Episode 45: Interface Errors and Duplex Mismatches
Interface-level problems can wreak havoc on network performance and are often the root cause of symptoms like slow connections, dropped packets, and unreliable links. This episode focuses on diagnosing errors reported by switch and router interfaces, such as CRC errors, late collisions, input errors, and output drops. These indicators reveal underlying issues that often stem from bad cables, failing hardware, or misconfigured ports. Understanding how to interpret these counters is essential for identifying performance bottlenecks.
A major focus of this episode is duplex mismatches, where one device operates in full-duplex mode while the other uses half-duplex, resulting in collisions and retransmissions. We explain how to spot these mismatches using CLI commands and interface logs, and we demonstrate how to manually set duplex and speed settings for consistent behavior. This is a high-impact topic that appears frequently on the exam and in real-world support calls.
