I am running a debian box and i use it as a sandbox for developing web applications etc. In 7-8 days the server loses all network connectivity and i have to reboot it by hand, it cannot get connection and i cannot SSH to my server. I have tried things like restarting networking and for this week i have disabled a few features of the server's NIC (tx checksum). Could this be a dns issue?.
Could be DNS. The way to test this is to ssh to the IP address, not the name. If you can get to the IP address but not the name, then DNS is partially guilty.
Do you get the address with DHCP? If so, how long is the DHCP lease?