[c-nsp] 3560 cpu load question

Cord MacLeod cordmacleod at gmail.com
Thu May 21 19:20:31 EDT 2009

It sits in the middle of a network.  Below are layer 2 2960 switches  
at the top of rack which the machines plug in to.  Above are routers  
announcing BGP default at it in the confederation.  The machines use  
the 3560 to traverse vlans, it is also the root switch in spanning  
tree and has around 110 inbound acls applied on the interface leading  
to the edge routers.  As far as STP is concerned, the topology never  
changes so we can rule out convergence.

That's every function the switch is performing.  These spikes are  
abnormal spikes, and they do not show up on my graphs, nor can I find  
the process causing them.  There is no correlation I find between the  
CPU spikes and any network traffic.

On May 21, 2009, at 4:09 PM, Peter Rathlev wrote:

> On Thu, 2009-05-21 at 15:18 -0700, Cord MacLeod wrote:
>> My graphs show cpu spikes up to 20% every now and again, but the
>> following command shows 100% spikes.  Question being is this normal
>> behavior, how would I track the cause (assuming my traffic is
>> relatively stable throughout the day) and should I be worried this  
>> may
>> be impacting traffic?
> Is it normal: Probably not. But that depends on what the device is
> doing.
> Will there be traffic impact: Probably not. Traffic forwarding is not
> CPU bound. Traffic forwarding of course relies on the CPU executing
> certain algorithms depending of protocols in use. (STP, IGP, BGP etc.)
> which it might not be able to do in a timely fashion if busy doing
> something else.
> Tracking the cause: Start looking at "show proc cpu sorted" and see  
> what
> processes take up most CPU when the spike is occuring.
> What is the device configured to do, apart from forwarding traffic?
> Regards,
> Peter

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