Ask the Expert: High CPU on IOS Questions with Cisco Expert Vinit Jain

[Lisa Latour]

This is an opportunity to learn and ask questions about high CPU condition that you might be facing your environment and troubleshooting the same with the tools and techniques available within the platform with Cisco expert Vinit Jain.

Ask questions from Monday, May 11th, 2015 to Friday, May 22, 2015

High CPU condition is a very common problem seen in production environments which can cause a huge impact on the services if not taken care on time. High CPU can be classified in primarily in two categories – 1) High CPU due to process and 2) High CPU due to interrupt (traffic). Cisco expert Vinit Jain will cover and answer all of your questions about troubleshooting High CPU on Cisco IOS.

Vinit Jain, 3X CCIE #22854 is a Technical Lead in HTTS (High Touch Technical Support) team supporting customers in areas of routing, MPLS, TE, IPv6, multicast and a wide variety of platform issues like High CPU, Memory leak, etc IOS, IOS XE, IOS XR and NxOS code base. Has been delivering trainings within Cisco on various technology as well as platform troubleshooting topics. He has also written workbook on IOS XR fundamentals on Cisco Support Community. Vinit has CCIE in R&S, SP and Sec and holds multiple certifications on programming and databases.

Vinit Jain will also be speaking at Cisco Live in June 2015 on Troubleshooting BGP (BRKRST-3320). 
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[Vinit Jain]

Hello,

First of all, i would like to know on which device you are seeing the high CPU - on 4500 or 3945? Also, could you please share the below outputs from both the devices:

- show process cpu sort | ex 0.0
- show interface
- show version
- show inv
- show run

Please capture the above outputs in files and upload. Further understanding the problem, if you are seeing high CPU due to IP Input process, are you also seeing input-queue drops on any of the interfaces?

Looking forward for the logs.

Thanks,

Vinit

[narendrabimo]

CPU Process on SM-ES3G-16-P (3945 switch Module) is high. Sorry i have not capture the cpu proccess when it was at peak, because the link went intermittent. So i rolled the scenario back quickly. There was a output drop on tunnel interface, for further information i have attached some configurations and topology. Thanks for your help

[Vinit Jain]

Thanks for the logs. Please note the output drops will not cause the CPU to spike. it can be due to qos policy drops or due to the other side not being able to process the packets quickly (so buffer issue).

Regarding the other logs, its more important to look at the physical interface out of which the tunnel is going and also its necessary to capture logs during problematic condition.

If you can share the complete "show interface" output, we can get some idea on which interface might have got input-queue drops and we can correlate it to the time of the issue. 

But, as I said again, its more important to troubleshoot when the problem is live. Its hard to say without relevant logs as what could be possibly going wrong during the high cpu condition.

Thanks,

Vinit