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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-11) exists of draft-ietf-isis-te-metric-extensions-06 == Outdated reference: A later version (-22) exists of draft-ietf-spring-segment-routing-mpls-01 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 TEAS Working Group A. Atlas 3 Internet-Draft J. Drake 4 Intended status: Informational Juniper Networks 5 Expires: December 11, 2015 S. Giacalone 6 Unaffiliated 7 D. Ward 8 S. Previdi 9 C. Filsfils 10 Cisco Systems 11 June 9, 2015 13 Performance-based Path Selection for Explicitly Routed LSPs using TE 14 Metric Extensions 15 draft-ietf-teas-te-express-path-02 17 Abstract 19 In certain networks, it is critical to consider network performance 20 criteria when selecting the path for an explicitly routed RSVP-TE 21 LSP. Such performance criteria can include latency, jitter, and loss 22 or other indications such as the conformance to link performance 23 objectives and non-RSVP TE traffic load. This specification uses 24 network performance data, such as is advertised via the OSPF and ISIS 25 TE metric extensions (defined outside the scope of this document) to 26 perform such path selections. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on December 11, 2015. 45 Copyright Notice 47 Copyright (c) 2015 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 63 1.1. Basic Requirements . . . . . . . . . . . . . . . . . . . 4 64 1.2. Oscillation and Stability Considerations . . . . . . . . 4 65 2. Using Performance Data Constraints . . . . . . . . . . . . . 5 66 2.1. End-to-End Constraints . . . . . . . . . . . . . . . . . 5 67 2.2. Link Constraints . . . . . . . . . . . . . . . . . . . . 6 68 2.3. Links out of compliance with Link Performance Objectives 6 69 2.3.1. Use of Anomalous Links for New Paths . . . . . . . . 7 70 2.3.2. Links entering the Anomalous State . . . . . . . . . 7 71 2.3.3. Links leaving the Anomalous State . . . . . . . . . . 8 72 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 73 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 74 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 75 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 6.1. Normative References . . . . . . . . . . . . . . . . . . 8 77 6.2. Informative References . . . . . . . . . . . . . . . . . 9 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 80 1. Introduction 82 In certain networks, such as financial information networks, network 83 performance information is becoming as critical to data path 84 selection as other existing metrics. Network performance information 85 can be obtained via either the TE Metric Extensions in OSPF [RFC7471] 86 or ISIS [I-D.ietf-isis-te-metric-extensions] or via a management 87 system. As with other TE information flooded via OSPF or ISIS, the 88 TE metric extensions have a flooding scope limited to the local area 89 or level. This document describes how a path computation function, 90 whether in an ingress LSR or a PCE[RFC4655] , can use that 91 information for path selection for explicitly routed LSPs. The 92 selected path may be signaled via RSVP-TE [RFC3209] or simply used by 93 the ingress with segment routing 94 [I-D.ietf-spring-segment-routing-mpls] to properly forward the 95 packet. Methods of optimizing path selection for multiple parameters 96 are generally computationally complex. However, there are good 97 heuristics for the delay-constrained lowest-cost (DCLC) computation 98 problem [k-Paths_DCLC] that can be applied to consider both path cost 99 and a maximum delay bound. Some of the network performance 100 information can also be used to prune links from a topology before 101 computing the path. 103 The path selection mechanisms described in this document apply to 104 paths that are fully computed by the head-end of the LSP and then 105 signaled in an ERO where every sub-object is strict. This allows the 106 head-end to consider IGP-distributed performance data without 107 requiring the ability to signal the performance constraints in an 108 object of the RSVP Path message. 110 When considering performance-based data, it is obvious that there are 111 additional contributors to latency beyond just the links. Clearly 112 end-to-end latency is a combination of router latency (e.g. latency 113 from traversing a router without queueing delay), queuing latency, 114 physical link latency and other factors. While traversing a router 115 can cause delay, that router latency can be included in the 116 advertised link delay. As described in [RFC7471] and 117 [I-D.ietf-isis-te-metric-extensions], queuing delay must not be 118 included in the measurements advertised by OSPF or ISIS. 120 Queuing latency is specifically excluded to insure freedom from 121 oscillations and stability issues that have plagued prior attempts to 122 use delay as a routing metric. If application traffic follows a path 123 based upon latency constraints, the same traffic might be in an 124 Expedited Forwarding Per-Hop-Behavior [RFC3246] with minimal queuing 125 delay or another PHB with potentially very substantial per-hop 126 queuing delay. Only traffic which experiences relatively low 127 congestion, such as Expedited Forwarding traffic, will experience 128 delays very close to the sum of the reported link delays. 130 This document does not specify how a router determines what values to 131 advertise by the IGP; it does assume that the constraints specified 132 in [RFC7471] and [I-D.ietf-isis-te-metric-extensions] are followed. 133 Additionally, the end-to-end performance that is computed for an LSP 134 path should be built from the individual link data. Any end-to-end 135 characterization used to determine an LSP's performance compliance 136 should be fully reflected in the Traffic Engineering Database so that 137 a path calculation can also determine whether a path under 138 consideration would be in compliance. 140 1.1. Basic Requirements 142 The following are the requirements that motivate this solution. 144 1. Select a TE tunnel's path based upon a combination of existing 145 constraints as well as on link-latency, packet loss, jitter, link 146 performance objectives conformance, and bandwidth consumed by 147 non-RSVP-TE traffic. 149 2. Ability to define different end-to-end performance requirements 150 for each TE tunnel regardless of common use of resources. 152 3. Ability to periodically verify with the TE LSDB that a TE 153 tunnel's current LSP complies with its configured end-to-end 154 performance requirements. 156 4. Ability to move tunnels, using make-before-break, based upon 157 computed end-to-end performance complying with constraints. 159 5. Ability to move tunnels away from any link that is violating an 160 underlying link performance objective. 162 6. Ability to optionally avoid setting up tunnels using any link 163 that is violating a link performance objective, regardless of 164 whether end-to-end performance would still meet requirements. 166 7. Ability to revert back using make-before-break to the best path 167 after a configurable period. 169 1.2. Oscillation and Stability Considerations 171 Past attempts to use unbounded delay or loss as metric sufferred from 172 severe oscillations. The use of performance based data must be such 173 that undampened oscillations are not possible and stability cannot be 174 impacted. 176 The use of timers is often cited as a cure. Oscillation that is 177 damped by timers is known as "slosh". If advertisement timers are 178 very short relative to the jitter applied to RSVP-TE CSPF timers, 179 then a partial oscillation occurs. If RSVP-TE CSPF timers are short 180 relative to advertisement timers, full oscillation (all traffic 181 moving back and forth) can occur. Even a partial oscillation causes 182 unnecessary reordering which is considered at least minimally 183 disruptive. 185 Delay variation or jitter is affected by even small traffic levels. 186 At even tiny traffic levels, the probability of a queue occupancy of 187 one can produce a measured jitter proportional to or equal to the 188 packet serialization delay. Very low levels of traffic can increase 189 the probability of queue occupancies of two or three packets enough 190 to further increase the measured jitter. Because jitter measurement 191 is extremely sensitive to even very low traffic levels, any use of 192 jitter is likely to oscillate. There may be legitimate use of a 193 jitter measurement in path computation that can be considered free of 194 oscillation. 196 Delay measurements that are not sensitive to traffic loads may be 197 safely used in path computation. Delay measurements made at the link 198 layer or measurements made at a queuing priority higher than any 199 significant traffic (such as DSCP CS7 or CS6 [RFC4594], but not CS2 200 if traffic levels at CS3 and higher or EF and AF can affect the 201 measurement). Making delay measurements at the same priority as the 202 traffic on affected paths is likely to cause oscillations. 204 2. Using Performance Data Constraints 206 2.1. End-to-End Constraints 208 The per-link performance data available in the IGP [RFC7471] 209 [I-D.ietf-isis-te-metric-extensions] includes: unidirectional link 210 delay, unidirectional delay variation, and link loss. Each (or all) 211 of these parameters can be used to create the path-level link-based 212 parameter. 214 It is possible to compute a CSPF where the link latency values are 215 used instead of TE metrics, this results in ignoring the TE metrics 216 and causing LSPs to prefer the lowest-latency paths. In practical 217 scenarios, latency constraints are typically a bound constraint 218 rather than a minimization objective. An end-to-end latency upper 219 bound merely requires that the path computed be no more than that 220 bound and does not require that it be the minimum latency path. The 221 latter is exactly the delay-constrained lowest-cost (DCLC) problem to 222 which good heuristics have been proposed in the literature (e.g. 223 [k-Paths_DCLC]). 225 An end-to-end bound on delay variation can be used similarly as a 226 constraint in the path computation on what links to explore where the 227 path's delay variation is the sum of the used links' delay 228 variations. 230 For link loss, the path loss is not the sum of the used links' 231 losses. Instead, the path loss fraction is 1 - (1 - loss_L1)*(1 - 232 loss_L2)*...*(1 - loss_Ln), where the links along the path are L1 to 233 Ln with loss_Li in fractions. This computation is discussed in more 234 detail in Sections 5.1.4 and 5.1.5 in [RFC6049]. The end-to-end link 235 loss bound, computed in this fashion, can also be used as a 236 constraint in the path computation. 238 The heuristic algorithms for DCLC only address one constraint bound 239 but having a CSPF that limits the paths explored (i.e. based on hop- 240 count) can be combined [hop-count_DCLC]. 242 2.2. Link Constraints 244 In addition to selecting paths that conform to a bound on performance 245 data, it is also useful to avoid using links that do not meet a 246 necessary constraint. Naturally, if such a parameter were a known 247 fixed value, then resource attribute flags could be used to express 248 this behavior. However, when the parameter associated with a link 249 may vary dynamically, there is not currently a configuration-time 250 mechanism to enforce such behavior. An example of this is described 251 in Section 2.3, where links may move in and out of conformance for 252 link performance objectives with regards to latency, delay variation, 253 and link loss. 255 When doing path selection for TE tunnels, it has not been possible to 256 know how much actual bandwidth is available that includes the 257 bandwidth used by non-RSVP-TE traffic. In [RFC7471] 258 [I-D.ietf-isis-te-metric-extensions], the Unidirectional Available 259 Bandwidth is advertised as is the Residual Bandwidth. When computing 260 the path for a TE tunnel, only links with at least a minimum amount 261 of Unidirectional Available Bandwidth might be permitted. 263 Similarly, only links whose loss is under a configurable value might 264 be acceptable. For these constraints, each link can be tested 265 against the constraint and only explored in the path computation if 266 the link passes. In essence, a link that fails the constraint test 267 is treated as if it contained a resource attribute in the exclude-any 268 filter. 270 2.3. Links out of compliance with Link Performance Objectives 272 Link conformance to a link performance objective can change as a 273 result of rerouting at lower layers. This could be due to optical 274 regrooming or simply rerouting of a FA-LSP. When this occurs, there 275 are two questions to be asked: 277 a. Should the link be trusted and used for the setup of new LSPs? 279 b. Should LSPs using this link automatically be moved to a secondary 280 path? 282 2.3.1. Use of Anomalous Links for New Paths 284 If the answer to (a) is no for link latency performance objectives, 285 then any link which has the Anomalous bit set in the Unidirectional 286 Link Delay sub-TLV[RFC7471] [I-D.ietf-isis-te-metric-extensions] 287 should be removed from the topology before a path calculation is used 288 to compute a new path. In essence, the link should be treated 289 exactly as if it fails the exclude-any resource attributes 290 filter.[RFC3209]. 292 Similarly, if the answer to (a) is no for link loss performance 293 objectives, then any link which has the Anomalous bit set in the Link 294 Los sub-TLV should be treated as if it fails the exclude-any resource 295 attributes filter. If the answer to (a) is no for link jitter 296 performance objectives, then any link that has the Anomalous bit set 297 in the Unidirectional Delay Variation sub- 298 TLV[I-D.ietf-isis-te-metric-extensions] should be treated as if it 299 fails the exclude-any resource attributes filter. 301 2.3.2. Links entering the Anomalous State 303 When a link enters the Anomalous state with respect to a parameter, 304 this is an indication that LSPs using that link might also no longer 305 be in compliance with their performance bounds. It can also be 306 considered an indication that something is changing that link and so 307 it might no longer be trustworthy to carry performance-critical 308 traffic. Naturally, which performance criteria are important for a 309 particular LSP is dependent upon the LSP's configuration and thus the 310 compliance of a link with respect to a particular link performance 311 objective is indicated per performance criterion. 313 At the ingress of a TE tunnel, a TE tunnel may be configured to be 314 sensitive to the Anomalous state of links in reference to latency, 315 delay variation, and/or loss. Additionally, such a TE tunnel may be 316 configured to either verify continued compliance, to switch 317 immediately to a standby LSP, or to move to a different path. 319 When a sub-TLV is received with the Anomalous bit set when previously 320 it was clear, the list of interested TE tunnels must be scanned. 321 Each such TE tunnel should either have its continued compliance 322 verified, be switched to a hot standby, or do a make-before-break to 323 a secondary path. 325 It is not sufficient to just look at the Anomalous bit in order to 326 determine when TE tunnels must have their compliance verified. When 327 changing to set, the Anomalous bit merely provides a hint that 328 interested TE tunnels should have their continued compliance 329 verified. 331 2.3.3. Links leaving the Anomalous State 333 When a link leaves the Anomalous state with respect to a parameter, 334 this can serve as an indication that those TE tunnels, whose LSPs 335 were changed due to administrative policy when the link entered the 336 Anomalous state, may want to reoptimize to a better path. The hint 337 provided by the Anomalous state change may help optimize when to 338 recompute for a better path. 340 3. IANA Considerations 342 This document includes no request to IANA. 344 4. Security Considerations 346 This document is not currently believed to introduce new security 347 concerns. 349 5. Acknowledgements 351 The authors would like to thank Curtis Villamizar for his extensive 352 detailed comments and suggested text in the Section 1 and 353 Section 1.2. The authors would like to thank Dhruv Dhody for his 354 useful comments, and his care and persistence in making sure that 355 these important corrections weren't missed. The authors would also 356 like to thank Xiaohu Xu and Sriganesh Kini for their review. 358 6. References 360 6.1. Normative References 362 [I-D.ietf-isis-te-metric-extensions] 363 Previdi, S., Giacalone, S., Ward, D., Drake, J., Atlas, 364 A., Filsfils, C., and W. Wu, "IS-IS Traffic Engineering 365 (TE) Metric Extensions", draft-ietf-isis-te-metric- 366 extensions-06 (work in progress), April 2015. 368 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 369 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 370 Tunnels", RFC 3209, December 2001. 372 [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. 373 Previdi, "OSPF Traffic Engineering (TE) Metric 374 Extensions", RFC 7471, March 2015. 376 6.2. Informative References 378 [hop-count_DCLC] 379 Agrawal, H., Grah, M., and M. Gregory, "Optimization of 380 QoS Routing", 6th IEEE/AACIS International Conference on 381 Computer and Information Science 2007, 2007, 382 . 385 [I-D.ietf-spring-segment-routing-mpls] 386 Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 387 Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J., 388 and E. Crabbe, "Segment Routing with MPLS data plane", 389 draft-ietf-spring-segment-routing-mpls-01 (work in 390 progress), May 2015. 392 [k-Paths_DCLC] 393 Jia, Z. and P. Varaiya, "Heuristic methods for delay 394 constrained least cost routing using k-shortest-paths", 395 IEEE Transactions on Automatic Control 51(4), 2006, 396 . 399 [RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec, 400 J., Courtney, W., Davari, S., Firoiu, V., and D. 401 Stiliadis, "An Expedited Forwarding PHB (Per-Hop 402 Behavior)", RFC 3246, March 2002. 404 [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration 405 Guidelines for DiffServ Service Classes", RFC 4594, August 406 2006. 408 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 409 Element (PCE)-Based Architecture", RFC 4655, August 2006. 411 [RFC6049] Morton, A. and E. Stephan, "Spatial Composition of 412 Metrics", RFC 6049, January 2011. 414 Authors' Addresses 416 Alia Atlas 417 Juniper Networks 418 10 Technology Park Drive 419 Westford, MA 01886 420 USA 422 Email: akatlas@juniper.net 423 John Drake 424 Juniper Networks 425 1194 N. Mathilda Ave. 426 Sunnyvale, CA 94089 427 USA 429 Email: jdrake@juniper.net 431 Spencer Giacalone 432 Unaffiliated 434 Email: spencer.giacalone@gmail.com 436 Dave Ward 437 Cisco Systems 438 170 West Tasman Dr. 439 San Jose, CA 95134 440 USA 442 Email: dward@cisco.com 444 Stefano Previdi 445 Cisco Systems 446 Via Del Serafico 200 447 Rome 00142 448 Italy 450 Email: sprevidi@cisco.com 452 Clarence Filsfils 453 Cisco Systems 454 Brussels 455 Belgium 457 Email: cfilsfil@cisco.com