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Versions: (draft-rabadan-bess-dci-evpn-overlay) 00 01 02 03 04 05 06 07 08 09 10 Draft is active
In: MissingRef
BESS Workgroup                                                J. Rabadan
Internet Draft                                              S. Sathappan
Intended status: Standards Track                           W. Henderickx
                                                         S. Palislamovic
R. Shekhar                                                         Nokia
A. Lohiya
J. Drake
Juniper                                                       A. Sajassi
                                                                  D. Cai
                                                                   Cisco


Expires: March 12, 2017                                September 8, 2016



            Interconnect Solution for EVPN Overlay networks
                  draft-ietf-bess-dci-evpn-overlay-04

Abstract

   This document describes how Network Virtualization Overlay networks
   (NVO) can be connected to a Wide Area Network (WAN) in order to
   extend the layer-2 connectivity required for some tenants. The
   solution analyzes the interaction between NVO networks running EVPN
   and other L2VPN technologies used in the WAN, such as VPLS/PBB-VPLS
   or EVPN/PBB-EVPN, and proposes a solution for the interworking
   between both.

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
   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



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   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on March 12, 2017.

Copyright Notice

   Copyright (c) 2016 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. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Decoupled Interconnect solution for EVPN overlay networks . . .  3
     2.1. Interconnect requirements . . . . . . . . . . . . . . . . .  4
     2.2. VLAN-based hand-off . . . . . . . . . . . . . . . . . . . .  5
     2.3. PW-based (Pseudowire-based) hand-off  . . . . . . . . . . .  5
     2.4. Multi-homing solution on the GWs  . . . . . . . . . . . . .  6
     2.5. Gateway Optimizations . . . . . . . . . . . . . . . . . . .  6
       2.5.1. MAC Address Advertisement Control . . . . . . . . . . .  6
       2.5.2. ARP flooding control  . . . . . . . . . . . . . . . . .  7
       2.5.3. Handling failures between GW and WAN Edge routers . . .  7
   3. Integrated Interconnect solution for EVPN overlay networks  . .  8
     3.1. Interconnect requirements . . . . . . . . . . . . . . . . .  8
     3.2. VPLS Interconnect for EVPN-Overlay networks . . . . . . . .  9
       3.2.1. Control/Data Plane setup procedures on the GWs  . . . .  9
       3.2.2. Multi-homing procedures on the GWs  . . . . . . . . . . 10
     3.3. PBB-VPLS Interconnect for EVPN-Overlay networks . . . . . . 10
       3.3.1. Control/Data Plane setup procedures on the GWs  . . . . 10
       3.3.2. Multi-homing procedures on the GWs  . . . . . . . . . . 11
     3.4. EVPN-MPLS Interconnect for EVPN-Overlay networks  . . . . . 11
       3.4.1. Control Plane setup procedures on the GWs . . . . . . . 11
       3.4.2. Data Plane setup procedures on the GWs  . . . . . . . . 13
       3.4.3. Multi-homing procedure extensions on the GWs  . . . . . 14
       3.4.4. Impact on MAC Mobility procedures . . . . . . . . . . . 16
       3.4.5. Gateway optimizations . . . . . . . . . . . . . . . . . 16
       3.4.6. Benefits of the EVPN-MPLS Interconnect solution . . . . 17
     3.5. PBB-EVPN Interconnect for EVPN-Overlay networks . . . . . . 18



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       3.5.1. Control/Data Plane setup procedures on the GWs  . . . . 18
       3.5.2. Multi-homing procedures on the GWs  . . . . . . . . . . 18
       3.5.3. Impact on MAC Mobility procedures . . . . . . . . . . . 18
       3.5.4. Gateway optimizations . . . . . . . . . . . . . . . . . 19
     3.6. EVPN-VXLAN Interconnect for EVPN-Overlay networks . . . . . 19
       3.6.1. Globally unique VNIs in the Interconnect network  . . . 20
       3.6.2. Downstream assigned VNIs in the Interconnect network  . 20
   5. Conventions and Terminology . . . . . . . . . . . . . . . . . . 20
   6. Security Considerations . . . . . . . . . . . . . . . . . . . . 21
   7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 21
   8. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     8.1. Normative References  . . . . . . . . . . . . . . . . . . . 21
     8.2. Informative References  . . . . . . . . . . . . . . . . . . 22
   9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 22
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22
   11. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 23



1. Introduction

   [EVPN-Overlays] discusses the use of EVPN as the control plane for
   Network Virtualization Overlay (NVO) networks, where VXLAN, NVGRE or
   MPLS over GRE can be used as possible data plane encapsulation
   options.

   While this model provides a scalable and efficient multi-tenant
   solution within the Data Center, it might not be easily extended to
   the WAN in some cases due to the requirements and existing deployed
   technologies. For instance, a Service Provider might have an already
   deployed (PBB-)VPLS or (PBB-)EVPN network that must be used to
   interconnect Data Centers and WAN VPN users. A Gateway (GW) function
   is required in these cases.

   This document describes a Interconnect solution for EVPN overlay
   networks, assuming that the NVO Gateway (GW) and the WAN Edge
   functions can be decoupled in two separate systems or integrated into
   the same system. The former option will be referred as "Decoupled
   Interconnect solution" throughout the document, whereas the latter
   one will be referred as "Integrated Interconnect solution".

2. Decoupled Interconnect solution for EVPN overlay networks

   This section describes the interconnect solution when the GW and WAN
   Edge functions are implemented in different systems. Figure 1 depicts
   the reference model described in this section.





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                                   +--+
                                   |CE|
                                   +--+
                                     |
                                  +----+
                             +----| PE |----+
           +---------+       |    +----+    |       +---------+
   +----+  |        +---+  +----+        +----+  +---+        |  +----+
   |NVE1|--|        |   |  |WAN |        |WAN |  |   |        |--|NVE3|
   +----+  |        |GW1|--|Edge|        |Edge|--|GW3|        |  +----+
           |        +---+  +----+        +----+  +---+        |
           |  NVO-1   |      |     WAN      |      |   NVO-2  |
           |        +---+  +----+        +----+  +---+        |
           |        |   |  |WAN |        |WAN |  |   |        |
   +----+  |        |GW2|--|Edge|        |Edge|--|GW4|        |  +----+
   |NVE2|--|        +---+  +----+        +----+  +---+        |--|NVE4|
   +----+  +---------+       |              |       +---------+  +----+
                             +--------------+

   |<-EVPN-Overlay-->|<-VLAN->|<-WAN L2VPN->|<--PW-->|<--EVPN-Overlay->|
                      hand-off               hand-off

                         Figure 1 Decoupled Interconnect model

   The following section describes the interconnect requirements for
   this model.

2.1. Interconnect requirements

   This proposed Interconnect architecture will be normally deployed in
   networks where the EVPN-Overlay and WAN providers are different
   entities and a clear demarcation is needed. The solution must observe
   the following requirements:

   o A simple connectivity hand-off must be provided between the EVPN-
     Overlay network provider and the WAN provider so that QoS and
     security enforcement are easily accomplished.

   o The solution must be independent of the L2VPN technology deployed
     in the WAN.

   o Multi-homing between GW and WAN Edge routers is required. Per-
     service load balancing MUST be supported. Per-flow load balancing
     MAY be supported but it is not a strong requirement since a
     deterministic path per service is usually required for an easy QoS
     and security enforcement.

   o Ethernet OAM and Connectivity Fault Management (CFM) functions must



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     be supported between the EVPN-Overlay network and the WAN network.

   o The following optimizations MAY be supported at the GW:
     + Flooding reduction of unknown unicast traffic sourced from the DC
       Network Virtualization Edge devices (NVEs).
     + Control of the WAN MAC addresses advertised to the DC.
     + ARP flooding control for the requests coming from the WAN.

2.2. VLAN-based hand-off

   In this option, the hand-off between the GWs and the WAN Edge routers
   is based on 802.1Q VLANs. This is illustrated in Figure 1 (between
   the GWs in NVO-1 and the WAN Edge routers). Each MAC-VRF in the GW is
   connected to a different VSI/MAC-VRF instance in the WAN Edge router
   by using a different C-TAG VLAN ID or a different combination of
   S/C-TAG VLAN IDs that matches at both sides.

   This option provides the best possible demarcation between the DC and
   WAN providers and it does not require control plane interaction
   between both providers. The disadvantage of this model is the
   provisioning overhead since the service must be mapped to a S/C-TAG
   VLAN ID combination at both, GW and WAN Edge routers.

   In this model, the GW acts as a regular Network Virtualization Edge
   (NVE) towards the DC. Its control plane, data plane procedures and
   interactions are described in [EVPN-Overlays].

   The WAN Edge router acts as a (PBB-)VPLS or (PBB-)EVPN PE with
   attachment circuits (ACs) to the GWs. Its functions are described in
   [RFC4761][RFC4762][RFC6074] or [RFC7432][RFC7623].

2.3. PW-based (Pseudowire-based) hand-off

   If MPLS can be enabled between the GW and the WAN Edge router, a PW-
   based Interconnect solution can be deployed. In this option the
   hand-off between both routers is based on FEC128-based PWs or FEC129-
   based PWs (for a greater level of network automation). Note that this
   model still provides a clear demarcation boundary between DC and WAN,
   and security/QoS policies may be applied on a per PW basis. This
   model provides better scalability than a C-TAG based hand-off and
   less provisioning overhead than a combined C/S-TAG hand-off. The
   PW-based hand-off interconnect is illustrated in Figure 1 (between
   the NVO-2 GWs and the WAN Edge routers).

   In this model, besides the usual MPLS procedures between GW and WAN
   Edge router, the GW MUST support an interworking function in each
   MAC-VRF that requires extension to the WAN:




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   o If a FEC128-based PW is used between the MAC-VRF (GW) and the VSI
     (WAN Edge), the provisioning of the VCID for such PW MUST be
     supported on the MAC-VRF and must match the VCID used in the peer
     VSI at the WAN Edge router.

   o If BGP Auto-discovery [RFC6074] and FEC129-based PWs are used
     between the GW MAC-VRF and the WAN Edge VSI, the provisioning of
     the VPLS-ID MUST be supported on the MAC-VRF and must match the
     VPLS-ID used in the WAN Edge VSI.

2.4. Multi-homing solution on the GWs

   As already discussed, single-active multi-homing, i.e. per-service
   load-balancing multi-homing MUST be supported in this type of
   interconnect. All-active multi-homing may be considered in future
   revisions of this document.

   The GWs will be provisioned with a unique ESI per WAN interconnect
   and the hand-off attachment circuits or PWs between the GW and the
   WAN Edge router will be assigned to such ESI. The ESI will be
   administratively configured on the GWs according to the procedures in
   [RFC7432]. This Interconnect ESI will be referred as "I-ESI"
   hereafter.

   The solution (on the GWs) MUST follow the single-active multi-homing
   procedures as described in [EVPN-Overlays] for the provisioned I-ESI,
   i.e. Ethernet A-D routes per ESI and per EVI will be advertised to
   the DC NVEs. The MAC addresses learned (in the data plane) on the
   hand-off links will be advertised with the I-ESI encoded in the ESI
   field.

2.5. Gateway Optimizations

   The following features MAY be supported on the GW in order to
   optimize the control plane and data plane in the DC.

2.5.1. MAC Address Advertisement Control

   The use of EVPN in the NVO networks brings a significant number of
   benefits as described in [EVPN-Overlays].  However, if multiple DCs
   are interconnected into a single EVI, each DC will have to import all
   of the MAC addresses from each of the other DCs.

   Even if optimized BGP techniques like RT-constraint are used, the
   number of MAC addresses to advertise or withdraw (in case of failure)
   by the GWs of a given DC could overwhelm the NVEs within that DC,
   particularly when the NVEs reside in the hypervisors.




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   The solution specified in this document uses the 'Unknown MAC' route
   which is advertised into a given DC by each of the DC's GWs.  This
   route is a regular EVPN MAC/IP Advertisement route in which the MAC
   Address Length is set to 48, the MAC address is set to
   00:00:00:00:00:00, the IP length is set to 0, and the ESI field is
   set to the DC GW's I-ESI.

   An NVE within that DC that understands the Unknown MAC route will
   send (unicast) a packet with an unknown unicast MAC address to one of
   the DCs GWs which will then forward that packet to the correct egress
   PE.  I.e., because the ESI is set to the DC GW's I-ESI, all-active
   multi-homing can be applied to unknown unicast MAC addresses.

   This document proposes that administrative policy determines whether
   and which external MAC addresses and/or the Unknown MAC route are to
   be advertised into a given DC. E.g., when all the DC MAC addresses
   are learned in the control/management plane, it may be appropriate to
   advertise the Unknown MAC route.

2.5.2. ARP flooding control

   Another optimization mechanism, naturally provided by EVPN in the
   GWs, is the Proxy ARP/ND function. The GWs SHOULD build a Proxy
   ARP/ND cache table as per [RFC7432]. When the active GW receives an
   ARP/ND request/solicitation coming from the WAN, the GW does a Proxy
   ARP/ND table lookup and replies as long as the information is
   available in its table.

   This mechanism is especially recommended on the GWs since it protects
   the DC network from external ARP/ND-flooding storms.

2.5.3. Handling failures between GW and WAN Edge routers

   Link/PE failures MUST be handled on the GWs as specified in
   [RFC7432]. The GW detecting the failure will withdraw the EVPN routes
   as per [RFC7432].

   Individual AC/PW failures should be detected by OAM mechanisms. For
   instance:

   o If the Interconnect solution is based on a VLAN hand-off,
     802.1ag/Y.1731 Ethernet-CFM MAY be used to detect individual AC
     failures on both, the GW and WAN Edge router. An individual AC
     failure will trigger the withdrawal of the corresponding A-D per
     EVI route as well as the MACs learned on that AC.

   o If the Interconnect solution is based on a PW hand-off, the LDP PW
     Status bits TLV MAY be used to detect individual PW failures on



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     both, the GW and WAN Edge router.

3. Integrated Interconnect solution for EVPN overlay networks

   When the DC and the WAN are operated by the same administrative
   entity, the Service Provider can decide to integrate the GW and WAN
   Edge PE functions in the same router for obvious CAPEX and OPEX
   saving reasons. This is illustrated in Figure 2. Note that this model
   does not provide an explicit demarcation link between DC and WAN
   anymore.

                             +--+
                             |CE|
                             +--+
                               |
                            +----+
                       +----| PE |----+
           +---------+ |    +----+    | +---------+
   +----+  |        +---+            +---+        |  +----+
   |NVE1|--|        |   |            |   |        |--|NVE3|
   +----+  |        |GW1|            |GW3|        |  +----+
           |        +---+            +---+        |
           |  NVO-1   |       WAN      |   NVO-2  |
           |        +---+            +---+        |
           |        |   |            |   |        |
   +----+  |        |GW2|            |GW4|        |  +----+
   |NVE2|--|        +---+            +---+        |--|NVE4|
   +----+  +---------+ |              | +---------+  +----+
                       +--------------+

   |<--EVPN-Overlay--->|<-----VPLS--->|<---EVPN-Overlay-->|
                       |<--PBB-VPLS-->|
     Interconnect  ->  |<-EVPN-MPLS-->|
      options          |<--EVPN-Ovl-->|
                       |<--PBB-EVPN-->|

               Figure 2 Integrated Interconnect model

3.1. Interconnect requirements

   The solution must observe the following requirements:

   o The GW function must provide control plane and data plane
     interworking between the EVPN-overlay network and the L2VPN
     technology supported in the WAN, i.e. (PBB-)VPLS or (PBB-)EVPN, as
     depicted in Figure 2.

   o Multi-homing MUST be supported. Single-active multi-homing with



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     per-service load balancing MUST be implemented. All-active multi-
     homing, i.e. per-flow load-balancing, MUST be implemented as long
     as the technology deployed in the WAN supports it.

   o If EVPN is deployed in the WAN, the MAC Mobility, Static MAC
     protection and other procedures (e.g. proxy-arp) described in
     [RFC7432] must be supported end-to-end.

   o Any type of inclusive multicast tree MUST be independently
     supported in the WAN as per [RFC7432], and in the DC as per [EVPN-
     Overlays].

3.2. VPLS Interconnect for EVPN-Overlay networks

3.2.1. Control/Data Plane setup procedures on the GWs

   Regular MPLS tunnels and TLDP/BGP sessions will be setup to the WAN
   PEs and RRs as per [RFC4761][RFC4762][RFC6074] and overlay tunnels
   and EVPN will be setup as per [EVPN-Overlays]. Note that different
   route-targets for the DC and for the WAN are normally required. A
   single type-1 RD per service may be used.

   In order to support multi-homing, the GWs will be provisioned with an
   I-ESI (see section 2.4), that will be unique per interconnection. All
   the [RFC7432] procedures are still followed for the I-ESI, e.g. any
   MAC address learned from the WAN will be advertised to the DC with
   the I-ESI in the ESI field.

   A MAC-VRF per EVI will be created in each GW. The MAC-VRF will have
   two different types of tunnel bindings instantiated in two different
   split-horizon-groups:

      o VPLS PWs will be instantiated in the "WAN split-horizon-group".

      o Overlay tunnel bindings (e.g. VXLAN, NVGRE) will be instantiated
      in the "DC split-horizon-group".

   Attachment circuits are also supported on the same MAC-VRF, but they
   will not be part of any of the above split-horizon-groups.

   Traffic received in a given split-horizon-group will never be
   forwarded to a member of the same split-horizon-group.

   As far as BUM flooding is concerned, a flooding list will be created
   with the sub-list created by the inclusive multicast routes and the
   sub-list created for VPLS in the WAN. BUM frames received from a
   local attachment circuit will be flooded to both sub-lists. BUM
   frames received from the DC or the WAN will be forwarded to the



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   flooding list observing the split-horizon-group rule described above.

   Note that the GWs are not allowed to have an EVPN binding and a PW to
   the same far-end within the same MAC-VRF in order to avoid loops and
   packet duplication. This is described in [EVPN-VPLS-INTEGRATION].

   The optimizations procedures described in section 2.5 can also be
   applied to this model.


3.2.2. Multi-homing procedures on the GWs

   Single-active multi-homing MUST be supported on the GWs. All-active
   multi-homing is not supported by VPLS.

   All the single-active multi-homing procedures as described by [EVPN-
   Overlays] will be followed for the I-ESI.

   The non-DF GW for the I-ESI will block the transmission and reception
   of all the bindings in the "WAN split-horizon-group" for BUM and
   unicast traffic.

3.3. PBB-VPLS Interconnect for EVPN-Overlay networks

3.3.1. Control/Data Plane setup procedures on the GWs

   In this case, there is no impact on the procedures described in
   [RFC7041] for the B-component. However the I-component instances
   become EVI instances with EVPN-Overlay bindings and potentially local
   attachment circuits. M MAC-VRF instances can be multiplexed into the
   same B-component instance. This option provides significant savings
   in terms of PWs to be maintained in the WAN.

   The I-ESI concept described in section 3.2.1 will also be used for
   the PBB-VPLS-based Interconnect.

   B-component PWs and I-component EVPN-overlay bindings established to
   the same far-end will be compared. The following rules will be
   observed:

      o Attempts to setup a PW between the two GWs within the B-
      component context will never be blocked.

      o If a PW exists between two GWs for the B-component and an
      attempt is made to setup an EVPN binding on an I-component linked
      to that B-component, the EVPN binding will be kept operationally
      down. Note that the BGP EVPN routes will still be valid but not
      used.



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      o The EVPN binding will only be up and used as long as there is no
      PW to the same far-end in the corresponding B-component. The EVPN
      bindings in the I-components will be brought down before the PW in
      the B-component is brought up.

   The optimizations procedures described in section 2.5 can also be
   applied to this Interconnect option.

3.3.2. Multi-homing procedures on the GWs

   Single-active multi-homing MUST be supported on the GWs.

   All the single-active multi-homing procedures as described by [EVPN-
   Overlays] will be followed for the I-ESI for each EVI instance
   connected to B-component.

3.4. EVPN-MPLS Interconnect for EVPN-Overlay networks

   If EVPN for MPLS tunnels, EVPN-MPLS hereafter, is supported in the
   WAN, an end-to-end EVPN solution can be deployed. The following
   sections describe the proposed solution as well as the impact
   required on the [RFC7432] procedures.

3.4.1. Control Plane setup procedures on the GWs

   The GWs MUST establish separate BGP sessions for sending/receiving
   EVPN routes to/from the DC and to/from the WAN. Normally each GW will
   setup one (two) BGP EVPN session(s) to the DC RR(s) and one(two)
   session(s) to the WAN RR(s).

   In order to facilitate separate BGP processes for DC and WAN, EVPN
   routes sent to the WAN SHOULD carry a different route-distinguisher
   (RD) than the EVPN routes sent to the DC. In addition, although
   reusing the same value is possible, different route-targets are
   expected to be handled for the same EVI in the WAN and the DC. Note
   that the EVPN service routes sent to the DC RRs will normally include
   a [RFC5512] BGP encapsulation extended community with a different
   tunnel type than the one sent to the WAN RRs.

   As in the other discussed options, an I-ESI will be configured on the
   GWs for multi-homing. This I-ESI represents the WAN to the DC but
   also the DC to the WAN. Optionally, different I-ESI values MAY be
   configured for representing the WAN and the DC. If different EVPN-
   Overlay networks are connected to the same group of GWs, each EVPN-
   Overlay network MUST get assigned a different I-ESI.

   Received EVPN routes will never be reflected on the GWs but consumed
   and re-advertised (if needed):



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      o Ethernet A-D routes, ES routes and Inclusive Multicast routes
        are consumed by the GWs and processed locally for the
        corresponding [RFC7432] procedures.

      o MAC/IP advertisement routes will be received, imported and if
        they become active in the MAC-VRF MAC FIB, the information will
        be re-advertised as new routes with the following fields:

        + The RD will be the GW's RD for the MAC-VRF.

        + The ESI will be set to the I-ESI.

        + The Ethernet-tag value will be kept from the received NLRI.

        + The MAC length, MAC address, IP Length and IP address values
        will be kept from the received NLRI.

        + The MPLS label will be a local 20-bit value (when sent to the
        WAN) or a DC-global 24-bit value (when sent to the DC).

        + The appropriate Route-Targets (RTs) and [RFC5512] BGP
        Encapsulation extended community will be used according to
        [EVPN-Overlays].

   The GWs will also generate the following local EVPN routes that will
   be sent to the DC and WAN, with their corresponding RTs and [RFC5512]
   BGP Encapsulation extended community values:

      o ES route(s) for the I-ESI(s).

      o Ethernet A-D routes per ESI and EVI for the I-ESI(s). The A-D
        per-EVI routes sent to the WAN and the DC will have consistent
        Ethernet-Tag values.

      o Inclusive Multicast routes with independent tunnel type value
        for the WAN and DC. E.g. a P2MP LSP may be used in the WAN
        whereas ingress replication may be used in the DC. The routes
        sent to the WAN and the DC will have a consistent Ethernet-Tag.

      o MAC/IP advertisement routes for MAC addresses learned in local
        attachment circuits. Note that these routes will not include the
        I-ESI, but ESI=0 or different from 0 for local multi-homed
        Ethernet Segments (ES). The routes sent to the WAN and the DC
        will have a consistent Ethernet-Tag.

   Assuming GW1 and GW2 are peer GWs of the same DC, each GW will
   generate two sets of local service routes: Set-DC will be sent to the
   DC RRs and will include A-D per EVI, Inclusive Multicast and MAC/IP



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   routes for the DC encapsulation and RT. Set-WAN will be sent to the
   WAN RRs and will include the same routes but using the WAN RT and
   encapsulation. GW1 and GW2 will receive each other's set-DC and set-
   WAN. This is the expected behavior on GW1 and GW2 for locally
   generated routes:

      o Inclusive multicast routes: when setting up the flooding lists
        for a given MAC-VRF, each GW will include its DC peer GW only in
        the EVPN-MPLS flooding list (by default) and not the EVPN-
        Overlay flooding list. That is, GW2 will import two Inclusive
        Multicast routes from GW1 (from set-DC and set-WAN) but will
        only consider one of the two, having the set-WAN route higher
        priority. An administrative option MAY change this preference so
        that the set-DC route is selected first.

      o MAC/IP advertisement routes for local attachment circuits: as
        above, the GW will select only one, having the route from the
        set-WAN a higher priority. As for the Inclusive multicast
        routes, an administrative option MAY change this priority.

   Note that, irrespective of the encapsulation, EVPN routes always have
   higher priority than VPLS AD routes as per [EVPN-VPLS-INTEGRATION].

3.4.2. Data Plane setup procedures on the GWs

   The procedure explained at the end of the previous section will make
   sure there are no loops or packet duplication between the GWs of the
   same EVPN-Overlay network (for frames generated from local ACs) since
   only one EVPN binding per EVI (or per Ethernet Tag in case of VLAN-
   aware bundle services) will be setup in the data plane between the
   two nodes. That binding will by default be added to the EVPN-MPLS
   flooding list.

   As for the rest of the EVPN tunnel bindings, they will be added to
   one of the two flooding lists that each GW sets up for the same MAC-
   VRF:

      o EVPN-overlay flooding list (composed of bindings to the remote
        NVEs or multicast tunnel to the NVEs).

      o EVPN-MPLS flooding list (composed of MP2P or LSM tunnel to the
        remote PEs)

   Each flooding list will be part of a separate split-horizon-group:
   the WAN split-horizon-group or the DC split-horizon-group. Traffic
   generated from a local AC can be flooded to both
   split-horizon-groups. Traffic from a binding of a split-horizon-group
   can be flooded to the other split-horizon-group and local ACs, but



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   never to a member of its own split-horizon-group.

   When either GW1 or GW2 receive a BUM frame on an MPLS tunnel
   including an ESI label at the bottom of the stack, they will perform
   an ESI label lookup and split-horizon filtering as per [RFC7432] in
   case the ESI label identifies a local ESI (I-ESI or any other non-
   zero ESI).


3.4.3. Multi-homing procedure extensions on the GWs

   Single-active as well as all-active multi-homing MUST be supported.

   All the [RFC7432] multi-homing procedures for the DF election on I-
   ESI(s) as well as the backup-path (single-active) and aliasing (all-
   active) procedures will be followed on the GWs. Remote PEs in the
   EVPN-MPLS network will follow regular [RFC7432] aliasing or backup-
   path procedures for MAC/IP routes received from the GWs for the same
   I-ESI. So will NVEs in the EVPN-Overlay network for MAC/IP routes
   received with the same I-ESI.

   As far as the forwarding plane is concerned, by default, the EVPN-
   Overlay network will have an analogous behavior to the access ACs in
   [RFC7432] multi-homed Ethernet Segments.

   The forwarding behavior on the GWs is described below:

      o Single-active multi-homing; assuming a WAN split-horizon-group
        (comprised of EVPN-MPLS bindings), a DC split-horizon-group
        (comprised of EVPN-Overlay bindings) and local ACs on the GWs:

        + Forwarding behavior on the non-DF: the non-DF MUST block
          ingress and egress forwarding on the EVPN-Overlay bindings
          associated to the I-ESI. The EVPN-MPLS network is considered
          to be the core network and the EVPN-MPLS bindings to the
          remote PEs and GWs will be active.

        + Forwarding behavior on the DF: the DF MUST NOT forward BUM or
          unicast traffic received from a given split-horizon-group to a
          member of his own split-horizon group. Forwarding to other
          split-horizon-groups and local ACs is allowed (as long as the
          ACs are not part of an ES for which the node is non-DF). As
          per [RFC7432] and for split-horizon purposes, when receiving
          BUM traffic on the EVPN-Overlay bindings associated to an I-
          ESI, the DF GW SHOULD add the I-ESI label when forwarding to
          the peer GW over EVPN-MPLS.

        + When receiving EVPN MAC/IP routes from the WAN, the non-DF



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          MUST NOT re-originate the EVPN routes and advertise them to
          the DC peers. In the same way, EVPN MAC/IP routes received
          from the DC MUST NOT be advertised to the WAN peers. This is
          consistent with [RFC7432] and allows the remote PE/NVEs know
          who the primary GW is, based on the reception of the MAC/IP
          routes.

      o All-active multi-homing; assuming a WAN split-horizon-group
        (comprised of EVPN-MPLS bindings), a DC split-horizon-group
        (comprised of EVPN-Overlay bindings) and local ACs on the GWs:

        + Forwarding behavior on the non-DF: the non-DF follows the same
          behavior as the non-DF in the single-active case but only for
          BUM traffic. Unicast traffic received from a split-horizon-
          group MUST NOT be forwarded to a member of its own split-
          horizon-group but can be forwarded normally to the other
          split-horizon-groups and local ACs. If a known unicast packet
          is identified as a "flooded" packet, the procedures for BUM
          traffic MUST be followed.

        + Forwarding behavior on the DF: the DF follows the same
          behavior as the DF in the single-active case but only for BUM
          traffic. Unicast traffic received from a split-horizon-group
          MUST NOT be forwarded to a member of its own split-horizon-
          group but can be forwarded normally to the other split-
          horizon-group and local ACs. If a known unicast packet is
          identified as a "flooded" packet, the procedures for BUM
          traffic MUST be followed. As per [RFC7432] and for split-
          horizon purposes, when receiving BUM traffic on the EVPN-
          Overlay bindings associated to an I-ESI, the DF GW MUST add
          the I-ESI label when forwarding to the peer GW over EVPN-MPLS.

        + Contrary to the single-active multi-homing case, both DF and
          non-DF re-originate and advertise MAC/IP routes received from
          the WAN/DC peers, adding the corresponding I-ESI so that the
          remote PE/NVEs can perform regular aliasing as per [RFC7432].

   The example in Figure 3 illustrates the forwarding of BUM traffic
   originated from an NVE on a pair of all-active multi-homing GWs.












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        |<--EVPN-Overlay--->|<--EVPN-MPLS-->|

                +---------+ +--------------+
         +----+ BUM       +---+             |
         |NVE1+----+----> |   +-+-----+     |
         +----+  | |   DF |GW1| |     |     |
                 | |      +-+-+ |     |    ++--+
                 | |        |   |     +--> |PE1|
                 | +--->X +-+-+ |          ++--+
                 |     NDF|   | |           |
         +----+  |        |GW2<-+           |
         |NVE2+--+        +-+-+             |
         +----+  +--------+ |  +------------+
                            v
                          +--+
                          |CE|
                          +--+

               Figure 3 Multi-homing BUM forwarding

   GW2 is the non-DF for the I-ESI and blocks the BUM forwarding. GW1 is
   the DF and forwards the traffic to PE1 and GW2. GW2 will only forward
   the packets to local ACs (CE in the example).

3.4.4. Impact on MAC Mobility procedures

   MAC Mobility procedures described in [RFC7432] are not modified by
   this document.

   Note that an intra-DC MAC move still leaves the MAC attached to the
   same I-ESI, so under the rules of [RFC7432] this is not considered a
   MAC mobility event. Only when the MAC moves from the WAN domain to
   the DC domain (or from one DC to another) the MAC will be learned
   from a different ES and the MAC Mobility procedures will kick in.

   The sticky bit indication in the MAC Mobility extended community MUST
   be propagated between domains.

3.4.5. Gateway optimizations

   All the Gateway optimizations described in section 2.5 MAY be applied
   to the GWs when the Interconnect is based on EVPN-MPLS.

   In particular, the use of the Unknown MAC route, as described in
   section 2.5.1, solves some transient packet duplication issues in
   cases of all-active multi-homing, as explained below.

   Consider the diagram in Figure 2 for EVPN-MPLS Interconnect and all-



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   active multi-homing, and the following sequence:

      a) MAC Address M1 is advertised from NVE3 in EVI-1.

      b) GW3 and GW4 learn M1 for EVI-1 and re-advertise M1 to the WAN
         with I-ESI-2 in the ESI field.

      c) GW1 and GW2 learn M1 and install GW3/GW4 as next-hops following
         the EVPN aliasing procedures.

      d) Before NVE1 learns M1, a packet arrives at NVE1 with
         destination M1. If the Unknown MAC route had not been
         advertised into the DC, NVE1 would have flooded the packet
         throughout the DC, in particular to both GW1 and GW2.  If the
         same VNI/VSID is used for both known unicast and BUM traffic,
         as is typically the case, there is no indication in the packet
         that it is a BUM packet and both GW1 and GW2 would have
         forwarded it. However, because the Unknown MAC route had been
         advertised into the DC, NVE1 will unicast the packet to either
         GW1 or GW2.

      e) Since both GW1 and GW2 know M1, the GW receiving the packet
         will forward it to either GW3 or GW4.

3.4.6. Benefits of the EVPN-MPLS Interconnect solution

   Besides retaining the EVPN attributes between Data Centers and
   throughout the WAN, the EVPN-MPLS Interconnect solution on the GWs
   has some benefits compared to pure BGP EVPN RR or Inter-AS model B
   solutions without a gateway:

      o The solution supports the connectivity of local attachment
        circuits on the GWs.

      o Different data plane encapsulations can be supported in the DC
        and the WAN.

      o Optimized multicast solution, with independent inclusive
        multicast trees in DC and WAN.

      o MPLS Label aggregation: for the case where MPLS labels are
        signaled from the NVEs for MAC/IP Advertisement routes, this
        solution provides label aggregation. A remote PE MAY receive a
        single label per GW MAC-VRF as opposed to a label per NVE/MAC-
        VRF connected to the GW MAC-VRF. For instance, in Figure 2, PE
        would receive only one label for all the routes advertised for a
        given MAC-VRF from GW1, as opposed to a label per NVE/MAC-VRF.




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      o The GW will not propagate MAC mobility for the MACs moving
        within a DC. Mobility intra-DC is solved by all the NVEs in the
        DC. The MAC Mobility procedures on the GWs are only required in
        case of mobility across DCs.

      o Proxy-ARP/ND function on the DC GWs can be leveraged to reduce
        ARP/ND flooding in the DC or/and in the WAN.

3.5. PBB-EVPN Interconnect for EVPN-Overlay networks

   PBB-EVPN [RFC7623] is yet another Interconnect option. It requires
   the use of GWs where I-components and associated B-components are
   part of EVI instances.

3.5.1. Control/Data Plane setup procedures on the GWs

   EVPN will run independently in both components, the I-component MAC-
   VRF and B-component MAC-VRF. Compared to [RFC7623], the DC C-MACs are
   no longer learned in the data plane on the GW but in the control
   plane through EVPN running on the I-component. Remote C-MACs coming
   from remote PEs are still learned in the data plane. B-MACs in the B-
   component will be assigned and advertised following the procedures
   described in [RFC7623].

   An I-ESI will be configured on the GWs for multi-homing, but it will
   only be used in the EVPN control plane for the I-component EVI. No
   non-reserved ESIs will be used in the control plane of the B-
   component EVI as per [RFC7623].

   The rest of the control plane procedures will follow [RFC7432] for
   the I-component EVI and [RFC7623] for the B-component EVI.

   From the data plane perspective, the I-component and B-component EVPN
   bindings established to the same far-end will be compared and the I-
   component EVPN-overlay binding will be kept down following the rules
   described in section 3.3.1.

3.5.2. Multi-homing procedures on the GWs

   Single-active as well as all-active multi-homing MUST be supported.

   The forwarding behavior of the DF and non-DF will be changed based on
   the description outlined in section 3.4.3, only replacing the "WAN
   split-horizon-group" for the B-component.

3.5.3. Impact on MAC Mobility procedures

   C-MACs learned from the B-component will be advertised in EVPN within



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   the I-component EVI scope. If the C-MAC was previously known in the
   I-component database, EVPN would advertise the C-MAC with a higher
   sequence number, as per [RFC7432]. From a Mobility perspective and
   the related procedures described in [RFC7432], the C-MACs learned
   from the B-component are considered local.

3.5.4. Gateway optimizations

   All the considerations explained in section 3.4.5 are applicable to
   the PBB-EVPN Interconnect option.

3.6. EVPN-VXLAN Interconnect for EVPN-Overlay networks

   If EVPN for Overlay tunnels is supported in the WAN and a GW function
   is required, an end-to-end EVPN solution can be deployed. This
   section focuses on the specific case of EVPN for VXLAN (EVPN-VXLAN
   hereafter) and the impact on the [RFC7432] procedures.

   This use-case assumes that NVEs need to use the VNIs or VSIDs as a
   globally unique identifiers within a data center, and a Gateway needs
   to be employed at the edge of the data center network to translate
   the VNI or VSID when crossing the network boundaries. This GW
   function provides VNI and tunnel IP address translation. The use-case
   in which local downstream assigned VNIs or VSIDs can be used (like
   MPLS labels) is described by [EVPN-Overlays].

   While VNIs are globally significant within each DC, there are two
   possibilities in the Interconnect network:

      a) Globally unique VNIs in the Interconnect network:
         In this case, the GWs and PEs in the Interconnect network will
         agree on a common VNI for a given EVI. The RT to be used in the
         Interconnect network can be auto-derived from the agreed
         Interconnect VNI. The VNI used inside each DC MAY be the same
         as the Interconnect VNI.

      b) Downstream assigned VNIs in the Interconnect network.
         In this case, the GWs and PEs MUST use the proper RTs to
         import/export the EVPN routes. Note that even if the VNI is
         downstream assigned in the Interconnect network, and unlike
         option B, it only identifies the <Ethernet Tag, GW> pair and
         not the <Ethernet Tag, egress PE> pair. The VNI used inside
         each DC MAY be the same as the Interconnect VNI. GWs SHOULD
         support multiple VNI spaces per EVI (one per Interconnect
         network they are connected to).

   In both options, NVEs inside a DC only have to be aware of a single
   VNI space, and only GWs will handle the complexity of managing



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   multiple VNI spaces. In addition to VNI translation above, the GWs
   will provide translation of the tunnel source IP for the packets
   generated from the NVEs, using their own IP address. GWs will use
   that IP address as the BGP next-hop in all the EVPN updates to the
   Interconnect network.

   The following sections provide more details about these two options.

3.6.1. Globally unique VNIs in the Interconnect network

   Considering Figure 2, if a host H1 in NVO-1 needs to communicate with
   a host H2 in NVO-2, and assuming that different VNIs are used in each
   DC for the same EVI, e.g. VNI-10 in NVO-1 and VNI-20 in NVO-2, then
   the VNIs must be translated to a common Interconnect VNI (e.g. VNI-
   100) on the GWs. Each GW is provisioned with a VNI translation
   mapping so that it can translate the VNI in the control plane when
   sending BGP EVPN route updates to the Interconnect network. In other
   words, GW1 and GW2 must be configured to map VNI-10 to VNI-100 in the
   BGP update messages for H1's MAC route. This mapping is also used to
   translate the VNI in the data plane in both directions, that is, VNI-
   10 to VNI-100 when the packet is received from NVO-1 and the reverse
   mapping from VNI-100 to VNI-10 when the packet is received from the
   remote NVO-2 network and needs to be forwarded to NVO-1.

   The procedures described in section 3.4 will be followed, considering
   that the VNIs advertised/received by the GWs will be translated
   accordingly.

3.6.2. Downstream assigned VNIs in the Interconnect network

   In this case, if a host H1 in NVO-1 needs to communicate with a host
   H2 in NVO-2, and assuming that different VNIs are used in each DC for
   the same EVI, e.g. VNI-10 in NVO-1 and VNI-20 in NVO-2, then the VNIs
   must be translated as in section 3.6.1. However, in this case, there
   is no need to translate to a common Interconnect VNI on the GWs. Each
   GW can translate the VNI received in an EVPN update to a locally
   assigned VNI advertised to the Interconnect network. Each GW can use
   a different Interconnect VNI, hence this VNI does not need to be
   agreed on all the GWs and PEs of the Interconnect network.

   The procedures described in section 3.4 will be followed, taking the
   considerations above for the VNI translation.

5. Conventions and Terminology

   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].



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   AC: Attachment Circuit

   BUM: it refers to the Broadcast, Unknown unicast and Multicast
   traffic

   DF: Designated Forwarder

   GW: Gateway or Data Center Gateway

   DCI: Data Center Interconnect

   ES: Ethernet Segment

   ESI: Ethernet Segment Identifier

   I-ESI: Interconnect ESI defined on the GWs for multi-homing to/from
   the WAN

   EVI: EVPN Instance

   MAC-VRF: it refers to an EVI instance in a particular node

   NVE: Network Virtualization Edge

   PW: Pseudowire

   RD: Route-Distinguisher

   RT: Route-Target

   TOR: Top-Of-Rack switch

   VNI/VSID: refers to VXLAN/NVGRE virtual identifiers

   VSI: Virtual Switch Instance or VPLS instance in a particular PE


6. Security Considerations

   This section will be completed in future versions.

7. IANA Considerations


8. References

8.1. Normative References




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   [RFC4761]Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private LAN
   Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC 4761,
   DOI 10.17487/RFC4761, January 2007, <http://www.rfc-
   editor.org/info/rfc4761>.

   [RFC4762]Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private
   LAN Service (VPLS) Using Label Distribution Protocol (LDP)
   Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
   <http://www.rfc-editor.org/info/rfc4762>.

   [RFC6074]Rosen, E., Davie, B., Radoaca, V., and W. Luo,
   "Provisioning, Auto-Discovery, and Signaling in Layer 2 Virtual
   Private Networks (L2VPNs)", RFC 6074, DOI 10.17487/RFC6074, January
   2011, <http://www.rfc-editor.org/info/rfc6074>.

   [RFC7041]Balus, F., Ed., Sajassi, A., Ed., and N. Bitar, Ed.,
   "Extensions to the Virtual Private LAN Service (VPLS) Provider Edge
   (PE) Model for Provider Backbone Bridging", RFC 7041, DOI
   10.17487/RFC7041, November 2013, <http://www.rfc-
   editor.org/info/rfc7041>.

   [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>.


   [RFC7623] Sajassi et al., "Provider Backbone Bridging Combined with
   Ethernet VPN (PBB-EVPN)", RFC 7623, September, 2015, <http://www.rfc-
   editor.org/info/rfc7623>.


8.2. Informative References

   [EVPN-Overlays] Sajassi-Drake et al., "A Network Virtualization
   Overlay Solution using EVPN", draft-ietf-bess-evpn-overlay-04.txt,
   work in progress, June, 2016

   [EVPN-VPLS-INTEGRATION] Sajassi et al., "(PBB-)EVPN Seamless
   Integration with (PBB-)VPLS", draft-ietf-bess-evpn-vpls-integration-
   00.txt, work in progress, February, 2015

9. Acknowledgments

   The authors would like to thank Neil Hart for their valuable comments
   and feedback.

10. Contributors



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   In addition to the authors listed on the front page, the following
   co-authors have also contributed to this document:

   Florin Balus
   Wen Lin
   Patrice Brissette


11. Authors' Addresses


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

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

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

   Senad Palislamovic
   Nokia
   Email: senad.palislamovic@nokia.com

   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com

   Ravi Shekhar
   Juniper
   Email: rshekhar@juniper.net

   Anil Lohiya
   Juniper
   Email: alohiya@juniper.net

   Dennis Cai
   Cisco Systems
   Email: dcai@cisco.com

   John Drake
   Juniper
   Email: jdrake@juniper.net



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