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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 14, 2012                                  July 14, 2012


                      BGP MPLS Based Ethernet VPN
                        draft-ietf-l2vpn-evpn-01

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) 2012 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
   (E-VPN).

Table of Contents

   1. Specification of requirements . . . . . . . . . . . . . . . . .  5
   2. Contributors  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5. BGP MPLS Based E-VPN Overview . . . . . . . . . . . . . . . . .  6
   6. Ethernet Segment  . . . . . . . . . . . . . . . . . . . . . . .  7
   7. Ethernet Tag  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     7.1 VLAN Based Service Interface . . . . . . . . . . . . . . . .  9
     7.2 VLAN Bundle Service Interface  . . . . . . . . . . . . . . .  9
       7.2.1 Port Based Service Interface . . . . . . . . . . . . . .  9
     7.3 VLAN Aware Bundle Service Interface  . . . . . . . . . . . .  9
   8. BGP E-VPN NLRI  . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1. Ethernet Auto-Discovery Route . . . . . . . . . . . . . . . 10
     8.2.  MAC Advertisement Route  . . . . . . . . . . . . . . . . . 11
     8.3. Inclusive Multicast Ethernet Tag Route  . . . . . . . . . . 11
     8.4 Ethernet Segment Route . . . . . . . . . . . . . . . . . . . 12
     8.5 ESI MPLS Label Extended Community  . . . . . . . . . . . . . 12
     8.6 ES-Import Extended Community . . . . . . . . . . . . . . . . 13
     8.7 MAC Mobility Extended Community  . . . . . . . . . . . . . . 13
   9. Multi-homing Functions  . . . . . . . . . . . . . . . . . . . . 13
     9.1 Multi-homed Ethernet Segment Auto-Discovery  . . . . . . . . 13
       9.1.1 Constructing the Ethernet Segment Route  . . . . . . . . 14
     9.2 Fast Convergence . . . . . . . . . . . . . . . . . . . . . . 14
       9.2.1 Constructing the Ethernet A-D Route per Ethernet
             Segment  . . . . . . . . . . . . . . . . . . . . . . . . 15
         9.2.1.1. Ethernet A-D Route Targets  . . . . . . . . . . . . 15
     9.3 Split Horizon  . . . . . . . . . . . . . . . . . . . . . . . 16
       9.3.1 ESI MPLS Label Assignment  . . . . . . . . . . . . . . . 16
         9.3.1.1 Ingress Replication  . . . . . . . . . . . . . . . . 16
         9.3.1.2. P2MP MPLS LSPs  . . . . . . . . . . . . . . . . . . 17
         9.3.1.3. MP2MP LSPs  . . . . . . . . . . . . . . . . . . . . 18



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     9.4 Aliasing . . . . . . . . . . . . . . . . . . . . . . . . . . 18
       9.4.1 Constructing the Ethernet A-D Route per EVI  . . . . . . 18
         9.4.1.1 Ethernet A-D Route Targets . . . . . . . . . . . . . 19
     9.5 Designated Forwarder Election  . . . . . . . . . . . . . . . 20
       9.5.1 Default DF Election Procedure  . . . . . . . . . . . . . 21
       9.5.2 DF Election with Service Carving . . . . . . . . . . . . 21
   10. Determining Reachability to Unicast MAC Addresses  . . . . . . 22
     10.1. Local Learning . . . . . . . . . . . . . . . . . . . . . . 23
     10.2. Remote learning  . . . . . . . . . . . . . . . . . . . . . 23
       10.2.1. Constructing the BGP E-VPN MAC Address Advertisement . 23
   11. ARP and ND . . . . . . . . . . . . . . . . . . . . . . . . . . 25
   12. Handling of Multi-Destination Traffic  . . . . . . . . . . . . 26
     12.1. Construction of the Inclusive Multicast Ethernet Tag
           Route  . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     12.2. P-Tunnel Identification  . . . . . . . . . . . . . . . . . 27
   13. Processing of Unknown Unicast Packets  . . . . . . . . . . . . 28
     13.1. Ingress Replication  . . . . . . . . . . . . . . . . . . . 28
     13.2. P2MP MPLS LSPs . . . . . . . . . . . . . . . . . . . . . . 29
   14. Forwarding Unicast Packets . . . . . . . . . . . . . . . . . . 29
     14.1. Forwarding packets received from a CE  . . . . . . . . . . 29
     14.2. Forwarding packets received from a remote PE . . . . . . . 30
       14.2.1. Unknown Unicast Forwarding . . . . . . . . . . . . . . 30
       14.2.2. Known Unicast Forwarding . . . . . . . . . . . . . . . 31
   15. Load Balancing of Unicast Frames . . . . . . . . . . . . . . . 31
     15.1. Load balancing of traffic from an PE to remote CEs . . . . 31
       15.1.1 Active-Standby Redundancy Mode  . . . . . . . . . . . . 31
       15.1.2 All-Active Redundancy Mode  . . . . . . . . . . . . . . 32
     15.2. Load balancing of traffic between an PE and a local CE . . 33
       15.2.1. Data plane learning  . . . . . . . . . . . . . . . . . 34
       15.2.2. Control plane learning . . . . . . . . . . . . . . . . 34
   16. MAC Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 34
   17. Multicast  . . . . . . . . . . . . . . . . . . . . . . . . . . 36
     17.1. Ingress Replication  . . . . . . . . . . . . . . . . . . . 36
     17.2. P2MP LSPs  . . . . . . . . . . . . . . . . . . . . . . . . 36
     17.3. MP2MP LSPs . . . . . . . . . . . . . . . . . . . . . . . . 36
       17.3.1. Inclusive Trees  . . . . . . . . . . . . . . . . . . . 36
       17.3.2. Selective Trees  . . . . . . . . . . . . . . . . . . . 37
     17.4. Explicit Tracking  . . . . . . . . . . . . . . . . . . . . 38
   18. Convergence  . . . . . . . . . . . . . . . . . . . . . . . . . 38
     18.1. Transit Link and Node Failures between PEs . . . . . . . . 38
     18.2. PE Failures  . . . . . . . . . . . . . . . . . . . . . . . 38
       18.2.1. Local Repair . . . . . . . . . . . . . . . . . . . . . 38
     18.3. PE to CE Network Failures  . . . . . . . . . . . . . . . . 39
   19. LACP State Synchronization . . . . . . . . . . . . . . . . . . 39
   20. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 40
   21. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
   21. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 41




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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. 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

3. Introduction

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

4. Terminology

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

   E-VPN Instance (EVI):  An E-VPN routing and forwarding instance on a
   PE.

   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 E-VPN instance consists of one or more
   broadcast domains. Ethernet tag(s) are assigned to the broadcast
   domains of a given E-VPN instance by the provider of that E-VPN, and
   each PE in that E-VPN instance performs a mapping between broadcast



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   domain identifier(s) understood by each of its attached CEs and the
   corresponding Ethernet tag.

   Link Aggregation Control Protocol (LACP):

   Multipoint to Multipoint (MP2MP):

   Point to Multipoint (P2MP):

   Point to Point (P2P):


5. BGP MPLS Based E-VPN Overview

   This section provides an overview of E-VPN.

   An E-VPN 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 E-VPNs 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
   PSN tunneling technology.

   In an E-VPN, 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 E-VPN, 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.



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   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 E-VPN are very similar to those of IP-VPN.
   An EVI requires a Route-Distinguisher (RD) and one or more Route-
   Targets (RTs). A CE attaches to an E-VPN instance (EVI) on an PE, on
   an Ethernet interface which may be configured for one or more
   Ethernet Tags, e.g., VLANs. Some deployment scenarios guarantee
   uniqueness of VLANs across E-VPNs: all points of attachment of a
   given EVI use the same VLAN, and no other EVI uses this VLAN.  This
   document refers to this case as a "Unique VLAN E-VPN" 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
   encoded as a ten octets integer.  A single-homed CE is considered to
   be attached to an Ethernet segment with ESI 0. Otherwise, an Ethernet
   segment MUST have a unique non-zero ESI.  The ESI can be assigned
   using various mechanisms:
      1. The ESI may be configured. For instance when E-VPNs are used to
      provide a VPLS service the ESI is fairly analogous to the Multi-
      homing site ID in [BGP-VPLS-MH].

      2. 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.




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      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.

      3. If LLDP is used between the PEs and CEs that are hosts, then
      the ESI is determined by LLDP. The ESI will be specified in a
      following version.

      4. 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)}

7. Ethernet Tag

   An Ethernet Tag identifies a particular broadcast domain, e.g. a
   VLAN, in an EVI.  An EVI consists of one or more broadcast domains.
   Ethernet Tags are assigned to the broadcast domains of a given EVI by
   the provider of the E-VPN service. Each PE, in a given EVI, performs
   a mapping between the Ethernet Tag and the corresponding broadcast
   domain identifier(s) understood by each of its attached CEs (e.g. CE
   VLAN Identifiers or CE-VIDs).

   If the broadcast domain identifiers(s) are understood consistently by
   all of the CEs in an EVI, the broadcast domain identifier(s) MAY be
   used as the corresponding Ethernet Tag(s). In other words, the
   Ethernet Tag ID assigned by the provider is numerically equal to the
   broadcast domain identifier (e.g., CE-VID = Ethernet Tag).

   Further, some deployment scenarios guarantee uniqueness of broadcast
   domain identifiers across all EVIs;  all points of attachment of a
   given EVI use the same broadcast domain identifier(s) and no other
   EVI uses these broadcast domain identifier(s).  This allows the RT(s)
   for each EVI to be derived automatically, as described in section
   9.4.1.1.1 "Auto-Derivation from the Ethernet Tag ID".

   The following subsections discuss the relationship between Ethernet
   Tags, EVIs and broadcast domain identifiers as well as the setting of
   the Ethernet Tag Identifier, in the various E-VPN BGP routes (defined
   in section 8), for the different types of service interfaces



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   described in [EVPN-REQ].

7.1 VLAN Based Service Interface

   With this service interface, there is a one-to-one mapping between
   the broadcast domain identifier understood by a CE on a port (e.g.
   CE-VID) and an EVI. Furthermore, there is a single bridge domain per
   PE for the EVI. Different CEs connected to different PE ports MAY use
   different broadcast domain identifiers (e.g. CE-VIDs) for the same
   EVI. If said identifiers are different, the frames SHOULD remain
   tagged with the originating CE's broadcast domain identifier (e.g.
   CE-VID). When the CE broadcast domain identifiers are not consistent,
   a tag translation function MUST be supported in the data path and
   MUST be performed on the disposition PE. The Ethernet Tag Identifier
   in all E-VPN routes MUST be set to 0.

7.2 VLAN Bundle Service Interface

   With this service interface, there is a many-to-one mapping between
   the broadcast domain identifier understood by a CE on a port (e.g.
   CE-VID) and an EVI. Furthermore, there is a single bridge domain per
   PE for the EVI. Different CEs connected to different PE ports MUST
   use the same broadcast domain identifiers (e.g. CE-VIDs) for the same
   EVI. The MPLS encapsulated frames MUST remain tagged with the
   originating CE's broadcast domain identifier (e.g. CE-VID). Tag
   translation is NOT permitted. The Ethernet Tag Identifier in all E-
   VPN 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, there is a many-to-one mapping between
   the broadcast domain identifier understood by a CE on a port (e.g.
   CE-VID) and an EVI. Furthermore, there are multiple bridge domains
   per PE for the EVI: one broadcast domain per CE broadcast domain
   identifier. In the case where the CE broadcast domain identifiers are
   not consistent for different CEs, a normalized Ethernet Tag 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 on both the imposition as well as the disposition PEs. The
   Ethernet Tag Identifier in all E-VPN routes MUST be set to the
   normalized Ethernet Tag assigned by the E-VPN provider.



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8. BGP E-VPN NLRI

   This document defines a new BGP NLRI, called the E-VPN NLRI.

   Following is the format of the E-VPN NLRI:

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

   The Route Type field defines encoding of the rest of the E-VPN NLRI
   (Route Type specific E-VPN NLRI).

   The Length field indicates the length in octets of the Route Type
   specific field of E-VPN 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 E-VPN NLRI is carried in BGP [RFC4271] using BGP Multiprotocol
   Extensions [RFC4760] with an AFI of TBD and an SAFI of E-VPN (To be
   assigned by IANA). The NLRI field in the
   MP_REACH_NLRI/MP_UNREACH_NLRI attribute contains the E-VPN NLRI
   (encoded as specified above).

   In order for two BGP speakers to exchange labeled E-VPN 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 TBD and an SAFI of E-VPN.

8.1. Ethernet Auto-Discovery Route

   A Ethernet A-D route type specific E-VPN 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 E-VPN 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 (n * 3 octets)            |
                   +---------------------------------------+

   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

   An Inclusive Multicast Ethernet Tag route type specific E-VPN NLRI
   consists of the following:







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                   +---------------------------------------+
                   |      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 E-VPN 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)|
                   +---------------------------------------+

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

8.5 ESI MPLS Label Extended Community

   This extended community is a new transitive extended community. 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 MPLS Label 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | 0x44        |   Sub-Type    | Flags (One Octet)  |Reserved=0  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Reserved = 0|          ESI MPLS label                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The low order bit of the flags octet is defined as the "Active-



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   Standby" bit and may be set to 1. The other bits must be set to 0.

8.6 ES-Import Extended Community

   This is a new transitive 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 Extended Community.
   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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | 0x44        |   Sub-Type    |          ES-Import              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     ES-Import Cont'd                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

8.7 MAC Mobility Extended Community

   This extended community is a new transitive extended community. 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0x44          | Sub-Type      | Reserved=0                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Sequence Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

9. Multi-homing Functions

   This section discusses the functions, procedures and associated BGP
   routes used to support multi-homing in E-VPN. 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



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   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.

   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.

   Note that the new ES-Import extended community is not the same as the
   Route Target Extended Community. The Ethernet Segment route carries
   this new ES-Import extended community. The PEs apply filtering on
   this new extended community. As a result the Ethernet Segment route
   is imported only by the PEs that are connected to the same Ethernet
   segment.

9.2 Fast Convergence

   In E-VPN, 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, E-VPN 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



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   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
   MPLS label used for split-horizon filtering (as discussed in section
   9.2). Support of this route flavor is MANDATORY.

   Route-Distinguisher (RD) MUST be a Type 1 RD [RFC4364]. The value
   field comprises an IP address of the PE (typically, the loopback
   address) followed by 0.  The reason for such encoding is that the RD
   cannot be that of a given EVI since the ESI can span across one or
   more EVIs.

   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 MPLS 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 MPLS 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 9.2.

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

9.2.1.1. Ethernet A-D Route Targets




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   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
   EVIs 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. If the CE sends a multicast, broadcast or unknown
   unicast packet to a particular PE, say PE1, then PE1 will forward
   that packet to all or subset of the other PEs in the EVI. In this
   case the PEs, other than PE1, that the CE is multi-homed to MUST drop
   the packet and not forward back to the CE. This is referred to as
   "split horizon" filtering in this document.

   In order to achieve this split horizon function, every multicast,
   broadcast or unknown unicast packet is encapsulated with an MPLS
   label that identifies the Ethernet segment of origin (i.e. the
   segment from which the frame entered the E-VPN network). This label
   is referred to as the ESI MPLS label, and is distributed using the
   "Ethernet A-D route per Ethernet Segment" as per the procedures in
   section 9.1.1 above. This route is imported by the PEs connected to
   the Ethernet Segment and also by the PEs that have at least one EVI
   in common with the Ethernet Segment in the route. As described in
   section 9.1.1, the route MUST carry an ESI MPLS Label Extended
   Community with a valid ESI MPLS label. The disposition PEs rely on
   the value of the ESI MPLS label to determine whether or not a flooded
   frame is allowed to egress a specific Ethernet segment.

9.3.1 ESI MPLS Label Assignment

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

9.3.1.1 Ingress Replication

   An PE that is using ingress replication for sending broadcast,
   multicast or unknown unicast traffic, distributes to other PEs, that
   belong to the Ethernet segment, a downstream assigned "ESI MPLS
   label" in the Ethernet A-D route. 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. Further
   consider that PE1 is using P2P or MP2P LSPs to send packets to PE2.



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   Consider that PE1 receives a multicast, broadcast or unknown unicast
   packet from CE1 on VLAN1 on ESI1. In this scenario, PE2 distributes
   an Inclusive Multicast Ethernet Tag route for VLAN1 in the associated
   EVI. So, when PE1 sends a multicast, broadcast or unknown unicast
   packet, that it receives from CE1, it MUST first push onto the MPLS
   label stack the ESI label that PE2 has distributed for ESI1. It MUST
   then push on the MPLS label distributed by PE2 in the Inclusive
   Multicast Ethernet Tag route for 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 ESI1, then PE2
   MUST NOT forward the packet onto ESI1.

9.3.1.2. P2MP MPLS LSPs

   An PE that is using P2MP LSPs for sending broadcast, multicast or
   unknown unicast traffic, distributes to other PEs, that belong to the
   Ethernet segment or have an E-VPN in common with the Ethernet
   Segment, an upstream assigned "ESI MPLS 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. Also
   consider PE3 that is in the same EVI as one of the EVIs to which ES1
   belongs.  Further, assume that PE1 is using P2MP MPLS LSPs to send
   broadcast, multicast or uknown unicast packets. When PE1 sends a
   multicast, broadcast or unknown unicast 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 E-VPN. 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 ESI1, then PE2 MUST NOT forward the
   packet onto ESI1. When PE3 receives this packet, it de-capsulates the
   top MPLS label and forwards the packet using the context label space



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   determined by the top label. If the next label is the ESI label
   assigned by PE1 to ESI1 and PE3 is not connected to ESI1, then PE3
   MUST pop the label and flood the packet over all local ESIs in the
   EVI.

9.3.1.3. MP2MP LSPs

   The procedures for ESI MPLS Label assignment and usage for MP2MP LSPs
   will be described in a future version.

9.4 Aliasing

   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, E-VPN introduces the concept of 'Aliasing'.
   Aliasing refers to the ability of an 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-zero ESI SHOULD consider the advertised
   MAC address as reachable via all PEs which have advertised
   reachability to the relevant Segment using Ethernet A-D routes with
   the same ESI (and Ethernet Tag if applicable).

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



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   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 E-VPN 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 E-
   VPN.  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
        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



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

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 E-VPN 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:

        -   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.
   Optional mechanisms, which will be specified in the future, will
   allow selecting a DF at the granularity of <ESI, EVI, S, G>.

   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 E-VPN
   via switches, then the support of all-active points of attachments,



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   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 granularity of the DF election MUST be at least the Ethernet
   segment via which the CE is multi-homed to the PEs. If the DF
   election is done at the Ethernet segment granularity then a single PE
   MUST be elected as the DF on the Ethernet segment.

   If there are one or more EVIs enabled on the Ethernet segment, then
   the granularity of the DF election SHOULD be the combination of the
   Ethernet segment and EVI on that Ethernet segment. In this case a
   single PE MUST be elected as the DF for a particular EVI on that
   Ethernet segment.

   The detailed procedures for DF election are described next.

9.5.1 Default DF Election Procedure

   As a PE discovers the other PEs that are connected to the same
   Ethernet Segment, using the Ethernet Segment routes, it starts
   building an ordered list based on the originating PE IP addresses.
   This list is used to select a DF and a backup DF (BDF) on a per
   Ethernet Segment basis. By default, the PE with the numerically
   highest IP address is considered the DF for that Ethernet Segment and
   the next PE in the list is considered the BDF.

   If the Ethernet Segment is a multi-homed device, then the elected DF
   is the only PE that must forward flooded multi-destination packets
   towards the segment. All other PE nodes must not permit multi-
   destination packets to egress to the segment. In the case where the
   DF fails, the BDF takes over its functionality.

   This procedure enables the election of a single DF per Ethernet
   Segment, for all EVIs enabled on the segment. It is possible to
   achieve more granular load-balancing of traffic among the PE nodes by
   employing Service Carving, as discussed in the next section.

9.5.2 DF Election with Service Carving



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   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.

   2. The PE then starts a timer to allow the reception of Ethernet
   Segment routes from other PE nodes 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. 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 EVI 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 EVI V when (V mod N) = i.

   The above procedure results in the entire EVI range being divided up
   among the PEs in the RG, regardless of whether a given EVI is
   configured/enabled on the associated Ethernet Segment or not.

   4. The PE that is elected as a DF for a given EVI will unblock
   traffic for that EVI only if the EVI is configured/enabled on the
   Segment. 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 EVIs) 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. 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.

10. Determining Reachability to Unicast MAC Addresses




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   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 E-VPN 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.

   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 the same PE or 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 the EVI, using MP-BGP and specifically
   the MAC Advertisement route.

10.2.1. Constructing the BGP E-VPN MAC Address Advertisement



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   BGP is extended to advertise these MAC addresses using the MAC
   Advertisement route type in the E-VPN 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 EVI (e.g., the PE needs to perform qualified learning
   for the VLANs in that EVI).

   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 E-
   VPN 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 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 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 Length field value is set to the number of octets in
   the IP Address field.

   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 is included, it is encoded as specified in
   section 12.

   The MPLS label field carries one or more labels (that corresponds to
   the stack of labels [MPLS-ENCAPS]).  Each label is encoded as 3
   octets, where the high-order 20 bits contain the label value, and the
   low order bit contains "Bottom of Stack" (as defined in [MPLS-
   ENCAPS]). The MPLS label stack MUST be the downstream assigned E-VPN
   MPLS label stack that is used by the PE to forward MPLS-encapsulated
   Ethernet frames received from remote PEs, where the destination MAC



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   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 E-VPN 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
   E-VPN 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 E-
   VPN label per MAC address. All of these methodologies have their
   tradeoffs.

   Per EVI label assignment requires the least number of E-VPN 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
   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 E-VPN".

   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.

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 E-VPN 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



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   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 and respond to the ARP request.

   Further detailed procedures will be specified in a later version.

12. Handling of Multi-Destination Traffic

   Procedures are required for a given PE to send broadcast or multicast
   traffic, received from a CE encapsulated in a given Ethernet Tag in
   an EVI, to all the other PEs that span that Ethernet Tag in the EVI.
   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 E-VPN 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 E-VPN 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



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   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 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
   E-VPN 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 E-VPN on
   the PE, the PMSI Tunnel attribute of the Inclusive 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 E-VPN, 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 E-VPN, the route MUST
          include the PMSI Tunnel attribute with the Tunnel Type set to
          Ingress Replication and Tunnel Identifier set to a routable



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          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 E-VPN
          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. Flooding 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 [RFC 4761, RFC
   4762].  When an PE capable of flooding (say PEx) receives a broadcast
   or multicast Ethernet frame, or one with an unknown destination MAC
   address, it must flood 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 the EVI, 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 the EVI. 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 broadcast and multicast
   packets, as well as packets to an unknown MAC address.

   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 E-VPN may use ingress replication using RSVP-
   TE P2P LSPs or LDP MP2P LSPs for sending broadcast, multicast and
   unknown unicast traffic to other PEs. Or they may use RSVP-TE P2MP or
   LDP P2MP or LDP MP2MP LSPs 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 EVI, specifies



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   the downstream label that the other PEs can use to send unknown
   unicast, multicast or broadcast traffic for the EVI 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 EVI 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 EVIs, may use the same P2MP
   LSP, using upstream labels [VPLS-MCAST]. This is the 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

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.




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   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 E-VPN 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 <EVI, Ethernet Tag> combination. The Ethernet
           Tag in the route must be the same as the 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 EVI. If the same P2MP LSP is used
           for all Ethernet Tags, then all the PEs in the EVI MUST
           be the leaves of the P2MP LSP. If a distinct P2MP LSP is
           used for a given Ethernet Tag in the EVI, 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
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 EVI or 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 unknown unicast, broadcast
   or multicast 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



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   that the destination MAC address is unknown unicast, broadcast or
   multicast and 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 unknown
   unicast 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 E-VPN 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 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 Active-Standby 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 MPLS Label Extended Community is set, then the remote
   PE MUST deduce that the Ethernet segment is operating in Active-
   Standby 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.

   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



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   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.

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 MPLS 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 ESI1 as well as an Ethernet A-D route per EVI for



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   <ESI1, VLAN1>.

   The MPLS label stack to send the packets to PE1 is the MPLS LSP stack
   to get to PE1 and the E-VPN 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.

   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 E-VPN
   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.



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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.

   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 E-VPN 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 E-VPN 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.



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   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 E-VPN 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.

   Since the sequence number is an unsigned 32 bit integer, all sequence
   number comparisons must be performed modulo 2**32. This unsigned
   arithmetic preserves the relationship of sequence numbers as they
   cycle from 2**32 - 1 to 0.

   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 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 sequence number in the received MAC
      Advertisement route, if the received route is tagged with a MAC
      Mobility extended community attribute.

   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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17. Multicast

   The PEs in a particular E-VPN 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 unknown unicast,
   multicast or broadcast traffic as described in section "Handling of
   Multi-Destination Traffic". A given unknown unicast or 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.

17.2. P2MP LSPs

   An PE may use an "Inclusive" tree for sending an unknown unicast,
   broadcast or multicast packet or a "Selective" tree. 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. For selective P-
   Multicast trees, only unicast PE-PE tunnels (using MPLS or IP/GRE
   encapsulation) and P2MP LSPs are supported, and the supported P2MP
   LSP signaling protocols are RSVP-TE, and mLDP.

17.3. MP2MP LSPs

   The root of the MP2MP LDP LSP advertises the Inclusive Multicast Tag
   route with the PMSI Tunnel attribute set to the MP2MP Tunnel
   identifier.  This advertisement is then sent to all PEs in the E-VPN.
    Upon receiving the Inclusive Multicast Tag routes with a PMSI Tunnel
   attribute that contains the MP2MP Tunnel identifier, the receiving
   PEs initiate the setup of the MP2MP tunnel towards the root using the
   procedures in [MLDP].

17.3.1. 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 EVIs on a
   given PE. A particular P-Multicast tree can be set up to carry the
   traffic originated by sites belonging to a single E-VPN, or to carry
   the traffic originated by sites belonging to different E-VPNs. The



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   ability to carry the traffic of more than one E-VPN on the same tree
   is termed 'Aggregation'. The tree needs to include every PE that is a
   member of any of the E-VPNs 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 E-VPN 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
   EVIs 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 E-VPN Inclusive Multicast routes.

17.3.2. Selective Trees

   A Selective P-Multicast tree is used by an PE to send IP multicast
   traffic for one or more specific IP multicast streams, originated by
   CEs connected to the PE, that belong to the same or different E-VPNs,
   to a subset of the PEs that belong to those E-VPNs. Each of the PEs
   in the subset should be on the path to a receiver of one or more
   multicast streams that are mapped onto the tree. The ability to use
   the same tree for multicast streams that belong to different E-VPNs
   is termed an PE the ability to create separate SP multicast trees for
   specific multicast streams, e.g. high bandwidth multicast streams.
   This allows traffic for these multicast streams to reach only those
   PE routers that have receivers in these streams. This avoids flooding
   other PE routers in the E-VPN.

   An SP can use both Inclusive P-Multicast trees and Selective P-
   Multicast trees or either of them for a given E-VPN on an PE, based
   on local configuration.

   The granularity of a selective tree is <RD, PE, S, G> where S is an
   IP multicast source address and G is an IP multicast group address or
   G is a multicast MAC address. Wildcard sources and wildcard groups
   are supported. Selective trees require explicit tracking as described
   below.

   A E-VPN PE advertises a selective tree using a E-VPN selective A-D
   route. The procedures are the same as those in [VPLS-MCAST] with S-



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   PMSI A-D routes in [VPLS-MCAST] replaced by E-VPN Selective A-D
   routes. The information elements of the E-VPN selective  A-D route
   are similar to those of the VPLS S-PMSI A-D route with the following
   differences. A E-VPN Selective A-D route includes an optional
   Ethernet Tag field. Also an E-VPN selective A-D route may encode a
   MAC address in the Group field. The encoding details of the E-VPN
   selective A-D route will be described in the next revision.

   Selective trees can also be aggregated on the same P2MP LSP using
   aggregation as described in [VPLS-MCAST].

17.4. Explicit Tracking

   [VPLS-MCAST] describes procedures for explicit tracking that rely on
   Leaf A-D routes. The same procedures are used for explicit tracking
   in this specification with VPLS Leaf A-D routes replaced with E-VPN
   Leaf A-D routes.  These procedures allow a root PE to request
   multicast membership information for a given (S, G), from leaf PEs.
   Leaf PEs rely on IGMP snooping or PIM snooping between the PE and the
   CE to determine the multicast membership information. Note that the
   procedures in [VPLS-MCAST] do not describe how explicit tracking is
   performed if the CEs are enabled with join suppression. The
   procedures for this case will be described in a future version.

18. Convergence

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

18.1. Transit Link and Node Failures between PEs

   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.

18.2.1. Local Repair



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   It is possible to perform local repair in the case of PE failures.
   Details will be specified in the future.

18.3. 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. LACP State Synchronization

   This section requires review and discussion amongst the authors and
   will be revised in the next version.

   To support CE multi-homing with multi-chassis Ethernet bundles, the
   PEs connected to a given CE should synchronize [802.1AX] LACP state
   amongst each other. This ensures that the PEs can present a single
   LACP bundle to the CE. This is required for initial system bring-up
   and upon any configuration change.

   This includes at least the following LACP specific configuration
   parameters:

      - System Identifier (MAC Address): uniquely identifies a LACP
        speaker.
      - System Priority: determines which LACP speaker's port
        priorities are used in the Selection logic.
      - Aggregator Identifier: uniquely identifies a bundle within
        a LACP speaker.
      - Aggregator MAC Address: identifies the MAC address of the
        bundle.
      - Aggregator Key: used to determine which ports can join an
        Aggregator.
      - Port Number: uniquely identifies an interface within a LACP
        speaker.
      - Port Key: determines the set of ports that can be bundled.
      - Port Priority: determines a port's precedence level to join



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        a bundle in case the number of eligible ports exceeds the
        maximum number of links allowed in a bundle.

   Furthermore, the PEs should also synchronize operational (run-time)
   data, in order for the LACP Selection logic state-machines to
   execute. This operational data includes the following LACP
   operational parameters, on a per port basis:

      - Partner System Identifier: this is the CE System MAC address.
      - Partner System Priority: the CE LACP System Priority
      - Partner Port Number: CE's AC port number.
      - Partner Port Priority: CE's AC Port Priority.
      - Partner Key: CE's key for this AC.
      - Partner State: CE's LACP State for the AC.
      - Actor State: PE's LACP State for the AC.
      - Port State: PE's AC port status.

   The above state needs to be communicated between PEs forming a multi-
   chassis bundle during LACP initial bringup, upon any configuration
   change and upon the occurrence of a failure.

   It should be noted that the above configuration and operational state
   is localized in scope and is only relevant to PEs which connect to
   the same multi-homed CE over a given Ethernet bundle.

   Furthermore, the communication of state changes, upon failures, must
   occur with minimal latency, in order to minimize the switchover time
   and consequent service disruption. The protocol details for
   synchronizing the LACP state will be described in the following
   version.


20. Acknowledgements

   We would like to thank Yakov Rekhter, 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 for his review.

21. References
   [E-VPN-REQ] A. Sajassi, R. Aggarwal et. al., "Requirements for
              Ethernet VPN", draft-sajassi-raggarwa-l2vpn-evpn-req-
              00.txt

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

   [VPLS-MCAST] "Multicast in VPLS". R. Aggarwal et.al., draft-ietf-



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              l2vpn-vpls-mcast-04.txt

   [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.

   [VPLS-MULTIHOMING] "BGP based Multi-homing in Virtual Private LAN
              Service", K. Kompella et. al., draft-ietf-l2vpn-vpls-
              multihoming-00.txt

   [PIM-SNOOPING] "PIM Snooping over VPLS", V. Hemige et. al., draft-
              ietf-l2vpn-vpls-pim-snooping-01

   [IGMP-SNOOPING] "Considerations for Internet Group Management
              Protocol (IGMP) and Multicast Listener Discovery (MLD)
              Snooping Switches", M. Christensen et. al., RFC4541,

   [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

   [EVPN-SEGMENT-ROUTE] A. Sajassi et. al., "E-VPN Ethernet Segment
              Route", draft-sajassi-l2vpn-evpn-segment-route-00.txt,
              work in progress.



21. Author's Address

      Rahul Aggarwal
      Email: raggarwa_1@yahoo.com


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


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



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      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


      Samer Salam
      Cisco
      595 Burrard Street, Suite 2123
      Vancouver, BC V7X 1J1, Canada



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      Email: ssalam@cisco.com


















































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