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.

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[light1001]

We are using a 2821 router as a centralized TDM-to-SIP voice gateway for a few remote facilities. The voice traffic is first sent as H323 between a Vendor_B voice gateway at the remote site to a central Vendor_B voice gateway through GRE tunnels. The GRE tunnels from the remote facilities terminate on the 2821, which then routes the traffic to the central Vendor_B voice gateway. The voice traffic is then processed by a central PBX and handed back to the 2821 as TDM through 2 MFT T1 ports. The 2821 then sends the calls as SIP to the ITSP.

The router is overloading at around 40-50 concurrent calls due to interrupt traffic. All calls are G.711 and, even though the voice traffic is being hairpinned, the bandwidth rarely exceeds 7mbps. Please see attached diagram. Thanks so much for your help! 

[Vinit Jain]

Hello,

the first thing we need to understand is if the traffic coming on the router is hitting the CPU or not and if yes, then why? Could you please share the following outputs:

- show process cpu sort | ex 0.0    // capture this output 2-3 times
- show interface
- show interface switching
- Running config of all relevant interfaces

You can attach the above outputs as a file.