Internet DRAFT - draft-ietf-bess-evpn-mvpn-seamless-interop

draft-ietf-bess-evpn-mvpn-seamless-interop







BESS Working Group                                            A. Sajassi
Internet-Draft                                       K. Thiruvenkatasamy
Intended status: Standards Track                               S. Thoria
Expires: 25 April 2024                                             Cisco
                                                                A. Gupta
                                                                  VMware
                                                                L. Jalil
                                                                 Verizon
                                                         23 October 2023


     Seamless Multicast Interoperability between EVPN and MVPN PEs
             draft-ietf-bess-evpn-mvpn-seamless-interop-06

Abstract

   Ethernet Virtual Private Network (EVPN) solution is becoming
   pervasive for Network Virtualization Overlay (NVO) services in data
   center (DC) and Enterprise networks as well as the next generation
   VPN services in service provider (SP) networks.

   As service providers transform their networks in their Central
   Offices (COs) towards the next generation data center with Software
   Defined Networking (SDN) based fabric and Network Function
   Virtualization (NFV), they want to be able to maintain their offered
   services including Multicast VPN (MVPN) service between their
   existing network and their new Service Provider Data Center (SPDC)
   network seamlessly without the use of gateway devices.  They want to
   have such seamless interoperability between their new SPDCs and their
   existing networks for a) reducing cost, b) having optimum forwarding,
   and c) reducing provisioning.  This document describes a unified
   solution based on RFCs 6513 & 6514 for seamless interoperability of
   Multicast VPN between EVPN and MVPN PEs.  Furthermore, it describes
   how the proposed solution can be used as a routed multicast solution
   in data centers with only EVPN PEs.

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/.






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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 25 April 2024.

Copyright Notice

   Copyright (c) 2023 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
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   5
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Optimum Forwarding  . . . . . . . . . . . . . . . . . . .   7
     4.2.  Optimum Replication . . . . . . . . . . . . . . . . . . .   7
     4.3.  All-Active and Single-Active Multi-Homing . . . . . . . .   8
     4.4.  Inter-AS Tree Stitching . . . . . . . . . . . . . . . . .   8
     4.5.  EVPN Service Interfaces . . . . . . . . . . . . . . . . .   8
     4.6.  Distributed Anycast Gateway . . . . . . . . . . . . . . .   8
     4.7.  Selective & Aggregate Selective Tunnels . . . . . . . . .   9
     4.8.  Tenants' (S,G) or (*,G) states  . . . . . . . . . . . . .   9
     4.9.  Zero Disruption upon BD/Subnet Addition . . . . . . . . .   9
     4.10. No Changes to Existing EVPN Service Interface Models  . .   9
     4.11. External source and receivers . . . . . . . . . . . . . .   9
     4.12. Tenant RP placement . . . . . . . . . . . . . . . . . . .   9
   5.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  IRB Unicast versus IRB Multicast  . . . . . . . . . . . .  10
       5.1.1.  IRB multicast in seamless interop mode  . . . . . . .  10
     5.2.  Operational Model for EVPN IRB PEs  . . . . . . . . . . .  11
     5.3.  Unicast Route Advertisements for IP multicast Source  . .  14
     5.4.  Multi-homing of IP Multicast Source and Receivers . . . .  16
       5.4.1.  Single-Active Multi-Homing  . . . . . . . . . . . . .  16
       5.4.2.  All-Active Multi-Homing . . . . . . . . . . . . . . .  17
     5.5.  Mobility for Tenant's Sources and Receivers . . . . . . .  19



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   6.  Control Plane Operation . . . . . . . . . . . . . . . . . . .  19
     6.1.  Intra-ES Subnet Tunnel  . . . . . . . . . . . . . . . . .  20
     6.2.  Intra-Subnet BUM Tunnel . . . . . . . . . . . . . . . . .  21
     6.3.  Inter-Subnet IP Multicast Tunnel  . . . . . . . . . . . .  21
     6.4.  IGMP Hosts as TSes  . . . . . . . . . . . . . . . . . . .  22
     6.5.  PIM Routers as TSes . . . . . . . . . . . . . . . . . . .  23
   7.  Data Plane Operation  . . . . . . . . . . . . . . . . . . . .  23
     7.1.  Intra-Subnet L2 Switching . . . . . . . . . . . . . . . .  24
     7.2.  Inter-Subnet L3 Routing . . . . . . . . . . . . . . . . .  24
   8.  DCs with only EVPN PEs  . . . . . . . . . . . . . . . . . . .  25
     8.1.  Setup of overlay multicast delivery . . . . . . . . . . .  25
     8.2.  Handling of different encapsulations  . . . . . . . . . .  27
       8.2.1.  MPLS Encapsulation  . . . . . . . . . . . . . . . . .  27
       8.2.2.  VxLAN Encapsulation . . . . . . . . . . . . . . . . .  27
       8.2.3.  Other Encapsulation . . . . . . . . . . . . . . . . .  27
   9.  DCI with MPLS in WAN and VxLAN in DCs . . . . . . . . . . . .  28
     9.1.  Control plane inter-connect . . . . . . . . . . . . . . .  28
     9.2.  Data plane inter-connect  . . . . . . . . . . . . . . . .  29
   10. Interop with L2 EVPN PEs  . . . . . . . . . . . . . . . . . .  29
     10.1.  Interaction with L2EVPN PE and Seamless interop capable
            PE . . . . . . . . . . . . . . . . . . . . . . . . . . .  30
     10.2.  Network having L2EVPN PE, Seamless interop capable PE and
            MVPN PE  . . . . . . . . . . . . . . . . . . . . . . . .  32
   11. Connecting external Multicast networks or PIM routers.  . . .  33
   12. TS RP options . . . . . . . . . . . . . . . . . . . . . . . .  33
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  33
   14. Security Considerations . . . . . . . . . . . . . . . . . . .  34
   15. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  34
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     16.2.  Informative References . . . . . . . . . . . . . . . . .  35
   Appendix A.  Supporting application with TTL value 1  . . . . . .  35
     A.1.  Policy based model  . . . . . . . . . . . . . . . . . . .  35
     A.2.  Exercising BUM procedure for VLAN/BD  . . . . . . . . . .  36
     A.3.  Intra-subnet bridging . . . . . . . . . . . . . . . . . .  36
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  37

1.  Introduction

   Ethernet Virtual Private Network (EVPN) solution is becoming
   pervasive for Network Virtualization Overlay (NVO) services in data
   center (DC) and Enterprise networks as well as the next generation
   VPN services in service provider (SP) networks.

   As service providers transform their networks in their Central
   Offices (COs) towards the next generation data center with Software
   Defined Networking (SDN) based fabric and Network Function
   Virtualization (NFV), they want to be able to maintain their offered



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   services including Multicast VPN (MVPN) service between their
   existing network and their new SPDC network seamlessly without the
   use of gateway devices.  There are several reasons for having such
   seamless interoperability between their new DCs and their existing
   networks:

   - Lower Cost: gateway devices need to have very high scalability to
   handle VPN services for their DCs and as such need to handle large
   number of VPN instances (in tens or hundreds of thousands) and very
   large number of routes (e.g., in tens of millions).  For the same
   speed and feed, these high scale gateway boxes are relatively much
   more expensive than the edge devices (e.g., PEs and TORs) that
   support a much lower number of routes and VPN instances.

   - Optimum Forwarding: in a given Central Office(CO), both EVPN PEs
   and MVPN PEs can be connected to the same fabric/network (e.g., same
   IGP domain).  In such scenarios, the service providers want to have
   optimum forwarding among these PE devices without the use of gateway
   devices.  If gateway devices are used, then the IP multicast traffic
   between an EVPN and MVPN PEs can no longer be optimum and in some
   cases, it may even get tromboned.  Furthermore, when an SPDC network
   spans across multiple LATA (multiple geographic areas) and gateways
   are used between EVPN and MVPN PEs, then with respect to IP multicast
   traffic, only one GW can be designated forwarder (DF) between EVPN
   and MVPN PEs.  Such scenarios not only result in non- optimum
   forwarding but also it can result in the tromboning of IP multicast
   traffic between the two LATAs when both source and destination PEs
   are in the same LATA and the DF gateway is elected to be in a
   different LATA.

   - Less Provisioning: If gateways are used, then the operator needs to
   configure per-tenant info on the gateways.  In other words, for each
   tenant that is configured, one (or maybe two) additional touchpoints
   are needed.

   In datacenter deployments, inter-subnet multicast traffic within an
   EVPN based fabric/data center is unoptimized.  When there are
   multiple receivers in different broadcast domains of the same tenant
   system, a router attached to an EVPN PE would send multiple copies
   into the EVPN fabric resulting in bandwidth wastage.  [RFC9135] only
   covers procedures for efficient inter-subnet connectivity among these
   Tenant Systems and End Devices while maintaining the multi-homing
   capabilities of EVPN only for unicast traffic.  There is a need to
   support efficient inter-subnet multicast forwarding within the data
   center.






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   This document describes a unified solution based on [RFC6513] and
   [RFC6514] for seamless interoperability of multicast VPN between EVPN
   and MVPN PEs.  Furthermore, it describes how the proposed solution
   can be used as a routed multicast solution in data centers with only
   EVPN PEs (e.g., routed multicast VPN only among EVPN PEs) to do
   optimized multicast forwarding.

   The document is organized such that seamless interop mode covered
   first followed by how the same model can be used as an optimized
   multicast forwarding solution for data center networks.

   Section 5 provides the solution overview in detail.  This section
   assumes that all EVPN PEs have IRB capability and operating in IRB
   mode for both unicast and multicast traffic (e.g., all EVPN PEs are
   homogenous in terms of their capabilities and operational modes).
   Section 6 and 7 covers control plane and data plane respectively.

   Section 8 describes how the proposed solution can be used to achieve
   optimized multicast forwarding within the EVPN domain/Data center
   only networks.  Section 9 discusses DCI use cases.

   An EVPN network can consist of a mix of L2 and L3 PEs.  The multicast
   operation of such a heterogeneous EVPN network will be an extension
   of an EVPN homogenous network.  Section 10 discusses the multicast
   IRB solution description for the EVPN heterogeneous network.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
   be interpreted as described in [RFC2119] only when they appear in all
   upper case.  They may also appear in lower or mixed case as English
   words, without any normative meaning.

3.  Terminology

   Most of the terminology used in this document comes from [RFC8365]

   Broadcast Domain (BD): In a bridged network, the broadcast domain
   corresponds to a Virtual LAN (VLAN), where a VLAN is typically
   represented by a single VLAN ID (VID) but can be represented by
   several VIDs where Shared VLAN Learning (SVL) is used per [802.1Q].

   Bridge Table (BT): An instantiation of a broadcast domain on a MAC-
   VRF.

   VXLAN: Virtual Extensible LAN




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   PoD: Point of Delivery

   NV: Network Virtualization

   NVO: Network Virtualization Overlay

   NVE: Network Virtualization Endpoint

   NVGRE: Network Virtualization using Generic Routing Encapsulation

   GENEVE: Generic Network Virtualization Encapsulation

   VNI: Virtual Network Identifier (for VXLAN)

   EVPN: Ethernet VPN

   EVI: An EVPN instance spanning the Provider Edge (PE) devices
   participating in that EVPN

   MAC-VRF: A Virtual Routing and Forwarding Table for Media Access
   Control (MAC) addresses on a PE

   IP-VRF: A Virtual Routing and Forwarding Table for Internet Protocol
   (IP) addresses on a PE

   Ethernet Segment (ES): When a customer site (device or network) is
   connected to one or more PEs via a set of Ethernet links, then that
   set of links is referred to as an 'Ethernet segment'.

   Ethernet Segment Identifier (ESI): A unique non-zero identifier that
   identifies an Ethernet segment is called an 'Ethernet Segment
   Identifier'.

   Ethernet Tag: An Ethernet tag identifies a particular broadcast
   domain, e.g., a VLAN.  An EVPN instance consists of one or more
   broadcast domains.

   PE: Provider Edge device.

   Single-Active Redundancy Mode: When only a single PE, among all the
   PEs attached to an Ethernet segment are allowed to forward traffic
   to/from that Ethernet segment for a given VLAN, then the Ethernet
   segment is defined to be operating in Single-Active redundancy mode.

   All-Active Redundancy Mode: When all PEs are attached to an Ethernet
   segment are allowed to forward known unicast traffic to/from that
   Ethernet segment for a given VLAN, then the Ethernet segment is
   defined to be operating in All-Active redundancy mode.



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   PIM-SM: Protocol Independent Multicast - Sparse-Mode

   PIM-SSM: Protocol Independent Multicast - Source Specific Multicast
   Bidir PIM: Bidirectional PIM

   FHR: First Hop Router

   LHR: Last Hop Router

   CO: Central Office of a service provider

   SPDC: Service Provider Data Center

   LATA: Local Access and Transport Area

   Border Leafs: A set of EVPN PEs acting as an exit point for EVPN
   fabric.

   EC: BGP Extended Community

   UMH: Upstream Multicast Hop

   TS: Tenant Systems

4.  Requirements

   This section describes the requirements specific to providing
   seamless multicast VPN service between MVPN and EVPN capable
   networks.

4.1.  Optimum Forwarding

   The solution SHALL support optimum multicast forwarding between EVPN
   and MVPN PEs within a network.  The network can be confined to a CO
   or it can span across multiple LATAs.  The solution SHALL support
   optimum multicast forwarding with both ingress replication tunnels
   and P2MP tunnels.

4.2.  Optimum Replication

   For EVPN PEs with IRB capability, the solution SHALL use only a
   single multicast tunnel among EVPN and MVPN PEs for IP multicast
   traffic, when both PEs use the same tunnel type.  Multicast tunnels
   can be either ingress replication tunnels or P2MP tunnels.  The the
   solution MUST support optimum replication for both Intra-subnet and
   Inter-subnet IP multicast traffic:





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   - Non-IP traffic SHALL be forwarded per EVPN baseline [RFC7432] or
   [RFC8365]

   - If a Multicast VPN spans across both Intra and Inter subnets, then
   for Ingress replication regardless of whether the traffic is Intra or
   Inter subnet, only a single copy of IP multicast traffic SHALL be
   sent from the source PE to the destination PE.

   - If a Multicast VPN spans across both Intra and Inter subnets, then
   for P2MP tunnels regardless of whether the traffic is Intra or Inter
   subnet, only a single copy of multicast data SHALL be transmitted by
   the source PE.  Source PE can be either EVPN or MVPN PE and receiving
   PEs can be a mix of EVPN and MVPN PEs - i.e., a multicast VPN can be
   spread across both EVPN and MVPN PEs.

4.3.  All-Active and Single-Active Multi-Homing

   The solution MUST support multi-homing of source devices and
   receivers that are sitting in the same subnet (e.g., VLAN) and are
   multi-homed to EVPN PEs.  The solution SHALL allow for both Single-
   Active and All-Active multi-homing.

4.4.  Inter-AS Tree Stitching

   The solution SHALL support multicast tree stitching when the tree
   spans across multiple Autonomous Systems.

4.5.  EVPN Service Interfaces

   The solution MUST support all EVPN service interfaces listed in
   section 6 of [RFC7432]:

   *  VLAN-based service interface

   *  VLAN-bundle service interface

   *  VLAN-aware bundle service interface.

4.6.  Distributed Anycast Gateway

   The solution SHALL support distributed anycast gateways for tenant
   workloads on NVE devices operating in EVPN-IRB mode.









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4.7.  Selective & Aggregate Selective Tunnels

   The solution SHALL support selective and aggregate selective P-
   tunnels as well as inclusive and aggregate inclusive P-tunnels.  When
   selective tunnels are used, multicast traffic SHOULD only be
   forwarded to the remote PEs that have receivers - i.e., if there are
   no receivers at a remote PE, the multicast traffic SHOULD NOT be
   forwarded to that PE.  If there are no receivers on any remote PEs,
   then the multicast traffic SHOULD NOT be forwarded to the core.

4.8.  Tenants' (S,G) or (*,G) states

   The solution SHOULD store (C-S,C-G) and (C-*,C-G) states only on PE
   devices that have an interest in such states hence reducing memory
   and processing requirements - i.e., PE devices that have sources and/
   or receivers interested in such multicast groups.

4.9.  Zero Disruption upon BD/Subnet Addition

   In DC environments, various broadcast domains (BDs) are provisioned
   and removed on a regular basis due to host mobility, policy, and
   tenant changes.  Such change in BD configuration should not affect
   existing flows within the same BD or any other BD in the network.

4.10.  No Changes to Existing EVPN Service Interface Models

   VLAN-aware bundle service as defined in [RFC7432] typically does not
   require any VLAN ID translation from one tenant site to another -
   i.e., the same set of VLAN IDs are configured consistently on all
   tenant segments.  In such scenarios, EVPN-IRB multicast service MUST
   maintain the same mode of operation and SHALL NOT require any VLAN ID
   translation.

4.11.  External source and receivers

   The solution SHALL support sources and receivers external to the
   tenant domain. i.e., multicast source inside the tenant domain can
   have receiver outside the tenant domain and vice versa.

4.12.  Tenant RP placement

   The solution SHALL support a tenant to have RP anywhere in the
   network.  RP can be placed inside the EVPN network or MVPN network or
   external domain.







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5.  Solution Overview

   This section describes a multicast VPN solution based on [RFC6513]
   and [RFC6514] for EVPN PEs operating in IRB mode that want to perform
   seamless interoperability with their counterparts MVPN PEs.

   In order to enable seamless integration of EVPN and MVPN PEs, traffic
   originated/received from an EVPN PE needs to be modeled very similar
   to a MVPN PE.  Hence, there are some differences in handling IRB
   multicast defined in this document in comparison to IRB unicast
   defined in [RFC9135].  The next section covers differences.

5.1.  IRB Unicast versus IRB Multicast

   [RFC9135] describes the operation for EVPN PEs in IRB mode for
   unicast traffic.  The same IRB model is used for unicast traffic,
   where an IP-VRF in an EVPN PE is attached to one or more bridge
   tables (BTs) via virtual IRB interfaces, is also applicable for
   multicast traffic.

   For unicast traffic, the intra-subnet traffic is bridged within the
   MAC-VRF associated with that subnet (i.e., a lookup based on MAC-DA
   is performed); whereas, the inter-subnet traffic is routed in the
   corresponding IP-VRF (i.e. a lookup based on IP-DA is performed).

   A given tenant can have one or more IP-VRFs; however, without loss of
   generality, this document assumes one IP-VRF per tenant.  In context
   of a given tenant's multicast traffic, the intra-subnet traffic is
   bridged for non-IP traffic and it is Layer-2 switched for IP traffic.
   Whereas, the tenant's inter-subnet multicast traffic is always routed
   in the corresponding IP-VRF.  The difference between bridging and
   L2-switching for multicast traffic is that the former uses MAC-DA
   lookup for forwarding the multicast traffic; whereas, the latter uses
   IP-DA lookup for such forwarding where the forwarding states are
   built in the MAC-VRF using IGMP/MLD or PIM snooping.

5.1.1.  IRB multicast in seamless interop mode

   EVPN does not provide a Virtual LAN (VLAN) service per [IEEE802.1Q]
   but rather an emulated VLAN service.  This VLAN service emulation is
   not only done for unicast traffic but also extended for intra- subnet
   multicast traffic described in [RFC9251].  For intra-subnet
   multicast, an EVPN PE builds multicast forwarding states in its
   bridge table (BT) based on snooping of IGMP/MLD and/or PIM messages
   and the forwarding is performed based on the destination IP multicast
   address of the Ethernet frame rather than destination MAC address as
   noted above.




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   In order to enable seamless integration of EVPN and MVPN PEs, this
   document extends the concept of an emulated VLAN service for
   multicast IRB applications such that the intra-subnet IP multicast
   traffic can get treated the same as inter-subnet IP multicast traffic
   which means intra-subnet IP multicast traffic destined to remote PEs
   gets routed instead of being L2-switched - i.e., TTL value gets
   decremented and the Ethernet header of the L2 frame is de-capsulated
   and encapsulated at both ingress and egress PEs.

   It should be noted that the non-IP multicast or L2 broadcast traffic
   still gets bridged and frames get forwarded based on their
   destination MAC addresses.

   Link local IP multicast traffic consists of IPv4 traffic with a
   destination address prefix of 224/8 and IPv6 traffic with a
   destination address prefix of FF02/16.  Such IP multicast traffic
   along with non-IP multicast/broadcast traffic are sent per EVPN
   [RFC7432] BUM procedures and does not get routed via IP-VRF for
   multicast addresses.  So, such BUM traffic will be limited to a given
   EVI/VLAN (e.g., a given subnet); whereas, IP multicast traffic, will
   be locally L2 switched for local interfaces attached on the same
   subnet and will be routed for local interfaces attached to a
   different subnet or for forwarding traffic to other EVPN PEs (refer
   to section 7 for data plane operation).

5.2.  Operational Model for EVPN IRB PEs

   Without the loss of generality, this section assumes that all EVPN
   PEs have IRB capability and operating in IRB mode for both unicast
   and multicast traffic (e.g., all EVPN PEs are homogenous in terms of
   their capabilities and operational modes).  As it will be seen later,
   an EVPN network can consist of a mix of PEs where some are capable of
   multicast IRB and some are not and the multicast operation of such
   heterogeneous EVPN network will be an extension of an EVPN homogenous
   network.  Therefore, we start with the multicast IRB solution
   description for the EVPN homogenous network.















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   The EVPN PEs terminate IGMP/MLD messages from tenant host devices or
   PIM messages from tenant routers on their IRB interfaces, thus avoid
   sending these messages over MPLS/IP core.  A tenant virtual/physical
   router (e.g., CE) attached to an EVPN PE becomes a multicast routing
   the adjacency of that PE.  Furthermore, the PE uses MVPN BGP protocol
   and procedures per [RFC6513] and [RFC6514].  With respect to
   multicast routing protocol between the tenant's virtual/physical
   router and the PE that it is attached to, any of the following PIM
   protocols is supported per [RFC6513]: PIM-SM with Any Source
   Multicast (ASM) mode, PIM-SM with Source Specific Multicast (SSM)
   mode, and PIM Bidirectional (BIDIR) mode.  Support of PIM-DM (Dense
   Mode) is excluded in this document per [RFC6513].

   The EVPN PEs use MVPN BGP routes defined in [RFC6514] to convey
   tenant (S,G) or (*,G) states to other MVPN or EVPN PEs and to set up
   overlay trees (inclusive or selective) for a given MVPN instance.
   The root or a leaf of such an overlay tree is terminated on an EVPN
   or MVPN PE.  Furthermore, this inclusive or selective overlay tree is
   terminated on a single IP-VRF of the EVPN or MVPN PE.  In case of
   EVPN PE, these overlay trees never get terminated on MAC-VRFs of that
   PE.

   Overlay trees are instantiated by underlay provider tunnels (P-
   tunnels) - e.g., P2MP, MP2MP, or unicast tunnels per [RFC6513].  When
   there are several overlay trees mapped to a single underlay P-tunnel,
   the tunnel is referred to as an aggregate tunnel.

   Figure-1 below depicts a scenario where a tenant's multicast VPN
   spans across both EVPN and MVPN PEs; where all EVPN PEs have
   multicast IRB capability.  An EVPN PE (with multicast IRB capability)
   can be modeled as an MVPN PE where the virtual IRB interface of an
   EVPN PE (virtual interface between a BT and IP-VRF) can be considered
   a routed interface for the MVPN PE.


















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                        EVPN PE1
                     +------------+
           Src1 +----|(MAC-VRF1)  |                   MVPN PE3
          Rcvr1 +----|      \     |    +---------+   +--------+
                     |    (IP-VRF)|----|         |---|(IP-VRF)|--- Rcvr5
                     |      /     |    |         |   +--------+
           Rcvr2 +---|(MAC-VRF2)  |    |         |
                     +------------+    |         |
                                       |  MPLS/  |
                        EVPN PE2       |  IP     |
                     +------------+    |         |
           Rcvr3 +---|(MAC-VRF1)  |    |         |    MVPN PE4
                     |       \    |    |         |   +--------+
                     |    (IP-VRF)|----|         |---|(IP-VRF)|--- Rcvr6
                     |       /    |    +---------+   +--------+
           Rcvr4 +---|(MAC-VRF3)  |
                     +------------+

                   Figure 1: & MVPN PEs Seamless Interop

   Figure 2 depicts the modeling of EVPN PEs based on MVPN PEs where an
   EVPN PE can be modeled as a PE that consists of an MVPN PE whose
   routed interfaces (e.g., attachment circuits) are replaced with IRB
   interfaces connecting each IP-VRF of the MVPN PE to a set of BTs.
   Similar to an MVPN PE where an attachment circuit serves as a routed
   multicast interface for an IP-VRF associated with an MVPN instance,
   an IRB interface serves as a routed multicast interface for the IP-
   VRF associated with the MVPN instance.  Since EVPN PEs run MVPN
   protocols (e.g., [RFC6513] and [RFC6514] ), for all practical
   purposes, they look just like MVPN PEs to other PE devices.  Such
   modeling of EVPN PEs transforms the multicast VPN operation of EVPN
   PEs to that of MVPN and thus simplifies the interoperability between
   EVPN and MVPN PEs to that of running a single unified solution based
   on MVPN.

















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                        EVPN PE1
                     +------------+
           Src1 +----|(MAC-VRF1)  |
                     |     \      |
          Rcvr1 +----|  +--------+|    +---------+   +--------+
                     |  |MVPN PE1||----|         |---|MVPN PE3|--- Rcvr5
                     |  +--------+|    |         |   +--------+
                     |      /     |    |         |
           Rcvr2 +---|(MAC-VRF2)  |    |         |
                     +------------+    |         |
                                       |  MPLS/  |
                        EVPN PE2       |  IP     |
                     +------------+    |         |
           Rcvr3 +---|(MAC-VRF1)  |    |         |
                     |       \    |    |         |
                     |  +--------+|    |         |   +--------+
                     |  |MVPN PE2||----|         |---|MVPN PE4|--- Rcvr6
                     |  +--------+|    |         |   +--------+
                     |       /    |    +---------+
           Rcvr4 +---|(MAC-VRF3)  |
                     +------------+

                       Figure 2: EVPN PEs as MVPN PEs

   Although modeling an EVPN PE as a MVPN PE, conceptually simplifies
   the operation to that of a solution based on MVPN, the following
   operational aspects of EVPN need to be factored in when considering
   seamless integration between EVPN and MVPN PEs.

   *  Unicast route advertisements for IP multicast source

   *  Multi-homing of IP multicast sources and receivers

   *  Mobility for Tenant's sources and receivers

5.3.  Unicast Route Advertisements for IP multicast Source

   When an IP multicast source is attached to an EVPN PE, the unicast
   route for that IP multicast source needs to be advertised.  When the
   the source is attached to a Single-Active multi-homed Ethernet
   Segment (ES), then the EVPN DF PE is the PE that advertises a unicast
   route corresponding to the source IP address with VRF Route Import
   extended community which in turn is used as the Route Target for Join
   (S,G) messages sent toward the source PE by the remote PEs.  The EVPN
   PE advertises this unicast route using EVPN route type 2 and IPVPN
   unicast route along with VRF Route Import extended community.  EVPN
   route type 2 is advertised with the Route Targets corresponding to
   both IP-VRF and MAC-VRF/BT; whereas, the IPVPN unicast route is



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   advertised with RT corresponding to the IP-VRF.  When unicast routes
   are advertised by MVPN PEs, they are advertised using IPVPN unicast
   route along with VRF Route Import extended community per [RFC6514].

   When the source is attached to an All-Active multi-homed ES, then the
   PE that learns the source advertises the unicast route for that
   source using EVPN route type 2 and IPVPN unicast route along with VRF
   Route Import extended community.  EVPN route type 2 is advertised
   with the Route Targets corresponding to both IP-VRF and MAC-VRF/BT;
   whereas, the IPVPN unicast route is advertised with RT corresponding
   to the IP-VRF.  When the other multi-homing EVPN PEs for that ES
   receive this unicast EVPN route, they import the route and check to
   see if they have learned the route locally for that ES, if they have,
   then they do nothing.  But if they have not, then they add the IP and
   MAC addresses to their IP-VRF and MAC-VRF/BT tables respectively with
   the local interface corresponding to that ES as the corresponding
   route adjacency.  Furthermore, these PEs advertise an IPVPN unicast
   route along with VRF Route Import extended community and Route Target
   corresponding to IP-VRF to other remote PEs for that MVPN.
   Therefore, the remote PEs learn the unicast route corresponding to
   the source from all multi-homing PEs associated with that All-Active
   ES even though one of the multi-homing PEs may only have directly
   learned the IP address of the source.

   EVPN PEs advertise unicast routes as host routes using EVPN route
   type 2 for sources that are directly attached to a tenant BD that has
   been extended in the EVPN fabric.  EVPN PE may summarize sources (IP
   networks) behind a router that is attached to itself or sources that
   are connected to a BD, which is not extended across EVPN fabric and
   advertises those routes with EVPN route type 5.  EVPN host routes are
   also advertised as IPVPN host routes to MVPN PEs only in case of
   seamless interop mode.

   Section 8 extends seamless interop procedures to EVPN only fabrics as
   an IRB solution for multicast.  L3VPN provisioning is not needed
   among EVPN PEs.  EVPN PEs only need to advertise unicast routes using
   EVPN route-type 2 or route-type 5 with VRF Route Import extended
   community and don't need to advertise IPVPN routes within EVPN only
   fabric.

   Section 9 discusses DCI use cases, where EVPN and MVPN networks are
   connected using a gateway model.  In the gateway model, EVPN PE
   advertises unicast routes as IPVPN routes along with VRI extended
   community for all multicast sources are attached behind EVPN PEs.
   All IPVPN routes SHOULD be summarized while adverting to MVPN PEs.






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5.4.  Multi-homing of IP Multicast Source and Receivers

   EVPN [RFC7432] has extensive multi-homing capabilities that allow
   Tenant Systems (TSes) to be multi-homed to two or more EVPN PEs in
   Single-Active or All-Active mode.  In Single-Active mode, only one of
   the multi-homing EVPN PEs can receive/transmit traffic for a given
   subnet (a given BD) for that multi-homed Ethernet Segment (ES).  In
   All-Active mode, any of the multi-homing EVPN PEs can receive/
   transmit unicast traffic but only one of them (the DF PE) can send
   BUM traffic to the multi-homed ES for a given subnet.

   The multi-homing mode (Single-Active versus All-Active) of a TS
   source can impact the MVPN procedures as described below.

5.4.1.  Single-Active Multi-Homing

   When a TS source resides on an ES that is multi-homed to two or more
   EVPN PEs operating in Single-Active mode, only one of the EVPN PEs
   can be active for the source subnet on that ES.  Therefore, only one
   of the multi-homing PE learns the unicast route of the TS source and
   advertises that using EVPN and IPVPN to other PEs as described
   previously.

   A downstream PE that receives a Join/Prune message from a TS host/
   router, selects an Upstream Multicast Hop (UMH) which is the upstream
   PE that receives the IP multicast flow in the case of Singe-Active
   multi-homing.  An IP multicast flow belongs to either a source-
   specific tree (S,G) or to a shared tree (*,G).  We use the notation
   (X,G) to refer to either (S,G) or (*,G); where X refers to S in case
   of (S,G) and X refers to the Rendezvous Point (RP) for G in the case
   of (*,G).  Since the active PE (which is also the UMH PE) has been
   advertised unicast route for X along with the VRF Route Import EC,
   the downstream PEs select the UMH without any ambiguity based on MVPN
   procedures described in section 5.1 of [RFC6513].

   The multi-homing PE that receives the IP multicast flow on its local
   AC performs the following tasks:

   - L2 switches the multicast traffic in its BT associated with the
   local AC over which it received the flow if there are any interested
   receivers for that subnet.

   - L3 routes the multicast traffic to other BTs for other subnets if
   there are any interested receivers for those subnets.

   *  L3 routes the multicast traffic to other PEs per MVPN procedures.





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   The multicast traffic can be sent on Inclusive, Selective, or
   Aggregate-Selective tree.  Regardless of what type of tree is used,
   only a single copy of the multicast traffic is received by the
   downstream PEs and the multicast traffic is forwarded optimally from
   the upstream PE to the downstream PEs.

5.4.2.  All-Active Multi-Homing

   When a TS source resides on an ES that is multi-homed to two or more
   EVPN PEs operating in All-Active mode, then any of the multi-homing
   PEs can learn the TS source's unicast route; however, PE may not be
   the same PE that receives the IP multicast flow.  Therefore, the
   procedures for Single-Active Multi-homing need to be augmented for
   All-Active scenario as below.

   The multi-homing EVPN PE that receives the IP multicast flow on its
   local AC needs to do the following tasks in addition to the ones
   listed in the previous section for Single-Active multi-homing: L2
   switch the multicast traffic to other multi-homing EVPN PEs for that
   ES via a multicast tunnel which is called intra-ES subnet tunnel.
   There will be a dedicated tunnel for this purpose which is different
   from inter-subnet overlay tree/tunnel setup by MVPN procedures.

   When the multi-homing EVPN PEs receive the IP multicast flow via this
   tunnel, they treat it as if they receive the flow via their local ACs
   and thus perform the tasks mentioned in the previous section for
   Single-Active multi-homing.  The tunnel type for this intra-ES subnet
   tunnel can be any of the supported tunnel types such as ingress-
   replication, P2MP tunnel, BIER, and Assisted Replication; however,
   given that the vast majority of multi-homing ESes are just dual-
   homing, a simple ingress replication tunnel can serve well.  For a
   given ES, since multicast traffic that is locally received by one
   multi-homing PE is sent to other multi-homing PEs via this intra-ES
   subnet tunnel, there is no need for sending the multicast traffic via
   MVPN tunnel to these multi-homing PEs - i.e., MVPN multicast tunnels
   are used only for remote EVPN and MVPN PEs.  Multicast traffic sent
   over this intra-ES subnet tunnel to other multi-homing PEs for a
   given ES can be either fixed or on a demand basis.

   By feeding IP multicast flow received on one of the EVPN multi-homing
   PEs to the interested EVPN PEs in the same multi-homing group, we
   have essentially enabled all the EVPN PEs in the multi-homing group
   to serve as UMH for that IP multicast flow.  Each of these UMH PEs
   advertises unicast route for X in (X,G) along with the VRF Route
   Import EC to all PEs for that MVPN instance.  The downstream PEs
   build a candidate UMH set based on procedures described in the
   section 5.1 of [RFC6513] and pick a UMH from the set.  It should be
   noted that both the default UMH selection procedure based on the



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   highest UMH PE IP address and the UMH selection algorithm based on a
   hash function specified in section 5.1.3 of [RFC6513] (which is also
   a MUST implement algorithm) result in the same UMH PE be selected by
   all downstream PEs running the same algorithm.  However, in order to
   allow a form of "equal cost load balancing", the hash algorithm is
   recommended to be used among all EVPN and MVPN PEs.  This hash
   algorithm distributes UMH selection for different IP multicast flows
   among the multi-homing PEs for a given ES.

   Since all downstream PEs (EVPN and MVPN) use the same hash-based
   algorithm for UMH determination, they all choose the same upstream PE
   as their UMH for a given (X,G) flow and thus they all send their
   (X,G) join message via BGP to the same upstream PE.  This results in
   one of the multi-homing PEs to receive the join message and thus send
   the IP multicast flow for (X,G) over its associated overlay tree even
   though all of the multi-homing PEs in the All-Active redundancy group
   have received the IP multicast flow (one of them directly via its
   local AC and the rest indirectly via the associated intra-ES subnet
   tunnel).  Therefore, only a single copy of the routed IP multicast
   flow is sent over the network regardless of overlay tree type
   supported by the PEs - i.e., the overlay tree can be of type
   selective or aggregate selective or inclusive tree.  This gives the
   network operator the maximum flexibility for choosing any overlay
   tree type that is suitable for its network operation and still be
   able to deliver only a single copy of the IP multicast flows to the
   egress PEs.  In other words, an egress PE only receives a single copy
   of the IP multicast flow over the network, because it either receives
   it via the EVPN intra-ES subnet tunnel or MVPN inter-subnet tunnel.
   Furthermore, if it receives it via MVPN inter-subnet tunnel, then
   only one of the multi-homing PEs associated with the source ES, sends
   the IP multicast traffic.

   Since the network of interest for seamless interoperability between
   EVPN and MVPN PEs is MPLS, the EVPN handling of BUM traffic for MPLS
   network needs to be considered.  EVPN [RFC7432] uses ESI MPLS label
   for split-horizon filtering of Broadcast/Unknown unicast/multicast
   (BUM) traffic from an All-Active multi-homing Ethernet Segment to
   ensure that BUM traffic doesn't get looped back to the same Ethernet
   Segment that it came from.  This split-horizon filtering mechanism
   applies as-is for multicast IRB scenarios because of using the intra-
   ES tunnel among multi-homing PEs.  Since the multicast traffic
   received from a TS source on an All-Active ES by a multi-homing PE is
   bridged to all other multi-homing PEs in that group, the standard
   EVPN split-horizon filtering described in [RFC7432] applies as-is.







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5.5.  Mobility for Tenant's Sources and Receivers

   When a tenant system (TS), source or receiver, is multi-homed behind
   a group of multi-homing EVPN PEs, then TS mobility SHALL be supported
   among EVPN PEs.  Furthermore, such TS mobility SHALL only cause an
   temporary disruption to the related multicast service among EVPN and
   MVPN PEs.  If a source is moved from one EVPN PE to another PE, then
   the EVPN mobility procedure SHALL discover this move and a new
   unicast route advertisement (using both EVPN and IPVPN routes) is
   made by the EVPN PE where the source has moved to per section 5.3
   above and unicast route withdrawal (for both EVPN and IPVPN routes)
   is performed by the EVPN PE where the source has moved from.

   The move of a source results in disruption of the IP multicast flow
   for the corresponding (S,G) flow till the new unicast route
   associated with the source is advertised by the new PE along with the
   VRF Route Import EC, the join messages sent by the egress PEs are
   received by the new PE, the multicast state for that flow is
   installed in the new PE and a new overlay tree is built for that
   source from the new PE to the egress PEs that are interested in
   receiving that IP multicast flow.

   The move of a receiver results in disruption of the IP multicast flow
   to that receiver only till the new PE for that receiver discovers the
   source and joins the overlay tree for that flow.

6.  Control Plane Operation

   In seamless interop between EVPN and MVPN PEs, the control plane
   needs to setup the following three types of multicast tunnels.  The
   first two are among EVPN PEs and are associated with the attached BD,
   but the third one is among EVPN and MVPN PEs and is associated with
   tenant-VRF

   1) Intra-ES subnet tunnel

   2) Intra-subnet BUM tunnel

   3) Inter-subnet IP multicast tunnel

   While advertising IMET routes, all seamless interop capable PEs
   should attach EVPN Multicast Flags Extended Community with "EVPN/MVPN
   Seamless Interop Supported" flag set.








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6.1.  Intra-ES Subnet Tunnel

   As described in section 5.4.2, when a multicast source is sitting
   behind an All-Active ES, then an intra-subnet multicast tunnel is
   needed among the multi-homing EVPN PEs for that ES to carry multicast
   flow received by one of the multi-homing PEs to the other PEs in that
   ES.  We refer to this multicast tunnel as an Intra-ES subnet tunnel.
   The vast majority of All-Active multi-homing for TOR devices in DC
   networks are just dual-homing which means the multicast flow received
   by one of the dual-homing PE only needs to be sent to the other dual-
   homing PE.  Therefore, a simple ingress replication tunnel is all
   that is needed.  In case of multi-homing to three or more EVPN PEs,
   then other tunnel types such as P2MP, MP2MP, BIER, and Assisted
   Replication can be considered.  It should be noted that this intra-ES
   subnet tunnel is only needed for All-Active multi-homing and it is
   not required for Single-Active multi-homing.

   The EVPN PEs belonging to a given All-Active ES discover each other
   using EVPN Ethernet Segment route per procedures described in
   [RFC7432].  These EVPN PEs perform DF election per [RFC7432],
   [RFC8584], or other DF election algorithms to decide who is a DF for
   a given BD.  If the BD belongs to a tenant that has IRB IP multicast
   enabled for it, then for fixed-mode, each PE sets up an intra-ES
   subnet tunnel to forward IP multicast traffic received locally on
   that BD to other multi-homing PE(s) for that ES.  Therefore, IP
   multicast traffic received via a local attachment circuit is sent on
   this tunnel and on the associated IRB interface for that BT and other
   local attachment circuits if there are interested receivers for them.
   The other multi-homing EVPN PEs treat this intra-ES subnet tunnel
   just like their local ACs - i.e., the multicast traffic received over
   this tunnel is treated as if it is received via its local AC.  Thus,
   the multi-homing PEs cannot receive the same IP multicast flow from
   an MVPN tunnel (e.g., over an IRB interface for that BD) because
   between a source behind a local AC versus a source behind a remote
   PE, the PE always chooses its local AC.

 When all multihomed PE support  [RFC9251],
 traffic may be forwarded on demand basis.  Based on IGMP
 synchronization procedure specified in
 [I-D.ietf-bess-evpn-igmp-mld-proxy], the join state may be synchronized
 between all multihomed PEs.  Multihomed PE which receives the
 multicast traffic from its attached circuit, may send the traffic
 towards intra-ES subnet tunnel, only if it has received an IGMP sync
 message from one of the multihomed PEs.  Such extension is outside
 the scope of this document and may be covered in a separate document
 if required.





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   In case of a TS, receiver sits behind an All-Active Multihoming ES
   and a TS source sits behind an inter-subnet tunnel (with respect to
   the multihomed PE), it is possible that more than one multihomed PEs
   sends MVPN join toward remote PE based on incoming join on their
   local interfaces.  When the traffic is received on the inter-subnet
   tunnel, it is sent towards locally attached receivers.  Only DF sends
   traffic towards multihomed ethernet segment.  Traffic received on the
   inter-subnet tunnel, should not be sent towards Intra-ES subnet
   tunnel.

   When ingress replication is used for intra-ES subnet tunnel, every PE
   in the All-Active multi-homing ES has all the information to setup
   these tunnels - i.e., a) each PE knows what are the other multi-
   homing PEs for that ES via EVPN Ethernet Segment route and can use
   this information to setup intra-ES subnet tunnel among themselves.

6.2.  Intra-Subnet BUM Tunnel

   As the name implies, this tunnel is setup to carry BUM traffic for a
   given subnet/BD among EVPN PEs.  In [RFC7432], this overlay tunnel is
   used for transmission of all BUM traffic including tenant IP
   multicast traffic.

   When an EVPN IRB PE operates in seamless interop mode, this tunnel is
   used for all broadcast, unknown-unicast, non-IP multicast traffic,
   and link-local IP multicast traffic - i.e., it is used for all BUM
   traffic except for tenant IP multicast traffic.  This tunnel is setup
   using the IMET route for a given EVI/BD.  The composition and
   advertisement of IMET routes are exactly per [RFC7432].  It should be
   noted that when an EVPN All-Active multi-homing PE uses both this
   tunnel as well as intra-ES subnet tunnel, there SHALL be no
   duplication of multicast traffic over the network because they carry
   different types of multicast traffic - i.e., intra-ES subnet tunnel
   among multi-homing PEs carries only tenant IP multicast traffic;
   whereas, intra-subnet BUM tunnel carries link-local IP multicast
   traffic and BUM traffic (w/ non-IP multicast).

6.3.  Inter-Subnet IP Multicast Tunnel

   As its name implies, this tunnel is setup to carry IP-only multicast
   traffic for a given tenant across all its subnets (BDs) among EVPN
   and MVPN PEs.

   The following NLRIs from [RFC6514] is used for setting up this inter-
   subnet tunnel in the network.

       Intra-AS I-PMSI A-D route is used for the setup of default




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       underlay tunnel (also called inclusive tunnel) for a tenant IP-
       VRF.  The tunnel attributes are indicated using the PMSI
       attribute with this route.

       S-PMSI A-D route is used for the setup of Customer flow specific
       underlay tunnels.  This enables selective delivery of data to PEs
       having active receivers and optimizing fabric bandwidth
       utilization.  The tunnel attributes are indicated using PMSI
       attribute with this route.

   Each EVPN PE supporting a specific MVPN instance discovers the set of
   other PEs in its AS that are attached to sites of that MVPN using
   Intra-AS I-PMSI A-D route (route type 1) per [RFC6514].  It can also
   discover the set of other ASes that have PEs attached to sites of
   that MVPN using Inter-AS I-PMSI A-D route (route type 2) per
   [RFC6514].  After the discovery of PEs that are attached to sites of
   the MVPN, an inclusive overlay tree (I-PMSI) can be setup for
   carrying tenant multicast flows for that MVPN; however, this is not a
   requirement per [RFC6514] and it is possible to adopt a policy in
   which all tenant flows are carried on S-PMSIs.

   An EVPN-IRB PE sends a tenant IP multicast flow to other EVPN and
   MVPN PEs over this inter-subnet tunnel that is instantiated using
   MVPN I-PMSI or S-PMSI.  This tunnel can be considered as being
   originated and terminated from/to among IP-VRFs of EVPN/MVPN PEs;
   whereas, intra-subnet tunnel originated/terminated among MAC-VRFs of
   EVPN PEs.

6.4.  IGMP Hosts as TSes

   IGMP messages are terminated by the EVPN-IRB PE and tenant (*,G) or
   (S,G) join messages are sent via MVPN Shared Tree Join route (route
   type 6) or Source Tree Join route (route type 7) respectively of
   MCAST-VPN NLRI per [RFC6514].

   Here, IGMP states are terminated at IRB interfaces, and local
   interest are expressed in the context of IP-VRF to remote PEs.

   In the case of a network with only IGMP hosts, the preferred mode of
   operation is that of Shortest Path Tree(SPT) per section 14 of
   [RFC6514].  This mode is only supported for PIM-SM and avoids the RP
   configuration overhead.  Such mode is chosen by provisioning/
   configuration.








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6.5.  PIM Routers as TSes

   Just like an MVPN PE, an EVPN PE runs a separate tenant multicast
   routing instance (VPN-specific) per MVPN instance and the following
   tenant multicast routing instances are supported:

      -  PIM Sparse Mode (PIM-SM) with the ASM service model

      -  PIM Sparse Mode with the SSM service model

      -  PIM Bidirectional Mode (BIDIR-PIM), which uses bidirectional
         tenant-trees to support the ASM service model

   A given tenant's PIM join messages for (*,G) or (S, G) are processed
   by the corresponding tenant multicast routing protocol and they are
   advertised over MPLS/IP network using the Shared Tree Join route
   (route type 6) and Source Tree Join route (route type 7) respectively
   of MCAST-VPN NLRI per [RFC6514].

7.  Data Plane Operation

   When an EVPN-IRB PE receives an IGMP/MLD join message over one of its
   Attachment Circuits (ACs), it adds that AC to its Layer-2 (L2) OIF
   list.  This L2 OIF list is associated with the MAC-VRF/BT
   corresponding to the subnet of the tenant device that sent the IGMP/
   MLD join.  Therefore, tenant (S,G) or (*,G) forwarding entries are
   created/updated for the corresponding MAC-VRF/BT based on these
   source and group IP addresses.  Furthermore, the IGMP/MLD join
   message is propagated over the corresponding IRB interface and it is
   processed by the tenant multicast routing instance which creates the
   corresponding tenant (S,G) or (*,G) Layer-3 (L3) forwarding entries.
   It adds this IRB interface to the L3 OIF list.  An IRB is removed as
   a L3 OIF when all L2 tenant (S,G) or (*,G) forwarding states is
   removed for the MAC-VRF/BT associated with that IRB.  Furthermore,
   tenant (S,G) or (*,G) L3 forwarding state is removed when all of its
   L3 OIFs are removed - i.e., all the IRB and L3 interfaces associated
   with that tenant (S,G) or (*,G) are removed.

   When an EVPN PE receives IP multicast traffic from one of its AC, if
   it has any attached receivers for that subnet, it performs L2
   switching of the intra-subnet traffic within the BT attached to that
   AC.  If the multicast flow is received over an AC that belongs to an
   All-Active ES, then the multicast flow is also sent over the intra-
   ES subnet tunnel among multi-homing PEs.  The EVPN PE then sends the
   multicast traffic over the corresponding IRB interface.  The
   multicast traffic then gets routed in the corresponding IP-VRF and it
   gets forwarded to interfaces in the L3 OIF list which can include
   other IRB interfaces, other L3 interfaces directly connected to TSes,



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   and the MVPN Inter-Subnet tunnel which is instantiated by an I-PMSI
   or S-PMSI tunnel.  When the multicast packet is routed within the IP-
   VRF of the EVPN PE, its Ethernet header is stripped and its TTL gets
   decremented as the result of this IP routing.  Remote multicast
   traffic that is received from MVPN Inter-Subnet tunnel gets routed
   towards all L3 OIFs.  When the multicast traffic is received on an
   IRB interface by the BT corresponding to that interface, it gets L2
   switched and sent over ACs that belong to the L2 OIF list.

7.1.  Intra-Subnet L2 Switching

   Rcvr1 in Figure 1 is connected to PE1 in MAC-VRF1 (same as Src1) and
   sends IGMP join for (C-S, C-G), IGMP snooping will record this state
   in the local bridging entry.  A routing entry will be formed as well
   which will point to MAC-VRF1 as RPF for Src1.  We assume that Src1 is
   known via ARP or similar procedures.  Rcvr1 will get a locally
   bridged copy of multicast traffic from Src1.  Rcvr3 is also connected
   in MAC-VRF1 but to PE2 and hence would send IGMP join which will be
   recorded at PE2.  PE2 will also form routing entry and RPF will be
   assumed as Tenant Tunnel "Tenant1" formed beforehand using MVPN
   procedures.  Also, this would cause the multicast control plane to
   initiate a BGP MCAST-VPN type 7 route which would include VRI for PE1
   and hence be accepted on PE1.  PE1 will include Tenant1 tunnel as
   Outgoing Interface (OIF) in the routing entry.  Now, since it has
   knowledge of remote receivers via MVPN control plane it will
   encapsulate original multicast traffic in Tenant1 tunnel towards
   core.

7.2.  Inter-Subnet L3 Routing

   Rcvr2 in Figure 1 is connected to PE1 in MAC-VRF2 and hence PE1 will
   record its membership in MAC-VRF2.  Since MAC-VRF2 is enabled with
   IRB, gets added as another OIF to the routing entry formed for (C-S,
   C-G).  Rcvr2 and Rcvr4 are also in different MAC-VRFs than multicast
   speaker Src1 and hence need Inter-subnet forwarding.  PE2 now adds
   another OIF 'MAC-VRF2' to its existing routing entry.  But there is
   no change in control plane states since it is already sent MVPN route
   and no further signaling is required.  Traffic received by the tenant
   tunnel interface gets routed towards both MAC-VRF1 and MAC-VRF3.  PE3
   forms routing entry very similar to PE2.  It is to be noted that PE3
   does not have MAC-VRF1 configured locally but still can receive the
   multicast data traffic over the Tenant1 tunnel formed due to MVPN
   procedures and routes traffic towards its L3 OIFs for that (C-S,C-G).








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8.  DCs with only EVPN PEs

   As mentioned earlier, the proposed solution can be used as a routed
   multicast solution in data center networks with only EVPN PEs (e.g.,
   routed multicast VPN only among EVPN PEs).

   As per section 5.2, EVPN PE is modeled as a PE that consists of a
   MVPN PE whose routed interfaces (e.g., attachment circuits) are
   replaced with IRB interfaces connecting each IP-VRF of the MVPN PE to
   a set of BTs.  Due to this, the IP multicast traffic that needs to be
   forwarded from the source PE to remote PEs is routed to remote PEs
   regardless of whether the traffic is intra-subnet or inter-subnet.
   As a result, the TTL value for intra-subnet traffic that spans across
   two or more PEs get decremented.

   However, if there are applications that require intra-subnet
   multicast traffic to be L2 forwarded, Appendix A discusses some
   options to support applications having TTL value 1.  The procedure
   discussed in Appendix A may be used to support applications that
   require intra-subnet multicast traffic to be L2 forwarded.

8.1.  Setup of overlay multicast delivery

   It must be emphasized that this solution poses no restriction on the
   setup of the tenant BDs and that neither the source PE, nor the
   receiver PEs do not need to know/learn about the BD configuration on
   other PEs in the tenant IP-VRF ( Since EVPN PE is modeled as MVPN PE,
   source and receivers are announced to remote PE in the context of
   tenant IP-VRF(MVPN) as opposed to BD context).  The Reverse Path
   Forwarder (RPF) is selected per the tenant multicast source and the
   IP-VRF in compliance with the procedures in [RFC6514], using the
   incoming EVPN route type 2 or 5 NLRI per [RFC7432].

   The VRF Route Import (VRI) extended community that is carried with
   the IPVPN routes in [RFC6514] MUST be carried with the EVPN unicast
   routes when these routes are used.  The construction and processing
   of the VRI are consistent with [RFC6514].  The VRI MUST uniquely
   identify the PE which is advertising a multicast source and the IP-
   VRF it resides in.

   VRI is constructed as following:
       *  The 4-octet Global Administrator field MUST be set to an IP
          address of the PE.  This address SHOULD be common for all the
          IP-VRFs on the PE (e.g., this address may be the PE's loopback
          address or VTEP address).






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       *  The 2-octet Local Administrator field associated with a given
          IP-VRF contains a number that uniquely identifies that IP-VRF
          within the PE that contains the IP-VRF.

   EVPN PE MUST have Route Target Extended Community to import/export
   MVPN routes.  In a data center environment, it is desirable to have
   this RT is configured using an auto-generated method rather than a
   static configuration.

   The following is one recommended model to auto-generate MVPN RT:
      *  The Global Administrator field of the MVPN RT MAY be set to BGP
         AS Number.

      *  The Local Administrator field of the MVPN RT MAY be set to the
         VNI associated with the tenant IP-VRF.

   Every PE that detects a local receiver via a local IGMP join or a
   local PIM join for a specific source (overlay SSM mode) MUST
   terminate the IGMP/PIM signaling at the IP-VRF and generate a (C-S,C-
   G) via the BGP MCAST-VPN route type 7 per [RFC6514] if and only if
   the RPF for the source points to the fabric.  If the RPF points to a
   local multicast source on the same MAC-VRF or a different MAC-VRF on
   that PE, the MCAST-VPN MUST NOT be advertised and data traffic will
   be locally routed/bridged to the receiver.

   The VRI received with EVPN route type 2 or 5 NLRI from source PE will
   be appended as an export route-target extended community.  The PE
   which has advertised the unicast route with VRI, will import the
   incoming MCAST-VPN NLRI in the IP-VRF with the same import route-
   target extended-community and other PEs SHOULD ignore it.  Following
   such procedure the source PE learns about the existence of at least
   one remote receiver in the tenant overlay and programs data plane
   accordingly, so that a single copy of multicast data is forwarded
   into the fabric using tenant VRF tunnel(i.e. inter-subnet tunnel/mvpn
   tunnel).

   If the multicast source is unknown (overlay ASM mode), the MCAST-VPN
   route type 6 (C-*,C-G) join SHOULD be targeted towards the designated
   overlay Rendezvous Point (RP) by appending the received RP VRI as an
   export route-target extended community.  Every PE which detects a a
   local source, registers with its RP PE.  That is how the RP learns
   about the tenant source(s) and group(s) within the MVPN.  Once the
   overlay RP PE receives either the first remote (C-RP,C-G) join or a
   local IGMP/PIM join, it will trigger an MCAST-VPN route type 7 (C-
   S,C-G) towards the actual source PE for which it has received PIM
   register messages in full compliance with regular PIM procedures.
   This involves the source PE to advertise the MCAST-VPN Source Active
   A-D route (MCAST-VPN route-type 5) towards all PEs.  The Source



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   Active A-D route is used to inform all PEs in a given MVPN about the
   active multicast source for switching from RPT to SPT when MVPNs use
   tenant RP-shared trees (i.e., rooted at tenant's RP) per section 13
   of [RFC6514].

8.2.  Handling of different encapsulations

   Just as in [RFC6514] the MVPN I-PMSI and S-PMSI A-D routes are used
   to form the overlay multicast tunnels and signal the tunnel type
   using the P-Multicast Service Interface Tunnel (PMSI Tunnel)
   attribute.

8.2.1.  MPLS Encapsulation

   The [RFC6514] assumes MPLS/IP core and there is no modification to
   the signaling procedures and encoding for PMSI tunnel formation
   therein.  Also, there is no need for a gateway to inter-operate with
   non-EVPN PEs supporting [RFC6514] based MVPN over IP/MPLS.

8.2.2.  VxLAN Encapsulation

   In order to signal VXLAN, the corresponding BGP encapsulation
   extended community [RFC9012] SHOULD be appended to the MVPN I-PMSI
   and S-PMSI A-D routes.  The MPLS label in the PMSI Tunnel Attribute
   MUST be the Virtual Network Identifier (VNI) associated with the
   customer MVPN.  The supported PMSI tunnel types with VXLAN
   encapsulation are: PIM-SSM Tree, PIM-SM Tree, BIDIR-PIM Tree, Ingress
   Replication [RFC6514].  Further details are in [RFC8365].

   In this case, a gateway is needed for inter-operation between the
   EVPN MVPN-capable PEs and non-EVPN MVPN PEs.  The gateway should re-
   originate the control plane signaling with the relevant tunnel
   encapsulation on either side.  In the data plane, the gateway
   terminates the tunnels formed on either side and performs the
   relevant stitching/re- encapsulation on data packets.

8.2.3.  Other Encapsulation

   In order to signal a different tunneling encapsulation such as NVGRE,
   GPE, or GENEVE the corresponding BGP encapsulation extended community
   [RFC9012] SHOULD be appended to the MVPN I-PMSI and S-PMSI A-D
   routes.  If the Tunnel Type field in the encapsulation extended-
   community is set to a type that requires Virtual Network Identifier
   (VNI), e.g., VXLAN-GPE or NVGRE [RFC9012], then the MPLS label in the
   PMSI Tunnel Attribute MUST be the VNI associated with the customer
   MVPN.  Same as in the VXLAN case, a gateway is needed for inter-
   operation between the EVPN MVPN-capable PEs and non-EVPN MVPN PEs.




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9.  DCI with MPLS in WAN and VxLAN in DCs

   This section describes the inter-operation between MVPN PEs in WAN
   using MPLS encapsulation with EVPN PEs in a DC network using VxLAN
   encapsulation.  Since the tunnel encapsulation between these networks
   are different, we must have at least one gateway in between.
   Usually, two or more are required for redundancy and load balancing
   purposes.  In such scenarios, a DC network can be represented as a
   customer network that is multi-homed to two or more MVPN PEs via L3
   interfaces and thus standard MVPN multi-homing procedures are
   applicable here.  It should be noted that an MVPN overlay tunnel over
   the DC network is terminated on the IP-VRF of the gateway and not the
   MAC-VRF/BTs.  Therefore, the considerations for loop prevention and
   split-horizon filtering described in [RFC9014] are not applicable
   here.  .

9.1.  Control plane inter-connect

   The gateway(s) MUST be setup with the inclusive set of all the IP-
   VRFs that span across the two domains.  On each gateway, there will
   be at least two BGP sessions: one towards the DC side and the other
   towards the WAN side.  Usually for redundancy purposes, more sessions
   are setup on each side.  The unicast route propagation follows the
   exact same procedures in [RFC9014].  Hence, a multicast host located
   in either domain, is advertised with the gateway IP address as the
   next-hop to the other domain.  As a result, PEs view the hosts in the
   other domain as directly attached to the gateway and all inter-domain
   multicast signaling is directed towards the gateway(s).  Received
   MVPN routes type 1-7 from either side of the gateway(s), MUST NOT be
   reflected back to the same side but processed locally and re-
   advertised (if needed) to the other side:

   *  Intra-AS/Inter-AS I-PMSI A-D Route: these are distributed within
      each domain to form the overlay tunnels which terminate at
      gateway(s).  They are not passed to the other side of the
      gateway(s).

   *  C-Multicast Route: joins are imported into the corresponding IP-
      VRF on each gateway and advertised as a new route to the other
      side with the following modifications (the rest of NLRI fields and
      path attributes remain on-touched):

      -  Route-Distinguisher is set to that of the IP-VRF

      -  Route-target is set to the exported route-target list on IP-VRF

      -  The PMSI tunnel attribute and BGP Encapsulation extended
         community will be modified according to section 8



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      -  Next-hop will be set to the IP address which represents the
         gateway on either domain

   *  Source Active A-D Route: same as joins

   *  S-PMSI A-D Route: these are passed to the other side to form
      selective PMSI tunnels per every (C-S,C-G) from the gateway to the
      PEs in the other domain provided it contains receivers for the
      given (C-S, C-G).  Similar modifications made to joins are made to
      the newly originated S-PMSI.

   In addition, the Originating Router's IP address is set to GW's IP
   address.  Multicast signaling from/to hosts on local ACs on the
   gateway(s) are generated and propagated in both domains (if needed)
   per the procedures in section 6 in this document and in [RFC6514]
   with no change.  It must be noted that for a locally attached source,
   the gateway will program an OIF per every domain from which it
   receives a remote join in its forwarding plane and different
   encapsulation will be used on the data packets.

9.2.  Data plane inter-connect

   Traffic forwarding procedures on gateways are the same as those
   described for PEs in section 5 except that, unlike a non-border leaf
   PE, the gateway will not only route the incoming traffic from one
   side to its local receivers, but will also send it to the remote
   receivers in the other domain after de-capsulation and appending the
   right encapsulation.  The OIF and IIF are programmed in FIB based on
   the received joins from either side and the RPF calculation to the
   source or RP.  The de-capsulation and encapsulation actions are
   programmed based on the received I-PMSI or S-PMSI A-D routes from
   either side.

   The multicast traffic from local sources on each gateway may flow to
   the other gateway with either of the tunnel encapsulation.  But, it
   is recommended to use VxLAN tunnel than MPLS in this case.

10.  Interop with L2 EVPN PEs

   A gateway device is needed to do interop between EVPN PEs that
   support seamless interop procedure specified in this document and
   L2EVPN PEs.  A tenant domain can be provisioned with one or more such
   gateway devices are known as "Seamless interop EVPN Multicast Gateway
   (SEMG)".  PE that is configured as SEMG must be provisioned with all
   BDs that are available in the tenant domain.






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   When advertising the IMET route for a BD, PE configured as SEMG
   advertises EVPN Multicast Flags Extended Community with SEMG flag
   set.  Given a set of eligible PEs, one PE is selected as the SEMG
   designated forwarder (SEMG-DF).  PE should use the procedure
   specified in [RFC8584] for the SEMG DF election.

   There are multiple possibilities that need to be considered here.

   *  L2EVPN PE may or may not have support for [RFC9251]

   *  Seamless interop PE may or may not support [RFC9251]

   *  Network may only have L2EVPN PE and Seamless interop capable PE

   *  Network may have L2EVPN PE, Seamless interop capable PE, and MVPN
      PE.

   Multicast sources and receivers can exist anywhere in the network.
   These usecases are discussed below.

10.1.  Interaction with L2EVPN PE and Seamless interop capable PE

   The following cases are considered in this section.

   *  Case1: [RFC9251] is supported both at seamless interop capable PE
      and L2EVPN PE.

   *  Case2: [RFC9251] is supported only at seamless interop capable PE.

   *  Case3: [RFC9251] is not supported at interop capable PE.

   [RFC9251] support is recommended for seamless interop capable PE.
   SEMG can group L2 EVPN PEs into two separate groups ( one that
   supports the [RFC9251] and another that doesn't) from IMET routes
   that it receives from the remote peers.  The interop procedure for
   handling these two different sets of remote L2 EVPN PEs are captured
   in case 1 and 2.

   Case 1: [RFC9251] is supported both at seamless interop capable PE
   and L2EVPN PE

   This may be the most common usecase.

   SEMG-DF has the following special responsibilities on a BD for which
   it is the DF.






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   *  Process EVPN SMET routes from the remote L2 EVPN PEs that support
      [RFC9251] and creates L2 multicast state.  SMET route in-turn
      triggers the creation of L3 multicast state similar to the IGMP
      join received on the local AC.  SEMG-DF exercises the MVPN
      procedures for the join.

   *  It should not process IGMP control packets from L2EVPN PE that
      supports [RFC9251].

   *  Originate SMET(*,*) route towards L2 EVPN PEs.  This is to receive
      traffic from multicast sources that are connected behind L2 EVPN
      PEs.

   *  When SEMG-DF receives traffic from L2 EVPN PE on the intra-subnet
      tunnel on BD-X, it does the following

      -  Performs FHR functionality

      -  Advertises the host route with L3 label and VRF Route-Import
         corresponds to the tenant domain.

      -  Sends the traffic towards the locally attached receivers.

      -  Sends the traffic towards L2EVPN receiver on BDs other than
         incoming BD(after multicast routing)

      -  Sends the traffic towards remote seamless interop capable PEs,
         where receivers are attached/connected behind that PE.

   *  When SEMG-DF receives traffic from the MVPN tunnel, it does the
      following

      -  Sends the traffic toward the IRB interfaces, where the receiver
         exists

      -  BD corresponding to the IRB interfaces may have local receivers
         or remote receivers behind L2 EVPN PE.  SEMG-DF sends the
         traffic on the intra-subnet tunnel for remote receivers.

   Case 2: [RFC9251] is not supported at L2 EVPN PE

   This case only differs from case 1 in terms of the way it learns
   receivers behind L2 EVPN PEs and how SEMG-DF attracts traffic from
   sources behind L2 EVPN PE.  The rest of the procedures specified
   above is applicable for this case.

   SEMG-DF has the following special responsibilities on a BD for which
   it is the DF



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   *  Process IGMP control packets from remote L2 EVPN PEs that doesn't
      support [RFC9251] and create L2 and L3 state.

   *  When an IGMP query is received on the intra-subnet tunnel on BD-X,
      SEMG-DF needs to send proxy IGMP reports for all groups that it
      has learned from remote L2-EVPN PEs on that BD.

   *  Connecting multicast router behind L2 EVPN PE is not recommended.
      If a multicast router is connected behind L2 EVPN PE, the BD
      corresponds to the VRF tunnel needs to be configured in the L2
      EVPN PE so that the PIM router may get all joins that are received
      in the BD corresponds to the MVPN tunnel interface at SEMG-DF.

   *  SEMG-DF should get all multicast traffic from L2EVPN PEs.  This
      may be achieved by sending an IGMP query or PIM hello on the
      intra- subnet tunnel

   Case 3: [RFC9251] is not supported at seamless interop capable PE

   The procedure for handling this use case is exactly the same as the
   case 2.

   All seamless interop capable PEs other than SEMG should discard SMET
   routes that are coming from L2EVPN PEs and must discard all IGMP
   control packets, if any received on the intra-subnet tunnel.  SEMG
   should discard incoming SMET routes and IGMP joins from L2EVPN PEs,
   if it is not the DF for the incoming BD.

   When [RFC9251] is supported both at seamless interop capable PE and
   L2EVPN PE, selective forwarding is done based on receiver interest at
   the egress-PE, when overlay tunnel type is Ingress-replication or
   selective tunnel.

10.2.  Network having L2EVPN PE, Seamless interop capable PE and MVPN PE

   Since MVPN PE can only interact with Seamless interop capable PEs,
   SEMG-DF acts as FHR and LHR for sources and receivers behind L2 EVPN
   PE.  Only SEMG-DF advertises the IPVPN unicast route along with the
   VRF Route Import extended community for hosts behind L2 EVPN PE.  No
   additional procedures are required when they all co-exist.











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11.  Connecting external Multicast networks or PIM routers.

   External multicast networks or PIM routers can be attached to any
   EVPN MVPN-capable PEs or MVPN PEs.  Multicast network or PIM router
   can also be attached to any IRB enabled interface or set of
   interfaces.  The fabric can be used as a Transit network for
   connecting the external multicast networks.  All PIM signaling is
   terminated at PE's IRB interfaces.

   No additional procedures are required while connecting external
   multicast networks.

12.  TS RP options

   RP can be configured in the EVPN PE itself in the tenant VRF or in
   the external multicast networks connected behind an EVPN PE or in the
   MVPN network.  When RPF is not local to EVPN PE, EVPN PE operates in
   rpt-spt mode as PER procedures specified in section 13 of [RFC6514].

   EVPN fabric without having any external multicast network/attached
   MVPN network doesn't need RP configuration.  A configuration option
   SHALL be provided to the end user to operate the fabric in RP less
   mode.  When an EVPN PE is operating in RP-less mode, EVPN PE MUST
   advertise all attached sources to remote EVPN PEs using the procedure
   specified in [RFC6514].

   In RP less mode, (C-*,C-G) RPF may be set to NULL or may be set to
   wild card interface( Any interface on the tenant VRF).  In RP-less
   mode, traffic is always forwarded based on (C-S,C-G) state.

13.  IANA Considerations

   IANA has allocated the codepoint for Multicast Flags Extended
   Community which is defined in [RFC9251].

   The Multicast Flags Extended Community contains a 16-bit Flags field.
   The bits are numbered 0-15, from high-order to low-order.  IANA has
   allocated the following flags for this document.

     Bit   Name                                 Reference
     ----  --------------                       -------------
     5    SEMG                                  This document
     6    EVPN/MVPN Seamless Interop Supported  This document








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14.  Security Considerations

   All the security considerations in [RFC7432], [RFC6513] and [RFC6514]
   apply directly to this document because this document leverages these
   RFCs control planes and their associated procedures.

15.  Acknowledgements

   The authors would like to thank Niloofar Fazlollahi, Aamod
   Vyavaharkar, Raunak Banthia, and Swadesh Agrawal for their
   discussions and contributions.

16.  References

16.1.  Normative References

   [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>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <https://www.rfc-editor.org/info/rfc6513>.

   [RFC6514]  Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
              Encodings and Procedures for Multicast in MPLS/BGP IP
              VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
              <https://www.rfc-editor.org/info/rfc6514>.

   [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>.

   [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>.

   [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>.





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   [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>.

   [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>.

   [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>.

   [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>.

16.2.  Informative References

Appendix A.  Supporting application with TTL value 1

   It is possible that some deployments may have a host on the tenant
   domain that sends multicast traffic with TTL value 1.  The interested
   receiver for that traffic flow may be attached to different PEs on
   the same subnet.  The procedures specified in Section 5 always routes
   the traffic between PEs for both intra and inter subnet traffic.
   Hence traffic with TTL value 1 is dropped due to the nature of
   routing.

   This section discusses a few possible ways to support traffic having
   TTL value 1 or traffic that requires L2 bridging behavior.  An
   implementation MAY support any of the following models.

A.1.  Policy based model

   Policies may be used to enforce EVPN BUM procedure for traffic flows
   with TTL value 1.  Traffic flow that matches the policy is excluded
   from seamless interop procedure specified in this document, hence TTL
   decrement issue will not apply.








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A.2.  Exercising BUM procedure for VLAN/BD

   Servers/hosts sending the traffic with TTL value 1 may be attached to
   a separate VLAN/BD, where multicast routing is disabled.  When
   multicast routing is disabled, EVPN BUM procedure may be applied to
   all traffic ingressing on that VLAN/BD.  On the Egress PE, the RPF
   for such traffic may be set to BD interface, where the source is
   attached.

A.3.  Intra-subnet bridging

   The procedure specified in the section enables a PE to detect an
   attached subnet source (i.e., source that is directly attached in the
   tenant BD/VLAN).  By applying the following procedure for the
   attached source, Traffic flows having TTL value 1 can be supported.

      -  On the ingress PE, do the bridging on the interface towards the
         core interface

      -  On the egress side, make a decision whether to bridge or route
         at the outgoing interface (OIF) based on whether the source is
         attached to the OIF's BD/VLAN or not.

   Recent ASIC supports single lookup forwarding for bridging and
   routing (L2+L3).  The procedure mentioned here leverages this ASIC
   capability.

                       PE1
                      +------------+
              S11 +---+(BD1)       |  +---------+
                      |  \         |  |         |
                      |(IP-VRF)-(CORE)|         |
                      |  /         |  |         |
              R12 +---+(BD2)       |  |         |
                      +------------+  |         |
                                      |         |
                       PE2            | VXLAN.  |
                      +------------+  |         |
              R21 +---+(BD1)       |  |         |
                      |  \         |  |         |
                      |(IP-VRF)-(CORE)|         |
                      |  /         |  |         |
              R22+----+(BD3)       |  +---------+
                      +------------+

                      Figure 3: Intra-subnet bridging

   Consider the above picture.  In the picture



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        - PE1 and PE2 are seamless interop capable PEs
        - S11 is a multicast host directly attached to PE1 in BD1
        - Source S11 sends traffic to Group G11
        - R21, R22 are IGMP receivers for group G11
        - R21 and R22 are attached to BD1 and BD3 respectively at PE2.

   When source S11 starts sending the traffic, PE1 learns the source and
   announces the source using MVPN procedures to the remote PEs.

   At PE2, IGMP joins from R21, R22 result the creation of (*,G11) entry
   with outgoing OIF as IRB interface of BD1 and BD3.  When PE2 learns
   the source information from PE1, it installs the route (S11, G11) at
   the tenant VRF with RPF as the CORE interface.

   PE2 inherits (*, G11) OIFs to (S11, G11) entry.  While inheriting
   OIF, PE2 checks whether the source is attached to OIF's subnet.  OIF
   matching source subnet is added with a flag indicating bridge only
   interface.  In the case of (S11, G11) entry, BD1 is added as the
   bridge only OIF, while BD3 is added as normal OIF(L3 OIF).  PEs (PE2)
   sends MVPN join (S11, G11) towards PE1, since it has local receivers.

   At Ingress PE(PE1), CORE interface is added to (S11, G11) entry as an
   OIF (outgoing interface) with a flag indicating that bridge only
   interface.  With this procedure, ingress PE(PE1) bridges the traffic
   on the CORE interface.  (PE1 retains the TTL and source-MAC).  The
   traffic is encapsulated with VNI associated with the CORE interface.
   PE1 also routes the traffic for R12 which is attached to BD2 on the
   same device.

   PE2 decapsulates the traffic from PE1 and does an inner lookup on the
   tenant VRF associated with incoming VNI.  Traffic lookup on the
   tenant VRF yields (S11, G11) entry as the matching entry.  Traffic
   gets bridged on BD1 (PE2 retains the TTL and source-MAC) since the
   OIF is marked as a bridge only interface.  Traffic gets routed on
   BD2.

Authors' Addresses

   Ali Sajassi
   Cisco
   170 West Tasman Drive
   San Jose, CA 95134, US
   Email: sajassi@cisco.com








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   Kesavan Thiruvenkatasamy
   Cisco
   170 West Tasman Drive
   San Jose, CA 95134, US
   Email: kethiruv@cisco.com


   Samir Thoria
   Cisco
   170 West Tasman Drive
   San Jose, CA 95134, US
   Email: sthoria@cisco.com


   Ashutosh Gupta
   VMware
   3401 Hillview Ave, Palo Alto, CA 94304
   Email: ashutoshgupta@vmware.com


   Luay Jalil
   Verizon
   Email: luay.jalil@verizon.com




























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