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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group S. Aldrin 3 Internet-Draft Google, Inc 4 Intended status: Informational C. Pignataro 5 Expires: October 17, 2016 Cisco 6 G. Mirsky 7 Ericsson 8 N. Kumar 9 Cisco 10 April 15, 2016 12 Seamless Bidirectional Forwarding Detection (S-BFD) Use Cases 13 draft-ietf-bfd-seamless-use-case-05 15 Abstract 17 This document describes various use cases for a Seamless 18 Bidirectional Forwarding Detection (S-BFD), and provides requirements 19 such that protocol mechanisms allow for a simplified detection of 20 forwarding failures. 22 These use cases support S-BFD, as a simplified mechanism to use 23 Bidirectional Forwarding Detection (BFD) with large portions of 24 negotiation aspects eliminated, accelerating the establishment of a 25 BFD session. S-BFD benefits include quick provisioning as well as 26 improved control and flexibility to network nodes initiating the path 27 monitoring. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on October 17, 2016. 46 Copyright Notice 48 Copyright (c) 2016 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 64 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 66 2. Introduction to Seamless BFD . . . . . . . . . . . . . . . . 4 67 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5 68 3.1. Unidirectional Forwarding Path Validation . . . . . . . . 5 69 3.2. Validation of the Forwarding Path Prior to Switching 70 Traffic . . . . . . . . . . . . . . . . . . . . . . . . . 6 71 3.3. Centralized Traffic Engineering . . . . . . . . . . . . . 7 72 3.4. BFD in Centralized Segment Routing . . . . . . . . . . . 8 73 3.5. Efficient BFD Operation under Resource Constraints . . . 8 74 3.6. BFD for Anycast Addresses . . . . . . . . . . . . . . . . 8 75 3.7. BFD Fault Isolation . . . . . . . . . . . . . . . . . . . 9 76 3.8. Multiple BFD Sessions to the Same Target Node . . . . . . 9 77 3.9. An MPLS BFD Session Per ECMP Path . . . . . . . . . . . . 10 78 4. Detailed Requirements for a Seamless BFD . . . . . . . . . . 10 79 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 80 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 81 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 82 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12 83 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 84 9.1. Normative References . . . . . . . . . . . . . . . . . . 12 85 9.2. Informative References . . . . . . . . . . . . . . . . . 13 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 88 1. Introduction 90 Bidirectional Forwarding Detection (BFD) is a lightweight protocol, 91 as defined in [RFC5880], used to detect forwarding failures. Various 92 protocols and applications rely on BFD as its clients for failure 93 detection. Even though the protocol is lightweight and simple, there 94 are certain use cases where faster setting up of sessions and faster 95 continuity check of the data forwarding paths is necessary. This 96 document identifies these use cases and consequent requirements, such 97 that enhancements and extensions result in a Seamless BFD (S-BFD) 98 protocol. 100 BFD is a simple lightweight "Hello" protocol to detect data plane 101 failures. With dynamic provisioning of forwarding paths on a large 102 scale, establishing BFD sessions for each of those paths not only 103 creates operational complexity, but also causes undesirable delay in 104 establishing or deleting sessions. The existing session 105 establishment mechanism of the BFD protocol has to be enhanced in 106 order to minimize the time for the session to come up to validate the 107 forwarding path. 109 This document specifically identifies various use cases and 110 corresponding requirements in order to enhance BFD and other 111 supporting protocols. Specifically, one key goal is removing the 112 time delay (i.e., the "seam") between a network node wants to perform 113 a continuity test and the node completes that continuity test. 114 Consequently, "Seamless BFD" (S-BFD) has been chosen as the name for 115 this mechanism. 117 While the identified requirements could meet various use cases, it is 118 outside the scope of this document to identify all of the possible 119 and necessary requirements. Solutions to the identified uses cases 120 and protocol specific enhancements or proposals are outside the scope 121 of this document as well. Protocol definitions to support these use 122 cases can be found at [I-D.ietf-bfd-seamless-base] and 123 [I-D.ietf-bfd-seamless-ip]. 125 1.1. Terminology 127 The reader is expected to be familiar with the BFD [RFC5880], IP 128 [RFC0791] [RFC2460], MPLS [RFC3031], and Segment Routing (SR) 129 [I-D.ietf-spring-segment-routing] terminologies and protocol 130 constructs. 132 1.2. Requirements Language 134 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 135 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 136 "OPTIONAL" in this document are to be interpreted as described in 137 [RFC2119]. 139 2. Introduction to Seamless BFD 141 BFD, as defined in [RFC5880], requires two network nodes to exchange 142 locally allocated discriminators. These discriminators enable the 143 identification of the sender and the receiver of BFD packets over the 144 particular session. Subsequently, BFD performs proactive continuity 145 monitoring of the forwarding path between the two. Several 146 specifications describe BFD's multiple deployment uses: 148 [RFC5881] defines BFD over IPv4 and IPv6 for single IP hops 150 [RFC5883] defines BFD over multihop paths 152 [RFC5884] defines BFD for MPLS Label Switched Paths (LSPs) 154 [RFC5885] defines BFD for MPLS Pseudowires (PWs) 156 Currently, BFD is best suited to verify that two endpoints are 157 mutually reachable or that an existing connection continues to be up 158 and alive. In order for BFD to be able to initially verify that a 159 connection is valid and that it connects the expected set of 160 endpoints, it is necessary to provide each endpoint with the 161 discriminators associated with the connection at each endpoint prior 162 to initiating BFD sessions. The discriminators are used to verify 163 that the connection is up and verifiable. Currently, the exchange of 164 discriminators and the demultiplexing of the initial BFD packets is 165 application dependent. 167 If this information is already known to the end-points of a potential 168 BFD session, the initial handshake including an exchange of 169 discriminators is unnecessary and it is possible for the endpoints to 170 begin BFD messaging seamlessly. A key objective of the S-BFD use 171 cases described in this document is to avoid needing to exchange the 172 initial packets before the BFD session can be established, with the 173 goal of getting to the established state more quickly; in other 174 words, the initial exchange of discriminator information is an 175 unnecessary extra step that may be avoided for these cases. 177 In a given scenario, an entity (such as an operator, or a centralized 178 controller) determines a set of network entities to which BFD 179 sessions might need to be established. In traditional BFD, each of 180 those network entities chooses a BFD discriminator for each BFD 181 session that the entity will participate in (see Section 6.3 of 182 [RFC5880]). However, a key goal of a Seamless BFD is to provide 183 operational simplification. In this context, for S-BFD, each of 184 those network entities is assigned one or more BFD discriminators, 185 and allowing those network entities to use one discriminator value 186 for multiple sessions. Therefore, there may be only one or a few 187 discriminators assigned to a node. These network entities will 188 create an S-BFD listener session instance that listens for incoming 189 BFD control packets. When the mappings between specific network 190 entities and their corresponding BFD discriminators are known to 191 other network nodes belonging to the same administrative domain, 192 then, without having received any BFD packet from a particular 193 target, a network entity in this network is able to send a BFD 194 control packet to the target's assigned discriminator in the Your 195 Discriminator field. The target network node, upon reception of such 196 BFD control packet, will transmit a response BFD control packet back 197 to the sender. 199 3. Use Cases 201 As per the BFD protocol [RFC5880], BFD sessions are established using 202 handshake mechanism prior to validating the forwarding path. This 203 section outlines some use cases where the existing mechanism may not 204 be able to satisfy the requirements identified. In addition, some of 205 the use cases also stress the need for expedited BFD session 206 establishment while preserving benefits of forwarding failure 207 detection using existing BFD mechanics. Both these high-level goals 208 result in the S-BFD use cases. 210 3.1. Unidirectional Forwarding Path Validation 212 Even though bidirectional verification of forwarding path is useful, 213 there are scenarios where verification is only required in one 214 direction between a pair of nodes. One such case is, when a static 215 route uses BFD to validate reachability to the next-hop IP router. 216 In this case, the static route is established from one network entity 217 to another. The requirement in this case is only to validate the 218 forwarding path for that statically established unidirectional path. 219 Validation of the forwarding path in the direction of the target 220 entity to the originating entity is not required, in this scenario. 221 Many LSPs have the same unidirectional characteristics and 222 unidirectional validation requirements. Such LSPs are common in 223 Segment Routing and LDP based MPLS networks. A final example is when 224 a unidirectional tunnel uses BFD to validate reachability of an 225 egress node. 227 Additionally, there are operational implications to the 228 unidirectional path validation. If the traditional BFD is to be 229 used, the target network entity has to be provisioned as well as an 230 initiator, even though the reverse path validation with the BFD 231 session is not required. However, in the case of unidirectional BFD, 232 there is no need for provisioning on the target network entity, only 233 the source one. 235 In this use case, a BFD session could be established in a single 236 direction. When the targeted network entity receives the packet, the 237 Your Discriminator value in the packet instructs the network entity 238 to process it, and send a response based on the source address of the 239 packet. This does not necessitate the requirement for establishment 240 of a bi-directional session, hence the two way handshake to exchange 241 discriminators is not needed. The target node does not need to know 242 the My Discriminator of the source node. 244 Thus, a requirement for BFD for this use case is to enable session 245 establishment from source network entity to target network entity 246 without the need to have a session (and state) for the reverse 247 direction. Further, another requirement is that the BFD response 248 from target back to sender can take any (in-band or out-of-band) 249 path. The target network entity (for the BFD session), upon receipt 250 of BFD packet, starts processing the BFD packet based on the 251 discriminator received. The source network entity can therefore 252 establish a unidirectional BFD session without the bidirectional 253 handshake of discriminators for session establishment. 255 3.2. Validation of the Forwarding Path Prior to Switching Traffic 257 This use case is when BFD is used to verify reachability before 258 sending traffic via a path/LSP. This comes with a cost, which is 259 that traffic is prevented to use the path/LSP until BFD is able to 260 validate the reachability, which could take seconds due to BFD 261 session bring-up sequences [RFC5880], LSP ping bootstrapping 262 [RFC5884], etc. This use case would be better supported by 263 eliminating the need for the initial BFD session negotiation. 265 All it takes to be able to send BFD packets to a target, and the 266 target properly demultiplexing these, is for the source network 267 entities to know what the discriminator values to be used for the 268 session. The same is the case for S-BFD: the three-way handshake 269 mechanism is eliminated during the bootstrap of BFD sessions. 270 However, this information is required at each entity to verify that 271 BFD messages are being received from the expected end-points, hence 272 the handshake mechanism serves no purpose. Elimination of the 273 unnecessary handshake mechanism allows for faster reachability 274 validation of BFD provisioned paths/LSPs. 276 In addition, it is expected that some MPLS technologies will require 277 traffic engineered LSPs to be created dynamically, perhaps driven by 278 external applications, as e.g. in Software Defined Networks (SDN). 279 It will be desirable to perform BFD validation as soon as the LSPs 280 are created, so as to use them. 282 In order to support this use case, an S-BFD session is established 283 without the need for session negotiation and exchange of 284 discriminators. 286 3.3. Centralized Traffic Engineering 288 Various technologies in the SDN domain that involve controller-based 289 networks have evolved such that the intelligence, traditionally 290 placed in a distributed and dynamic control plane, is separated from 291 the networking entities themselves; instead, it resides in a 292 (logically) centralized place. There are various controllers that 293 perform the function in establishment of forwarding paths for the 294 data flow. Traffic engineering (TE) is one important function, where 295 the path of the traffic flow is engineered, depending upon various 296 attributes and constraints of the traffic paths as well as the 297 network state. 299 When the intelligence of the network resides in a centralized entity, 300 the ability to manage and maintain the dynamic network and its 301 multiple data paths and node reachability becomes a challenge. One 302 way to ensure the forwarding paths are valid and working is done by 303 validation using BFD. When traffic engineered tunnels are created, 304 it is operationally critical to ensure that the forwarding paths are 305 working, prior to switching the traffic onto the engineered tunnels. 306 In the absence of distributed control plane protocols, it may be 307 desirable to verify any arbitrary forwarding path in the network. 308 With tunnels being engineered by a centralized entity, when the 309 network state changes, traffic has to be switched with minimum 310 latency and without black-holing of the data. 312 It is highly desirable in this centralized traffic engineering use 313 case that the traditional BFD session establishment and validation of 314 the forwarding path does not become a bottleneck. If the controller 315 or other centralized entity is able to very rapidly verify the 316 forwarding path of a traffic engineered tunnel, it could steer the 317 traffic onto the traffic engineered tunnel very quickly thus 318 minimizing adverse effect on a service. This is even more useful and 319 necessary when the scale of the network and number of traffic 320 engineered tunnels grows. 322 The cost associated with the time required for BFD session 323 negotiation and establishment of BFD sessions to identify valid paths 324 is very high when providing network redundancy is a critical issue. 326 3.4. BFD in Centralized Segment Routing 328 A monitoring technique of a Segment Routing network based on a 329 centralized controller is described in [I-D.ietf-spring-oam-usecase]. 330 Specific OAM requirements for Segment Routing are captured in 331 [I-D.ietf-spring-sr-oam-requirement]. In validating this use case, 332 one of the requirements is to ensure that the BFD packet's behavior 333 is according to the monitoring specified for the segment, and that 334 the packet is U-turned at the expected node. This criteria ensures 335 the continuity check to the adjacent segment-id. 337 To support this use case, the operational requirement is for BFD, 338 initiated from a centralized controller, to perform liveness 339 detection for any given segment under its domain. 341 3.5. Efficient BFD Operation under Resource Constraints 343 When BFD sessions are being setup, torn down or modified (i.e., when 344 parameters such as interval and multiplier are being modified), BFD 345 requires additional packets other than scheduled packet transmissions 346 to complete the negotiation procedures (i.e., P/F bits). There are 347 scenarios where network resources are constrained: a node may require 348 BFD to monitor very large number of paths, or BFD may need to operate 349 in low powered and traffic sensitive networks; these include 350 microwave, low powered nano-cells, and others. In these scenarios, 351 it is desirable for BFD to slow down, speed up, stop, or resume at- 352 will and with minimal number of additional BFD packets exchanged to 353 modify the session or establish a new one. 355 The established BFD session parameters and attributes like 356 transmission interval, receiver interval, etc., need to be modifiable 357 without changing the state of the session. 359 3.6. BFD for Anycast Addresses 361 The BFD protocol requires two endpoints to host BFD sessions, both 362 sending packets to each other. This BFD model does not fit well with 363 anycast address monitoring, as BFD packets transmitted from a network 364 node to an anycast address will reach only one of potentially many 365 network nodes hosting the anycast address. 367 This use case verifies that a source node can send a packet to an 368 anycast address, and that the target node to which the packet is 369 delivered can send a response packet to the source node. Traditional 370 BFD cannot fulfill this requirement, since it does not provide for a 371 set of BFD agents to collectively form one endpoint of a BFD session. 372 The concept of a Target Listener in S-BFD solves this requirement. 374 To support this use case, the BFD sender transmits BFD packets, which 375 are received by any of the nodes hosting the anycast address to which 376 the BFD packets being sent. The anycast target that receives the BFD 377 packet, responds. This use case does not imply the BFD session 378 establishment with every node hosting the anycast address. 379 Consequently, in this any cast use case, target nodes that do not 380 happen to receive any of the BFD packets do not need to maintain any 381 state, and the source node does not need to maintain separate state 382 for each target node. 384 3.7. BFD Fault Isolation 386 BFD for multihop paths [RFC5883] and BFD for MPLS LSPs [RFC5884] 387 perform end-to-end validation, traversing multiple network nodes. 388 BFD has been designed to declare failure upon lack of consecutive 389 packet reception, which can be caused by a fault anywhere along these 390 path. Fast failure detection allows for rapid fault detection and 391 consequent rapid path recovery procedures. However, operators often 392 have to follow up, manually or automatically, to attempt to identify 393 and localize the fault that caused BFD sessions to fail (i.e., fault 394 isolation). The usage of other tools to isolate the fault (e.g., 395 traceroute) may cause the packets to traverse a different path 396 through the network, if Equal-Cost Multipath (ECMP) is used. In 397 addition, the longer it takes from BFD session failure to starting 398 fault isolation, the more likely that the fault will not be able to 399 be isolated (e.g., a fault can get corrected or routed around). If 400 BFD had built-in fault isolation capability, fault isolation can get 401 triggered at the earliest sign of fault detection. This embedded 402 fault isolation will be more effective when those BFD fault isolation 403 packets are load balanced in the same way as the BFD packets that 404 were dropped, detecting the fault. 406 This use case describes S-BFD fault isolation capabilities using 407 status indicating fields. 409 3.8. Multiple BFD Sessions to the Same Target Node 411 BFD is capable of providing very fast failure detection, as relevant 412 network nodes continuously transmit BFD packets at the negotiated 413 rate. If BFD packet transmission is interrupted, even for a very 414 short period of time, BFD can declare a failure irrespective of path 415 liveliness. It is possible, on a system where BFD is running, for 416 certain events (intentionally or unintentionally) to cause a short 417 interruption of BFD packet transmissions. With distributed 418 architectures of BFD implementations, this case can be protected. In 419 this case, the use case of an S-BFD node running multiple BFD 420 sessions to a targets, with those sessions hosted on different system 421 modules (e.g., in different CPU instances). This can reduce BFD 422 false failures, resulting in more stable network. 424 To support this use case, a mapping between the multiple 425 discriminators on a single system, and the specific entity within the 426 system is required. 428 3.9. An MPLS BFD Session Per ECMP Path 430 BFD for MPLS LSPs, defined in [RFC5884], describes procedures to run 431 BFD as LSP in-band continuity check mechanism, through usage of MPLS 432 echo request [RFC4379] to bootstrap the BFD session on the target 433 (i.e., egress) node. Section 4 of [RFC5884] also describes a 434 possibility of running multiple BFD sessions per alternative paths of 435 LSP. [RFC7726] further clarified the procedures, both for ingress 436 and egress nodes, of how to bootstrap, maintain, and remove multiple 437 BFD sessions for the same tuple. However, this 438 mechanism still requires the use of MPLS LSP Ping for bootstrapping, 439 round-trips for initialization, and keeping state at the receiver. 441 In the presence of ECMP within an MPLS LSP, it may be desirable to 442 run in-band monitoring that exercises every path of this ECMP. 443 Otherwise there will be scenarios where in-band BFD session remains 444 up through one path but traffic is black-holing over another path. A 445 BFD session per ECMP path of an LSP requires the definition of 446 procedures that update [RFC5884] in terms of how to bootstrap and 447 maintain the correct set of BFD sessions on the egress node. 448 However, for traditional BFD, that requires the constant use of MPLS 449 Echo Request messages to create and delete BFD sessions on the egress 450 node, when ECMP paths and/or corresponding load balance hash keys 451 change. If a BFD session over any paths of the LSP can be 452 instantiated, stopped and resumed without requiring additional 453 procedures of bootstrapping via an MPLS echo request message, it 454 would greatly simplify both implementations and operations, and 455 benefits network devices as less processing are required by them. 457 To support this requirement, multiple S-BFD sessions need to be 458 established over different ECMP paths from the same source to target 459 node. 461 4. Detailed Requirements for a Seamless BFD 463 REQ#1: A target network entity (for the S-BFD session), upon 464 receipt of the S-BFD packet, MUST process the packet based 465 on the discriminator received in the BFD packet. If the 466 S-BFD context is found, the target network entity MUST be 467 able to send a response. 469 REQ#2: The source network entity MUST be able to establish a 470 unidirectional S-BFD session without the bidirectional 471 handshake of discriminators for session establishment. 473 REQ#3: The S-BFD session MUST be able to be established without the 474 need for exchange of discriminators in session negotiation. 476 REQ#4: In a Segment Routed network, S-BFD MUST be able to perform 477 liveness detection initiated from a centralized controller 478 for any given segment under its domain. 480 REQ#5: The established S-BFD session parameters and attributes, 481 such as transmission interval, reception interval, etc., 482 MUST be modifiable without changing the state of the 483 session. 485 REQ#6: An S-BFD source network entity MUST be able to send S-BFD 486 control packets to an anycast address which are received by 487 any node hosting that address, and must be able to receive 488 responses from any of these anycast nodes, without 489 establishing a separate BFD session with every node hosing 490 the anycast address. 492 REQ#7: S-BFD SHOULD support fault isolation capability, which MAY 493 be triggered when a fault is encountered. 495 REQ#8: S-BFD SHOULD be able to establish multiple sessions between 496 the same pair of source and target nodes. This requirement 497 enables but does not guarantee the ability to monitor 498 diverge paths in ECMP environments. It also provides 499 resiliency in distributed router architectures. The mapping 500 between BFD discriminators and particular entities (e.g., 501 ECMP paths, or Line Cards) is out the scope of the S-BFD 502 specification. 504 REQ#9: The S-BFD protocol MUST provide mechanisms for loop 505 detection and prevention, protecting against malicious 506 attacks attempting to create packet loops. 508 REQ#10: S-BFD MUST incorporate robust security protections against 509 impersonators, malicions actors, and various attacks. The 510 simple and accelerated establishment of an S-BFD session 511 should not negatively affect security. 513 5. Security Considerations 515 This document details the use cases and identifies various associated 516 requirements. Some of these requirements are security related. The 517 use cases herein described do not expose a system to abuse or to 518 additional security risks. The proposed new protocols, extensions, 519 and enhancements for a Seamless BFD supporting these use cases and 520 realizing these requirements will address the associated security 521 considerations. A Seamless BFD should not have reduced security 522 capabilities as compared to traditional BFD. 524 6. IANA Considerations 526 There are no IANA considerations introduced by this document. 528 7. Acknowledgements 530 The authors would like to thank Tobias Gondrom and Eric Gray, for 531 their insightful and useful comments. The authors appreciate the 532 thorough review and comments provided by Dale R. Worley. 534 8. Contributors 536 The following are key contributors to this document: 538 Manav Bhatia, Ionos Networks 539 Satoru Matsushima, Softbank 540 Glenn Hayden, ATT 541 Santosh P K 542 Mach Chen, Huawei 543 Nobo Akiya, Big Switch Networks 545 9. References 547 9.1. Normative References 549 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 550 Requirement Levels", BCP 14, RFC 2119, 551 DOI 10.17487/RFC2119, March 1997, 552 . 554 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 555 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 556 . 558 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 559 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 560 DOI 10.17487/RFC5881, June 2010, 561 . 563 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 564 (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, 565 June 2010, . 567 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 568 "Bidirectional Forwarding Detection (BFD) for MPLS Label 569 Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, 570 June 2010, . 572 [RFC5885] Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional 573 Forwarding Detection (BFD) for the Pseudowire Virtual 574 Circuit Connectivity Verification (VCCV)", RFC 5885, 575 DOI 10.17487/RFC5885, June 2010, 576 . 578 9.2. Informative References 580 [I-D.ietf-bfd-seamless-base] 581 Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J. 582 Networks, "Seamless Bidirectional Forwarding Detection 583 (S-BFD)", draft-ietf-bfd-seamless-base-09 (work in 584 progress), April 2016. 586 [I-D.ietf-bfd-seamless-ip] 587 Akiya, N., Pignataro, C., and D. Ward, "Seamless 588 Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6 589 and MPLS", draft-ietf-bfd-seamless-ip-04 (work in 590 progress), April 2016. 592 [I-D.ietf-spring-oam-usecase] 593 Geib, R., Filsfils, C., Pignataro, C., and N. Kumar, "A 594 scalable and topology aware MPLS data plane monitoring 595 system", draft-ietf-spring-oam-usecase-02 (work in 596 progress), April 2016. 598 [I-D.ietf-spring-segment-routing] 599 Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., 600 and R. Shakir, "Segment Routing Architecture", draft-ietf- 601 spring-segment-routing-07 (work in progress), December 602 2015. 604 [I-D.ietf-spring-sr-oam-requirement] 605 Kumar, N., Pignataro, C., Akiya, N., Geib, R., Mirsky, G., 606 and S. Litkowski, "OAM Requirements for Segment Routing 607 Network", draft-ietf-spring-sr-oam-requirement-01 (work in 608 progress), December 2015. 610 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 611 DOI 10.17487/RFC0791, September 1981, 612 . 614 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 615 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 616 December 1998, . 618 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol 619 Label Switching Architecture", RFC 3031, 620 DOI 10.17487/RFC3031, January 2001, 621 . 623 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 624 Label Switched (MPLS) Data Plane Failures", RFC 4379, 625 DOI 10.17487/RFC4379, February 2006, 626 . 628 [RFC7726] Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S. 629 Aldrin, "Clarifying Procedures for Establishing BFD 630 Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726, 631 DOI 10.17487/RFC7726, January 2016, 632 . 634 Authors' Addresses 636 Sam Aldrin 637 Google, Inc 639 Email: aldrin.ietf@gmail.com 641 Carlos Pignataro 642 Cisco Systems, Inc. 644 Email: cpignata@cisco.com 646 Greg Mirsky 647 Ericsson 649 Email: gregory.mirsky@ericsson.com 650 Nagendra Kumar 651 Cisco Systems, Inc. 653 Email: naikumar@cisco.com