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carl_townshend
Frequent Contributor

cpu 100% on 3850

Hi All

It appears we have hit an issue with our 3850s running an old version of code, the fed process seems to be maxing out the CPU.

Can anyone tell me if this will have any impact when forwarding traffic?

As forwarding is done in hardware I would expect not, however 100% cpu must me having an impact somewhere?

what is the best fix, IOS upgrade ?

cheers

1 ACCEPTED SOLUTION

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Yes i believe so it definitely wouldn't help and if it stays like that the switch may just tip itself over and reboot too anyway as Reza said especially if 4 are maxed out constantly

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6 REPLIES 6
Joseph W. Doherty
Hall of Fame Expert

The impact of a process consuming all the available CPU depends on how that process is prioritized. As Cisco doesn't, as far as I know, publicly document priorities of their processes, unable to say whether such a high CPU for the FED process would adversely impact traffic forwarding (or other control plane functions, for the matter).

Often an IOS upgrade is the fix, especially if the release notes document it fixing the issue being seen. (Depending where you are in the life cycle of the IOS, often an IOS upgrade may generally be a good thing.)

Ye i hit a FED bug issue before on 3.6.2 went to 3.6.6 an it fixed it cpu dropped back to normal , I think there's 4 cores if I remember right , so it shouldn't hugely impact forwarding unless there all maxed with FED as the culprit

good doc on it from CL regarding architecture and how to tshoot it
http://d2zmdbbm9feqrf.cloudfront.net/2016/usa/pdf/BRKCRS-3146.pdf

same again specific just to cpu
https://www.cisco.com/c/en/us/support/docs/switches/catalyst-3850-series-switches/117594-technote-hicpu3850-00.html

Hi

just for info, all 4 cpus are running at 100%.

would this cause traffic forwarding issues ?

Yes i believe so it definitely wouldn't help and if it stays like that the switch may just tip itself over and reboot too anyway as Reza said especially if 4 are maxed out constantly
Reza Sharifi
Hall of Fame Expert

Hi,

If this switch is in production, it is critical to your environment and the CPU is100%, all the time, you need to fix it right away as it will crash sooner than later. As Mark said, 3.6.6 is pretty good. With 3.6.6 the CPU will be ok, but the memory still at 40% on a simple layer-2 box which is not good. Oh, well 40 is better than 80 or 90. In general, Cisco 3850s run high on CPU or memory or both.

HTH

Leo L
VIP Community Legend