# Gunter Van de Velde, RTG AD, comments for draft-ietf-bess-evpn-irb-extended-mobility-17
Many thanks to Donald Eastlake for his Early RTGDIR review for draft-ietf-bess-evpn-irb-extended-mobility-10. The review improved the document quality. The enhancements to the document have been resolved to satisfaction according https://mailarchive.ietf.org/arch/msg/bess/ZAqF_aVRjbYi9H2hs6SgeZVU2-8/ Thanks to Stephane Litkowski for his detailed Shepherd write-up. The document technical content seems complete, although it was not always easy to process. I tried to proposed alternate textblobs to improve readability while trying to keep the original message content. During this review process i noted observations when something was not clear and needed potentially clarification or correction. Great success to learn that there are at least 2 implementations of the draft #issues #====== # This document is not mentioning SRv6 anywhere. Is that the intent? If yes, then maybe that should be explicit mentioned early in the document. # figure 3 seems to be missing some components: PE3, PE4 and ESI-2? # The abstract seems overly detailed. Please consider the suggested alternate abstract, higher level and more generic, with focus upon detailing more abstract the objective of draft-ietf-bess-evpn-irb-extended-mobility-17 #DETAILED COMMENTS #================= ##classified as [minor] and [major] and [re-edit] 17 Abstract 19 The procedure to handle host mobility in a layer 2 Network with EVPN 20 control plane is defined as part of RFC7432. 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 RFC7432 are extensible to 24 IRB use cases if a fixed 1:1 mapping between host IP and MAC is 25 assumed across host moves. Generic mobility support for IP and MAC 26 addresses that allows these bindings to change across moves IS 27 REQUIRED to support a broader set of EVPN IRB use cases. EVPN all- 28 active multi-homing further introduces scenarios that require 29 additional consideration from mobility perspective. This document 30 enumerates a set of design considerations applicable to mobility 31 across these EVPN IRB use cases and updates sequence number 32 assignment procedures defined in RFC7432 to address these IRB use 33 cases. [major] This abstract is very detailed and makes it hard to understand on a high level what exactly the content of the draft is all about. I view upon a abstract as the textblob one gives to your people manager to make him/het understand what the document is all about. What about the following abstract textblob proposal, making high level draft intent better understandable for non-EVPN technology wizards " This document specifies extensions to RFC7432 Ethernet VPN (EVPN) Integrated Routing and Bridging (IRB) procedures to enhance the mobility mechanisms for EVPN IRB-based networks. The proposed extensions improve the handling of IP address mobility across EVPN networks by introducing a mechanism to track the movement of IP addresses and ensure seamless forwarding. These enhancements address the limitations in the existing EVPN IRB mobility procedures by providing more efficient and scalable solutions. The extensions are backward compatible with existing EVPN IRB implementations and aim to optimize network performance in scenarios involving frequent IP address mobility. " 127 1. Introduction 128 129 EVPN-IRB enables advertising both MAC and IP routes via a single 130 MAC+IP RT-2 advertisement. The MAC address is imported into the 131 local bridge MAC table and enables L2 bridged traffic across the 132 network overlay. The IP address is imported into the local ARP table 133 in an asymmetric IRB design or imported into the IP routing table in 134 a symmetric IRB design, and enables routed traffic across the layer 2 135 network overlay. Please refer to [RFC9135] for more background on 136 EVPN IRB forwarding modes. [re-edit] EVPN-IRB facilitates the advertisement of both MAC and IP routes via a single MAC+IP Route Type 2 (RT-2) advertisement. The MAC address is integrated into the local bridge MAC table, enabling Layer 2 (L2) bridged traffic across the network overlay. The IP address is incorporated into the local ARP table in an asymmetric IRB design, or into the IP routing table in a symmetric IRB design, facilitating routed traffic across the L2 network overlay. For additional context on EVPN IRB forwarding modes, refer to [RFC9135]. 138 To support EVPN mobility procedure, a single sequence number mobility 139 attribute is advertised with the combined MAC+IP route. A single 140 sequence number advertised with the combined MAC+IP route to resolve 141 both MAC and IP reachability implicitly assumes a 1:1 fixed mapping 142 between IP and MAC. While a fixed 1:1 mapping between IP and MAC is 143 a common use case that is addressed via existing MAC mobility 144 procedure defined in [RFC7432], additional IRB scenarios need to be 145 considered, that don't necessarily adhere to this assumption. Such 146 use cases are common in a virtualized host environment where hosts 147 attached to an EVPN network are virtual machines (VM) or 148 containerized workloads. Following IRB mobility scenarios are 149 considered: 150 151 * VM move results in VM IP and MAC moving together 152 153 * VM move results in VM IP moving to a new MAC association 154 155 * VM move results in VM MAC moving to a new IP association [re-edit] To support the EVPN mobility procedure, a single sequence number mobility attribute is advertised with the combined MAC+IP route. This approach, which resolves both MAC and IP reachability with a single sequence number, inherently assumes a fixed 1:1 mapping between IP and MAC. While this fixed 1:1 mapping is a common use case and is addressed via the existing MAC mobility procedure defined in [RFC7432], there are additional IRB scenarios that do not adhere to this assumption. Such scenarios are prevalent in virtualized host environments where hosts connected to an EVPN network are virtual machines (VMs) or containerized workloads. The following IRB mobility scenarios are considered: * A VM move results in the VM's IP and MAC moving together. * A VM move results in the VM's IP moving to a new MAC association. * A VM move results in the VM's MAC moving to a new IP association. 157 While existing MAC mobility procedure can be used for MAC+IP move in 158 the first scenario, subsequent scenarios result in a new MAC- IP 159 association. As a result, a single sequence number assigned 160 independently per-{MAC, IP} is not sufficient to determine most 161 recent reachability for both MAC and IP, unless the sequence number 162 assignment algorithm allows for changing MAC-IP bindings across 163 moves. 163 165 This document updates sequence number assignment procedures defined 166 in [RFC7432] to adequately address mobility support across EVPN-IRB 167 overlay use cases that allow MAC-IP bindings to change across VM 168 moves and can support mobility for both MAC and IP components carried 169 in an EVPN RT-2 for these use cases. [re-edit] While the existing MAC mobility procedure can manage the MAC+IP move in the first scenario, the subsequent scenarios lead to new MAC-IP associations. Therefore, a single sequence number assigned independently per-{MAC, IP} is insufficient to determine the most recent reachability for both MAC and IP unless the sequence number assignment algorithm allows for changing MAC-IP bindings across moves. This document updates the sequence number assignment procedures defined in [RFC7432] to adequately address mobility support across EVPN-IRB overlay use cases that permit MAC-IP bindings to change across VM moves and support mobility for both MAC and IP components carried in an EVPN RT-2 for these use cases. 171 In addition, for hosts on an ESI multi-homed to multiple PE devices, 172 additional procedures are specified to ensure synchronized sequence 173 number assignments across the multi-homing devices. 174 175 This document covers mobility for the following cases, independent of 176 the overlay encapsulation (e.g.: MPLS, NVO Tunnel): 177 178 * Symmetric EVPN IRB overlay 179 180 * Asymmetric EVPN IRB overlay 181 182 * Routed EVPN overlay [re-edit] Additionally, for hosts on an ESI multi-homed to multiple PE devices, additional procedures are specified to ensure synchronized sequence number assignments across the multi-homing devices. This document addresses mobility for the following cases, independent of the overlay encapsulation (e.g., MPLS, NVO Tunnel): * Symmetric EVPN IRB overlay * Asymmetric EVPN IRB overlay * Routed EVPN overlay 184 1.1. Document Structure 185 186 Following sections of the document are informative: 187 188 * section 3 provides the necessary background and problem statement 189 being addressed in this document. 190 191 * section 4 lists the resulting design considerations for the 192 document. 193 194 Following sections of the document are normative: 195 196 * section 6 describes the mobility and sequence number assigment 197 procedures in an EVPN-IRB overlay required to address the 198 scenarios described in section 4. 199 200 * section 7 describes the mobility procedures for a routed overlay 201 network as opposed to an IRB overlay. 202 203 * section 8 describes corresponding duplicate detection procedures 204 for EVPN-IRB and routed overlays. [minor] What about section 5? it exists in the draft. I assume the intent is informational 217 * Underlay: IP or MPLS fabric core network that provides IP or MPLS 218 routed reachability between EVPN PEs. [major] Is SRv6 intentionally missing from this list? 220 * Overlay: VPN or service layer network consisting of EVPN PEs OR 221 VPN provider-edge (PE) switch-router devices that runs on top of 222 an underlay routed core. [major] I believe that this is ambigious terminology. add RFC references to the base RFC that documents each type of overlay PE 233 * Symmetric EVPN-IRB: An overlay fabric first-hop routing 234 architecture as defined in [RFC9135], wherein, overlay host-to- 235 host routed inter-subnet flows are routed at both ingress and 236 egress EVPN PEs. [re-edit] Symmetric EVPN-IRB: is a specific design approach used in EVPN-based networks [RFC9135] to handle both Layer 2 (L2) and Layer 3 (L3) forwarding within the same network infrastructure. The key characteristic of symmetric EVPN-IRB is that both ingress and egress PE routers perform routing for inter-subnet traffic. 238 * Asymmetric EVPN-IRB: An overlay fabric first-hop routing 239 architecture as defined in [RFC9135], wherein, overlay host-to- 240 host routed inter-subnet flows are routed and bridged at ingress 241 PE and bridged at egress PEs. [re-edit] Asymmetric EVPN-IRB: is a design approach used in EVPN-based networks [RFC9135] to handle Layer 2 (L2) and Layer 3 (L3) forwarding. In this approach, only the ingress Provider Edge (PE) router performs routing for inter-subnet traffic, while the egress PE router performs bridging. 248 * Ethernet-Segment: physical Ethernet or LAG port that connects an 249 access device to an EVPN PE, as defined in [RFC7432]. [minor] s/physical Ethernet/Physical ethernet/ 251 * EVPN all-active multi-homing: PE-CE all-active multi-homing 252 achieved via a multi-homed layer-2 LAG interface on a CE with 253 member links to multiple PEs and related EVPN procedures on the 254 PEs. [re-edit] EVPN all-active multi-homing: is a redundancy and load-sharing mechanism used in EVPN networks. This method allows multiple PE devices to simultaneously provide Layer 2 and Layer 3 connectivity to a single CE device or network segment. 256 * RT-2: EVPN route type 2 carrying both MAC and IP reachability. 257 258 * RT-5: EVPN route type 5 carrying IP prefix reachability. [minor] add references to RFC7432 260 * MAC-IP: IP association for a MAC, referred to in this document may 261 be IPv4, IPv6 or both. [minor] Is this specified in a document somewhere, or is this explicit to this document itself? 263 * SYNC MAC route: In the context of EVPN multi-homing, this refers 264 to a local MAC route SYNCed from another PE sharing the same ESI. 265 266 * SYNC MAC-IP route: In the context of EVPN multi-homing, this 267 refers to a local MAC-IP route SYNCed from another PE sharing the 268 same ESI. 269 270 * SYNC MAC sequence number: In the context of EVPN multi-homing, 271 this refers to sequence number received with a SYNC MAC route. 272 273 * SYNC MAC-IP sequence number: In the context of EVPN multi-homing, 274 this refers to sequence number received with a SYNC MAC-IP route. [minor] Is the SYNC something outlined in this draft itself, or is this procedure specified in another document? I assume this is based upon the priciples of RFC7432 using the MAC Mobility Extended Community 279 3.1. Optional MAC only RT-2 280 281 In an EVPN IRB scenario, where a single MAC+IP RT-2 advertisement 282 carries both IP and MAC routes, a MAC only RT-2 advertisement is 283 redundant for host MACs that are advertised via MAC+IP RT-2. As a 284 result, advertisement of a local MAC only RT-2 is an optional at an 285 EVPN PE. This is an important consideration for mobility scenarios 286 discussed in subsequent sections. Note that a local MAC and its 287 assigned sequence number is still maintained locally on a PE, and it 288 is just the advertisement of this route to other PEs that is 289 optional. 291 MAC only RT-2 may still be advertised for non-IP host MACs that are 292 not advertised via MAC+IP RT-2. [re-edit] In an EVPN IRB scenario, where a single MAC+IP RT-2 advertisement carries both IP and MAC routes, a MAC-only RT-2 advertisement becomes redundant for host MACs already advertised via MAC+IP RT-2. Consequently, the advertisement of a local MAC-only RT-2 is optional at an EVPN PE. This consideration is important for mobility scenarios discussed in subsequent sections. It is noteworthy that a local MAC and its assigned sequence number are still maintained locally on a PE, and only the advertisement of this route to other PEs is optional. MAC-only RT-2 advertisements may still be issued for non-IP host MACs that are not included in MAC+IP RT-2 advertisements. 294 3.2. Mobility Use Cases 295 296 This section describes the IRB mobility use cases considered in this 297 document. Procedures to address them are covered later in section 6 298 and section 7. 299 300 * Host move results in Host IP and MAC moving together 301 302 * Host move results in Host IP moving to a new MAC association 303 304 * Host move results in Host MAC moving to a new IP association [re-edit] This section outlines the IRB mobility use cases addressed in this document. Detailed procedures to handle these scenarios are provided in Sections 6 and 7. * A host move results in both the host's IP and MAC addresses moving together. * A host move results in the host's IP address moving to a new MAC address association. * A host move results in the host's MAC address moving to a new IP address association. 306 3.2.1. Host MAC+IP Move 307 308 This is the baseline case, wherein a host move results in both host 309 MAC and IP moving together with no change in MAC-IP binding across a 310 move. Existing MAC mobility defined in [RFC7432] may be leveraged to 311 apply to corresponding MAC+IP route to support this mobility 312 scenario. 313 314 3.2.2. Host IP Move to new MAC 315 316 This is the case, where a host move results in VM IP moving to a new 317 MAC binding. 318 319 3.2.2.1. VM Reload 320 321 A host reload or an orchestrated host move that results in a host 322 being re-spawned at a new location may result in host getting a new 323 MAC assignment, while maintaining its existing IP address. This 324 results in a host IP move to a new MAC binding: 325 326 IP-a, MAC-a ---> IP-a, MAC-b 327 328 3.2.2.2. MAC Sharing 329 330 This takes into account scenarios, where multiple hosts, each with a 331 unique IP, may share a common MAC binding, and a host move results in 332 a new MAC binding for the host IP. 333 334 As an example, hosts running on a single physical server, each with a 335 unique IP, may share the same physical server MAC. In yet another 336 scenario, an L2 access network may be behind a firewall, such that 337 all hosts IPs on the access network are learnt with a common firewall 338 MAC. In all such "shared MAC" use cases, multiple local MAC-IP ARP 339 entries may be learnt with the same MAC. A host IP move, in such 340 scenarios (for example, to a new physical server), could result in 341 new MAC association for the host IP. 342 343 3.2.2.3. Problem 344 345 In both of the above scenarios, a combined MAC+IP EVPN RT-2 346 advertised with a single sequence number attribute implicitly assumes 347 a fixed IP to MAC mapping. A host IP move to a new MAC breaks this 348 assumption and results in a new MAC+IP route. If this new MAC+IP 349 route is independently assigned a new sequence number, the sequence 350 number can no longer be used to determine most recent host IP 351 reachability in a symmetric EVPN-IRB design OR the most recent IP to 352 MAC binding in an asymmetric EVPN-IRB design. 353 354 +------------------------+ 355 | Underlay Network Fabric| 356 +------------------------+ 358 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 359 | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | 360 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 361 \ / \ / \ / 362 \ ESI-1 / \ ESI-2 / \ ESI-3 / 363 \ / \ / \ / 364 +\---/+ +\---/+ +\---/+ 365 | \ / | | \ / | | \ / | 366 +--+--+ +--+--+ +--+--+ 367 | | | 368 Server-M1 Server-M2 Server-M3 369 | | | 370 VM-IP1, VM-IP2 VM-IP3, VM-IP4 VM-IP5, VM-IP6 371 372 Figure 1 373 374 As an example, consider a topology shown in Figure 1, with host VMs 375 sharing the physical server MAC. In steady state, IP1-M1 route is 376 learnt at PE1, PE2 and advertised to remote PEs with a sequence 377 number N. Now, VM-IP1 is moved to MAC Server-M2. ARP or ND based 378 local learning at PE3, PE4 would now result in a new IP1-M2 route 379 being learnt. If route IP1-M2 is learnt as a new MAC+IP route and 380 assigned a new sequence number of say 0, mobility procedure for VM- 381 IP1 will not trigger across the overlay network. 382 383 A sequence number assignment procedure needs to be defined to 384 unambiguously determine the most recent IP reachability, IP to MAC 385 binding, and MAC reachability for such a MAC sharing scenario. [re-edit] 3.2.1. Host MAC+IP Move This is the baseline scenario where a host move results in both the host's MAC and IP addresses moving together without altering the MAC-IP binding. The existing MAC mobility procedures defined in [RFC7432] can be leveraged to support this MAC+IP mobility scenario. 3.2.2. Host IP Move to a New MAC This scenario involves a host move where the host's IP address is reassigned to a new MAC address. 3.2.2.1. VM Reload A host reload or orchestrated move may cause a host to be re-spawned at a new location, resulting in a new MAC assignment while retaining the existing IP address. This results in the host's IP moving to a new MAC binding, as shown below: IP-a, MAC-a ---> IP-a, MAC-b 3.2.2.2. MAC Sharing This scenario considers cases where multiple hosts, each with a unique IP address, share a common MAC address. A host move results in a new MAC binding for the host IP. For example, hosts running on a single physical server might share the same MAC. Alternatively, an L2 access network behind a firewall may have all host IPs learned with a common firewall MAC. In these "shared MAC" scenarios, multiple local MAC-IP ARP entries may be learned with the same MAC. A host IP move to a new physical server could result in a new MAC association for the host IP. 3.2.2.3. Problem In the aforementioned scenarios, a combined MAC+IP EVPN RT-2 advertised with a single sequence number attribute assumes a fixed IP-to-MAC mapping. A host IP move to a new MAC breaks this assumption and results in a new MAC+IP route. If this new route is independently assigned a new sequence number, the sequence number can no longer determine the most recent host IP reachability in a symmetric EVPN-IRB design or the most recent IP-to-MAC binding in an asymmetric EVPN-IRB design. +------------------------+ | Underlay Network Fabric| +------------------------+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ \ / \ / \ / \ ESI-1 / \ ESI-2 / \ ESI-3 / \ / \ / \ / +\---/+ +\---/+ +\---/+ | \ / | | \ / | | \ / | +--+--+ +--+--+ +--+--+ | | | Server-M1 Server-M2 Server-M3 | | | VM-IP1, VM-IP2 VM-IP3, VM-IP4 VM-IP5, VM-IP6 Figure 1 Figure 1 illustrates a topology with host VMs sharing the physical server MAC. In steady state, the IP1-M1 route is learned at PE1 and PE2 and advertised to remote PEs with a sequence number N. If VM-IP1 moves to Server-M2, ARP or ND-based local learning at PE3 and PE4 would result in a new IP1-M2 route. If this new route is assigned a sequence number of 0, the mobility procedure for VM-IP1 will not trigger across the overlay network. A sequence number assignment procedure must be defined to unambiguously determine the most recent IP reachability, IP-to-MAC binding, and MAC reachability for such MAC sharing scenarios. 387 3.2.3. Host MAC move to new IP 388 389 This is a scenario where a host move or re-provisioning behind a new 390 gateway location may result in the host getting a new IP address 391 assigned, while keeping the same MAC. 392 393 3.2.3.1. Problem 394 395 The complication with this scenario is that MAC reachability could be 396 carried via a combined MAC+IP route while a MAC only route may not be 397 advertised at all. A single sequence number association with the 398 MAC+IP route again implicitly assumes a fixed mapping between MAC and 399 IP. A MAC move resulting in a new IP association for the host MAC 400 breaks this assumption and results in a new MAC+IP route. If this 401 new MAC+IP route independently assumes a new sequence number, this 402 mobility attribute can no longer be used to determine the most recent 403 host MAC reachability. 404 405 +------------------------+ 406 | Underlay Network Fabric| 407 +------------------------+ 408 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 409 | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | 410 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 411 \ / \ / \ / 412 \ ESI-1 / \ ESI-2 / \ ESI-3 / 413 \ / \ / \ / 414 +\---/+ +\---/+ +\---/+ 415 | \ / | | \ / | | \ / | 416 +--+--+ +--+--+ +--+--+ 417 | | | 418 Server1 Server2 Server3 419 | | | 420 VM-IP1-M1, VM-IP2-M2 VM-IP3-M3, VM-IP4-M4 VM-IP5-M5, VM-IP6-M6 421 Figure 2 422 423 As an example, consider a host VM IP1-M1 that is learnt locally at 424 PE1, PE2 and advertised to remote hosts with a sequence number N. 425 Consider a scenario where this VM with MAC M1 is re-provisioned at 426 server 2, however, as part of this re-provisioning, assigned a 427 different IP address say IP7. IP7-M1 is learnt as a new route at 428 PE3, PE4 and advertised to remote PEs with a sequence number of 0. 429 As a result, L3 reachability to IP7 would be established across the 430 overlay, however, MAC mobility procedure for M1 will not trigger as a 431 result of this MAC-IP route advertisement. If an optional MAC only 432 route is also advertised, sequence number associated with the MAC 433 only route would trigger MAC mobility as per [RFC7432]. However, in 434 the absence of an additional MAC only route advertisement, a single 435 sequence number advertised with a combined MAC+IP route may not be 436 sufficient to update MAC reachability across the overlay. 437 438 A MAC-IP sequence number assignment procedure needs to be defined to 439 unambiguously determine the most recent MAC reachability in such a 440 scenario without a MAC only route being advertised. 441 442 Further, PE1/PE2, on learning new reachability for IP7-M1 via PE3/PE4 443 MUST probe and delete any local IPs associated with MAC M1, such as 444 IP1-M1 in the above example. 445 446 Arguably, MAC mobility sequence number defined in [RFC7432], could be 447 interpreted to apply only to the MAC part of MAC-IP route, and would 448 hence cover this scenario. This interpretation could be considered a 449 clarification to [RFC7432] and one of the reasons for the common 450 sequence number assignment procedure across all MAC-IP mobility 451 scenarios detailed in this document. [re-edit] 3.2.3. Host MAC move to new IP The complication in this scenario arises because MAC reachability can be carried via a combined MAC+IP route, whereas a MAC-only route may not be advertised. Associating a single sequence number with the MAC+IP route implicitly assumes a fixed MAC-to-IP mapping. A MAC move that results in a new IP association breaks this assumption and creates a new MAC+IP route. If this new route independently receives a new sequence number, the sequence number can no longer reliably indicate the most recent host MAC reachability. +------------------------+ | Underlay Network Fabric| +------------------------+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ \ / \ / \ / \ ESI-1 / \ ESI-2 / \ ESI-3 / \ / \ / \ / +\---/+ +\---/+ +\---/+ | \ / | | \ / | | \ / | +--+--+ +--+--+ +--+--+ | | | Server1 Server2 Server3 | | | VM-IP1-M1, VM-IP2-M2 VM-IP3-M3, VM-IP4-M4 VM-IP5-M5, VM-IP6-M6 Figure 2 For instance, consider host VM IP1-M1 learned locally at PE1 and PE2 and advertised to remote hosts with sequence number N. If this VM with MAC M1 is re-provisioned at Server2 and assigned a different IP address (e.g., IP7), the new IP7-M1 route learned at PE3 and PE4 would be advertised with sequence number 0. Consequently, L3 reachability to IP7 would be established across the overlay, but the MAC mobility procedure for M1 would not trigger due to the new MAC-IP route advertisement. Advertising an optional MAC-only route with its sequence number would trigger MAC mobility per [RFC7432]. However, without this additional advertisement, a single sequence number associated with a combined MAC+IP route may be insufficient to update MAC reachability across the overlay. A MAC-IP sequence number assignment procedure is required to unambiguously determine the most recent MAC reachability in such scenarios without advertising a MAC-only route. Furthermore, PE1 and PE2, upon learning new reachability for IP7-M1 via PE3 and PE4, must probe and delete any local IPs associated with MAC M1, such as IP1-M1. It could be argued that the MAC mobility sequence number defined in [RFC7432] applies only to the MAC part of a MAC-IP route, thus covering this scenario. This interpretation could serve as a clarification to [RFC7432] and supports the need for a common sequence number assignment procedure across all MAC-IP mobility scenarios detailed in this document. 453 3.3. EVPN All Active multi-homed ES 454 +------------------------+ 455 | Underlay Network Fabric| 456 +------------------------+ 457 458 +-----+ +-----+ 459 | PE1 | | PE2 | 460 +-----+ +-----+ 461 \\ // 462 \\ ESI-1 // 463 \\ /X 464 +\\---//+ 465 | \\ // | 466 +---+---+ 467 | 468 CE1 469 470 Figure 3 471 472 Consider an EVPN-IRB overlay network shown in Figure 2, with hosts 473 multi-homed to two or more PE devices via an all-active multi-homed 474 ES. MAC and ARP entries learnt on a local ES may also be 475 synchronized across the multi-homing PE devices sharing this ES. 476 This MAC and ARP SYNC enables local switching of intra and inter 477 subnet ECMP traffic flows from remote hosts. In other words, local 478 MAC and ARP entries on a given ES may be learnt via local learning 479 and / or via sync from another PE device sharing the same ES. 480 481 For a host that is multi-homed to multiple PE devices via an all- 482 active ES interface, local learning of host MAC and MAC-IP at each PE 483 device is an independent asynchronous event, that is dependent on 484 traffic flow and or ARP / ND response from the host hashing to a 485 directly connected PE on the MC-LAG interface. As a result, sequence 486 number mobility attribute value assigned to a locally learnt MAC or 487 MAC-IP route at each device may not always be the same, depending on 488 transient states on the device at the time of local learning. 489 490 As an example, consider a host VM that is deleted from ESI-2 and 491 moved to ESI-1. It is possible for host to be learnt on PE1 492 following deletion of the remote route from PE3, PE4, while being 493 learnt on PE2 prior to deletion of remote route from PE3, PE4. If 494 so, PE1 would process local host route learning as a new route and 495 assign a sequence number of 0, while PE2 would process local host 496 route learning as a remote to local move and assign a sequence number 497 of N+1, N being the existing sequence number assigned at PE3, PE4. 498 499 Inconsistent sequence numbers advertised from multi-homing devices 500 introduces: 501 502 * Ambiguity with respect to how the remote PEs should handle paths 503 with same ESI and different sequence numbers. A remote PE might 504 not program ECMP paths if it receives routes with different 505 sequence numbers from a set of multi-homing PEs sharing the same 506 ESI. 507 508 * Breaks consistent route versioning across the network overlay that 509 is needed for EVPN mobility procedures to work. 510 511 As an example, in this inconsistent state, PE2 would drop a remote 512 route received for the same host with sequence number N (as its local 513 sequence number is N+1), while PE1 would install it as the best route 514 (as its local sequence number is 0). 515 516 There is need for a mechanism to ensure consistency of sequence 517 numbers advertised from a set of multi-homing devices for EVPN 518 mobility to work reliably. 519 520 In order to support mobility for multi-homed hosts using the sequence 521 number mobility attribute, local MAC and MAC-IP routes learnt on a 522 multi-homed ES MUST be advertised with the same sequence number by 523 all PE devices that the ES is multi-homed to. There is need for a 524 mechanism to ensure consistency of sequence numbers assigned across 525 these PEs. [major] * The text talks about PE3 and PE4 and about ESI-2, but the figure does not show this. Can figure be corrected to show these components? This will make it more clear how inconsistency with sequence numbers manifests. [minor] unsure why in thi informational section in the last paragraph uppercase MUST is used. BCP14 language does not apply to informational textblobs [re-edit] 3.3. EVPN All Active multi-homed ES +------------------------+ | Underlay Network Fabric| +------------------------+ +-----+ +-----+ | PE1 | | PE2 | +-----+ +-----+ \\ // \\ ESI-1 // \\ /X +\\---//+ | \\ // | +---+---+ | CE1 Figure 3 Consider an EVPN-IRB overlay network illustrated in Figure 3, where hosts are multi-homed to two or more PE devices via an all-active multi-homed ES. MAC and ARP entries learned on a local ES may also be synchronized across the multi-homing PE devices sharing this ES. This synchronization enables local switching of intra- and inter-subnet ECMP traffic flows from remote hosts. Thus, local MAC and ARP entries on a given ES may be learned through local learning and/or synchronization from another PE device sharing the same ES. For a host that is multi-homed to multiple PE devices via an all-active ES interface, the local learning of host MAC and MAC-IP at each PE device is an independent asynchronous event, dependent on traffic flow or ARP/ND response from the host hashing to a directly connected PE on the MC-LAG interface. Consequently, the sequence number mobility attribute value assigned to a locally learned MAC or MAC-IP route at each device may not always be the same, depending on transient states on the device at the time of local learning. For example, consider a host VM that is deleted from ESI-2 and moved to ESI-1. It is possible for the host to be learned on PE1 following the deletion of the remote route from PE3 and PE4, while being learned on PE2 prior to the deletion of the remote route from PE3 and PE4. In this case, PE1 would process local host route learning as a new route and assign a sequence number of 0, while PE2 would process local host route learning as a remote-to-local move and assign a sequence number of N+1, where N is the existing sequence number assigned at PE3 and PE4. Inconsistent sequence numbers advertised from multi-homing devices introduce: * Ambiguity regarding how remote PEs should handle paths with the same ESI but different sequence numbers. A remote PE might not program ECMP paths if it receives routes with different sequence numbers from a set of multi-homing PEs sharing the same ESI. * Disruption of consistent route versioning across the network overlay, which is necessary for EVPN mobility procedures to function correctly. For instance, in this inconsistent state, PE2 would drop a remote route received for the same host with sequence number N (since its local sequence number is N+1), while PE1 would install it as the best route (since its local sequence number is 0). To support mobility for multi-homed hosts using the sequence number mobility attribute, local MAC and MAC-IP routes learned on a multi-homed ES must be advertised with the same sequence number by all PE devices to which the ES is multi-homed. There is a need for a mechanism to ensure the consistency of sequence numbers assigned across these PEs. 527 4. Design Considerations 528 529 To summarize, sequence number assignment scheme and implementation 530 must take following considerations into account: 531 532 * MAC+IP may be learnt on an ES multi-homed to multiple PE devices, 533 hence requires sequence numbers to be synchronized across multi- 534 homing PE devices. 535 536 * MAC only RT-2 is optional in an IRB scenario and may not 537 necessarily be advertised in addition to MAC+IP RT-2. 538 539 * A single MAC may be associated with multiple IPs, i.e., multiple 540 host IPs may share a common MAC. 541 542 * A host IP move could result in host moving to a new MAC, resulting 543 in a new IP to MAC association and a new MAC+IP route. 544 545 * A host MAC move to a new location could result in host MAC being 546 associated with a different IP address, resulting in a new MAC to 547 IP association and a new MAC+IP route. 548 549 * Local MAC-IP learn via ARP would always accompanied by a local MAC 550 learn event resulting from the ARP packet. MAC and MAC-IP 551 learning, however, could happen in any order. 552 553 * Use cases discussed earlier that do not maintain a constant 1:1 554 MAC-IP mapping across moves could potentially be addressed by 555 using separate sequence numbers associated with MAC and IP 556 components of MAC+IP route. Maintaining two separate sequence 557 numbers however adds significant overhead with respect to 558 complexity, debugability, and backward compatibility. Hence, this 559 document addresses these requirements via a single sequence number 560 attribute. [re-edit] To summarize, the sequence number assignment scheme and implementation must consider the following: * Synchronization Across Multi-Homing PE Devices: MAC+IP may be learned on an ES multi-homed to multiple PE devices, requiring synchronized sequence numbers across these devices. * Optional MAC-Only RT-2: In an IRB scenario, MAC-only RT-2 is optional and may not be advertised alongside MAC+IP RT-2. * Multiple IPs Associated with a Single MAC: A single MAC may be linked to multiple IP addresses, indicating multiple host IPs sharing a common MAC. * Host IP Movement: A host IP move may result in a new MAC association, necessitating a new IP to MAC association and a new MAC+IP route. * Host MAC Movement: A host MAC move may result in a new IP association, requiring a new MAC to IP association and a new MAC+IP route. * Local MAC-IP Learning via ARP: Local MAC-IP learning via ARP always accompanies a local MAC learning event resulting from the ARP packet. However, MAC and MAC-IP learning can occur in any order. * Separate Sequence Numbers for MAC and IP: Use cases that do not maintain a constant 1:1 MAC-IP mapping across moves could potentially be addressed by using separate sequence numbers for MAC and IP components of the MAC+IP route. However, maintaining two separate sequence numbers adds significant complexity, debugging challenges, and backward compatibility issues. Therefore, this document addresses these requirements using a single sequence number attribute. 562 5. Solution Components 563 564 This section goes over the main components of the EVPN IRB mobility 565 solution specified in this document. Later sections will specify 566 exact sequence number assignment procedures resulting from concepts 567 described in this section. 568 569 5.1. Sequence Number Inheritance 570 571 The main idea presented here is to view a local MAC-IP route as a 572 child of the corresponding local MAC route within the local context 573 of a PE, such that the local MAC-IP route inherits the sequence 574 number attribute from the parent local MAC only route: 575 576 Mx-IPx -----> Mx (seq# = N) 578 578 As a result, both parent MAC and child MAC-IP routes share one common 579 sequence number associated with the parent MAC route. Doing so 580 ensures that a single sequence number attribute carried in a combined 581 MAC+IP route represents sequence number for both a MAC only route as 582 well as a MAC+IP route, and hence makes advertisement of the MAC only 583 route truly optional. As a result, optional MAC only route with its 584 own sequence number is not required to establish the most recent 585 reachability for a MAC in the overlay network. Specifically, this 586 enables a MAC to assume a different IP address on a move, and still 587 be able to establish the most recent reachability to the MAC across 588 the overlay network via the mobility attribute associated with the 589 MAC+IP route advertisement. As an example, when Mx moves to a new 590 location, it would result in local Mx being assigned a higher 591 sequence number at its new location as per [RFC7432]. If this move 592 results in Mx assuming a different IP address, IPz, local Mx+IPz 593 route would inherit the new sequence number from Mx. 594 595 Local MAC and local MAC-IP routes would typically be sourced from 596 data plane learning and ARP learning respectively, and could get 597 learnt in the control plane in any order. Implementation could 598 either replicate the inherited sequence number in each MAC-IP entry 599 OR maintain a single attribute in the parent MAC by creating a 600 forward reference local MAC object for cases where a local MAC-IP is 601 learnt before the local MAC. 602 603 5.2. MAC Sharing 605 Further, for the shared MAC scenario, this results in multiple local 606 MAC-IP siblings inheriting a sequence number attribute from the 607 common parent MAC route: 608 609 Mx-IP1 ----- 610 | | 611 Mx-IP2 ----- 612 . | 613 . +---> Mx (seq# = N) 614 . | 615 Mx-IPw ----- 616 | | 617 Mx-IPx ----- 627 619 Figure 4 620 621 In such a case, a host-IP move to a different physical server would 622 result in IP moving to a new MAC binding. A new MAC-IP route 623 resulting from this move must now be advertised with a sequence 624 number that is higher than the previous MAC-IP route for this IP, 625 advertised from the prior location. As an example, consider a route 626 Mx-IPx that is currently advertised with sequence number N from PE1. 627 IPx moving to a new physical server behind PE2 results in IPx being 628 associated with MAC Mz. A new local Mz-IPx route resulting from this 629 move at PE2 must now be advertised with a sequence number higher than 630 N and higher than the previous Mz sequence number M. This is so that 631 PE devices, including PE1, PE2, and other remote PE devices that are 632 part of the overlay can clearly determine and program the most recent 633 MAC binding and reachability for the IP. PE1, on receiving this new 634 Mz-IPx route with sequence number say, N+1, for symmetric IRB case, 635 would update IPx reachability via PE2 in forwarding, for asymmetric 636 IRB case, would update IPx's ARP binding to Mz. In addition, PE1 637 would clear and withdraw the stale Mx-IPx route with the lower 638 sequence number. 639 640 This also implies that sequence number associated with local MAC Mz 641 and all local MAC-IP children of Mz at PE2 must now be incremented to 642 N+1 or to M+1 if the previous Mz sequence number M is greater than N, 643 and re-advertised across the overlay. While this re-advertisement of 644 all local MAC-IP children routes affected by the parent MAC route is 645 an overhead, it avoids the need for two separate sequence number 646 attributes to be maintained and advertised for IP and MAC components 647 of MAC+IP RT-2. Implementation would need to be able to lookup MAC- 648 IP routes for a given IP and update sequence number for it's parent 649 MAC and its MAC-IP children. 650 651 5.3. Multi-homing Mobility Synchronization 652 653 In order to support mobility for multi-homed hosts, local MAC and 654 MAC-IP routes learnt on a shared ES MUST be advertised with the same 655 sequence number by all PE devices that the ES is multi-homed to. 656 This also applies to local MAC only routes. local MAC and MAC-IP may 657 be learnt natively via data plane and ARP/ND respectively as well as 658 via SYNC from another multi-homing PE to achieve local switching. 659 Local and SYNC route learning can happen in any order. Local MAC-IP 660 routes advertised by all multi-homing PE devices sharing the ES must 661 carry the same sequence number, independent of the order in which 662 they are learnt. This implies: 663 664 * On local or SYNC MAC-IP route learning, sequence number for the 665 local MAC-IP route MUST be compared and updated to the higher 666 value. 667 668 * On local or SYNC MAC route learning, sequence number for the local 669 MAC route MUST be compared and updated to the higher value. 670 671 If an update to local MAC-IP sequence number is required as a result 672 of the above comparison with SYNC MAC-IP route, it would essentially 673 amount to a sequence number update on the parent local MAC, resulting 674 in inherited sequence number update on the MAC-IP route. [major] * is the arrow used in the small figure correct? Should it not be the other way around if the sequence number is inherited? w.o.w. Mx (seq# = N) -----> Mx-IPx ? * similar with the other figure in section 5.2 [re-edit] 5. Solution Components This section outlines the main components of the EVPN IRB mobility solution specified in this document. Subsequent sections will detail the exact sequence number assignment procedures based on the concepts described here. 5.1. Sequence Number Inheritance The key concept presented here is to treat a local MAC-IP route as a child of the corresponding local MAC route within the local context of a PE. This ensures that the local MAC-IP route inherits the sequence number attribute from the parent local MAC-only route: Mx-IPx -----> Mx (seq# = N) Thus, both the parent MAC and child MAC-IP routes share a common sequence number associated with the parent MAC route. This ensures that a single sequence number attribute carried in a combined MAC+IP route represents the sequence number for both a MAC-only route and a MAC+IP route, making the advertisement of the MAC-only route truly optional. This enables a MAC to assume a different IP address upon moving and still establish the most recent reachability to the MAC across the overlay network via the mobility attribute associated with the MAC+IP route advertisement. For instance, when Mx moves to a new location, it would be assigned a higher sequence number at its new location per [RFC7432]. If this move results in Mx assuming a different IP address, IPz, the local Mx+IPz route would inherit the new sequence number from Mx. Local MAC and local MAC-IP routes are typically sourced from data plane learning and ARP learning, respectively, and can be learned in the control plane in any order. Implementation can either replicate the inherited sequence number in each MAC-IP entry or maintain a single attribute in the parent MAC by creating a forward reference local MAC object for cases where a local MAC-IP is learned before the local MAC. 5.2. MAC Sharing For the shared MAC scenario, multiple local MAC-IP siblings inherit the sequence number attribute from the common parent MAC route: Mx-IP1 ----- | | Mx-IP2 ----- . | . +---> Mx (seq# = N) . | Mx-IPw ----- | | Mx-IPx ----- In such cases, a host-IP move to a different physical server results in the IP moving to a new MAC binding. A new MAC-IP route resulting from this move must be advertised with a sequence number higher than the previous MAC-IP route for this IP, advertised from the prior location. For example, consider a route Mx-IPx currently advertised with sequence number N from PE1. If IPx moves to a new physical server behind PE2 and is associated with MAC Mz, the new local Mz-IPx route must be advertised with a sequence number higher than N and the previous Mz sequence number M. This allows PE devices, including PE1, PE2, and other remote PE devices, to determine and program the most recent MAC binding and reachability for the IP. PE1, upon receiving this new Mz-IPx route with sequence number N+1, would update IPx reachability via PE2 for symmetric IRB and update IPx's ARP binding to Mz for asymmetric IRB, while clearing and withdrawing the stale Mx-IPx route with the lower sequence number. This implies that the sequence number associated with local MAC Mz and all local MAC-IP children of Mz at PE2 must be incremented to N+1 or M+1 if the previous Mz sequence number M is greater than N and re-advertised across the overlay. While this re-advertisement of all local MAC-IP children routes affected by the parent MAC route adds overhead, it avoids the need for maintaining and advertising two separate sequence number attributes for IP and MAC components of MAC+IP RT-2. Implementation must be able to look up MAC-IP routes for a given IP and update the sequence number for its parent MAC and its MAC-IP children. 5.3. Multi-Homing Mobility Synchronization To support mobility for multi-homed hosts, local MAC and MAC-IP routes learned on a shared ES must be advertised with the same sequence number by all PE devices to which the ES is multi-homed. This applies to local MAC-only routes as well. Local MAC and MAC-IP may be learned natively via data plane and ARP/ND respectively, as well as via SYNC from another multi-homing PE to achieve local switching. Local and SYNC route learning can occur in any order. Local MAC-IP routes advertised by all multi-homing PE devices sharing the ES must carry the same sequence number, independent of the order in which they are learned. This implies: * On local or SYNC MAC-IP route learning, the sequence number for the local MAC-IP route must be compared and updated to the higher value. * On local or SYNC MAC route learning, the sequence number for the local MAC route must be compared and updated to the higher value. If an update to the local MAC-IP sequence number is required as a result of the comparison with the SYNC MAC-IP route, it essentially amounts to a sequence number update on the parent local MAC, resulting in an inherited sequence number update on the MAC-IP route. 676 6. Requirements for Sequence Number Assignment 677 678 Following sections specify sequence number assignment procedure 679 needed on local and SYNC MAC and MAC-IP route learning events in 680 order to accomplish the above. 681 682 6.1. Local MAC-IP learning 683 684 A local Mx-IPx learning via ARP or ND should result in computation OR 685 re-computation of the parent MAC Mx's sequence number, following 686 which the MAC-IP route Mx-IPx would simply inherit parent MAC's 687 sequence number. The parent MAC Mx Sequence number MUST be computed 688 as follows: 689 690 * MUST be higher than any existing remote MAC route for Mx, as per 691 [RFC7432]. 692 693 * MUST be at least equal to corresponding SYNC MAC sequence number 694 if one is present. 695 696 * If the IP is also associated with a different remote MAC "Mz", 697 MUST be higher than the "Mz" sequence number. 698 699 Once the new sequence number for MAC route Mx is computed as per 700 above, all local MAC-IPs associated with MAC Mx MUST inherit the 701 updated sequence number. 702 703 6.2. Local MAC learning 704 705 The local MAC Mx Sequence number MUST be computed as follows: 705 707 * MUST be higher than any existing remote MAC route for Mx, as per 708 [RFC7432]. 709 710 * MUST be at least equal to the corresponding SYNC MAC sequence 711 number if one is present. 712 713 * Once the new sequence number for MAC route Mx is computed as per 714 above, all local MAC-IPs associated with MAC Mx MUST inherit the 715 updated sequence number. 716 717 Note that the local MAC sequence number might already be present if 718 there was a local MAC-IP learnt prior to the local MAC, in which case 719 the above may not result in any change in local MAC's sequence 720 number. 721 722 6.3. Remote MAC or MAC-IP Update 723 724 On receiving a remote MAC OR MAC-IP route update associated with a 725 MAC Mx with a sequence number that is 726 727 * either higher than the sequence number assigned to a local route 728 for MAC Mx, 729 730 * or equal to the sequence number assigned to a local route for MAC 731 Mx, but the remote route is selected as best because of lower VTEP 732 IP as per [RFC7432], 733 734 following handling IS REQUIRED on the receiving PE: 735 736 * the PE MUST trigger probe and deletion procedure for all local IPs 737 associated with MAC Mx. 738 739 * the PE MUST trigger deletion procedure for local MAC route for Mx. 740 741 6.4. REMOTE (SYNC) MAC update 742 743 On receiving a REMOTE SYNC, the corresponding local MAC Mx (if 744 present) sequence number should be re- computed as follows: 745 746 * If the current sequence number is less than the received SYNC MAC 747 sequence number, it MUST be increased to be equal to received SYNC 748 MAC sequence number. 749 750 * If a local MAC sequence number is updated as a result of the 751 above, all local MAC-IPs associated with MAC Mx MUST inherit the 752 updated sequence number. 753 754 6.5. REMOTE (SYNC) MAC-IP update 755 756 Receiving a SYNC MAC-IP for a locally attached host results in a 757 derived SYNC MAC Mx route entry, as MAC only RT-2 advertisement is 758 optional. The corresponding local MAC Mx (if present) sequence 759 number should be re-computed as follows: 760 761 * If the current sequence number is less than the received SYNC MAC 762 sequence number, it MUST be increased to be equal to received SYNC 763 MAC sequence number. 764 765 * If a local MAC sequence number is updated as a result of the 766 above, all local MAC-IPs associated with MAC Mx MUST inherit the 767 updated sequence number. 768 769 6.6. Interoperability 770 771 In general, if all PE nodes in the overlay network follow the above 772 sequence number assignment procedures, and the PE is advertising both 773 MAC+IP and MAC routes, sequence numbers advertised with the MAC and 774 MAC+IP routes with the same MAC would always be the same. However, 775 an inter-op scenario with a different implementation could arise, 776 where a PE implementation non-compliant with this document or with 777 [RFC7432] assigns and advertises independent sequence numbers to MAC 778 and MAC+IP routes. To handle this case, if different sequence 779 numbers are received for remote MAC+IP and corresponding remote MAC 780 routes from a remote PE, sequence number associated with the remote 781 MAC route MUST be computed as: 782 783 * Highest of all the received sequence numbers with remote MAC+IP 784 and MAC routes with the same MAC. 785 786 * MAC sequence number would be re-computed on a MAC or MAC+IP route 787 withdraw as per above. 788 789 A MAC and / or IP move to the local PE would now result in the MAC 790 (and hence all MAC-IP) sequence numbers being incremented from the 791 above computed remote MAC sequence number. 792 793 If MAC only routes are not advertised at all, and different sequence 794 numbers are received with multiple MAC+IP routes for a given MAC, the 795 sequence number associated with the derived remote MAC route should 796 still be computed as the highest of all of the received MAC+IP 797 sequence numbers with the same MAC. 798 799 6.7. MAC Sharing Race Condition 800 801 In a MAC sharing use case described in section 5.2, a race condition 802 is possible with simultaneous host moves between a pair of PEs. As 803 an example, consider PE1 with local host IPs I1 and I2 sharing MAC 804 M1, and PE2 with local host IPs I3 and I4 sharing MAC M2. A 805 simultaneous move of I1 from PE1 to PE2 and of I3 from PE2 to PE1, 806 such that I3 is learnt on PE1 before I1's local entry has been probed 807 out on PE1 and/or I1 is learnt on PE2 before I3's local entry has 808 been probed out on PE2 may trigger a race condition. This race 809 condition together with MAC sequence number assignment rules defined 810 in section 6.1 can cause new mac-ip routes I1-M2 and I3-M1 to bounce 811 a couple of times with an incremented sequence number until stale 812 entries I1-M1 and I3-M2 have been probed out from PE1 and PE2 813 respectively. An implementation MUST ensure proper probing 814 procedures to remove stale ARP, ND, and local MAC entries, following 815 a move, on learning remote routes as defined in section 6.3 (and as 816 per [RFC9135]) to minimize exposure to this race condition. 817 818 6.8. Mobility Convergence 819 820 This sections is optional and details ARP and ND probing procedures 821 that MAY be implemented to achieve faster host re- learning and 822 convergence on mobility events. 822 824 * Following a host move from PE1 to PE2, the host's MAC is 825 discovered at PE2 as a local MAC via a data frames received from 826 the host. If PE2 has a prior remote MAC-IP host route for this 827 MAC from PE1, an ARP/ND probe MAY be triggered at PE2 to learn the 828 MAC-IP as a local adjacency and trigger EVPN RT-2 advertisement 829 for this MAC-IP across the overlay with new reachability via PE2. 830 This results in a reliable "event based" host IP learning 831 triggered by a "MAC learning event" across the overlay, and hence 832 faster convergence of overlay routed flows to the host. 833 834 * Following a host move from PE1 to PE2, once PE1 receives a MAC or 835 MAC-IP route from PE2 with a higher sequence number, an ARP/ND 836 probe MAY be triggered at PE1 to clear the stale local MAC-IP 837 neighbor adjacency or to re-learn the local MAC-IP in case the 838 host has moved back or is duplicate. 838 840 * Following a local MAC age-out, if there is a local IP adjacency 841 with this MAC, an ARP/ND probe MAY be triggered for this IP to 842 either re-learn the local MAC and maintain local l3 and l2 843 reachability to this host or to clear the ARP/ND entry in case the 844 host is indeed no longer local. Note that this accomplishes 845 clearance of stale ARP entries, triggered by a MAC age-out event 846 even when the ARP refresh timer was longer than the MAC age-out 847 timer. Clearing of stale IP neighbor entries in-turn facilitates 848 traffic convergence in the event that the host was silent and not 849 discovered at its new location. Once the stale neighbor entry for 850 the host is cleared, routed traffic flow destined for the host can 851 re-trigger ARP/ND discovery for this host at the new location. 852 853 6.8.1. Generalized Probing Logic 854 855 The above probing logic may be generalized as probing for an IP 856 neighbor anytime a resolving parent MAC route is "inconsistent" with 857 the MAC- IP neighbor route, where being inconsistent is defined as 858 being not present or conflicting in terms of the route source being 859 local OR remote. The MAC-IP to MAC parent relationship described 860 earlier in this document in section 5.1 MAY be used to achieve this 861 logic. [major] * for my own understanding: in section 6.2 first bullet point, make me wonder if the connected ESI is share between two PEs. Would the requirement potentially lead to a count to infinity when two PEs connect to a shared ESI? * section 6.6: How would an implementation detect that the remote implementation does not support the behavior? Could that be explicit explained in the text? * section 6.7: THis section i did not understand. Too many moving parts. Can this be explained more explicit or elaborative? * section 6.8: What network figure is referenced towards? [re-edit] 6. Requirements for Sequence Number Assignment The following sections specify the sequence number assignment procedures required for local and SYNC MAC and MAC-IP route learning events to achieve the objectives outlined. 6.1. Local MAC-IP Learning A local Mx-IPx learning via ARP or ND should result in the computation or re-computation of the parent MAC Mx's sequence number, following which the MAC-IP route Mx-IPx inherits the parent MAC's sequence number. The parent MAC Mx sequence number MUST be computed as follows: * MUST be higher than any existing remote MAC route for Mx, as per [RFC7432]. * MUST be at least equal to the corresponding SYNC MAC sequence number, if present. * If the IP is also associated with a different remote MAC "Mz," it MUST be higher than the "Mz" sequence number. Once the new sequence number for MAC route Mx is computed as per the above criteria, all local MAC-IPs associated with MAC Mx MUST inherit the updated sequence number. 6.2. Local MAC Learning The local MAC Mx sequence number MUST be computed as follows: * MUST be higher than any existing remote MAC route for Mx, as per [RFC7432]. * MUST be at least equal to the corresponding SYNC MAC sequence number, if present. Once the new sequence number for MAC route Mx is computed as per the above criteria, all local MAC-IPs associated with MAC Mx MUST inherit the updated sequence number. Note that the local MAC sequence number might already be present if there was a local MAC-IP learned prior to the local MAC, in which case the above may not result in any change in the local MAC's sequence number. 6.3. Remote MAC or MAC-IP Update Upon receiving a remote MAC or MAC-IP route update associated with a MAC Mx with a sequence number that is: * Either higher than the sequence number assigned to a local route for MAC Mx, * Or equal to the sequence number assigned to a local route for MAC Mx, but the remote route is selected as best due to a lower VTEP IP as per [RFC7432], the following actions are REQUIRED on the receiving PE: * The PE MUST trigger a probe and deletion procedure for all local IPs associated with MAC Mx. * The PE MUST trigger a deletion procedure for the local MAC route for Mx. 6.4. REMOTE (SYNC) MAC Update Upon receiving a REMOTE SYNC, the corresponding local MAC Mx (if present) sequence number should be re-computed as follows: * If the current sequence number is less than the received SYNC MAC sequence number, it MUST be increased to be equal to the received SYNC MAC sequence number. * If a local MAC sequence number is updated as a result of the above, all local MAC-IPs associated with MAC Mx MUST inherit the updated sequence number. 6.5. REMOTE (SYNC) MAC-IP Update Receiving a SYNC MAC-IP for a locally attached host results in a derived SYNC MAC Mx route entry, as the MAC-only RT-2 advertisement is optional. The corresponding local MAC Mx (if present) sequence number should be re-computed as follows: * If the current sequence number is less than the received SYNC MAC sequence number, it MUST be increased to be equal to the received SYNC MAC sequence number. * If a local MAC sequence number is updated as a result of the above, all local MAC-IPs associated with MAC Mx MUST inherit the updated sequence number. 6.6. Interoperability Generally, if all PE nodes in the overlay network follow the above sequence number assignment procedures and the PE is advertising both MAC+IP and MAC routes, the sequence numbers advertised with the MAC and MAC+IP routes with the same MAC would always be the same. However, an interoperability scenario with a different implementation could arise, where a non-compliant PE implementation assigns and advertises independent sequence numbers to MAC and MAC+IP routes. To handle this case, if different sequence numbers are received for remote MAC+IP and corresponding remote MAC routes from a remote PE, the sequence number associated with the remote MAC route MUST be computed as: * The highest of all received sequence numbers with remote MAC+IP and MAC routes with the same MAC. * The MAC sequence number would be re-computed on a MAC or MAC+IP route withdraw as per the above. A MAC and/or IP move to the local PE would then result in the MAC (and hence all MAC-IP) sequence numbers being incremented from the above computed remote MAC sequence number. If MAC-only routes are not advertised at all, and different sequence numbers are received with multiple MAC+IP routes for a given MAC, the sequence number associated with the derived remote MAC route should still be computed as the highest of all received MAC+IP sequence numbers with the same MAC. 6.7. MAC Sharing Race Condition ************************************************************* ****This section i was not able to process and understand**** ************************************************************* In a MAC sharing use case described in section 5.2, a race condition is possible with simultaneous host moves between a pair of PEs. As an example, consider PE1 with local host IPs I1 and I2 sharing MAC M1, and PE2 with local host IPs I3 and I4 sharing MAC M2. A simultaneous move of I1 from PE1 to PE2 and of I3 from PE2 to PE1, such that I3 is learnt on PE1 before I1's local entry has been probed out on PE1 and/or I1 is learnt on PE2 before I3's local entry has been probed out on PE2 may trigger a race condition. This race condition together with MAC sequence number assignment rules defined in section 6.1 can cause new mac-ip routes I1-M2 and I3-M1 to bounce a couple of times with an incremented sequence number until stale entries I1-M1 and I3-M2 have been probed out from PE1 and PE2 respectively. An implementation MUST ensure proper probing procedures to remove stale ARP, ND, and local MAC entries, following a move, on learning remote routes as defined in section 6.3 (and as per [RFC9135]) to minimize exposure to this race condition. 6.8. Mobility Convergence This section is optional and details ARP and ND probing procedures that MAY be implemented to achieve faster host re-learning and convergence on mobility events. * Following a host move from PE1 to PE2, the host's MAC is discovered at PE2 as a local MAC via data frames received from the host. If PE2 has a prior remote MAC-IP host route for this MAC from PE1, an ARP/ND probe MAY be triggered at PE2 to learn the MAC-IP as a local adjacency and trigger EVPN RT-2 advertisement for this MAC-IP across the overlay with new reachability via PE2. This results in a reliable "event-based" host IP learning triggered by a "MAC learning event" across the overlay, and hence faster convergence of overlay routed flows to the host. * Following a host move from PE1 to PE2, once PE1 receives a MAC or MAC-IP route from PE2 with a higher sequence number, an ARP/ND probe MAY be triggered at PE1 to clear the stale local MAC-IP neighbor adjacency or to re-learn the local MAC-IP in case the host has moved back or is duplicated. * Following a local MAC age-out, if there is a local IP adjacency with this MAC, an ARP/ND probe MAY be triggered for this IP to either re-learn the local MAC and maintain local L3 and L2 reachability to this host or to clear the ARP/ND entry if the host is no longer local. This accomplishes the clearance of stale ARP entries triggered by a MAC age-out event even when the ARP refresh timer is longer than the MAC age-out timer. Clearing stale IP neighbor entries facilitates traffic convergence if the host was silent and not discovered at its new location. Once the stale neighbor entry for the host is cleared, routed traffic flow destined for the host can re-trigger ARP/ND discovery for this host at the new location. 6.8.1. Generalized Probing Logic The above probing logic may be generalized as probing for an IP neighbor anytime a resolving parent MAC route is inconsistent with the MAC-IP neighbor route, where inconsistency is defined as being not present or conflicting in terms of the route source being local or remote. The MAC-IP to MAC parent relationship described in section 5.1 MAY be used to achieve this logic. 863 7. Routed Overlay 864 865 An additional use case is possible, such that traffic to an end host 866 in the overlay is always IP routed. In a purely routed overlay such 867 as this: 868 869 * A host MAC is never advertised in the EVPN overlay control plane. 870 871 * Host /32 or /128 IP reachability is distributed across the overlay 872 via EVPN route type 5 (RT-5) along with a zero or non- zero ESI. 873 874 * An overlay IP subnet may still be stretched across the underlay 875 fabric, however, intra-subnet traffic across the stretched overlay 876 is never bridged. 877 878 * Both inter-subnet and intra-subnet traffic, in the overlay is IP 879 routed at the EVPN PE. 880 881 Please refer to [RFC7814] for more details. 882 883 Host mobility within the stretched subnet would still need to be 884 supported for this use. In the absence of any host MAC routes, 885 sequence number mobility Extended Community specified in [RFC7432], 886 section 7.7 may be associated with a /32 OR /128 host IP prefix 887 advertised via EVPN route type 5. MAC mobility procedures defined in 888 [RFC7432] can now be applied as is to host IP prefixes: 889 890 * On local learning of a host IP, on a new ESI, the host IP MUST be 891 advertised with a sequence number attribute that is higher than 892 what is currently advertised with the old ESI. 893 894 * On receiving a host IP route advertisement with a higher sequence 895 number, a PE MUST trigger ARP/ND probe and deletion procedures on 896 any local route for that IP with a lower sequence number. A PE 897 would essentially move the forwarding entry to point to the remote 898 route with a higher sequence number and send an ARP/ND PROBE for 899 the local IP route. If the IP has indeed moved, PROBE would 900 timeout and the local IP host route would be deleted. 901 902 Note that there is still only one sequence number associated with a 903 host route at any time. For earlier use cases where a host MAC is 904 advertised along with the host IP, a sequence number is only 905 associated with a MAC. Only if the MAC is not advertised at all, as 906 in this use case, is a sequence number associated with a host IP. 907 908 Note that this mobility procedure would not apply to "anycast IPv6" 909 hosts advertised via NA messages with 0-bit=0. Please refer to 910 [RFC9161]. [major] * Unsure what purpose of 0-bit=0 is and where it is explained in RFC9161. Some explicit reference and explanation could help the draft [re-edit] 7. Routed Overlay An additional use case involves traffic to an end host in the overlay being entirely IP routed. In such a purely routed overlay: * A host MAC is never advertised in the EVPN overlay control plane. * Host /32 or /128 IP reachability is distributed across the overlay via EVPN Route Type 5 (RT-5) along with a zero or non-zero ESI. * An overlay IP subnet may still be stretched across the underlay fabric; however, intra-subnet traffic across the stretched overlay is never bridged. * Both inter-subnet and intra-subnet traffic in the overlay is IP routed at the EVPN PE. Refer to [RFC7814] for more details. Host mobility within the stretched subnet still needs support. In the absence of host MAC routes, the sequence number mobility Extended Community specified in [RFC7432], section 7.7, MAY be associated with a /32 or /128 host IP prefix advertised via EVPN Route Type 5. MAC mobility procedures defined in [RFC7432] can be applied to host IP prefixes as follows: * On local learning of a host IP on a new ESI, the host IP MUST be advertised with a sequence number higher than what is currently advertised with the old ESI. * On receiving a host IP route advertisement with a higher sequence number, a PE MUST trigger ARP/ND probe and deletion procedures on any local route for that IP with a lower sequence number. The PE will update the forwarding entry to point to the remote route with a higher sequence number and send an ARP/ND probe for the local IP route. If the IP has moved, the probe will time out, and the local IP host route will be deleted. Note that there is only one sequence number associated with a host route at any time. For previous use cases where a host MAC is advertised along with the host IP, a sequence number is only associated with the MAC. If the MAC is not advertised, as in this use case, a sequence number is associated with the host IP. This mobility procedure does not apply to "anycast IPv6" hosts advertised via NA messages with 0-bit=0. Refer to [RFC9161] for more details. 912 8. Duplicate Host Detection 913 914 Duplicate host detection scenarios across EVPN IRB can be classified 915 as follows: 916 917 * Scenario A: where two hosts have the same MAC (host IPs may or may 918 not be duplicate). 919 920 * Scenario B: where two hosts have the same IP but different MACs. 920 922 * Scenario C: where two hosts have the same IP and host MAC is not 923 advertised at all. 924 925 Duplicate detection procedures for scenario B and C would not apply 926 to "anycast IPv6" hosts advertised via NA messages with 0-bit=0. 927 Please refer to [RFC9161]. 928 929 8.1. Scenario A 920 931 For all use cases where duplicate hosts have the same MAC, the MAC is 932 detected as duplicate via the duplicate MAC detection procedure 933 described in [RFC7432]. Corresponding MAC-IP routes with the same 934 MAC do not require duplicate detection and MUST simply inherit the 935 duplicate property from the corresponding MAC route. In other words, 936 if a MAC route is in duplicate state, all corresponding MAC-IP routes 937 MUST also be treated as duplicate. Duplicate detection procedure 938 need only be applied to MAC routes. 939 940 8.2. Scenario B 941 942 Due to misconfiguration, a situation may arise where hosts with 943 different MACs are configured with the same IP. This scenario would 944 not be detected by [RFC7432] duplicate MAC detection procedures and 945 would result in incorrect forwarding of routed traffic destined to 946 this IP. 947 948 Such a situation, on local MAC-IP learning, would be detected as a 949 move scenario via the following local MAC sequence number computation 950 procedure described earlier in section 6.1: 951 952 * If the IP is also associated with a different remote MAC "Mz", 953 MUST be higher than "Mz" sequence number. 954 955 Such a move that results in sequence number increment on local MAC 956 because of a remote MAC-IP route associated with a different MAC MUST 957 be counted as an "IP move" against the "IP" independent of the MAC. 958 Duplicate detection procedure described in [RFC7432] can now be 959 applied to an "IP" entity independent of MAC. Once an IP is detected 960 as duplicate, corresponding MAC-IP route should be treated as 961 duplicate. Associated MAC routes and any other MAC-IP routes 962 associated with this MAC should not be affected. 963 964 8.2.1. Duplicate IP Detection Procedure for Scenario B 065 966 The duplicate IP detection procedure for such a scenario are 967 specified in [RFC9161]. What counts as an "IP move" in this scenario 968 is further clarified as follows: 969 970 * On learning a local MAC-IP route Mx-IPx, check if there is an 971 existing remote or local route for IPx with a different MAC 972 association, say, Mz-IPx. If so, count this as an "IP move" count 973 for IPx, independent of the MAC. 974 975 * On learning a remote MAC-IP route Mz-IPx, check if there is an 976 existing local route for IPx with a different MAC association, 977 say, Mx-IPx. If so, count this as an "IP move" count for IPx, 978 independent of the MAC. 979 980 A MAC-IP route SHOULD be treated as duplicate if either of the 981 following two conditions are met: 982 983 * The corresponding MAC route is marked as duplicate via existing 984 duplicate detection procedure. 985 986 * The corresponding IP is marked as duplicate via extended procedure 987 described above. 988 989 8.3. Scenario C 990 991 For a purely routed overlay scenario described in section 7, where 992 only a host IP is advertised via EVPN RT-5, together with a sequence 993 number mobility attribute, duplicate MAC detection procedures 994 specified in [RFC7432] can be intuitively applied to IP only host 995 routes for the purpose of duplicate IP detection. 996 997 * On learning a local host IP route IPx, check if there is an 998 existing remote or local route for IPx with a different ESI 999 association. If so, count this as an "IP move" count for IPx. 1000 1001 * On learning a remote host IP route IPx, check if there is an 1002 existing local route for IPx with a different ESI association. If 1003 so, count this as an "IP move" count for IPx. 1004 1005 * With configurable parameters "N" and "M", if "N" IP moves are 1006 detected within "M" seconds for IPx, treat IPx as duplicate. 1007 1008 8.4. Duplicate Host Recovery 1009 1010 Once a MAC or IP is marked as duplicate and frozen, corrective action 1011 must be taken to un-provision one of the duplicate MAC or IP. Un- 1012 provisioning a duplicate MAC or IP in this context refers to a 1013 corrective action taken on the host side. Once one of the duplicate 1014 MAC or IP is un-provisioned, normal operation would not resume until 1015 the duplicate MAC or IP ages out, following this correction, unless 1016 additional action is taken to speed up recovery. 1017 1018 This section lists possible additional corrective actions that could 1019 be taken to achieve faster recovery to normal operation. 1020 1021 8.4.1. Route Un-freezing Configuration 1022 1023 Unfreezing the duplicate or frozen MAC or IP via a CLI can be used to 1024 recover from duplicate and frozen state following corrective un- 1025 provisioning of the duplicate MAC or IP. 1026 1027 Unfreezing the frozen MAC or IP via a CLI at a PE should result in 1028 that MAC or IP being advertised with a sequence number that is higher 1029 than the sequence number advertised from the other location of that 1030 MAC or IP. 1031 1032 Two possible corrective un-provisioning scenarios exist: 1033 1034 * Scenario A: A duplicate MAC or IP may have been un-provisioned at 1035 the location where it was NOT marked as duplicate and frozen. 1036 1037 * Scenario B: A duplicate MAC or IP may have been un-provisioned at 1038 the location where it was marked as duplicate and frozen. 1039 1040 Unfreezing the duplicate and frozen MAC or IP, following the above 1041 corrective un-provisioning scenarios would result in recovery to 1042 steady state as follows: 1043 1044 * Scenario A: If the duplicate MAC or IP was un-provisioned at the 1045 location where it was NOT marked as duplicate, unfreezing the 1046 route at the frozen location will result in the route being 1047 advertised with a higher sequence number. This would in-turn 1048 result in automatic clearing of local route at the PE location, 1049 where the host was un-provisioned via ARP/ND PROBE and DELETE 1050 procedure specified earlier in section 6 and in [RFC7432]. 1051 1052 * Scenario B: If the duplicate host is un-provisioned at the 1053 location where it was marked as duplicate, unfreezing the route 1054 will trigger an advertisement with a higher sequence number to the 1055 other location. This would in-turn trigger re-learning of local 1056 route at the remote location, resulting in another advertisement 1057 with a higher sequence number from the remote location. Route at 1058 the local location would now be cleared on receiving this remote 1059 route advertisement, following the ARP/ND PROBE. 1060 1061 Note that the probes referred to in the above scenarios are event 1062 driven probes resulting from receiving a route with a higher sequence 1063 number. Periodic probes resulting from refresh timers may also occur 1064 in addition as completely independent probes. 1065 1066 8.4.2. Route Clearing Configuration 1067 1068 In addition to the above, route clearing CLIs may also be used to 1069 clear the local MAC or IP route, to be executed AFTER the duplicate 1070 host is un-provisioned: 1071 1072 * clear MAC CLI: A clear MAC CLI can be used to clear a duplicate 1073 MAC route, to recover from a duplicate MAC scenario. 1074 1075 * clear ARP/ND: A clear ARP/ND CLI may be used to clear a duplicate 1076 IP route to recover from a duplicate IP scenario. 1077 1078 Note that the route unfreeze CLI may still need to be run if the 1079 route was un-provisioned and cleared from the non-duplicate / non- 1080 frozen location. Given that unfreezing of the route via the un- 1081 freeze CLI would any ways result in auto-clearing of the route from 1082 the "un- provisioned" location, as explained in the prior section, 1083 need for a route clearing CLI for recovery from duplicate / frozen 1084 state is truly optional. [major] * what is the 0-bit=0? please add a specific reference [re-edit] 8. Duplicate Host Detection Duplicate host detection scenarios across EVPN IRB can be classified as follows: * Scenario A: Two hosts have the same MAC address (host IPs may or may not be duplicates). * Scenario B: Two hosts have the same IP address but different MAC addresses. * Scenario C: Two hosts have the same IP address, and the host MAC is not advertised. Duplicate detection procedures for Scenarios B and C do not apply to "anycast IPv6" hosts advertised via NA messages with 0-bit=0, as per [RFC9161]. 8.1. Scenario A In cases where duplicate hosts share the same MAC address, the MAC is detected as duplicate using the duplicate MAC detection procedure described in [RFC7432]. Corresponding MAC-IP routes with the same MAC do not require separate duplicate detection and MUST inherit the duplicate property from the MAC route. If a MAC route is marked as duplicate, all associated MAC-IP routes MUST also be treated as duplicates. Duplicate detection procedures need only be applied to MAC routes. 8.2. Scenario B Misconfigurations may lead to different MAC addresses being assigned the same IP address. This scenario is not detected by [RFC7432] duplicate MAC detection procedures and can result in incorrect routing of traffic destined for the IP address. Such situations, when detected locally, are identified as a move scenario through the local MAC sequence number computation procedure described in section 6.1: * If the IP is associated with a different remote MAC "Mz," the sequence number MUST be higher than the "Mz" sequence number. This move results in a sequence number increment for the local MAC due to the remote MAC-IP route associated with a different MAC, counting as an "IP move" against the IP, independent of the MAC. The duplicate detection procedure described in [RFC7432] can then be applied to the IP entity independent of the MAC. Once an IP is detected as duplicate, the corresponding MAC-IP route should be treated as duplicate. Associated MAC routes and any other MAC-IP routes related to this MAC should not be affected. 8.2.1. Duplicate IP Detection Procedure for Scenario B The duplicate IP detection procedure for this scenario is specified in [RFC9161]. An "IP move" is further clarified as follows: * Upon learning a local MAC-IP route Mx-IPx, check for existing remote or local routes for IPx with a different MAC association (Mz-IPx). If found, count this as an "IP move" for IPx, independent of the MAC. * Upon learning a remote MAC-IP route Mz-IPx, check for existing local routes for IPx with a different MAC association (Mx-IPx). If found, count this as an "IP move" for IPx, independent of the MAC. A MAC-IP route SHOULD be treated as duplicate if either: * The corresponding MAC route is marked as duplicate via the existing detection procedure. * The corresponding IP is marked as duplicate via the extended procedure described above. 8.3. Scenario C In a purely routed overlay scenario, as described in section 7, where only a host IP is advertised via EVPN RT-5 with a sequence number mobility attribute, duplicate MAC detection procedures specified in [RFC7432] can be applied intuitively to IP-only host routes for duplicate IP detection. * Upon learning a local host IP route IPx, check for existing remote or local routes for IPx with a different ESI association. If found, count this as an "IP move" for IPx. * Upon learning a remote host IP route IPx, check for existing local routes for IPx with a different ESI association. If found, count this as an "IP move" for IPx. * Using configurable parameters "N" and "M," if "N" IP moves are detected within "M" seconds for IPx, IPx should be treated as duplicate. 8.4. Duplicate Host Recovery Once a MAC or IP is marked as duplicate and frozen, corrective action must be taken to un-provision one of the duplicate MAC or IP addresses. Un-provisioning refers to corrective action taken on the host side. Following this correction, normal operation will not resume until the duplicate MAC or IP ages out unless additional action is taken to expedite recovery. Possible additional corrective actions for faster recovery include: 8.4.1. Route Unfreezing Configuration Unfreezing the duplicate or frozen MAC or IP via a CLI can be used to recover from the duplicate and frozen state following corrective un-provisioning of the duplicate MAC or IP. Unfreezing the MAC or IP should result in advertising it with a sequence number higher than that advertised from the other location. Two scenarios exist: * Scenario A: The duplicate MAC or IP is un-provisioned at the location where it was not marked as duplicate. * Scenario B: The duplicate MAC or IP is un-provisioned at the location where it was marked as duplicate. Unfreezing the duplicate and frozen MAC or IP will result in recovery to a steady state as follows: * Scenario A: If the duplicate MAC or IP is un-provisioned at the non-duplicate location, unfreezing the route at the frozen location results in advertising with a higher sequence number, leading to automatic clearing of the local route at the un-provisioned location via ARP/ND PROBE and DELETE procedures. * Scenario B: If the duplicate host is un-provisioned at the duplicate location, unfreezing the route triggers an advertisement with a higher sequence number to the other location, prompting re-learning and clearing of the local route at the original location upon receiving the remote route advertisement. Probes referred to in these scenarios are event-driven probes resulting from receiving a route with a higher sequence number. Periodic probes resulting from refresh timers may also occur independently. 8.4.2. Route Clearing Configuration In addition to the above, route clearing CLIs may be used to clear the local MAC or IP route after the duplicate host is un-provisioned: * Clear MAC CLI: Used to clear a duplicate MAC route. * Clear ARP/ND: Used to clear a duplicate IP route. The route unfreeze CLI may still need to be executed if the route was un-provisioned and cleared from the non-duplicate location. Given that unfreezing the route via the CLI would result in auto-clearing from the un-provisioned location, as explained earlier, using a route clearing CLI for recovery from the duplicate state is optional. Kind Regards, Gunter Van de Velde Routing Area Director _______________________________________________ BESS mailing list -- bess@ietf.org To unsubscribe send an email to bess-le...@ietf.org
