[c-nsp] 3750 High Cpu IP Input

[Peter Rathlev]

On Thu, 2009-04-23 at 13:51 -0400, Chris Lane wrote:
> Having a high cpu with my 3750 not in stack. sh proc cpu | exclude 0.00
> CPU utilization for five seconds: 68%/43%; one minute: 69%; five minutes:
> 70%
>  PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
> 168    40336940  92166921        437 15.49% 15.76% 15.97%   0 IP Input
> 
> WS-C3750-48TS      12.2(35)SE2             C3750-ADVIPSERVICESK
> 
> According to some old threads this was a bug in some older IOS which was
> fixed in 12.2(25)
> 
> Egress port is quiet:
> 5 minute input rate 11171000 bits/sec, 1353 packets/sec
>   5 minute output rate 2821000 bits/sec, 681 packets/sec
> 
> Sure i can upgrade IOS!
> Looking to know WHY this box is so hot!

When you see the box spending processor time in "IP Input" it's because
it cannot hardware switch the traffic it moves. This is (almost) always
a bad thing when you're looking at a L3 switch.

There can be several reasons for this. Features not supported in
hardware (= most features, e.g. GRE or NAT) is one possible thing. TCAM
starvation/overflow could also make the box do software switching.

It depends on your configuration. Has it always done this?

Regards,
Peter