|Do you see in your ipconfig /all the line that says:|
dhcp enable =yes?
This means the modem is giving out the ip address.
You set the routers wan port to the same so it gets the ip address. This is standard feature on all routers.
You clone the workstations mac address to the routers wan port. Again this should be covered in the routers docs. Some have a place to manually enter the info. Others have a button to clone the wkst mac address.
Have you logged into the router and looked at the configuration pages?