Debian losing network connection
 

I have a very frustrating issue with my debian server box. Every few days, it loses the network connection. 'ifconfig' shows a normal result (IP address and everything), but any network action gives "network is unreachable".
A plain "ifdown eth0" followed by "ifup eth0" solves the problem. dmesg gives no clue, neither does /var/log/messages.

Well as long as you haven't found the problem you might want to run a cron job that does the ifdown and ifup every so often. Like a couple of seconds planned downtime is better than hours not planned. But could it be that your dhcp lease runs out?

Yes, I was thinking about a cronjob too, but I figured there must be a solution to the problem.
The DHCP lease runs out every 3600 seconds, and the problem occurs every 2-3 days. I found that in /var/log/daemon there is a nice renewal every hour, but when the problem occurs the computer doesn't seem to get a new lease (which is probably not the DHCP servers fault, as 100+ windows computers continue to run fine all the time)

Well let's see. Ifup only sets everything up again you have in the /etc/interfaces file. I'd also say some setting is going wrong. In my network I usually get the same IP both for my computer local and my router's IP so it could be ifconfig does not show that it's not working and simply display the old address.

I must admit I'm not really an expert on this thing so I'm guessing a bit too if you don't mind ;) Which program is trying to get the dhcp lease every hour or is it a script?