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Versions: 00

INTERNET-DRAFT                                         L. Krattiger, Ed.
Intended Status: Informational                           A. Sajassi, Ed.
Expires: January 22, 2020                                      S. Thoria
                                                           Cisco Systems

                                                              J. Rabadan
                                                                   Nokia

                                                                J. Drake
                                                                 Juniper

                                                           July 21, 2019


                      EVPN Interoperability Modes
                 draft-krattiger-evpn-modes-interop-00


Abstract

   Ethernet VPN (EVPN) provides different functional modes in the area
   of Service Interface, Integrated Route and Bridge (IRB) and IRB Core
   connectivity. This document specifies how the different EVPN
   functional modes and types can interoperate with each other. This
   document doesn't aim to redefine the existing functional modes but
   extend them for interoperability.



Status of this Memo

   This Internet-Draft is submitted to IETF 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/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at



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


Copyright and License Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Requirements Language . . . . . . . . . . . . . . . . . . .  3
   2.  Valid Combinations for Interoperability  . . . . . . . . . . .  3
   3.  Service Interface Interoperability . . . . . . . . . . . . . .  5
     3.1.  VLAN-Aware Bundle and VLAN-Based . . . . . . . . . . . . .  5
       3.1.1.  VLAN-Aware Bundle Service PE . . . . . . . . . . . . .  6
       3.1.2.  VLAN-Based Service PE  . . . . . . . . . . . . . . . .  7
     3.2. Service Interface Interop Mode of Operation . . . . . . . .  7
   4.  Interoperability for different IRB Types . . . . . . . . . . .  8
     4.1.  Asymmetric IRB and Symmetric IRB . . . . . . . . . . . . .  8
       4.1.1.  Asymmetric IRB PE  . . . . . . . . . . . . . . . . . . 10
       4.1.2.  Symmetric IRB PE . . . . . . . . . . . . . . . . . . . 10
     4.2. IRB Interop Mode of Operation . . . . . . . . . . . . . . . 11
   5.  Interoperability for different IRB Core Connectivity Modes . . 12
     5.1.  Interface-Less and Interface-Ful Unnumbered IRB  . . . . . 12
       5.1.1.  Interface-Less PE  . . . . . . . . . . . . . . . . . . 15
       5.1.2.  Interface-Ful Unnumbered IRB . . . . . . . . . . . . . 15
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 18
   9. Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     9.1.  Demonstration of Applicability . . . . . . . . . . . . . . 19
       9.1.1.  Service Interface Interoperability . . . . . . . . . . 19
       9.1.2.  IRB Types  . . . . . . . . . . . . . . . . . . . . . . 19
       9.1.3.  IRB Core Connectivity Types  . . . . . . . . . . . . . 19
   10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 19



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1.  Introduction

   Ethernet VPN (EVPN) provides different functional modes in the area
   of Service Interface, Integrated Route and Bridge (IRB) and IRB
   connection model. It is understood that the different modes are
   defined with different use-cases in mind. Even with the specific use-
   cases and the resulting mode definition, the aim of interoperability
   is critical.
   The following EVPN modes are considered for interoperability. It is
   limited to most pertinent interop modes as oppose to all
   permutations. In the future if other modes are identified, it will be
   addressed in future revisions.

   - For Service Interfaces, the VLAN Aware Bundle and VLAN Based types.

   - In Integrated Routing and Bridging (IRB) the Asymmetric IRB and
   Symmetric IRB type.

   - Within the IRB connectivity types, interface-less and the
   interface-ful Unnumbered IRB.

1.1  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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.


2.  Valid Combinations for Interoperability

   The tables below provide an overview of the valid combinations for
   interoperability described in this Internet-Draft.

   For the Service Interface Types as described in [RFC7432] section 6
   and [RFC8365] section 5.1.2. Interoperability considerations are
   provided for the VLAN-Based Service interface ([RFC7432], section
   6.1) and the VLAN-Aware Bundle Service Interface type ([RFC7432]
   section 6.3). The VLAN Bundle Service Interface ([RFC7432] section
   6.2) is not considered at this time.

   Table 1 represent the considered Service Interface Types
   interoperability:







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   +-------------------+------------+-------------+--------------------+
   |                   | VLAN-Based | VLAN Bundle | VLAN-Aware Bundle  |
   +-------------------+------------+-------------+--------------------+
   | VLAN-Based        |    YES     |    NO       |    YES             |
   +-------------------+------------+-------------+--------------------+
   | VLAN Bundle       |    NO      |    YES      |    NO              |
   +-------------------+------------+-------------+--------------------+
   | VLAN-Aware Bundle |    YES     |    NO       |    YES             |
   +-------------------+------------+-------------+--------------------+
   Table 1

   In regards to Integrated Route and Bridge (IRB), two different modes
   are defined in [EVPN-INTERSUBNET], with section 3.2 describing
   Symmetric IRB and section 3.3 Asymmetric IRB:

      The interoperability considerations for Asymmetric IRB and
      Symmetric IRB mode are represented within this Internet-Draft.

   For the IRB Core Connectivity, from all the available modes as
   described in [EVPN-PREFIX], considered for interoperability is the
   interface-less mode (section 4.4.1) in conjunction with only one of
   the interface-ful modes, namely interface-ful IP-VRF-to-IP-VRF with
   Unnumbered SBD IRB (section 4.4.3). With the implementation
   proximation between the two interface-ful modes, considerations for
   interoperability between interface-less and interface-ful Numbered
   are currently not considered. Similarly, the interoperability between
   the two interface-ful modes is currently not being considered, given
   the already close relation and to limit permutations. Future
   revisions of this Internet-Draft might address further variations of
   interoperability.

   Table 2 represent the considered IRB Core Connectivity
   interoperability.

   +-----------------+----------------+---------------+----------------+
   |                 | Interface-Less | Interface-Ful | Interface-Ful  |
   |                 |                | Numbered IRB  | Unnumbered IRB |
   +-----------------+----------------+---------------+----------------+
   | Interface-Less  |      YES       |      NO       |      YES       |
   +-----------------+----------------+---------------+----------------+
   | Interface-Ful   |      NO        |      YES      |      NO        |
   | Numbered IRB    |                |               |                |
   +-----------------+----------------+---------------+----------------+
   | Interface-Ful   |      YES       |      NO       |      YES       |
   | Unnumbered IRB  |                |               |                |
   +-----------------+----------------+---------------+----------------+
   Table 2




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3.  Service Interface Interoperability


3.1.  VLAN-Aware Bundle and VLAN-Based

   [RFC7432] section 6 describes three different Service Interface
   Types. The two modes in focus for interoperability are namely the
   VLAN-Based Service Interface as defined in [RFC7432] section 6.1 and
   the VLAN-Aware Bundle Service Interface as defined in [RFC7432]
   section 6.3. The VLAN Bundle Service Interface is not considered.

   The VLAN-Based Service Interface defines an EVPN instance consisting
   of only a single broadcast domain or "Single Broadcast Domain per
   EVI" as described in [RFC8365] section 5.1.2 Option 1. In this mode,
   individual BGP Route Distinguisher (RD) and Route Target (RT) are
   required for each EVI. Each EVI corresponds to a single MAC-VRF
   identified by the RT, which provides the advantage of an BGP RT
   constraint mechanisms in order to limit the propagation and import of
   routes to only the PE that are interested. With VLAN-Based, the MAC-
   VRF corresponds to only a single bridge table. The VLAN-Based Service
   Interface uses the EVPN MAC/IP Advertisement route ([RFC7432],
   section 7.2) with the MUST requirement of the Ethernet Tag ID being
   set to zero.

   Differently, the VLAN-Aware Bundle Service Interface follows a
   bundling of multiple broadcast domains, with each having its own
   bridge table, into a single EVI. This refers to the definition of
   "Multiple Broadcast Domain per EVI" as described in [RFC8365] section
   5.1.2 Option 2. The advantage of this model is that it doesn't
   require the provisioning of an RD/RT per broadcast domain, which is a
   moot point when VLAN-Base uses auto-derivation of RD/RT. With VLAN-
   Aware Bundle Service, RT Constraint, as defined in [RFC4684], does
   not help to reduce the dissemination of routes for a BD to the Pes
   attached to that BD. This is given by the nature of the bundle
   service where the RT is not sufficient to identify the MAC-VRF and
   corresponding bridge table. The differences between the two modes of
   Service Interfaces, namely VLAN-Based and VLAN-Aware Bundle Service
   Interface, lie in the definition of the Ethernet Tag field in the
   EVPN routes. While VLAN-Based Service Interface defines the EtherTag
   as "must be set to zero", the VLAN-Aware Bundle Service interface
   uses the VID within the EtherTag to identify the bridge table within
   the MAC-VRF. These two requirements are orthogonal and as a result
   make the interoperability of the two types mutually exclusive, an
   interoperability is not achievable (Figure 1).







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   VLAN-Aware Bundle                                          VLAN-Based
   Service Interface                                   Service Interface
    +--------------------------+        +--------------------------+
    | PE1                      |        |                      PE2 |
    |  +---------+  +--------+ |        | +--------+  +---------+  |
    |  | +-----+ |  |        | |        | |        |  |         |  |
   +-----| BD2 | +--+        | |--------| |        +--+         |---+
   ||  | +-----+ |  |        | |        | |        |  |         |  ||
   ||  |         |  |        | |        | |        |  |         |  ||
   ||  |MAC-VRF1 |  |IP-VRF1 | |        | |IP-VRF1 |  |MAC-VRF1 |  ||
   ||  +---------+  +--------+ |        | +--------+  +---------+  ||
   ||                          |        |                          ||
   ||                  +-----+ |        | +-----+                  ||
   ||                  | BGP | |        | | BGP |                  ||
   ||                  +-----+ |        | +-----+                  ||
   |+--------------------------+        +--------------------------+|
   |            2|EthTag [2]| -----><----- 2|EthTag [0]|            |
   |                                                                |
   | +------+                                              +------+ |
   +-|M1/IP1!                                              |M2/IP2!-+
     +------+                                              +------+

   Figure 1: Interop of different Service Interface Types

   As illustrated in Figure 1, the MAC/IP routes exchanged by PE1 and
   PE2 contain Ethernet Tags 2 and 0 respectively. The receiving PE will
   not process these routes and will normally discard them (treat-as-
   withdraw)."

   By extending the requirements currently present, an interoperability
   is achievable. The adjustment would be as follows (Figure 2).


3.1.1.  VLAN-Aware Bundle Service PE

   In case of VLAN Aware Bundle Service Interface on the receiving PE
   and with the consideration of VLAN Based Service Interface on the
   advertising PE:

   - MUST Operate in Single Broadcast Domain per EVI.

   - Multiple Broadcast Domain per EVI case is not considered.

   - MUST allow to receive zero EtherTag.

   - The import of routes is performed based on the import policy
   (route-target).




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   - With single bridge table per MAC-VRF, additional evaluation of the
   EtherTag field is not required; the bridge table is sufficiently
   defined by the import route-target.

   - No Change to data-plane operation, the MPLS label identifies MAC-
   VRF + bridge-table, or the VNI identifies the MAC-VRF + the bridge-
   table.


3.1.2.  VLAN-Based Service PE

   - Operates in Single Broadcast Domain per EVI.

   In case of VLAN Based Service Interface on the receiving PE and with
   the consideration of VLAN Based Service Interface on the advertising
   PE:

   - Operates in Single Broadcast Domain per EVI.

   - MUST allow receiving of non-zero EtherTag.

   - No Change in control-plane operation, the EVI import policy (route-
   target) identifies the broadcast domain (bridge-table) within a MAC-
   VRF.

   - No Change to data-plane operation, the MPLS label identifies MAC-
   VRF + bridge-table, or the VNI identifies the MAC-VRF + the bridge-
   table.

   While the expansion introduces additional configuration requirement
   for the VLAN-Aware Bundle Service Interface, it also allows for
   broader interoperability in the eventuality of Vendor "A" only
   implemented VLAN-Based while Vendor "B" only implemented VLAN-Aware
   Bundle Service Interface.


3.2. Service Interface Interop Mode of Operation

   When Service Interface interoperability is required, a given PE
   should follow this section's procedures for all its broadcast domains
   (BDs) and not just the BDs that need interoperability.

   For those BDs where interoperability between VLAN-Aware Bundle and
   VLAN-Based Service Interface is needed, ignoring the presence of the
   EVPN routes Ethernet Tag ID on the PEs supporting VLAN-Based mode is
   not enough. Each PE needs to clearly signal what mode it supports, so
   that all the PEs attached to the same EVI can understand in what mode
   the EVI operates.



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   Consider a scenario where PE1 is attached to the BD range BD1-10 and
   it operates in VLAN-Aware mode, whereas PE2 is attached to the BD
   range BD7-20 and operates in VLAN-Based mode. Interoperability is
   required for the intersecting BDs, I.e., BD7-10.

   For PE1, this means BD7-10 need to be separated into a dedicated MAC-
   VRF each. EVPN routes for each of these three MAC-VRFs MUST be
   advertised by PE1 with an Ethernet Tag ID of zero. In this way, PE1
   indicates the use of VLAN-Based mode for those BDs. On reception, PE1
   imports the BD7-10 routes based on the Route Target and ignoring the
   Ethernet Tag ID, as the Route Target alone is sufficient to identify
   the correct MAC-VRF and Bridge Table. The remaining BDs on PE1 (range
   BD1-6) continue operating in VLAN-Aware Bundle mode.

   In the same example, other PEs attached to BD1-6 must still process
   the received Ethernet Tag ID in the EVPN routes from PE1, so that
   they can identify the correct Bridge Table in a given MAC-VRF.

   PE2 operates in VLAN-Based mode for BD7-20, as per [RFC7432] and
   [RFC8365]. PE2's EVPN route advertisements for BD7-20 will include
   individual Route Targets per BD and an Ethernet Tag ID of zero. On
   reception, PE2 identifies the MAC-VRF and Bridge Table solely based
   on the Route Target.


4.  Interoperability for different IRB Types

4.1.  Asymmetric IRB and Symmetric IRB

   The differences in the two inter-subnet forwarding modes, namely
   Asymmetric IRB and Symmetric IRB, are beyond just the information
   difference in the control-plane from an EVPN Route Type 2
   perspective. The two IRB modes have significant differences in inter-
   subnet forwarding behavior and as a result different operation during
   label imposition or encapsulation.

   With the Asymmetric IRB mode, the ingress PE performs a "bridge-and-
   route" operation while the egress PE follows a "bridge-only"
   approach. Differently, the forwarding behavior in Symmetric IRB mode
   performs a "bridge-and-route" operation on the ingress PE followed by
   a "route-and bridge" operation at the egress PE. The significance in
   difference is not only in the forwarding behavior itself but also
   around how the respective EVPN attribute are used for driving the
   inter-subnet operation. More specifically, in the case of inter-
   subnet forwarding with Asymmetric IRB, MPLS Label1 is used towards
   the egress PE to specify the MAC-VRF and respective Bridge-Domain for
   forwarding. In inter-subnet forwarding with Symmetric IRB, MPLS
   Label2 associated with the IP-VRF is used for the inter-subnet



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   forwarding operation towards egress PE.

   The respective forwarding behaviors are described in [EVPN-
   INTERSUBNET]. The following steps are required to ensure the
   interoperability between the Asymmetric and Symmetric IRB modes.


   Asymmetric IRB                                         Symmetric IRB
    +--------------------------+        +--------------------------+
    | PE1                      |        |                      PE2 |
    |  +---------+             |        |             +---------+  |
    |  | +-----+ |             |        |             | +-----+ |  |
   +-----| BD0 | +-IRB0-+      |        |     +-IRB0--+ | BD0 | |  |
   ||  | +-----+ |      |      |        |     |       | +-----+ |  |
   ||  |         |  +---+----+ |        | +---+----+  |         |  |
   ||  |MAC-VRF1 |  |        | |        | |        |  |MAC-VRF1 |  |
   ||  +---------+  |IP-VRF1 | |--------| |IP-VRF1 |  +---------+  |
   ||               |        | |        | |        |               |
   ||  +---------+  +---+----+ |        | +---+----+  +---------+  |
   ||  | +-----+ |      |      |        |     |       | +-----+ |  |
   ||  | | BD2 | +-IRB2-+      |        |     +-IRB2--+ | BD2 |-----+
   ||  | +-----+ |             |        |             | +-----+ |  ||
   ||  |         |     +-----+ |        | +-----+     |         |  ||
   ||  |MAC-VRF2 |     | BGP | |        | | BGP |     |MAC-VRF2 |  ||
   ||  +---------+     +-----+ |        | +-----+     +---------+  ||
   ||                          |        |                          ||
   |+--------------------------+        +--------------------------+|
   |       2|MAC/IP, 1 Label| -----><----- 2|MAC/IP, 2 Label|       |
   |                                                                |
   | +------+                                              +------+ |
   +-|M1/IP1!                                              |M2/IP2!-+
     +------+                                              +------+

   Figure 2: Asymmetric IRB and Symmetric IRB


   Figure 2 illustrates the overview of and Asymmetric IRB PE (PE1) and
   a Symmetric IRB PE (PE2) within a interoperability deployment
   scenario. Attached to PE1, end-point M1/IP1 is attached to BD0 within
   MAC-VRF1. Respectively, on PE2 end-point M2/IP2 is connected via
   attachment circuit to BD2 positioned within MAC-VRF2. IRB0 and IRB2
   represent the host-facing IRB interface for inter-subnet
   communication between the different end-points located in the
   different IP Subnets. The IRB interfaces for a common MAC-VRF/BD on
   PE1 and PE2 use the same IP address. With the difference of the IRB
   modes between PE1 (Asymmetric IRB) and PE2 (Symmetric IRB), there is
   a difference in the MPLS Label presence as part of the MAC/IP routes
   exchanged between the PEs. PE1s update contains a single label,



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   representing MPLS Label1 used for bridging purposes. PE2s
   advertisement contains two labels, one for bridging and one for
   routing, as part of the MAC/IP route. While PE1 receives all
   information necessary from PE2, PE2 is missing information necessary
   for its routing operation. As a result, Inter-Subnet routing between
   PE1 and PE2 is not achieved.

   By following the current existing forwarding behavior as described in
   [EVPN-INTERSUBNET], interoperability is theoretically achievable
   without changes in the control-plane format. Nevertheless, there are
   steps required that involve predominantly the local behavior of the
   PE with Symmetric IRB mode.


4.1.1.  Asymmetric IRB PE

   In case of Asymmetric IRB as the advertising PE and with Symmetric
   IRB on the receiving PE:

   - Asymmetric IRB PE MUST send MAC and IP information with MPLS
   Label1.

   In case of Symmetric IRB as the advertising PE and with Asymmetric
   IRB on the receiving PE:

   - Asymmetric IRB PE MUST be able to ignore MPLS Label2.


4.1.2.  Symmetric IRB PE

   In case of Symmetric IRB as the advertising PE and with Asymmetric
   IRB on the receiving PE:

   - Symmetric IRB PE has no additional requirements.

   In case of Asymmetric IRB as the advertising PE and with Symmetric
   IRB on the receiving PE:

   - Symmetric IRB PE requires to add the host-binding information, MAC
   and IP, and associates them to the adjacency (ARP/ND) table facing
   the PE with Asymmetric IRB; this is in addition of adding the MAC
   address into the MAC-VRF table. Since there is no MPLS Label2 or
   Route-Target for the IP-VRF, the Host IP is not specifically added to
   IP-VRF table.







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4.2. IRB Interop Mode of Operation

   Interoperability between the Asymmetric IRB and Symmetric IRB mode
   follows specific defined behavior that is predominantly required on
   the PE that operates in the Symmetric IRB mode. Nevertheless, in
   support for the interoperability, the PE operating in Asymmetric IRB
   MUST accommodate the following two minimal requirements (with
   references to Figure 2): 1) The PE that operates in Asymmetric IRB
   mode (PE1), MUST send the MAC/IP route including the Host IP address.
   2) The PE with Asymmetric IRB (PE1) MUST accept the MAC/IP routes
   sent from PE2 (Symmetric IRB), while ignoring the additional
   information of MPLS Label2 and Route-Target of the IP-VRF.

   In reference to 1), the PE MUST always send the end-point MAC
   address, Host IP address and related MPLS Label1 as part of the
   MAC/IP route towards the PE with Symmetric IRB (PE2). This route will
   be sent only with MPLS Label1 and the Route-Target of the matching
   MAC-VRF. In reference to the illustration in Figure 2, PE1 MUST
   generate and advertise an EVPN MAC/IP route using:

   - MAC Length of 48

   - MAC Address of M1

   - IP Length of 32 / 128

   - IP Address of IP1

   - Label for MAC-VRF1

   - Route-Target of MAC-VRF1

   - Next-Hop PE1

   For completeness of the requirements and in reference of 2), the
   MAC/IP route advertised from the PE operating in Symmetric IRB (PE2)
   is as follow:

   - MAC Length of 48

   - MAC Address of M2

   - IP Length of 32 /128

   - IP Address of IP2

   - Label for MAC-VRF2, IP-VRF1




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   - Route-Target of MAC-VRF2, IP-VRF1

   - Next-Hop PE2

   As defined in 2), the Label and Route-Target information for IP-VRF1
   MUST be ignored by PE1 (PE with Asymmetric IRB).

   With PE2 operating in Symmetric IRB and with enabled interop mode,
   the MAC/IP route from PE1 (Asymmetric IRB) is processed in the
   respective bridging, routing and adjacency table. Based on the Route-
   Target for MAC-VRF1, the MAC address M1 will be imported into MAC-
   VRF1 respectively and placed within BD0. In addition, the host-
   binding information M1/IP1 MUST be installed within PE2s adjacency
   table. Subsequent, on PE2 the MAC address M1 and the host-binding
   information (adjacency table entry) of M1/IP1 MUST point towards PE1
   as the next-hop. With no presence of the Route-Target for IP-VRF1,
   the IP address IP1 will not be specifically imported into IP-VRF1 and
   is not associated with a MPLS Label2. As a result of the
   interoperability, the additional efficiency provided by Symmetric IRB
   in regards of preserving adjacency table exhaustion is reduced; this
   is specifically when communicating with an Asymmetric IRB based
   egress PE. In contrary, the interop mode allows for communication
   between the different IRB modes. As a result, in the eventuality that
   Vendor "A" only provides Asymmetric IRB, while Vendor "B" only has
   Symmetric IRB available, interoperability for inter-subnet forwarding
   can be seamlessly achieved. In addition, two further benefits are
   present by implementing an Asymmetric/Symmetric Co-Existence on the
   same PE (dual-mode PE).

   - A dual-mode PE can seamlessly communicate with PE's that are either
   in Asymmetric or in Symmetric IRB mode.

   - A dual-mode PE can act as Anchor for interconnecting Symmetric IRB
   and Asymmetric IRB based PE's (deployment restrictions might apply).


5.  Interoperability for different IRB Core Connectivity Modes

5.1.  Interface-Less and Interface-Ful Unnumbered IRB

   The two modes, namely interface-less and interface-ful Unnumbered SBD
   IRB, are closely related in regards to the information required in
   the EVPN Route Type 5. While interface-less provides all information
   for the IP prefix advertisement within the EVPN Route Type 5, in the
   case of interface-ful Unnumbered SBD IRB, an additional EVPN Route
   Type 2 is required for the next-hop recursive lookup. From a
   forwarding behavior, both approaches are similar and follow a
   symmetric routing approach but are not interoperable. Note as per



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   [EVPN-PREFIX] the interface-ful Unnumbered SBD IRB is an OPTIONAL
   mode.

                                                          Interface-Ful
   Interface-Less                                        Unnumbered IRB
    +--------------------------+        +--------------------------+
    | PE1                      |        |                      PE2 |
    |               +--------+ |        | +--------+               |
    |               |        | |        | |        |               |
   +----------------+        | |--------| |        +----------------+
   ||               |        | |        | |        |               ||
   ||               |        | |        | |        |               ||
   ||               |IP-VRF1 | |        | |IP-VRF1 |               ||
   ||               +--------+ |        | +--------+               ||
   ||                          |        |                          ||
   ||                  +-----+ |        | +-----+                  ||
   ||                  | BGP | |        | | BGP |                  ||
   ||                  +-----+ |        | +-----+                  ||
   |+--------------------------+        +--------------------------+|
   |                  2|None| ----->                                |
   |                                <----- 5|No Label|              |
   |                                                                |
   | +-------+                                            +-------+ |
   +-|TS1/SN1|                                            |TS2/SN2!-+
     +-------+                                            +-------+

   Figure 3: Interoperability of different IRB Core Connectivity Mode
   (unnumbered)


   The illustration in Figure 3 represents the possible deployment
   scenario between two different Core IRB Connectivity modes.
   Specifically, PE1 is operating with interface-less Core IRB Mode
   while PE2 operates with the interface-ful Unnumbered SDB IRB mode;
   both operate without interoperability capabilities. Attached to PE1
   and PE2 respectively, Tenant System 1 (TS1) and Tenant System 2 (TS2)
   with different IP Subnets are present. TS1 attached on PE1 as well as
   TS2 attached to PE2 are represented in a common IP-VRF (IP-VRF1),
   sharing a common Route-Target between the PEs. With the different IRB
   Core Connectivity modes on PE1 and PE2 respectively, the differences
   in IP prefix advertisements as described in [EVPN-PREFIX] are
   present. PE1 advertises only a single EVPN Route Type 5 (IP Prefix
   Route) for TS1 using the fields following the interface-less mode:

   EVPN Route Type 5:

   - IP Length of 0 to 32 / 0 to 128




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   - IP Address of SN1

   - Label for IP-VRF1

   - GW IP Address set to zero

   - Route-Target of IP-VRF1

   - Router's MAC Extended Community of PE1

   - Next-Hop PE1

   Differently, PE2 advertises an EVPN Route Type 2 (MAC/IP Route) next
   to the EVPN Route Type 5 (IP Prefix Route). The MAC/IP Route supports
   the requirement for recursive next-hop resolution for the next-hop
   used in the IP Prefix Route. Below the fields used in the Route Type
   5 and respective Route Type 2 according to the interface-ful
   Unnumbered IRB mode:

   EVPN Route Type 5:

   - IP Length of 0 to 32 / 0 to 128

   - IP Address of SN1

   - Label SHOULD be set to 0

   - GW IP Address SHOULD be set to "

   - Route-Target of IP-VRF1

   - Router's MAC Extended Community of PE2

   - Next-Hop PE2

   EVPN Route Type 2:

   - MAC Length of 48

   - MAC Address of PE2

   - IP Length of 32 / 128

   - IP Address of PE2

   - Label for IP-VRF1

   - Route-Target of IP-VRF1



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   - Next-Hop PE2


   While PE1 is missing the MPLS Label for the IP-VRF from PE2, PE2 is
   missing the MPLS Label information and the necessary info for the
   next-hop recursion. As a result, Routing with IP Prefix Advertisement
   between PE1 and PE2 is not achieved.

   By advertising an additional EVPN Route Type 2 from interface-less
   (PE1) and by advertising the MPLS Label as part of EVPN Route Type 5
   from PE2, interoperability is achievable. The specific mode of
   operation would be as per the following two section and refers to
   Figure 3 and Figure 4.


5.1.1.  Interface-Less PE

   In case of interface-less on the advertising PE and with the
   consideration of interface-ful Unnumbered IRB as the receiving PE:

   Shall generate and Advertise EVPN Route Type 2 for every IP-VRF
   using.

   - MAC Length of 48

   - MAC Address with "Router MAC"

   - IP Length of 32

   - IP Address with NVE IP

   - Label for IP-VRF

   - Route-Target of IP-VRF

   - Router-MAC Extended Community

   In case of interface-less on the receiving PE and with the
   consideration of interface-ful Unnumbered IRB as the advertising PE:

   - MUST ignore EVPN Route Type 2 with MPLS Label and route-target
   matching the IP-VRF because there is no MAC-VRF defined matching
   these information.


5.1.2.  Interface-Ful Unnumbered IRB

   In case of interface-ful Unnumbered on the advertising PE and with



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   the consideration of interface-less as the receiving PE:

   - Shall advertise MPLS Label for IP-VRF in EVPN Route Type 5 with
   matching route-target.

   In case of interface-ful Unnumbered on the receiving PE and with the
   consideration of interface-less as the advertising PE:

   - No Additions Required.

                                                           Interface-Ful
   Interface-Less                                        Unnumbered IRB
    +--------------------------+        +--------------------------+
    | PE1                      |        |                      PE2 |
    |               +--------+ |        | +--------+               |
    |               |        | |        | |        |               |
   +----------------+        | |--------| |        +----------------+
   ||               |        | |        | |        |               ||
   ||               |        | |        | |        |               ||
   ||               | IP-VRF | |        | | IP-VRF |               ||
   ||               +--------+ |        | +--------+               ||
   ||                          |        |                          ||
   ||                  +-----+ |        | +-----+                  ||
   ||                  | BGP | |        | | BGP |                  ||
   ||                  +-----+ |        | +-----+                  ||
   |+--------------------------+        +--------------------------+|
   |              2|RMAC/RIP| ----->                                |
   |                                <----- 5|Label|                 |
   |                                                                |
   | +-------+                                            +-------+ |
   +-|TS1/SN1|                                            |TS2/SN2!-+
     +-------+                                            +-------+

   Figure 4: Interop of different IRB Core Connectivity Types
   (unnumbered)


   Illustrated in Figure 4 are the additional requirements for
   interface-less IRB Core Connectivity mode, specifically the MAC/IP
   Route (EVPN Route Type 2) necessary for PE2s next-hop recursion.
   Also, the MPLS Label addition within PE2s IP Prefix route (EVPN Route
   Type 5) is represented, which is required for interface-ful
   Unnumbered IRBs advertisement towards an interface-less PE (PE1)

   The interop mode introduces additional control-plane advertisements
   from an Interface-less perspective. This is necessary to allow
   interface-ful Unnumbered SBD IRB to perform the recursive lookup
   required. From a EVPN Type 5 perspective between the two types, most



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   of the fields are already equally defined and populated as per [EVPN-
   PREFIX]. Exception is the IP-VRF Label, which is required to be added
   in the interface-ful Unnumbered SBD IRB's EVPN Type 5. In addition,
   the Interface-less plus addition allows the Co-Existence of both
   types on the same PE (dual-mode PE). Such a dual-mode PE can
   communicate at the same time with PE's that are in Interface-less or
   in interface-ful Unnumbered SBD IRB mode.

   The disadvantage of the additional advertisement has to be put into
   relation to advantage of successful interoperability where
   eventuality of Vendor "A" only implemented interface-less while
   Vendor "B" only implemented interface-ful Unnumbered SBD IRB.

6.  Security Considerations

   TBD.


7.  IANA Considerations

   TBD.


8.  References

8.1.  Normative References

   [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>.

   [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>.

   [EVPN-INTERSUBNET]  Sajassi et al., "Integrated Routing and Bridging
              in EVPN", draft-ietf-bess-evpn-inter-subnet-forwarding-08,
              work in progress, March, 2019.

   [EVPN-PREFIX] Rabadan et al., "IP Prefix Advertisement in EVPN",
              draft-ietf-bess-evpn-prefix-advertisement-11, May 2018.

   [KEYWORDS] 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-



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              editor.org/info/rfc2119>.

   [RFC1776]  Crocker, S., "The Address is the Message", RFC 1776, DOI
              10.17487/RFC1776, April 1 1995, <https://www.rfc-
              editor.org/info/rfc1776>.

   [TRUTHS]   Callon, R., "The Twelve Networking Truths", RFC 1925, DOI
              10.17487/RFC1925, April 1 1996, <https://www.rfc-
              editor.org/info/rfc1925>.


8.2.  Informative References

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

   [EANTC] EANTC, "Multi-Vendor Interoperability Test", February 2019,
              <http://www.eantc.de/fileadmin/eantc/downloads/News/2019/EANTC-
              MPLSSDNNFV2019-WhitePaper-v1.2.pdf>.

   [EVILBIT]  Bellovin, S., "The Security Flag in the IPv4 Header",
              RFC 3514, DOI 10.17487/RFC3514, April 1 2003,
              <https://www.rfc-editor.org/info/rfc3514>.

   [RFC5513]  Farrel, A., "IANA Considerations for Three Letter
              Acronyms", RFC 5513, DOI 10.17487/RFC5513, April 1 2009,
              <https://www.rfc-editor.org/info/rfc5513>.

   [RFC5514]  Vyncke, E., "IPv6 over Social Networks", RFC 5514, DOI
              10.17487/RFC5514, April 1 2009, <https://www.rfc-
              editor.org/info/rfc5514>.



9. Conclusion

   With minimal additions, the most common EVPN types for Virtual
   Identifiers to EVI Mapping, Integrated Routing and Bridging and IP
   Prefix Advertisement can be made interoperable. The aim for
   interoperability doesn't remove the requirement for optimized types
   for different use-cases but allows flexibility and basic
   interoperability.





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9.1.  Demonstration of Applicability

   Cisco, Juniper and Nokia demonstrated successfully the ability of
   EVPN interoperability modes during EANTCs yearly "Multi-Vendor
   Interoperability Test". The Whitepaper can be obtained through EANTC
   with the latest version being available at [EANTC].


9.1.1.  Service Interface Interoperability

   A proof of the benefit with this interoperability mode has already
   been demonstrated during EVPN Multi-Vendor interoperability testing
   and also, in production environments. Specifically, Cisco and Nokia's
   VLAN-Based Service Interface successful proofed interoperability with
   Junipers VLAN-Aware Bundle Service Interface.

9.1.2.  IRB Types

   A proof of the benefit with this interoperability mode has already
   successfully demonstrated during EVPN Multi-Vendor interoperability
   testing. Specifically, Cisco operated in a Hybrid IRB (Dual-Mode)
   mode while other Vendor operated in an Asymmetric IRB mode.
   Forwarding was achieved through dynamic detection of the alternate
   Vendor PE's mode and adjustment to Asymmetric IRB for these specific
   BDs. Communication for all other BDs continued to be Symmetric IRB.

9.1.3.  IRB Core Connectivity Types

   A proof of an interoperability mode between interface-less and
   interface-ful Unnumbered SBD IRB has already been demonstrated in
   production environments and during EVPN Multi-Vendor interoperability
   testing. Specifically, Cisco's addition for Interface-less is
   successfully deployed with Nokia's and Nuage's interface-ful
   Unnumbered SBD IRB at customers


10. Authors' Addresses


   Lukas Krattiger
   Cisco
   USA
   EMail: lkrattig@cisco.com



   Ali Sajassi
   Cisco



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   USA
   EMail: sajassi@cisco.com



   Samir Thoria
   Cisco
   USA
   EMail: sthoria@cisco.com



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



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




























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