| Internet-Draft | Abbreviated Title | March 2021 |
| Brissette, et al. | Expires 23 September 2021 | [Page] |
This document specifies mechanisms for backward compatibility of Ethernet VPN Virtual Private Wire Service (EVPN-VPWS) solutions with legacy Virtual Private Wire Service (VPWS). It provides mechanisms for seamless integration in the same MPLS/IP network on a per-pseudowire or per flexible-crossconnect service basis. Implementation of this document enables service providers to introduce EVPN-VPWS PEs in their brown-field deployments of legacy VPWS networks. This document specifies control-plane and forwarding behaviour needed for auto-discovery of a pseudowire in order to enable seamless integration between EVPN-VPWS and VPWS PEs.¶
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Virtual Private Wire Service (VPWS) is a widely-deployed Layer-2 VPN (L2VPN) technology. Many service providers, who are looking at adopting Ethernet VPN Virtual Private Wire Service (EVPN-VPWS), want to preserve their investment in the VPWS networks. Hence, they require mechanisms by which EVPN-VPWS can be introduced into their brown-field legacy VPWS networks without requiring any upgrades (software or hardware) to these networks. This document specifies control-plane and forwarding behaviour needed for auto-discovery of a pseudowire in order to enable seamless integration between EVPN-VPWS Provider Edge(PE) devices and PEs running legacy VPWS services in the same MPLS/IP network.¶
MPLS/IP Core
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2| Legacy VPWS
| |----|---+ | +---+
+---+ | | |
EVPN-VPWS & | +--PW2---+ | +---+
Legacy VPWS | +--|---|PE3| EVPN-VPWS
(hybrid) | | +---+
+---------------+
Seamless Integration of EVPN-VPWS.¶
Figure 1 shows a simple network where PE1 runs in hybrid mode (EVPN-VPWS and legacy VPWS). It provides a pseudowire (PW1) with PE2 running legacy VPWS. It also provides a pseudowire (PW2) with PE3 running EVPN-VPWS. PE2 may be upgraded to EVPN-VPWS seamlessly. Legacy PEs may be setting up PWs per [RFC8077] or may be setting up a VPWS service by first auto-discovering VPN members using [RFC6074] and then setting up the PWs using [RFC8077] or [RFC6624].¶
The seamless integration solution described in this document has the following attributes:¶
- It is backward compatible with [RFC8214] and EVPN Flexible crossconnect Service [evpn_fxc] document.¶
- New PEs can leverage the multi-homing mechanisms and provisioning simplifications of EVPN Ethernet-Segment:¶
Figure 2 illustrates how legacy VPWS brown-field network migration to EVPN-VPWS is achieved. For example, let say PE1 and PE2 have a legacy PW established between them. First, network operator may upgrade PE2 to support EVPN-VPWS. Once upgraded, PE2 which now have the EVPN-VPWS capability still runs legacy VPWS PW with PE1. Later on, network operator may decide to upgrade PE1 to support EVPN-VPWS. As soon as the upgrade is completed, EVPN-VPWS service takes high-precedence over legacy VPWS network. The network operator can safely remove any legacy configuration related to that PW from PE1 and PE2 nodes. PW remains established as an EVPN-VPWS service.¶
MPLS/IP Core
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | Legacy | +---+
Legacy | | Legacy
VPWS +---------------+ VPWS
....
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | Legacy | +---+
Legacy | | Legacy VPWS
VPWS +---------------+ + EVPN-VPWS
....
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | EVPN-VPWS | +---+
Legacy VPWS | | Legacy VPWS
+ EVPN-VPWS +---------------+ + EVPN-VPWS
....
+---------------+
+---+ | | +---+
|PE1|----|----- PW1 -----|---|PE2|
+---+ | EVPN-VPWS | +---+
EVPN-VPWS | | EVPN-VPWS
+---------------+
Migration from Legacy to EVPN-VPWS.¶
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 [RFC2119].¶
Following are the key requirements for backward compatibility between EVPN-VPWS and VPWS:¶
These requirements collectively allow for the seamless insertion of the EVPN-VPWS technology into brown-field VPWS deployments.¶
In order to support seamless integration with Legacy PEs, this document may require Legacy PEs to setup PWs per [RFC8077] or may require Legacy PEs to setup VPWS service by auto-discovering VPN members using [RFC6074] and then setting up the PWs using [RFC8077] or [RFC6624]. Furthermore, EVPN-VPWS PEs must support BGP EVPN routes per [RFC8214] and one of method of legacy VPWS technologies. All the logic for seamless integration SHALL reside on the EVPN-VPWS PEs.¶
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.¶
In the case of VPWS PEs running VPWS A-D, they may advertise the BGP VPWS A-D route, per the procedures specified in [RFC4664] and [RFC6074]. The operator may decide to use the same BGP Route Target (RT) to identify a pseudowire on both EVPN-VPWS and VPWS networks. In this case, when a VPWS 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 VPWS network and another for EVPN-VPWS network and employ RT-constrained [RFC4684] in order to prevent BGP EVPN routes from reaching the VPWS 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 the purpose of discovery. This ensures that, at the end of the route exchange, all EVPN-VPWS capable PEs discover other EVPN-VPWS capable PEs. Furthermore, all the VPWS-only PEs discover the EVPN-VPWS PEs as if they are standard VPWS PEs. In other words, when the discovery phase is completed, the EVPN-VPWS PEs have discovered the remote PE per pseudowire along with their associated capability (EVPN-VPWS or VPWS-only), whereas the VPWS PE have discovered the remote PE per pseudowire as if it is VPWS-only PEs.¶
Figure 3 demonstrates a typical brown-field deployment where PE2 is a legacy PE and PE1 is an EVPN-VPWS PE.¶
EVPN-VPWS & MPLS/IP
Legacy VPWS Core Legacy VPWS
+---------------+
+---+ | | +---+
|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 forwarding state setup procedures over VPWS PEs are per [RFC8077], [RFC4761] and [RFC4762].¶
The EVPN-VPWS PE procedures are as follow:¶
Figure 4 below demonstrates multi-homing scenarios. CE1 is connected to PE1 and PE2 where PE1 is the designated forwarder while PE2 is the non designated forwarder.¶
EVPN-VPWS & MPLS/IP
Legacy VPWS Core Legacy VPWS
+---------+
DF +---+ | | +---+ +---+
+--|PE1|----|---------|---|PE3|---|CE2|
+---+/ +---+ | PW1 /| +---+ +---+
|CE1| | / |
+---+\ +---+ | / |
+--|PE2|----|-----+ |
NDF +---+ | |
+---------+
EVPN-VPWS Port-Active 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 EVPN port-active document [evpn_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 Legacy PW. Finally, PE2 advertises corresponding VPWS A-D route or LDP-LM message for that PW1 and re-establish Legacy 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 supports EVPN-VPWS, seamless integration procedures are applied. Higher precedence of EVPN-VPWS over VPWS allow all PEs to avoid the usage of legacy circuit. At that point in time, non-preferred legacy VPWS protocols and configuration may be removed from all PEs.¶
Single-active operation is similar to Port-active load-balancing mode described above but at the VLAN level instead being of at the port/interface level.¶
The main difference resides on the support of Legacy PW VC-type 4 vs PW VC-Type 5 mode on the EVPN-VPWS PE as per [RFC4448]. While services running in port-active load-balancing mode require raw mode, services running single-active load-balancing mode use tagged mode.¶
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 PEs running Legacy VPWS do NOT support all-active peering PEs as remote endpoint.¶
EVPN-VPWS PE discovering remote PE running VPWS PW MAY fallback into port-active load-balancing mode. In that case, following rules are applied:¶
One privilege option is the asymmetric forwarding while peering PEs run in all-active load-balancing mode. In the example of Figure 3, 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 should get forwarded to PE3 using that same VPN label. Traffic coming from CE3 to PE3 gets forwarded only over the primary PW towards PE1; the DF PE.¶
Supporting asymmetric forwarding with purely LDP as per [RFC8077] requires extensions to EVPN-VPWS MH procedures. These procedures are NOT restricted only to LDP and may be applied to VPWS A-D.¶
Following rules are applied to achieve expected behaviour:¶
This document has no actions for IANA.¶
The same Security Considerations described in [RFC8214] are valid for this document.¶
The authors would like to acknowledge Sylvain Masse for his feedback and contribution to this document.¶