Ethernet VPN Signalling Extensions for Bit-stream VPWS

Introduction and Motivation 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 for Frame Relay, ATM, HDLC, PPP, Ethernet, TDM and SONET/SDH. How Ethernet VPWS can be signalled using Ethernet VPN has already been specified in . This document is defining necessary signalling extensions for Ethernet VPN to also support the following bit-stream VPWS instance types:

TDM services using SAToP
TDM services using CESoP
SONET/SDH services using CEP
Private line services using PLE

A generic VPWS reference model similar to the one defined in and is shown in . Data received from 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.

VPWS Reference Model | | +-----------------------------+ | | | | | +---+ v +---+ +---+ v +---+ |CE1|-----| |.......... VPWS1 ........|PE2|-----|CE3| +---+ | | +---+ +---+ |PE1| packet switched network | +---- | | +---+ +---+ |CE2|-----| |.......... VPWS2 ........|PE3|-----|CE4| +---+ +---+ +---+ +---+ ^ | | ^ | +-----------------------------+ | | | attachment attachment circuits circuits | | |<------ emulated services ------>| ]]>

Requirements Notation 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 BCP14 when, and only when, they appear in all capitals, as shown here.

Terminology

AIS - Alarm Indication Signal
AFI - Address Family Identifier
ATM - Asynchronous Transfer Mode
BGP - Border Gateway Protocol
CBR - Constant Bit Rate
CE - Customer Edge
CEP - SONET/SDH Circuit Emulation over Packet
CESoP - Structure-aware TDM Circuit Emulation Service over Packet Switched Network
DF - Designated Forwarder
EAD - Ethernet Auto Discovery
FC - Fibre Channel
EBM - Equipped Bit Mask
EVI - EVPN Instance
EVPN - Ethernet Virtual Private Network
HDLC - High-level Data Link Control
LDP - Label Distribution Protocol
MPLS - Multi Protocol Label Switching
MTU - Maximum Transmission Unit
NDF - Non-Designated Forwarder
NLRI - Network Layer Reachability Information
OC - Optical Carrier
ODUk - Optical Data Unit k
PDH - Plesiochronous Digital Hierarchy
PE - Provider Edge
PLE - Private Line Emulation
PPP - Point-to-Point Protocol
PSN - Packet Switched Network
PW - Pseudo Wire
PWE3 - Pseudowire Emulation Edge-to-Edge
P2P - Point-to-Point
RTP - Realtime Transport Protocol
SAFI - Subsequent Address Family Identifier
SAToP - Structure Agnostic TDM over Packet
SDH - Synchronous Digital Hierarchy
SONET - Synchronous Optical Network
SRv6 - Segment Routing over IPv6 Dataplane
STM - Synchronous Transport Module
STS - Synchronous Transport Signal
TDM - Time Division Multiplexing
TLV - Type Length Value
UNE - Unequipped
VC - Virtual Circuit
VPWS - Virtual Private Wire Service
VT - Virtual Tributary

Solution Requirements To avoid redefining PW types for the notion of "PW type" from is maintained and only a new PW type for has been assigned by IANA.

TBD1 - Private Line Emulation (PLE) over Packet

The concept of "CEP type" from 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 in . To unambiguously identify the rate of an attachment circuit, also the concept of "CEP/TDM bitrate" from is adopted and called "PLE/CEP/TDM bitrate" herein. The VPWS signalling requirements are as follows:

Implementations MUST support MPLS for service multiplexing and as PSN underlay.
The VPWS instance MAY be signalled as SRv6 overlay service per leveraging the mechanisms specified in and considering
- Use of endpoint and encapsulation behaviors specified in
- SRv6 as underlay PSN
The use of control word MUST be signalled, as defined in , , and .
The PW type MUST be signalled and the PE nodes MUST validate that the PW type is identical on both endpoints.
For CEP and PLE the PLE/CEP type MUST be signalled and the PE nodes MUST validate that the PLE/CEP type is identical on both endpoints.
The PLE/CEP/TDM bitrate MUST be signalled if the attachment circuit cannot be unambiguously identified from the PW type alone and the PE nodes MUST validate that the attachment circuit is identical on both endpoints.
A non-default payload size MAY be signalled. Both PE nodes MUST validate that the payload size is identical on both endpoints.
A locally configured connection identifier as defined in 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.
The multi-homed PE scenarios per and SHOULD be supported where the load-balancing mode single-active MUST be supported. Port-active load-balancing mode MAY also be supported.
Multi-homed PE scenarios non-revertive mode MUST and revertive mode SHOULD be supported in compliance to .

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

Ethernet Service Types Ethernet Service Types

Service Type	PW Type	PLE/CEP Type	PLE/CEP/TDM Bitrate
1000Base-X	TBD1	0x3	1,250,000
10GBASE-R	TBD1	0x3	10,312,500
25GBASE-R	TBD1	0x3	25,791,300
40GBASE-R	TBD1	0x3	41,250,000
50GBASE-R	TBD1	0x3	51,562,500
100GBASE-R	TBD1	0x3	103,125,000
200GBASE-R	TBD1	0x3	212,500,000
400GBASE-R	TBD1	0x3	425,000,000

Fibre Channel Service Types Fibre Channel Service Types

Service Type	PW Type	PLE/CEP Type	PLE/CEP/TDM Bitrate
1GFC	TBD1	0x3	1,062,500
2GFC	TBD1	0x3	2,125,000
4GFC	TBD1	0x3	4,250,000
8GFC	TBD1	0x3	8,500,000
10GFC	TBD1	0x3	10,518,750
16GFC	TBD1	0x3	14,025,000
32GFC	TBD1	0x3	28,050,000
64GFC	TBD1	0x3	57,800,000
128GFC	TBD1	0x3	112,200,000

OTN Service Types OTN Service Types

Service Type	PW Type	PLE/CEP Type	PLE/CEP/TDM Bitrate
ODU0	TBD1	0x4	1,244,160
ODU1	TBD1	0x4	2,498,775
ODU2	TBD1	0x4	10,037,273
ODU2e	TBD1	0x4	10,399,525
ODU3	TBD1	0x4	40,319,218
ODU4	TBD1	0x4	104,794,445

TDM Service Types TDM Service Types

Service Type	PW Type	PLE/CEP Type	PLE/CEP/TDM Bitrate
CESoPSN basic mode	0x0015	N/A	N
CESoPSN with CAS	0x0017	N/A	N
E1	0x0011	N/A	32
DS1	0x0012	N/A	24
DS1 octet-aligned	0x0012	N/A	25
E3	0x0013	N/A	535
T3	0x0014	N/A	699

SONET/SDH Service Types Ethernet Service Types

Service Type	PW Type	PLE/CEP Type	PLE/CEP/TDM Bitrate
VT1.5/VC-11	0x0010	0x1	26
VT2/VC-12	0x0010	0x1	35
VT3	0x0010	0x1	53
VT6/VC-2	0x0010	0x1	107
STS-Nc	0x0010	0x0	783*N
VC-4-Mc	0x0010	0x0	7833M
Fract. STS1/VC-3	0x0010	0x2	783
Fract. VC-4	0x0010	0x2	783*4
Async STS1/VC-3	0x0010	0x2	783
OC3/STM1	TBD1	0x3	155,520
OC12/STM4	TBD1	0x3	622,080
OC48/STM16	TBD1	0x3	2,488,320
OC192/STM64	TBD1	0x3	9,953,280
OC768/STM256	TBD1	0x3	39,813,120

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

C bit set to 1 to indicate Control Word MUST be present.
P and B bits are set by dual-homing PEs as per and
L2 MTU MUST be set to zero and ignored by the receiver

For SRv6 related aspects see .

BGP Bit-stream Attribute To exchange and validate bit-stream specific attachment circuit parameters during the VPWS setup, a new BGP path attribute called "BGP Bit-stream attribute" is defined. The BGP Bit-stream attribute is an optional and transitive BGP path attribute with the attribute type codepoint TBD2. The BGP Bit-stream attribute can only be attached to Ethernet Auto-Discovery (A-D) routes (Route type 1) defined in . The usage for other route types and Address Family Identifier (AFI) / Subsequent Address Family Identifier (SAFI) combinations is not allowed unless specified in future specifications. The format is defined as a set of Type/Length/Value (TLV) triplets, described in the following sections and listed in . This attribute SHOULD only be included with EVPN Network Layer Reachability Information (NLRI). BGP Bit-stream attribute TLV

TLV Type	Name	Length	Mandatory
1	PW Type TLV	3	Y
2	PLE/CEP/TDM Bitrate 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

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 is expected to happen.

PW Type TLV The PW Type TLV MUST be present in the BGP Bit-stream 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 . The PW Type TLV format is shown in

PW Type TLV Type : 1 Length : 6

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].

PLE/CEP/TDM Bitrate TLV The PLE/CEP/TDM Bitrate 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 Bitrate TLV format is shown in .

PLE/CEP/TDM Bitrate TLV Type : 2 Length : 8

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 Bitrate :

A four byte field denoting the data rate of the emulated service. Rules defined in do apply for signalling TDM VPWS. Rules for CEP VPWS are defined in .

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

- Guidelines for setting the bitrate for SAToP VPWS and CESoP VPWS can be found in . And for CEP VPWS in .

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 .

PLE/CEP Options TLV Type : 3 Length : 6

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

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

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 . Two new values for PLE are defined in this document:

- 0x3 - Basic 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

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 . The TDM Options TLV format is shown in .

TDM Options TLV Type : 4 Length : 16

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}

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 , , and [PLE] MUST be assumed. The format of the PLE/CEP/TDM Payload Bytes TLV is shown in .

PLE/CEP/TDM Payload Bytes TLV Type : 5 Length : 6

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 do apply for signalling TDM VPWS. Rules for CEP VPWS are defined in .

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

Endpoint-ID TLV Type : 6 Length : 3-83

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.

Control Plane Operations The deployment model shown in figure 3 of does equally apply to the operations defined in this document.

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 its 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 Bit-stream 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 Bit-stream 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:

The mandatory PW type parameter MUST be identical
The mandatory PLE/CEP/TDM Bitrate parameter MUST be identical. This MAY be skipped if this parameter was not signalled because the attachment circuit rate can be unambiguously derived from the PW type .
For CEP and PLE, the mandatory CEP/PLE Type parameter signalled via the CEP/PLE Options TLV MUST be identical
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.

If any of the previous statements is not 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 cannot 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 apply but are limited to the single-active and port-active scenarios. Whenever the VPWS instance configuration is removed, the PE node MUST withdraw its associated per-EVI ethernet A-D route.

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 . 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.

Failure Scenarios

Single-homed CEs Whenever a attachment circuit does declare a local fault the following operations MUST happen:

Operations defined in , , and MUST happen
The per-EVI ethernet A-D route MAY be withdrawn

Whenever the CE-bound IWF does enter packet loss state the operations defined in , , and MUST happen.

Multi-homed CEs 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.

EVPN-VPWS Multi-homing Redundancy In 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 whereas PE2 is the Non-Designated Forwarder (NDF) for that segment. The signalling of primary / backup follows exactly the procedure defined in 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 and 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 unconfigured. 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.

Mandatory Control Word Both and do provide guidance on when the use of control should be signalled. As the bit-stream VPWS types signalled via the mechanisms described in this document mandate a control word to be present, the use of control word MUST always be signalled independent of the underlying PSN characteristics.

Security Considerations The same Security Considerations described in are valid for this document.

IANA Considerations This document defines a new BGP path attribute known as the "Bit-stream attribute". IANA is requested to assign the following from the "BGP Path Attributes" registry (see https://www.iana.org/assignments/bgp-parameters/bgp-parameters.xhtml#bgp-parameters-2).

Value	Code	Reference
TBD2	Bit-stream	this document

This document also defines a new PW Type for PLE VPWS. IANA is requested to assign the following from the "MPLS Pseudowire Types" registry (see https://www.iana.org/assignments/pwe3-parameters/pwe3-parameters.xhtml#pwe3-parameters-2).

PW Type	Description	Reference
TBD2	Bit-stream	this document

Acknowledgements The authors would like to thank all reviewers, contributors and the working group for reviewing this document and providing useful comments and suggestions.