>>/956255/
Modem should not have an IP.
These days ISPs that use modem give modems that are routers as well. These have inner and outer IPs. They have a webpage with their settings that is reachable just with any commercially available basic home router. Some has an option to turn off the router and function as a modem. But some doesn't have this feature and have to request the ISP to switch the router functionality off.

 >>/956257/
No.