[Search] [txt|html|xml|pdf|bibtex] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01                                                         
BESS WG                                                          Y. Wang
Internet-Draft                                                    Q. Niu
Intended status: Standards Track                         ZTE Corporation
Expires: 27 April 2022                                   24 October 2021


                 Distributed Bump-in-the-wire Use Case
          draft-wang-bess-evpn-distributed-bump-in-the-wire-01

Abstract

   The Bump-in-the-wire use-case of Section 4.3 of [RFC9136] is a
   centerlized inter-subnet forwarding solution.  The centerlized inter-
   subnet forwarding burdens the DGWs with the L3 traffics among
   different subnets inside the same DC.

   This draft extends the Bump-in-the-wire use-case of Section 4.3 of
   [RFC9136] in order to achieve a distributed inter-subnet forwarding
   solution.

Status of This Memo

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

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

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

   This Internet-Draft will expire on 27 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.










Wang & Niu                Expires 27 April 2022                 [Page 1]


Internet-Draft            Bump-in-the-wire SBD              October 2021


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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology and Acronyms  . . . . . . . . . . . . . . . .   4
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Centerlized Inter-subnet Forwarding . . . . . . . . . . .   5
     2.2.  RT-1 Confliction among Multiple Bump-in-the-wires . . . .   6
   3.  Solutions . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.1.  Supplementary BD for Bump-in-the-wire . . . . . . . . . .   8
     3.2.  Constructing IP Prefix Advertisement Route  . . . . . . .   9
     3.3.  ACI-specific Supplementary Overlay Index Extended
           Community . . . . . . . . . . . . . . . . . . . . . . . .  11
     3.4.  Determining the Aliasing Pathes for RT-5E . . . . . . . .  13
     3.5.  Other Considerations  . . . . . . . . . . . . . . . . . .  13
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   As shown in Figure 1, the Bump-in-the-wire use-case of Section 4.3 of
   [RFC9136] is a centerlized inter-subnet forwarding solution.  The
   centerlized inter-subnet forwarding burdens the DGWs with the L3
   traffics among different subnets (e.g.  SN1 and H3 of Figure 2)
   inside the same DC.














Wang & Niu                Expires 27 April 2022                 [Page 2]


Internet-Draft            Bump-in-the-wire SBD              October 2021


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

                        Figure 1: RFC9136's Figure 7

   When a SBD is added (see Figure 4) for the IP-VRF instance, using
   this SBD and its SBD IRB, we can extend the Bump-in-the-wire use case
   to form a distributed inter-subnet forwarding solution which will not
   burden the DGWs with the L3 traffics among different subnets inside
   the same DC.

   But when multiple Bump-in-the-wires are integrated into the same IP-
   VRF (as shown in Figure 3), the above extension is not enough, the
   details are discribed in Section 2.2, thus some futher extensions are
   introduced to solve that problem.

   The RT-5 route that specifies an ESI as overlay index is first
   defined in Section 4.3 of [RFC9136], where the Bump-in-the-wire use
   case (which is called the first type RT-5E usage) is also defined
   there.

   Note that the RT-5E routes (which are called the second type RT-5E
   usage) of Section 4.3.2 of
   [I-D.wang-bess-evpn-arp-nd-synch-without-irb] and Section 1.3 of
   [I-D.sajassi-bess-evpn-ip-aliasing] are different from these RT-5E
   routes of Bump-in-the-wire use case in the following factors:

   *  Source MAC - The ethernet header can not be absent in the first
      type usage even if the data plane is MPLS.  The source MAC MUST be
      set to the MAC address of the IRB interface of BD-10 in Bump-in-
      the-wire usecase.  But in the second type usage the ethernet
      header can be absent if the data plane is MPLS.

   *  Recursive Resolution - The recursive resolution of the first type
      usage are done in the context of a BD, But the recursive
      resolution of the second type usage are done in the context of a
      IP-VRF.



Wang & Niu                Expires 27 April 2022                 [Page 3]


Internet-Draft            Bump-in-the-wire SBD              October 2021


   *  EVPN label - The EVPN label of the corresponding RT-1 per EVI
      route of the first type usage is a MPLS label which identifies a
      BD, But the EVPN label of the corresponding RT-1 per EVI route of
      the second type usage is a MPLS label which identifies an IP-VRF.

   *  ESI - The ESI of the first type usage is attached to a BD, But
      ESIs of the second type usage are attached to IP-VRFs.

   The Bump-in-the-wire use case is a special form of EVPN IRB use case,
   that's why its corresponding RT-1 per EVI routes are resolved in BD
   context.

1.1.  Terminology and Acronyms

   Most of the acronyms and terms used in this documents comes from
   [RFC9136] and [I-D.wang-bess-evpn-ether-tag-id-usage] except for the
   following:

   * VRF AC -  An Attachment Circuit (AC) that attaches a CE to an
         IP-VRF but is not an IRB interface.

   * VRF Interface -  An IRB interface or a VRF-AC or an IRC
         interface.  Note that a VRF interface will be bound to the
         routing space of an IP-VRF.

   * L3 EVI -  An EVPN instance spanning the Provider Edge (PE)
         devices participating in that EVPN which contains VRF ACs and
         maybe contains IRB interfaces or IRC interfaces.

   * RT-1 per EVI -  Ethernet Auto-Discovery route per EVI, and the
         EVI here is an IP-VRF.  Note that the Ethernet Tag ID of an
         RT-1 per EVI route may be not zero.

   * IP-AD/ES -  Ethernet Auto-Discovery route per ES, and the EVI
         for one of its route targets is an IP-VRF.

   * RMAC -  Router's MAC, which is signaled in the Router's MAC
         extended community.

   * ESI Overlay Index -  ESI as overlay index.

   * ET-ID -  Ethernet Tag ID, it is also called ETI for short in
         this document.

   * RT-5E -  An EVPN Prefix Advertisement Route with a non-reserved
         ESI as its overlay index (the ESI-as-Overlay-Index-style RT-5)
         .




Wang & Niu                Expires 27 April 2022                 [Page 4]


Internet-Draft            Bump-in-the-wire SBD              October 2021


   * CE-BGP -  The BGP session between PE and CE.  Note that CE-BGP
         route doesn't have a RD or Route-Target.

   * CE-Prefix -  An IP Prefixes behind a CE is called as that CE's
         CE-Prefix.

   * ETI-Agnostic BD -  A Broadcast Domain (BD) whose data packets
         can be received along with any Ethernet Tag ID (ETI).  Note
         that a broadcast domain of an L2 EVI of VLAN-aware bundle
         service interface is a good example of an ETI-Specific BD.

   * ETI-Specific BD -  A Broadcast Domain (BD) whose data packets
         are expected to be received along with a normalized Ethernet
         Tag ID (ETI).  Note that a broadcast domain of an L2 EVI of
         VLAN-bundle or VLAN-based service interface is a good example
         of an ETI-Agnostic BD.

   * BDI-Specific EADR -  When the <ESI, BD> uses BDI-Specific
         Ethernet Auto-discovery mode, the only Ethernet A-D per EVI
         route of that <ESI, BD> is called as a BDI-Specific EADR in
         this draft.

   * ACI-Specific EADR -  When the <ESI, BD> uses ACI-Specific
         Ethernet Auto-discovery mode, the Ethernet A-D per EVI routes
         of that <ESI, BD> are called as ACI-Specific EADRs in this
         draft.

2.  Problem Statement

2.1.  Centerlized Inter-subnet Forwarding





















Wang & Niu                Expires 27 April 2022                 [Page 5]


Internet-Draft            Bump-in-the-wire SBD              October 2021


                     NVE2                              DGW1
              M2 +-----------+   +----------+   +-------------+
    +--TS2(VA1)--|  (BD-10)  |---|          |   | (BD-30)     |
    |      ESI23 +-----------+   |          |   |     \ IRB3  |
    |        +                   |          |---|    (IP-VRF) +---+
    |        |                   |          |   |     / IRB1  |   |
   SN1       |                   |          |   | (BD-10)     |   |
    |        |                   |          |   +-------------+  _|_
    |        +      NVE3         |          |                   (   )
    |      ESI23 +-----------+   |    DC    |                  ( WAN )
    +--TS3(VA1)--|  (BD-10)  |---| Underlay |          DGW2     (___)
              M3 +-----------+   |          |   +-------------+   |
                                 |          |   | (BD-10)     |   |
                    NVE8         |          |   |     \ IRB1  |   |
            +----------------+   |          |---|    (IP-VRF) +---+
      H3----+(BD-30)-(IP-VRF)|---|          |   |     / IRB3  |
            |      IRB3      |   |          |   | (BD-30)     |
            +----------------+   +----------+   +-------------+

              Figure 2: Centerlized Bump-in-the-wire Use Case

   As shown in Figure 2, SN1 and H3 are both internal hosts of the same
   DC.  But the communication between them have to pass through a DGW,
   that's why the DGWs will be burdened with inter-subnet forwarding of
   the internal hosts.

   The Section 4.3 of [RFC9136] defined the Bump-in-the-wire use-case,
   where a style (which is called as RT-5E in this draft) of RT-5 routes
   (whose overlay index is a non-zero ESI), is used to advertise the IP
   prefix of subnet SN1 (see Figure 3).  The RT-5E routes (whose IP
   prefix is SN1, and ESI is ESI23) of Section 4.3 of [RFC9136] is
   called as RT5E_SN1 in this draft.  And the RT-1 routes (whose ESI is
   ESI23) corresponding to the RT5E_SN1 is called as RT1_ESI23 in this
   draft.

   Note that when DGW1 or DGW2 receives RT5E_SN1, it should know (before
   the recursive resolution) that RT5E_SN1's ESI (ESI23) should be
   resolved in the context of BD-10, not in BD-30 (whether BD-30 is
   another Bump-in-the-wire BD or not).  Because of RT5E_SN1's Route
   target (which identifies BD-10), DGW1 can know that before the
   recursive resolution.

2.2.  RT-1 Confliction among Multiple Bump-in-the-wires








Wang & Niu                Expires 27 April 2022                 [Page 6]


Internet-Draft            Bump-in-the-wire SBD              October 2021


             TS2                          NVE2
         +------------+           +------------+
         |            |           |            |
   SN7----(VA2-M4)__  |           |  __(BD-20) |
   |     |          \ |       IF2 | /          |
   |     |           >=============<           +---+
   |     |        __/ |   ESI23   | \__        |   |
   |  +---(VA1-M2)    |     +     |    (BD-10) |   |        NVE8
   |  |  |            |     |     |            |   |     +---------+
   |  |  +------------+     |     +------------+  _+_    | (SBD)   |
   |  |                     |                    (   )   |   |     |
   | SN1                    |                   ( DC  )--|   |IRB8 |
   |  |      TS3            |             NVE3   (_ _)   |   |     |
   |  |  +------------+     |     +------------+   +     |(IP-VRF)-+-+H3
   |  |  |            |     |     |            |   |     +---------+
   |  +---(VA1-M3)__  |     +     |  __(BD-10) |   |
   |     |          \ |   ESI23   | /          |   |
   |     |           >=============<           +---+
   |     |        __/ |       IF3 | \__        |
   SN7----(VA2-M5)    |           |    (BD-20) |
         |            |           |            |
         +------------+           +------------+

              Figure 3: ET-ID Confliction of Bump-in-the-wire

   This network is another view of a part of Figure 4, and it is similar
   to Section 4.3 of [RFC9136] with a few notable exceptions as below:

   The NVE2,NVE3,BD-10,ESI23,TS2,TS3 and SN1 here is the NVE2,NVE3,BD-
   10,ESI23,TS2,TS3 and SN1 there (Section 4.3 of [RFC9136]).  The VA1
   here is the Virtual Appliance (whose VA-MAC is M2/M3 on TS2/TS3)
   there.  The NVE8 here is the DGW1 there.  The IRB8 here takes the
   place of the IRB1 there.

   But here we have another Bump-in-the-wire instance for Virtual
   Appliance VA2, which are attached to another Broadcast Domain BD-20.
   Both BD-10 and BD-20 are integrated into the same IP-VRF by DGW1.
   But the subnet SN1 can only be reached through BD-10, while the
   subnet SN7 can only be reached through BD-20.

   RT5E_SN1 (whose route-target identifying BD-10) is imported into the
   BD-10 at first, although it can be imported into the IP-VRF following
   BD-10's IRB interface, RT5E_SN1 will not be imported into the IP-VRF
   on other PEs which don't have an instance of BD-10.  Thus such PEs
   are precluded from connecting to the hosts of SN1 by such rules.

   Note that both BD-10 and BD-20 are L2 EVIs of VLAN-based Service
   Interfaces.



Wang & Niu                Expires 27 April 2022                 [Page 7]


Internet-Draft            Bump-in-the-wire SBD              October 2021


   The solution for this problem is decribed in Section 3.5.

3.  Solutions

3.1.  Supplementary BD for Bump-in-the-wire

   As shown in Figure 4, the SN1, BD-10, IP-VRF are the same as
   Figure 2, except that the TS2, TS3 and ESI23 are not shown in
   Figure 4, but they are still there unchanged.  Then we add a SBD for
   the IP-VRF instance, and each SBD will be configured with an IRB
   interface (which is called its SBD IRB).  Using this SBD and its SBD
   IRB, we can extend the Bump-in-the-wire use case to form a
   distributed inter-subnet forwarding solution which will not burden
   the DGWs with the L3 traffics among different subnets inside the same
   DC.

                  NVE2                        DGW1
          +----------------+ +--------+ +----------------+
          |       IRB8b    | |        | |     IRB8d      |
          |(IP-VRF)-(SBD)  | |        | | (SBD)-(IP-VRF) |-----+
          |  / IRB1        | |        | |                |     |
      +---+(BD-10)         | |        | +----------------+    _+_
      |   +----------------+ |        |                      (   )
   SN1|                      |        |                     ( WAN )
      |           NVE3       |        |                      (___)
      |   +----------------+ |        |        DGW2            +
      +---+(BD-10)         | |   DC   | +----------------+     |
          |  \ IRB2        | |Underlay| |                |     |
          |(IP-VRF)-(SBD)  | |        | | (SBD)-(IP-VRF) |-----+
          |       IRB8c    | |        | |     IRB8e      |
          +----------------+ |        | +----------------+
                             |        |
                  NVE8       |        |
          +----------------+ |        |
    H3----+(IP-VRF)-(SBD)  | |        |
          |       IRB8     | |        |
          +----------------+ +--------+

              Figure 4: Distributed Bump-in-the-wire Use Case

   The RT-5 route (say RT5E_SN1) advertised by NVE2/NVE3 for SN1 is the
   same as Section 4.3 of [RFC9136] except for the following notable
   differentces:

   *  The route-targets of RT5E_SN1 is set to the export-RT of the SBD.

   *  The RT-1 route of ESI23 MUST be advertised both for BD-10 and the




Wang & Niu                Expires 27 April 2022                 [Page 8]


Internet-Draft            Bump-in-the-wire SBD              October 2021


      SBD, when they are advertised for the SBD, the EVPN label of the
      RT-1 per EVI route should be set to the EVPN label of the BD-10,
      as if it is advertised for BD-10.

      Note that when it is advertised for the SBD, it may use different
      RD than it is advertised for BD-10.

   *  In order to process the RT5E_SN1 properly, the DGW1 and DGW2
      don't have to change its behavior of Section 4.3 of [RFC9136].
      But the configurations of DGW1 and DGW2 must be changed, because
      that the BD-10 is removed and the SBD takes its place.

   Note that to the RT5E_SN1 route, the NVE8 is actually no different
   from DGW1 and DGW2.  NVE8 is not a DC gateway, but whether NVE8 is a
   DC gateway is not awared by NVE1 and NVE2.

3.2.  Constructing IP Prefix Advertisement Route

   The RT5E_SN1 is constructed following Section 4.3 of [RFC9136] except
   for the following differences:

   * Route target and RD
     The route target of RT5E_SN1 MUST be set to the route-target which
     identifies the SBD.  In other words, RT5E_SN1 is advertise for the
     SBD, or we can see RT5E_SN1 is advertised in the context of the
     SBD.

     The RD of RT5E_SN1 can be set to the RD of SBD too.

   * ESI and ET-ID

     No matter whether BD-10 is an ETI-agnostic BD or ETI-specific BD,
     it will be enough to configure the SBD as an ETI-agnostic BD.  But
     the Ethernet Tag ID of the Ethernet A-D per EVI routes of the SBD
     may be set to non-reserved ET-IDs.

     When an CE-prefix of a Bump-in-the-wire instance is advertised by a
     RT-5E route, The RT-5E route is advertised in the SBD's context.
     The RT-5E route's ESI MUST be determined by the CE-prefix's VA MAC
     (which will be known by policy).  Take SN1 of Figure 4 for example,
     by policy, we can know that the VA MAC M1 is in BD-10, then we can
     know that VA MAC M1 is learnt over <ESI23, BD-10>, so the ESI of
     RT5E_SN1 should be set to ESI23.








Wang & Niu                Expires 27 April 2022                 [Page 9]


Internet-Draft            Bump-in-the-wire SBD              October 2021


     If BD-10 is an ETI-agnostic BD (e.g.  BD-10 is of VLAN-based
     service interface), the ET-ID of RT5E_SN1 MUST be set to 0.  If
     BD-10 is an ETI-specific BD (e.g.  BD-10 is of VLAN-aware bundle
     service interface), the ET-ID of RT5E_SN1 MUST be set to the BD-ID
     of BD-10 (even if the SBD is ETI-agnostic).

     Note that the ET-ID of RT5E_SN1 is not used to resolve (as
     described in Section 3.4) RT5E_SN1's ESI overlay index to a proper
     Ethernet A-D per EVI route.

   * ACI-Specific Supplementary Overlay Index

     When an IP Prefix Advertisement is advertised, The ACI-Specific
     Supplementary Overlay Index (SOI) extended community is always
     recommanded to be carried along with it, if it is not clear that
     whether there will be conflictions among Ethernet A-D per EVI
     routes inside the SBD in the future.

     Note that the ACI-Specific SOI here is not used to isolate IP
     address spaces.  It is just used to resolve (as described in
     Section 3.4) RT5E_SN1's ESI overlay index to a proper Ethernet A-D
     per EVI route.

     ACI-specific Overlay Index extended community should be advertised
     along with the RT-5E routes.  Thus the ET-ID of these RT-5E routes
     can be set to zero if BD-10 and BD-20 are ETI-agnostic BDs.

     Note that the combination of <ESI, SOI> will be used to select the
     corresponding RT-1 per EVI routes (in SBD) for these RT-5E routes
     on other PEs.

     Note that in the data plane, the EVPN label that is encapsulated by
     NVE8 for NVE2 or NVE3 will be a label that identifies BD-10.  So
     when BD-10 is an ETI-Specific BD, the ET-ID of RT5E_SN1 MUST be
     encapsulated into the ethernet header of the data packets.
     Otherwise such data packets won't be received by BD-10 (of NVE2 or
     NVE3).














Wang & Niu                Expires 27 April 2022                [Page 10]


Internet-Draft            Bump-in-the-wire SBD              October 2021


3.3.  ACI-specific Supplementary Overlay Index Extended Community

   A new EVPN BGP Extended Community called Supplementary Overlay Index
   is introduced.  This new extended community is a transitive extended
   community with the Type field of 0x06 (EVPN) and the Sub-Type of TBD.
   It is advertised along with EVPN MAC/IP Advertisement Route (Route
   Type 2) per [RFC7432] in ACI-Sepecific Ethernet Auto-Discovery mode.
   It may also be advertised along with EVPN Prefix Advertisement Route
   (Route Type 5) as per [RFC9136].  Generically speaking, the new
   extended community must be attached to any routes which are leant
   over an <ESI, EVI> of ACI-specific Ethernet Auto-Discovery.

   The Supplementary Overlay Index Extended Community is encoded as an
   8-octet value as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Type=0x06     | Sub-Type=TBD  | Type  |O|Z|F=1| Flags |  MBZ  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  MBZ(Cont.)   |         VLAN2         |         VLAN1         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 5: Supplementary Overlay Index Extended Community

   o F:  Format Indicator, its value is always 1 in this draft.  Other
     values are reserved.

   o Type:  .

     * 0:  VLAN-based AC-ID.
         +=====+===========+========+=======+=======+=====+
         | No. | Use Cases | Type   | VLAN2 | VLAN1 | MBZ |
         +=====+===========+========+=======+=======+=====+
         | 1   | untag     | type 0 |   0   |   0   | 0   |
         +-----+-----------+--------+-------+-------+-----+
         | 2   | default   | type 0 |   0   |  FFF  | 0   |
         +-----+-----------+--------+-------+-------+-----+
         | 3   | dot1q     | type 0 |   0   |   E   | 0   |
         +-----+-----------+--------+-------+-------+-----+
         | 4   | QinQ      | type 0 |   E   |   I   | 0   |
         +-----+-----------+--------+-------+-------+-----+

                      Table 1: VLAN-based AOIs
         Notes:
         E :  That field is the External VLAN of the AC.
         I :  That field is the Internal VLAN of the AC.
         0 :  The tag corresponding to that field is absent.



Wang & Niu                Expires 27 April 2022                [Page 11]


Internet-Draft            Bump-in-the-wire SBD              October 2021


         FFF :  The AC is the default subinterface (Section 3.3) of the
             corresponding ES.
         untag :  An untagged subinterface should be matched by that
             format.
         default :  A default subinterface should be matched by that
             format.  When the AC is a default subinterface, it will
             match all the remaining VLAN-tags (which are left over by
             other subinterfaces) on its main-interface.
         dot1q :  A dot1q subinterface should be matched by that format.
         QinQ :  A QinQ subinterface should be matched by that format.
     * 1-15:  Reserved.

   o O Flag:  Overlay Index Flag, this extended community is used as
     overlay index.

     When type field is 0-1: For ACI-Specific Ethernet auto-discovery
     mode, when it is carried along with a RT-2 route, the O Flag should
     be set to 1, For BDI-Specific Ethernet auto-discovery, when it is
     carried along with a RT-2 route, the O Flag should be set to 0.

     When the O Flag is set to 1, this AC-ID is also called as AOI (ACI-
     Specific Overlay Index), and the <ESI, AOI> of that RT-2R or RT-5E
     should be used to determine ECMP pathes.  At the same time, the AOI
     should also be used like Attachment Circuit ID Extended Community
     too.

     Note that only the lowest 8 bits of MBZ field should be used to
     select RT-1 per EVI routes.  <lowest 8 bits of MBZ, VLAN2, VLAN1>
     of a type-0 AOI forms an Ethernet Tag ID of an ACI-Specific EADR.

   o Z Flag:  Must be zero.  Reserved for future use, the receiver
     should ignore this extended coummunity if Z flag is not zero at
     now.

   o Flags:  Reserved for future use. it is set to 0 on advertising, and
     ignored on receiving.

   Note that although this extended community is similar to the AC-ID
   extended community (as per
   [I-D.sajassi-bess-evpn-ac-aware-bundling]), we can assume that they
   may be of different Sub-Types because that they have different
   behaviors.









Wang & Niu                Expires 27 April 2022                [Page 12]


Internet-Draft            Bump-in-the-wire SBD              October 2021


3.4.  Determining the Aliasing Pathes for RT-5E

   No matter whether a RT-5 route is constructed following Section 4.3
   of [RFC9136] or Section 3.2 of this draft, the RT-1 per EVI routes
   corresponding to that RT-5E route will be resolved in the context of
   a BD, not in an IP-VRF.

   When resolving corresponding RT-1 per EVI routes for a RT-5E route,
   the AOI (ACI-specific SOI) Extended Community of the RT-5E route can
   be used.

   Note that when the RT-5E's AOI is Y (Y!=0), the ET-IDs of the
   selected Ethernet A-D per EVI routes (of that RT-5E) should be all Y.

   Note that when the RT-5E's ET-ID is not 0, and an AOI is advertised
   along with the RT-5E, the Ethernet A-D per EVI routes of that RT-5E
   should be selected according to the <ESI,AOI>.

   Note that when a data packet is load-balanced according to <ESI,
   AOI>, in Bump-in-the-wire use case, it is the RT-5E's ET-ID which
   should be encapsulated into the data packet (as 802.1q Tag), not the
   AOI.

   Note that [I-D.sajassi-bess-evpn-ac-aware-bundling] requires the
   Presence of Attachment Circuit ID Extended Community MUST be ignored
   by non multihoming PEs.  It requires the remote PE (non-multihome PE,
   e.g.  PE3) MUST process MAC route as defined in [RFC7432].  But the
   AOI of this case should be used to select ETI-Specific EADRs.  This
   is non-compatible with the Attachment Circuit Extended Community,
   thus the new ACI-Specific Overlay Index Extended Community is
   defined.

3.5.  Other Considerations

   We can assume that maybe neither BD-10 nor BD-20 will be configured
   on NVE8, as illustrated in Figure 4.  In such case, we assume that a
   SBD (Supplementary BD) can be provisoned on NVE8.

   The SBD is similar to the combination of the SBD of Section 4.4.3 of
   [RFC9136] and the BD-10 of Section 4.3 of [RFC9136], except for the
   following factors:

      The RT-1 per EVI routes advertised for SBD is originated from the
      BD-10.  and the SBD don't have to advertise any EVPN routes (e.g.
      IMET route) of its own.  because there are no hosts (even the IP
      address of SBD IRB will not be provisoned in this case) in the
      SBD.




Wang & Niu                Expires 27 April 2022                [Page 13]


Internet-Draft            Bump-in-the-wire SBD              October 2021


   Note that DGWs will advertise their own IP prefixes using their own
   L3 EVPN label and route-targets.  They don't have to expect any data
   packets to be received from such SBD.

   The route advertisement behavior of NVE2 and NVE3 should also be
   changed:

   *  When BD-10 advertised a RT-1 per EVI route RT1a, another RT-1 per
      EVI route RT1b (which is the mirroring of RT1a) should be
      advertised for the SBD.  Although RT1b is advertised for the SBD,
      RT1b's EVPN label should be set to BD-10's EVPN label, not the
      SBD's EVPN label.  RT1b's ET-ID MUST be set to the AC-ID of the AC
      corresponding to RT1a.

      Otherwise the RT-1 per EVI routes for BD-10 and BD-20 will
      conflict with each other, because that both BD-10 and BD-20 are of
      VLAN-based Servcice Interface.


   *  The MAC addresses of IRB interface of each Bump-in-the-wire BD
      (e.g.  BD-10 and BD-20) should be the same as the SBD IRB
      interface of the same L3 EVI, otherwise the source MAC may be not
      expected to be learnt by the CE-side L2 switches.

4.  IANA Considerations

   A new transitive extended community Type of 0x06 and Sub-Type of TBD
   for EVPN Supplementary Overlay Index Extended Community needs to be
   allocated by IANA.

5.  Security Considerations

   TBD.

6.  References

6.1.  Normative References

   [I-D.sajassi-bess-evpn-ac-aware-bundling]
              Sajassi, A., Brissette, P., Mishra, M., Thoria, S.,
              Rabadan, J., and J. Drake, "AC-Aware Bundling Service
              Interface in EVPN", Work in Progress, Internet-Draft,
              draft-sajassi-bess-evpn-ac-aware-bundling-04, 11 July
              2021, <https://datatracker.ietf.org/doc/html/draft-
              sajassi-bess-evpn-ac-aware-bundling-04>.






Wang & Niu                Expires 27 April 2022                [Page 14]


Internet-Draft            Bump-in-the-wire SBD              October 2021


   [I-D.sajassi-bess-evpn-ip-aliasing]
              Sajassi, A., Badoni, G., Warade, P., Pasupula, S., Drake,
              J., and J. Rabadan, "EVPN Support for L3 Fast Convergence
              and Aliasing/Backup Path", Work in Progress, Internet-
              Draft, draft-sajassi-bess-evpn-ip-aliasing-02, 8 June
              2021, <https://datatracker.ietf.org/doc/html/draft-
              sajassi-bess-evpn-ip-aliasing-02>.

   [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>.

   [RFC9135]  Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
              Rabadan, "Integrated Routing and Bridging in Ethernet VPN
              (EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
              <https://www.rfc-editor.org/info/rfc9135>.

   [RFC9136]  Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
              A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
              (EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
              <https://www.rfc-editor.org/info/rfc9136>.

6.2.  Informative References

   [I-D.wang-bess-evpn-arp-nd-synch-without-irb]
              Wang, Y. and Z. Zhang, "ARP/ND Synching And IP Aliasing
              without IRB", Work in Progress, Internet-Draft, draft-
              wang-bess-evpn-arp-nd-synch-without-irb-08, 1 September
              2021, <https://datatracker.ietf.org/doc/html/draft-wang-
              bess-evpn-arp-nd-synch-without-irb-08>.

   [I-D.wang-bess-evpn-ether-tag-id-usage]
              Wang, Y., "Ethernet Tag ID Usage Update for Ethernet A-D
              per EVI Route", Work in Progress, Internet-Draft, draft-
              wang-bess-evpn-ether-tag-id-usage-03, 26 August 2021,
              <https://datatracker.ietf.org/doc/html/draft-wang-bess-
              evpn-ether-tag-id-usage-03>.

   [I-D.wz-bess-evpn-vpws-as-vrf-ac]
              Wang, Y. and Z. Zhang, "EVPN VPWS as VRF Attachment
              Circuit", Work in Progress, Internet-Draft, draft-wz-bess-
              evpn-vpws-as-vrf-ac-02, 28 August 2021,
              <https://datatracker.ietf.org/doc/html/draft-wz-bess-evpn-
              vpws-as-vrf-ac-02>.

Authors' Addresses




Wang & Niu                Expires 27 April 2022                [Page 15]


Internet-Draft            Bump-in-the-wire SBD              October 2021


   Yubao Wang
   ZTE Corporation
   No.68 of Zijinghua Road, Yuhuatai Distinct
   Nanjing
   China

   Email: wang.yubao2@zte.com.cn


   Qibo Niu
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: niu.qibo@zte.com.cn



































Wang & Niu                Expires 27 April 2022                [Page 16]