Network Interface Health
Use this skill when a network symptom might be caused by a physical link, switch port, cable, transceiver, duplex setting, or congested interface.
When to Use
- A host or VLAN has packet loss, latency spikes, or intermittent reachability.
- A switch or router interface shows CRCs, runts, giants, drops, resets, or flaps.
- You need to compare both ends of a link before replacing hardware.
- A change window needs before/after interface counter evidence.
- Monitoring reports rising
ifInErrors,ifOutErrors, orifOutDiscards.
How It Works
Interface counters are evidence, but the trend matters more than the absolute number. Capture a baseline, wait a measurement interval, capture again, then compare increments.
show interfaces <interface>
show interfaces <interface> status
show logging | include <interface>|changed state|line protocol
On Linux hosts:
ip -s link show <interface>
ethtool <interface>
ethtool -S <interface>
Counter Reference
| Counter | Meaning | Common cause |
|---|---|---|
| CRC | Received frame checksum failed | Bad cable, dirty fiber, bad optic, duplex mismatch |
| input errors | Aggregate … |
