Layer 1
show ip interface brief
| Problem | Solution |
|---|---|
| administratively down | no shutdown |
| down/down | Layer 1 issue; check cables and device power (or interface is shutdown on other side) |
| up/down | Layer 2 issue; check interface config matches on both sides (including duplex and speed) |
 |
show interface <interface> <port/port>
If the interface is reporting an excessively high number of errors it is possible that this is caused by high collision rates due to speed/duplex mismatches. Additionally, speed mismatches will cause the interface to operate below max speed and often bring it down entirely.