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Applicability of EVPN to NVO3 Networks
draft-ietf-nvo3-evpn-applicability-05

Document Type Active Internet-Draft (nvo3 WG)
Authors Jorge Rabadan , Matthew Bocci , Sami Boutros , Ali Sajassi
Last updated 2022-09-01
Replaces draft-rabadan-nvo3-evpn-applicability
Stream Internet Engineering Task Force (IETF)
Intended RFC status Informational
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Stream WG state Submitted to IESG for Publication
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IANA IANA review state Version Changed - Review Needed
draft-ietf-nvo3-evpn-applicability-05
NVO3 Workgroup                                           J. Rabadan, Ed.
Internet-Draft                                                  M. Bocci
Intended status: Informational                                     Nokia
Expires: 5 March 2023                                         S. Boutros
                                                                   Ciena
                                                              A. Sajassi
                                                                   Cisco
                                                        1 September 2022

                 Applicability of EVPN to NVO3 Networks
                 draft-ietf-nvo3-evpn-applicability-05

Abstract

   In Network Virtualization Over Layer-3 (NVO3) networks, Network
   Virtualization Edge devices (NVEs) sit at the edge of the underlay
   network and provide Layer-2 and Layer-3 connectivity among Tenant
   Systems (TSes) of the same tenant.  The NVEs need to build and
   maintain mapping tables so that they can deliver encapsulated packets
   to their intended destination NVE(s).  While there are different
   options to create and disseminate the mapping table entries, NVEs may
   exchange that information directly among themselves via a control-
   plane protocol, such as Ethernet Virtual Private Network (EVPN).
   EVPN provides an efficient, flexible and unified control-plane option
   that can be used for Layer-2 and Layer-3 Virtual Network (VN) service
   connectivity.  This document describes the applicability of EVPN to
   NVO3 networks and how EVPN solves the challenges in those networks.
   This document does not introduce any new procedures in EVPN.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 5 March 2023.

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Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  EVPN and NVO3 Terminology . . . . . . . . . . . . . . . . . .   3
   3.  Why is EVPN Needed in NVO3 Networks?  . . . . . . . . . . . .   7
   4.  Applicability of EVPN to NVO3 Networks  . . . . . . . . . . .   9
     4.1.  EVPN Route Types Used in NVO3 Networks  . . . . . . . . .   9
     4.2.  EVPN Basic Applicability for Layer-2 Services . . . . . .  10
       4.2.1.  Auto-Discovery and Auto-Provisioning  . . . . . . . .  12
       4.2.2.  Remote NVE Auto-Discovery . . . . . . . . . . . . . .  13
       4.2.3.  Distribution of Tenant MAC and IP Information . . . .  14
     4.3.  EVPN Basic Applicability for Layer-3 Services . . . . . .  14
     4.4.  EVPN as Control Plane for NVO3 Encapsulations and
           GENEVE  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     4.5.  EVPN OAM and Application to NVO3  . . . . . . . . . . . .  18
     4.6.  EVPN as the Control Plane for NVO3 Security . . . . . . .  18
     4.7.  Advanced EVPN Features for NVO3 Networks  . . . . . . . .  18
       4.7.1.  Virtual Machine (VM) Mobility . . . . . . . . . . . .  18
       4.7.2.  MAC Protection, Duplication Detection and Loop
               Protection  . . . . . . . . . . . . . . . . . . . . .  19
       4.7.3.  Reduction/Optimization of BUM Traffic in Layer-2
               Services  . . . . . . . . . . . . . . . . . . . . . .  19
       4.7.4.  Ingress Replication (IR) Optimization for BUM
               Traffic . . . . . . . . . . . . . . . . . . . . . . .  20
       4.7.5.  EVPN Multi-Homing . . . . . . . . . . . . . . . . . .  21
       4.7.6.  EVPN Recursive Resolution for Inter-Subnet Unicast
               Forwarding  . . . . . . . . . . . . . . . . . . . . .  22
       4.7.7.  EVPN Optimized Inter-Subnet Multicast Forwarding  . .  23
       4.7.8.  Data Center Interconnect (DCI)  . . . . . . . . . . .  24
   5.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  24
   6.  Conventions Used in this Document . . . . . . . . . . . . . .  24
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  25

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     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  25
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  25
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  29
   Appendix B.  Contributors . . . . . . . . . . . . . . . . . . . .  29
   Appendix C.  Authors' Addresses . . . . . . . . . . . . . . . . .  29
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   In Network Virtualization Over Layer-3 (NVO3) networks, Network
   Virtualization Edge devices (NVEs) sit at the edge of the underlay
   network and provide Layer-2 and Layer-3 connectivity among Tenant
   Systems (TSes) of the same tenant.  The NVEs need to build and
   maintain mapping tables so that they can deliver encapsulated packets
   to their intended destination NVE(s).  While there are different
   options to create and disseminate the mapping table entries, NVEs may
   exchange that information directly among themselves via a control-
   plane protocol, such as EVPN.  EVPN provides an efficient, flexible
   and unified control-plane option that can be used for Layer-2 and
   Layer-3 Virtual Network (VN) service connectivity.  This document
   does not introduce any new procedures in EVPN.

   In this document, we assume that the EVPN control-plane module
   resides in the NVEs.  The NVEs can be virtual switches in
   hypervisors, TOR/Leaf switches or Data Center Gateways.  As described
   in [RFC7365], Network Virtualization Authorities (NVAs) may be used
   to provide the forwarding information to the NVEs, and in that case,
   EVPN could be used to disseminate the information across multiple
   federated NVAs.  The applicability of EVPN would then be similar to
   the one described in this document.  However, for simplicity, the
   description assumes control-plane communication among NVE(s).

2.  EVPN and NVO3 Terminology

   This document uses the terminology of [RFC7365], in addition to the
   terms that follow.

   *  AC: Attachment Circuit or logical interface associated to a given
      BT.  To determine the AC on which a packet arrived, the NVE will
      examine the physical/logical port and/or VLAN tags (where the VLAN
      tags can be individual c-tags, s-tags or ranges of both).

   *  ARP and ND: Address Resolution Protocol (IPv4) and Neighbor
      Discovery protocol (IPv6).

   *  BD: or Broadcast Domain, it corresponds to a tenant IP subnet.  If
      no suppression techniques are used, a BUM frame that is injected
      in a Broadcast Domain will reach all the NVEs that are attached to

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      that Broadcast Domain.  An EVI may contain one or multiple
      Broadcast Domains depending on the service model [RFC7432].  This
      document will use the term Broadcast Domain to refer to a tenant
      subnet.

   *  BT: a Bridge Table, as defined in [RFC7432].  A BT is the
      instantiation of a Broadcast Domain in an NVE.  When there is a
      single Broadcast Domain on a given EVI, the MAC-VRF is equivalent
      to the BT on that NVE.  Although a Broadcast Domain spans multiple
      NVEs, and a BT is really the instantiation of a Broadcast Domain
      in an NVE, this document uses BT and Broadcast Domain
      interchangeably.

   *  BUM: Broadcast, Unknown unicast and Multicast frames.

   *  CLOS: a multistage network topology described in [CLOS1953], where
      all the edge switches (or Leafs) are connected to all the core
      switches (or Spines).  Typically used in Data Centers.

   *  DF and NDF: they refer to Designated Forwarder and Non-Designated
      Forwarder, which are the roles that a given PE can have in a given
      ES.

   *  ECMP: Equal Cost Multi-Path.

   *  EVPN: Ethernet Virtual Private Networks, as described in
      [RFC7432].

   *  EVI: EVPN Instance.

   *  EVPN VLAN-based service model: one of the three service models
      defined in [RFC7432].  It is characterized as a Broadcast Domain
      that uses a single VLAN per physical access port to attach tenant
      traffic to the Broadcast Domain.  In this service model, there is
      only one Broadcast Domain per EVI.

   *  EVPN VLAN-bundle service model: similar to VLAN-based but uses a
      bundle of VLANs per physical port to attach tenant traffic to the
      Broadcast Domain.  As in VLAN-based, in this model there is a
      single Broadcast Domain per EVI.

   *  EVPN VLAN-aware bundle service model: similar to the VLAN-bundle
      model but each individual VLAN value is mapped to a different
      Broadcast Domain.  In this model there are multiple Broadcast
      Domains per EVI for a given tenant.  Each Broadcast Domain is
      identified by an "Ethernet Tag", that is a control-plane value
      that identifies the routes for the Broadcast Domain within the
      EVI.

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   *  ES: Ethernet Segment.  When a Tenant System (TS) is connected to
      one or more NVEs via a set of Ethernet links, then that set of
      links is referred to as an 'Ethernet segment'.  Each ES is
      represented by a unique Ethernet Segment Identifier (ESI) in the
      NVO3 network and the ESI is used in EVPN routes that are specific
      to that ES.

   *  Ethernet Tag: Used to represent a Broadcast Domain that is
      configured on a given ES for the purpose of Designated Forwarder
      election.  Note that any of the following may be used to represent
      a Broadcast Domain: VIDs (including Q-in-Q tags), configured IDs,
      VNIs (Virtual Extensible Local Area Network (VXLAN) Network
      Identifiers), normalized VIDs, I-SIDs (Service Instance
      Identifiers), etc., as long as the representation of the Broadcast
      Domains is configured consistently across the multihomed PEs
      attached to that ES.  The Ethernet Tag value MUST be different
      from zero.

   *  EVI: or EVPN Instance.  It is a Layer-2 Virtual Network that uses
      an EVPN control-plane to exchange reachability information among
      the member NVEs.  It corresponds to a set of MAC-VRFs of the same
      tenant.  See MAC-VRF in this section.

   *  GENEVE: Generic Network Virtualization Encapsulation, an NVO3
      encapsulation defined in [RFC8926].

   *  IP-VRF: an IP Virtual Routing and Forwarding table, as defined in
      [RFC4364].  It stores IP Prefixes that are part of the tenant's IP
      space, and are distributed among NVEs of the same tenant by EVPN.
      Route-Distinghisher (RD) and Route-Target(s) (RTs) are required
      properties of an IP-VRF.  An IP-VRF is instantiated in an NVE for
      a given tenant, if the NVE is attached to multiple subnets of the
      tenant and local inter-subnet-forwarding is required across those
      subnets.

   *  IRB: Integrated Routing and Bridging interface.  It refers to the
      logical interface that connects a Broadcast Domain instance (or a
      BT) to an IP- VRF and allows to forward packets with destination
      in a different subnet.

   *  MAC-VRF: a MAC Virtual Routing and Forwarding table, as defined in
      [RFC7432].  The instantiation of an EVI (EVPN Instance) in an NVE.
      Route Distinghisher (RD) and Route Target(s) (RTs) are required
      properties of a MAC-VRF and they are normally different than the
      ones defined in the associated IP-VRF (if the MAC-VRF has an IRB
      interface).

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   *  NVE: Network Virtualization Edge device, a network entity that
      sits at the edge of an underlay network and implements Layer-2
      and/or Layer-3 network virtualization functions.  The network-
      facing side of the NVE uses the underlying Layer-3 network to
      tunnel tenant frames to and from other NVEs.  The tenant-facing
      side of the NVE sends and receives Ethernet frames to and from
      individual Tenant Systems.  In this document, an NVE could be
      implemented as a virtual switch within a hypervisor, a switch or a
      router, and runs EVPN in the control-plane.

   *  NVO3 tunnels: Network Virtualization Over Layer-3 tunnels.  In
      this document, NVO3 tunnels or simply Overlay tunnels will be used
      interchangeably.  Both terms refer to a way to encapsulate tenant
      frames or packets into IP packets whose IP Source Addresses (SA)
      or Destination Addresses (DA) belong to the underlay IP address
      space, and identify NVEs connected to the same underlay network.
      Examples of NVO3 tunnel encapsulations are VXLAN [RFC7348], GENEVE
      [RFC8926] or MPLSoUDP [RFC7510].

   *  PE: Provider Edge router.

   *  PMSI: Provider Multicast Service Interface.

   *  PTA: Provider Multicast Service Interface Tunnel Attribute.

   *  RT and RD: Route Target and Route Distinguisher.

   *  RT-1, RT-2, RT-3, etc.: they refer to Route Type followed by the
      type number as defined in the IANA registry for EVPN route types.

   *  SA and DA: Source Address and Destination Address.  They are used
      along with MAC or IP, e.g.  IP SA or MAC DA.

   *  SBD: Supplementary Broadcast Domain.  Defined in [RFC9136], it is
      a Broadcast Domain that does not have any Attachment Circuits,
      only IRB interfaces, and provides connectivity among all the IP-
      VRFs of a tenant in the Interface-ful IP-VRF-to-IP-VRF models.

   *  TS: Tenant System.  A physical or virtual system that can play the
      role of a host or a forwarding element such as a router, switch,
      firewall, etc.  It belongs to a single tenant and connects to one
      or more Broadcast Domains of that tenant.

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   *  VNI: Virtual Network Identifier.  Irrespective of the NVO3
      encapsulation, the tunnel header always includes a VNI that is
      added at the ingress NVE (based on the mapping table lookup) and
      identifies the BT at the egress NVE.  This VNI is called VNI in
      VXLAN or GENEVE, VSID in nvGRE or Label in MPLSoGRE or MPLSoUDP.
      This document will refer to VNI as a generic Virtual Network
      Identifier for any NVO3 encapsulation.

   *  VXLAN: Virtual eXtensible Local Area Network, an NVO3
      encapsulation defined in [RFC7348].

3.  Why is EVPN Needed in NVO3 Networks?

   Data Centers have adopted NVO3 architectures mostly due to the issues
   discussed in [RFC7364].  The architecture of a Data Center is
   nowadays based on a CLOS design, where every Leaf is connected to a
   layer of Spines, and there is a number of Equal Cost Multi-Paths
   between any two leaf nodes.  All the links between Leaf and Spine
   nodes are routed links, forming what we also know as an underlay IP
   Fabric.  The underlay IP Fabric does not have issues with loops or
   flooding (like old Spanning Tree Data Center designs did),
   convergence is fast and Equal Cost Multi-Path provides a fairly
   optimal bandwidth utilization on all the links.

   On this architecture and as discussed by [RFC7364], multi-tenant
   intra-subnet and inter-subnet connectivity services are provided by
   NVO3 tunnels, being VXLAN [RFC7348] or GENEVE [RFC8926] two examples
   of such tunnels.

   Why is a control-plane protocol along with NVO3 tunnels required?
   There are three main reasons:

   a.  Auto-discovery of the remote NVEs that are attached to the same
       VPN instance (Layer-2 and/or Layer-3) as the ingress NVE is.

   b.  Dissemination of the MAC/IP host information so that mapping
       tables can be populated on the remote NVEs.

   c.  Advanced features such as MAC Mobility, MAC Protection, BUM and
       ARP/ND traffic reduction/suppression, Multi-homing, Prefix
       Independent Convergence (PIC) like functionality, Fast
       Convergence, etc.

   A possible approach to achieve points (a) and (b) above for
   multipoint Ethernet services, is "flood and learn".  "Flood and
   learn" refers to not using a specific control-plane on the NVEs, but
   rather "flood" BUM traffic from the ingress NVE to all the egress
   NVEs attached to the same Broadcast Domain.  The egress NVEs may then

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   use data path source MAC address "learning" on the frames received
   over the NVO3 tunnels.  When the destination host replies back and
   the frames arrive at the NVE that initially flooded BUM frames, the
   NVE will also "learn" the source MAC address of the frame
   encapsulated on the NVO3 tunnel.  This approach has the following
   drawbacks:

   *  In order to flood a given BUM frame, the ingress NVE must know the
      IP addresses of the remote NVEs attached to the same Broadcast
      Domain.  This may be done as follows:

      -  The remote tunnel IP addresses can be statically provisioned on
         the ingress NVE.  If the ingress NVE receives a BUM frame for
         the Broadcast Domain on an ingress Attachment Circuit, it will
         do ingress replication and will send the frame to all the
         configured egress NVE destination IP addresss in the Broadcast
         Domain.

      -  All the NVEs attached to the same Broadcast Domain can
         subscribe to an underlay IP Multicast Group that is dedicated
         to that Broadcast Domain.  When an ingress NVE receives a BUM
         frame on an ingress Attachment Circuit, it will send a single
         copy of the frame encapsulated into an NVO3 tunnel, using the
         multicast address as destination IP address of the tunnel.
         This solution requires Protocol Independent Multicast (PIM) in
         the underlay network and the association of individual
         Broadcast Domains to underlay IP multicast groups.

   *  "Flood and learn" solves the issues of auto-discovery and learning
      of the MAC to VNI/tunnel IP mapping on the NVEs for a given
      Broadcast Domain.  However, it does not provide a solution for
      advanced features and it does not scale well (mostly due to the
      need for constant flooding and the underlay PIM states that are
      needed to maintain).

   EVPN provides a unified control-plane that solves the NVE auto-
   discovery, tenant MAP/IP dissemination and advanced features in a
   scalable way and keeping the independence of the underlay IP Fabric,
   i.e., there is no need to enable PIM in the underlay network and
   maintain multicast states for tenant Broadcast Domains.

   Section 4 describes how EVPN can be used to meet the control-plane
   requirements in an NVO3 network.

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4.  Applicability of EVPN to NVO3 Networks

   This section discusses the applicability of EVPN to NVO3 networks.
   The intent is not to provide a comprehensive explanation of the
   protocol itself but give an introduction and point at the
   corresponding reference document, so that the reader can easily find
   more details if needed.

4.1.  EVPN Route Types Used in NVO3 Networks

   EVPN supports multiple Route Types and each type has a different
   function.  For convenience, Table 1 shows a summary of all the
   existing EVPN route types and its usage.  In this document we may
   refer to these route types as RT-x routes, where x is the type number
   included in the first column of Table 1.

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   +======+=====================+======================================+
   | Type | Description         | Usage                                |
   +======+=====================+======================================+
   | 1    | Ethernet Auto-      | Multi-homing: Per-ES: Mass           |
   |      | Discovery           | withdrawal, Per-EVI: aliasing/backup |
   +------+---------------------+--------------------------------------+
   | 2    | MAC/IP              | Host MAC/IP dissemination, supports  |
   |      | Advertisement       | MAC mobility and protection          |
   +------+---------------------+--------------------------------------+
   | 3    | Inclusive           | NVE discovery and BUM flooding tree  |
   |      | Multicast           | setup                                |
   |      | Ethernet Tag        |                                      |
   +------+---------------------+--------------------------------------+
   | 4    | Ethernet            | Multi-homing: ES auto-discovery and  |
   |      | Segment             | DF Election                          |
   +------+---------------------+--------------------------------------+
   | 5    | IP Prefix           | IP Prefix dissemination              |
   +------+---------------------+--------------------------------------+
   | 6    | Selective           | Indicate interest for a multicast    |
   |      | Multicast           | S,G or *,G                           |
   |      | Ethernet Tag        |                                      |
   +------+---------------------+--------------------------------------+
   | 7    | Multicast Join      | Multi-homing: S,G or *,G state synch |
   |      | Synch               |                                      |
   +------+---------------------+--------------------------------------+
   | 8    | Multicast           | Multi-homing: S,G or *,G leave synch |
   |      | Leave Synch         |                                      |
   +------+---------------------+--------------------------------------+
   | 9    | Per-Region          | BUM tree creation across regions     |
   |      | I-PMSI A-D          |                                      |
   +------+---------------------+--------------------------------------+
   | 10   | S-PMSI A-D          | Multicast tree for S,G or *,G states |
   +------+---------------------+--------------------------------------+
   | 11   | Leaf A-D            | Used for responses to explicit       |
   |      |                     | tracking                             |
   +------+---------------------+--------------------------------------+

                         Table 1: EVPN route types

4.2.  EVPN Basic Applicability for Layer-2 Services

   Although the applicability of EVPN to NVO3 networks spans multiple
   documents, EVPN's baseline specification is [RFC7432].  [RFC7432]
   allows multipoint layer-2 VPNs to be operated as [RFC4364] IP-VPNs,
   where MACs and the information to setup flooding trees are
   distributed by MP-BGP [RFC4760].  Based on [RFC7432], [RFC8365]
   describes how to use EVPN to deliver Layer-2 services specifically in
   NVO3 Networks.

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   Figure 1 represents a Layer-2 service deployed with an EVPN Broadcast
   Domain in an NVO3 network.

                                 +--TS2---+
                                 *        | Single-Active
                                 *        |   ESI-1
                               +----+  +----+
                               |BD1 |  |BD1 |
                 +-------------|    |--|    |-----------+
                 |             +----+  +----+           |
                 |              NVE2    NVE3          NVE4
                 |           EVPN NVO3 Network       +----+
            NVE1(IP-A)                               | BD1|-----+
           +-------------+      RT-2                 |    |     |
           |             |    +-------+              +----+     |
           |   +----+    |    |MAC1   |               NVE5     TS3
    TS1--------|BD1 |    |    |IP1    |              +----+     |
    MAC1   |   +----+    |    |Label L|--->          | BD1|-----+
    IP1    |             |    |NH IP-A|              |    | All-Active
           | Hypervisor  |    +-------+              +----+  ESI-2
           +-------------+                              |
                 +--------------------------------------+

             Figure 1: EVPN for L2 in an NVO3 Network - example

   In a simple NVO3 network, such as the example of Figure 1, these are
   the basic constructs that EVPN uses for Layer-2 services (or Layer-2
   Virtual Networks):

   *  BD1 is an EVPN Broadcast Domain for a given tenant and TS1, TS2
      and TS3 are connected to it.  The five represented NVEs are
      attached to BD1 and are connected to the same underlay IP network.
      That is, each NVE learns the remote NVEs' loopback addresses via
      underlay routing protocol.

   *  NVE1 is deployed as a virtual switch in a Hypervisor with IP-A as
      underlay loopback IP address.  The rest of the NVEs in Figure 1
      are physical switches and TS2/TS3 are multi-homed to them.  TS1 is
      a virtual machine, identified by MAC1 and IP1.  TS2 and TS3 are
      physically dual-connected to NVEs, hence they are normally not
      considered virtual machines.

   *  The terms Single-Active and All-Active in Figure 1 refer to the
      mode in which the TS2 and TS3 are multi-homed to the NVEs in BD1.
      In All-Active mode, all the multi-homing links are active and can
      send or receive traffic.  In Single-Active mode, only one link (of
      the set of links connected to the NVEs) is active.

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4.2.1.  Auto-Discovery and Auto-Provisioning

   Auto-discovery is one of the basic capabilities of EVPN.  The
   provisioning of EVPN components in NVEs is significantly automated,
   simplifying the deployment of services and minimizing manual
   operations that are prone to human error.

   These are some of the Auto-Discovery and Auto-Provisioning
   capabilities available in EVPN:

   *  Automation on Ethernet Segments (ES): an Ethernet Segment is
      defined as a group of NVEs that are attached to the same Tenant
      System or network.  An Ethernet Segment is identified by an
      Ethernet Segment Identifier (ESI) in the control plane, but
      neither the ESI nor the NVEs that share the same Ethernet Segment
      are required to be manually provisioned in the local NVE:

      -  If the multi-homed Tenant System or network are running
         protocols such as LACP (Link Aggregation Control Protocol)
         [IEEE.802.1AX_2014], MSTP (Multiple-instance Spanning Tree
         Protocol), G.8032, etc. and all the NVEs in the Ethernet
         Segment can listen to the protocol PDUs to uniquely identify
         the multi-homed Tenant System/network, then the ESI can be
         "auto-sensed" or "auto-provisioned" following the guidelines in
         [RFC7432] section 5.  The ESI can also be auto-derived out of
         other parameters that are common to all NVEs attached to the
         same Ethernet Segment.

      -  As described in [RFC7432], EVPN can also auto-derive the BGP
         parameters required to advertise the presence of a local
         Ethernet Segment in the control plane (RT and RD).  Local
         Ethernet Segments are advertised using Ethernet Segment routes
         and the ESI-import Route-Target used by Ethernet Segment routes
         can be auto-derived based on the procedures of [RFC7432],
         section 7.6.

      -  By listening to other Ethernet Segment routes that match the
         local ESI and import Route Target, an NVE can also auto-
         discover the other NVEs participating in the multi-homing for
         the Ethernet Segment.

      -  Once the NVE has auto-discovered all the NVEs attached to the
         same Ethernet Segment, the NVE can automatically perform the
         Designated Forwarder Election algorithm (which determines the
         NVE that will forward traffic to the multi-homed Tenant System/
         network).  EVPN guarantees that all the NVEs in the Ethernet
         Segment have a consistent Designated Forwarder Election.

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   *  Auto-provisioning of services: when deploying a Layer-2 Service
      for a tenant in an NVO3 network, all the NVEs attached to the same
      subnet must be configured with a MAC-VRF and the Broadcast Domain
      for the subnet, as well as certain parameters for them.  Note
      that, if the EVPN service model is VLAN-based or VLAN-bundle,
      implementations do not normally have a specific provisioning for
      the Broadcast Domain (since it is in that case the same construct
      as the MAC-VRF).  EVPN allows auto-deriving as many MAC-VRF
      parameters as possible.  As an example, the MAC-VRF's Route Target
      and Route Distinguisher for the EVPN routes may be auto-derived.
      Section 5.1.2.1 in [RFC8365] specifies how to auto-derive a MAC-
      VRF's Route Target as long as VLAN-based service model is
      implemented.  [RFC7432] specifies how to auto-derive the Route
      Distinguisher.

4.2.2.  Remote NVE Auto-Discovery

   Auto-discovery via MP-BGP [RFC4760] is used to discover the remote
   NVEs attached to a given Broadcast Domain, the NVEs participating in
   a given redundancy group, the tunnel encapsulation types supported by
   an NVE, etc.

   In particular, when a new MAC-VRF and Broadcast Domain are enabled,
   the NVE will advertise a new Inclusive Multicast Ethernet Tag route.
   Besides other fields, the Inclusive Multicast Ethernet Tag route will
   encode the IP address of the advertising NVE, the Ethernet Tag (which
   is zero in case of VLAN-based and VLAN-bundle models) and also a PMSI
   Tunnel Attribute (PTA) that indicates the information about the
   intended way to deliver BUM traffic for the Broadcast Domain.

   In the example of Figure 1, when BD1 is enabled, NVE1 will send an
   Inclusive Multicast Ethernet Tag route including its own IP address,
   Ethernet-Tag for BD1 and the PMSI Tunnel Attribute to the remote
   NVEs.  Assuming Ingress Replication (IR) is used, the Inclusive
   Multicast Ethernet Tag route will include an identification for
   Ingress Replication in the PMSI Tunnel Attribute and the Virtual
   Network Identifier that the other NVEs in the Broadcast Domain must
   use to send BUM traffic to the advertising NVE.  The other NVEs in
   the Broadcast Domain will import the Inclusive Multicast Ethernet Tag
   route and will add NVE1's IP address to the flooding list for BD1.
   Note that the Inclusive Multicast Ethernet Tag route is also sent
   with a BGP encapsulation attribute [RFC9012] that indicates what NVO3
   encapsulation the remote NVEs should use when sending BUM traffic to
   NVE1.

   Refer to [RFC7432] for more information about the Inclusive Multicast
   Ethernet Tag route and forwarding of BUM traffic, and to [RFC8365]
   for its considerations on NVO3 networks.

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4.2.3.  Distribution of Tenant MAC and IP Information

   Tenant MAC/IP information is advertised to remote NVEs using MAC/IP
   Advertisement routes.  Following the example of Figure 1:

   *  In a given EVPN Broadcast Domain, Tenant Systems' MAC addresses
      are first learned at the NVE they are attached to, via data path
      or management plane learning.  In Figure 1 we assume NVE1 learns
      MAC1/IP1 in the management plane (for instance, via Cloud
      Management System) since the NVE is a virtual switch.  NVE2, NVE3,
      NVE4 and NVE5 are TOR/Leaf switches and they normally learn MAC
      addresses via data path.

   *  Once NVE1's BD1 learns MAC1/IP1, NVE1 advertises that information
      along with a Virtual Network Identifier and Next Hop IP-A in an
      MAC/IP Advertisement route.  The EVPN routes are advertised using
      the Route Distinguisher/Route Targets of the MAC-VRF where the
      Broadcast Domain belongs.  All the NVEs in BD1 learn local MAC/IP
      addresses and advertise them in MAC/IP Advertisement routes in a
      similar way.

   *  The remote NVEs can then add MAC1 to their mapping table for BD1
      (BT).  For instance, when TS3 sends frames to NVE4 with
      destination MAC address = MAC1, NVE4 does a MAC lookup on the
      Bridge Table that yields IP-A and Label L.  NVE4 can then
      encapsulate the frame into an NVO3 tunnel with IP-A as the tunnel
      destination IP address and L as the Virtual Network Identifier.
      Note that the MAC/IP Advertisement route may also contain the
      host's IP address (as in the example of Figure 1).  While the MAC
      of the received MAC/IP Advertisement route is installed in the
      Bridge Table, the IP address may be installed in the Proxy-ARP/ND
      table (if enabled) or in the ARP/IP-VRF tables if the Broadcast
      Domain has an IRB.  See Section 4.7.3 to see more information
      about Proxy-ARP/ND and Section 4.3. for more details about IRB and
      Layer-3 services.

   Refer to [RFC7432] and [RFC8365] for more information about the MAC/
   IP Advertisement route and forwarding of known unicast traffic.

4.3.  EVPN Basic Applicability for Layer-3 Services

   [RFC9136] and [RFC9135] are the reference documents that describe how
   EVPN can be used for Layer-3 services.  Inter Subnet Forwarding in
   EVPN networks is implemented via IRB interfaces between Broadcast
   Domains and IP-VRFs.  An EVPN Broadcast Domain corresponds to an IP
   subnet.  When IP packets generated in a Broadcast Domain are destined
   to a different subnet (different Broadcast Domain) of the same
   tenant, the packets are sent to the IRB attached to the local

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   Broadcast Domain in the source NVE.  As discussed in [RFC9135],
   depending on how the IP packets are forwarded between the ingress NVE
   and the egress NVE, there are two forwarding models: Asymmetric and
   Symmetric model.

   The Asymmetric model is illustrated in the example of Figure 2 and it
   requires the configuration of all the Broadcast Domains of the tenant
   in all the NVEs attached to the same tenant.  In that way, there is
   no need to advertise IP Prefixes between NVEs since all the NVEs are
   attached to all the subnets.  It is called Asymmetric because the
   ingress and egress NVEs do not perform the same number of lookups in
   the data plane.  In Figure 2, if TS1 and TS2 are in different
   subnets, and TS1 sends IP packets to TS2, the following lookups are
   required in the data path: a MAC lookup (on BD1's table), an IP
   lookup (on the IP-VRF) and a MAC lookup (on BD2's table) at the
   ingress NVE1 and then only a MAC lookup at the egress NVE.  The two
   IP-VRFs in Figure 2 are not connected by tunnels and all the
   connectivity between the NVEs is done based on tunnels between the
   Broadcast Domains.

                  +-------------------------------------+
                  |             EVPN NVO3               |
                  |                                     |
                NVE1                                 NVE2
          +--------------------+            +--------------------+
          | +---+IRB +------+  |            |  +------+IRB +---+ |
    TS1-----|BD1|----|IP-VRF|  |            |  |IP-VRF|----|BD1| |
          | +---+    |      |  |            |  |      |    +---+ |
          | +---+    |      |  |            |  |      |    +---+ |
          | |BD2|----|      |  |            |  |      |----|BD2|----TS2
          | +---+IRB +------+  |            |  +------+IRB +---+ |
          +--------------------+            +--------------------+
                  |                                     |
                  +-------------------------------------+

        Figure 2: EVPN for L3 in an NVO3 Network - Asymmetric model

   In the Symmetric model, depicted in Figure 3, the same number of data
   path lookups is needed at the ingress and egress NVEs.  For example,
   if TS1 sends IP packets to TS3, the following data path lookups are
   required: a MAC lookup at NVE1's BD1 table, an IP lookup at NVE1's
   IP-VRF and then IP lookup and MAC lookup at NVE2's IP-VRF and BD3
   respectively.  In the Symmetric model, the Inter Subnet connectivity
   between NVEs is done based on tunnels between the IP-VRFs.

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                  +-------------------------------------+
                  |             EVPN NVO3               |
                  |                                     |
                NVE1                                 NVE2
          +--------------------+            +--------------------+
          | +---+IRB +------+  |            |  +------+IRB +---+ |
    TS1-----|BD1|----|IP-VRF|  |            |  |IP-VRF|----|BD3|-----TS3
          | +---+    |      |  |            |  |      |    +---+ |
          | +---+IRB |      |  |            |  +------+          |
    TS2-----|BD2|----|      |  |            +--------------------+
          | +---+    +------+  |                        |
          +--------------------+                        |
                  |                                     |
                  +-------------------------------------+

         Figure 3: EVPN for L3 in an NVO3 Network - Symmetric model

   The Symmetric model scales better than the Asymmetric model because
   it does not require the NVEs to be attached to all the tenant's
   subnets.  However, it requires the use of NVO3 tunnels on the IP-VRFs
   and the exchange of IP Prefixes between the NVEs in the control
   plane.  EVPN uses MAC/IP Advertisement and IP Prefix routes for the
   exchange of host IP routes (in the case of the MAC/IP Advertisement
   and the IP Prefix routes) and IP Prefixes (IP Prefix routes) of any
   length.  As an example, in Figure 3, NVE2 needs to advertise TS3's
   host route and/or TS3's subnet, so that the IP lookup on NVE1's IP-
   VRF succeeds.

   [RFC9135] specifies the use of MAC/IP Advertisement routes for the
   advertisement of host routes.  Section 4.4.1 in [RFC9136] specifies
   the use of IP Prefix routes for the advertisement of IP Prefixes in
   an "Interface-less IP-VRF-to-IP-VRF Model".  The Symmetric model for
   host routes can be implemented following either approach:

   a.  [RFC9135] uses MAC/IP Advertisement routes to convey the
       information to populate Layer-2, ARP/ND and Layer-3 Forwarding
       Information Base tables in the remote NVE.  For instance, in
       Figure 3, NVE2 would advertise a MAC/IP Advertisement route with
       TS3's IP and MAC addresses, and including two labels/Virtual
       Network Identifiers: a label-3/VNI-3 that identifies BD3 for MAC
       lookup (that would be used for Layer-2 traffic in case NVE1 was
       attached to BD3 too) and a label-1/VNI-1 that identifies the IP-
       VRF for IP lookup (and will be used for Layer-3 traffic).  NVE1
       imports the MAC/IP Advertisement route and installs TS3's IP in
       the IP-VRF route table with label-1/VNI-1.  Traffic from e.g.,
       TS2 to TS3, will be encapsulated with label-1/VNI-1 and forwarded
       to NVE2.

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   b.  [RFC9136] uses MAC/IP Advertisement routes to convey the
       information to populate the Layer-2 Forwarding Information Base
       and ARP/ND tables, and IP Prefix routes to populate the IP-VRF
       Layer-3 Forwarding Information Base table.  For instance, in
       Figure 3, NVE2 would advertise a MAC/IP Advertisement route
       including TS3's MAC and IP addresses with a single label-3/VNI-3.
       In this example, this MAC/IP Advertisement route wouldn't be
       imported by NVE1 because NVE1 is not attached to BD3.  In
       addition, NVE2 would advertise a IP Prefix route with TS3's IP
       address and label-1/VNI-1.  This IP Prefix route would be
       imported by NVE1's IP-VRF and the host route installed in the
       Layer-3 Forwarding Information Base associated to label-1/VNI-1.
       Traffic from TS2 to TS3 would be encapsulated with label-1/VNI-1.

4.4.  EVPN as Control Plane for NVO3 Encapsulations and GENEVE

   [RFC8365] describes how to use EVPN for NVO3 encapsulations, such us
   VXLAN, nvGRE or MPLSoGRE.  The procedures can be easily applicable to
   any other NVO3 encapsulation, in particular GENEVE.

   The Generic Network Virtualization Encapsulation [RFC8926] has been
   recommended to be the proposed standard for NVO3 Encapsulation.  The
   EVPN control plane can signal the GENEVE encapsulation type in the
   BGP Tunnel Encapsulation Extended Community (see [RFC9012]).

   The NVO3 encapsulation design team has made a recommendation in
   [I-D.ietf-nvo3-encap] for a control plane to:

   1.  Negotiate a subset of GENEVE option TLVs that can be carried on a
       GENEVE tunnel

   2.  Enforce an order for GENEVE option TLVs and

   3.  Limit the total number of options that could be carried on a
       GENEVE tunnel.

   The EVPN control plane can easily extend the BGP Tunnel Encapsulation
   Attribute sub-TLV [RFC9012] to specify the GENEVE tunnel options that
   can be received or transmitted over a GENEVE tunnels by a given NVE.
   [I-D.ietf-bess-evpn-geneve] describes the EVPN control plane
   extensions to support GENEVE.

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4.5.  EVPN OAM and Application to NVO3

   EVPN OAM (as in [I-D.ietf-bess-evpn-lsp-ping]) defines mechanisms to
   detect data plane failures in an EVPN deployment over an MPLS
   network.  These mechanisms detect failures related to P2P and P2MP
   connectivity, for multi-tenant unicast and multicast Layer-2 traffic,
   between multi-tenant access nodes connected to EVPN PE(s), and in a
   single-homed, single-active or all-active redundancy model.

   In general, EVPN OAM mechanisms defined for EVPN deployed in MPLS
   networks are equally applicable for EVPN in NVO3 networks.

4.6.  EVPN as the Control Plane for NVO3 Security

   EVPN can be used to signal the security protection capabilities of a
   sender NVE, as well as what portion of an NVO3 packet (taking a
   GENEVE packet as an example) can be protected by the sender NVE, to
   ensure the privacy and integrity of tenant traffic carried over the
   NVO3 tunnels [I-D.sajassi-bess-secure-evpn].

4.7.  Advanced EVPN Features for NVO3 Networks

   This section describes how EVPN can be used to deliver advanced
   capabilities in NVO3 networks.

4.7.1.  Virtual Machine (VM) Mobility

   [RFC7432] replaces the traditional Ethernet Flood-and-Learn behavior
   among NVEs with BGP-based MAC learning, which in return provides more
   control over the location of MAC addresses in the Broadcast Domain
   and consequently advanced features, such as MAC Mobility.  If we
   assume that VM Mobility means the VM's MAC and IP addresses move with
   the VM, EVPN's MAC Mobility is the required procedure that
   facilitates VM Mobility.  According to [RFC7432] section 15, when a
   MAC is advertised for the first time in a Broadcast Domain, all the
   NVEs attached to the Broadcast Domain will store Sequence Number zero
   for that MAC.  When the MAC "moves" within the same Broadcast Domain
   but to a remote NVE, the NVE that just learned locally the MAC,
   increases the Sequence Number in the MAC/IP Advertisement route's MAC
   Mobility extended community to indicate that it owns the MAC now.
   That makes all the NVE in the Broadcast Domain change their tables
   immediately with no need to wait for any aging timer.  EVPN
   guarantees a fast MAC Mobility without flooding or black-holes in the
   Broadcast Domain.

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4.7.2.  MAC Protection, Duplication Detection and Loop Protection

   The advertisement of MACs in the control plane, allows advanced
   features such as MAC protection, Duplication Detection and Loop
   Protection.

   [RFC7432] MAC Protection refers to EVPN's ability to indicate - in a
   MAC/IP Advertisement route - that a MAC must be protected by the NVE
   receiving the route.  The Protection is indicated in the "Sticky bit"
   of the MAC Mobility extended community sent along the MAC/IP
   Advertisement route for a MAC.  NVEs' Attachment Circuits that are
   connected to subject-to-be-protected servers or VMs, may set the
   Sticky bit on the MAC/IP Advertisement routes sent for the MACs
   associated to the Attachment Circuits.  Also, statically configured
   MAC addresses should be advertised as Protected MAC addresses, since
   they are not subject to MAC Mobility procedures.

   [RFC7432] MAC Duplication Detection refers to EVPN's ability to
   detect duplicate MAC addresses.  A "MAC move" is a relearn event that
   happens at an access Attachment Circuit or through a MAC/IP
   Advertisement route with a Sequence Number that is higher than the
   stored one for the MAC.  When a MAC moves a number of times N within
   an M-second window between two NVEs, the MAC is declared as Duplicate
   and the detecting NVE does not re-advertise the MAC anymore.

   [RFC7432] provides MAC Duplication Detection, and with an extension
   it can protect the Broadcast Domain against loops created by backdoor
   links between NVEs.  The same principle (based on the Sequence
   Number) may be extended to protect the Broadcast Domain against
   loops.  When a MAC is detected as duplicate, the NVE may install it
   as a black-hole MAC and drop received frames with source MAC address
   and destination MAC address matching that duplicate MAC.  The MAC
   Duplication extension to support Loop Protection is described in
   [I-D.ietf-bess-rfc7432bis].

4.7.3.  Reduction/Optimization of BUM Traffic in Layer-2 Services

   In Broadcast Domains with a significant amount of flooding due to
   Unknown unicast and Broadcast frames, EVPN may help reduce and
   sometimes even suppress the flooding.

   In Broadcast Domains where most of the Broadcast traffic is caused by
   ARP (Address Resolution Protocol) and ND (Neighbor Discovery)
   protocols on the Tenant Systems, EVPN's Proxy-ARP and Proxy-ND
   capabilities may reduce the flooding drastically.  The use of Proxy-
   ARP/ND is specified in [RFC9161].

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   Proxy-ARP/ND procedures along with the assumption that Tenant Systems
   always issue a GARP (Gratuitous ARP) or an unsolicited Neighbor
   Advertisement message when they come up in the Broadcast Domain, may
   drastically reduce the unknown unicast flooding in the Broadcast
   Domain.

   The flooding caused by Tenant Systems' IGMP/MLD or PIM messages in
   the Broadcast Domain may also be suppressed by the use of IGMP/MLD
   and PIM Proxy functions, as specified in [RFC9251] and
   [I-D.skr-bess-evpn-pim-proxy].  These two documents also specify how
   to forward IP multicast traffic efficiently within the same Broadcast
   Domain, translate soft state IGMP/MLD/PIM messages into hard state
   BGP routes and provide fast-convergence redundancy for IP Multicast
   on multi-homed Ethernet Segments (ESes).

4.7.4.  Ingress Replication (IR) Optimization for BUM Traffic

   When an NVE attached to a given Broadcast Domain needs to send BUM
   traffic for the Broadcast Domain to the remote NVEs attached to the
   same Broadcast Domain, Ingress Replication is a very common option in
   NVO3 networks, since it is completely independent of the multicast
   capabilities of the underlay network.  Also, if the optimization
   procedures to reduce/suppress the flooding in the Broadcast Domain
   are enabled (Section 4.7.3), in spite of creating multiple copies of
   the same frame at the ingress NVE, Ingress Replication may be good
   enough.  However, in Broadcast Domains where Multicast (or Broadcast)
   traffic is significant, Ingress Replication may be very inefficient
   and cause performance issues on virtual-switch-based NVEs.

   [I-D.ietf-bess-evpn-optimized-ir] specifies the use of AR (Assisted
   Replication) NVO3 tunnels in EVPN Broadcast Domains.  AR retains the
   independence of the underlay network while providing a way to forward
   Broadcast and Multicast traffic efficiently.  AR uses AR-REPLICATORs
   that can replicate the Broadcast/Multicast traffic on behalf of the
   AR-LEAF NVEs.  The AR-LEAF NVEs are typically virtual-switches or
   NVEs with limited replication capabilities.  AR can work in a single-
   stage replication mode (Non-Selective Mode) or in a dual-stage
   replication mode (Selective Mode).  Both modes are detailed in
   [I-D.ietf-bess-evpn-optimized-ir].

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   In addition, [I-D.ietf-bess-evpn-optimized-ir] also describes a
   procedure to avoid sending Broadcast, Multicast or Unknown unicast to
   certain NVEs that do not need that type of traffic.  This is done by
   enabling PFL (Pruned Flood Lists) on a given Broadcast Domain.  For
   instance, an virtual-switch NVE that learns all its local MAC
   addresses for a Broadcast Domain via Cloud Management System, does
   not need to receive the Broadcast Domain's Unknown unicast traffic.
   Pruned Flood Lists help optimize the BUM flooding in the Broadcast
   Domain.

4.7.5.  EVPN Multi-Homing

   Another fundamental concept in EVPN is multi-homing.  A given Tenant
   System can be multi-homed to two or more NVEs for a given Broadcast
   Domain, and the set of links connected to the same Tenant System is
   defined as Ethernet Segment (ES).  EVPN supports single-active and
   all-active multi-homing.  In single-active multi-homing only one link
   in the Ethernet Segment is active.  In all-active multi-homing all
   the links in the Ethernet Segment are active for unicast traffic.
   Both modes support load-balancing:

   *  Single-active multi-homing means per-service load-balancing to/
      from the Tenant System.  For example, in Figure 1, for BD1, only
      one of the NVEs can forward traffic from/to TS2.  For a different
      Broadcast Domain, the other NVE may forward traffic.

   *  All-active multi-homing means per-flow load-balanding for unicast
      frames to/from the Tenant System.  That is, in Figure 1 and for
      BD1, both NVE4 and NVE5 can forward known unicast traffic to/from
      TS3.  For BUM traffic only one of the two NVEs can forward traffic
      to TS3, and both can forward traffic from TS3.

   There are two key aspects in the EVPN multi-homing procedures:

   *  DF (Designated Forwarder) election: the Designated Forwarder is
      the NVE that forwards the traffic to the Ethernet Segment in
      single-active mode.  In case of all-active, the Designated
      Forwarder is the NVE that forwards the BUM traffic to the Ethernet
      Segment.

   *  Split-horizon function: prevents the Tenant System from receiving
      echoed BUM frames that the Tenant System itself sent to the
      Ethernet Segment.  This is especially relevant in all-active
      Ethernet Segments, where the Tenant System may forward BUM frames
      to a non-Designated Forwarder NVE that can flood the BUM frames
      back to the Designated Forwarder NVE and then the Tenant System.
      As an example, in Figure 1, assuming NVE4 is the Designated
      Forwarder for ES-2 in BD1, BUM frames sent from TS3 to NVE5 will

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      be received at NVE4 and, since NVE4 is the Designated Forwarder
      for DB1, it will forward them back to TS3.  Split-horizon allows
      NVE4 (and any multi-homed NVE for that matter) to identify if an
      EVPN BUM frame is coming from the same Ethernet Segment or
      different, and if the frame belongs to the same ES2, NVE4 will not
      forward the BUM frame to TS3, in spite of being the Designated
      Forwarder.

   While [RFC7432] describes the default algorithm for the Designated
   Forwarder Election, [RFC8584] and [I-D.ietf-bess-evpn-pref-df]
   specify other algorithms and procedures that optimize the Designated
   Forwarder Election.

   The Split-horizon function is specified in [RFC7432] and it is
   carried out by using a special ESI-label that it identifies in the
   data path, all the BUM frames being originated from a given NVE and
   Ethernet Segment.  Since the ESI-label is an MPLS label, it cannot be
   used in all the non-MPLS NVO3 encapsulations, therefore [RFC8365]
   defines a modified Split-horizon procedure that is based on the
   source IP address of the NVO3 tunnel, and it is known as "Local-
   Bias".  It is worth noting that Local-Bias only works for all-active
   multi-homing, and not for single-active multi-homing.

4.7.6.  EVPN Recursive Resolution for Inter-Subnet Unicast Forwarding

   Section 4.3 describes how EVPN can be used for Inter Subnet
   Forwarding among subnets of the same tenant.  MAC/IP Advertisement
   routes and IP Prefix routes allow the advertisement of host routes
   and IP Prefixes (IP Prefix route) of any length.  The procedures
   outlined by Section 4.3 are similar to the ones in [RFC4364], only
   for NVO3 tunnels.  However, [RFC9136] also defines advanced Inter
   Subnet Forwarding procedures that allow the resolution of IP Prefix
   routes to not only BGP next-hops but also "overlay indexes" that can
   be a MAC, a GW IP or an ESI, all of them in the tenant space.

   Figure 4 illustrates an example that uses Recursive Resolution to a
   GW-IP as per [RFC9136] section 4.4.2.  In this example, IP-VRFs in
   NVE1 and NVE2 are connected by a SBD (Supplementary Broadcast
   Domain).  An SBD is a Broadcast Domain that connects all the IP-VRFs
   of the same tenant, via IRB, and has no Attachment Circuits.  NVE1
   advertises the host route TS2-IP/L (IP address and Prefix Length of
   TS2) in an IP Prefix route with overlay index GWIP=IP1.  Also, IP1 is
   advertised in an MAC/IP Advertisement route associated to M1, VNI-S
   and BGP next-hop NVE1.  Upon importing the two routes, NVE2 installs
   TS2-IP/L in the IP-VRF with a next-hop that is the GWIP IP1.  NVE2
   also installs M1 in the Supplementary Broadcast Domain, with VNI-S
   and NVE1 as next-hop.  If TS3 sends a packet with IP DA=TS2, NVE2
   will perform a Recursive Resolution of the IP Prefix route prefix

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   information to the forwarding information of the correlated MAC/IP
   Advertisement route.  The IP Prefix route's Recursive Resolution has
   several advantages such as better convergence in scaled networks
   (since multiple IP Prefix routes can be invalidated with a single
   withdrawal of the overlay index route) or the ability to advertise
   multiple IP Prefix routes from an overlay index that can move or
   change dynamically.  [RFC9136] describes a few use-cases.

                  +-------------------------------------+
                  |             EVPN NVO3               |
                  |                                     +
                NVE1                                 NVE2
          +--------------------+            +--------------------+
          | +---+IRB +------+  |            |  +------+IRB +---+ |
    TS1-----|BD1|----|IP-VRF|  |            |  |IP-VRF|----|BD3|-----TS3
          | +---+    |      |-(SBD)------(SBD)-|      |    +---+ |
          | +---+IRB |      |IRB(IP1/M1)    IRB+------+          |
    TS2-----|BD2|----|      |  |            +-----------+--------+
          | +---+    +------+  |                        |
          +--------------------+                        |
                  |   RT-2(M1,IP1,VNI-S,NVE1)-->        |
                  |     RT-5(TS2-IP/L,GWIP=IP1)-->      |
                  +-------------------------------------+

            Figure 4: EVPN for L3 - Recursive Resolution example

4.7.7.  EVPN Optimized Inter-Subnet Multicast Forwarding

   The concept of the Supplementary Broadcast Domain described in
   Section 4.7.6 is also used in [I-D.ietf-bess-evpn-irb-mcast] for the
   procedures related to Inter Subnet Multicast Forwarding across
   Broadcast Domains of the same tenant.  For instance,
   [I-D.ietf-bess-evpn-irb-mcast] allows the efficient forwarding of IP
   multicast traffic from any Broadcast Domain to any other Broadcast
   Domain (or even to the same Broadcast Domain where the Source
   resides).  The [I-D.ietf-bess-evpn-irb-mcast] procedures are
   supported along with EVPN multi-homing, and for any tree allowed on
   NVO3 networks, including IR or AR.  [I-D.ietf-bess-evpn-irb-mcast]
   also describes the interoperability between EVPN and other multicast
   technologies such as MVPN (Multicast VPN) and PIM for inter-subnet
   multicast.

   [I-D.ietf-bess-evpn-mvpn-seamless-interop] describes another
   potential solution to support EVPN to MVPN interoperability.

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4.7.8.  Data Center Interconnect (DCI)

   Tenant Layer-2 and Layer-3 services deployed on NVO3 networks must be
   extended to remote NVO3 networks that are connected via non-NOV3 Wide
   Area Networks (mostly MPLS based Wide Area Networks).  [RFC9014]
   defines some architectural models that can be used to interconnect
   NVO3 networks via MPLS Wide Area Networks.

   When NVO3 networks are connected by MPLS Wide Area Networks,
   [RFC9014] specifies how EVPN can be used end-to-end, in spite of
   using a different encapsulation in the Wide Area Network.  [RFC9014]
   also supports the use of NVO3 or Segment Routing (encoding 32-bit or
   128-bit Segment Identifiers into labels or IPv6 addresses
   respectively) transport tunnels in the Wide Area Network.

   Even if EVPN can also be used in the Wide Area Network for Layer-2
   and Layer-3 services, there may be a need to provide a Gateway
   function between EVPN for NVO3 encapsulations and IPVPN for MPLS
   tunnels, if the operator uses IPVPN in the Wide Area Network.
   [I-D.ietf-bess-evpn-ipvpn-interworking] specifies the interworking
   function between EVPN and IPVPN for unicast Inter Subnet Forwarding.
   If Inter Subnet Multicast Forwarding is also needed across an IPVPN
   Wide Area Network, [I-D.ietf-bess-evpn-irb-mcast] describes the
   required interworking between EVPN and MVPN (Multicast Virtual
   Private Networks).

5.  Conclusion

   EVPN provides a unified control-plane that solves the NVE auto-
   discovery, tenant MAP/IP dissemination and advanced features required
   by NVO3 networks, in a scalable way and keeping the independence of
   the underlay IP Fabric, i.e. there is no need to enable PIM in the
   underlay network and maintain multicast states for tenant Broadcast
   Domains.

   This document justifies the use of EVPN for NVO3 networks, discusses
   its applicability to basic Layer-2 and Layer-3 connectivity
   requirements, as well as advanced features such as MAC-mobility, MAC
   Protection and Loop Protection, multi-homing, DCI and much more.

6.  Conventions Used in this Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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7.  Security Considerations

   This document does not introduce any new procedure or additional
   signaling in EVPN, and relies on the security considerations of the
   individual specifications used as a reference throughout the
   document.  In particular, and as mentioned in [RFC7432], control
   plane and forwarding path protection are aspects to secure in any
   EVPN domain, when applied to NVO3 networks.

   [RFC7432] mentions security techniques such as those discussed in
   [RFC5925] to authenticate BGP messages, and those included in
   [RFC4271], [RFC4272] and [RFC6952] to secure BGP are relevant for
   EVPN in NVO3 networks as well.

8.  IANA Considerations

   None.

9.  References

9.1.  Normative References

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC7365]  Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
              Rekhter, "Framework for Data Center (DC) Network
              Virtualization", RFC 7365, DOI 10.17487/RFC7365, October
              2014, <https://www.rfc-editor.org/info/rfc7365>.

   [RFC7364]  Narten, T., Ed., Gray, E., Ed., Black, D., Fang, L.,
              Kreeger, L., and M. Napierala, "Problem Statement:
              Overlays for Network Virtualization", RFC 7364,
              DOI 10.17487/RFC7364, October 2014,
              <https://www.rfc-editor.org/info/rfc7364>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

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   [RFC9136]  Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
              A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
              (EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
              <https://www.rfc-editor.org/info/rfc9136>.

   [RFC9135]  Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
              Rabadan, "Integrated Routing and Bridging in Ethernet VPN
              (EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
              <https://www.rfc-editor.org/info/rfc9135>.

   [RFC8365]  Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
              Uttaro, J., and W. Henderickx, "A Network Virtualization
              Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
              DOI 10.17487/RFC8365, March 2018,
              <https://www.rfc-editor.org/info/rfc8365>.

   [RFC8926]  Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
              "Geneve: Generic Network Virtualization Encapsulation",
              RFC 8926, DOI 10.17487/RFC8926, November 2020,
              <https://www.rfc-editor.org/info/rfc8926>.

   [I-D.ietf-nvo3-encap]
              Boutros, S. and D. E. Eastlake, "Network Virtualization
              Overlays (NVO3) Encapsulation Considerations", Work in
              Progress, Internet-Draft, draft-ietf-nvo3-encap-08, 30
              April 2022, <https://www.ietf.org/archive/id/draft-ietf-
              nvo3-encap-08.txt>.

   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

   [I-D.ietf-bess-evpn-lsp-ping]
              Jain, P., Sajassi, A., Salam, S., Boutros, S., and G.
              Mirsky, "LSP-Ping Mechanisms for EVPN and PBB-EVPN", Work
              in Progress, Internet-Draft, draft-ietf-bess-evpn-lsp-
              ping-08, 8 July 2022, <https://www.ietf.org/archive/id/
              draft-ietf-bess-evpn-lsp-ping-08.txt>.

   [RFC9161]  Rabadan, J., Ed., Sathappan, S., Nagaraj, K., Hankins, G.,
              and T. King, "Operational Aspects of Proxy ARP/ND in
              Ethernet Virtual Private Networks", RFC 9161,
              DOI 10.17487/RFC9161, January 2022,
              <https://www.rfc-editor.org/info/rfc9161>.

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   [RFC9251]  Sajassi, A., Thoria, S., Mishra, M., Patel, K., Drake, J.,
              and W. Lin, "Internet Group Management Protocol (IGMP) and
              Multicast Listener Discovery (MLD) Proxies for Ethernet
              VPN (EVPN)", RFC 9251, DOI 10.17487/RFC9251, June 2022,
              <https://www.rfc-editor.org/info/rfc9251>.

   [I-D.skr-bess-evpn-pim-proxy]
              Rabadan, J., Kotalwar, J., Sathappan, S., Zhang, Z., and
              A. Sajassi, "PIM Proxy in EVPN Networks", Work in
              Progress, Internet-Draft, draft-skr-bess-evpn-pim-proxy-
              01, 30 October 2017, <https://www.ietf.org/archive/id/
              draft-skr-bess-evpn-pim-proxy-01.txt>.

   [I-D.ietf-bess-evpn-optimized-ir]
              Rabadan, J., Sathappan, S., Lin, W., Katiyar, M., and A.
              Sajassi, "Optimized Ingress Replication Solution for
              Ethernet VPN (EVPN)", Work in Progress, Internet-Draft,
              draft-ietf-bess-evpn-optimized-ir-12, 25 January 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-
              optimized-ir-12.txt>.

   [RFC8584]  Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
              J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
              VPN Designated Forwarder Election Extensibility",
              RFC 8584, DOI 10.17487/RFC8584, April 2019,
              <https://www.rfc-editor.org/info/rfc8584>.

   [I-D.ietf-bess-evpn-pref-df]
              Rabadan, J., Sathappan, S., Przygienda, T., Lin, W.,
              Drake, J., Sajassi, A., and S. Mohanty, "Preference-based
              EVPN DF Election", Work in Progress, Internet-Draft,
              draft-ietf-bess-evpn-pref-df-09, 6 July 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-
              pref-df-09.txt>.

   [I-D.ietf-bess-evpn-irb-mcast]
              Lin, W., Zhang, Z., Drake, J., Rosen, E. C., Rabadan, J.,
              and A. Sajassi, "EVPN Optimized Inter-Subnet Multicast
              (OISM) Forwarding", Work in Progress, Internet-Draft,
              draft-ietf-bess-evpn-irb-mcast-07, 23 June 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-irb-
              mcast-07.txt>.

   [RFC9014]  Rabadan, J., Ed., Sathappan, S., Henderickx, W., Sajassi,
              A., and J. Drake, "Interconnect Solution for Ethernet VPN
              (EVPN) Overlay Networks", RFC 9014, DOI 10.17487/RFC9014,
              May 2021, <https://www.rfc-editor.org/info/rfc9014>.

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   [I-D.ietf-bess-evpn-ipvpn-interworking]
              Rabadan, J., Sajassi, A., Rosen, E., Drake, J., Lin, W.,
              Uttaro, J., and A. Simpson, "EVPN Interworking with
              IPVPN", Work in Progress, Internet-Draft, draft-ietf-bess-
              evpn-ipvpn-interworking-07, 6 July 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-
              ipvpn-interworking-07.txt>.

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
              <https://www.rfc-editor.org/info/rfc7348>.

   [RFC7510]  Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
              "Encapsulating MPLS in UDP", RFC 7510,
              DOI 10.17487/RFC7510, April 2015,
              <https://www.rfc-editor.org/info/rfc7510>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [CLOS1953] Clos, C., "A Study of Non-Blocking Switching Networks",
              March 1953.

   [I-D.ietf-bess-evpn-geneve]
              Boutros, S., Sajassi, A., Drake, J., Rabadan, J., and S.
              Aldrin, "EVPN control plane for Geneve", Work in Progress,
              Internet-Draft, draft-ietf-bess-evpn-geneve-04, 23 May
              2022, <https://www.ietf.org/archive/id/draft-ietf-bess-
              evpn-geneve-04.txt>.

   [I-D.ietf-bess-evpn-mvpn-seamless-interop]
              Sajassi, A., Thiruvenkatasamy, K., Thoria, S., Gupta, A.,
              and L. Jalil, "Seamless Multicast Interoperability between
              EVPN and MVPN PEs", Work in Progress, Internet-Draft,
              draft-ietf-bess-evpn-mvpn-seamless-interop-04, 28 June
              2022, <https://www.ietf.org/archive/id/draft-ietf-bess-
              evpn-mvpn-seamless-interop-04.txt>.

   [I-D.sajassi-bess-secure-evpn]
              Sajassi, A., Banerjee, A., Thoria, S., Carrel, D., Weis,
              B., and J. Drake, "Secure EVPN", Work in Progress,
              Internet-Draft, draft-sajassi-bess-secure-evpn-05, 25
              October 2021, <https://www.ietf.org/archive/id/draft-
              sajassi-bess-secure-evpn-05.txt>.

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   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <https://www.rfc-editor.org/info/rfc4272>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [I-D.ietf-bess-rfc7432bis]
              Sajassi, A., Burdet, L. A., Drake, J., and J. Rabadan,
              "BGP MPLS-Based Ethernet VPN", Work in Progress, Internet-
              Draft, draft-ietf-bess-rfc7432bis-04, 7 March 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-
              rfc7432bis-04.txt>.

   [IEEE.802.1AX_2014]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Link Aggregation", 24 December 2014.

Appendix A.  Acknowledgments

   The authors want to thank Aldrin Isaac for his comments.

Appendix B.  Contributors

Appendix C.  Authors' Addresses

Authors' Addresses

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   Jorge Rabadan (editor)
   Nokia
   520 Almanor Ave
   Sunnyvale, CA 94085
   United States of America
   Email: jorge.rabadan@nokia.com

   Matthew Bocci
   Nokia
   Email: matthew.bocci@nokia.com

   Sami Boutros
   Ciena
   Email: sboutros@ciena.com

   Ali Sajassi
   Cisco Systems, Inc.
   Email: sajassi@cisco.com

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