CRC errors increment in the show interface command output on a Cisco IOS-based switch due to a duplex mismatch.
If Cyclic Redundancy Check (CRC) errors are incrementing in the show interface command output check the port speed and duplex
settings.
Ensure that both devices are configured identically. Both sides should be set to auto speed and auto duplex,or hard set to the
same speed and duplex settings.
This is an explanation of CRC errors:
a.. CRC errors indicate that the cyclic redundancy checksum generated by the originating LAN device does not match the
checksum calculated from the data received. On a LAN, this usually indicates noise or transmission problems on the LAN interface
or the LAN bus itself. A high number of CRCs is usually the result of collisions or a station transmitting bad data.
On Cisco IOS-based switches, the interface configuration commands to set the speed and duplex to auto are speed auto and
duplex auto.
To hard set the speed and duplex settings, issue the duplex and speed commands specifying the desired settings.
For example, to set the interface to 100/full, issue the speed 100 and duplex full commands. Never mix a hard set and an auto
command on the same interface. For example, the speed auto and duplex full commands should never be issued on the same
interface.
If the speed and duplex settings are correct, yet the CRC counters continue to increase, perform these steps:
a.. Verify that the connected Network Interface Card (NIC) is good and has the latest drivers.
b.. Verify that the cable connecting the devices is good, using a cable tester or by replacing it with a known good cable.
c.. Verify that no interference is occurring on the line.
You can refer to:
http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00800a7af0.shtml
Hope this helps
