It seems openVPN is to blaim for this problem. Some need to make openVPN connections with this server. But when doing so, the connection failed and that is the moment eth1 goes down. After re-installing the openVPN server eth1 is still up (for about 13 hours now), while openVPN connections work again.
Still don't know what was wrong but it seems solved, eth1 is still up and the openVPN server is running fine.
Last edited by colweb; Jun 9th, 2009 at 5:23 am.