Core issue
This issue is caused by a bad cable, Network Interface Card (NIC) or duplex configuration.
The show port counters mod#/port# command shows Frame Check Sequence (FCS)-errors incrementing on a port.
FCS errors can be caused by any of these options:
- Collisions
- Duplex mismatch
- Hardware (NIC, cable or port)
- Frames with bad FCS being generated by the connected device
Resolution
To resolve this issue, perform these steps:
- If possible, hard set the speed and duplex settings on both the port and the connected device.
On the switch, issue the set port speed mod#/port# speed and set port duplex mod#/port# duplex commands.
For example, to set the speed to 100 and the duplex to full on port 5 of module 4, the commands would be as shown:
set port speed 4/5 100
set port duplex 4/5 full
- Check the cable with a tester or replace it with a known good cable.
If the connection is to a patch panel, bypass the patch panel and connect directly to the end device.
- Check the NIC drivers on the end device to make sure they support the required duplex and speed settings.
For compatibility information, refer to Troubleshooting Cisco Catalyst Switches to NIC Compatibility Issues.
- Check the port by connecting the end device to a different port on the switch.
Monitor the port counters to see if the FCS-err count is incrementing.
Problem frequency
Always
Device connected to switch
Host
Server
Another Switch
External router
Non Cisco
Show port errors
FCS-Err
Show interface counters
CrcAlign-Err
