Core issue
Malformed packets cause Cisco Catalyst OS (CatOS) 7.x code to display %SYS-4-SUPERVISOR_ERR:Forwarding engine IP errors.
These error message counters are recorded in the syslog:
%SYS-4-SUPERVISOR_ERR:Forwarding engine IP length error counter =4
%SYS-4-SUPERVISOR_ERR:Forwarding engine IP too short error counter =1
%SYS-4-SUPERVISOR_ERR:Forwarding engine IP check sum error counter = 38
These messages indicate the switch forwarding engine has received an IP packet which is below the minimum length of the allowed IP packets, and the forwarding engine is dropping it. In older CatOS code, the packet was silently dropped with no corresponding error messages and counted in the forwarding engine statistics. In newer supervisor codes (CatOS 7.x and later), this message error is recorded in the syslog once every 30 minutes.
Resolution
The switch normally drops malformed packets. The root cause is not the switch itself, but a device connected to it. A connected device sends the malformed packets. The causes of this issue include a bad Network Interface Card (NIC) driver, a NIC driver bug, or a misbehaving application.
Note: Use a network sniffer to track down the source address.
To disable these error messages, issue the set errordetection portcounters disable command on the switch. This action does not fix the root cause; to fix the cause, the offending device must be discovered.
For more information, refer to Common CatOS Error Messages on Catalyst 6500/6000 Series Switches.
