I have finally been able to release and re-new my cable IP address after speaking with my cable provider. It was a real nightmare.
I have a linksys router WRT54G and connected with a cable modem. For the last 2.5 years, my IP adddress has not changed as my network is always on.
Anyway, I have decided to change my IP address.
my router was giving the IP 126.96.36.199XX and when I connected a laptop to the modem direcly I got the same IP 188.8.131.52XX .
Anyway, I did remove the coaxial cable from the cable modem, and turn off the modem.
2 hours later, reconnected the coaxial cable to the cable modem, then went to command promt (laptop connected directly to the cable modem, did ipconfig/release then ipconfig/renew.
to my surpise the IP address got release and was getting a new IP address 184.108.40.206X from my cable modem instead 220.127.116.11XX
I connected the modem back to the router and did a ping, and to my surprised thru the router I got the original IP 18.104.22.168XX. I can not understand why, I did a hard for the router, and reconfigure it, and still that IP address keep popping up, while the cable modem is 22.214.171.124X if I still connect the laptop to the modem.
Do I need to something in Vista to sort this problem? I want my router to give the new IP address of the cable modem?
I believe this has something to do with MAC address of the router, as the modem stores such information and makes a lease query based off that address (the modem itself most likely doesn't receive own external IP, yet in most cases accessible via web-interface - i.e. http://192.168.100.1 for Motorola models, google for your make. For this, I presume, you must be directly connected to the modem with one of your systems). One of the ways to resolve it would be spoofing router's MAC (if possible at all), another - reseting the cable modem to the factory default to clear MACs stored in modem's memory, which is easier to do via web-interface, but I wouldn't recommend it without notifying and hence receiving a blessing from your ISP first, as I'm not a professional and have only a vague understanding of the consequences, moreover never tried it before myself. As for what can you do to make the IP release/renewal easier next time - as far as I understand there is nothing to be done on the user side except what was already mentioned: reseting to factory defaults or spoofing router's MAC, which is probably not that easy to do, if that option is not openly available on your model.