Which interconnectivity method offers the fastest convergence in the event of a unidirectional issue between three Layer 2 switches connected together with trunk links?

Fiber optic links are uniquely susceptible to unidirectional failures when one strand breaks while the other remains intact; UDLD (Unidirectional Link Detection) is a Layer 2 protocol purpose-built to detect these conditions and immediately disable the affected port, providing the fastest possible Layer 2 convergence for this specific failure type on trunk links between switches.

BFD (Bidirectional Forwarding Detection) operates at Layer 3 to accelerate routing protocol convergence and does not detect Layer 2 unidirectional trunk link issues; copper is also inherently less prone to unidirectional failures.

BFD is a Layer 3 failure detection mechanism and cannot detect Layer 2 unidirectional conditions that UDLD is specifically designed to address on fiber links.

Copper Ethernet relies on auto-negotiation which typically detects failures bidirectionally, and UDLD's primary benefit targets fiber where independent TX and RX strands make unidirectional failures most common.