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Resolving High CPU Occupancy on Cisco C3850 Switches
Mar 27 , 2023 1501

Upgrading Cisco C3850 Switches to Solves the Problem of High CPU Occupancy

According to our customer's feedback, the CPU usage rate of a Cisco aggregation switch has increased recently.

Problem analysis process

1. Checked from the monitoring software, the CPU usage is high


2. According to the switch logs, after searching for related processes, we can find that the occupancy rate of FED and stack-mgr processes is high


 Analyze the cause of the failure and provide solutions

1. Since the device has never been restarted after running for a long time, abnormalities is caused by long-term operation. Thus, it is recommended to restart. 

2. Given that the current version is too old, it is recommended to upgrade SW to fix known bugs



First, troubleshooting solution description

According to Cisco, upgrading the current version of C3850SW to a higher version can solve the problem of high CPU occupancy rate of the switch.

The following is description


Second, upgrading preparation

1.The client provides a computer that installs TFTP software and USB flash disk, so we need to prepare the console control line, network cable, and send the IOS version file to the client for downloading.

2. Through the show switch command, we can confirm the current active and standby switches according to the figure shown as below,.


3. Use the show version command to view the current version of the switch and confirm that the switch is running in INSTALL mode.


4. Backup the configuration file of the C3850 in the network, and put a temporary label on the interface cable of the C3850 switch, indicating the corresponding switch port information on the label. For example, the description of port 1 of switch 1 is SW1-1.

Third, upgrading procedures and process

1. Download and copy the IOS version file to a USB flash drive, and connect it to the USB port of the C3850 switch.

2. Use the console to connect to the switch and log in, and enter the following command to copy the IOS file to the flash of the switch:

copy usbflash0: cat3k_caa-universalk9.SPA.03.07.05.E.152-3.E5.bin flash: cat3k_caa-universalk9.SPA.03.07.05.E.152-3.E5.binn

3. Log in to the switch through the console, and enter the upgrade command:

3.1 First upgrade the standby switch


Switch# software install file flash: cat3k_caa-universalk9.16.06.09.spa.bin switch 2 force


3.2 After the upgrading process is completed, the standby switch automatically restarts. Wait for the standby switch to go online again, and then upgrade the active switch.


Switch# software install file flash: cat3k_caa-universalk9.SPA.03.07.05.E.152-3.E5.bin


3.3 The active switch automatically restarts after the upgrading process ends. Wait for the switch to go online again, and use the following command to confirm that the two switches have been upgraded to the target version.

Switch# show switch


Switch# show version 

So far, the IT equipment maintenance technical support has been successfully completed, and the customer's equipment has returned to normal operation.

Related Reading:

10 Questions About The Cisco Catalyst 3850 Series Switches

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