The OP stated they were using an Unlocked HG612 Modem. Which implies it would have an external IP Address.
Not unless he's switched the modem into router mode and is doing the PPP connection on the modem.
Unlocking a modem by default only gives access to the web interface using a private address on the LAN side of the modem.
I don't know, maybe i'm not explaining things well so i'll try again.
Imagine a really wide pipe. One end is the LAN port on your modem and the other end is the equipment in the fibre cabinet. This big pipe is not connected to the Internet, it goes nowhere near it, it's just a way of providing a path.
Inside the big pipe is a narrower pipe. It extends beyond the big pipe at both ends. One end is connected to the WAN port on your router, the other end is connected to your ISP. It also has no connection to the Internet and just provides a path between your router and ISP.
Inside the small pipe is a cable. It extends slightly beyond the small pipe. One end is attached to a PPP client running on the WAN port of your router and the other end is attached to a PPP server running on a machine at your ISP. Each end of the cable has a global IP and it is this that provides your Internet connection. The big and small pipes are just ways of getting the cable from one end to the other.
This is very simplified but hopefully it'll help the OP understand why this is not an issue at all and that they shouldn't mess around with the settings in the modem. If you've unlocked your modem just use it for stat gathering and don't mess with anything else.
Edited by deleted (Wed 06-Aug-14 21:04:05)