First determine if the problem is real or is there a perceived problem. If determined to be real (e.g. performance is not as expected), start troubleshooting. Try and isolate the problem to a particular link, device or component. After you have narrowed down the problem to a specific area, propose a solution and test it.
The main functions a router CPU performs are packet forwarding and executing control plane and management processes. When high CPU utilization occurs it is important to understand when it is a potential problem and when temporary high CPU utilization might be normal. High CPU utilization could be attributable to short network burst which would be considered normal or if CPU utilization is consistently high it will be impacting performance and needs to be investigated.
When the CPU is too busy network performance suffers. Things such as packet loss can occur as buffers fill up, jitter (variations in packet delay) as the CPU is not processing packets in a timely manner and higher than normal delays due to the same problem as just mentioned.
Numerous problems can arise due to high CPU utilization. Some common problems are listed on the slide above.
Some of the common causes to high router CPU utilization are listed on the slide above.
Listed on the slide above are just a handful of examples that can cause high router CPU utilization.
The show processes cpu command displays overall router CPU utilization as well as the CPU utilization of each of the processes running on the router. The output CPU utilization for the past 5 seconds, past 1 minute and past 5 minutes.
The show processes cpu history command is similar to the show processes cpu command although it displays router utilization for the past 1 minute, 60 minutes and 72 hours.
In the example on the slide, in order to utilize the Advanced Enterprise Services version of IOS your 3800 series router would need to have a minimum of 256MB of DRAM and 64MB of Flash.