Very High CPU Utilization on VOIP transit router

[howard.cisco]

We have several 5300's running VOIP with a Fastethernet link to a 2600 then on through another Fastethernet link to an ISP.

When one particular 5300 starts passing VOIP traffic through the 2600, the CPU utilization goes from about 20% to 99%. About 30% of the trafffic is UDP process switched on 64-80 byte packets. The Ethernet load is only 1.5 Mbit/s.

I cannot see any particular difference between the offending AS5300 and the others.

Any Ideas?

[Chester Rieman]

Is there a reason why you are rpocess switching? Turn on fast switching and this should reduce the cpu load greatly.

[howard.cisco]

Hi, All interfaces are Fast switching and I have tried Flow switching but no change.

I think the packets are not cacheing properly or the packet header is changing some how, but I do not know why. Its only 1 AS5300 creating the problem out of 4 others. In order to access the 2600 I sometimes add traffic shaping to reduce the load, but need to bring the traffic down to 100kbit/s to drop the cpu load to 50%. We thought it may be a DOS attack and I have looked at "traffic to local host" but its only incrementing by 2-5 pps.

[hburgos]

HiWhat version code are you using ? Are you nating on this unit ?What features are you running on the high CPU router ?Hankb@tampabay.rr.com">Hankb@tampabay.rr.com