Interface counters and what they actually tell you
Every error counter has a specific meaning. Knowing which is which turns guessing into diagnosis.
Writing
ethernet
Cable faults that look like software faults
Hours get spent in configuration for problems that live in the first metre of the path.
Duplex mismatch: the fault that hides in plain sight
The link is up, the speed is right, and throughput is terrible. Check the counters, not the status.