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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-08) exists of draft-ietf-sfc-proof-of-transit-02 Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force S. Aldrin 3 Internet-Draft Google 4 Intended status: Informational C. Pignataro, Ed. 5 Expires: January 26, 2020 N. Kumar, Ed. 6 Cisco 7 R. Krishnan 8 VMware 9 A. Ghanwani 10 Dell 11 July 25, 2019 13 Service Function Chaining (SFC) 14 Operations, Administration and Maintenance (OAM) Framework 15 draft-ietf-sfc-oam-framework-10 17 Abstract 19 This document provides a reference framework for Operations, 20 Administration and Maintenance (OAM) for Service Function Chaining 21 (SFC). 23 Requirements Language 25 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 26 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 27 "OPTIONAL" in this document are to be interpreted as described in RFC 28 2119 [RFC2119] RFC 8174 [RFC8174] when and only when, they appear in 29 all capitals, as shown here. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on January 26, 2020. 48 Copyright Notice 50 Copyright (c) 2019 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (https://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 1.1. Document Scope . . . . . . . . . . . . . . . . . . . . . 4 67 1.2. Acronyms and Terminology . . . . . . . . . . . . . . . . 4 68 1.2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . 4 69 1.2.2. Terminology . . . . . . . . . . . . . . . . . . . . . 4 70 2. SFC Layering Model . . . . . . . . . . . . . . . . . . . . . 5 71 3. SFC OAM Components . . . . . . . . . . . . . . . . . . . . . 6 72 3.1. The SF Component . . . . . . . . . . . . . . . . . . . . 7 73 3.1.1. SF Availability . . . . . . . . . . . . . . . . . . . 7 74 3.1.2. SF Performance Measurement . . . . . . . . . . . . . 8 75 3.2. The SFC Component . . . . . . . . . . . . . . . . . . . . 8 76 3.2.1. SFC Availability . . . . . . . . . . . . . . . . . . 8 77 3.2.2. SFC Performance Measurement . . . . . . . . . . . . . 9 78 3.3. The Classifier Component . . . . . . . . . . . . . . . . 9 79 4. SFC OAM Functions . . . . . . . . . . . . . . . . . . . . . . 9 80 4.1. Connectivity Functions . . . . . . . . . . . . . . . . . 10 81 4.2. Continuity Functions . . . . . . . . . . . . . . . . . . 10 82 4.3. Trace Functions . . . . . . . . . . . . . . . . . . . . . 11 83 4.4. Performance Management Functions . . . . . . . . . . . . 11 84 5. Gap Analysis . . . . . . . . . . . . . . . . . . . . . . . . 12 85 5.1. Existing OAM Functions . . . . . . . . . . . . . . . . . 12 86 5.2. Missing OAM Functions . . . . . . . . . . . . . . . . . . 12 87 5.3. Required OAM Functions . . . . . . . . . . . . . . . . . 13 88 6. Candidate SFC OAM Tools . . . . . . . . . . . . . . . . . . . 13 89 6.1. SFC OAM Packet Marker . . . . . . . . . . . . . . . . . . 13 90 6.2. OAM Packet Processing and Forwarding Semantic . . . . . . 13 91 6.3. OAM Function Types . . . . . . . . . . . . . . . . . . . 14 92 6.4. OAM Toolset Applicability . . . . . . . . . . . . . . . . 14 93 6.4.1. ICMP . . . . . . . . . . . . . . . . . . . . . . . . 14 94 6.4.2. BFD/Seamless-BFD . . . . . . . . . . . . . . . . . . 15 95 6.4.3. In-Situ OAM . . . . . . . . . . . . . . . . . . . . . 15 96 6.4.4. SFC Traceroute . . . . . . . . . . . . . . . . . . . 15 97 7. Manageability Considerations . . . . . . . . . . . . . . . . 15 98 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 99 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 100 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 101 11. Contributing Authors . . . . . . . . . . . . . . . . . . . . 17 102 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 103 12.1. Normative References . . . . . . . . . . . . . . . . . . 17 104 12.2. Informative References . . . . . . . . . . . . . . . . . 18 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 107 1. Introduction 109 Service Function Chaining (SFC) enables the creation of composite 110 services that consist of an ordered set of Service Functions (SF) 111 that are to be applied to packets and/or frames selected as a result 112 of classification [RFC7665]. SFC is a concept that provides for more 113 than just the application of an ordered set of SFs to selected 114 traffic; rather, it describes a method for deploying SFs in a way 115 that enables dynamic ordering and topological independence of those 116 SFs as well as the exchange of metadata between participating 117 entities. The foundations of SFC are described in the following 118 documents: 120 o SFC Problem Statement [RFC7498] 122 o SFC Architecture [RFC7665] 124 The reader is assumed to be familiar with the material in these 125 documents. 127 This document provides a reference framework for Operations, 128 Administration and Maintenance (OAM, [RFC6291]) of SFC. 129 Specifically, this document provides: 131 o In Section 2, an SFC layering model; 133 o In Section 3, aspects monitored by SFC OAM; 135 o In Section 4, functional requirements for SFC OAM; 137 o In Section 5, a gap analysis for SFC OAM. 139 SFC OAM solution documents should refer to this document to indicate 140 the SFC OAM component and the functionality they target. 142 OAM controllers are assumed to be within the same administrative 143 domain as the target SFC enabled domain. 145 1.1. Document Scope 147 The focus of this document is to provide an architectural framework 148 for SFC OAM, particularly focused on the aspect of the Operations 149 component within OAM. Actual solutions and mechanisms are outside 150 the scope of this document. 152 1.2. Acronyms and Terminology 154 1.2.1. Acronyms 156 SFC: Service Function Chain 158 SFF: Service Function Forwarder 160 SF: Service Function 162 SFP: Service Function Path 164 RSP: Rendered Service Path 166 NSH: Network Service Header 168 VM: Virtual Machines 170 OAM: Operations, Administration and Maintenance 172 IPPM: IP Performance Measurement 174 BFD: Bidirectional Forwarding Detection 176 NVo3: Network Virtualization over Layer3 178 SNMP: Simple Network Management Protocol 180 NETCONF: Network Configuration Protocol 182 E-OAM: Ethernet OAM 184 MPLS_PM: MPLS Performance Measurement 186 1.2.2. Terminology 188 This document uses the terminologies defined in [RFC7665], [RFC8300], 189 and so the readers are expected to be familiar with the same. 191 2. SFC Layering Model 193 Multiple layers come into play for implementing the SFC. These 194 include the service layer and the underlying layers (Network Layer, 195 Link Layer, etc.). 197 o The service layer, which consists of SFC data plane elements that 198 includes classifiers, Service Functions (SF), Service Function 199 Forwarders (SFF), and SFC Proxies. This layer uses the overlay 200 network for ensuring connectivity between SFC data plane elements. 202 o The overlay network layer, which leverages various overlay network 203 technologies interconnecting SFC data plane elements and allows 204 establishing Service Function Paths (SFPs). This layer is mostly 205 transparent to the SFC data plane elements. 207 o The underlay network layer, which is dictated by the networking 208 technology deployed within a network (e.g., IP, MPLS) 210 o The link layer, which is dependent upon the physical technology 211 used. Ethernet is a popular choice for this layer, but other 212 alternatives are deployed (e.g. POS, DWDM). The same or distinct 213 link layer technologies may be used in each leg shown in Figure 1. 215 o----------------------Service Layer----------------------o 217 +------+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ 218 |Classi|---|SF1|---|SF2|---|SF3|---|SF4|---|SF5|---|SF6|---|SF7| 219 |fier | +---+ +---+ +---+ +---+ +---+ +---+ +---+ 220 +------+ 221 <------VM1------> <--VM2--> <--VM3--> 223 ^-----------------^-------------------^---------------^ Overlay N/W 225 o-----------------o-------------------o---------------o Underlay N/W 227 o--------o--------o--------o--------o--------o--------o Link 229 Figure 1: SFC Layering Example 231 In Figure 1, the service layer element such as classifier and SF are 232 depicted as virtual machines that are interconnected using an overlay 233 network. The underlay network may comprise of multiple intermediate 234 nodes but not shown in the figure that provides underlay connectivity 235 between the service layer elements. 237 While Figure 1 depicts a sample example where SFs are enabled as 238 virtual entities, the SFC architecture does not make any assumptions 239 on how the SFC data plane elements are deployed. The SFC 240 architecture is flexible and accommodates physical or virtual entity 241 deployment. SFC OAM accounts for this flexibility and accordingly it 242 is applicable whether SFC data plane elements are deployed directly 243 on physical hardware, as one or more Virtual Machines, or any 244 combination thereof. 246 3. SFC OAM Components 248 The SFC operates at the service layer. For the purpose of defining 249 the OAM framework, the service layer is broken up into three distinct 250 components: 252 1. SF component: OAM functions applicable at this component includes 253 testing the SFs from any SFC-aware network devices (e.g., 254 classifiers, controllers, other service nodes). Testing an SF 255 may not be restricted to connectivity to the SF, but also whether 256 the SF is providing its intended service. Refer to Section 3.1.1 257 for a more detailed discussion. 259 2. SFC component: OAM functions applicable at this component 260 includes (but are not limited to) testing the service function 261 chains and the SFPs, validaion of the correlation between an SFC 262 and the actual forwarding path followed by a packet matching that 263 SFC, i.e. the Rendered Service Path (RSP). Some of the hops of 264 an SFC may not be visible when Hierarchical Service Function 265 Chaining (hSFC) [RFC8459] is in use. In such schemes, it is the 266 responsibility of the Internal Boundary Node (IBN) to glue the 267 connectivity between different levels for end-to-end OAM 268 functionality. 270 3. Classifier component: OAM functions applicable at this component 271 includes testing the validity of the classification rules and 272 detecting any incoherence among the rules installed in different 273 classifiers. 275 Figure 2 illustrates an example where OAM for the three defined 276 components are used within the SFC environment. 278 +-Classifier +-Service Function Chain OAM 279 | OAM | 280 | | ___________________________________________ 281 | \ /\ Service Function Chain \ 282 | \ / \ +---+ +---+ +-----+ +---+ \ 283 | \ / \ |SF1| |SF2| |Proxy|--|SF3| \ 284 | +------+ \/ \ +---+ +---+ +-----+ +---+ \ 285 +----> | |....(+-> ) | | | ) 286 |Classi| \ / +-----+ +-----+ +-----+ / 287 |fier | \ / | SFF1|----| SFF2|----| SFF3| / 288 | | \ / +--^--+ +-----+ +-----+ / 289 +----|-+ \/_________|________________________________/ 290 | | 291 +-------SF_OAM-------+ 292 +---+ +---+ 293 +SF_OAM>|SF3| |SF5| 294 | +-^-+ +-^-+ 295 +------|---+ | | 296 |Controller| +-SF_OAM+ 297 +----------+ 298 Service Function OAM (SF_OAM) 300 Figure 2: SFC OAM Components 302 It is expected that multiple SFC OAM solutions will be defined, each 303 targeting one specific component of the service layer. However, it 304 is critical that SFC OAM solutions together provide the coverage of 305 all three SFC OAM components: the SF component, the SFC component, 306 and the classifier component. 308 3.1. The SF Component 310 3.1.1. SF Availability 312 One SFC OAM requirement for the SF component is to allow an SFC-aware 313 network device to check the availability of a specific SF (instance), 314 located on the same or different network device(s). The SF 315 availability may be performed to check the availability of any 316 instance of a specific SFn or it can be a specific instance of a SF. 317 SF availability is an aspect that raises an interesting question -- 318 How to determine that a service function is available?. On one end 319 of the spectrum, one might argue that an SF is sufficiently available 320 if the service node (physical or virtual) hosting the SF is available 321 and is functional. On the other end of the spectrum, one might argue 322 that the SF's availability can only be concluded if the packet, after 323 passing through the SF, was examined and it was verified that the 324 packet did indeed get the got expected service. 326 The former approach will likely not provide sufficient confidence to 327 the actual SF availability, i.e. a service node and a SF are two 328 different entities. The latter approach is capable of providing an 329 extensive verification, but comes at a cost. Some SFs make direct 330 modifications to packets, while others do not. Additionally, the 331 purpose of some SFs may be to, conditionally, drop packets 332 intentionally. In such cases, it is normal behavior that certain 333 packets will not be egressing out from the service function. The OAM 334 mechanism needs to take into account such SF specifics when assessing 335 SF availability. Note that there are many flavors of SFs available, 336 and many more that are likely be introduced in future. Even a given 337 SF may introduce a new functionality (e.g., a new signature in a 338 firewall). The cost of this approach is that the OAM mechanism for 339 some SF will need to be continuously modified in order to "keep up" 340 with new functionality being introduced: lack of extendibility. 342 This framework document provides a RECOMMENDED framework where a 343 generalized approach is taken to verify that a SF is sufficiently 344 available (i.e., an adequate granularity to provide a basic SF 345 service). More specifics on the mechanism to characterize SF- 346 specific OAM to validate the service offering are outside the scope 347 of this document. Those fine-grained mechanisms are implementation- 348 and deployment-specific. 350 3.1.2. SF Performance Measurement 352 The second SFC OAM requirement for the SF component is to allow an 353 SFC-aware network device to check the performance metrics such as 354 loss and delay induced by a specific SF for processing legitimate 355 traffic. The performance can be a passive measurement by using live 356 traffic or can be active measurement by using synthetic probe 357 packets. 359 On the one hand, the performance of any specific SF can be quantified 360 by measuring the loss and delay metrics of the traffic from SFF to 361 the respective SF, while on the other hand, the performance can be 362 measured by leveraging the loss and delay metrics from the respective 363 SFs. The latter requires SF involvement to perform the measurement 364 while the former does not. 366 3.2. The SFC Component 368 3.2.1. SFC Availability 370 An SFC could be comprised of varying SFs and so the OAM layer is 371 required to perform validation and verification of SFs within an SFP, 372 in addition to connectivity verification and fault isolation. 374 In order to perform service connectivity verification of an SFC/SFP, 375 the OAM functions could be initiated from any SFC-aware network 376 devices of an SFC-enabled domain for end-to-end paths, or partial 377 paths terminating on a specific SF, within the SFC/SFP. The goal of 378 this OAM function is to ensure the SFs chained together have 379 connectivity as was intended at the time when the SFC was 380 established. The necessary return codes should be defined for 381 sending back in the response to the OAM packet, in order to complete 382 the verification. 384 When ECMP is in use at the service layer for any given SFC, there 385 MUST be the ability to discover and traverse all available paths. 387 A detailed explanation of the mechanism is outside the scope of this 388 document and is expected to be included in the actual solution 389 document. 391 3.2.2. SFC Performance Measurement 393 Any SFC-aware network device SHOULD have the ability to make 394 performance measurements over the entire SFC (i.e., end-to-end) or to 395 a specific segment of SFs within the SFC. 397 3.3. The Classifier Component 399 A classifier maintains the classification rules that map a flow to a 400 specific SFC. It is vital that the classifier is correctly 401 configured with updated classification rules and is functioning as 402 expected. The SFC OAM must be able to validate the classification 403 rules by assessing whether a flow is appropriately mapped to the 404 relevant SFC. Sample OAM packets can be presented to the classifiers 405 to assess the behavior with regard to a given classification entry. 407 4. SFC OAM Functions 409 Section 3 described SFC OAM operations that are required on each SFC 410 component. This section explores SFC OAM functions that are 411 applicable for more than one SFC components. 413 The various SFC OAM requirements listed in Section 3 highlighted the 414 need for various OAM functions at different layers. As listed in 415 Section 5.1, various OAM functions are in existence that are defined 416 to perform OAM functionality at different layers. In order to apply 417 such OAM functions at the service layer, they need to be enhanced to 418 operate a single SF/SFF to multiple SFs/SFFs in an SFC and also in 419 multiple SFCs. 421 4.1. Connectivity Functions 423 Connectivity is mainly an on-demand function to verify that the 424 connectivity exists between certain network elements and that the SFs 425 are available. For example, LSP Ping [RFC8029] is a common tool used 426 to perform this function for an MPLS underlay network. OAM messages 427 SHOULD be encapsulated with necessary SFC header and with OAM 428 markings when testing the SFC component. OAM messages MAY be 429 encapsulated with the necessary SFC header and with OAM markings when 430 testing the SF component. Some of the OAM functions performed by 431 connectivity functions are as follows: 433 o Verify the Path MTU from a source to the destination SF or through 434 the SFC. This requires the ability for the OAM packet to be of 435 variable length packet size. 437 o Verify any packet re-ordering and corruption. 439 o Verify the policy of an SFC or SF. 441 o Verification and validation of forwarding paths. 443 o Proactively test alternate or protected paths to ensure 444 reliability of network configurations. 446 4.2. Continuity Functions 448 Continuity is a model where OAM messages are sent periodically to 449 validate or verify the reachability to a given SF within an SFC or 450 for the entire SFC. This allows a monitoring network device (such as 451 the classifier or controller) to quickly detect failures such as link 452 failures, network element failures, SF outages, or SFC outages. BFD 453 [RFC5880] is one such function which helps in detecting failures 454 quickly. OAM functions supported by continuity function are as 455 follows: 457 o Ability to provision continuity check to a given SF within an SFC 458 or for the entire SFC. 460 o Proactively test alternate or protected paths to ensure 461 reliability of network configurations. 463 o Notifying the detected failures to other OAM functions or 464 applications to take appropriate action. 466 4.3. Trace Functions 468 Tracing is an OAM function that allows the operation to trigger an 469 action (e.g. response generation) from every transit device (e.g. 470 SFF, SF, SFC Proxy) on the tested layer. This function is typically 471 useful for gathering information from every transit devices or for 472 isolating the failure point to a specific SF within an SFC or for an 473 entire SFC. Some of the OAM functions supported by trace functions 474 are: 476 o Ability to trigger action from every transit device at the SFC 477 layer, using TTL or other means. 479 o Ability to trigger every transit device at the SFC layer to 480 generate a response with OAM code(s), using TTL or other means. 482 o Ability to discover and traverse ECMP paths within an SFC. 484 o Ability to skip SFs that do not support OAM while tracing SFs in 485 an SFC. 487 4.4. Performance Management Functions 489 Performance management functions involve measuring of packet loss, 490 delay, delay variance, etc. These performance metrics may be 491 measured pro-actively or on-demand. 493 SFC OAM should provide the ability to measure packet loss for an SFC. 494 On-demand measurement can be used to estimate packet loss using 495 statistical methods. Measuring the loss of OAM packets, an 496 approximation of packet loss for a given SFC can be derived. 498 Delay within an SFC could be measured based on the time it takes for 499 a packet to traverse the SFC from the ingress SFC node to the egress 500 SFF. As SFCs are unidirectional in nature, measurement of one-way 501 delay [RFC7679] is important. In order to measure one-way delay, 502 time synchronization MUST be supported by means such as NTP, PTP, 503 GPS, etc. 505 One-way delay variation [RFC3393] could also be calculated by sending 506 OAM packets and measuring the jitter between the packets passing 507 through an SFC. 509 Some of the OAM functions supported by the performance measurement 510 functions are: 512 o Ability to measure the packet processing delay induced by a single 513 SF or the one-way delay to traverse an SFP bound to a given SFC. 515 o Ability to measure the packet loss [RFC7680] within an SF or an 516 SFP bound to a given SFC. 518 5. Gap Analysis 520 This section identifies various OAM functions available at different 521 levels introduced in Section 2. It also identifies various gaps that 522 exist within the current toolset for performing OAM functions 523 required for SFC. 525 5.1. Existing OAM Functions 527 There are various OAM tool sets available to perform OAM functions 528 within various layers. These OAM functions may be used to validate 529 some of the underlay and overlay networks. Tools like ping and trace 530 are in existence to perform connectivity check and tracing of 531 intermediate hops in a network. These tools support different 532 network types like IP, MPLS, TRILL, etc. There is also an effort to 533 extend the tool set to provide connectivity and continuity checks 534 within overlay networks. BFD is another tool which helps in 535 detecting data forwarding failures. The orchestration tool may be 536 used for network and service orchestration function. Tables 3 and 4 537 are not exhaustive. 539 Table 3: OAM Tool GAP Analysis 540 +----------------+--------------+-------------+--------+------------+ 541 | Layer | Connectivity | Continuity | Trace | Performance| 542 +----------------+--------------+-------------+--------+------------+ 543 | Underlay N/w | Ping |E-OAM, BFD | Trace | IPPM, | 544 | | | | | MPLS_PM | 545 +----------------+--------------+-------------+--------+------------+ 546 | Overlay N/w | Ping |BFD, NVo3 OAM| Trace | IPPM | 547 +----------------+--------------+-------------+--------+------------+ 548 | SF | None + None + None + None | 549 +----------------+--------------+-------------+--------+------------+ 550 | SFC | None + None + None + None | 551 +----------------+--------------+-------------+--------+------------+ 553 5.2. Missing OAM Functions 555 As shown in Table 3, there are no standards-based tools available for 556 the verification of SFs and SFCs. 558 5.3. Required OAM Functions 560 Primary OAM functions exist for underlying layers. Tools like ping, 561 trace, BFD, etc. exist in order to perform these OAM functions. 563 6. Candidate SFC OAM Tools 565 This section describes the operational aspects of SFC OAM at the 566 service layer to perform the SFC OAM function defined in Section 4 567 and analyzes the applicability of various existing OAM toolsets in 568 the service layer. 570 6.1. SFC OAM Packet Marker 572 The SFC OAM function described in Section 4 performed at the service 573 layer or overlay network layer must mark the packet as an OAM packet 574 so that relevant nodes can differentiate an OAM packet from data 575 packets. The base header defined in Section 2.2 of [RFC8300] assigns 576 a bit to indicate OAM packets. When NSH encapsulation is used at the 577 service layer, the O bit must be set to differentiate the OAM packet. 578 Any other overlay encapsulations used in future must have a way to 579 mark the packet as OAM packet. 581 6.2. OAM Packet Processing and Forwarding Semantic 583 Upon receiving an OAM packet, SFC-aware SFs may choose to discard the 584 packet if it does not support OAM functionality or if the local 585 policy prevents them from processing the OAM packet. When an SF 586 supports OAM functionality, it is desirable to process the packet and 587 provide an appropriate response to allow end-to-end verification. To 588 limit performance impact due to OAM, SFC-aware SFs should rate limit 589 the number of OAM packets processed. 591 An SFF may choose not to forward the OAM packet to an SF if the SF 592 does not support OAM or if the policy does not allow to forward OAM 593 packet to an SF. The SFF may choose to skip the SF, modify the 594 header and forward to next SFC node in the chain. It should be noted 595 that skipping an SF might have implication on some OAM functions 596 (e.g. the delay measurement may not be accurate). The method by 597 which an SFF detects if the connected SF supports or is allowed to 598 process OAM packets is outside the scope of this document. It could 599 be a configuration parameter instructed by the controller or it can 600 be done by dynamic negotiation between the SF and SFF. 602 If the SFF receiving the OAM packet bound to a given SFC is the last 603 SFF in the chain, it must send a relevant response to the initiator 604 of the OAM packet. Depending on the type of OAM solution and tool 605 set used, the response could be a simple response (such as ICMP 606 reply) or could include additional data from the received OAM packet 607 (like statistical data consolidated along the path). The details are 608 expected to be covered in the solution documents. 610 Any SFC-aware node that initiates an OAM packet must set the OAM 611 marker in the overlay encapsulation. 613 6.3. OAM Function Types 615 As described in Section 4, there are different OAM functions that may 616 require different OAM solutions. While the presence of the OAM 617 marker in the overlay header (e.g., O bit in the NSH header) 618 indicates it as OAM packet, it is not sufficient to indicate what OAM 619 function the packet is intended for. The Next Protocol field in NSH 620 header may be used to indicate what OAM function is intended to or 621 what toolset is used. 623 6.4. OAM Toolset Applicability 625 As described in Section 5.1, there are different tool sets available 626 to perform OAM functions at different layers. This section describes 627 the applicability of some of the available toolsets in the service 628 layer. 630 6.4.1. ICMP 632 [RFC0792] and [RFC4443] describes the use of ICMP in IPv4 and IPv6 633 network respectively. It explains how ICMP messages can be used to 634 test the network reachability between different end points and 635 perform basic network diagnostics. 637 ICMP could be leveraged for connectivity function (defined in 638 Section 4.1) to verify the availability of SF or SFC. The Initiator 639 can generate an ICMP echo request message and control the service 640 layer encapsulation header to get the response from relevant node. 641 For example, a classifier initiating OAM can generate ICMP echo 642 request message, can set the TTL field in NSH header to 255 to get 643 the response from last SFF and thereby test the SFC availability. 644 Alternately, the initiator can set the TTL to some other value to get 645 the response from a specific SFs and there by test partial SFC 646 availability. Alternately, the initiator could send OAM packets with 647 sequentially incrementing the TTL in the NSH to trace the SFP. 649 It could be observed that ICMP at its current stage may not be able 650 to perform all required SFC OAM functions, but as explained above, it 651 can be used for some of the connectivity functions. 653 6.4.2. BFD/Seamless-BFD 655 [RFC5880] defines Bidirectional Forwarding Detection (BFD) mechanism 656 for fast failure detection. [RFC5881] and [RFC5884] defines the 657 applicability of BFD in IPv4, IPv6 and MPLS networks. [RFC7880] 658 defines Seamless BFD (S-BFD), a simplified mechanism of using BFD. 659 [RFC7881] explains its applicability in IPv4, IPv6 and MPLS network. 661 BFD or S-BFD could be leveraged to perform continuity function for SF 662 or SFC. An initiator could generate a BFD control packet and set the 663 "Your Discriminator" value as last SFF in the control packet. Upon 664 receiving the control packet, the last SFF in the SFC will reply back 665 with relevant DIAG code. The TTL field in the NSH header could be 666 used to perform partial SFC availability. For example, the initiator 667 can set the "Your Discriminator" value to the SF that is intended to 668 be tested and set the TTL field in NSH header in a way that it expire 669 at the relevant SF. How the initiator gets the Discriminator value 670 of the SF is outside the scope of this document. 672 6.4.3. In-Situ OAM 674 [I-D.ietf-sfc-proof-of-transit] defines a mechanism to perform proof 675 of transit to securely verify if a packet traversed the relevant SFP 676 or SFC. While the mechanism is defined inband (i.e., it will be 677 included in data packets), it may be used to perform various SFC OAM 678 functions as well. 680 In-Situ OAM could be used with O bit set to perform SF availability 681 and SFC availability or performance measurement. 683 6.4.4. SFC Traceroute 685 [I-D.penno-sfc-trace] defines a protocol that checks for path 686 liveliness and traces the service hops in any SFP. Section 3 of 687 [I-D.penno-sfc-trace] defines the SFC trace packet format while 688 Sections 4 and 5 of [I-D.penno-sfc-trace] defines the behavior of SF 689 and SFF respectively. 691 An initiator can control the Service Index Limit (SIL) in SFC trace 692 packet to perform SF and SFC availability test. 694 7. Manageability Considerations 696 This document does not define any new manageability tools but 697 consolidates the manageability tool gap analysis for SF and SFC. 699 Table 4: OAM Tool GAP Analysis 700 +----------------+--------------+-------------+--------+-------------+ 701 | Layer |Configuration |Orchestration|Topology|Notification | 702 +----------------+--------------+-------------+--------+-------------+ 703 | Underlay N/w |CLI, NETCONF | CLI, NETCONF|SNMP |SNMP, Syslog,| 704 | | | | |NETCONF | 705 +----------------+--------------+-------------+--------+-------------+ 706 | Overlay N/w |CLI, NETCONF | CLI, NETCONF|SNMP |SNMP, Syslog | 707 | | | | |NETCONF | 708 +----------------+--------------+-------------+--------+-------------+ 709 | SF |CLI, NETCONF + CLI, NETCONF| None | None | 710 +----------------+--------------+-------------+--------+-------------+ 711 | SFC |CLI, NETCONF + CLI, NETCONF| None | None | 712 +----------------+--------------+-------------+--------+-------------+ 714 Configuration, orchestration and manageability of SF and SFC could be 715 performed using CLI, NETCONF, etc. 717 As depicted in Tables 4, information and data models are needed for 718 configuration, manageability and orchestration for SFC. With 719 virtualized SF and SFC, manageability needs to be done 720 programmatically. 722 8. Security Considerations 724 Any security consideration defined in [RFC7665] and [RFC8300] are 725 applicable for this document. 727 The OAM information from service layer at different components may 728 collectively or independently reveal sensitive information. The 729 information may reveal the type of service functions hosted in the 730 network, the classification rules and the associated service chains, 731 specific service function paths etc. The sensitivity of the 732 information from SFC layer raises a need for careful security 733 considerations 735 The mapping and the rules information at the classifier component may 736 reveal the traffic rules and the traffic mapped to the SFC. The SFC 737 information collected at an SFC component may reveal the SF 738 associated within each chain and this information together with 739 classifier rules may be used to manipulate the header of synthetic 740 attack packets that may be used to bypass the SFC and trigger any 741 internal attacks. 743 The SF information at the SF component may be used by a malicious 744 user to trigger Denial of Service (DoS) attack by overloading any 745 specific SF using rogue OAM traffic. 747 To address the above concerns, SFC and SF OAM may provide mechanism 748 for: 750 o Misuse of the OAM channel for denial-of-services, 752 o Leakage of OAM packets across SFC instances, and 754 o Leakage of SFC information beyond the SFC domain. 756 The documents proposing the OAM solution for SF component should 757 consider rate-limiting the OAM probes at a frequency guided by the 758 implementation choice. Rate-limiting may be applied at the SFF or 759 the SF . The OAM initiator may not receive a response for the probes 760 that are rate-limited resulting in false negatives and the 761 implementation should be aware of this. 763 The documents proposing the OAM solution for any service layer 764 components should consider some form of message filtering to prevent 765 leaking any internal service layer information outside the 766 administrative domain. 768 9. IANA Considerations 770 No action is required by IANA for this document. 772 10. Acknowledgements 774 We would like to thank Mohamed Boucadair, Adrian Farrel, and Greg 775 Mirsky for their review and comments. 777 11. Contributing Authors 779 Nobo Akiya 780 Ericsson 781 Email: nobo.akiya.dev@gmail.com 783 12. References 785 12.1. Normative References 787 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 788 Requirement Levels", BCP 14, RFC 2119, 789 DOI 10.17487/RFC2119, March 1997, 790 . 792 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 793 Chaining (SFC) Architecture", RFC 7665, 794 DOI 10.17487/RFC7665, October 2015, 795 . 797 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 798 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 799 May 2017, . 801 [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., 802 "Network Service Header (NSH)", RFC 8300, 803 DOI 10.17487/RFC8300, January 2018, 804 . 806 [RFC8459] Dolson, D., Homma, S., Lopez, D., and M. Boucadair, 807 "Hierarchical Service Function Chaining (hSFC)", RFC 8459, 808 DOI 10.17487/RFC8459, September 2018, 809 . 811 12.2. Informative References 813 [I-D.ietf-sfc-proof-of-transit] 814 Brockners, F., Bhandari, S., Dara, S., Pignataro, C., 815 Leddy, J., Youell, S., Mozes, D., Mizrahi, T., Aguado, A., 816 and D. Lopez, "Proof of Transit", draft-ietf-sfc-proof-of- 817 transit-02 (work in progress), March 2019. 819 [I-D.penno-sfc-trace] 820 Penno, R., Quinn, P., Pignataro, C., and D. Zhou, 821 "Services Function Chaining Traceroute", draft-penno-sfc- 822 trace-03 (work in progress), September 2015. 824 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 825 RFC 792, DOI 10.17487/RFC0792, September 1981, 826 . 828 [RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation 829 Metric for IP Performance Metrics (IPPM)", RFC 3393, 830 DOI 10.17487/RFC3393, November 2002, 831 . 833 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 834 Control Message Protocol (ICMPv6) for the Internet 835 Protocol Version 6 (IPv6) Specification", STD 89, 836 RFC 4443, DOI 10.17487/RFC4443, March 2006, 837 . 839 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 840 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 841 . 843 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 844 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 845 DOI 10.17487/RFC5881, June 2010, 846 . 848 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 849 "Bidirectional Forwarding Detection (BFD) for MPLS Label 850 Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, 851 June 2010, . 853 [RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu, 854 D., and S. Mansfield, "Guidelines for the Use of the "OAM" 855 Acronym in the IETF", BCP 161, RFC 6291, 856 DOI 10.17487/RFC6291, June 2011, 857 . 859 [RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for 860 Service Function Chaining", RFC 7498, 861 DOI 10.17487/RFC7498, April 2015, 862 . 864 [RFC7679] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton, 865 Ed., "A One-Way Delay Metric for IP Performance Metrics 866 (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January 867 2016, . 869 [RFC7680] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton, 870 Ed., "A One-Way Loss Metric for IP Performance Metrics 871 (IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January 872 2016, . 874 [RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. 875 Pallagatti, "Seamless Bidirectional Forwarding Detection 876 (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016, 877 . 879 [RFC7881] Pignataro, C., Ward, D., and N. Akiya, "Seamless 880 Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6, 881 and MPLS", RFC 7881, DOI 10.17487/RFC7881, July 2016, 882 . 884 [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., 885 Aldrin, S., and M. Chen, "Detecting Multiprotocol Label 886 Switched (MPLS) Data-Plane Failures", RFC 8029, 887 DOI 10.17487/RFC8029, March 2017, 888 . 890 Authors' Addresses 892 Sam K. Aldrin 893 Google 895 Email: aldrin.ietf@gmail.com 897 Carlos Pignataro (editor) 898 Cisco Systems, Inc. 900 Email: cpignata@cisco.com 902 Nagendra Kumar (editor) 903 Cisco Systems, Inc. 905 Email: naikumar@cisco.com 907 Ram Krishnan 908 VMware 910 Email: ramkri123@gmail.com 912 Anoop Ghanwani 913 Dell 915 Email: anoop@alumni.duke.edu