EVPN Virtual Ethernet Segment
draft-ietf-bess-evpn-virtual-eth-segment-14

BESS WorkGroup                                                A. Sajassi
Internet-Draft                                              P. Brissette
Intended status: Standards Track                           Cisco Systems
Expires: 26 March 2024                                         R. Schell
                                                                 Verizon
                                                                J. Drake
                                                                 Juniper
                                                              J. Rabadan
                                                                   Nokia
                                                       23 September 2023

                     EVPN Virtual Ethernet Segment
              draft-ietf-bess-evpn-virtual-eth-segment-14

Abstract

   Etheret VPN (EVPN) and Provider Backbone EVPN (PBB-EVPN) introduce a
   family of solutions for Ethernet services over MPLS/IP network with
   many advanced features including multi-homing capabilities.  These
   solutions introduce Single-Active and All-Active redundancy modes for
   an Ethernet Segment (ES), itself defined as a set of physical links
   between the multi-homed device/network and a set of PE devices that
   they are connected to.  This document extends the Ethernet Segment
   concept so that an ES can be associated to a set of Ethernet Virtual
   Circuits (EVCs e.g., VLANs) or other objects such as MPLS Label
   Switch Paths (LSPs) or Pseudowires (PWs).  Such an ES is referred to
   as Virtual Ethernet Segments (vES).  This draft describes the
   requirements and the extensions needed to support vES in EVPN and
   PBB-EVPN.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] and
   [RFC8174].

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/.

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   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
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   This Internet-Draft will expire on 26 March 2024.

Copyright Notice

   Copyright (c) 2023 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
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   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Virtual Ethernet Segments in Access Ethernet Networks . .   3
     1.2.  Virtual Ethernet Segments in Access MPLS Networks . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Single-Homed and Multi-Homed vES  . . . . . . . . . . . .   8
     3.2.  Local Switching . . . . . . . . . . . . . . . . . . . . .   8
     3.3.  EVC Service Types . . . . . . . . . . . . . . . . . . . .   8
     3.4.  Designated Forwarder (DF) Election  . . . . . . . . . . .   9
     3.5.  OAM . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.6.  Failure and Recovery  . . . . . . . . . . . . . . . . . .  10
     3.7.  Fast Convergence  . . . . . . . . . . . . . . . . . . . .  10
   4.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  EVPN DF Election for vES  . . . . . . . . . . . . . . . .  11
     4.2.  Grouping and Route Coloring for vES . . . . . . . . . . .  13
       4.2.1.  EVPN Route Coloring for vES . . . . . . . . . . . . .  13
       4.2.2.  PBB-EVPN Route Coloring for vES . . . . . . . . . . .  14
   5.  Failure Handling and Recovery . . . . . . . . . . . . . . . .  14
     5.1.  EVC Failure Handling for Single-Active vES in EVPN  . . .  16
     5.2.  EVC Failure Handling for Single-Active vES in PBB-EVPN  .  16
     5.3.  Port Failure Handling for Single-Active vESes in EVPN . .  17
     5.4.  Port Failure Handling for Single-Active vESes in
           PBB-EVPN  . . . . . . . . . . . . . . . . . . . . . . . .  18
     5.5.  Fast Convergence in (PBB-)EVPN  . . . . . . . . . . . . .  19
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21

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   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  21
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   Ethernet VPN (EVPN, [RFC7432]) and Provider Backbone EVPN (PBB-EVPN,
   [RFC7623]) introduce a family of solutions for Ethernet services over
   MPLS/IP network with many advanced features including multi-homing
   capabilities.  These solutions introduce Single-Active and All-Active
   redundancy modes for an Ethernet Segment (ES), itself defined as a
   set of links between the multi-homed device/network and a set of PE
   devices that they are connected to.

   An Ethernet Segment, as defined in [RFC7432], represents a set of
   Ethernet links connecting customer site to one or more PE.  This
   document extends the Ethernet Segment concept so that an ES can be
   associated to a set of Ethernet Virtual Circuits (EVCs e.g., VLANs)
   or other objects such as MPLS Label Switch Paths (LSPs) or
   Pseudowires (PWs).  Such an ES is referred to as Virtual Ethernet
   Segments (vES).  This draft describes the requirements and the
   extensions needed to support vES in EVPN and PBB-EVPN.

1.1.  Virtual Ethernet Segments in Access Ethernet Networks

   Some Service Providers (SPs) want to extend the concept of the
   physical links in an ES to Ethernet Virtual Circuits (EVCs) where
   many of such EVCs (e.g., VLANs) can be aggregated on a single
   physical External Network-to-Network Interface (ENNI).  An ES that
   consists of a set of EVCs instead of physical links is referred to as
   a virtual ES (vES).  Figure-1 depicts two PE devices (PE1 and PE2)
   each with an ENNI that aggregates several EVCs.  Some of the EVCs on
   a given ENNI can be associated with vESes.  For example, the multi-
   homed vES in Figure-1 consists of EVC4 on ENNI1 and EVC5 on ENNI2.

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                     3rd Party
       +-----+       EAP
       | CE11|EVC1  +---------+
       +-----+   \  |         |       +---+
       Cust. A    \-0=========0--ENNI1|   |
       +-----+      |         |  ENNI1|   |   +-------+   +---+
       | CE12|EVC2--0=========0--ENNI1|PE1|---|       |   |   |
       +-----+      |         |  ENNI1|   |   |SP     |---|PE3|-
                    |       ==0--ENNI1|   |   |IP/MPLS|   |   | \  +---+
       +-----+      |      /  |       +---+   |Core   |   +---+  \-|   |
       | CE22|EVC3--0==== /   |               |Network|            |CE4|
       +-----+      |    X    |               |       |   +---+    |   |
       Cust. B      |   / \   |       +---+   |       |   |   |  /-|   |
       +-----+     -0===   ===0--ENNI2|   |   |       |---|PE4|-/  +---+
       | CE3 |EVC4/ |         |  ENNI2|PE2|---|       |   |   |
       |     |EVC5--0=========0--ENNI2|   |   +-------+   +---+
       +-----+      |         |       +---+
       Cust. C      +---------+   /\
              /\                  ||
              ||                  ENNI
              EVCs             Interface
       <--------802.1Q---------->  <---- EVPN Network -----> <-802.1Q->

   Figure 1: Dual-homed Device/Network (both SA/AA) and SH on same ENNI

   ENNIs are commonly used to reach remote customer sites via
   independent Ethernet access networks or third- party Ethernet Access
   Providers (EAP).  ENNIs can aggregate traffic from many vESes (e.g.,
   hundreds to thousands), where each vES is represented by its
   associated EVC on that ENNI.  As a result, ENNIs and their associated
   EVCs are a key element of SP external boundaries that are carefully
   designed and closely monitored.  As a reminder, the ENNI is the
   demarcation between the SP (IP/MPLS Core Network) and the third-party
   Ethernet Access Provider.

   To meet customers' Service Level Agreements (SLA), SPs build
   redundancy via multiple EVPN PEs and across multiple ENNIs (as shown
   in Figure 1) where a given vES can be multi-homed to two or more EVPN
   PE devices (on two or more ENNIs) via their associated EVCs.  Just
   like physical ESs in [RFC7432] and [RFC7623] solutions, these vESes
   can be single-homed or multi-homed ESs and when multi-homed, then can
   operate in either Single-Active or All-Active redundancy modes.  In a
   typical SP external-boundary scenario (e.g., with an EAP), an ENNI
   can be associated with several thousands of single-homed vESes,
   several hundreds of Single- Active vESes and it may also be

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   associated with tens or hundreds of All-Active vESes.  Specific
   numbers (hundreds, thousands, etc.) being used through this document
   are used to describe the relation of various elements between them at
   time of writing.

1.2.  Virtual Ethernet Segments in Access MPLS Networks

   Other Service Providers (SPs) want to extend the concept of the
   physical links in an ES to individual Pseudowires (PWs) or to MPLS
   Label Switched Paths (LSPs) in Access MPLS networks - i.e., a vES
   consisting of a set of PWs or a set of LSPs.  Figure 2 illustrates
   this concept.

                    MPLS Aggregation
                    Network
      +-----+      +-----------------+
      | CE11|EVC1  |                 |
      +-----+   \ +AG1-+  PW1      +-+---+
      Cust. A    -0----|===========|     |
      +-----+     | ---+===========|     |   +-------+   +---+
      | CE12|EVC2-0/   |  PW2   /\ | PE1 +---+       |   |   |
      +-----+     ++---+      /=||=|     |   |       +---+PE3+-
                   |         //=||=|     |   |IP/MPLS|   |   | \  +---+
                   |        //  \/ +-+---+   |Core   |   +---+  \-+   |
      +-----+EVC3  |    PW3//  LSP1  |       |Network|            |CE4|
      | CE13|    \+AG2-+==//         |       |       |   +---+    |   |
      +-----+     0    |==/PW4  /\ +-+---+   |       |   |   |  /-+   |
                  0    |==PW5===||=|     |   |       +---+PE4+-/  +---+
      +-----+    /++---+==PW6===||=| PE2 +---+       |   |   |
      | CE14|EVC4  |            \/ |     |   +-------+   +---+
      +-----+      |           LSP2+-+---+
      Cust. C      +-----------------+
             /\
             ||
             EVCs
      <--802.1Q--> <-----MPLS Agg----> <--- EVPN Network ---> <-802.1Q->

               Figure 2: Dual-Homed and Single-homed Network
                         on MPLS Aggregation networks

   In some cases, Service Providers use MPLS Aggregation Networks that
   belong to separate administrative entities or third parties to get
   access to their own IP/MPLS Core network infrastructure.  This is the
   case illustrated in Figure 2.

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   In such scenarios, a virtual ES (vES) is defined as a set of
   individual PWs if they cannot be aggregated.  If the aggregation of
   PWs is possible, the vES can be associated to a group of PWs that
   share the same unidirectional LSP pair (by LSP pair we mean the
   ingress and egress LSPs between the same endpoints).

   In the example of Figure 2, EVC3 is connected to a VPWS instance in
   AG2 that is connected to PE1 and PE2 via PW3 and PW5 respectively.
   EVC4 is connected to another VPWS instance on AG2 that is connected
   to PE1 and PE2 via PW4 and PW6, respectively.  Since the PWs for the
   two VPWS instances can be aggregated into the same LSP pair going to
   and coming from the MPLS network, a common virtual ES (vES) can be
   defined for the four mentioned PWs.  In Figure 2, LSP1 and LSP2
   represent the two LSP pairs between PE1 and AG2, and between PE2 and
   AG2, respectively.  The vES consists of these two LSP pairs (LSP1 and
   LSP2) and each LSP pair has two PWs.  This vES will be shared by two
   separate EVPN instances (e.g., EVI-1 and EVI-2) in the EVPN network.
   PW3 and PW4 are associated with EVI-1 and EVI-2 respectively on PE1,
   and PW5 and PW6 are associated with EVI-1 and EVI-2 respectively on
   PE2.

   In some cases, the aggregation of PWs that share the same LSP pair
   may not be possible.  For instance, if PW3 were terminated into a
   third PE, e.g.  PE3, instead of PE1, the vES would need to be defined
   on a per individual PW on each PE.

   For MPLS/IP access networks where a vES represents a set of LSP pairs
   or a set of PWs, this document extends Single-Active multi-homing
   procedures of [RFC7432] and [RFC7623] to vES.  The vES extension to
   All-Active multi-homing is outside of the scope of this document for
   MPLS/IP access networks.

   This draft defines the concept of a vES and additional extensions
   needed to support a vES in [RFC7432] and [RFC7623].  Section 3 lists
   the set of requirements for a vES.  Section 4 describes extensions
   for a vES that are applicable to EVPN solutions including [RFC7432]
   and [RFC7209].  Furthermore, these extensions meet the requirements
   described in Section 3.  Section 4 gives solution overview and
   Section 5 describes failure handling, recovery, scalability, and fast
   convergence of [RFC7432] and [RFC7623] for vESes.

2.  Terminology

   AC:       Attachment Circuit

   B-MAC:    Backbone MAC Address

   CE:       Customer Edge Device

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   C-MAC:    Customer/Client MAC Address

   DF:       Designated Forwarder

   ENNI:     External Network-Network Interface

   ES:       Ethernet Segment

   ESI:      Ethernet Segment Identifier

   Ethernet A-D:  Ethernet Auto-Discovery Route

   EVC:      Ethernet Virtual Circuit, [MEF63]

   EVI:      EVPN Instance

   EVPN:     Ethernet VPN

   I-SID:    Service Instance Identifier (24 bits and global within a
             PBB network see [RFC7080])

   PBB:      Provider Backbone Bridge

   PBB-EVPN:  Provider Backbone Bridge EVPN

   PE:       Provider Edge Device

   VPWS:     Virtual Pseudowire Service

   Single-Active Redundancy Mode (SA):  When only a single PE, among a
             group of PEs attached to an Ethernet Segment, is allowed to
             forward traffic to/from that Ethernet Segment, then the
             Ethernet Segment is defined to be operating in Single-
             Active redundancy mode.

   All-Active Redundancy Mode (AA):  When all PEs attached to an
             Ethernet segment, are allowed to forward traffic to/from
             that Ethernet Segment, then the Ethernet Segment is defined
             to be operating in All-Active redundancy mode.

3.  Requirements

   This section describes the requirements specific to virtual Ethernet
   Segment (vES) for (PBB-)EVPN solutions.  These requirements are in
   addition to the ones described in [RFC8214], [RFC7432], and
   [RFC7623].

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3.1.  Single-Homed and Multi-Homed vES

   A PE needs to support the following types of vESes:

   (R1a) A PE MUST handle single-homed vESes on a single physical port
   (e.g., single ENNI)

   (R1b) A PE MUST handle a mix of Single-Homed vESes and Single-Active
   multi-homed vESes simultaneously on a single physical port (e.g.,
   single ENNI).  Single-Active multi-homed vESes will be simply
   referred to as Single-Active vESes through the rest of this document.

   (R1c) A PE MAY handle All-Active multi-homed vESes on a single
   physical port.  All-Active multi-homed vESes will be simply referred
   to as All-Active vESes through the rest of this document.

   (R1d) A PE MAY handle a mix of All-Active vESes along with other
   types of vESes on a single physical port.

   (R1e) A Multi-Homed vES (Single-Active or All-Active) can be spread
   across two or more ENNIs, on any two or more PEs.

3.2.  Local Switching

   Many vESes of different types can be aggregated on a single physical
   port on a PE device and some of these vESes can belong to the same
   service instance (e.g., EVI).  This translates into the need for
   supporting local switching among the vESes for the same service
   instance on the same physical port (e.g., ENNI) of the PE.

   (R3a) A PE that supports vES function, MUST support local switching
   among different vESes belonging to the same service instance (or
   customer) on a single physical port.  For example, in Figure 1, PE1
   must support local switching between CE11 and CE12 (both belonging to
   customer A) that are mapped to two Single-homed vESes on ENNI1.  In
   case of Single-Active vESes, the local switching is performed among
   active EVCs belonging to the same service instance on the same ENNI.

3.3.  EVC Service Types

   A physical port (e.g., ENNI) of a PE can aggregate many EVCs each of
   which is associated with a vES.  Furthermore, an EVC may carry one or
   more VLANs.  Typically, an EVC carries a single VLAN and thus it is
   associated with a single broadcast domain.  However, there is no
   restriction preventing an EVC from carrying more than one VLAN.

   (R4a) An EVC can be associated with a single broadcast domain - e.g.,
   VLAN-based service or VLAN bundle service.

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   (R4b) An EVC MAY be associated with several broadcast domains - e.g.,
   VLAN-aware bundle service.

   In the same way, a PE can aggregate many LSPs and PWs.  In the case
   of individual PWs per vES, typically a PW is associated with a single
   broadcast domain, but there is no restriction preventing the PW from
   carrying more than one VLAN if the PW is of type Raw mode.

   (R4c) A PW can be associated with a single broadcast domain - e.g.,
   VLAN-based service or VLAN bundle service.

   (R4d) An PW MAY be associated with several broadcast domains - e.g.,
   VLAN-aware bundle service.

3.4.  Designated Forwarder (DF) Election

   Section 8.5 of [RFC7432] describes the default procedure for DF
   election in EVPN which is also used in [RFC7623] and [RFC8214].
   [RFC8584] describes the additional procedures for DF election in
   EVPN.  These DF election procedures is performed at the granularity
   of (ESI, Ethernet Tag).  In case of a vES, the same EVPN default
   procedure for DF election also applies; however, at the granularity
   of (vESI, Ethernet Tag); where vESI is the virtual Ethernet Segment
   Identifier and the Ethernet Tag field is represented by and I-SID in
   PBB-EVPN and by a VLAN ID (VID) in EVPN.  As in [RFC7432], this
   default procedure for DF election at the granularity of (vESI,
   Ethernet Tag) is also referred to as "service carving".  With service
   carving, it is desirable to evenly partition the DFs for different
   vESes among different PEs, thus evenly distributing the traffic among
   different PEs.  The following list the requirements apply to DF
   election of vESes for (PBB-)EVPN.

   (R5a) A PE that supports vES function, MUST support a vES with m EVCs
   among n ENNIs belonging to p PEs in any arbitrary order; where n >= p
   >= m >=2.  For example, if there is a vES with 2 EVCs and there are 5
   ENNIs on 5 PEs (PE1 through PE5), then vES can be dual homed to PE2
   and PE4 and the DF election must be performed between PE2 and PE4.

   (Rbc) Each vES MUST be identified by its own virtual ESI (vESI).

3.5.  OAM

   To detect the failure of an individual EVC and perform DF election
   for its associated vES as the result of this failure, each EVC should
   be monitored independently.

   (R6a) Each EVC SHOULD be monitored for its health independently.

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   (R6b) A single EVC failure (among many aggregated on a single
   physical port/ENNI) MUST trigger DF election for its associated vES.

3.6.  Failure and Recovery

   (R7a) Failure and failure recovery of an EVC for a Single-homed vES
   SHALL NOT impact any other EVCs within its service instance or any
   other service instances.  In other words, for PBB-EVPN, it SHALL NOT
   trigger any MAC flushing both within its own I-SID as well as other
   I-SIDs.

   (R7b) In case of All-Active vES, failure and failure recovery of an
   EVC for that vES SHALL NOT impact any other EVCs within its service
   instance or any other service instances.  In other words, for PBB-
   EVPN, it SHALL NOT trigger any MAC flushing both within its own I-SID
   as well as other I-SIDs.

   (R7c) Failure and failure recovery of an EVC for a Single-Active vES
   SHALL impact only its own service instance.  In other words, for PBB-
   EVPN, MAC flushing SHALL be limited to the associated I-SID only and
   SHALL NOT impact any other I-SIDs.

   (R7d) Failure and failure recovery of an EVC for a Single-Active vES
   MUST only impact C-MACs associated with multi-homed device/network
   for that service instance.  In other words, MAC flushing MUST be
   limited to single service instance (I-SID in the case of PBB-EVPN)
   and only C-MACs for Single-Active multi-homed device/network.

3.7.  Fast Convergence

   Since many EVCs (and their associated vESes) are aggregated via a
   single physical port (e.g., ENNI), then the failure of that physical
   port impacts many vESes and triggers equally many ES route
   withdrawals.  Formulating, sending, receiving, and processing such
   large number of BGP messages can introduce delay in DF election and
   convergence time.  As such, it is highly desirable to have a
   mass-withdraw mechanism similar to the one in [RFC7432] for
   withdrawing many Ethernet A-D per ES routes.

   (R8a) There SHOULD be a mechanism equivalent to EVPN mass-withdraw
   such that upon an ENNI failure, only a single BGP message is needed
   to indicate to the remote PEs to trigger DF election for all impacted
   vES associated with that ENNI.

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4.  Solution Overview

   The solutions described in [RFC7432] and [RFC7623] are leveraged
   as-is with the modification that the ESI assignment is performed for
   an EVC or a group of EVCs or LSPs/PWs instead of a link or a group of
   physical links.  In other words, the ESI is associated with a virtual
   ES (vES), hereby referred to as vESI.

   For the EVPN solution, everything basically remains the same except
   for the handling of physical port failure where many vESes can be
   impacted.  Sections 5.1 and 5.3 below describe the handling of
   physical port/link failure for EVPN.  In a typical multi-homed
   operation, MAC addresses are learned behind a vES and are advertised
   with the ESI corresponding to the vES (i.e., vESI).  EVPN aliasing
   and mass-withdraw operations are performed with respect to vES
   identifier: the Ethernet A-D routes for these operations are
   advertised with vESI instead of ESI.

   For PBB-EVPN solution, the main change is with respect to the B-MAC
   address assignment which is performed similar to what is described in
   section 7.2.1.1 of [RFC7623] with the following refinements:

   *  One shared B-MAC address SHOULD be used per PE for the
      single-homed vESes.  In other words, a single B-MAC is shared for
      all single-homed vESes on that PE.

   *  One shared B-MAC address SHOULD be used per PE per physical port
      (e.g., ENNI) for the Single-Active vESes.  In other words, a
      single B-MAC is shared for all Single-Active vESes that share the
      same ENNI.

   *  One shared B-MAC address MAY be used for all Single-Active vESes
      on that PE.

   *  One B-MAC address SHOULD be used per set of EVCs representing an
      All-Active vES.  In other words, a single B-MAC address is used
      per vES for All-Active scenarios.

   *  A single B-MAC address MAY also be used per vES per PE for Single-
      Active scenarios.

4.1.  EVPN DF Election for vES

   The procedure for service carving for virtual Ethernet Segments is
   almost the same as the ones outlined in section 8.5 of [RFC7432] and
   [RFC8584] except for the fact that ES is replaced with vES.

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   For the sake of clarity and completeness, the default DF election
   procedure of [RFC7432] is repeated below with the necessary changes:

   1.  When a PE discovers the vESI or is configured with the vESI
       associated with its attached vES, it advertises an Ethernet
       Segment route with the associated ES-Import extended community
       attribute.

   2.  The PE then starts a timer (default value = 3 seconds) to allow
       the reception of Ethernet Segment routes from other PE nodes
       connected to the same vES.  This timer value MUST be same across
       all PEs connected to the same vES.

   3.  When the timer expires, each PE builds an ordered list of the IP
       addresses of all the PE nodes connected to the vES (including
       itself), in increasing numeric value.  Each IP address in this
       list is extracted from the "Originator Router's IP address" field
       of the advertised Ethernet Segment route.  Every PE is then given
       an ordinal indicating its position in the ordered list, starting
       with 0 as the ordinal for the PE with the numerically lowest IP
       address.  The ordinals are used to determine which PE node will
       be the DF for a given EVPN instance on the vES using the
       following rule: Assuming a redundancy group of N PE nodes, the PE
       with ordinal i is the DF for an EVPN instance with an associated
       Ethernet Tag value of V when (V mod N) = i.  It should be noted
       that using "Originator Router's IP address" field in the Ethernet
       Segment route to get the PE IP address needed for the ordered
       list, allows for a CE to be multi-homed across different ASes if
       such need ever arises.

   4.  The PE that is elected as a DF for a given EVPN instance will
       unblock traffic for that EVPN instance.  Note that the DF PE
       unblocks all traffic in both ingress and egress directions for
       Single-Active vES and unblocks multi-destination in egress
       direction for All-Active Multi-homed vES.  All non-DF PEs block
       all traffic in both ingress and egress directions for Single-
       Active vES and block multi-destination traffic in the egress
       direction for All-Active vES.

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   In case of an EVC failure, the affected PE withdraws its Virtual
   Ethernet Segment route if there are no more EVCs associated to the
   vES in the PE.  This will re-trigger the DF Election procedure on all
   the PEs in the Redundancy Group.  For PE node failure, or upon PE
   commissioning or decommissioning, the PEs re-trigger the DF Election
   procedure across all affected vESes.  In case of a Single-Active,
   when a service moves from one PE in the Redundancy Group to another
   PE because of DF re-election, the PE, which ends up being the elected
   DF for the service, MUST trigger a MAC address flush notification
   towards the associated vES if the multi-homing device is a bridge or
   the multi-homing network is an Ethernet bridged network.

   For LSP-based and PW-based vES, the non-DF PE SHOULD signal PW-status
   'standby' to the Aggregation PE (e.g., AG1 and AG2 in Figure 2), and
   a new DF PE MAY send an LDP MAC withdraw message as a MAC address
   flush notification.  It should be noted that the PW-status is
   signaled for the scenarios where there is a one-to-one mapping
   between EVI (EVPN instance) and the PW.

4.2.  Grouping and Route Coloring for vES

   Physical ports (e.g.  ENNI) which aggregate many EVCs are 'colored'
   to enable the grouping schemes described below.

   By default, the MAC address of the corresponding port (e.g.  ENNI) is
   used to represent the 'color' of the port, and the EVPN Router's MAC
   Extended Community defined in [RFC9135] is used to signal this color.

   The difference between coloring mechanism for EVPN and PBB-EVPN is
   that for EVPN, the extended community is advertised with the Ethernet
   A-D per ES route whereas for PBB-EVPN, the extended community may be
   advertised with the B-MAC route.

   The following sections describe Grouping Ethernet A-D per ES and
   Grouping B-MAC, will become crucial for port failure handling as seen
   in Section 5.3, Section 5.4, and Section 5.5 below.

4.2.1.  EVPN Route Coloring for vES

   When a PE discovers the vESI or is configured with the vESI
   associated with its attached vES, an Ethernet-Segment route and
   Ethernet A-D per ES route are generated using the vESI identifier.

   These Ethernet-Segment and Ethernet A-D per ES routes specific to
   each vES are colored with an attribute representing their association
   to a physical port (e.g.  ENNI).

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   The corresponding port 'color' is encoded in the EVPN Router's MAC
   Extended Community defined in [RFC9135] and advertised along with the
   Ethernet Segment and Ethernet A-D per ES routes for this vES.

   The PE also constructs a special Grouping Ethernet A-D per ES route
   which represents all the vES associated with the port (e.g.  ENNI).
   The corresponding port 'color' is encoded in the ESI field.  For this
   encoding, Type 3 ESI (Section 5 of [RFC7432]) is used with the MAC
   field set to the color (MAC address) of the port and the 3-octet
   local discriminator field set to 0xFFFFFF.

   The ESI label extended community (Section 7.5 of [RFC7432]) is not
   relevant to Grouping Ethernet A-D per ES route.  The label value is
   not used for encapsulating BUM (Broadcast, Unknown-unicast,
   Multicast) packets for any split-horizon function.  The ESI label
   extended community SHOULD NOT be added to Grouping Ethernet A-D per
   ES route and SHOULD be ignored on receiving PE.

   This Grouping Ethernet A-D per ES route is advertised with a list of
   Route Targets corresponding to the impacted service instances.  If
   the number of attached Route Targets exceeds the limit than can fit
   into a single route, then a set of Grouping Ethernet A-D per ES
   routes are advertised.

4.2.2.  PBB-EVPN Route Coloring for vES

   For PBB-EVPN, especially where there are large number of service
   instances (i.e., I-SIDs) associated with each EVC the PE MAY color
   each vES B-MAC route with an attribute representing their association
   to a physical port (e.g.  ENNI).

   The corresponding port 'color' is encoded in the EVPN Router's MAC
   Extended Community defined in [RFC9135] and advertised along with the
   B-MAC for this vES in PBB-EVPN.

   The PE MAY then also construct a special Grouping B-MAC route which
   represents all the vES associated with the port (e.g.  ENNI).  The
   corresponding port 'color' is encoded directly into this special
   Grouping B-MAC route.

5.  Failure Handling and Recovery

   There are several failure scenarios to consider such as:

   A:  CE uplink port failure

   B:  Ethernet Access Network failure

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   C:  PE access-facing port or link failure

   D:  PE node failure

   E:  PE isolation from IP/MPLS network

   [RFC7432], [RFC7623], and [RFC8214] solutions provide protection
   against such failures as described in the corresponding references.
   In the presence of virtual Ethernet Segments (vESes) in these
   solutions, besides the above failure scenarios, individual EVC
   failure is an additional scenario to consider.  Handling vES failure
   scenarios implies that individual EVCs or PWs need to be monitored
   and upon detection of failure or restoration of services, appropriate
   DF election and failure recovery mechanisms are executed.

   [RFC7023] is used for monitoring EVCs and upon failure detection of a
   given EVC, DF election procedure per Section 4.1 is executed.  For
   PBB-EVPN, some extensions are needed to handle the failure and
   recovery procedures of [RFC7623] to meet the above requirements.
   These extensions are described in the next section.

   [RFC4377] and [RFC6310] are used for monitoring the status of LSPs
   and/or PWs associated to vES.

                         B            D
                         ||           ||
                         \/           \/
                       +-----+
          +-----+      |     |       +---+
          | CE1 |EVC2--0=====0--ENNI1|   |   +-------+
          +-----+      |    =0--ENNI1|PE1|---|       |  +---+  +---+
          Cust. A      |   / |       |   |   |IP/MPLS|--|PE3|--|CE4|
          +-----+      |  /  |       +---+   |Network|  |   |  +---+
          |     |EVC2--0==   |               |       |  +---+
          | CE2 |      |     |       +---+   |       |
          |     |EVC3--0=====0--ENNI2|PE2|---|       |
          +-----+      |     |       |   |   +-------+
                       +-----+       +---+
                 /\                /\     /\
                 ||                ||     ||
                 A                 C      E

      Figure 4: Failure Scenarios A,B,C,D and E

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5.1.  EVC Failure Handling for Single-Active vES in EVPN

   In [RFC7432], when a DF PE connected to a Single-Active multi-homed
   Ethernet Segment loses connectivity to the segment, due to link or
   port failure, it signals to the remote PEs to invalidate all MAC
   addresses associated with that Ethernet Segment.  This is done by
   means of a mass-withdraw message, by withdrawing the Ethernet A-D per
   ES route.  It should be noted that for dual-homing use cases where
   there is only a single backup path, MAC invalidating can be avoided
   by the remote PEs as they can update their next hop associated with
   the affected MAC entries to the backup path per procedure described
   in section 8.2 of [RFC7432].

   In case of an EVC failure which impacts a single vES, this same EVPN
   procedure is used.  In this case, the mass-withdraw is conveyed by
   withdrawing the Ethernet A-D per vES route carrying the vESI
   representing the failed EVC.  The remote PEs upon receiving this
   message perform the same procedures outlined in section 8.2 of
   [RFC7432].

5.2.  EVC Failure Handling for Single-Active vES in PBB-EVPN

   In [RFC7432] when a PE connected to a Single-Active Ethernet Segment
   loses connectivity to the segment, due to link or port failure, it
   signals the remote PE to flush all C-MAC addresses associated with
   that Ethernet Segment.  This is done by updating the advertised a
   B-MAC route's MAC Mobility Extended community.

   In case of an EVC failure that impacts a single vES, if the above
   PBB-EVPN procedure is used, it results in excessive C-MAC flushing
   because a single physical port can support large number of EVCs (and
   their associated vESes) and thus updating the advertised B-MAC
   corresponding to the physical port, with MAC mobility Extended
   community, will result in flushing C-MAC addresses not just for the
   impacted EVC but for all other EVCs on that port.

   To reduce the scope of C-MAC flushing to only the impacted service
   instances (the service instance(s) impacted by the EVC failure), the
   PBB-EVPN C-MAC flushing needs to be adapted on a per service instance
   basis (i.e., per I-SID).  [I-D.ietf-bess-pbb-evpn-isid-cmacflush]
   introduces B-MAC/I-SID route where existing PBB-EVPN B-MAC route is
   modified to carry an I-SID in the "Ethernet Tag ID" field instead of
   NULL value.  This field indicates to the receiving PE, to flush all
   C-MAC addresses associated with that I-SID for that B-MAC.  This
   C-MAC flushing mechanism per I-SID SHOULD be used in case of EVC
   failure impacting a vES.  Since typically an EVC maps to a single
   broadcast domain and thus, a single service instance, the affected PE
   only needs to advertise a single B-MAC/I-SID route.  However, if the

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   failed EVC carries multiple VLANs each with its own broadcast domain,
   then the affected PE needs to advertise multiple B-MAC/I-SID routes -
   one for each VLAN (broadcast domain) - i.e., one for each I-SID.
   Each B-MAC/I-SID route basically instructs the remote PEs to perform
   flushing for C-MACs corresponding to the advertised B-MAC only for
   the advertised I-SID.

   The C-MAC flushing based on B-MAC/I-SID route works fine when there
   are only a few VLANs (e.g., I-SIDs) per EVC.  However if the number
   of I-SIDs associated with a failed EVC is large, then it is
   RECOMMENDED to assign a B-MAC per vES and upon EVC failure, the
   affected PE simply withdraws this B-MAC message to other PEs.

5.3.  Port Failure Handling for Single-Active vESes in EVPN

   When many EVCs are aggregated via a single physical port on a PE,
   where each EVC corresponds to a vES, then the port failure impacts
   all the associated EVCs and their corresponding vESes.  If the number
   of EVCs corresponding to the Single-Active vESes for that physical
   port is in thousands, then thousands of service instances are
   impacted.  Therefore, the propagation of failure in BGP needs to
   address all these impacted service instances.  In order to achieve
   this, the following extensions are added to the baseline EVPN
   mechanism:

   1.  The PE MAY color each Ethernet A-D per ES route for a given vES,
       as described in Section 4.2.1.  PE SHOULD use the physical port
       MAC by default.  The receiving PEs take note of this color and
       create a list of vESes for this color.

   2.  The PE MAY advertises a special Grouping Ethernet A-D per ES
       route for that color, which represents all the vES associated
       with the port.

   3.  Upon a port failure (e.g., ENNI failure), the PE MAY send a
       mass-withdraw message by withdrawing the Grouping Ethernet A-D
       per ES route.

   4.  When this message is received, the remote PE MAY detect the
       special vES mass-withdraw message by identifying the Grouping
       Ethernet A-D per ES route.  The remote PEs MAY then access the
       list created in (1) of the vESes for the specified color, and
       initiate locally MAC address invalidating procedures for each of
       the vESes in the list.

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   In scenarios where a logical ENNI is used the above procedure equally
   applies.  The logical ENNI is represented by a Grouping Ethernet A-D
   per ES where the Type 3 ESI and the 6 bytes used in the ENNI's ESI
   MAC address field is used as a color for vESes as described above and
   in Section 4.2.1.

5.4.  Port Failure Handling for Single-Active vESes in PBB-EVPN

   When many EVCs are aggregated via a single physical port on a PE,
   where each EVC corresponds to a vES, then the port failure impacts
   all the associated EVCs and their corresponding vESes.  If the number
   of EVCs corresponding to the Single-Active vESes for that physical
   port is in thousands, then thousands of service instances (I-SIDs)
   are impacted.  In such failure scenarios, the following two MAC
   flushing mechanisms per [RFC7623] can be performed.

   1.  If the MAC address of the physical port is used for PBB
       encapsulation as B-MAC SA, then upon the port failure, the PE
       MUST use the EVPN MAC route withdrawal message to signal the
       flush.

   2.  If the PE shared MAC address is used for PBB encapsulation as
       B-MAC SA, then upon the port failure, the PE MUST re-advertise
       this MAC route with the MAC Mobility Extended Community to signal
       the flush.

   The first method is recommended because it reduces the scope of
   flushing the most.

   As noted above, the advertisement of the extended community along
   with B-MAC route for coloring purposes is optional and only
   recommended when there are many vESes per physical port and each vES
   is associated with very large number of service instances (i.e.,
   large number of I-SIDs).

   If there are large number of service instances (i.e., I-SIDs)
   associated with each EVC, and if there is a B-MAC assigned per vES as
   recommended in the above section, then to handle port failure
   efficiently, the following extensions are added to the baseline PBB-
   EVPN mechanism:

   1.  Each vES MAY be colored with a MAC address representing the
       physical port like the coloring mechanism for EVPN.  In other
       words, each B-MAC representing a vES is advertised with the
       'color' of the physical port per Section 4.2.2.  The receiving
       PEs take note of this color being advertised along with the B-MAC
       route and for each such color, create a list of vESes associated
       with this color.

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   2.  The PE MAY advertise a special Grouping B-MAC route for that
       color (consisting by default of port MAC address), which
       represents all the vES associated with the port.

   3.  Upon a port failure (e.g., ENNI failure), the PE MAY send a
       mass-withdraw message by withdrawing the Grouping B-MAC route.

   4.  When this message is received, the remote PE MAY detect the
       special vES mass-withdraw message by identifying the Grouping
       B-MAC route.  The remote PEs MAY then access the list created in
       (1) for the specified color, and flush all C-MACs associated with
       the failed physical port.

5.5.  Fast Convergence in (PBB-)EVPN

   As described above, when many EVCs are aggregated via a physical port
   on a PE, and where each EVC corresponds to a vES, then the port
   failure impacts all the associated EVCs and their corresponding
   vESes.  Two actions must be taken as the result of such port failure:

   *  For EVPN initiate mass-withdraw procedure for all vESes associated
      with the failed port to invalidate MACs and for PBB-EVPN flush all
      C-MACs associated with the failed port across all vESes and the
      impacted I-SIDs

   *  DF election for all impacted vESes associated with the failed port

   Section 5.3 already describes how to perform mass-withdraw for all
   affected vESes and invalidating MACs using a single BGP withdrawal of
   the Grouping Ethernet A-D per ES route.  Section 5.4 describes how to
   only flush C-MAC address associated with the failed physical port
   (e.g., optimum C-MAC flushing) as well as, optionally, the withdrawal
   of a Grouping B-MAC route.

   This section describes how to perform DF election in the most optimal
   way - e.g., to trigger DF election for all impacted vESes (which can
   be very large) among the participating PEs via a single BGP message
   as opposed to sending large number of BGP messages (one per vES).
   This section assumes that the MAC flushing mechanism described in
   Section 5.4 is used and route coloring is used.

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                     +-----+
          +----+     |     |       +---+
          | CE1|AC1--0=====0--ENNI1|   |  +-------+
          |    |AC2--0     |       |PE1|--|       |
          +----+     |\  ==0--ENNI2|   |  |       |
                     | \/  |       +---+  |       |
                     | /\  |              |IP/MPLS|
          +----+     |/  \ |       +---+  |Network|   +---+  +---+
          | CE2|AC4--0    =0--ENNI3|   |  |       |---|PE4|--|CE4|
          |    |AC4--0=====0--ENNI3|PE2|--|       |   +---+  +---+
          +----+     | ====0--ENNI3|   |  |       |
                     |/    |       +---+  |       |
                     0     |              |       |
          +----+    /|     |       +---+  |       |
          | CE3|AC5- |     |       |PE3|--|       |
          |    |AC6--0=====0--ENNI4|   |  +-------+
          +----+     |     |       +---+
                     +-----+

      Figure 5: Fast Convergence Upon ENNI Failure

   The procedure for coloring vES Ethernet Segment routes is described
   in Section 4.2.  The following describes the procedure for fast
   convergence for DF election using these colored routes:

   1.  When a vES is configured, the PE SHOULD advertise the Ethernet
       Segment route for this vES with a color corresponding to the
       physical port.

   2.  All receiving PEs (in the redundancy group) SHOULD take note of
       this color and create a list of vESes for this color.

   3.  Recall, that the PE SHOULD also advertise a Grouping Ethernet A-D
       per ES (for EVPN) and a Grouping B-MAC (for PBB-EVPN)
       representing this color and vES grouping.

   4.  Upon a port failure (e.g., ENNI failure), the PE SHOULD withdraw
       this previously advertised Grouping Ethernet A-D per ES or
       Grouping B-MAC associated with the failed port.  The PE SHOULD
       prioritize sending these Grouping routes withdraw message over
       individual vES route withdrawal messages of impacted vESes.  For
       example, in Figure 5, when the physical port associated with
       ENNI3 fails on PE2, it withdraws the previously advertised
       Grouping Ethernet A-D per ES route.  When other multi-homing
       PEs(i.e., PE1 and PE3) receives this withdrawal message, they

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       know that the vESes associated with CE1 and CE3 are impacted
       (because of the associated color), and thus to initiate DF
       election procedure for these vESes.  Furthermore, the remote PEs
       (i.e., PE4) upon receiving this withdrawal message, it intiates
       failover procedure for vESes associated with CE1, CE3, and
       switches over to the other PE for each vES redundancy group.

   5.  On reception of Grouping Ethernet A-D per ES or Grouping B-MAC
       route withdrawal, other PEs in the redundancy group SHOULD
       initiate DF election procedures across all their affected vESes.

   6.  The PE with the physical port failure (ENNI failure), SHOULD send
       vES route withdrawal for every impacted vES.  The other PEs upon
       receiving these messages, clear up their BGP tables.  It should
       be noted the vES route withdrawal messages are not used for
       executing DF election procedures by the receiving PEs when
       Grouping Ethernet A-D per ES or Grouping B-MAC withdrawal has
       been previously received.

6.  Acknowledgements

   The authors would like to thank Mei Zhang, Jose Liste, and
   Luc Andre Burdet for their reviews of this document and feedback.

7.  Security Considerations

   All the security considerations in [RFC7432] and [RFC7623] apply
   directly to this document because this document leverages the control
   and data plane procedures described in those documents.

   This document does not introduce any new security considerations
   beyond that of [RFC7432] and [RFC7623] because advertisements and
   processing of Ethernet Segment route for vES in this document follows
   that of physical ES in those RFCs.

8.  IANA Considerations

   This document requests no actions from IANA.

9.  References

9.1.  Normative References

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   [I-D.ietf-bess-pbb-evpn-isid-cmacflush]
              Rabadan, J., Sathappan, S., Nagaraj, K., Miyake, M., and
              T. Matsuda, "PBB-EVPN ISID-based C-MAC-Flush", Work in
              Progress, Internet-Draft, draft-ietf-bess-pbb-evpn-isid-
              cmacflush-08, 5 July 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bess-
              pbb-evpn-isid-cmacflush-08>.

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

   [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>.

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

   [RFC8214]  Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
              Rabadan, "Virtual Private Wire Service Support in Ethernet
              VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
              <https://www.rfc-editor.org/info/rfc8214>.

   [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>.

9.2.  Informative References

   [MEF63]    Metro Ethernet Forum, MEF., "[MEF6.3]: Subscriber Ethernet
              Services Definitions", 2019.

   [RFC4377]  Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
              Matsushima, "Operations and Management (OAM) Requirements
              for Multi-Protocol Label Switched (MPLS) Networks",
              RFC 4377, DOI 10.17487/RFC4377, February 2006,
              <https://www.rfc-editor.org/info/rfc4377>.

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   [RFC6310]  Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
              Nadeau, T., and Y. Stein, "Pseudowire (PW) Operations,
              Administration, and Maintenance (OAM) Message Mapping",
              RFC 6310, DOI 10.17487/RFC6310, July 2011,
              <https://www.rfc-editor.org/info/rfc6310>.

   [RFC7023]  Mohan, D., Ed., Bitar, N., Ed., Sajassi, A., Ed., DeLord,
              S., Niger, P., and R. Qiu, "MPLS and Ethernet Operations,
              Administration, and Maintenance (OAM) Interworking",
              RFC 7023, DOI 10.17487/RFC7023, October 2013,
              <https://www.rfc-editor.org/info/rfc7023>.

   [RFC7080]  Sajassi, A., Salam, S., Bitar, N., and F. Balus, "Virtual
              Private LAN Service (VPLS) Interoperability with Provider
              Backbone Bridges", RFC 7080, DOI 10.17487/RFC7080,
              December 2013, <https://www.rfc-editor.org/info/rfc7080>.

   [RFC7209]  Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
              Henderickx, W., and A. Isaac, "Requirements for Ethernet
              VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,
              <https://www.rfc-editor.org/info/rfc7209>.

   [RFC8584]  Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
              J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
              VPN Designated Forwarder Election Extensibility",
              RFC 8584, DOI 10.17487/RFC8584, April 2019,
              <https://www.rfc-editor.org/info/rfc8584>.

Authors' Addresses

   Ali Sajassi
   Cisco Systems
   Email: sajassi@cisco.com

   Patrice Brissette
   Cisco Systems
   Email: pbrisset@cisco.com

   Rick Schell
   Verizon
   Email: richard.schell@verizon.com

   John E Drake
   Juniper
   Email: jdrake@juniper.net

Sajassi, et al.           Expires 26 March 2024                [Page 23]
Internet-Draft        EVPN Virtual Ethernet Segment       September 2023

   Jorge Rabadan
   Nokia
   Email: jorge.rabadan@nokia.com

Sajassi, et al.           Expires 26 March 2024                [Page 24]