[cisco-nas] High CPU usage on IP INPUT process

[Gert Doering]

Hi,

On Fri, Jan 28, 2005 at 02:09:13PM +0700, Souphonh wrote:
> I am using Cisco 3620, IOS 12.2-17 as NAT, and found that the CPU utilisation for IP INPUT is very high. I need to clear IP NAT TRANSLATION every day. Could you please suggest how can I check for the cause of high CPU utilisation.

We've recently discovered that 12.2 seems to be affected by CSCsa51150
as well:

On a customer 1600, upgrading IOS from 12.0->12.2 made the NAT table
virtually explode.  All entries were legitimately-looking web sessions, 
but the translation entries just did not go away after the TCP FIN came 
along - the bug ID above lists only 12.3(x) as affected, so we're not 
fully sure whether it's the same bug, but it's definitely the same 
behaviour.  

Symptoms are similar: high CPU load, large NAT table, "clear ip nat tra *" 
makes it go away for a few hours, then the CPU load is up again (while
the number of NAT translation entries grows and grows and grows...).

We downgraded back to 12.0(recent), and haven't seen any NAT issues on
that router since.

gert


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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de