[c-nsp] IP Input high CPU utilization

[Rodney Dunn]

Yep. A routing loop with TTL==1 would do it.

Rodney

On Mon, Jan 29, 2007 at 10:19:43PM -0500, David Coulson wrote:
> David Coulson wrote:
> > So, I decided to make core1 the active router in HSRP. It started to
> > utilize 100% cpu on core1 due to the 'IP Input' process. I know this is
> > caused by process switched packets, however since the config for the
> > interfaces is the same on both routers, I can't figure out why it would
> > behave differently on the two routers. For all intents and purposes,
> > these two routers are identical (same IOS, same RSPs, same VIP/PAs).
> > Even when I have HSRP move onto core2, we still have outbound traffic to
> > that interface on core1, and traffic which would previously have been
> > routed via core1 (e.g. directly connected customers) will come in on
> > another GigE interface sub-interface and end up on core1 anyway.
> 
> After some digging around, I was able to fix this issue, although I'm 
> not entirely sure how I fixed it... Why it would be different on the 
> GigE Vs. FastEthernet is anyone's guess, although Rodney's suggestion 
> that CEF is distributed across sub-interfaces may contribute to it.
> 
> Basically there were a bunch of routes on core1 that caused a routing 
> loop, and of course, TTL <=1 traffic is punted to the processor. Once I 
> removed these routes, CPU usage dropped significantly and I was able to 
> bring up the GigE sub interface under HSRP without any issues. I've been 
> consistently under 8% CPU utilization (process + interrupt) all day, 
> which is much better than we've seen in the past.
> 
> David
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