A Series Switches - CPU Utilization Excessively High when No Device
Connected as Well as After Devices Connected
Environment
All A-Series switches
Issue
Switch with no configuration reporting 10% CPU utilization
No devices are connected to any of the interfaces with exception to the console connection reporting 10%+ CPU utilization
With devices attached the CPU utilization increases significantly
Cause
The initial CPU utilization that is reported with no devices connected to interfaces (with the exception of the console) is a baseline of
the switch resources being used. Even though the switch is not doing anything, it is still monitoring interfaces, memory,
buffer handling and other operating system functions. The CPU utilization being reported would be viewed as the baseline
utilization.
As devices are added to interfaces or as features are implemented and the amount of traffic traversing the unit increases the CPU
utilization will increase. The increase in devices added to the switch may not necessarily be a linear increase of CPU utilization .
Resolution
If there is a significantly high baseline CPU utilization being reported, review the Release Notes of the latest build of software.
Perhaps there gave been modifications to the algorithm used to calculate CPU utilization that may be available.
If the CPU utilization is excessively high with devices attached, there may be a process that is using a significant level of CPU
cycles. Examination of the logbuffer may result in a diagnostic message describing a possible condition that could lead to excessive
CPU utilization. An example would be if a switch is operating in a Spanning Tree environment. If an examination of the logbuffer
reveals a high occurrance of Topology Change Notification (TCN's) messages, that could indicate that the switch is in an unstable
STP network and that due the frequency of TCN messages, the CPU utilization will increase.