Server randomly not reachable. Can't detect the problem
we run ISPConfig on Debian to manage our webserver with several virtual hosts. Everythings running fine, but the webserver suddenly isn't reachable any more. Login to ISPConfig or Webmail (on Port 81) still works fine. From the command line I can't see any problems. No heavy load, apache running normal, tcpdump shows normal connections.
After doing a /etc/init.d/apache2 restart the webserver is accesible via web again immediately. I don't even have to push reload in browser, the established connections is being finished at this moment.
The Firewall works fine, disabling doesn't fix the problem. There is enough space on the servers hds. The problem doesn't appear consistently, but randomly.
Does somebody have an idea whats going wrong?