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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7432

Network Working Group                                         A. Sajassi
INTERNET-DRAFT                                                     Cisco
Category: Standards Track
                                                             R. Aggarwal
N. Bitar                                                          Arktan
Verizon
                                                           W. Henderickx
S. Boutros                                                      F. Balus
K. Patel                                                  Alcatel-Lucent
S. Salam
Cisco                                                       Aldrin Isaac
                                                               Bloomberg
J. Drake
R. Shekhar                                                     J. Uttaro
Juniper Networks                                                    AT&T

Expires: January 15, 2014                                  July 15, 2013


                      BGP MPLS Based Ethernet VPN
                        draft-ietf-l2vpn-evpn-04

Status of this Memo

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

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Copyright and License Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors. All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Abstract

   This document describes procedures for BGP MPLS based Ethernet VPNs
   (EVPN).

Table of Contents

   1. Specification of requirements . . . . . . . . . . . . . . . . .  5
   2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4. Contributors  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5. BGP MPLS Based EVPN Overview  . . . . . . . . . . . . . . . . .  6
   6. Ethernet Segment  . . . . . . . . . . . . . . . . . . . . . . .  7
   7. Ethernet Tag  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1 VLAN Based Service Interface . . . . . . . . . . . . . . . .  9
     7.2 VLAN Bundle Service Interface  . . . . . . . . . . . . . . .  9
       7.2.1 Port Based Service Interface . . . . . . . . . . . . . . 10
     7.3 VLAN Aware Bundle Service Interface  . . . . . . . . . . . . 10
       7.3.1 Port Based VLAN Aware Service Interface  . . . . . . . . 10
   8. BGP EVPN NLRI . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1. Ethernet Auto-Discovery Route . . . . . . . . . . . . . . . 11
     8.2.  MAC Advertisement Route  . . . . . . . . . . . . . . . . . 12
     8.3. Inclusive Multicast Ethernet Tag Route  . . . . . . . . . . 12
     8.4 Ethernet Segment Route . . . . . . . . . . . . . . . . . . . 13
     8.5 ESI Label Extended Community . . . . . . . . . . . . . . . . 13
     8.6 ES-Import Route Target . . . . . . . . . . . . . . . . . . . 14
     8.7 MAC Mobility Extended Community  . . . . . . . . . . . . . . 14
     8.8 Default Gateway Extended Community . . . . . . . . . . . . . 15
   9. Multi-homing Functions  . . . . . . . . . . . . . . . . . . . . 15
     9.1 Multi-homed Ethernet Segment Auto-Discovery  . . . . . . . . 15
       9.1.1 Constructing the Ethernet Segment Route  . . . . . . . . 15
     9.2 Fast Convergence . . . . . . . . . . . . . . . . . . . . . . 16
       9.2.1 Constructing the Ethernet A-D Route per Ethernet
             Segment  . . . . . . . . . . . . . . . . . . . . . . . . 16
         9.2.1.1. Ethernet A-D Route Targets  . . . . . . . . . . . . 17
     9.3 Split Horizon  . . . . . . . . . . . . . . . . . . . . . . . 17
       9.3.1 ESI Label Assignment . . . . . . . . . . . . . . . . . . 18
         9.3.1.1 Ingress Replication  . . . . . . . . . . . . . . . . 18



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         9.3.1.2. P2MP MPLS LSPs  . . . . . . . . . . . . . . . . . . 19
     9.4 Aliasing and Backup-Path . . . . . . . . . . . . . . . . . . 20
       9.4.1 Constructing the Ethernet A-D Route per EVI  . . . . . . 21
         9.4.1.1 Ethernet A-D Route Targets . . . . . . . . . . . . . 22
     9.5 Designated Forwarder Election  . . . . . . . . . . . . . . . 22
     9.6. Interoperability with Single-homing PEs . . . . . . . . . . 24
   10. Determining Reachability to Unicast MAC Addresses  . . . . . . 25
     10.1. Local Learning . . . . . . . . . . . . . . . . . . . . . . 25
     10.2. Remote learning  . . . . . . . . . . . . . . . . . . . . . 26
       10.2.1. Constructing the BGP EVPN MAC Address Advertisement  . 26
       10.2.2 Route Resolution  . . . . . . . . . . . . . . . . . . . 28
   11. ARP and ND . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     11.1 Default Gateway . . . . . . . . . . . . . . . . . . . . . . 29
   12. Handling of Multi-Destination Traffic  . . . . . . . . . . . . 30
     12.1. Construction of the Inclusive Multicast Ethernet Tag
           Route  . . . . . . . . . . . . . . . . . . . . . . . . . . 31
     12.2. P-Tunnel Identification  . . . . . . . . . . . . . . . . . 31
   13. Processing of Unknown Unicast Packets  . . . . . . . . . . . . 32
     13.1. Ingress Replication  . . . . . . . . . . . . . . . . . . . 33
     13.2. P2MP MPLS LSPs . . . . . . . . . . . . . . . . . . . . . . 33
   14. Forwarding Unicast Packets . . . . . . . . . . . . . . . . . . 34
     14.1. Forwarding packets received from a CE  . . . . . . . . . . 34
     14.2. Forwarding packets received from a remote PE . . . . . . . 35
       14.2.1. Unknown Unicast Forwarding . . . . . . . . . . . . . . 35
       14.2.2. Known Unicast Forwarding . . . . . . . . . . . . . . . 35
   15. Load Balancing of Unicast Frames . . . . . . . . . . . . . . . 36
     15.1. Load balancing of traffic from an PE to remote CEs . . . . 36
       15.1.1 Single-Active Redundancy Mode . . . . . . . . . . . . . 36
       15.1.2 All-Active Redundancy Mode  . . . . . . . . . . . . . . 37
     15.2. Load balancing of traffic between an PE and a local CE . . 38
       15.2.1. Data plane learning  . . . . . . . . . . . . . . . . . 38
       15.2.2. Control plane learning . . . . . . . . . . . . . . . . 39
   16. MAC Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 39
     16.1. MAC Duplication Issue  . . . . . . . . . . . . . . . . . . 41
     16.2. Sticky MAC addresses . . . . . . . . . . . . . . . . . . . 41
   17. Multicast & Broadcast  . . . . . . . . . . . . . . . . . . . . 41
     17.1. Ingress Replication  . . . . . . . . . . . . . . . . . . . 41
     17.2. P2MP LSPs  . . . . . . . . . . . . . . . . . . . . . . . . 42
       17.2.1. Inclusive Trees  . . . . . . . . . . . . . . . . . . . 42
   18. Convergence  . . . . . . . . . . . . . . . . . . . . . . . . . 42
     18.1. Transit Link and Node Failures between PEs . . . . . . . . 42
     18.2. PE Failures  . . . . . . . . . . . . . . . . . . . . . . . 43
     18.2. PE to CE Network Failures  . . . . . . . . . . . . . . . . 43
   19. Frame Ordering . . . . . . . . . . . . . . . . . . . . . . . . 43
   20. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
   21.  Security Considerations . . . . . . . . . . . . . . . . . . . 44
   22.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
   23. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45



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     23.1 Normative References  . . . . . . . . . . . . . . . . . . . 45
     23.2 Informative References  . . . . . . . . . . . . . . . . . . 45
   24. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 45
















































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1. Specification of requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2. Terminology

   Bridge Domain:

   Broadcast Domain:

   CE: Customer Edge device e.g., host or router or switch

   EVI:  An EVPN instance spanning across the PEs participating in that
   VPN

   MAC-VRF:  A Virtual Routing and Forwarding table for MAC addresses on
   a PE for an EVI

   Ethernet Segment Identifier (ESI):  If a CE is multi-homed to two or
   more PEs, the set of Ethernet links that attaches the CE to the PEs
   is an 'Ethernet segment'.   Ethernet segments MUST have a unique non-
   zero identifier, the '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. Ethernet tag(s) are assigned to the broadcast
   domains of a given EVPN instance by the provider of that EVPN, and
   each PE in that EVPN instance performs a mapping between broadcast
   domain identifier(s) understood by each of its attached CEs and the
   corresponding Ethernet tag.

   LACP: Link Aggregation Control Protocol

   MP2MP: Multipoint to Multipoint

   P2MP: Point to Multipoint

   P2P: Point to Point

   Single-Active Mode: When a device or a network is multi-homed to two
   or more PEs and when only a single PE in such redundancy group can
   forward traffic to/from the multi-homed device or network for a given
   VLAN, then such multi-homing or redundancy is referred to as "Single-
   Active".




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   All-Active Mode: When a device is multi-homed to two or more PEs and
   when all PEs in such redundancy group can forward traffic to/from the
   multi-homed device for a given VLAN, then such multi-homing or
   redundancy is referred to as "All-Active".


3. Introduction

   This document describes procedures for BGP MPLS based Ethernet VPNs
   (EVPN).  The procedures described here are intended to meet the
   requirements specified in [EVPN-REQ].  Please refer to [EVPN-REQ] for
   the detailed requirements and motivation. EVPN requires extensions to
   existing IP/MPLS protocols as described in this document. In addition
   to these extensions EVPN uses several building blocks from existing
   MPLS technologies.


4. Contributors

   In addition to the authors listed above, the following individuals
   also contributed to this document:

      Quaizar Vohra
      Kireeti Kompella
      Apurva Mehta
      Nadeem Mohammad
      Juniper Networks

      Clarence Filsfils
      Dennis Cai
      Cisco


5. BGP MPLS Based EVPN Overview

   This section provides an overview of EVPN. An EVPN instance comprises
   CEs that are connected to PEs that form the edge of the MPLS
   infrastructure. A CE may be a host, a router or a switch. The PEs
   provide virtual Layer 2 bridged connectivity between the CEs. There
   may be multiple EVPN instances in the provider's network.

   The PEs may be connected by an MPLS LSP infrastructure which provides
   the benefits of MPLS technology such as fast-reroute, resiliency,
   etc.  The PEs may also be connected by an IP infrastructure in which
   case IP/GRE tunneling or other IP tunneling can be used between the
   PEs. The detailed procedures in this version of this document are
   specified only for MPLS LSPs as the tunneling technology. However
   these procedures are designed to be extensible to IP tunneling as the



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   PSN tunneling technology.

   In an EVPN, MAC learning between PEs occurs not in the data plane (as
   happens with traditional bridging) but in the control plane. Control
   plane learning offers greater control over the MAC learning process,
   such as restricting who learns what, and the ability to apply
   policies.  Furthermore, the control plane chosen for advertising MAC
   reachability information is multi-protocol (MP) BGP (similar to IP
   VPNs (RFC 4364)). This provides greater scalability and the ability
   to preserve the "virtualization" or isolation of groups of
   interacting agents (hosts, servers, virtual machines) from each
   other. In EVPN, PEs advertise the MAC addresses learned from the CEs
   that are connected to them, along with an MPLS label, to other PEs in
   the control plane using MP-BGP. Control plane learning enables load
   balancing of traffic to and from CEs that are multi-homed to multiple
   PEs. This is in addition to load balancing across the MPLS core via
   multiple LSPs between the same pair of PEs.  In other words it allows
   CEs to connect to multiple active points of attachment. It also
   improves convergence times in the event of certain network failures.

   However, learning between PEs and CEs is done by the method best
   suited to the CE: data plane learning, IEEE 802.1x, LLDP, 802.1aq,
   ARP, management plane or other protocols.

   It is a local decision as to whether the Layer 2 forwarding table on
   an PE is populated with all the MAC destination addresses known to
   the control plane, or whether the PE implements a cache based scheme.
   For instance the MAC forwarding table may be populated only with the
   MAC destinations of the active flows transiting a specific PE.

   The policy attributes of EVPN are very similar to those of IP-VPN. A
   EVPN instance requires a Route-Distinguisher (RD) which is unique per
   PE and one or more globally unique Route-Targets (RTs). A CE attaches
   to a MAC-VRF on an PE, on an Ethernet interface which may be
   configured for one or more Ethernet Tags, e.g., VLAN IDs. Some
   deployment scenarios guarantee uniqueness of VLAN IDs across EVPN
   instances: all points of attachment for a given EVPN instance use the
   same VLAN ID, and no other EVPN instance uses this VLAN ID.  This
   document refers to this case as a "Unique VLAN EVPN" and describes
   simplified procedures to optimize for it.


6. Ethernet Segment

   If a CE is multi-homed to two or more PEs, the set of Ethernet links
   constitutes an "Ethernet Segment". An Ethernet segment may appear to
   the CE as a Link Aggregation Group (LAG).  Ethernet segments have an
   identifier, called the "Ethernet Segment Identifier" (ESI) which is



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   encoded as a ten octets integer.  The following two ESI values are
   reserved:

   - ESI 0 denotes a single-homed CE.

   - ESI {0xFF} (repeated 10 times) is known as MAX-ESI and is reserved.

   In general, an Ethernet segment MUST have a non-reserved ESI that is
   unique network wide (e.g., across all EVPN instances on all the PEs).
   If the CE(s) constituting an Ethernet Segment is (are) managed by the
   network operator, then ESI uniqueness should be guaranteed; however,
   if the CE(s) is (are) not managed, then the operator MUST configure a
   network-wide unique ESI for that Ethernet Segment.  This is required
   to enable auto-discovery of Ethernet Segments and DF election. The
   ESI can be assigned using various mechanisms:

      1. If IEEE 802.1AX LACP is used between the PEs and CEs, then
      the ESI is determined from LACP by concatenating the following
      parameters:

        + CE LACP System Identifier comprised of two octets of System
          Priority and six octets of System MAC address, where the
          System Priority is encoded in the most significant two octets.
          The CE LACP identifier MUST be encoded in the high order eight
          octets of the ESI.

        + CE LACP two octets Port Key. The CE LACP port key MUST be
          encoded in the low order two octets of the ESI.

      As far as the CE is concerned, it would treat the multiple PEs
      that it is connected to as the same switch. This allows the CE
      to aggregate links that are attached to different PEs in the
      same bundle.

      This mechanism could be used only if it produces ESIs that satisfy
      the uniqueness requirement specified above.

      2. In the case of indirectly connected hosts via a bridged LAN
      between the CEs and the PEs, the ESI is determined based on the
      Layer 2 bridge protocol as follows: If MST is used in the bridged
      LAN then the value of the ESI is derived by listening to BPDUs on
      the Ethernet segment. To achieve this the PE is not required to
      run MST. However the PE must learn the Root Bridge MAC address
      and Bridge Priority of the root of the Internal Spanning Tree
      (IST) by listening to the BPDUs. The ESI is constructed as
      follows:

      {Bridge Priority (16 bits) , Root Bridge MAC Address (48 bits)}



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      This mechanism could be used only if it produces ESIs that satisfy
      the uniqueness requirement specified above.

      3. The ESI may be configured.

7. Ethernet Tag

   An Ethernet Tag identifies a particular broadcast domain, e.g. a
   VLAN, in an EVPN Instance.  An EVPN Instance consists of one or more
   broadcast domains (one or more VLANs). VLANs are assigned to a given
   EVPN Instance by the provider of the EVPN service. A given VLAN can
   itself be represented by multiple VLAN IDs (VIDs). In such cases, the
   PEs participating in that VLAN for a given EVPN instance are
   responsible for performing VLAN ID translation to/from locally
   attached CE devices.

   If a VLAN is represented by a single VID across all PE devices
   participating in that VLAN for that EVPN instance, then there is no
   need for VID translation at the PEs. Furthermore, some deployment
   scenarios guarantee uniqueness of VIDs across all EVPN instances;
   all points of attachment for a given EVPN instance use the same VID
   and no other EVPN instances use that VID.  This allows the RT(s) for
   each EVPN instance to be derived automatically from the corresponding
   VID, as described in section 9.4.1.1.1 "Auto-Derivation from the
   Ethernet Tag ID".

   The following subsections discuss the relationship between broadcast
   domains (e.g., VLANs), Ethernet Tags (e.g., VIDs), and MAC-VRFs as
   well as the setting of the Ethernet Tag Identifier, in the various
   EVPN BGP routes (defined in section 8), for the different types of
   service interfaces described in [EVPN-REQ].

7.1 VLAN Based Service Interface

   With this service interface, an EVPN instance consists of only a
   single broadcast domain (e.g., a single VLAN). Therefore, there is a
   one to one mapping between a VID on this interface and a MAC-VRF.
   Since a MAC-VRF corresponds to a single VLAN, it consists of a single
   bridge domain corresponding to that VLAN. If the VLAN is represented
   by different VIDs on different PEs, then each PE needs to perform VID
   translation for frames destined to its attached CEs. In such
   scenarios, the Ethernet frames transported over MPLS/IP network
   SHOULD remain tagged with the originating VID and a VID translation
   MUST be supported in the data path and MUST be performed on the
   disposition PE. The Ethernet Tag Identifier in all EVPN routes MUST
   be set to 0.

7.2 VLAN Bundle Service Interface



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   With this service interface, an EVPN instance corresponds to several
   broadcast domains (e.g., several VLANs); however, only a single
   bridge domain is maintained per MAC-VRF which means multiple VLANs
   share the same bridge domain. This implies MAC addresses MUST be
   unique across different VLANs for this service to work. In other
   words, there is a many-to-one mapping between VLANs and a MAC-VRF,
   and the MAC-VRF consists of a single bridge domain. Furthermore, a
   single VLAN must be represented by a single VID - e.g., no VID
   translation is allowed for this service interface type. The MPLS
   encapsulated frames MUST remain tagged with the originating VID. Tag
   translation is NOT permitted. The Ethernet Tag Identifier in all EVPN
   routes MUST be set to 0.

7.2.1 Port Based Service Interface

   This service interface is a special case of the VLAN Bundle service
   interface, where all of the VLANs on the port are part of the same
   service and map to the same bundle. The procedures are identical to
   those described in section 7.2.

7.3 VLAN Aware Bundle Service Interface

   With this service interface, an EVPN instance consists of several
   broadcast domains (e.g., several VLANs) with each VLAN having its own
   bridge domain - e.g., multiple bridge domains (one per VLAN) is
   maintained by a single MAC-VRF corresponding to the EVPN instance. In
   the case where a single VLAN is represented by different VIDs on
   different CEs and thus tag (VID) translation is required, a
   normalized Ethernet Tag (VID) MUST be carried in the MPLS
   encapsulated frames and a tag translation function MUST be supported
   in the data path. This translation MUST be performed in data path on
   both the imposition as well as the disposition PEs (translating to
   normalized tag on imposition PE and translating to local tag on
   disposition PE). The Ethernet Tag Identifier in all EVPN routes MUST
   be set to the normalized Ethernet Tag assigned by the EVPN provider.

7.3.1 Port Based VLAN Aware Service Interface

   This service interface is a special case of the VLAN Aware Bundle
   service interface, where all of the VLANs on the port are part of the
   same service and map to the same bundle. The procedures are identical
   to those described in section 7.3.

8. BGP EVPN NLRI

   This document defines a new BGP NLRI, called the EVPN NLRI.

   Following is the format of the EVPN NLRI:



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                   +-----------------------------------+
                   |    Route Type (1 octet)           |
                   +-----------------------------------+
                   |     Length (1 octet)              |
                   +-----------------------------------+
                   | Route Type specific (variable)    |
                   +-----------------------------------+

   The Route Type field defines encoding of the rest of the EVPN NLRI
   (Route Type specific EVPN NLRI).

   The Length field indicates the length in octets of the Route Type
   specific field of EVPN NLRI.

   This document defines the following Route Types:

        + 1 - Ethernet Auto-Discovery (A-D) route
        + 2 - MAC advertisement route
        + 3 - Inclusive Multicast Route
        + 4 - Ethernet Segment Route

   The detailed encoding and procedures for these route types are
   described in subsequent sections.

   The EVPN NLRI is carried in BGP [RFC4271] using BGP Multiprotocol
   Extensions [RFC4760] with an AFI of 25 (L2VPN) and a SAFI of 70
   (EVPN). The NLRI field in the MP_REACH_NLRI/MP_UNREACH_NLRI attribute
   contains the EVPN NLRI (encoded as specified above).

   In order for two BGP speakers to exchange labeled EVPN NLRI, they
   must use BGP Capabilities Advertisement to ensure that they both are
   capable of properly processing such NLRI. This is done as specified
   in [RFC4760], by using capability code 1 (multiprotocol BGP) with an
   AFI of 25 (L2VPN) and a SAFI of 70 (EVPN).

8.1. Ethernet Auto-Discovery Route

   A Ethernet A-D route type specific EVPN NLRI consists of the
   following:












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                   +---------------------------------------+
                   |      RD   (8 octets)                  |
                   +---------------------------------------+
                   |Ethernet Segment Identifier (10 octets)|
                   +---------------------------------------+
                   |  Ethernet Tag ID (4 octets)           |
                   +---------------------------------------+
                   |  MPLS Label (3 octets)                |
                   +---------------------------------------+

   For procedures and usage of this route please see section 9.2 "Fast
   Convergence" and section 9.4 "Aliasing".

8.2.  MAC Advertisement Route

   A MAC advertisement route type specific EVPN NLRI consists of the
   following:

                   +---------------------------------------+
                   |      RD   (8 octets)                  |
                   +---------------------------------------+
                   |Ethernet Segment Identifier (10 octets)|
                   +---------------------------------------+
                   |  Ethernet Tag ID (4 octets)           |
                   +---------------------------------------+
                   |  MAC Address Length (1 octet)         |
                   +---------------------------------------+
                   |  MAC Address (6 octets)               |
                   +---------------------------------------+
                   |  IP Address Length (1 octet)          |
                   +---------------------------------------+
                   |  IP Address (4 or 16 octets)          |
                   +---------------------------------------+
                   |  MPLS Label (3 octets)                |
                   +---------------------------------------+

   For the purpose of BGP route key processing, only the Ethernet Tag
   ID, MAC Address Length, MAC Address, IP Address Length, and IP
   Address Address fields are considered to be part of the prefix in the
   NLRI. The Ethernet Segment Identifier and MPLS Label fields are to be
   treated as route attributes as opposed to being part of the "route".

   For procedures and usage of this route please see section 10
   "Determining Reachability to Unicast MAC Addresses" and section 15
   "Load Balancing of Unicast Packets".

8.3. Inclusive Multicast Ethernet Tag Route




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   An Inclusive Multicast Ethernet Tag route type specific EVPN NLRI
   consists of the following:

                   +---------------------------------------+
                   |      RD   (8 octets)                  |
                   +---------------------------------------+
                   |  Ethernet Tag ID (4 octets)           |
                   +---------------------------------------+
                   |  IP Address Length (1 octet)          |
                   +---------------------------------------+
                   |   Originating Router's IP Addr        |
                   |          (4 or 16 octets)             |
                   +---------------------------------------+

   For procedures and usage of this route please see section 12
   "Handling of Multi-Destination Traffic", section 13 "Processing of
   Unknown Unicast Traffic" and section 17 "Multicast".

8.4 Ethernet Segment Route

   The Ethernet Segment Route is encoded in the EVPN NLRI using the
   Route Type value of 4. The Route Type Specific field of the NLRI is
   formatted as follows:

                   +---------------------------------------+
                   |      RD   (8 octets)                  |
                   +---------------------------------------+
                   |Ethernet Segment Identifier (10 octets)|
                   +---------------------------------------+
                   |  IP Address Length (1 octet)          |
                   +---------------------------------------+
                   |   Originating Router's IP Addr        |
                   |          (4 or 16 octets)             |
                   +---------------------------------------+

   For procedures and usage of this route please see section 9.5
   "Designated Forwarder Election".

8.5 ESI Label Extended Community

   This extended community is a new transitive extended community with
   the Type field is 0x06, and the Sub-Type of 0x01. It may be
   advertised along with Ethernet Auto-Discovery routes and it enables
   split-horizon procedures for multi-homed sites as described in
   section 9.3 "Split Horizon".

   Each ESI Label Extended Community is encoded as a 8-octet value as
   follows:



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        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Type=0x06   | Sub-Type=0x01 | Flags (One Octet)  |Reserved=0  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Reserved = 0|          ESI Label                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The low order bit of the flags octet is defined as the "Active-
   Standby" bit and may be set to 1. A value of 0 means that the multi-
   homed site is operating in All-Active mode; whereas, a value of 1
   means that the multi-homed site is operating in Single-Active mode.

   The second low order bit of the flags octet is defined as the "Root-
   Leaf". A value of 0 means that this label is associated with a Root
   site; whereas, a value of 1 means that this label is associate with a
   Leaf site. The other bits must be set to 0.

8.6 ES-Import Route Target

   This is a new transitive Route Target extended community carried with
   the Ethernet Segment route. When used, it enables all the PEs
   connected to the same multi-homed site to import the Ethernet Segment
   routes. The value is derived automatically from the ESI by encoding
   the 6-byte MAC address portion of the ESI in the ES-Import Route
   Target. The format of this extended community is as follows:

       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type=0x06   | Sub-Type=0x02 |          ES-Import              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     ES-Import Cont'd                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This document expands the definition of the Route Target extended
   community to allow the value of high order octet (Type field) to be
   0x06 (in addition to the values specified in rfc4360). The value of
   low order octet (Sub-Type field) of 0x02 indicates that this extended
   community is of type "Route Target". The new value for Type field of
   0x06 indicates that the structure of this RT is a six bytes value
   (e.g., a MAC address). A BGP speaker that implements RT-Constrain
   (RFC4684) MUST apply the RT-Constrain procedures to the ES-import RT
   as-well.

   For procedures and usage of this attribute, please see section 9.1
   "Redundancy Group Discovery".

8.7 MAC Mobility Extended Community




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   This extended community is a new transitive extended community with
   the Type field of 0x06 and the Sub-Type of 0x00. It may be advertised
   along with MAC Advertisement routes. The procedures for using this
   Extended Community are described in section 16 "MAC Mobility".

   The MAC Mobility Extended Community is encoded as a 8-octet value as
   follows:

   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type=0x06     | Sub-Type=0x00 |Flags(1 octet)|  Reserved=0    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Sequence Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The low order bit of the flags octet is defined as the
   "Sticky/static" flag and may be set to 1. A value of 1 means that the
   MAC address is static and cannot move.


8.8 Default Gateway Extended Community

   The Default Gateway community is an Extended Community of an Opaque
   Type (see 3.3 of rfc4360). It is a transitive community, which means
   that the first octet is 0x03. The value of the second octet (Sub-
   Type) is 0x030d (Default Gateway) as defined by IANA. The Value field
   of this community is reserved (set to 0 by the senders, ignored by
   the receivers).


9. Multi-homing Functions

   This section discusses the functions, procedures and associated BGP
   routes used to support multi-homing in EVPN. This covers both multi-
   homed device (MHD) as well as multi-homed network (MHN) scenarios.

9.1 Multi-homed Ethernet Segment Auto-Discovery

   PEs connected to the same Ethernet segment can automatically discover
   each other with minimal to no configuration through the exchange of
   the Ethernet Segment route.

9.1.1 Constructing the Ethernet Segment Route

   The Route-Distinguisher (RD) MUST be a Type 1 RD [RFC4364]. The value
   field comprises an IP address of the MES (typically, the loopback
   address) followed by 0's.




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   The Ethernet Segment Identifier MUST be set to the ten octet ESI
   identifier described in section 6.

   The BGP advertisement that advertises the Ethernet Segment route MUST
   also carry an ES-Import extended community attribute, as defined in
   section 8.6.

   The Ethernet Segment Route filtering MUST be done such that the
   Ethernet Segment Route is imported only by the PEs that are multi-
   homed to the same Ethernet Segment. To that end, each PE that is
   connected to a particular Ethernet segment constructs an import
   filtering rule to import a route that carries the ES-Import extended
   community, constructed from the ESI.

9.2 Fast Convergence

   In EVPN, MAC address reachability is learnt via the BGP control-plane
   over the MPLS network. As such, in the absence of any fast protection
   mechanism, the network convergence time is a function of the number
   of MAC Advertisement routes that must be withdrawn by the PE
   encountering a failure. For highly scaled environments, this scheme
   yields slow convergence.

   To alleviate this, EVPN defines a mechanism to efficiently and
   quickly signal, to remote PE nodes, the need to update their
   forwarding tables upon the occurrence of a failure in connectivity to
   an Ethernet segment. This is done by having each PE advertise an
   Ethernet A-D Route per Ethernet segment for each locally attached
   segment (refer to section 9.2.1 below for details on how this route
   is constructed). Upon a failure in connectivity to the attached
   segment, the PE withdraws the corresponding Ethernet A-D route. This
   triggers all PEs that receive the withdrawal to update their next-hop
   adjacencies for all MAC addresses associated with the Ethernet
   segment in question. If no other PE had advertised an Ethernet A-D
   route for the same segment, then the PE that received the withdrawal
   simply invalidates the MAC entries for that segment. Otherwise, the
   PE updates the next-hop adjacencies to point to the backup PE(s).

9.2.1 Constructing the Ethernet A-D Route per Ethernet Segment

   This section describes procedures to construct the Ethernet A-D route
   when a single such route is advertised by an PE for a given Ethernet
   Segment. This flavor of the Ethernet A-D route is used for fast
   convergence (as discussed above) as well as for advertising the ESI
   label used for split-horizon filtering (as discussed in section 9.3).
   Support of this route flavor is MANDATORY.

   Route-Distinguisher (RD) MUST be a Type 1 RD [RFC4364]. The value



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   field comprises an IP address of the PE (typically, the loopback
   address) followed by 0.

   The Ethernet Segment Identifier MUST be a ten octet entity as
   described in section "Ethernet Segment". This document does not
   specify the use of the Ethernet A-D route when the Segment Identifier
   is set to 0.

   The Ethernet Tag ID MUST be set to 0.

   The MPLS label in the NLRI MUST be set to 0.

   The "ESI Label Extended Community" MUST be included in the route. If
   all-Active multi-homing is desired, then the "Active-Standby" bit in
   the flags of the ESI Label Extended Community MUST be set to 0 and
   the MPLS label in that extended community MUST be set to a valid MPLS
   label value. The MPLS label in this Extended Community is referred to
   as an "ESI label". This label MUST be a downstream assigned MPLS
   label if the advertising PE is using ingress replication for
   receiving multicast, broadcast or unknown unicast traffic from other
   PEs. If the advertising PE is using P2MP MPLS LSPs for sending
   multicast, broadcast or unknown unicast traffic, then this label MUST
   be an upstream assigned MPLS label. The usage of this label is
   described in section 9.3.

   If the Ethernet Segment is connected to more than one PE and Single-
   Active multi-homing is desired, then the "Active-Standby" bit in the
   flags of the ESI Label Extended Community MUST be set to 1 and ESI
   label MUST be set to zero.

9.2.1.1. Ethernet A-D Route Targets

   The Ethernet A-D route MUST carry one or more Route Target (RT)
   attributes. These RTs MUST be the set of RTs associated with all the
   EVPN instances to which the Ethernet Segment, corresponding to the
   Ethernet A-D route, belongs.

9.3 Split Horizon

   Consider a CE that is multi-homed to two or more PEs on an Ethernet
   segment ES1 operating in All-Active mode. If the CE sends a
   broadcast, unknown unicast, or multicast (BUM) packet to one of the
   non-DF (Designated Forwarder) PEs, say PE1, then PE1 will forward
   that packet to all or subset of the other PEs in that EVPN instance
   including the DF PE for that Ethernet segment. In this case the DF PE
   that the CE is multi-homed to MUST drop the packet and not forward
   back to the CE. This filtering is referred to as "split horizon"
   filtering in this document.



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   In order to achieve this split horizon function, every BUM packet
   originating from a non-DF PE is encapsulated with an MPLS label that
   identifies the Ethernet segment of origin (i.e. the segment from
   which the frame entered the EVPN network). This label is referred to
   as the ESI label, and MUST be distributed by all PEs when operating
   in All-Active multi-homing mode using the "Ethernet A-D route per
   Ethernet Segment" as per the procedures in section 9.2.1 above. This
   route is imported by the PEs connected to the Ethernet Segment and
   also by the PEs that have at least one EVPN instance in common with
   the Ethernet Segment in the route. As described in section 9.1.1, the
   route MUST carry an ESI Label Extended Community with a valid ESI
   label. The disposition DF PE rely on the value of the ESI label to
   determine whether or not a BUM frame is allowed to egress a specific
   Ethernet segment. It should be noted that if the BUM frame is
   originated from the DF PE operating in All-Active multi-homing mode,
   then the DF PE MAY not encapsulate the frame with the ESI label.
   Furthermore, if the multi-homed PEs operate in active/standby mode,
   then the packet MUST NOT be encapsulated with the ESI label and the
   label value MUST be set to zero in ESI Label Extended Community per
   section 9.2.1 above.

9.3.1 ESI Label Assignment

   The following subsections describe the assignment procedures for the
   ESI label, which differ depending on the type of tunnels being used
   to deliver multi-destination packets in the EVPN network.

9.3.1.1 Ingress Replication

   All PEs operating in an All-Active multi-homing mode that rely on
   ingress replication for the reception of BUM traffic, distribute to
   other PEs, that belong to the Ethernet segment, a downstream assigned
   "ESI label" in the Ethernet A-D route per ESI. This label MUST be
   programmed in the platform label space by the advertising PE. Further
   the forwarding entry for this label must result in NOT forwarding
   packets received with this label onto the Ethernet segment that the
   label was distributed for.

   Consider PE1 and PE2 that are multi-homed to CE1 on ES1 and operating
   in All-Active multi-homing mode. Further consider that PE1 is using
   P2P or MP2P LSPs to send packets to PE2. Consider that PE1 is the
   non-DF for VLAN1 and PE2 is the DF for VLAN1, and PE1 receives a BUM
   packet from CE1 on VLAN1 on ES1. In this scenario, PE2 distributes an
   Inclusive Multicast Ethernet Tag route for VLAN1 corresponding to an
   EVPN instance. So, when PE1 sends a BUM packet, that it receives from
   CE1, it MUST first push onto the MPLS label stack the ESI label that
   PE2 has distributed for ES1. It MUST then push on the MPLS label
   distributed by PE2 in the Inclusive Multicast Ethernet Tag route for



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   VLAN1. The resulting packet is further encapsulated in the P2P or
   MP2P LSP label stack required to transmit the packet to PE2.  When
   PE2 receives this packet, it determines the set of ESIs to replicate
   the packet to from the top MPLS label, after any P2P or MP2P LSP
   labels have been removed. If the next label is the ESI label assigned
   by PE2 for ES1, then PE2 MUST NOT forward the packet onto ES1. If the
   next label is an ESI label which has not been assigned by PE2, then
   PE2 MUST drop the packet. It should be noted that in this scenario,
   if PE2 receives a BUM traffic for VLAN1 from CE1, then it doesn't
   need to encapsulate the packet with an ESI label when sending it to
   the PE1 since PE1 can use its DF logic to filter the BUM packets and
   thus doesn't need to use split-horizon filtering for ES1.

9.3.1.2. P2MP MPLS LSPs

   The non-DF PEs operating in an All-Active multi-homing mode that is
   using P2MP LSPs for sending BUM traffic, distribute to other PEs,
   that belong to the Ethernet segment or have an EVPN instance in
   common with the Ethernet Segment, an upstream assigned "ESI label" in
   the Ethernet A-D route. This label is upstream assigned by the PE
   that advertises the route. This label MUST be programmed by the other
   PEs, that are connected to the ESI advertised in the route, in the
   context label space for the advertising PE. Further the forwarding
   entry for this label must result in NOT forwarding packets received
   with this label onto the Ethernet segment that the label was
   distributed for. This label MUST also be programmed by the other PEs,
   that import the route but are not connected to the ESI advertised in
   the route, in the context label space for the advertising PE. Further
   the forwarding entry for this label must be a POP with no other
   associated action.

   Consider PE1 and PE2 that are multi-homed to CE1 on ES1 and operating
   in All-Active multi-homing mode. Also consider PE3 belongs to one of
   the EVPN instances of ES1.  Further, assume that PE1 which is the
   non-DF, using P2MP MPLS LSPs to send BUM packets. When PE1 sends a
   BUM packet, that it receives from CE1, it MUST first push onto the
   MPLS label stack the ESI label that it has assigned for the ESI that
   the packet was received on. The resulting packet is further
   encapsulated in the P2MP MPLS label stack necessary to transmit the
   packet to the other PEs. Penultimate hop popping MUST be disabled on
   the P2MP LSPs used in the MPLS transport infrastructure for EVPN.
   When PE2 receives this packet, it de-capsulates the top MPLS label
   and forwards the packet using the context label space determined by
   the top label. If the next label is the ESI label assigned by PE1 to
   ES1, then PE2 MUST NOT forward the packet onto ES1. When PE3 receives
   this packet, it de-capsulates the top MPLS label and forwards the
   packet using the context label space determined by the top label. If
   the next label is the ESI label assigned by PE1 to ES1 and PE3 is not



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   connected to ES1, then PE3 MUST pop the label and flood the packet
   over all local ESIs in that EVPN instance. It should be noted that
   when PE2 sends a BUM frame over a P2MP LSP, it does not need to
   encapsulate the frame with an ESI label because it is the DF for that
   VLAN.


9.4 Aliasing and Backup-Path

   In the case where a CE is multi-homed to multiple PE nodes, using a
   LAG with All-Active redundancy, it is possible that only a single PE
   learns a set of the MAC addresses associated with traffic transmitted
   by the CE. This leads to a situation where remote PE nodes receive
   MAC advertisement routes, for these addresses, from a single PE even
   though multiple PEs are connected to the multi-homed segment. As a
   result, the remote PEs are not able to effectively load-balance
   traffic among the PE nodes connected to the multi-homed Ethernet
   segment. This could be the case, for e.g. when the PEs perform data-
   path learning on the access, and the load-balancing function on the
   CE hashes traffic from a given source MAC address to a single PE.
   Another scenario where this occurs is when the PEs rely on control
   plane learning on the access (e.g. using ARP), since ARP traffic will
   be hashed to a single link in the LAG.

   To alleviate this issue, EVPN introduces the concept of 'Aliasing'.
   Aliasing refers to the ability of a PE to signal that it has
   reachability to a given locally attached Ethernet segment, even when
   it has learnt no MAC addresses from that segment. The Ethernet A-D
   route per EVI is used to that end. Remote PEs which receive MAC
   advertisement routes with non-reserved ESI SHOULD consider the
   advertised MAC address as reachable via all PEs which have advertised
   reachability to the relevant Segment using: (1) Ethernet A-D routes
   per EVI with the same ESI (and Ethernet Tag if applicable) AND
   (2)Ethernet A-D routes per ESI with the same ESI and with the
   Active/Standby bit set to 0 in the ESI Label Extended Community.

   This flavor of Ethernet A-D route per EVI, associated with aliasing,
   can arrive at target PEs asynchronously relative to the flavor of
   Ethernet A-D route associated with split-horizon and mass-withdraw
   (i.e. per ESI). Therefore, if the Ethernet A-D route per EVI arrives
   ahead of the Ethernet A-D route per ESI, then the former must NOT be
   used for traffic forwarding till the latter arrives. This will take
   care of corner cases and race conditions where the Ethernet A-D route
   associated with mass-withdraw is withdrawn but a PE still receives
   the route associated with aliasing.

   Backup-Path is a closely related function, albeit it applies to the
   case where the redundancy mode is Active/Standby. In this case, the



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   PE advertises that it has reachability to a given locally attached
   Ethernet Segment using the Ethernet A-D route as well. Remote PEs
   which receive the MAC advertisement routes, with non-reserved ESI,
   MUST consider the MAC address as reachable via the advertising PE.
   Furthermore, the remote PEs SHOULD install a Backup-Path, for said
   MAC, to the PE which had advertised reachability to the relevant
   Segment using (1) an Ethernet A-D routes per EVI with the same ESI
   (and Ethernet Tag if applicable) AND (2) Ethernet A-D routes per ESI
   with the same ESI and with the Active/Standby bit set to 1 in the ESI
   Label Extended Community.

9.4.1 Constructing the Ethernet A-D Route per EVI

   This section describes procedures to construct the Ethernet A-D route
   when one or more such routes are advertised by an PE for a given EVI.
   This flavor of the Ethernet A-D route is used for aliasing, and
   support of this route flavor is OPTIONAL.

   Route-Distinguisher (RD) MUST be set to the RD of the EVI that is
   advertising the NLRI. An RD MUST be assigned for a given EVI on an
   PE. This RD MUST be unique across all EVIs on an PE. It is
   RECOMMENDED to use the Type 1 RD [RFC4364]. The value field comprises
   an IP address of the PE (typically, the loopback address) followed by
   a number unique to the PE.  This number may be generated by the PE.
   Or in the Unique VLAN EVPN case, the low order 12 bits may be the 12
   bit VLAN ID, with the remaining high order 4 bits set to 0.

   The Ethernet Segment Identifier MUST be a ten octet entity as
   described in section "Ethernet Segment Identifier". This document
   does not specify the use of the Ethernet A-D route when the Segment
   Identifier is set to 0.

   The Ethernet Tag ID is the identifier of an Ethernet Tag on the
   Ethernet segment. This value may be a 12 bit VLAN ID, in which case
   the low order 12 bits are set to the VLAN ID and the high order 20
   bits are set to 0. Or it may be another Ethernet Tag used by the
   EVPN.  It MAY be set to the default Ethernet Tag on the Ethernet
   segment or to the value 0.

   Note that the above allows the Ethernet A-D route to be advertised
   with one of the following granularities:

      + One Ethernet A-D route for a given <ESI, Ethernet Tag ID> tuple
        per EVI. This is applicable when the PE uses MPLS-based
        disposition.

      + One Ethernet A-D route per <ESI, EVI> (where the Ethernet
        Tag ID is set to 0). This is applicable when the PE uses



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        MAC-based disposition, or when the PE uses MPLS-based
        disposition when no VLAN translation is required.

   The usage of the MPLS label is described in the section on "Load
   Balancing of Unicast Packets".

   The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
   be set to the IPv4 or IPv6 address of the advertising PE.

9.4.1.1 Ethernet A-D Route Targets

   The Ethernet A-D route MUST carry one or more Route Target (RT)
   attributes. RTs may be configured (as in IP VPNs), or may be derived
   automatically.

   If an PE uses Route Target Constrain [RT-CONSTRAIN], the PE SHOULD
   advertise all such RTs using Route Target Constrains. The use of RT
   Constrains allows each Ethernet A-D route to reach only those PEs
   that are configured to import at least one RT from the set of RTs
   carried in the Ethernet A-D route.

9.4.1.1.1 Auto-Derivation from the Ethernet Tag ID

   The following is the procedure for deriving the RT attribute
   automatically from the Ethernet Tag ID associated with the
   advertisement:

        +    The Global Administrator field of the RT MUST
             be set to the Autonomous System (AS) number that the PE
             belongs to.

        +    The Local Administrator field of the RT contains a 4
             octets long number that encodes the Ethernet Tag-ID. If the
             Ethernet Tag-ID is a two octet VLAN ID then it MUST be
             encoded in the lower two octets of the Local Administrator
             field and the higher two octets MUST be set to zero.

   For the "Unique VLAN EVPN" this results in auto-deriving the RT from
   the Ethernet Tag, e.g., VLAN ID for that EVPN.

9.5 Designated Forwarder Election

   Consider a CE that is a host or a router that is multi-homed directly
   to more than one PE in an EVPN instance on a given Ethernet segment.
   One or more Ethernet Tags may be configured on the Ethernet segment.
   In this scenario only one of the PEs, referred to as the Designated
   Forwarder (DF), is responsible for certain actions:




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        -   Sending multicast and broadcast traffic, on a given Ethernet
            Tag on a particular Ethernet segment, to the CE.

        -   Flooding unknown unicast traffic (i.e. traffic for
            which an PE does not know the destination MAC address),
            on a given Ethernet Tag on a particular Ethernet segment
            to the CE, if the environment requires flooding of
            unknown unicast traffic.

   Note that this behavior, which allows selecting a DF at the
   granularity of <ESI, EVI> for multicast, broadcast and unknown
   unicast traffic, is the default behavior in this specification.

   Note that a CE always sends packets belonging to a specific flow
   using a single link towards an PE. For instance, if the CE is a host
   then, as mentioned earlier, the host treats the multiple links that
   it uses to reach the PEs as a Link Aggregation Group (LAG). The CE
   employs a local hashing function to map traffic flows onto links in
   the LAG.

   If a bridged network is multi-homed to more than one PE in an EVPN
   network via switches, then the support of All-Active points of
   attachments, as described in this specification, requires the bridge
   network to be connected to two or more PEs using a LAG. In this case
   the reasons for doing DF election are the same as those described
   above when a CE is a host or a router.

   If a bridged network does not connect to the PEs using LAG, then only
   one of the links between the switched bridged network and the PEs
   must be the active link for a given Ethernet Tag. In this case, the
   Ethernet A-D route per Ethernet segment MUST be advertised with the
   "Active-Standby" flag set to one. Procedures for supporting All-
   Active points of attachments, when a bridge network connects to the
   PEs using LAG, are for further study.

   The default procedure for DF election at the granularity of <ESI,
   EVI> is referred to as "service carving". With service carving, it is
   possible to elect multiple DFs per Ethernet Segment (one per EVI) in
   order to perform load-balancing of multi-destination traffic destined
   to a given Segment. The load-balancing procedures carve up the EVI
   space among the PE nodes evenly, in such a way that every PE is the
   DF for a disjoint set of EVIs. The procedure for service carving is
   as follows:

   1. When a PE discovers the ESI of the attached Ethernet Segment, it
   advertises an Ethernet Segment route with the associated ES-Import
   extended community attribute.




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   2. The PE then starts a timer (default value = 3 seconds) to allow
   the reception of Ethernet Segment routes from other PE nodes
   connected to the same Ethernet Segment. This timer value MUST be same
   across all PEs connected to the same Ethernet Segment.

   3. When the timer expires, each PE builds an ordered list of the IP
   addresses of all the PE nodes connected to the Ethernet Segment
   (including itself), in increasing numeric value. Each IP address in
   this list is extracted from the "Originator Router's IP address"
   field of the advertised Ethernet Segment route. Every PE is then
   given an ordinal indicating its position in the ordered list,
   starting with 0 as the ordinal for the PE with the numerically lowest
   IP address. The ordinals are used to determine which PE node will be
   the DF for a given EVPN instance on the Ethernet Segment using the
   following rule: Assuming a redundancy group of N PE nodes, the PE
   with ordinal i is the DF for an EVPN instance with an associated
   Ethernet Tag value V when (V mod N) = i. In the case where multiple
   Ethernet Tags are associated with a single EVPN instance, then the
   numerically lowest Ethernet Tag value in that EVPN instance MUST be
   used in the modulo function.

   It should be noted that using "Originator Router's IP address" field
   in the Ethernet Segment route to get the PE IP address needed for the
   ordered list, allows for a CE to be multi-homed across different ASes
   if such need every arises.

   4. The PE that is elected as a DF for a given EVPN instance will
   unblock traffic for the Ethernet Tags associated with that EVPN
   instance. Note that the DF PE unblocks multi-destination traffic in
   the egress direction towards the Segment. All non-DF PEs continue to
   drop multi-destination traffic (for the associated EVPN instances) in
   the egress direction towards the Segment.

   In the case of link or port failure, the affected PE withdraws its
   Ethernet Segment route. This will re-trigger the service carving
   procedures on all the PEs in the RG. For PE node failure, or upon PE
   commissioning or decommissioning, the PEs re-trigger the service
   carving. In case of a Single-Active multi-homing, when a service
   moves from one PE in the RG to another PE as a result of re-carving,
   the PE, which ends up being the elected DF for the service, must
   trigger a MAC address flush notification towards the associated
   Ethernet Segment. This can be done, for e.g. using IEEE 802.1ak MVRP
   'new' declaration.


9.6. Interoperability with Single-homing PEs

   Let's refer to PEs that only support single-homed CE devices as



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   single-homing PEs. For single-homing PEs, all the above multi-homing
   procedures can be omitted; however, to allow for single-homing PEs to
   fully inter-operate with multi-homing PEs, some of the multi-homing
   procedures described above SHOULD be supported even by single-homing
   PEs:

   - procedures related to processing Ethernet A-D route for the purpose
   of Fast Convergence (9.2 Fast Convergence), to let single-homing PEs
   benefit from fast convergence

   - procedures related to processing Ethernet A-D route for the purpose
   of Aliasing (9.4 Aliasing and Backup-path), to let single-homing PEs
   benefit from load balancing

   - procedures related to processing Ethernet A-D route for the purpose
   of Backup-path (9.4 Aliasing and Backup-path), to let single-homing
   PEs to benefit from the corresponding convergence improvement


10. Determining Reachability to Unicast MAC Addresses

   PEs forward packets that they receive based on the destination MAC
   address. This implies that PEs must be able to learn how to reach a
   given destination unicast MAC address.

   There are two components to MAC address learning, "local learning"
   and "remote learning":

10.1. Local Learning

   A particular PE must be able to learn the MAC addresses from the CEs
   that are connected to it. This is referred to as local learning.

   The PEs in a particular EVPN instance MUST support local data plane
   learning using standard IEEE Ethernet learning procedures. An PE must
   be capable of learning MAC addresses in the data plane when it
   receives packets such as the following from the CE network:

        - DHCP requests

        - ARP request for its own MAC.

        - ARP request for a peer.

   Alternatively PEs MAY learn the MAC addresses of the CEs in the
   control plane or via management plane integration between the PEs and
   the CEs.




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   There are applications where a MAC address that is reachable via a
   given PE on a locally attached Segment (e.g. with ESI X) may move
   such that it becomes reachable via another PE on another Segment
   (e.g. with ESI Y).  This is referred to as a "MAC Mobility".
   Procedures to support this are described in section "MAC Mobility".

10.2. Remote learning

   A particular PE must be able to determine how to send traffic to MAC
   addresses that belong to or are behind CEs connected to other PEs
   i.e. to remote CEs or hosts behind remote CEs. We call such MAC
   addresses as "remote" MAC addresses.

   This document requires an PE to learn remote MAC addresses in the
   control plane. In order to achieve this, each PE advertises the MAC
   addresses it learns from its locally attached CEs in the control
   plane, to all the other PEs in that EVPN instance, using MP-BGP and
   specifically the MAC Advertisement route.

10.2.1. Constructing the BGP EVPN MAC Address Advertisement

   BGP is extended to advertise these MAC addresses using the MAC
   Advertisement route type in the EVPN NLRI.

   The RD MUST be the RD of the EVI that is advertising the NLRI. The
   procedures for setting the RD for a given EVI are described in
   section 9.4.1.

   The Ethernet Segment Identifier is set to the ten octet ESI described
   in section "Ethernet Segment".

   The Ethernet Tag ID may be zero or may represent a valid Ethernet Tag
   ID.  This field may be non-zero when there are multiple bridge
   domains in the MAC-VRF (e.g., the PE needs to perform qualified
   learning for the VLANs in that MAC-VRF).

   When the the Ethernet Tag ID in the NLRI is set to a non-zero value,
   for a particular bridge domain, then this Ethernet Tag may either be
   the Ethernet tag value associated with the CE, e.g., VLAN ID, or it
   may be the Ethernet Tag Identifier, e.g., VLAN ID assigned by the
   EVPN provider and mapped to the CE's Ethernet tag. The latter would
   be the case if the CE Ethernet tags, e.g., VLAN ID, for a particular
   bridge domain are different on different CEs.

   The MAC address length field is in bits and it is typically set to
   48. However this specification enables specifying the MAC address as
   a prefix; in which case, the MAC address length field is set to the
   length of the prefix. This provides the ability to aggregate MAC



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   addresses if the deployment environment supports that.  The encoding
   of a MAC address MUST be the 6-octet MAC address specified by
   [802.1D-ORIG] [802.1D-REV]. If the MAC address is advertised as a
   prefix then the trailing bits of the prefix MUST be set to 0 to
   ensure that the entire prefix is encoded as 6 octets.

   The IP Address field is optional. By default, the IP Address Length
   field is set to 0 and the IP address field is omitted from the route.
   When a valid IP address or address prefix needs to be advertised
   (e.g., for ARP suppression purposes or for inter-subnet switching),
   it is then encoded in this route.

   The IP Address Length field is in bits and it is the length of the IP
   prefix. This provides the ability to advertise IP address prefixes
   when the deployment environment supports that. The encoding of an IP
   address MUST be either 4 octets for IPv4 or 16 octets for IPv6. When
   the IP address is advertised as a prefix, then the trailing bits of
   the prefix MUST be set to 0 to ensure that the entire prefix is
   encoded as either 4 or 16 octets. The length field of EVPN NLRI
   (which is in octets and is described in section 8) is sufficient to
   determine whether an IP address/prefix is encoded in this route and
   if so, whether the encoded IP address/prefix is IPV4 or IPv6.

   The MPLS label field carries a single label and it is encoded as 3
   octets, where the high-order 20 bits contain the label value. The
   MPLS label  MUST be the downstream assigned that is used by the PE to
   forward MPLS-encapsulated Ethernet frames, where the destination MAC
   address in the Ethernet frame is the MAC address advertised in the
   above NLRI. The forwarding procedures are specified in section
   "Forwarding Unicast Packets" and "Load Balancing of Unicast Packets".

   An PE may advertise the same single EVPN label for all MAC addresses
   in a given EVI. This label assignment methodology is referred to as a
   per EVI label assignment. Alternatively, an PE may advertise a unique
   EVPN label per <ESI, Ethernet Tag> combination. This label assignment
   methodology is referred to as a per <ESI, Ethernet Tag> label
   assignment. As a third option, an PE may advertise a unique EVPN
   label per MAC address. All of these methodologies have their
   tradeoffs. The choice of a particular label assignment methodology is
   purely local to the PE that originates the route.

   Per EVI label assignment requires the least number of EVPN labels,
   but requires a MAC lookup in addition to an MPLS lookup on an egress
   PE for forwarding. On the other hand, a unique label per <ESI,
   Ethernet Tag> or a unique label per MAC allows an egress PE to
   forward a packet that it receives from another PE, to the connected
   CE, after looking up only the MPLS labels without having to perform a
   MAC lookup. This includes the capability to perform appropriate VLAN



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   ID translation on egress to the CE.

   The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
   be set to the IPv4 or IPv6 address of the advertising PE.

   The BGP advertisement for the MAC advertisement route MUST also carry
   one or more Route Target (RT) attributes.  RTs may be configured (as
   in IP VPNs), or may be derived automatically from the Ethernet Tag
   ID, in the Unique VLAN case, as described in section "Ethernet A-D
   Route per EVPN".

   It is to be noted that this document does not require PEs to create
   forwarding state for remote MACs when they are learnt in the control
   plane. When this forwarding state is actually created is a local
   implementation matter.

10.2.2 Route Resolution

   If the Ethernet Segment Identifier field in a received MAC
   Advertisement route is set to the reserved ESI value of 0 or MAX-ESI,
   then the receiving PE MUST install forwarding state for the
   associated MAC Address based on the MAC Advertisement route alone.

   If the Ethernet Segment Identifier field in a received MAC
   Advertisement route is set to a non-reserved ESI, and the receiving
   PE is locally attached to the same ESI, then the PE does not alter
   its forwarding state based on the received route. This ensures that
   local routes are preferred to remote routes.

   If the Ethernet Segment Identifier field in a received MAC
   Advertisement route is set to a non-reserved ESI, then the receiving
   PE MUST install forwarding state for a given MAC address only when
   both the MAC Advertisement route AND the associated Ethernet A-D
   route per ESI have been received.

   To illustrate this with an example, consider two PEs (PE1 and PE2)
   connected to a multi-homed Ethernet Segment ES1. All-Active
   redundancy mode is assumed. A given MAC address M1 is learnt by PE1
   but not PE2. On PE3, the following states may arise:

   T1- When the MAC Advertisement Route from PE1 and the Ethernet A-D
   routes per ESI from PE1 and PE2 are received, PE3 can forward traffic
   destined to M1 to both PE1 and PE2.

   T2- If after T1, PE1 withdraws its Ethernet A-D route per ESI, then
   PE3 forwards traffic destined to M1 to PE2 only.

   T3- If after T1, PE2 withdraws its Ethernet A-D route per ESI, then



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   PE3 forwards traffic destined to M1 to PE1 only.

   T4- If after T1, PE1 withdraws its MAC Advertisement route, then PE3
   treats traffic to M1 as unknown unicast. Note, here, that had PE2
   also advertised a MAC route for M1 before PE1 withdraws its MAC
   route, then PE3 would have continued forwarding traffic destined to
   M1 to PE2.

11. ARP and ND

   The IP address field in the MAC advertisement route may optionally
   carry one of the IP addresses associated with the MAC address. This
   provides an option which can be used to minimize the flooding of ARP
   or Neighbor Discovery (ND) messages over the MPLS network and to
   remote CEs. This option also minimizes ARP (or ND) message processing
   on end-stations/hosts connected to the EVPN network. An PE may learn
   the IP address associated with a MAC address in the control or
   management plane between the CE and the PE. Or, it may learn this
   binding by snooping certain messages to or from a CE. When an PE
   learns the IP address associated with a MAC address, of a locally
   connected CE, it may advertise this address to other PEs by including
   it in the MAC Advertisement route. The IP Address may be an IPv4
   address encoded using four octets, or an IPv6 address encoded using
   sixteen octets. The IP Address length field MUST be set to 32 for an
   IPv4 address or to 128 for an IPv6 address.

   If there are multiple IP addresses associated with a MAC address,
   then multiple MAC advertisement routes MUST be generated, one for
   each IP address. For instance, this may be the case when there are
   both an IPv4 and an IPv6 address associated with the MAC address.
   When the IP address is dissociated with the MAC address, then the MAC
   advertisement route with that particular IP address MUST be
   withdrawn.

   When an PE receives an ARP request for an IP address from a CE, and
   if the PE has the MAC address binding for that IP address, the PE
   SHOULD perform ARP proxy by responding to the ARP request.

11.1 Default Gateway

   When a PE needs to perform inter-subnet forwarding where each subnet
   is represented by a different broadcast domain (e.g., different VLAN)
   the inter-subnet forwarding is performed at layer 3 and the PE that
   performs such function is called the default gateway. In this case
   when the PE receives an ARP Request for the IP address of the default
   gateway, the PE originates an ARP Reply.

   Each PE that acts as a default gateway for a given EVPN instance MAY



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   advertise in the EVPN control plane its default gateway MAC address
   using the MAC advertisement route, and indicates that such route is
   associated with the default gateway.  This is accomplished by
   requiring the route to carry the Default Gateway extended community
   defined in [Section 8.8 Default Gateway Extended Community]. The IP
   address field (4 octets for IPv4, 16 octets for IPv6) is set to zero
   when advertising the MAC route with the Default Gateway extended
   community. Both ESI and Ethernet Tag fields are also set to zero for
   this advertisement.

   Unless it is known a priori (by means outside of this document) that
   all PEs of a given EVPN instance act as a default gateway for that
   EVPN instance, the MPLS label MUST be set to a valid downstream
   assigned label.

   Furthermore, even if all PEs of a given EVPN instance do act as a
   default gateway for that EVPN instance, but only some, but not all,
   of these PEs have sufficient (routing) information to provide inter-
   subnet routing for all the inter-subnet traffic originated within the
   subnet associated with the EVPN instance, then when such PE
   advertises in the EVPN control plane its default gateway MAC address
   using the MAC advertisement route, and indicates that such route is
   associated with the default gateway, the route MUST carry a valid
   downstream assigned label.

   If all PEs of a given EVPN instance act as a default gateway for that
   EVPN instance, and the same default gateway MAC address is used
   across all gateway devices, then no such advertisement is needed.
   However, if each default gateway uses a different MAC address, then
   each default gateway needs to be aware of other gateways' MAC
   addresses and thus the need for such advertisement. This is called
   MAC address aliasing since a single default GW can be represented by
   multiple MAC addresses.

   Each PE that receives this route and imports it as per procedures
   specified in this document follows the procedures in this section
   when replying to ARP Requests that it receives if such Requests are
   for the IP address in the received EVPN route.

   Each PE that acts as a default gateway for a given EVPN instance that
   receives this route and imports it as per procedures specified in
   this document MUST create MAC forwarding state that enables it to
   apply IP forwarding to the packets destined to the MAC address
   carried in the route.


12. Handling of Multi-Destination Traffic




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   Procedures are required for a given PE to send broadcast or multicast
   traffic, received from a CE encapsulated in a given Ethernet Tag
   (VLAN) in an EVPN instance, to all the other PEs that span that
   Ethernet Tag (VLAN) in that EVPN instance. In certain scenarios,
   described in section "Processing of Unknown Unicast Packets", a given
   PE may also need to flood unknown unicast traffic to other PEs.

   The PEs in a particular EVPN instance may use ingress replication,
   P2MP LSPs or MP2MP LSPs to send unknown unicast, broadcast or
   multicast traffic to other PEs.

   Each PE MUST advertise an "Inclusive Multicast Ethernet Tag Route" to
   enable the above. The following subsection provides the procedures to
   construct the Inclusive Multicast Ethernet Tag route. Subsequent
   subsections describe in further detail its usage.

12.1. Construction of the Inclusive Multicast Ethernet Tag Route

   The RD MUST be the RD of the EVI that is advertising the NLRI. The
   procedures for setting the RD for a given EVPN instance on a PE are
   described in section 9.4.1.

   The Ethernet Tag ID is the identifier of the Ethernet Tag. It MAY be
   set to 0 or to a valid Ethernet Tag value.

   The Originating Router's IP address MUST be set to an IP address of
   the PE.  This address SHOULD be common for all the EVIs on the PE
   (e.,g., this address may be PE's loopback address). The IP Address
   Length field is in bits.

   The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
   be set to the same IP address as the one carried in the Originating
   Router's IP Address field.

   The BGP advertisement for the Inclusive Multicast Ethernet Tag route
   MUST also carry one or more Route Target (RT) attributes. The
   assignment of RTs described in the section on "Constructing the BGP
   EVPN MAC Address Advertisement" MUST be followed.

12.2. P-Tunnel Identification

   In order to identify the P-Tunnel used for sending broadcast, unknown
   unicast or multicast traffic, the Inclusive Multicast Ethernet Tag
   route MUST carry a "PMSI Tunnel Attribute" as specified in [BGP
   MVPN].

   Depending on the technology used for the P-tunnel for the EVPN
   instance on the PE, the PMSI Tunnel attribute of the Inclusive



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   Multicast Ethernet Tag route is constructed as follows.

        + If the PE that originates the advertisement uses a
          P-Multicast tree for the P-tunnel for EVPN, the PMSI
          Tunnel attribute MUST contain the identity of the tree
          (note that the PE could create the identity of the
          tree prior to the actual instantiation of the tree).

        + An PE that uses a P-Multicast tree for the P-tunnel MAY
          aggregate two or more Ethernet Tags in the same or different
          EVIs present on the PE onto the same tree. In this case, in
          addition to carrying the identity of the tree, the PMSI Tunnel
          attribute MUST carry an MPLS upstream assigned label which
          the PE has bound uniquely to the Ethernet Tag for the EVI
          associated with this update (as determined by its RTs).

          If the PE has already advertised Inclusive Multicast
          Ethernet Tag routes for two or more Ethernet Tags that it
          now desires to aggregate, then the PE MUST re-advertise
          those routes. The re-advertised routes MUST be the same
          as the original ones, except for the PMSI Tunnel attribute
          and the label carried in that attribute.

        + If the PE that originates the advertisement uses ingress
          replication for the P-tunnel for EVPN, the route MUST
          include the PMSI Tunnel attribute with the Tunnel Type set to
          Ingress Replication and Tunnel Identifier set to a routable
          address of the PE. The PMSI Tunnel attribute MUST carry a
          downstream assigned MPLS label. This label is used to
          demultiplex the broadcast, multicast or unknown unicast EVPN
          traffic received over a MP2P tunnel by the PE.

        + The Leaf Information Required flag of the PMSI Tunnel
          attribute MUST be set to zero, and MUST be ignored on receipt.

13. Processing of Unknown Unicast Packets

   The procedures in this document do not require the PEs to flood
   unknown unicast traffic to other PEs. If PEs learn CE MAC addresses
   via a control plane protocol, the PEs can then distribute MAC
   addresses via BGP, and all unicast MAC addresses will be learnt prior
   to traffic to those destinations.

   However, if a destination MAC address of a received packet is not
   known by the PE, the PE may have to flood the packet. When flooding,
   one must take into account "split horizon forwarding" as follows: The
   principles behind the following procedures are borrowed from the
   split horizon forwarding rules in VPLS solutions [RFC4761] and



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   [RFC4762].  When an PE capable of flooding (say PEx) receives an
   unknown destination MAC address, it floods the frame.  If the frame
   arrived from an attached CE, PEx must send a copy of the frame to
   every other attached CE participating in that EVPN instance, on a
   different ESI than the one it received the frame on, as long as the
   PE is the DF for the egress ESI. In addition, the PE must flood the
   frame to all other PEs participating in that EVPN instance. If, on
   the other hand, the frame arrived from another PE (say PEy), PEx must
   send a copy of the packet only to attached CEs as long as it is the
   DF for the egress ESI. PEx MUST NOT send the frame to other PEs,
   since PEy would have already done so. Split horizon forwarding rules
   apply to unknown MAC addresses.

   Whether or not to flood packets to unknown destination MAC addresses
   should be an administrative choice, depending on how learning happens
   between CEs and PEs.

   The PEs in a particular EVPN instance may use ingress replication
   using RSVP-TE P2P LSPs or LDP MP2P LSPs for sending unknown unicast
   traffic to other PEs. Or they may use RSVP-TE P2MP or LDP P2MP for
   sending such traffic to other PEs.

13.1. Ingress Replication

   If ingress replication is in use, the P-Tunnel attribute, carried in
   the Inclusive Multicast Ethernet Tag routes for the EVPN instance,
   specifies the downstream label that the other PEs can use to send
   unknown unicast, multicast or broadcast traffic for that EVPN
   instance to this particular PE.

   The PE that receives a packet with this particular MPLS label MUST
   treat the packet as a broadcast, multicast or unknown unicast packet.
   Further if the MAC address is a unicast MAC address, the PE MUST
   treat the packet as an unknown unicast packet.

13.2. P2MP MPLS LSPs

   The procedures for using P2MP LSPs are very similar to VPLS
   procedures [VPLS-MCAST]. The P-Tunnel attribute used by an PE for
   sending unknown unicast, broadcast or multicast traffic for a
   particular EVPN instance is advertised in the Inclusive Ethernet Tag
   Multicast route as described in section "Handling of Multi-
   Destination Traffic".

   The P-Tunnel attribute specifies the P2MP LSP identifier. This is the
   equivalent of an Inclusive tree in [VPLS-MCAST]. Note that multiple
   Ethernet Tags, which may be in different EVPN instances, may use the
   same P2MP LSP, using upstream labels [VPLS-MCAST]. This is the



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   equivalent of an Aggregate Inclusive tree in [VPLS-MCAST]. When P2MP
   LSPs are used for flooding unknown unicast traffic, packet re-
   ordering is possible.

   The PE that receives a packet on the P2MP LSP specified in the PMSI
   Tunnel Attribute MUST treat the packet as a broadcast, multicast or
   unknown unicast packet. Further if the MAC address is a unicast MAC
   address, the PE MUST treat the packet as an unknown unicast packet.

14. Forwarding Unicast Packets

   This section describes procedures for forwarding unicast packets by
   PEs, where such packets are received from either directly connected
   CEs, or from some other PEs.

14.1. Forwarding packets received from a CE

   When an PE receives a packet from a CE, on a given Ethernet Tag, it
   must first look up the source MAC address of the packet. In certain
   environments the source MAC address MAY be used to authenticate the
   CE and determine that traffic from the host can be allowed into the
   network. Source MAC lookup MAY also be used for local MAC address
   learning.

   If the PE decides to forward the packet, the destination MAC address
   of the packet must be looked up. If the PE has received MAC address
   advertisements for this destination MAC address from one or more
   other PEs or learned it from locally connected CEs, it is considered
   as a known MAC address. Otherwise, the MAC address is considered as
   an unknown MAC address.

   For known MAC addresses the PE forwards this packet to one of the
   remote PEs or to a locally attached CE. When forwarding to a remote
   PE, the packet is encapsulated in the EVPN MPLS label advertised by
   the remote PE, for that MAC address, and in the MPLS LSP label stack
   to reach the remote PE.

   If the MAC address is unknown and if the administrative policy on the
   PE requires flooding of unknown unicast traffic then:

   - The PE MUST flood the packet to other PEs. The PE MUST first
   encapsulate the packet in the ESI MPLS label as described in section
   9.3. If ingress replication is used, the packet MUST be replicated
   one or more times to each remote PE with the outermost label being an
   MPLS label determined as follows: This is the MPLS label advertised
   by the remote PE in a PMSI Tunnel Attribute in the Inclusive
   Multicast Ethernet Tag route for an <EVPN instance, Ethernet Tag>
   combination. The Ethernet Tag in the route must be the same as the



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   Ethernet Tag associated with the interface on which the ingress PE
   receives the packet. If P2MP LSPs are being used the packet MUST be
   sent on the P2MP LSP that the PE is the root of for the Ethernet Tag
   in the EVPN instance. If the same P2MP LSP is used for all Ethernet
   Tags, then all the PEs in the EVPN instance MUST be the leaves of the
   P2MP LSP. If a distinct P2MP LSP is used for a given Ethernet Tag in
   the EVPN instance, then only the PEs in the Ethernet Tag MUST be the
   leaves of the P2MP LSP. The packet MUST be encapsulated in the P2MP
   LSP label stack.

   If the MAC address is unknown then, if the administrative policy on
   the PE does not allow flooding of unknown unicast traffic:

   - The PE MUST drop the packet.

14.2. Forwarding packets received from a remote PE

   This section described the procedures for forwarding known and
   unknown unicast packets received from a remote PE.

14.2.1. Unknown Unicast Forwarding

   When an PE receives an MPLS packet from a remote PE then, after
   processing the MPLS label stack, if the top MPLS label ends up being
   a P2MP LSP label associated with an EVPN instance or in case of
   ingress replication the downstream label advertised in the P-Tunnel
   attribute, and after performing the split horizon procedures
   described in section "Split Horizon":

   - If the PE is the designated forwarder of BUM traffic on a
   particular set of ESIs for the Ethernet Tag, the default behavior is
   for the PE to flood the packet on these ESIs. In other words, the
   default behavior is for the PE to assume that for BUM traffic, it is
   not required to perform a destination MAC address lookup. As an
   option, the PE may perform a destination MAC lookup to flood the
   packet to only a subset of the CE interfaces in the Ethernet Tag. For
   instance the PE may decide to not flood an BUM packet on certain
   Ethernet segments even if it is the DF on the Ethernet segment, based
   on administrative policy.

   - If the PE is not the designated forwarder on any of the ESIs for
   the Ethernet Tag, the default behavior is for it to drop the packet.

14.2.2. Known Unicast Forwarding

   If the top MPLS label ends up being an EVPN label that was advertised
   in the unicast MAC advertisements, then the PE either forwards the
   packet based on CE next-hop forwarding information associated with



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   the label or does a destination MAC address lookup to forward the
   packet to a CE.

15. Load Balancing of Unicast Frames

   This section specifies the load balancing procedures for sending
   known unicast frames to a multi-homed CE.

15.1. Load balancing of traffic from an PE to remote CEs

   Whenever a remote PE imports a MAC advertisement for a given <ESI,
   Ethernet Tag> in an EVI, it MUST examine all imported Ethernet A-D
   routes for that ESI in order to determine the load-balancing
   characteristics of the Ethernet segment.

15.1.1 Single-Active Redundancy Mode

   For a given ESI, if the remote PE has imported an Ethernet A-D route
   per Ethernet Segment from at least one PE, where the "Active-Standby"
   flag in the ESI Label Extended Community is set, then the remote PE
   MUST deduce that the Ethernet segment is operating in Single-Active
   redundancy mode. As such, the MAC address will be reachable only via
   the PE announcing the associated MAC Advertisement route - this is
   referred to as the primary PE. The set of other PE nodes advertising
   Ethernet A-D routes per Ethernet Segment for the same ESI serve as
   backup paths, in case the active PE encounters a failure. These are
   referred to as the backup PEs. It should be noted that the primary PE
   for a given <ESI, EVI> is the DF for that <ESI, EVI>.

   If the primary PE encounters a failure, it MAY withdraw its Ethernet
   A-D route for the affected segment prior to withdrawing the entire
   set of MAC Advertisement routes.

   In the case where only a single other backup PE in the network had
   advertised an Ethernet A-D route for the same ESI, the remote PE can
   then use the Ethernet A-D route withdrawal as a trigger to update its
   forwarding entries, for the associated MAC addresses, to point
   towards the backup PE. As the backup PE starts learning the MAC
   addresses over its attached Ethernet segment, it will start sending
   MAC Advertisement routes while the failed PE withdraws its own. This
   mechanism minimizes the flooding of traffic during fail-over events.

   In the case where multiple other backup PE in the network had
   advertised an Ethernet A-D route for the same ESI, the remote PE MUST
   then use the Ethernet A-D route withdrawal as a trigger to start
   flooding traffic destined to the associated MAC addresses (as long as
   flooding of unknown unicast is administratively allowed). It is not
   possible to select a single backup path in this case.



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15.1.2 All-Active Redundancy Mode

   If for the given ESI, none of the  Ethernet A-D routes per Ethernet
   Segment imported by the remote PE have the "Active-Standby" flag set
   in the ESI Label Extended Community, then the remote PE MUST treat
   the Ethernet segment as operating in All-Active redundancy mode. The
   remote PE would then treat the MAC address as reachable via all of
   the PE nodes from which it has received both an Ethernet A-D route
   per Ethernet Segment as well as an Ethernet A-D route per EVI for the
   ESI in question. The remote PE MUST use the MAC advertisement and
   eligible Ethernet A-D routes to construct the set of next-hops that
   it can use to send the packet to the destination MAC. Each next-hop
   comprises an MPLS label stack that is to be used by the egress PE to
   forward the packet. This label stack is determined as follows:

   -If the next-hop is constructed as a result of a MAC route then this
   label stack MUST be used. However, if the MAC route doesn't exist,
   then the next-hop and MPLS label stack is constructed as a result of
   the Ethernet A-D routes. Note that the following description applies
   to determining the label stack for a particular next-hop to reach a
   given PE, from which the remote PE has received and imported Ethernet
   A-D routes that have the matching ESI and Ethernet Tag as the one
   present in the MAC advertisement. The Ethernet A-D routes mentioned
   in the following description refer to the ones imported from this
   given PE.

   -If an Ethernet A-D route per Ethernet Segment for that ESI exists,
   together with an Ethernet A-D route per EVI, then the label from that
   latter route must be used.

   The following example explains the above.

   Consider a CE (CE1) that is dual-homed to two PEs (PE1 and PE2) on a
   LAG interface (ES1), and is sending packets with MAC address MAC1 on
   VLAN1. A remote PE, say PE3, is able to learn that MAC1 is reachable
   via PE1 and PE2. Both PE1 and PE2 may advertise MAC1 in BGP if they
   receive packets with MAC1 from CE1. If this is not the case, and if
   MAC1 is advertised only by PE1, PE3 still considers MAC1 as reachable
   via both PE1 and PE2 as both PE1 and PE2 advertise a Ethernet A-D
   route per ESI for ES1 as well as an Ethernet A-D route per EVI for
   <ES1, VLAN1>.

   The MPLS label stack to send the packets to PE1 is the MPLS LSP stack
   to get to PE1 and the EVPN label advertised by PE1 for CE1's MAC.

   The MPLS label stack to send packets to PE2 is the MPLS LSP stack to
   get to PE2 and the MPLS label in the Ethernet A-D route advertised by
   PE2 for <ES1, VLAN1>, if PE2 has not advertised MAC1 in BGP.



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   We will refer to these label stacks as MPLS next-hops.

   The remote PE (PE3) can now load balance the traffic it receives from
   its CEs, destined for CE1, between PE1 and PE2.  PE3 may use N-Tuple
   flow information to hash traffic into one of the MPLS next-hops for
   load balancing of IP traffic. Alternatively PE3 may rely on the
   source MAC addresses for load balancing.

   Note that once PE3 decides to send a particular packet to PE1 or PE2
   it can pick one out of multiple possible paths to reach the
   particular remote PE using regular MPLS procedures. For instance, if
   the tunneling technology is based on RSVP-TE LSPs, and PE3 decides to
   send a particular packet to PE1, then PE3 can choose from multiple
   RSVP-TE LSPs that have PE1 as their destination.

   When PE1 or PE2 receive the packet destined for CE1 from PE3, if the
   packet is a unicast MAC packet it is forwarded to CE1.  If it is a
   multicast or broadcast MAC packet then only one of PE1 or PE2 must
   forward the packet to the CE. Which of PE1 or PE2 forward this packet
   to the CE is determined based on which of the two is the DF.

   If the connectivity between the multi-homed CE and one of the PEs
   that it is attached to fails, the PE MUST withdraw the Ethernet Tag
   A-D routes, that had been previously advertised, for the Ethernet
   Segment to the CE. When the MAC entry on the PE ages out, the PE MUST
   withdraw the MAC address from BGP. Note that to aid convergence, the
   Ethernet Tag A-D routes MAY be withdrawn before the MAC routes. This
   enables the remote PEs to remove the MPLS next-hop to this particular
   PE from the set of MPLS next-hops that can be used to forward traffic
   to the CE. For further details and procedures on withdrawal of EVPN
   route types in the event of PE to CE failures please section "PE to
   CE Network  Failures".

15.2. Load balancing of traffic between an PE and a local CE

   A CE may be configured with more than one interface connected to
   different PEs or the same PE for load balancing, using a technology
   such as LAG. The PE(s) and the CE can load balance traffic onto these
   interfaces using one of the following mechanisms.

15.2.1. Data plane learning

   Consider that the PEs perform data plane learning for local MAC
   addresses learned from local CEs. This enables the PE(s) to learn a
   particular MAC address and associate it with one or more interfaces,
   if the technology between the PE and the CE supports multi-pathing.
   The PEs can now load balance traffic destined to that MAC address on
   the multiple interfaces.



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   Whether the CE can load balance traffic that it generates on the
   multiple interfaces is dependent on the CE implementation.

15.2.2. Control plane learning

   The CE can be a host that advertises the same MAC address using a
   control protocol on both interfaces. This enables the PE(s) to learn
   the host's MAC address and associate it with one or more interfaces.
   The PEs can now load balance traffic destined to the host on the
   multiple interfaces. The host can also load balance the traffic it
   generates onto these interfaces and the PE that receives the traffic
   employs EVPN forwarding procedures to forward the traffic.

16. MAC Mobility

   It is possible for a given host or end-station (as defined by its MAC
   address) to move from one Ethernet segment to another;  this is
   referred to as 'MAC Mobility' or 'MAC move' and it is different from
   the multi-homing situation in which a given MAC address is reachable
   via multiple PEs for the same Ethernet segment.  In a MAC move, there
   would be two sets of MAC Advertisement routes, one set with the new
   Ethernet segment and one set with the previous Ethernet segment, and
   the MAC address would appear to be reachable via each of these
   segments.

   In order to allow all of the PEs in the EVPN instance to correctly
   determine the current location of the MAC address, all advertisements
   of it being reachable via the previous Ethernet segment MUST be
   withdrawn by the PEs, for the previous Ethernet segment, that had
   advertised it.

   If local learning is performed using the data plane, these PEs will
   not be able to detect that the MAC address has moved to another
   Ethernet segment and the receipt of MAC Advertisement routes, with
   the MAC Mobility extended community attribute, from other PEs serves
   as the trigger for these PEs to withdraw their advertisements.  If
   local learning is performed using the control or management planes,
   these interactions serve as the trigger for these PEs to withdraw
   their advertisements.

   In a situation where there are multiple moves of a given MAC,
   possibly between the same two Ethernet segments, there may be
   multiple withdrawals and re-advertisements.  In order to ensure that
   all PEs in the EVPN instance receive all of these correctly through
   the intervening BGP infrastructure, it is necessary to introduce a
   sequence number into the MAC Mobility extended community attribute.

   An implementation MUST handle the scenarios where the sequence number



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   wraps around to process mobility event correctly.

   Every MAC mobility event for a given MAC address will contain a
   sequence number that is set using the following rules:

   - A PE advertising a MAC address for the first time advertises it
   with no MAC Mobility extended community attribute.

   - A PE detecting a locally attached MAC address for which it had
   previously received a MAC Advertisement route with a different
   Ethernet segment identifier advertises the MAC address in a MAC
   Advertisement route tagged with a MAC Mobility extended community
   attribute with a sequence number one greater than the sequence number
   in the MAC mobility attribute of the received MAC Advertisement
   route. In the case of the first mobility event for a given MAC
   address, where the received MAC Advertisement route does not carry a
   MAC Mobility attribute, the value of the sequence number in the
   received route is assumed to be 0 for purpose of this processing.

   - A PE detecting a locally attached MAC address for which it had
   previously received a MAC Advertisement route with the same non-zero
   Ethernet segment identifier advertises it with:
      i.  no MAC Mobility extended community attribute, if the received
      route did not carry said attribute.

      ii. a MAC Mobility extended community attribute with the sequence
      number equal to the highest of the sequence number(s) in the
      received MAC Advertisement route(s), if the received route(s) is
      (are) tagged with a MAC Mobility extended community attribute.

   - A PE detecting a locally attached MAC address for which it had
   previously received a MAC Advertisement route with the same zero
   Ethernet segment identifier (single-homed scenarios) advertises it
   with MAC mobility extended community attribute with the sequence
   number set properly. In case of single-homed scenarios, there is no
   need for ESI comparison. The reason ESI comparison is done for multi-
   homing, is to prevent false detection of MAC move among the PEs
   attached to the same multi-homed site.

   A PE receiving a MAC Advertisement route for a MAC address with a
   different Ethernet segment identifier and a higher sequence number
   than that which it had previously advertised, withdraws its MAC
   Advertisement route. If two (or more) PEs advertise the same MAC
   address with same sequence number but different Ethernet segment
   identifiers, a PE that receives these routes selects the route
   advertised by the PE with lowest IP address as the best route.





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16.1. MAC Duplication Issue

   A situation may arise where the same MAC address is learned by
   different PEs in the same VLAN because of two (or more hosts) being
   mis-configured with the same (duplicate) MAC address. In such
   situation, the traffic originating from these hosts would trigger
   continuous MAC moves among the PEs attached to these hosts. It is
   important to recognize such situation and avoid incrementing the
   sequence number (in the MAC Mobility attribute) to infinity. In order
   to remedy such situation, a PE that detects a MAC mobility event by
   way of local learning starts an M-second timer (default value of M =
   5) and if it detects N MAC moves before the timer expires (default
   value for N = 3), it concludes that a duplicate MAC situation has
   occurred. The PE MUST alert the operator and stop sending and
   processing any BGP MAC Advertisement routes for that MAC address till
   a corrective action is taken by the operator. The values of M and N
   MUST be configurable to allow for flexibility in operator control.
   Note that the other PEs in the E-VPN instance will forward the
   traffic for the duplicate MAC address to one of the PEs advertising
   the duplicate MAC address.


16.2. Sticky MAC addresses

   There are scenarios in which it is desired to configure some MAC
   addresses as static so that they are not subjected to MAC move. In
   such scenarios, these MAC addresses are advertised with MAC Mobility
   Extended Community where static flag is set to 1 and sequence number
   is set to zero. If a PE receives such advertisements and later learns
   the same MAC address(es) via local learning, then the PE MUST alert
   the operator.


17. Multicast & Broadcast

   The PEs in a particular EVPN instance may use ingress replication or
   P2MP LSPs to send multicast traffic to other PEs.

17.1. Ingress Replication

   The PEs may use ingress replication for flooding BUM traffic as
   described in section "Handling of Multi-Destination Traffic". A given
   broadcast packet must be sent to all the remote PEs. However a given
   multicast packet for a multicast flow may be sent to only a subset of
   the PEs. Specifically a given multicast flow may be sent to only
   those PEs that have receivers that are interested in the multicast
   flow. Determining which of the PEs have receivers for a given
   multicast flow is done using explicit tracking described below.



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17.2. P2MP LSPs

   An PE may use an "Inclusive" tree for sending an BUM packet. This
   terminology is borrowed from [VPLS-MCAST].

   A variety of transport technologies may be used in the SP network.
   For inclusive P-Multicast trees, these transport technologies include
   point-to-multipoint LSPs created by RSVP-TE or mLDP.

17.2.1. Inclusive Trees

   An Inclusive Tree allows the use of a single multicast distribution
   tree, referred to as an Inclusive P-Multicast tree, in the SP network
   to carry all the multicast traffic from a specified set of EVPN
   instances on a given PE. A particular P-Multicast tree can be set up
   to carry the traffic originated by sites belonging to a single EVPN
   instance, or to carry the traffic originated by sites belonging to
   different EVPN instances. The ability to carry the traffic of more
   than one EVPN instance on the same tree is termed 'Aggregation'. The
   tree needs to include every PE that is a member of any of the EVPN
   instances that are using the tree. This implies that an PE may
   receive multicast traffic for a multicast stream even if it doesn't
   have any receivers that are interested in receiving traffic for that
   stream.

   An Inclusive P-Multicast tree as defined in this document is a P2MP
   tree.  A P2MP tree is used to carry traffic only for EVPN CEs that
   are connected to the PE that is the root of the tree.

   The procedures for signaling an Inclusive Tree are the same as those
   in [VPLS-MCAST] with the VPLS-AD route replaced with the Inclusive
   Multicast Ethernet Tag route. The P-Tunnel attribute [VPLS-MCAST] for
   an Inclusive tree is advertised in the Inclusive Multicast route as
   described in section "Handling of Multi-Destination Traffic". Note
   that an PE can "aggregate" multiple inclusive trees for different
   EVPN instances on the same P2MP LSP using upstream labels. The
   procedures for aggregation are the same as those described in [VPLS-
   MCAST], with VPLS A-D routes replaced by EVPN Inclusive Multicast
   routes.


18. Convergence

   This section describes failure recovery from different types of
   network failures.

18.1. Transit Link and Node Failures between PEs




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   The use of existing MPLS Fast-Reroute mechanisms can provide failure
   recovery in the order of 50ms, in the event of transit link and node
   failures in the infrastructure that connects the PEs.

18.2. PE Failures

   Consider a host host1 that is dual homed to PE1 and PE2. If PE1
   fails, a remote PE, PE3, can discover this based on the failure of
   the BGP session.  This failure detection can be in the sub-second
   range if BFD is used to detect BGP session failure. PE3 can update
   its forwarding state to start sending all traffic for host1 to only
   PE2. It is to be noted that this failure recovery is potentially
   faster than what would be possible if data plane learning were to be
   used. As in that case PE3 would have to rely on re-learning of MAC
   addresses via PE2.

18.2. PE to CE Network Failures

   When an Ethernet segment connected to an PE fails or when a Ethernet
   Tag is decommissioned on an Ethernet segment, then the PE MUST
   withdraw the Ethernet A-D route(s) announced for the <ESI, Ethernet
   Tags> that are impacted by the failure or decommissioning. In
   addition, the PE MUST also withdraw the MAC advertisement routes that
   are impacted by the failure or decommissioning.

   The Ethernet A-D routes should be used by an implementation to
   optimize the withdrawal of MAC advertisement routes. When an PE
   receives a withdrawal of a particular Ethernet A-D route from an PE
   it SHOULD consider all the MAC advertisement routes, that are learned
   from the same <ESI, Ethernet Tag> as in the Ethernet A-D route, from
   the advertising PE, as having been withdrawn. This optimizes the
   network convergence times in the event of PE to CE failures.


19. Frame Ordering

   In a MAC address, bit-1 of the most significant byte is used for
   unicast/multicast indication and bit-2 is used for globally unique
   versus locally administered MAC address. If the value of the 2nd
   nibble (bits 4 thorough 8) of the most significant byte of the
   destination MAC address (which follows the last MPLS label) happens
   to be 0x4 or 0x6, then the Ethernet frame can be misinterpreted as an
   IPv4 or IPv6 packet by intermediate P nodes performing ECMP resulting
   in load balancing packets belonging to the same flow on different
   ECMP paths, thus subjecting them to different delays. Therefore,
   packets belonging to the same flow can arrive at the destination out
   of order. This out of order delivery can happen during steady state
   in absence of any failures resulting in significant impact to the



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   network operation.

   In order to avoid any such mis-ordering, the usage of control word
   SHALL adhere to the following rules:

   - A PE MUST use the control world when sending EVPN encapsulated
   packets over a MP2P or a P2P LSP

   - A PE MUST NOT use the control world when sending EVPN encapsulated
   packets over a P2MP LSP


   The control word is defined as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0 0 0|   Reserved            |       Sequence Number         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   In the above diagram the first 4 bits MUST be set to 0.  The rest of
   the first 16 bits are reserved for future use. They MUST be set to 0
   when transmitting, and MUST be ignored upon receipt. The next 16 bits
   provide a sequence number that MUST also be set to zero by default.


20. Acknowledgements

   Special thanks to Yakov Rekhter for reviewing this draft several
   times and providing valuable comments and for his very engaging
   discussions on several topics of this draft that helped shape this
   document. We would also like to thank Pedro Marques, Kaushik Ghosh,
   Nischal Sheth, Robert Raszuk, Amit Shukla and Nadeem Mohammed for
   discussions that helped shape this document. We would also like to
   thank Han Nguyen for his comments and support of this work. We would
   also like to thank Steve Kensil and Reshad Rahman for their reviews.
   Last but not least, many thanks to Jakob Heitz for his help to
   improve several sections of this draft.

21.  Security Considerations



22.  IANA Considerations






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23. References

23.1 Normative References

   [RFC4364] "BGP/MPLS IP VPNs", Rosen, Rekhter, et. al., February 2006

   [RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
              (VPLS) Using BGP for Auto-Discovery and Signaling", RFC
              4761, January 2007.

   [RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
              (VPLS) Using Label Distribution Protocol (LDP) Signaling",
              RFC 4762, January 2007.

   [RFC4271] Y. Rekhter et. al., "A Border Gateway Protocol 4 (BGP-4)",
              RFC 4271, January 2006

   [RFC4760] T. Bates et. al., "Multiprotocol Extensions for BGP-4", RFC
              4760, January 2007


23.2 Informative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [EVPN-REQ] A. Sajassi, R. Aggarwal et. al., "Requirements for
              Ethernet VPN", draft-ietf-l2vpn-evpn-req-04.txt, July
              2013.

   [VPLS-MCAST] "Multicast in VPLS". R. Aggarwal et.al., draft-ietf-
              l2vpn-vpls-mcast-14.txt, July 2013.

   [RT-CONSTRAIN] P. Marques et. al., "Constrained Route Distribution
              for Border Gateway Protocol/MultiProtocol Label Switching
              (BGP/MPLS) Internet Protocol (IP) Virtual Private Networks
              (VPNs)", RFC 4684, November 2006

24. Author's Address

      Ali Sajassi
      Cisco
      Email: sajassi@cisco.com


      Rahul Aggarwal
      Email: raggarwa_1@yahoo.com




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      Wim Henderickx
      Alcatel-Lucent
      e-mail: wim.henderickx@alcatel-lucent.com


      Aldrin Isaac
      Bloomberg
      Email: aisaac71@bloomberg.net


      James Uttaro
      AT&T
      200 S. Laurel Avenue
      Middletown, NJ  07748
      USA
      Email: uttaro@att.com


      Nabil Bitar
      Verizon Communications
      Email : nabil.n.bitar@verizon.com


      Ravi Shekhar
      Juniper Networks
      1194 N. Mathilda Ave.
      Sunnyvale, CA  94089 US
      Email: rshekhar@juniper.net


      Florin Balus
      Alcatel-Lucent
      e-mail: Florin.Balus@alcatel-lucent.com


      Keyur Patel
      Cisco
      170 West Tasman Drive
      San Jose, CA  95134, US
      Email: keyupate@cisco.com


      Sami Boutros
      Cisco
      170 West Tasman Drive
      San Jose, CA  95134, US
      Email: sboutros@cisco.com




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      Samer Salam
      Cisco
      Email: ssalam@cisco.com


      John Drake
      Juniper Networks
      Email: jdrake@juniper.net











































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