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[Archive] [ScreenOS] How to troubleshoot increasing Input errors, CRC and overrun counters on a Cisco switch connected to Netscreen firewall



Article ID: KB5058 KB Last Updated: 21 Mar 2020Version: 5.0

Input errors, CRC and overrun counter are increasing on Cisco Switch. How do I interpret the counters data?

  • Transparent mode
  • Juniper firewall
  • Cisco Catalyst Switches
Symptoms & Errors:
  • Input errors counter is increasing on Cisco Switches
  • CRC counter is increasing on Cisco Switches
  • Overrun counter is increasing on Cisco Switches

Input error: Includes runts, giants, no buffer, CRC, frame, overrun, and ignored counts. Other input-related errors can also cause the input error count to be increased, and some datagrams may have more than one error; therefore, this sum may not balance with the sum of enumerated input error counts.

CRC: Indicates that the cyclic redundancy checksum generated by the originating LAN station or far-end 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.
Overrun: Shows the number of times that the receiver hardware was incapable of handing received data to a hardware buffer because the input rate exceeded the receiver's capability to handle the data.


In order to troubleshoot this issue,

  1. Swap the cable between Firewall and Cisco Catalyst, then check if these counters are still increasing

  2. Swap the Cisco Catalyst switch port to another port, then check if these counters are still increasing.

  3. Remove the Firewall temporarily, and check if counters are increasing. If counters are still increasing, it is not a Firewall problem. Check the traffic pattern using packet capturing tool and contact the switch vendor for more troubleshooting assistance.

  4. If counters are NOT increasing, please capture the traffic pattern using packet capturing tool, and analyze the data for oddities in the data. Send the captured data to Juniper Support for further troubleshooting.

Modification History:
2020-03-21: Archived article.
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