Posted 25 February 2012 - 09:01
There are different networks in play. You have control of the network between your PC and your Router (Internal network), Your ISP has control the network between your Router and their Router (External Network/Internet), Your ISP will connect to other networks they don't have control over.
What is displayed on whatismyip.com is controlled by Your ISP.
Some ISPs offer Dynamic IP addresses (They can change your IP address whenever they like), other offer static IP addresses (Your IP address never changes unless you ask them to change it).
Do not change the MAC address on a Cable modem, Most cable companies look at the MAC address to allow you onto their network.
If you wish to change the IP address that your ISP assigns you, there are a few things you can try:
1. Release/Renew the IP address on the modem, or reboot it. It is quite likely that the ISP will simply issue the same IP address again in this case.
2. Release the IP address or switch off the modem completely for a few days. Somebody else's modem in the area might be due for a new IP address to be handed out and hopefully will be issued with your old one instead of getting the same one again. When you plug back in/renew the IP address you could then get their one (or someone else has taken their old one you get someone else's, and so on).
3. Asking your ISP to give you a Static IP address if you are currently on Dynamic. There is usually and extra charge for this and not all ISPs offer it. Check if they will issue you with a new IP address if you do this.
4. If you already have a Static IP, request that the ISP gives you a new static IP. My ISP allows me to change my Static IP (included for free) using their online toolbox up to 50 times for free.
5. If you still can't change the IP address, get a new ISP. That will definitely give you a new IP address.
If you received a copyright infringement notice showing your IP address, this won't help you. Most ISPs keep a date/time log of when you had a particular IP address so they can still track you even if you change IP addresses. Also if you have been banned from something, sometimes the whole IP block is banned (so even if you change, if your new IP address is similar to the old it will be blocked also).