Cisco 6509 SUP32 SNMP Meltdown With CatOS

Fri Nov 2 21:12:26 UTC 2012

On 11/02/2012 04:52 PM, Nick Hilliard wrote:

> E.g. a fully loaded 6509 with 384 ports would take ~3000 queries every
> several minutes to perform full port diagnostic polling, and you'd want to
> be doing this every couple of seconds to cause serious CPU impact.  Are you
> doing something like full DFZ or MAC table polling?

I bet you're close toward the end there.  My guess is he's carrying a
large BGP feed and querying the ipRouteTable.  The caveat below is for
IOS 12.4(20)T but equivalent issues surely exist for CatOS:

http://www.cisco.com/en/US/docs/ios/12_4t/release/notes/124TCAVS3.html#wp2057950

The killer in this case is not the SNMP traffic or anything resulting
directly from it, but the CPU overhead from constantly re-sorting the
ipRouteTable since that's generated from the FIB when CEF is enabled.
Workaround is to disable CEF (heh) or configure a MIB view that excludes
the ipRouteTable.  This one bites an OpenNMS support customer a few
times a year -- happened again just today, in fact, at a shop that just
enabled topology discovery.

> Also, you may want to consider moving away from CatOS, as it's now
> basically abandonware (or at least will formally be in Jan 2013), and
> hasn't even seen maintenance updates in the last 4 years.

What you said :)

-jeff