"Change IP address @ large ISP"
The short answer is that if you don't have a configurable router then for large cable/DSL ISPs you may well be stuck with the IP you are assigned. If you have a configurable router then the long answer follows. Comcast is my ISP and the method below works for me.
The advice below should apply to most large cable and DSL ISPs, but your ISP could be different. YMMV.
Usually large ISPs will assign your IP address based on your MAC address. A MAC address is an identifier that is hard wired into the hardware of any device that connects to a network … for example your router and the network interface card in your PC. Probably your PC doesn't have a separate network interface card and the connection is right on your motherboard/laptop.
Info on MAC addresses
–> http://en.wikipedia.org/wiki/MAC_address
If you reconnect, even after releasing the IP, the ISP's network hardware can/will read your MAC address (it's in EVERY packet) and look up that MAC address in it's network info tables and simply give you back the address you had on your last connect. If you don't connect for 1/2/3 months the old table entry will have been purged during that time and you will get a new IP address.
So, how to change your MAC address in order to get a new IP?
Many routers have the ability to clone your PC MAC address to overlay the MAC address in the router. Routers that do that usually will also allow you to specify the MAC address to use.
About MAC addresses … it's a bad thing if two computers on the same network use the same MAC address. So, be a bit careful about what MAC address you program into your router. If you use your neighbor's MAC address your ISP's network equipment may get rather confused. Try to avoid that.
If you have two (or more) computers at home you can find out the MAC addresses of the computers using the "clone to router" feature I mentioned. Another way is to use the "ipconfig /all" DOS command (no quotes). It's listed as "Physical Address."
Detailed instructions for seeing the MAC address on your PC/Mac/Linux box are at the URL below.
http://www.tvcc.cc.or.us/ISS/Find-MAC-Address.cfm
Scenario 1 - you do not own a router
Routers have their own native MAC address. So, if you don't have a router and then you go out and buy one and start using it then that will almost certainly change your MAC address.
When deciding on which router to get look for a feature where the router will allow you to either clone or program the MAC address into the router. Read the router manuals online before buying. That router feature will allow you to at least toggle between two IPs in the future and possibly will let you change your IP at will.
A $40 - $60 wireless router from Newegg/Best Buy/etc. should do you just fine. BTW - wireless routers are also "wired routers." You won't be using it right now, but look for WPA2 as a feature for your future wireless connections. I notice Newegg has the dual antenna Linksys WRT54GL (good brand) on sale for $50 ("see price in cart"/"blow 'em out the door"). It has 802.11b and g, but no n. Do you really need 802.11n? Probably not (unless your gonna stream HDTV wirelessly). It has wireless MAC address filtering … a very nice security feature. It has WPA2 and MAC address programmability. That last feature is the one you need.
For the "no router" situation do the following:
A - Buy a router (preferably MAC address programmable).
B - Power off your cable/DSL modem and your computer.
C - Connect the cable/DSL modem to the "internet" connection on the router.
D - Connect your PC to an "ethernet" connection on the router (pick any one).
E - Don't power on the router quite yet.
F - follow steps 10 through 13 below
Scenario 2 - you own a router
So, you want to program your router in order to get a new IP address from your cable/DSL ISP. You can use the steps below.
1 - Power off your cable/DSL modem.
2 - From your web browser login to your router (see the router manual).
3 - In the router web pages navigate to the "program MAC address" web page.
4 - Program in the new MAC address by any of the methods below.
A. clone the MAC address from the current computer
B. type in the new MAC address manually
C. revert back to using the native MAC address of the router
[[ Your cable/DSL modem is powered off, right?]]
5 - Save the router changes (normally causes the router to reboot–you wait).
6 - Login to the router again.
7 - In the router check that the new MAC address is on that MAC address page.
8 - Power the router off.
9 - Shutdown your computer.
10 - Power on the cable/DSL modem. Wait until the appropriate lights are on.
11 - Power on your router. Wait until the appropriate lights are on.
12 - Boot your computer and login.
13 - On the net check your IP address. Many websites will do this for you.
http://whatismyipaddress.com/
http://www.ipchecking.com/
You should have a new IP address.
Routers are good, cheap hardware firewalls. I recommend getting one if you don't have one. One thing about them is that they complicate the setup of P2P programs (if you do that sort of thing). For proper setup in that situation see the portforward.com website.
Please use a GOOD router password. If it is the default password change it to a GOOD password. This is an important line of defense for you. It's probably best to put the new GOOD router password on a sticky note in the router manual because most folks will forget a password that is onlyused once every 6 months.
For future IP address changes you can either toggle between using the router's MAC address and the PC MAC address or you can explicitly program MAC addresses into the router. Each time you change your MAC address most large ISPs will store that new MAC address and the IP address that goes with it. Each time you go back to a MAC address they'll give you the IP address associated with that MAC address … unless you wait a LONG time between MAC address changes (?1/2/3 months?).
For future IP address changes just follow steps 1 through 13 and also make sure your cable/DSL modem was powered off for 45 - 60 seconds. On Comcast near Chicago 20 seconds works fine for me. Digerati's suggestion of 10 minutes for the power off couldn't hurt, but it's a long time to wait.
