Hey, I was struggling with this as well, until I found some info in another forum (it may be here too, but I wasn't able to locate it). I'm currently on DSL, but here is what I do, and I can pull a new IP in about 2 minutes...
1 - Login to my DSL modem (done by navigating to my current IP address)
2 - On the home screen, it shows my connection status as "CONNECTED"
3 - I click on that, and it shows me that I am setup on PPPOE, and right next to that is a button labeled "RELEASE"
4 - I click on the RELEASE button, and my Internet connection goes down
5 - I then login to my wireless router, change the MAC address, which automatically reboots the router
6 - Once rebooted, toggle the power on the DSL modem, and bingo - New IP Address
Again, all of this takes about 2 minutes total. I was able to change my IP address 4 times yesterday with no problems whatsoever.
Unfortunately for me, by keeping track of the MAC addresses I use, I am not able to pull the same IP address again. I guess Verizon DSL just doesn't work that way. So, what I do is keep a spreadsheet, with all of my eBay IDs as column headers. Then I just record whatever IP address I get in those columns. Each time I pull a new IP I just search the spreadsheet to see if it's ever been used before. It's pretty simple really.
Apparently you have to release the PPOE session so it'll give your old IP address back to the pool. Otherwise, the session will stay open, waiting for you to reconnect until whatever timeout period that has been setup by your ISP has expired. That can be anywhere from a few minutes to a few days.
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