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Versions: (draft-rabadan-bess-dci-evpn-overlay) 00 01 02 03 04 05 06 07 08 09 10

BESS Workgroup                                          J. Rabadan (Ed.)
Internet Draft                                              S. Sathappan
Intended status: Standards Track                           W. Henderickx
                                                                   Nokia

                                                              A. Sajassi
                                                                   Cisco

                                                                J. Drake
                                                                 Juniper



Expires: September 3, 2018                                 March 2, 2018



            Interconnect Solution for EVPN Overlay networks
                  draft-ietf-bess-dci-evpn-overlay-10

Abstract

   This document describes how Network Virtualization Overlays (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 Ethernet Virtual Private
   Networks (EVPN) and other L2VPN technologies used in the WAN, such as
   Virtual Private LAN Services (VPLS), VPLS extensions for Provider
   Backbone Bridging (PBB-VPLS), EVPN or PBB-EVPN. It also describes how
   the existing technical specifications apply to the Interconnection
   and extends the EVPN procedures needed in some cases. In particular,
   this document describes how EVPN routes are processed on Gateways
   (GWs) that interconnect EVPN-Overlay and EVPN-MPLS networks, as well
   as the Interconnect Ethernet Segment (I-ES) to provide multi-homing,
   and the use of the Unknown MAC route to avoid MAC scale issues on
   Data Center Network Virtualization Edge (NVE) devices.


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.




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   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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   The list of current Internet-Drafts can be accessed at
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   This Internet-Draft will expire on September 3, 2018.

Copyright Notice

   Copyright (c) 2018 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. Conventions and Terminology . . . . . . . . . . . . . . . . . .  3
   2. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3. Decoupled Interconnect solution for EVPN overlay networks . . .  6
     3.1. Interconnect requirements . . . . . . . . . . . . . . . . .  7
     3.2. VLAN-based hand-off . . . . . . . . . . . . . . . . . . . .  8
     3.3. PW-based (Pseudowire-based) hand-off  . . . . . . . . . . .  8
     3.4. Multi-homing solution on the GWs  . . . . . . . . . . . . .  9
     3.5. Gateway Optimizations . . . . . . . . . . . . . . . . . . .  9
       3.5.1. MAC Address Advertisement Control . . . . . . . . . . .  9
       3.5.2. ARP/ND flooding control . . . . . . . . . . . . . . . . 10
       3.5.3. Handling failures between GW and WAN Edge routers . . . 11
   4. Integrated Interconnect solution for EVPN overlay networks  . . 11
     4.1. Interconnect requirements . . . . . . . . . . . . . . . . . 12
     4.2. VPLS Interconnect for EVPN-Overlay networks . . . . . . . . 13
       4.2.1. Control/Data Plane setup procedures on the GWs  . . . . 13
       4.2.2. Multi-homing procedures on the GWs  . . . . . . . . . . 14
     4.3. PBB-VPLS Interconnect for EVPN-Overlay networks . . . . . . 14



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       4.3.1. Control/Data Plane setup procedures on the GWs  . . . . 14
       4.3.2. Multi-homing procedures on the GWs  . . . . . . . . . . 15
     4.4. EVPN-MPLS Interconnect for EVPN-Overlay networks  . . . . . 15
       4.4.1. Control Plane setup procedures on the GWs . . . . . . . 15
       4.4.2. Data Plane setup procedures on the GWs  . . . . . . . . 17
       4.4.3. Multi-homing procedure extensions on the GWs  . . . . . 18
       4.4.4. Impact on MAC Mobility procedures . . . . . . . . . . . 20
       4.4.5. Gateway optimizations . . . . . . . . . . . . . . . . . 20
       4.4.6. Benefits of the EVPN-MPLS Interconnect solution . . . . 21
     4.5. PBB-EVPN Interconnect for EVPN-Overlay networks . . . . . . 22
       4.5.1. Control/Data Plane setup procedures on the GWs  . . . . 22
       4.5.2. Multi-homing procedures on the GWs  . . . . . . . . . . 22
       4.5.3. Impact on MAC Mobility procedures . . . . . . . . . . . 23
       4.5.4. Gateway optimizations . . . . . . . . . . . . . . . . . 23
     4.6. EVPN-VXLAN Interconnect for EVPN-Overlay networks . . . . . 23
       4.6.1. Globally unique VNIs in the Interconnect network  . . . 24
       4.6.2. Downstream assigned VNIs in the Interconnect network  . 24
   5. Security Considerations . . . . . . . . . . . . . . . . . . . . 25
   6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 26
   7. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     7.1. Normative References  . . . . . . . . . . . . . . . . . . . 26
     7.2. Informative References  . . . . . . . . . . . . . . . . . . 27
   8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 28
   9. Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . 28
   10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 29



1. Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   AC: Attachment Circuit.

   ARP: Address Resolution Protocol.

   BUM: refers to Broadcast, Unknown unicast and Multicast traffic.

   CE: Customer Equipment.

   CFM: Connectivity Fault Management.

   DC and DCI: Data Center and Data Center Interconnect.




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   DC RR(s) and WAN RR(s): refers to the Data Center and Wide Area
   Network Route Reflectors, respectively.

   DF and NDF: Designated Forwarder and Non-Designated Forwarder.

   EVPN: Ethernet Virtual Private Network, as in [RFC7432].

   EVI: EVPN Instance.

   EVPN Tunnel binding: refers to a tunnel to a remote PE/NVE for a
   given EVI. Ethernet packets in these bindings are encapsulated with
   the Overlay or MPLS encapsulation and the EVPN label at the bottom of
   the stack.

   ES and vES: Ethernet Segment and virtual Ethernet Segment.

   ESI: Ethernet Segment Identifier.

   GW: Gateway or Data Center Gateway.

   I-ES and I-ESI: Interconnect Ethernet Segment and Interconnect
   Ethernet Segment Identifier. An I-ES is defined on the GWs for multi-
   homing to/from the WAN.

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

   MP2P and LSM tunnels: refer to Multi-Point to Point and Label
   Switched Multicast tunnels.

   ND: Neighbor Discovery protocol.

   NVE: Network Virtualization Edge.

   NVGRE: Network Virtualization using Generic Routing Encapsulation.

   NVO: refers to Network Virtualization Overlays.

   OAM: Operations and Maintenance.

   PBB: Provider Backbone Bridging.

   PE: Provider Edge.

   PW: Pseudowire.

   RD: Route-Distinguisher.

   RT: Route-Target.



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   S/C-TAG: refers to a combination of Service Tag and Customer Tag in a
   802.1Q frame.

   TOR: Top-Of-Rack switch.

   UMR: Unknown MAC Route.

   VNI/VSID: refers to VXLAN/NVGRE virtual identifiers.

   VPLS: Virtual Private LAN Service.

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

   VXLAN: Virtual eXtensible LAN.


2. Introduction

   [EVPN-Overlays] discusses the use of Ethernet Virtual Private
   Networks (EVPN) [RFC7432] as the control plane for Network
   Virtualization Overlays (NVO), where VXLAN [RFC7348], NVGRE [RFC7637]
   or MPLS over GRE [RFC4023] 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 Wide Area Network (WAN) in some cases due to the requirements and
   existing deployed technologies. For instance, a Service Provider
   might have an already deployed Virtual Private LAN Service (VPLS)
   [RFC4761][RFC4762], VPLS extensions for Provider Backbone Bridging
   (PBB-VPLS) [RFC7041], EVPN [RFC7432] or PBB-EVPN [RFC7623] network
   that has to be used to interconnect Data Centers and WAN VPN users. A
   Gateway (GW) function is required in these cases. In fact, [EVPN-
   Overlays] discusses two main Data Center Interconnect solution
   groups: "DCI using GWs" and "DCI using ASBRs". This document
   specifies the solutions that correspond to the "DCI using GWs" group.

   It is assumed 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".

   The specified procedures are local to the redundant GWs connecting a
   DC to the WAN. The document does not preclude any combination across
   different DCs for the same tenant. For instance, a "Decoupled"
   solution can be used in GW1 and GW2 (for DC1) and an "Integrated"
   solution can be used in GW3 and GW4 (for DC2).



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   While the Gateways and WAN PEs use existing specifications in some
   cases, the document also defines extensions that are specific to DCI.
   In particular, those extensions are:

   o The Interconnect Ethernet Segment (I-ES), an Ethernet Segment that
     can be associated to a set of PWs or other tunnels. I-ES defined in
     this document is not associated with a set of Ethernet links, as
     per [RFC7432], but rather with a set of virtual tunnels (e.g., a
     set of PWs). This set of virtual tunnels is referred to as vES
     [VIRTUAL-ES].

   o The use of the Unknown MAC route in a DCI scenario.

   o The processing of EVPN routes on Gateways with MAC-VRFs connecting
     EVPN-Overlay and EVPN-MPLS networks, or EVPN-Overlay and EVPN-
     Overlay networks.


3. 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. Note that, although
   not shown in Figure 1, GWs may have local ACs (Attachment Circuits).



























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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.

3.1. Interconnect requirements

   The Decoupled Interconnect architecture is intended to be deployed in
   networks where the EVPN-Overlay and WAN providers are different
   entities and a clear demarcation is needed. This solution solves the
   following requirements:

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

   o Independence of the Layer Two VPN (L2VPN) technology deployed in
     the WAN.

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

   o Support of Ethernet OAM and Connectivity Fault Management (CFM)
     [802.1AG][Y.1731] functions between the GW and the WAN Edge router



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     to detect individual AC failures.

   o Support for the following optimizations 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.
     + Address Resolution Protocol (ARP) and Neighbor Discovery (ND)
       flooding control for the requests coming from the WAN.


3.2. VLAN-based hand-off

   In this option, the hand-off between the GWs and the WAN Edge routers
   is based on VLANs [802.1Q-2014]. 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 has to be mapped to a C-TAG
   or 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].

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

   If MPLS between the GW and the WAN Edge router is an option, a PW-
   based Interconnect solution can be deployed. In this option the
   hand-off between both routers is based on FEC128-based PWs [RFC4762]
   or FEC129-based PWs (for a greater level of network automation)
   [RFC6074]. Note that this model still provides a clear demarcation
   boundary between DC and WAN (since there is a single PW between each
   MAC-VRF and peer VSI), 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



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   Edge router [RFC3031], the GW MUST support an interworking function
   in each MAC-VRF that requires extension to the WAN:

   o If a FEC128-based PW is used between the MAC-VRF (GW) and the VSI
     (WAN Edge), the corresponding VCID MUST be provisioned on the MAC-
     VRF and 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.

   If a PW-based handoff is used, the GW's AC (or point of attachment to
   the EVPN Instance) uses a combination of a PW label and VLAN IDs. PWs
   are treated as service interfaces defined in [RFC7432].


3.4. Multi-homing solution on the GWs

   EVPN single-active multi-homing, i.e. per-service load-balancing
   multi-homing is required in this type of interconnect.

   The GWs will be provisioned with a unique ES per WAN interconnect,
   and the hand-off attachment circuits or PWs between the GW and the
   WAN Edge router will be assigned an ESI for such ES. The ESI will be
   administratively configured on the GWs according to the procedures in
   [RFC7432]. This Interconnect ES will be referred as "I-ES" hereafter,
   and its identifier will be referred as "I-ESI". [RFC7432] describes
   different ESI Types. The use of Type 0 for the I-ESI is RECOMMENDED
   in this document.

   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 ES and per EVI will be advertised to the
   DC NVEs for the multi-homing functions, ES routes will be advertised
   so that ES discovery and Designated Forwarder (DF) procedures can be
   followed. 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.

3.5. Gateway Optimizations

   The following GW features are optional and optimize the control plane
   and data plane in the DC.

3.5.1. MAC Address Advertisement Control

   The use of EVPN in NVO networks brings a significant number of
   benefits as described in [EVPN-Overlays]. However, if multiple DCs



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   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 [RFC4684] 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.

   The solution specified in this document uses the 'Unknown MAC Route'
   (UMR) which is advertised into a given DC by each of the DC's GWs.
   This route is defined in [RFC7543] and is a regular EVPN MAC/IP
   Advertisement route in which the MAC Address Length is set to 48, the
   MAC address is set to 0, and the ESI field is set to the DC GW's I-
   ESI.

   An NVE within that DC that understands and process the UMR will send
   unknown unicast frames to one of the DCs GWs, which will then forward
   that packet to the correct egress PE. Note that, because the ESI is
   set to the DC GW's I-ESI, all-active multi-homing can be applied to
   unknown unicast MAC addresses. An NVE that does not understand the
   Unknown MAC route will handle unknown unicast as described in
   [RFC7432].

   This document proposes that local policy determines whether MAC
   addresses and/or the UMR are advertised into a given DC. As an
   example, when all the DC MAC addresses are learned in the
   control/management plane, it may be appropriate to advertise only the
   UMR. Advertising all the DC MAC addresses in the control/management
   plane is usually the case when the NVEs reside in hypervisors. Refer
   to [EVPN-Overlays] section 7.

   It is worth noting that the UMR usage in [RFC7543] and the UMR usage
   in this document are different. In the former, a Virtual Spoke (V-
   spoke) does not necessarily learn all the MAC addresses pertaining to
   hosts in other V-spokes of the same network. The communication
   between two V-spokes is done through the DMG, until the V-spokes
   learn each other's MAC addresses. In this document, two leaf switches
   in the same DC are recommended to learn each other's MAC addresses
   for the same EVI. The leaf to leaf communication is always direct and
   does not go through the GW.


3.5.2. ARP/ND 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



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   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.

3.5.3. Handling failures between GW and WAN Edge routers

   Link/PE failures are 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 may be detected by OAM mechanisms. For
   instance:

   o If the Interconnect solution is based on a VLAN hand-off, Ethernet-
     CFM [802.1AG][Y.1731] 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 Label
     Distribution Protocol (LDP) PW Status bits TLV [RFC6870] may be
     used to detect individual PW failures on both, the GW and WAN Edge
     router.

4. 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. Although not shown in Figure 2, note that the GWs may have
   local ACs.
















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                             +--+
                             |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

   * EVPN-Ovl stands for EVPN-Overlay (and it's an Interconnect option).

4.1. Interconnect requirements

   The Integrated Interconnect solution meets the following
   requirements:

   o Control plane and data plane interworking between the EVPN-overlay
     network and the L2VPN technology supported in the WAN, irrespective
     of the technology choice, i.e. (PBB-)VPLS or (PBB-)EVPN, as
     depicted in Figure 2.

   o Multi-homing, including single-active multi-homing with per-service
     load balancing or all-active multi-homing, i.e. per-flow load-
     balancing, as long as the technology deployed in the WAN supports
     it.

   o Support for end-to-end MAC Mobility, Static MAC protection and
     other procedures (e.g. proxy-arp) described in [RFC7432] as long as
     EVPN-MPLS is the technology of choice in the WAN.




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   o Independent inclusive multicast trees in the WAN and in the DC.
     That is, the inclusive multicast tree type defined in the WAN does
     not need to be the same as in the DC.

4.2. VPLS Interconnect for EVPN-Overlay networks

4.2.1. 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 (unless [RFC4762] is used in the WAN, in which case no WAN
   route-target is needed). 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 3.4), that will be unique per interconnection. The
   I-ES in this case will represent the group of PWs to the WAN PEs and
   GWs. All the [RFC7432] procedures are still followed for the I-ES,
   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 (although
   not shown in Figure 2), 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 composed
   of 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 (AC) will be forwarded to the flooding list.
   BUM frames received from the DC or the WAN will be forwarded to the
   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, so that loops and packet
   duplication are avoided. In case a GW can successfully establish



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   both, an EVPN binding and a PW to the same far-end PE, the EVPN
   binding will prevail and the PW will be brought operationally down.

   The optimizations procedures described in section 3.5 can also be
   applied to this model.


4.2.2. Multi-homing procedures on the GWs

   This model supports single-active multi-homing on the GWs. All-active
   multi-homing is not supported by VPLS, therefore it cannot be used on
   the GWs.

   In this case, for a given EVI, all the PWs in the WAN split-horizon-
   group are assigned to I-ES. All the single-active multi-homing
   procedures as described by [EVPN-Overlays] will be followed for the
   I-ES.

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

4.3. PBB-VPLS Interconnect for EVPN-Overlay networks

4.3.1. 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. A number of 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 4.2.1 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 3.5 can also be
   applied to this Interconnect option.

4.3.2. Multi-homing procedures on the GWs

   This model supports single-active multi-homing on the GWs. All-active
   multi-homing is not supported by this scenario.

   The single-active multi-homing procedures as described by [EVPN-
   Overlays] will be followed for the I-ES for each EVI instance
   connected to the B-component. Note that in this case, for a given
   EVI, all the EVPN bindings in the I-component are assigned to the I-
   ES. The non-DF GW for the I-ES will block the transmission and
   reception of all the I-component EVPN bindings for BUM and unicast
   traffic. When learning MACs from the WAN, the non-DF MUST NOT
   advertise EVPN MAC/IP routes for those MACs.


4.4. 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.

4.4.1. 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 BGP EVPN session to the DC RR (or two BGP EVPN sessions if
   there are redundant DC RRs) and one session to the WAN RR (or two
   sessions if there are redundant WAN RRs).

   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 [TUNNEL-ENCAP] 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-ES and its assigned I-ESI



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   will be configured on the GWs for multi-homing. This I-ES represents
   the WAN EVPN-MPLS PEs to the DC but also the DC EVPN-Overlay NVEs to
   the WAN. Optionally, different I-ESI values are 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):

      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, 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 for
        encapsulations using a VNI).

        + The appropriate Route-Targets (RTs) and [TUNNEL-ENCAP] 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 [TUNNEL-
   ENCAP] BGP Encapsulation extended community values:

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

      o Ethernet A-D routes per ES 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



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        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 the above local service routes: Set-DC will be
   sent to the DC RRs and will include A-D per EVI, Inclusive Multicast
   and MAC/IP 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 with the Inclusive multicast
        routes, an administrative option MAY change this priority.

4.4.2. 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).




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      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
   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).


4.4.3. Multi-homing procedure extensions on the GWs

   This model supports single-active as well as all-active multi-homing.

   All the [RFC7432] multi-homing procedures for the DF election on I-
   ES(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-ES. 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



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          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-
          ES, 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
          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-ES, 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-ES and blocks the BUM forwarding. GW1 is
   the DF and forwards the traffic to PE1 and GW2. Packets sent to GW2
   will include the ESI-label for the I-ES. Based on the ESI-label, GW2
   identifies the packets as I-ES-generated packets and will only
   forward them to local ACs (CE in the example) and not back to the
   EVPN-Overlay network.


4.4.4. 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-ES, 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.

4.4.5. Gateway optimizations

   All the Gateway optimizations described in section 3.5 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



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   section 3.5.1, 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-
   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, creating packet duplication. 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.


4.4.6. Benefits of the EVPN-MPLS Interconnect solution

   The [EVPN-Overlays] "DCI using ASBRs" solution and the GW solution
   with EVPN-MPLS Interconnect may be seen similar since they both
   retain the EVPN attributes between Data Centers and throughout the
   WAN. However the EVPN-MPLS Interconnect solution on the GWs has
   significant benefits compared to the "DCI using ASBRs" solution:

      o As in any of the described GW models, this solution supports the
        connectivity of local attachment circuits on the GWs. This is
        not possible in a "DCI using ASBRs" solution.

      o Different data plane encapsulations can be supported in the DC
        and the WAN, while a uniform encapsulation is needed in the "DCI
        using ASBRs" solution.

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




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      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.

      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.


4.5. 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.

4.5.1. 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-ES will be configured on the GWs for multi-homing, but its I-ESI
   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], that is, the I-ES will be represented
   to the WAN PBB-EVPN PEs using shared or dedicated B-MACs.

   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 4.3.1.

4.5.2. Multi-homing procedures on the GWs



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   This model supports single-active as well as all-active multi-homing.

   The forwarding behavior of the DF and non-DF will be changed based on
   the description outlined in section 4.4.3, only replacing the "WAN
   split-horizon-group" for the B-component, and using [RFC7623]
   procedures for the traffic sent or received on the B-component.

4.5.3. Impact on MAC Mobility procedures

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

4.5.4. Gateway optimizations

   All the considerations explained in section 4.4.5 are applicable to
   the PBB-EVPN Interconnect option.

4.6. 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. While
   multiple Overlay tunnel combinations at the WAN and the DC are
   possible (MPLSoGRE, nvGRE, etc.), VXLAN is described here, given its
   popularity in the industry. This section focuses on the specific case
   of EVPN for VXLAN (EVPN-VXLAN hereafter) and the impact on the
   [RFC7432] procedures.

   The procedures described in section 4.4 apply to this section too,
   only replacing EVPN-MPLS for EVPN-VXLAN control plane specifics and
   using [EVPN-Overlays] "Local Bias" procedures instead of section
   4.4.3. Since there are no ESI-labels in VXLAN, GWs need to rely on
   "Local Bias" to apply split-horizon on packets generated from the I-
   ES and sent to the peer GW.

   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:



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      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 (a), 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
   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.

4.6.1. 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 4.4 will be followed, considering
   that the VNIs advertised/received by the GWs will be translated
   accordingly.

4.6.2. Downstream assigned VNIs in the Interconnect network



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   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 4.6.1. 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 4.4 will be followed, taking the
   considerations above for the VNI translation.


5. Security Considerations

   This document applies existing specifications to a number of
   Interconnect models. The Security Considerations included in those
   documents, such as [RFC7432], [EVPN-Overlays], [RFC7623], [RFC4761]
   and [RFC4762] apply to this document whenever those technologies are
   used.

   As discussed, [EVPN-Overlays] discusses two main DCI solution groups:
   "DCI using GWs" and "DCI using ASBRs". This document specifies the
   solutions that correspond to the "DCI using GWs" group. It is
   important to note that the use of GWs provide a superior level of
   security on a per tenant basis, compared to the use of ASBRs. This is
   due to the fact that GWs need to perform a MAC lookup on the frames
   being received from the WAN, and they apply security procedures, such
   as filtering of undesired frames, filtering of frames with a source
   MAC that matches a protected MAC in the DC or application of MAC
   duplication procedures defined in [RFC7432]. On ASBRs though, traffic
   is forwarded based on a label or VNI swap and there is usually no
   visibility of the encapsulated frames, which can carry malicious
   traffic.

   In addition, the GW optimizations specified in this document, provide
   additional protection of the DC Tenant Systems. For instance, the MAC
   address advertisement control and Unknown MAC Route defined in
   section 3.5.1 protect the DC NVEs from being overwhelmed with an
   excessive number MAC/IP routes being learned on the GWs from the WAN.
   The ARP/ND flooding control described in 3.5.2 can reduce/suppress
   broadcast storms being injected from the WAN.

   Finally, the reader should be aware of the potential security
   implications of designing a DCI with the Decoupled Interconnect
   solution (section 3) or the Integrated Interconnect solution (section
   4). In the Decoupled Interconnect solution the DC is typically easier



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   to protect from the WAN, since each GW has a single logical link to
   one WAN PE, whereas in the Integrated solution, the GW has logical
   links to all the WAN PEs that are attached to the tenant. In either
   model, proper control plane and data plane policies should be put in
   place in the GWs in order to protect the DC from potential attacks
   coming from the WAN.


6. IANA Considerations

   This document has no IANA actions.

7. References

7.1. Normative References


   [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>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March
   1997, <http://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC



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   2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
   <http://www.rfc-editor.org/info/rfc8174>.

   [TUNNEL-ENCAP]  Rosen et al., "The BGP Tunnel Encapsulation
   Attribute", draft-ietf-idr-tunnel-encaps-08, work in progress,
   January 11, 2018.

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

   [EVPN-Overlays]  Sajassi-Drake et al., "A Network Virtualization
   Overlay Solution using EVPN", draft-ietf-bess-evpn-overlay-11.txt,
   work in progress, January 2018.

   [RFC7543]  Jeng, H., Jalil, L., Bonica, R., Patel, K., and L. Yong,
   "Covering Prefixes Outbound Route Filter for BGP-4", RFC 7543, DOI
   10.17487/RFC7543, May 2015, <https://www.rfc-
   editor.org/info/rfc7543>.


7.2. Informative References

   [RFC4684]  Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
   R., Patel, K., and J. Guichard, "Constrained Route Distribution for
   Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS)
   Internet Protocol (IP) Virtual Private Networks (VPNs)", RFC 4684,
   DOI 10.17487/RFC4684, November 2006, <http://www.rfc-
   editor.org/info/rfc4684>.

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
   L., Sridhar, T., Bursell, M., and C. Wright, "Virtual eXtensible
   Local Area Network (VXLAN): A Framework for Overlaying Virtualized
   Layer 2 Networks over Layer 3 Networks", RFC 7348, DOI
   10.17487/RFC7348, August 2014, <http://www.rfc-
   editor.org/info/rfc7348>.

   [RFC7637]  Garg, P., et al., "NVGRE: Network Virtualization using
   Generic Routing Encapsulation", RFC 7637, September, 2015

   [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
   "Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE)",
   RFC 4023, DOI 10.17487/RFC4023, March 2005, <http://www.rfc-
   editor.org/info/rfc4023>.

   [Y.1731]  ITU-T Recommendation Y.1731, "OAM functions and mechanisms
   for Ethernet based networks", July 2011.




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   [802.1AG]  IEEE 802.1AG_2007, "IEEE Standard for Local and
   Metropolitan Area Networks - Virtual Bridged Local Area Networks
   Amendment 5: Connectivity Fault Management", January 2008.

   [802.1Q-2014]  IEEE 802.1Q-2014, "IEEE Standard for Local and
   metropolitan area networks--Bridges and Bridged Networks", December
   2014.

   [RFC6870]  Muley, P., Ed., and M. Aissaoui, Ed., "Pseudowire
   Preferential Forwarding Status Bit", RFC 6870, DOI 10.17487/RFC6870,
   February 2013, <http://www.rfc-editor.org/info/rfc6870>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
   Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031,
   January 2001, <http://www.rfc-editor.org/info/rfc3031>.

   [VIRTUAL-ES]  Sajassi et al., "EVPN Virtual Ethernet Segment", draft-
   sajassi-bess-evpn-virtual-eth-segment-03, work in progress, February
   2018.

8. Acknowledgments

   The authors would like to thank Neil Hart, Vinod Prabhu and Kiran
   Nagaraj for their valuable comments and feedback. We would also like
   to thank Martin Vigoureux and Alvaro Retana for his detailed review
   and comments.

9. Contributors

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

   Ravi Shekhar
   Anil Lohiya
   Wen Lin
   Juniper Networks

   Florin Balus
   Patrice Brissette
   Cisco

   Senad Palislamovic
   Nokia

   Dennis Cai
   Alibaba





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10. 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

   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com

   John Drake
   Juniper
   Email: jdrake@juniper.net



























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