My Ubuntu 11.04 server on the internet has some strange behavior since a few days. It runs perfectly fine with some Java web applications. Then, suddenly it does not accept connections anymore. When I try to ssh or to http-connect my server I get no response, until I get timeout. But ping works perfectly. nmap also works:
Starting Nmap 5.21 ( http://nmap.org ) at 2011-08-29 10:52 CEST Nmap scan report for ... Host is up (0.020s latency). Not shown: 994 closed ports PORT STATE SERVICE 22/tcp open ssh 25/tcp open smtp 53/tcp open domain 443/tcp open https 3000/tcp open ppp 3128/tcp open squid-http
After reboot, everything works again for some hours.
What could this be? Or how to analyse this problem?