A city clerk reports one-way fiber between wiring closets: frames leave one switch but never return. Which Layer-2 feature is specifically meant to detect that unidirectional condition?
Select an answer to reveal the explanation.
Short Explanation
One-way fiber is like a hallway with doors that only swing outward—you can leave but never get back. Neighbor discovery chats won’t catch that trap. UDLD is the feature that checks both directions so a silent one-way link doesn’t keep pretending it’s fine.
Full Explanation
UDLD (Unidirectional Link Detection) exchanges probes to confirm the link is bidirectional; when fiber or copper fails in only one direction, UDLD can errdisable the port before STP or EtherChannel assumes a healthy path. CDP and LLDP discover neighbors and capabilities but are not the primary unidirectional-link safety mechanism. PortFast only changes STP edge-port timing. For closet fiber that passes light one way, enable and tune UDLD rather than relying on discovery protocols.