



Internet Engineering Task Force (IETF)                   A. Sajassi, Ed.
Request for Comments: 9744                                  P. Brissette
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                                J. Uttaro
                                                              Individual
                                                                J. Drake
                                                             Independent
                                                              S. Boutros
                                                                   Ciena
                                                              J. Rabadan
                                                                   Nokia
                                                              March 2025


 EVPN Virtual Private Wire Service (VPWS) Flexible Cross-Connect (FXC)
                                Service

Abstract

   This document describes a new EVPN Virtual Private Wire Service
   (VPWS) service type specifically for multiplexing multiple attachment
   circuits across different Ethernet Segments (ESs) and physical
   interfaces into a single EVPN-VPWS service tunnel and still providing
   Single-Active and All-Active multi-homing.  This new service is
   referred to as the EVPN-VPWS Flexible Cross-Connect (FXC) service.
   This document specifies a solution based on extensions to EVPN-VPWS
   (RFC 8214), which in turn is based on extensions to EVPN (RFC 7432).
   Therefore, a thorough understanding of RFCs 7432 and 8214 are
   prerequisites for this document.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9744.

Copyright Notice

   Copyright (c) 2025 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 Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Terminology
     1.2.  Requirements Language
   2.  Requirements
   3.  Solution
     3.1.  VPWS Service Identifiers
     3.2.  Default Flexible Cross-Connect
       3.2.1.  Multi-homing
     3.3.  VLAN-Signaled FXC
       3.3.1.  Local Switching
     3.4.  Service Instantiation
   4.  BGP Extensions
   5.  Failure Scenarios
     5.1.  EVPN-VPWS Service Failure
     5.2.  Attachment Circuit Failure
     5.3.  PE Port Failure
     5.4.  PE Node Failure
   6.  Security Considerations
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Contributors
   Authors' Addresses

1.  Introduction

   [RFC8214] describes a solution to deliver point-to-point (P2P)
   services using BGP constructs defined in [RFC7432].  It delivers this
   P2P service between a pair of Attachment Circuits (ACs), where an AC
   on a PE can represent a port, a VLAN on a port, or a group of VLANs
   on a port.  It also leverages multi-homing and fast convergence
   capabilities of [RFC7432] in delivering these VPWS services.  Multi-
   homing capabilities include the support of Single-Active and All-
   Active redundancy mode, and fast convergence is provided using a
   "mass withdrawal" message in control plane and fast protection
   switching using prefix-independent convergence in a data plane upon
   node or link failure [BGP-PIC].  Furthermore, the use of EVPN BGP
   constructs eliminates the need for multi-segment pseudowire auto-
   discovery and signaling if the VPWS service need to span across
   multiple Autonomous Systems (ASes) [RFC5659].

   Service providers have a very large number of ACs (in millions) that
   need to be backhauled across their MPLS/IP network.  These ACs may or
   may not require tag manipulation (e.g., VLAN translation).  These
   service providers want to multiplex a large number of ACs across
   several physical interfaces spread across one or more PEs (e.g.,
   several ESs) onto a single VPWS service tunnel in order to a) reduce
   the number of EVPN service labels associated with EVPN-VPWS service
   tunnels and thus the associated Operations, Administration, and
   Maintenance (OAM) monitoring and b) reduce EVPN BGP signaling (e.g.,
   not to signal each AC as it is the case in [RFC8214]).

   Service providers want the above functionality without sacrificing
   any of the capabilities of [RFC8214] including Single-Active and All-
   Active multi-homing and fast convergence.

   This document specifies a solution based on extensions to EVPN-VPWS
   [RFC8214] to meet the above requirements.  Furthermore, [RFC8214] is
   itself based on extensions to EVPN [RFC7432].  Therefore, a thorough
   understanding of [RFC7432] and [RFC8214] are prerequisites for this
   document.

1.1.  Terminology

   AC:  Attachment Circuit

   ES:  Ethernet Segment

   ESI:  Ethernet Segment Identifier

   EVI:  EVPN Instance Identifier

   EVPN:  Ethernet Virtual Private Network

   Ethernet A-D:  Ethernet Auto-Discovery (per EVI or per Ethernet A-D
      per ESI routes, as defined in [RFC7432] and [RFC8214])

   FXC:  Flexible Cross-Connect

   MAC:  Media Access Control

   MPLS:  Multiprotocol Label Switching

   OAM:  Operations, Administration, and Maintenance

   PE:  Provider Edge

   VCCV:  Virtual Circuit Connectivity Verification

   VID:  VLAN ID

   VPWS:  Virtual Private Wire Service

   VRF:  VPN Routing and Forwarding

   IP-VRF:  VPN Routing and Forwarding for IP lookup

   MAC-VRF:  VPN Routing and Forwarding for MAC lookup

   VID-VRF:  VPN Routing and Forwarding for normalized VID lookup

   VPWS Service Tunnel:  It is represented by a pair of EVPN service
      labels associated with a pair of endpoints.  Each label is
      downstream assigned and advertised by the disposition PE through
      an Ethernet A-D per EVI route.  The downstream label identifies
      the endpoint on the disposition PE.  A VPWS service tunnel can be
      associated with many VPWS service identifiers where each
      identifier is a normalized VID.

   Single-Active Redundancy Mode:  When a device or a network is multi-
      homed to two or more PEs and when only a single PE in such
      redundancy group can forward traffic to/from the multi-homed
      device or network for a given VLAN, then such multi-homing or
      redundancy is referred to as "Single-Active".

   All-Active Redundancy Mode:  When a device or a network is multi-
      homed to two or more PEs and when all PEs in such redundancy group
      can forward traffic to/from the multi-homed device or network for
      a given VLAN, then such multi-homing or redundancy is referred to
      as "All-Active".

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Requirements

   Two of the main motivations for service providers seeking a new
   solution are: 1) to reduce the number of VPWS service tunnels by
   multiplexing a large number of ACs across different physical
   interfaces instead of having one VPWS service tunnel per AC and 2) to
   reduce the signaling of ACs as much as possible.  Besides these two
   requirements, they also want the multi-homing and fast convergence
   capabilities of [RFC8214].

   In [RFC8214], a PE signals an AC indirectly by first associating that
   AC to a VPWS service tunnel (e.g., a VPWS service instance) and then
   signaling the VPWS service tunnel via an Ethernet A-D per EVI route
   with the Ethernet Tag field set to a 24-bit VPWS service instance
   identifier (which is unique within the EVI) and the ESI field set to
   a 10-octet identifier of the ES corresponding to that AC.

   Therefore, a PE device that receives such EVPN routes can associate
   the VPWS service tunnel to the remote ES using the ESI field.
   Additionally, when the remote ES fails and the PE receives the "mass
   withdrawal" message associated with the failed ES per [RFC7432], a PE
   device can quickly update its next-hop adjacency list (adjacency
   list) for all VPWS service tunnels sharing the ESI field and achieve
   fast convergence for multi-homing scenarios.  Even if fast
   convergence were not needed, there would still be a need for
   signaling each AC failure (via its corresponding VPWS service tunnel)
   associated with the failed ES so that the adjacency list gets updated
   and the packets are sent to a backup PE (in case of Single-Active
   multi-homing) or to other PEs in the redundancy group (in case of
   All-Active multi-homing).  In the absence of updating the adjacency
   list properly, the traffic for that VPWS service tunnel will be
   dropped by the egress PE with a failed ES/AC.

   When a single VPWS service tunnel carries multiple ACs across various
   ESs (physical interfaces) without signaling the ACs via EVPN BGP to
   remote PE devices, those remote PE devices lack the information to
   associate the received ES with these ACs or with their local ACs.
   They also lack the association between the VPWS service tunnel (e.g.,
   EVPN service label) and the far-end ACs.  This means that, while the
   remote PEs can associate their local ACs with the VPWS service
   tunnel, they cannot make similar associations for the far-end ACs.

   Consequently, in case of a connectivity failure to the ES, the remote
   PEs are unable to redirect traffic via another multi-homing PE to
   that ES.  In other words, even if an ES failure is signaled via EVPN
   to the remote PE devices, they cannot effectively respond because
   they do not know the relationship between the remote ES, the remote
   ACs, and the VPWS service tunnel.

   To address this issue when multiplexing a large number of ACs onto a
   single VPWS service tunnel, two mechanisms have been developed: one
   to support VPWS services between two single-homed endpoints and
   another one to support VPWS services where one of the endpoints is
   multi-homed.

   For single-homed endpoints, it is acceptable not to signal each AC in
   BGP because, in the event of a connection failure to the ES, there is
   no alternative path to that endpoint.  However, the implication of
   not signaling an AC failure is that the traffic destined for the
   failed AC is sent over the MPLS/IP core and then discarded at the
   destination PE, thereby potentially wasting network resources.

   This waste of network resources during a connection failure may be
   transient, as it can be detected and prevented at the application
   layer in certain cases.  Section 3.2 outlines a solution for such
   single-homing VPWS services.

   For VPWS services where one of the endpoints is multi-homed, there
   are two options:

   1.  Signal each AC via BGP, allowing the adjacency list to be updated
       upon a failure affecting those ACs.  This solution is described
       in Section 3.3 and is referred to as the "VLAN-signaled FXC
       service".

   2.  Bundle several ACs on an ES together per destination endpoint
       (e.g., ES, MAC-VRF, etc.) and associate such a bundle with a
       single VPWS service tunnel.  This approach is similar to the VLAN
       bundle service interface described in [RFC8214].  This solution
       is described in Section 3.2.1.

3.  Solution

   This section specifies how to provide a new VPWS service between two
   PE devices where a large number of ACs (such as VLANs) that span
   across multiple ESs (physical interfaces) on each PE are multiplexed
   onto a single P2P EVPN service tunnel.  Since the multiplexing
   involves several physical interfaces, there can be overlapping VLAN
   IDs (VIDs) across these interfaces.  In such cases, the VIDs must be
   translated into unique VIDs to prevent collisions.  Furthermore, if
   the number of VLANs being multiplexed onto a single VPWS service
   tunnel exceeds 4095, then a single tag to double tag translation must
   be performed.  This translation of VIDs into unique VIDs (either
   single or double) results in a "normalized VID".

   When a single normalized VID is used, the lower 12 bits of the
   Ethernet Tag ID field in EVPN routes MUST be set to that VID.  When a
   double normalized VID is used, the lower 12 bits of the Ethernet Tag
   ID field MUST be set to the inner VID, while the higher 12 bits are
   set to the outer VID.  24-bit VPWS service instance identifiers
   [RFC8214] as well as 12-bit VPWS service instance identifiers
   representing normalized VIDs MUST be right-aligned.

   Since there is only a single EVPN-VPWS service tunnel associated with
   many normalized VIDs (either single or double) across multiple
   physical interfaces, an MPLS lookup at the disposition PE is no
   longer sufficient to forward the packet to the correct egress
   endpoint or interface.  Therefore, in addition to an EVPN label
   lookup corresponding to the VPWS service tunnel, a VID lookup (either
   single or double) is also required.  At the disposition PE, the EVPN
   label lookup identifies a VID-VRF, and the lookup of the normalized
   VIDs within that table identifies the appropriate egress endpoint or
   interface.  The tag manipulation (translation from normalized VIDs to
   the local VID) SHOULD be performed either as part of the VID table
   lookup or at the egress interface itself.

   Since the VID lookup (single or double) needs to be performed at the
   disposition PE, VID normalization MUST be completed prior to MPLS
   encapsulation on the ingress PE.  This requires that both the
   imposition and disposition PE devices be capable of VLAN tag
   manipulation, such as rewriting (single or double), adding, or
   deleting (single or double) at their endpoints (e.g., their ESs, MAC-
   VRFs, IP-VRFs, etc.).  Operators should be informed of potential
   trade-offs from a performance standpoint, compared to typical
   pseudowire processing.

3.1.  VPWS Service Identifiers

   In [RFC8214], a unique value identifying the service is signaled in
   the context of each PE's EVI.  The 32-bit Ethernet Tag ID field MUST
   be set to this VPWS service instance identifier value.  Translation
   at an Autonomous System Border Router (ASBR) is needed if re-
   advertising to another AS affects uniqueness.

   For FXC, this same Ethernet Tag ID field value is an identifier that
   may represent:

   *  VLAN Bundle Service Interface: a unique value for a group of VLANs

   *  VLAN-Aware Bundle Service Interface: a unique value for individual
      VLANs and is considered the same as the normalized VID

   Both the VPWS service instance identifier and normalized VID are
   carried in the Ethernet Tag ID field of the Ethernet A-D per EVI
   route.  For FXC, in the case of a 12-bit ID, the VPWS service
   instance identifier is the same as the single-tag normalized VID and
   will be the same on both VPWS service endpoints.  Similarly in the
   case of a 24-bit ID, the VPWS service instance identifier is the same
   as the double-tag normalized VID.

3.2.  Default Flexible Cross-Connect

   In this mode of operation, many ACs across several ESs are
   multiplexed into a single EVPN-VPWS service tunnel represented by a
   single VPWS service ID.  This is the default mode of operation for
   FXC, and the participating PEs do not need to signal the VLANs
   (normalized VIDs) in EVPN BGP.

   Regarding the data plane aspects of this solution, the imposition PE
   performs VID normalization, and the disposition PE carries out VID
   lookup and translation.  Both imposition and disposition PE devices
   MUST be aware of the VLANs through configuration.  There should
   ideally be a single point-to-point (P2P) EVPN-VPWS service tunnel
   between a pair of PEs for a specific set of ACs.

   As previously mentioned, because the EVPN-VPWS service tunnel is
   employed to multiplex ACs across various ESs or physical interfaces,
   the EVPN label alone is not sufficient for accurate forwarding of the
   received packets over the MPLS/IP network to egress interfaces.
   Therefore, normalized VID lookup is REQUIRED in the disposition
   direction to forward packets to their proper egress endpoints; the
   EVPN label lookup identifies a VID-VRF, and a subsequent normalized
   VID lookup in that table identifies the egress interface.

   In this solution, for each PE, the single-homing ACs represented by
   their normalized VIDs are associated with a single VPWS service
   instance within a specific EVI.  The generated EVPN route is an
   Ethernet A-D per-EVI route with an ESI of 0, the Ethernet Tag field
   is set to a VPWS service instance ID, and the MPLS label field is set
   to a dynamically generated EVPN service label representing the EVPN-
   VPWS service tunnel.  This route is sent with a Route Target (RT)
   that represents the EVI, which can be auto-generated from the EVI
   according to Section 5.1.2.1 of [RFC8365].  Additionally, this route
   is sent with the EVPN Layer 2 Attributes Extended Community defined
   in Section 3.1 of [RFC8214] with two new flags (outlined in
   Section 4) that indicate: 1) the VPW service tunnel (set to default
   Flexible Cross-Connect) and 2) the normalized VID type (set to
   normalized single VID or double VID).  The receiving PE uses these
   new flags for a consistency check and MAY generate an alarm if it
   detects inconsistencies, but it will not disrupt the VPWS service.

   It should be noted that in this mode of operation, a single Ethernet
   A-D per-EVI route is transmitted upon the configuration of the first
   AC with the normalized VID.  As additional ACs are configured and
   associated with this EVPN-VPWS service tunnel, the PE does not
   advertise any additional EVPN BGP routes and only locally associates
   these ACs with the pre-established VPWS service tunnel.

3.2.1.  Multi-homing

   The default FXC mode can also be used for multi-homing.  In this
   mode, a group of normalized VIDs representing ACs on a single ES, all
   destined to a single endpoint, are multiplexed into a single EVPN-
   VPWS service tunnel, which is identified by a unique VPWS service ID.
   When employing the default FXC mode for multi-homing, rather than
   using a single EVPN-VPWS service tunnel, there may be multiple
   service tunnels per pair of PEs.  Specifically, there is one tunnel
   for each group of VIDs per pair of PEs, and there can be many such
   groups between a pair of PEs, resulting in numerous EVPN service
   tunnels.

3.3.  VLAN-Signaled FXC

   In this mode of operation, similar to the default FXC mode described
   in Section 3.2, many normalized VIDs representing ACs across several
   ESs and interfaces are multiplexed into a single EVPN-VPWS service
   tunnel.  However, this single tunnel is represented by multiple VPWS
   service IDs (one per normalized VID), and these normalized VIDs are
   signaled using EVPN BGP.

   In this solution, on each PE, the multi-homing ACs represented by
   their normalized VIDs are configured with a single EVI.  There is no
   need to configure a separate VPWS service instance ID in here, as it
   corresponds to the normalized VID.  For each normalized VID on each
   ES, the PE generates an Ethernet A-D per-EVI route where the ESI
   field represents the ES ID, the Ethernet Tag field is set to the
   normalized VID, and the MPLS label field is set to a dynamically
   generated EVPN label representing the P2P EVPN service tunnel.  This
   label is the same for all ACs multiplexed into a single EVPN-VPWS
   service tunnel.  This route is sent with an RT representing the EVI.
   As before, this RT can be auto-generated from the EVI per
   Section 5.1.2.1 of [RFC8365].  Additionally, this route includes the
   EVPN Layer 2 Attributes Extended Community defined in Section 3.1 of
   [RFC8214] with two new flags (outlined in Section 4) that indicate:
   1) this VPWS service tunnel for VLAN-signaled FXC and 2) the
   normalized VID type (single versus double).  The receiving PE uses
   these new flags for a consistency check and may generate an alarm if
   it detects inconsistency, but it will not disrupt the VPWS service.

   It should be noted that in this mode of operation, the PE sends a
   single Ethernet A-D per-EVI route for each AC that is configured.
   Each normalized VID that is configured per ES results in generation
   of an Ethernet A-D per EVI.

   This mode of operation enabled automatic cross-checking of normalized
   VIDs used for Ethernet Virtual Private Line (EVPL) services because
   these VIDs are signaled in EVPN BGP.  For instance, if the same
   normalized VID is configured on three PE devices (instead of two) for
   the same EVI, then when a PE receives the second remote Ethernet A-D
   per EVI route, it generates an error message unless the two Ethernet
   A-D per EVI routes include the same ESI.  Such cross-checking is not
   feasible in the default FXC mode because the normalized VIDs are not
   signaled.

3.3.1.  Local Switching

   When cross-connection occurs between two ACs belonging to two multi-
   homed ESs on the same set of multi-homing PEs, the forwarding between
   the two ACs must be performed locally during normal operation (e.g.,
   in absence of a local link failure).  This means that traffic between
   the two ACs MUST be locally switched within the PE.

   In terms of control plane processing, this means that when the
   receiving PE processes an Ethernet A-D per-EVI route whose ESI is a
   local ESI, the PE does not modify its forwarding state based on the
   received route.  This approach ensures that local switching takes
   precedence over forwarding via the MPLS/IP network.  This method of
   prioritizing locally switched traffic aligns with the baseline EVPN
   principles described in [RFC7432], where locally switched preference
   is specified for MAC/IP routes.

   In such scenarios, the Ethernet A-D per-EVI route should be
   advertised with the MPLS label either associated with the destination
   AC or with the destination ES in order to avoid any ambiguity in
   forwarding.  In other words, the MPLS label cannot represent the same
   VID-VRF outlined in Section 3.3, as the same normalized VID can be
   reachable via two ESs.  In the case of using an MPLS label per
   destination AC, this approach can also be applied to VLAN-based VPWS
   or VLAN bundle VPWS services as per [RFC8214].

3.4.  Service Instantiation

   The V field defined in Section 4 is OPTIONAL.  However, if
   transmitted, its value may indicate an error condition that could
   lead to operational issues.  In such cases, merely notifying the
   operator of an error is insufficient; the VPWS service tunnel must
   not be established.

   If both endpoints of a VPWS tunnel are signaling a matching
   normalized VID in the control plane, but one is operating in single-
   tag mode and the other in double-tag mode, then the signaling of the
   V-bit facilitates the detection and prevention of this tunnel's
   instantiation.

   If single VID normalization is signaled in the Ethernet Tag ID field
   (12 bits), yet the data plane is operating based on double tags, the
   VID normalization applies only to the outer tag.  Conversely, if
   double VID normalization is signaled in the Ethernet Tag ID field (24
   bits), VID normalization applies to both the inner and outer tags.

4.  BGP Extensions

   This document uses the EVPN Layer 2 Attributes Extended Community as
   defined in [RFC8214] with two additional flags incorporated into this
   Extended Community (EC) as detailed below.  This EC is sent with
   Ethernet A-D per-EVI route per Section 3 and SHOULD be sent for both
   Single-Active and All-Active redundancy modes.

       +-------------------------------------------+
       | Type (0x06) / Sub-type (0x04) (2 octets)  |
       +-------------------------------------------+
       | Control Flags (2 octets)                  |
       +-------------------------------------------+
       | L2 MTU (2 octets)                         |
       +-------------------------------------------+
       | Reserved (2 octets)                       |
       +-------------------------------------------+

                            1 1 1 1 1 1
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | MBZ           | V | M | |C|P|B|    (MBZ = MUST Be Zero)
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The following bits in the Control Flags are defined; the remaining
   bits MUST be set to zero when sending and MUST be ignored when
   receiving this community.

         +=======+==============================================+
         | Name  | Meaning                                      |
         +=======+==============================================+
         | B,P,C | per definition in [RFC8214]                  |
         +-------+----------------------------------------------+
         | M     | 00 mode of operation as defined in [RFC8214] |
         |       +----------------------------------------------+
         |       | 01 VLAN-Signaled FXC                         |
         |       +----------------------------------------------+
         |       | 10 Default FXC                               |
         +-------+----------------------------------------------+
         | V     | 00 operating per [RFC8214]                   |
         |       +----------------------------------------------+
         |       | 01 single-VID normalization                  |
         |       +----------------------------------------------+
         |       | 10 double-VID normalization                  |
         +-------+----------------------------------------------+

                                 Table 1

   The M and V fields are OPTIONAL.  The M field is ignored at reception
   for forwarding purposes and is used for error notifications.

5.  Failure Scenarios

   The two following examples analyze the failure scenarios.

   The first scenario is a default Flexible Cross-Connect with a multi-
   homing solution, and it is depicted in Figure 1.  In this case, VID
   normalization is performed, and a single Ethernet A-D per-EVI route
   is sent for the bundle of ACs on an ES.  That is, PE1 will advertise
   two Ethernet A-D per-EVI routes: The first one will identify the ACs
   on port p1's ES, and the second one will identify the AC2 in port
   p2's ES.  Similarly, PE2 will advertise two Ethernet A-D per-EVI
   routes.

                    N.VID 1,2,3 +---------------------+
                            PE1 |                     |
                        +---------+     IP/MPLS       |
      +-----+ VID1   p1 | +-----+ | sv.T1             +
      | CE1 |-------------| FXC |======+            PE3         +-----+
      |     |        /\ | |     | |    \     +----------+    +--| CE3 |
      +-----+\      +||---|     | sv.T2 \    |          |  1/   |     |
          VID3\    / ||---|     |=====+  \   | +-----+  |  /    +-----+
               \  // \/ | +-----+ |    \  +====| FXC |----+
                \ /  p2 +---------+     +======|     |  |   2   +-----+
                /\                           | |     |----------| CE4 |
               / /\    +---------+       +=====|     |  |       |     |
              / /  \p3 | +-----+ sv.T3  / +====|     |  |       +-----+
       VIDs1,2 /    +----| FXC |=======+ /   | |     |---+
      +-----+ /   /\   | |     | |      /    | +-----+  |\3    +-----+
      | CE2 |-----||---| |     | sv.T4 /     |          | \    | CE5 |
      |     |-----||---| |     |======+      +----------+  +---|     |
      +--VIDs3,4  \/   | +-----+ |                  |          +-----+
                  p4   +---------+                  |
                            PE2 |                   |
                    N.VID 1,2,3 +-------------------+

                  Figure 1: Default Flexible Cross-Connect

   The second scenario, depicted in Figure 2, illustrates the VLAN-
   signaled FXC mode with multi-homing.  In this example:

   *  CE1 is connected to PE1 and PE2 via (port,VID)=(p1,1) and (p3,3),
      respectively.  CE1's VIDs are normalized to value 1 on both PEs,
      and CE1 is cross-connected to CE3's VID 1 at the remote end.

   *  CE2 is connected to PE1 and PE2 via ports p2 and p4, respectively:

      -  The combinations (p2,1) and (p4,3) identify the ACs used to
         cross-connect CE2 to CE4's VID 2 and are normalized to value 2.

      -  The combinations (p2,2) and (p4,4) identify the ACs used to
         cross-connect CE2 to CE5's VID 3 and are normalized to value 3.

   In this scenario, PE1 and PE2 advertise an Ethernet A-D per EVI route
   for each normalized VID (values 1, 2, and 3).  However, only two VPWS
   Service Tunnels are required: 1) VPWS Service Tunnel 1 (sv.T1)
   between PE1's FXC and PE3's FXC and 2) VPWS Service Tunnel 2 (sv.T2)
   between PE2's FXC and PE3's FXC.

                    N.VID 1,2,3 +---------------------+
                            PE1 |                     |
                        +---------+     IP/MPLS       |
       +-----+ VID1  p1 | +-----+ |                   +
       | CE1 |------------| FXC | |     sv.T1       PE3          +-----+
       |     |       /\ | |     |=======+     +----------+    +--| CE3 |
       +-----+\     +||---|     | |     \     |          |  1/   |     |
           VID3\   / ||---|     | |      \    | +-----+  |  /    +-----+
                \ / /\/ | +-----+ |       +=====| FXC |----+
                 \ / p2 +---------+           | |     |  |   2   +-----+
                 /\                           | |     |----------| CE4 |
                / /\    +---------+      +======|     |  |       |     |
               / /  \p3 | +-----+ |     /     | |     |  |       +-----+
        VIDs1,2 /    +----| FXC |      /      | |     |---+
       +-----+ /   /\   | |     |======+      | +-----+  |\3    +-----+
       | CE2 |-----||-----|     | |     sv.T2 |          | \    | CE5 |
       |     |-----||-----|     | |           +----------+  +---|     |
       +-----+     \/   | +-----+ |                 |           +-----+
          VIDs3,4  p4   +---------+                 |
                             PE2 |                  |
                     N.VID 1,2,3 +------------------+

                        Figure 2: VLAN-Signaled FXC

5.1.  EVPN-VPWS Service Failure

   The failure detection of an EVPN-VPWS service can be performed via
   OAM mechanisms such as Bidirectional Forwarding Detection (BFD) for
   the pseudowire Virtual Circuit Connectivity Verification (VCCV)
   [RFC5885], and upon such failure detection, the switch over procedure
   to the backup PE is the same as the one described above.

5.2.  Attachment Circuit Failure

   In the event of an AC failure, the VLAN-Signaled and default FXC
   modes exhibit distinct behaviors:

   *  Default FXC (Figure 1): In the default mode, a VLAN or AC failure
      is not signaled.  Consequently, in case of an AC failure, such as
      VID1 on CE2, there is nothing to prevent PE3 from directing
      traffic from CE4 to PE1, leading to a potential packet loss at the
      egress PE with a failed AC.  Application layer OAM may be utilized
      if per-VLAN fault propagation is necessary in this scenario.

   *  VLAN-Signaled FXC (Figure 2): In the case of a VLAN or AC failure,
      such as VID1 on CE2, this triggers the withdrawal of the Ethernet
      A-D per-EVI route for the corresponding Normalized VID,
      specifically Ethernet-Tag 2.  Upon receiving the route withdrawal,
      PE3 will remove PE1 from its outgoing adjacency list for traffic
      originating from CE4.

5.3.  PE Port Failure

   In the event of a PE port failure, the failure will be signaled, and
   the other PE will assume forwarding in both scenarios:

   *  Default FXC (Figure 1): In the case of a port failure, such as p2,
      the route for Service Tunnel 2 (sv.T2) will be withdrawn.  Upon
      receiving the fault notification, PE3 will remove PE1 from its
      adjacency list for traffic originating from CE4 and CE5.

   *  VLAN-Signaled FXC (Figure 2): A port failure, such as p2, triggers
      the withdrawal of the Ethernet A-D per EVI routes for normalized
      VIDs 2 and 3, along with the withdrawal of the Ethernet A-D per-ES
      route for p2's ES.  Upon receiving the fault notification, PE3
      will remove PE1 from its adjacency list for the traffic
      originating from CE4 and CE5.

5.4.  PE Node Failure

   In the case of PE node failure, the operation is similar to the steps
   described above, albeit that EVPN route withdrawals are performed by
   the route reflector instead of the PE.

6.  Security Considerations

   Since this document describes a muxing capability that leverages
   EVPN-VPWS signaling, no additional functionality beyond the muxing
   service is added, and thus no additional security considerations are
   needed beyond what is already specified in [RFC8214].

7.  IANA Considerations

   This document has allocated bits 8-11 in the "EVPN Layer 2 Attributes
   Control Flags" registry with names M and V:

   M  Signaling mode of operation (bits 10-11)
   V  VLAN-ID normalization (bits 8-9)

8.  References

8.1.  Normative References

   [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>.

   [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>.

8.2.  Informative References

   [BGP-PIC]  Bashandy, A., Ed., Filsfils, C., and P. Mohapatra, "BGP
              Prefix Independent Convergence", Work in Progress,
              Internet-Draft, draft-ietf-rtgwg-bgp-pic-21, 7 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-
              bgp-pic-21>.

   [RFC5659]  Bocci, M. and S. Bryant, "An Architecture for Multi-
              Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
              DOI 10.17487/RFC5659, October 2009,
              <https://www.rfc-editor.org/info/rfc5659>.

   [RFC5885]  Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional
              Forwarding Detection (BFD) for the Pseudowire Virtual
              Circuit Connectivity Verification (VCCV)", RFC 5885,
              DOI 10.17487/RFC5885, June 2010,
              <https://www.rfc-editor.org/info/rfc5885>.

   [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>.

Contributors

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

   Wen Lin
   Juniper Networks
   Email: wlin@juniper.net


   Luc Andre Burdet
   Cisco
   Email: lburdet@cisco.com


Authors' Addresses

   Ali Sajassi (editor)
   Cisco Systems
   Email: sajassi@cisco.com


   Patrice Brissette
   Cisco Systems
   Email: pbrisset@cisco.com


   James Uttaro
   Individual
   Email: juttaro@ieee.org


   John Drake
   Independent
   Email: je_drake@yahoo.com


   Sami Boutros
   Ciena
   Email: sboutros@ciena.com


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