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

Versions: 00 01 02 03

BESS WG                                                          Y. Wang
Internet-Draft                                                   R. Chen
Intended status: Standards Track                         ZTE Corporation
Expires: 18 May 2021                                    14 November 2020


                    Reduction of EVPN C-MAC Overload
            draft-wang-bess-evpn-cmac-overload-reduction-02

Abstract

   When there are too many customer-MACs (C-MACs), the RRs and/or ASBRs
   will be overloaded by the RT-2 routes for these MACs according to
   [RFC7432].  This issue can be simply solved by making the remote
   C-MAC entries learnt via data-plane MAC learning (like what PBB VPLS
   have done since [RFC7041]) rather than received from RT-2 routes.
   This simplified solution will works as well as PBB VPLS.  But this
   simplified solution will lose many important features that based on
   the ESI concept.  Because the ingress-ESI can't be learnt via data-
   plane MAC learning at the egress PE.  So when the data packets is
   forwarded following these MAC entries, they can't benefit from the
   EAD/EVI routes as per RFC7432.  So the All-Active Redundancy mode for
   ES can't be supported.  This make the simplified solution can't work
   as well as PBB EVPN ([RFC7623]).

   This document proposes some new extensions to [RFC7432] to achieve
   all-active mode ES redundancy on TPEs and reduce the C-MAC loads for
   RRs and ASBRs at the same time.  The new solution will work even more
   better than PBB EVPN under the help of these extensions, especially
   when there is no deployment of MPLS dataplane.

   Furthermore, it naturally brings the benefits of high scalability,
   faster network convergence, and reduced operational complexity, and
   we call it light-weighted EVPNs because of these advantages.

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/.







Wang & Chen                Expires 18 May 2021                  [Page 1]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   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 18 May 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  No C-MAC Awareness in the Backbone  . . . . . . . . . . .   6
     2.2.  EVPN IRB Support  . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Unified Encapsulation per Scenario  . . . . . . . . . . .   6
     2.4.  ESI Features Remain Supported . . . . . . . . . . . . . .   7
     2.5.  Flexible Multi-homing Remains Supported . . . . . . . . .   7
     2.6.  C-MAC Address Learning and Confinement  . . . . . . . . .   7
     2.7.  No C-MAC Flushing for All-Active ESes . . . . . . . . . .   8
     2.8.  Independent C-MAC Flushing for Single-Active ESes . . . .   8
     2.9.  Independent Convergency per <ESI, EVI>  . . . . . . . . .   8
     2.10. Route Aggregation and Default Route in Backbone . . . . .   8
     2.11. Applicable to SRv6 BE use-cases . . . . . . . . . . . . .   8
     2.12. ARP Suppression . . . . . . . . . . . . . . . . . . . . .   8
     2.13. ESI Indicator Aggregation . . . . . . . . . . . . . . . .   9
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   9
     3.1.  Common Overview . . . . . . . . . . . . . . . . . . . . .   9
     3.2.  VXLAN over IP-VRF overview  . . . . . . . . . . . . . . .  10
     3.3.  VXLAN Solution Overview . . . . . . . . . . . . . . . . .  10
     3.4.  MPLS Solution Overview  . . . . . . . . . . . . . . . . .  12
     3.5.  SRv6 Solution Overview  . . . . . . . . . . . . . . . . .  14
   4.  Dataplane-specific Procedures . . . . . . . . . . . . . . . .  15
     4.1.  Packet Walkthrough  . . . . . . . . . . . . . . . . . . .  15
     4.2.  VXLAN over IP-VRF . . . . . . . . . . . . . . . . . . . .  16



Wang & Chen                Expires 18 May 2021                  [Page 2]


Internet-Draft            EVPN C-MAC Reduction             November 2020


     4.3.  NVO3-specific EVPN-lite Procedures  . . . . . . . . . . .  17
     4.4.  MPLS-specific EVPN-lite Procedures  . . . . . . . . . . .  17
     4.5.  SRv6-specific EVPN-lite Procedures  . . . . . . . . . . .  18
       4.5.1.  End.ESI Function and Arg.EGD  . . . . . . . . . . . .  19
   5.  Other Considerations  . . . . . . . . . . . . . . . . . . . .  20
     5.1.  ESI Indicator Advertisement Optimization  . . . . . . . .  20
     5.2.  C-MAC Flush Notification Procedure  . . . . . . . . . . .  21
     5.3.  E-Tree Support Considerations . . . . . . . . . . . . . .  21
     5.4.  EVPN IRB Support Considerations . . . . . . . . . . . . .  21
     5.5.  Use End.ESI SID in MAC/IP Advertisement Routes  . . . . .  22
     5.6.  Hierarchical VPLS in EVPN-lite  . . . . . . . . . . . . .  22
   6.  Comparison with Other Solutions . . . . . . . . . . . . . . .  23
     6.1.  Questions . . . . . . . . . . . . . . . . . . . . . . . .  23
     6.2.  Summary Comparisons . . . . . . . . . . . . . . . . . . .  25
     6.3.  Detailed Comparisons with Anycast Node SID  . . . . . . .  25
     6.4.  Detailed Comparisons with Anycast VTEP IP . . . . . . . .  25
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
     8.1.  END.ESI SID . . . . . . . . . . . . . . . . . . . . . . .  26
     8.2.  Global Unique ESI-label in EAD per ES Route . . . . . . .  26
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  26
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  26
   11. Informative References  . . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   In [RFC7432], the C-MACs is advertised via RT-2 route.  This behavior
   is inheritted by [RFC8365] and [I-D.ietf-bess-srv6-services].  but in
   order to solve the C-MAC overload problem for RRs and ASBRs, we have
   to return to a PBB-like dataplane C-MAC learning procedures.

   We discuss all the requirements for a light-weighted EVPN solution
   which pushes no C-MAC entries into the backbone network in Section 2.
   Note that some of these requirements is not supported well by PBB
   EVPN.

   In this document, the light-weighted EVPN solutions are also called
   as EVPN-lite for short.  A total of four EVPN-lite solutions are
   proposed in Section 3.  These solutions are VXLAN over EVPN IP-VRF,
   light-weighted VXLAN EVPN, light-weighted MPLS EVPN, light-weighted
   SRv6 EVPN.

   Note that the VXLAN-based EVPN-lite and MPLS-based EVPN-lite are both
   a evolution of VXLAN over IP-VRF.  The former takes the MPLS factors
   off the VXLAN over IP-VRF solution, and becomes a pure VXLAN
   solution.  The latter takes the VXLAN factors off the VXLAN over IP-
   VRF solution, and becomes a pure MPLS solution.



Wang & Chen                Expires 18 May 2021                  [Page 3]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   In order to compare these five solutions with [RFC7348] and [RFC7623]
   whose C-MAC entries are also not pushed into the backbone network,
   two terms are introduced in this document, because the comparisons
   need to be done in unified terminology.  One term is "Global ESI
   Indicator (GEI)", which is called as B-MAC in PBB EVPN.  The other
   term is "EVI's Global Dicreminator (EGD)", which is called as I-SID
   in PBB EVPN.

   Note that the EVI here corresponds to the I-Component of [RFC7623],
   not the B-Component.  In fact, there will be no typical B-components
   in some of the above seven solutions.

   Note that the GEI and EGD in different EVPN-lite solutions are very
   different.  The details will be described in Section 3.

   On the basis of GEI concept, then we define two route-types for EVPN-
   lite: The first route type is GEI/ES route, which is called as RT-2
   route in PBB EVPN.  The second route type is GEI/EVI route, which is
   called as EAD/EVI roue in [RFC7432].

   The details of these terms are described in Section 1.1.

1.1.  Terminology

   Most of the terminology used in this documents comes from [RFC7432]
   and [I-D.ietf-bess-srv6-services] except for the following:

   *  Light-weighted EVPN: The EVPN solution with high scalability and
      reduced operational complexity.

   *  EVPN-lite: The Light-weighted EVPN is also called EVPN-lite for
      short.

   *  C-MAC: Customer MAC, it is the same as the C-MAC of PBB EVPN.

   *  ISID: a broadcast domain identifier in PBB I-Component.

   *  LDV: Local Discreminating Value.  It is similar to the Local
      Discreminating Value of type 3 ESI.

   *  GDV: Global Discreminating Value.  An identifier with global
      uniqueness.

   *  EGD: EVI-GDV, an EVI's Global Discreminator, it is a GDV for an
      EVI instance.  A EGD is used to idenfify an EVPN Instance (EVI) in
      data plane.  The EGD is a Global Discreminating Value (GDV) of
      that EVI, so it is also the abbreviation of EVI-GDV.  e.g.  The
      EGD of [RFC7348] is a global VNI.



Wang & Chen                Expires 18 May 2021                  [Page 4]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   *  ESI Indicator: A Global ID for an ESI.  Note that different PE may
      assign different ESI-indicator for the same ESI, espacially when
      the ES redundancy mode is single-active.  e.g.  The ESI indicator
      of [RFC7623] is B-MAC.

   *  GEI: Global ESI Indicator.  It is the same as the "ESI Indicator"
      except for the emphasization to its global uniqueness.  A GEI is
      used in data plane to identify an ESI, because it have global
      uniqueness across the service domain of a corresponding EVPN
      Instance (EVI).  But an ESI may have a few GEIs, each for a TPE,
      espacially in the single-active mode of ES redundancy.  And in
      E-Tree scenarios, an ESI may have two GEIs on the same PE, one for
      Root ACs, one for Leaf ACs.  e.g.  The GEIs for an ESI of
      [RFC8317] is two B-MACs, one for root ACs, one for Leaf ACs.

   *  GEI/ES: The EVPN route which is used to advertise the relation
      between ESE and its GEI.  Note that the GEI/ES route is advertised
      per ESI basis on a specified PE.  In PBB EVPN, the GEI/ES route is
      the MAC Advertisement Route.  Note that different solutions may
      have different GEI/ES routes.  Note that a GEI/ES don't have to be
      an EAD/ES route.

   *  EAD/EVI: An Ethernet A-D route per EVI.

   *  GEI/EVI: The EVPN route which is used to advertise the relation
      between <ESI/GEI, EVI> and its EVPN label and MPLS nexthops.  Note
      that in PBB EVPN, such route is not used.  Note that different
      solutions may have different GEI/EVI routes.  Note that a GEI/EVI
      don't have to be an EAD/EVI route.

   *  ARG.EGD: The argument part of a SID of the End.ESI function is
      called as ARG.EGD, because the value of that argument will be a
      EGD.

   *  RT-2: MAC/IP Advertise Route.

   *  MAC Entry: An entry in the EVPN MAC table in data-plane.

   *  ESI SID: An SRv6 SID whose function type is End.ESI.  Note that
      when the ESI is all-active mode, the ESI SID is the same on all
      PEs of that ES, according to Section 3.5.  In such case, the ESI
      SID can be called as ES anycast SID too.

   *  ESI IP: An End.ESI SID with its Argument part being set to zero.

   *  VXLAN EVPN: EVPN per [RFC8365].





Wang & Chen                Expires 18 May 2021                  [Page 5]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   *  EVPN VXLAN: A broadcast domain per [RFC7348], but use IMET routes
      of [RFC8365] to construct VXLAN tunnels.  Note that an EVPN VXLAN
      will not use EAD/EVI routes or MAC/IP Advertisement Routes.

   *  SPE - Stitching PE, the PEs to do label swapping operation for the
      EVPN labels.  It is similar to the SPE of MS-PWs.

   *  TPE - Target PE, the PEs to do EVPN forwarding for the overlay
      network.

   *  PLR - A router at the point of local repair in the underlay
      network.  In egress node protection, it is the penultimate hop
      router on an anycast tunnel.

2.  Requirements

   EVPN C-MAC Reduction should be provided together with the following
   requirements:

2.1.  No C-MAC Awareness in the Backbone

   In typical operation, an EVPN PE sends a BGP MAC Advertisement route
   per C-MAC address.  In certain applications, this poses scalability
   challenges, as is the case in data center interconnect (DCI)
   scenarios where the number of virtual machines (VMs), and hence the
   number of C-MAC addresses, can be in the millions.  This is called as
   C-MAC overload of DC Backbone.  In such scenarios, it is required to
   reduce the number of BGP MAC Advertisement routes by relying on a
   'EVPN-lite' scheme, as is provided by ESI and its equivalents (e.g.
   Pseudo B-MAC, ESI IP).

2.2.  EVPN IRB Support

   The PBB-VPLS/PBB-EVPN is not friendly to IRB usecase because of its
   complicated Protocol Stack, so it is used just in pure L2VPN usecase
   up to now in the industry.

   The solution should provider efficient forwarding performance in EVPN
   IRB use cases.

2.3.  Unified Encapsulation per Scenario

   PBB EVPN, especially the MPLS encapsulation of its B-VPLS, is
   typically not used in DC Scenario.  So we bring PBB and MPLS
   encapsulation to DC Backbone just due to the C-MAC overload problem.
   EVPN IRB is widely deplyed in DC scenarios, but PBB EVPN is not
   friendly for EVPN IRB use cases.  So we have to use different
   solutions in EVPN IRB and C-MAC reduction use cases.  We believe that



Wang & Chen                Expires 18 May 2021                  [Page 6]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   if we choose VXLAN/Geneve data-plane, we will prefer to use the same
   data-plane in all use cases, e.g.  EVPN IRB, C-MAC reduction.  So it
   is necessary to make NVO3/MPLS/SRv6 EVPN to support Section 2.1 in
   order to provider a unified solution for data center and other
   secenarios.

2.4.  ESI Features Remain Supported

   Two redundancy modes are defined in [RFC7432].  They are All-Active
   mode and Single-Active mode.

   In All-active mode, the C-MAC movement among the different adjacent
   PE nodes of the same ESI should not be considered as C-MAC mobility.
   In Single-Active mode, such movements can be considered as C-MAC
   mobility.

2.5.  Flexible Multi-homing Remains Supported

   Flexible multi-homing means that different ES instances can have
   different adjacent-PEs.  We call all the adjacent-PEs of the same ES
   instances as that ES's location-set in this document.  Flexible
   multi-homing means that different ES can have different location-set.

   For example, ES1's location-set is {PE1}, ES2's location-set is {PE2,
   PE3}, ES3's location-set is {PE1, PE3}, and ES4's location-set is
   {PE2,PE4}.

2.6.  C-MAC Address Learning and Confinement

   In EVPN, all the PE nodes participating in the same EVPN instance are
   exposed to all the C-MAC addresses learned by any one of these PE
   nodes because a C-MAC learned by one of the PE nodes is advertised in
   BGP to other PE nodes in that EVPN instance.  This is the case even
   if some of the PE nodes for that EVPN instance are not involved in
   forwarding traffic to, or from, these C-MAC addresses.  Even if an
   implementation does not install hardware forwarding entries for C-MAC
   addresses that are not part of active traffic flows on that PE, the
   device memory is still consumed by keeping record of the C-MAC
   addresses in the routing information base (RIB) table.  In network
   applications with millions of C-MAC addresses, this introduces a non-
   trivial waste of PE resources.  As such, it is required to confine
   the scope of visibility of C-MAC addresses to only those PE nodes
   that are actively involved in forwarding traffic to, or from, these
   addresses.







Wang & Chen                Expires 18 May 2021                  [Page 7]


Internet-Draft            EVPN C-MAC Reduction             November 2020


2.7.  No C-MAC Flushing for All-Active ESes

   Just as in [RFC7432], it is required to avoid C-MAC address flushing
   upon link, port, or node failure for remote All-Active multihomed
   segments.

2.8.  Independent C-MAC Flushing for Single-Active ESes

   Just as in [RFC7432], upon singel-active ES1's link or port failure,
   the C-MACs of other single-active ESes from the same PE will not be
   flushed.

2.9.  Independent Convergency per <ESI, EVI>

   When the physical port of an All-Active ES works well, but a single
   Ethernet Tag ID (ETI) of that ES fails, The traffic to that ETI of
   that ES will be re-routed to other adjacent PE of the same ES, but
   the traffic to other ETIs of the same ES will not be affected.

   Note that when AC (ES link) fails but PE node still works well, there
   should not be steady bypassing traffic either.  The steady bypassing
   problem is discussed in [I-D.wang-bess-evpn-egress-protection-03].

2.10.  Route Aggregation and Default Route in Backbone

   The routes per ESIs can be aggregated in Backbone network.  Even the
   default route should be supported when the B-Component is an EVPN IP-
   VRF (e.g. in VXLAN over IP-VRF solutions).

2.11.  Applicable to SRv6 BE use-cases

   The leight-weighted SRv6 EVPN mechanisms should be applicable to SRv6
   BE use-cases, not just the SRv6 TE use-cases.

2.12.  ARP Suppression

   The ARP suppression requires <IP,MAC> entries to be steadily held on
   all TPEs, So it conflicts with Section 2.6.  But if the C-MAC
   confinement requirements is not so important in some scenarios, The
   ARP Suppression can be activated.  This is an option.











Wang & Chen                Expires 18 May 2021                  [Page 8]


Internet-Draft            EVPN C-MAC Reduction             November 2020


2.13.  ESI Indicator Aggregation

   When two ESes are attached to the same group of PEs, they can share
   the same ESI indicator.  But this will bring out some issues too.
   One of these issues is that they may be attached to different groups
   of PEs in the future.  Another issue is that when only one of the
   ESes fails, the ESI indicator can't be withdrawn by that PE, so the
   steady bypass of that ES arises immediately after its failture on
   that PE.  If these issues are not so important in some scenarios, The
   ESI Indicator Aggregation may be activated.  This is an option.

   Note that when ESI Indicator Aggregation is activated, the local-bias
   ES split-horizon procedures or its variations (like what
   [I-D.eastlake-bess-evpn-vxlan-bypass-vtep] does) should be used.

   Note that ESI Indicator Aggregation works well with single-active
   ESIs (see Section 4.5), its steadby bypassing problem will arise with
   all-active ESIs only.

3.  Solution Overview

3.1.  Common Overview

   We assign a Global Discreminator EGD1 to an EVI instance EVI1, the
   EGD1 is a number consists of N bits.  We assign an ESI-indicator GEI1
   to ESI1 on PE1, and we assign an ESI-indicator GEI2 to ESI1 on PE2.
   We call the relationship between ESI1 and its two ESI-indicators as
   ESI1_GEI1 and ESI1_GEI2 respectively.  The EGD and GEIs MUST have
   global uniqueness in EVI1's service domain.

                                    +----------+
                      PE1           |          |
                 +-------------+    |          |
                 | ESI1_GEI1   |    |          |         PE3
                /|             |----|          |   +-------------+
               / |             |    | IP/MPLS  |   |             |
          LAG /  +-------------+    | Backbone |   |   ESI2_GEI3 |---CE2
      CE1=====                      |   with   |   |             |
              \  +-------------+    |   EVPN   |---|             |
               \ |             |    |   RRs    |   +-------------+
                \|             |----|   and    |
                 | ESI1_GEI2   |    |   SPEs   |
                 +-------------+    |          |
                      PE2           |          |
                                    +----------+

                    Figure 1: EVPN MAC Reduction Usecase




Wang & Chen                Expires 18 May 2021                  [Page 9]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   We use IMET routes to build a broadcast-list.  The broadcast-list is
   used to forward BUM traffics.  The data-plane MAC learning for BUM
   traffics produces the first batch of C-MAC entries.  The subsequent
   C-MAC entries can be learnt from Unicast traffics and/or BUM
   traffics.  It is clear that we don't use MAC/IP routes to advertise
   C-MAC entries as usual, that is for fear that the RRs and/or ASBRs
   are overloaded by these C-MACs.

3.2.  VXLAN over IP-VRF overview

   We can replace the data plane of PBB EVPN with VXLAN data plane, but
   keep its control plane and management plane unchanged from [RFC7623].
   This is called Pseudo PBB EVPN, and its details are defined in
   [Revision-01_section3.2].

   But it is a bit weird to use PBB EVPN management plane together with
   VXLAN over IP-VRF data-plane.  So we can make a step forward and use
   VXLAN over IP-VRF management/control plane instead.

   We configure ESI-IP and VTEP IP instead of B-MAC, VXLAN instance
   instead of I-VPLS, Backbone IP-VRF instead of B-VPLS, VNI instead of
   I-SID.

   The ESI-IP and VTEP IP are advertised by RT-5 routes, not RT-2
   routes.  Although these IPs can be carried in the RT-2 route's IP
   address field too, it may be a bit weird.  So we choose RT-5 route to
   do the advertisement.

   Note that the GEI/ES route in VXLAN over IP-VRF will be RT-5 route,
   And the ESI may be not advertised together with its GEI.

3.3.  VXLAN Solution Overview

   Although the VXLAN encapsulation is used in Pseudo PBB-EVPN, the MPLS
   data plane is also needed, because that the B-Component of Pseudo
   PBB-EVPN is an IP-VRF.  So we introduce a completely VXLAN
   encapsulation in this section, it is called as VXLAN solution.

   In VXLAN solution, the GEI is composed of a VTEP IP and an ESI label.
   It is illustrated as the following:

       |           32 bits                     |      16 bits      |
       +----+----+----+----+----+----+----+----+----+----+----+----+
       |           VTEP IP                     |     ESI Label     |
       +----+----+----+----+----+----+----+----+----+----+----+----+

                         Figure 2: VXLAN GEI Format




Wang & Chen                Expires 18 May 2021                 [Page 10]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   The VTEP IP is PE1/PE2/PE3's IP address, the ESI label is a local
   discreminating value (LDV) that is used to identify a ESI.  So the
   GEI has global uniqueness in the EVPN domain.

   Note that the GEIs (on PE1 and PE2) of ESI1 don't have to be the
   same.  But if we let them to be the same through configuration, it
   will work well too.

   We use the following encapsulation in this solution:

                +----------------------------------------+
                | IPv4 Header (SIP=VTEP IP)              |
                +----------------------------------------+
                | UDP Header (Source Port ^= ESI label) |
                +----------------------------------------+
                | VXLAN Header (VNI=EGD)                 |
                +----------------------------------------+
                | Ethernet Header                        |
                +----------------------------------------+
                | Ethernet Payload                       |
                +----------------------------------------+
                | Ethernet FCS                           |
                +----------------------------------------+

                Figure 3: VXLAN Encapsulation for EVPN-lite

   Note that only the ingress GEI will be encapsulated in data-plane,
   the VTEP IP of ingress GEI is encapsulated as source IP, the ESI
   label is encrypted into the source port.

   Note that the cryptographic key for ESI label of the inner packet's
   intrinsic entropy.  The intrinsic entropy is a 16 bits unsigned
   integer that is computed from nothing but the inner packet's fields.
   When the ESI label is encrypted into the source port, then the source
   port will contain both the context entropy and the intrinsic entropy
   of the inner packet.  The source port is now called as the
   compositive entropy of the inner packet.

   The GEI/ES route of VXLAN-based EVPN-lite is the RT-1 per ES route.
   The ESI-label attribute is used to carry the GEI1's ESI-label field.
   The OPE TLV or nexthop is used to carry the GEI1's VTEP IP field.










Wang & Chen                Expires 18 May 2021                 [Page 11]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   On receiving the RT-1 per ESI1 route R1 from PE1, PE3 will install a
   GEI mapping entry ME1 into the data-plane.  On receiving a VXLAN
   packet VP1 of Figure 3 format, PE3 recomputes the intrinsic entropy
   of VP1 by the same algorithm, the PE3 decrypts GEI1's ESI label part
   from VP1's UDP source port using the intrinsic entropy.  Then PE3
   learn's VP1's inner S-MAC MAC1 whose destination ESI is ESI1
   according to the GEI mapping entry ME1.

   Note that the simplest encryption algorithm may be the bitwise XOR.
   And it is good enough for our use case.

   On receiving a ethernet packet EP1 whose D-MAC is MAC1, PE3 will
   forwarded EP1 to PE1/PE2 following ESI1's RT-1 per EVI routes for
   EVI1.

   On receiving the RT-1 per ESI route R2 from PE1, PE2 will install a
   GEI mapping entry ME2 into the data-plane.  Then, on receiving a
   VXLAN packet VP2 of Figure 3 format, when VP2 is about to be
   forwarded to ESI1, PE2 will drop VP2 because that its ingress GEI is
   ESI1 (according to the GEI mapping entry ME2) too.

   The conceptual comparisons between light-weighted VXLAN EVPN and
   (Pseudo-) PBB EVPN is illustrated in [Revision-01_section3.6].

3.4.  MPLS Solution Overview

   In MPLS EVPN control plane, we use a 24 bits unsigned number as the
   EGD of EVI1, and it has global uniqueness in EVI1's service domain.
   In data plane, we use QinQ tags to carry the EGD.

   We use a Global Unique Label (GUL) to identify a ESI in EVI1's
   service domain.  So the ESI-GUL is also its Global ESI Indicator.
   The ESI-GULs are avertised through RT-1 per ES routes, and they are
   considered to be an ESI-label by these routes.  The label in RT-3
   route's PMSI-Tunnel Attribute (PTA-Label) whose tunnel type is
   ingress replication is called as Ingress Replication Multicast Label
   (IRML) in this document.

   We use the following encapsulation in MPLS-based EVPN-lite:












Wang & Chen                Expires 18 May 2021                 [Page 12]


Internet-Draft            EVPN C-MAC Reduction             November 2020


            Format #1                    Format #2
       +-----------------------+     +----------------------------+
       | PSN Labels            |     | PSN Labels                 |
       +-----------------------+     +----------------------------+
       | IRML (EVI1)           |     | Destination-ESI GUL (ESI1) |
       +-----------------------+     +----------------------------+
       | Source-ESI GUL (ESI1) |     | Source-ESI GUL (ESI2)      |
       +-----------------------+     +----------------------------+
       | Ethernet Header       |     | Ethernet Header (EVI1)     |
       +-----------------------+     +----------------------------+
       | Ethernet Payload      |     | Ethernet Payload           |
       +-----------------------+     +----------------------------+
       | Ethernet FCS          |     | Ethernet FCS               |
       +-----------------------+     +----------------------------+

                 Figure 4: MPLS Encapsulation for EVPN-lite

   Note that the GUL can be a single Label Stack Entry (LSE), in such
   case, it should be allocated in DCB label space.  Given that the ESIs
   and vESIs may be too many to be allocated in DCB in certain
   scenarios, so the GUL should be allocated in a few context-specific
   label spaces, each identified by a Context Label Space ID (CLS-ID)
   per [I-D.ietf-bess-mvpn-evpn-aggregation-label] in such case.  In
   such case, the ESI-GUL is the entirety of ESI-label and its Context
   Label Space ID (CLS-ID), so it means two LSEs in the Label Stack at
   that time.

   Note that the ESI GULs are assigned by a center authority, which may
   be a DC controller or an administrator.

   Note that the ESI-label (ESI-GUL) should be pushed onto the Label
   Stack whether the packet is BUM or not.  The ESI-GUL can't identify
   the EVPN Instance EVI1, so we have to use the EGD in the inner
   ethernet header of "Format #2" to find EVI1 out.

   Note that the GUL concept is very different with the "upstream-
   assigned label (UAL)" concept.  Because that when a SPE receives a
   GUL from a remote PE, the GUL is considered as an outgoing-label to
   that remote PE, and although the GUL is also considered as a
   incoming-label of the current SPE, and the label operation for the
   GUL will be a "swap", to be precise, The SPE will swap it to itself
   and then push the MPLS Label Stack to that remote PE.  When the same
   GUL is received from different remote PEs, MPLS ECMP or FRR
   procedures will be applied.







Wang & Chen                Expires 18 May 2021                 [Page 13]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   So when the GUL is two LSEs in the label stack, we can say that the
   Context-specific Label Space (CLS) of the ESI-label (inside the GUL)
   takes the role of B-MAC of PBB EVPN, and the CLS-ID label inside the
   GUL takes the role of the B-VPLS label of PBB EVPN.  So no B-VPLS
   instances will be found here.

   Note that the GEI/ES route of MPLS-based EVPN-lite is the RT-1 per ES
   route.

   Note that the light-weighted MPLS EVPN solutions can be used whether
   or not the SR-MPLS LSPs are used in the underlay network.

   The conceptual comparisons between light-weighted MPLS EVPN and
   (Pseudo-) PBB EVPN is illustrated in [Revision-01_section3.6].

3.5.  SRv6 Solution Overview

   We introduce a SRv6 function named End.ESI to carry the ESI-indicator
   in SRv6 dataplane.  A SID with the End.ESI function is called as an
   "ESI SID" in this document.  The GEI is the locator and fuction part
   of its corresponding ESI SID.  The argument part of the ESI SID is
   the EGD for an EVI.  The EGD works like the function part of an
   End.DT2U/DT2M SID.  But the EGD has a global meaning like a global
   VNI or an PBB ISID but the function part for an End.DT2U/DT2M SID
   typically is only a local discreminator on the egress PE.  The
   argument part of the ESI SID is called as ARG.EGD in this document,
   where the EGD is the abbreviation of EVI-GDV.

   The SRv6 SID in IMET route is an End.DT2M SID with a zero argument
   length.  The GEI1 and GEI2 are SRv6 SID of End.ESI function that is
   defined in the following figure.  We use IGP protocols to advertise
   GEI1 and GEI2 to PE3 respectively in SRv6 underlay.  So we don't use
   EAD/ES route or EAD/EVI route in SRv6 EVPN in this section.  If ESI1
   is single-active mode, GEI1 is different from GEI2, but if ESI1 is
   all-active mode, GEI1 is the same as GEI2.

   Note that when PE1 node fails and the ESI is all active, the PLR node
   will do underlay anycast FRR switching for GEI1(=GEI2).  This will
   bring out fast network convergency.

   Note that when the PE-CE link of GEI1 fails, the IGP route of GEI1
   will be withdrawn, So there will be no steady bypassing for that ES,
   but a temporary bypassing can be performed to further improve the
   convergency.







Wang & Chen                Expires 18 May 2021                 [Page 14]


Internet-Draft            EVPN C-MAC Reduction             November 2020


       |       ESI-Indicator(128-N bits)     |        N bits           |
       +------------+------------+-----------+-------------------------+
       |    Block   |   Node     | ESI.LDV   |        ARG.EGD          |
       +------------+------------+-----------+-------------------------+

                        Figure 5: End.ESI SID Format

   Note that an ESI-indicator is composed of Locator and Function, an
   ESI IP is an 128 bits SID with a zero argument.  The function part is
   a Local Discreminating Value (LDV) on that PE for the ESI.  The
   argument part is a EVI-GDV (EGD) for the EVPN Instance.  The argument
   part is also called ARG.EGD in this document.

   Note that although the EGD can be carried in the VLAN-IDs of the
   inner ethernet packet (like MPLS EVPN-lite solutions), it will be
   better to make it be carried in the SRv6 SID.

   The conceptual comparisons between light-weighted SRv6 EVPN and
   (Pseudo-) PBB EVPN is illustrated in [Revision-01_section3.6].

4.  Dataplane-specific Procedures

4.1.  Packet Walkthrough

   #1 [PE1 forward ARP Request to PE2/PE3]

   *  When CE1 requests CE2's ARP, PE1 will receive the ARP Request BUM1
      from a AC (say AC1) of ESI1.  PE1 will forward the ARP Request
      following the broadcast-list of AC1's EVI instance(say EVI1).  The
      broadcast-list is constructed by IMET routes from PE2/PE3.

      PE1 will forward the ARP Request to PE2/PE3.  The ARP Request is
      encapsulated with GEI1 and EVI1_GDV1.  The inner SMAC of the ARP
      request is M1 which is CE1's MAC address.

   #2  [PE2/PE3's Dataplane MAC Learning]

   *  When PE2/PE3 receives the ARP Request packet BUM1, they do
      dataplane MAC learning independently.  They will learn that M1 is
      behind GEI1.

      Note that when PE2 learns that M1 is behind GEI1, it will assume
      that M1 is behind the local AC whose ESI-indicator is GEI1 too.
      The local AC may have more higher priority than the remote one.

      After the dataplane MAC learning, the ARP request packet BUM1 is
      broadcasted to the local ACs, behind one of which is CE2.




Wang & Chen                Expires 18 May 2021                 [Page 15]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   #3  [PE2 Discard ARP Request to CE1]

   *  On receiving BUM1 from PE1, PE2 use the ingress GEI information in
      BUM1 to determine its ingress ESI ESI1, When ESI1 is all-active
      mode and PE2 is about to forward the ARP request to CE1, PE2 will
      find that the ESI for the outgoing AC is also ESI1, so PE2
      discards it for ESI loop-free considerations.

      When ESI1 is single-active mode, the outgoing AC may be in
      blocking state, otherwise its corresponding sub-interface on CE1
      will take charge of packet-drop behavior instead.  So alghough the
      ESI for the outgoing AC is not the same as ESI1, no loop will
      arise in the Ethernet Segment.

   #4  [PE3 Forward ARP Replay to PE1/PE2]

   *  When CE2 replies to CE1 for the ARP request, PE3 will forward the
      ARP reply U1 according to the MAC entry M1 learned previously as
      above.

      PE3 will forward the ARP reply U1 to PE1 or PE2 according to
      ESI1's RT-1 per EVI routes and RT-1 per ES routes:

      When ESI1 is all-active mode, GEI1 may be the same as GEI2, in
      such case, we call both of them GEI21 instead.  The traffics to M1
      will be load-balanced between PE1 and PE2.  Because that GEI21 is
      advertised by both PE1 and PE2l.

   #5  [PE1 Forward ARP Replay to CE1]

   *  Whe PE1 received the ARP reply packet U1 from PE3, PE1 first match
      the packet to the its EVI instance EVI1 by U1's EGD information.
      And PE1 will not discard it because the egress ESI is not the same
      as the ingress ESI which is determined by U1's GEI information.

4.2.  VXLAN over IP-VRF

   We don't use multicast IP address as the underlay destination IP
   address of the BUM packets.  We use the VTEP IP address per each
   egress PE instead.  But the IMET route is not advertised for the
   backbone IP-VRF instance, they are advertised for the VXLAN instance.
   We use the Originator Router's IP (ORIP) field of the IMET route as
   the underlay destination IP address instead of the nexthop.  It means
   that ORIP should be advertised for the backbone IP-VRF instance, and
   the ORIP should be the VTEP IP address of corresponding PE.

   There are no other changes from Pseudo PBB-EVPN in data-plane.  So it
   is also a MPLS-based solution.



Wang & Chen                Expires 18 May 2021                 [Page 16]


Internet-Draft            EVPN C-MAC Reduction             November 2020


4.3.  NVO3-specific EVPN-lite Procedures

   In Section 3.3, We use VXLAN encapsulation as an example for NVO3
   EVPN.  But when GENEVE or MPLSoGRE encapsulation is used, the ESI-
   label will have its own space in packet headers, so we don't have to
   encapsulate ESI-label in UDP Source port.

   Note that in step #4 the egress GEI is not encapsulated in U1.  U1's
   underlay DIP will be determined by these RT-1 per EVI routes.

4.4.  MPLS-specific EVPN-lite Procedures

   According to [RFC7432], When the IMET route's PTA's tunnel type is
   ingress replication, the ESI-label is considered to be downstream-
   assigned too.  Because that nothing of RT-1 per ES route will
   indicate whether the ESI-label is upstream-assigned or not.

   Alghough ESI-GUL can be a single LSE or two LSEs in the Label Stack,
   we assume that it is a single LSE by default in this section, it is
   for simplification purpose.

   [M1]  In Step #1, "Format #1" of Figure 4 will be used.

         Although the Ingress Replication Multicat Label (IRML) of
         "Format #1" can identify EVI1 by itself, we suppose that the
         ethernet header of it should also carry EGD as what [M4] does.

         Note that there isn't a B-VPLS here, so the IRML identifies the
         EVI1 itself.  The EVI1 here equals I-VPLS of PBB EVPN.

         Note that when that ARP Request packet comes from a SHD
         (single-homed device), the ESI of its AC will be null.  The
         Source-ESI GUL in "Format #1" will be replaced with a MPLS
         label identifying the ingress TPE.  When we assume that the
         underlay network is a SR-MPLS network, that TPE-identifying
         label can be the node SID label of that ingress TPE.  This
         method follows [I-D.wang-bess-evpn-context-label-02], and the
         context of the TPE-identifying label is identified by the
         EVI1's IRML of "Format #1".

         Note that the TPE-identifying label typically will do nothing
         to the all-active ESes, they are used just for the single-homed
         ESes.  But when Section 2.13 is activated, and all ESIs share
         the same ESI indicator, an anycast TPE-identifying label in the
         DCB can be used as that ESI indicator.






Wang & Chen                Expires 18 May 2021                 [Page 17]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   [M2]  In Step #2, "Format #1" of Figure 4 will be received.  PE3
         knows the packet is for EVI1 with the help of the IRML label.
         Then PE3 can learn the relation between the ingress-GEI
         (ingress-ESI GUL) and S-MAC of BUM1 directly, no GEI to ESI
         lookup needed.

   [M3]  In Step #3, PE2 can compare the ingress-GEI (ingress-ESI GUL)
         of BUM1 and the egress-GEI (ESI-GUL of outgoing AC) directly,
         no GEI to ESI lookup needed.

   [M4]  In Step #4, "Format #2" of Figure 4 will be used.  The source-
         ESI GUL, from which the corresponding MAC entry M1 is
         previously learnt, will be encapsulated as the destination-ESI
         GUL directly.  No GEI to ESI lookup needed only if we don't
         care the requirements of Section 2.9.  Otherwise we should
         refer the corresponding RT-1 per EVI routes of ESI1 to forward
         the packet.  These RT-1 per EVI routes are advertised for EVI1,
         so the Ethernet Tag ID (ETI) of these routes don't have to be
         the EGD.

         Note that when ESI1 is single-active mode, ESI-GUL of ESI1 will
         be different on PE1 and PE2.  But the MAC entry M1 will use the
         newest one only, the swithover between them is called as MAC-
         move.

   [M5]  In Step #5, Whe PE1 received the ARP reply packet from PE3, PE1
         first match the packet to ESI1 by Destination-ESI GUL, then
         match the packet to the EVI instance EVI1 by the QinQ tags of
         Ethernet header.

         Note that we suppose that the original tags from ingress AC
         will be processed following the Raw mode per [RFC4448].
         Although the tagged mode can be used technically.  Note that
         the original tags (if they are kept in the packet) will be the
         inner tags of the EGD.

         Note that when RT-1 per EVI route are used, as specified in
         [M4].  There is no need to carry EGD in unicast data-packets
         too.

4.5.  SRv6-specific EVPN-lite Procedures

   [6A]  In Step #1, PE1 will forward the ARP Request to PE2/PE3 with
         the following SRv6 BE encapsulation: It's underlay Source IP is
         the End.ESI SID on PE1 for ESI1; It's underlay Destination IP
         is the End.DT2M SID on PE2/PE3.  The locator and function part
         of the End.ESI SID is GEI1.  The Argument part of the End.ESI
         SID is 0.



Wang & Chen                Expires 18 May 2021                 [Page 18]


Internet-Draft            EVPN C-MAC Reduction             November 2020


         Note that the underlay SIP will be the End.DT2U SID (because
         they don't need an ESI SID) for the single-homed ingress ACs.
         The multi-homed ingress ACs with single-active behavior may not
         be assigned with an dedicated ESI-indicator either.  In such
         situations, the underlay SIP will be the End.DT2U SID too.
         Note that in such situations, the ESI indicator of all single-
         active ESIs for the same EVI are aggregated into the same IPv6
         address.

   [6B]  In Step #3, PE2 can compare the ingress-GEI of BUM1 and the GEI
         of outgoing AC directly, no GEI to ESI lookup needed.

   [6C]  In Step #4, PE3 will forward the ARP reply to PE1 with the
         following SRv6 BE encapsulation: It's underlay Source IP is the
         End.ESI SID on PE3 for ESI2; It's underlay Destination IP is
         the End.ESI SID on PE1 for ESI1 according to the MAC entry M1.
         The ARG.EGD for the End.ESI SID in DIP is the EGD configured on
         PE3.  Note that the EGD for the same EVI is configured with the
         same value on PE1/PE2/PE3.

         When ESI1 is all-active mode, GEI1 will be the same as GEI2, so
         we call both of them GEI21 instead.  The traffics to M1 will be
         load-balanced between PE1 and PE2 by the underlay network on
         PE3.  Because GEI21 is advertised by both PE1 and PE2 in the
         underlay IGP protocol.

         Note that if the DIP is the anycast node SID of PE1 and PE2,
         when the PE-CE link of ESI1 fails, the traffic will be steadily
         bypassed untill that link recovers again.

   [6D]  In Step #5, Whe PE1 received the SRv6 encapsulated ARP reply
         packet from PE3, PE1 first match the packet to the End.ESI SID
         of ESI1 by DIP, then match the packet to the EVI instance EVI1
         by ARG.EGD.

4.5.1.  End.ESI Function and Arg.EGD

   The "Endpoint with decapsulation and ESI-specific L2 table
   forwarding" behavior (End.ESI for short) is a variant of the End.DX2
   behavior.

   Two of the applications of the End.ESI behavior are the EVPN VPLS
   [RFC7432] and the EVPN ETREE [RFC8317]use-cases.

   Any SID instance of this behavior is associated with an ESI E.  The
   behavior also takes an argument: "Arg.EGD".  This argument provides a
   local mapping to an EVI V and its L2 tabel T.  The outgoing AC-
   interface corresponding to <E,V> (ESI E and EVI V) is OIF.



Wang & Chen                Expires 18 May 2021                 [Page 19]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   The End.ESI SID MUST be the last segment in a SR Policy.

   When N receives a packet whose IPv6 DA is S and S is a local End.ESI
   SID, the processing is identical to the End.DX2 behavior except for
   the Upper-layer header processing which is as follows:

    S01. If (Upper-Layer Header type == 143(Ethernet) ) {
    S02.    Remove the outer IPv6 Header with all its extension headers.
    S03.    Learn the exposed MAC Source Address in L2 Table T.
    S04.    Find out the OIF, and forward the Ethernet frame to the OIF.
    S05. } Else {
    S06.    Process as per Section 4.1.1
                of [I-D.ietf-spring-srv6-network-programming].
    S07. }

   Note that the EVI V is determined by the End.ESI SID's ARG.EGD
   argument.

   Note that the MAC learning should not be applied unless the EVI V is
   an E-LAN service.

   Note that the OIF may be found out using the MAC-entries in L2
   Table T, when the EVI V is an E-LAN service and the AC-aware service
   interface is used.

   Note that we can use the ARG.EGD to find out whether the EVI V is an
   E-LAN service or not.

5.  Other Considerations

5.1.  ESI Indicator Advertisement Optimization

   Although we can advertise End.ESI SID in underlay IGP protocols, But
   it is better to use the SRv6 SID Structure Sub-Sub-TLV to indicate
   the length of the ARG.EGD in the End.ESI SID at the same time.
   Otherwise we have to keep the consistence between the length of
   ARG.EGD and the length of local EGD by means of manual
   configurations.

   So we can use EAD/ES route (or EAD/EVI route) to advertise Global ESI
   Indicator (GEI) (and EGD), these EAD routes is called as GEI/ES or
   GEI/EVI route in this document.  When the GEI/EVI route is used to
   advertise GEI, the End.ESI SID is advertised in its SRv6 L2 Service
   TLV, not in its nexthop.  The EGD may be carried in the ARG.EGD field
   of the End.ESI SID, or it can also be determined from its EVI-RTs.






Wang & Chen                Expires 18 May 2021                 [Page 20]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   Either GEI/EVI routes (or GEI/ES) routes will be advertised/imported
   for Global Routing Table (GRT), so their Route-Targets (RT) will be
   configured with GRT.  Because there isn't a dedicated B-component
   like PBB VPLS and PBB EVPN.  Note that the GEI/EVI routes can be
   installed as /128 routes and the ARG.EGD part can be set to the
   actual EGD of the corresponding EVI.  In such case, when a C-MAC is
   learnt over an End.ESI SID (as IPv6 SA) in the data-plane, the
   ARG.EGD field of that SID should be set to the EVI's EGD when the
   C-MAC entry is installed.

   Although GEIs is imported to GRT, they are awared only on PE nodes,
   the transit nodes in underlay network won't be aware of GEIs (they
   can aware the common prefix of these GEIs) in order to reduce the FIB
   consumption.  We can use the argument length in the SRv6 SID
   Structure Sub-Sub-TLV to check whether the EGD is too big for the
   End.ESI SID, So we can avoid the destruction to the function part of
   the End.ESI and we can use flexible EGD length.

5.2.  C-MAC Flush Notification Procedure

   The withdraw of GEI Advertisement can be used as C-MAC flush
   notification like what have been done by [RFC8317] and
   [I-D.ietf-bess-pbb-evpn-isid-cmacflush].

   Note that even if the GEI/EVI routes of Section 5.1 are not
   advertised, the withdraw of those GEI/EVI route can still be used as
   a C-MAC flush notification of their <ESI,EVI>.

5.3.  E-Tree Support Considerations

   E-tree Supprot extensions is similar to [RFC8317] section 5 except
   for the following notable differences: The leaf B-MACs are replaced
   by leaf GEIs, the root B-MACs are replaced by root GEIs.  the PBB
   encapsulation is replaced by other encapsulations, the B-component is
   replaced by an IP-VRF or the underlay GRT.  The B-MAC Advertisement
   Route is replaced by GEI/EVI route or ESI/IP Route.

5.4.  EVPN IRB Support Considerations

   The dataplane in this draft is no more complex with typical SRv6
   EVPN.  So it will work as efficient as we should expect in SRv6 EVPN
   IRB usecase.









Wang & Chen                Expires 18 May 2021                 [Page 21]


Internet-Draft            EVPN C-MAC Reduction             November 2020


5.5.  Use End.ESI SID in MAC/IP Advertisement Routes

   In [I-D.ietf-bess-srv6-services] the downstream assigned ESI label is
   encapsulated in the Arg.FE2 part of End.DT2M SID, And the ESI label
   present as Arg.FE2 only when the egress PE is adjacent with the
   ingress ESI.  So it is difficult (if not impossible) to do data-plane
   C-MAC learning via End.DT2M SID and its unwarranted Arg.FE2 presence.
   Alghough upstream assigned ESI label (like NVO3-specific EVPN-lite
   solutions) may be used to learn ingress ESI-indicator on egress PE
   node, that will be difficult.

   But the End.ESI SID can be used in MAC/IP advertisement route, even
   if C-MAC overload is not a real threat.  By doing this, the data-
   plane can be unified among these usecases.  The details for using
   End.ESI SID in MAC/IP Advertisement Route will be described in future
   versions.

5.6.  Hierarchical VPLS in EVPN-lite

   In hierachical topology (as illustrated in the following figure), the
   PEs are separated into two groups, the Target PEs (TPEs) and the
   Superstratum PEs (SPEs).

              ___TPE5___        SPE3       ___TPE4_____
             /AC5       \      /   \      /            \AC4
          CE3            \    /     \    /              >=====CE2
             \___         \  /       \  /          ____/AC2
              ___TPE3----SPE1-------SPE2-------TPE2
             /AC3          /                       \
          CE1         ____/                         \
             \____TPE1                               \___CE6
              AC1


                         Figure 6: EVPN-lite H-VPLS

   The TPEs works like the IB-BEB-PE in PBB VPLS, the SPE works like the
   BCB-PE in PBB VPLS.  The BCB-PEs in PBB VPLS do BUM replication based
   on the PBB header.  There are no PBB hearder in EVPN-lite solutions,
   but the SPEs won't learn the C-MACs, which is the same as BCB-PEs in
   PBB VPLS.  The forwarding behaviors of these EVPN-lite solutions are
   very different from each other:

   *  The SPE in Pseudo PBB-EVPN do BUM replication based on the
      Multicast Group IP address.






Wang & Chen                Expires 18 May 2021                 [Page 22]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   *  The SPEs in VXLAN over IP-VRF needn't aware of the BUM packets,
      because the destination IP address of the BUM packets will be an
      ingress replication tunnel address to the egress TPE.

   *  The SPEs in MPLS-based EVPN-lite don't have to aware of the BUM
      packets, because that, for IMET routes, they work like the ASBRs
      in inter-AS option B.  In such case, the TPEs do ingress-
      replication for all other TPEs by themselves.

      The SPEs in MPLS-based EVPN-lite may terminate the IMET routes
      that were received from their TPEs.  These IMET routes are
      imported into an corresponding BD, but may not be passed through
      other SPEs, so as not to cause duplicated BUM packets.  In such
      case, take SPE1 for example, there are two split-horizon-groups,
      one group is TPE1/TPE3/TPE5, another split-horizon-group is SPE1/
      SPE2.  The BUM packets are replicated between different split-
      horizon-groups.  In such case, the TPEs do ingress-replication for
      its directly connected TPEs and SPEs, not for the indirectly
      connected TPEs and SPEs.  But the unicast packet will not be
      forwarded by that BD on the SPEs.  The unicast packets will be
      label-swapped in the context-specific label-space for the
      corresponding GULs.

      Note that the BCB-PE in PBB VPLS is typically supported in the
      industry, But it seems that the BCB-PE in PBB EVPN is typically
      not supported in the industry up to now.  Because the BCB-PE
      function can be replaced in MPLS EVPN by a label-swapping
      operation which is like the inter-AS option B scenarios.

   Note that the BUM packets here are defined based on the destination
   C-MAC addresses.

6.  Comparison with Other Solutions

6.1.  Questions

   We compare EVPN-lite with other solutions in this section.  These
   solutions are:

   *  Anycast VTEP IP - [RFC7348] plus IMET routes of [RFC8365], VTEP
      group of [I-D.eastlake-bess-evpn-vxlan-bypass-vtep] and bypass
      tunnel of [I-D.wang-bess-evpn-egress-protection-03].  Data plane
      C-MAC learning is used and the RT-2 routes are eliminated.  But
      RT-1 per ES route may still be used for local-bias ES split-
      horizon.






Wang & Chen                Expires 18 May 2021                 [Page 23]


Internet-Draft            EVPN C-MAC Reduction             November 2020


      Note that the bypass-tunnel is used for the communication between
      the single-homed CEs of the same VTEP group.  The bypass-tunnels
      should not use anycast VTEP IP as their destination addresses.

   *  SRv6 Anycast Node SID - The transplantation of Anycast-VTEP-IP
      solution in SRv6 data-plane, where the Anycast Node SID is the
      equivalent of the Anycast VTEP IP address.  SRv6 Anycast Node SID
      is the ultimate Aggregation of ESI indicators.

   We use the following questions for these solutions to do the
   comparison:

   [CMAC-Reduction]
   #1  No C-MAC Awareness in the Backbone ?

   [EVPN-IRB]
   #2  EVPN IRB Support ?

   [Unified-Encap]
   #3  Unified Encapsulation per Scenario ?

   [ESI-Retained]
   #4  ESI Features Remain Supported ?

   [Flexible-MH]
   #5  Flexible Multi-homing Remains Supported ?

   [Learn-Confined]
   #6  C-MAC Address Learning and Confinement ?

   [AA-no-flush]
   #7  No C-MAC Flushing for All-Active ESes ?

   [SA-independent]
   #8  Independent C-MAC Flushing for Single-Active ESes ?

   [<ESI,EVI> Converge]
   #9  Independent Convergency per <ESI, EVI> ?

   [Route Aggregation]
   #10 Route Aggregation and Default Route in Backbone ?










Wang & Chen                Expires 18 May 2021                 [Page 24]


Internet-Draft            EVPN C-MAC Reduction             November 2020


6.2.  Summary Comparisons

   We place the detailed comparisons about the answers of these
   questions for each solution in separated sections, but we place the
   brief comparisons in the following table:

   +===================+==========+=================+==================+
   | Questions         |EVPN-lite | Anycast-VTEP-IP | Anycast-Node-SID |
   +===================+==========+=================+==================+
   | CMAC-Reduction    |   Yes    |       Yes       |       Yes        |
   +-------------------+----------+-----------------+------------------+
   | EVPN-IRB          |   Yes    |       Yes       |       Yes        |
   +-------------------+----------+-----------------+------------------+
   | Unified-Encap     |   Yes    |       Yes       |       Yes        |
   +-------------------+----------+-----------------+------------------+
   | ESI-Retained      |   Yes    |        No       |        No        |
   +-------------------+----------+-----------------+------------------+
   | Flexible-MH       |   Yes    |        No       |        No        |
   +-------------------+----------+-----------------+------------------+
   | Learn-Confined    |   Yes    |       Yes       |       Yes        |
   +-------------------+----------+-----------------+------------------+
   | AA-no-flush       |   Yes    |       Yes       |       Yes        |
   +-------------------+----------+-----------------+------------------+
   | SA-independent    |   Yes    |        No       |        No        |
   +-------------------+----------+-----------------+------------------+
   | ESI-EVI-Converge  |   Yes    |        No       |        No        |
   +-------------------+----------+-----------------+------------------+
   | Route-Aggregation |   Yes    |       N/A       |       N/A        |
   +-------------------+----------+-----------------+------------------+

                       Table 1: Solution Comparisons

   Note that the comparisons with PBB-EVPN and PBB-VPLS can be found in
   [Revision-01_section6.2].

6.3.  Detailed Comparisons with Anycast Node SID

   TBD.

6.4.  Detailed Comparisons with Anycast VTEP IP

   TBD.

7.  Security Considerations

   Security considerations will be added in future versions.





Wang & Chen                Expires 18 May 2021                 [Page 25]


Internet-Draft            EVPN C-MAC Reduction             November 2020


8.  IANA Considerations

8.1.  END.ESI SID

   IANA is requested to allocate a new code points for the new SRv6
   Endpoint Behaviors defined in this document.

                  +------+-------------+---------------+
                  | Type | Description | Reference     |
                  +------+-------------+---------------+
                  | TBD1 | END.ESI     | This Document |
                  +------+-------------+---------------+


                             Figure 7: END.ESI

8.2.  Global Unique ESI-label in EAD per ES Route

   When we use Global Unique ESI-label in EAD per ES route, especially
   in ingress-replication use case, It should be explicitly indicated in
   the EAD per ES route.  The details will be added in future versions.

9.  Acknowledgements

   The authors would like to thank the following for their comments and
   review of this document:

   Ye Shu.

10.  Normative References

   [I-D.ietf-bess-mvpn-evpn-aggregation-label]
              Zhang, Z., Rosen, E., Lin, W., Li, Z., and I. Wijnands,
              "MVPN/EVPN Tunnel Aggregation with Common Labels", Work in
              Progress, Internet-Draft, draft-ietf-bess-mvpn-evpn-
              aggregation-label-03, 24 October 2019,
              <https://tools.ietf.org/html/draft-ietf-bess-mvpn-evpn-
              aggregation-label-03>.

   [I-D.ietf-bess-srv6-services]
              Dawra, G., Filsfils, C., Talaulikar, K., Raszuk, R.,
              Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based
              Overlay services", Work in Progress, Internet-Draft,
              draft-ietf-bess-srv6-services-05, 2 November 2020,
              <https://tools.ietf.org/html/draft-ietf-bess-srv6-
              services-05>.





Wang & Chen                Expires 18 May 2021                 [Page 26]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              Work in Progress, Internet-Draft, draft-ietf-spring-srv6-
              network-programming-24, 7 October 2020,
              <https://tools.ietf.org/html/draft-ietf-spring-srv6-
              network-programming-24>.

   [RFC4448]  Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
              "Encapsulation Methods for Transport of Ethernet over MPLS
              Networks", RFC 4448, DOI 10.17487/RFC4448, April 2006,
              <https://www.rfc-editor.org/info/rfc4448>.

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

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC7623]  Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
              Henderickx, "Provider Backbone Bridging Combined with
              Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
              September 2015, <https://www.rfc-editor.org/info/rfc7623>.

   [RFC8317]  Sajassi, A., Ed., Salam, S., Drake, J., Uttaro, J.,
              Boutros, S., and J. Rabadan, "Ethernet-Tree (E-Tree)
              Support in Ethernet VPN (EVPN) and Provider Backbone
              Bridging EVPN (PBB-EVPN)", RFC 8317, DOI 10.17487/RFC8317,
              January 2018, <https://www.rfc-editor.org/info/rfc8317>.

   [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>.

11.  Informative References








Wang & Chen                Expires 18 May 2021                 [Page 27]


Internet-Draft            EVPN C-MAC Reduction             November 2020


   [I-D.eastlake-bess-evpn-vxlan-bypass-vtep]
              Eastlake, D., Li, Z., and S. Zhuang, "EVPN VXLAN Bypass
              VTEP", Work in Progress, Internet-Draft, draft-eastlake-
              bess-evpn-vxlan-bypass-vtep-06, 19 October 2020,
              <https://tools.ietf.org/html/draft-eastlake-bess-evpn-
              vxlan-bypass-vtep-06>.

   [I-D.ietf-bess-pbb-evpn-isid-cmacflush]
              Rabadan, J., Sathappan, S., Nagaraj, K., Miyake, M., and
              T. Matsuda, "PBB-EVPN ISID-based CMAC-Flush", Work in
              Progress, Internet-Draft, draft-ietf-bess-pbb-evpn-isid-
              cmacflush-01, 30 October 2020,
              <https://tools.ietf.org/html/draft-ietf-bess-pbb-evpn-
              isid-cmacflush-01>.

   [I-D.wang-bess-evpn-context-label-02]
              Wang, Y., "'SR-MPLS signalling for CSL-based Context VC'
              in I-D.wang-bess-evpn-context-label-02", 10 June 2020,
              <https://tools.ietf.org/html/draft-wang-bess-evpn-context-
              label-02#section-4.2>.

   [I-D.wang-bess-evpn-egress-protection-03]
              Wang, Y., "'Steady Bypassing Problems' in I-D.wang-bess-
              evpn-egress-protection-03", 22 August 2020,
              <https://tools.ietf.org/html/draft-wang-bess-evpn-egress-
              protection-03#section-6.3>.

   [Revision-01_section3.2]
              "Pseudo PBB EVPN", 1 July 2020,
              <https://tools.ietf.org/html/draft-wang-bess-evpn-cmac-
              overload-reduction-01#section-3.2>.

   [Revision-01_section3.6]
              "Comparisons of Relative Concepts", 1 July 2020,
              <https://tools.ietf.org/html/draft-wang-bess-evpn-cmac-
              overload-reduction-01#section-3.6>.

   [Revision-01_section6.2]
              "Comparisons with PBB EVPN and PBB VPLS", 1 July 2020,
              <https://tools.ietf.org/html/draft-wang-bess-evpn-cmac-
              overload-reduction-01#section-6.2>.

   [RFC7041]  Balus, F., Ed., Sajassi, A., Ed., and N. Bitar, Ed.,
              "Extensions to the Virtual Private LAN Service (VPLS)
              Provider Edge (PE) Model for Provider Backbone Bridging",
              RFC 7041, DOI 10.17487/RFC7041, November 2013,
              <https://www.rfc-editor.org/info/rfc7041>.




Wang & Chen                Expires 18 May 2021                 [Page 28]


Internet-Draft            EVPN C-MAC Reduction             November 2020


Authors' Addresses

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

   Email: wang.yubao2@zte.com.cn


   Ran Chen
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: chen.ran@zte.com.cn

































Wang & Chen                Expires 18 May 2021                 [Page 29]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/