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Cisco 3900 Router - high CPU utilization

Level 1
Level 1

Hi All,

I am having Cisco 3900 router (C3900-SPE150/K9)  running with SW Version 15.0(1r)M13.

During the peak hours in night time the user number touches at 1000 in numbers and consuming around 145 Mbps of bandwidth. During that period the CPU consumption of router touches at 99% and ping latency to router(LAN) crosses 100. During the day time the CPU runs at around 50% in average with 100 Mbps bandwidth consumption.


I would like to know is it common for this model of router and in that case do I need to upgrade router or Is there any solution so that I can reduce the CPU consumption during the peak time?






8 Replies 8

Leo Laohoo
Hall of Fame
Hall of Fame

@cleetusant wrote:

consuming around 145 Mbps of bandwidth.  

I think I know what is causing the high CPU.  

What is the WAN bandwidth?  Is it >150 Mbps?

Hi Leo,

Total Bandwidth is 150 Mbps.




What is the exact model of the router?

RTR#sh ver
Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.1(4)M4, REL EASE SOFTWARE (fc1)
Technical Support:
Copyright (c) 1986-2012 by Cisco Systems, Inc.
Compiled Tue 20-Mar-12 21:28 by prod_rel_team

ROM: System Bootstrap, Version 15.0(1r)M13, RELEASE SOFTWARE (fc1)

GV-RTR uptime is 2 days, 23 hours, 44 minutes
System returned to ROM by reload at 21:00:15 AFT Wed Dec 5 2018
System restarted at 21:02:00 AFT Wed Dec 5 2018
System image file is "flash0:c3900-universalk9-mz.SPA.151-4.M4.bin"
Last reload type: Normal Reload
Last reload reason: Reload Command

This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:

If you require further assistance please contact us by sending email to

Cisco CISCO3945-CHASSIS (revision 1.0) with C3900-SPE150/K9 with 987136K/61440K bytes of memory.
Processor board ID FGL1625108U
3 Gigabit Ethernet interfaces
1 terminal line
DRAM configuration is 72 bits wide with parity enabled.
255K bytes of non-volatile configuration memory.
250880K bytes of ATA System CompactFlash 0 (Read/Write)

License Info:

License UDI:

Device# PID SN
*0 C3900-SPE150/K9 FOC16237K7W

Technology Package License Information for Module:'c3900'

Technology Technology-package Technology-package
Current Type Next reboot
ipbase ipbasek9 Permanent ipbasek9
security None None None
uc None None None
data None None None

Configuration register is 0x2102

CISCO3945 - is capable of handling that traffic.


did you see show process cpu  what is causing issue that time ?


To understand better what is the this router does in the network, it is internet edge router processing all the request.

we need to closely look is this normal, if this is normal we can not tweak, consider upgrading to ISR / ASR higher models depends in requirement.





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Hi Balaji,

Yes, This is the Edge router does process all the internet request. last week I have upgraded bandwidth from 120 to 150 Mbps due to the sudden increase of user numbers. From that time this issue started.

Is there anything else we need to consider in the interface configuration ? CEF is configured globally as well as in the interface. There is not much drops also I can find in the LAN interface.


Any idea ?




As you have mentioned after upgrading the internet facing bandwidth from 120Mb to 150MB and users increased using, from then  you have start observing the cpu high process. to confirm again  We need to collect some samplings and analyse what is causing this issue.  ( also post the configuration), then we can suggest some tuning config.


show processes cpu sorted 5sec  - collect the data


Consider below document for reference :




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Hi Balaji,

Please see the attached conf file.