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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BESS WorkGroup N. Malhotra, Ed. 3 Internet-Draft A. Sajassi 4 Intended status: Standards Track A. Pattekar 5 Expires: September 16, 2021 Cisco Systems 6 J. Rabadan 7 Nokia 8 A. Lingala 9 ATT 10 J. Drake 11 Juniper Networks 12 March 15, 2021 14 Extended Mobility Procedures for EVPN-IRB 15 draft-ietf-bess-evpn-irb-extended-mobility-05 17 Abstract 19 Procedure to handle host mobility in a layer 2 Network with EVPN 20 control plane is defined as part of RFC 7432. EVPN has since evolved 21 to find wider applicability across various IRB use cases that include 22 distributing both MAC and IP reachability via a common EVPN control 23 plane. MAC Mobility procedures defined in RFC 7432 are extensible to 24 IRB use cases if a fixed 1:1 mapping between VM IP and MAC is assumed 25 across VM moves. Generic mobility support for IP and MAC that allows 26 these bindings to change across moves is required to support a 27 broader set of EVPN IRB use cases, and requires further 28 consideration. EVPN all-active multi-homing further introduces 29 scenarios that require additional consideration from mobility 30 perspective. This document enumerates a set of design considerations 31 applicable to mobility across these EVPN IRB use cases and defines 32 generic sequence number assignment procedures to address these IRB 33 use cases. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at https://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on September 16, 2021. 51 Copyright Notice 53 Copyright (c) 2021 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (https://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Requirements Language and Terminology . . . . . . . . . . . . 3 69 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 70 2.1. Document Structure . . . . . . . . . . . . . . . . . . . 5 71 3. Optional MAC only RT-2 . . . . . . . . . . . . . . . . . . . 6 72 4. Mobility Use Cases . . . . . . . . . . . . . . . . . . . . . 6 73 4.1. Host MAC+IP Move . . . . . . . . . . . . . . . . . . . . 6 74 4.2. Host IP Move to new MAC . . . . . . . . . . . . . . . . . 7 75 4.2.1. VM Reload . . . . . . . . . . . . . . . . . . . . . . 7 76 4.2.2. MAC Sharing . . . . . . . . . . . . . . . . . . . . . 7 77 4.2.3. Problem . . . . . . . . . . . . . . . . . . . . . . . 7 78 4.3. Host MAC move to new IP . . . . . . . . . . . . . . . . . 8 79 4.3.1. Problem . . . . . . . . . . . . . . . . . . . . . . . 8 80 5. EVPN All Active multi-homed ES . . . . . . . . . . . . . . . 10 81 6. Design Considerations . . . . . . . . . . . . . . . . . . . . 11 82 7. Solution Components . . . . . . . . . . . . . . . . . . . . . 12 83 7.1. Sequence Number Inheritance . . . . . . . . . . . . . . . 12 84 7.2. MAC Sharing . . . . . . . . . . . . . . . . . . . . . . . 13 85 7.3. Multi-homing Mobility Synchronization . . . . . . . . . . 14 86 8. Requirements for Sequence Number Assignment . . . . . . . . . 14 87 8.1. LOCAL MAC-IP learning . . . . . . . . . . . . . . . . . . 15 88 8.2. LOCAL MAC learning . . . . . . . . . . . . . . . . . . . 15 89 8.3. Remote MAC OR MAC-IP Update . . . . . . . . . . . . . . . 15 90 8.4. REMOTE (SYNC) MAC update . . . . . . . . . . . . . . . . 16 91 8.5. REMOTE (SYNC) MAC-IP update . . . . . . . . . . . . . . . 16 92 8.6. Inter-op . . . . . . . . . . . . . . . . . . . . . . . . 16 93 8.7. MAC Sharing Race Condition . . . . . . . . . . . . . . . 17 94 8.8. Mobility Convergence . . . . . . . . . . . . . . . . . . 17 95 8.8.1. Generalized Probing Logic . . . . . . . . . . . . . . 18 96 9. Routed Overlay . . . . . . . . . . . . . . . . . . . . . . . 18 97 10. Duplicate Host Detection . . . . . . . . . . . . . . . . . . 19 98 10.1. Scenario A . . . . . . . . . . . . . . . . . . . . . . . 19 99 10.2. Scenario B . . . . . . . . . . . . . . . . . . . . . . . 20 100 10.2.1. Duplicate IP Detection Procedure for Scenario B . . 20 101 10.3. Scenario C . . . . . . . . . . . . . . . . . . . . . . . 21 102 10.4. Duplicate Host Recovery . . . . . . . . . . . . . . . . 21 103 10.4.1. Route Un-freezing Configuration . . . . . . . . . . 21 104 10.4.2. Route Clearing Configuration . . . . . . . . . . . . 22 105 11. Security Considerations . . . . . . . . . . . . . . . . . . . 23 106 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 107 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23 108 14. Normative References . . . . . . . . . . . . . . . . . . . . 23 109 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 111 1. Requirements Language and Terminology 113 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 114 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 115 document are to be interpreted as described in [RFC2119]. 117 o EVPN-IRB: A BGP-EVPN distributed control plane based integrated 118 routing and bridging fabric overlay discussed in [EVPN-IRB] 120 o Underlay: IP or MPLS fabric core network that provides IP or MPLS 121 routed reachability between EVPN PEs. 123 o Overlay: VPN or service layer network consisting of EVPN PEs OR 124 VPN provider-edge (PE) switch-router devices that runs on top of 125 an underlay routed core. 127 o EVPN PE: A PE switch-router in a data-center fabric that runs 128 overlay BGP-EVPN control plane and connects to overlay CE host 129 devices. An EVPN PE may also be the first-hop layer-3 gateway for 130 CE/host devices. This document refers to EVPN PE as a logical 131 function in a data-center fabric. This EVPN PE function may be 132 physically hosted on a top-of-rack switching device (ToR) OR at 133 layer(s) above the ToR in the Clos fabric. An EVPN PE is 134 typically also an IP or MPLS tunnel end-point for overlay VPN flow 136 o Symmetric EVPN-IRB: An overlay fabric first-hop routing 137 architecture as defined in [EVPN-IRB], wherein, overlay host-to- 138 host routed inter-subnet flows are routed at both ingress and 139 egress EVPN PEs. 141 o Asymmetric EVPN-IRB: An overlay fabric first-hop routing 142 architecture as defined in [EVPN-IRB], wherein, overlay host-to- 143 host routed inter-subnet flows are routed and bridged at ingress 144 PE and bridged at egress PEs. 146 o ARP: Address Resolution Protocol [RFC 826]. ARP references in 147 this document are equally applicable to ND as well. 149 o ND: IPv6 Neighbor Discovery Protocol [RFC 4861]. 151 o Ethernet-Segment: physical Ethernet or LAG port that connects an 152 access device to an EVPN PE, as defined in [RFC 7432]. 154 o ESI: Ethernet Segment Identifier as defined in [RFC 7432]. 156 o LAG: Layer-2 link-aggregation, also known as layer-2 bundle port- 157 channel, or bond interface. 159 o EVPN all-active multi-homing: PE-CE all-active multi-homing 160 achieved via a multi-homed layer-2 LAG interface on a CE with 161 member links to multiple PEs and related EVPN procedures on the 162 PEs. 164 o RT-2: EVPN route type 2 carrying both MAC and IP reachability. 166 o RT-5: EVPN route type 5 carrying IP prefix reachability. 168 o MAC-IP: IP association for a MAC, referred to in this document may 169 be IPv4, IPv6 or both. 171 2. Introduction 173 EVPN-IRB enables capability to advertise both MAC and IP routes via a 174 single MAC+IP RT-2 advertisement. MAC is imported into local bridge 175 MAC table and enables L2 bridged traffic across the network overlay. 176 IP is imported into the local ARP table in an asymmetric IRB design 177 OR imported into the IP routing table in a symmetric IRB design, and 178 enables routed traffic across the layer 2 network overlay. Please 179 refer to [EVPN-IRB] for more background on EVPN IRB forwarding modes. 181 To support EVPN mobility procedure, a single sequence number mobility 182 attribute is advertised with the combined MAC+IP route. A single 183 sequence number advertised with the combined MAC+IP route to resolve 184 both MAC and IP reachability implicitly assumes a 1:1 fixed mapping 185 between IP and MAC. While a fixed 1:1 mapping between IP and MAC is 186 a common use case that could be addressed via existing MAC mobility 187 procedure, additional IRB scenarios need to be considered, that don't 188 necessarily adhere to this assumption. Following IRB mobility 189 scenarios are considered: 191 o VM move results in VM IP and MAC moving together 193 o VM move results in VM IP moving to a new MAC association 194 o VM move results in VM MAC moving to a new IP association 196 While existing MAC mobility procedure can be leveraged for MAC+IP 197 move in the first scenario, subsequent scenarios result in a new MAC- 198 IP association. As a result, a single sequence number assigned 199 independently per-[MAC, IP] is not sufficient to determine most 200 recent reachability for both MAC and IP, unless the sequence number 201 assignment algorithm is designed to allow for changing MAC-IP 202 bindings across moves. 204 Purpose of this draft is to define additional sequence number 205 assignment and handling procedures to adequately address generic 206 mobility support across EVPN-IRB overlay use cases that allow MAC-IP 207 bindings to change across VM moves and can support mobility for both 208 MAC and IP components carried in an EVPN RT-2 for these use cases. 210 In addition, for hosts on an ESI multi-homed to multiple GW devices, 211 additional procedure is proposed to ensure synchronized sequence 212 number assignments across the multi-homing devices. 214 Content presented in this draft is independent of data plane 215 encapsulation used in the overlay being MPLS or NVO Tunnels. It is 216 also largely independent of the EVPN IRB solution being based on 217 symmetric OR asymmetric IRB design as defined in [EVPN-INTER-SUBNET]. 219 In addition to symmetric and asymmetric IRB, mobility solution for a 220 routed overlay, where traffic to an end host in the overlay is always 221 IP routed using EVPN RT-5 is also presented in this document. 223 To summarize, this draft covers mobility mobility for the following 224 independent of the overlay encapsulation being MPLS or an NVO Tunnel: 226 o Symmetric EVPN IRB overlay 228 o Asymmetric EVPN IRB overlay 230 o Routed EVPN overlay 232 2.1. Document Structure 234 Following sections of the document should be condidered informnative: 236 o section 4 and 5 provide the necessary background and problem 237 statement being addressed in this document. 239 o section 6 lists the resulting design considerations for the 240 document. 242 Following sections of the document should be condidered normative: 244 o section 8 describes the mobility and sequence number assigment 245 procedures in an EVPN-IRB overlay required to address the 246 scenarios described in section 4. 248 o section 9 describes the mobility procedures for a routed overlay 249 nextwork as opposed to an IRB overlay. 251 o section 10 describes corresponding duplicate detection procedures 252 for EVPN-IRB and routed overlays. 254 3. Optional MAC only RT-2 256 In an EVPN IRB scenario, where a single MAC+IP RT-2 advertisement 257 carries both IP and MAC routes, a MAC only RT-2 advertisement is 258 redundant for host MACs that are advertised via MAC+IP RT-2. As a 259 result, a MAC only RT-2 is an optional route that may not be 260 advertised from or received at an EVPN PE. This is an important 261 consideration for mobility scenarios discussed in subsequent 262 sections. 264 MAC only RT-2 may still be advertised for non-IP host MACs that are 265 not advertised via MAC+IP RT-2. 267 4. Mobility Use Cases 269 This section describes the IRB mobility use cases considered in this 270 document. Procedures to address them are covered later in section 6 271 and section 7. 273 o Host move results in Host IP and MAC moving together 275 o Host move results in Host IP moving to a new MAC association 277 o Host move results in Host MAC moving to a new IP association 279 4.1. Host MAC+IP Move 281 This is the baseline case, wherein a host move results in both host 282 MAC and IP moving together with no change in MAC-IP binding across a 283 move. Existing MAC mobility defined in RFC 7432 may be leveraged to 284 apply to corresponding MAC+IP route to support this mobility 285 scenario. 287 4.2. Host IP Move to new MAC 289 This is the case, where a host move results in VM IP moving to a new 290 MAC binding. 292 4.2.1. VM Reload 294 A host reload or an orchestrated host move that results in host being 295 re-spawned at a new location may result in host getting a new MAC 296 assignment, while maintaining existing IP address. This results in a 297 host IP move to a new MAC binding: 299 IP-a, MAC-a ---> IP-a, MAC-b 301 4.2.2. MAC Sharing 303 This takes into account scenarios, where multiple hosts, each with a 304 unique IP, may share a common MAC binding, and a host move results in 305 a new MAC binding for the host IP. 307 As an example, hosts running on a single physical server, each with a 308 unique IP, may share the same physical server MAC. In yet another 309 scenario, an L2 access network may be behind a firewall, such that 310 all hosts IPs on the access network are learnt with a common firewall 311 MAC. In all such "shared MAC" use cases, multiple local MAC-IP ARP 312 entries may be learnt with the same MAC. A host IP move, in such 313 scenarios (for e.g., to a new physical server), could result in new 314 MAC association for the host IP. 316 4.2.3. Problem 318 In both of the above scenarios, a combined MAC+IP EVPN RT-2 319 advertised with a single sequence number attribute implicitly assumes 320 a fixed IP to MAC mapping. A host IP move to a new MAC breaks this 321 assumption and results in a new MAC+IP route. If this new MAC+IP 322 route is independently assigned a new sequence number, the sequence 323 number can no longer be used to determine most recent host IP 324 reachability in a symmetric EVPN-IRB design OR the most recent IP to 325 MAC binding in an asymmetric EVPN-IRB design. 327 +------------------------+ 328 | Underlay Network Fabric| 329 +------------------------+ 331 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 332 | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | 333 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 334 \ / \ / \ / 335 \ ESI-1 / \ ESI-2 / \ ESI-3 / 336 \ / \ / \ / 337 +\---/+ +\---/+ +\---/+ 338 | \ / | | \ / | | \ / | 339 +--+--+ +--+--+ +--+--+ 340 | | | 341 Server-MAC1 Server-MAC2 Server-MAC3 342 | | | 343 [VM-IP1, VM-IP2] [VM-IP3, VM-IP4] [VM-IP5, VM-IP6] 345 Figure 1 347 As an example, consider a topology shown in Figure 1, with host VMs 348 sharing the physical server MAC. In steady state, [IP1, MAC1] route 349 is learnt at [PE1, PE2] and advertised to remote PEs with a sequence 350 number N. Now, VM-IP1 is moved to Server-MAC2. ARP or ND based 351 local learning at [PE3, PE4] would now result in a new [IP1, MAC2] 352 route being learnt. If route [IP1, MAC2] is learnt as a new MAC+IP 353 route and assigned a new sequence number of say 0, mobility procedure 354 for VM-IP1 will not trigger across the overlay network. 356 A sequence number assignment procedure needs to be defined to 357 unambiguously determine the most recent IP reachability, IP to MAC 358 binding, and MAC reachability for such a MAC sharing scenario. 360 4.3. Host MAC move to new IP 362 This is a scenario where host move or re-provisioning behind a new 363 gateway location may result in host getting a new IP address 364 assigned, while keeping the same MAC. 366 4.3.1. Problem 368 Complication with this scenario is that MAC reachability could be 369 carried via a combined MAC+IP route while a MAC only route may not be 370 advertised at all. A single sequence number association with the 371 MAC+IP route again implicitly assumes a fixed mapping between MAC and 372 IP. A MAC move resulting in a new IP association for the host MAC 373 breaks this assumption and results in a new MAC+IP route. If this 374 new MAC+IP route independently assumes a new sequence number, this 375 mobility attribute can no longer be used to determine most recent 376 host MAC reachability. 378 +------------------------+ 379 | Underlay Network Fabric| 380 +------------------------+ 381 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 382 | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | 383 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 384 \ / \ / \ / 385 \ ESI-1 / \ ESI-2 / \ ESI-3 / 386 \ / \ / \ / 387 +\---/+ +\---/+ +\---/+ 388 | \ / | | \ / | | \ / | 389 +--+--+ +--+--+ +--+--+ 390 | | | 391 Server1 Server2 Server3 392 | | | 393 [VM-IP1-M1, VM-IP2-M2] [VM-IP3-M3, VM-IP4-M4] [VM-IP5-M5, VM-IP6-M6] 395 Figure 2 397 As an example, consider a host VM IP1-M1 that is learnt locally at 398 [PE1, PE2] and advertised to remote hosts with a sequence number N. 399 Consider a scenario where this VM with MAC M1 is re-provisioned at 400 server 2, however, as part of this re-provisioning, assigned a 401 different IP address say IP7. [IP7, M1] is learnt as a new route at 402 [PE3, PE4] and advertised to remote PEs with a sequence number of 0. 403 As a result, L3 reachability to IP7 would be established across the 404 overlay, however, MAC mobility procedure for MAC1 will not trigger as 405 a result of this MAC-IP route advertisement. If an optional MAC only 406 route is also advertised, sequence number associated with the MAC 407 only route would trigger MAC mobility as per [RFC7432]. However, in 408 the absence of an additional MAC only route advertisement, a single 409 sequence number advertised with a combined MAC+IP route would not be 410 sufficient to update MAC reachability across the overlay. 412 A MAC-IP sequence number assignment procedure needs to be defined to 413 unambiguously determine the most recent MAC reachability in such a 414 scenario without a MAC only route being advertised. 416 Further, PE1/PE2, on learning new reachability for [IP7, M1] via PE3/ 417 PE4 MUST probe and delete any local IPs associated with MAC M1, such 418 as [IP1, M1] in the above example. 420 Arguably, MAC mobility sequence number defined in [RFC7432], could be 421 interpreted to apply only to the MAC part of MAC-IP route, and would 422 hence cover this scenario. It could hence be interpreted as a 423 clarification to [RFC7432] and one of the considerations for a common 424 sequence number assignment procedure across all MAC-IP mobility 425 scenarios detailed in this document. 427 5. EVPN All Active multi-homed ES 429 +------------------------+ 430 | Underlay Network Fabric| 431 +------------------------+ 433 +-----+ +-----+ 434 | PE1 | | PE2 | 435 +-----+ +-----+ 436 \\ // 437 \\ ESI-1 // 438 \\ /X 439 +\\---//+ 440 | \\ // | 441 +---+---+ 442 | 443 CE1 445 Figure 3 447 Consider an EVPN-IRB overlay network shown in Figure 2, with hosts 448 multi-homed to two or more PE devices via an all-active multi-homed 449 ES. MAC and ARP entries learnt on a local ES may also be 450 synchronized across the multi-homing PE devices sharing this ES. 451 This MAC and ARP SYNC enables local switching of intra and inter 452 subnet ECMP traffic flows from remote hosts. In other words, local 453 MAC and ARP entries on a given ES may be learnt via local learning 454 and / or via sync from another PE device sharing the same ES. 456 For a host that is multi-homed to multiple PE devices via an all- 457 active ES interface, local learning of host MAC and MAC-IP at each PE 458 device is an independent asynchronous event, that is dependent on 459 traffic flow and or ARP / ND response from the host hashing to a 460 directly connected PE on the MC-LAG interface. As a result, sequence 461 number mobility attribute value assigned to a locally learnt MAC or 462 MAC-IP route at each device may not always be the same, depending on 463 transient states on the device at the time of local learning. 465 As an example, consider a host VM that is deleted from ESI-2 and 466 moved to ESI-1. It is possible for host to be learnt on say, PE1 467 following deletion of the remote route from [PE3, PE4], while being 468 learnt on PE2 prior to deletion of remote route from [PE3, PE4]. If 469 so, PE1 would process local host route learning as a new route and 470 assign a sequence number of 0, while PE2 would process local host 471 route learning as a remote to local move and assign a sequence number 472 of N+1, N being the existing sequence number assigned at [PE3, PE4]. 474 Inconsistent sequence numbers advertised from multi-homing devices 475 introduces: 477 o Ambiguity with respect to how the remote PEs should handle paths 478 with same ESI and different sequence numbers. A remote PE may not 479 program ECMP paths if it receives routes with different sequence 480 numbers from a set of multi-homing PEs sharing the same ESI. 482 o Breaks consistent route versioning across the network overlay that 483 is needed for EVPN mobility procedures to work. 485 As an example, in this inconsistent state, PE2 would drop a remote 486 route received for the same host with sequence number N (as its local 487 sequence number is N+1), while PE1 would install it as the best route 488 (as its local sequence number is 0). 490 There is need for a mechanism to ensure consistency of sequence 491 numbers advertised from a set of multi-homing devices for EVPN 492 mobility to work reliably. 494 In order to support mobility for multi-homed hosts using the sequence 495 number mobility attribute, local MAC and MAC-IP routes learnt on a 496 multi-homed ES MUST be advertised with the same sequence number by 497 all PE devices that the ES is multi-homed to. There is need for a 498 mechanism to ensure consistency of sequence numbers assigned across 499 these PEs. 501 6. Design Considerations 503 To summarize, sequence number assignment scheme and implementation 504 must take following considerations into account: 506 o MAC+IP may be learnt on an ES multi-homed to multiple PE devices, 507 hence requires sequence numbers to be synchronized across multi- 508 homing PE devices. 510 o MAC only RT-2 is optional in an IRB scenario and may not 511 necessarily be advertised in addition to MAC+IP RT-2. 513 o Single MAC may be associated with multiple IPs, i.e., multiple 514 host IPs may share a common MAC. 516 o Host IP move could result in host moving to a new MAC, resulting 517 in a new IP to MAC association and a new MAC+IP route. 519 o Host MAC move to a new location could result in host MAC being 520 associated with a different IP address, resulting in a new MAC to 521 IP association and a new MAC+IP route. 523 o LOCAL MAC-IP learn via ARP would always accompanied by a LOCAL MAC 524 learn event resulting from the ARP packet. MAC and MAC-IP 525 learning, however, could happen in any order. 527 o Use cases discussed earlier that do not maintain a constant 1:1 528 MAC-IP mapping across moves could potentially be addressed by 529 using separate sequence numbers associated with MAC and IP 530 components of MAC+IP route. Maintaining two separate sequence 531 numbers however adds significant overhead with respect to 532 complexity, debugability, and backward compatibility. Hence, this 533 document addresses these requirements via a single sequence number 534 attribute. 536 7. Solution Components 538 This section goes over main components of the EVPN IRB mobility 539 solution proposed in this draft. Later sections will go over exact 540 sequence number assignment procedures resulting from concepts 541 described in this section. 543 7.1. Sequence Number Inheritance 545 Main idea presented here is to view a LOCAL MAC-IP route as a child 546 of the corresponding LOCAL MAC only route that inherits the sequence 547 number attribute from the parent LOCAL MAC only route: 549 Mx-IPx -----> Mx (seq# = N) 551 As a result, both parent MAC and child MAC-IP routes share one common 552 sequence number associated with the parent MAC route. Doing so 553 ensures that a single sequence number attribute carried in a combined 554 MAC+IP route represents sequence number for both a MAC only route as 555 well as a MAC+IP route, and hence makes the MAC only route truly 556 optional. As a result, optional MAC only route with its own sequence 557 number is not required to establish most recent reachability for a 558 MAC in the overlay network. Specifically, this enables a MAC to 559 assume a different IP address on a move, and still be able to 560 establish most recent reachability to the MAC across the overlay 561 network via mobility attribute associated with the MAC+IP route 562 advertisement. As an example, when Mx moves to a new location, it 563 would result in LOCAL Mx being assigned a higher sequence number at 564 its new location as per RFC 7432. If this move results in Mx 565 assuming a different IP address, IPz, LOCAL Mx+IPz route would 566 inherit the new sequence number from Mx. 568 LOCAL MAC and LOCAL MAC-IP routes would typically be sourced from 569 data plane learning and ARP learning respectively, and could get 570 learnt in control plane in any order. Implementation could either 571 replicate inherited sequence number in each MAC-IP entry OR maintain 572 a single attribute in the parent MAC by creating a forward reference 573 LOCAL MAC object for cases where a LOCAL MAC-IP is learnt before the 574 LOCAL MAC. 576 Arguably, this inheritance may be assumed from RFC 7432, in which 577 case, the above may be interpreted as a clarification with respect to 578 interpretation of a MAC sequence number in a MAC-IP route. 580 7.2. MAC Sharing 582 Further, for the shared MAC scenario, this would result in multiple 583 LOCAL MAC-IP siblings inheriting sequence number attribute from a 584 common parent MAC route: 586 Mx-IP1 ----- 587 | | 588 Mx-IP2 ----- 589 . | 590 . +---> Mx (seq# = N) 591 . | 592 Mx-IPw ----- 593 | | 594 Mx-IPx ----- 596 Figure 4 598 In such a case, a host-IP move to a different physical server would 599 result in IP moving to a new MAC binding. A new MAC-IP route 600 resulting from this move must now be advertised with a sequence 601 number that is higher than the previous MAC-IP route for this IP, 602 advertised from the prior location. As an example, consider a route 603 Mx-IPx that is currently advertised with sequence number N from PE1. 604 IPx moving to a new physical server behind PE2 results in IPx being 605 associated with MAC Mz. A new local Mz-IPx route resulting from this 606 move at PE2 must now be advertised with a sequence number higher than 607 N. This is so that PE devices, including PE1, PE2, and other remote 608 PE devices that are part of the overlay can clearly determine and 609 program the most recent MAC binding and reachability for the IP. 610 PE1, on receiving this new Mz-IPx route with sequence number say, 611 N+1, for symmetric IRB case, would update IPx reachability via PE2 in 612 forwarding, for asymmetric IRB case, would update IPx's ARP binding 613 to Mz. In addition, PE1 would clear and withdraw the stale Mx-IPx 614 route with the lower sequence number. 616 This also implies that sequence number associated with local MAC Mz 617 and all local MAC-IP children of Mz at PE2 must now be incremented to 618 N+1, and re-advertised across the overlay. While this re- 619 advertisement of all local MAC-IP children routes affected by the 620 parent MAC route is an overhead, it avoids the need for two separate 621 sequence number attributes to be maintained and advertised for IP and 622 MAC components of MAC+IP RT-2. Implementation would need to be able 623 to lookup MAC-IP routes for a given IP and update sequence number for 624 it's parent MAC and its MAC-IP children. 626 7.3. Multi-homing Mobility Synchronization 628 In order to support mobility for multi-homed hosts, local MAC and 629 MAC-IP routes learnt on a shared ES MUST be advertised with the same 630 sequence number by all PE devices that the ES is multi-homed to. 631 This also applies to local MAC only routes. LOCAL MAC and MAC-IP may 632 be learnt natively via data plane and ARP/ND respectively as well as 633 via SYNC from another multi-homing PE to achieve local switching. 634 Local and SYNC route learning can happen in any order. Local MAC-IP 635 routes advertised by all multi-homing PE devices sharing the ES must 636 carry the same sequence number, independent of the order in which 637 they are learnt. This implies: 639 o On local or sync MAC-IP route learning, sequence number for the 640 local MAC-IP route MUST be compared and updated to the higher 641 value. 643 o On local or sync MAC route learning, sequence number for the local 644 MAC route MUST be compared and updated to the higher value. 646 If an update to local MAC-IP sequence number is required as a result 647 of above comparison with sync MAC-IP route, it would essentially 648 amount to a sequence number update on the parent local MAC, resulting 649 in inherited sequence number update on the MAC-IP route. 651 8. Requirements for Sequence Number Assignment 653 Following sections summarize sequence number assignment procedure 654 needed on local and sync MAC and MAC-IP route learning events in 655 order to accomplish the above. 657 8.1. LOCAL MAC-IP learning 659 A local Mx-IPx learning via ARP or ND should result in computation OR 660 re-computation of parent MAC Mx's sequence number, following which 661 the MAC-IP route Mx-IPx would simply inherit parent MAC's sequence 662 number. Parent MAC Mx Sequence number should be computed as follows: 664 o MUST be higher than any existing remote MAC route for Mx, as per 665 RFC 7432. 667 o MUST be at least equal to corresponding SYNC MAC sequence number 668 if one is present. 670 o If the IP is also associated with a different remote MAC "Mz", 671 MUST be higher than "Mz" sequence number. 673 Once new sequence number for MAC route Mx is computed as per above, 674 all LOCAL MAC-IPs associated with MAC Mx MUST inherit the updated 675 sequence number. 677 8.2. LOCAL MAC learning 679 Local MAC Mx Sequence number should be computed as follows: 681 o MUST be higher than any existing remote MAC route for Mx, as per 682 RFC 7432. 684 o MUST be at least equal to corresponding SYNC MAC sequence number 685 if one is present. 687 o Once new sequence number for MAC route Mx is computed as per 688 above, all LOCAL MAC-IPs associated with MAC Mx MUST inherit the 689 updated sequence number. 691 Note that the local MAC sequence number might already be present if 692 there was a local MAC-IP learnt prior to the local MAC, in which case 693 the above may not result in any change in local MAC's sequence 694 number. 696 8.3. Remote MAC OR MAC-IP Update 698 On receiving a remote MAC OR MAC-IP route update associated with a 699 MAC Mx with a sequence number that is higher than or equal to 700 sequence number assigned to a LOCAL route for MAC Mx: 702 o PE MUST trigger probe and deletion procedure for all LOCAL IPs 703 associated with MAC Mx. 705 o PE MUST trigger deletion procedure for LOCAL MAC route for Mx. 707 8.4. REMOTE (SYNC) MAC update 709 Corresponding local MAC Mx (if present) sequence number should be re- 710 computed as follows: 712 o If the current sequence number is less than the received SYNC MAC 713 sequence number, it MUST be increased to be equal to received SYNC 714 MAC sequence number. 716 o If a LOCAL MAC sequence number is updated as a result of the 717 above, all LOCAL MAC-IPs associated with MAC Mx MUST inherit the 718 updated sequence number. 720 8.5. REMOTE (SYNC) MAC-IP update 722 If this is a SYNCed MAC-IP on a local ES, it would also result in a 723 derived SYNC MAC Mx route entry, as MAC only RT-2 advertisement is 724 optional. Corresponding local MAC Mx (if present) sequence number 725 should be re-computed as follows: 727 o If the current sequence number is less than the received SYNC MAC 728 sequence number, it MUST be increased to be equal to received SYNC 729 MAC sequence number. 731 o If a LOCAL MAC sequence number is updated as a result of the 732 above, all LOCAL MAC-IPs associated with MAC Mx MUST inherit the 733 updated sequence number. 735 8.6. Inter-op 737 In general, if all PE nodes in the overlay network follow the above 738 sequence number assignment procedure, and the PE is advertising both 739 MAC+IP and MAC routes, sequence number advertised with the MAC and 740 MAC+IP routes with the same MAC would always be the same. However, 741 an inter-op scenario with a different implementation could arise, 742 where a PE implementation non-compliant with this document or with 743 RFC 7432 assigns and advertises independent sequence numbers to MAC 744 and MAC+IP routes. To handle this case, if different sequence 745 numbers are received for remote MAC+IP and corresponding remote MAC 746 routes from a remote PE, sequence number associated with the remote 747 MAC route should be computed as: 749 o Highest of the all received sequence numbers with remote MAC+IP 750 and MAC routes with the same MAC. 752 o MAC sequence number would be re-computed on a MAC or MAC+IP route 753 withdraw as per above. 755 A MAC and / or IP move to the local PE would now result in the MAC 756 (and hence all MAC-IP) sequence numbers incremented from the above 757 computed remote MAC sequence number. 759 8.7. MAC Sharing Race Condition 761 In a MAC sharing use case described in section 6.2, a race condition 762 is possible with simultaneous host moves between a pair of PEs. As 763 an example, consider PE1 with local host IPs I1 and I2 sharing MAC 764 M1, and PE2 with local host IPs I3 and I4 sharing MAC M2. A 765 simultaneous move of I1 from PE1 to PE2 and of I3 from PE2 to PE1, 766 such that I3 is learnt on PE1 before I1's local entry has been probed 767 out on PE1 and/or I1 is learnt on PE2 before I3's local entry has 768 been probed out on PE2 may trigger a race condition. This race 769 condition together with MAC sequence number assignment rules defined 770 in section 7.1 can cause new mac-ip routes [I1, M2] and [I3, M1] to 771 bounce a couple of times with an incremented sequence number until 772 stale entries [I1, M1] and [I3, M2] have been probed out from PE1 and 773 PE2 respectively. An implementation MUST ensure proper probing 774 procedures to remove stale ARP, ND, and local MAC entries, following 775 a move, on learning remote routes as defined in section 7.3 (and as 776 per [EVPN-IRB]) to minimize exposure to this race condition. 778 8.8. Mobility Convergence 780 This sections is to be treated as optional and details ARP and ND 781 probing procedures that MAY be implemented to achieve faster host re- 782 learning and convergence on mobility events. 784 o Following a host move from PE1 to PE2, the host's MAC is 785 discovered at PE2 as a local MAC via a data frames received from 786 the host. If PE2 has a prior REMOTE MAC-IP host route for this 787 MAC from PE1, an ARP/ND probe MAY be triggered at PE2 to learn the 788 MAC-IP as a local adjacency and trigger EVPN RT-2 advertisement 789 for this MAC-IP across the overlay with new reachability via PE2. 790 This results in a reliable "event based" host IP learning 791 triggered by a "MAC learning event" across the overlay, and hence 792 faster convergence of overlay routed flows to the host. 794 o Following a host move from PE1 to PE2, once PE1 receives a MAC or 795 MAC-IP route from PE2 with a higher sequence number, an ARP/ND 796 probe MAY be triggered at PE1 to clear the stale local MAC-IP 797 neighbor adjacency OR re-learn the local MAC-IP in case the host 798 has moved back or is duplicate. 800 o Following a local MAC age-out, if there is a local IP adjacency 801 with this MAC, an ARP/ND probe MAY be triggered for this IP to 802 either re-learn the local MAC and maintain local l3 and l2 803 reachability to this host OR to clear the ARP/ND entry in case the 804 host is indeed no longer local. Note that this accomplishes 805 clearing of stale ARP entries, triggered by a MAC age-out event 806 even when the ARP refresh timer was longer than the MAC age-out 807 timer. Clearing of stale IP neighbor entries in-turn facilitates 808 traffic convergence in the event that the host was silent and not 809 discovered at its new location. Once stale neighbor entry for the 810 host is cleared, routed traffic flow destined for the host can re- 811 trigger ARP/ND discovery for this host at the new location. 813 8.8.1. Generalized Probing Logic 815 Above probing logic may be generalized as probing for an IP neighbor 816 anytime a resolving parent MAC route is "inconsistent" with the MAC- 817 IP neighbor route, where being inconsistent is defined as being not 818 present OR conflicting in terms of the route source being local OR 819 remote. MAC-IP to MAC parent relationship described earlier in this 820 document in section 6.1 MAY be used to achieve this logic. 822 9. Routed Overlay 824 An additional use case is possible, such that traffic to an end host 825 in the overlay is always IP routed. In a purely routed overlay such 826 as this: 828 o A host MAC is never advertised in EVPN overlay control plane. 830 o Host /32 or /128 IP reachability is distributed across the overlay 831 via EVPN route type 5 (RT-5) along with a zero or non- zero ESI. 833 o An overlay IP subnet may still be stretched across the underlay 834 fabric, however, intra-subnet traffic across the stretched overlay 835 is never bridged. 837 o Both inter-subnet and intra-subnet traffic, in the overlay is IP 838 routed at the EVPN PE. 840 Please refer to [RFC 7814] for more details. 842 Host mobility within the stretched subnet would still need to be 843 supported for this use. In the absence of any host MAC routes, 844 sequence number mobility EXT-COMM specified in [RFC7432], section 7.7 845 may be associated with a /32 OR /128 host IP prefix advertised via 846 EVPN route type 5. MAC mobility procedures defined in RFC 7432 can 847 now be applied as is to host IP prefixes: 849 o On LOCAL learning of a host IP, on a new ESI, host IP MUST be 850 advertised with a sequence number attribute that is higher than 851 what is currently advertised with the old ESI. 853 o On receiving a host IP route advertisement with a higher sequence 854 number, a PE MUST trigger ARP/ND probe and deletion procedure on 855 any LOCAL route for that IP with a lower sequence number. A PE 856 would essentially move the forwarding entry to point to the remote 857 route with a higher sequence number and send an ARP/ND PROBE for 858 the local IP route. If the IP has indeed moved, PROBE would 859 timeout and the local IP host route would be deleted. 861 Note that there is still only one sequence number associated with a 862 host route at any time. For earlier use cases where a host MAC is 863 advertised along with the host IP, a sequence number is only 864 associated with a MAC. Only if the MAC is not advertised at all, as 865 in this use case, is a sequence number associated with a host IP. 867 Note that this mobility procedure would not apply to "anycast IPv6" 868 hosts advertised via NA messages with 0-bit=0. Please refer to 869 [EVPN-PROXY-ARP]. 871 10. Duplicate Host Detection 873 Duplicate host detection scenarios across EVPN IRB can be classified 874 as follows: 876 o Scenario A: where two hosts have the same MAC (host IPs may or may 877 not be duplicate). 879 o Scenario B: where two hosts have the same IP but different MACs. 881 o Scenario C: where two hosts have the same IP and host MAC is not 882 advertised at all. 884 Duplicate detection procedures for scenario B and C would not apply 885 to "anycast IPv6" hosts advertised via NA messages with 0-bit=0. 886 Please refer to [EVPN-PROXY-ARP]. 888 10.1. Scenario A 890 For all use cases where duplicate hosts have the same MAC, MAC is 891 detected as duplicate via duplicate MAC detection procedure described 892 in RFC 7432. Corresponding MAC-IP routes with the same MAC do not 893 require duplicate detection and MUST simply inherit the DUPLICATE 894 property from the corresponding MAC route. In other words, if a MAC 895 route is in DUPLICATE state, all corresponding MAC-IP routes MUST 896 also be treated as DUPLICATE. Duplicate detection procedure need 897 only be applied to MAC routes. 899 10.2. Scenario B 901 Due to misconfiguration, a situation may arise where hosts with 902 different MACs are configured with the same IP. This scenario would 903 not be detected by existing duplicate MAC detection procedure and 904 would result in incorrect forwarding of routed traffic destined to 905 this IP. 907 Such a situation, on LOCAL MAC-IP learning, would be detected as a 908 move scenario via the following local MAC sequence number computation 909 procedure described earlier in section 6.1: 911 o If the IP is also associated with a different remote MAC "Mz", 912 MUST be higher than "Mz" sequence number. 914 Such a move that results in sequence number increment on local MAC 915 because of a remote MAC-IP route associated with a different MAC MUST 916 be counted as an "IP move" against the "IP" independent of MAC. 917 Duplicate detection procedure described in RFC 7432 can now be 918 applied to an "IP" entity independent of MAC. Once an IP is detected 919 as DUPLICATE, corresponding MAC-IP route should be treated as 920 DUPLICATE. Associated MAC routes and any other MAC-IP routes 921 associated with this MAC should not be affected. 923 10.2.1. Duplicate IP Detection Procedure for Scenario B 925 Duplicate IP detection procedure for such a scenario is specified in 926 [EVPN-PROXY-ARP]. What counts as an "IP move" in this scenario is 927 further clarified as follows: 929 o On learning a LOCAL MAC-IP route Mx-IPx, check if there is an 930 existing REMOTE OR LOCAL route for IPx with a different MAC 931 association, say, Mz-IPx. If so, count this as an "IP move" count 932 for IPx, independent of the MAC. 934 o On learning a REMOTE MAC-IP route Mz-IPx, check if there is an 935 existing LOCAL route for IPx with a different MAC association, 936 say, Mx-IPx. If so, count this as an "IP move" count for IPx, 937 independent of the MAC. 939 A MAC-IP route SHOULD be treated as DUPLICATE if either of the 940 following two conditions are met: 942 o Corresponding MAC route is marked as DUPLICATE via existing 943 duplicate detection procedure. 945 o Corresponding IP is marked as DUPLICATE via extended procedure 946 described above. 948 10.3. Scenario C 950 For a purely routed overlay scenario described in section 8, where 951 only a host IP is advertised via EVPN RT-5, together with a sequence 952 number mobility attribute, duplicate MAC detection procedures 953 specified in RFC 7432 can be intuitively applied to IP only host 954 routes for the purpose of duplicate IP detection. 956 o On learning a LOCAL host IP route IPx, check if there is an 957 existing REMOTE OR LOCAL route for IPx with a different ESI 958 association. If so, count this as an "IP move" count for IPx. 960 o On learning a REMOTE host IP route IPx, check if there is an 961 existing LOCAL route for IPx with a different ESI association. If 962 so, count this as an "IP move" count for IPx. 964 o With configurable parameters "N" and "M", If "N" IP moves are 965 detected within "M" seconds for IPx, treat IPx as DUPLICATE. 967 10.4. Duplicate Host Recovery 969 Once a MAC or IP is marked as DUPLICATE and FROZEN, corrective action 970 must be taken to un-provision one of the duplicate MAC or IP. Un- 971 provisioning a duplicate MAC or IP in this context refers to a 972 corrective action taken on the host side. Once one of the duplicate 973 MAC or IP is un-provisioned, normal operation would not resume until 974 the duplicate MAC or IP ages out, following this correction, unless 975 additional action is taken to speed up recovery. 977 This section lists possible additional corrective actions that could 978 be taken to achieve faster recovery to normal operation. 980 10.4.1. Route Un-freezing Configuration 982 Unfreezing the DUPLICATE OR FROZEN MAC or IP via a CLI can be 983 leveraged to recover from DUPLICATE and FROZEN state following 984 corrective un-provisioning of the duplicate MAC or IP. 986 Unfreezing the frozen MAC or IP via a CLI at a PE should result in 987 that MAC OR IP being advertised with a sequence number that is higher 988 than the sequence number advertised from the other location of that 989 MAC or IP. 991 Two possible corrective un-provisioning scenarios exist: 993 o Scenario A: A duplicate MAC or IP may have been un-provisioned at 994 the location where it was NOT marked as DUPLICATE and FROZEN. 996 o Scenario B: A duplicate MAC or IP may have been un-provisioned at 997 the location where it was marked as DUPLICATE and FROZEN. 999 Unfreezing the DUPLICATE and FROZEN MAC or IP, following the above 1000 corrective un-provisioning scenarios would result in recovery to 1001 steady state as follows: 1003 o Scenario A: If the duplicate MAC or IP was un-provisioned at the 1004 location where it was NOT marked as DUPLICATE, unfreezing the 1005 route at the FROZEN location will result in the route being 1006 advertised with a higher sequence number. This would in-turn 1007 result in automatic clearing of local route at the PE location, 1008 where the host was un-provisioned via ARP/ND PROBE and DELETE 1009 procedure specified earlier in section 8 and in [RFC 7432]. 1011 o Scenario B: If the duplicate host is un-provisioned at the 1012 location where it was marked as DUPLICATE, unfreezing the route 1013 will trigger an advertisement with a higher sequence number to the 1014 other location. This would in-turn trigger re-learning of local 1015 route at the remote location, resulting in another advertisement 1016 with a higher sequence number from the remote location. Route at 1017 the local location would now be cleared on receiving this remote 1018 route advertisement, following the ARP/ND PROBE. 1020 10.4.2. Route Clearing Configuration 1022 In addition to the above, route clearing CLIs may also be leveraged 1023 to clear the local MAC or IP route, to be executed AFTER the 1024 duplicate host is un-provisioned: 1026 o clear mac CLI: A clear MAC CLI can be leveraged to clear a 1027 DUPLICATE MAC route, to recover from a duplicate MAC scenario. 1029 o clear ARP/ND: A clear ARP/ND CLI may be leveraged to clear a 1030 DUPLICATE IP route to recover from a duplicate IP scenario. 1032 Note that the route unfreeze CLI may still need to be run if the 1033 route was un-provisioned and cleared from the NON-DUPLICATE / NON- 1034 FROZEN location. Given that unfreezing of the route via the un- 1035 freeze CLI would any ways result in auto-clearing of the route from 1036 the "un- provisioned" location, as explained in the prior section, 1037 need for a route clearing CLI for recovery from DUPLICATE / FROZEN 1038 state is truly optional. 1040 11. Security Considerations 1042 This document raises no new security issues for EVPN. 1044 12. IANA Considerations 1046 None. 1048 13. Acknowledgements 1050 Authors would like to thank Vibov Bhan and Patrice Brisset for 1051 feedback the process of design and implementation of procedures 1052 defined in this document. Authors would like to thank Wen Lin for a 1053 detailed review and valuable comments related to MAC sharing race 1054 conditions. 1056 14. Normative References 1058 [EVPN-IRB] 1059 Sajassi, A., Salam, S., Thoria, S., Drake, J., and J. 1060 Rabadan, "Integrated Routing and Bridging in EVPN", draft- 1061 ietf-bess-evpn-inter-subnet-forwarding-13 (work in 1062 progress), February 2021. 1064 [EVPN-PROXY-ARP] 1065 Rabadan, J., Sathappan, S., Nagaraj, K., Hankins, G., and 1066 T. King, "Operational Aspects of Proxy-ARP/ND in EVPN 1067 Networks", draft-ietf-bess-evpn-proxy-arp-nd-11 (work in 1068 progress), Jan 2021. 1070 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1071 Requirement Levels", BCP 14, RFC 2119, 1072 DOI 10.17487/RFC2119, March 1997, 1073 . 1075 [RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A., 1076 Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based 1077 Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February 1078 2015, . 1080 [RFC7814] Xu, X., Jacquenet, C., Raszuk, R., Boyes, T., and B. Fee, 1081 "Virtual Subnet: A BGP/MPLS IP VPN-Based Subnet Extension 1082 Solution", RFC 7814, DOI 10.17487/RFC7814, March 2016, 1083 . 1085 Authors' Addresses 1087 Neeraj Malhotra (editor) 1088 Cisco Systems 1089 170 W. Tasman Drive 1090 San Jose, CA 95134 1091 USA 1093 Email: nmalhotr@cisco.com 1095 Ali Sajassi 1096 Cisco Systems 1097 170 W. Tasman Drive 1098 San Jose, CA 95134 1099 USA 1101 Email: sajassi@cisco.com 1103 Aparna Pattekar 1104 Cisco Systems 1105 170 W. Tasman Drive 1106 San Jose, CA 95134 1107 USA 1109 Email: apjoshi@cisco.com 1111 Jorge Rabadan 1112 Nokia 1113 777 E. Middlefield Road 1114 Mountain View, CA 94043 1115 USA 1117 Email: jorge.rabadan@nokia.com 1119 Avinash Lingala 1120 ATT 1121 200 S. Laurel Avenue 1122 Middletown, CA 07748 1123 USA 1125 Email: ar977m@att.com 1126 John Drake 1127 Juniper Networks 1129 Email: jdrake@juniper.net