High CPU utilization clears after router reboot

[Jeffj12345]

Dear Members,

We had an issue with one of our routers wherein the CPU utilization on the router was around 98%. The utilization of the processes running was around 25%. Hence we could conclude that the high CPU was due to interrupts.

We were using a very old IOS which was released in 2012 and it was buggy,hence we decided to go with the IOS upgrade to the latest one suggested by Cisco.

I have a few questions here

1> When trying to load the new IOS it took atleast one hour as we are getting a lot of zeroes in the output which i believe that the packets were out of form. Why would this happen due to high cpu utilization

2>How did the CPU utilisation drop after reboot even without ios upgrade

Thanks for your help

[Reza Sharifi]

Hi,

Getting a lot of zeroes is not because of high CPU.  It may be the file is not loading correctly or it is corrupted.

If you just reboot the IOS without upgrading to a different version, it takes sometime for the CPU to  spike again.

If you are upgrading to a different version, make sure to read the release note for that version, as you may be encounter a different bug in the OS.

HTH

[Jeffj12345]

Hi Reza,

Thanks for getting back,, after the reboot we did not encounter any problem for more than a week, what i believe the problem was that we started observing the issue afer HWIC removal for Cisco 3945, thinking that it was hot swappable, but later observed that 3945 series router support OIR and we need to follow those steps when removing HWIC