EVPN-VPWS Seamless Integration with L2VPN VPWS
draft-brissette-bess-evpn-vpws-seamless-07
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Patrice Brissette , Wen Lin , Jorge Rabadan , Jim Uttaro , Bin Wen | ||
| Last updated | 2023-05-17 | ||
| Replaces | draft-brissette-bess-vpws-seamless | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-brissette-bess-evpn-vpws-seamless-07
BESS Working Group P. Brissette
Internet-Draft Cisco Systems
Intended status: Standards Track W. Lin
Expires: 18 November 2023 Juniper
J. Rabadan
Nokia
J. Uttaro
ATT
B. Wen
Comcast
17 May 2023
EVPN-VPWS Seamless Integration with L2VPN VPWS
draft-brissette-bess-evpn-vpws-seamless-07
Abstract
This document presents a solution for migrating L2VPN Virtual Private
Wire Service (VPWS) to Ethernet VPN Virtual Private Wire Service
(EVPN-VPWS) services. The solution allows the coexistence of EVPN
and L2VPN services under the same point-to-point VPN instance. By
using this seamless integration solution, a service provider can
introduce EVPN into their existing L2VPN network or migrate from an
existing L2VPN based network to EVPN. The migration may be done per
pseudowire or per flexible-crossconnect (FXC) service basis. This
document specifies control-plane and forwarding behaviors.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119] and
RFC 8174 [RFC8174].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 18 November 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terms and Abbreviations . . . . . . . . . . . . . . . . . . . 5
3. L2VPN PE, EVPN-VPWS PE and Composite PE . . . . . . . . . . . 6
4. Solution Requirements . . . . . . . . . . . . . . . . . . . . 7
5. Seamless Integration Solution . . . . . . . . . . . . . . . . 8
6. Capability Discovery . . . . . . . . . . . . . . . . . . . . 8
7. Data Plane Operations . . . . . . . . . . . . . . . . . . . . 9
8. Control Plane Operations . . . . . . . . . . . . . . . . . . 11
9. Multi-homed Operations . . . . . . . . . . . . . . . . . . . 12
9.1. Operations with Port-Active MH PEs . . . . . . . . . . . 13
9.2. Operation with Single-Active MH PEs . . . . . . . . . . . 13
9.3. Operation with All-Active MH PEs . . . . . . . . . . . . 14
9.3.1. Falling back to port-active . . . . . . . . . . . . . 14
9.3.2. Asymmetric forwarding . . . . . . . . . . . . . . . . 14
10. Route Optimization . . . . . . . . . . . . . . . . . . . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12. Security Considerations . . . . . . . . . . . . . . . . . . . 15
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
14.1. Normative References . . . . . . . . . . . . . . . . . . 16
14.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
Point-to-point L2VPN solutions are specified in [RFC8077] when LDP-
based pseudowire are offered. BGP-based L2VPN service may also offer
point-to-point service using [RFC6624] or by setting up auto-
discovered VPN members using [RFC6074] and then the pseudowires using
[RFC8077].
EVPN-VPWS leverages the latest EVPN technology and brings extra
functions to Layer 2 point-to-point Ethernet service, such as all-
active redundancy, load balancing and mass withdrawal. All-active
redundancy also makes it easier to achieve fast convergence on an
access link or node failure.
When expanding an existing L2VPN network with Ethernet encapsulation,
a service provider may want to deploy EVPN-VPWS to provide additional
Layer 2 point-to-point Ethernet services, and at the same time some
of the customer traffic may still need to be terminated on the
existing L2VPN PEs within the service provider network.
This document describes a seamless-integration solution that allows
the co-existence of L2VPN point-to-point Ethernet services and EVPN-
VPWS procedure per [RFC8214] under the same VPN network and over the
same MPLS/IP network. Service providers may also use the seamless
integration solution to migrate traditional L2VPN network to EVPN-
VPWS based network.
MPLS/IP Core
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2| L2VPN VPWS
| |----|---+ | +---+
+---+ | | |
EVPN-VPWS & | +--PW2---+ | +---+
L2VPN VPWS | +--|---|PE3| EVPN-VPWS
(Composite) | | +---+
+---------------+
Figure 1
Seamless Integration of EVPN-VPWS.
Figure 1 shows a network where PE1 runs in hybrid mode (EVPN-VPWS and
legacy L2VPN VPWS). PE1 has established a pseudowire (PW1) with PE2
running L2VPN VPWS. Also, it has initiated another pseudowire (PW2)
with PE3 running EVPN-VPWS. In the future, PE2 may be upgraded to
EVPN-VPWS seamlessly. The seamless integration solution described in
this document has the following attributes:
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- It is backward compatible with [RFC8214] and EVPN Flexible
crossconnect service [I-D.ietf-bess-evpn-vpws-fxc] documents.
- New PEs can leverage the multi-homing mechanisms and provisioning
simplifications of EVPN Ethernet-Segment framework:
a. Auto-sensing of MHN / MHD
b. Auto-discovery of redundancy groups
c. Auto-election of Designated Forwarder and VLAN carving
d. Support of various load-balancing modes such as port-active,
single-active and all-active
MPLS/IP Core
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | L2VPN | +---+
L2VPN | | L2VPN
VPWS +---------------+ VPWS
...
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | L2VPN | +---+
L2VPN | | L2VPN VPWS
VPWS +---------------+ + EVPN-VPWS
....
+---------------+
+---+ | | +---+
|PE1|----|--(PW1->PW2)---|---|PE2|
+---+ | EVPN-VPWS | +---+
L2VPN VPWS | | L2VPN VPWS
+ EVPN-VPWS +---------------+ + EVPN-VPWS
....
+---------------+
+---+ | | +---+
|PE1|----|----- PW2 -----|---|PE2|
+---+ | EVPN-VPWS | +---+
EVPN-VPWS | | EVPN-VPWS
+---------------+
Figure 2
Migration from L2VPN to EVPN-VPWS.
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Figure 2 illustrates the migration of a L2VPN VPWS brownfield network
to EVPN-VPWS. Initially PE1 and PE2 have a L2VPN PW established
between them. First, a network operator may upgrade PE2 to enable
EVPN-VPWS. Once upgraded, PE2 which now has the EVPN-VPWS capability
still runs L2VPN PW with PE1. Later on, a network operator may
decide to upgrade PE1 to support EVPN-VPWS. As soon as the upgrade
is completed, PE1 and PE2 auto-discover their respective EVPN routes
and the corresponding point-to-point service. That EVPN-VPWS service
takes higher precedence over existing legacy L2VPN pseudowire.
Finally, the network operator may safely remove any legacy
configurations from PE1 and PE2 nodes while PW remains established
using EVPN-VPWS.
2. Terms and Abbreviations
* CE: A Customer Edge device, e.g., a host, router, or switch.
* DF: EVPN Ethernet Segment Designated Forwarder.
* NDF: EVPN Ethernet Segment Non-Designated Forwarder.
* Ethernet Segment (ES): Refers to a set of Ethernet links
connecting a customer site (device or network of devices) to one
or more PEs.
* Virtual Ethernet Segment (vES): Refers to a subset of Ethernet
links connecting customer site (device or network of devices) to
one or more PEs. All procedures listed in all-active and single-
active mutli-homing apply; but not port-active.
* Ethernet Tag: An Ethernet Tag identifies a particular pseudowire,
e.g. a PW-ID as per [RFC8214].
* FEC: Forwarding Equivalence Class.
* homogeneous PEs: Refers to PEs that are of the same types.
* LDP-LM: LDP Label Mapping Message.
* LDP-LW: LDP Label Withdraw Message.
* LSP: Label Switched Path.
* MHD: Multi-Homed Device.
* MHN: Multi-Homed Network.
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* P2P: Point to Point - a P2P LSP typically refers to a LSP for
Layer2 pseudowire.
* PE: Provider Edge device.
* VPWS: Virtual Private Wire Service. It refers to L2VPN VPWS
circuit where pseudowires are signaled using LDP or BGP-AD
protocol. The latter is referred as VPWS A-D.
* EVPN-VPWS: Ethernet-VPN Virtual Private Wire Service. It refers
to EVPN-VPWS circuit where pseudowires are signaled via BGP-EVPN.
It can also refer to [I-D.ietf-bess-evpn-vpws-fxc].
* EVPN-FXC: Ethernet-VPN Flexible Cross-connect Service
[I-D.ietf-bess-evpn-vpws-fxc].
* Port-Active Redundancy Mode: When only a single PE, among all the
PEs attached to an Ethernet segment, is allowed to forward traffic
to/from that Ethernet segment for a given interface, then the
Ethernet Segment is defined to be operating in Port-Active
redundancy mode.
* Single-Active Redundancy Mode: When only a single PE, among all
the PEs attached to an Ethernet segment, is allowed to forward
traffic to/from that Ethernet segment for a given VLAN, then the
Ethernet Segment is defined to be operating in Single-Active
redundancy mode.
* All-Active Redundancy Mode: When all PEs attached to an Ethernet
Segment are allowed to forward traffic to/from that Ethernet
segment for a given VLAN, then the Ethernet segment is defined to
be operating in All-Active redundancy mode.
* VPWS A-D: Refers to Virtual Private Wire Services with BGP-based
Auto Discovery as in [RFC6074].
* PW: Pseudowire
3. L2VPN PE, EVPN-VPWS PE and Composite PE
There are three types of PEs defined in the seamless integration
solution: L2VPN PE, EVPN-VPWS PE and composite PE. Under a given
Layer 2 Ethernet VPN, the type of PE is categorized by the technology
it is provisioned for. For instance, a PE that is provisioned to use
L2VPN and EVPN-VPWS on the same VPN service is considered a composite
PE.
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Also in this document, in the context of a given Layer 2 Ethernet
VPN, an EVPN-VPWS PE is a PE that is provisioned to provide only the
EVPN solution per [RFC8214] or [I-D.ietf-bess-evpn-vpws-fxc] but not
a seamless integration solution. It is irrelevant whether an EVPN-
VPWS PE is capable to support a seamless integration solution.
For example, for a non-L2VPN PE, a network administrator may know a
priori that the PE does not need to establish any P2P Ethernet
service that involves L2VPN PE under a given Layer 2 Ethernet VPN
instance. In this case, the PE can be provisioned to act only as an
EVPN-VPWS PE for that VPN even though it is capable of providing
seamless integration procedure. If such prior knowledge is
unavailable, then a PE SHALL be provisioned to act as a composite PE
if it is capable of. Otherwise, it is unable to establish a P2P
Ethernet service with a L2VPN PE.
Unless explicitly specified in this specification, a PE's type
applies to a given Layer 2 Ethernet VPN instance. A PE may act as an
EVPN-VPWS PE for one VPN, but as a composite PE for another VPN.
4. Solution Requirements
The seamless integration solution for point-to-point Ethernet VPN
meets the following requirements:
* It must allow L2VPN, EVPN-VPWS and composite PEs to participate in
the same Layer 2 Ethernet VPN instance.
* The solution MUST allow for staged migration towards EVPN-VPWS on
a site-by-site basis - e.g., new EVPN-VPWS sites to be provisioned
on EVPN-VPWS Provider Edge devices (PEs). Migration SHOULD be
possible on a per-pseudowire basis.
* The solution MUST NOT require any changes to existing L2VPN PEs
running Legacy VPWS, unless it is to upgrade them to EVPN-VPWS and
make them composite PE.
* The solution MUST allow for the co-existence of composite PE
devices running EVPN-VPWS and L2VPN VPWS for the same single-homed
and/or multi-homed segments.
* The solution MUST support port-active redundancy of multi-homed
networks and multi-homed devices for L2VPN, EVPN-VPWS and
composite PEs.
* The solution MUST support single-active redundancy of multi-homed
networks and multi-homed devices for L2VPN, EVPN-VPWS and
composite PEs.
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* The solution SHOULD support all-active redundancy of multi-homed
Ethernet Segments for L2VPN, EVPN-VPWS and composite PEs.
* Composite PEs provisioned for all-active multihoming for their
multihomed CE(s) MAY work with L2VPN PE(s) working in single home
or active-standby multihoming.
These requirements collectively allow for the seamless insertion of
the EVPN-VPWS technology into brownfield L2VPN VPWS deployments.
5. Seamless Integration Solution
To support seamless integration, the solution may require L2VPN PEs
to setup PWs per [RFC8077] or [RFC6624] or may require L2VPN PEs to
setup VPWS service by auto-discovering VPN members using [RFC6074]
and then setting up the PWs using [RFC8077]. Furthermore, composite
PEs must support BGP EVPN routes per [RFC8214] and as per
[I-D.ietf-bess-evpn-vpws-fxc] and one of a method of legacy VPWS
technologies. All the logic for seamless integration SHALL reside on
the composite PEs.
A PE participating in a point-to-point Ethernet VPN offers P2P
Ethernet services with different remote PEs. By nature of point-to-
point service, there is no requirement for full-mesh among all the
PEs participating in the same point-to-point Ethernet VPN instance.
The seamless integration solution allows the coexistence of composite
PE, L2VPN PE and EVPN-VPWS PE under the same VPN instance. It allows
the establishment of P2P Ethernet services over the same MPLS/IP
core: (a) between two homogenous PEs, or (b) between a composite PE
and a L2VPN PE, or (c) between a composite PE and a EVPN-VPWS PE.
A composite PE can establish a P2P Ethernet service with a L2VPN PE
and different a P2P service with the same or a different EVPN-VPWS
PE. It is the sole responsibility of a composite PE to seamless
integrate with L2VPN PEs and EVPN-VPWS PEs.
There will be no P2P service between an EVPN-VPWS PE and a L2VPN PE
in the same L2 Ethernet VPN as an EVPN-VPWS PE is provisioned only to
provide the procedure/function per EVPN-VPWS.
6. Capability Discovery
The EVPN-VPWS PEs MUST advertise both BGP VPWS Auto-Discovery (VPWS
A-D) route or LDP-LM message as well as the BGP EVPN Ethernet AD per
EVI route for a given pseudowire. Auto-discovery is only meaningful
to PEs participating in the same VPN.
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In the case of L2VPN PEs running VPWS A-D, they may advertise the BGP
VPWS A-D route, per the procedures specified in [RFC4664] and
[RFC6074] or [RFC6624]. The operator may decide to use the same BGP
Route Target (RT) to identify a pseudowire on both EVPN-VPWS and
L2VPN networks. In this case, when a L2VPN PE receives the EVPN
Ethernet AD per EVI route, it MUST ignore it on the basis that it
belongs to an unknown SAFI. However, the operator may choose to use
two RTs - one to identify the pseudowire on L2VPN network and another
for EVPN-VPWS network and employ RT-constrained route distribution
[RFC4684] in order to prevent BGP EVPN routes from reaching the L2VPN
PEs.
When an EVPN-VPWS PE receives both a VPWS A-D route or a LDP-LM
message as well as an EVPN-VPWS Ethernet AD per EVI route from a
given remote PE for the same pseudowire, it MUST give preference to
the EVPN-VPWS route for discovery. This ensures that, at the end of
the route exchange, all EVPN-VPWS capable PEs discover other EVPN-
VPWS capable PEs.
When the discovery phase is completed, the composite PEs have
discovered the remote PE per pseudowire along with their associated
capability (EVPN-VPWS or L2VPN), whereas the L2VPN PE have discovered
the remote PE per pseudowire as if they are L2VPN-only PEs.
Basically, a L2VPN PE discovers all L2VPN PEs and all composite PEs
participating in the same VPN. However, a L2VPN cannot distinguish a
L2VPN from a composite PE. From a point of L2VPN PE, all composite
PEs are L2VPN PEs.
Also, an EVPN-VPWS PE discovers all EVPN PEs and all composite PEs
participating in the same VPN. Similarly, an EVPN-VPWS PE cannot
distinguish an EVPN-VPWS PE from a composite PE. From a point of
EVPN-VPWS PE, all composite PEs are EVPN-VPWS PEs.
7. Data Plane Operations
When a packet arrives at an ingress composite PE, the composite PE
adds a VPN service label based on the AC that packet arrives at, and
it encapsulates the packet and sends it through a pseudowire to the
egress PE.
* A composite PE will not forward customer traffic to the L2VPN PE
playing a non-DF role
* If a composite PE detects that two or more EVPN-VPWS PEs are
attached to the same ES and they are working in all-active mode,
it will load balance the traffic among the EVPN-VPWS PEs.
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* If a composite PE detects that two or more EVPN-VPWS PEs are
attached to the same ES and they are working in single-active
mode, it will only forward the traffic to the EVPN-VPWS PE playing
a DF role. Similar logic is followed with port-active mode.
* If a set of composites PEs work in all-active multihoming mode for
the same multihomed CE, then regardless of DF or Non-DF role each
composite PE plays, it may forward the packet received from its
multihomed CE to the remote L2VPN DF PE. Detailed description is
done in Section 9.3.
* If a composite PE receives both L2VPN and EVPN A-D routes from a
remote PE for the same p2p Ethernet service, the composite should
install forwarding routes in a make-before-break fashion:
a. For the traffic coming from the remote PE to its local access
interface direction, to achieve a fast failover, the composite
may install forwarding routes based on both L2VPN and EVPN A-D
routes. However, to save system resources in a scaled setup,
the composite may choose to install only the forwarding route
for the EVPN A-D route and it should do so before it deletes
the forwarding route for the L2VPN A-D route if it was
installed beforehand.
b. For traffic coming from its local access interface to the
remote PE direction, only one route can be installed for the
same local access interface. Forwarding should be based on
the EVPN A-D route. The composite PE should update the
forwarding route in a make-before-break fashion if the
forwarding route for L2VPN A-D route has already been
installed before the processing of the incoming EVPN A-D
route.
* If a composite PE receives both L2VPN and EVPN A-D routes from a
remote PE for the same p2p Ethernet service, and later on the
remote PE has reverted back to a L2VPN only PE and withdraws its
EVPN A-D route, the composite PE should also update the forwarding
route accordingly in a make-before-break fashion:
a. For the traffic coming from the remote PE to its local access
interface direction, if the forwarding route for the L2VPN A-D
route is not there, the composite PE should install the
forwarding route for the L2VPN A-D route before it tears down
the forwarding route for the EVPN A-D route.
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b. For the traffic coming from its local access interface to the
remote PE direction, only one route can be installed for the
same local access interface. The composite PE should update
the forwarding route based on the L2VPN A-D route in a make-
before-break fashion.
8. Control Plane Operations
Figure 3 demonstrates a typical brown-field deployment where PE1 is a
composite PE and PE2 is a L2VPN PE.
MPLS/IP
Composite PE Core L2VPN PE
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | | +---+
+---------------+
VPWS A-D route ] TX TX [ VPWS A-D route
or ] ---> <--- [ or
LDP Label Mapping ] [ LDP Label Mapping
AND
TX
EVPN A-D per EVI ] --->
Figure 3
EVPN-VPWS Single-Homed
The control plane procedures of L2VPN PEs are per [RFC8077],
[RFC8214] and [RFC4762].
The EVPN-VPWS PE procedures are as follows:
* The composite PE MUST establish a PW to each remote PE from which
it has received only a VPWS A-D route or a LDP-LM message for the
corresponding pseudowire, and MUST set up the label stack
corresponding to the PW FEC.
* If an composite PE receives a VPWS A-D route or a LDP-LM message
from a given PE, it sets up a L2VPN VPWS PW to that PE. If it
then receives an EVPN Ethernet AD per EVI route for that PW from
the same PE, then the composite PE may bring the L2VPN PW
operationally down and MUST forward traffic using the label
information from the EVPN Ethernet AD per EVI route.
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* If an composite PE receives an EVPN Ethernet AD per EVI route
followed by a VPWS A-D route or a LDP-LM message from the same PE,
then the composite PE will setup the EVPN-VPWS PW. It may keep
the L2VPN VPWS PW operationally down and MUST forward traffic
using the reachability information from that EVPN Ethernet AD per
EVI route.
* For L2VPN PEs not using VPWS A-D or LDP signaling, the composite
PEs need to be provisioned manually with PWs to those remote L2VPN
PEs for each pseudowire. In that case, if an composite PE
receives an EVPN Ethernet AD per EVI route from a PE to which a PW
exists, it may keep VPWS PW operationally down and MUST forward
traffic using the reachability information from that EVPN Ethernet
AD per EVI route.
In the case where a composite PE receives an EVPN Ethernet AD per EVI
route for an established L2VPN PW from a different PE, the result
should be directed by a local configuration. This is to avoid any
security breach where a malicious user may want to steer an existing
connection to a different PE.
9. Multi-homed Operations
Figure 4 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.
MPLS/IP
Composite PE Core L2VPN PE
+---------+
DF +---+ | | +---+ +---+
+--|PE1|----|---------|---|PE3|---|CE2|
+---+/ +---+ | PW1 /| +---+ +---+
|CE1| | / |
+---+\ +---+ | / |
+--|PE2|----|-----+ |
NDF +---+ | |
+---------+
Figure 4
EVPN-VPWS Multi-homing Redundancy
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9.1. Operations with Port-Active MH PEs
In Figure 4, PE1 and PE2 are configured in port-active load-balancing
mode. Both PEs are advertising EVPN Ethernet AD per ES route with
the single-active bit set as described in [I-D.ietf-bess-evpn-mh-pa].
In this example, PE1 is DF elected for the shared Ethernet-Segment
identifier.
* Only PE1, as DF, advertises the VPWS A-D route or LDP-LM message
towards remote PE3.
* PE1 advertises the EVPN Ethernet AD per EVI route for PW1 towards
remote PE3. The P-bit in L2 Attributes Extended Community is set
for PE1 as per [RFC8214]. The purpose is to have all required
EVPN-VPWS routes on remote PE. During an upgrade from L2VPN to
EVPN-VPWS, those remote nodes are immediately upgraded.
* PE2, as NDF, only advertises its EVPN Ethernet AD per EVI route
corresponding to that same PW1. The B-bit in L2 Attributes
Extended Community is set for PE2 as per [RFC8214]
* If PE3 is running 2-way pseudowire redundancy and PW-status is
enabled, PE2 may leverage the existence of standby/backup PW with
PE3. In this particular scenario, PE2 may advertise VPWS A-D
route or LDP-LM message along with PW-status message
Upon link failure between CE1 and PE1, PE1 and PE2 follow EVPN
Ethernet Segment DF Election procedures described in [RFC8214] for
EVPN-VPWS. Furthermore, PE1 withdraws its VPWS A-D route or sends
LDP-LW message to remote PE3 to teardown the L2VPN PW. Finally, PE2
advertises corresponding VPWS A-D route or LDP-LM message for that
PW1 and re-establish L2VPN PW with new PE2 destination.
Once PE3 is upgraded and support EVPN-VPWS, seamless integration
procedures are applied. Higher precedence of EVPN-VPWS over L2VPN
VPWS allow all PEs to avoid the usage of legacy circuit. Then, non-
preferred L2VPN VPWS protocols and configuration may be removed from
all PEs.
9.2. Operation with Single-Active MH PEs
Single-active operation is similar to Port-active load-balancing mode
described above. The main difference resides in the Designated
Forwarder election where the carving is performed at the circuit
level instead being of at the port/interface level.
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9.3. Operation with All-Active MH PEs
In EVPN-VPWS all-active load-balancing mode, all PEs participating in
a redundancy group forward traffic bidirectionally, reducing the
importance of DF and NDF PE. However, L2VPN PEs do NOT support all-
active peering PEs as remote endpoints.
9.3.1. Falling back to port-active
Composite PE discovering remote L2VPN PE MAY fallback into port-
active load-balancing mode. That can be achieved dynamically or by
enforcing network operators to configure port-active instead of all-
active load-balacing mode. In both cases, port-active multi-homing
operations, as described before, apply here
9.3.2. Asymmetric forwarding
As per Figure 4, peering PEs run in all-active load-balancing mode
while PE3 behaves as single-homed PE. Asymmetric forwarding consists
of transmitting traffic in an all-active manner from peering PEs to
PE3 while the reverse direction is done in port-active or single-
active manner.
Traffic from CE1 going to PE1 is forwarded to PE3 using the VPN label
learned from VPWS AD route or LDP-LM message received from PE3.
Traffic from CE1 going to PE2 is forwarded to PE3 using that same VPN
label. Traffic coming from CE2 to PE3 gets forwarded only over the
primary PW towards PE1; the DF PE. Supporting asymmetric forwarding
with L2VPN PE requires extensions to EVPN-VPWS MH procedures.
For BGP VPWS, PE1 and PE2 naturally receive the same label from PE3
via BGP. They can use the same label when sending to PE3. There is
no direct need for alias label signaling. For LDP VPWS, since the
LDP sessions are targeted, PE1 and PE2 always receive different
labels, hence the alias label procedure is needed.
Following rules are applied to achieve expected behavior:
* Peering PEs advertise EVPN Ethernet AD per ES route with the
single-active bit unset. That is to get the network ready when
remote L2VPN PE are upgraded to composite PE.
* DF PE advertises VPWS AD routes or LDP-LM message and EVPN
Ethernet AD per EVI route per PW.
* NDF PE advertises only EVPN Ethernet AD per EVI route per PW.
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* If PE3 is running 2-ways pseudowire redundancy, PE2 may leverage
the existence of standby/backup PW with PE3. PE2 may advertise
VPWS AD route or LDP-LM message with proper PW-status message.
* If PE3 is not running pseudowire redundancy, the tunnel
encapsulation attribute [RFC9012] is used to synchronize alias PW
label between peering PEs. The tunnel encapsulation attribute,
specifying the alias PW label and tunnel endpoint (nexthop) of the
remote PE (PE3), is transmitted along with EVPN Ethernet AD per
EVI route. The NDF PEs uses that alias VPN label per L2VPN PW as
DF PE when transmitting traffic coming from CE (CE1) towards
remote PE(PE3).
* Composite PE1 and PE2 do not need similar mechanism for EVPN-VPWS
since the same route advertised by PW is received on both PEs.
10. Route Optimization
If a composite PE does not know at priori whether the remote PE for a
given P2P service is a L2VPN PE or an EVPN PE, the composite needs to
participate in the auto-discovery and signaling procedures for both
L2VPN and EVPN-VPWS. This works well as it allows a composite PE to
establish a P2P service with different types of PEs, and to switch
from using a L2VPN PW to EVPN-VPWS dynamically during the migration
process.
A composite PE originates twice as many A-D routes as they are
required to establish the number of P2P services it is provisioned
to. Therefore in some scenarios, a composite PE should be optimized
to perform either L2VPN or EVPN-VPWS procedure for a given P2P
service, but not both.
For a composite PE, if a Service Provider has prior knowledge about
the types of remote PEs for some or all of its P2P Ethernet services,
reducing the number of routes a composite PE originates can be
achieved through the configuration. Based on the configuration, a
composite may advertise EVPN route but not L2VPN A-D route for a P2P
Ethernet service, or vice versa. It is up to the Service Provider to
decide based on the network requirement.
11. IANA Considerations
This document has no actions for IANA.
12. Security Considerations
The same Security Considerations described in [RFC8214] are valid for
this document.
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13. Contributors
In addition to the authors listed on the front page, the following
coauthors have also contributed to this document:
Ali Sajassi
Cisco Systems
Email: sajassi@cisco.com
Luc Andre Burdet
Cisco Systems
Email: lburdet@cisco.com
Daniel Voyer
Bell Canada
Email: daniel.voyer@bell.ca
Iman Ghamari
Linkedin
Email: iman@linkedin.com
Edward Leyton
Verizon Wireless
Email: edward.leyton@verizonwireless.com
14. References
14.1. 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>.
[RFC6074] Rosen, E., Davie, B., Radoaca, V., and W. Luo,
"Provisioning, Auto-Discovery, and Signaling in Layer 2
Virtual Private Networks (L2VPNs)", RFC 6074,
DOI 10.17487/RFC6074, January 2011,
<https://www.rfc-editor.org/info/rfc6074>.
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[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>.
[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>.
14.2. Informative References
[I-D.ietf-bess-evpn-mh-pa]
Brissette, P., Burdet, L. A., Wen, B., Leyton, E., and J.
Rabadan, "EVPN multi-homing port-active load-balancing",
Work in Progress, Internet-Draft, draft-ietf-bess-evpn-mh-
pa-07, 5 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-mh-pa-07>.
[I-D.ietf-bess-evpn-vpws-fxc]
Sajassi, A., Brissette, P., Uttaro, J., Drake, J.,
Boutros, S., and J. Rabadan, "EVPN VPWS Flexible Cross-
Connect Service", Work in Progress, Internet-Draft, draft-
ietf-bess-evpn-vpws-fxc-08, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-vpws-fxc-08>.
[RFC4664] Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
2 Virtual Private Networks (L2VPNs)", RFC 4664,
DOI 10.17487/RFC4664, September 2006,
<https://www.rfc-editor.org/info/rfc4664>.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
[RFC4762] Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
<https://www.rfc-editor.org/info/rfc4762>.
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[RFC6624] Kompella, K., Kothari, B., and R. Cherukuri, "Layer 2
Virtual Private Networks Using BGP for Auto-Discovery and
Signaling", RFC 6624, DOI 10.17487/RFC6624, May 2012,
<https://www.rfc-editor.org/info/rfc6624>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
Authors' Addresses
Patrice Brissette
Cisco Systems
Email: pbrisset@cisco.com
Wen Lin
Juniper
Email: wlin@juniper.com
J. Rabadan
Nokia
Email: jorge.rabadan@nokia.com
James Uttaro
ATT
Email: uttaro@att.com
Bin Wen
Comcast
Email: bin_wen@comcast.com
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