Overview of Headend Termination for EVPN VPWS for Business Services

Single Pseudowire Headend Termination

The pseudowire subscriber transport logical interface is used as the access interface for EVPN-VPWS instance. EVPN establishes a point-to-point Ethernet service with pseudowire subscriber transport logical interface as an access interface in the control plane.

Active-Standby Pseudowire Headend Termination

As shown in Figure 2, to achieve resilience for pseudowire headend termination into Layer 3 VPN or BGP-VPLS, you can use a pair of redundant pseudowires on the EVPN-VPWS side. Also, in Figure 2, Layer 3 VPN or BGP-VPLS is treated as if it is multi-homed to the set of redundant service edge routers, PE1 and PE2. PE1 and PE2 work in active-standby mode for EVPN-VPWS. One of them is elected as the primary PE per EVPN normal designated forwarder (DF) election procedure. Only the primary PE is used to forward Layer 2 traffic.

Figure 2: EVPN-VPWS Active/standby with Pseudowire Subscriber Interface

Following are the reasons for the pseudowire failure, when redundancy is provided by the EVPN-VPWS active-standby interface:

• Service edge router node failure.

• Pseudowire subscriber transport logical interface failure on the primary PE.

• Failure on the path towards the primary PE.

The EVPN-VPWS also supports the service side of the network multi-homing to EVPN-VPWS through the pseudowire subscriber logical interface in an active-standby mode.

To achieve active-standby pseudowire headend termination, the following is required:

• Ethernet segment identifier (ESI) support on the pseudowire subscriber transport logical interface.

• Synchronizing data path between active pseudowire and Layer 3 VPN.

• MAC flush in the BGP-VPLS when the active-standby pseudowires switch. MAC flush is triggered when the active service edge node suffers a node failure.

[edit]
routing-instances {
    l3vpn_1 {
        instance-type vrf;
        interface ps0.1;
        interface lo0.1;
        route-distinguisher 2.2.2.3:6500;
        vrf-import l3vpn1_import;
        vrf-export l3vpn1_export;
        vrf-table-label;
        protocols {
             bgp {
                group toPW-CE1 {
                    type external;
                    export send-direct;
                    peer-as 1;
                    neighbor 10.1.1.1;
                }
            }
        }
    }
}
policy-options {
    policy-statement l3vpn_1_export {
        term 1 {
            from condition primary;
            then {
                local-preference add 300;
                community set l3vpn_1;
                accept;
            }
        }
        term 2 {
            from condition standby;
            then {
                community set l3vpn_1;
                accept;
            }
        }
    }
    policy-statement l3vpn1_import {
        term 1 {
            from community l3vpn_1;
            then accept;
        }
        term default {
            then reject;
        }
    }
    community l3vpn_1 members target:65056:100;
    condition primary {
        if-route-exists {
            address-family {
                ccc {
                    ps0.0;
                    table mpls.0;
                }
            }
        }
    }
    condition standby {
        if-route-exists {
            address-family {
                ccc {
                    ps0.0;
                    table mpls.0;
                    standby;
                }
            }
        }
    }
}

[edit]
routing-instances {
    vpls-1 {
        instance-type vpls;
        interface ps0.1;
        route-distinguisher 100:2;
        vrf-target target:100:100;
        protocols {
            vpls {
                site ce3 {
                    site-identifier 3;
                }
            }
        }
    }
}

Active-Active Pseudowire Headend Termination

Active-active pseudowire headend termination is supported only in Layer 3 VPN and not supported in BGP-VPLS.

vMX

A vMX can have active and backup VCP with one or more VFPs. The VCP is the RE and the VFP is the line-card. The communication between VCP and VFP is facilitated through vRouter, if the VCP and VFP reside on the same server. Else, it is through the external network to which the servers are connected. There is no direction communication between VFPs.

Service Isolation

For a given point-to-point pseudowire with only one VFP per vMX, the data traffic is handled by one VFP for both ingress and egress traffic.

Active-Standby Pseudowire Headend Termination into VMX

The vMX acts as a regular MX for the overlay point-to-point Ethernet service. Similar to physical MX router, redundancy is achieved by using multiple vMXs, and only active-standby pseudowire headend termination is supported. The pseudowire is terminated at the loopback IP address that is used as the protocol nexthop address for the pseudowire.