Refer to the exhibit.

BFD with tuned timers is the correct fault-detection solution when OSPF traffic must fail over in milliseconds and cannot wait for the OSPF dead interval. Cisco describes Bidirectional Forwarding Detection as a lightweight mechanism that detects forwarding-path failures rapidly and notifies the routing protocol. OSPF can then bring down the adjacency and switch to an alternate route without waiting for the normal hello and dead timer process. Tuning SPF delay or LSA timers improves the control-plane calculation phase after OSPF has learned about a failure, but it does not provide the fastest failure detection by itself. IP SLA tracking can detect reachability problems, but it is not the standard per-neighbor OSPF millisecond detection mechanism. Decreasing SPF timers alone does not solve the requirement to avoid waiting for the dead interval. Therefore, BFD with appropriate 100 ms timers is the correct design choice. Reference topics: OSPF high availability, BFD, fast failure detection, dead interval avoidance, subsecond convergence.