Common Cisco switch port errors
Table of contents
Common network problems
From my experience the most network problems are on Layer One (Physical layer aka “The cable”). Cisco switches provide a lot of information of the switch interfaces and typically I check:
swt-3750g#show interfaces counters errors
swt-3750g#show interfaces status
swt-3750g#show interfaces GigabitEthernet x/x/x
Overview
| Error | Possible cause |
|---|---|
| Align-Err | Malformed frames, bad hardware, duplex mismatch, half duplex collisions |
| FCS-Err | Bad frame checksum, duplex mismatch, bad hardware |
| Xmit-Err | Speed settings mismatch |
| Rcv-Err | Duplex mismatch, backplane congestion |
| UnderSize | Received frames which are less than 64 bytes |
| OutDiscards | Occur when transmit buffer is full and packets are dropped |
| Single-Col | Half duplex, duplex mismatch, high utilization of port |
| Multi-Col | Half duplex, duplex mismatch, high utilization of port |
| Late-Col | Cable length, duplex mismatch |
| Excess-Col | Switch rehad 16 collisions in row, high utilization of port |
| Carri-Sen | Duplex settings |
| Runts | Frame is smaller than 64 bytes and has bad CRC, duplex settings, physical port |
| Giants | Frame is larger than 1518 bytes and has bad FCS, device source |