automatic IP address

[dragos_iliescu_2005]

When I use an automatic network configuration under ubuntu, dhcp returns somethink like 89.136....but under windows returns something like 83.103...
Only the last one really work. I could not understand why dhcp returns two different addresses from the some isp. Is there anyone that could offer me some informations on that?
Things are getting more interesting when I see that under Windows, there are blocked connections attempts by firewall on address 89.136...even that the current IP is 83.103...