[c-nsp] 3750 stack with high CPU from IP Input process.

[Bill]

    Hi,

    I have a 3750 stack that has 3 Cisco 3750's in it. Attached to the stack
via a 1 gig trunking port is a Cisco 2950. That 2950 doesn't have anything
plugged into it except a 24 port Alcatel switch. I recently moved that
Alcatel switch from the 2950 to the 3750. That left the 2950 empty. For some
reason the 3750 CPU went from loafing at about 5 or 6% CPU to 50% CPU.
Sometimes even higher. I can't figure out why but I did notice that when I
do a "show interface stats" it shows that all of the interfaces are doing
"process switching". Fast and CEF switching is enabled on all interfaces but
according to the "show interface stats" the stack is doing "process
switching". I assume this is the reason for the high CPU usage.

    This switch stack has 1 routed interface as the gateway for the entire
stack. It connects to a 3662 router. And it has 3 VLANs for routing specific
networks.

    I've talked to Cisco and the only answer I get is change the "SDM
PREFER" to "routing" and reboot. That's a bunch of bilogna because the stack
ran at 5 or 6% before I moved that ethernet cable to the 3750. Earlier today
I moved the Alcatel ethernet cable back to the 2950 and the CPU continues to
run high. That 2950 loafs along at 1 or 2% but doesn't do any routing. The
load thru the 3750 is the same no matter where that Alcatel ethernet is
plugged in at.

    Anyone have any ideas? So far Cisco tech has been no help.

    Bill