI 1199 indicates the point at which to enter that path. 1201 The Change Sequence SFT is just another SFT that may appear in a set 1202 of SFI/SFT tuples within an SI and is selected as described in 1203 Section 5. 1205 Note that Special Purpose SFTs MUST NOT be advertised in SFIRs. 1207 6.2. Implications for Forwarding State 1209 Support for looping and jumping requires that the SFF has forwarding 1210 state established to an SFF that provides access to an instance of 1211 the appropriate SF. This means that the SFF must have seen the 1212 relevant SFIR advertisements and known that it needed to create the 1213 forwarding state. This is a matter of local configuration and 1214 implementation: for example, an implementation could be configured to 1215 install forwarding state for specific looping/jumping. 1217 Support for branching requires that the SFF has forwarding state 1218 established to an SFF that provides access to an instance of the 1219 appropriate entry SF on the other SFP. This means that the SFF must 1220 have seen the relevant SFIR and SFPR advertisements and known that it 1221 needed to create the forwarding state. This is a matter of local 1222 configuration and implementation: for example, an implementation 1223 could be configured to install forwarding state for specific 1224 branching (identified by SPI and SI). 1226 7. Advanced Topics 1228 This section highlights several advanced topics introduced elsewhere 1229 in this document. 1231 7.1. Preserving Entropy 1233 Forwarding decisions in the underlay network in the presence of equal 1234 cost multipath (ECMP) are usually made by inspecting key invariant 1235 fields in a packet header so that all packets from the same packet 1236 flow receive the same forwarding treatment. However, when an NSH is 1237 included in a packet, those key fields may be inaccessible. For 1238 example, the fields may be too far inside the packet for a forwarding 1239 engine to quickly find them and extract their values, or the node 1240 performing the examination may be unaware of the format and meaning 1241 of the NSH and so unable to parse far enough into the packet. 1243 Various mechanisms exist within forwarding technologies to include an 1244 "entropy indicator" within a forwarded packet. For example, in MPLS 1245 there is the entropy label [RFC6790], while for encapsulations in UDP 1246 the source port field is often used to carry an entropy indicator 1247 (such as for MPLS in UDP [RFC7510]). 1249 Implementations of this specification are RECOMMENDED to include an 1250 entropy indicator within the packet's underlay network header, and 1251 SHOULD preserve any entropy indicator from a received packet for use 1252 on the same packet when it is forwarded along the path but MAY choose 1253 to generate a new entropy indicator so long as the method used is 1254 constant for all packets. Note that preserving per packet entropy 1255 may require that the entropy indicator is passed to and returned by 1256 the SFI to prevent the SFF from having to maintain per-packet state. 1258 7.2. Correlating Service Function Path Instances 1260 It is often useful to create bidirectional SFPs to enable packet 1261 flows to traverse the same set of SFs, but in the reverse order. 1262 However, packets on SFPs in the data plane (per [I-D.ietf-sfc-nsh]) 1263 do not contain a direction indicator, so each direction must use a 1264 different SPI. 1266 As described in Section 3.2.1.1 an SFPR can contain one or more 1267 correlators encoded in Association TLVs. If the Association Type 1268 indicates "Bidirectional SFP" then the SFP advertised in the SFPR is 1269 one direction of a bidirectional pair of SFPs where the other in the 1270 pair is advertised in the SFPR with RD as carried in the Associated 1271 SFPR-RD field of the Association TLV. The SPI carried in the 1272 Associated SPI field of the Association TLV provides a cross-check 1273 and should match the SPI advertised in the SFPR with RD as carried in 1274 the Associated SFPR-RD field of the Association TLV. 1276 As noted in Section 3.2.1.1 SFPRs reference each other one SFPR 1277 advertisement will be received before the other. Therefore 1278 processing of an association will require that the first SFPR is not 1279 rejected simply because the Associated SFPR-RD it carries is unknown. 1280 However, the SFP defined by the first SFPR is valid and SHOULD be 1281 available for use as a unidirectional SFP even in the absence of an 1282 advertisement of its partner. 1284 Furthermore, in error cases where SFPR-a associates with SFPR-b, but 1285 SFPR-b associates with SFPR-c such that a bidirectional pair of SFPs 1286 cannot be formed, the individual SFPs are still valid and SHOULD be 1287 available for use as unidirectional SFPs. An implementation SHOULD 1288 log this situation because it represents a Controller error. 1290 Usage of a bidirectional SFP may be programmed into the Classifiers 1291 by the Controller. Alternatively, a Classifier may look at incoming 1292 packets on a bidirectional packet flow, extract the SPI from the 1293 received NSH, and look up the SFPR to find the reverse direction SFP 1294 to use when it sends packets. 1296 See Section 8 for an example of how this works. 1298 7.3. Considerations for Stateful Service Functions 1300 Some service functions are stateful. That means that they build and 1301 maintain state derived from configuration or from the packet flows 1302 that they handle. In such cases it can be important or necessary 1303 that all packets from a flow continue to traverse the same instance 1304 of a service function so that the state can be leveraged and does not 1305 need to be regenerated. 1307 In the case of bidirectional SFPs, it may be necessary to traverse 1308 the same instances of a stateful service function in both directions. 1309 A firewall is a good example of such a service function. 1311 This issue becomes a concern where there are multiple parallel 1312 instances of a service function and a determination of which one to 1313 use could normally be left to the SFF as a load-balancing or local 1314 policy choice. 1316 For the forward direction SFP, the concern is that the same choice of 1317 service function is made for all packets of a flow under normal 1318 network conditions. It may be possible to guarantee that the load 1319 balancing functions applied in the SFFs are stable and repeatable, 1320 but a controller that constructs SFPs might not want to trust to 1321 this. The controller can, in these cases, build a number of more 1322 specific SFPs each traversing a specific instance of the stateful 1323 SFs. In this case, the load balancing choice can be left up to the 1324 Classifier. Thus the Classifier selects which instance of a stateful 1325 SF is used by a particular flow by selecting the SFP that the flow 1326 uses. 1328 For bidirectional SFPs where the same instance of a stateful SF must 1329 be traversed in both directions, it is not enough to leave the choice 1330 of service function instance as a local choice even if the load 1331 balancing is stable because coordination would be required between 1332 the decision points in the forward and reverse directions and this 1333 may be hard to achieve in all cases except where it is the same SFF 1334 that makes the choice in both directions. 1336 Note that this approach necessarily increases the amount of SFP state 1337 in the network (i.e., there are more SFPs). It is possible to 1338 mitigate this effect by careful construction of SFPs built from a 1339 concatenation of other SFPs. 1341 Section 8.9 includes some simple examples of SFPs for stateful 1342 service functions. 1344 7.4. VPN Considerations and Private Service Functions 1346 Likely deployments include reserving specific instances of Service 1347 Functions for specific customers or allowing customers to deploy 1348 their own Service Functions within the network. Building Service 1349 Functions in such environments requires that suitable identifiers are 1350 used to ensure that SFFs distinguish which SFIs can be used and which 1351 cannot. 1353 This problem is similar to how VPNs are supported and is solved in a 1354 similar way. The RT field is used to indicate a set of Service 1355 Functions from which all choices must be made. 1357 7.5. Flow Spec for SFC Classifiers 1359 [RFC5575] defines a set of BGP routes that can be used to identify 1360 the packets in a given flow using fields in the header of each 1361 packet, and a set of actions, encoded as extended communities, that 1362 can be used to disposition those packets. This document enables the 1363 use of RFC 5575 mechanisms by SFC Classifiers by defining a new 1364 action extended community called "Flow Spec for SFC classifiers" 1365 identified by the value TBD4. Note that other action extended 1366 communities may also be present. 1368 This extended community is encoded as an 8-octet value, as shown in 1369 Figure 10: 1371 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 1372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1373 | Type=0x80 | Sub-Type=TBD4 | SPI | 1374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1375 | SPI (cont.) | SI | SFT | 1376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1378 Figure 10: The Format of the Flow Spec for SFC Classifiers Extended 1379 Community 1381 The extended community contains the Service Path Identifier (SPI), 1382 Service Index (SI), and Service Function Type (SFT) as defined 1383 elsewhere in this document. Thus, each action extended community 1384 defines the entry point (not necessarily the first hop) into a 1385 specific service function path. This allows, for example, different 1386 flows to enter the same service function path at different points. 1388 Note that a given Flow Spec update according to [RFC5575] may include 1389 multiple of these action extended communities, and that if a given 1390 action extended community does not contain an installed SFPR with the 1391 specified [SPI, SI, SFT] it MUST NOT be used for dispositioning the 1392 packets of the specified flow. 1394 The normal case of packet classification for SFC will see a packet 1395 enter the SFP at its first hop. In this case the SI in the extended 1396 community is superfluous and the SFT may also be unnecessary. To 1397 allow these cases to be handled, a special meaning is assigned to a 1398 Service Index of zero (not a valid value) and an SFT of zero (a 1399 reserved value in the registry - see Section 10.5). 1401 o If an SFC Classifiers Extended Community is received with SI = 0 1402 then it means that the first hop of the SFP indicated by the SPI 1403 MUST be used. 1405 o If an SFC Classifiers Extended Community is received with SFT = 0 1406 then there are two sub-cases: 1408 * If there is a choice of SFT in the hop indicated by the value 1409 of the SI (including SI = 0) then SFT = 0 means there is a free 1410 choice according to local policy of which SFT to use). 1412 * If there is no choice of SFT in the hop indicated by the value 1413 of SI, then SFT = 0 means that the value of the SFT at that hop 1414 as indicated in the SPFR for the indicated SPI MUST be used. 1416 7.6. Choice of Data Plane SPI/SI Representation 1418 This document ties together the control and data planes of an SFC 1419 overlay network through the use of the SPI/SI which is nominally 1420 carried in the NSH of a given packet. However, in order to handle 1421 situations in which the NSH is not ubiquitously deployed, it is also 1422 possible to use alternative data plane representations of the SPI/SI 1423 by carrying the identical semantics in other protocol fields such as 1424 MPLS labels [I-D.farrel-mpls-sfc]. 1426 This document defines a new sub-TLV for the Tunnel Encapsulation 1427 attribute, the SPI/SI Representation sub-TLV of type TBD5. This sub- 1428 TLV MAY be present in each Tunnel TLV contained in a Tunnel 1429 Encapsulation attribute when the attribute is carried by an SFIR. 1430 The value field of this sub-TLV is a two octet field of flags, each 1431 of which describes how the originating SFF expects to see the SPI/SI 1432 represented in the data plane for packets carried in the tunnels 1433 described by the Tunnel TLV. 1435 The following bits are defined by this document: 1437 Bit 0: If this bit is set the NSH is to be used to carry the SPI/SI 1438 in the data plane. 1440 Bit 1: If this bit is set two labels in an MPLS label stack are to 1441 be used as described in Section 7.6.1. 1443 If a given Tunnel TLV does not contain an SPI/SI Representation sub- 1444 TLV then it MUST be processed as if such a sub-TLV is present with 1445 Bit 0 set and no other bits set. That is, the absence of the sub-TLV 1446 SHALL be interpreted to mean that the NSH is to be used. 1448 If a given Tunnel TLV contains an SPI/SI Representation sub-TLV with 1449 value field that has no flag set then the tunnel indicated by the 1450 Tunnel TLV MUST NOT be used for forwarding SFC packets. If a given 1451 Tunnel TLV contains an SPI/SI Representation sub-TLV with both bit 0 1452 and bit 1 set then the tunnel indicated by the Tunnel TLV MUST NOT be 1453 used for forwarding SFC packets. The meaning and rules for presence 1454 of other bits is to be defined in future documents, but 1455 implementations of this specification MUST set other bits to zero and 1456 ignore them on receipt. 1458 If a given Tunnel TLV contains more than one SPI/SI Representation 1459 sub-TLV then the first one MUST be considered and subsequent 1460 instances MUST be ignored. 1462 Note that the MPLS representation of the logical NSH may be used even 1463 if the tunnel is not an MPLS tunnel. Conversely, MPLS tunnels may be 1464 used to carry other encodings of the logical NSH (specifically, the 1465 NSH itself). It is a requirement that both ends of a tunnel over the 1466 underlay network know that the tunnel is used for SFC and know what 1467 form of NSH representation is used. The signaling mechanism 1468 described here allows coordination of this information. 1470 7.6.1. MPLS Representation of the SPI/SI 1472 If bit 1 is set in the in the SPI/SI Representation sub-TLV then 1473 labels in the MPLS label stack are used to indicate SFC forwarding 1474 and processing instructions to achieve the semantics of a logical 1475 NSH. The label stack is encoded as shown in [I-D.farrel-mpls-sfc]. 1477 7.7. MPLS Label Swapping/Stacking Operation 1479 When a classifier constructs an MPLS label stack for an SFP it starts 1480 with that SFP' last hop. If the last hop requires an {SPI, SI} label 1481 pair for label swapping, it pushes the SI (set to the SI value of the 1482 last hop) and the SFP's SPI onto the MPLS label stack. If the last 1483 hop requires a {context label, SFI label} label pair for label 1484 stcking it selects a specific SFIR and pushes that SFIR's SFI label 1485 and context label onto the MPLS label stack. 1487 The classifier then moves sequentially back through the SFP one hop 1488 at a time. For each hop, if the hop requires an {SPI, SI]} and there 1489 is an {SPI, SI} at the top of the MPLS label stack, the SI is set to 1490 the SI value of the current hop. If there is not an {SPI, SI} at the 1491 top of the MPLS label stack, it pushes the SI (set to the SI value of 1492 the current hop) and the SFP's SPI onto the MPLS label stack. 1494 If the hop requires a {context label, SFI label}, it selects a 1495 specific SFIR and pushes that SFIR's SFI label and context label onto 1496 the MPLS label stack. 1498 8. Examples 1500 Assume we have a service function overlay network with four SFFs 1501 (SFF1, SFF3, SFF3, and SFF4). The SFFs have addresses in the 1502 underlay network as follows: 1504 SFF1 192.0.2.1 1505 SFF2 192.0.2.2 1506 SFF3 192.0.2.3 1507 SFF4 192.0.2.4 1509 Each SFF provides access to some SFIs from the four Service Function 1510 Types SFT=41, SFT=42, SFT=43, and SFT=44 as follows: 1512 SFF1 SFT=41 and SFT=42 1513 SFF2 SFT=41 and SFT=43 1514 SFF3 SFT=42 and SFT=44 1515 SFF4 SFT=43 and SFT=44 1517 The service function network also contains a Controller with address 1518 198.51.100.1. 1520 This example service function overlay network is shown in Figure 11. 1522 -------------- 1523 | Controller | 1524 | 198.51.100.1 | ------ ------ ------ ------ 1525 -------------- | SFI | | SFI | | SFI | | SFI | 1526 |SFT=41| |SFT=42| |SFT=41| |SFT=43| 1527 ------ ------ ------ ------ 1528 \ / \ / 1529 --------- --------- 1530 ---------- | SFF1 | | SFF2 | 1531 Packet --> | | |192.0.2.1| |192.0.2.2| 1532 Flows --> |Classifier| --------- --------- -->Dest 1533 | | --> 1534 ---------- --------- --------- 1535 | SFF3 | | SFF4 | 1536 |192.0.2.3| |192.0.2.4| 1537 --------- --------- 1538 / \ / \ 1539 ------ ------ ------ ------ 1540 | SFI | | SFI | | SFI | | SFI | 1541 |SFT=42| |SFT=44| |SFT=43| |SFT=44| 1542 ------ ------ ------ ------ 1544 Figure 11: Example Service Function Overlay Network 1546 The SFFs advertise routes to the SFIs they support. So we see the 1547 following SFIRs: 1549 RD = 192.0.2.1,1, SFT = 41 1550 RD = 192.0.2.1,2, SFT = 42 1551 RD = 192.0.2.2,1, SFT = 41 1552 RD = 192.0.2.2,2, SFT = 43 1553 RD = 192.0.2.3,7, SFT = 42 1554 RD = 192.0.2.3,8, SFT = 44 1555 RD = 192.0.2.4,5, SFT = 43 1556 RD = 192.0.2.4,6, SFT = 44 1558 Note that the addressing used for communicating between SFFs is taken 1559 from the Tunnel Encapsulation attribute of the SFIR and not from the 1560 SFIR-RD. 1562 8.1. Example Explicit SFP With No Choices 1564 Consider the following SFPR. 1566 SFP1: RD = 198.51.100.1,101, SPI = 15, 1567 [SI = 255, SFT = 41, RD = 192.0.2.1,1], 1568 [SI = 250, SFT = 43, RD = 192.0.2.2,2] 1570 The Service Function Path consists of an SF of type 41 located at 1571 SFF1 followed by an SF of type 43 located at SFF2. This path is 1572 fully explicit and each SFF is offered no choice in forwarding packet 1573 along the path. 1575 SFF1 will receive packets on the path from the Classifier and will 1576 identify the path from the SPI (15). The initial SI will be 255 and 1577 so SFF1 will deliver the packets to the SFI for SFT 41. 1579 When the packets are returned to SFF1 by the SFI the SI will be 1580 decreased to 250 for the next hop. SFF1 has no flexibility in the 1581 choice of SFF to support the next hop SFI and will forward the packet 1582 to SFF2 which will send the packets to the SFI that supports SFT 43 1583 before forwarding the packets to their destinations. 1585 8.2. Example SFP With Choice of SFIs 1587 SFP2: RD = 198.51.100.1,102, SPI = 16, 1588 [SI = 255, SFT = 41, RD = 192.0.2.1,], 1589 [SI = 250, SFT = 43, {RD = 192.0.2.2,2, 1590 RD = 192.0.2.4,5 } ] 1592 In this example the path also consists of an SF of type 41 located at 1593 SFF1 and this is followed by an SF of type 43, but in this case the 1594 SI = 250 contains a choice between the SFI located at SFF2 and the 1595 SFI located at SFF4. 1597 SFF1 will receive packets on the path from the Classifier and will 1598 identify the path from the SPI (16). The initial SI will be 255 and 1599 so SFF1 will deliver the packets to the SFI for SFT 41. 1601 When the packets are returned to SFF1 by the SFI the SI will be 1602 decreased to 250 for the next hop. SFF1 now has a choice of next hop 1603 SFF to execute the next hop in the path. It can either forward 1604 packets to SFF2 or SFF4 to execute a function of type 43. It uses 1605 its local load balancing algorithm to make this choice. The chosen 1606 SFF will send the packets to the SFI that supports SFT 43 before 1607 forwarding the packets to their destinations. 1609 8.3. Example SFP With Open Choice of SFIs 1611 SFP3: RD = 198.51.100.1,103, SPI = 17, 1612 [SI = 255, SFT = 41, RD = 192.0.2.1,1], 1613 [SI = 250, SFT = 44, RD = 0] 1615 In this example the path also consists of an SF of type 41 located at 1616 SFF1 and this is followed by an SI with an RD of zero and SF of type 1617 44. This means that a choice can be made between any SFF that 1618 supports an SFI of type 44. 1620 SFF1 will receive packets on the path from the Classifier and will 1621 identify the path from the SPI (17). The initial SI will be 255 and 1622 so SFF1 will deliver the packets to the SFI for SFT 41. 1624 When the packets are returned to SFF1 by the SFI the SI will be 1625 decreased to 250 for the next hop. SFF1 now has a free choice of 1626 next hop SFF to execute the next hop in the path selecting between 1627 all SFFs that support SFs of type 44. Looking at the SFIRs it has 1628 received, SFF1 knows that SF type 44 is supported by SFF3 and SFF4. 1629 SFF1 uses its local load balancing algorithm to make this choice. 1630 The chosen SFF will send the packets to the SFI that supports SFT 44 1631 before forwarding the packets to their destinations. 1633 8.4. Example SFP With Choice of SFTs 1634 SFP4: RD = 198.51.100.1,104, SPI = 18, 1635 [SI = 255, SFT = 41, RD = 192.0.2.1,1], 1636 [SI = 250, {SFT = 43, RD = 192.0.2.2,2, 1637 SFT = 44, RD = 192.0.2.3,8 } ] 1639 This example provides a choice of SF type in the second hop in the 1640 path. The SI of 250 indicates a choice between SF type 43 located 1641 through SF2 and SF type 44 located at SF3. 1643 SFF1 will receive packets on the path from the Classifier and will 1644 identify the path from the SPI (18). The initial SI will be 255 and 1645 so SFF1 will deliver the packets to the SFI for SFT 41. 1647 When the packets are returned to SFF1 by the SFI the SI will be 1648 decreased to 250 for the next hop. SFF1 now has a free choice of 1649 next hop SFF to execute the next hop in the path selecting between 1650 all SFF2 that support an SF of type 43 and SFF3 that supports an SF 1651 of type 44. These may be completely different functions that are to 1652 be executed dependent on specific conditions, or may be similar 1653 functions identified with different type identifiers (such as 1654 firewalls from different vendors). SFF1 uses its local policy and 1655 load balancing algorithm to make this choice, and may use additional 1656 information passed back from the local SFI to help inform its 1657 selection. The chosen SFF will send the packets to the SFI that 1658 supports the chose SFT before forwarding the packets to their 1659 destinations. 1661 8.5. Example Correlated Bidirectional SFPs 1663 SFP5: RD = 198.51.100.1,105, SPI = 19, 1664 Assoc-Type = 1, Assoc-RD = 198.51.100.1,106, Assoc-SPI = 20, 1665 [SI = 255, SFT = 41, RD = 192.0.2.1,1], 1666 [SI = 250, SFT = 43, RD = 192.0.2.2,2] 1668 SFP6: RD = 198.51.100.1,106, SPI = 20, 1669 Assoc-Type = 1, Assoc-RD = 198.51.100.1,105, Assoc-SPI = 19, 1670 [SI = 254, SFT = 43, RD = 192.0.2.2,2], 1671 [SI = 249, SFT = 41, RD = 192.0.2.1,1] 1673 This example demonstrates correlation of two SFPs to form a 1674 bidirectional SFP as described in Section 7.2. 1676 Two SFPRs are advertised by the Controller. They have different SPIs 1677 (19 and 20) so they are known to be separate SFPs, but they both have 1678 Association TLVs with Association Type set to 1 indicating 1679 bidirectional SFPs. Each has an Associated SFPR-RD fields containing 1680 the value of the other SFPR-RD to correlated the two SFPs as a 1681 bidirectional pair. 1683 As can be seen from the SFPRs in this example, the paths are 1684 symmetric: the hops in SFP5 appear in the reverse order in SFP6. 1686 8.6. Example Correlated Asymmetrical Bidirectional SFPs 1688 SFP7: RD = 198.51.100.1,107, SPI = 21, 1689 Assoc-Type = 1, Assoc-RD = 198.51.100.1,108, Assoc-SPI = 22, 1690 [SI = 255, SFT = 41, RD = 192.0.2.1,1], 1691 [SI = 250, SFT = 43, RD = 192.0.2.2,2] 1693 SFP8: RD = 198.51.100.1,108, SPI = 22, 1694 Assoc-Type = 1, Assoc-RD = 198.51.100.1,107, Assoc-SPI = 21, 1695 [SI = 254, SFT = 44, RD = 192.0.2.4,6], 1696 [SI = 249, SFT = 41, RD = 192.0.2.1,1] 1698 Asymmetric bidirectional SFPs can also be created. This example 1699 shows a pair of SFPs with distinct SPIs (21 and 22) that are 1700 correlated in the same way as in the example in Section 8.5. 1702 However, unlike in that example, the SFPs are different in each 1703 direction. Both paths include a hop of SF type 41, but SFP7 includes 1704 a hop of SF type 43 supported at SFF2 while SFP8 includes a hop of SF 1705 type 44 supported at SFF4. 1707 8.7. Example Looping in an SFP 1709 SFP9: RD = 198.51.100.1,109, SPI = 23, 1710 [SI = 255, SFT = 41, RD = 192.0.2.1,1], 1711 [SI = 250, SFT = 44, RD = 192.0.2.4,5], 1712 [SI = 245, SFT = 1, RD = {SPI=23, SI=255, Rsv=0}], 1713 [SI = 245, SFT = 42, RD = 192.0.2.3,7] 1715 Looping and jumping are described in Section 6. This example shows 1716 an SFP that contains an explicit loop-back instruction that is 1717 presented as a choice within an SFP hop. 1719 The first two hops in the path (SI = 255 and SI = 250) are normal. 1720 That is, the packets will be delivered to SFF1 and SFF4 in turn for 1721 execution of SFs of type 41 and 44 respectively. 1723 The third hop (SI = 245) presents SFF4 with a choice of next hop. It 1724 can either forward the packets to SFF3 for an SF of type 42 (the 1725 second choice), or it can loop back. 1727 The loop-back entry in the SFPR for SI = 245 is indicated by the 1728 special purpose SFT value 1 ("Change Sequence"). Within this hop, 1729 the RD is interpreted as encoding the SPI and SI of the next hop (see 1730 Section 6.1. In this case the SPI is 23 which indicates that this is 1731 loop or branch: i.e., the next hop is on the same SFP. The SI is set 1732 to 255: this is a higher number than the current SI (245) indicating 1733 a loop. 1735 SFF4 must make a choice between these two next hops. Either the 1736 packets will be forwarded to SFF3 with the NSH SI decreased to 245 or 1737 looped back to SFF1 with the NSH SI reset to 255. This choice will 1738 be made according to local policy, information passed back by the 1739 local SFI, and details in the packets' metadata that are used to 1740 prevent infinite looping. 1742 8.8. Example Branching in an SFP 1744 SFP10: RD = 198.51.100.1,110, SPI = 24, 1745 [SI = 254, SFT = 42, RD = 192.0.2.3,7], 1746 [SI = 249, SFT = 43, RD = 192.0.2.2,2] 1748 SFP11: RD = 198.51.100.1,111, SPI = 25, 1749 [SI = 255, SFT = 41, RD = 192.0.2.1,1], 1750 [SI = 250, SFT = 1, RD = {SPI=24, SI=254, Rsv=0}] 1752 Branching follows a similar procedure to that for looping (and 1753 jumping) as shown in Section 8.7 however there are two SFPs involved. 1755 SFP10 shows a normal path with packets forwarded to SFF3 and SFF2 for 1756 execution of service functions of type 42 and 43 respectively. 1758 SFP11 starts as normal (SFF1 for an SF of type 41), but then SFF1 1759 processes the next hop in the path and finds a "Change Sequence" 1760 Special Purpose SFT. The SFIR-RD field includes an SPI of 24 which 1761 indicates SFP10, not the current SFP. The SI in the SFIR-RD is 254, 1762 so SFF1 knows that it must set the SPI/SI in the NSH to 24/254 and 1763 send the packets to the appropriate SFF as advertised in the SFPR for 1764 SFP10 (that is, SFF3). 1766 8.9. Examples of SFPs with Stateful Service Functions 1768 This section provides some examples to demonstrate establishing SFPs 1769 when there is a choice of service functions at a particular hop, and 1770 where consistency of choice is required in both directions. The 1771 scenarios that give rise to this requirement are discussed in 1772 Section 7.3. 1774 8.9.1. Forward and Reverse Choice Made at the SFF 1776 Consider the topology shown in Figure 12. There are three SFFs 1777 arranged neatly in a line, and the middle one (SFF2) supports three 1778 SFIs all of SFT 42. These three instances can be used by SFF2 to 1779 load balance so that no one instance is swamped. 1781 ------ ------ ------ ------ ------ 1782 | SFI | | SFIa | | SFIb | | SFIc | | SFI | 1783 |SFT=41| |SFT=42| |SFT=42| |SFT=42| |SFT=43| 1784 ------ ------\ ------ /------ ------ 1785 \ \ | / / 1786 --------- --------- --------- 1787 ---------- | SFF1 | | SFF2 | | SFF3 | 1788 --> | |..|192.0.2.1|...|192.0.2.2|...|192.0.2.3|--> 1789 --> |Classifier| --------- --------- --------- 1790 | | 1791 ---------- 1793 Figure 12: Example Where Choice is Made at the SFF 1795 This leads to the following SFIRs being advertised. 1797 RD = 192.0.2.1,11, SFT = 41 1798 RD = 192.0.2.2,11, SFT = 42 (for SFIa) 1799 RD = 192.0.2.2,12, SFT = 42 (for SFIb) 1800 RD = 192.0.2.2,13, SFT = 42 (for SFIc) 1801 RD = 192.0.2.3,11, SFT = 43 1803 The controller can create a single forward SFP giving SFF2 the choice 1804 of which SFI to use to provide function of SFT 42 as follows. The 1805 load-balancing choice between the three available SFIs is assumed to 1806 be within the capabilities of the SFF and if the SFs are stateful it 1807 is assumed that the SFF knows this and arranges load balancing in a 1808 stable, flow-dependent way. 1810 SFP12: RD = 198.51.100.1,112, SPI = 26, 1811 Assoc-Type = 1, Assoc-RD = 198.51.100.1,113, Assoc-SPI = 27, 1812 [SI = 255, SFT = 41, RD = 192.0.2.1,11], 1813 [SI = 254, SFT = 42, {RD = 192.0.2.2,11, 1814 192.0.2.2,12, 1815 192.0.2.2,13 }], 1816 [SI = 253, SFT = 43, RD = 192.0.2.3,11] 1818 The reverse SFP in this case may also be created as shown below using 1819 association with the forward SFP and giving the load-balancing choice 1820 to SFF2. This is safe, even in the case that the SFs of type 42 are 1821 stateful because SFF2 is doing the load balancing in both directions 1822 and can apply the same algorithm to ensure that packets associated 1823 with the same flow use the same SFI regardless of the direction of 1824 travel. 1826 SFP13: RD = 198.51.100.1,113, SPI = 27, 1827 Assoc-Type = 1, Assoc-RD = 198.51.100.1,112, Assoc-SPI = 26, 1828 [SI = 255, SFT = 43, RD = 192.0.2.3,11], 1829 [SI = 254, SFT = 42, {RD = 192.0.2.2,11, 1830 192.0.2.2,12, 1831 192.0.2.2,13 }], 1832 [SI = 253, SFT = 41, RD = 192.0.2.1,11] 1834 8.9.2. Parallel End-to-End SFPs with Shared SFF 1836 The mechanism described in Section 8.9.1 might not be desirable 1837 because of the functional assumptions it places on SFF2 to be able to 1838 load balance with suitable flow identification, stability, and 1839 equality in both directions. Instead, it may be desirable to place 1840 the responsibility for flow classification in the Classifier and let 1841 it determine load balancing with the implied choice of SFIs. 1843 Consider the network graph as shown in Figure 12 and with the same 1844 set of SFIRs as listed in Section 8.9.1. In this case the controller 1845 could specify three forward SFPs with their corresponding associated 1846 reverse SFPs. Each bidirectional pair of SFPs uses a different SFI 1847 for the SF of type 42. The controller can instruct the Classifier 1848 how to place traffic on the three bidirectional SFPs, or can treat 1849 them as a group leaving the Classifier responsible for balancing the 1850 load. 1852 SFP14: RD = 198.51.100.1,114, SPI = 28, 1853 Assoc-Type = 1, Assoc-RD = 198.51.100.1,117, Assoc-SPI = 31, 1854 [SI = 255, SFT = 41, RD = 192.0.2.1,11], 1855 [SI = 254, SFT = 42, RD = 192.0.2.2,11], 1856 [SI = 253, SFT = 43, RD = 192.0.2.3,11] 1858 SFP15: RD = 198.51.100.1,115, SPI = 29, 1859 Assoc-Type = 1, Assoc-RD = 198.51.100.1,118, Assoc-SPI = 32, 1860 [SI = 255, SFT = 41, RD = 192.0.2.1,11], 1861 [SI = 254, SFT = 42, RD = 192.0.2.2,12], 1862 [SI = 253, SFT = 43, RD = 192.0.2.3,11] 1864 SFP16: RD = 198.51.100.1,116, SPI = 30, 1865 Assoc-Type = 1, Assoc-RD = 198.51.100.1,119, Assoc-SPI = 33, 1866 [SI = 255, SFT = 41, RD = 192.0.2.1,11], 1867 [SI = 254, SFT = 42, RD = 192.0.2.2,13], 1868 [SI = 253, SFT = 43, RD = 192.0.2.3,11] 1870 SFP17: RD = 198.51.100.1,117, SPI = 31, 1871 Assoc-Type = 1, Assoc-RD = 198.51.100.1,114, Assoc-SPI = 28, 1872 [SI = 255, SFT = 43, RD = 192.0.2.3,11], 1873 [SI = 254, SFT = 42, RD = 192.0.2.2,11], 1874 [SI = 253, SFT = 41, RD = 192.0.2.1,11] 1876 SFP18: RD = 198.51.100.1,118, SPI = 32, 1877 Assoc-Type = 1, Assoc-RD = 198.51.100.1,115, Assoc-SPI = 29, 1878 [SI = 255, SFT = 43, RD = 192.0.2.3,11], 1879 [SI = 254, SFT = 42, RD = 192.0.2.2,12], 1880 [SI = 253, SFT = 41, RD = 192.0.2.1,11] 1882 SFP19: RD = 198.51.100.1,119, SPI = 33, 1883 Assoc-Type = 1, Assoc-RD = 198.51.100.1,116, Assoc-SPI = 30, 1884 [SI = 255, SFT = 43, RD = 192.0.2.3,11], 1885 [SI = 254, SFT = 42, RD = 192.0.2.2,13], 1886 [SI = 253, SFT = 41, RD = 192.0.2.1,11] 1888 8.9.3. Parallel End-to-End SFPs with Separate SFFs 1890 While the examples in Section 8.9.1 and Section 8.9.2 place the 1891 choice of SFI as subtended from the same SFF, it is also possible 1892 that the SFIs are ach subtended from a different SFF as shown in 1893 Figure 13. In this case it is harder to coordinate the choices for 1894 forward and reverse paths without some form of coordination between 1895 SFF1 and SFF3. Therefore it would be normal to consider end-to-end 1896 parallel SFPs as described in Section 8.9.2. 1898 ------ 1899 | SFIa | 1900 |SFT=42| 1901 ------ 1902 ------ | 1903 | SFI | --------- 1904 |SFT=41| | SFF5 | 1905 ------ ..|192.0.2.5|.. 1906 | ..: --------- :.. 1907 ---------.: :.--------- 1908 ---------- | SFF1 | --------- | SFF3 | 1909 --> | |..|192.0.2.1|....| SFF6 |....|192.0.2.3| --> 1910 --> |Classifier| ---------: |192.0.2.6| :--------- 1911 | | : --------- : | 1912 ---------- : | : ------ 1913 : ------ : | SFI | 1914 :.. | SFIb | ..: |SFT=43| 1915 :.. |SFT=42| ..: ------ 1916 : ------ : 1917 :.---------.: 1918 | SFF7 | 1919 |192.0.2.7| 1920 --------- 1921 | 1922 ------ 1923 | SFIc | 1924 |SFT=42| 1925 ------ 1927 Figure 13: Second Example With Parallel End-to-End SFPs 1929 In this case, five SFIRs are advertised as follows: 1931 RD = 192.0.2.1,11, SFT = 41 1932 RD = 192.0.2.5,11, SFT = 42 (for SFIa) 1933 RD = 192.0.2.6,11, SFT = 42 (for SFIb) 1934 RD = 192.0.2.7,11, SFT = 42 (for SFIc) 1935 RD = 192.0.2.3,11, SFT = 43 1937 In this case the controller could specify three forward SFPs with 1938 their corresponding associated reverse SFPs. Each bidirectional pair 1939 of SFPs uses a different SFF and SFI for middle hop (for an SF of 1940 type 42). The controller can instruct the Classifier how to place 1941 traffic on the three bidirectional SFPs, or can treat them as a group 1942 leaving the Classifier responsible for balancing the load. 1944 SFP20: RD = 198.51.100.1,120, SPI = 34, 1945 Assoc-Type = 1, Assoc-RD = 198.51.100.1,123, Assoc-SPI = 37, 1946 [SI = 255, SFT = 41, RD = 192.0.2.1,11], 1947 [SI = 254, SFT = 42, RD = 192.0.2.5,11], 1948 [SI = 253, SFT = 43, RD = 192.0.2.3,11] 1950 SFP21: RD = 198.51.100.1,121, SPI = 35, 1951 Assoc-Type = 1, Assoc-RD = 198.51.100.1,124, Assoc-SPI = 38, 1952 [SI = 255, SFT = 41, RD = 192.0.2.1,11], 1953 [SI = 254, SFT = 42, RD = 192.0.2.6,11], 1954 [SI = 253, SFT = 43, RD = 192.0.2.3,11] 1956 SFP22: RD = 198.51.100.1,122, SPI = 36, 1957 Assoc-Type = 1, Assoc-RD = 198.51.100.1,125, Assoc-SPI = 39, 1958 [SI = 255, SFT = 41, RD = 192.0.2.1,11], 1959 [SI = 254, SFT = 42, RD = 192.0.2.7,11], 1960 [SI = 253, SFT = 43, RD = 192.0.2.3,11] 1962 SFP23: RD = 198.51.100.1,123, SPI = 37, 1963 Assoc-Type = 1, Assoc-RD = 198.51.100.1,120, Assoc-SPI = 34, 1964 [SI = 255, SFT = 43, RD = 192.0.2.3,11], 1965 [SI = 254, SFT = 42, RD = 192.0.2.5,11], 1966 [SI = 253, SFT = 41, RD = 192.0.2.1,11] 1968 SFP24: RD = 198.51.100.1,124, SPI = 38, 1969 Assoc-Type = 1, Assoc-RD = 198.51.100.1,121, Assoc-SPI = 35, 1970 [SI = 255, SFT = 43, RD = 192.0.2.3,11], 1971 [SI = 254, SFT = 42, RD = 192.0.2.6,11], 1972 [SI = 253, SFT = 41, RD = 192.0.2.1,11] 1974 SFP25: RD = 198.51.100.1,125, SPI = 39, 1975 Assoc-Type = 1, Assoc-RD = 198.51.100.1,122, Assoc-SPI = 36, 1976 [SI = 255, SFT = 43, RD = 192.0.2.3,11], 1977 [SI = 254, SFT = 42, RD = 192.0.2.7,11], 1978 [SI = 253, SFT = 41, RD = 192.0.2.1,11] 1980 8.9.4. Parallel SFPs Downstream of the Choice 1982 The mechanism of parallel SFPs demonstrated in Section 8.9.3 is 1983 perfectly functional and may be practical in many environments. 1984 However, there may be scaling concerns because of the large amount of 1985 state (knowledge of SFPs, i.e., SFPR advertisements retained) if 1986 there is a very large amount of choice of SFIs (for example, tens of 1987 instances of the same stateful SF), or if there are multiple choices 1988 of stateful SF along a path. This situation may be mitigated using 1989 SFP fragments that are combined to form the end to end SFPs. 1991 The example presented here is necessarily simplistic, but should 1992 convey the basic principle. The example presented in Figure 14 is 1993 similar to that in Section 8.9.3 but with an additional first hop. 1995 ------ 1996 | SFIa | 1997 |SFT=43| 1998 ------ 1999 ------ ------ | 2000 | SFI | | SFI | --------- 2001 |SFT=41| |SFT=42| | SFF5 | 2002 ------ ------ ..|192.0.2.5|.. 2003 | | ..: --------- :.. 2004 --------- ---------.: :.--------- 2005 ------ | SFF1 | | SFF2 | --------- | SFF3 | 2006 -->|Class-|.|192.0.2.1|.|192.0.2.2|....| SFF6 |....|192.0.2.3|--> 2007 -->| ifier| --------- ---------: |192.0.2.6| :--------- 2008 ------ : --------- : | 2009 : | : ------ 2010 : ------ : | SFI | 2011 :.. | SFIb | ..: |SFT=44| 2012 :.. |SFT=43| ..: ------ 2013 : ------ : 2014 :.---------.: 2015 | SFF7 | 2016 |192.0.2.7| 2017 --------- 2018 | 2019 ------ 2020 | SFIc | 2021 |SFT=43| 2022 ------ 2024 Figure 14: Example With Parallel SFPs Downstream of Choice 2026 The six SFIs are advertised as follows: 2028 RD = 192.0.2.1,11, SFT = 41 2029 RD = 192.0.2.2,11, SFT = 42 2030 RD = 192.0.2.5,11, SFT = 43 (for SFIa) 2031 RD = 192.0.2.6,11, SFT = 43 (for SFIb) 2032 RD = 192.0.2.7,11, SFT = 43 (for SFIc) 2033 RD = 192.0.2.3,11, SFT = 44 2035 SFF2 is the point at which a load balancing choice must be made. So 2036 "tail-end" SFPs are constructed as follows. Each takes in a 2037 different SFF that provides access to an SF of type 43. 2039 SFP26: RD = 198.51.100.1,126, SPI = 40, 2040 Assoc-Type = 1, Assoc-RD = 198.51.100.1,130, Assoc-SPI = 44, 2041 [SI = 255, SFT = 43, RD = 192.0.2.5,11], 2042 [SI = 254, SFT = 44, RD = 192.0.2.3,11] 2044 SFP27: RD = 198.51.100.1,127, SPI = 41, 2045 Assoc-Type = 1, Assoc-RD = 198.51.100.1,131, Assoc-SPI = 45, 2046 [SI = 255, SFT = 43, RD = 192.0.2.6,11], 2047 [SI = 254, SFT = 44, RD = 192.0.2.3,11] 2049 SFP28: RD = 198.51.100.1,128, SPI = 42, 2050 Assoc-Type = 1, Assoc-RD = 198.51.100.1,132, Assoc-SPI = 46, 2051 [SI = 255, SFT = 43, RD = 192.0.2.7,11], 2052 [SI = 254, SFT = 44, RD = 192.0.2.3,11] 2054 Now an end-to-end SFP with load balancing choice can be constructed 2055 as follows. The choice made by SFF2 is expressed in terms of 2056 entering one of the three "tail end" SFPs. 2058 SFP29: RD = 198.51.100.1,129, SPI = 43, 2059 [SI = 255, SFT = 41, RD = 192.0.2.1,11], 2060 [SI = 254, SFT = 42, RD = 192.0.2.2,11], 2061 [SI = 253, {SFT = 1, RD = {SPI=40, SI=255, Rsv=0}, 2062 RD = {SPI=41, SI=255, Rsv=0}, 2063 RD = {SPI=42, SI=255, Rsv=0} } ] 2065 Now, despite the load balancing choice being made other than at the 2066 initial classifier, it is possible for the reverse SFPs to be well- 2067 constructed without any ambiguity. The three reverse paths appear as 2068 follows. 2070 SFP30: RD = 198.51.100.1,130, SPI = 44, 2071 Assoc-Type = 1, Assoc-RD = 198.51.100.1,126, Assoc-SPI = 40, 2072 [SI = 255, SFT = 44, RD = 192.0.2.4,11], 2073 [SI = 254, SFT = 43, RD = 192.0.2.5,11], 2074 [SI = 253, SFT = 42, RD = 192.0.2.2,11], 2075 [SI = 252, SFT = 41, RD = 192.0.2.1,11] 2077 SFP31: RD = 198.51.100.1,131, SPI = 45, 2078 Assoc-Type = 1, Assoc-RD = 198.51.100.1,127, Assoc-SPI = 41, 2079 [SI = 255, SFT = 44, RD = 192.0.2.4,11], 2080 [SI = 254, SFT = 43, RD = 192.0.2.6,11], 2081 [SI = 253, SFT = 42, RD = 192.0.2.2,11], 2082 [SI = 252, SFT = 41, RD = 192.0.2.1,11] 2084 SFP32: RD = 198.51.100.1,132, SPI = 46, 2085 Assoc-Type = 1, Assoc-RD = 198.51.100.1,128, Assoc-SPI = 42, 2086 [SI = 255, SFT = 44, RD = 192.0.2.4,11], 2087 [SI = 254, SFT = 43, RD = 192.0.2.7,11], 2088 [SI = 253, SFT = 42, RD = 192.0.2.2,11], 2089 [SI = 252, SFT = 41, RD = 192.0.2.1,11] 2091 9. Security Considerations 2093 This document inherits all the security considerations discussed in 2094 the documents that specify BGP, the documents that specify BGP 2095 Multiprotocol Extensions, and the documents that define the 2096 attributes that are carried by BGP UPDATEs of the SFC AFI/SAFI. For 2097 more information look in [RFC4271], [RFC4760], and 2098 [I-D.ietf-idr-tunnel-encaps]. 2100 Service Function Chaining provides a significant attack opportunity: 2101 packets can be diverted from their normal paths through the network, 2102 can be made to execute unexpected functions, and the functions that 2103 are instantiated in software can be subverted. However, this 2104 specification does not change the existence of Service Function 2105 Chaining and security issues specific to Service Function Chaining 2106 are covered in [RFC7665] and [I-D.ietf-sfc-nsh]. 2108 This document defines a control plane for Service Function Chaining. 2109 Clearly, this provides an attack vector for a Service Function 2110 Chaining system as an attack on this control plane could be used to 2111 make the system misbehave. Thus, the security of the BGP system is 2112 critically important to the security of the whole Service Function 2113 Chaining system. 2115 10. IANA Considerations 2117 10.1. New BGP AF/SAFI 2119 IANA maintains a registry of "Address Family Numbers". IANA is 2120 requested to assign a new Address Family Number from the "Standards 2121 Action" range called "BGP SFC" (TBD1 in this document) with this 2122 document as a reference. 2124 IANA maintains a registry of "Subsequent Address Family Identifiers 2125 (SAFI) Parameters". IANA is requested to assign a new SAFI value 2126 from the "Standards Action" range called "BGP SFC" (TBD2 in this 2127 document) with this document as a reference. 2129 10.2. New BGP Path Attribute 2131 IANA maintains a registry of "Border Gateway Protocol (BGP) 2132 Parameters" with a subregistry of "BGP Path Attributes". IANA is 2133 requested to assign a new Path attribute called "SFP attribute" (TBD3 2134 in this document) with this document as a reference. 2136 10.3. New SFP Attribute TLVs Type Registry 2138 IANA maintains a registry of "Border Gateway Protocol (BGP) 2139 Parameters". IANA is request to create a new subregistry called the 2140 "SFP Attribute TLVs" registry. 2142 Valid values are in the range 0 to 65535. 2144 o Values 0 and 65535 are to be marked "Reserved, not to be 2145 allocated". 2147 o Values 1 through 65524 are to be assigned according to the "First 2148 Come First Served" policy [RFC8126]. 2150 This document should be given as a reference for this registry. 2152 The new registry should track: 2154 o Type 2156 o Name 2158 o Reference Document or Contact 2160 o Registration Date 2162 The registry should initially be populated as follows: 2164 Type | Name | Reference | Date 2165 ------+-------------------------+---------------+--------------- 2166 1 | Association TLV | [This.I-D] | Date-to-be-set 2167 2 | Hop TLV | [This.I-D] | Date-to-be-set 2168 3 | SFT TLV | [This.I-D] | Date-to-be-set 2169 4 | MPLS Swapping/Stacking | [This.I-D] | Date-to-be-set 2170 5 | SFP Traversal With MPLS | [This.I-D] | Date-to-be-set 2172 10.4. New SFP Association Type Registry 2174 IANA maintains a registry of "Border Gateway Protocol (BGP) 2175 Parameters". IANA is request to create a new subregistry called the 2176 "SFP Association Type" registry. 2178 Valid values are in the range 0 to 65535. 2180 o Values 0 and 65535 are to be marked "Reserved, not to be 2181 allocated". 2183 o Values 1 through 65524 are to be assigned according to the "First 2184 Come First Served" policy [RFC8126]. 2186 This document should be given as a reference for this registry. 2188 The new registry should track: 2190 o Association Type 2192 o Name 2194 o Reference Document or Contact 2196 o Registration Date 2198 The registry should initially be populated as follows: 2200 Association Type | Name | Reference | Date 2201 -----------------+--------------------+------------+--------------- 2202 1 | Bidirectional SFP | [This.I-D] | Date-to-be-set 2204 10.5. New Service Function Type Registry 2206 IANA is request to create a new top-level registry called "Service 2207 Function Chaining Service Function Types". 2209 Valid values are in the range 0 to 65535. 2211 o Values 0 and 65535 are to be marked "Reserved, not to be 2212 allocated". 2214 o Values 1 through 31 are to be assigned by "Standards Action" 2215 [RFC8126] and are referred to as the Special Purpose SFT values. 2217 o Other values (32 through 65534) are to be assigned according to 2218 the "First Come First Served" policy [RFC8126]. 2220 This document should be given as a reference for this registry. 2222 The new registry should track: 2224 o Value 2226 o Name 2228 o Reference Document or Contact 2230 o Registration Date 2232 The registry should initially be populated as follows: 2234 Value | Name | Reference | Date 2235 ------+-----------------------+---------------+--------------- 2236 1 | Change Sequence | [This.I-D] | Date-to-be-set 2238 10.6. New Generic Transitive Experimental Use Extended Community Sub- 2239 Types 2241 IANA maintains a registry of "Border Gateway Protocol (BGP) 2242 Parameters" with a subregistry of "Generic Transitive Experimental 2243 Use Extended Community Sub-Type". IANA is requested to assign a new 2244 sub-types as follows: 2246 "Flow Spec for SFC Classifiers" (TBD4 in this document) with this 2247 document as the reference. 2249 "SFI Pool Identifier" (TBD6 in this document) with this document 2250 as the reference. 2252 "MPLS Label Stack Mixed Swapping/Stacking Labels" (TBD7 in this 2253 document) with this document as the reference. 2255 10.7. SPI/SI Representation 2257 IANA is requested to assign a codepoint from the "BGP Tunnel 2258 Encapsulation Attribute Sub-TLVs" registry for the "SPI/SI 2259 Representation Sub-TLV" (TBD5 in this document) with this document 2260 being the reference. 2262 11. Contributors 2264 Stuart Mackie 2265 Juniper Networks 2267 Email: wsmackie@juinper.net 2269 Keyur Patel 2270 Arrcus, Inc. 2272 Email: keyur@arrcus.com 2274 Avinash Lingala 2275 AT&T 2277 Email: ar977m@att.com 2279 12. Acknowledgements 2281 Thanks to Tony Przygienda for helpful comments, and to Joel Halpern 2282 for discussions that improved this document. 2284 13. References 2286 13.1. Normative References 2288 [I-D.ietf-idr-tunnel-encaps] 2289 Rosen, E., Patel, K., and G. Velde, "The BGP Tunnel 2290 Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-07 2291 (work in progress), July 2017. 2293 [I-D.ietf-sfc-nsh] 2294 Quinn, P., Elzur, U., and C. Pignataro, "Network Service 2295 Header (NSH)", draft-ietf-sfc-nsh-27 (work in progress), 2296 October 2017. 2298 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2299 Requirement Levels", BCP 14, RFC 2119, 2300 DOI 10.17487/RFC2119, March 1997, 2301 . 2303 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 2304 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 2305 DOI 10.17487/RFC4271, January 2006, 2306 . 2308 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 2309 Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2310 2006, . 2312 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 2313 "Multiprotocol Extensions for BGP-4", RFC 4760, 2314 DOI 10.17487/RFC4760, January 2007, 2315 . 2317 [RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J., 2318 and D. McPherson, "Dissemination of Flow Specification 2319 Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009, 2320 . 2322 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2323 Writing an IANA Considerations Section in RFCs", BCP 26, 2324 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2325 . 2327 13.2. Informative References 2329 [I-D.farrel-mpls-sfc] 2330 Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based 2331 Forwarding Plane for Service Function Chaining", draft- 2332 farrel-mpls-sfc-02 (work in progress), October 2017. 2334 [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and 2335 L. Yong, "The Use of Entropy Labels in MPLS Forwarding", 2336 RFC 6790, DOI 10.17487/RFC6790, November 2012, 2337 . 2339 [RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for 2340 Service Function Chaining", RFC 7498, 2341 DOI 10.17487/RFC7498, April 2015, 2342 . 2344 [RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black, 2345 "Encapsulating MPLS in UDP", RFC 7510, 2346 DOI 10.17487/RFC7510, April 2015, 2347 . 2349 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 2350 Chaining (SFC) Architecture", RFC 7665, 2351 DOI 10.17487/RFC7665, October 2015, 2352 . 2354 Authors' Addresses 2356 Adrian Farrel 2357 Juniper Networks 2359 Email: afarrel@juniper.net 2361 John Drake 2362 Juniper Networks 2364 Email: jdrake@juniper.net 2366 Eric Rosen 2367 Juniper Networks 2369 Email: erosen@juniper.net 2371 Jim Uttaro 2372 AT&T 2374 Email: ju1738@att.com 2376 Luay Jalil 2377 Verizon 2379 Email: luay.jalil@verizon.com