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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BESS Workgroup J. Rabadan, Ed. 3 Internet Draft S. Sathappan 4 Intended status: Standards Track Nokia 6 S. Boutros T. Przygienda 7 VMware W. Lin 8 J. Drake 9 Juniper Networks 11 A. Sajassi 12 S. Mohanty 13 Cisco Systems 15 Expires: December 23, 2017 June 21, 2017 17 Preference-based EVPN DF Election 18 draft-ietf-bess-evpn-pref-df-00 20 Abstract 22 RFC7432 defines the Designated Forwarder (DF) in (PBB-)EVPN networks 23 as the PE responsible for sending broadcast, multicast and unknown 24 unicast traffic (BUM) to a multi-homed device/network in the case of 25 an all-active multi-homing ES, or BUM and unicast in the case of 26 single-active multi-homing. 28 The DF is selected out of a candidate list of PEs that advertise the 29 Ethernet Segment Identifier (ESI) to the EVPN network, according to 30 the 'service-carving' algorithm. 32 While 'service-carving' provides an efficient and automated way of 33 selecting the DF across different EVIs or ISIDs in the ES, there are 34 some use-cases where a more 'deterministic' and user-controlled 35 method is required. At the same time, Service Providers require an 36 easy way to force an on-demand DF switchover in order to carry out 37 some maintenance tasks on the existing DF or control whether a new 38 active PE can preempt the existing DF PE. 40 This document proposes an extension to the current RFC7432 DF 41 election procedures so that the above requirements can be met. 43 Status of this Memo 45 This Internet-Draft is submitted in full conformance with the 46 provisions of BCP 78 and BCP 79. 48 Internet-Drafts are working documents of the Internet Engineering 49 Task Force (IETF), its areas, and its working groups. Note that 50 other groups may also distribute working documents as Internet- 51 Drafts. 53 Internet-Drafts are draft documents valid for a maximum of six months 54 and may be updated, replaced, or obsoleted by other documents at any 55 time. It is inappropriate to use Internet-Drafts as reference 56 material or to cite them other than as "work in progress." 58 The list of current Internet-Drafts can be accessed at 59 http://www.ietf.org/ietf/1id-abstracts.txt 61 The list of Internet-Draft Shadow Directories can be accessed at 62 http://www.ietf.org/shadow.html 64 This Internet-Draft will expire on December 23, 2017. 66 Copyright Notice 68 Copyright (c) 2017 IETF Trust and the persons identified as the 69 document authors. All rights reserved. 71 This document is subject to BCP 78 and the IETF Trust's Legal 72 Provisions Relating to IETF Documents 73 (http://trustee.ietf.org/license-info) in effect on the date of 74 publication of this document. Please review these documents 75 carefully, as they describe your rights and restrictions with respect 76 to this document. Code Components extracted from this document must 77 include Simplified BSD License text as described in Section 4.e of 78 the Trust Legal Provisions and are provided without warranty as 79 described in the Simplified BSD License. 81 Table of Contents 83 1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3 84 2. Solution requirements . . . . . . . . . . . . . . . . . . . . . 3 85 3. EVPN BGP Attributes for Deterministic DF Election . . . . . . . 4 86 4. Solution description . . . . . . . . . . . . . . . . . . . . . 5 87 4.1 Use of the Preference algorithm . . . . . . . . . . . . . . 5 88 4.2 Use of the Preference algorithm in RFC7432 89 Ethernet-Segments . . . . . . . . . . . . . . . . . . . . . 7 90 4.3 The Non-Revertive option . . . . . . . . . . . . . . . . . . 7 91 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 10 92 11. Conventions used in this document . . . . . . . . . . . . . . 10 93 12. Security Considerations . . . . . . . . . . . . . . . . . . . 11 94 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 95 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 96 15.1 Normative References . . . . . . . . . . . . . . . . . . . 11 97 15.2 Informative References . . . . . . . . . . . . . . . . . . 11 98 16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 99 17. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11 100 17. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11 102 1. Problem Statement 104 RFC7432 defines the Designated Forwarder (DF) in (PBB-)EVPN networks 105 as the PE responsible for sending broadcast, multicast and unknown 106 unicast traffic (BUM) to a multi-homed device/network in the case of 107 an all-active multi-homing ES or BUM and unicast traffic to a multi- 108 homed device or network in case of single-active multi-homing. 110 The DF is selected out of a candidate list of PEs that advertise the 111 Ethernet Segment Identifier (ESI) to the EVPN network and according 112 to the 'service-carving' algorithm. 114 While 'service-carving' provides an efficient and automated way of 115 selecting the DF across different EVIs or ISIDs in the ES, there are 116 some use-cases where a more 'deterministic' and user-controlled 117 method is required. At the same time, Service Providers require an 118 easy way to force an on-demand DF switchover in order to carry out 119 some maintenance tasks on the existing DF or control whether a new 120 active PE can preempt the existing DF PE. 122 This document proposes an extension to the current RFC7432 DF 123 election procedures so that the above requirements can be met. 125 2. Solution requirements 127 This document proposes an extension of the RFC7432 'service-carving' 128 DF election algorithm motivated by the following requirements: 130 a) The solution MUST provide an administrative preference option so 131 that the user can control in what order the candidate PEs may 132 become DF, assuming they are all operationally ready to take over. 134 b) This extension MUST work for RFC7432 Ethernet Segments (ES) and 135 virtual ES, as defined in [vES]. 137 c) The user MUST be able to force a PE to preempt the existing DF for 138 a given EVI/ISID without re-configuring all the PEs in the ES. 140 d) The solution SHOULD allow an option to NOT preempt the current DF, 141 even if the former DF PE comes back up after a failure. This is 142 also known as "non-revertive" behavior, as opposed to the RFC7432 143 DF election procedures that are always revertive. 145 e) The solution MUST work for single-active and all-active multi- 146 homing Ethernet Segments. 148 3. EVPN BGP Attributes for Deterministic DF Election 150 This solution reuses and extends the DF Election Extended Community 151 defined in [EVPN-HRW-DF] that is advertised along with the ES route: 153 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 155 | Type=0x06 | Sub-Type(TBD) | DF Type |DP| Reserved=0 | 156 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 157 | Reserved = 0 | DF Preference (2 octets) | 158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 Where the following fields are re-defined as follows: 162 o DF Type can have the following values: 164 - Type 0 - Default, mod based DF election as per RFC7432. 165 - Type 1 - HRW algorithm as per [EVPN-HRW-DF] 166 - Type 2 - Preference algorithm (this document) 168 o DP or 'Don't Preempt' bit, determines if the PE advertising the ES 169 route requests the remote PEs in the ES not to preempt it as DF. 170 The default value is DP=0, which is compatible with the current 171 'preempt' or 'revertive' behavior in RFC7432. The DP bit SHOULD be 172 ignored if the DF Type is different than 2. 174 o DF Preference defines a 2-octet value that indicates the PE 175 preference to become the DF in the ES. The allowed values are 176 within the range 0-65535, and default value MUST be 32767. This 177 value is the midpoint in the allowed Preference range of values, 178 which gives the operator the flexibility of choosing a significant 179 number of values, above or below the default Preference. 181 4. Solution description 183 Figure 1 illustrates an example that will be used in the description 184 of the solution. 186 EVPN network 187 +-------------------+ 188 | +-------+ ENNI Aggregation 189 | <---ESI1,500 | PE1 | /\ +----Network---+ 190 | <-----ESI2,100 | |===||=== | 191 | | |===||== \ vES1 | +----+ 192 +-----+ | | \/ |\----------------+CE1 | 193 CE3--+ PE4 | +-------+ | \ ------------+ | 194 +-----+ | | \ / | +----+ 195 | | | X | 196 | <---ESI1,255 +-----+============ \ | 197 | <-----ESI2,200 | PE2 |========== \ vES2 | +----+ 198 | +-----+ | \ ----------+CE2 | 199 | | | --------------| | 200 | +-----+ ----------------------+ | 201 | <-----ESI2,300 | PE3 +--/ | | +----+ 202 | +-----+ +--------------+ 203 --------------------+ 205 Figure 1 ES and Deterministic DF Election 207 Figure 1 shows three PEs that are connecting EVCs coming from the 208 Aggregation Network to their EVIs in the EVPN network. CE1 is 209 connected to vES1 - that spans PE1 and PE2 - and CE2 is connected to 210 vES2, that is defined in PE1, PE2 and PE3. 212 If the algorithm chosen for vES1 and vES2 is type 2, i.e. Preference- 213 based, the PEs may become DF irrespective of their IP address and 214 based on an administrative Preference value. The following sections 215 provide some examples of the new defined procedures and how they are 216 applied in the use-case in Figure 1. 218 4.1 Use of the Preference algorithm 220 Assuming the operator wants to control - in a flexible way - what PE 221 becomes the DF for a given vES and the order in which the PEs become 222 DF in case of multiple failures, the following procedure may be used: 224 a) vES1 and vES2 are now configurable with three optional parameters 225 that are signaled in the DF Election extended community. These 226 parameters are the Preference, Preemption option (or "Don't 227 Preempt Me" option) and DF algorithm type. We will represent these 228 parameters as [Pref,DP,type]. Let's assume vES1 is configured as 229 [500,0,Pref] in PE1, and [255,0,Pref] in PE2. vES2 is configured 230 as [100,0,Pref], [200,0,Pref] and [300,0,Pref] in PE1, PE2 and PE3 231 respectively. 233 b) The PEs will advertise an ES route for each vES, including the 3 234 parameters in the DF Election Extended Community. 236 c) According to RFC7432, each PE will wait for the DF timer to expire 237 before running the DF election algorithm. After the timer expires, 238 each PE runs the Preference-based DF election algorithm as 239 follows: 241 o The PE will check the DF type in each ES route, and assuming all 242 the ES routes are consistent in this DF type and the value is 2 243 (Preference-based), the PE will run the new extended procedure. 244 Otherwise, the procedure will fall back to RFC7432 'service- 245 carving'. 247 o In this extended procedure, each PE builds a list of candidate 248 PEs, ordered based on the Preference. E.g. PE1 will build a list 249 of candidate PEs for vES1 ordered by the Preference, from high 250 to low: PE1>PE2. Hence PE1 will become the DF for vES1. In the 251 same way, PE3 becomes the DF for vES2. 253 d) Note that, by default, the Highest-Preference is chosen for each 254 ES or vES, however the ES configuration can be changed to the 255 Lowest-Preference algorithm as long as this option is consistent 256 in all the PEs in the ES. E.g. vES1 could have been explicitly 257 configured as type Preference-based with Lowest-Preference, in 258 which case, PE2 would have been the DF. 260 e) Assuming some maintenance tasks had to be executed on PE3, the 261 operator could set vES2's preference to e.g. 50 so that PE2 is 262 forced to take over as DF for vES2. Once the maintenance on PE3 is 263 over, the operator could decide to leave the existing preference 264 or configure the old preference back. 266 f) In case of equal Preference in two or more PEs in the ES, the tie- 267 breakers will be the DP bit and the lowest IP PE in that order. 268 For instance: 270 o If vES1 parameters were [500,0,Pref] in PE1 and [500,1,Pref] in 271 PE2, PE2 would be elected due to the DP bit. 273 o If vES1 parameters were [500,0,Pref] in PE1 and [500,0,Pref] in 274 PE2, PE1 would be elected, assuming PE1's IP address is lower 275 than PE2's. 277 g) The Preference is an administrative option that MUST be configured 278 on a per-ES basis from the management plane, but MAY also be 279 dynamically changed based on the use of local policies. For 280 instance, on PE1, ES1's Preference can be lowered from 500 to 100 281 in case the bandwidth on the ENNI port is decreased a 50% (that 282 could happen if e.g. the 2-port LAG between PE1 and the 283 Aggregation Network loses one port). Policies MAY also trigger 284 dynamic Preference changes based on the PE's bandwidth 285 availability in the core, of specific ports going operationally 286 down, etc. The definition of the actual local policies is out of 287 scope of this document. The default Preference value is 32767. 289 4.2 Use of the Preference algorithm in RFC7432 Ethernet-Segments 291 While the Preference-based DF type described in section 4.1 is 292 typically used in virtual ES scenarios where there is normally an 293 individual EVI per vES, the existing RFC7432 definition of ES allows 294 potentially up to thousands of EVIs on the same ES. If this is the 295 case, and the operator still wants to control who the DF is for a 296 given EVI, the use of the Preference-based DF type can also provide 297 the desired level of load balancing. 299 In this type of scenarios, the ES is configured with an 300 administrative Preference value, but then a range of EVI/ISIDs can be 301 defined to use the Highest-Preference or the Lowest-Preference 302 depending on the desired behavior. With this option, the PE will 303 build a list of candidate PEs ordered by the Preference, however the 304 DF for a given EVI/ISID will be determined by the local 305 configuration. 307 For instance: 309 o Assuming ES3 is defined in PE1 and PE2, PE1 may be configured as 310 [500,0,Preference] for ES3 and PE2 as [100,0,Preference]. 312 o In addition, assuming vlan-based service interfaces, the PEs will 313 be configured with (vlan/ISID-range,high_or_low), e.g. (1- 314 2000,high) and (2001-4000, low). 316 o This will result in PE1 being DF for EVI/ISIDs 1-2000 and PE2 being 317 DF for EVI/ISIDs 2001-4000. 319 4.3 The Non-Revertive option 321 As discussed in section 2(d), an option to NOT preempt the existing 322 DF for a given EVI/ISID is required and therefore added to the DF 323 Election extended community. This option will allow a non-revertive 324 behavior in the DF election. 326 Note that, when a given PE in an ES is taken down for maintenance 327 operations, before bringing it back, the Preference may be changed in 328 order to provide a non-revertive behavior. The DP bit and the 329 mechanism explained in this section will be used for those cases when 330 a former DF comes back up without any controlled maintenance 331 operation, and the non-revertive option is desired in order to avoid 332 service impact. 334 In Figure 1, we assume that based on the Highest-Pref, PE3 is the DF 335 for ESI2. 337 If PE3 has a link, EVC or node failure, PE2 would take over as DF. 338 If/when PE3 comes back up again, PE3 will take over, causing some 339 unnecessary packet loss in the ES. 341 The following procedure avoids preemption upon failure recovery 342 (please refer to Figure 1): 344 1) A new "Don't Preempt Me" parameter is defined on a per-PE per-ES 345 basis, as described in section 3. If "Don't Preempt Me" is 346 disabled (default behavior) the advertised DP bit will be 0. If 347 "Don't Preempt Me" is enabled, the ES route will be advertised 348 with DP=1 ("Don't Preempt Me"). 350 2) Assuming we want to avoid 'preemption', the three PEs are 351 configured with the "Don't Preempt Me" option. Note that each PE 352 individually MAY be configured with different preemption value. In 353 this example, we assume ESI2 is configured as 'DP=enabled' in the 354 three PEs. 356 3) Assuming EVI1 uses Highest-Pref in vES2 and EVI2 uses Lowest-Pref, 357 when vES2 is enabled in the three PEs, the PEs will exchange the 358 ES routes and select PE3 as DF for EVI1 (due to the Highest-Pref 359 type), and PE1 as DF for EVI2 (due to the Lowest-Pref). 361 4) If PE3's vES2 goes down (due to EVC failure - detected by OAM, or 362 port failure or node failure), PE2 will become the DF for EVI1. No 363 changes will occur for EVI2. 365 5) When PE3's vES2 comes back up, PE3 will start a boot-timer (if 366 booting up) or hold-timer (if the port or EVC recovers). That 367 timer will allow some time for PE3 to receive the ES routes from 368 PE1 and PE2. PE3 will then: 370 o Select two "reference-PEs" among the ES routes in the vES, the 371 "Highest-PE" and the "Lowest-PE": 373 - The Highest-PE is the PE with higher Preference, using the DP 374 bit first (with DP=1 being better) and, after that, the lower 375 PE-IP address as tie-breakers. PE3 will select PE2 as Highest- 376 PE over PE1, since, when comparing [Pref,DP,PE-IP], 377 [200,1,PE2-IP] wins over [100,1,PE1-IP]. 379 - The Lowest-PE is the PE with lower Preference, using the DP 380 bit first (with DP=1 being better) and, after that, the lower 381 PE-IP address as tie-breakers. PE3 will select PE1 as Lowest- 382 PE over PE2, since [100,1,PE1-IP] wins over [200,1,PE2-IP]. 384 - Note that if there were only one remote PE in the ES, Lowest 385 and Highest PE would be the same PE. 387 o Check its own administrative Pref and compares it with the one 388 of the Highest-PE and Lowest-PE that have DP=1 in their ES 389 routes. Depending on this comparison PE3 will send the ES route 390 with a [Pref,DP] that may be different from its administrative 391 [Pref,DP]: 393 - If PE3's Pref value is higher than the Highest-PE's, PE3 will 394 send the ES route with an 'in-use' operational Pref equal to 395 the Highest-PE's and DP=0. 397 - If PE3's Pref value is lower than the Lowest-PE's, PE3 will 398 send the ES route with an 'in-use' operational Preference 399 equal to the Lowest-PE's and DP=0. 401 - If PE3's Pref value is neither higher nor lower than the 402 Highest-PE's or the Lowest-PE's respectively, PE3 will send 403 the ES route with its administrative [Pref,DP]=[300,1]. 405 - In this example, PE3's administrative Pref=300 is higher than 406 the Highest-PE with DP=1, that is, PE2 (Pref=200). Hence PE3 407 will inherit PE2's preference and send the ES route with an 408 operational 'in-use' [Pref,DP]=[200,0]. 410 Note that, a PE will always send DP=0 as long as the advertised 411 Pref is the 'in-use' operational Pref (as opposed to the 412 'administrative' Pref). 414 This ES route update sent by PE3 (with [200,0,PE3-IP]) will not 415 cause any DF switchover for any EVI/ISID. PE2 will continue being 416 DF for EVI1. This is because the DP bit will be used as a tie- 417 breaker in the DF election. That is, if a PE has two candidate PEs 418 with the same Pref, it will pick up the one with DP=1. There are 419 no DF changes for EVI2 either. 421 6) Subsequently, if PE2 fails, upon receiving PE2's ES route 422 withdrawal, PE3 and PE1 will go through the process described in 423 (5) to select new Highest and Lowest-PEs (considering their own 424 active ES route) and then they will run the DF Election. 426 o If a PE selects itself as new Highest or Lowest-PE and it was 427 not before, the PE will then compare its operational 'in-use' 428 Pref with its administrative Pref. If different, the PE will 429 send an ES route update with its administrative Pref and DP 430 values. In the example, PE3 will be the new Highest-PE, 431 therefore it will send an ES route update with 432 [Pref,DP]=[300,1]. 434 o After running the DF Election, PE3 will become the new DF for 435 EVI1. No changes will occur for EVI2. 437 Note that, irrespective of the DP bit, when a PE or ES comes back and 438 the PE advertises a DF Election type different than 2 (Preference 439 algorithm), the rest of the PEs in the ES MUST fall back to the 440 default RFC7432 service-carving modulo-based DF Election. 442 5. Conclusions 444 Service Providers are seeking for options where the DF election can 445 be controlled by the user in a deterministic way and with a non- 446 revertive behavior. This document defines the use of a Preference 447 algorithm that can be configured and used in a flexible manner to 448 achieve those objectives. 450 11. Conventions used in this document 452 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 453 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 454 document are to be interpreted as described in RFC-2119 [RFC2119]. 456 In this document, these words will appear with that interpretation 457 only when in ALL CAPS. Lower case uses of these words are not to be 458 interpreted as carrying RFC-2119 significance. 460 In this document, the characters ">>" preceding an indented line(s) 461 indicates a compliance requirement statement using the key words 462 listed above. This convention aids reviewers in quickly identifying 463 or finding the explicit compliance requirements of this RFC. 465 12. Security Considerations 467 This section will be added in future versions. 469 13. IANA Considerations 471 This document solicits the allocation of DF type = 2 in the registry 472 created by [EVPN-HRW-DF] for the DF type field. 474 15. References 476 15.1 Normative References 478 [RFC7432]Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A., 479 Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet 480 VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015, . 483 15.2 Informative References 485 [vES] Sajassi et al. "EVPN Virtual Ethernet Segment", draft-sajassi- 486 bess-evpn-virtual-eth-segment-01, work-in-progress, July 6, 2015. 488 [EVPN-HRW-DF] Mohanty S. et al. "A new Designated Forwarder Election 489 for the EVPN", draft-mohanty-bess-evpn-df-election-02, work-in- 490 progress, October 19, 2015. 492 16. Acknowledgments 494 The authors would like to thank Kishore Tiruveedhula for his review 495 and comments. 497 17. Contributors 499 In addition to the authors listed, the following individuals also 500 contributed to this document: 502 Kiran Nagaraj, Nokia 503 Vinod Prabhu, Nokia 504 Selvakumar Sivaraj, Juniper 506 17. Authors' Addresses 507 Jorge Rabadan 508 Nokia 509 777 E. Middlefield Road 510 Mountain View, CA 94043 USA 511 Email: jorge.rabadan@nokia.com 513 Senthil Sathappan 514 Alcatel-Lucent 515 Email: senthil.sathappan@nokia.com 517 Tony Przygienda 518 Juniper Networks, Inc. 519 Email: prz@juniper.net 521 John Drake 522 Juniper Networks, Inc. 523 Email: jdrake@juniper.net 525 Wen Lin 526 Juniper Networks, Inc. 527 Email: wlin@juniper.net 529 Ali Sajassi 530 Cisco Systems, Inc. 531 Email: sajassi@cisco.com 533 Satya Ranjan Mohanty 534 Cisco Systems, Inc. 535 Email: satyamoh@cisco.com 537 Sami Boutros 538 VMware, Inc. 539 Email: sboutros@vmware.com