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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BESS Working Group N. Malhotra, Ed. 3 INTERNET-DRAFT Arrcus 5 Intended Status: Proposed Standard A. Sajassi 6 A. Pattekar 7 Cisco 9 A. Lingala 10 AT&T 12 J. Rabadan 13 Nokia 15 J. Drake 16 Juniper Networks 18 Expires: Dec 21, 2019 June 19, 2019 20 Extended Mobility Procedures for EVPN-IRB 21 draft-ietf-bess-evpn-irb-extended-mobility-01 23 Abstract 25 Procedure to handle host mobility in a layer 2 Network with EVPN 26 control plane is defined as part of RFC 7432. EVPN has since evolved 27 to find wider applicability across various IRB use cases that include 28 distributing both MAC and IP reachability via a common EVPN control 29 plane. MAC Mobility procedures defined in RFC 7432 are extensible to 30 IRB use cases if a fixed 1:1 mapping between VM IP and MAC is assumed 31 across VM moves. Generic mobility support for IP and MAC that allows 32 these bindings to change across moves is required to support a 33 broader set of EVPN IRB use cases, and requires further 34 consideration. EVPN all-active multi-homing further introduces 35 scenarios that require additional consideration from mobility 36 perspective. This document enumerates a set of design considerations 37 applicable to mobility across these EVPN IRB use cases and defines 38 generic sequence number assignment procedures to address these IRB 39 use cases. 41 Status of this Memo 43 This Internet-Draft is submitted to IETF in full conformance with the 44 provisions of BCP 78 and BCP 79. 46 Internet-Drafts are working documents of the Internet Engineering 47 Task Force (IETF), its areas, and its working groups. Note that 48 other groups may also distribute working documents as 49 Internet-Drafts. 51 Internet-Drafts are draft documents valid for a maximum of six months 52 and may be updated, replaced, or obsoleted by other documents at any 53 time. It is inappropriate to use Internet-Drafts as reference 54 material or to cite them other than as "work in progress." 56 The list of current Internet-Drafts can be accessed at 57 http://www.ietf.org/1id-abstracts.html 59 The list of Internet-Draft Shadow Directories can be accessed at 60 http://www.ietf.org/shadow.html 62 Copyright and License Notice 64 Copyright (c) 2017 IETF Trust and the persons identified as the 65 document authors. All rights reserved. 67 This document is subject to BCP 78 and the IETF Trust's Legal 68 Provisions Relating to IETF Documents 69 (http://trustee.ietf.org/license-info) in effect on the date of 70 publication of this document. Please review these documents 71 carefully, as they describe your rights and restrictions with respect 72 to this document. Code Components extracted from this document must 73 include Simplified BSD License text as described in Section 4.e of 74 the Trust Legal Provisions and are provided without warranty as 75 described in the Simplified BSD License. 77 Table of Contents 79 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 80 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5 81 2. Optional MAC only RT-2 . . . . . . . . . . . . . . . . . . . . 6 82 3. Mobility Use Cases . . . . . . . . . . . . . . . . . . . . . . 6 83 3.1 Host MAC+IP Move . . . . . . . . . . . . . . . . . . . . . 6 84 3.2 Host IP Move to new MAC . . . . . . . . . . . . . . . . . . 6 85 3.2.1 VM Reload . . . . . . . . . . . . . . . . . . . . . . . 7 86 3.2.2 MAC Sharing . . . . . . . . . . . . . . . . . . . . . . 7 87 3.2.3 Problem . . . . . . . . . . . . . . . . . . . . . . . . 7 88 3.3 Host MAC move to new IP . . . . . . . . . . . . . . . . . . 8 89 3.3.1 Problem . . . . . . . . . . . . . . . . . . . . . . . . 8 90 4. EVPN All Active multi-homed ES . . . . . . . . . . . . . . . . 11 91 5. Design Considerations . . . . . . . . . . . . . . . . . . . . 12 92 6. Solution Components . . . . . . . . . . . . . . . . . . . . . 13 93 6.1 Sequence Number Inheritance . . . . . . . . . . . . . . . . 13 94 6.2 MAC Sharing . . . . . . . . . . . . . . . . . . . . . . . . 14 95 6.3 Multi-homing Mobility Synchronization . . . . . . . . . . . 15 96 7. Requirements for Sequence Number Assignment . . . . . . . . . 15 97 7.1 LOCAL MAC-IP learning . . . . . . . . . . . . . . . . . . . 15 98 7.2 LOCAL MAC learning . . . . . . . . . . . . . . . . . . . . 16 99 7.3 Remote MAC OR MAC-IP Update . . . . . . . . . . . . . . . . 16 100 7.4 REMOTE (SYNC) MAC update . . . . . . . . . . . . . . . . . 16 101 7.5 REMOTE (SYNC) MAC-IP update . . . . . . . . . . . . . . . . 17 102 7.6 Inter-op . . . . . . . . . . . . . . . . . . . . . . . . . 17 103 7.7 MAC Sharing Race Condition . . . . . . . . . . . . . . . . 18 104 8. Routed Overlay . . . . . . . . . . . . . . . . . . . . . . . . 18 105 9. Duplicate Host Detection . . . . . . . . . . . . . . . . . . . 19 106 9.1 Scenario A . . . . . . . . . . . . . . . . . . . . . . . . . 19 107 9.2 Scenario B . . . . . . . . . . . . . . . . . . . . . . . . . 20 108 9.2.1 Duplicate IP Detection Procedure for Scenario B . . . . 20 109 9.3 Scenario C . . . . . . . . . . . . . . . . . . . . . . . . . 21 110 9.4 Duplicate Host Recovery . . . . . . . . . . . . . . . . . . 21 111 9.4.1 Route Un-freezing Configuration . . . . . . . . . . . . 21 112 9.4.2 Route Clearing Configuration . . . . . . . . . . . . . 22 113 10. Security Considerations . . . . . . . . . . . . . . . . . . . 22 114 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 115 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 116 12.1 Normative References . . . . . . . . . . . . . . . . . . . 23 117 12.2 Informative References . . . . . . . . . . . . . . . . . . 23 118 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23 119 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 120 Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 122 1 Introduction 124 EVPN-IRB enables capability to advertise both MAC and IP routes via a 125 single MAC+IP RT-2 advertisement. MAC is imported into local bridge 126 MAC table and enables L2 bridged traffic across the network overlay. 127 IP is imported into the local ARP table in an asymmetric IRB design 128 OR imported into the IP routing table in a symmetric IRB design, and 129 enables routed traffic across the layer 2 network overlay. Please 130 refer to [EVPN-IRB] for more background on EVPN IRB forwarding modes. 132 To support EVPN mobility procedure, a single sequence number mobility 133 attribute is advertised with the combined MAC+IP route. A single 134 sequence number advertised with the combined MAC+IP route to resolve 135 both MAC and IP reachability implicitly assumes a 1:1 fixed mapping 136 between IP and MAC. While a fixed 1:1 mapping between IP and MAC is a 137 common use case that could be addressed via existing MAC mobility 138 procedure, additional IRB scenarios need to be considered, that don't 139 necessarily adhere to this assumption. Following IRB mobility 140 scenarios are considered: 142 o VM move results in VM IP and MAC moving together 144 o VM move results in VM IP moving to a new MAC association 146 o VM move results in VM MAC moving to a new IP association 148 While existing MAC mobility procedure can be leveraged for MAC+IP 149 move in the first scenario, subsequent scenarios result in a new MAC- 150 IP association. As a result, a single sequence number assigned 151 independently per-[MAC, IP] is not sufficient to determine most 152 recent reachability for both MAC and IP, unless the sequence number 153 assignment algorithm is designed to allow for changing MAC-IP 154 bindings across moves. 156 Purpose of this draft is to define additional sequence number 157 assignment and handling procedures to adequately address generic 158 mobility support across EVPN-IRB overlay use cases that allow MAC-IP 159 bindings to change across VM moves and can support mobility for both 160 MAC and IP components carried in an EVPN RT-2 for these use cases. 162 In addition, for hosts on an ESI multi-homed to multiple GW devices, 163 additional procedure is proposed to ensure synchronized sequence 164 number assignments across the multi-homing devices. 166 Content presented in this draft is independent of data plane 167 encapsulation used in the overlay being MPLS or NVO Tunnels. It is 168 also largely independent of the EVPN IRB solution being based on 169 symmetric OR asymmetric IRB design as defined in [EVPN-INTER-SUBNET]. 171 In addition to symmetric and asymmetric IRB, mobility solution for a 172 routed overlay, where traffic to an end host in the overlay is always 173 IP routed using EVPN RT-5 is also presented in section 8. 175 To summarize, this draft covers mobility mobility for the following 176 independent of the overlay encapsulation being MPLS or an NVO Tunnel: 178 o Symmetric EVPN IRB overlay 180 o Asymmetric EVPN IRB overlay 182 o Routed EVPN overlay 184 1.1 Terminology 186 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 187 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 188 document are to be interpreted as described in RFC 2119 [RFC2119]. 190 o EVPN-IRB: A BGP-EVPN distributed control plane based integrated 191 routing and bridging fabric overlay discussed in [EVPN-IRB] 192 o Underlay: IP or MPLS fabric core network that provides IP or 193 MPLS routed reachability between EVPN PEs. 194 o Overlay: VPN or service layer network consisting of EVPN PEs 195 OR VPN provider-edge (PE) switch-router devices that runs on top 196 of an underlay routed core. 197 o EVPN PE: A PE switch-router in a data-center fabric that 198 runs overlay BGP-EVPN control plane and connects to overlay CE 199 host devices. An EVPN PE may also be the first-hop layer-3 200 gateway for CE/host devices. This document refers to EVPN PE as a 201 logical function in a data-center fabric. This EVPN PE function 202 may be physically hosted on a top-of-rack switching device (ToR) 203 OR at layer(s) above the ToR in the Clos fabric. An EVPN PE is 204 typically also an IP or MPLS tunnel end-point for overlay VPN 205 flow 206 o Symmetric EVPN-IRB: An overlay fabric first-hop routing 207 architecture as defined in [EVPN-IRB], wherein, overlay host-to- 208 host routed inter-subnet flows are routed at both ingress and 209 egress EVPN PEs. 210 o Asymmetric EVPN-IRB: An overlay fabric first-hop routing 211 architecture as defined in [EVPN-IRB], wherein, overlay host-to- 212 host routed inter-subnet flows are routed and bridged at ingress 213 PE and bridged at egress PEs. 214 o ARP: Address Resolution Protocol [RFC 826]. ARP references in 215 this document are equally applicable to ND as well. 216 o ND: IPv6 Neighbor Discovery Protocol [RFC 4861]. 217 o Ethernet-Segment: physical Ethernet or LAG port that connects an 218 access device to an EVPN PE, as defined in [RFC 7432]. 220 o ESI: Ethernet Segment Identifier as defined in [RFC 7432]. 221 o LAG: Layer-2 link-aggregation, also known as layer-2 bundle 222 port-channel, or bond interface. 223 o EVPN all-active multi-homing: PE-CE all-active multi-homing 224 achieved via a multi-homed layer-2 LAG interface on a CE with 225 member links to multiple PEs and related EVPN procedures on the 226 PEs. 227 o RT-2: EVPN route type 2 carrying both MAC and IP reachability. 228 o RT-5: EVPN route type 5 carrying IP prefix reachability. 229 o MAC-IP: IP association for a MAC, referred to in this document 230 may be IPv4, IPv6 or both. 232 2. Optional MAC only RT-2 234 In an EVPN IRB scenario, where a single MAC+IP RT-2 advertisement 235 carries both IP and MAC routes, a MAC only RT-2 advertisement is 236 redundant for host MACs that are advertised via MAC+IP RT-2. As a 237 result, a MAC only RT-2 is an optional route that may not be 238 advertised from or received at an EVPN PE. This is an important 239 consideration for mobility scenarios discussed in subsequent 240 sections. 242 MAC only RT-2 may still be advertised for non-IP host MACs that are 243 not advertised via MAC+IP RT-2. 245 3. Mobility Use Cases 247 This section describes the IRB mobility use cases considered in this 248 document. Procedures to address them are covered later in section 6 249 and section 7. 251 o Host move results in Host IP and MAC moving together 253 o Host move results in Host IP moving to a new MAC association 255 o Host move results in Host MAC moving to a new IP association 257 3.1 Host MAC+IP Move 259 This is the baseline case, wherein a host move results in both host 260 MAC and IP moving together with no change in MAC-IP binding across a 261 move. Existing MAC mobility defined in RFC 7432 may be leveraged to 262 apply to corresponding MAC+IP route to support this mobility 263 scenario. 265 3.2 Host IP Move to new MAC 267 This is the case, where a host move results in VM IP moving to a new 268 MAC binding. 270 3.2.1 VM Reload 272 A host reload or an orchestrated host move that results in host being 273 re-spawned at a new location may result in host getting a new MAC 274 assignment, while maintaining existing IP address. This results in a 275 host IP move to a new MAC binding: 277 IP-a, MAC-a ---> IP-a, MAC-b 279 3.2.2 MAC Sharing 281 This takes into account scenarios, where multiple hosts, each with a 282 unique IP, may share a common MAC binding, and a host move results in 283 a new MAC binding for the host IP. 285 As an example, hosts running on a single physical server, each with a 286 unique IP, may share the same physical server MAC. In yet another 287 scenario, an L2 access network may be behind a firewall, such that 288 all hosts IPs on the access network are learnt with a common firewall 289 MAC. In all such "shared MAC" use cases, multiple local MAC-IP ARP 290 entries may be learnt with the same MAC. A host IP move, in such 291 scenarios (for e.g., to a new physical server), could result in new 292 MAC association for the host IP. 294 3.2.3 Problem 296 In both of the above scenarios, a combined MAC+IP EVPN RT-2 297 advertised with a single sequence number attribute implicitly assumes 298 a fixed IP to MAC mapping. A host IP move to a new MAC breaks this 299 assumption and results in a new MAC+IP route. If this new MAC+IP 300 route is independently assigned a new sequence number, the sequence 301 number can no longer be used to determine most recent host IP 302 reachability in a symmetric EVPN-IRB design OR the most recent IP to 303 MAC binding in an asymmetric EVPN-IRB design. 305 +------------------------+ 306 | Underlay Network Fabric| 307 +------------------------+ 309 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 310 | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | 311 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 312 \ / \ / \ / 313 \ ESI-1 / \ ESI-2 / \ ESI-3 / 314 \ / \ / \ / 315 +\---/+ +\---/+ +\---/+ 316 | \ / | | \ / | | \ / | 317 +--+--+ +--+--+ +--+--+ 318 | | | 319 Server-MAC1 Server-MAC2 Server-MAC3 320 | | | 321 [VM-IP1, VM-IP2] [VM-IP3, VM-IP4] [VM-IP5, VM-IP6] 323 Figure 1 325 As an example, consider a topology shown in Figure 1, with host VMs 326 sharing the physical server MAC. In steady state, [IP1, MAC1] route 327 is learnt at [PE1, PE2] and advertised to remote PEs with a sequence 328 number N. Now, VM-IP1 is moved to Server-MAC2. ARP or ND based local 329 learning at [PE3, PE4] would now result in a new [IP1, MAC2] route 330 being learnt. If route [IP1, MAC2] is learnt as a new MAC+IP route 331 and assigned a new sequence number of say 0, mobility procedure for 332 VM-IP1 will not trigger across the overlay network. 334 A sequence number assignment procedure needs to be defined to 335 unambiguously determine the most recent IP reachability, IP to MAC 336 binding, and MAC reachability for such a MAC sharing scenario. 338 3.3 Host MAC move to new IP 340 This is a scenario where host move or re-provisioning behind a new 341 gateway location may result in host getting a new IP address 342 assigned, while keeping the same MAC. 344 3.3.1 Problem 346 Complication with this scenario is that MAC reachability could be 347 carried via a combined MAC+IP route while a MAC only route may not be 348 advertised at all. A single sequence number association with the 349 MAC+IP route again implicitly assumes a fixed mapping between MAC and 350 IP. A MAC move resulting in a new IP association for the host MAC 351 breaks this assumption and results in a new MAC+IP route. If this new 352 MAC+IP route independently assumes a new sequence number, this 353 mobility attribute can no longer be used to determine most recent 354 host MAC reachability. 356 +------------------------+ 357 | Underlay Network Fabric| 358 +------------------------+ 359 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 360 | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | 361 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 362 \ / \ / \ / 363 \ ESI-1 / \ ESI-2 / \ ESI-3 / 364 \ / \ / \ / 365 +\---/+ +\---/+ +\---/+ 366 | \ / | | \ / | | \ / | 367 +--+--+ +--+--+ +--+--+ 368 | | | 369 Server1 Server2 Server3 370 | | | 371 [VM-IP1-M1, VM-IP2-M2] [VM-IP3-M3, VM-IP4-M4] [VM-IP5-M5, VM-IP6-M6] 373 As an example, consider a host VM IP1-M1 that is learnt locally at 374 [PE1, PE2] and advertised to remote hosts with a sequence number N. 375 Consider a scenario where this VM with MAC M1 is re-provisioned at 376 server 2, however, as part of this re-provisioning, assigned a 377 different IP address say IP7. [IP7, M1] is learnt as a new route at 378 [PE3, PE4] and advertised to remote PEs with a sequence number of 0. 379 As a result, L3 reachability to IP7 would be established across the 380 overlay, however, MAC mobility procedure for MAC1 will not trigger as 381 a result of this MAC-IP route advertisement. If an optional MAC only 382 route is also advertised, sequence number associated with the MAC 383 only route would trigger MAC mobility as per [RFC7432]. However, in 384 the absence of an additional MAC only route advertisement, a single 385 sequence number advertised with a combined MAC+IP route would not be 386 sufficient to update MAC reachability across the overlay. 388 A MAC-IP sequence number assignment procedure needs to be defined to 389 unambiguously determine the most recent MAC reachability in such a 390 scenario without a MAC only route being advertised. 392 Further, PE1/PE2, on learning new reachability for [IP7, M1] via 393 PE3/PE4 MUST probe and delete any local IPs associated with MAC M1, 394 such as [IP1, M1] in the above example. 396 Arguably, MAC mobility sequence number defined in [RFC7432], could be 397 interpreted to apply only to the MAC part of MAC-IP route, and would 398 hence cover this scenario. It could hence be interpreted as a 399 clarification to [RFC7432] and one of the considerations for a common 400 sequence number assignment procedure across all MAC-IP mobility 401 scenarios detailed in this document. 403 4. EVPN All Active multi-homed ES 405 +------------------------+ 406 | Underlay Network Fabric| 407 +------------------------+ 409 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 410 | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | 411 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ 412 \ / \ / \ / 413 \ ESI-1 / \ ESI-2 / \ ESI-3 / 414 \ / \ / \ / 415 +\---/+ +\---/+ +\---/+ 416 | \ / | | \ / | | \ / | 417 +--+--+ +--+--+ +--+--+ 418 | | | 419 Server-1 Server-2 Server-3 421 Figure 2 423 Consider an EVPN-IRB overlay network shown in Figure 2, with hosts 424 multi-homed to two or more PE devices via an all-active multi-homed 425 ES. MAC and ARP entries learnt on a local ES may also be synchronized 426 across the multi-homing PE devices sharing this ES. This MAC and ARP 427 SYNC enables local switching of intra and inter subnet ECMP traffic 428 flows from remote hosts. In other words, local MAC and ARP entries on 429 a given ES may be learnt via local learning and / or via sync from 430 another PE device sharing the same ES. 432 For a host that is multi-homed to multiple PE devices via an all- 433 active ES interface, local learning of host MAC and MAC-IP at each PE 434 device is an independent asynchronous event, that is dependent on 435 traffic flow and or ARP / ND response from the host hashing to a 436 directly connected PE on the MC-LAG interface. As a result, sequence 437 number mobility attribute value assigned to a locally learnt MAC or 438 MAC-IP route at each device may not always be the same, depending on 439 transient states on the device at the time of local learning. 441 As an example, consider a host VM that is deleted from ESI-2 and 442 moved to ESI-1. It is possible for host to be learnt on say, PE1 443 following deletion of the remote route from [PE3, PE4], while being 444 learnt on PE2 prior to deletion of remote route from [PE3, PE4]. If 445 so, PE1 would process local host route learning as a new route and 446 assign a sequence number of 0, while PE2 would process local host 447 route learning as a remote to local move and assign a sequence number 448 of N+1, N being the existing sequence number assigned at [PE3, PE4]. 450 Inconsistent sequence numbers advertised from multi-homing devices 451 introduces: 453 o Ambiguity with respect to how the remote PEs should handle 454 paths with same ESI and different sequence numbers. A remote PE 455 may not program ECMP paths if it receives routes with different 456 sequence numbers from a set of multi-homing PEs sharing the same 457 ESI. 459 o Breaks consistent route versioning across the network overlay 460 that is needed for EVPN mobility procedures to work. 462 As an example, in this inconsistent state, PE2 would drop a remote 463 route received for the same host with sequence number N (as its local 464 sequence number is N+1), while PE1 would install it as the best route 465 (as its local sequence number is 0). 467 There is need for a mechanism to ensure consistency of sequence 468 numbers advertised from a set of multi-homing devices for EVPN 469 mobility to work reliably. 471 In order to support mobility for multi-homed hosts using the sequence 472 number mobility attribute, local MAC and MAC-IP routes learnt on a 473 multi-homed ES MUST be advertised with the same sequence number by 474 all PE devices that the ES is multi-homed to. There is need for a 475 mechanism to ensure consistency of sequence numbers assigned across 476 these PEs. 478 5. Design Considerations 480 To summarize, sequence number assignment scheme and implementation 481 must take following considerations into account: 483 o MAC+IP may be learnt on an ES multi-homed to multiple PE 484 devices, hence requires sequence numbers to be synchronized 485 across multi-homing PE devices. 487 o MAC only RT-2 is optional in an IRB scenario and may not 488 necessarily be advertised in addition to MAC+IP RT-2 490 o Single MAC may be associated with multiple IPs, i.e., multiple 491 host IPs may share a common MAC 493 o Host IP move could result in host moving to a new MAC, resulting 494 in a new IP to MAC association and a new MAC+IP route. 496 o Host MAC move to a new location could result in host MAC being 497 associated with a different IP address, resulting in a new MAC to 498 IP association and a new MAC+IP route 500 o LOCAL MAC-IP learn via ARP would always accompanied by a LOCAL 501 MAC learn event resulting from the ARP packet. MAC and MAC-IP 502 learning, however, could happen in any order 504 o Use cases discussed earlier that do not maintain a constant 1:1 505 MAC-IP mapping across moves could potentially be addressed by 506 using separate sequence numbers associated with MAC and IP 507 components of MAC+IP route. Maintaining two separate sequence 508 numbers however adds significant overhead with respect to 509 complexity, debugability, and backward compatibility. Hence, this 510 document addresses these requirements via a single sequence 511 number attribute. 513 6. Solution Components 515 This section goes over main components of the EVPN IRB mobility 516 solution proposed in this draft. Later sections will go over exact 517 sequence number assignment procedures resulting from concepts 518 described in this section. 520 6.1 Sequence Number Inheritance 522 Main idea presented here is to view a LOCAL MAC-IP route as a child 523 of the corresponding LOCAL MAC only route that inherits the sequence 524 number attribute from the parent LOCAL MAC only route: 526 Mx-IPx -----> Mx (seq# = N) 528 As a result, both parent MAC and child MAC-IP routes share one common 529 sequence number associated with the parent MAC route. Doing so 530 ensures that a single sequence number attribute carried in a combined 531 MAC+IP route represents sequence number for both a MAC only route as 532 well as a MAC+IP route, and hence makes the MAC only route truly 533 optional. As a result, optional MAC only route with its own sequence 534 number is not required to establish most recent reachability for a 535 MAC in the overlay network. Specifically, this enables a MAC to 536 assume a different IP address on a move, and still be able to 537 establish most recent reachability to the MAC across the overlay 538 network via mobility attribute associated with the MAC+IP route 539 advertisement. As an example, when Mx moves to a new location, it 540 would result in LOCAL Mx being assigned a higher sequence number at 541 its new location as per RFC 7432. If this move results in Mx assuming 542 a different IP address, IPz, LOCAL Mx+IPz route would inherit the new 543 sequence number from Mx. 545 LOCAL MAC and LOCAL MAC-IP routes would typically be sourced from 546 data plane learning and ARP learning respectively, and could get 547 learnt in control plane in any order. Implementation could either 548 replicate inherited sequence number in each MAC-IP entry OR maintain 549 a single attribute in the parent MAC by creating a forward reference 550 LOCAL MAC object for cases where a LOCAL MAC-IP is learnt before the 551 LOCAL MAC. 553 Arguably, this inheritance may be assumed from RFC 7432, in which 554 case, the above may be interpreted as a clarification with respect to 555 interpretation of a MAC sequence number in a MAC-IP route. 557 6.2 MAC Sharing 559 Further, for the shared MAC scenario, this would result in multiple 560 LOCAL MAC-IP siblings inheriting sequence number attribute from a 561 common parent MAC route: 563 Mx-IP1 ----- 564 | | 565 Mx-IP2 ----- 566 . | 567 . +---> Mx (seq# = N) 568 . | 569 Mx-IPw ----- 570 | | 571 Mx-IPx ----- 573 In such a case, a host-IP move to a different physical server would 574 result in IP moving to a new MAC binding. A new MAC-IP route 575 resulting from this move must now be advertised with a sequence 576 number that is higher than the previous MAC-IP route for this IP, 577 advertised from the prior location. As an example, consider a route 578 Mx-IPx that is currently advertised with sequence number N from PE1. 579 IPx moving to a new physical server behind PE2 results in IPx being 580 associated with MAC Mz. A new local Mz-IPx route resulting from this 581 move at PE2 must now be advertised with a sequence number higher than 582 N. This is so that PE devices, including PE1, PE2, and other remote 583 PE devices that are part of the overlay can clearly determine and 584 program the most recent MAC binding and reachability for the IP. PE1, 585 on receiving this new Mz-IPx route with sequence number say, N+1, for 586 symmetric IRB case, would update IPx reachability via PE2 in 587 forwarding, for asymmetric IRB case, would update IPx's ARP binding 588 to Mz. In addition, PE1 would clear and withdraw the stale Mx-IPx 589 route with the lower sequence number. 591 This also implies that sequence number associated with local MAC Mz 592 and all local MAC-IP children of Mz at PE2 must now be incremented to 593 N+1, and re-advertised across the overlay. While this re- 594 advertisement of all local MAC-IP children routes affected by the 595 parent MAC route is an overhead, it avoids the need for two separate 596 sequence number attributes to be maintained and advertised for IP and 597 MAC components of MAC+IP RT-2. Implementation would need to be able 598 to lookup MAC-IP routes for a given IP and update sequence number for 599 it's parent MAC and its MAC-IP children. 601 6.3 Multi-homing Mobility Synchronization 603 In order to support mobility for multi-homed hosts, local MAC and 604 MAC-IP routes learnt on a shared ES MUST be advertised with the same 605 sequence number by all PE devices that the ES is multi-homed to. This 606 also applies to local MAC only routes. LOCAL MAC and MAC-IP may be 607 learnt natively via data plane and ARP/ND respectively as well as via 608 SYNC from another multi-homing PE to achieve local switching. Local 609 and SYNC route learning can happen in any order. Local MAC-IP routes 610 advertised by all multi-homing PE devices sharing the ES must carry 611 the same sequence number, independent of the order in which they are 612 learnt. This implies: 614 o On local or sync MAC-IP route learning, sequence number for the 615 local MAC-IP route MUST be compared and updated to the higher 616 value. 618 o On local or sync MAC route learning, sequence number for the 619 local MAC route MUST be compared and updated to the higher value. 621 If an update to local MAC-IP sequence number is required as a result 622 of above comparison with sync MAC-IP route, it would essentially 623 amount to a sequence number update on the parent local MAC, resulting 624 in inherited sequence number update on the MAC-IP route. 626 7. Requirements for Sequence Number Assignment 628 Following sections summarize sequence number assignment procedure 629 needed on local and sync MAC and MAC-IP route learning events in 630 order to accomplish the above. 632 7.1 LOCAL MAC-IP learning 634 A local Mx-IPx learning via ARP or ND should result in computation OR 635 re-computation of parent MAC Mx's sequence number, following which 636 the MAC-IP route Mx-IPx would simply inherit parent MAC's sequence 637 number. Parent MAC Mx Sequence number should be computed as follows: 639 o MUST be higher than any existing remote MAC route for Mx, as per 640 RFC 7432. 642 o MUST be at least equal to corresponding SYNC MAC sequence number 643 if one is present. 645 o If the IP is also associated with a different remote MAC "Mz", 646 MUST be higher than "Mz" sequence number 648 Once new sequence number for MAC route Mx is computed as per above, 649 all LOCAL MAC-IPs associated with MAC Mx MUST inherit the updated 650 sequence number. 652 7.2 LOCAL MAC learning 654 Local MAC Mx Sequence number should be computed as follows: 656 o MUST be higher than any existing remote MAC route for Mx, as per 657 RFC 7432. 659 o MUST be at least equal to corresponding SYNC MAC sequence number 660 if one is present. 662 o Once new sequence number for MAC route Mx is computed as per 663 above, all LOCAL MAC-IPs associated with MAC Mx MUST inherit the 664 updated sequence number. 666 Note that the local MAC sequence number might already be present if 667 there was a local MAC-IP learnt prior to the local MAC, in which case 668 the above may not result in any change in local MAC's sequence 669 number. 671 7.3 Remote MAC OR MAC-IP Update 673 On receiving a remote MAC OR MAC-IP route update associated with a 674 MAC Mx with a sequence number that is higher than or equal to 675 sequence number assigned to a LOCAL route for MAC Mx: 677 o PE MUST trigger probe and deletion procedure for all LOCAL IPs 678 associated with MAC Mx 680 o PE MUST trigger deletion procedure for LOCAL MAC route for Mx 682 7.4 REMOTE (SYNC) MAC update 684 Corresponding local MAC Mx (if present) sequence number should be re- 685 computed as follows: 687 o If the current sequence number is less than the received SYNC 688 MAC sequence number, it MUST be increased to be equal to received 689 SYNC MAC sequence number. 691 o If a LOCAL MAC sequence number is updated as a result of the 692 above, all LOCAL MAC-IPs associated with MAC Mx MUST inherit the 693 updated sequence number. 695 7.5 REMOTE (SYNC) MAC-IP update 697 If this is a SYNCed MAC-IP on a local ES, it would also result in a 698 derived SYNC MAC Mx route entry, as MAC only RT-2 advertisement is 699 optional. Corresponding local MAC Mx (if present) sequence number 700 should be re-computed as follows: 702 o If the current sequence number is less than the received SYNC 703 MAC sequence number, it MUST be increased to be equal to received 704 SYNC MAC sequence number. 706 o If a LOCAL MAC sequence number is updated as a result of the 707 above, all LOCAL MAC-IPs associated with MAC Mx MUST inherit the 708 updated sequence number. 710 7.6 Inter-op 712 In general, if all PE nodes in the overlay network follow the above 713 sequence number assignment procedure, and the PE is advertising both 714 MAC+IP and MAC routes, sequence number advertised with the MAC and 715 MAC+IP routes with the same MAC would always be the same. However, an 716 inter-op scenario with a different implementation could arise, where 717 a PE implementation non-compliant with this document or with RFC 7432 718 assigns and advertises independent sequence numbers to MAC and MAC+IP 719 routes. To handle this case, if different sequence numbers are 720 received for remote MAC+IP and corresponding remote MAC routes from a 721 remote PE, sequence number associated with the remote MAC route 722 should be computed as: 724 o Highest of the all received sequence numbers with remote MAC+IP 725 and MAC routes with the same MAC. 727 o MAC sequence number would be re-computed on a MAC or MAC+IP 728 route withdraw as per above. 730 A MAC and / or IP move to the local PE would now result in the MAC 731 (and hence all MAC-IP) sequence numbers incremented from the above 732 computed remote MAC sequence number. 734 7.7 MAC Sharing Race Condition 736 In a MAC sharing use case described in section 6.2, a race condition 737 is possible with simultaneous host moves between a pair of PEs. As an 738 example, consider PE1 with local host IPs I1 and I2 sharing MAC M1, 739 and PE2 with local host IPs I3 and I4 sharing MAC M2. A simultaneous 740 move of I1 from PE1 to PE2 and of I3 from PE2 to PE1, such that I3 is 741 learnt on PE1 before I1's local entry has been probed out on PE1 742 and/or I1 is learnt on PE2 before I3's local entry has been probed 743 out on PE2 may trigger a race condition. This race condition together 744 with MAC sequence number assignment rules defined in section 7.1 can 745 cause new mac-ip routes [I1, M2] and [I3, M1] to bounce a couple of 746 times with an incremented sequence number until stale entries [I1, 747 M1] and [I3, M2] have been probed out from PE1 and PE2 respectively. 748 An implementation MUST ensure proper probing procedures to remove 749 stale ARP, ND, and local MAC entries, following a move, on learning 750 remote routes as defined in section 7.3 (and as per [EVPN-IRB]) to 751 minimize exposure to this race condition. 753 8. Routed Overlay 755 An additional use case is possible, such that traffic to an end host 756 in the overlay is always IP routed. In a purely routed overlay such 757 as this: 759 o A host MAC is never advertised in EVPN overlay control plane 761 o Host /32 or /128 IP reachability is distributed across the 762 overlay via EVPN route type 5 (RT-5) along with a zero or non- 763 zero ESI 765 o An overlay IP subnet may still be stretched across the underlay 766 fabric, however, intra-subnet traffic across the stretched 767 overlay is never bridged 769 o Both inter-subnet and intra-subnet traffic, in the overlay is 770 IP routed at the EVPN PE. 772 Please refer to [RFC 7814] for more details. 774 Host mobility within the stretched subnet would still need to be 775 supported for this use. In the absence of any host MAC routes, 776 sequence number mobility EXT-COMM specified in [RFC7432], section 7.7 777 may be associated with a /32 OR /128 host IP prefix advertised via 778 EVPN route type 5. MAC mobility procedures defined in RFC 7432 can 779 now be applied as is to host IP prefixes: 781 o On LOCAL learning of a host IP, on a new ESI, host IP MUST be 782 advertised with a sequence number attribute that is higher than 783 what is currently advertised with the old ESI 785 o on receiving a host IP route advertisement with a higher 786 sequence number, a PE MUST trigger ARP/ND probe and deletion 787 procedure on any LOCAL route for that IP with a lower sequence 788 number. A PE would essentially move the forwarding entry to point 789 to the remote route with a higher sequence number and send an 790 ARP/ND PROBE for the local IP route. If the IP has indeed moved, 791 PROBE would timeout and the local IP host route would be deleted. 793 Note that there is still only one sequence number associated with a 794 host route at any time. For earlier use cases where a host MAC is 795 advertised along with the host IP, a sequence number is only 796 associated with a MAC. Only if the MAC is not advertised at all, as 797 in this use case, is a sequence number associated with a host IP. 799 Note that this mobility procedure would not apply to "anycast IPv6" 800 hosts advertised via NA messages with 0-bit=0. Please refer to [EVPN- 801 PROXY-ARP]. 803 9. Duplicate Host Detection 805 Duplicate host detection scenarios across EVPN IRB can be classified 806 as follows: 808 o Scenario A: where two hosts have the same MAC (host IPs may or 809 may not be duplicate) 811 o Scenario B: where two hosts have the same IP but different MACs 813 o Scenario C: where two hosts have the same IP and host MAC is not 814 advertised at all 816 Duplicate detection procedures for scenario B and C would not apply 817 to "anycast IPv6" hosts advertised via NA messages with 0-bit=0. 818 Please refer to [EVPN-PROXY-ARP]. 820 9.1 Scenario A 822 For all use cases where duplicate hosts have the same MAC, MAC is 823 detected as duplicate via duplicate MAC detection procedure described 824 in RFC 7432. Corresponding MAC-IP routes with the same MAC do not 825 require duplicate detection and MUST simply inherit the DUPLICATE 826 property from the corresponding MAC route. In other words, if a MAC 827 route is in DUPLICATE state, all corresponding MAC-IP routes MUST 828 also be treated as DUPLICATE. Duplicate detection procedure need only 829 be applied to MAC routes. 831 9.2 Scenario B 833 Due to misconfiguration, a situation may arise where hosts with 834 different MACs are configured with the same IP. This scenario would 835 not be detected by existing duplicate MAC detection procedure and 836 would result in incorrect forwarding of routed traffic destined to 837 this IP. 839 Such a situation, on LOCAL MAC-IP learning, would be detected as a 840 move scenario via the following local MAC sequence number computation 841 procedure described earlier in section 5.1: 843 o If the IP is also associated with a different remote MAC "Mz", 844 MUST be higher than "Mz" sequence number 846 Such a move that results in sequence number increment on local MAC 847 because of a remote MAC-IP route associated with a different MAC MUST 848 be counted as an "IP move" against the "IP" independent of MAC. 849 Duplicate detection procedure described in RFC 7432 can now be 850 applied to an "IP" entity independent of MAC. Once an IP is detected 851 as DUPLICATE, corresponding MAC-IP route should be treated as 852 DUPLICATE. Associated MAC routes and any other MAC-IP routes 853 associated with this MAC should not be affected. 855 9.2.1 Duplicate IP Detection Procedure for Scenario B 857 Duplicate IP detection procedure for such a scenario is specified in 858 [EVPN-PROXY-ARP]. What counts as an "IP move" in this scenario is 859 further clarified as follows: 861 o On learning a LOCAL MAC-IP route Mx-IPx, check if there is an 862 existing REMOTE OR LOCAL route for IPx with a different MAC 863 association, say, Mz-IPx. If so, count this as an "IP move" count 864 for IPx, independent of the MAC 866 o On learning a REMOTE MAC-IP route Mz-IPx, check if there is an 867 existing LOCAL route for IPx with a different MAC association, 868 say, Mx-IPx. If so, count this as an "IP move" count for IPx, 869 independent of the MAC 871 A MAC-IP route SHOULD be treated as DUPLICATE if either of the 872 following two conditions are met: 874 o Corresponding MAC route is marked as DUPLICATE via existing 875 duplicate detection procedure 877 o Corresponding IP is marked as DUPLICATE via extended procedure 878 described above 880 9.3 Scenario C 882 For a purely routed overlay scenario described in section 8, where 883 only a host IP is advertised via EVPN RT-5, together with a sequence 884 number mobility attribute, duplicate MAC detection procedures 885 specified in RFC 7432 can be intuitively applied to IP only host 886 routes for the purpose of duplicate IP detection. 888 o On learning a LOCAL host IP route IPx, check if there is an 889 existing REMOTE OR LOCAL route for IPx with a different ESI 890 association. If so, count this as an "IP move" count for IPx. 892 o On learning a REMOTE host IP route IPx, check if there is an 893 existing LOCAL route for IPx with a different ESI association. If 894 so, count this as an "IP move" count for IPx 896 o With configurable parameters "N" and "M", If "N" IP moves are 897 detected within "M" seconds for IPx, treat IPx as DUPLICATE 899 9.4 Duplicate Host Recovery 901 Once a MAC or IP is marked as DUPLICATE and FROZEN, corrective action 902 must be taken to un-provision one of the duplicate MAC or IP. Un- 903 provisioning a duplicate MAC or IP in this context refers to a 904 corrective action taken on the host side. Once one of the duplicate 905 MAC or IP is un-provisioned, normal operation would not resume until 906 the duplicate MAC or IP ages out, following this correction, unless 907 additional action is taken to speed up recovery. 909 This section lists possible additional corrective actions that could 910 be taken to achieve faster recovery to normal operation. 912 9.4.1 Route Un-freezing Configuration 914 Unfreezing the DUPLICATE OR FROZEN MAC or IP via a CLI can be 915 leveraged to recover from DUPLICATE and FROZEN state following 916 corrective un-provisioning of the duplicate MAC or IP. 918 Unfreezing the frozen MAC or IP via a CLI at a PE should result in 919 that MAC OR IP being advertised with a sequence number that is higher 920 than the sequence number advertised from the other location of that 921 MAC or IP. 923 Two possible corrective un-provisioning scenarios exist: 925 o Scenario A: A duplicate MAC or IP may have been un-provisioned 926 at the location where it was NOT marked as DUPLICATE and FROZEN 928 o Scenario B: A duplicate MAC or IP may have been un-provisioned 929 at the location where it was marked as DUPLICATE and FROZEN 931 Unfreezing the DUPLICATE and FROZEN MAC or IP, following the above 932 corrective un-provisioning scenarios would result in recovery to 933 steady state as follows: 935 o Scenario A: If the duplicate MAC or IP was un-provisioned at 936 the location where it was NOT marked as DUPLICATE, unfreezing the 937 route at the FROZEN location will result in the route being 938 advertised with a higher sequence number. This would in-turn 939 result in automatic clearing of local route at the PE location, 940 where the host was un-provisioned via ARP/ND PROBE and DELETE 941 procedure specified earlier in section 8 and in [RFC 7432]. 943 o Scenario B: If the duplicate host is un-provisioned at the 944 location where it was marked as DUPLICATE, unfreezing the route 945 will trigger an advertisement with a higher sequence number to 946 the other location. This would in-turn trigger re-learning of 947 local route at the remote location, resulting in another 948 advertisement with a higher sequence number from the remote 949 location. Route at the local location would now be cleared on 950 receiving this remote route advertisement, following the ARP/ND 951 PROBE. 953 9.4.2 Route Clearing Configuration 955 In addition to the above, route clearing CLIs may also be leveraged 956 to clear the local MAC or IP route, to be executed AFTER the 957 duplicate host is un-provisioned: 959 o clear mac CLI: A clear MAC CLI can be leveraged to clear a 960 DUPLICATE MAC route, to recover from a duplicate MAC scenario 962 o clear ARP/ND: A clear ARP/ND CLI may be leveraged to clear a 963 DUPLICATE IP route to recover from a duplicate IP scenario 965 Note that the route unfreeze CLI may still need to be run if the 966 route was un-provisioned and cleared from the NON-DUPLICATE / NON- 967 FROZEN location. Given that unfreezing of the route via the un-freeze 968 CLI would any ways result in auto-clearing of the route from the "un- 969 provisioned" location, as explained in the prior section, need for a 970 route clearing CLI for recovery from DUPLICATE / FROZEN state is 971 truly optional. 973 10. Security Considerations 974 11. IANA Considerations 976 12. References 978 12.1 Normative References 980 [RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A., 981 Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based 982 Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February 983 2015, . 985 [EVPN-PROXY-ARP] Rabadan et al., "Operational Aspects of Proxy- 986 ARP/ND in EVPN Networks", draft-ietf-bess-evpn-proxy-arp- 987 nd-06, work in progress, April 2019, 988 . 991 [EVPN-IRB] Sajassi et al., "Integrated Routing and Bridging in 992 EVPN", draft-ietf-bess-evpn-inter-subnet-forwarding-08, 993 work in progress, March 2019, 994 . 997 [RFC7814] Xu, X., Jacquenet, C., Raszuk, R., Boyes, T., Fee, B., 998 "Virtual Subnet: A BGP/MPLS IP VPN-Based Subnet Extension 999 Solution", RFC 7814, March 2016, 1000 . 1002 12.2 Informative References 1004 13. Acknowledgements 1006 Authors would like to thank Vibov Bhan and Patrice Brisset for 1007 feedback the process of design and implementation of procedures 1008 defined in this document. Authors would like to thank Wen Lin for a 1009 detailed review and valuable comments related to MAC sharing race 1010 conditions. 1012 Authors' Addresses 1014 Neeraj Malhotra (Editor) 1015 Arrcus 1016 EMail: neeraj.ietf@gmail.com 1018 Ali Sajassi 1019 Cisco 1020 EMail: sajassi@cisco.com 1021 Aparna Pattekar 1022 Cisco 1023 Email: apjoshi@cisco.com 1025 Jorge Rabadan 1026 Nokia 1027 Email: jorge.rabadan@nokia.com 1029 Avinash Lingala 1030 AT&T 1031 Email: ar977m@att.com 1033 John Drake 1034 Juniper Networks 1035 EMail: jdrake@juniper.net 1037 Appendix A 1039 An alternative approach considered was to associate two independent 1040 sequence number attributes with MAC and IP components of a MAC-IP 1041 route. However, the approach of enabling IRB mobility procedures 1042 using a single sequence number associated with a MAC, as specified in 1043 this document was preferred for the following reasons: 1045 o Procedural overhead and complexity associated with maintaining 1046 two separate sequence numbers all the time, only to address 1047 scenarios with changing MAC-IP bindings is a big overhead for 1048 topologies where MAC-IP bindings never change. 1050 o Using a single sequence number associated with MAC is much 1051 simpler and adds no overhead for topologies where MAC-IP bindings 1052 never change. 1054 o Using a single sequence number associated with MAC is aligned 1055 with existing MAC mobility implementations. On other words, it is 1056 an easier implementation extension to existing MAC mobility 1057 procedure.