CPU High Utilization

[bssmith10]

Every day I have a router that spikes high CPU utilization (above 80%) in the morning, usually after everyone has begun work and done their logins, that lasts for maybe a couple of hours. It then drops back down to below 10%. It happened again today, so I telneted into the router and did a show proc cpu. The only process that showed above 1% was tty background. What is that? And if that was me telneted into the router, what else could be causing the router cpu to spike when there isn't a tty session on it?

[sspangle]

A TTY process at 1% is nothing to be concerned about. I'd graph your bandwidth and pps on all interfaces over a couple of days. I'll bet you get a spike in both of those during this time period. You'd then need to determine what is causing the spike in traffic with Ethereal or some other method.

Regards,

Steve

www.networking-forum.com

[bssmith10]

Sorry, I should have elaborated more. When I examined the proc cpu, the tty background was above 60%, but all other process were below 1%. I examined the bandwidth at the time and did not see high usage. I will perform more detailed monitoring of the interfaces over the next couple of days as suggested to be sure.

[johansens]

This may very well be due to a bug which is resolved with issuing the command "no logging synchronous" under the "con 0" line. Check this bug-id (req. entitled CCO-login):

http://www.cisco.com/cgi-bin/Support/Bugtool/onebug.pl?bugid=CSCdy01705

And see this link for info from Cisco TAC:

http://www.ciscotaccc.com/core/showcase?case=K11858846

For more information, do a search like this:

http://www.cisco.com/cgi-bin/search/search.pl?searchPhrase=troubleshooting%20high%20cpu

[arnichol]

Hi,

As CPU is going Hight only during High Traffic Time,I may suggest to check your Switching.make sure you are using better switching method in your High Traffic interface."show interface stat" and "show interface switching" should give you brief information about switching.

understand from your message that Traffic in this PVC is in Line rate,if this condition seen many time in the day,better to upgrade PVC.

but if it is only Spikes during the Peak Period may try Frame-relay Traffic-shaping to smoothern Traffic and avoid congestion.

Arul.

[gauravprakash]

Well, You can do some research on the reasons for high CPU utilization , but please check if you have a good version of IOS.

[jroyster]

Many times it is not a process, but interrupts.

CPU utilization for five seconds: 3%/1%; one minute: 2%; five minutes: 3%

Notice the "for five seconds: 3%/1%" The firs number 3% is total processor utilization, the second is processor utilization for interrupts.

So you could be reading 80%/75% which means you have excessive interrupts. You can search cisco.com for "troubleshoot high cpu" for a good document.

things to look for:

1) using process switching can hit the cpu hard

2) access lists or complicated access lists that are process switched

3) excessive logging or debugging, especially if logging to console

hope this helps

[sdoremus33]

I would ask the following questions

1. What is the networsk enviroment, are u running in a static en, with a few connections, are U running in an IGP env ie... OSPF,EIGRP, are you running BGP, are there any route flapping.

check each int sh ip int br, and run proc utilization while running all interfaces, is one causing this, could you please eloborate more on the network infrastructure. Thanks

[bssmith10]

This router is at the spoke end of a frame relay hub and spoke topology. A single FastE and serial link with single PVC. port speed is 128k. Running eigrp. No routing flaps recently. Right now proc cpu showsCPU utilization for five seconds: 1%/0%; one minute: 1%; five minutes: 0% TTY background as per first post is 0% vs. over 60% when cpu goes high. I checked on the bug also mentioned, but that command is not configured so it is not the bug.

[jhiggins]

I am having a similar problem with high cpu utilization. It is being caused by my serial interface connection as I moved it to another router and it is causing the same problem. I am incrementing "Total output drops" on the serial interface. I think that my problem is being caused by a saturated serial interface as the output of interface bits per second match the line speed of the serial interface. I am still trying to determine how I can limit the packets per second trying to go out that serial interface.

[johansens]

You won't see the command as it's a default setting.. just do a "no logging synchronous" on the "line con 0" if you have a IOS version which matches one in the "versions affected" list in the BugTool.

[farhadsoltani]

Are you have "logging synchronous" in "line vty"? If it's exists please remove it.

Farhad