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BFD Support for VCCV for Layer 2 VPNs, Layer 2 Circuits, and VPLS

Bidirectional Forwarding Detection (BFD) support for virtual circuit connectivity verification (VCCV) on MX Series devices enables you to configure a control channel for a pseudowire, in addition to the corresponding operations, administration, and management functions to be used over that control channel.

BFD provides a low resource mechanism for the continuous monitoring of the pseudowire data path and for detecting data plane failures. This feature provides support for asynchronous mode BFD for VCCV as described in RFC 5885, Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity Verification (VCCV). Alternatively, you can use a ping operation to detect pseudowire failures. However, the processing resources required for a ping operation are greater than what is needed for BFD. In addition, BFD is capable of detecting data plane failure faster than a VCCV ping. BFD for pseudowires is supported for Layer 2 circuits (LDP-based), Layer 2 VPNs (BGP-based), and VPLS (LDP-based or BGP-based).

Starting with Release 12.1, Junos OS introduces a distributed model for the BFD for VCCV. Unlike in previous releases where the BFD for VCCV followed a Routing Engine-based implementation, in Release 12.1 and later, the BFD for VCCV follows a distributed implementation over PIC concentrators, such as DPC, FPC, and MPC.

For distributed BFD, you need to configure the lo0 interface with unit 0 and the appropriate family enabled.

Note:

For the distributed BFD for VCCV to work, you must configure MPLS family (family mpls) on the loopback interface.

Note:

On ACX Series routers, to enable BFD sessions over VCCV, you need configure control word. For VPLS, include the control-word statement at the [edit routing-instances routing-instance-name protocols vpls] hierarchy level. For Layer 2 VPN, include the control-word statement at the [edit routing-instances routing-instance-name protocols l2vpn] hierarchy level. For Layer 2 Circuit, include the control-word statement at the [edit protocols l2circuit neighbor neighbor-ip-address interface interface-name] hierarchy level. The control-word statement must also be configured at the peer device for control word negotiation to happen between the pseudowire peers.

In Junos OS Release 12.1 and later, the periodic packet management process (ppmd) on the PIC concentrators handles the periodic packet management (send and receive) for BFD for VCCV. This enables Junos OS to create more BFD for VCCV sessions, and to reduce the time taken for error detection. Similarly, the distributed implementation improves the performance of Routing Engines because the Routing Engine resources used for BFD for VCCV implementation become available for Routing Engine-related applications when the BFD for VCCV-related processing moves to the PIC concentrators. The distributed BFD for VCCV implementation also enables the BFD for VCCV sessions to remain across graceful restarts.

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