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Versions: (draft-rabadan-l2vpn-evpn-prefix-advertisement) 00 01 02 03 04 05 06 07 08

BESS Workgroup                                           J. Rabadan, Ed.
Internet Draft                                             W. Henderickx
Intended status: Standards Track                                   Nokia

                                                                J. Drake
                                                                  W. Lin
                                                                 Juniper

                                                              A. Sajassi
                                                                   Cisco


Expires: April 23, 2018                                 October 20, 2017



                    IP Prefix Advertisement in EVPN
              draft-ietf-bess-evpn-prefix-advertisement-08


Abstract

   EVPN provides a flexible control plane that allows intra-subnet
   connectivity in an MPLS and/or NVO-based network. In some networks,
   there is also a need for a dynamic and efficient inter-subnet
   connectivity across Tenant Systems and End Devices that can be
   physical or virtual and do not necessarily participate in dynamic
   routing protocols. This document defines a new EVPN route type for
   the advertisement of IP Prefixes and explains some use-case examples
   where this new route-type is used.

Status of this Memo

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

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

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

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



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

   This Internet-Draft will expire on April 23, 2018.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Introduction and Problem Statement  . . . . . . . . . . . . . .  4
     2.1 Inter-Subnet Connectivity Requirements in Data Centers . . .  4
     2.2 The Requirement for a New EVPN Route Type  . . . . . . . . .  7
   3. The BGP EVPN IP Prefix Route  . . . . . . . . . . . . . . . . .  8
     3.1 IP Prefix Route Encoding . . . . . . . . . . . . . . . . . .  9
     3.2 Overlay Indexes and Recursive Lookup Resolution  . . . . . . 10
   4. Overlay Index Use-Cases . . . . . . . . . . . . . . . . . . . . 13
     4.1 TS IP Address Overlay Index Use-Case . . . . . . . . . . . . 13
     4.2 Floating IP Overlay Index Use-Case . . . . . . . . . . . . . 15
     4.3 Bump-in-the-Wire Use-Case  . . . . . . . . . . . . . . . . . 17
     4.4 IP-VRF-to-IP-VRF Model . . . . . . . . . . . . . . . . . . . 20
       4.4.1 Interface-less IP-VRF-to-IP-VRF Model  . . . . . . . . . 21
       4.4.2 Interface-ful IP-VRF-to-IP-VRF with SBD IRB  . . . . . . 24
       4.4.3 Interface-ful IP-VRF-to-IP-VRF with Unnumbered SBD IRB . 27
   5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 30
   6. Conventions used in this document . . . . . . . . . . . . . . . 31
   7. Security Considerations . . . . . . . . . . . . . . . . . . . . 31
   8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 31
   9. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 31
     9.1 Normative References . . . . . . . . . . . . . . . . . . . . 31
     9.2 Informative References . . . . . . . . . . . . . . . . . . . 31
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 32
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 32
   12. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 32




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1. Terminology

   GW IP: Gateway IP Address.

   IPL: IP address length.

   ML: MAC address length.

   NVE: Network Virtualization Edge.

   TS: Tenant System.

   VA: Virtual Appliance.

   RT-2: EVPN route type 2, i.e. MAC/IP advertisement route.

   RT-5: EVPN route type 5, i.e. IP Prefix route.

   AC: Attachment Circuit.

   ARP: Address Resolution Protocol.

   ND: Neighbor Discovery Protocol.

   Ethernet NVO tunnel: it refers to Network Virtualization Overlay
      tunnels with Ethernet payload. Examples of this type of tunnels
      are VXLAN or nvGRE.

   IP NVO tunnel: it refers to Network Virtualization Overlay tunnels
      with IP payload (no MAC header in the payload).

   EVI: EVPN Instance spanning the NVE/PE devices that are participating
      on that EVPN.

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

   BD: Broadcast Domain. As per [RFC7432], an EVI consists of a single
      or multiple BDs. In case of VLAN-bundle and VLAN-based service
      models (see [RFC7432]), a BD is equivalent to an EVI. In case of
      VLAN-aware bundle service model, an EVI contains multiple BDs.
      Also, in this document, BD and subnet are equivalent terms.

   BT: Bridge Table. The instantiation of a BD in a MAC-VRF.

   IP-VRF: A VPN Routing and Forwarding table for IP routes on an
      NVE/PE. The IP routes could be populated by EVPN and IP-VPN
      address families.



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

   SBD: Supplementary Broadcast Domain. A BD that does not have any ACs,
      only IRB interfaces, and it is used to provide connectivity among
      all the IP-VRFs of the tenant. The SBD is only required in IP-VRF-
      to-IP-VRF use-cases (see section 4.4.).


2. Introduction and Problem Statement

   Inter-subnet connectivity is used for certain tenants within the Data
   Center. [EVPN-INTERSUBNET] defines some fairly common inter-subnet
   forwarding scenarios where TSes can exchange packets with TSes
   located in remote subnets. In order to achieve this,
   [EVPN-INTERSUBNET] describes how MAC/IPs encoded in TS RT-2 routes
   are not only used to populate MAC-VRF and overlay ARP tables, but
   also IP-VRF tables with the encoded TS host routes (/32 or /128). In
   some cases, EVPN may advertise IP Prefixes and therefore provide
   aggregation in the IP-VRF tables, as opposed to program individual
   host routes. This document complements the scenarios described in
   [EVPN-INTERSUBNET] and defines how EVPN may be used to advertise IP
   Prefixes. Interoperability between EVPN and L3VPN [RFC4364] IP Prefix
   routes is out of the scope of this document.

   Section 2.1 describes the inter-subnet connectivity requirements in
   Data Centers. Section 2.2 explains why a new EVPN route type is
   required for IP Prefix advertisements. Once the need for a new EVPN
   route type is justified, sections 3, 4 and 5 will describe this route
   type and how it is used in some specific use cases.

2.1 Inter-Subnet Connectivity Requirements in Data Centers

   [RFC7432] is used as the control plane for a Network Virtualization
   Overlay (NVO3) solution in Data Centers (DC), where Network
   Virtualization Edge (NVE) devices can be located in Hypervisors or
   TORs, as described in [EVPN-OVERLAY].

   If we use the term Tenant System (TS) to designate a physical or
   virtual system identified by MAC and maybe IP addresses, and
   connected to a BD by an Attachment Circuit, the following
   considerations apply:

   o The Tenant Systems may be Virtual Machines (VMs) that generate
     traffic from their own MAC and IP.

   o The Tenant Systems may be Virtual Appliance entities (VAs) that
     forward traffic to/from IP addresses of different End Devices



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     sitting behind them.

        o These VAs can be firewalls, load balancers, NAT devices, other
          appliances or virtual gateways with virtual routing instances.

        o These VAs do not necessarily participate in dynamic routing
          protocols and hence rely on the EVPN NVEs to advertise the
          routes on their behalf.

        o In all these cases, the VA will forward traffic to other TSes
          using its own source MAC but the source IP will be the one
          associated to the End Device sitting behind or a translated IP
          address (part of a public NAT pool) if the VA is performing
          NAT.

        o Note that the same IP address could exist behind two of these
          TS. One example of this would be certain appliance resiliency
          mechanisms, where a virtual IP or floating IP can be owned by
          one of the two VAs running the resiliency protocol (the master
          VA). Virtual Router Redundancy Protocol (VRRP), RFC5798, is
          one particular example of this. Another example is multi-homed
          subnets, i.e. the same subnet is connected to two VAs.

        o Although these VAs provide IP connectivity to VMs and subnets
          behind them, they do not always have their own IP interface
          connected to the EVPN NVE, e.g. layer-2 firewalls are examples
          of VAs not supporting IP interfaces.

   Figure 1 illustrates some of the examples described above.






















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                       NVE1
                    +-----------+
           TS1(VM)--|  (BD-10)  |-----+
             IP1/M1 +-----------+     |               DGW1
                                  +---------+    +-------------+
                                  |         |----|  (BD-10)    |
     SN1---+           NVE2       |         |    |    IRB1\    |
           |        +-----------+ |         |    |     (IP-VRF)|---+
     SN2---TS2(VA)--|  (BD-10)  |-|         |    +-------------+  _|_
           | IP2/M2 +-----------+ |  VXLAN/ |                    (   )
     IP4---+  <-+                 |  nvGRE  |         DGW2      ( WAN )
                |                 |         |    +-------------+ (___)
             vIP23 (floating)     |         |----|  (BD-10)    |   |
                |                 +---------+    |    IRB2\    |   |
     SN1---+  <-+      NVE3         |  |  |      |     (IP-VRF)|---+
           | IP3/M3 +-----------+   |  |  |      +-------------+
     SN3---TS3(VA)--|  (BD-10)  |---+  |  |
           |        +-----------+      |  |
     IP5---+                           |  |
                                       |  |
                    NVE4               |  |      NVE5            +--SN5
              +---------------------+  |  | +-----------+        |
     IP6------|  (BD-1)             |  |  +-|  (BD-10)  |--TS4(VA)--SN6
              |       \             |  |    +-----------+        |
              |    (IP-VRF)         |--+                ESI4     +--SN7
              |       /  \IRB3      |
          |---|  (BD-2)  (BD-10)    |
       SN4|   +---------------------+

                    Figure 1 DC inter-subnet use-cases

   Where:

   NVE1, NVE2, NVE3, NVE4, NVE5, DGW1 and DGW2 share the same BD for a
   particular tenant. BD-10 is comprised of the collection of BD
   instances defined in all the NVEs. All the hosts connected to BD-10
   belong to the same IP subnet. The hosts connected to BD-10 are listed
   below:

   o TS1 is a VM that generates/receives traffic from/to IP1, where IP1
     belongs to the BD-10 subnet.

   o TS2 and TS3 are Virtual Appliances (VA) that send/receive traffic
     from/to the subnets and hosts sitting behind them (SN1, SN2, SN3,
     IP4 and IP5). Their IP addresses (IP2 and IP3) belong to the BD-10
     subnet and they can also generate/receive traffic. When these VAs
     receive packets destined to their own MAC addresses (M2 and M3)
     they will route the packets to the proper subnet or host. These VAs



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     do not support routing protocols to advertise the subnets connected
     to them and can move to a different server and NVE when the Cloud
     Management System decides to do so. These VAs may also support
     redundancy mechanisms for some subnets, similar to VRRP, where a
     floating IP is owned by the master VA and only the master VA
     forwards traffic to a given subnet. E.g.: vIP23 in figure 1 is a
     floating IP that can be owned by TS2 or TS3 depending on who the
     master is. Only the master will forward traffic to SN1.

   o Integrated Routing and Bridging interfaces IRB1, IRB2 and IRB3 have
     their own IP addresses that belong to the BD-10 subnet too. These
     IRB interfaces connect the BD-10 subnet to Virtual Routing and
     Forwarding (IP-VRF) instances that can route the traffic to other
     subnets for the same tenant (within the DC or at the other end of
     the WAN).

   o TS4 is a layer-2 VA that provides connectivity to subnets SN5, SN6
     and SN7, but does not have an IP address itself in the BD-10. TS4
     is connected to a physical port on NVE5 assigned to Ethernet
     Segment Identifier 4.

   All the above DC use cases require inter-subnet forwarding and
   therefore the individual host routes and subnets:

   a) MUST be advertised from the NVEs (since VAs and VMs do not
      participate in dynamic routing protocols) and
   b) MAY be associated to an Overlay Index that can be a VA IP address,
      a floating IP address, a MAC address or an ESI. An Overlay Index
      is a next-hop that requires a recursive resolution and it is
      described in section 3.2.


2.2 The Requirement for a New EVPN Route Type

   [RFC7432] defines a MAC/IP route (also referred as RT-2) where a MAC
   address can be advertised together with an IP address length (IPL)
   and IP address (IP). While a variable IPL might have been used to
   indicate the presence of an IP prefix in a route type 2, there are
   several specific use cases in which using this route type to deliver
   IP Prefixes is not suitable.

   One example of such use cases is the "floating IP" example described
   in section 2.1. In this example we need to decouple the advertisement
   of the prefixes from the advertisement of MAC address of either M2 or
   M3", otherwise the solution gets highly inefficient and does not
   scale.

   E.g.: if we are advertising 1k prefixes from M2 (using RT-2) and the



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   floating IP owner changes from M2 to M3, we would need to withdraw 1k
   routes from M2 and re-advertise 1k routes from M3. However if we use
   a separate route type, we can advertise the 1k routes associated to
   the floating IP address (vIP23) and only one RT-2 for advertising the
   ownership of the floating IP, i.e. vIP23 and M2 in the route type 2.
   When the floating IP owner changes from M2 to M3, a single RT-2
   withdraw/update is required to indicate the change. The remote DGW
   will not change any of the 1k prefixes associated to vIP23, but will
   only update the ARP resolution entry for vIP23 (now pointing at M3).

   Other reasons to decouple the IP Prefix advertisement from the MAC/IP
   route are listed below:

   o Clean identification, operation and troubleshooting of IP Prefixes,
     independent of and not subject to the interpretation of the IPL and
     the IP value. E.g.: a default IP route 0.0.0.0/0 must always be
     easily and clearly distinguished from the absence of IP
     information.

   o In MAC/IP routes, the MAC information is part of the NLRI, so if IP
     Prefixes were to be advertised using MAC/IP routes, the MAC
     information would always be present and part of the route key.

   The following sections describe how EVPN is extended with a new route
   type for the advertisement of IP prefixes and how this route is used
   to address the current and future inter-subnet connectivity
   requirements existing in the Data Center.


3. The BGP EVPN IP Prefix Route

   The current BGP EVPN NLRI as defined in [RFC7432] is shown below:

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

   Where the route type field can contain one of the following specific
   values (refer to the IANA "EVPN Route Types registry):

   + 1 - Ethernet Auto-Discovery (A-D) route

   + 2 - MAC/IP advertisement route




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   + 3 - Inclusive Multicast Route

   + 4 - Ethernet Segment Route

   This document defines an additional route type that IANA has added to
   the registry, and will be used for the advertisement of IP Prefixes:

   + 5 - IP Prefix Route

   The support for this new route type is OPTIONAL.

   Since this new route type is OPTIONAL, an implementation not
   supporting it MUST ignore the route, based on the unknown route type
   value, as specified by Section 5.4 in [RFC7606].

   The detailed encoding of this route and associated procedures are
   described in the following sections.


3.1 IP Prefix Route Encoding

   An IP Prefix advertisement route NLRI consists of the following
   fields:

    +---------------------------------------+
    |      RD   (8 octets)                  |
    +---------------------------------------+
    |Ethernet Segment Identifier (10 octets)|
    +---------------------------------------+
    |  Ethernet Tag ID (4 octets)           |
    +---------------------------------------+
    |  IP Prefix Length (1 octet)           |
    +---------------------------------------+
    |  IP Prefix (4 or 16 octets)           |
    +---------------------------------------+
    |  GW IP Address (4 or 16 octets)       |
    +---------------------------------------+
    |  MPLS Label (3 octets)                |
    +---------------------------------------+

   Where:

   o RD, Ethernet Tag ID and MPLS Label fields will be used as defined
     in [RFC7432] and [EVPN-OVERLAY].

   o The Ethernet Segment Identifier will be a non-zero 10-byte
     identifier if the ESI is used as an Overlay Index (see the
     definition of Overlay Index in section 3.2). It will be zero



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     otherwise.

   o The IP Prefix Length can be set to a value between 0 and 32 (bits)
     for ipv4 and between 0 and 128 for ipv6, and specifies the number
     of bits in the Prefix.

   o The IP Prefix will be a 32 or 128-bit field (ipv4 or ipv6). The
     size of this field does not depend on the value of the IP Prefix
     Length field.

   o The GW IP (Gateway IP Address) will be a 32 or 128-bit field (ipv4
     or ipv6), and will encode an IP address as an overlay index for the
     IP Prefixes. The GW IP field SHOULD be zero if it is not used as an
     Overlay Index. Refer to section 3.2 for the definition and use of
     the Overlay Index.

   o The MPLS Label field is encoded as 3 octets, where the high-order
     20 bits contain the label value. When sending, the label value
     SHOULD be zero if recursive resolution based on overlay index is
     used. If the received MPLS Label value is zero, the route MUST
     contain an Overlay Index and the ingress NVE/PE MUST do recursive
     resolution to find the egress NVE/PE. If the received Label value
     is non-zero, the route will not be used for recursive resolution
     unless a local policy says so.

   o The total route length will indicate the type of prefix (ipv4 or
     ipv6) and the type of GW IP address (ipv4 or ipv6). Note that the
     IP Prefix + the GW IP should have a length of either 64 or 256
     bits, but never 160 bits (ipv4 and ipv6 mixed values are not
     allowed).

   The RD, Eth-Tag ID, IP Prefix Length and IP Prefix will be part of
   the route key used by BGP to compare routes. The rest of the fields
   will not be part of the route key.

   An IP Prefix Route MAY be sent along with a Router's MAC Extended
   Community (defined in [EVPN-INTERSUBNET]) to carry the MAC address
   that is used as the overlay index. Note that the MAC address may be
   that of an TS.


3.2 Overlay Indexes and Recursive Lookup Resolution

   RT-5 routes support recursive lookup resolution through the use of
   Overlay Indexes as follows:

   o An Overlay Index can be an ESI, IP address in the address space of
     the tenant or MAC address and it is used by an NVE as the next-hop



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     for a given IP Prefix. An Overlay Index always needs a recursive
     route resolution on the NVE/PE that installs the RT-5 into one of
     its IP-VRFs, so that the NVE knows to which egress NVE/PE it needs
     to forward the packets. It is important to note that recursive
     resolution of the Overlay Index applies upon installation into an
     IP-VRF, and not upon BGP propagation (for instance, on an ASBR).
     Also, as a result of the recursive resolution, the egress NVE/PE is
     not necessarily the same NVE that originated the RT-5.

   o The Overlay Index is indicated along with the RT-5 in the ESI
     field, GW IP field or Router's MAC Extended Community, depending on
     whether the IP Prefix next-hop is an ESI, IP address or MAC address
     in the tenant space. The Overlay Index for a given IP Prefix is set
     by local policy at the NVE that originates an RT-5 for that IP
     Prefix (typically managed by the Cloud Management System).

   o In order to enable the recursive lookup resolution at the ingress
     NVE, an NVE that is a possible egress NVE for a given Overlay Index
     must originate a route advertising itself as the BGP next hop on
     the path to the system denoted by the Overlay Index. For instance:

     . If an NVE receives an RT-5 that specifies an Overlay Index, the
       NVE cannot use the RT-5 in its IP-VRF unless (or until) it can
       recursively resolve the Overlay Index.
     . If the RT-5 specifies an ESI as the Overlay Index, recursive
       resolution can only be done if the NVE has received and installed
       an RT-1 (Auto-Discovery per-EVI) route specifying that ESI.
     . If the RT-5 specifies a GW IP address as the Overlay Index,
       recursive resolution can only be done if the NVE has received and
       installed an RT-2 (MAC/IP route) specifying that IP address in
       the IP address field of its NLRI.
     . If the RT-5 specifies a MAC address as the Overlay Index,
       recursive resolution can only be done if the NVE has received and
       installed an RT-2 (MAC/IP route) specifying that MAC address in
       the MAC address field of its NLRI.

     Note that the RT-1 or RT-2 routes needed for the recursive
     resolution may arrive before or after the given RT-5 route.

   o Irrespective of the recursive resolution, if there is no IGP or BGP
     route to the BGP next-hop of an RT-5, BGP SHOULD fail to install
     the RT-5 even if the Overlay Index can be resolved.

   o The ESI and GW IP fields MAY both be zero, however they MUST NOT
     both be non-zero at the same time. A route containing a non-zero GW
     IP and a non-zero ESI (at the same time) will be treated as-
     withdraw.




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   The indirection provided by the Overlay Index and its recursive
   lookup resolution is required to achieve fast convergence in case of
   a failure of the object represented by the Overlay Index (see the
   example described in section 2.2).

   Table 1 shows the different RT-5 field combinations allowed by this
   specification and what Overlay Index must be used by the receiving
   NVE/PE in each case. When the Overlay Index is "None" in Table 1, the
   receiving NVE/PE will not perform any recursive resolution, and the
   actual next-hop is given by the RT-5's BGP next-hop.

   +----------+----------+----------+------------+----------------+
   | ESI      | GW-IP    | MAC*     | Label      | Overlay Index  |
   |--------------------------------------------------------------|
   | Non-Zero | Zero     | Zero     | Don't Care | ESI            |
   | Non-Zero | Zero     | Non-Zero | Don't Care | ESI            |
   | Zero     | Non-Zero | Zero     | Don't Care | GW-IP          |
   | Zero     | Zero     | Non-Zero | Zero       | MAC            |
   | Zero     | Zero     | Non-Zero | Non-Zero   | MAC or None**  |
   | Zero     | Zero     | Zero     | Non-Zero   | None***        |
   +----------+----------+----------+------------+----------------+

          Table 1 - RT-5 fields and Indicated Overlay Index

   Table NOTES:

   *   MAC with Zero value means no Router's MAC extended community is
       present along with the RT-5. Non-Zero indicates that the extended
       community is present and carries a valid MAC address. Examples of
       invalid MAC addresses are broadcast or multicast MAC addresses.
       The presence of the Router's MAC extended community alone is not
       enough to indicate the use of the MAC address as the overlay
       index, since the extended community can be used for other
       purposes.

   **  In this case, the Overlay Index may be the RT-5's MAC address or
       None, depending on the local policy of the receiving NVE/PE.

   *** The Overlay Index is None. This is a special case used for IP-
       VRF-to-IP-VRF where the NVE/PEs are connected by IP NVO tunnels
       as opposed to Ethernet NVO tunnels.

   Table 2 shows the different inter-subnet use-cases described in this
   document and the corresponding coding of the Overlay Index in the
   route type 5 (RT-5).






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   +---------+---------------------+----------------------------+
   | Section | Use-case            | Overlay Index in the RT-5  |
   +-------------------------------+----------------------------+
   |   4.1   | TS IP address       | GW IP                      |
   |   4.2   | Floating IP address | GW IP                      |
   |   4.3   | "Bump in the wire"  | ESI or MAC                 |
   |   4.4   | IP-VRF-to-IP-VRF    | GW IP, MAC or None         |
   +---------+---------------------+----------------------------+

      Table 2 - Use-cases and Overlay Indexes for Recursive Resolution

   The above use-cases are representative of the different Overlay
   Indexes supported by RT-5 (GW IP, ESI, MAC or None). Any other use-
   case using a given Overlay Index, SHOULD follow the procedures
   described in this document for the same Overlay Index.



4. Overlay Index Use-Cases

   This section describes some use-cases for the Overlay Index types
   used with the IP Prefix route.

4.1 TS IP Address Overlay Index Use-Case

   The following figure illustrates an example of inter-subnet
   forwarding for subnets sitting behind Virtual Appliances (on TS2 and
   TS3).

   IP4---+           NVE2                            DGW1
         |        +-----------+ +---------+    +-------------+
   SN2---TS2(VA)--|  (BD-10)  |-|         |----|  (BD-10)    |
         | IP2/M2 +-----------+ |         |    |    IRB1\    |
    -+---+                      |         |    |     (IP-VRF)|---+
     |                          |         |    +-------------+  _|_
    SN1                         |  VXLAN/ |                    (   )
     |                          |  nvGRE  |         DGW2      ( WAN )
    -+---+           NVE3       |         |    +-------------+ (___)
         | IP3/M3 +-----------+ |         |----|  (BD-10)    |   |
   SN3---TS3(VA)--|  (BD-10)  |-|         |    |    IRB2\    |   |
         |        +-----------+ +---------+    |     (IP-VRF)|---+
   IP5---+                                     +-------------+

                  Figure 2 TS IP address use-case

   An example of inter-subnet forwarding between subnet SN1/24 and a
   subnet sitting in the WAN is described below. NVE2, NVE3, DGW1 and
   DGW2 are running BGP EVPN. TS2 and TS3 do not participate in dynamic



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   routing protocols, and they only have a static route to forward the
   traffic to the WAN. We assume SN1/24 is dual-homed to NVE2 and NVE3.

   In this case, a GW IP is used as an Overlay Index. Although a
   different Overlay Index type could have been used, this use-case
   assumes that the operator knows the VA's IP addresses beforehand,
   whereas the VA's MAC address is unknown and the VA's ESI is zero.
   Because of this, the GW IP is the suitable Overlay Index to be used
   with the RT-5s. The NVEs know the GW IP to be used for a given Prefix
   by policy.

   (1) NVE2 advertises the following BGP routes on behalf of TS2:

        o Route type 2 (MAC/IP route) containing: ML=48, M=M2, IPL=32,
          IP=IP2 and [RFC5512] BGP Encapsulation Extended Community with
          the corresponding Tunnel-type. The MAC and IP addresses may be
          learned via ARP-snooping (ND-snooping if IPv6).

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=0, GW IP address=IP2. The prefix and GW IP are learned by
          policy.

   (2) Similarly, NVE3 advertises the following BGP routes on behalf of
       TS3:

        o Route type 2 (MAC/IP route) containing: ML=48, M=M3, IPL=32,
          IP=IP3 (and BGP Encapsulation Extended Community).

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=0, GW IP address=IP3.

   (3) DGW1 and DGW2 import both received routes based on the
       route-targets:

        o Based on the BD-10 route-target in DGW1 and DGW2, the MAC/IP
          route is imported and M2 is added to the BD-10 along with its
          corresponding tunnel information. For instance, if VXLAN is
          used, the VTEP will be derived from the MAC/IP route BGP next-
          hop and VNI from the MPLS Label1 field. IP2 - M2 is added to
          the ARP table. Similarly, M3 is added to BD-10 and IP3 - M3 to
          the ARP table.

        o Based on the BD-10 route-target in DGW1 and DGW2, the IP
          Prefix route is also imported and SN1/24 is added to the IP-
          VRF with Overlay Index IP2 pointing at the local BD-10. In
          this example, we assume the RT-5 from NVE2 is preferred over
          the RT-5 from NVE3. If both routes were equally preferable and
          ECMP enabled, SN1/24 would also be added to the routing table



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          with Overlay Index IP3.

   (4) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table and Overlay Index=IP2 is found. Since IP2 is an
          Overlay Index a recursive route resolution is required for
          IP2.

        o IP2 is resolved to M2 in the ARP table, and M2 is resolved to
          the tunnel information given by the BD FIB (e.g. remote VTEP
          and VNI for the VXLAN case).

        o The IP packet destined to IPx is encapsulated with:

             . Source inner MAC = IRB1 MAC.

             . Destination inner MAC = M2.

             . Tunnel information provided by the BD (VNI, VTEP IPs and
               MACs for the VXLAN case).

   (5) When the packet arrives at NVE2:

        o Based on the tunnel information (VNI for the VXLAN case), the
          BD-10 context is identified for a MAC lookup.

        o Encapsulation is stripped-off and based on a MAC lookup
          (assuming MAC forwarding on the egress NVE), the packet is
          forwarded to TS2, where it will be properly routed.

   (6) Should TS2 move from NVE2 to NVE3, MAC Mobility procedures will
       be applied to the MAC route IP2/M2, as defined in [RFC7432].
       Route type 5 prefixes are not subject to MAC mobility procedures,
       hence no changes in the DGW IP-VRF routing table will occur for
       TS2 mobility, i.e. all the prefixes will still be pointing at IP2
       as Overlay Index. There is an indirection for e.g. SN1/24, which
       still points at Overlay Index IP2 in the routing table, but IP2
       will be simply resolved to a different tunnel, based on the
       outcome of the MAC mobility procedures for the MAC/IP route
       IP2/M2.

   Note that in the opposite direction, TS2 will send traffic based on
   its static-route next-hop information (IRB1 and/or IRB2), and regular
   EVPN procedures will be applied.

4.2 Floating IP Overlay Index Use-Case



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   Sometimes Tenant Systems (TS) work in active/standby mode where an
   upstream floating IP - owned by the active TS - is used as the
   Overlay Index to get to some subnets behind. This redundancy mode,
   already introduced in section 2.1 and 2.2, is illustrated in Figure
   3.

                    NVE2                           DGW1
                 +-----------+ +---------+    +-------------+
    +---TS2(VA)--|  (BD-10)  |-|         |----|  (BD-10)    |
    |     IP2/M2 +-----------+ |         |    |    IRB1\    |
    |      <-+                 |         |    |     (IP-VRF)|---+
    |        |                 |         |    +-------------+  _|_
   SN1    vIP23 (floating)     |  VXLAN/ |                    (   )
    |        |                 |  nvGRE  |         DGW2      ( WAN )
    |      <-+      NVE3       |         |    +-------------+ (___)
    |     IP3/M3 +-----------+ |         |----|  (BD-10)    |   |
    +---TS3(VA)--|  (BD-10)  |-|         |    |    IRB2\    |   |
                 +-----------+ +---------+    |     (IP-VRF)|---+
                                              +-------------+

            Figure 3 Floating IP Overlay Index for redundant TS

   In this use-case, a GW IP is used as an Overlay Index for the same
   reasons as in 4.1. However, this GW IP is a floating IP that belongs
   to the active TS. Assuming TS2 is the active TS and owns IP23:

   (1) NVE2 advertises the following BGP routes for TS2:

        o Route type 2 (MAC/IP route) containing: ML=48, M=M2, IPL=32,
          IP=IP23 (and BGP Encapsulation Extended Community). The MAC
          and IP addresses may be learned via ARP-snooping.

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=0, GW IP address=IP23. The prefix and GW IP are learned by
          policy.

   (2) NVE3 advertises the following BGP route for TS3 (it does not
       advertise an RT-2 for IP23/M3):

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=0, GW IP address=IP23. The prefix and GW IP are learned by
          policy.

   (3) DGW1 and DGW2 import both received routes based on the route-
       target:

        o M2 is added to the BD-10 FIB along with its corresponding
          tunnel information. For the VXLAN use case, the VTEP will be



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          derived from the MAC/IP route BGP next-hop and VNI from the
          VNI/VSID field. IP23 - M2 is added to the ARP table.

        o SN1/24 is added to the IP-VRF in DGW1 and DGW2 with Overlay
          index IP23 pointing at M2 in the local BD-10.

   (4) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table and Overlay Index=IP23 is found. Since IP23 is
          an Overlay Index, a recursive route resolution for IP23 is
          required.

        o IP23 is resolved to M2 in the ARP table, and M2 is resolved to
          the tunnel information given by the BD (remote VTEP and VNI
          for the VXLAN case).

        o The IP packet destined to IPx is encapsulated with:

             . Source inner MAC = IRB1 MAC.

             . Destination inner MAC = M2.

             . Tunnel information provided by the BD FIB (VNI, VTEP IPs
               and MACs for the VXLAN case).

   (5) When the packet arrives at NVE2:

        o Based on the tunnel information (VNI for the VXLAN case), the
          BD-10 context is identified for a MAC lookup.

        o Encapsulation is stripped-off and based on a MAC lookup
          (assuming MAC forwarding on the egress NVE), the packet is
          forwarded to TS2, where it will be properly routed.

   (6) When the redundancy protocol running between TS2 and TS3 appoints
       TS3 as the new active TS for SN1, TS3 will now own the floating
       IP23 and will signal this new ownership (GARP message or
       similar). Upon receiving the new owner's notification, NVE3 will
       issue a route type 2 for M3-IP23 and NVE2 will withdraw the RT-2
       for M2-IP23. DGW1 and DGW2 will update their ARP tables with the
       new MAC resolving the floating IP. No changes are made in the IP-
       VRF routing table.


4.3 Bump-in-the-Wire Use-Case




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   Figure 5 illustrates an example of inter-subnet forwarding for an IP
   Prefix route that carries a subnet SN1. In this use-case, TS2 and TS3
   are layer-2 VA devices without any IP address that can be included as
   an Overlay Index in the GW IP field of the IP Prefix route. Their MAC
   addresses are M2 and M3 respectively and are connected to BD-10. Note
   that IRB1 and IRB2 (in DGW1 and DGW2 respectively) have IP addresses
   in a subnet different than SN1.


                      NVE2                           DGW1
               M2 +-----------+ +---------+    +-------------+
     +---TS2(VA)--|  (BD-10)  |-|         |----|  (BD-10)    |
     |      ESI23 +-----------+ |         |    |    IRB1\    |
     |        +                 |         |    |     (IP-VRF)|---+
     |        |                 |         |    +-------------+  _|_
    SN1       |                 |  VXLAN/ |                    (   )
     |        |                 |  nvGRE  |         DGW2      ( WAN )
     |        +      NVE3       |         |    +-------------+ (___)
     |      ESI23 +-----------+ |         |----|  (BD-10)    |   |
     +---TS3(VA)--|  (BD-10)  |-|         |    |    IRB2\    |   |
               M3 +-----------+ +---------+    |     (IP-VRF)|---+
                                               +-------------+

                    Figure 5 Bump-in-the-wire use-case

   Since neither TS2 nor TS3 can participate in any dynamic routing
   protocol and have no IP address assigned, there are two potential
   Overlay Index types that can be used when advertising SN1:

   a) an ESI, i.e. ESI23, that can be provisioned on the attachment
      ports of NVE2 and NVE3, as shown in Figure 5.
   b) or the VA's MAC address, that can be added to NVE2 and NVE3 by
      policy.

   The advantage of using an ESI as Overlay Index as opposed to the VA's
   MAC address, is that the forwarding to the egress NVE can be done
   purely based on the state of the AC in the ES (notified by the AD
   per-EVI route) and all the EVPN multi-homing redundancy mechanisms
   can be re-used. For instance, the [RFC7432] mass-withdrawal mechanism
   for fast failure detection and propagation can be used. This section
   assumes that an ESI Overlay Index is used in this use-case but it
   does not prevent the use of the VA's MAC address as an Overlay Index.
   If a MAC is used as Overlay Index, the control plane must follow the
   procedures described in section 4.4.3.

   The model supports VA redundancy in a similar way as the one
   described in section 4.2 for the floating IP Overlay Index use-case,
   except that it uses the EVPN Ethernet A-D per-EVI route instead of



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   the MAC advertisement route to advertise the location of the Overlay
   Index. The procedure is explained below:

   (1) Assuming TS2 is the active TS in ESI23, NVE2 advertises the
   following BGP routes:

        o Route type 1 (Ethernet A-D route for BD-10) containing:
          ESI=ESI23 and the corresponding tunnel information (VNI/VSID
          field), as well as the BGP Encapsulation Extended Community as
          per [EVPN-OVERLAY].

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=ESI23, GW IP address=0. The Router's MAC Extended
          Community defined in [EVPN-INTERSUBNET] is added and carries
          the MAC address (M2) associated to the TS behind which SN1
          sits. M2 may be learned by policy.

   (2) NVE3 advertises the following BGP route for TS3 (no AD per-EVI
          route is advertised):

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=23, GW IP address=0. The Router's MAC Extended Community
          is added and carries the MAC address (M3) associated to the TS
          behind which SN1 sits. M3 may be learned by policy.

   (3) DGW1 and DGW2 import the received routes based on the route-
       target:

        o The tunnel information to get to ESI23 is installed in DGW1
          and DGW2. For the VXLAN use case, the VTEP will be derived
          from the Ethernet A-D route BGP next-hop and VNI from the
          VNI/VSID field (see [EVPN-OVERLAY]).

        o The RT-5 coming from the NVE that advertised the RT-1 is
          selected and SN1/24 is added to the IP-VRF in DGW1 and DGW2
          with Overlay Index ESI23 and MAC = M2.

   (4) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table and Overlay Index=ESI23 is found. Since ESI23 is
          an Overlay Index, a recursive route resolution is required to
          find the egress NVE where ESI23 resides.

        o The IP packet destined to IPx is encapsulated with:

             . Source inner MAC = IRB1 MAC.



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             . Destination inner MAC = M2 (this MAC will be obtained
               from the Router's MAC Extended Community received along
               with the RT-5 for SN1). Note that the Router's MAC
               Extended Community is used in this case to carry the TS'
               MAC address, as opposed to the NVE/PE's MAC address.

             . Tunnel information for the NVO tunnel is provided by the
               Ethernet A-D route per-EVI for ESI23 (VNI and VTEP IP for
               the VXLAN case).

   (5) When the packet arrives at NVE2:

        o Based on the tunnel demultiplexer information (VNI for the
          VXLAN case), the BD-10 context is identified for a MAC lookup
          (assuming MAC disposition model) or the VNI MAY directly
          identify the egress interface (for a label or VNI disposition
          model).

        o Encapsulation is stripped-off and based on a MAC lookup
          (assuming MAC forwarding on the egress NVE) or a VNI lookup
          (in case of VNI forwarding), the packet is forwarded to TS2,
          where it will be forwarded to SN1.

   (6) If the redundancy protocol running between TS2 and TS3 follows an
       active/standby model and there is a failure, appointing TS3 as
       the new active TS for SN1, TS3 will now own the connectivity to
       SN1 and will signal this new ownership. Upon receiving the new
       owner's notification, NVE3's AC will become active and issue a
       route type 1 for ESI23, whereas NVE2 will withdraw its Ethernet
       A-D route for ESI23. DGW1 and DGW2 will update their tunnel
       information to resolve ESI23. The destination inner MAC will be
       changed to M3.

4.4 IP-VRF-to-IP-VRF Model

   This use-case is similar to the scenario described in "IRB forwarding
   on NVEs for Tenant Systems" in [EVPN-INTERSUBNET], however the new
   requirement here is the advertisement of IP Prefixes as opposed to
   only host routes.

   In the examples described in sections 4.1, 4.2 and 4.3, the BD
   instance can connect IRB interfaces and any other Tenant Systems
   connected to it. EVPN provides connectivity for:

   1. Traffic destined to the IRB or TS IP interfaces as well as

   2. Traffic destined to IP subnets sitting behind the TS, e.g. SN1 or
      SN2.



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   In order to provide connectivity for (1), MAC/IP routes (RT-2) are
   needed so that IRB or TS MACs and IPs can be distributed.
   Connectivity type (2) is accomplished by the exchange of IP Prefix
   routes (RT-5) for IPs and subnets sitting behind certain Overlay
   Indexes, e.g. GW IP or ESI or TS MAC.

   In some cases, IP Prefix routes may be advertised for subnets and IPs
   sitting behind an IRB. We refer to this use-case as the "IP-VRF-to-
   IP-VRF" model.

   [EVPN-INTERSUBNET] defines an asymmetric IRB model and a symmetric
   IRB model, based on the required lookups at the ingress and egress
   NVE: the asymmetric model requires an ip-lookup and a mac-lookup at
   the ingress NVE, whereas only a mac-lookup is needed at the egress
   NVE; the symmetric model requires ip and mac lookups at both, ingress
   and egress NVE. From that perspective, the IP-VRF-to-IP-VRF use-case
   described in this section is a symmetric IRB model.

   Note that, in an IP-VRF-to-IP-VRF scenario, out of the many subnets
   that a tenant may have, it may be the case that only a few are
   attached to a given NVE/PE's IP-VRF. In order to provide inter-subnet
   connectivity among the set of NVE/PEs where the tenant is connected,
   a new "Supplementary Broadcast Domain" (SBD) is created on all of
   them if recursive resolution is needed. This SBD is instantiated as a
   regular BD (with no ACs) in each NVE/PE and has a IRB interfaces that
   connect the SBD to the IP-VRF. The IRB interface's IP or MAC address
   is used as the overlay index for recursive resolution.

   Depending on the existence and characteristics of the SBD and IRB
   interfaces for the IP-VRFs, there are three different IP-VRF-to-IP-
   VRF scenarios identified and described in this document:


   1) Interface-less model: no SBD and no overlay indexes required.
   2) Interface-ful with SBD IRB model: it requires SBD, as well as GW
      IP addresses as overlay indexes.
   3) Interface-ful with unnumbered SBD IRB model: it requires SBD, as
      well as MAC addresses as overlay indexes.

   Inter-subnet IP multicast is outside the scope of this document.


4.4.1 Interface-less IP-VRF-to-IP-VRF Model

   Figure 6 will be used for the description of this model.






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                      NVE1(M1)
             +------------+
     IP1+----|  (BD-1)    |                DGW1(M3)
             |      \     |    +---------+ +--------+
             |    (IP-VRF)|----|         |-|(IP-VRF)|----+
             |      /     |    |         | +--------+    |
         +---|  (BD-2)    |    |         |              _+_
         |   +------------+    |         |             (   )
      SN1|                     |  VXLAN/ |            ( WAN )--H1
         |            NVE2(M2) |  nvGRE/ |             (___)
         |   +------------+    |  MPLS   |               +
         +---|  (BD-2)    |    |         | DGW2(M4)      |
             |       \    |    |         | +--------+    |
             |    (IP-VRF)|----|         |-|(IP-VRF)|----+
             |       /    |    +---------+ +--------+
     SN2+----|  (BD-3)    |
             +------------+




         Figure 6 Interface-less IP-VRF-to-IP-VRF model

   In this case:

   a) The NVEs and DGWs must provide connectivity between hosts in SN1,
      SN2, IP1 and hosts sitting at the other end of the WAN, for
      example, H1. We assume the DGWs import/export IP and/or VPN-IP
      routes from/to the WAN.

   b) The IP-VRF instances in the NVE/DGWs are directly connected
      through NVO tunnels, and no IRBs and/or BD instances are
      instantiated to connect the IP-VRFs.

   c) The solution must provide layer-3 connectivity among the IP-VRFs
      for Ethernet NVO tunnels, for instance, VXLAN or nvGRE.

   d) The solution may provide layer-3 connectivity among the IP-VRFs
      for IP NVO tunnels, for example, VXLAN GPE (with IP payload).

   In order to meet the above requirements, the EVPN route type 5 will
   be used to advertise the IP Prefixes, along with the Router's MAC
   Extended Community as defined in [EVPN-INTERSUBNET] if the
   advertising NVE/DGW uses Ethernet NVO tunnels. Each NVE/DGW will
   advertise an RT-5 for each of its prefixes with the following fields:

        o RD as per [RFC7432].




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        o Eth-Tag ID=0.

        o IP address length and IP address, as explained in the previous
          sections.

        o GW IP address=0.

        o ESI=0

        o MPLS label or VNI corresponding to the IP-VRF.

   Each RT-5 will be sent with a route-target identifying the tenant
   (IP-VRF) and two BGP extended communities:

        o The first one is the BGP Encapsulation Extended Community, as
          per [RFC5512], identifying the tunnel type.

        o The second one is the Router's MAC Extended Community as per
          [EVPN-INTERSUBNET] containing the MAC address associated to
          the NVE advertising the route. This MAC address identifies the
          NVE/DGW and MAY be re-used for all the IP-VRFs in the NVE. The
          Router's MAC Extended Community MUST be sent if the route is
          associated to an Ethernet NVO tunnel, for instance, VXLAN. If
          the route is associated to an IP NVO tunnel, for instance
          VXLAN GPE with IP payload, the Router's MAC Extended Community
          SHOULD NOT be sent.

   The following example illustrates the procedure to advertise and
   forward packets to SN1/24 (ipv4 prefix advertised from NVE1):

   (1) NVE1 advertises the following BGP route:

        o Route type 5 (IP Prefix route) containing:

          . IPL=24, IP=SN1, Label=10.

          . GW IP= SHOULD be set to 0.

          . [RFC5512] BGP Encapsulation Extended Community.

          . Router's MAC Extended Community that contains M1.

          . Route-target identifying the tenant (IP-VRF).

   (2) DGW1 imports the received routes from NVE1:

        o DGW1 installs SN1/24 in the IP-VRF identified by the RT-5
          route-target.



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        o Since GW IP=ESI=0, the Label is a non-zero value and the local
          policy indicates this interface-less model, DGW1 will use the
          Label and next-hop of the RT-5, as well as the MAC address
          conveyed in the Router's MAC Extended Community (as inner
          destination MAC address) to set up the forwarding state and
          later encapsulate the routed IP packets.

   (3) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table. The lookup yields SN1/24.

        o Since the RT-5 for SN1/24 had a GW IP=ESI=0, a non-zero Label
          and next-hop and the model is interface-less, DGW1 will not
          need a recursive lookup to resolve the route.

        o The IP packet destined to IPx is encapsulated with: Source
          inner MAC = DGW1 MAC, Destination inner MAC = M1, Source outer
          IP (tunnel source IP) = DGW1 IP, Destination outer IP (tunnel
          destination IP) = NVE1 IP. The Source and Destination inner
          MAC addresses are not needed if IP NVO tunnels are used.

   (4) When the packet arrives at NVE1:

        o NVE1 will identify the IP-VRF for an IP-lookup based on the
          Label (the Destination inner MAC is not needed to identify the
          IP-VRF).

        o An IP lookup is performed in the routing context, where SN1
          turns out to be a local subnet associated to BD-2. A
          subsequent lookup in the ARP table and the BD FIB will provide
          the forwarding information for the packet in BD-2.

   The model described above is called Interface-less model since the
   IP-VRFs are connected directly through tunnels and they don't require
   those tunnels to be terminated in SBDs instead, like in sections
   4.4.2 or 4.4.3. An EVPN IP-VRF-to-IP-VRF implementation is REQUIRED
   to support the ingress and egress procedures described in this
   section.


4.4.2 Interface-ful IP-VRF-to-IP-VRF with SBD IRB

   Figure 7 will be used for the description of this model.






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                    NVE1
           +------------+                       DGW1
   IP10+---+(BD-1)      | +---------------+ +------------+
           |  \         | |               | |            |
           |(IP-VRF)-(SBD)|               |(SBD)-(IP-VRF)|-----+
           |  /    IRB(IP1/M1)           IRB(IP3/M3)     |     |
       +---+(BD-2)      | |               | +------------+    _+_
       |   +------------+ |               |                  (   )
    SN1|                  |     VXLAN/    |                 ( WAN )--H1
       |            NVE2  |     nvGRE/    |                  (___)
       |   +------------+ |     MPLS      |     DGW2           +
       +---+(BD-2)      | |               | +------------+     |
           |  \         | |               | |            |     |
           |(IP-VRF)-(SBD)|               |(SBD)-(IP-VRF)|-----+
           |  /    IRB(IP2/M2)           IRB(IP4/M4)     |
   SN2+----+(BD-3)      | +---------------+ +------------+
           +------------+


         Figure 7 Interface-ful with SBD IRB model

   In this model:

   a) As in section 4.4.1, the NVEs and DGWs must provide connectivity
      between hosts in SN1, SN2, IP1 and hosts sitting at the other end
      of the WAN.

   b) However, the NVE/DGWs are now connected through Ethernet NVO
      tunnels terminated in the SBD instance. The IP-VRFs use IRB
      interfaces for their connectivity to the SBD.

   c) Each SBD IRB has an IP and a MAC address, where the IP address
      must be reachable from other NVEs or DGWs.

   d) The SBD is attached to all the NVE/DGWs in the tenant domain BDs.

   e) The solution must provide layer-3 connectivity for Ethernet NVO
      tunnels, for instance, VXLAN or nvGRE.

   EVPN type 5 routes will be used to advertise the IP Prefixes, whereas
   EVPN RT-2 routes will advertise the MAC/IP addresses of each SBD IRB
   interface. Each NVE/DGW will advertise an RT-5 for each of its
   prefixes with the following fields:

        o RD as per [RFC7432].

        o Eth-Tag ID=0.




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        o IP address length and IP address, as explained in the previous
          sections.

        o GW IP address=IRB-IP (this is the Overlay Index that will be
          used for the recursive route resolution).

        o ESI=0

        o Label value SHOULD be zero since the RT-5 route requires a
          recursive lookup resolution to an RT-2 route. It is ignored on
          reception, and, when forwarding packets, the MPLS label or VNI
          from the RT-2's MPLS Label1 field is used.


   Each RT-5 will be sent with a route-target identifying the tenant
   (IP-VRF). The Router's MAC Extended Community SHOULD NOT be sent in
   this case.

   The following example illustrates the procedure to advertise and
   forward packets to SN1/24 (ipv4 prefix advertised from NVE1):

   (1) NVE1 advertises the following BGP routes:

        o Route type 5 (IP Prefix route) containing:

          . IPL=24, IP=SN1, Label= SHOULD be set to 0.

          . GW IP=IP1 (sBD IRB's IP)

          . Route-target identifying the tenant (IP-VRF).

        o Route type 2 (MAC/IP route for the SBD IRB) containing:

          . ML=48, M=M1, IPL=32, IP=IP1, Label=10.

          . A [RFC5512] BGP Encapsulation Extended Community.

          . Route-target identifying the SBD. This route-target MAY be
            the same as the one used with the RT-5.

   (2) DGW1 imports the received routes from NVE1:

        o DGW1 installs SN1/24 in the IP-VRF identified by the RT-5
          route-target.

          . Since GW IP is different from zero, the GW IP (IP1) will be
            used as the Overlay Index for the recursive route resolution
            to the RT-2 carrying IP1.



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   (3) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table. The lookup yields SN1/24, which is associated
          to the Overlay Index IP1. The forwarding information is
          derived from the RT-2 received for IP1.

        o The IP packet destined to IPx is encapsulated with: Source
          inner MAC = M3, Destination inner MAC = M1, Source outer IP
          (source VTEP) = DGW1 IP, Destination outer IP (destination
          VTEP) = NVE1 IP.

   (4) When the packet arrives at NVE1:

        o NVE1 will identify the IP-VRF for an IP-lookup based on the
          Label and the inner MAC DA.

        o An IP lookup is performed in the routing context, where SN1
          turns out to be a local subnet associated to BD-2. A
          subsequent lookup in the ARP table and the BD FIB will provide
          the forwarding information for the packet in BD-2.

   The model described above is called 'Interface-ful with SBD IRB
   model' since the tunnels connecting the DGWs and NVEs need to be
   terminated into the SBD. The SBD is connected to the IP-VRFs via SBD
   IRB interfaces, and that allows the recursive resolution of RT-5s to
   GW IP addresses. An EVPN IP-VRF-to-IP-VRF implementation is REQUIRED
   to support the ingress and egress procedures described in this
   section.

4.4.3 Interface-ful IP-VRF-to-IP-VRF with Unnumbered SBD IRB

   Figure 8 will be used for the description of this model. Note that
   this model is similar to the one described in section 4.4.2, only
   without IP addresses on the SBD IRB interfaces.















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                    NVE1
           +------------+                       DGW1
   IP1+----+(BD-1)      | +---------------+ +------------+
           |  \         | |               | |            |
           |(IP-VRF)-(SBD)|               (SBD)-(IP-VRF) |-----+
           |  /    IRB(M1)|               | IRB(M3)      |     |
       +---+(BD-2)      | |               | +------------+    _+_
       |   +------------+ |               |                  (   )
    SN1|                  |     VXLAN/    |                 ( WAN )--H1
       |            NVE2  |     nvGRE/    |                  (___)
       |   +------------+ |     MPLS      |     DGW2           +
       +---+(BD-2)      | |               | +------------+     |
           |  \         | |               | |            |     |
           |(IP-VRF)-(SBD)|               (SBD)-(IP-VRF) |-----+
           |  /    IRB(M2)|               | IRB(M4)      |
   SN2+----+(BD-3)      | +---------------+ +------------+
           +------------+


         Figure 8 Interface-ful with unnumbered SBD IRB model

   In this model:

   a) As in section 4.4.1 and 4.4.2, the NVEs and DGWs must provide
      connectivity between hosts in SN1, SN2, IP1 and hosts sitting at
      the other end of the WAN.

   b) As in section 4.4.2, the NVE/DGWs are connected through Ethernet
      NVO tunnels terminated in the SBD instance. The IP-VRFs use IRB
      interfaces for their connectivity to the SBD.

   c) However, each SBD IRB has a MAC address only, and no IP address
      (that is why the model refers to an 'unnumbered' SBD IRB). In this
      model, there is no need to have IP reachability to the SBD IRB
      interfaces themselves and there is a requirement to save IP
      addresses on those interfaces.

   d) As in section 4.4.2, the SBD is composed of all the NVE/DGW BDs of
      the tenant that need inter-subnet-forwarding.

   e) As in section 4.4.2, the solution must provide layer-3
      connectivity for Ethernet NVO tunnels, for instance, VXLAN or
      nvGRE.

   This model will also make use of the RT-5 recursive resolution. EVPN
   type 5 routes will advertise the IP Prefixes along with the Router's
   MAC Extended Community used for the recursive lookup, whereas EVPN
   RT-2 routes will advertise the MAC addresses of each SBD IRB



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   interface (this time without an IP).

   Each NVE/DGW will advertise an RT-5 for each of its prefixes with the
   same fields as described in 4.4.2 except for:

        o GW IP address= SHOULD be set to 0.

   Each RT-5 will be sent with a route-target identifying the tenant
   (IP-VRF) and the Router's MAC Extended Community containing the MAC
   address associated to SBD IRB interface. This MAC address MAY be re-
   used for all the IP-VRFs in the NVE.

   The example is similar to the one in section 4.4.2:

   (1) NVE1 advertises the following BGP routes:

        o Route type 5 (IP Prefix route) containing the same values as
          in the example in section 4.4.2, except for:

          . GW IP= SHOULD be set to 0.

          . Router's MAC Extended Community containing M1 (this will be
            used for the recursive lookup to a RT-2).

        o Route type 2 (MAC route for the SBD IRB) with the same values
          as in section 4.4.2 except for:

          . ML=48, M=M1, IPL=0, Label=10.

   (2) DGW1 imports the received routes from NVE1:

        o DGW1 installs SN1/24 in the IP-VRF identified by the RT-5
          route-target.

          . The MAC contained in the Router's MAC Extended Community
            sent along with the RT-5 (M1) will be used as the Overlay
            Index for the recursive route resolution to the RT-2
            carrying M1.

   (3) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table. The lookup yields SN1/24, which is associated
          to the Overlay Index M1. The forwarding information is derived
          from the RT-2 received for M1.

        o The IP packet destined to IPx is encapsulated with: Source



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          inner MAC = M3, Destination inner MAC = M1, Source outer IP
          (source VTEP) = DGW1 IP, Destination outer IP (destination
          VTEP) = NVE1 IP.

   (4) When the packet arrives at NVE1:

        o NVE1 will identify the IP-VRF for an IP-lookup based on the
          Label and the inner MAC DA.

        o An IP lookup is performed in the routing context, where SN1
          turns out to be a local subnet associated to BD-2. A
          subsequent lookup in the ARP table and the BD FIB will provide
          the forwarding information for the packet in BD-2.

   The model described above is called Interface-ful with SBD IRB model
   (as in section 4.4.2), only this time the SBD IRB does not have an IP
   address. This model is OPTIONAL for an EVPN IP-VRF-to-IP-VRF
   implementation.

5. Conclusions

   An EVPN route (type 5) for the advertisement of IP Prefixes is
   described in this document. This new route type has a differentiated
   role from the RT-2 route and addresses the Data Center (or NVO-based
   networks in general) inter-subnet connectivity scenarios described in
   this document. Using this new RT-5, an IP Prefix may be advertised
   along with an Overlay Index that can be a GW IP address, a MAC or an
   ESI, or without an Overlay Index, in which case the BGP next-hop will
   point at the egress NVE/ASBR/ABR and the MAC in the Router's MAC
   Extended Community will provide the inner MAC destination address to
   be used. As discussed throughout the document, the EVPN RT-2 does not
   meet the requirements for all the DC use cases, therefore this EVPN
   route type 5 is required.

   The EVPN route type 5 decouples the IP Prefix advertisements from the
   MAC/IP route advertisements in EVPN, hence:

   a) Allows the clean and clear advertisements of ipv4 or ipv6 prefixes
      in an NLRI with no MAC addresses.

   b) Since the route type is different from the MAC/IP Advertisement
      route, the current [RFC7432] procedures do not need to be
      modified.

   c) Allows a flexible implementation where the prefix can be linked to
      different types of Overlay/Underlay Indexes: overlay IP address,
      overlay MAC addresses, overlay ESI, underlay BGP next-hops, etc.




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   d) An EVPN implementation not requiring IP Prefixes can simply
      discard them by looking at the route type value.


6. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

7. Security Considerations

   The security considerations discussed in [RFC7432] apply to this
   document.

8. IANA Considerations

   This document requests the allocation of value 5 in the "EVPN Route
   Types" registry defined by [RFC7432]:

   Value     Description         Reference
   5         IP Prefix route     [this document]



9. References

9.1 Normative References

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

   [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>.

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


9.2 Informative References

   [EVPN-INTERSUBNET] Sajassi et al., "IP Inter-Subnet Forwarding in
   EVPN", draft-ietf-bess-evpn-inter-subnet-forwarding-03.txt, work in
   progress, February, 2017



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   [EVPN-OVERLAY] Sajassi-Drake et al., "A Network Virtualization
   Overlay Solution using EVPN", draft-ietf-bess-evpn-overlay-08.txt,
   work in progress, March, 2017



10. Acknowledgments

   The authors would like to thank Mukul Katiyar and Jeffrey Zhang for
   their valuable feedback and contributions. The following people also
   helped improving this document with their feedback: Tony Przygienda
   and Thomas Morin. Special THANK YOU to Eric Rosen for his detailed
   review, it really helped improve the readability and clarify the
   concepts.

11. Contributors

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

   Senthil Sathappan
   Florin Balus
   Aldrin Isaac
   Senad Palislamovic


12. Authors' Addresses

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

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

   John E. Drake
   Juniper
   Email: jdrake@juniper.net

   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com

   Wen Lin
   Juniper



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   Email: wlin@juniper.net


















































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