The UDLD protocol allows devices connected through fiber-optic or copper Ethernet cables (for example, Category 5 cabling) to monitor the physical configuration of the cables and detect when a unidirectional link exists. When a unidirectional link is detected, UDLD shuts down the affected port and alerts the user. A unidirectional link occurs whenever traffic transmitted by the local device over a link is received by the neighbor but traffic transmitted from the neighbor is not received by the local device. For example, if one of the fiber strands in a pair is disconnected, as long as autonegotiation is active the link does not stay up. In this situation, the logical link is undetermined, and UDLD does not take any actions. If both fibers are working normally at Layer 1, then UDLD at Layer 2 determines whether those fibers are connected correctly and whether traffic is flowing bidirectionally between the correct neighbors. I posts the UDLD explanation because knowing that the best way to isolate is move the same cable to another port with UDLD enabled, if the cable is the cause the UDLD will follow. In short, of running diagnostics on the line card by re-seating it, there is not command to see the health of the port. diagnostic is run at boot-up not online. Please rate if it helps.
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