| Internet-Draft | EVPN-VPWS Seamless Integration | July 2021 |
| Brissette, et al. | Expires 12 January 2022 | [Page] |
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 flexible-crossconnext (FXC) service basis. This document specifies control-plane and forwarding behaviors.¶
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].¶
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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) | | +---+
+---------------+
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:¶
- 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:¶
MPLS/IP Core
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | L2VPN | +---+
L2VPN | | L2VPN
VPWS +---------------+ VPWS
...
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | L2VPN | +---+
L2VPN | | L2VPN VPWS
VPWS +---------------+ + EVPN-VPWS
....
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | EVPN-VPWS | +---+
L2VPN VPWS | | L2VPN VPWS
+ EVPN-VPWS +---------------+ + EVPN-VPWS
....
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | EVPN-VPWS | +---+
EVPN-VPWS | | EVPN-VPWS
+---------------+
Migration from L2VPN to EVPN-VPWS.¶
Figure 2 illustrates the migration of a L2VPN VPWS brownfield network to EVPN-VPWS. For example, let say 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 taked 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.¶
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.¶
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.¶
The seamless integration solution for point-to-point Ethernet VPN meets the following requirements:¶
These requirements collectively allow for the seamless insertion of the EVPN-VPWS technology into brownfield L2VPN VPWS deployments.¶
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.¶
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.¶
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 [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.¶
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.¶
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:¶
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:¶
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 per EVI/EAD ] --->
EVPN-VPWS Single-Homed¶
The control plane procedures of L2VPN PEs are per [RFC8077], [RFC4761] and [RFC4762].¶
The EVPN-VPWS PE procedures are as follow:¶
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.¶
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 +---+ | |
+---------+
EVPN-VPWS Multi-homing Redundancy¶
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.¶
Upon link failure between CE1 and PE1, PE1 and PE2 follows 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.¶
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.¶
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.¶
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.¶
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.¶
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¶
As per figure 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:¶
With the simplest provisioning model, if a composite PE does not know a 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 to establish a P2P service with different types of PEs composite PE, and to switch from using a L2VPN PW to EVPN-VPWS dynamically during the migration process.¶
The simples provisioning model may not be optimal though, in that 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 scenario,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.¶
This document has no actions for IANA.¶
The same Security Considerations described in [RFC8214] are valid for this document.¶