So I recently set up an apache server on Ubuntu 11.04 in my apartment. I plug directly into the wall and I know that this goes to a router because I can connect to it via 192.168.1.1. I set up port forwarding and everything was running smoothly until the next day. The server was down and when I did an ifconfig I found that the ip had changed to 66.XX.XXX.XXX wheres the day before it was 69.XX.XXX.XXX. I am not able to connect to the router. When I unplug and re plug it into the wall port I get a 192 number for a day then it changes again. Is there anything that would of caused the ip to change and is there a way to fix it?
To begin with, this is hard to say for sure due to the ips in the example.
My guess is one of the following:
All this being said, unless you are using static IP addresses, if a machine is not on when the DHCP lease expires, it is possible to loose your reservation and that IP address.
I hope this helps a little, but, again, it sounds a little weird from what you have said and to help you further, I really need to know more about your network topology.