[c-nsp] 3560 cpu load question

Peter Rathlev peter at rathlev.dk
Fri May 22 05:49:12 EDT 2009

On Thu, 2009-05-21 at 16:20 -0700, Cord MacLeod wrote:
> 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.

Would this switch happen to have a L3 interface in a VLAN with other
hosts? Broadcasts are always sent to the CPU, so user traffic then might
cause spikes.

> 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.

Strange. What are the graphs graphing? Maybe the 5 min avg. every 5
minutes? That would explain why spikes couldn't be seen there at least.

You can setup rmon to alert you specifically when the CPU load exceeds
some threshold:

rmon event 1 trap SecretCommunity description "Rising Event for busyPer" owner admin
rmon event 2 trap SecretCommunity description "Falling Event for busyPer" owner admin
rmon alarm 1 lsystem.56.0 60 absolute rising-threshold 90 1 falling-threshold 70 2 owner admin

With EEM or a script on the trap receiver you could extract the process
table at exactly the moment the CPU spikes occur.


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