Bidirectional Forwarding Detection (BFD) is used in conjunction with OSPF to provide sub-second failure detection. However, running standard BFD (Control Mode) for many neighbors can place a significant load on the switch ' s Control Plane CPU, as the CPU must process every BFD control packet.
Control Mode vs. Echo Mode:
Control Mode: Both peers exchange BFD packets that are processed by their respective CPUs. This ensures the BFD state machine is synchronized but is CPU-intensive.
Echo Mode: The switch sends a BFD Echo packet to its neighbor. The neighbor simply " reflects " the packet back in the data plane (ASIC) without sending it to its own CPU. The originating switch then processes the returned packet.
Efficiency of Echo Mode: In the Aruba AOS-CX architecture, BFD Echo Mode is highly efficient because it offloads the " heartbeat " processing from the CPU to the hardware (ASIC) on supported platforms. By enabling echo mode, the frequency of control packets reaching the CPU is reduced, which effectively resolves high CPU utilization issues while maintaining fast failover.
Evaluating Other Options:
Option A: ICMP is not part of the BFD mechanism for OSPF adjacency tracking.
Option B: OSPF does not form adjacencies on passive interfaces, so BFD would not run there and would not contribute to CPU usage.
Option D: ICMP redirects are unrelated to the BFD protocol ' s internal processing logic.
