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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-06) exists of draft-geib-spring-oam-usecase-03 ** Obsolete normative reference: RFC 4379 (Obsoleted by RFC 8029) Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Aldrin 3 Internet-Draft 4 Intended status: Informational M. Bhatia 5 Expires: October 30, 2015 Ionos Networks 6 S. Matsushima 7 Softbank 8 G. Mirsky 9 Ericsson 10 N. Kumar 11 Cisco 12 April 28, 2015 14 Seamless Bidirectional Forwarding Detection (BFD) Use Case 15 draft-ietf-bfd-seamless-use-case-02 17 Abstract 19 This document provides various use cases for Bidirectional Forwarding 20 Detection (BFD) such that extensions could be developed to allow for 21 simplified detection of forwarding failures. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on October 30, 2015. 40 Copyright Notice 42 Copyright (c) 2015 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Introduction to Seamless BFD . . . . . . . . . . . . . . . . 3 60 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 3.1. Unidirectional Forwarding Path Validation . . . . . . . . 4 62 3.2. Validation of forwarding path prior to traffic switching 5 63 3.3. Centralized Traffic Engineering . . . . . . . . . . . . . 5 64 3.4. BFD in Centralized Segment Routing . . . . . . . . . . . 6 65 3.5. BFD Efficient Operation Under Resource Constraints . . . 6 66 3.6. BFD for Anycast Address . . . . . . . . . . . . . . . . . 6 67 3.7. BFD Fault Isolation . . . . . . . . . . . . . . . . . . . 7 68 3.8. Multiple BFD Sessions to Same Target . . . . . . . . . . 7 69 3.9. MPLS BFD Session Per ECMP Path . . . . . . . . . . . . . 7 70 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 71 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 72 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 73 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 74 8. Normative References . . . . . . . . . . . . . . . . . . . . 9 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 77 1. Introduction 79 Bidirectional Forwarding Detection (BFD) is a lightweight protocol, 80 as defined in [RFC5880], used to detect forwarding failures. Various 81 protocols and applications rely on BFD for failure detection. Even 82 though the protocol is simple and lightweight, there are certain use 83 cases, where faster setting up of sessions and continuity check of 84 the data forwarding paths is necessary. This document identifies use 85 cases such that necessary enhancements could be made to BFD protocol 86 to meet those requirements. 88 BFD was designed to be a lightweight "Hello" protocol to detect data 89 plane failures. With dynamic provisioning of forwarding paths on a 90 large scale, establishing BFD sessions for each of those paths 91 creates complexity, not only from an operations point of view, but 92 also in terms of the speed at which these sessions could be 93 established or deleted. The existing session establishment mechanism 94 of the BFD protocol need to be enhanced in order to minimize the time 95 for the session to come up and validate the forwarding path. 97 This document specifically identifies those cases where certain 98 requirements could be derived to be used as reference, so that, 99 protocol enhancements could be developed to address them. While the 100 use cases could be used as reference for certain requirements, it is 101 outside the scope of this document to identify all of the 102 requirements for all possible enhancements. Specific solutions and 103 enhancement proposals are outside the scope of this document as well. 105 1.1. Terminology 107 The reader is expected to be familiar with the BFD, IP, MPLS and 108 Segment Routing (SR) terminology and protocol constructs. This 109 section identifies only the new terminology introduced. 111 2. Introduction to Seamless BFD 113 BFD, as defined in standard [RFC5880], requires two network nodes, to 114 exchange locally allocated discriminators. The discriminator enables 115 identification of the sender and receiver of BFD packets of the 116 particular session and proactive continuity monitoring of the 117 forwarding path between the two. [RFC5881] defines single hop BFD 118 whereas [RFC5883] and [RFC5884] defines multi-hop BFD. 120 Currently, BFD is best suited to verify that two end points are 121 reachable or that an existing connection continues to be valid. In 122 order for BFD to be able to initially verify that a connection is 123 valid and that it connects the expected set of end points, it is 124 necessary to provide the node information associated with the 125 connection at each end point prior to initiating BFD sessions, such 126 that this information can be used to verify that the connection is 127 valid. 129 If this information is already known to the end-points of a potential 130 BFD session, the initial handshake including an exchange of this 131 node-specific information is unnecessary and it is possible for the 132 end points to begin BFD messaging seamlessly. In fact, the initial 133 exchange of discriminator information is an unnecessary extra step 134 that may be avoided for these cases. 136 As an example of how Seamless BFD (S-BFD) might work, an entity (such 137 as an operator, or centralized controller) determines a set of 138 network entities to which BFD sessions might need to be established. 139 Each of those network entities is assigned a BFD discriminator, to 140 establish a BFD session. These network entities will create a BFD 141 session instance that listens for incoming BFD control packets. 142 Mappings between selected network entities and corresponding BFD 143 discriminators are known to other network nodes belonging in the same 144 network by some means. A network entity in this network is then able 145 to send a BFD control packet to a particular target with the 146 corresponding BFD discriminator. Target network node, upon reception 147 of such BFD control packet, will transmit a response BFD control 148 packet back to the sender. 150 3. Use Cases 152 As per the BFD protocol [RFC5880], BFD sessions are established using 153 handshake mechanism prior to validating the forwarding path. This 154 section outlines some use cases where the existing mechanism may not 155 be able to satisfy the requirements. In addition, some of the use 156 cases also be identify the need for expedited BFD session 157 establishment while preserving benefits of forwarding failure 158 detection using existing BFD specifications. 160 3.1. Unidirectional Forwarding Path Validation 162 Even though bidirectional verification of forwarding path is useful, 163 there are scenarios when verification is only required in one 164 direction between a pair of nodes. One such case is when a static 165 route uses BFD to validate reachability to the next-hop IP router. 166 In this case, the static route is established from one network entity 167 to another. The requirement in this case is only to validate the 168 forwarding path for that statically established path, and validation 169 by the target entity to the originating entity is not required. Many 170 LSPs have the same unidirectional characteristics and unidirectional 171 validation requirements. Such LSPs are common in Segment Routing and 172 LDP based networks. Another example is when a unidirectional tunnel 173 uses BFD to validate reachability of an egress node. 175 If the traditional BFD is to be used, the target network entity has 176 to be provisioned as well, even though the reverse path validation 177 with BFD session is not required. But with unidirectional BFD, the 178 need to provision on the target network entity is not needed. Once 179 the mechanism within the BFD protocol is in place, where the source 180 network entity knows the target network entity's discriminator, it 181 starts the session right away. When the targeted network entity 182 receives the packet, it knows that BFD packet, based on the 183 discriminator and processes it. That does not require establishment 184 of a bi-directional session, hence the two way handshake to exchange 185 discriminators is not needed as well. 187 The primary requirement in this use case is to enable session 188 establishment from source network entity to target network entity. 189 This translates to a need for the target network entity (for the BFD 190 session), should start processing for the discriminator received in 191 the BFD packet. This will enable the source network entity to 192 establish a unidirectional BFD session without the bidirectional 193 handshake of discriminators for session establishment. 195 3.2. Validation of forwarding path prior to traffic switching 197 BFD provides data delivery confidence when reachability validation is 198 performed prior to traffic utilizing specific paths/LSPs. However 199 this comes with a cost, where, traffic is prevented to use such 200 paths/LSPs until BFD is able to validate the reachability, which 201 could take seconds due to BFD session bring-up sequences [RFC5880], 202 LSP ping bootstrapping [RFC5884], etc. This use case does not 203 require to have sequences for session negotiation and discriminator 204 exchanges in order to establish the BFD session. 206 When these sequences for handshake are eliminated, the network 207 entities need to know what the discriminator values to be used for 208 the session. The same is the case for S-BFD, i.e., when the three- 209 way handshake mechanism is eliminated during bootstrap of BFD 210 sessions. However, this information is required at each entity to 211 verify that BFD messages are being received from the expected end- 212 points, hence the handshake mechanism serves no purpose. Elimination 213 of the unnecessary handshake mechanism allows for faster reachability 214 validation of BFD provisioned paths/LSPs. 216 In addition, it is expected that some MPLS technologies will require 217 traffic engineered LSPs to be created dynamically, perhaps driven by 218 external applications, e.g. in Software Defined Networks (SDN). It 219 will be desirable to perform BFD validation very quickly to allow 220 applications to utilize dynamically created LSPs in a timely manner. 222 3.3. Centralized Traffic Engineering 224 Various technologies in the SDN domain that involve controller based 225 networks have evolved where intelligence, traditionally placed in a 226 distributed and dynamic control plane, is separated from the data 227 plane and resides in a logically centralized place. There are 228 various controllers that perform this exact function in establishing 229 forwarding paths for the data flow. Traffic engineering is one 230 important function, where the traffic flow is engineered depending 231 upon various attributes of the traffic as well as the network state. 233 When the intelligence of the network resides in a centralized entity, 234 ability to manage and maintain the dynamic network becomes a 235 challenge. One way to ensure the forwarding paths are valid, and 236 working, is to establish BFD sessions within the network. When 237 traffic engineered tunnels are created, it is operationally critical 238 to ensure that the forwarding paths are working prior to switching 239 the traffic onto the engineered tunnels. In the absence of control 240 plane protocols, it may be desirable to verify the forwarding path 241 but also of any arbitrary path in the network. With tunnels being 242 engineered by a centralized entity, when the network state changes, 243 traffic has to be switched with minimum latency and black holing of 244 the data. 246 Traditional BFD session establishment and validation of the 247 forwarding path must not become a bottleneck in the case of 248 centralized traffic engineering. If the controller or other 249 centralized entity is able to instantly verify a forwarding path of 250 the TE tunnel , it could steer the traffic onto the traffic 251 engineered tunnel very quickly thus minimizing adverse effect on a 252 service. This is especially useful and needed when the scale of the 253 network and number of TE tunnels is very high. 255 The cost associated with BFD session negotiation and establishment of 256 BFD sessions to identify valid paths is very high and providing 257 network redundancy becomes a critical issue. 259 3.4. BFD in Centralized Segment Routing 261 A centralized controller based Segment Routing network monitoring 262 technique is described in [I-D.geib-spring-oam-usecase]. In 263 validating this use case, one of the requirements is to ensure the 264 BFD packet's behavior is according to the requirement and monitoring 265 of the segment, where the packet is U-turned at the expected node. 266 One of the criterion is to ensure the continuity check to the 267 adjacent segment-id. 269 3.5. BFD Efficient Operation Under Resource Constraints 271 When BFD sessions are being setup, torn down or modified (i.e. 272 parameters ? such as interval, multiplier, etc are being modified), 273 BFD requires additional packets other than scheduled packet 274 transmissions to complete the negotiation procedures (i.e. P/F 275 bits). There are scenarios where network resources are constrained: 276 a node may require BFD to monitor very large number of paths, or BFD 277 may need to operate in low powered and traffic sensitive networks, 278 i.e. microwave, low powered nano-cells, etc. In these scenarios, it 279 is desirable for BFD to slow down, speed up, stop or resume at will 280 witho minimal additional BFD packets exchanged to establish a new or 281 modified session. 283 3.6. BFD for Anycast Address 285 BFD protocol requires two endpoints to host BFD sessions, both 286 sending packets to each other. This BFD model does not fit well with 287 anycast address monitoring, as BFD packets transmitted from a network 288 node to an anycast address will reach only one of potentially many 289 network nodes hosting the anycast address. 291 3.7. BFD Fault Isolation 293 BFD multi-hop and BFD MPLS traverse multiple network nodes. BFD has 294 been designed to declare failure upon lack of consecutive packet 295 reception, which can be caused by a fault anywhere along the path. 296 Fast failure detection allows for rapid path recovery procedures. 297 However, operators often have to follow up, manually or 298 automatically, to attempt to identify and localize the fault that 299 caused BFD sessions to fail. Usage of other tools to isolate the 300 fault may cause the packets to traverse a different path through the 301 network (e.g. if ECMP is used). In addition, the longer it takes 302 from BFD session failure to fault isolation attempt, more likely that 303 the fault cannot be isolated, e.g. a fault can get corrected or 304 routed around. If BFD had built-in fault isolation capability, fault 305 isolation can get triggered at the earliest sign of fault and such 306 packets will get load balanced in very similar way, if not the same, 307 as BFD packets that went missing. 309 3.8. Multiple BFD Sessions to Same Target 311 BFD is capable of providing very fast failure detection, as relevant 312 network nodes continuously transmitting BFD packets at negotiated 313 rate. If BFD packet transmission is interrupted, even for a very 314 short period of time, that can result in BFD to declare failure 315 irrespective of path liveliness. It is possible, on a system where 316 BFD is running, for certain events, intentionally or unintentionally, 317 to cause a short interruption of BFD packet transmissions. With 318 distributed architectures of BFD implementations, this can be 319 protected, if a node was to run multiple BFD sessions to targets, 320 hosted on different parts of the system (ex: different CPU 321 instances). This can reduce BFD false failures, resulting in more 322 stable network. 324 3.9. MPLS BFD Session Per ECMP Path 326 BFD for MPLS, defined in [RFC5884], describes procedures to run BFD 327 as LSP in-band continuity check mechanism, through usage of MPLS echo 328 request [RFC4379] to bootstrap the BFD session on the egress node. 329 Section 4 of [RFC5884] also describes a possibility of running 330 multiple BFD sessions per alternative paths of LSP. However, details 331 on how to bootstrap and maintain correct set of BFD sessions on the 332 egress node is absent. 334 When an LSP has ECMP segment, it may be desirable to run in-band 335 monitoring that exercises every path of ECMP. Otherwise there will 336 be scenarios where in-band BFD session remains up through one path 337 but traffic is black-holing over another path. One way to achieve 338 BFD session per ECMP path of LSP is to define procedures that update 339 [RFC5884] in terms of how to bootstrap and maintain correct set of 340 BFD sessions on the egress node. However, that may require constant 341 use of MPLS Echo Request messages to create and delete BFD sessions 342 on the egress node, when ECMP paths and/or corresponding load balance 343 hash keys change. If a BFD session over any paths of the LSP can be 344 instantiated, stopped and resumed without requiring additional 345 procedures of bootstrapping via MPLS echo request, it would simplify 346 implementations and operations, and benefits network devices as less 347 processing are required by them. 349 4. Security Considerations 351 There are no new security considerations associated with this draft. 353 5. IANA Considerations 355 There are no IANA considerations introduced by this draft 357 6. Contributors 359 Carlos Pignataro 361 Cisco Systems 363 Email: cpignata@cisco.com 365 Glenn Hayden 367 ATT 369 Email: gh1691@att.com 371 Santosh P K 373 Juniper 375 Email: santoshpk@juniper.net 377 Mach Chen 379 Huawei 381 Email: mach.chen@huawei.com 383 Nobo Akiya 384 Cisco Systems 386 Email: nobo@cisco.com 388 7. Acknowledgements 390 The authors would like to thank Eric Gray for his useful comments. 392 8. Normative References 394 [I-D.geib-spring-oam-usecase] 395 ?, "Geib, R., Filsfils, C., Pignataro, C. and Kumar, N., 396 "SR MPLS monitoring use case", draft-geib-spring-oam- 397 usecase-03(work in progress), October 2014.", 1900. 399 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 400 Label Switched (MPLS) Data Plane Failures", RFC 4379, 401 February 2006. 403 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 404 (BFD)", RFC 5880, June 2010. 406 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 407 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June 408 2010. 410 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 411 (BFD) for Multihop Paths", RFC 5883, June 2010. 413 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 414 "Bidirectional Forwarding Detection (BFD) for MPLS Label 415 Switched Paths (LSPs)", RFC 5884, June 2010. 417 Authors' Addresses 419 Sam Aldrin 420 2330 Central Expressway 422 Email: aldrin.ietf@gmail.com 424 Manav Bhatia 425 Ionos Networks 427 Email: manav@ionosnetworks.com 428 Satoru Matsushima 429 Softbank 431 Email: satoru.matsushima@g.softbank.co.jp 433 Greg Mirsky 434 Ericsson 436 Email: gregory.mirsky@ericsson.com 438 Nagendra Kumar 439 Cisco 441 Email: naikumar@cisco.com