[c-nsp] troubleshooting SVI input drops on MSFC3

[Lincoln Dale (ltd)]

> Or, does the traffic hit the MSFC because the CEF adjacency is the
same
> interface for all prefixes, i.e. router-on-a-stick?
> 
> I've read references to both as being the reason one would see high
CPU on
> an MSFC along with SVI input drops, just trying to understand the
hardware
> better.  It seems the magic number is around 40-50 Mbps which resulted
in
> 75% CPU usage and input drops.  That just seems low for such powerful
> hardware...

you either have a feature enabled which isn't implemented in hardware
(hence h/w has to punt to software to process), or you've hit some kind
of bug that is causing your particular traffic to be sent to software
for processing.

beyond mentioning the hardware you have, you haven't mentioned what IOS
release, nor have you posted any configuration snippet from your SVI, so
it's a little difficult to provide any meaningful diagnosis as to which
of the above it may be.

as a suggestion, if you have a support contract, open a TAC case to
troubleshoot with the TAC.  alternately, have a look through release
notes for newer IOS releases and see if you can find a 'closed bug' that
matches the behavior you have seen.
alternately, search through the bug database to see what you can find.


I don't think "40Mbps" is a magical number. it just represents some
pkts/sec level.
as a general statement, you rarely want to be hitting software
switching, less so process-level switching within software switching!


cheers,

lincoln.