-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of chloe K i all I use linux as GiGE router and have 6 NIC on it Those days the NIC interrupt takes around 100% CPU but the system is 4G memroy and 8 CPU. I can't see any error packet in this NIC interface too After I block the udp, the %CPU drops. but the UDP only takes around 8M in general Is there any chance you have a routing loop problem? when your CPU jumps to 100% usage, is traffic still passing, and your applications working? (I am also assuming that all 8CPU's are at 100% usage) are you blocking the UDP traffic with iptables on your linux box? if so...maybe set it to be a log rule instead, then analyze those logs. as a side note, when your interrupts are taking 100% CPU...it is called "Live Lock" (in case you didn't know) We use UDP traffic for voice. Do you have any suggestion ? increase the kernel parameter? I take it that there was no interesting information in 'dmesg' as well. Mike