Network Operations Guide

Bill Nash billn at
Thu Aug 23 15:39:27 UTC 2007

On Thu, 23 Aug 2007, Sam Stickland wrote:

> Bill Nash wrote:
> > The single most important piece of advice I can offer when building your own
> > tools: Never poll the routing table with SNMP. Ever. Any OTS tool that says
> > it can, as a feature, well, it's a witch, burn it. (
> >   
> You mean like the Cisco Route Manager?
> *
> *
> I not used it myself but the datasheet does say it collects the routing tables
> via SNMP, with the one cavet:
> "Prior to a scan, the Cisco Route Manager checks the router's CPU and if the
> percentage is greater than a configured threshold then it does not scan the
> route table and moves onto the next router."

That 'feature' right there is a great indicator as to just how unhealthy 
such an action is. Even if your CPU load is below your threshold, you 
can't guarantee that the polling action isn't going to put it over that 
threshold to the point of impacting performance. 

Break out the Zebra/Quagga install and offload that CPU load. Don't use 
SNMP to read routing information.

Ok, I shouldn't be so declarative about it. You can do whatever you want 
with your network. I will continue to beat people if/when I catch them 
doing it. =)

- billn

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