I am encountering following problem. There is one server (DL160 G5) running Centos 6.3 with default kernel 2.6.32-220.2.1.el6.x86_64 - at this point I'd like to add that issue appeared also at older version - 6.1 and older kernel (do not remember exactly which version). There is cPanel installed and from time to time it becomes unavailable (network connection). What I've checked is (via KVMoIP): load average is completely normal it does not lack memory or disk space when problem occurs no console notifications checked all access logs and there is no sign that it can be caused by a client script cannot even access local interface (127.0.0.1) or main IP address running tcpdump I can only see packets arriving to server - no responses all services seem to be running properly (mail,sql,http,ssh) checked crontab and all clients' crontabs too network port utilisation is low ( up to several Mbits) arriving packet rate is low - hundreds per second (according to tcpdump) console (via kvmoip) works fine, no lags there is no conntrack at this server there is no ipv6 at this server flushing iptables, unloading modules does not resolve problem restarting network does not resolve problem, no errors appear it also occurs when two sepearate networks are configured (and multiple gateways) as well as one IP, one default gw and one network is configured - so it seems network configuration independent it seems to repeat randomly (load,packet rate,bandwith usage,load independent) checked server with different rootkit detection tools - it seems to be clean server has been rebooted, it did not change anything there are no interface errors it apperas randomly can be once a week or several times per day It usually works fine after 1-15 minutes. What I can also check? It is definitely OS issue - there is traffic at interface only in one direction when problem occurs, can not even ping loopback. Any ideas? Recommended checks? Anything I did not checked above.