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.
