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High CPU Utilization

Answered Question
Jun 6th, 2017
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Dear All,


I have 200mb live traffic running on Cisco 3845 router. But from past few days CPU utilization is going very high(80%). 

Normal cpu utilization was upto 20% earlier. 


I am not able to find out why utilization is going this high. 


Please explain. 

Correct Answer by Joseph W. Doherty about 2 months 6 days ago

Well, if shifting traffic away from the router has brought the CPU down, then the high CPU was likely due to the traffic itself.

As a personal rule, I try to avoid having a 3845 deal with more than 100 Mbps.  Normally, I would expect 200 Mbps to peg the CPU of a 3845.

The real question was whether your high CPU was almost all interrupt usage, normally indicating optimal performance, or whether there was another process driving the high CPU, like IP Input.  The latter can sometimes be corrected allowing a higher forwarding rate.

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Leo Laohoo Tue, 06/06/2017 - 15:28
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Please post the complete output to the command "sh proc cpu sort | ex 0.00".

praveenthakran92 Mon, 06/12/2017 - 05:05
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Router4#sh processes cpu sorted | ex 0.00
CPU utilization for five seconds: 27%/26%; one minute: 32%; five minutes: 23%
PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process
91 1900 9100 208 0.24% 0.24% 0.23% 0 IP Input
116 24 729 32 0.08% 0.06% 0.05% 0 CEF process
76 4 14429 0 0.08% 0.07% 0.06% 0 EAP Framework

Leo Laohoo Mon, 06/12/2017 - 14:04
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Looks OK to me. 

Joseph W. Doherty Tue, 06/13/2017 - 07:03
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Ideally, you want to capture the stats that Leo requested when the CPU is "very high(80%)."

praveenthakran92 Tue, 06/13/2017 - 19:18
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I got Leo's reply after a day. Before that I had shifted some traffic to Cisco asr1001x.  

Why would I keep working on a router with 80% cpu utilization? 

Now everything is normal. 

Correct Answer
Joseph W. Doherty Wed, 06/14/2017 - 02:43
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Well, if shifting traffic away from the router has brought the CPU down, then the high CPU was likely due to the traffic itself.

As a personal rule, I try to avoid having a 3845 deal with more than 100 Mbps.  Normally, I would expect 200 Mbps to peg the CPU of a 3845.

The real question was whether your high CPU was almost all interrupt usage, normally indicating optimal performance, or whether there was another process driving the high CPU, like IP Input.  The latter can sometimes be corrected allowing a higher forwarding rate.

Leo Laohoo Wed, 06/14/2017 - 16:13
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Well, if shifting traffic away from the router has brought the CPU down, then the high CPU was likely due to the traffic itself.

I concur with Joe.

Joseph W. Doherty Fri, 06/16/2017 - 04:08
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That depends on the model, and also depending on the model, what's installed in it or what performance it's licensed for.

The ASR 1K (and the ISR 4K) differ from their earlier counterparts in that they have built in performance caps.  This to try to insure they always can deliver the throughput noted in their data sheets.

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