problem with internet connection on debian VM

Hi all ,
First: please excuse for my bad English.
I am facing a problem with my Debian vm on proxmox 1.7, the Debina vm has a static ip address, in sometimes the internet connection stops, and can't access the VM using ssh connection, at this case i have to access the vm using VNC console from the Proxmox web-interface and to restart the Debian vm, after this step the internet connection is back.

please help .