These are common symptoms of high CPU utilization:

  • High percentages in the output of the show processes cpu commandIf you have the show processes cpu command output or a show tech-support command from enable mode, display potential issues and fixes from your Cisco device by referring to the Output Interpreter tool.
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  • Input queue drops
  • Slow performance

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  • Services on the router fail to respond, for instance: 
    • Slow response in Telnet or unable to Telnet to the router.
    • Slow or no response to the ping command.
    • The router does not send routing updates.
  • If the router is being overloaded with traffic or the traffic not taking the optimal switching path through the router, the issue can also be caused by the Blaster and Nachi worms.
  •    You can see what are the processes shooting your CPU utilization using following command:
  • You can also check your CPU history in graphical pattern using “show processes cpu history”  command to see High CPU spike.

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    Resolution

     

    To resolve this issue, determine the accessibility of the router by performing these steps:

    1. Determine if you are able to issue the show commands on the router. If so, start collecting more information immediately using these show commands.
    2. Determine if the router is inaccessible and if this problem is reproducible. If so, power-cycle the router. Before reproducing the problem, configure the scheduler interval 500 command; this schedules low priority processes to run every 500 ms. This provides time for you to run some commands, even if CPU usage is at 100 percent. On Cisco 7200 and Cisco 7500 series routers, issue the scheduler allocate 3000 1000 command.
    3. Determine if the router shows symptoms of high CPU utilization at brief and unpredictable intervals. If so, periodically collect the output of the show processes cpu command. This shows if the high CPU utilization is caused by interrupts or by a certain process. Use this UNIX script. Based on the first findings, modify the script to collect data needed for further investigation of the issue.