Private Line Emulation VPWS Signalling
draft-schmutzer-bess-ple-vpws-signalling-02

Document Type Active Internet-Draft (individual)
Authors Steven Gringeri  , Jeremy Whittaker  , Christian Schmutzer  , Patrice Brissette 
Last updated 2021-05-03
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BESS Working Group                                           S. Gringeri
Internet-Draft                                              J. Whittaker
Intended status: Standards Track                                 Verizon
Expires: November 4, 2021                              C. Schmutzer, Ed.
                                                            P. Brissette
                                                     Cisco Systems, Inc.
                                                             May 3, 2021

                 Private Line Emulation VPWS Signalling
              draft-schmutzer-bess-ple-vpws-signalling-02

Abstract

   This document specifies the mechanisms to allow for dynamic
   signalling of Virtual Private Wire Services (VPWS) carrying bit-
   stream signals over Packet Switched Networks (PSN).

Status of This Memo

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

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   Copyright (c) 2021 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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Solution Requirements . . . . . . . . . . . . . . . . . . . .   7
   3.  Service Types . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.1.  Ethernet Service Types  . . . . . . . . . . . . . . . . .   8
     3.2.  Fibre Channel Service Types . . . . . . . . . . . . . . .   8
     3.3.  OTN Service Types . . . . . . . . . . . . . . . . . . . .   9
     3.4.  TDM Service Types . . . . . . . . . . . . . . . . . . . .   9
     3.5.  SONET/SDH Service Types . . . . . . . . . . . . . . . . .   9
   4.  EVPN-VPWS signalling  . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Reuse of existing BGP EVPN-VPWS capabilities  . . . . . .  10
     4.2.  BGP PLE Attribute . . . . . . . . . . . . . . . . . . . .  10
       4.2.1.  PW Type TLV . . . . . . . . . . . . . . . . . . . . .  11
       4.2.2.  PLE/CEP/TDM Bit-rate TLV  . . . . . . . . . . . . . .  12
       4.2.3.  PLE/CEP Options TLV . . . . . . . . . . . . . . . . .  13
       4.2.4.  TDM options TLV . . . . . . . . . . . . . . . . . . .  14
       4.2.5.  PLE/CEP/TDM Payload Bytes TLV . . . . . . . . . . . .  15
       4.2.6.  Endpoint-ID TLV . . . . . . . . . . . . . . . . . . .  16
     4.3.  Control Plane Operations  . . . . . . . . . . . . . . . .  16
       4.3.1.  VPWS Setup and Teardown . . . . . . . . . . . . . . .  17
       4.3.2.  Misconnection Handling  . . . . . . . . . . . . . . .  18
       4.3.3.  Failure Scenarios . . . . . . . . . . . . . . . . . .  18
         4.3.3.1.  Single-homed CEs  . . . . . . . . . . . . . . . .  18
         4.3.3.2.  Multi-homed CEs . . . . . . . . . . . . . . . . .  18
   5.  VPWS signalling using LDP . . . . . . . . . . . . . . . . . .  19
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   Virtual Private Wire Service (VPWS) is a widely deployed technology
   for providing point-to-point (P2P) services for various layer 2 and
   also layer 1 technologies.  Initially VPWS were define in the
   Pseudowire Emulation Edge-to-Edge (PWE3) architecture [RFC3985] for
   Frame Relay, ATM, HDLC, PPP, Ethernet, TDM and SONET/SDH.

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   This document focuses on bit stream VPWS instance types which already
   got introduced in [RFC3985].  Possible bit stream VPWS instance types
   and their encapsulation specification documents are:

   o  TDM services using SAToP [RFC4553]

   o  TDM services using CESoP [RFC5086]

   o  SONET/SDH services using CEP [RFC4842]

   o  High-speed private line services using PLE [PLE]

   Signalling mechanisms and extensions to [RFC8077] required to
   dynamically signal TDM bit-stream services ([RFC4553], [RFC5086]) and
   SONET/SDH bit-stream services ([RFC4842]) are already described in
   [RFC5287].

   The scope of this document is to specify extensions to [RFC8077]
   required to dynamically signal PLE bit-stream services defined in
   [PLE] and to specify extensions required to use EVPN-VPWS [RFC8214]
   as a signalling protocol for all bit-stream services mentioned in
   this document.

   A generic VPWS reference model similar to the one defined in
   [RFC3985] and [PLE] is shown in Figure 1.  Data received from a CEs
   is encapsulated by PEs into the respective VPWS established between
   the attachment circuits of the local and remote PE and transmitted
   across the Packet Switched Network (PSN) using a PSN tunnel.

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       CE1 & CE2 physical                       CE3 & CE4 physical
          interfaces                                interfaces
               |      <------- PSN tunnels ----->      |
               |    +-----------------------------+    |
               |    |                             |    |
        +---+  v  +---+                         +---+  v  +---+
        |CE1|-----|   |.......... VPWS1 ........|PE2|-----|CE3|
        +---+     |   |                         +---+     +---+
                  |PE1| packet switched network   |
        +----     |   |                         +---+     +---+
        |CE2|-----|   |.......... VPWS2 ........|PE3|-----|CE4|
        +---+     +---+                         +---+     +---+
                  ^ |                             | ^
                  | +-----------------------------+ |
                  |                                 |
              attachment                       attachment
               circuits                         circuits
                  |                                 |
                  |<------ emulated services ------>|

                      Figure 1: VPWS Reference Model

   In the example shown in Figure 1 there are two CE nodes (CE1 and CE2)
   connected to the same PE node (PE1).  CE3 is connected to PE2 and CE4
   is connected to PE3.  There are two VPWS instances established.
   VPWS1 between CE1 and CE3 and VPWS2 between CE2 and CE4.  For traffic
   to be carried across the network PSN tunnels between PE1 and PE2 and
   between PE1 and PE3 are needed.

   In order for a bit stream VPWS instance to come up, the attachment
   circuit parameters must be identical on both endpoints.  The control
   plane mechanisms described in this document are leveraged to meet
   this requirement.  Mechanisms for misconnection detection and
   protection switch coordination are also described.

1.1.  Requirements Language

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

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1.2.  Terminology

   o  AIS - Alarm Indication Signal

   o  AFI - Address Family Identifier

   o  ATM - Asynchronous Transfer Mode

   o  BGP - Border Gateway Protocol

   o  CBR - Constant Bit Rate

   o  CE - Customer Edge

   o  CEP - SONET/SDH Circuit Emulation over Packet

   o  CESoP - Structure-aware TDM Circuit Emulation Service over Packet
      Switched Network

   o  DF - Designated Forwarder

   o  EAD - Ethernet Auto Discovery

   o  FC - Fibre Channel

   o  EBM - Equipped Bit Mask

   o  EVI - EVPN Instance

   o  EVPN - Ethernet Virtual Private Network

   o  HDLC - High-level Data Link Control

   o  LDP - Label Distribution Protocol

   o  MPLS - Multi Protocol Label Switching

   o  MTU - Maximum Transmission Unit

   o  NDF - Non-Designated Forwarder

   o  NLRI - Network Layer Reachability Information

   o  OC - Optical Carrier

   o  ODUk - Optical Data Unit k

   o  PDH - Plesynchronous Digital Hierarchy

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   o  PE - Provider Edge

   o  PLE - Private Line Emulation

   o  PPP - Point-to-Point Protocol

   o  PSN - Packet Switched Network

   o  PW - Pseudo Wire

   o  PWE3 - Pseudowire Emulation Edge-to-Edge

   o  P2P - Point-to-Point

   o  RTP - Realtime Transport Protocol

   o  SAFI - Subsequent Address Family Identifier

   o  SAToP - Structure Agnostic TDM over Packet

   o  SDH - Synchronous Digital Hierarchy

   o  SONET - Synchronous Optical Network

   o  SRv6 - Segment Routing over IPv6 Dataplane

   o  STM - Synchronous Transport Module

   o  STS - Synchronous Transport Signal

   o  TDM - Time Division Multiplexing

   o  TLV - Type Length Value

   o  UNE - Unequipped

   o  VC - Virtual Circuit

   o  VPWS - Virtual Private Wire Service

   o  VT - Virtual Tributary

   o

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2.  Solution Requirements

   To avoid redefining PW types for [RFC8214] the notion of "PW type"
   from [RFC8077] is maintained and only a new PW type for [PLE] has
   been assigned by IANA.

   o  TBD1 - Private Line Emulation (PLE) over Packet

   The concept of "CEP type" from [RFC5287] to distinguish different
   connection types that use the same PW type is adopted.  In this
   document it is referred to as "PLE/CEP type".  Two new connection
   types are defined (see Section 4.2.3).

   To unambiguously identify the rate of an attachment circuit, also the
   concept of "CEP/TDM bit-rate" from [RFC5287] is adopted and called
   "PLE bit-rate" herein.

   The VPWS signalling requirements are as follows:

   o  EVPN-VPWS [RFC8214] as signalling protocol MUST be supported

   o  LDP [RFC8077] MAY be supported as VPWS signalling protocol

   o  Implementations MUST support MPLS as underlay PSN

   o  The VPWS instance MAY be signalled as SRv6 overlay service per
      [srv6_overlay] leveraging on [srv6_netprog] using the End.DX2
      function.  In such case, the implementation MUST support SRv6 as
      underlay PSN.

   o  The use of control word MUST be signalled, as defined in
      [RFC4553], [RFC5086], [RFC4842] and [PLE].

   o  The PW type MUST be signalled and the PE nodes MUST validate that
      the PW type is identical on both endpoint.

   o  For CEP [RFC4842] and PLE [PLE] the PLE/CEP type MUST be signalled
      and the PE nodes MUST validate that the PLE/CEP type is identical
      on both endpoints.

   o  The PLE/CEP/TDM bit-rate MUST be signalled if the attachment
      circuit can not be unambiguously identified from the PW type alone
      and the PE nodes MUST validate that the attachment circuit is
      identical on both endpoints.

   o  A non-default payload size MAY be signalled.  Both PE nodes MUST
      validate that the payload size is identical on both endpoints.

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   o  A locally configured connection identifier as defined in
      Section 4.2.6 SHOULD be sent to the remote PE node.  A locally
      configured expected identifier MAY be used to identify a
      misconnection by comparing it with the identifier received from
      the remote PE node.

   o  When using EVPN-VPWS [RFC8214] as a signalling protocol, multi-
      homed PE scenarios per [RFC7432] and [RFC8214] SHOULD be supported
      where the load-balancing mode single-active MUST be supported.
      Port-active load-balancing mode MAY also be supported.

   o  For EVPN-VPWS [RFC8214] multi-homed PE scenarios non-revertive
      mode MUST and revertive mode SHOULD be supported in compliance to
      [pref_df].

3.  Service Types

   The following sections list all possible service types that are
   supported by the proposed signalling mechanisms.

3.1.  Ethernet Service Types

   +------------+-----------------+--------+-----------+---------------+
   | Service    |  Encapsulation  |   PW   |  PLE/CEP  |   PLE/CEP/TDM |
   | Type       |     Standard    |  Type  |    Type   |      Bit-rate |
   +------------+-----------------+--------+-----------+---------------+
   | 1000BASE-X |      [PLE]      |  TBD1  |    0x3    |     1,250,000 |
   | 10GBASE-R  |      [PLE]      |  TBD1  |    0x3    |    10,312,500 |
   | 25GBASE-R  |      [PLE]      |  TBD1  |    0x3    |    25,791,300 |
   | 40GBASE-R  |      [PLE]      |  TBD1  |    0x3    |    41,250,000 |
   | 100GBASE-R |      [PLE]      |  TBD1  |    0x3    |   103,125,000 |
   +------------+-----------------+--------+-----------+---------------+

3.2.  Fibre Channel Service Types

   +-----------+-----------------+--------+-----------+----------------+
   | Service   |  Encapsulation  |   PW   |  PLE/CEP  |    PLE/CEP/TDM |
   | Type      |     Standard    |  Type  |    Type   |       Bit-rate |
   +-----------+-----------------+--------+-----------+----------------+
   | 1GFC      |      [PLE]      |  TBD1  |    0x3    |      1,062,500 |
   | 2GFC      |      [PLE]      |  TBD1  |    0x3    |      2,125,000 |
   | 4GFC      |      [PLE]      |  TBD1  |    0x3    |      4,250,000 |
   | 8GFC      |      [PLE]      |  TBD1  |    0x3    |      8,500,000 |
   | 10GFC     |      [PLE]      |  TBD1  |    0x3    |     19,518,750 |
   | 16GFC     |      [PLE]      |  TBD1  |    0x3    |     14,025,000 |
   | 32GFC     |      [PLE]      |  TBD1  |    0x3    |     28,050,000 |
   | 128GFC    |      [PLE]      |  TBD1  |    0x3    |    112,200,000 |
   +-----------+-----------------+--------+-----------+----------------+

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3.3.  OTN Service Types

   +----------+----------------+-------+----------------+--------------+
   | Service  | Encapsulation  |   PW  |  PLE/CEP Type  |  PLE/CEP/TDM |
   | Type     |    Standard    |  Type |                |     Bit-rate |
   +----------+----------------+-------+----------------+--------------+
   | ODU0     |     [PLE]      |  TBD1 |      0x4       |    1,244,160 |
   | ODU1     |     [PLE]      |  TBD1 |      0x4       |    2,498,775 |
   | ODU2     |     [PLE]      |  TBD1 |      0x4       |   10,037,273 |
   | ODU2e    |     [PLE]      |  TBD1 |      0x4       |   10,399,525 |
   | ODU3     |     [PLE]      |  TBD1 |      0x4       |   40,319,218 |
   | ODU4     |     [PLE]      |  TBD1 |      0x4       |  104,794,445 |
   +----------+----------------+-------+----------------+--------------+

3.4.  TDM Service Types

   +------------------+---------------+--------+---------+-------------+
   | Service Type     | Encapsulation |   PW   | PLE/CEP | PLE/CEP/TDM |
   |                  |    Standard   |  Type  |   Type  |    Bit-rate |
   +------------------+---------------+--------+---------+-------------+
   | CESoPSN basic    |   [RFC5086]   | 0x0015 |   N/A   |           N |
   | mode             |               |        |         |             |
   | CESoPSN with CAS |   [RFC5086]   | 0x0017 |   N/A   |           N |
   | E1               |   [RFC4553]   | 0x0011 |   N/A   |          32 |
   | DS1              |   [RFC4553]   | 0x0012 |   N/A   |          24 |
   | DS1 octet-       |   [RFC4553]   | 0x0012 |   N/A   |          25 |
   | aligned          |               |        |         |             |
   | E3               |   [RFC4553]   | 0x0013 |   N/A   |         535 |
   | T3               |   [RFC4553]   | 0x0014 |   N/A   |         699 |
   +------------------+---------------+--------+---------+-------------+

         N is the number of DS0 channels in the attachment circuit

3.5.  SONET/SDH Service Types

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   +------------------+---------------+--------+---------+-------------+
   | Service Type     | Encapsulation |   PW   | PLE/CEP | PLE/CEP/TDM |
   |                  |    Standard   |  Type  |   Type  |    Bit-rate |
   +------------------+---------------+--------+---------+-------------+
   | VT1.5/VC-11      |   [RFC4842]   | 0x0010 |   0x1   |          26 |
   | VT2/VC-12        |   [RFC4842]   | 0x0010 |   0x1   |          35 |
   | VT3              |   [RFC4842]   | 0x0010 |   0x1   |          53 |
   | VT6/VC-2         |   [RFC4842]   | 0x0010 |   0x1   |         107 |
   | STS-Nc           |   [RFC4842]   | 0x0010 |   0x0   |       783*N |
   | VC-4-Mc          |   [RFC4842]   | 0x0010 |   0x0   |     783*3*M |
   | Fract. STS1/VC-3 |   [RFC4842]   | 0x0010 |   0x2   |         783 |
   | Fract. VC-4      |   [RFC4842]   | 0x0010 |   0x2   |       783*4 |
   | Async STS1/VC-3  |   [RFC4842]   | 0x0010 |   0x2   |         783 |
   | OC3/STM1         |     [PLE]     |  TBD1  |   0x3   |     155,520 |
   | OC12/STM4        |     [PLE]     |  TBD1  |   0x3   |     622,080 |
   | OC48/STM16       |     [PLE]     |  TBD1  |   0x3   |   2,488,320 |
   | OC192/STM64      |     [PLE]     |  TBD1  |   0x3   |   9,953,280 |
   | OC768/STM256     |     [PLE]     |  TBD1  |   0x3   |  39,813,120 |
   +------------------+---------------+--------+---------+-------------+

                  N=1,3,12,48,192,768 and M=1,4,16,64,256

4.  EVPN-VPWS signalling

4.1.  Reuse of existing BGP EVPN-VPWS capabilities

   A PLE VPWS instance is identified by a pair of per-EVI ethernet A-D
   routes advertised by two PE nodes establishing the VPWS in accordance
   to [RFC8214].

   The EVPN layer 2 attribute extended community defined in [RFC8214]
   MUST be supported and added to the per-EVI ethernet A-D route.

   o  C bit set to 1 to indicate Control Word MUST be present.

   o  P and B bits are set by dual-homing PEs as per [RFC8214] and
      [pref_df]

   o  L2 MTU MUST be set to zero and ignored by the receiver

4.2.  BGP PLE Attribute

   To exchange and validate bit-stream specific attachment circuit
   parameters during the VPWS setup, a new BGP path attribute called
   "BGP PLE attribute" is defined.

   The BGP PLE attribute defined in this document can be attached to
   EVPN VPWS routes [RFC8214].  The usage for other Address Family

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   Identifier (AFI) / Subsequent Address Family Identifier (SAFI)
   combinations is not defined herein but may be specified in future
   specifications.

   The BGP PLE attribute is an optional and transitive BGP path
   attribute.  The attribute type code TBD2 has been assigned by IANA
   (see section Section 6)

   The format is defined as a set of Type/Length/Value (TLV) triplets,
   described in the following sections and listed in Table 1.  This
   attribute SHOULD only be included with EVPN Network Layer
   Reachability Information (NLRI).

     +----------+-------------------------------+--------+-----------+
     | TLV Type | Name                          | Length | Mandatory |
     +----------+-------------------------------+--------+-----------+
     | 1        | PW Type TLV                   | 3      | Y         |
     | 2        | PLE/CEP/TDM Bit-rate TLV      | 5      | Y         |
     | 3        | PLE/CEP Options TLV           | 3      | Y 1*      |
     | 4        | TDM Options TLV               | 13     | Y 2*      |
     | 5        | PLE/CEP/TDM Payload Bytes TLV | 3      | N         |
     | 6        | Endpoint-ID TLV               | 0..80  | N         |
     +----------+-------------------------------+--------+-----------+

                       1* PLE/CEP only, 2* TDM only

                      Table 1: BGP PLE attribute TLVs

   For a particular PSN it is expected that the network operator will
   choose a common set of parameters per VPWS type, hence efficient BGP
   update packing as discussed in section 12 of [RFC4277] is expected to
   happen.

4.2.1.  PW Type TLV

   The PW Type TLV MUST be present in the BGP PLE attribute to signal
   what type of VPWS instance has to be established.  Valid PW types for
   the mechanisms described in this document can be found in Section 3.

   The PW Type TLV format is shown in Figure 2.

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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |             Length            |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |R|           PW Type           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 2: PW type TLV

   Type : 1

   Length : 3

      The total length in octets of the value portion of the TLV.

   Reserved / R :

      For future use.  MUST be set to ZERO and ignored by receiver.

   PW Type :

      A 15-bit quantity containing a value that represents the type of
      VPWS.  Assigned Values are specified in "IANA Allocations for
      Pseudowire Edge to Edge Emulation (PWE3)" [RFC4446].

4.2.2.  PLE/CEP/TDM Bit-rate TLV

   The PLE/CEP/TDM Bit-rate TLV is MANDATORY but MAY be omitted if the
   attachment circuit type can be unambiguously derived from the PW Type
   carried in the PW Type TLV.  The PLE/CEP/TDM Bit-rate TLV format is
   shown in Figure 3.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |             Length            |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     PLE/CEP/TDM Bit-rate                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 3: PLE/CEP/TDM Bit-rate TLV

   Type : 2

   Length : 5

      The total length in octets of the value portion of the TLV.

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   Reserved :

      8-bit field for future use.  MUST be set to ZERO and ignored by
      receiver.

   PLE/CEP/TDM Bit-rate :

      A four byte field denoting the desired payload size to be used.
      Rules defined in [RFC5287] do apply for signalling TDM VPWS.
      Rules for CEP VPWS are defined in [RFC4842].

      *  For PLE [PLE] the bit rate MUST be set to the data rate in
         units of 1-kbps of the PLE payload.

      *  Guidelines for setting the bit rate for SAToP VPWS and CESoP
         VPWS can be found in [RFC5287].  And for CEP VPWS in [RFC4842].

4.2.3.  PLE/CEP Options TLV

   The PLE/CEP Options TLV MUST be present when signalling CEP and PLE
   VPWS instances.  The PLE/CPE Options TLV format is shown in Figure 4.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |             Length            |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        PLE/CEP Options        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 4: PLE/CEP Options TLV

   Type : 3

   Length : 3

      The total length in octets of the value portion of the TLV.

   Reserved :

      8-bit field for future use.  MUST be set to ZERO and ignored by
      receiver.

   PLE/CEP Options :

      A two byte field with the format as shown in Figure 5

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       0                                       1
       0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
     |AIS|UNE|RTP|EBM|      Reserved [0:6]       |  PLE/CEP  | Async |
     |   |   |   |   |                           |    Type   |T3 |E3 |
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

                         Figure 5: PLE/CEP Options

      AIS, UNE, RTP, EBM :

         These bits MUST be set to zero and ignored by the receiver
         except for CEP VPWS.  Guidelines for CEP are defined in
         [RFC4842]

      Reserved :

         7-bit field for future use.  MUST be set to ZERO and ignored by
         receiver.

      CEP/PLE Type :

         Indicates the connection type for CEP and PLE.  CEP connection
         types are defined in [RFC4842].  Two new values for PLE are
         defined in this document:

            0x3 - Constand Bit Rate (CBR) PLE payload

            0x4 - Byte aligned PLE payload

      Async :

         These bits MUST be set to zero and ignored by the receiver
         except for CEP VPWS.  Guidelines for CEP are defined in
         [RFC4842]

4.2.4.  TDM options TLV

   Whether when signalling TDM VPWS the TDM Options TLV MUST be present
   or MAY be omitted when signalling TDM VPWS instances is defined in
   [RFC5287].  The TDM Options TLV format is shown in Figure 6.

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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |             Length            |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                         TDM Options                           |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 6: TDM Options TLV

   Type : 4

   Length : 13

      The total length in octets of the value portion of the TLV.

   Reserved :

      8-bit field for future use.  MUST be set to ZERO and ignored by
      receiver.

   TDM Options :

      A twelve byte field with the format as defined in section 3.8 of
      [RFC5287]

4.2.5.  PLE/CEP/TDM Payload Bytes TLV

   The PLE/CEP/TDM Payload Bytes TLV MAY be included if a non-default
   payload size is to be used.  If this TLV is omitted then the default
   payload sizes defined in [RFC4553], [RFC5086], [RFC4842] and [PLE]
   MUST be assumed.  The format of the PLE/CEP/TDM Payload Bytes TLV is
   shown in Figure 7.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |             Length            |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   PLE/CEP/TDM Payload Bytes   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 7: PLE/CEP/TDM Payload Bytes TLV

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   Type : 5

   Length : 3

      The total length in octets of the value portion of the TLV.

   Reserved :

      8-bit field for future use.  MUST be set to ZERO and ignored by
      receiver.

   PLE/CEP/TDM Payload Bytes :

      A two byte field denoting the desired payload size to be used.
      Rules defined in [RFC5287] do apply for signalling TDM VPWS.
      Rules for CEP VPWS are defined in [RFC4842].

4.2.6.  Endpoint-ID TLV

   The Endpoint-ID TLV MAY be included to allow for misconnection
   detection.  The Endpoint-ID TLV format is shown in Figure 8.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |             Length            |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
      //                Endpoint Identifier (variable)               //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 8: Endpoint-ID TLV

   Type : 6

   Length : 0-80

      The total length in octets of the value portion of the TLV.

   Endpoint Identifier :

      Arbitrary string of variable length from 0 to 80 octets used to
      describe the attachment circuit to the remote PE node.

4.3.  Control Plane Operations

   The deployment model shown in figure 3 of [RFC8214] does equally
   apply to the operations defined in this document.

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4.3.1.  VPWS Setup and Teardown

   After an attachment circuit has been configured to be part of a VPWS
   instance and has not declared any local defect, the PE node announces
   his endpoint using a per-EVI ethernet A-D route to other PEs in the
   PSN via BGP.  The Ethernet Tag ID is set to the VPWS instance
   identifier and the BGP PLE attribute is included to carry mandatory
   and optional bit-stream specific attachment circuit parameters.

   Both endpoints receiving the EVPN per-EVI A-D route, validate the end
   to end connectivity by comparing BGP PLE attributes.  Upon successful
   validation, the VPWS instance comes up and traffic can flow through
   the PSN.  In the scenario where the validation phase fails, the
   remote PE reachability information is simply ignored and dismissed as
   a destination candidate.  The VPWS instance validation is performed
   as follow:

   o  The mandatory PW type parameter MUST be identical

   o  The mandatory PLE/CEP/TDM Bit-rate parameter MUST be identical.
      This MAY be skipped if this parameter was not signaled because the
      attachment circuit rate can be unambiguously derived from the PW
      type [RFC5287].

   o  For CEP and PLE, the mandatory CEP/PLE Type parameter signalled
      via the CEP/PLE Options TLV MUST be identical

   o  If the payload size was signalled via the optional PLE/CEP/TDM
      Payload Bytes TLV it MUST be identical and supported by the PE
      node.  Else the default payload size MUST be assumed.

   o  If any of the previous statements is no true or any of the signal
      CEP/PLE or TDM options is not supported by the PE node, the VPWS
      instance must stay down and a appropriate defect MUST be declared.

   PLE is structure agnostic for SONET/SDH service types and hence can
   not validate whether a mix of SONET and SDH attachment circuits are
   connected (by incident) via VPWS.  The detection of such
   misconfiguration is the responsibility of the operator managing the
   CE nodes.

   In case of multi-homed CEs the mechanisms defined in [RFC8214] apply
   but are limited to the single-active and port-active scenarios.

   Whenever the VPWS instance configuration is removed, the PE node MUST
   widthdraw its associated per-EVI ethernet A-D route.

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4.3.2.  Misconnection Handling

   In circuit switched networks it is a common requirement to have the
   ability to check if the correct two endpoints got connected via a
   circuit.  To confirm that the established bit-stream VPWS service is
   connecting the appropriate pair of attachment circuits, a Endpoint-ID
   string MAY be configured on each attachment circuit and communicated
   to the peer PE node using the Endpoint-ID TLV defined in
   Section 4.2.6.

   Each endpoint MAY be configured to compare the Endpoint-ID received
   from the peer PE node to a locally configured expected Endpoint-ID
   and raise a fault (defect) when the IDs don't match.  When a fault is
   raised, the R bit in the control word must bet set to 1 (backward
   defect indication) for the VPWS packets sent to the peer PE node.
   Each endpoint MAY be configured to only compare and report
   mismatches, but not to raise a fault.

4.3.3.  Failure Scenarios

4.3.3.1.  Single-homed CEs

   Whenever a attachment circuit does declare a local fault the
   following operations MUST happen:

   o  Operations defined in [RFC4553], [RFC5086], [RFC4842] and [PLE]
      MUST happen

   o  The per-EVI ethernet A-D route MAY be withdrawn

   Whenever the CE-bound IWF does enter packet loss state the operations
   defined in [RFC4553], [RFC5086], [RFC4842] and [PLE] MUST happen.

4.3.3.2.  Multi-homed CEs

   Figure 9 demonstrates a multi-homing scenario.  CE1 is connected to
   PE1 and PE2 where PE1 is the designated forwarder while PE2 is the
   non designated forwarder.

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                            PSN
                         +---------+
            DF  +---+    |         |   +---+   +---+
             +--|PE1|----|---------|---|PE3|---|CE2|
       +---+/   +---+    |   VPWS1/|   +---+   +---+
       |CE1|             |       / |
       +---+\   +---+    |      /  |
             +--|PE2|----|-----+   |
           NDF  +---+    |         |
                         +---------+

                Figure 9: EVPN-VPWS multi-homing redundancy

   In Figure 9 PE1 and PE2 are configured for single-active load-
   balancing mode.  Both PEs are advertising a per-ES ethernet A-D route
   with the same non-zero Ethernet Segment (ES) value and the single-
   active bit set.  This non-zero ES value is called Ethernet Segment
   Identifier (ESI).

   In this example PE1 is elected as Designated Forwarder (DF) for the
   shared ESI where as PE2 is the Non-Designated Forwarder (NDF) for
   that segment.  The signalling of primary / backup follows exactly the
   procedure defined in [RFC8214] where P and B bits of the layer 2
   attribute extended community are used to settle proper connectivity.

   Upon link failure between CE1 and PE1, PE1 and PE2 follows EVPN
   Ethernet Segment DF Election procedures described in [RFC8214] and
   [pref_df] for EVPN-VPWS.  PE1 leverage mass-withdraw mechanism to
   tell PE3 to steer traffic over backup connectivity.  The per-EVI
   ethernet A-D route advertisement remains intact.  The main purpose is
   to keep reachability information available for fast convergence
   purpose.  Therefore, the per-EVI ethernet A-D route MAY be withdrawn
   only under local fault and MUST be withdraw when the circuit is un-
   configured.

   Port-active operation happens in the same way as single-active load-
   balancing mode described before but at the port level instead of
   being at the sub-interface level.

5.  VPWS signalling using LDP

   This section is already under construction and will be soon be
   publicly announced

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6.  IANA Considerations

   This document defines a new BGP path attribute known as the BGP PLE
   attribute.  IANA is requested to assign attribute code type TBD2 to
   the BGP PLE attribute from the "BGP Path Attributes" registry.

   This document defines a new PW Type for PLE VPWS.  IANA is requested
   to assign a PW type value TBD1 from the "MPLS Pseudowire Types"
   registry.

7.  Security Considerations

   The same Security Considerations described in [RFC8214] and [RFC5287]
   are valid for this document.

8.  Acknowledgements

9.  References

9.1.  Normative References

   [PLE]      Schmutzer, C., "draft-cisco-bess-mpls-ple-00", 2020.

   [pref_df]  IETF, "Preference-based EVPN DF Election",
              <https://tools.ietf.org/html/draft-ietf-bess-evpn-pref-
              df>.

   [RFC4446]  Martini, L., "IANA Allocations for Pseudowire Edge to Edge
              Emulation (PWE3)", BCP 116, RFC 4446,
              DOI 10.17487/RFC4446, April 2006,
              <https://www.rfc-editor.org/info/rfc4446>.

   [RFC4553]  Vainshtein, A., Ed. and YJ. Stein, Ed., "Structure-
              Agnostic Time Division Multiplexing (TDM) over Packet
              (SAToP)", RFC 4553, DOI 10.17487/RFC4553, June 2006,
              <https://www.rfc-editor.org/info/rfc4553>.

   [RFC4842]  Malis, A., Pate, P., Cohen, R., Ed., and D. Zelig,
              "Synchronous Optical Network/Synchronous Digital Hierarchy
              (SONET/SDH) Circuit Emulation over Packet (CEP)",
              RFC 4842, DOI 10.17487/RFC4842, April 2007,
              <https://www.rfc-editor.org/info/rfc4842>.

   [RFC5086]  Vainshtein, A., Ed., Sasson, I., Metz, E., Frost, T., and
              P. Pate, "Structure-Aware Time Division Multiplexed (TDM)
              Circuit Emulation Service over Packet Switched Network
              (CESoPSN)", RFC 5086, DOI 10.17487/RFC5086, December 2007,
              <https://www.rfc-editor.org/info/rfc5086>.

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   [RFC5287]  Vainshtein, A. and Y(J). Stein, "Control Protocol
              Extensions for the Setup of Time-Division Multiplexing
              (TDM) Pseudowires in MPLS Networks", RFC 5287,
              DOI 10.17487/RFC5287, August 2008,
              <https://www.rfc-editor.org/info/rfc5287>.

   [RFC8077]  Martini, L., Ed. and G. Heron, Ed., "Pseudowire Setup and
              Maintenance Using the Label Distribution Protocol (LDP)",
              STD 84, RFC 8077, DOI 10.17487/RFC8077, February 2017,
              <https://www.rfc-editor.org/info/rfc8077>.

   [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>.

   [srv6_netprog]
              IETF, "SRv6 Network Programming",
              <https://tools.ietf.org/html/draft-ietf-spring-srv6-
              network-programming>.

   [srv6_overlay]
              IETF, "SRv6 BGP based Overlay services",
              <https://tools.ietf.org/html/draft-ietf-bess-
              srv6-services>.

9.2.  Informative References

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,
              <https://www.rfc-editor.org/info/rfc3985>.

   [RFC4277]  McPherson, D. and K. Patel, "Experience with the BGP-4
              Protocol", RFC 4277, DOI 10.17487/RFC4277, January 2006,
              <https://www.rfc-editor.org/info/rfc4277>.

   [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>.

Authors' Addresses

   Steven Gringeri
   Verizon

   Email: steven.gringeri@verizon.com

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   Jeremy Whittaker
   Verizon

   Email: jeremy.whittaker@verizon.com

   Christian Schmutzer (editor)
   Cisco Systems, Inc.
   Vienna
   Austria

   Email: cschmutz@cisco.com

   Patrice Brissette
   Cisco Systems, Inc.
   Ottawa, ON
   Canada

   Email: pbrisset@cisco.com

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