100% CPU with no apparent cause on a 831

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Apr 17th, 2007
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Hi everyone. I have a strange situation where one of our 831b is showing 100% CPU usage and the users aren't complaining at all. I checked the processes and didn't see any that were taking up CPU. The traffic is negligible from what I can see. The router has been running at 100% CPU for more than a day now. The other thing is that another one of our 831 is doing the same thing. Is there any known issue with 831's?


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Overall Rating: 4 (1 ratings)
dgahm Tue, 04/17/2007 - 06:49
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Can you post the output from show proc cpu sorted?

I would suggest reloading the router, and checking the bug toolkit for issues with the version of code you are running.

Please rate helpful posts.


chris_moyzan Tue, 04/17/2007 - 06:59
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See attached for the show proc cpu sorted output. I guess I should have mentionned that when I look at the processes, none of them use up ANY CPU at all...

I did look at the bug toolkit but didn't find anything. As for rebooting the router, I would have to do that during the night, unfortunately.

Danilo Dy Tue, 04/17/2007 - 07:09
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Can you post "show ver" output?

chris_moyzan Tue, 04/17/2007 - 07:11
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here's the show ver output:

show ver

Cisco IOS Software, C831 Software (C831-K9O3SY6-M), Version 12.3(8)T4, RELEASE SOFTWARE (fc2)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2004 by Cisco Systems, Inc.

Compiled Fri 03-Sep-04 08:21 by eaarmas

ROM: System Bootstrap, Version 12.2(8r)YN, RELEASE SOFTWARE (fc1)

ST-RAYMOND uptime is 20 hours, 34 minutes

System returned to ROM by power-on

System image file is "flash:c831-k9o3sy6-mz.123-8.T4.bin"

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

[email protected].

Cisco C831 (MPC857DSL) processor (revision 0x400) with 44237K/4915K bytes of memory.

Processor board ID AMB082022NR (2764410859), with hardware revision 0000

CPU rev number 7

2 Ethernet interfaces

4 FastEthernet interfaces

128K bytes of NVRAM.

12288K bytes of processor board System flash (Read/Write)

2048K bytes of processor board Web flash (Read/Write)

Configuration register is 0x2102

Danilo Dy Tue, 04/17/2007 - 07:29
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There are multiple bugs and vulnerabilities reported for 12.3(8)T4. Though the 100% CPU util is not listed, it could be a symptom of a new bug or vulnerability. I recommend for you to upgrade your IOS to latest T series, 12.3(14)T7 or 12.4(11)T1

chris_moyzan Tue, 04/17/2007 - 08:45
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I guess I'll just reboot one of the router during the night and see if it helps. I ran a report with our monitoring tool to see the CPU usage in the last year and the average is about 4-5%... Nothing was changed recently on those routers to explain this.

chris_moyzan Tue, 04/17/2007 - 10:45
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no changes were made recently, that's what's so puzzling about this. I did see a reboot before the CPU went to 100%, though. Is it possible that there would be some kind of invisible process that wouldn't show with show proc cpu?

Ahmede Tue, 04/17/2007 - 10:53
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If you are runnig OPSF, please port the output of

show ip ospf max..

chris_moyzan Tue, 04/17/2007 - 11:12
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here's what it gave me:

AS System 1

Maxage delete timer due in NEVER


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