300-320 Question #186: Real Exam Question with Answer & Explanation

The correct answer is A: BFD. Bidirectional Forwarding Detection (BFD) is a lightweight, protocol-independent hello mechanism designed to rapidly detect link or path failures between two adjacent devices. It operates in milliseconds (configurable down to ~50ms) and notifies routing protocols like OSPF of the

Question

Refer to the exhibit. Which Layer 2 feature detects a link failure between the switch and router B that decreases OSPF reconvergence to approximately 50 milliseconds?

Exhibit

Options

ABFD
BUDLD
CRSTP
DPVST+

Explanation

Bidirectional Forwarding Detection (BFD) is a lightweight, protocol-independent hello mechanism designed to rapidly detect link or path failures between two adjacent devices. It operates in milliseconds (configurable down to ~50ms) and notifies routing protocols like OSPF of the failure far faster than OSPF's own hello/dead timers. UDLD detects unidirectional link conditions but does not accelerate OSPF reconvergence. RSTP and PVST+ are spanning-tree variants that operate at Layer 2 for loop prevention, not for accelerating Layer 3 routing protocol convergence.

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