If you are behind a router simply spoof the MAC address of the router and then do a DHCP release/renew on thr router. That should work. If not that then swap out you NIC in your computer and do a DHCP release/renew with the new NIC and it should work then too. Other than that shut all off for a time period of ??????? and then turn it all back on.
You turned it back on too quickly. When the IP is released, it is free for someone else to use. If nobody else turns their cable modem on, no IP is needed. You turn yours on and it needs one. It gets one that is still not in use. It might be tough to get a new IP without leaving the modem off for a few days, as it's likely most cable modem users leave the modem on
First, a clarification. Do you want the modem to get a new IP address, or the device (computer, router, etc.) connected to the modem to get a new IP address?
If you want the device attached to it to get a new IP address, you may need to see when the lease expires, and take the device off the network
*at least* until that time. The theory is that once it is no longer leased, someone else could take it. However, if your node has a pool with plenty of IP addresses, that may not happen. And if another device hasn't taken the available IP address, you'll get it back no matter how long it's been.
If you have a router, you can probably spoof a different MAC address. That will likely get you a new IP address. However (and isn't there always a "however"?), it would be unwise to just randomly come up with a new MAC address. This could potentially result in problems that could affect the network. In a case like that, getting you off the network will be the remedy the ISP takes. Only spoof MAC addresses of NIC cards in your possession.
If you're not using a router, the easiest way is to install a new NIC, or buy a router. (Of course don't spoof the IP address of the NIC you're putting behind the router!)
That's how to get a new IP address for the device connected to the cablemodem. But if you want the modem itself to get a new IP address, you're probably out of luck. While the modem gets it's IP address by DHCP, the customer account software used by most big cable Internet providers will keep the modem IP address and the account linked. That is, even if you went out and bought your own modem, once the modem is identified as being on your account, it will be given back the same IP address you had before. If there is a chance to change your cablemodem's IP address, it would be to get a new modem. But don't count on it.
Of course this all begs the question of why you would want a new IP address? What problem do you think this will solve?
Good firewall should keep anyone knowing your ip out of your box. Have it drop packets and they won't even affect your upstream rate. You are using a safer browser, Mozilla Thunderbird 0.8.
I have been on @home, attbi and comcast and always had my ip address in my posts. No problem so far. Quick google search shows Results 1 - 10 of about 12,600 English messages for author:bit author:twister. (0.40 seconds)
So you would want to change your IP address after every time you post?
And what does it matter that people know your IP address? (Unless you're with an ISP that has nothing in place to screen out DoS attacks, which would be unusual.) And, of course, you're using some kind of a firewall, aren't you?
Trust me when I say that it doesn't matter if people know your IP address. As some others around here can tell you, I've pissed-off plenty of people, and I haven't had any problems. (Of course if someone wants to prove me wrong, I'm sure they can find a way. But your typical psycho script kiddie isn't that bright.)
But if it really bothers you, post through an anonymous reposter. (Of course someone saying things that piss people off from behind anonymous reposters often don't have much credibility once someone calls them on it.)
Using a motorola surfboard 5100 all I need to do is to change the mac-address of my router, and turn off the surfboard for 5 secs... Sending an email to myself and checking the internet header I see my IP effectively changed afterwards