The above Topology represents a failure on a Fiber Optic Transmit / Receive cable pair on one cable, on one end of the link, which would leave the link up and Unidirectional. Here is an example of the SFP Transceiver and Fiber cable connecting to a switch: Source : This Cisco.com 2960x Fiber Stacking article … Continue reading STP – Fiber Cabling, Loop Guard and UDLD DEEP DIVE, and important notes for exam day!