Arsenal / Troubleshooting
Interface Counter Decoder
The switch already knows what's wrong. The counters are how it tells you.
Paste show interfaces output or load a sample. The decoder explains every counter, flags the ones that matter, and points to the likely cause. Then test yourself on five practice outputs.
- Network+ N10-009 · Troubleshooting
- Cisco IOS-style output
- Nothing leaves your browser
01 / Decode
Paste or pick an output
Works best with Cisco IOS show interfaces output. NX-OS-style “input discard” / “output discard” lines are read too. Your text stays on this page.
Counters found
| Counter | Value | What it means |
|---|
02 / Field guide
Counter glossary
Duplex mismatch, the classic pattern: the half-duplex side logs collisions and late collisions (it thinks it can only talk when the line is quiet). The full-duplex side logs CRC errors and runts (the half side keeps aborting frames). Throughput is terrible but the link stays up, which is why it hides so well.
Rule of thumb: errors on a full-duplex link point to Layer 1 (cable, connector, optic, interference, or a run longer than 328 feet (100 meters)). Drops with zero errors point to capacity (congestion). Always clear counters (clear counters) and watch them climb before you blame anything.
03 / Practice
What's wrong?
Read each output and pick the most likely cause. Your answer grades immediately; the explanation and a link to decode the output follow.