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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT Sam Aldrin 3 Intended Status: Informational (Huawei) 4 Expires: December 13, 2014 Manav Bhatia 5 (Ionos) 6 Greg Mirsky 7 (Ericsson) 8 Nagendra Kumar 9 (Cisco) 10 Satoru Matsushima 11 (Softbank) 13 June 11, 2014 15 Seamless Bidirectional Forwarding Detection (BFD) Use Case 16 draft-ietf-bfd-seamless-use-case-00 18 Abstract 20 This document provides various use cases for Bidirectional Forwarding 21 Detection (BFD) such that simplified solution and extensions could be 22 developed for detecting forwarding failures. 24 Status of this Memo 26 This Internet-Draft is submitted to IETF in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF), its areas, and its working groups. Note that 31 other groups may also distribute working documents as 32 Internet-Drafts. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 The list of current Internet-Drafts can be accessed at 40 http://www.ietf.org/1id-abstracts.html 42 The list of Internet-Draft Shadow Directories can be accessed at 43 http://www.ietf.org/shadow.html 45 Copyright and License Notice 46 Copyright (c) 2014 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Introduction to Seamless BFD . . . . . . . . . . . . . . . . . 3 64 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3.1. Unidirectional Forwarding Path Validation . . . . . . . . . 4 66 3.2. Validation of forwarding path prior to traffic switching . 5 67 3.3. Centralized Traffic Engineering . . . . . . . . . . . . . . 5 68 3.4. BFD in Centralized Segment Routing . . . . . . . . . . . . 6 69 3.5. BFD to Efficiently Operate under Resource Constraints . . . 6 70 3.6. BFD for Anycast Address . . . . . . . . . . . . . . . . . . 7 71 3.7. BFD Fault Isolation . . . . . . . . . . . . . . . . . . . . 7 72 3.8. Multiple BFD Sessions to Same Target . . . . . . . . . . . 7 73 3.9. MPLS BFD Session Per ECMP Path . . . . . . . . . . . . . . 8 74 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 9 75 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9 76 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 77 6.1. Normative References . . . . . . . . . . . . . . . . . . . 9 78 7. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 9 79 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10 81 1. Introduction 83 Bidirectional Forwarding Detection (BFD) is a lightweight protocol, 84 as defined in [RFC5880], used to detect forwarding failures. Various 85 protocols and applications rely on BFD for failure detection. Even 86 though the protocol is simple and lightweight, there are certain use 87 cases, where a much faster setting up of sessions and continuity 88 check of the data forwarding paths is necessary. This document 89 identifies those use cases such that necessary enhancements could be 90 made to BFD protocol to meet those requirements. 92 There are various ways to detecting faults and BFD protocol was 93 designed to be a lightweight "Hello" protocol to detect data plane 94 failures. With dynamic provisioning of forwarding paths at a large 95 scale, establishing BFD sessions for each of those paths creates 96 complexity, not only from operations point of view, but also the 97 speed at which these sessions could be established or deleted. The 98 existing session establishment mechanism of the BFD protocol need to 99 be enhanced in order to minimize the time for the session to come up 100 and validate the forwarding path. 102 This document specifically identifies those cases where certain 103 requirements could be derived to be used as reference, so that, 104 protocol enhancements could be developed to address them. Whilst the 105 use cases could be used as reference for certain requirements, it is 106 outside the scope of this document to identify all of the 107 requirements for all possible enhancements. Specific solutions and 108 enhancement proposals are outside the scope of this document as well. 110 1.1. Terminology 112 The reader is expected to be familiar with the BFD, IP, MPLS and SR 113 terminology and protocol constructs. This section identifies only 114 the new terminology introduced. 116 2. Introduction to Seamless BFD 118 BFD as defined in standard [RFC5880] requires two network nodes, as 119 part of handshake, exchange discriminators. This will enable the 120 sender and receiver of BFD packets of a session to be identified and 121 check the continuity of the forwarding path. [RFC5881] defines single 122 hop BFD whereas [RFC5883] and [RFC5884] defines multi-hop BFD. 124 In order to establish BFD sessions between network entities and 125 seamlessly be able to have the session up and running, BFD protocol 126 should be capable of doing that. These sessions have to be 127 established a priori to traffic flow and ensure the forwarding path 128 is available and connectivity is present. With handshake mechanism 129 within BFD protocol, establishing sessions at a rapid rate and 130 ensuring the validity or existence of working forwarding path, prior 131 to the session being up and running, becomes complex and time 132 consuming. In order to achieve seamless BFD sessions, it requires a 133 mechanism where the ability to specify the discriminators and the 134 ability to respond to the BFD control packets by the network node, 135 should already be negotiated ahead of the session becoming active. 136 Seamless BFD by definition will be able to provide those mechanisms 137 within the BFD protocol in order to meet the requirements and 138 establish BFD sessions seamlessly, with minimal overhead, in order to 139 detect forwarding failures. 141 As an example of how Seamless BFD (S-BFD) works, a set of network 142 entities are first identified, to which BFD sessions have to be 143 established. Each of those network nodes, will be assigned a special 144 BFD discriminator, to establish a BFD session. These network nodes 145 will also create a BFD session instance that listens for incoming BFD 146 control packets. Mappings between selected network entities and 147 corresponding special BFD discriminators are known to other network 148 nodes belonging in the same network. A network node in such network 149 is then able to send a BFD control packet to a particular target with 150 corresponding special BFD discriminator. Target network node, upon 151 reception of such BFD control packet, will transmit a response BFD 152 control packet back to the sender. 154 3. Use Cases 156 As per the BFD protocol [RFC5880], BFD sessions are established using 157 handshake mechanism prior to validating the forwarding path. This 158 section outlines some of the use cases where the existing mechanism 159 may not be able to satisfy the requirements. In addition, some of the 160 use cases will also be identifying the need for expedited BFD session 161 establishment with preserving benefits of forwarding failure 162 detection using existing BFD specifications. 164 3.1. Unidirectional Forwarding Path Validation 166 Even though bidirectional verification of forwarding path is useful, 167 there are scenarios when only one side of the BFD, not both, is 168 interested in verifying continuity of the data plane between a pair 169 of nodes. One such case is, when a static route uses BFD to validate 170 reachability to the next-hop IP router. In this case, the static 171 route is established from one network entity to another. The 172 requirement in this case is only to validate the forwarding path for 173 that statically established path. Validating the reverse direction is 174 not required in this case. Many of these network scenarios are being 175 proposed as part of segment routing [TBD]. Another example is when a 176 unidirectional tunnel uses BFD to validate reachability to the egress 177 node. 179 If the traditional BFD is to be used, the target network entity has 180 to be provisioned as well, even though the reverse path validation 181 with BFD session is not required. But with unidirectional BFD, the 182 need to provision on the target network entity is not needed. Once 183 the mechanism within the BFD protocol is in place, where the source 184 network entity knows the target network entity's discriminator, it 185 starts the session right away. When the targeted network entity 186 receives the packet, it knows that BFD packet, based on the 187 discriminator and processes it. That do not require to have a bi- 188 directional session establishment, hence the two way handshake to 189 exchange discriminators is not needed as well. 191 The primary requirement in this use case is to enable session 192 establishment from source network entity to target network entity. 193 This translates to, the target network entity for the BFD session, 194 upon receiving the BFD packet, should start processing for the 195 discriminator received. This will enable the source network entity to 196 establish a unidirectional BFD session without bidirectional 197 handshake of discriminators for session establishment. 199 3.2. Validation of forwarding path prior to traffic switching 201 BFD provides data delivery confidence when reachability validation is 202 performed prior to traffic utilizing specific paths/LSPs. However 203 this comes with a cost, where, traffic is prevented to use such 204 paths/LSPs until BFD is able to validate the reachability, which 205 could take seconds due to BFD session bring-up sequences [RFC5880], 206 LSP ping bootstrapping [RFC5884], etc. This use case does not 207 require to have sequences for session negotiation and discriminator 208 exchanges in order to establish the BFD session. 210 When these sequences for handshake are eliminated, the network 211 entities need to know what the discriminator values to be used for 212 the session. The same is the case for S-BFD, i.e., when the three-way 213 handshake mechanism is eliminated during bootstrap of BFD sessions. 214 Due to this faster reachability validation of BFD provisioned 215 paths/LSPs could be achieved. In addition, it is expected that some 216 MPLS technologies will require traffic engineered LSPs to get created 217 dynamically, driven by external applications, e.g. in Software 218 Defined Networks (SDN). It would be desirable to perform BFD 219 validation very quickly to allow applications to utilize dynamically 220 created LSPs in timely manner. 222 3.3. Centralized Traffic Engineering 224 Various technologies in the SDN domain have evolved which involves 225 controller based networks, where the intelligence, traditionally 226 placed in the distributed and dynamic control plane, is separated 227 from the data plane and resides in a logically centralized place. 228 There are various controllers which perform this exact function in 229 establishing forwarding paths for the data flow. Traffic engineering 230 is one important function, where the traffic 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 the centralized 234 entity, 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 traffic 237 engineering tunnels are created, it is operationally critical to 238 ensure that the forwarding paths are working prior to switching the 239 traffic onto the engineered tunnels. In the absence of control plane 240 protocols, it is not only the desire to verify the forwarding path 241 but also an arbitrary path in the network. With tunnels being 242 engineered from the centralized entity, when the network state 243 changes, traffic has to be switched without much latency and black 244 holing of the data. 246 Traditional BFD session establishment and validation of the 247 forwarding path must not become bottleneck in the case of centralized 248 traffic engineering. If the controller or other centralized entity is 249 able to instantly verify a forwarding path of the TE tunnel , it 250 could steer the traffic onto the traffic engineered tunnel very 251 quickly thus minimizing adverse effect on a service. This is 252 especially useful and needed when the scale of the network and number 253 of TE tunnels is too high. Session negotiation and establishment of 254 BFD sessions to identify valid paths is way to high in terms of time 255 and providing network redundancy becomes a critical issue. 257 3.4. BFD in Centralized Segment Routing 259 Centralized controller based Segment Routing network monitoring 260 technique, is described in [I-D.geib-spring-oam-usecase]. In 261 validating this use case, one of the requirements is to ensure the 262 BFD packet's behavior is according to the requirement and monitoring 263 of the segment, where the packet is U-turned at the expected node. 264 One of the criterion is to ensure the continuity check to the 265 adjacent segment-id. 267 3.5. BFD to Efficiently Operate under Resource Constraints 269 When BFD sessions are being setup, torn down or parameters (i.e. 270 interval, multiplier, etc) are being modified, BFD protocol requires 271 additional packets outside of scheduled packet transmissions to 272 complete the negotiation procedures (i.e. P/F bits). There are 273 scenarios where network resources are constrained: a node may require 274 BFD to monitor very large number of paths, or BFD may need to operate 275 in low powered and traffic sensitive networks, i.e. microwave, low 276 powered nano-cells, etc. In these scenarios, it is desirable for BFD 277 to slow down, speed up, stop or resume at will without requiring 278 additional BFD packets to be exchanged. 280 3.6. BFD for Anycast Address 282 BFD protocol requires the two endpoints to host BFD sessions, both 283 sending packets to each other. This BFD model does not fit well with 284 anycast address monitoring, as BFD packets transmitted from a network 285 node to an anycast address will reach only one of potentially many 286 network nodes hosting the anycast address. 288 3.7. BFD Fault Isolation 290 BFD multi-hop and BFD MPLS traverse multiple network nodes. BFD has 291 been designed to declare failure upon lack of consecutive packet 292 reception, which can be caused by any fault anywhere along the path. 293 Fast failure detection provides great benefits, as it can trigger 294 recovery procedures rapidly. However, operators often have to follow 295 up, manually or automatically, to attempt to identify and localize 296 the fault which caused the BFD sessions to fail. Usage of other tools 297 to isolate the fault may cause the packets to traverse differently 298 throughout the network (i.e. ECMP). In addition, longer it takes from 299 BFD session failure to fault isolation attempt, more likely that 300 fault cannot be isolated, i.e. fault can get corrected or routed 301 around. If BFD had built-in fault isolation capability, fault 302 isolation can get triggered at the earliest sign of fault and such 303 packets will get load balanced in very similar way, if not the same, 304 as BFD packets which went missing. 306 3.8. Multiple BFD Sessions to Same Target 308 BFD is capable of providing very fast failure detection, as relevant 309 network nodes continuously transmitting BFD packets at negotiated 310 rate. If BFD packet transmission is interrupted, even for a very 311 short period of time, that can result in BFD to declare failure 312 irrespective of path liveliness. It is possible, on a system where 313 BFD is running, for certain events, intentionally or unintentionally, 314 to cause a short interruption of BFD packet transmissions. With 315 distributed architectures of BFD implementations, this can be 316 protected, if a node was to run multiple BFD sessions to targets, 317 hosted on different parts of the system (ex: different CPU 318 instances). This can reduce BFD false failures, resulting in more 319 stable network. 321 3.9. MPLS BFD Session Per ECMP Path 323 BFD for MPLS, defined in [RFC5884], describes procedures to run BFD 324 as LSP in-band continuity check mechanism, through usage of MPLS echo 325 request [RFC4379] to bootstrap the BFD session on the egress node. 326 Section 4 of [RFC5884] also describes a possibility of running 327 multiple BFD sessions per alternative paths of LSP. However, details 328 on how to bootstrap and maintain correct set of BFD sessions on the 329 egress node is absent. 331 When an LSP has ECMP segment, it may be desirable to run in-band 332 monitoring that exercises every path of ECMP. Otherwise there will 333 be scenarios where in-band BFD session remains up through one path 334 but traffic is black-holing over another path. One way to achieve 335 BFD session per ECMP path of LSP is to define procedures that update 336 [RFC5884] in terms of how to bootstrap and maintain correct set of 337 BFD sessions on the egress node. However, that may require constant 338 use of MPLS Echo Request messages to create and delete BFD sessions 339 on the egress node, when ECMP paths and/or corresponding load balance 340 hash keys change. If a BFD session over any paths of the LSP can be 341 instantiated, stopped and resumed without requiring additional 342 procedures of bootstrapping via MPLS echo request, it would simplify 343 implementations and operations, and benefits network devices as less 344 processing are required by them. 346 4. Security Considerations 348 There are no new security considerations introduced by this draft. 350 5. IANA Considerations 352 There are no new IANA considerations introduced by this draft 354 6. References 356 6.1. Normative References 358 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 359 Requirement Levels", BCP 14, RFC 2119, March 1997. 361 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 362 Label Switched (MPLS) Data Plane Failures", RFC 4379, 363 February 2006. 365 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 366 (BFD)", RFC5880, June 2010. 368 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 369 (BFD)", RFC5881, June 2010. 371 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 372 (BFD) for Multihop Paths", RFC5883, June 2010. 374 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 375 "Bidirectional Forwarding Detection (BFD) for MPLS Label 376 Switched Paths (LSPs)", RFC5884, June 2010. 378 7. Authors' Addresses 380 Sam Aldrin 381 Huawei Technologies 382 2330 Central Expressway 383 Santa Clara, CA 95051 385 EMail: aldrin.ietf@gmail.com 387 Manav Bhatia 388 Ionos Networks 390 EMail: manav@ionosnetworks.com 392 Satoru Matsushima 393 Softbank 394 EMail: satoru.matsushima@g.softbank.co.jp 396 Greg Mirsky 397 Ericsson 399 EMail: gregory.mirsky@ericsson.com 401 Nagendra Kumar 402 Cisco 404 EMail: naikumar@cisco.com 406 8. Contributors 408 Carlos Pignataro 409 Cisco Systems 411 Email: cpignata@cisco.com 413 Glenn Hayden 414 ATT 416 Email: gh1691@att.com 418 Santosh P K 419 Juniper 421 Email: santoshpk@juniper.net 423 Mach Chen 424 Huawei 426 Email: mach.chen@huawei.com 428 Nobo Akiya 429 Cisco Systems 431 Email: nobo@cisco.com