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Versions: (draft-rabadan-bess-evpn-optimized-ir) 00 01 02

BESS Workgroup                                           J. Rabadan, Ed.
Internet Draft                                              S. Sathappan
Intended status: Standards Track                           W. Henderickx
                                                                   Nokia
R. Shekhar
N. Sheth                                                      A. Sajassi
W. Lin                                                             Cisco
M. Katiyar
Juniper                                                         A. Isaac
                                                                 Juniper
M. Tufail
Citibank

Expires: February 17, 2018                               August 16, 2017




            Optimized Ingress Replication solution for EVPN
                  draft-ietf-bess-evpn-optimized-ir-02


Abstract

   Network Virtualization Overlay (NVO) networks using EVPN as control
   plane may use ingress replication (IR) or PIM-based trees to convey
   the overlay BUM traffic. PIM provides an efficient solution to avoid
   sending multiple copies of the same packet over the same physical
   link, however it may not always be deployed in the NVO core network.
   IR avoids the dependency on PIM in the NVO network core. While IR
   provides a simple multicast transport, some NVO networks with
   demanding multicast applications require a more efficient solution
   without PIM in the core. This document describes a solution to
   optimize the efficiency of IR in NVO networks.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

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



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   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt


   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on February 17, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (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.


Table of Contents

   1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Solution requirements . . . . . . . . . . . . . . . . . . . . .  4
   3. EVPN BGP Attributes for optimized-IR  . . . . . . . . . . . . .  5
   4. Non-selective Assisted-Replication (AR) Solution Description  .  7
     4.1. Non-selective AR-REPLICATOR procedures  . . . . . . . . . .  8
     4.2. Non-selective AR-LEAF procedures  . . . . . . . . . . . . .  9
     4.3. RNVE procedures . . . . . . . . . . . . . . . . . . . . . . 11
     4.4. Forwarding behavior in non-selective AR EVIs  . . . . . . . 11
       4.4.1. Broadcast and Multicast forwarding behavior . . . . . . 11
         4.4.1.1. Non-selective AR-REPLICATOR BM forwarding . . . . . 11
         4.4.1.2. Non-selective AR-LEAF BM forwarding . . . . . . . . 12
         4.4.1.3. RNVE BM forwarding  . . . . . . . . . . . . . . . . 12
       4.4.2. Unknown unicast forwarding behavior . . . . . . . . . . 13
         4.4.2.1. Non-selective AR-REPLICATOR/LEAF Unknown unicast
                  forwarding  . . . . . . . . . . . . . . . . . . . . 13
         4.4.2.2. RNVE Unknown unicast forwarding . . . . . . . . . . 13
   5. Selective Assisted-Replication (AR) Solution Description  . . . 13
     5.1. Selective AR-REPLICATOR procedures  . . . . . . . . . . . . 14
     5.2. Selective AR-LEAF procedures  . . . . . . . . . . . . . . . 15



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     5.3. Forwarding behavior in selective AR EVIs  . . . . . . . . . 16
       5.3.1. Selective AR-REPLICATOR BM forwarding . . . . . . . . . 16
       5.3.2. Selective AR-LEAF BM forwarding . . . . . . . . . . . . 17
   6. Pruned-Flood-Lists (PFL)  . . . . . . . . . . . . . . . . . . . 18
     6.1. A PFL example . . . . . . . . . . . . . . . . . . . . . . . 18
   7. AR Procedures for single-IP AR-REPLICATORS  . . . . . . . . . . 19
   8. AR Procedures and EVPN Multi-homing Split-Horizon . . . . . . . 20
   9. Out-of-band distribution of Broadcast/Multicast traffic . . . . 21
   10. Benefits of the optimized-IR solution  . . . . . . . . . . . . 21
   11. Conventions used in this document  . . . . . . . . . . . . . . 21
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
   14. Terminology  . . . . . . . . . . . . . . . . . . . . . . . . . 22
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     15.1 Normative References  . . . . . . . . . . . . . . . . . . . 23
     15.2 Informative References  . . . . . . . . . . . . . . . . . . 23
   16. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 23
   17. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 23



1. Problem Statement

   EVPN may be used as the control plane for a Network Virtualization
   Overlay (NVO) network. Network Virtualization Edge (NVE) devices and
   PEs that are part of the same EVI use Ingress Replication (IR) or
   PIM-based trees to transport the tenant's BUM traffic. In NVO
   networks where PIM-based trees cannot be used, IR is the only
   alternative. Examples of these situations are NVO networks where the
   core nodes don't support PIM or the network operator does not want to
   run PIM in the core.

   In some use-cases, the amount of replication for BUM (Broadcast,
   Unknown unicast and Multicast traffic) is kept under control on the
   NVEs due to the following fairly common assumptions:

   a) Broadcast is greatly reduced due to the proxy-ARP and proxy-ND
      capabilities supported by EVPN on the NVEs. Some NVEs can even
      provide DHCP-server functions for the attached Tenant Systems (TS)
      reducing the broadcast even further.

   b) Unknown unicast traffic is greatly reduced in virtualized NVO
      networks where all the MAC and IP addresses are learnt in the
      control plane.

   c) Multicast applications are not used.

   If the above assumptions are true for a given NVO network, then IR



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   provides a simple solution for multi-destination traffic. However,
   the statement c) above is not always true and multicast applications
   are required in many use-cases.

   When the multicast sources are attached to NVEs residing in
   hypervisors or low-performance-replication TORs, the ingress
   replication of a large amount of multicast traffic to a significant
   number of remote NVEs/PEs can seriously degrade the performance of
   the NVE and impact the application.

   This document describes a solution that makes use of two IR
   optimizations:

   i) Assisted-Replication (AR)
   ii) Pruned-Flood-Lists (PFL)

   Both optimizations may be used together or independently so that the
   performance and efficiency of the network to transport multicast can
   be improved. Both solutions require some extensions to [RFC7432] that
   are described in section 3.

   Section 2 lists the requirements of the combined optimized-IR
   solution, whereas sections 4 and 5 describe the Assisted-Replication
   (AR) solution, and section 6 the Pruned-Flood-Lists (PFL) solution.

2. Solution requirements

   The IR optimization solution (optimized-IR hereafter) MUST meet the
   following requirements:

   a) The solution MUST provide an IR optimization for BM (Broadcast and
      Multicast) traffic, while preserving the packet order for unicast
      applications, i.e. known and unknown unicast traffic SHALL follow
      the same path.

   b) The solution MUST be compatible with [RFC7432] and [EVPN-OVERLAY]
      and have no impact on the EVPN procedures for BM traffic. In
      particular, the solution SHOULD support the following EVPN
      functions:

        o All-active multi-homing, including the split-horizon and
          Designated Forwarder (DF) functions.

        o Single-active multi-homing, including the DF function.

        o Handling of multi-destination traffic and processing of
          broadcast and multicast as per [RFC7432].




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   c) The solution MUST be backwards compatible with existing NVEs using
      a non-optimized version of IR. A given EVI can have NVEs/PEs
      supporting regular-IR and optimized-IR.

   d) The solution MUST be independent of the NVO specific data plane
      encapsulation and the virtual identifiers being used, e.g.: VXLAN
      VNIs, NVGRE VSIDs or MPLS labels.

3. EVPN BGP Attributes for optimized-IR

   This solution proposes some changes to the [RFC7432] Inclusive
   Multicast Ethernet Tag routes and attributes so that an NVE/PE can
   signal its optimized-IR capabilities.

   The Inclusive Multicast Ethernet Tag route (RT-3) and its PMSI Tunnel
   Attribute's (PTA) general format used in [RFC7432] are shown below:

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


                 +---------------------------------+
                 |  Flags (1 octet)                |
                 +---------------------------------+
                 |  Tunnel Type (1 octets)         |
                 +---------------------------------+
                 |  MPLS Label (3 octets)          |
                 +---------------------------------+
                 |  Tunnel Identifier (variable)   |
                 +---------------------------------+

   The Flags field is defined as follows:

                  0 1 2 3 4 5  6 7
                 +-+-+-+-+-+--+-+-+
                 |rsved| T |BM|U|L|
                 +-+-+-+-+-+--+-+-+

   Where a new type field (for AR) and two new flags (for PFL signaling)
   are defined:



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   - T is the AR Type field (2 bits) that defines the AR role of the
     advertising router:

     + 00 (decimal 0) = RNVE (non-AR support)

     + 01 (decimal 1) = AR-REPLICATOR

     + 10 (decimal 2) = AR-LEAF

     + 11 (decimal 3) = RESERVED

   - The PFL (Pruned-Flood-Lists) flags defined the desired behavior of
     the advertising router for the different types of traffic:

     + BM= Broadcast and Multicast (BM) flag. BM=1 means "prune-me" from
       the BM flooding list. BM=0 means regular behavior.

     + U= Unknown flag. U=1 means "prune-me" from the Unknown flooding
       list. U=0 means regular behavior.

   - Flag L is an existing flag defined in [RFC6514] (L=Leaf Information
     Required) and it will be used only in the Selective AR Solution.

   Please refer to section 10 for the IANA considerations related to the
   PTA flags.

   In this document, the above RT-3 and PTA can be used in two different
   modes for the same EVI/Ethernet Tag:

   o Regular-IR route: in this route, Originating Router's IP Address,
     Tunnel Type (0x06), MPLS Label, Tunnel Identifier and Flags MUST be
     used as described in [RFC7432]. The Originating Router's IP Address
     and Tunnel Identifier are set to an IP address that we denominate
     IR-IP in this document.

   o Replicator-AR route: this route is used by the AR-REPLICATOR to
     advertise its AR capabilities, with the fields set as follows.

     + Originating Router's IP Address as well as the Tunnel Identifier
       are set to the same routable IP address that we denominate AR-IP
       and SHOULD be different than the IR-IP for a given PE/NVE.

     + Tunnel Type = Assisted-Replication (AR). Section 11 provides the
       allocated type value.

     + T (AR role type) = 01 (AR-REPLICATOR).

     + L (Leaf Information Required) = 0 (for non-selective AR) or 1



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       (for selective AR).

   In addition, this document also uses the Leaf-AD route (RT-11)
   defined in [EVPN-BUM] in case the selective AR mode is used. The
   Leaf-AD route MAY be used by the AR-LEAF in response to a Replicator-
   AR route (with the L flag set) to advertise its desire to receive the
   multicast traffic from a specific AR-REPLICATOR. It is only used for
   selective AR and its fields are set as follows:

     + Originating Router's IP Address is set to the advertising IR-IP
       (same IP used by the AR-LEAF in regular-IR routes).

     + Route Key is the "Route Type Specific" NLRI of the Replicator-AR
       route for which this Leaf-AD route is generated.

     + The AR-LEAF constructs an IP-address-specific route-target as
       indicated in [EVPN-BUM], by placing the IP address carried in the
       Next Hop field of the received Replicator-AR route in the Global
       Administrator field of the Community, with the Local
       Administrator field of this Community set to 0. Note that the
       same IP-address-specific import route-target is auto-configured
       by the AR-REPLICATOR that sent the Replicator-AR, in order to
       control the acceptance of the Leaf-AD routes.

     + The leaf-AD route MUST include the PMSI Tunnel attribute with the
       Tunnel Type set to AR, type set to AR-LEAF and the Tunnel
       Identifier set to the IR-IP of the advertising AR-LEAF. The PMSI
       Tunnel attribute MUST carry a downstream-assigned MPLS label that
       is used by the AR-REPLICATOR to send traffic to the AR-LEAF.

   Each AR-enabled node MUST understand and process the AR type field in
   the PTA (Flags field) of the routes, and MUST signal the
   corresponding type (1 or 2) according to its administrative choice.

   Each node, part of the EVI, MAY understand and process the BM/U
   flags. Note that these BM/U flags may be used to optimize the
   delivery of multi-destination traffic and its use SHOULD be an
   administrative choice, and independent of the AR role.

   Non-optimized-IR nodes will be unaware of the new PMSI attribute flag
   definition as well as the new Tunnel Type (AR), i.e. they will ignore
   the information contained in the flags field for any RT-3 and will
   ignore the RT-3 routes with an unknown Tunnel Type (type AR in this
   case).


4. Non-selective Assisted-Replication (AR) Solution Description




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   The following figure illustrates an example NVO network where the
   non-selective AR function is enabled. Three different roles are
   defined for a given EVI: AR-REPLICATOR, AR-LEAF and RNVE (Regular
   NVE). The solution is called "non-selective" because the chosen AR-
   REPLICATOR for a given flow MUST replicate the multicast traffic to
   'all' the NVE/PEs in the EVI except for the source NVE/PE.

                           (           )
                          (_    WAN    _)
                       +---(_         _)----+
                       |     (_      _)     |
                 PE1   |                PE2 |
                +------+----+          +----+------+
           TS1--+  (EVI-1)  |          |  (EVI-1)  +--TS2
                |REPLICATOR |          |REPLICATOR |
                +--------+--+          +--+--------+
                         |                |
                      +--+----------------+--+
                      |                      |
                      |                      |
                 +----+ VXLAN/nvGRE/MPLSoGRE +----+
                 |    |      IP Fabric       |    |
                 |    |                      |    |
       NVE1      |    +-----------+----------+    |      NVE3
       Hypervisor|          TOR   |  NVE2         |Hypervisor
       +---------+-+        +-----+-----+       +-+---------+
       |  (EVI-1)  |        |  (EVI-1)  |       |  (EVI-1)  |
       |    LEAF   |        |   RNVE    |       |    LEAF   |
       +--+-----+--+        +--+-----+--+       +--+-----+--+
          |     |              |     |             |     |
         VM11  VM12           TS3   TS4           VM31  VM32

                      Figure 1 Optimized-IR scenario


4.1. Non-selective AR-REPLICATOR procedures

   An AR-REPLICATOR is defined as an NVE/PE capable of replicating
   ingress BM (Broadcast and Multicast) traffic received on an overlay
   tunnel to other overlay tunnels and local Attachment Circuits (ACs).
   The AR-REPLICATOR signals its role in the control plane and
   understands where the other roles (AR-LEAF nodes, RNVEs and other AR-
   REPLICATORs) are located. A given AR-enabled EVI service may have
   zero, one or more AR-REPLICATORs. In our example in figure 1, PE1 and
   PE2 are defined as AR-REPLICATORs. The following considerations apply
   to the AR-REPLICATOR role:

   a) The AR-REPLICATOR role SHOULD be an administrative choice in any



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      NVE/PE that is part of an AR-enabled EVI. This administrative
      option to enable AR-REPLICATOR capabilities MAY be implemented as
      a system level option as opposed to as a per-MAC-VRF option.

   b) An AR-REPLICATOR MUST advertise a Replicator-AR route and MAY
      advertise a Regular-IR route. The AR-REPLICATOR MUST NOT generate
      a Regular-IR route if it does not have local attachment circuits
      (AC).

   c) The Replicator-AR and Regular-IR routes will be generated
      according to section 3. The AR-IP and IR-IP used by the
      Replicator-AR will be different routable IP addresses.

   d) When a node defined as AR-REPLICATOR receives a packet on an
      overlay tunnel, it will do a tunnel destination IP lookup and
      apply the following procedures:

        o If the destination IP is the AR-REPLICATOR IR-IP Address the
          node will process the packet normally as in [RFC7432].

        o If the destination IP is the AR-REPLICATOR AR-IP Address the
          node MUST replicate the packet to local ACs and overlay
          tunnels (excluding the overlay tunnel to the source of the
          packet). When replicating to remote AR-REPLICATORs the tunnel
          destination IP will be an IR-IP. That will be an indication
          for the remote AR-REPLICATOR that it MUST NOT replicate to
          overlay tunnels. The tunnel source IP will be the AR-IP of the
          AR-REPLICATOR.


4.2. Non-selective AR-LEAF procedures

   AR-LEAF is defined as an NVE/PE that - given its poor replication
   performance - sends all the BM traffic to an AR-REPLICATOR that can
   replicate the traffic further on its behalf. It MAY signal its AR-
   LEAF capability in the control plane and understands where the other
   roles are located (AR-REPLICATOR and RNVEs). A given service can have
   zero, one or more AR-LEAF nodes. Figure 1 shows NVE1 and NVE3 (both
   residing in hypervisors) acting as AR-LEAF. The following
   considerations apply to the AR-LEAF role:

   a) The AR-LEAF role SHOULD be an administrative choice in any NVE/PE
      that is part of an AR-enabled EVI. This administrative option to
      enable AR-LEAF capabilities MAY be implemented as a system level
      option as opposed to as per-MAC-VRF option.

   b) In this non-selective AR solution, the AR-LEAF MUST advertise a
      single Regular-IR inclusive multicast route as in [RFC7432]. The



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      AR-LEAF SHOULD set the AR Type field to AR-LEAF. Note that
      although this flag does not make any difference for the egress
      nodes when creating an EVPN destination to the the AR-LEAF, it is
      RECOMMENDED the use of this flag for an easy operation and
      troubleshooting of the EVI.

   c) In a service where there are no AR-REPLICATORs, the AR-LEAF MUST
      use regular ingress replication. This will happen when a new
      update from the last former AR-REPLICATOR is received and contains
      a non-REPLICATOR AR type, or when the AR-LEAF detects that the
      last AR-REPLICATOR is down (next-hop tracking in the IGP or any
      other detection mechanism). Ingress replication MUST use the
      forwarding information given by the remote Regular-IR Inclusive
      Multicast Routes as described in [RFC7432].

   d) In a service where there is one or more AR-REPLICATORs (based on
      the received Replicator-AR routes for the EVI), the AR-LEAF can
      locally select which AR-REPLICATOR it sends the BM traffic to:

        o A single AR-REPLICATOR MAY be selected for all the BM packets
          received on the AR-LEAF attachment circuits (ACs) for a given
          EVI. This selection is a local decision and it does not have
          to match other AR-LEAF's selection within the same EVI.

        o An AR-LEAF MAY select more than one AR-REPLICATOR and do
          either per-flow or per-EVI load balancing.

        o In case of a failure on the selected AR-REPLICATOR, another
          AR-REPLICATOR will be selected.

        o When an AR-REPLICATOR is selected, the AR-LEAF MUST send all
          the BM packets to that AR-REPLICATOR using the forwarding
          information given by the Replicator-AR route for the chosen
          AR-REPLICATOR, with tunnel type = 0x0A (AR tunnel). The
          underlay destination IP address MUST be the AR-IP advertised
          by the AR-REPLICATOR in the Replicator-AR route.

        o AR-LEAF nodes SHALL send service-level BM control plane
          packets following regular IR procedures. An example would be
          IGMP, MLD or PIM multicast packets. The AR-REPLICATORs MUST
          not replicate these control plane packets to other overlay
          tunnels since they will use the regular IR-IP Address.

   e) The use of an AR-REPLICATOR-activation-timer (in seconds) on the
      AR-LEAF nodes is RECOMMENDED. Upon receiving a new Replicator-AR
      route where the AR-REPLICATOR is selected, the AR-LEAF will run a
      timer before programming the new AR-REPLICATOR. This will give the
      AR-REPLICATOR some time to program the AR-LEAF nodes before the



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      AR-LEAF sends BM traffic.


4.3. RNVE procedures

   RNVE (Regular Network Virtualization Edge node) is defined as an
   NVE/PE without AR-REPLICATOR or AR-LEAF capabilities that does IR as
   described in [RFC7432]. The RNVE does not signal any AR role and is
   unaware of the AR-REPLICATOR/LEAF roles in the EVI. The RNVE will
   ignore the Flags in the Regular-IR routes and will ignore the
   Replicator-AR routes (due to an unknown tunnel type in the PTA) and
   the Leaf-AD routes (due to the IP-address-specific route-target).

   This role provides EVPN with the backwards compatibility required in
   optimized-IR EVIs. Figure 1 shows NVE2 as RNVE.

4.4. Forwarding behavior in non-selective AR EVIs

   In AR EVIs, BM (Broadcast and Multicast) traffic between two NVEs may
   follow a different path than unicast traffic. This solution proposes
   the replication of BM through the AR-REPLICATOR node, whereas
   unknown/known unicast will be delivered directly from the source node
   to the destination node without being replicated by any intermediate
   node. Unknown unicast SHALL follow the same path as known unicast
   traffic in order to avoid packet reordering for unicast applications
   and simplify the control and data plane procedures. Section 4.4.1.
   describes the expected forwarding behavior for BM traffic in nodes
   acting as AR-REPLICATOR, AR-LEAF and RNVE. Section 4.4.2. describes
   the forwarding behavior for unknown unicast traffic.

   Note that known unicast forwarding is not impacted by this solution.

4.4.1. Broadcast and Multicast forwarding behavior

   The expected behavior per role is described in this section.

4.4.1.1. Non-selective AR-REPLICATOR BM forwarding

   The AR-REPLICATORs will build a flooding list composed of ACs and
   overlay tunnels to remote nodes in the EVI. Some of those overlay
   tunnels MAY be flagged as non-BM receivers based on the BM flag
   received from the remote nodes in the EVI.

   o When an AR-REPLICATOR receives a BM packet on an AC, it will
     forward the BM packet to its flooding list (including local ACs and
     remote NVE/PEs), skipping the non-BM overlay tunnels.

   o When an AR-REPLICATOR receives a BM packet on an overlay tunnel, it



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     will check the destination IP of the underlay IP header and:

      - If the destination IP matches its AR-IP, the AR-REPLICATOR will
        forward the BM packet to its flooding list (ACs and overlay
        tunnels) excluding the non-BM overlay tunnels. The AR-REPLICATOR
        will do source squelching to ensure the traffic is not sent back
        to the originating AR-LEAF. If the encapsulation is MPLSoGRE (or
        MPLSoUDP) and the EVI label is not the bottom of the stack, the
        AR-REPLICATOR MUST copy the rest of the labels and forward them
        to the egress overlay tunnels.

      - If the destination IP matches its IR-IP, the AR-REPLICATOR will
        skip all the overlay tunnels from the flooding list, i.e. it
        will only replicate to local ACs. This is the regular IR
        behavior described in [RFC7432].


4.4.1.2. Non-selective AR-LEAF BM forwarding

   The AR-LEAF nodes will build two flood-lists:

     1) Flood-list #1 - composed of ACs and an AR-REPLICATOR-set of
        overlay tunnels. The AR-REPLICATOR-set is defined as one or more
        overlay tunnels to the AR-IP Addresses of the remote AR-
        REPLICATOR(s) in the EVI. The selection of more than one AR-
        REPLICATOR is described in section 4.2. and it is a local AR-
        LEAF decision.

     2) Flood-list #2 - composed of ACs and overlay tunnels to the
        remote IR-IP Addresses.

   When an AR-LEAF receives a BM packet on an AC, it will check the
   AR-REPLICATOR-set:

   o If the AR-REPLICATOR-set is empty, the AR-LEAF will send the packet
     to flood-list #2.

   o If the AR-REPLICATOR-set is NOT empty, the AR-LEAF will send the
     packet to flood-list #1, where only one of the overlay tunnels of
     the AR-REPLICATOR-set is used.

   When an AR-LEAF receives a BM packet on an overlay tunnel, will
   forward the BM packet to its local ACs and never to an overlay
   tunnel. This is the regular IR behavior described in [RFC7432].

4.4.1.3. RNVE BM forwarding

   The RNVE is completely unaware of the AR-REPLICATORs, AR-LEAF nodes



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   and BM/U flags (that information is ignored). Its forwarding behavior
   is the regular IR behavior described in [RFC7432]. Any regular non-AR
   node is fully compatible with the RNVE role described in this
   document.

4.4.2. Unknown unicast forwarding behavior

   The expected behavior is described in this section.

4.4.2.1. Non-selective AR-REPLICATOR/LEAF Unknown unicast forwarding

   While the forwarding behavior in AR-REPLICATORs and AR-LEAF nodes is
   different for BM traffic, as far as Unknown unicast traffic
   forwarding is concerned, AR-LEAF nodes behave exactly in the same way
   as AR-REPLICATORs do.

   The AR-REPLICATOR/LEAF nodes will build a flood-list composed of ACs
   and overlay tunnels to the IR-IP Addresses of the remote nodes in the
   EVI. Some of those overlay tunnels MAY be flagged as non-U (Unknown
   unicast) receivers based on the U flag received from the remote nodes
   in the EVI.

   o When an AR-REPLICATOR/LEAF receives an unknown packet on an AC, it
     will forward the unknown packet to its flood-list, skipping the
     non-U overlay tunnels.

   o When an AR-REPLICATOR/LEAF receives an unknown packet on an overlay
     tunnel will forward the unknown packet to its local ACs and never
     to an overlay tunnel. This is the regular IR behavior described in
     [RFC7432].

4.4.2.2. RNVE Unknown unicast forwarding

   As described for BM traffic, the RNVE is completely unaware of the
   REPLICATORs, LEAF nodes and BM/U flags (that information is ignored).
   Its forwarding behavior is the regular IR behavior described in
   [RFC7432], also for Unknown unicast traffic. Any regular non-AR node
   is fully compatible with the RNVE role described in this document.


5. Selective Assisted-Replication (AR) Solution Description

   Figure 1 is also used to describe the selective AR solution, however
   in this section we consider NVE2 as one more AR-LEAF for EVI-1. The
   solution is called "selective" because a given AR-REPLICATOR MUST
   replicate the BM traffic to only the AR-LEAF that requested the
   replication (as opposed to all the AR-LEAF nodes) and MAY replicate
   the BM traffic to the RNVEs. The same AR roles defined in section 4



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   are used here, however the procedures are slightly different.

   The following sub-sections describe the differences in the procedures
   of AR-REPLICATOR/LEAFs compared to the non-selective AR solution.
   There is no change on the RNVEs.


5.1. Selective AR-REPLICATOR procedures

   In our example in figure 1, PE1 and PE2 are defined as Selective AR-
   REPLICATORs. The following considerations apply to the Selective AR-
   REPLICATOR role:

   a) The Selective AR-REPLICATOR capability SHOULD be an administrative
      choice in any NVE/PE that is part of an AR-enabled EVI, as the AR
      role itself. This administrative option MAY be implemented as a
      system level option as opposed to as a per-MAC-VRF option.

   b) Each AR-REPLICATOR will build a list of AR-REPLICATOR, AR-LEAF and
      RNVE nodes (AR-LEAF nodes that sent only a regular-IR route are
      accounted as RNVEs by the AR-REPLICATOR). In spite of the
      'Selective' administrative option, an AR-REPLICATOR MUST NOT
      behave as a Selective AR-REPLICATOR if at least one of the AR-
      REPLICATORs has the L flag NOT set. If at least one AR-REPLICATOR
      sends a Replicator-AR route with L=0 (in the EVI context), the
      rest of the AR-REPLICATORs will fall back to non-selective AR
      mode.

   b) The Selective AR-REPLICATOR MUST follow the procedures described
      in section 4.1, except for the following differences:

        o The Replicator-AR route MUST include L=1 (Leaf Information
          Required) in the Replicator-AR route. This flag is used by the
          AR-REPLICATORs to advertise their 'selective' AR-REPLICATOR
          capabilities. In addition, the AR-REPLICATOR auto-configures
          its IP-address-specific import route-target as described in
          section 3.

        o The AR-REPLICATOR will build a 'selective' AR-LEAF-set with
          the list of nodes that requested replication to its own AR-IP.
          For instance, assuming NVE1 and NVE2 advertise a Leaf-AD route
          with PE1's IP-address-specific route-target and NVE3
          advertises a Leaf-AD route with PE2's IP-address-specific
          route-target, PE1 MUST only add NVE1/NVE2 to its selective AR-
          LEAF-set for EVI-1, and exclude NVE3.

        o When a node defined and operating as Selective AR-REPLICATOR
          receives a packet on an overlay tunnel, it will do a tunnel



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          destination IP lookup and if the destination IP is the AR-
          REPLICATOR AR-IP Address, the node MUST replicate the packet
          to:

          + local ACs
          + overlay tunnels in the Selective AR-LEAF-set (excluding the
            overlay tunnel to the source AR-LEAF).
          + overlay tunnels to the RNVEs if the tunnel source IP is the
            IR-IP of an AR-LEAF (in any other case, the AR-REPLICATOR
            MUST NOT replicate the BM traffic to remote RNVEs). In other
            words, the first-hop selective AR-REPLICATOR will replicate
            to all the RNVEs.
          + overlay tunnels to the remote Selective AR-REPLICATORs if
            the tunnel source IP is an IR-IP of its own AR-LEAF-set (in
            any other case, the AR-REPLICATOR MUST NOT replicate the BM
            traffic to remote AR-REPLICATORs), where the tunnel
            destination IP is the AR-IP of the remote Selective AR-
            REPLICATOR. The tunnel destination IP AR-IP will be an
            indication for the remote Selective AR-REPLICATOR that the
            packet needs further replication to its AR-LEAFs.


5.2. Selective AR-LEAF procedures

   A Selective AR-LEAF chooses a single Selective AR-REPLICATOR per EVI
   and:

   o Sends all the EVI BM traffic to that AR-REPLICATOR and
   o Expects to receive the BM traffic for a given EVI from the same AR-
     REPLICATOR.

   In the example of Figure 1, we consider NVE1/NVE2/NVE3 as Selective
   AR-LEAFs. NVE1 selects PE1 as its Selective AR-REPLICATOR. If that is
   so, NVE1 will send all its BM traffic for EVI-1 to PE1. If other AR-
   LEAF/REPLICATORs send BM traffic, NVE1 will receive that traffic from
   PE1. These are the differences in the behavior of a Selective AR-LEAF
   compared to a non-selective AR-LEAF:

   a) The AR-LEAF role selective capability SHOULD be an administrative
      choice in any NVE/PE that is part of an AR-enabled EVI. This
      administrative option to enable AR-LEAF capabilities MAY be
      implemented as a system level option as opposed to as per-MAC-VRF
      option.

   b) The AR-LEAF MAY advertise a Regular-IR route if there are RNVEs in
      the EVI. The Selective AR-LEAF MUST advertise a Leaf-AD route
      after receiving a Replicator-AR route with L=1. It is recommended
      that the Selective AR-LEAF waits for a timer t before sending the



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      Leaf-AD route, so that the AR-LEAF receives all the Replicator-AR
      routes for the EVI.

   c) In a service where there is more than one Selective AR-REPLICATORs
      the Selective AR-LEAF MUST locally select a single Selective AR-
      REPLICATOR for the EVI. Once selected:

        o The Selective AR-LEAF will send a Leaf-AD route including the
          Route-key and IP-address-specific route-target of the selected
          AR-REPLICATOR.

        o The Selective AR-LEAF will send all the BM packets received on
          the attachment circuits (ACs) for a given EVI to that AR-
          REPLICATOR.

        o In case of a failure on the selected AR-REPLICATOR, another
          AR-REPLICATOR will be selected and a new Leaf-AD update will
          be issued for the new AR-REPLICATOR. This new route will
          update the selective list in the new Selective AR-REPLICATOR.
          In case of failure on the active Selective AR-REPLICATOR, it
          is recommended for the Selective AR-LEAF to revert to IR
          behavior for a timer t to speed up the convergence. When the
          timer expires, the Selective AR-LEAF will resume its AR mode
          with the new Selective AR-REPLICATOR.

   All the AR-LEAFs in an EVI are expected to be configured as either
   selective or non-selective. A mix of selective and non-selective AR-
   LEAFs SHOULD NOT coexist in the same EVI. In case there is a non-
   selective AR-LEAF, its BM traffic sent to a selective AR-REPLICATOR
   will not be replicated to other AR-LEAFs that are not in its
   Selective AR-LEAF-set.

5.3. Forwarding behavior in selective AR EVIs

   This section describes the differences of the selective AR forwarding
   mode compared to the non-selective mode. Compared to section 4.4,
   there are no changes for the forwarding behavior in RNVEs or for
   unknown unicast traffic.

5.3.1. Selective AR-REPLICATOR BM forwarding

   The Selective AR-REPLICATORs will build two flood-lists:

     1) Flood-list #1 - composed of ACs and overlay tunnels to the
        remote nodes in the EVI, always using the IR-IPs in the tunnel
        destination IP addresses. Some of those overlay tunnels MAY be
        flagged as non-BM receivers based on the BM flag received from
        the remote nodes in the EVI.



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     2) Flood-list #2 - composed of ACs, a Selective AR-LEAF-set and a
        Selective AR-REPLICATOR-set, where:

        o The Selective AR-LEAF-set is composed of the overlay tunnels
          to the AR-LEAFs that advertise a Leaf-AD route for the local
          AR-REPLICATOR. This set is updated with every Leaf-AD route
          received/withdrawn from a new AR-LEAF.

        o The Selective AR-REPLICATOR-set is composed of the overlay
          tunnels to all the AR-REPLICATORs that send a Replicator-AR
          route with L=1. The AR-IP addresses are used as tunnel
          destination IP.

   When a Selective AR-REPLICATOR receives a BM packet on an AC, it will
   forward the BM packet to its flood-list #1, skipping the non-BM
   overlay tunnels.

   When a Selective AR-REPLICATOR receives a BM packet on an overlay
   tunnel, it will check the destination and source IPs of the underlay
   IP header and:

      - If the destination IP matches its AR-IP and the source IP
        matches an IP of its own Selective AR-LEAF-set, the AR-
        REPLICATOR will forward the BM packet to its flood-list #2, as
        long as the list of AR-REPLICATORs for the EVI matches the
        Selective AR-REPLICATOR-set. If the Selective AR-REPLICATOR-set
        does not match the list of AR-REPLICATORs, the node reverts back
        to non-selective mode and flood-list #1 is used.

      - If the destination IP matches its AR-IP and the source IP does
        not match any IP of its Selective AR-LEAF-set, the AR-REPLICATOR
        will forward the BM packet to flood-list #2 but skipping the AR-
        REPLICATOR-set.

      - If the destination IP matches its IR-IP, the AR-REPLICATOR will
        use flood-list #1 but MUST skip all the overlay tunnels from the
        flooding list, i.e. it will only replicate to local ACs. This is
        the regular-IR behavior described in [RFC7432].

   In any case, non-BM overlay tunnels are excluded from flood-lists
   and, also, source squelching is always done in order to ensure the
   traffic is not sent back to the originating source. If the
   encapsulation is MPLSoGRE (or MPLSoUDP) and the EVI label is not the
   bottom of the stack, the AR-REPLICATOR MUST copy the rest of the
   labels when forwarding them to the egress overlay tunnels.


5.3.2. Selective AR-LEAF BM forwarding



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   The Selective AR-LEAF nodes will build two flood-lists:

     1) Flood-list #1 - composed of ACs and the overlay tunnel to the
        selected AR-REPLICATOR (using the AR-IP as the tunnel
        destination IP).

     2) Flood-list #2 - composed of ACs and overlay tunnels to the
        remote IR-IP Addresses.

   When an AR-LEAF receives a BM packet on an AC, it will check if there
   is any selected AR-REPLICATOR. If there is, flood-list #1 will be
   used. Otherwise, flood-list #2 will.

   When an AR-LEAF receives a BM packet on an overlay tunnel, will
   forward the BM packet to its local ACs and never to an overlay
   tunnel. This is the regular IR behavior described in [RFC7432].


6. Pruned-Flood-Lists (PFL)

   In addition to AR, the second optimization supported by this solution
   is the ability for the all the EVI nodes to signal Pruned-Flood-Lists
   (PFL). As described in section 3, an EVPN node can signal a given
   value for the BM and U PFL flags in the IR Inclusive Multicast
   Routes, where:

   + BM= Broadcast and Multicast (BM) flag. BM=1 means "prune-me" from
     the BM flood-list. BM=0 means regular behavior.

   + U= Unknown flag. U=1 means "prune-me" from the Unknown flood-list.
     U=0 means regular behavior.

   The ability to signal these PFL flags is an administrative choice.
   Upon receiving a non-zero PFL flag, a node MAY decide to honor the
   PFL flag and remove the sender from the corresponding flood-list. A
   given EVI node receiving BUM traffic on an overlay tunnel MUST
   replicate the traffic normally, regardless of the signaled PFL
   flags.

   This optimization MAY be used along with the AR solution.

6.1. A PFL example

   In order to illustrate the use of the solution described in this
   document, we will assume that EVI-1 in figure 1 is optimized-IR
   enabled and:

   o PE1 and PE2 are administratively configured as AR-REPLICATORs, due



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     to their high-performance replication capabilities. PE1 and PE2
     will send a Replicator-AR route with BM/U flags = 00.

   o NVE1 and NVE3 are administratively configured as AR-LEAF nodes, due
     to their low-performance software-based replication capabilities.
     They will advertise a Regular-IR route with type AR-LEAF. Assuming
     both NVEs advertise all the attached VMs in EVPN as soon as they
     come up and don't have any VMs interested in multicast
     applications, they will be configured to signal BM/U flags = 11 for
     EVI-1.

   o NVE2 is optimized-IR unaware; therefore it takes on the RNVE role
     in EVI-1.

   Based on the above assumptions the following forwarding behavior will
   take place:

   (1) Any BM packets sent from VM11 will be sent to VM12 and PE1. PE1
       will forward further the BM packets to TS1, WAN link, PE2 and
       NVE2, but not to NVE3. PE2 and NVE2 will replicate the BM packets
       to their local ACs but we will avoid NVE3 having to replicate
       unnecessarily those BM packets to VM31 and VM32.

   (2) Any BM packets received on PE2 from the WAN will be sent to PE1
       and NVE2, but not to NVE1 and NVE3, sparing the two hypervisors
       from replicating unnecessarily to their local VMs. PE1 and NVE2
       will replicate to their local ACs only.

   (3) Any Unknown unicast packet sent from VM31 will be forwarded by
       NVE3 to NVE2, PE1 and PE2 but not NVE1. The solution avoids the
       unnecessary replication to NVE1, since the destination of the
       unknown traffic cannot be at NVE1.

   (4) Any Unknown unicast packet sent from TS1 will be forwarded by PE1
       to the WAN link, PE2 and NVE2 but not to NVE1 and NVE3, since the
       target of the unknown traffic cannot be at those NVEs.

7. AR Procedures for single-IP AR-REPLICATORS

   The procedures explained in sections 4 (Non-selective AR) and 5
   (Selective AR) assume that the AR-REPLICATOR can use two local
   routable IP addresses to terminate and originate NVO tunnels, i.e.
   IR-IP and AR-IP addresses. This is usually the case for PE-based AR-
   REPLICATOR nodes.

   In some cases, the AR-REPLICATOR node does not support more than one
   IP address to terminate and originate NVO tunnels, i.e. the IR-IP and
   AR-IP are the same IP addresses. This may be the case in some



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   software-based or low-end AR-REPLICATOR nodes. If this is the case,
   the procedures in sections 4 and 5 must be modified in the following
   way:

   o The Replicator-AR routes generated by the AR-REPLICATOR use an AR-
     IP that will match its IR-IP. In order to differentiate the data
     plane packets that need to use IR from the packets that must use AR
     forwarding mode, the Replicator-AR route must advertise a different
     VNI/VSID than the one used by the Regular-IR route. For instance,
     the AR-REPLICATOR will advertise AR-VNI along with the Replicator-
     AR route and IR-VNI along with the Regular-IR route. Since both
     routes have the same key, different RDs are needed for both routes.

   o An AR-REPLICATOR will perform IR or AR forwarding mode for the
     incoming Overlay packets based on an ingress VNI lookup, as opposed
     to the tunnel IP DA lookup described in sections 4 and 5. Note
     that, when replicating to remote AR-REPLICATOR nodes, the use of
     the IR-VNI or AR-VNI advertised by the egress node will determine
     the IR or AR forwarding mode at the subsequent AR-REPLICATOR.

   The rest of the procedures will follow what is described in sections
   4 and 5.


8. AR Procedures and EVPN Multi-homing Split-Horizon

   If VXLAN or NVGRE are used, and if the Split-horizon is based on the
   tunnel IP SA and "Local-Bias" as described in [EVPN-OVERLAY], the
   Split-horizon check will not work if there is an Ethernet-Segment
   shared between two AR-LEAF nodes, and the AR-REPLICATOR changes the
   tunnel IP SA of the packets with its own AR-IP.

   In order to be compatible with the IP SA split-horizon check, the AR-
   REPLICATOR MAY keep the original received tunnel IP SA when
   replicating packets to a remote AR-LEAF or AR-REPLICATOR. This will
   allow DF (Designated Forwarder) AR-LEAF nodes to apply Split-horizon
   check procedures for BM packets, before sending them to the local
   Ethernet-Segment.

   When EVPN is used for MPLS over GRE (or UDP), the ESI-label based
   split-horizon procedure as in [RFC7432] will not work for multi-homed
   Ethernet-Segments defined on AR-LEAF nodes. "Local-Bias" is
   recommended in this case, as in the case of VXLAN or NVGRE explained
   above. The "Local-Bias" and tunnel IP SA preservation mechanisms
   provide the required split-horizon behavior in non-selective or
   selective AR.

   Note that if the AR-REPLICATOR implementation keeps the received



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   tunnel IP SA, the use of uRPF in the IP fabric based on the tunnel IP
   SA MUST be disabled.


9. Out-of-band distribution of Broadcast/Multicast traffic

   The use of out-of-band mechanisms to distribute BM traffic between
   AR-REPLICATORS MAY be used.


10. Benefits of the optimized-IR solution

   A solution for the optimization of Ingress Replication in EVPN is
   described in this document (optimized-IR). The solution brings the
   following benefits:

   o Optimizes the multicast forwarding in low-performance NVEs, by
     relaying the replication to high-performance NVEs (AR-REPLICATORs)
     and while preserving the packet ordering for unicast applications.

   o Reduces the flooded traffic in NVO networks where some NVEs do not
     need broadcast/multicast and/or unknown unicast traffic.

   o It is fully compatible with existing EVPN implementations and EVPN
     functions for NVO overlay tunnels. Optimized-IR NVEs and regular
     NVEs can be even part of the same EVI.

   o It does not require any PIM-based tree in the NVO core of the
     network.


11. Conventions used in this document

   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 RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

   In this document, the characters ">>" preceding an indented line(s)
   indicates a compliance requirement statement using the key words
   listed above. This convention aids reviewers in quickly identifying
   or finding the explicit compliance requirements of this RFC.

12. Security Considerations




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   This section will be added in future versions.

13. IANA Considerations

   IANA has allocated the following Border Gateway Protocol (BGP)
   Parameters:

   1) Allocation in the P-Multicast Service Interface Tunnel (PMSI
      Tunnel) Tunnel Types registry:

      Value     Meaning                        Reference
      0x0A      Assisted-Replication Tunnel    [This document]

   2) Allocations in the P-Multicast Service Interface (PMSI) Tunnel
      Attribute Flags registry:

      Value    Name                           Reference
      3-4      Assisted-Replication Type (T)  [This document]
      5        Broadcast and Multicast (BM)   [This document]
      6        Unknown (U)                    [This document]


14. Terminology

   Regular-IR: Refers to Regular Ingress Replication, where the source
          NVE/PE sends a copy to each remote NVE/PE part of the EVI.

   AR-IP: IP address owned by the AR-REPLICATOR and used to
          differentiate the ingress traffic that must follow the AR
          procedures.

   IR-IP: IP address used for Ingress Replication as in [RFC7432].

   AR-VNI: VNI advertised by the AR-REPLICATOR along with the
          Replicator-AR route. It is used to identify the ingress
          packets that must follow AR procedures ONLY in the Single-IP
          AR-REPLICATOR case.

   IR-VNI: VNI advertised along with the RT-3 for IR.

   AR forwarding mode: for an AR-LEAF, it means sending an AC BM packet
          to a single AR-REPLICATOR with tunnel destination IP AR-IP.
          For an AR-REPLICATOR, it means sending a BM packet to a
          selective number or all the overlay tunnels when the packet
          was previously received from an overlay tunnel.

   IR forwarding mode: it refers to the Ingress Replication behavior
          explained in [RFC7432]. It means sending an AC BM packet copy



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          to each remote PE/NVE in the EVI and sending an overlay BM
          packet only to the ACs and not other overlay tunnels.

   PTA: PMSI Tunnel Attribute

   RT-3: EVPN Route Type 3, Inclusive Multicast Ethernet Tag route


   RT-11: EVPN Route Type 11, Leaf Auto-Discovery (AD) route

15. References

15.1 Normative References


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

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


   [RFC7902]Rosen, E. and Morin, T., "Registry and Extensions for P-
   Multicast Service Interface Tunnel Attribute Flags", June 2016,
   <http://www.rfc-editor.org/info/rfc7902>.

   [EVPN-BUM] Zhang et al., "Updates on EVPN BUM Procedures", draft-
   ietf-bess-evpn-bum-procedure-updates-01.txt, work in progress,
   December 2016.

15.2 Informative References

   [EVPN-OVERLAY] Sajassi-Drake et al., "A Network Virtualization
   Overlay Solution using EVPN", draft-ietf-bess-evpn-overlay-07.txt,
   work in progress, December 2016.


16. Acknowledgments

   The authors would like to thank Neil Hart, David Motz, Kiran Nagaraj,
   Dai Truong, Thomas Morin, Jeffrey Zhang and Shankar Murthy for their
   valuable feedback and contributions.

17. Authors' Addresses



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   Jorge Rabadan (Editor)
   Nokia
   777 E. Middlefield Road
   Mountain View, CA 94043 USA
   Email: jorge.rabadan@nokia.com

   Senthil Sathappan
   Nokia
   Email: senthil.sathappan@nokia.com

   Mukul Katiyar
   Juniper Networks
   Email: mkatiyar@juniper.net

   Wim Henderickx
   Nokia
   Email: wim.henderickx@nokia.com

   Ravi Shekhar
   Juniper Networks
   Email: rshekhar@juniper.net

   Nischal Sheth
   Juniper Networks
   Email: nsheth@juniper.net

   Wen Lin
   Juniper Networks
   Email: wlin@juniper.net

   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com

   Aldrin Isaac
   Juniper
   Email: aisaac@juniper.net

   Mudassir Tufail
   Citibank
   mudassir.tufail@citi.com










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