About once a month or so my net goes toes up. After standing on my head under a desk to hook up a monitor and keyboard to my gw, I consistently learn that eth1 is disabled and invalid. On rebooting, something to the effect of "eth1 disabled, some other device has 192.168.1.1" scrolls by.
Aside from the fact that the DHCP server can't assign this address (it's limited to 100-254), I know what's on my net and nothing has that address. I fiddle with DHCP settings, reassign my gw to 192.168.1.2, change the default gw address and DNS server address, etc., then change them all back to what they should be and things work for another month or so.
The cable modem is a pretty dumb box that is on the eth0 (WAN) side of things. Its IP is 192.168.100.1. It offers 1 page of basic info. Hard to see how that could be a problem. eth1 is my LAN at 192.168.1.x.
I also had this problem when I first installed COS. At the time I thought it was a driver problem and reinstalled about 4 times. Eventually the problem went away, only to resurface later.
Thanks for thinking about this. It's a bit out of my league.