Cisco "show interfaces" Command Explained
show interfaces — shows full detail for interfaces — state, speed/duplex, and the error counters that reveal physical-layer problems. Runs in privileged EXEC mode.
Syntax and common variants
| Variant | Purpose |
|---|---|
show interfaces | All interfaces, full detail |
show interfaces gi0/1 | One interface |
show interfaces status | Switch summary: speed/duplex/VLAN per port |
show interfaces counters errors | Error counters table |
Reading the output
| Output field | Meaning |
|---|---|
Gi0/1 is up, line protocol is up | L1/L2 health at a glance |
Full-duplex, 1000Mb/s | Negotiated duplex and speed |
CRC / input errors | Corrupted frames — cabling/duplex suspects |
collisions / late collisions | Classic duplex-mismatch signature |
output drops | Congestion — traffic exceeding the interface |
When to use it
Where cable and duplex problems confess: climbing CRC errors mean bad cabling/SFP; late collisions scream duplex mismatch; growing output drops mean congestion. Clear counters, reproduce, re-check — that's the physical-layer troubleshooting loop. Browse more in the command reference or practise in the free labs.
Frequently asked questions
What causes CRC errors?
Corrupted frames — usually damaged cables, bad connectors/SFPs, interference, or a duplex mismatch.
What indicates a duplex mismatch?
Late collisions on the half-duplex side and CRC/runts on the full-duplex side — fix both ends to auto or matching manual settings.
How do I reset the counters?
clear counters [interface] — then watch whether errors keep climbing while you test.
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