What do you mean by disconnect? Do you mean disconnect the cable? IP addresses usually stay the same when using the same DHCP server over and over. The reason for this is, is that unless your MAC address changes, your IP really shouldn't/won't. That is one reason why cable users (though they use DHCP and dynamic IP) have been known to keep the same IP address for a year or more as long as the networking device (or it's MAC address) on the connection doesn't change.