[c-nsp] High CPU usage on 2621's

[andrew2 at one.net]

Can't seem to figure this one out.  I have a pair of 2621's on my
network that are maxing out their CPUs during a backup process every
evening.  The network layout looks like this:

Backup server <--> 2924XL-EN <--> 2621 <--> Firewall <--> 2621 <-->
2924XL-EN <--> Servers being backed up

During the backup, traffic through the two 2621's gets up to a little
more than 50Mb/s, which to my understanding shouldn't be anything they
aren't capable of handling.  There doesn't appear to be any degradation
of service, however the CPU's on both routers spike up to 100% during
the backup window.  During normal operations the traffic through each of
the routers is less than 10Mb/s and the CPU usage is negligible.
(Usually no more than 10%.)

Both routers have multiple secondary addresses configured on the FE port
connected to the switch.  Fast switching and CEF are enabled on both
routers on both FE interfaces, and same-interface switching is enabled
on the FE ports connected to the switch.  Is there anything else I
can/should be doing to help with this, or is this normal behavior.  As I
said, I haven't noticed any service degradation as a result of the CPU's
being pegged but I'm a bit concerned.

Thanks for any help,

Andrew