What is the approximate failure-detection time provided by BFD?

Bidirectional Forwarding Detection (BFD) is designed for very fast failure detection, often in milliseconds. This makes "less than a second" the most accurate answer. While other options like 1, 2, or 3 seconds represent relatively quick detection, BFD's primary advantage is its ability to detect failures significantly faster than traditional routing protocol hello mechanisms (which typically operate in seconds). BFD achieves this speed by using lightweight, rapid hello packets, making it ideal for applications requiring near-instantaneous fault detection to minimize network disruption.