BESS WorkGroup                                                A. Sajassi
Internet-Draft                                                  S. Salam
Intended status: Standards Track                               S. Thoria
Expires: January 27, 2022                                  Cisco Systems
                                                                J. Drake
                                                                 Juniper
                                                              J. Rabadan
                                                                   Nokia
                                                           July 26, 2021


                Integrated Routing and Bridging in EVPN
            draft-ietf-bess-evpn-inter-subnet-forwarding-15

Abstract

   Ethernet VPN (EVPN) provides an extensible and flexible multi-homing
   VPN solution over an MPLS/IP network for intra-subnet connectivity
   among Tenant Systems and End Devices that can be physical or virtual.
   However, there are scenarios for which there is a need for a dynamic
   and efficient inter-subnet connectivity among these Tenant Systems
   and End Devices while maintaining the multi-homing capabilities of
   EVPN.  This document describes an Integrated Routing and Bridging
   (IRB) solution based on EVPN to address such requirements.

Requirements Language

   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 RFC
   2119 [RFC2119] and RFC 8174 [RFC8174] when, and only when, they
   appear in all capitals, as shown here.

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).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."




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   This Internet-Draft will expire on January 27, 2022.

Copyright Notice

   Copyright (c) 2021 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
   (https://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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  EVPN PE Model for IRB Operation . . . . . . . . . . . . . . .   6
   4.  Symmetric and Asymmetric IRB  . . . . . . . . . . . . . . . .   7
     4.1.  IRB Interface and its MAC and IP addresses  . . . . . . .  10
     4.2.  Operational Considerations  . . . . . . . . . . . . . . .  12
   5.  Symmetric IRB Procedures  . . . . . . . . . . . . . . . . . .  13
     5.1.  Control Plane - Advertising PE  . . . . . . . . . . . . .  13
     5.2.  Control Plane - Receiving PE  . . . . . . . . . . . . . .  14
     5.3.  Subnet route advertisement  . . . . . . . . . . . . . . .  15
     5.4.  Data Plane - Ingress PE . . . . . . . . . . . . . . . . .  16
     5.5.  Data Plane - Egress PE  . . . . . . . . . . . . . . . . .  17
   6.  Asymmetric IRB Procedures . . . . . . . . . . . . . . . . . .  17
     6.1.  Control Plane - Advertising PE  . . . . . . . . . . . . .  17
     6.2.  Control Plane - Receiving PE  . . . . . . . . . . . . . .  18
     6.3.  Data Plane - Ingress PE . . . . . . . . . . . . . . . . .  19
     6.4.  Data Plane - Egress PE  . . . . . . . . . . . . . . . . .  19
   7.  Mobility Procedure  . . . . . . . . . . . . . . . . . . . . .  20
     7.1.  Initiating a gratutious ARP upon a Move . . . . . . . . .  21
     7.2.  Sending Data Traffic without an ARP Request . . . . . . .  22
     7.3.  Silent Host . . . . . . . . . . . . . . . . . . . . . . .  24
   8.  BGP Encoding  . . . . . . . . . . . . . . . . . . . . . . . .  24
     8.1.  Router's MAC Extended Community . . . . . . . . . . . . .  25
   9.  Operational Models for Symmetric Inter-Subnet Forwarding  . .  25
     9.1.  IRB forwarding on NVEs for Tenant Systems . . . . . . . .  25
       9.1.1.  Control Plane Operation . . . . . . . . . . . . . . .  27
       9.1.2.  Data Plane Operation  . . . . . . . . . . . . . . . .  28
     9.2.  IRB forwarding on NVEs for Subnets behind Tenant Systems   30
       9.2.1.  Control Plane Operation . . . . . . . . . . . . . . .  31



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       9.2.2.  Data Plane Operation  . . . . . . . . . . . . . . . .  32
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  33
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  33
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     13.2.  Informative References . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

1.  Terminology

   AC: Attachment Circuit

   ARP: Address Resolution Protocol

   ARP table: A logical view of a forwarding table on a PE that
   maintains an IP to MAC binding entry on an IP interface for both IPv4
   and IPv6.  These entries are learned through ARP/ND or through EVPN.

   Broadcast Domain: As per [RFC7432], an EVI consists of a single or
   multiple broadcast domains.  In the case of VLAN-bundle and VLAN-
   based service models (see [RFC7432]), a broadcast domain is
   equivalent to an EVI.  In the case of VLAN-aware bundle service
   model, an EVI contains multiple broadcast domains.  Also, in this
   document, broadcast domain and subnet are equivalent terms and
   wherever "subnet" is used, it means "IP subnet"

   Broadcast Domain Route Target: refers to the Broadcast Domain
   assigned Route Target [RFC4364].  In the case of VLAN-aware bundle
   service model, all the broadcast domain instances in the MAC-VRF
   share the same Route Target

   Bridge Table: The instantiation of a broadcast domain in a MAC-VRF,
   as per [RFC7432].

   Ethernet NVO tunnel: refers to Network Virtualization Overlay tunnels
   with Ethernet payload as specified for VxLAN in [RFC7348] and for
   NVGRE in [RFC7637].

   EVI: EVPN Instance spanning the NVE/PE devices that are participating
   on that EVPN, as per [RFC7432].

   EVPN: Ethernet Virtual Private Networks, as per [RFC7432].

   IP NVO tunnel: it refers to Network Virtualization Overlay tunnels
   with IP payload (no MAC header in the payload) as specified for GPE
   in [I-D.ietf-nvo3-vxlan-gpe].




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   IP-VRF: A Virtual Routing and Forwarding table for IP routes on an
   NVE/PE.  The IP routes could be populated by EVPN and IP-VPN address
   families.  An IP-VRF is also an instantiation of a layer 3 VPN in an
   NVE/PE.

   IRB: Integrated Routing and Bridging interface.  It connects an IP-
   VRF to a broadcast domain (or subnet).

   MAC-VRF: A Virtual Routing and Forwarding table for Media Access
   Control (MAC) addresses on an NVE/PE, as per [RFC7432].  A MAC-VRF is
   also an instantiation of an EVI in an NVE/PE.

   ND: Neighbor Discovery Protocol

   NVE: Network Virtualization Edge

   NVGRE: Network Virtualization Generic Routing Encapsulation,
   [RFC7637]

   NVO: Network Virtualization Overlays

   RT-2: EVPN route type 2, i.e., MAC/IP Advertisement route, as defined
   in [RFC7432]

   RT-5: EVPN route type 5, i.e., IP Prefix route.  As defined in
   Section 3 of [I-D.ietf-bess-evpn-prefix-advertisement]

   TS: Tenant System

   VA: Virtual Appliance

   VNI: Virtual Network Identifier.  As in [RFC8365], the term is used
   as a representation of a 24-bit NVO instance identifier, with the
   understanding that VNI will refer to a VXLAN Network Identifier in
   VXLAN, or Virtual Subnet Identifier in NVGRE, etc. unless it is
   stated otherwise.

   VTEP: VXLAN Termination End Point, as in [RFC7348].

   VXLAN: Virtual Extensible LAN, as in [RFC7348].

   This document also assumes familiarity with the terminology of
   [RFC7432], [RFC8365] and [RFC7365].








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2.  Introduction

   EVPN [RFC7432] provides an extensible and flexible multi-homing VPN
   solution over an MPLS/IP network for intra-subnet connectivity among
   Tenant Systems (TSes) and End Devices that can be physical or
   virtual; where an IP subnet is represented by an EVPN Instance (EVI)
   for a VLAN-based service or by an (EVI, VLAN) for a VLAN-aware bundle
   service.  However, there are scenarios for which there is a need for
   a dynamic and efficient inter-subnet connectivity among these Tenant
   Systems and End Devices while maintaining the multi-homing
   capabilities of EVPN.  This document describes an Integrated Routing
   and Bridging (IRB) solution based on EVPN to address such
   requirements.

   The inter-subnet communication is traditionally achieved at
   centralized L3 Gateway (L3GW) devices where all the inter-subnet
   forwarding is performed and all the inter-subnet communication
   policies are enforced.  When two TSes belonging to two different
   subnets connected to the same PE wanted to communicate with each
   other, their traffic needed to be backhauled from the PE all the way
   to the centralized gateway where inter-subnet switching is performed
   and then back to the PE.  For today's large multi-tenant data center,
   this scheme is very inefficient and sometimes impractical.

   In order to overcome the drawback of the centralized layer-3 GW
   approach, IRB functionality is needed on the PEs (also referred to as
   EVPN NVEs) attached to TSes in order to avoid inefficient forwarding
   of tenant traffic (i.e., avoid back-hauling and hair-pinning).  When
   a PE with IRB capability receives tenant traffic over an Attachment
   Circuit (AC), it can not only locally bridge the tenant intra-subnet
   traffic but also can locally route the tenant inter-subnet traffic on
   a packet by packet basis thus meeting the requirements for both intra
   and inter-subnet forwarding and avoiding non-optimal traffic
   forwarding associated with centralized layer-3 GW approach.

   Some TSes run non-IP protocols in conjunction with their IP traffic.
   Therefore, it is important to handle both kinds of traffic optimally
   - e.g., to bridge non-IP and intra-subnet traffic and to route inter-
   subnet IP traffic.  Therefore, the solution needs to meet the
   following requirements:

   R1: The solution must provide each tenant with IP routing of its
   inter-subnet traffic and Ethernet bridging of its intra-subnet
   traffic and non-routable traffic, where non-routable traffic refers
   both to non-IP traffic and IP traffic whose version differs from the
   IP version configured in the IP-VRF.  For example, if an IP-VRF in a
   NVE is configured for IPv6 and that NVE receives IPv4 traffic on the




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   corresponding VLAN, then the IPv4 traffic is treated as non-routable
   traffic.

   R2: The solution must allow IP routing of inter-subnet traffic to be
   disabled on a per-VLAN basis on those PEs that are backhauling that
   traffic to another PE for routing.

3.  EVPN PE Model for IRB Operation

   Since this document discusses IRB operation in relationship to EVPN
   MAC-VRF, IP-VRF, EVI, Broadcast Domain, Bridge Table, and IRB
   interfaces, it is important to understand the relationship between
   these components.  Therefore, the following PE model is illustrated
   below to a) describe these components and b) illustrate the
   relationship among them.


      +-------------------------------------------------------------+
      |                                                             |
      |              +------------------+                    IRB PE |
      | Attachment   | +------------------+                         |
      | Circuit(AC1) | |  +----------+    |                MPLS/NVO tnl
    ----------------------*Bridge    |    |                    +-----
      |              | |  |Table(BT1)|    |    +-----------+  / \    \
      |              | |  |          *---------*           |<--> |Eth|
      |              | |  |  VLAN x  |    |IRB1|           |  \ /    /
      |              | |  +----------+    |    |           |   +-----
      |              | |     ...          |    |  IP-VRF1  |        |
      |              | |  +----------+    |    |  RD2/RT2  |MPLS/NVO tnl
      |              | |  |Bridge    |    |    |           |   +-----
      |              | |  |Table(BT2)|    |IRB2|           |  / \    \
      |              | |  |          *---------*           |<--> |IP |
    ----------------------*  VLAN y  |    |    +-----------+  \ /    /
      |  AC2         | |  +----------+    |                    +-----
      |              | |    MAC-VRF1      |                         |
      |              +-+    RD1/RT1       |                         |
      |                +------------------+                         |
      |                                                             |
      |                                                             |
      +-------------------------------------------------------------+

                      Figure 1: EVPN IRB PE Model


   A tenant needing IRB services on a PE, requires an IP Virtual Routing
   and Forwarding table (IP-VRF) along with one or more MAC Virtual
   Routing and Forwarding tables (MAC-VRFs).  An IP-VRF, as defined in
   [RFC4364], is the instantiation of an IPVPN instance in a PE.  A MAC-



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   VRF, as defined in [RFC7432], is the instantiation of an EVI (EVPN
   Instance) in a PE.  A MAC-VRF consists of one or more bridge tables,
   where each bridge table corresponds to a VLAN (broadcast domain).  If
   service interfaces for an EVPN PE are configured in VLAN- Based mode
   (i.e., section 6.1 of RFC7432), then there is only a single bridge
   table per MAC-VRF (per EVI) - i.e., there is only one tenant VLAN per
   EVI.  However, if service interfaces for an EVPN PE are configured in
   VLAN-Aware Bundle mode (i.e., section 6.3 of RFC7432), then there are
   several bridge tables per MAC-VRF (per EVI) - i.e., there are several
   tenant VLANs per EVI.

   Each bridge table is connected to an IP-VRF via an L3 interface
   called IRB interface.  Since a single tenant subnet is typically (and
   in this document) represented by a VLAN (and thus supported by a
   single bridge table), for a given tenant there are as many bridge
   tables as there are subnets and thus there are also as many IRB
   interfaces between the tenant IP-VRF and the associated bridge tables
   as shown in the PE model above.

   IP-VRF is identified by its corresponding route target and route
   distinguisher and MAC-VRF is also identified by its corresponding
   route target and route distinguisher.  If operating in EVPN VLAN-
   Based mode, then a receiving PE that receives an EVPN route with MAC-
   VRF route target can identify the corresponding bridge table;
   however, if operating in EVPN VLAN-Aware Bundle mode, then the
   receiving PE needs both the MAC-VRF route target and VLAN ID in order
   to identify the corresponding bridge table.

4.  Symmetric and Asymmetric IRB

   This document defines and describes two types of IRB solutions -
   namely symmetric and asymmetric IRB.  The description of symmetric
   and asymmetric IRB procedures relating to data path operations and
   tables in this document is a logical view of data path lookups and
   related tables.  Actual implementations, while following this logical
   view, may not strictly adhere to it for performance tradeoffs.
   Specifically,

   o  References to ARP table in the context of asymmetric IRB is a
      logical view of a forwarding table that maintains an IP to MAC
      binding entry on a layer 3 interface for both IPv4 and IPv6.
      These entries are not subject to ARP or ND protocol.  For IP to
      MAC bindings learnt via EVPN, an implementation may choose to
      import these bindings directly to the respective forwarding table
      (such as an adjacency/next-hop table) as opposed to importing them
      to ARP or ND protocol tables.





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   o  References to host IP lookup followed by a host MAC lookup in the
      context of asymmetric IRB MAY be collapsed into a single IP lookup
      in a hardware implementation.

   In symmetric IRB as its name implies, the lookup operation is
   symmetric at both ingress and egress PEs - i.e., both ingress and
   egress PEs perform lookups on both MAC and IP addresses.  The ingress
   PE performs a MAC lookup followed by an IP lookup and the egress PE
   performs an IP lookup followed by a MAC lookup as depicted in the
   following figure.



                  Ingress PE                   Egress PE
            +-------------------+        +------------------+
            |                   |        |                  |
            |    +-> IP-VRF ----|---->---|-----> IP-VRF -+  |
            |    |              |        |               |  |
            |   BT1        BT2  |        |  BT3         BT2 |
            |    |              |        |               |  |
            |    ^              |        |               v  |
            |    |              |        |               |  |
            +-------------------+        +------------------+
                 ^                                       |
                 |                                       |
           TS1->-+                                       +->-TS2
                           Figure 2: Symmetric IRB


   In symmetric IRB as shown in figure-2, the inter-subnet forwarding
   between two PEs is done between their associated IP-VRFs.  Therefore,
   the tunnel connecting these IP-VRFs can be either IP-only tunnel
   (e.g., in case of MPLS or GPE encapsulation) or Ethernet NVO tunnel
   (e.g., in case of VxLAN encapsulation).  If it is an Ethernet NVO
   tunnel, the TS1's IP packet is encapsulated in an Ethernet header
   consisting of ingress and egress PEs MAC addresses - i.e., there is
   no need for ingress PE to use the destination TS2's MAC address.
   Therefore, in symmetric IRB, there is no need for the ingress PE to
   maintain ARP entries for destination TS2's IP and MAC addresses
   association in its ARP table.  Each PE participating in symmetric IRB
   only maintains ARP entries for locally connected hosts and maintains
   MAC-VRFs/bridge tables for only locally configured subnets.

   In asymmetric IRB, the lookup operation is asymmetric and the ingress
   PE performs three lookups; whereas the egress PE performs a single
   lookup - i.e., the ingress PE performs a MAC lookup, followed by an
   IP lookup, followed by a MAC lookup again; whereas, the egress PE
   performs just a single MAC lookup as depicted in figure 3 below.



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               Ingress PE                       Egress PE
            +-------------------+        +------------------+
            |                   |        |                  |
            |    +-> IP-VRF ->  |        |      IP-VRF      |
            |    |           |  |        |                  |
            |   BT1        BT2  |        |  BT3         BT2 |
            |    |           |  |        |              | | |
            |    |           +--|--->----|--------------+ | |
            |    |              |        |                v |
            +-------------------+        +----------------|-+
                 ^                                        |
                 |                                        |
           TS1->-+                                        +->-TS2
                           Figure 3: Asymmetric IRB


   In asymmetric IRB as shown in figure-3, the inter-subnet forwarding
   between two PEs is done between their associated MAC-VRFs/bridge
   tables.  Therefore, the MPLS or NVO tunnel used for inter-subnet
   forwarding MUST be of type Ethernet.  Since only MAC lookup is
   performed at the egress PE (e.g., no IP lookup), the TS1's IP packets
   need to be encapsulated with the destination TS2's MAC address.  In
   order for ingress PE to perform such encapsulation, it needs to
   maintain TS2's IP and MAC address association in its ARP table.
   Furthermore, it needs to maintain destination TS2's MAC address in
   the corresponding bridge table even though it may not have any TSes
   of the corresponding subnet locally attached.  In other words, each
   PE participating in asymmetric IRB MUST maintain ARP entries for
   remote hosts (hosts connected to other PEs) as well as maintain MAC-
   VRFs/bridge tables and IRB interfaces for ALL subnets in an IP VRF
   including subnets that may not be locally attached.  Therefore,
   careful consideration of PE scale aspects for its ARP table size, its
   IRB interfaces, number and size of its bridge tables should be given
   for the application of asymmetric IRB.

   It should be noted that whenever a PE performs a host IP lookup for a
   packet that is routed, IPv4 TTL or IPv6 hop limit for that packet is
   decremented by one and if it reaches zero, the packet is discarded.
   In the case of symmetric IRB, the TTL/hop limit is decremented by
   both ingress and egress PEs (once by each); whereas, in the case of
   asymmetric IRB, the TTL/hop limit is decremented only once by the
   ingress PE.

   The following sections define the control and data plane procedures
   for symmetric and asymmetric IRB on ingress and egress PEs.  The
   following figure is used to describe these procedures, showing a
   single IP-VRF and a number of broadcast domains on each PE for a
   given tenant.  I.e., an IP-VRF connects one or more EVIs, each EVI



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   contains one MAC-VRF, each MAC VRF consists of one or more bridge
   tables, one per broadcast domain, and a PE has an associated IRB
   interface for each broadcast domain.


                    PE 1         +---------+
              +-------------+    |         |
      TS1-----|         MACx|    |         |        PE2
    (IP1/M1)  |(BT1)        |    |         |   +-------------+
      TS5-----|      \      |    |  MPLS/  |   |MACy  (BT3)  |-----TS3
    (IP5/M5)  |IPx/Mx \     |    |  VxLAN/ |   |     /       | (IP3/M3)
              |    (IP-VRF1)|----|  NVGRE  |---|(IP-VRF1)    |
              |       /     |    |         |   |     \       |
      TS2-----|(BT2) /      |    |         |   |      (BT1)  |-----TS4
    (IP2/M2)  |             |    |         |   |             |  (IP4/M4)
              +-------------+    |         |   +-------------+
                                 |         |
                                 +---------+

                       Figure 4: IRB forwarding


4.1.  IRB Interface and its MAC and IP addresses

   To support inter-subnet forwarding on a PE, the PE acts as an IP
   Default Gateway from the perspective of the attached Tenant Systems
   where default gateway MAC and IP addresses are configured on each IRB
   interface associated with its subnet and falls into one of the
   following two options:

   1.  All the PEs for a given tenant subnet use the same anycast
       default gateway IP and MAC addresses.  On each PE, this default
       gateway IP and MAC addresses correspond to the IRB interface
       connecting the bridge table associated with the tenant's VLAN to
       the corresponding tenant's IP-VRF.

   2.  Each PE for a given tenant subnet uses the same anycast default
       gateway IP address but its own MAC address.  These MAC addresses
       are aliased to the same anycast default gateway IP address
       through the use of the Default Gateway extended community as
       specified in [RFC7432], which is carried in the EVPN MAC/IP
       Advertisement routes.  On each PE, this default gateway IP
       address along with its associated MAC addresses correspond to the
       IRB interface connecting the bridge table associated with the
       tenant's VLAN to the corresponding tenant's IP-VRF.

   It is worth noting that if the applications that are running on the
   TSes are employing or relying on any form of MAC security, then the



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   first option (i.e. using anycast MAC address) should be used to
   ensure that the applications receive traffic from the same IRB
   interface MAC address that they are sending to.  If the second option
   is used, then the IRB interface MAC address MUST be the one used in
   the initial ARP reply or ND Neighbor Advertisement (NA)for that TS.

   Although both of these options are applicable to both symmetric and
   asymmetric IRB, the option-1 is recommended because of the ease of
   anycast MAC address provisioning on not only the IRB interface
   associated with a given subnet across all the PEs corresponding to
   that VLAN but also on all IRB interfaces associated with all the
   tenant's subnets across all the PEs corresponding to all the VLANs
   for that tenant.  Furthermore, it simplifies the operation as there
   is no need for Default Gateway extended community advertisement and
   its associated MAC aliasing procedure.  Yet another advantage is that
   following host mobility, the host does not need to refresh the
   default GW ARP/ND entry.

   If option-1 is used, an implementation MAY choose to auto-derive the
   anycast MAC address.  If auto-derivation is used, the anycast MAC
   MUST be auto-derived out of the following ranges (which are defined
   in [RFC5798]):

   o  Anycast IPv4 IRB case: 00-00-5E-00-01-{VRID}

   o  Anycast IPv6 IRB case: 00-00-5E-00-02-{VRID}

   Where the last octet is generated based on a configurable Virtual
   Router ID (VRID, range 1-255)).  If not explicitly configured, the
   default value for the VRID octet is '1'.  Auto-derivation of the
   anycast MAC can only be used if there is certainty that the auto-
   derived MAC does not collide with any customer MAC address.

   In addition to IP anycast addresses, IRB interfaces can be configured
   with non-anycast IP addresses for the purpose of OAM (such as
   traceroute/ping to these interfaces) for both symmetric and
   asymmetric IRB.  These IP addresses need to be distributed as VPN
   routes when PEs operate in symmetric IRB mode.  However, they don't
   need to be distributed if the PEs are operating in asymmetric IRB
   mode as the non-anycast IP addresses are configured along with their
   individual MACs and they get distributed via EVPN route type-2
   advertisement.

   For option-1, irrespective of using only the anycast MAC address or
   both anycast and non-anycast MAC addresses (where the latter one is
   used for the purpose of OAM) on the same IRB, when a TS sends an ARP
   request or ND Neighbor Solicitation (NS) to the PE that is attached
   to, the request is sent for the anycast IP address of the IRB



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   interface associated with the TS's subnet and then the reply will use
   anycast MAC address (in both Source MAC in the Ethernet header and
   Sender hardware address in the payload).  For example, in figure 4,
   TS1 is configured with the anycast IPx address as its default gateway
   IP address and thus when it sends an ARP request for IPx (anycast IP
   address of the IRB interface for BT1), the PE1 sends an ARP reply
   with the MACx which is the anycast MAC address of that IRB interface.
   Traffic routed from IP-VRF1 to TS1 uses the anycast MAC address as
   source MAC address.

4.2.  Operational Considerations

   Symmetric and Asymmetric IRB modes may coexist in the same network,
   and an ingress PE that supports both forwarding modes for a given
   tenant can interwork with egress PEs that support either IRB mode.
   The egress PE will indicate the desired forwarding mode for a given
   host based on the presence of the Label2 field and the IP-VRF route-
   target in the EVPN MAC/IP Advertisement route.  If the Label2 field
   of the received MAC/IP Advertisement route for host H1 is non-zero,
   and one of its route-targets identifies the IP-VRF, the ingress PE
   will use Symmetric IRB mode when forwarding packets destined to H1.
   If the Label2 field is zero and the MAC/IP Advertisement route for H1
   does not carry any route-target that identifies the IP-VRF, the
   ingress PE will use Asymmetric mode when forwarding traffic to H1.

   As an example that illustrates the previous statement, suppose PE1
   and PE2 need to forward packets from TS2 to TS4 in the example of
   Figure 4.  Since both PEs are attached to the bridge table of the
   destination host, Symmetric and Asymmetric IRB modes are both
   possible as long as the ingress PE, PE1, supports both modes.  The
   forwarding mode will depend on the mode configured in the egress PE,
   PE2.  That is:

   1.  If PE2 is configured for Symmetric IRB mode, PE2 will advertise
       TS4 MAC/IP addresses in a MAC/IP Advertisement route with a non-
       zero Label2 field, e.g., Label2=Lx, and a route-target that
       identifies IP-VRF1 in PE1.  IP4 will be installed in PE1's IP-
       VRF1, TS4's ARP and MAC information will also be installed in
       PE1's IRB interface ARP table and BT1 respectively.  When a
       packet from TS2 destined to TS4 is looked up in PE1's IP-VRF
       route-table, a longest prefix match lookup will find IP4 in the
       IP-VRF, and PE1 will forward using the Symmetric IRB mode and
       Label Lx.

   2.  However, if PE2 is configured for Asymmetric IRB mode, PE2 will
       advertise TS4 MAC/IP information in a MAC/IP Advertisement route
       with a zero Label2 field and no route-target identifying IP-VRF1.
       In this case, PE2 will install TS4 information in its ARP table



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       and BT1.  When a packet from TS2 to TS4 arrives at PE1, a longest
       prefix match on IP-VRF1's route-table will yield the local IRB
       interface to BT1, where a subsequent ARP and bridge table lookup
       will provide the information for an Asymmetric forwarding mode to
       PE2.

   Refer to [I-D.ietf-bess-evpn-modes-interop] for more information
   about interoperability between Symmetric and Asymmetric forwarding
   modes.

   The choice between Symmetric or Asymmetric mode is based on the
   operator's preference and it is a trade-off between scale (better in
   the Symmetric IRB mode) and control plane simplicity (Asymmetric IRB
   mode simplifies the control plane).  In cases where a tenant has
   hosts for every subnet attached to all (or most) the PEs, the ARP and
   MAC entries need to be learned by all PEs anyway and therefore the
   Asymmetric IRB mode simplifies the forwarding model and saves space
   in the IP-VRF route-table, since host routes are not installed in the
   route-table.  However, if the tenant does not need to stretch subnets
   (broadcast domains) to multiple PEs and inter-subnet-forwarding is
   needed, the Symmetric IRB model will save ARP and bridge table space
   in all the PEs (in comparison with the Asymmetric IRB model).

5.  Symmetric IRB Procedures

5.1.  Control Plane - Advertising PE

   When a PE (e.g., PE1 in figure 4 above) learns MAC and IP address of
   a TS (e.g., via an ARP request or Neighbor Solicitation), it adds the
   MAC address to the corresponding MAC-VRF/bridge table of that
   tenant's subnet and adds the IP address to the IP-VRF for that
   tenant.  Furthermore, it adds this TS's MAC and IP address
   association to its ARP table or NDP cache.  It then builds an EVPN
   MAC/IP Advertisement route (type 2) as follows and advertises it to
   other PEs participating in that tenant's VPN.

   o  The Length field of the BGP EVPN NLRI for an EVPN MAC/IP
      Advertisement route MUST be either 40 (if IPv4 address is carried)
      or 52 (if IPv6 address is carried).

   o  Route Distinguisher (RD), Ethernet Segment Identifier, Ethernet
      Tag ID, MAC Address Length, MAC Address, IP Address Length, IP
      Address, and MPLS Label1 fields MUST be set per [RFC7432] and
      [RFC8365].

   o  The MPLS Label2 field is set to either an MPLS label or a VNI
      corresponding to the tenant's IP-VRF.  In the case of an MPLS




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      label, this field is encoded as 3 octets, where the high-order 20
      bits contain the label value.

   Just as in [RFC7432], the RD, Ethernet Tag ID, MAC Address Length,
   MAC Address, IP Address Length, and IP Address fields are part of the
   route key used by BGP to compare routes.  The rest of the fields are
   not part of the route key.

   This route is advertised along with the following two extended
   communities:

   1.  Encapsulation Extended Community

   2.  Router's MAC Extended Community

   This route is advertised with one or more Encapsulation extended
   communities [RFC9012], one for each encapsulation type supported by
   the advertising PE.  If one or more encapsulation types require an
   Ethernet frame, a single Router's MAC extended community, section
   8.1, is also advertised.  This extended community specifies the MAC
   address to be used as the inner destination MAC address in an
   Ethernet frame sent to the advertising PE.

   This route MUST be advertised with two route targets, one
   corresponding to the MAC-VRF of the tenant's subnet and another
   corresponding to the tenant's IP-VRF.

5.2.  Control Plane - Receiving PE

   When a PE (e.g., PE2 in figure 4 above) receives this EVPN MAC/IP
   Advertisement route, it performs the following:

   o  The MAC-VRF route target and Ethernet Tag, if the latter is non-
      zero, are used to identify the correct MAC-VRF and bridge table
      and if they are found the MAC address is imported.  The IP-VRF
      route target is used to identify the correct IP-VRF and if it is
      found the IP address is imported.

   If the MPLS label2 field is non-zero, it means that this route is to
   be used for symmetric IRB and the MPLS label2 value is to be used
   when sending a packet for this IP address to the advertising PE.

   If the receiving PE receives this route with both the MAC-VRF and IP-
   VRF route targets but the MAC/IP Advertisement route does not include
   MPLS label2 field and if the receiving PE supports asymmetric IRB
   mode, then the receiving PE installs the MAC address in the
   corresponding MAC-VRF and (IP, MAC) association in the ARP table for
   that tenant (identified by the corresponding IP-VRF route target).



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   If the receiving PE receives this route with both the MAC-VRF and IP-
   VRF route targets and if the receiving PE does not support either
   asymmetric or symmetric IRB modes, then if it has the corresponding
   MAC-VRF, it only imports the MAC address.

   If the receiving PE receives this route with both the MAC-VRF and IP-
   VRF route targets and the MAC/IP Advertisement route includes MPLS
   label2 field but the receiving PE only supports asymmetric IRB mode,
   then the receiving PE MUST ignore MPLS label2 field and install the
   MAC address in the corresponding MAC-VRF and (IP, MAC) association in
   the ARP table for that tenant (identified by the corresponding IP-VRF
   route target).

5.3.  Subnet route advertisement

   In the case of symmetric IRB, a layer-3 subnet and IRB interface
   corresponding to a MAC-VRF/bridge table is required to be provisioned
   at a PE only if that PE has locally attached hosts in that subnet.
   In order to enable inter-subnet routing across PEs in a deployment
   where not all subnets are provisioned at all PEs participating in an
   EVPN IRB instance, PEs MUST advertise local subnet routes as EVPN RT-
   5.  These subnet routes are required for bootstrapping host (MAC,IP)
   learning using gleaning procedures initiated by an inter-subnet data
   packet.

   I.e., if a given host's (MAC, IP) association is unknown, and an
   ingress PE needs to send a packet to that host, then that ingress PE
   needs to know which egress PEs are attached to the subnet in which
   the host resides in order to send the packet to one of those PEs,
   causing the PE receiving the packet to probe for that host.  For
   example, Consider a subnet A that is locally attached to PE1 and
   subnet B that is locally attached to PE2 and to PE3.  Host A in
   subnet A, that is attached to PE1 initiates a data packet destined to
   host B in subnet B that is attached to PE3.  If host B's (MAC, IP)
   has not yet been learnt either via a gratuitous ARP OR via a prior
   gleaning procedure, a new gleaning procedure MUST be triggered for
   host B's (MAC, IP) to be learnt and advertised across the EVPN
   network.  Since host B's subnet is not local to PE1, an IP lookup for
   host B at PE1 will not trigger this gleaning procedure for host B's
   (MAC, IP).  Therefore, PE1 MUST learn subnet B's prefix route via
   EVPN RT-5 advertised from PE2 and PE3, so it can route the packet to
   one of the PEs that have subnet B locally attached.  Once the packet
   is received at PE2 OR PE3, and the route lookup yields a glean
   result, an ARP request is triggered and flooded across the layer-2
   overlay.  This ARP request would be received and replied to by host
   B, resulting in host B (MAC, IP) learning at PE3, and its
   advertisement across the EVPN network.  Packets from host A to host B
   can now be routed directly from PE1 to PE3.  Advertisement of local



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   subnet EVPN RT-5 for an IP VRF MAY typically be achieved via
   provisioning connected route redistribution to BGP.

5.4.  Data Plane - Ingress PE

   When an Ethernet frame is received by an ingress PE (e.g., PE1 in
   figure 4 above), the PE uses the AC ID (e.g., VLAN ID) to identify
   the associated MAC-VRF/bridge table and it performs a lookup on the
   destination MAC address.  If the MAC address corresponds to its IRB
   Interface MAC address, the ingress PE deduces that the packet must be
   inter-subnet routed.  Hence, the ingress PE performs an IP lookup in
   the associated IP-VRF table.  The lookup identifies BGP next hop of
   egress PE along with the tunnel/encapsulation type and the associated
   MPLS/VNI values.  The ingress PE also decrements the TTL/hop limit
   for that packet by one and if it reaches zero, the ingress PE
   discards the packet.

   If the tunnel type is that of MPLS or IP-only NVO tunnel, then TS's
   IP packet is sent over the tunnel without any Ethernet header.
   However, if the tunnel type is that of Ethernet NVO tunnel, then an
   Ethernet header needs to be added to the TS's IP packet.  The source
   MAC address of this inner Ethernet header is set to the ingress PE's
   router MAC address and the destination MAC address of this inner
   Ethernet header is set to the egress PE's router MAC address learnt
   via Router's MAC extended community attached to the route.  MPLS VPN
   label is set to the received label2 in the route.  In the case of
   Ethernet NVO tunnel type, VNI may be set one of two ways:

   o  downstream mode: VNI is set to the received label2 in the route
      which is downstream assigned.

   o  global mode: VNI is set to the received label2 in the route which
      is domain-wide assigned.  This VNI value from received label2 MUST
      be the same as the locally configured VNI for the IP VRF as all
      PEs in the NVO MUST be configured with the same IP VRF VNI for
      this mode of operation.  If the received label2 value does not
      match the locally configured VNI value the route MUST NOT be used
      and an error message SHOULD logged.

   PEs may be configured to operate in one of these two modes depending
   on the administrative domain boundaries across PEs participating in
   the NVO, and PE's capability to support downstream VNI mode.

   In the case of NVO tunnel encapsulation, the outer source and
   destination IP addresses are set to the ingress and egress PE BGP
   next-hop IP addresses respectively.





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5.5.  Data Plane - Egress PE

   When the tenant's MPLS or NVO encapsulated packet is received over an
   MPLS or NVO tunnel by the egress PE, the egress PE removes NVO tunnel
   encapsulation and uses the VPN MPLS label (for MPLS encapsulation) or
   VNI (for NVO encapsulation) to identify the IP-VRF in which IP lookup
   needs to be performed.  If the VPN MPLS label or VNI identifies a
   MAC- VRF instead of an IP-VRF, then the procedures in section 6.4 for
   asymmetric IRB are executed.

   The lookup in the IP-VRF identifies a local adjacency to the IRB
   interface associated with the egress subnet's MAC-VRF/bridge table.
   The egress PE also decrements the TTL/hop limit for that packet by
   one and if it reaches zero, the egress PE discards the packet.

   The egress PE gets the destination TS's MAC address for that TS's IP
   address from its ARP table or NDP cache, it encapsulates the packet
   with that destination MAC address and a source MAC address
   corresponding to that IRB interface and sends the packet to its
   destination subnet MAC-VRF/bridge table.

   The destination MAC address lookup in the MAC-VRF/bridge table
   results in local adjacency (e.g., local interface) over which the
   Ethernet frame is sent on.

6.  Asymmetric IRB Procedures

6.1.  Control Plane - Advertising PE

   When a PE (e.g., PE1 in figure 4 above) learns MAC and IP address of
   an attached TS (e.g., via an ARP request or ND Neighbor
   Solicitation), it populates its MAC-VRF/bridge table, IP-VRF, and ARP
   table or NDP cache just as in the case for symmetric IRB.  It then
   builds an EVPN MAC/IP Advertisement route (type 2) as follows and
   advertises it to other PEs participating in that tenant's VPN.

   o  The Length field of the BGP EVPN NLRI for an EVPN MAC/IP
      Advertisement route MUST be either 37 (if IPv4 address is carried)
      or 49 (if IPv6 address is carried).

   o  Route Distinguisher (RD), Ethernet Segment Identifier, Ethernet
      Tag ID, MAC Address Length, MAC Address, IP Address Length, IP
      Address, and MPLS Label1 fields MUST be set per [RFC7432] and
      [RFC8365].

   o  The MPLS Label2 field MUST NOT be included in this route.





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   Just as in [RFC7432], the RD, Ethernet Tag ID, MAC Address Length,
   MAC Address, IP Address Length, and IP Address fields are part of the
   route key used by BGP to compare routes.  The rest of the fields are
   not part of the route key.

   This route is advertised along with the following extended community:

   o  Tunnel Type Extended Community

   For asymmetric IRB mode, Router's MAC extended community is not
   needed because forwarding is performed using destination TS's MAC
   address which is carried in this EVPN route type-2 advertisement.

   This route MUST always be advertised with the MAC-VRF route target.
   It MAY also be advertised with a second route target corresponding to
   the IP-VRF.

6.2.  Control Plane - Receiving PE

   When a PE (e.g., PE2 in figure 4 above) receives this EVPN MAC/IP
   Advertisement route, it performs the following:

   o  Using MAC-VRF route target, it identifies the corresponding MAC-
      VRF and imports the MAC address into it.  For asymmetric IRB mode,
      it is assumed that all PEs participating in a tenant's VPN are
      configured with all subnets (i.e., all VLANs) and corresponding
      MAC-VRFs/bridge tables even if there are no locally attached TSes
      for some of these subnets.  The reason for this is because ingress
      PE needs to do forwarding based on destination TS's MAC address
      and perform NVO tunnel encapsulation as a property of a lookup in
      MAC-VRF/bridge table.

   o  If only MAC-VRF route target is used, then the receiving PE uses
      the MAC-VRF route target to identify the corresponding IP-VRF --
      i.e., many MAC-VRF route targets map to the same IP-VRF for a
      given tenant.  In this case, MAC-VRF may be used by the receiving
      PE to identify the corresponding IP VRF via the IRB interface
      associated with the subnet MAC-VRF/bridge table.  In this case,
      the MAC-VRF route target may be used by the receiving PE to
      identify the corresponding IP VRF.

   o  Using MAC-VRF route target, the receiving PE identifies the
      corresponding ARP table or NDP cache for the tenant and it adds an
      entry to the ARP table or NDP cache for the TS's MAC and IP
      address association.  It should be noted that the tenant's ARP
      table or NDP cache at the receiving PE is identified by all the
      MAC- VRF route targets for that tenant.




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   o  If IP-VRF route target is included, it may be used to import the
      route to IP-VRF.  If IP-VRF route-target is not included, MAC-VRF
      is used to derive corresponding IP-VRF for import, as explained in
      the prior section.  In both cases, IP-VRF route is installed with
      the TS MAC binding included in the received route.

   If the receiving PE receives the MAC/IP Advertisement route with MPLS
   label2 field but the receiving PE only supports asymmetric IRB mode,
   then the receiving PE MUST ignore MPLS label2 field and install the
   MAC address in the corresponding MAC-VRF and (IP, MAC) association in
   the ARP table or NDP cache for that tenant (with IRB interface
   identified by the MAC-VRF).

6.3.  Data Plane - Ingress PE

   When an Ethernet frame is received by an ingress PE (e.g., PE1 in
   figure 4 above), the PE uses the AC ID (e.g., VLAN ID) to identify
   the associated MAC-VRF/bridge table and it performs a lookup on the
   destination MAC address.  If the MAC address corresponds to its IRB
   Interface MAC address, the ingress PE deduces that the packet must be
   inter-subnet routed.  Hence, the ingress PE performs an IP lookup in
   the associated IP-VRF table.  The lookup identifies a local adjacency
   to the IRB interface associated with the egress subnet's MAC-VRF/
   bridge table.  The ingress PE also decrements the TTL/hop limit for
   that packet by one and if it reaches zero, the ingress PE discards
   the packet.

   The ingress PE gets the destination TS's MAC address for that TS's IP
   address from its ARP table or NDP cache, it encapsulates the packet
   with that destination MAC address and a source MAC address
   corresponding to that IRB interface and sends the packet to its
   destination subnet MAC-VRF/bridge table.

   The destination MAC address lookup in the MAC-VRF/bridge table
   results in BGP next hop address of egress PE along with label1 (L2
   VPN MPLS label or VNI).  The ingress PE encapsulates the packet using
   Ethernet NVO tunnel of the choice (e.g., VxLAN or NVGRE) and sends
   the packet to the egress PE.  Because the packet forwarding is
   between ingress PE's MAC-VRF/bridge table and egress PE's MAC-VRF/
   bridge table, the packet encapsulation procedures follow that of
   [RFC7432] for MPLS and [RFC8365] for VxLAN encapsulations.

6.4.  Data Plane - Egress PE

   When a tenant's Ethernet frame is received over an NVO tunnel by the
   egress PE, the egress PE removes NVO tunnel encapsulation and uses
   the VPN MPLS label (for MPLS encapsulation) or VNI (for NVO




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   encapsulation) to identify the MAC-VRF/bridge table in which MAC
   lookup needs to be performed.

   The MAC lookup results in local adjacency (e.g., local interface)
   over which the packet needs to get sent.

   Note that the forwarding behavior on the egress PE is the same as
   EVPN intra-subnet forwarding described in [RFC7432] for MPLS and
   [RFC8365] for NVO networks.  In other words, all the packet
   processing associated with the inter-subnet forwarding semantics is
   confined to the ingress PE for asymmetric IRB mode.

   It should also be noted that [RFC7432] provides a different level of
   granularity for the EVPN label.  Besides identifying the bridge
   domain table, it can be used to identify the egress interface or a
   destination MAC address on that interface.  If EVPN label is used for
   egress interface or individual MAC address identification, then no
   MAC lookup is needed in the egress PE for MPLS encapsulation and the
   packet can be directly forwarded to the egress interface just based
   on EVPN label lookup.

7.  Mobility Procedure

   When a TS moves from one NVE (aka source NVE) to another NVE (aka
   target NVE), it is important that the MAC mobility procedures are
   properly executed and the corresponding MAC-VRF and IP-VRF tables on
   all participating NVEs are updated.  [RFC7432] describes the MAC
   mobility procedures for L2-only services for both single-homed TS and
   multi-homed TS.  This section describes the incremental procedures
   and BGP Extended Communities needed to handle the MAC mobility for
   IRB.  In order to place the emphasis on the differences between
   L2-only and IRB use cases, the incremental procedure is described for
   single-homed TS with the expectation that the additional steps needed
   for multi-homed TS, can be extended per section 15 of [RFC7432].
   This section describes mobility procedures for both symmetric and
   asymmetric IRB.  Although the language used in this section is for
   IPv4 ARP, it equally applies to IPv6 ND.

   When a TS moves from a source NVE to a target NVE, it can behave in
   one of the following three ways:

   1.  TS initiates an ARP request upon a move to the target NVE

   2.  TS sends data packet without first initiating an ARP request to
       the target NVE

   3.  TS is a silent host and neither initiates an ARP request nor
       sends any packets



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   Depending on the expexted TS's behavior, an NVE needs to handle at
   least the first bullet and should be able to handle the 2nd and the
   3rd bullet.  The following subsections describe the procedures for
   each of them where it is assumed that the MAC and IP addresses of a
   TS have one-to-one relationship (i.e., there is one IP address per
   MAC address and vice versa).  The procedures for host mobility
   detection in the presence of many-to-one relationship is outside the
   scope of this document and it is covered in
   [I-D.ietf-bess-evpn-irb-extended-mobility].  The many-to-one
   relationship means many host IP addresses corresponding to a single
   host MAC address or many host MAC addresses corresponding to a single
   IP address.  It should be noted that in case of IPv6, a Link Local IP
   address does not count in many-to-one relationship because that
   address is confined to single Ethernet Segment and it is not used for
   host moblity (i.e., by definition host mobility is between two
   different Ethernet Segments).  Therefore, when an IPv6 host is
   configured with both a Global Unicast address (or a Unique Local
   address) and a Link Local address, for the purpose of host mobility,
   it is considered with a single IP address.

7.1.  Initiating a gratutious ARP upon a Move

   In this scenario when a TS moves from a source NVE to a target NVE,
   the TS initiates a gratuitous ARP upon the move to the target NVE.

   The target NVE upon receiving this ARP message, updates its MAC-VRF,
   IP-VRF, and ARP table with the host MAC, IP, and local adjacency
   information (e.g., local interface).

   Since this NVE has previously learned the same MAC and IP addresses
   from the source NVE, it recognizes that there has been a MAC move and
   it initiates MAC mobility procedures per [RFC7432] by advertising an
   EVPN MAC/IP Advertisement route with both the MAC and IP addresses
   filled in (per sections 5.1 and 6.1) along with MAC Mobility Extended
   Community with the sequence number incremented by one.  The target
   NVE also exercises the MAC duplication detection procedure in section
   15.1 of [RFC7432].

   The source NVE upon receiving this MAC/IP Advertisement route,
   realizes that the MAC has moved to the target NVE.  It updates its
   MAC-VRF and IP-VRF table accordingly with the adjacency information
   of the target NVE.  In the case of the asymmetric IRB, the source NVE
   also updates its ARP table with the received adjacency information
   and in the case of the symmetric IRB, the source NVE removes the
   entry associated with the received (MAC, IP) from its local ARP
   table.  It then withdraws its EVPN MAC/IP Advertisement route.
   Furthermore, it sends an ARP probe locally to ensure that the MAC is
   gone.  If an ARP response is received, the source NVE updates its ARP



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   entry for that (IP, MAC) and re-advertises an EVPN MAC/IP
   Advertisement route for that (IP, MAC) along with MAC Mobility
   Extended Community with the sequence number incremented by one.  The
   source NVE also exercises the MAC duplication detection procedure in
   section 15.1 of [RFC7432].

   All other remote NVE devices upon receiving the MAC/IP Advertisement
   route with MAC Mobility extended community compare the sequence
   number in this advertisement with the one previously received.  If
   the new sequence number is greater than the old one, then they update
   the MAC/IP addresses of the TS in their corresponding MAC-VRF and IP-
   VRF tables to point to the target NVE.  Furthermore, upon receiving
   the MAC/IP withdraw for the TS from the source NVE, these remote PEs
   perform the cleanups for their BGP tables.

7.2.  Sending Data Traffic without an ARP Request

   In this scenario when a TS moves from a source NVE to a target NVE,
   the TS starts sending data traffic without first initiating an ARP
   request.

   The target NVE upon receiving the first data packet, learns the MAC
   address of the TS in the data plane and updates its MAC-VRF table
   with the MAC address and the local adjacency information (e.g., local
   interface) accordingly.  The target NVE realizes that there has been
   a MAC move because the same MAC address has been learned remotely
   from the source NVE.

   If EVPN-IRB NVEs are configured to advertise MAC-only routes in
   addition to MAC-and-IP EVPN routes, then the following steps are
   taken:

   o  The target NVE upon learning this MAC address in the data plane,
      updates this MAC address entry in the corresponding MAC-VRF with
      the local adjacency information (e.g., local interface).  It also
      recognizes that this MAC has moved and initiates MAC mobility
      procedures per [RFC7432] by advertising an EVPN MAC/IP
      Advertisement route with only the MAC address filled in along with
      MAC Mobility Extended Community with the sequence number
      incremented by one.

   o  The source NVE upon receiving this MAC/IP Advertisement route,
      realizes that the MAC has moved to the new NVE.  It updates its
      MAC-VRF table with the adjacency information for that MAC address
      to point to the target NVE and withdraws its EVPN MAC/IP
      Advertisement route that has only the MAC address (if it has
      advertised such route previously).  Furthermore, it searches for
      the corresponding MAC-IP entry and sends an ARP probe for this



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      (MAC,IP) pair.  The ARP request message is sent both locally to
      all attached TSes in that subnet as well as it is sent to other
      NVEs participating in that subnet including the target NVE.  Note
      that the PE needs to maintain a correlation between MAC and MAC-IP
      route entries in the MAC-VRF to accomplish this.

   o  The target NVE passes the ARP request to its locally attached TSes
      and when it receives the ARP response, it updates its IP-VRF and
      ARP table with the host (MAC, IP) information.  It also sends an
      EVPN MAC/IP Advertisement route with both the MAC and IP addresses
      filled in along with MAC Mobility Extended Community with the
      sequence number set to the same value as the one for MAC-only
      advertisement route it sent previously.

   o  When the source NVE receives the EVPN MAC/IP Advertisement route,
      it updates its IP-VRF table with the new adjacency information
      (pointing to the target NVE).  In the case of the asymmetric IRB,
      the source NVE also updates its ARP table with the received
      adjacency information and in the case of the symmetric IRB, the
      source NVE removes the entry associated with the received (MAC,
      IP) from its local ARP table.  Furthermore, it withdraws its
      previously advertised EVPN MAC/IP route with both the MAC and IP
      address fields filled in.

   o  All other remote NVE devices upon receiving the MAC/IP
      advertisement route with MAC Mobility extended community compare
      the sequence number in this advertisement with the one previously
      received.  If the new sequence number is greater than the old one,
      then they update the MAC/IP addresses of the TS in their
      corresponding MAC-VRF, IP-VRF, and ARP tables (in the case of
      asymmetric IRB) to point to the new NVE.  Furthermore, upon
      receiving the MAC/IP withdraw for the TS from the old NVE, these
      remote PEs perform the cleanups for their BGP tables.

   If EVPN-IRB NVEs are configured not to advertise MAC-only routes,
   then upon receiving the first data packet, it learns the MAC address
   of the TS and updates the MAC entry in the corresponding MAC-VRF
   table with the local adjacency information (e.g., local interface).
   It also realizes that there has been a MAC move because the same MAC
   address has been learned remotely from the source NVE.  It uses the
   local MAC route to find the corresponding local MAC-IP route, and
   sends a unicast ARP request to the host and when receiving an ARP
   response, it follows the procedure outlined in section 7.1.  In the
   prior case, where MAC-only routes are also advertised, this procedure
   of triggering a unicast ARP probe at the target PE MAY also be used
   in addition to the source PE broadcast ARP probing procedure
   described earlier for better convergence.




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7.3.  Silent Host

   In this scenario when a TS moves from a source NVE to a target NVE,
   the TS is silent and it neither initiates an ARP request nor it sends
   any data traffic.  Therefore, neither the target nor the source NVEs
   are aware of the MAC move.

   On the source NVE, an age-out timer (for the silent host that has
   moved) is used to trigger an ARP probe.  This age-out timer can be
   either ARP timer or MAC age-out timer and this is an implementation
   choice.  The ARP request gets sent both locally to all the attached
   TSes on that subnet as well as it gets sent to all the remote NVEs
   (including the target NVE) participating in that subnet.  The source
   NVE also withdraw the EVPN MAC/IP Advertisement route with only the
   MAC address (if it has previously advertised such a route).

   The target NVE passes the ARP request to its locally attached TSes
   and when it receives the ARP response, it updates its MAC-VRF, IP-
   VRF, and ARP table with the host (MAC, IP) and local adjacency
   information (e.g., local interface).  It also sends an EVPN MAC/IP
   advertisement route with both the MAC and IP address fields filled in
   along with MAC Mobility Extended Community with the sequence number
   incremented by one.

   When the source NVE receives the EVPN MAC/IP Advertisement route, it
   updates its IP-VRF table with the new adjacency information (pointing
   to the target NVE).  In the case of the asymmetric IRB, the source
   NVE also updates its ARP table with the received adjacency
   information and in the case of the symmetric IRB, the source NVE
   removes the entry associated with the received (MAC, IP) from its
   local ARP table.  Furthermore, it withdraws its previously advertised
   EVPN MAC/IP route with both the MAC and IP address fields filled in.

   All other remote NVE devices upon receiving the MAC/IP Advertisement
   route with MAC Mobility extended community compare the sequence
   number in this advertisement with the one previously received.  If
   the new sequence number is greater than the old one, then they update
   the MAC/IP addresses of the TS in their corresponding MAC-VRF, IP-
   VRF, and ARP (in the case of asymmetric IRB) tables to point to the
   new NVE.  Furthermore, upon receiving the MAC/IP withdraw for the TS
   from the old NVE, these remote PEs perform the cleanups for their BGP
   tables.

8.  BGP Encoding

   This document defines one new BGP Extended Community for EVPN.





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8.1.  Router's MAC Extended Community

   A new EVPN BGP Extended Community called Router's MAC is introduced
   here.  This new extended community is a transitive extended community
   with the Type field of 0x06 (EVPN) and the Sub-Type of 0x03.  It may
   be advertised along with Encapsulation Extended Community defined in
   section 4.1 of [I-D.ietf-idr-tunnel-encaps].

   The Router's MAC Extended Community is encoded as an 8-octet value as
   follows:


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Type=0x06     | Sub-Type=0x03 |        Router's MAC           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Router's MAC Cont'd                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 5: Router's MAC Extended Community


   This extended community is used to carry the PE's MAC address for
   symmetric IRB scenarios and it is sent with EVPN RT-2.  The
   advertising PE SHALL only attach a single Router's MAC Extended
   Community to a route.  In case the receiving PE receives more than
   one Router's MAC Extended Community with a route, it SHALL process
   the first one in the list and not store and propagate the others.

9.  Operational Models for Symmetric Inter-Subnet Forwarding

   The following sections describe two main symmetric IRB forwarding
   scenarios (within a DC -- i.e., intra-DC) along with the
   corresponding procedures.  In the following scenarios, without loss
   of generality, it is assumed that a given tenant is represented by a
   single IP-VPN instance.  Therefore, on a given PE, a tenant is
   represented by a single IP-VRF table and one or more MAC-VRF tables.

9.1.  IRB forwarding on NVEs for Tenant Systems

   This section covers the symmetric IRB procedures for the scenario
   where each Tenant System (TS) is attached to one or more NVEs and its
   host IP and MAC addresses are learned by the attached NVEs and are
   distributed to all other NVEs that are interested in participating in
   both intra-subnet and inter-subnet communications with that TS.





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   In this scenario, without loss of generality, it is assumed that NVEs
   operate in VLAN-based service interface mode with one bridge table(s)
   per MAC-VRF.  Thus, for a given tenant, an NVE has one MAC-VRF for
   each tenant subnet (e.g., each VLAN) that is configured for extension
   via VxLAN or NVGRE encapsulation.  In the case of VLAN-aware
   bundling, then each MAC-VRF consists of multiple Bridge Tables (e.g.,
   one bridge table per VLAN).  The MAC-VRFs on an NVE for a given
   tenant are associated with an IP-VRF corresponding to that tenant (or
   IP-VPN instance) via their IRB interfaces.

   Since VxLAN and NVGRE encapsulations require inner Ethernet header
   (inner MAC SA/DA), and since for inter-subnet traffic, TS MAC address
   cannot be used, the ingress NVE's MAC address is used as inner MAC
   SA.  The NVE's MAC address is the device MAC address and it is common
   across all MAC-VRFs and IP-VRFs.  This MAC address is advertised
   using the new EVPN Router's MAC Extended Community (section 8.1).

   Figure 6 below illustrates this scenario where a given tenant (e.g.,
   an IP-VPN instance) has three subnets represented by MAC-VRF1, MAC-
   VRF2, and MAC-VRF3 across two NVEs.  There are five TSes that are
   associated with these three MAC-VRFs -- i.e., TS1, TS4, and TS5 are
   on the same subnet (e.g., same MAC-VRF/VLAN).  TS1 and TS5 are
   associated with MAC-VRF1 on NVE1, while TS4 is associated with MAC-
   VRF1 on NVE2.  TS2 is associated with MAC-VRF2 on NVE1, and TS3 is
   associated with MAC-VRF3 on NVE2.  MAC-VRF1 and MAC-VRF2 on NVE1 are
   in turn associated with IP-VRF1 on NVE1 and MAC-VRF1 and MAC-VRF3 on
   NVE2 are associated with IP-VRF1 on NVE2.  When TS1, TS5, and TS4
   exchange traffic with each other, only the L2 forwarding (bridging)
   part of the IRB solution is exercised because all these TSes belong
   to the same subnet.  However, when TS1 wants to exchange traffic with
   TS2 or TS3 which belong to different subnets, both bridging and
   routing parts of the IRB solution are exercised.  The following
   subsections describe the control and data planes operations for this
   IRB scenario in details.

















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                     NVE1         +---------+
               +-------------+    |         |
       TS1-----|         MACx|    |         |        NVE2
     (IP1/M1)  |(MAC-        |    |         |   +-------------+
       TS5-----| VRF1)\      |    |  MPLS/  |   |MACy  (MAC-  |-----TS3
     (IP5/M5)  |       \     |    |  VxLAN/ |   |     / VRF3) | (IP3/M3)
               |    (IP-VRF1)|----|  NVGRE  |---|(IP-VRF1)    |
               |       /     |    |         |   |     \       |
       TS2-----|(MAC- /      |    |         |   |      (MAC-  |-----TS4
     (IP2/M2)  | VRF2)       |    |         |   |       VRF1) | (IP4/M4)
               +-------------+    |         |   +-------------+
                                  |         |
                                  +---------+

          Figure 6: IRB forwarding on NVEs for Tenant Systems


9.1.1.  Control Plane Operation

   Each NVE advertises a MAC/IP Advertisement route (i.e., Route Type 2)
   for each of its TSes with the following field set:

   o  RD and ESI per [RFC7432]

   o  Ethernet Tag = 0; assuming VLAN-based service

   o  MAC Address Length = 48

   o  MAC Address = Mi ; where i = 1,2,3,4, or 5 in the above example

   o  IP Address Length = 32 or 128

   o  IP Address = IPi ; where i = 1,2,3,4, or 5 in the above example

   o  Label1 = MPLS Label or VNI corresponding to MAC-VRF

   o  Label2 = MPLS Label or VNI corresponding to IP-VRF

   Each NVE advertises an EVPN RT-2 route with two Route Targets (one
   corresponding to its MAC-VRF and the other corresponding to its IP-
   VRF.  Furthermore, the EVPN RT-2 is advertised with two BGP Extended
   Communities.  The first BGP Extended Community identifies the tunnel
   type and it is called Encapsulation Extended Community as defined in
   [I-D.ietf-idr-tunnel-encaps] and the second BGP Extended Community
   includes the MAC address of the NVE (e.g., MACx for NVE1 or MACy for
   NVE2) as defined in section 8.1.  The Router's MAC Extended community
   MUST be added when Ethernet NVO tunnel is used.  If IP NVO tunnel
   type is used, then there is no need to send this second Extended



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   Community.  It should be noted that IP NVO tunnel type is only
   applicable to symmetric IRB procedures.

   Upon receiving this advertisement, the receiving NVE performs the
   following:

   o  It uses Route Targets corresponding to its MAC-VRF and IP-VRF for
      identifying these tables and subsequently importing the MAC and IP
      addresses into them respectively.

   o  It imports the MAC address from MAC/IP Advertisement route into
      the MAC-VRF with BGP Next Hop address as the underlay tunnel
      destination address (e.g., VTEP DA for VxLAN encapsulation) and
      Label1 as VNI for VxLAN encapsulation or EVPN label for MPLS
      encapsulation.

   o  If the route carries the new Router's MAC Extended Community, and
      if the receiving NVE uses Ethernet NVO tunnel, then the receiving
      NVE imports the IP address into IP-VRF with NVE's MAC address
      (from the new Router's MAC Extended Community) as inner MAC DA and
      BGP Next Hop address as the underlay tunnel destination address,
      VTEP DA for VxLAN encapsulation and Label2 as IP-VPN VNI for VxLAN
      encapsulation.

   o  If the receiving NVE uses MPLS encapsulation, then the receiving
      NVE imports the IP address into IP-VRF with BGP Next Hop address
      as the underlay tunnel destination address, and Label2 as IP-VPN
      label for MPLS encapsulation.

   If the receiving NVE receives an EVPN RT-2 with only Label1 and only
   a single Route Target corresponding to IP-VRF, or if it receives an
   EVPN RT-2 with only a single Route Target corresponding to MAC-VRF
   but with both Label1 and Label2, or if it receives an EVPN RT-2 with
   MAC Address Length of zero, then it MUST use the treat-as-withdraw
   approach [RFC7606] and SHOULD log an error message.

9.1.2.  Data Plane Operation

   The following description of the data-plane operation describes just
   the logical functions and the actual implementation may differ.  Lets
   consider data-plane operation when TS1 in subnet-1 (MAC-VRF1) on NVE1
   wants to send traffic to TS3 in subnet-3 (MAC-VRF3) on NVE2.

   o  NVE1 receives a packet with MAC DA corresponding to the MAC-VRF1
      IRB interface on NVE1 (the interface between MAC-VRF1 and IP-
      VRF1), and VLAN-tag corresponding to MAC-VRF1.





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   o  Upon receiving the packet, the NVE1 uses VLAN-tag to identify the
      MAC-VRF1.  It then looks up the MAC DA and forwards the frame to
      its IRB interface.

   o  The Ethernet header of the packet is stripped and the packet is
      fed to the IP-VRF where an IP lookup is performed on the
      destination IP address.  NVE1 also decrements the TTL/hop limit
      for that packet by one and if it reaches zero, NVE1 discards the
      packet.  This lookup yields the outgoing NVO tunnel and the
      required encapsulation.  If the encapsulation is for Ethernet NVO
      tunnel, then it includes the egress NVE's MAC address as inner MAC
      DA, the egress NVE's IP address (e.g., BGP Next Hop address) as
      the VTEP DA, and the VPN-ID as the VNI.  The inner MAC SA and VTEP
      SA are set to NVE's MAC and IP addresses respectively.  If it is a
      MPLS encapsulation, then corresponding EVPN and LSP labels are
      added to the packet.  The packet is then forwarded to the egress
      NVE.

   o  On the egress NVE, if the packet arrives on Ethernet NVO tunnel
      (e.g., it is VxLAN encapsulated), then the NVO tunnel header is
      removed.  Since the inner MAC DA is the egress NVE's MAC address,
      the egress NVE knows that it needs to perform an IP lookup.  It
      uses the VNI to identify the IP-VRF table.  If the packet is MPLS
      encapsulated, then the EVPN label lookup identifies the IP-VRF
      table.  Next, an IP lookup is performed for the destination TS
      (TS3) which results in an access-facing IRB interface over which
      the packet is sent.  Before sending the packet over this
      interface, the ARP table is consulted to get the destination TS's
      MAC address.  NVE2 also decrements the TTL/hop limit for that
      packet by one and if it reaches zero, NVE2 discards the packet.

   o  The IP packet is encapsulated with an Ethernet header with MAC SA
      set to that of IRB interface MAC address (i.e, IRB interface
      between MAC-VRF3 and IP-VRF1 on NVE2) and MAC DA set to that of
      destination TS (TS3) MAC address.  The packet is sent to the
      corresponding MAC-VRF (i.e., MAC-VRF3) and after a lookup of MAC
      DA, is forwarded to the destination TS (TS3) over the
      corresponding interface.

   In this symmetric IRB scenario, inter-subnet traffic between NVEs
   will always use the IP-VRF VNI/MPLS label.  For instance, traffic
   from TS2 to TS4 will be encapsulated by NVE1 using NVE2's IP-VRF VNI/
   MPLS label, as long as TS4's host IP is present in NVE1's IP-VRF.








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9.2.  IRB forwarding on NVEs for Subnets behind Tenant Systems

   This section covers the symmetric IRB procedures for the scenario
   where some Tenant Systems (TSes) support one or more subnets and
   these TSes are associated with one or more NVEs.  Therefore, besides
   the advertisement of MAC/IP addresses for each TS which can be multi-
   homed with All-Active redundancy mode, the associated NVE needs to
   also advertise the subnets statically configured on each TS.

   The main difference between this solution and the previous one is the
   additional advertisement corresponding to each subnet.  These subnet
   advertisements are accomplished using the EVPN IP Prefix route
   defined in [I-D.ietf-bess-evpn-prefix-advertisement].  These subnet
   prefixes are advertised with the IP address of their associated TS
   (which is in overlay address space) as their next hop.  The receiving
   NVEs perform recursive route resolution to resolve the subnet prefix
   with its advertising NVE so that they know which NVE to forward the
   packets to when they are destined for that subnet prefix.

   The advantage of this recursive route resolution is that when a TS
   moves from one NVE to another, there is no need to re-advertise any
   of the subnet prefixes for that TS.  All it is needed is to advertise
   the IP/MAC addresses associated with the TS itself and exercise MAC
   mobility procedures for that TS.  The recursive route resolution
   automatically takes care of the updates for the subnet prefixes of
   that TS.

   Figure 7 illustrates this scenario where a given tenant (e.g., an IP-
   VPN service) has three subnets represented by MAC-VRF1, MAC-VRF2, and
   MAC-VRF3 across two NVEs.  There are four TSes associated with these
   three MAC-VRFs -- i.e., TS1 is connected to MAC-VRF1 on NVE1, TS2 is
   connected to MAC-VRF2 on NVE1, TS3 is connected to MAC- VRF3 on NVE2,
   and TS4 is connected to MAC-VRF1 on NVE2.  TS1 has two subnet
   prefixes (SN1 and SN2) and TS3 has a single subnet prefix, SN3.  The
   MAC-VRFs on each NVE are associated with their corresponding IP-VRF
   using their IRB interfaces.  When TS4 and TS1 exchange intra- subnet
   traffic, only L2 forwarding (bridging) part of the IRB solution is
   used (i.e., the traffic only goes through their MAC- VRFs); however,
   when TS3 wants to forward traffic to SN1 or SN2 sitting behind TS1
   (inter-subnet traffic), then both bridging and routing parts of the
   IRB solution are exercised (i.e., the traffic goes through the
   corresponding MAC-VRFs and IP-VRFs).  If TS4, for example, wants to
   reach SN1, it uses its default route and sends the packet to the MAC
   address associated with the IRB interface on NVE2, NVE2 then makes an
   IP lookup in its IP- VRF, and finds an entry for SN1.  The following
   subsections describe the control and data planes operations for this
   IRB scenario in details.




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                                NVE1      +----------+
        SN1--+          +-------------+   |          |
             |--TS1-----|(MAC- \      |   |          |
        SN2--+ IP1/M1   | VRF1) \     |   |          |
                        |     (IP-VRF)|---|          |
                        |       /     |   |          |
                TS2-----|(MAC- /      |   |  MPLS/   |
               IP2/M2   | VRF2)       |   |  VxLAN/  |
                        +-------------+   |  NVGRE   |
                        +-------------+   |          |
        SN3--+--TS3-----|(MAC-\       |   |          |
               IP3/M3   | VRF3)\      |   |          |
                        |     (IP-VRF)|---|          |
                        |       /     |   |          |
                TS4-----|(MAC- /      |   |          |
               IP4/M4   | VRF1)       |   |          |
                        +-------------+   +----------+
                               NVE2


           Figure 7: IRB forwarding on NVEs for subnets behind TSes


   Note that in figure 7, above, SN1 and SN2 are configured on NVE1,
   which then advertises each in an IP Prefix route.  Similarly, SN3 is
   configured on NVE2, which then advertises it in an IP Prefix route.

9.2.1.  Control Plane Operation

   Each NVE advertises a Route Type-5 (EVPN RT-5, IP Prefix route
   defined in [I-D.ietf-bess-evpn-prefix-advertisement]) for each of its
   subnet prefixes with the IP address of its TS as the next hop
   (gateway address field) as follows:

   o  RD associated with the IP-VRF

   o  ESI = 0

   o  Ethernet Tag = 0;

   o  IP Prefix Length = 0 to 32 or 0 to 128

   o  IP Prefix = SNi

   o  Gateway Address = IPi; IP address of TS

   o  MPLS Label = 0




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   This EVPN RT-5 is advertised with one or more Route Targets
   associated with the IP-VRF from which the route is originated.

   Each NVE also advertises an EVPN RT-2 (MAC/IP Advertisement Route)
   along with their associated Route Targets and Extended Communities
   for each of its TSes exactly as described in section 9.1.1.

   Upon receiving the EVPN RT-5 advertisement, the receiving NVE
   performs the following:

   o  It uses the Route Target to identify the corresponding IP-VRF

   o  It imports the IP prefix into its corresponding IP-VRF that is
      configured with an import RT that is one of the RTs being carried
      by the EVPN RT-5 route along with the IP address of the associated
      TS as its next hop.

   When receiving the EVPN RT-2 advertisement, the receiving NVE imports
   MAC/IP addresses of the TS into the corresponding MAC-VRF and IP-VRF
   per section 9.1.1.  When both routes exist, recursive route
   resolution is performed to resolve the IP prefix (received in EVPN
   RT-5) to its corresponding NVE's IP address (e.g., its BGP next hop).
   BGP next hop will be used as the underlay tunnel destination address
   (e.g., VTEP DA for VxLAN encapsulation) and Router's MAC will be used
   as inner MAC for VxLAN encapsulation.

9.2.2.  Data Plane Operation

   The following description of the data-plane operation describes just
   the logical functions and the actual implementation may differ.  Lets
   consider data-plane operation when a host on SN1 sitting behind TS1
   wants to send traffic to a host sitting behind SN3 behind TS3.

   o  TS1 send a packet with MAC DA corresponding to the MAC-VRF1 IRB
      interface of NVE1, and VLAN-tag corresponding to MAC-VRF1.

   o  Upon receiving the packet, the ingress NVE1 uses VLAN-tag to
      identify the MAC-VRF1.  It then looks up the MAC DA and forwards
      the frame to its IRB interface just like section 9.1.1.

   o  The Ethernet header of the packet is stripped and the packet is
      fed to the IP-VRF; where, IP lookup is performed on the
      destination address.  This lookup yields the fields needed for
      VxLAN encapsulation with NVE2's MAC address as the inner MAC DA,
      NVE'2 IP address as the VTEP DA, and the VNI.  MAC SA is set to
      NVE1's MAC address and VTEP SA is set to NVE1's IP address.  NVE1
      also decrements the TTL/hop limit for that packet by one and if it
      reaches zero, NVE1 discards the packet.



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   o  The packet is then encapsulated with the proper header based on
      the above info and is forwarded to the egress NVE (NVE2).

   o  On the egress NVE (NVE2), assuming the packet is VxLAN
      encapsulated, the VxLAN and the inner Ethernet headers are removed
      and the resultant IP packet is fed to the IP-VRF associated with
      that the VNI.

   o  Next, a lookup is performed based on IP DA (which is in SN3) in
      the associated IP-VRF of NVE2.  The IP lookup yields the access-
      facing IRB interface over which the packet needs to be sent.
      Before sending the packet over this interface, the ARP table is
      consulted to get the destination TS (TS3) MAC address.  NVE2 also
      decrements the TTL/hop limit for that packet by one and if it
      reaches zero, NVE2 discards the packet.

   o  The IP packet is encapsulated with an Ethernet header with the MAC
      SA set to that of the access-facing IRB interface of the egress
      NVE (NVE2) and the MAC DA is set to that of destination TS (TS3)
      MAC address.  The packet is sent to the corresponding MAC-VRF3 and
      after a lookup of MAC DA, is forwarded to the destination TS (TS3)
      over the corresponding interface.

10.  Acknowledgements

   The authors would like to thank Sami Boutros, Jeffrey Zhang,
   Krzysztof Szarkowicz, Lukas Krattiger and Neeraj Malhotra for their
   valuable comments.  The authors would also like to thank Linda
   Dunbar, Florin Balus, Yakov Rekhter, Wim Henderickx, Lucy Yong, and
   Dennis Cai for their feedback and contributions.

11.  Security Considerations

   The security considerations for layer-2 forwarding in this document
   follow that of [RFC7432] for MPLS encapsulation and it follows that
   of [RFC8365] for VxLAN or NVGRE encapsulations.  This section
   describes additional considerations.

   This document describes a set of procedures for Inter-Subnet
   Forwarding of tenant traffic across PEs (or NVEs).  These procedures
   include both layer-2 forwarding and layer-3 routing on a packet by
   packet basis.  The security consideration for layer-3 routing in this
   document follows that of [RFC4365] with the exception for the
   application of routing protocols between CEs and PEs.  Contrary to
   [RFC4364], this document does not describe route distribution
   techniques between CEs and PEs, but rather considers the CEs as TSes
   or VAs that do not run dynamic routing protocols.  This can be
   considered a security advantage, since dynamic routing protocols can



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   be blocked on the NVE/PE ACs, not allowing the tenant to interact
   with the infrastructure's dynamic routing protocols.

   The VPN scheme described in this document does not provide the
   quartet of security properties mentioned in [RFC4365]
   (confidentiality protection, source authentication, integrity
   protection, replay protection).  If these are desired, they must be
   provided by mechanisms that are outside the scope of the VPN
   mechanisms.

   In this document, the EVPN RT-5 is used for certain scenarios.  This
   route uses an Overlay Index that requires a recursive resolution to a
   different EVPN route (an EVPN RT-2).  Because of this, it is worth
   noting that any action that ends up filtering or modifying the EVPN
   RT-2 route used to convey the Overlay Indexes, will modify the
   resolution of the EVPN RT-5 and therefore the forwarding of packets
   to the remote subnet.

12.  IANA Considerations

   IANA has allocated a new transitive extended community Type of 0x06
   and Sub-Type of 0x03 for EVPN Router's MAC Extended Community.

   This document has been listed as an additional reference for the MAC/
   IP Advertisement route in the EVPN Route Type registry.

13.  References

13.1.  Normative References

   [I-D.ietf-bess-evpn-prefix-advertisement]
              Rabadan, J., Henderickx, W., Drake, J., Lin, W., and A.
              Sajassi, "IP Prefix Advertisement in EVPN", draft-ietf-
              bess-evpn-prefix-advertisement-11 (work in progress), May
              2018.

   [I-D.ietf-idr-tunnel-encaps]
              Patel, K., Velde, G., Sangli, S., and J. Scudder, "The BGP
              Tunnel Encapsulation Attribute", draft-ietf-idr-tunnel-
              encaps-22 (work in progress), January 2021.

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






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   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [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,
              <https://www.rfc-editor.org/info/rfc7348>.

   [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, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.

   [RFC7637]  Garg, P., Ed. and Y. Wang, Ed., "NVGRE: Network
              Virtualization Using Generic Routing Encapsulation",
              RFC 7637, DOI 10.17487/RFC7637, September 2015,
              <https://www.rfc-editor.org/info/rfc7637>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8365]  Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
              Uttaro, J., and W. Henderickx, "A Network Virtualization
              Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
              DOI 10.17487/RFC8365, March 2018,
              <https://www.rfc-editor.org/info/rfc8365>.

13.2.  Informative References

   [I-D.ietf-bess-evpn-irb-extended-mobility]
              Malhotra, N., Sajassi, A., Pattekar, A., Lingala, A.,
              Rabadan, J., and J. Drake, "Extended Mobility Procedures
              for EVPN-IRB", draft-ietf-bess-evpn-irb-extended-
              mobility-03 (work in progress), May 2020.

   [I-D.ietf-nvo3-vxlan-gpe]
              Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
              Extension for VXLAN (VXLAN-GPE)", draft-ietf-nvo3-vxlan-
              gpe-10 (work in progress), July 2020.



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   [RFC4365]  Rosen, E., "Applicability Statement for BGP/MPLS IP
              Virtual Private Networks (VPNs)", RFC 4365,
              DOI 10.17487/RFC4365, February 2006,
              <https://www.rfc-editor.org/info/rfc4365>.

   [RFC5798]  Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
              Version 3 for IPv4 and IPv6", RFC 5798,
              DOI 10.17487/RFC5798, March 2010,
              <https://www.rfc-editor.org/info/rfc5798>.

   [RFC7365]  Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
              Rekhter, "Framework for Data Center (DC) Network
              Virtualization", RFC 7365, DOI 10.17487/RFC7365, October
              2014, <https://www.rfc-editor.org/info/rfc7365>.

Authors' Addresses

   Ali Sajassi
   Cisco Systems

   Email: sajassi@cisco.com


   Samer Salam
   Cisco Systems

   Email: ssalam@cisco.com


   Samir Thoria
   Cisco Systems

   Email: sthoria@cisco.com


   John E Drake
   Juniper

   Email: jdrake@juniper.net


   Jorge Rabadan
   Nokia

   Email: jorge.rabadan@nokia.com






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