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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (June 19, 2020) is 1400 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-15) exists of draft-ietf-bess-evpn-virtual-eth-segment-06 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). 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 5 Expires: December 21, 2020 T. Przygienda 6 W. Lin 7 J. Drake 8 Juniper Networks 9 A. Sajassi 10 S. Mohanty 11 Cisco Systems 12 June 19, 2020 14 Preference-based EVPN DF Election 15 draft-ietf-bess-evpn-pref-df-06 17 Abstract 19 The Designated Forwarder (DF) in Ethernet Virtual Private Networks 20 (EVPN) is defined as the PE responsible for sending Broadcast, 21 Unknown unicast and Broadcast traffic (BUM) to a multi-homed device/ 22 network in the case of an all-active multi-homing Ethernet Segment 23 (ES), or BUM and unicast in the case of single-active multi-homing. 25 The DF is selected out of a candidate list of PEs that advertise the 26 same Ethernet Segment Identifier (ESI) to the EVPN network, according 27 to the Default DF Election algorithm. 29 While the Default Algorithm provides an efficient and automated way 30 of selecting the DF across different Ethernet Tags in the ES, there 31 are some use-cases where a more 'deterministic' and user-controlled 32 method is required. At the same time, Service Providers require an 33 easy way to force an on-demand DF switchover in order to carry out 34 some maintenance tasks on the existing DF or control whether a new 35 active PE can preempt the existing DF PE. 37 This document proposes an extension to the Default DF election 38 procedures so that the above requirements can be met. 40 Status of This Memo 42 This Internet-Draft is submitted in full conformance with the 43 provisions of BCP 78 and BCP 79. 45 Internet-Drafts are working documents of the Internet Engineering 46 Task Force (IETF). Note that other groups may also distribute 47 working documents as Internet-Drafts. The list of current Internet- 48 Drafts is at https://datatracker.ietf.org/drafts/current/. 50 Internet-Drafts are draft documents valid for a maximum of six months 51 and may be updated, replaced, or obsoleted by other documents at any 52 time. It is inappropriate to use Internet-Drafts as reference 53 material or to cite them other than as "work in progress." 55 This Internet-Draft will expire on December 21, 2020. 57 Copyright Notice 59 Copyright (c) 2020 IETF Trust and the persons identified as the 60 document authors. All rights reserved. 62 This document is subject to BCP 78 and the IETF Trust's Legal 63 Provisions Relating to IETF Documents 64 (https://trustee.ietf.org/license-info) in effect on the date of 65 publication of this document. Please review these documents 66 carefully, as they describe your rights and restrictions with respect 67 to this document. Code Components extracted from this document must 68 include Simplified BSD License text as described in Section 4.e of 69 the Trust Legal Provisions and are provided without warranty as 70 described in the Simplified BSD License. 72 Table of Contents 74 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 75 1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 3 76 1.2. Solution requirements . . . . . . . . . . . . . . . . . . 3 77 2. Requirements Language and Terminology . . . . . . . . . . . . 4 78 3. EVPN BGP Attributes Extensions . . . . . . . . . . . . . . . 5 79 4. Solution description . . . . . . . . . . . . . . . . . . . . 6 80 4.1. Use of the Preference algorithm . . . . . . . . . . . . . 7 81 4.2. Use of the Preference algorithm in [RFC7432] Ethernet 82 Segments . . . . . . . . . . . . . . . . . . . . . . . . 9 83 4.3. The Non-Revertive Capability . . . . . . . . . . . . . . 10 84 5. Security Considerations . . . . . . . . . . . . . . . . . . . 13 85 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 86 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 87 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13 88 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 89 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 90 9.2. Informative References . . . . . . . . . . . . . . . . . 14 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 93 1. Introduction 94 1.1. Problem Statement 96 [RFC7432] defines the Designated Forwarder (DF) in (PBB-)EVPN 97 networks as the PE responsible for sending broadcast, multicast and 98 unknown unicast traffic (BUM) to a multi-homed device/network in the 99 case of an all-active multi-homing ES or BUM and unicast traffic to a 100 multi-homed device or network in case of single-active multi-homing. 102 The DF is selected out of a candidate list of PEs that advertise the 103 Ethernet Segment Identifier (ESI) to the EVPN network and according 104 to the DF Election Algorithm, or DF Alg as per [RFC8584]. 106 While the Default DF Alg [RFC7432] or HRW [RFC8584] provide an 107 efficient and automated way of selecting the DF across different 108 Ethernet Tags in the ES, there are some use-cases where a more 109 'deterministic' and user-controlled method is required. At the same 110 time, Service Providers require an easy way to force an on-demand DF 111 switchover in order to carry out some maintenance tasks on the 112 existing DF or control whether a new active PE can preempt the 113 existing DF PE. 115 This document proposes a new DF Alg and capability to address the 116 above needs. 118 1.2. Solution requirements 120 The procedures described in this document meet the following 121 requirements: 123 a. The solution provides an administrative preference option so that 124 the user can control in what order the candidate PEs may become 125 DF, assuming they are all operationally ready to take over as DF. 127 b. This extension works for [RFC7432] Ethernet Segments and virtual 128 ES, as defined in [I-D.ietf-bess-evpn-virtual-eth-segment]. 130 c. The user may force a PE to preempt the existing DF for a given 131 Ethernet Tag without re-configuring all the PEs in the ES. 133 d. The solution allows an option to NOT preempt the current DF, even 134 if the former DF PE comes back up after a failure. This is also 135 known as "non-revertive" behavior, as opposed to the [RFC7432] DF 136 election procedures that are always revertive. 138 e. The solution works for single-active and all-active multi-homing 139 Ethernet Segments. 141 2. Requirements Language and Terminology 143 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 144 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 145 "OPTIONAL" in this document are to be interpreted as described in 146 BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all 147 capitals, as shown here. 149 o AC - Attachment Circuit. An AC has an Ethernet Tag associated to 150 it. 152 o BUM - refers to the Broadcast, Unknown unicast and Multicast 153 traffic. 155 o DF, NDF and BDF - Designated Forwarder, Non-Designated Forwarder 156 and Backup Designated Forwarder. 158 o DF Alg or simply Alg - refers to Designated Forwarder Election 159 Algorithm. 161 o HRW - Highest Random Weight, as per [RFC8584]. 163 o ES, vES and ESI - Ethernet Segment, virtual Ethernet Segment and 164 Ethernet Segment Identifier. 166 o EVI - EVPN Instance. 168 o ISID - refers to Service Instance Identifiers in Provider Backbone 169 Bridging (PBB) networks. 171 o MAC-VRF - A Virtual Routing and Forwarding table for Media Access 172 Control (MAC) addresses on a PE. 174 o BD - Broadcast Domain. An EVI may be comprised of one (VLAN-Based 175 or VLAN Bundle services) or multiple (VLAN-Aware Bundle services) 176 Broadcast Domains. 178 o EVC - Ethernet Virtual Circuit. 180 o DP - refers to the "Don't Preempt me" capability in the DF 181 Election extended community. 183 o OAM - refers to Operations And Maintenance protocols. 185 o Ethernet A-D per ES route - refers to [RFC7432] route type 1 or 186 Auto-Discovery per Ethernet Segment route. 188 o Ethernet A-D per EVI route - refers to [RFC7432] route type 1 or 189 Auto-Discovery per EVPN Instance route. 191 o Ethernet Tag - used to represent a Broadcast Domain that is 192 configured on a given ES for the purpose of DF election. Note 193 that any of the following may be used to represent a Broadcast 194 Domain: VIDs (including Q-in-Q tags), configured IDs, VNI (VXLAN 195 Network Identifiers), normalized VID, I-SIDs (Service Instance 196 Identifiers), etc., as long as the representation of the broadcast 197 domains is configured consistently across the multi-homed PEs 198 attached to that ES. The Ethernet Tag value MUST be different 199 from zero. 201 3. EVPN BGP Attributes Extensions 203 This solution reuses and extends the DF Election Extended Community 204 defined in [RFC8584] that is advertised along with the ES route: 206 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 1 207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 208 | Type=0x06 | Sub-Type(0x06)| RSV | DF Alg | Bitmap ~ 209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 210 ~ Bitmap | Reserved | DF Preference (2 octets) | 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 213 Figure 1: DF Election Extended Community 215 Where the following fields are defined as follows: 217 o DF Alg can have the following values: 219 - Alg 0 - Default DF Election algorithm, or modulus-based 220 algorithm as per [RFC7432]. 222 - Alg 1 - HRW algorithm as per [RFC8584]. 224 - Alg 2 - Preference algorithm (this document). 226 o Bitmap (2 octets) can have the following values: 228 1 1 1 1 1 1 229 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 231 |D|A| | 232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 234 Figure 2: Bitmap field in the DF Election Extended Community 236 - Bit 0 (corresponds to Bit 24 of the DF Election Extended 237 Community and it is defined by this document): D bit or 'Don't 238 Preempt' bit (DP hereafter), determines if the PE advertising 239 the ES route requests the remote PEs in the ES not to preempt 240 it as DF. The default value is DP=0, which is compatible with 241 the 'preempt' or 'revertive' behavior in the Default DF Alg 242 [RFC7432]. The DP bit SHOULD be ignored if the DF Alg is 243 different than 2. 245 - Bit 1: AC-DF or AC-Influenced DF Election, as explained in 246 [RFC8584]. When set to 1, it indicates the desire to use AC- 247 Influenced DF Election with the rest of the PEs in the ES. The 248 AC-DF capability bit MAY be set along with the DP capability 249 and DF Alg 2. 251 o DF Preference (defined in this document): defines a 2-octet value 252 that indicates the PE preference to become the DF in the ES. The 253 allowed values are within the range 0-65535, and the default value 254 MUST be 32767. This value is the midpoint in the allowed 255 Preference range of values, which gives the operator the 256 flexibility of choosing a significant number of values, above or 257 below the default Preference. The DF Preference field is specific 258 to DF Alg 2 and does not represent any Preference value for other 259 Algs. If the DF Alg is different than Alg 2, these two octets can 260 be encoded differently. 262 4. Solution description 264 Figure 3 illustrates an example that will be used in the description 265 of the solution. 267 EVPN network 268 +-------------------+ 269 | +-------+ ENNI Aggregation 270 | <---ESI1,500 | PE1 | /\ +----Network---+ 271 | <-----ESI2,100 | |===||=== | 272 | | |===||== \ vES1 | +----+ 273 +-----+ | | \/ |\----------------+CE1 | 274 CE3--+ PE4 | +-------+ | \ ------------+ | 275 +-----+ | | \ / | +----+ 276 | | | X | 277 | <---ESI1,255 +-----+============ \ | 278 | <-----ESI2,200 | PE2 |========== \ vES2 | +----+ 279 | +-----+ | \ ----------+CE2 | 280 | | | --------------| | 281 | +-----+ ----------------------+ | 282 | <-----ESI2,300 | PE3 +--/ | | +----+ 283 | +-----+ +--------------+ 284 --------------------+ 286 Figure 3: Preference-based DF Election 288 Figure 3 shows three PEs that are connecting EVCs coming from the 289 Aggregation Network to their EVIs in the EVPN network. CE1 is 290 connected to vES1 - that spans PE1 and PE2 - and CE2 is connected to 291 vES2, that is defined in PE1, PE2 and PE3. 293 If the algorithm chosen for vES1 and vES2 is Alg 2, i.e., Preference- 294 based, the PEs may become DF irrespective of their IP address and 295 based on an administrative Preference value. The following sections 296 provide some examples of the procedures and how they are applied in 297 the use-case of Figure 3. 299 4.1. Use of the Preference algorithm 301 Assuming the operator wants to control - in a flexible way - what PE 302 becomes the DF for a given vES and the order in which the PEs become 303 DF in case of multiple failures, the following procedure may be used: 305 a. vES1 and vES2 are now configurable with three optional parameters 306 that are signaled in the DF Election extended community. These 307 parameters are the Preference, Preemption option (or "Don't 308 Preempt Me" option) and DF Alg. We will represent these 309 parameters as (Pref,DP,Alg). Let's assume vES1 is configured as 310 (500,0,Pref) in PE1, and (255,0,Pref) in PE2. vES2 is configured 311 as (100,0,Pref), (200,0,Pref) and (300,0,Pref) in PE1, PE2 and 312 PE3 respectively. 314 b. The PEs will advertise an ES route for each vES, including the 3 315 parameters in the DF Election Extended Community. 317 c. According to [RFC8584], each PE will run the DF election 318 algorithm upon expiration of the DF Wait timer. In this case, 319 each PE runs the Preference-based DF Alg for each ES as follows: 321 - The PE will check the DF Alg value in each ES route, and 322 assuming all the ES routes are consistent in this DF Alg and 323 the value is 2 (Preference-based), the PE will run the 324 procedure in this section. Otherwise, the procedure will fall 325 back to [RFC7432] Default Alg. 327 - In this Preference-based Alg, each PE builds a list of 328 candidate PEs, ordered by Preference. E.g. PE1 will build a 329 list of candidate PEs for vES1 ordered by the Preference, from 330 high to low: PE1>PE2. Hence PE1 will become the DF for vES1. 331 In the same way, PE3 becomes the DF for vES2. 333 d. Note that, by default, the Highest-Preference is chosen for each 334 ES or vES, however the ES configuration can be changed to the 335 Lowest-Preference algorithm as long as this option is consistent 336 in all the PEs in the ES. E.g. vES1 could have been explicitly 337 configured as Alg Preference-based with Lowest-Preference, in 338 which case, PE2 would have been the DF. 340 e. Assuming some maintenance tasks had to be executed on PE3, the 341 operator could set vES2's Preference to e.g., 50 so that PE2 is 342 forced to take over as DF for vES2 (irrespective of the DP 343 capability). Once the maintenance on PE3 is over, the operator 344 could decide to leave the existing preference or configure the 345 old preference back. 347 f. In case of equal Preference in two or more PEs in the ES, the DP 348 bit and the lowest IP of the candidate PEs are used as tie- 349 breakers. After selecting the PEs with the highest Preference 350 value, an implementation MUST first select the PE advertising the 351 DP bit set, and then select the PE with the lowest IP address (if 352 the DP bit selection does not yield a unique candidate). The 353 PE's IP address is the address used in the candidate list and it 354 is derived from the Originating Router's IP address of the ES 355 route. Some examples of the use of the DP bit and IP address 356 tie-breakers follow: 358 - If vES1 parameters were (500,0,Pref) in PE1 and (500,1,Pref) 359 in PE2, PE2 would be elected due to the DP bit. 361 - If vES1 parameters were (500,0,Pref) in PE1 and (500,0,Pref) 362 in PE2, PE1 would be elected, assuming PE1's IP address is 363 lower than PE2's. 365 g. The Preference is an administrative option that MUST be 366 configured on a per-ES basis from the management plane, but MAY 367 also be dynamically changed based on the use of local policies. 368 For instance, on PE1, ES1's Preference can be lowered from 500 to 369 100 in case the bandwidth on the ENNI port is decreased a 50% 370 (that could happen if e.g. the 2-port LAG between PE1 and the 371 Aggregation Network loses one port). Policies MAY also trigger 372 dynamic Preference changes based on the PE's bandwidth 373 availability in the core, specific ports going operationally 374 down, etc. The definition of the actual local policies is out of 375 scope of this document. The default Preference value is 32767. 377 The Preference Alg MAY be used along with the AC-DF capability. 378 Assuming all the PEs in the ES are configured consistently with 379 Preference Alg and AC-DF capability, a given PE in the ES is not 380 considered as candidate for DF Election until its corresponding 381 Ethernet A-D per ES and Ethernet A-D per EVI routes are not received, 382 as described in [RFC8584]. 384 The procedures in this document can be used in [RFC7432] based ES or 385 vES as in [I-D.ietf-bess-evpn-virtual-eth-segment], and including 386 EVPN networks as in [RFC8214], [RFC7623] or [RFC8365]. 388 4.2. Use of the Preference algorithm in [RFC7432] Ethernet Segments 390 While the Preference-based DF Alg described in Section 4.1 is 391 typically used in virtual ES scenarios where there is normally an 392 individual Ethernet Tag per vES, the existing [RFC7432] definition of 393 ES allows potentially up to thousands of Ethernet Tags on the same 394 ES. If this is the case, and the operator still wants to control who 395 the DF is for a given Ethernet Tag, the use of the Preference-based 396 DF Alg can also provide some level of load balancing. 398 In this type of scenarios, the ES is configured with an 399 administrative Preference value, but then a range of Ethernet Tags 400 can be defined to use the Highest-Preference or the Lowest-Preference 401 depending on the desired behavior. With this option, the PE will 402 build a list of candidate PEs ordered by Preference, however the DF 403 for a given Ethernet Tag will be determined by the local 404 configuration. 406 For instance: 408 o Assuming ES3 is defined in PE1 and PE2, PE1 may be configured as 409 (500,0,Preference) for ES3 and PE2 as (100,0,Preference). 411 o In addition, assuming VLAN-based service interfaces, the PEs will 412 be configured with (Ethernet Tag-range,high_or_low), E.g., 413 (1-2000,high) and (2001-4000, low). 415 o This will result in PE1 being DF for Ethernet Tags 1-2000 and PE2 416 being DF for Ethernet Tags 2001-4000. 418 For Ethernet Segments attached to three or more PEs, any other logic 419 that provides a fair distribution of the DF function among the PEs is 420 valid, as long as that logic is consistent in all the PEs in the ES. 422 4.3. The Non-Revertive Capability 424 As discussed in Section 1.2 (d), a capability to NOT preempt the 425 existing DF for a given Ethernet Tag is required and therefore added 426 to the DF Election extended community. This option will allow a non- 427 revertive behavior in the DF election. 429 Note that, when a given PE in an ES is taken down for maintenance 430 operations, before bringing it back, the Preference may be changed in 431 order to provide a non-revertive behavior. The DP bit and the 432 mechanism explained in this section will be used for those cases when 433 a former DF comes back up without any controlled maintenance 434 operation, and the non-revertive option is desired in order to avoid 435 service impact. 437 In Figure 3, we assume that based on the Highest-Pref, PE3 is the DF 438 for ESI2. 440 If PE3 has a link, EVC or node failure, PE2 would take over as DF. 441 If/when PE3 comes back up again, PE3 will take over, causing some 442 unnecessary packet loss in the ES. 444 The following procedure avoids preemption upon failure recovery 445 (please refer to Figure 1): 447 1. A new "Don't Preempt Me" capability is defined on a per-PE/per-ES 448 basis, as described in Section 3. If "Don't Preempt Me" is 449 disabled (default behavior), the advertised DP bit will be 0. If 450 "Don't Preempt Me" is enabled, the ES route will be advertised 451 with DP=1 ("Don't Preempt Me"). All the PEs in an ES SHOULD be 452 consistent in their configuration of the DP capability, however 453 this document do not enforce the consistency across all the PEs. 454 In case of inconsistency in the support of the DP capability in 455 the PEs of the same ES, non-revertive behavior is not guaranteed. 457 2. Assuming we want to avoid 'preemption' in all the PEs in the ES, 458 the three PEs are configured with the "Don't Preempt Me" 459 capability. In this example, we assume ESI2 is configured as 460 'DP=enabled' in the three PEs. 462 3. Assuming Ethernet Tag-1 uses Highest-Pref in vES2 and Ethernet 463 Tag-2 uses Lowest-Pref, when vES2 is enabled in the three PEs, 464 the PEs will exchange the ES routes and select PE3 as DF for 465 Ethernet Tag-1 (due to the Highest-Pref type), and PE1 as DF for 466 Ethernet Tag-2 (due to the Lowest-Pref). 468 4. If PE3's vES2 goes down (due to EVC failure - detected by OAM, or 469 port failure or node failure), PE2 will become the DF for 470 Ethernet Tag-1. No changes will occur for Ethernet Tag-2. 472 5. When PE3's vES2 comes back up, PE3 will start a boot-timer (if 473 booting up) or hold-timer (if the port or EVC recovers). That 474 timer will allow some time for PE3 to receive the ES routes from 475 PE1 and PE2. This timer is applied between the INIT and the 476 DF_WAIT states in the DF Election Finite State Machine described 477 in [RFC8584]. PE3 will then: 479 - Select two "reference-PEs" among the ES routes in the vES, the 480 "Highest-PE" and the "Lowest-PE": 482 * The Highest-PE is the PE with higher Preference, using the 483 DP bit first (with DP=1 being better) and, after that, the 484 lower PE-IP address as tie-breakers. PE3 will select PE2 485 as Highest-PE over PE1, since, when comparing (Pref,DP,PE- 486 IP), (200,1,PE2-IP) wins over (100,1,PE1-IP). 488 * The Lowest-PE is the PE with lower Preference, using the DP 489 bit first (with DP=1 being better) and, after that, the 490 lower PE-IP address as tie-breakers. PE3 will select PE1 491 as Lowest-PE over PE2, since (100,1,PE1-IP) wins over 492 (200,1,PE2-IP). 494 * Note that if there were only one remote PE in the ES, 495 Lowest and Highest PE would be the same PE. 497 - Check its own administrative Pref and compares it with the one 498 of the Highest-PE and Lowest-PE that have DP=1 in their ES 499 routes. Depending on this comparison PE3 will send the ES 500 route with a (Pref,DP) that may be different from its 501 administrative (Pref,DP): 503 * If PE3's Pref value is higher than the Highest-PE's, PE3 504 will send the ES route with an 'in-use' operational Pref 505 equal to the Highest-PE's and DP=0. 507 * If PE3's Pref value is lower than the Lowest-PE's, PE3 will 508 send the ES route with an 'in-use' operational Preference 509 equal to the Lowest-PE's and DP=0. 511 * If PE3's Pref value is neither higher nor lower than the 512 Highest-PE's or the Lowest-PE's respectively, PE3 will send 513 the ES route with its administrative (Pref,DP)=(300,1). 515 * In this example, PE3's administrative Pref=300 is higher 516 than the Highest-PE with DP=1, that is, PE2 (Pref=200). 517 Hence PE3 will inherit PE2's preference and send the ES 518 route with an operational 'in-use' (Pref,DP)=(200,0). 520 - Note that, a PE will always send DP=0 as long as the 521 advertised Pref is the 'in-use' operational Pref (as opposed 522 to the 'administrative' Pref). 524 - This ES route update sent by PE3, with (200,0,PE3-IP), will 525 not cause any DF switchover for any Ethernet Tag. PE2 will 526 continue being DF for Ethernet Tag-1. This is because the DP 527 bit will be used as a tie-breaker in the DF election. That 528 is, if a PE has two candidate PEs with the same Pref, it will 529 pick up the one with DP=1. There are no DF changes for 530 Ethernet Tag-2 either. 532 6. For any subsequent update/withdraw in the ES, the PEs will go 533 through the process described in (5) to select Highest and 534 Lowest-PEs. For instance, if PE2 fails, upon receiving PE2's ES 535 route withdrawal, PE3 and PE1 will go through the selection of 536 new Highest and Lowest-PEs (considering their own active ES 537 route) and then they will run the DF Election. 539 - If a PE selects itself as new Highest or Lowest-PE and it was 540 not before, the PE will then compare its operational 'in-use' 541 Pref with its administrative Pref. If different, the PE will 542 send an ES route update with its administrative Pref and DP 543 values. In the example, PE3 will be the new Highest-PE, 544 therefore it will send an ES route update with 545 (Pref,DP)=(300,1). 547 - After running the DF Election, PE3 will become the new DF for 548 Ethernet Tag-1. No changes will occur for Ethernet Tag-2. 550 Note that, irrespective of the DP bit, when a PE or ES comes back and 551 the PE advertises a DF Election Alg different than 2 (Preference 552 algorithm), the rest of the PEs in the ES MUST fall back to the 553 Default [RFC7432] Alg. 555 This document does not modify the use of the P and B bits in the 556 Ethernet A-D per EVI routes [RFC8214] advertised by the PEs in the ES 557 after running the DF Election, irrespective of the revertive or non- 558 revertive behavior in the PE. 560 5. Security Considerations 562 This document describes a DF Election Algorithm that provides 563 absolute control (by configuration) over what PE is the DF for a 564 given Ethernet Tag. While this control is desired in many situations, 565 a malicious user that gets access to the configuration of a PE in the 566 ES may change the behavior of the network. In other DF Algs such as 567 HRW, the DF Election is more automated and cannot be determined by 568 configuration. 570 The non-revertive capability described in this document may be seen 571 as a security improvement over the regular EVPN revertive DF 572 Election: an intentional link (or node) "flapping" on a PE will only 573 cause service disruption once, when the PE goes to NDF state. 575 6. IANA Considerations 577 This document solicits the allocation of the following values: 579 o DF Alg = 2 in the [RFC8584] "DF Alg" registry, with name 580 "Preference Algorithm". 582 o Bit 0 in the [RFC8584] DF Election Capabilities registry, with 583 name "D (Don't Preempt) Capability" for Non-revertive ES. 585 7. Acknowledgments 587 The authors would like to thank Kishore Tiruveedhula for his review 588 and comments. 590 8. Contributors 592 In addition to the authors listed, the following individuals also 593 contributed to this document: 595 Kiran Nagaraj, Nokia 597 Vinod Prabhu, Nokia 598 Selvakumar Sivaraj, Juniper 600 Sami Boutros, VMWare 602 9. References 604 9.1. Normative References 606 [RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A., 607 Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based 608 Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February 609 2015, . 611 [RFC8584] Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake, 612 J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet 613 VPN Designated Forwarder Election Extensibility", 614 RFC 8584, DOI 10.17487/RFC8584, April 2019, 615 . 617 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 618 Requirement Levels", BCP 14, RFC 2119, 619 DOI 10.17487/RFC2119, March 1997, 620 . 622 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 623 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 624 May 2017, . 626 [I-D.ietf-bess-evpn-virtual-eth-segment] 627 Sajassi, A., Brissette, P., Schell, R., Drake, J., and J. 628 Rabadan, "EVPN Virtual Ethernet Segment", draft-ietf-bess- 629 evpn-virtual-eth-segment-06 (work in progress), March 630 2020. 632 9.2. Informative References 634 [RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J. 635 Rabadan, "Virtual Private Wire Service Support in Ethernet 636 VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017, 637 . 639 [RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R., 640 Uttaro, J., and W. Henderickx, "A Network Virtualization 641 Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365, 642 DOI 10.17487/RFC8365, March 2018, 643 . 645 [RFC7623] Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W. 646 Henderickx, "Provider Backbone Bridging Combined with 647 Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623, 648 September 2015, . 650 Authors' Addresses 652 J. Rabadan (editor) 653 Nokia 654 777 Middlefield Road 655 Mountain View, CA 94043 656 USA 658 Email: jorge.rabadan@nokia.com 660 S. Sathappan 661 Nokia 663 Email: senthil.sathappan@nokia.com 665 T. Przygienda 666 Juniper Networks 668 Email: prz@juniper.net 670 W. Lin 671 Juniper Networks 673 Email: wlin@juniper.net 675 J. Drake 676 Juniper Networks 678 Email: jdrake@juniper.net 680 A. Sajassi 681 Cisco Systems 683 Email: sajassi@cisco.com 684 S. Mohanty 685 Cisco Systems 687 Email: satyamoh@cisco.com