[c-nsp] RANCID Spiking CPUs

[Justin Shore]

Nick,

I run RANCID on my SP network and I too see the high CPU spikes.  Mine 
actually clock in at 100% (high enough that it makes my 1m average 
register 80% on some devices via sh pr cpu his (which means that it's 
actually between 80 and 89%)).  I have a couple devices in particular 
that it hits hard.  One is a 7206 (G1) with almost 15,000 lines of 
config.  That other is a 3660 with over 18,000 lines of config.  I've 
never had any trouble though and I poll my devices hourly.

I'm not aware of any way of throttling the access that VTYs have to the 
control-plane.  In general I think the best approach is to make sure 
that your IOS device is well-configured and tuned with performance in 
mind.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/cs/csprtf/csprtf4/csperfrm.htm

For example, have you configured your routers to use the Nagle 
algorithm?  I'd highly recommend looking into it.

http://www.google.com/search?hl=en&q=service+nagle&btnG=Google+Search

The first couple of hits (especially the Cisco Press one) give you good 
info.

Justin


Nick Davey wrote:
> Hi All,
> I've deployed rancid on a fairly large metro network, and am seeing some
> pretty high CPU averages. When RANCID runs the CPU's on a large number of
> our boxes spike to about 95% for several seconds. Although they have never
> hit 100%, or caused any issues (dropped OSPF hello's, stp bpdu's) I'm
> concerned that this could happen under the right combination of events this
> could result is dropped OSPF neighbor adjacency's or other badness.
> 
> I've tried to replicate the high CPU issue by pasting the commands in
> manually however I haven't come anywhere close to the 95% I'm seeing when
> RANCID runs them. I'm assuming this is just the frequency at which the
> commands are run. Does anyone have any experience with this or any insight
> they can provide?