Two routers R1 and R2 are directly connected through an Ethernet link. Both routers are running OSPF. OSPF has been registered with BFD and BFD is running in asynchronous mode with the echo function…

BFD echo packets are originated by the local forwarding engine, transmitted to the remote device, and looped back at Layer 2 by the remote device without involving the remote BFD control plane, effectively testing the bidirectional data-plane path.

The echo function causes BFD control packets to be sent at a slower rate, not a higher rate, because echo packets assume responsibility for data-plane detection.

The remote BFD session does not actively participate in the processing or forwarding of echo packets - the remote device simply loops them back at Layer 2 with no BFD control plane involvement on that end.

Because the echo function offloads failure detection to the forwarding plane, BFD control packets no longer need to be exchanged at a high rate - the Required Min Echo RX Interval allows the control packet interval to be negotiated slower since echo packets are performing the actual liveness detection.

When the echo function is enabled, echo packets are sent from the forwarding engine in addition to control packets; a control-packet-only mode describes asynchronous operation without the echo function.