[c-nsp] Interface ignored errors - sizing and allocating buffers

[Brian Feeny]

On Nov 23, 2004, at 7:10 PM, Sam Stickland wrote:

> Hi,
>
> I've got a C7206-NPE200 router that's seeing a regular amount of 
> ignored errors on a policed interface (input). There's also the 
> occassional overun.
>
> The CPU on this router is currently:
>
> CPU utilization for five seconds: 65%/63%; one minute: 62%; five 
> minutes: 62%
>
> Is this caused by not having enough buffers available, or the CPU 
> usage? The only interface I see this on is the one with the policer - 
> there's another interface that carries a similar amount of traffic and 
> it doesn't exhibit these issues.

You need more info to determine the problem.  Alot of times, CPU can go 
up, because your running out of buffers.  But usually there is another 
problem which is why your running out of buffers in the first place.

>
> Is there anyway to size and allocate extra internal buffers to the 
> ethernet interface to prevent the errors?
>

You probably don't want to mess with interface level buffers, just 
stick to the global buffer stuff.

Are you sure the traffic is kosher going thru that interface?  I ask 
because sometimes there is wierd stuff
like DoS attacks and the like, which causes buffer exhaustion.  
Somethings I like to do are like enable
netflow on the interface and then do like "sh ip cache f0/0 flow" or 
whatever the interface is, and just look
for wierdness in the src/dst, or packet sizes, or a higher pps than 
normal.

Also definitely check "show interface switching" and make sure you 
don't have alot of process switched packets.

I assume  your running CEF too.


> Sam
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---------------------------------------------
Brian Feeny, CCIE #8036, CISSP
Network Engineer
ShreveNet Inc.