Episode 166: Link Layer Diagnostics — Duplexing, Transceivers, and LEDs

Link-level problems are easy to overlook but frequently cause intermittent issues. This episode explores duplex mismatches—where one device is set to full duplex and the other to half—leading to collisions, retransmissions, and degraded performance. We explain how to spot and correct these mismatches using port configuration and interface statistics.

We also examine the diagnostic value of physical indicators like LED lights and link lights, which can show speed, connectivity, and activity status at a glance. Finally, we discuss SFP and GBIC transceivers, their compatibility requirements, and how to troubleshoot them. These Layer 1 and 2 indicators are your first line of defense in network diagnostics.