I got a strange problem with the network connection of a Centos 6 server: From LAN everything works as expected (SSH, httpd) but outside connections fail if the server has been idle for a few minutes. After sending a ping from another computer over lan, outside connections work as long as the server isn't idle. Some minutes later the server stops responding again.
The router configuration/port forwarding should be ok (connecting to a nas in the same network never failed) and over lan there haven't been any problems.
Does anyone know what i could have missed in the configuration that causes this behaviour?