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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 L2VPN Workgroup A. Sajassi (Editor) 3 INTERNET-DRAFT Cisco 4 Intended Status: Standards Track J. Drake (Editor) 5 Juniper 6 N. Bitar 7 Nokia 8 A. Isaac 9 Juniper 10 J. Uttaro 11 AT&T 12 W. Henderickx 13 Nokia 15 Expires: November 24, 2016 May 24, 2016 17 A Network Virtualization Overlay Solution using EVPN 18 draft-ietf-bess-evpn-overlay-03 20 Abstract 22 This document describes how Ethernet VPN (EVPN) [RFC7432] can be used 23 as an Network Virtualization Overlay (NVO) solution and explores the 24 various tunnel encapsulation options over IP and their impact on the 25 EVPN control-plane and procedures. In particular, the following 26 encapsulation options are analyzed: VXLAN, NVGRE, and MPLS over GRE. 28 Status of this Memo 30 This Internet-Draft is submitted to IETF in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF), its areas, and its working groups. Note that 35 other groups may also distribute working documents as 36 Internet-Drafts. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 The list of current Internet-Drafts can be accessed at 44 http://www.ietf.org/1id-abstracts.html 46 The list of Internet-Draft Shadow Directories can be accessed at 47 http://www.ietf.org/shadow.html 49 Copyright and License Notice 51 Copyright (c) 2012 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 2 Specification of Requirements . . . . . . . . . . . . . . . . . 5 68 3 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 4 EVPN Features . . . . . . . . . . . . . . . . . . . . . . . . . 6 70 5 Encapsulation Options for EVPN Overlays . . . . . . . . . . . . 7 71 5.1 VXLAN/NVGRE Encapsulation . . . . . . . . . . . . . . . . . 7 72 5.1.1 Virtual Identifiers Scope . . . . . . . . . . . . . . . 8 73 5.1.1.1 Data Center Interconnect with Gateway . . . . . . . 8 74 5.1.1.2 Data Center Interconnect without Gateway . . . . . . 9 75 5.1.2 Virtual Identifiers to EVI Mapping . . . . . . . . . . . 9 76 5.1.2.1 Auto Derivation of RT . . . . . . . . . . . . . . . 10 77 5.1.3 Constructing EVPN BGP Routes . . . . . . . . . . . . . 11 78 5.2 MPLS over GRE . . . . . . . . . . . . . . . . . . . . . . . 13 79 6 EVPN with Multiple Data Plane Encapsulations . . . . . . . . . 13 80 7 NVE Residing in Hypervisor . . . . . . . . . . . . . . . . . . 14 81 7.1 Impact on EVPN BGP Routes & Attributes for VXLAN/NVGRE 82 Encapsulation . . . . . . . . . . . . . . . . . . . . . . . 14 83 7.2 Impact on EVPN Procedures for VXLAN/NVGRE Encapsulation . . 15 84 8 NVE Residing in ToR Switch . . . . . . . . . . . . . . . . . . 15 85 8.1 EVPN Multi-Homing Features . . . . . . . . . . . . . . . . 16 86 8.1.1 Multi-homed Ethernet Segment Auto-Discovery . . . . . . 16 87 8.1.2 Fast Convergence and Mass Withdraw . . . . . . . . . . . 16 88 8.1.3 Split-Horizon . . . . . . . . . . . . . . . . . . . . . 16 89 8.1.4 Aliasing and Backup-Path . . . . . . . . . . . . . . . . 17 90 8.1.5 DF Election . . . . . . . . . . . . . . . . . . . . . . 17 91 8.2 Impact on EVPN BGP Routes & Attributes . . . . . . . . . . . 18 92 8.3 Impact on EVPN Procedures . . . . . . . . . . . . . . . . . 18 93 8.3.1 Split Horizon . . . . . . . . . . . . . . . . . . . . . 19 94 8.3.2 Aliasing and Backup-Path . . . . . . . . . . . . . . . . 19 96 9 Support for Multicast . . . . . . . . . . . . . . . . . . . . . 20 97 10 Data Center Interconnections - DCI . . . . . . . . . . . . . . 20 98 10.1 DCI using GWs . . . . . . . . . . . . . . . . . . . . . . . 21 99 10.2 DCI using ASBRs . . . . . . . . . . . . . . . . . . . . . . 21 100 10.2.1 ASBR Functionality with NVEs in Hypervisors . . . . . . 22 101 10.2.2 ASBR Functionality with NVEs in TORs . . . . . . . . . 22 102 11 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 24 103 12 Security Considerations . . . . . . . . . . . . . . . . . . . 24 104 13 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 105 14 References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 106 14.1 Normative References . . . . . . . . . . . . . . . . . . . 25 107 14.2 Informative References . . . . . . . . . . . . . . . . . . 26 108 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 109 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 111 1 Introduction 113 In the context of this document, a Network Virtualization Overlay 114 (NVO) is a solution to address the requirements of a multi-tenant 115 data center, especially one with virtualized hosts, e.g., Virtual 116 Machines (VMs). The key requirements of such a solution, as described 117 in [Problem-Statement], are: 119 - Isolation of network traffic per tenant 121 - Support for a large number of tenants (tens or hundreds of 122 thousands) 124 - Extending L2 connectivity among different VMs belonging to a given 125 tenant segment (subnet) across different PODs within a data center or 126 between different data centers 128 - Allowing a given VM to move between different physical points of 129 attachment within a given L2 segment 131 The underlay network for NVO solutions is assumed to provide IP 132 connectivity between NVO endpoints (NVEs). 134 This document describes how Ethernet VPN (EVPN) can be used as an NVO 135 solution and explores applicability of EVPN functions and procedures. 136 In particular, it describes the various tunnel encapsulation options 137 for EVPN over IP, and their impact on the EVPN control-plane and 138 procedures for two main scenarios: 140 a) when the NVE resides in the hypervisor, and 141 b) when the NVE resides in a Top of Rack (ToR) device 143 Note that the use of EVPN as an NVO solution does not necessarily 144 mandate that the BGP control-plane be running on the NVE. For such 145 scenarios, it is still possible to leverage the EVPN solution by 146 using XMPP, or alternative mechanisms, to extend the control-plane to 147 the NVE as discussed in [L3VPN-ENDSYSTEMS]. 149 The possible encapsulation options for EVPN overlays that are 150 analyzed in this document are: 152 - VXLAN and NVGRE 153 - MPLS over GRE 155 Before getting into the description of the different encapsulation 156 options for EVPN over IP, it is important to highlight the EVPN 157 solution's main features, how those features are currently supported, 158 and any impact that the encapsulation has on those features. 160 2 Specification of Requirements 162 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 163 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 164 document are to be interpreted as described in [RFC2119]. 166 3 Terminology 168 NVO: Network Virtualization Overlay 170 NVE: Network Virtualization Endpoint 172 VNI: Virtual Network Identifier (for VXLAN) 174 VSID: Virtual Subnet Identifier (for NVGRE) 176 EVPN: Ethernet VPN 178 EVI: An EVPN instance spanning the Provider Edge (PE) devices 179 participating in that EVPN. 181 MAC-VRF: A Virtual Routing and Forwarding table for Media Access 182 Control (MAC) addresses on a PE. 184 Ethernet Segment (ES): When a customer site (device or network) is 185 connected to one or more PEs via a set of Ethernet links, then that 186 set of links is referred to as an 'Ethernet segment'. 188 Ethernet Segment Identifier (ESI): A unique non-zero identifier that 189 identifies an Ethernet segment is called an 'Ethernet Segment 190 Identifier'. 192 Ethernet Tag: An Ethernet tag identifies a particular broadcast 193 domain, e.g., a VLAN. An EVPN instance consists of one or more 194 broadcast domains. 196 PE: Provider Edge device. 198 Single-Active Redundancy Mode: When only a single PE, among all the 199 PEs attached to an Ethernet segment, is allowed to forward traffic 200 to/from that Ethernet segment for a given VLAN, then the Ethernet 201 segment is defined to be operating in Single-Active redundancy mode. 203 All-Active Redundancy Mode: When all PEs attached to an Ethernet 204 segment are allowed to forward known unicast traffic to/from that 205 Ethernet segment for a given VLAN, then the Ethernet segment is 206 defined to be operating in All-Active redundancy mode. 208 4 EVPN Features 210 EVPN was originally designed to support the requirements detailed in 211 [RFC7209] and therefore has the following attributes which directly 212 address control plane scaling and ease of deployment issues. 214 1) Control plane traffic is distributed with BGP and Broadcast and 215 Multicast traffic is sent using a shared multicast tree or with 216 ingress replication. 218 2) Control plane learning is used for MAC (and IP) addresses instead 219 of data plane learning. The latter requires the flooding of unknown 220 unicast and ARP frames; whereas, the former does not require any 221 flooding. 223 3) Route Reflector is used to reduce a full mesh of BGP sessions 224 among PE devices to a single BGP session between a PE and the RR. 225 Furthermore, RR hierarchy can be leveraged to scale the number of BGP 226 routes on the RR. 228 4) Auto-discovery via BGP is used to discover PE devices 229 participating in a given VPN, PE devices participating in a given 230 redundancy group, tunnel encapsulation types, multicast tunnel type, 231 multicast members, etc. 233 5) All-Active multihoming is used. This allows a given customer 234 device (CE) to have multiple links to multiple PEs, and traffic 235 to/from that CE fully utilizes all of these links. This set of links 236 is termed an Ethernet Segment (ES). 238 6) When a link between a CE and a PE fails, the PEs for that EVI are 239 notified of the failure via the withdrawal of a single EVPN route. 240 This allows those PEs to remove the withdrawing PE as a next hop for 241 every MAC address associated with the failed link. This is termed 242 'mass withdrawal'. 244 7) BGP route filtering and constrained route distribution are 245 leveraged to ensure that the control plane traffic for a given EVI is 246 only distributed to the PEs in that EVI. 248 8) When a 802.1Q interface is used between a CE and a PE, each of the 249 VLAN ID (VID) on that interface can be mapped onto a bridge table 250 (for upto 4094 such bridge tables). All these bridge tables may be 251 mapped onto a single MAC-VRF (in case of VLAN-aware bundle service). 253 9) VM Mobility mechanisms ensure that all PEs in a given EVI know 254 the ES with which a given VM, as identified by its MAC and IP 255 addresses, is currently associated. 257 10) Route Targets are used to allow the operator (or customer) to 258 define a spectrum of logical network topologies including mesh, hub & 259 spoke, and extranets (e.g., a VPN whose sites are owned by different 260 enterprises), without the need for proprietary software or the aid of 261 other virtual or physical devices. 263 11) Because the design goal for NVO is millions of instances per 264 common physical infrastructure, the scaling properties of the control 265 plane for NVO are extremely important. EVPN and the extensions 266 described herein, are designed with this level of scalability in 267 mind. 269 5 Encapsulation Options for EVPN Overlays 271 5.1 VXLAN/NVGRE Encapsulation 273 Both VXLAN and NVGRE are examples of technologies that provide a data 274 plane encapsulation which is used to transport a packet over the 275 common physical IP infrastructure between Network Virtualization 276 Edges (NVEs) - e.g., VXLAN Tunnel End Points (VTEPs) in VXLAN 277 network. Both of these technologies include the identifier of the 278 specific NVO instance, Virtual Network Identifier (VNI) in VXLAN and 279 Virtual Subnet Identifier (VSID) in NVGRE, in each packet. In the 280 remainder of this document we use VNI as the representation for NVO 281 instance with the understanding that VSID can equally be used if the 282 encapsulation is NVGRE unless it is stated otherwise. 284 Note that a Provider Edge (PE) is equivalent to a NVE/VTEP. 286 VXLAN encapsulation is based on UDP, with an 8-byte header following 287 the UDP header. VXLAN provides a 24-bit VNI, which typically provides 288 a one-to-one mapping to the tenant VLAN ID, as described in 289 [RFC7348]. In this scenario, the ingress VTEP does not include an 290 inner VLAN tag on the encapsulated frame, and the egress VTEP 291 discards the frames with an inner VLAN tag. This mode of operation in 292 [RFC7348] maps to VLAN Based Service in [RFC7432], where a tenant 293 VLAN ID gets mapped to an EVPN instance (EVI). 295 VXLAN also provides an option of including an inner VLAN tag in the 296 encapsulated frame, if explicitly configured at the VTEP. This mode 297 of operation can map to VLAN Bundle Service in [RFC7432] because all 298 the tenant's tagged frames map to a single bridge table / MAC-VRF, 299 and the inner VLAN tag is not used for lookup by the disposition PE 300 when performing VXLAN decapsulation as described in section 6 of 301 [RFC7348]. 303 [NVGRE] encapsulation is based on [GRE] and it mandates the inclusion 304 of the optional GRE Key field which carries the VSID. There is a one- 305 to-one mapping between the VSID and the tenant VLAN ID, as described 306 in [NVGRE] and the inclusion of an inner VLAN tag is prohibited. This 307 mode of operation in [NVGRE] maps to VLAN Based Service in 308 [RFC7432]. 310 As described in the next section there is no change to the encoding 311 of EVPN routes to support VXLAN or NVGRE encapsulation except for the 312 use of BGP Encapsulation extended community to indicate the 313 encapsulation type (e.g., VxLAN or NVGRE). However, there is 314 potential impact to the EVPN procedures depending on where the NVE is 315 located (i.e., in hypervisor or TOR) and whether multi-homing 316 capabilities are required. 318 5.1.1 Virtual Identifiers Scope 320 Although VNIs are defined as 24-bit globally unique values, there are 321 scenarios in which it is desirable to use a locally significant value 322 for VNI, especially in the context of data center interconnect: 324 5.1.1.1 Data Center Interconnect with Gateway 326 In the case where NVEs in different data centers need to be 327 interconnected, and the NVEs need to use VNIs as a globally unique 328 identifiers within a data center, then a Gateway needs to be employed 329 at the edge of the data center network. This is because the Gateway 330 will provide the functionality of translating the VNI when crossing 331 network boundaries, which may align with operator span of control 332 boundaries. As an example, consider the network of Figure 1 below. 333 Assume there are three network operators: one for each of the DC1, 334 DC2 and WAN networks. The Gateways at the edge of the data centers 335 are responsible for translating the VNIs between the values used in 336 each of the data center networks and the values used in the WAN. 338 +--------------+ 339 | | 340 +---------+ | WAN | +---------+ 341 +----+ | +---+ +----+ +----+ +---+ | +----+ 342 |NVE1|--| | | |WAN | |WAN | | | |--|NVE3| 343 +----+ |IP |GW |--|Edge| |Edge|--|GW | IP | +----+ 344 +----+ |Fabric +---+ +----+ +----+ +---+ Fabric | +----+ 345 |NVE2|--| | | | | |--|NVE4| 346 +----+ +---------+ +--------------+ +---------+ +----+ 348 |<------ DC 1 ------> <------ DC2 ------>| 350 Figure 1: Data Center Interconnect with Gateway 352 5.1.1.2 Data Center Interconnect without Gateway 354 In the case where NVEs in different data centers need to be 355 interconnected, and the NVEs need to use locally assigned VNIs (e.g., 356 similar to MPLS labels), then there may be no need to employ Gateways 357 at the edge of the data center network. More specifically, the VNI 358 value that is used by the transmitting NVE is allocated by the NVE 359 that is receiving the traffic (in other words, this is similar to 360 "downstream assigned" MPLS label). This allows the VNI space to be 361 decoupled between different data center networks without the need for 362 a dedicated Gateway at the edge of the data centers. This topics is 363 covered in section 10.2. 365 +--------------+ 366 | | 367 +---------+ | WAN | +---------+ 368 +----+ | | +----+ +----+ | | +----+ 369 |NVE1|--| | |ASBR| |ASBR| | |--|NVE3| 370 +----+ |IP Fabric|---| | | |--|IP Fabric| +----+ 371 +----+ | | +----+ +----+ | | +----+ 372 |NVE2|--| | | | | |--|NVE4| 373 +----+ +---------+ +--------------+ +---------+ +----+ 375 |<------ DC 1 -----> <---- DC2 ------>| 377 Figure 2: Data Center Interconnect with ASBR 379 5.1.2 Virtual Identifiers to EVI Mapping 381 When the EVPN control plane is used in conjunction with VXLAN (or 382 NVGRE encapsulation), two options for mapping the VXLAN VNI (or NVGRE 383 VSID) to an EVI are possible: 385 1. Option 1: Single Subnet per EVI 387 In this option, a single subnet represented by a VNI is mapped to a 388 unique EVI. This corresponds to the VLAN Based service in [RFC7432], 389 where a tenant VLAN ID gets mapped to an EVPN instance (EVI). As 390 such, a BGP RD and RT is needed per VNI on every NVE. The advantage 391 of this model is that it allows the BGP RT constraint mechanisms to 392 be used in order to limit the propagation and import of routes to 393 only the NVEs that are interested in a given VNI. The disadvantage of 394 this model may be the provisioning overhead if RD and RT are not 395 derived automatically from VNI. 397 In this option, the MAC-VRF table is identified by the RT in the 398 control plane and by the VNI in the data-plane. In this option, the 399 specific the MAC-VRF table corresponds to only a single bridge table. 401 2. Option 2: Multiple Subnets per EVI 403 In this option, multiple subnets each represented by a unique VNI are 404 mapped to a single EVI. For example, if a tenant has multiple 405 segments/subnets each represented by a VNI, then all the VNIs for 406 that tenant are mapped to a single EVI - e.g., the EVI in this case 407 represents the tenant and not a subnet . This corresponds to the 408 VLAN-aware bundle service in [RFC7432]. The advantage of this model 409 is that it doesn't require the provisioning of RD/RT per VNI. 410 However, this is a moot point if option 1 with auto-derivation is 411 used. The disadvantage of this model is that routes would be imported 412 by NVEs that may not be interested in a given VNI. 414 In this option the MAC-VRF table is identified by the RT in the 415 control plane and a specific bridge table for that MAC-VRF is 416 identified by the in the control plane. In this 417 option, the VNI in the data-plane is sufficient to identify a 418 specific bridge table - e.g., no need to do a lookup based on VNI and 419 Ethernet Tag ID fields to identify a bridge table. 421 5.1.2.1 Auto Derivation of RT 423 When the option of a single VNI per EVI is used, it is important to 424 auto-derive RT for EVPN BGP routes in order to simplify configuration 425 for data center operations. RD can be auto generated as described in 426 [RFC7432] and RT can be auto-derived as described next. 428 Since a gateway PE as depicted in figure-1 participates in both the 429 DCN and WAN BGP sessions, it is important that when RT values are 430 auto-derived for VNIs, there is no conflict in RT spaces between DCN 431 and WAN networks assuming that both are operating within the same AS. 432 Also, there can be scenarios where both VXLAN and NVGRE 433 encapsulations may be needed within the same DCN and their 434 corresponding VNIs are administered independently which means VNI 435 spaces can overlap. In order to ensure that no such conflict in RT 436 spaces arises, RT values for DCNs are auto-derived as follow: 438 0 1 2 3 4 439 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 0 440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---+ 441 | AS # |A| TYPE| D-ID |Service Instance ID| 442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---+ 444 - 2 bytes of global admin field of the RT is set to the AS number. 446 - Three least significant bytes of the local admin field of the RT is 447 set to the VNI, VSID, I-SID, or VID. 449 - The most significant bit of the local admin field of the RT is set 450 as follow: 451 0: auto-derived 452 1: manually-derived 454 - The next 3 bits of the most significant byte of the local admin 455 field of the RT identifies the space in which the other 3 bytes are 456 defined. The following spaces are defined: 457 0 : VID 458 1 : VXLAN 459 2 : NVGRE 460 3 : I-SID 461 4 : EVI 462 5 : dual-VID 464 - The remaining 4 bits of the most significant byte of the local 465 admin field of the RT identifies the domain-id. The default value of 466 domain-id is zero indicating that only a single numbering space exist 467 for a given technology. However, if there are more than one number 468 space exist for a given technology (e.g., overlapping VXLAN spaces), 469 then each of the number spaces need to be identify by their 470 corresponding domain-id starting from 1. 472 5.1.3 Constructing EVPN BGP Routes 474 In EVPN, an MPLS label is distributed by the egress PE via the EVPN 475 control plane and is placed in the MPLS header of a given packet by 476 the ingress PE. This label is used upon receipt of that packet by the 477 egress PE for disposition of that packet. This is very similar to the 478 use of the VNI by the egress NVE, with the difference being that an 479 MPLS label has local significance while a VNI typically has global 480 significance. Accordingly, and specifically to support the option of 481 locally assigned VNIs, the MPLS label field in the MAC Advertisement, 482 Ethernet AD per EVI, and Inclusive Multicast Ethernet Tag routes is 483 used to carry the VNI. For the balance of this memo, the MPLS label 484 field will be referred to as the VNI field. The VNI field is used for 485 both local and global VNIs, and for either case the entire 24-bit 486 field is used to encode the VNI value. 488 For the VLAN-based service (a single VNI per MAC-VRF), the Ethernet 489 Tag field in the MAC/IP Advertisement, Ethernet AD per EVI, and 490 Inclusive Multicast route MUST be set to zero just as in the VLAN 491 Based service in [RFC7432]. 493 For the VLAN-aware bundle service (multiple VNIs per MAC-VRF with 494 each VNI associated with its own bridge table), the Ethernet Tag 495 field in the MAC Advertisement, Ethernet AD per EVI, and Inclusive 496 Multicast route MUST identify a bridge table within a MAC-VRF and the 497 set of Ethernet Tags for that EVI needs to be configured consistently 498 on all PEs within that EVI. For local VNIs, the value advertised in 499 the Ethernet Tag field MUST be set to a VID just as in the VLAN-aware 500 bundle service in [RFC7432]. Such setting must be done consistently 501 on all PE devices participating in that EVI within a given domain. 502 For global VNIs, the value advertised in the Ethernet Tag field 503 SHOULD be set to a VNI as long as it matches the existing semantics 504 of the Ethernet Tag, i.e., it identifies a bridge table within a MAC- 505 VRF and the set of VNIs are configured consistently on each PE in 506 that EVI. 508 In order to indicate that which type of data plane encapsulation 509 (i.e., VXLAN, NVGRE, MPLS, or MPLS in GRE) is to be used, the BGP 510 Encapsulation extended community defined in [RFC5512] is included 511 with all EVPN routes (i.e. MAC Advertisement, Ethernet AD per EVI, 512 Ethernet AD per ESI, Inclusive Multicast Ethernet Tag, and Ethernet 513 Segment) advertised by an egress PE. Five new values have been 514 assigned by IANA to extend the list of encapsulation types defined in 515 [RFC5512]: 517 + 8 - VXLAN Encapsulation 518 + 9 - NVGRE Encapsulation 519 + 10 - MPLS Encapsulation 520 + 11 - MPLS in GRE Encapsulation 521 + 12 - VXLAN GPE Encapsulation 523 Note that the MPLS encapsulation tunnel type is needed in order to 524 distinguish between an advertising node that only supports non-MPLS 525 encapsulations and one that supports MPLS and non-MPLS 526 encapsulations. An advertising node that only supports MPLS 527 encapsulation does not need to advertise any encapsulation tunnel 528 types; i.e., if the BGP Encapsulation extended community is not 529 present, then either MPLS encapsulation or a statically configured 530 encapsulation is assumed. 532 The Ethernet Segment and Ethernet AD per ESI routes MAY be advertised 533 with multiple encapsulation types as long as they use the same EVPN 534 multi-homing procedures - e.g., the mix of VXLAN and NVGRE 535 encapsulation types is a valid one but not the mix of VXLAN and MPLS 536 encapsulation types. 538 The Next Hop field of the MP_REACH_NLRI attribute of the route MUST 539 be set to the IPv4 or IPv6 address of the NVE. The remaining fields 540 in each route are set as per [RFC7432]. 542 5.2 MPLS over GRE 544 The EVPN data-plane is modeled as an EVPN MPLS client layer sitting 545 over an MPLS PSN-tunnel server layer. Some of the EVPN functions 546 (split-horizon, aliasing, and backup-path) are tied to the MPLS 547 client layer. If MPLS over GRE encapsulation is used, then the EVPN 548 MPLS client layer can be carried over an IP PSN tunnel transparently. 549 Therefore, there is no impact to the EVPN procedures and associated 550 data-plane operation. 552 The existing standards for MPLS over GRE encapsulation as defined by 553 [RFC4023] can be used for this purpose; however, when it is used in 554 conjunction with EVPN the GRE key field SHOULD be present, and SHOULD 555 be used to provide a 32-bit entropy field. The Checksum and Sequence 556 Number fields are not needed and their corresponding C and S bits 557 MUST be set to zero. 559 6 EVPN with Multiple Data Plane Encapsulations 561 The use of the BGP Encapsulation extended community per [RFC5512] 562 allows each NVE in a given EVI to know each of the encapsulations 563 supported by each of the other NVEs in that EVI. i.e., each of the 564 NVEs in a given EVI may support multiple data plane encapsulations. 565 An ingress NVE can send a frame to an egress NVE only if the set of 566 encapsulations advertised by the egress NVE in the subject MAC/IP 567 Advertisement or per EVI Ethernet AD route, forms a non-empty 568 intersection with the set of encapsulations supported by the ingress 569 NVE, and it is at the discretion of the ingress NVE which 570 encapsulation to choose from this intersection. (As noted in 571 section 5.1.3, if the BGP Encapsulation extended community is not 572 present, then the default MPLS encapsulation or a statically 573 configured encapsulation is assumed.) 575 An ingress node that uses shared multicast trees for sending 576 broadcast or multicast frames MUST maintain distinct trees for each 577 different encapsulation type. 579 It is the responsibility of the operator of a given EVI to ensure 580 that all of the NVEs in that EVI support at least one common 581 encapsulation. If this condition is violated, it could result in 582 service disruption or failure. The use of the BGP Encapsulation 583 extended community provides a method to detect when this condition is 584 violated but the actions to be taken are at the discretion of the 585 operator and are outside the scope of this document. 587 7 NVE Residing in Hypervisor 589 When a NVE and its hosts/VMs are co-located in the same physical 590 device, e.g., when they reside in a server, the links between them 591 are virtual and they typically share fate; i.e., the subject 592 hosts/VMs are typically not multi-homed or if they are multi-homed, 593 the multi-homing is a purely local matter to the server hosting the 594 VM and the NVEs, and need not be "visible" to any other NVEs residing 595 on other servers, and thus does not require any specific protocol 596 mechanisms. The most common case of this is when the NVE resides on 597 the hypervisor. 599 In the sub-sections that follow, we will discuss the impact on EVPN 600 procedures for the case when the NVE resides on the hypervisor and 601 the VXLAN (or NVGRE) encapsulation is used. 603 7.1 Impact on EVPN BGP Routes & Attributes for VXLAN/NVGRE Encapsulation 605 In the scenario where all data centers are under a single 606 administrative domain, and there is a single global VNI space, the RD 607 MAY be set to zero in the EVPN routes. However, in the scenario where 608 different groups of data centers are under different administrative 609 domains, and these data centers are connected via one or more 610 backbone core providers as described in [NOV3-Framework], the RD must 611 be a unique value per EVI or per NVE as described in [RFC7432]. In 612 other words, whenever there is more than one administrative domain 613 for global VNI, then a non-zero RD MUST be used, or whenever the VNI 614 value have local significance, then a non-zero RD MUST be used. It is 615 recommend to use a non-zero RD at all time. 617 When the NVEs reside on the hypervisor, the EVPN BGP routes and 618 attributes associated with multi-homing are no longer required. This 619 reduces the required routes and attributes to the following subset of 620 four out of eight: 622 - MAC/IP Advertisement Route 623 - Inclusive Multicast Ethernet Tag Route 624 - MAC Mobility Extended Community 625 - Default Gateway Extended Community 627 However, as noted in section 8.6 of [RFC7432] in order to enable a 628 single-homing ingress NVE to take advantage of fast convergence, 629 aliasing, and backup-path when interacting with multi-homed egress 630 NVEs attached to a given Ethernet segment, the single-homing ingress 631 NVE SHOULD be able to receive and process Ethernet AD per ES and 632 Ethernet AD per EVI routes. 634 7.2 Impact on EVPN Procedures for VXLAN/NVGRE Encapsulation 636 When the NVEs reside on the hypervisors, the EVPN procedures 637 associated with multi-homing are no longer required. This limits the 638 procedures on the NVE to the following subset of the EVPN procedures: 640 1. Local learning of MAC addresses received from the VMs per section 641 10.1 of [RFC7432]. 643 2. Advertising locally learned MAC addresses in BGP using the MAC/IP 644 Advertisement routes. 646 3. Performing remote learning using BGP per Section 10.2 of 647 [RFC7432]. 649 4. Discovering other NVEs and constructing the multicast tunnels 650 using the Inclusive Multicast Ethernet Tag routes. 652 5. Handling MAC address mobility events per the procedures of Section 653 16 in [RFC7432]. 655 However, as noted in section 8.6 of [RFC7432] in order to enable a 656 single-homing ingress NVE to take advantage of fast convergence, 657 aliasing, and back-up path when interacting with multi-homed egress 658 NVEs attached to a given Ethernet segment, a single-homing ingress 659 NVE SHOULD implement the ingress node processing of Ethernet AD per 660 ES and Ethernet AD per EVI routes as defined in sections 8.2 Fast 661 Convergence and 8.4 Aliasing and Backup-Path of [RFC7432]. 663 8 NVE Residing in ToR Switch 664 In this section, we discuss the scenario where the NVEs reside in the 665 Top of Rack (ToR) switches AND the servers (where VMs are residing) 666 are multi-homed to these ToR switches. The multi-homing may operate 667 in All-Active or Single-Active redundancy mode. If the servers are 668 single-homed to the ToR switches, then the scenario becomes similar 669 to that where the NVE resides on the hypervisor, as discussed in 670 Section 7, as far as the required EVPN functionality are concerned. 672 [RFC7432] defines a set of BGP routes, attributes and procedures to 673 support multi-homing. We first describe these functions and 674 procedures, then discuss which of these are impacted by the VxLAN 675 (or NVGRE) encapsulation and what modifications are required. 677 8.1 EVPN Multi-Homing Features 679 In this section, we will recap the multi-homing features of EVPN to 680 highlight the encapsulation dependencies. The section only describes 681 the features and functions at a high-level. For more details, the 682 reader is to refer to [RFC7432]. 684 8.1.1 Multi-homed Ethernet Segment Auto-Discovery 686 EVPN NVEs (or PEs) connected to the same Ethernet Segment (e.g. the 687 same server via LAG) can automatically discover each other with 688 minimal to no configuration through the exchange of BGP routes. 690 8.1.2 Fast Convergence and Mass Withdraw 692 EVPN defines a mechanism to efficiently and quickly signal, to remote 693 NVEs, the need to update their forwarding tables upon the occurrence 694 of a failure in connectivity to an Ethernet segment (e.g., a link or 695 a port failure). This is done by having each NVE advertise an 696 Ethernet A-D Route per Ethernet segment for each locally attached 697 segment. Upon a failure in connectivity to the attached segment, the 698 NVE withdraws the corresponding Ethernet A-D route. This triggers all 699 NVEs that receive the withdrawal to update their next-hop adjacencies 700 for all MAC addresses associated with the Ethernet segment in 701 question. If no other NVE had advertised an Ethernet A-D route for 702 the same segment, then the NVE that received the withdrawal simply 703 invalidates the MAC entries for that segment. Otherwise, the NVE 704 updates the next-hop adjacency list accordingly. 706 8.1.3 Split-Horizon 708 If a server is multi-homed to two or more NVEs (represented by an 709 Ethernet segment ES1) and operating in an all-active redundancy mode, 710 sends a BUM packet (ie, Broadcast, Unknown unicast, or Multicast) 711 packet to one of these NVEs, then it is important to ensure the 712 packet is not looped back to the server via another NVE connected to 713 this server. The filtering mechanism on the NVE to prevent such loop 714 and packet duplication is called "split horizon filtering'. 716 8.1.4 Aliasing and Backup-Path 718 In the case where a station is multi-homed to multiple NVEs, it is 719 possible that only a single NVE learns a set of the MAC addresses 720 associated with traffic transmitted by the station. This leads to a 721 situation where remote NVEs receive MAC advertisement routes, for 722 these addresses, from a single NVE even though multiple NVEs are 723 connected to the multi-homed station. As a result, the remote NVEs 724 are not able to effectively load-balance traffic among the NVEs 725 connected to the multi-homed Ethernet segment. This could be the 726 case, for e.g. when the NVEs perform data-path learning on the 727 access, and the load-balancing function on the station hashes traffic 728 from a given source MAC address to a single NVE. Another scenario 729 where this occurs is when the NVEs rely on control plane learning on 730 the access (e.g. using ARP), since ARP traffic will be hashed to a 731 single link in the LAG. 733 To alleviate this issue, EVPN introduces the concept of Aliasing. 734 This refers to the ability of an NVE to signal that it has 735 reachability to a given locally attached Ethernet segment, even when 736 it has learnt no MAC addresses from that segment. The Ethernet A-D 737 route per EVI is used to that end. Remote NVEs which receive MAC 738 advertisement routes with non-zero ESI SHOULD consider the MAC 739 address as reachable via all NVEs that advertise reachability to the 740 relevant Segment using Ethernet A-D routes with the same ESI and with 741 the Single-Active flag reset. 743 Backup-Path is a closely related function, albeit it applies to the 744 case where the redundancy mode is Single-Active. In this case, the 745 NVE signals that it has reachability to a given locally attached 746 Ethernet Segment using the Ethernet A-D route as well. Remote NVEs 747 which receive the MAC advertisement routes, with non-zero ESI, SHOULD 748 consider the MAC address as reachable via the advertising NVE. 749 Furthermore, the remote NVEs SHOULD install a Backup-Path, for said 750 MAC, to the NVE which had advertised reachability to the relevant 751 Segment using an Ethernet A-D route with the same ESI and with the 752 Single-Active flag set. 754 8.1.5 DF Election 756 If a host is multi-homed to two or more NVEs on an Ethernet segment 757 operating in all-active redundancy mode, then for a given EVI only 758 one of these NVEs, termed the Designated Forwarder (DF) is 759 responsible for sending it broadcast, multicast, and, if configured 760 for that EVI, unknown unicast frames. 762 This is required in order to prevent duplicate delivery of multi- 763 destination frames to a multi-homed host or VM, in case of all-active 764 redundancy. 766 In NVEs where .1Q tagged frames are received from hosts, the DF 767 election is performed on host VLAN IDs (VIDs). It is assumed that for 768 a given Ethernet Segment, VIDs are unique and consistent (e.g., no 769 duplicate VIDs exist). 771 In GWs where VxLAN encapsulated frames are received, the DF election 772 is performed on VNIs. Again, it is assumed that for a given Ethernet 773 Segment, VNIs are unique and consistent (e.g., no duplicate VNIs 774 exist). 776 8.2 Impact on EVPN BGP Routes & Attributes 778 Since multi-homing is supported in this scenario, then the entire set 779 of BGP routes and attributes defined in [RFC7432] are used. The 780 setting of the Ethernet Tag field in the MAC Advertisement, Ethernet 781 AD per EVI, and Inclusive Multicast routes follows that of section 782 5.1.3. Furthermore, the setting of the VNI field in the MAC 783 Advertisement and Ethernet AD per EVI routes follows that of section 784 5.1.3. 786 8.3 Impact on EVPN Procedures 788 Two cases need to be examined here, depending on whether the NVEs are 789 operating in Active/Standby or in All-Active redundancy. 791 First, lets consider the case of Active/Standby redundancy, where the 792 hosts are multi-homed to a set of NVEs, however, only a single NVE is 793 active at a given point of time for a given VNI. In this case, the 794 aliasing is not required and the split-horizon may not be required, 795 but other functions such as multi-homed Ethernet segment auto- 796 discovery, fast convergence and mass withdraw, backup path, and DF 797 election are required. 799 Second, let's consider the case of All-Active redundancy. In this 800 case, out of all the EVPN multi-homing features listed in section 801 8.1, the use of the VXLAN or NVGRE encapsulation impacts the split- 802 horizon and aliasing features, since those two rely on the MPLS 803 client layer. Given that this MPLS client layer is absent with these 804 types of encapsulations, alternative procedures and mechanisms are 805 needed to provide the required functions. Those are discussed in 806 detail next. 808 8.3.1 Split Horizon 810 In EVPN, an MPLS label is used for split-horizon filtering to support 811 All-Active multi-homing where an ingress NVE adds a label 812 corresponding to the site of origin (aka ESI Label) when 813 encapsulating the packet. The egress NVE checks the ESI label when 814 attempting to forward a multi-destination frame out an interface, and 815 if the label corresponds to the same site identifier (ESI) associated 816 with that interface, the packet gets dropped. This prevents the 817 occurrence of forwarding loops. 819 Since the VXLAN or NVGRE encapsulation does not include this ESI 820 label, other means of performing the split-horizon filtering function 821 MUST be devised. The following approach is recommended for split- 822 horizon filtering when VXLAN (or NVGRE) encapsulation is used. 824 Every NVE track the IP address(es) associated with the other NVE(s) 825 with which it has shared multi-homed Ethernet Segments. When the NVE 826 receives a multi-destination frame from the overlay network, it 827 examines the source IP address in the tunnel header (which 828 corresponds to the ingress NVE) and filters out the frame on all 829 local interfaces connected to Ethernet Segments that are shared with 830 the ingress NVE. With this approach, it is required that the ingress 831 NVE performs replication locally to all directly attached Ethernet 832 Segments (regardless of the DF Election state) for all flooded 833 traffic ingress from the access interfaces (i.e. from the hosts). 834 This approach is referred to as "Local Bias", and has the advantage 835 that only a single IP address needs to be used per NVE for split- 836 horizon filtering, as opposed to requiring an IP address per Ethernet 837 Segment per NVE. 839 In order to prevent unhealthy interactions between the split horizon 840 procedures defined in [RFC7432] and the local bias procedures 841 described in this document, a mix of MPLS over GRE encapsulations on 842 the one hand and VXLAN/NVGRE encapsulations on the other on a given 843 Ethernet Segment is prohibited. 845 8.3.2 Aliasing and Backup-Path 847 The Aliasing and the Backup-Path procedures for VXLAN/NVGRE 848 encapsulation is very similar to the ones for MPLS. In case of MPLS, 849 two different Ethernet A-D routes are used for this purpose. The one 850 used for Aliasing has a VPN scope (per EVI) and carries a VPN label 851 but the one used for Backup-Path has Ethernet segment scope (per ES) 852 and doesn't carry any VPN specific info (e.g., Ethernet Tag and MPLS 853 label are set to zero). In case of VxLAN/NVGRE, the same two routes 854 are used for the Aliasing and the Backup-Path. In case of Aliasing, 855 the Ethernet Tag and VNI fields in Ethernet A-D per EVI route is set 856 as described in section 5.1.3. 858 9 Support for Multicast 860 The E-VPN Inclusive Multicast BGP route is used to discover the 861 multicast tunnels among the endpoints associated with a given EVI 862 (e.g., given VNI) for VLAN-based service and a given for 863 VLAN-aware bundle service. The Ethernet Tag field of this route is 864 set as described in section 5.1.3. The Originating router's IP 865 address field is set to the NVE's IP address. This route is tagged 866 with the PMSI Tunnel attribute, which is used to encode the type of 867 multicast tunnel to be used as well as the multicast tunnel 868 identifier. The tunnel encapsulation is encoded by adding the BGP 869 Encapsulation extended community as per section 5.1.1. The following 870 tunnel types as defined in [RFC6514] can be used in the PMSI tunnel 871 attribute for VXLAN/NVGRE: 873 + 3 - PIM-SSM Tree 874 + 4 - PIM-SM Tree 875 + 5 - BIDIR-PIM Tree 876 + 6 - Ingress Replication 878 Except for Ingress Replication, this multicast tunnel is used by the 879 PE originating the route for sending multicast traffic to other PEs, 880 and is used by PEs that receive this route for receiving the traffic 881 originated by hosts connected to the PE that originated the route. 883 In the scenario where the multicast tunnel is a tree, both the 884 Inclusive as well as the Aggregate Inclusive variants may be used. In 885 the former case, a multicast tree is dedicated to a VNI. Whereas, in 886 the latter, a multicast tree is shared among multiple VNIs. This is 887 done by having the NVEs advertise multiple Inclusive Multicast routes 888 with different VNI encoded in the Ethernet Tag field, but with the 889 same tunnel identifier encoded in the PMSI Tunnel attribute. 891 10 Data Center Interconnections - DCI 893 For DCI, the following two main scenarios are considered when 894 connecting data centers running evpn-overlay (as described here) over 895 MPLS/IP core network: 897 - Scenario 1: DCI using GWs 898 - Scenario 2: DCI using ASBRs 899 The following two subsections describe the operations for each of 900 these scenarios. 902 10.1 DCI using GWs 904 This is the typical scenario for interconnecting data centers over 905 WAN. In this scenario, EVPN routes are terminated and processed in 906 each GW and MAC/IP routes are always re-advertised from DC to WAN but 907 from WAN to DC, they are not re-advertised if unknown MAC address 908 (and default IP address) are utilized in NVEs. In this scenario, each 909 GW maintains a MAC-VRF (and/or IP-VRF) for each EVI. The main 910 advantage of this approach is that NVEs do not need to maintain MAC 911 and IP addresses from any remote data centers when default IP route 912 and unknown MAC routes are used - i.e., they only need to maintain 913 routes that are local to their own DC. When default IP route and 914 unknown MAC route are used, any unknown IP and MAC packets from NVEs 915 are forwarded to the GWs where all the VPN MAC and IP routes are 916 maintained. This approach reduces the size of MAC-VRF and IP-VRF 917 significantly at NVEs. Furthermore, it results in a faster 918 convergence time upon a link or NVE failure in a multi-homed network 919 or device redundancy scenario, because the failure related BGP routes 920 (such as mass withdraw message) do not need to get propagated all the 921 way to the remote NVEs in the remote DCs. This approach is described 922 in details in section 3.4 of [DCI-EVPN-OVERLAY]. 924 10.2 DCI using ASBRs 926 This approach can be considered as the opposite of the first approach 927 and it favors simplification at DCI devices over NVEs such that 928 larger MAC-VRF (and IP-VRF) tables are need to be maintained on NVEs; 929 whereas, DCI devices don't need to maintain any MAC (and IP) 930 forwarding tables. Furthermore, DCI devices do not need to terminate 931 and processed routes related to multi-homing but rather to relay 932 these messages for the establishment of an end-to-end LSP path. In 933 other words, DCI devices in this approach operate similar to ASBRs 934 for inter-AS options B. This requires locally assigned VNIs to be 935 used just like downstream assigned MPLS VPN label where for all 936 practical purposes the VNIs function like 24-bit VPN labels. This 937 approach is equally applicable to data centers (or Carrier Ethernet 938 networks) with MPLS encapsulation. 940 In inter-AS option B, when ASBR receives an EVPN route from its DC 941 over iBGP and re-advertises it to other ASBRs, it re-advertises the 942 EVPN route by re-writing the BGP next-hops to itself, thus losing the 943 identity of the PE that originated the advertisement. This re-write 944 of BGP next-hop impacts the EVPN Mass Withdraw route (Ethernet A-D 945 per ES) and its procedure adversely. However, it does not impact EVPN 946 Aliasing mechanism/procedure because when the Aliasing routes (Ether 947 A-D per EVI) are advertised, the receiving PE first resolves a MAC 948 address for a given EVI into its corresponding and 949 subsequently, it resolves the into multiple paths (and their 950 associated next hops) via which the is reachable. Since 951 Aliasing and MAC routes are both advertised per EVI basis and they 952 use the same RD and RT (per EVI), the receiving PE can associate them 953 together on a per BGP path basis (e.g., per originating PE) and thus 954 perform recursive route resolution - e.g., a MAC is reachable via an 955 which in turn, is reachable via a set of BGP paths, thus the 956 MAC is reachable via the set of BGP paths. Since on a per EVI basis, 957 the association of MAC routes and the corresponding Aliasing route is 958 fixed and determined by the same RD and RT, there is no ambiguity 959 when the BGP next hop for these routes is re-written as these routes 960 pass through ASBRs - i.e., the receiving PE may receive multiple 961 Aliasing routes for the same EVI from a single next hop (a single 962 ASBR), and it can still create multiple paths toward that . 964 However, when the BGP next hop address corresponding to the 965 originating PE is re-written, the association between the Mass 966 Withdraw route (Ether A-D per ES) and its corresponding MAC routes 967 cannot be made based on their RDs and RTs because the RD for Mass 968 Withdraw route is different than the one for the MAC routes. 969 Therefore, the functionality needed at the ASBRs and the receiving 970 PEs depends on whether the Mass Withdraw route is originated and 971 whether there is a need to handle route resolution ambiguity for this 972 route. The following two subsections describe the functionality 973 needed by the ASBRs and the receiving PEs depending on whether the 974 NVEs reside in a Hypervisors or in TORs. 976 10.2.1 ASBR Functionality with NVEs in Hypervisors 978 When NVEs reside in hypervisors as described in section 7.1, there is 979 no multi-homing and thus there is no need for the originating NVE to 980 send Ethernet A-D per ES or Ethernet A-D per EVI routes. However, as 981 noted in section 7, in order to enable a single-homing ingress NVE to 982 take advantage of fast convergence, aliasing, and backup-path when 983 interacting with multi-homing egress NVEs attached to a given 984 Ethernet segment, the single-homing NVE SHOULD be able to receive and 985 process Ethernet AD per ES and Ethernet AD per EVI routes. The 986 handling of these routes are described in the next section. 988 10.2.2 ASBR Functionality with NVEs in TORs 990 When NVEs reside in TORs and operate in multi-homing redundancy mode, 991 then as described in section 8, there is a need for the originating 992 NVE to send Ethernet A-D per ES route(s) (used for mass withdraw) and 993 Ethernet A-D per EVI routes (used for aliasing). As described above, 994 the re-write of BGP next-hop by ASBRs creates ambiguities when 995 Ethernet A-D per ES routes are received by the remote NVE in a 996 different ASBR because the receiving NVE cannot associated that route 997 with the MAC/IP routes of that Ethernet Segment advertised by the 998 same originating NVE. This ambiguity inhibits the function of mass- 999 withdraw per ES by the receiving NVE in a different AS. 1001 As an example consider a scenario where CE is multi-homed to PE1 and 1002 PE2 where these PEs are connected via ASBR1 and then ASBR2 to the 1003 remote PE3. Furthermore, consider that PE1 receives M1 from CE1 but 1004 not PE2. Therefore, PE1 advertises Eth A-D per ES1, Eth A-D per EVI1, 1005 and M1; whereas, PE2 only advertises Eth A-D per ES1 and Eth A-D per 1006 EVI1. ASBR1 receives all these five advertisements and passes them to 1007 ASBR2 (with itself as the BGP next hop). ASBR2, in turn, passes them 1008 to the remote PE3 with itself as the BGP next hop. PE3 receives these 1009 five routes where all of them have the same BGP next-hop (i.e., 1010 ASBR2). Furthermore, the two Ether A-D per ES routes received by PE3 1011 have the same info - i.e., same ESI and the same BGP next hop. 1012 Although both of these routes are maintained by the BGP process in 1013 PE3 (because they have different RDs and thus treated as different 1014 BGP routes), information from only one of them is used in the L2 1015 routing table (L2 RIB). 1017 PE1 1018 / \ 1019 CE ASBR1---ASBR2---PE3 1020 \ / 1021 PE2 1023 Figure 1: Inter-AS Option B 1025 Now, when the AC between the PE2 and the CE fails and PE2 sends NLRI 1026 withdrawal for Ether A-D per ES route and this withdrawal gets 1027 propagated and received by the PE3, the BGP process in PE3 removes 1028 the corresponding BGP route; however, it doesn't remove the 1029 associated info (namely ESI and BGP next hop) from the L2 routing 1030 table (L2 RIB) because it still has the other Ether A-D per ES route 1031 (originated from PE1) with the same info. That is why the mass- 1032 withdraw mechanism does not work when doing DCI with inter-AS option 1033 B. However, as described previoulsy, the aliasing function works and 1034 so does "mass-withdraw per EVI" (which is associated with withdrawing 1035 the EVPN route associated with Aliasing - i.e., Ether A-D per EVI 1036 route). 1038 In the above example, the PE3 receives two Aliasing routes with the 1039 same BGP next hop (ASBR2) but different RDs. One of the Alias route 1040 has the same RD as the advertised MAC route (M1). PE3 follows the 1041 route resolution procedure specified in [RFC7432] upon receiving the 1042 two Aliasing route - ie, it resolves M1 to and 1043 subsequently it resolves to a BGP path list with two paths 1044 along with the corresponding VNIs/MPLS labels (one associated with 1045 PE1 and the other associated with PE2). It should be noted that even 1046 though both paths are advertised by the same BGP next hop (ASRB2), 1047 the receiving PE3 can handle them properly. Therefore, M1 is 1048 reachable via two paths. This creates two end-to-end LSPs from PE3 to 1049 PE1 for M1 such that when PE3 wants to forward traffic destined to 1050 M1, it can load balanced between the two paths. Although route 1051 resolution for Aliasing routes with the same BGP next hop is not 1052 explicitly mentioned in [RFC7432], the is the expected operation and 1053 thus it is elaborated here. 1055 When the AC between the PE2 and the CE fails and PE2 sends NLRI 1056 withdrawal for Ether A-D per EVI routes and these withdrawals get 1057 propagated and received by the PE3, the PE3 removes the Aliasing 1058 route and updates the path list - ie, it removes the path 1059 corresponding to the PE2. Therefore, all the corresponding MAC routes 1060 for that that point to that path list will now have the 1061 updated path list with a single path associated with PE1. This action 1062 can be considered as the mass-withdraw at the per-EVI level. The 1063 mass-withdraw at per-EVI level has longer convergence time than the 1064 mass-withdraw at per-ES level; however, it is much faster than the 1065 convergence time when the withdraw is done on a per-MAC basis. 1067 In summary, it can be seen that aliasing (and backup path) 1068 functionality should work as is for inter-AS option B without 1069 requiring any addition functionality in ASBRs or PEs. However, the 1070 mass-withdraw functionality falls back from per-ES mode to per-EVI 1071 mode for inter-AS option B - i.e., PEs receiving mass-withdraw route 1072 from the same AS use Ether A-D per ES route; whereas, PEs receiving 1073 mass-withdraw route from different AS use Ether A-D per EVI route. 1075 11 Acknowledgement 1077 The authors would like to thank David Smith, John Mullooly, Thomas 1078 Nadeau for their valuable comments and feedback. The authors would 1079 also like to thank Jakob Heitz for his contribution on section 10. 1081 12 Security Considerations 1083 This document uses IP-based tunnel technologies to support data 1084 plane transport. Consequently, the security considerations of those 1085 tunnel technologies apply. This document defines support for VXLAN 1086 and NVGRE encapsulations. The security considerations from those 1087 documents as well as [RFC4301] apply to the data plane aspects of 1088 this document. 1090 As with [RFC5512], any modification of the information that is used 1091 to form encapsulation headers, to choose a tunnel type, or to choose 1092 a particular tunnel for a particular payload type may lead to user 1093 data packets getting misrouted, misdelivered, and/or dropped. 1095 More broadly, the security considerations for the transport of IP 1096 reachability information using BGP are discussed in [RFC4271] and 1097 [RFC4272], and are equally applicable for the extensions described 1098 in this document. 1100 If the integrity of the BGP session is not itself protected, then an 1101 imposter could mount a denial-of-service attack by establishing 1102 numerous BGP sessions and forcing an IPsec SA to be created for each 1103 one. However, as such an imposter could wreak havoc on the entire 1104 routing system, this particular sort of attack is probably not of 1105 any special importance. 1107 It should be noted that a BGP session may itself be transported over 1108 an IPsec tunnel. Such IPsec tunnels can provide additional security 1109 to a BGP session. The management of such IPsec tunnels is outside 1110 the scope of this document. 1112 13 IANA Considerations 1114 IANA has allocated the following BGP Tunnel Encapsulation Attribute 1115 Tunnel Types: 1117 8 VXLAN Encapsulation 1118 9 NVGRE Encapsulation 1119 10 MPLS Encapsulation 1120 11 MPLS in GRE Encapsulation 1121 12 VXLAN GPE Encapsulation 1123 14 References 1125 14.1 Normative References 1127 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 1128 Requirement Levels", BCP 14, RFC 2119, March 1997. 1130 [RFC4271] Y. Rekhter, Ed., T. Li, Ed., S. Hares, Ed., "A Border 1131 Gateway Protocol 4 (BGP-4)", January 2006. 1133 [RFC4272] S. Murphy, "BGP Security Vulnerabilities Analysis.", 1134 January 2006. 1136 [RFC4301] S. Kent, K. Seo., "Security Architecture for the 1137 Internet Protocol.", December 2005. 1139 [RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation 1140 Subsequent Address Family Identifier (SAFI) and the BGP 1141 Tunnel Encapsulation Attribute", RFC 5512, April 2009. 1143 [RFC7432] Sajassi et al., "BGP MPLS Based Ethernet VPN", RFC 7432, 1144 February 2014 1146 14.2 Informative References 1148 [RFC7209] Sajassi et al., "Requirements for Ethernet VPN (EVPN)", RFC 1149 7209, May 2014 1151 [RFC7348] Mahalingam, M., et al, "VXLAN: A Framework for Overlaying 1152 Virtualized Layer 2 Networks over Layer 3 Networks", RFC 7348, August 1153 2014 1155 [NVGRE] Garg, P., et al., "NVGRE: Network Virtualization using 1156 Generic Routing Encapsulation", draft-sridharan-virtualization-nvgre- 1157 07.txt, November 11, 2014 1159 [Problem-Statement] Narten et al., "Problem Statement: Overlays for 1160 Network Virtualization", draft-ietf-nvo3-overlay-problem-statement- 1161 01, September 2012. 1163 [L3VPN-ENDSYSTEMS] Marques et al., "BGP-signaled End-system IP/VPNs", 1164 draft-ietf-l3vpn-end-system, work in progress, October 2012. 1166 [NOV3-FRWK] Lasserre et al., "Framework for DC Network 1167 Virtualization", draft-ietf-nvo3-framework-01.txt, work in progress, 1168 October 2012. 1170 [DCI-EVPN-OVERLAY] Rabadan et al., "Interconnect Solution for EVPN 1171 Overlay networks", draft-ietf-bess-dci-evpn-overlay-02, work in 1172 progress, February 29, 2016. 1174 Contributors 1176 S. Salam K. Patel D. Rao S. Thoria D. Cai Cisco 1178 Y. Rekhter R. Shekhar Wen Lin Nischal Sheth Juniper 1179 L. Yong Huawei 1181 Authors' Addresses 1183 Ali Sajassi 1184 Cisco 1185 Email: sajassi@cisco.com 1187 John Drake 1188 Juniper Networks 1189 Email: jdrake@juniper.net 1191 Nabil Bitar 1192 Nokia 1193 Email : nabil.bitar@nokia.com 1195 Aldrin Isaac 1196 Juniper 1197 Email: aisaac@juniper.net 1199 James Uttaro 1200 AT&T 1201 Email: uttaro@att.com 1203 Wim Henderickx 1204 Alcatel-Lucent 1205 e-mail: wim.henderickx@nokia.com