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The %C4K_PKTPROCESSING-4-ERRORPACKET: and "%C4K_HWACLMAN-4-WARNINGSTRING:" error messages and high CPU utilization in Catalyst 4000/4500 Series Switches running Cisco IOS system software


Core issue

The error message looks similar to this:

%C4K_PKTPROCESSING-4-ERRORPACKET: Warning - Unexpected packet hitting input acl

%C4K_HWACLMAN-4-WARNINGSTRING: Entry: 48 PacketCount: 7

The software is unable to process a packet. Instead, the packets are forwarded to the CPU. Since this event is unexpected, the packet is being dropped. This ternary content addressable memory (TCAM) error indicates that the packet cannot be handled by ASIC hardware in Cisco Express Forwarding (CEF) with TCAM.

The impact that you see is in the CPU utilization and increases because of the extra packets that are forwarded.

In some scenarios, these messages appear even though you do not have an access-list applied on any interface.

The most possible cause is the hardware issue with the Supervisor Engine.


As a workaround, during the maintenance window, physically pull out and reseat the Supervisor firmly and reload the supervisor to make sure the TCAM is reprogrammed without ACL in the configuration.

In order to run a complete diagnostic test on the Supvervisor module and check for any hardware problems, complete these steps:

  1. Issue the diagnostic level complete command in the global configuration mode in order to set the diagnostics level to complete.       
  2. Issue the hw-module 1 reset command in order to soft-reset the module. After the module is up again, capture the output of the show module 1 command and the show diagnostic module 1 command.

For further assistance and support, use the TAC Service Request Tool in order to open a case with Cisco Technical Support.